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The present study reports on the development of a new binary filler system for rubber composites, SiO2@Al2O3, where Al2O3 sheets are grown onto SiO2 nanoparticles aggregates by a sustainable water-based soft-chemistry approach. The aim is to synergistically integrate the intrinsic thermal conductivity properties of Al2O3 with the peculiar reinforcement ability of SiO2 in an easy one-pot solution, which has been exploited to prepare polybutadiene (PB) model composites by a simple solvent casting technique. More in detail, the binary filler was used as-prepared or suitably surface functionalized with 3-(Trimethoxysilyl)propylmethacrylate (TMSPM). The filler compatibilization and interplay with the polymeric matrix have been inspected by solid state NMR in conjunction with scanning electron microscopy. These investigations highlighted that the presence of alumina in the binary filler does not undermine the capability of silica in generating polymer chains stiffening and indicated a significant effect of the silanization in providing better filler networking and interaction with the PB host ensuring, in principle, an enhanced thermal transport. Accordingly, thermal conductivity measurements revealed that SiO2@Al2O3 introduction in PB induces a remarkable upgrade of the heat transfer, which becomes much more relevant upon surface modification with TMSPM. These results appear encouraging, paving the possibility of applying SiO2@Al2O3 model system to more complex case studies, where both improved thermal conductivity and enhanced reinforcement are required, such as tires tread formulations. Highlights: A new SiO2@Al2O3 binary filler system was proposed following a soft-chemistry approach. The binary filler was functionalized to enhance its compatibilization. Fillers were dispersed in polybutadiene by a simple solvent casting technique. Thermal conductivity measurements revealed a remarkable upgrade of the heat transfer ability.

Impact of residual stresses on the thermal shock resistance of alumina–zirconia multi-layer ceramics is investigated within the framework of finite fracture mechanics, using a stress-energy criterion. The critical temperature difference (Tc) for crack formation is strongly dependent on the magnitude of residual stress and the material’s strength. The predicted minimal spacing between cracks, critical time for crack initiation, and initial depth of the induced cracks are compared and discussed for different designs. An increase of up to 40 % in Tc is predicted for multi-material ceramics with a thin alumina surface layer with compressive stresses, compared to bulk reference alumina.

Welding or brazing of metals to ceramics often leads to failures under aggressive conditions due to abrupt changes in physical, chemical, and thermal properties at the metal-ceramic interface. Metal-ceramic Functional Graded Materials (FGMs) replace the strict interface with a gradual transition of composition and properties, which protects the material from failures. The powder-blown Laser-Directed Energy Deposition (DED-LB) is one of the widely known Additive Manufacturing (AM) processes that offer unique features like developing FGMs and multi-material structures. Various studies have been conducted to process metalceramic FGMs using the DED-LB process but significant differences in thermal properties, varying laser-material interactions, and the possibility of formation of complex reaction products make the processing of metal-ceramic FGMs challenging. This study aims to understand the effect of laser power on a ceramic substrate, and its interaction with a metal powder introduced in the melt pool. A single track of nickel-based superalloy Alloy 718 powder was deposited on an Alumina substrate with different laser powers. The deposition was performed with and without substrate pre-heat to understand the effect of pre-treatment on deposition. Metallographic analysis was performed to reveal the microstructure of the resolidified metal mixed ceramic region, CC BY NC 4.0

Density functional theory based positron lifetime (PL) calculations for cation and oxygen monovacancies in a range of oxides – hematite, magnetite, hercynite, and alumina – have been conducted to compare the impact of defect chemistry and crystal structure on the predicted lifetimes. The role of defect charge state has also been examined. A comparison across the same type of crystalline structure but different composition shows that oxygen vacancies only induce a slight increase in the positron-electron overlap and thus barely modify the PL as compared to the bulk. A much more substantial increase of PL is observed for cation monovacancies, regardless of crystal structure or the elemental nature of the vacancy, which we ascribe to an enhanced localization of charge density around the vacant site. The structural and compositional richness of the oxide leads to longer defect PLs, with defected hercynite exhibiting the longest PLs. The charge state of cation monovacancies modifies only by a small percentage the positron localization, relegating to secondary importance the metal defect’s oxidation state in modifying the lifetime of positrons within vacancy traps.

Impact of residual stresses on the thermal shock resistance of alumina–zirconia multi-layer ceramics is investigated within the framework of finite fracture mechanics, using a stress-energy criterion. The critical temperature difference (Tc) for crack formation is strongly dependent on the magnitude of residual stress and the material’s strength. The predicted minimal spacing between cracks, critical time for crack initiation, and initial depth of the induced cracks are compared and discussed for different designs. An increase of up to 40 % in Tc is predicted for multi-material ceramics with a thin alumina surface layer with compressive stresses, compared to bulk reference alumina.

The study investigated the oxidation behaviour and grain boundary diffusion of minor/major elements of FeCrAl alloys, doped with over-critical concentrations of reactive elements (REs) Zr and Hf. While the formation of ?-Al2O3 scale on these alloys is conventionally attributed to inward oxygen transport along grain boundaries, this research proposes that metal ion outward diffusion also contributes to the development of oxide scales and their microstructural characteristics. Samples were analyzed after thermal exposure at 1100 °C using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom probe tomography (APT). Results revealed increased oxide growth, deeper internal oxidation, and RE-oxide formation near and at oxide grain boundaries due to enhanced inward and outward diffusion resulting from overdoping. The impact of overdoping varied with RE type and concentration, influenced by solubility, ionic size, and electronic structure of alumina. Notably, Zr-doped samples maintained alumina adhesion to the alloy after thermal exposure, whereas severe spallation occurred in Hf-doped samples.

Welding or brazing of metals to ceramics often leads to failures under aggressive conditions due to abrupt changes in physical, chemical, and thermal properties at the metal-ceramic interface. Metal-ceramic Functional Graded Materials (FGMs) replace the strict interface with a gradual transition of composition and properties, which protects the material from failures. The powder-blown Laser-Directed Energy Deposition (DED-LB) is one of the widely known Additive Manufacturing (AM) processes that offer unique features like developing FGMs and multi-material structures. Various studies have been conducted to process metalceramic FGMs using the DED-LB process but significant differences in thermal properties, varying laser-material interactions, and the possibility of formation of complex reaction products make the processing of metal-ceramic FGMs challenging. This study aims to understand the effect of laser power on a ceramic substrate, and its interaction with a metal powder introduced in the melt pool. A single track of nickel-based superalloy Alloy 718 powder was deposited on an Alumina substrate with different laser powers. The deposition was performed with and without substrate pre-heat to understand the effect of pre-treatment on deposition. Metallographic analysis was performed to reveal the microstructure of the resolidified metal mixed ceramic region, CC BY NC 4.0

Welding or brazing of metals to ceramics often leads to failures under aggressive conditions due to abrupt changes in physical, chemical, and thermal properties at the metal-ceramic interface. Metal-ceramic Functional Graded Materials (FGMs) replace the strict interface with a gradual transition of composition and properties, which protects the material from failures. The powder-blown Laser-Directed Energy Deposition (DED-LB) is one of the widely known Additive Manufacturing (AM) processes that offer unique features like developing FGMs and multi-material structures. Various studies have been conducted to process metalceramic FGMs using the DED-LB process but significant differences in thermal properties, varying laser-material interactions, and the possibility of formation of complex reaction products make the processing of metal-ceramic FGMs challenging. This study aims to understand the effect of laser power on a ceramic substrate, and its interaction with a metal powder introduced in the melt pool. A single track of nickel-based superalloy Alloy 718 powder was deposited on an Alumina substrate with different laser powers. The deposition was performed with and without substrate pre-heat to understand the effect of pre-treatment on deposition. Metallographic analysis was performed to reveal the microstructure of the resolidified metal mixed ceramic region, CC BY NC 4.0

Welding or brazing of metals to ceramics often leads to failures under aggressive conditions due to abrupt changes in physical, chemical, and thermal properties at the metal-ceramic interface. Metal-ceramic Functional Graded Materials (FGMs) replace the strict interface with a gradual transition of composition and properties, which protects the material from failures. The powder-blown Laser-Directed Energy Deposition (DED-LB) is one of the widely known Additive Manufacturing (AM) processes that offer unique features like developing FGMs and multi-material structures. Various studies have been conducted to process metalceramic FGMs using the DED-LB process but significant differences in thermal properties, varying laser-material interactions, and the possibility of formation of complex reaction products make the processing of metal-ceramic FGMs challenging. This study aims to understand the effect of laser power on a ceramic substrate, and its interaction with a metal powder introduced in the melt pool. A single track of nickel-based superalloy Alloy 718 powder was deposited on an Alumina substrate with different laser powers. The deposition was performed with and without substrate pre-heat to understand the effect of pre-treatment on deposition. Metallographic analysis was performed to reveal the microstructure of the resolidified metal mixed ceramic region, CC BY NC 4.0

Ru/Na2O/Al2O3 dual-function materials were prepared by varying the support synthesis method and Ru load. Different sol-gel-type and precipitation/ hydrothermal preparation methods were employed in order to synthesize materials with variable nanostructure, surface chemistry and textural properties, thereby effectively tuning the material activity for the methanation of pre-adsorbed CO2. The materials were thoroughly characterized and evaluated during the integrated CO2 capture and methanation process. It was found that the Pechini sol-gel synthesis method led to the structure with the highest porosity, basic site population and high dispersion of methanation and adsorption active Ru0 and Al-O--Na+ sites. The corresponding material displayed the highest CH4 yield (0.47 mmol/g) and fastest CH4 production kinetics, while stable performance was achieved under successive adsorption-hydrogenation cycles and under the co-presence of O2 and H2O during CO2 adsorption. Lastly, the increase in Ru load (0.25 wt% - 4 wt% range) could incrementally improve the CH4 production kinetics during hydrogenation.

Aqueous slurries of alumina doped with manganese and titanium oxides were developed. The powders and tapes were investigated by scanning electron (SEM) microscopy, X-ray diffractometry (XRD), and thermal analyses (TG/DSC). The stability and rheology of colloidal suspensions of undoped and doped alumina suspensions were investigated. At neutral pH of 7, pure alumina and MnO–TiO2 dopant particles present positive and negative surface charges and are prone to heterocoagulation. Optimized colloidal processing through proper adjustment of parameters was achieved to reach particle stabilization. The surface charge of the oxide particles was negative, and the suspensions did not agglomerate at a pH of 7 and higher. Tapes were cast, dried, and burned out. The thermal analyses revealed the release of residual water and decomposition of short-chain organics at temperatures under 215°C and of long-chain additives over 300°C., Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES), Deutscher Akademischer Austauschdienst (DAAD)

Welding or brazing of metals to ceramics often leads to failures under aggressive conditions due to abrupt changes in physical, chemical, and thermal properties at the metal-ceramic interface. Metal-ceramic Functional Graded Materials (FGMs) replace the strict interface with a gradual transition of composition and properties, which protects the material from failures. The powder-blown Laser-Directed Energy Deposition (DED-LB) is one of the widely known Additive Manufacturing (AM) processes that offer unique features like developing FGMs and multi-material structures. Various studies have been conducted to process metalceramic FGMs using the DED-LB process but significant differences in thermal properties, varying laser-material interactions, and the possibility of formation of complex reaction products make the processing of metal-ceramic FGMs challenging. This study aims to understand the effect of laser power on a ceramic substrate, and its interaction with a metal powder introduced in the melt pool. A single track of nickel-based superalloy Alloy 718 powder was deposited on an Alumina substrate with different laser powers. The deposition was performed with and without substrate pre-heat to understand the effect of pre-treatment on deposition. Metallographic analysis was performed to reveal the microstructure of the resolidified metal mixed ceramic region, CC BY NC 4.0

We would like to offer our gratitude to the employees of Analytical Laboratory: Aldona Nowicka, Ph.D., Anna Sobieszek, M.Sc., and Marcin Ku´smierz, Ph.D., for the SEM-EDX elemental mapping, and XPS measurements. The Authors would also like to acknowledge that the work was supported by subsidy from the Polish Ministry of Education and Science for the Faculty of Chemistry of Wroclaw University of Science and Technology as well as for the Institute of Chemical Sciences, Faculty of Chemistry, Maria Curie-Skłodowska University in Lublin. Eduardo Guzman acknowledge the support by MICINN under Grant PID2019-106557GB-C21., The specific physico-chemical properties of chitosan (Ch), a biopolymer isolated from chitin, and its impact on the stability of colloidal dispersity have focused the interest of science and industry. However, in some cases chitosan alone is not enough to provide high stability to dispersions, making it necessary to add surfactant to the chitosan/oxide system, leading to superior stabilizing properties due to the association of polymer and surfactant molecules to form complexes that can modify the ability of bare chitosan for adsorbing on colloidal materials. This study explores the interactions between chitosan and alumina in the presence of three different anionic surfactants: the hydrocarbon SDS (sodium dodecyl sulfate), the fluorocarbon FS-91 (Capstone® FS-91), and the silicone A-Si (Silphos A-100). Different analytical methods evidenced chitosan adsorption on the alumina surface, forming hybrid organic–inorganic materials. This process can be enhanced by adding surfactant, with SDS leading to a strong increase of chitosan adsorption. Elemental mapping and scanning electron microscope imaging have provided a confirmation of the co-adsorption of polymer and surfactant on the alumina surface. The latter emerges as a very important finding because the results have shown that small quantities of surfactant (as low as 0.002% v/v) can strongly influence the adsorption and stability of multicomponent colloidal systems. This allows decreasing the chitosan amount required for the enhancement of the colloidal stability in relation to dispersions without added surfactants, providing the basis for reducing the production costs of colloidal dispersion, which opens new opportunities to chemical industry, Faculty of Chemistry of Wroclaw University of Science and Technology, Institute of Chemical Sciences, Faculty of Chemistry, Maria Curie-Skłodowska University in Lublin MICINN, MICINN, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Reliable thermophysical properties of core melt (corium) are essential for the accurate prediction of the severe accident progression in light water reactors. Zirconia is one of the most important materials in corium. Despite the high interest in the viscosity of molten zirconia, few experimental data have been reported due to its high melting temperature and high vapor pressure. In the present study, the viscosity of molten zirconia was measured using aerodynamic levitation, laser heating and droplet oscillation techniques. A material sample was levitated by argon gas flow in a conical nozzle and then melted into a droplet by laser beams. The initial quiescent droplet was forced to oscillate by the excitation of a loudspeaker, and the viscosity was deduced based on the characteristics of the droplet damped oscillation after the loudspeaker was turned off. The viscosity of molten alumina was first measured for verification of the measurement system. Afterwards the viscosity of molten zirconia was measured. The results showed that the viscosity of molten zirconia at melting temperature (2988K) was 12.87 ± 1.03 mPa s and decreased with increasing temperature. The measurement uncertainties are within 21 %., QC 20240110

Hierarchically porous structures in nature, such as bamboo and bone, have remarkable strength and stiffness-to-density properties. Direct Ink Writing (DIW) or robocasting, an Additive Manufacturing (AM) material extrusion technique, is able to synthetically create near-net-shaped complex geometries. In this research, DIW and colloidal processing are synergized to fabricate multiscale porous ceramic scaffolds with tailorable properties. 100-micron scale porosity is produced by the 3D printed scaffold architecture. By applying particle-stabilized emulsions or capillary suspensions as feedstock for printing, a secondary level of smaller porosity is created within the scaffold filaments via soft templating of the oil phase. A third scale of porosity of sub-micron pores is formed by partial sintering of ceramic particles. Several ceramic systems are investigated in this work, namely clay, alumina, as well as hydroxyapatite and beta-tricalcium phosphate (bio-compatible and bio-resorbable ceramics). In Chapter 3, possible criteria for obtaining suitable ceramic paste feedstocks for DIW are developed by studying the relationships between paste formulation, rheological properties and print parameters. The study demonstrates that storage modulus and apparent yield stress from visco-elastic rheological measurements could be indicators of “printability” of the feedstock. This is further strengthened by the results in Chapter 4 of a different material. The particle size, surfactant concentration, oil fraction, and mixing speed are shown to influence the rheological properties, which can be adjusted to improve printing. In Chapter 4, the primary focus is to understand how to control the pore sizes within the filament microstructure. The study shows that by increasing the oil fraction and particle size, but reducing the surfactant concentration and mixing speed, produces larger micropore sizes within the filaments. The pore morphology is also determined to morph from sphere-like p

A novel and simple electrochemical sensor for the determination of gallic acid is presented. The alumina sample was char acterized by X-ray difraction, FTIR, and particle size distribution analysis. The carbon paste electrode was modifed with alumina and used as a sensor. The performances of the sensor were assessed by cyclic voltammetry and square-wave voltam metry techniques. The oxidation of gallic acid on alumina-modifed carbon paste electrode was an irreversible difusion controlled process. The linear relationship of peak current and concentration was obtained for the concentration range of 1.4 to 115 µM with the limit of detection of 0.8 µM. The sensor’s ability to test gallic aid in real systems was successfully tested in wine samples.

Aquest projete presenta un estudi detallat sobre l'ús de la técnica d’impressió “Direct Ink Writing” (DIW) per a la fabricació de monòlits d'alumina per a aplicacions de catalisis. L'objectiu principal d'aquesta investigació és investigar els efectes de la variació de la càrrega ceràmica en la tinta d'impressió en les propietats reològiques de les mostres impreses. Amb l'objectiu d'assolir aquest objectiu, es van dur a terme una sèrie d'experiments en què es van imprimir mostres amb diferents nivells de càrrega ceràmica i es van provar les seves propietats. Les propietats reològiques estudiades inclouen la contracció, la duresa i la rugositat. Els resultats d'aquestes proves indiquen que a mesura que augmenta la càrrega ceràmica en la tinta, es redueix la contracció i augmenta la duresa i la rugositat. Això indica que l'augment de la càrrega ceràmica en la tinta d'impressió condueix a una estructura més densa i compacta en les mostres impreses, el que resulta en una major duresa i rugositat. Els resultats d'aquesta investigació demostren el potencial d'utilitzar la DIW com un mètode viable per fabricar monòlits d'alumina amb propietats desitjables per a aplicacions de catalisis. La capacitat de controlar les propietats de les mostres impreses ajustant la càrrega ceràmica en la tinta proporciona una eina poderosa per adaptar les propietats dels monòlits d'alumina a aplicacions específiques de catalisis. A més, l'estudi proporciona una idea de com la càrrega ceràmica afecta les propietats reològiques de les mostres impreses, el que pot ser útil per a una major optimització del procés d'impressió i el desenvolupament de noves tintes. En general, aquesta tesi proporciona una comprensió completa de l'ús de la DIW per imprimir monòlits d'alumina per a aplicacions de catalisis i demostra el potencial d'aquesta tecnologia per ser utilitzada en la fabricació de materials ceràmics avançats per a diverses aplicacions., Este proyecto se basa en un estudio detallado sobre el uso de la técnica de impresión “Direct Ink Writing” (DIW) para la fabricación de monolitos de alúmina para aplicaciones de catalisis. El objetivo principal de esta investigación es investigar los efectos de la variación de la carga cerámica en la tinta de impresión en las propiedades reológicas de las muestras impresas. Con el fin de lograr este objetivo, se llevaron a cabo una serie de experimentos en los que se imprimieron muestras con diferentes niveles de carga cerámica y se probaron sus propiedades. Las propiedades reológicas estudiadas incluyen la contracción, la dureza y la rugosidad. Los resultados de estas pruebas indican que a medida que se aumenta la carga cerámica en la tinta, se reduce la contracción y aumenta la dureza y la rugosidad. Esto indica que el aumento de la carga cerámica en la tinta de impresión conduce a una estructura más densa y compacta en las muestras impresas, lo que resulta en una mayor dureza y rugosidad. Los resultados de esta investigación demuestran el potencial de utilizar la DIW como un método viable para fabricar monolitos de alúmina con propiedades deseables para aplicaciones de catalisis. La capacidad de controlar las propiedades de las muestras impresas ajustando la carga cerámica en la tinta proporciona una herramienta poderosa para adaptar las propiedades de los monolitos de alúmina a aplicaciones específicas de catalisis. Además, el estudio proporciona una idea de cómo la carga cerámica afecta las propiedades reológicas de las muestras impresas, lo cual puede ser útil para una mayor optimización del proceso de impresión y el desarrollo de nuevas tintas. En general, esta tesis proporciona una comprensión completa del uso de la DIW para imprimir monolitos de alúmina para aplicaciones de catalisis y demuestra el potencial de esta tecnología para ser utilizada en la fabricación de materiales cerámicos avanzados para varias aplicaciones., This project presents a detailed study on the use of Direct Ink Writing (DIW) for the fabrication of alumina monoliths for catalysis applications. The main objective of this research is to investigate the effects of varying ceramic charge in the printing ink on the rheological properties of the printed samples. In order to achieve this goal, a series of experiments were conducted in which samples with different ceramic charge levels were printed and their properties were tested. The rheological properties studied include shrinkage, hardness, and roughness. The results of these tests indicate that as the ceramic charge in the ink is increased, shrinkage is reduced and hardness and roughness increase. This indicates that increasing the ceramic charge in the printing ink leads to a denser and more compact structure in the printed samples, which results in higher hardness and roughness. The results of this research demonstrate the potential of using DIW as a viable method for fabricating alumina monoliths with desirable properties for catalysis applications. The ability to control the properties of the printed samples by adjusting the ceramic charge in the ink provides a powerful tool for tailoring the properties of the alumina monoliths to specific catalysis applications. Additionally, the study provides insight into how the ceramic charge affects the rheological properties of the printed samples, which can be useful for further optimization of the printing process and the development of new inks. To conclude, this thesis provides a comprehensive understanding of the use of DIW for printing alumina monoliths for catalysis applications and demonstrates the potential for this technology to be used in the fabrication of advanced ceramic materials for various applications.

A hetero-bimetallic alkoxide CrAl3(OiPr)12 was synthesised through metathesis of achromium(III)chloride THF complex (CrCl3 . 3 THF) and 3 KAl(OiPr)4.It was used as a single sourceprecursor to make oxide powders and films with 1:3 chromium/aluminium compositionthrough sol-gel synthesis. The final materials obtained and heat-treated samples of these wasstudied with thermogravimetric analysis (TG), X-ray diffraction (XRD) and IR spectroscopy. Itwas found that the as synthesised material was amorphous and elementally homogeneousand could be described as hydrated (oxo)-hydroxide with some loosely bonded carbonate,but no organics remaining. Above 600 oC crystallisation starts and eventually splits into twocorundum structured phases starting around 800 oC. At 1400 oC, the phases had joined backtogether in accordance with the Cr-Al-O phase diagram. Scanning Transmission ElectronMicroscopy with Electron Dispersive X-ray (STEM-EDX) tomography showed that the powderswere homogenous up to 800 oC, while after heating to 1000 oC showed chromiumenrichment in some crystals. Gracing Incidence X-ray diffraction (GI-XRD) on spin-coated filmsshowed that epitaxial growth might be achieved based on -Al2O3 (0001) substrate. The results show that the synthesis of the precursor and subsequent oxides was successful andyielded highly homogeneous gels that could be converted into oxide at ca. 600 oC andsubsequently be phase separated through spinodal decomposition at 1000 oC. The next stepwould be to try the precursor in the industrially used chemical vapour deposition (CVD)method.

Aluminum alloys have widespread use in the aerospace and maritime industries due to their high specific strength, good corrosion resistance, and low cost. Gas dynamic cold spray, cold spray for short, is a thermal spray technique that is used for in-field repair of metallic surfaces to include aluminum. To improve the wear resistance of aluminum, the metal must be reinforced with a filler. Additionally, to prevent delamination issues with cold sprayed coatings, a compositionally graded coating is required. To date, there has not been a study on the cold spray of compositionally graded, dual-reinforced aluminum metal matrix composites (Al-MMC). Al reinforced with aluminum oxide (Al2O3) and boron nitride nanotubes (BNNT) were cold-sprayed onto aircraft-grade aluminum (Al-7075) alloy. High energy ball milling was used to create coating compositions of 10, 20, and 30 vol.% Al2O3, 2 vol.% BNNTs, as well as 1 vol.% BNNT with 10 vol.% Al2O3. The different coating compositions were then graded over one another by means of cold spray and their subsequent properties of adhesion strength and wear resistance were studied. Results from these tests were also qualitatively evaluated using optical and scanning electron microscopy, as well as optical profilometry. All four graded coating compositions experienced equal or increased adhesion strength, while failing cohesively, leaving the base cold spray composition intact (i.e., still adhered to the substrate)., Office Of Naval Research, Young Investigator Program. Arlington, VA, 22217, Lieutenant Commander, United States Navy, Approved for public release. Distribution is unlimited.

As technologies like hypersonics develop, the need for advanced ceramic and composite materials becomes more urgent. These materials must have unique geometries and exceptional materials properties like high melting (or decomposition) temperature, low thermal conductivity, and high thermal shock resistance. In many cases, the only way to achieve the required geometry is by additive manufacturing. Furthermore, ceramic parts often need to be reinforced with nanoparticles to achieve the desired properties. This presents an issue since the high temperature of ceramic post-processing can degrade or even destroy these nanoparticles. This thesis sought to identify a method to sinter a 3D-printed ceramic while keeping the embedded nanoparticles intact. This work focused on hydroxyapatite [Ca10(PO4)6(OH)2] embedded with boron nitride nanotubes (BNNTs). The samples were heat treated in argon using a tube furnace. The temperature and the sintering medium were varied to determine the ideal process. After post-processing, the samples were evaluated using X-ray diffraction, scanning electron microscope analysis, and the Archimedes method. No significant trends in the density were noted throughout testing; however, it was found that samples that were sintered in a boron nitride powder medium displayed intact BNNTs post-sintering. This demonstrated that BNNTs can survive temperatures far above their oxidation point if the environment is carefully controlled., Ensign, United States Navy, Approved for public release. Distribution is unlimited.

Polymethyl methacrylate (PMMA) is a polymer material widely used in dental applications due to its excellent biocompatibility, stable physicochemical properties, easy manipulation, and low cost. The combination of biocompatible polymers and ceramics has great potential for the development of materials in the dental industry with improved mechanical properties. The addition of Al2O3 nanoparticles to PMMA can significantly improve its compressive and flexural strengths and wear resistance. Since this material is used in dental applications, it requires a high degree of product sterility. This can easily be achieved with gamma radiation treatment. Gamma radiation not only ensures the sterility of the product but can also affects changes in numerous material properties. The aim of this paper is to determine the influence of different doses of gamma radiation on the microbiological purity and changes in the mechanical and thermal properties of the PMMA/Al2O3 composite as well as the microstructural and color changes. It was found that the dose of radiation of 25 kGy is sufficient for complete sterilization of the product. This radiation dose improves the mechanical properties of the material and thermal stability. On the other hand, the dose of 25 kGy does not affect the morphology of the exposed sample and has small effect on the color change.

In the literature, a magnetic “easy” axis perpendicular to the film plane at room temperature (i.e., perpendicular magnetic anisotropy - PMA) has been reported in Ni (nickel) layers with thicknesses below ≈15 nm. In this work, we observed room-temperature PMA in a-Si/Ni/a-Si (where a-Si denotes amorphous silicon) thin film structures with nickel layer thicker than 15 nm. Two layered structures were prepared by DC/RF triode sputtering: [a-Si/Ni/a-Si] sandwich structure and [a-Si/Ni/a-Si]5 multilayer structure. The cross sectional STEM revealed uniform Ni layers with thicknesses of ≈17 nm in [a-Si/Ni/a-Si]5 – multilayer and ≈28 nm in [a-Si/Ni/a-Si] – single-layer whereas amorphous Si layers were ≈15 nm and 170 nm thick, respectively. An amorphous Ni–Si interphase was also observed in the layered structures. The XRD showed patterns for fcc-Ni with dominant (111) orientation. No other crystalline phases were observed in the XRD patterns. To our knowledge, there are no literature reports of easy magnetization direction perpendicular to the film plane at room temperature for Ni layers with thickness of ≈28 nm as presented in this work. The origin of PMA in a-Si/Ni/a-Si films may be mainly attributed to the magnetoelastic anisotropy whereas the secondary source of PMA is believed to be the surface anisotropy and magnetocrystalline anisotropy of [111] columnar grains. Amorphous silicon layers (substrate) do not have a well-defined lattice structure like crystalline substrates. Therefore, they do not induce strains in the nickel layers through lattice mismatch as in the case of epitaxy. The strains can be caused by other factors such as diffusion-induced strain, thermal expansion mismatch or intrinsic stresses during the growth process. These results could be important for applications in memory devices, sensors, logic chips, magneto-optic, magneto-electronic and spintronic devices and in fundamental research, as well as first step toward preparation and understanding of the

Today, far too many products are scrapped due to surface related issues, products with perfect function but with minor surface blemishes. The complaints are often offset by goodwill commitments from suppliers at great cost to them and delivery delays and lead time costs for customers. The reason is that the industry relies on several non-standardized classification systems for surface quality that are based on various combinations of and designations for surface defects, assessed by visual inspections at a defined distance to determine the severity of any detected surface deviations. These similar classification systems provide far too much scope for subjective and non-repeatable assessments causing communication problems between customer and producer at all stages in the supply chain. To challenge this situation, a common toolbox to communicate, describe and define surface quality should be developed, i.e. a standardisation of surface quality assessment including various effects and defects with a jointly established nomenclature and evaluation parameters. This work presents the first step of a research project bringing together 11 suppliers and OEMs along the supply chain, from the delivery of raw aluminium to finished alumina profiles included in consumer products. The final goal of the project is to develop an ‘objective classification of visual requirements’ on alumina profiles towards increased sustainability and decreased material wastage. Presented result is a common terminology with links to the process chain, surface defect geometry and visual appearance aiming at making the communication between producers and buyers of the aluminium profiles clearer and more unambiguous when it comes to specification and requirements of profile surfaces in each of the supply-chain links. Future work will add measurable parameters specifying surface quality.

Gamma-alumina (gamma-Al2O3) powder was characterized by hard x-ray photoelectron spectroscopy with an Ag L-alpha (2984.2 eV) excitation source. The sample was fixed to a stainless-steel sample holder with copper double-sided adhesive tape. Survey spectrum, C 1s, O 1s, Al 1s, Al KLL, Al 2s, and Al 2p core levels spectra were acquired., Prášek gama-aluminy (gama-Al2O3) byl charakterizován pomocí rentgenové foto-elektronové spektroskopie s využitím Ag L-alfa (2984.2 eV) excitačního zdroje. Vzorek byl připevněn k nerezovému držáku vzorků pomocí oboustranné měděné pásky. V rámci měření bylo pořízeno survey spektrum a core level spektra C 1s, O 1s, Al 1s, Al KLL, Al 2s, a Al 2p.

Pd-In2O3 catalysts are among the most promising alternatives to Cu-ZnO-Al2O3 for synthesis of CH3OH from CO2. However, the intrinsic activity and stability of In2O3 per unit mass should be increased to reduce the content of this scarcely available element and to enhance the catalyst lifetime. Herein, we propose and demonstrate a strategy for obtaining highly dispersed Pd and In2O3 nanoparticles onto an Al2O3 matrix by a one-step coprecipitation followed by calcination and activation. The activity of this catalyst is comparable with that of a Pd-In2O3 catalyst (0.52 vs 0.55 gMeOH h−1 gcat-1 at 300 °C, 30 bar, 40,800 mL h−1 gcat-1) but the In2O3 loading decreases from 98 to 12 wt% while improving the long-term stability by threefold at 30 bar. In the new Pd-In2O3-Al2O3 system, the intrinsic activity of In2O3 is highly increased both in terms of STY normalized to In specific surface area and In2O3 mass (4.32 vs 0.56 g gMeOH h−1 gIn2O3-1 of a Pd- In2O3 catalyst operating at 300 °C, 30 bar, 40,800 mL h−1 gcat-1).The combination of ex situ and in situ catalyst characterizations during reduction provides insights into the interaction between Pd and In and with the support. The enhanced activity is likely related to the close proximity of Pd and In2O3, wherein the H2 splitting activity of Pd promotes, in combination with CO2 activation over highly dispersed In2O3 particles, facile formation of CH3OH.

One of the main relevant limitations of the use of polymer-based materials in modern technological applications (e.g., electronics and optoelectronics, photonics, automotive) is their intrinsic low thermal conductivity that does not allow polymers to counteract the occurrence of the thermal degradation due to the in-service overheating phenomenon. To overcome this thermal constraint, polymer-based materials containing highly thermally conductive fillers are receiving great attention as they show an improved heat dissipation ability. However, recent studies report that a significant improvement of thermal conductivity in polymeric nanocomposites can be achieved only at high filler loadings, but this negatively affects both the mechanical behavior and density of the materials. Moreover, to achieve an efficient heat management, a continuous network of thermally conductive fillers crossing the entire composite is mandatory. In this context, interfacial phenomena play a major role as they favor the homogeneous distribution of the conductive fillers within the polymer matrix. In a previous study, it has been already verified that the surface functionalization of inorganic fillers (i.e., silica) with Polyhedral Oligosilsesquioxane (POSS) units, a family of hybrid inorganic-organic systems composed of an inorganic core of cage-like silicon oxide and several organic functional groups, significantly improved the dispersion and compatibilization of the inorganic fillers in the polymer matrix. Hence, the present contribution reports on the recent results obtained by introducing different types of alumina-based hybrid fillers decorated at the surface with either metacrylate silane or octa-methacryl-POSS units at low filler loadings in a polybutadiene polymer matrix. Even if displaying a modest intrinsic thermal conductivity, alumina can represent a valid and appealing thermally conductive filler, due to its low cost, stable chemical performance and negligible toxicity. The promi

A hetero-bimetallic alkoxide CrAl3(OiPr)12 was synthesised through metathesis of achromium(III)chloride THF complex (CrCl3 . 3 THF) and 3 KAl(OiPr)4.It was used as a single sourceprecursor to make oxide powders and films with 1:3 chromium/aluminium compositionthrough sol-gel synthesis. The final materials obtained and heat-treated samples of these wasstudied with thermogravimetric analysis (TG), X-ray diffraction (XRD) and IR spectroscopy. Itwas found that the as synthesised material was amorphous and elementally homogeneousand could be described as hydrated (oxo)-hydroxide with some loosely bonded carbonate,but no organics remaining. Above 600 oC crystallisation starts and eventually splits into twocorundum structured phases starting around 800 oC. At 1400 oC, the phases had joined backtogether in accordance with the Cr-Al-O phase diagram. Scanning Transmission ElectronMicroscopy with Electron Dispersive X-ray (STEM-EDX) tomography showed that the powderswere homogenous up to 800 oC, while after heating to 1000 oC showed chromiumenrichment in some crystals. Gracing Incidence X-ray diffraction (GI-XRD) on spin-coated filmsshowed that epitaxial growth might be achieved based on -Al2O3 (0001) substrate. The results show that the synthesis of the precursor and subsequent oxides was successful andyielded highly homogeneous gels that could be converted into oxide at ca. 600 oC andsubsequently be phase separated through spinodal decomposition at 1000 oC. The next stepwould be to try the precursor in the industrially used chemical vapour deposition (CVD)method.

The present study reports on the development and exploitation of an original filler system, based on alumina nanoparticles (NPs) and polyhedral silsesquioxane (POSS) units, namely Al2O3@POSS, where the remarkable compatibilization and thermomechanical features imparted by the silsesquioxane cage units “makes an alliance” with the enhanced thermal conductivity of Al2O3 NPs. The target is to supply rubber nanocomposites with improved heat transport and mechanical properties potentially applicable in tires formulation. The hybrid filler was prepared by a double-step approach consisting of a first silanization of Al2O3 with a methacrylate silane and subsequent grafting of OctaMethacrylPOSS through a radical reaction mediated by dicumyl peroxide as radical initiator. The material was characterized in depth in terms of structure, surface, and morphology and then used for producing, by solvent-casting technique, polybutadiene composites. The idea is to supply and test a model alumina-rubber based system which allows to better unveil the role played by the silsesquioxane units, thanks to the absence of other components (i.e. rubber polymers, vulcanization curatives and filler) usually included in real rubber formulations for tires. The comprehensive thermomechanical and morphological characterization of the nanocomposites highlighted the key role played by POSS units decorating the alumina surface, which assure both the compatibility between filler and polymer host, and an homogeneous distribution and continuous networking of the alumina NPs. This positively influences not only the heat transport, providing thermal conductive pathways that raise the thermal diffusivity even at low filler loadings (+60–70% with respect to composite enclosing bare alumina at a concentration of 15–10 v/v %) but also the storage modulus, paving the way toward a potential exploitation of Al2O3@POSS hybrid filler in large-scale formulations of rubber composites, namely those employed for tires.

Polymethyl methacrylate (PMMA) is a polymer material widely used in dental applications due to its excellent biocompatibility, stable physicochemical properties, easy manipulation, and low cost. The combination of biocompatible polymers and ceramics has great potential for the development of materials in the dental industry with improved mechanical properties. The addition of Al2O3 nanoparticles to PMMA can significantly improve its compressive and flexural strengths and wear resistance. Since this material is used in dental applications, it requires a high degree of product sterility. This can easily be achieved with gamma radiation treatment. Gamma radiation not only ensures the sterility of the product but can also affects changes in numerous material properties.The aim of this paper is to determine the influence of different doses of gamma radiation on the microbio-logical purity and changes in the mechanical and thermal properties of the PMMA/Al2O3 composite as well as the microstructural and color changes. It was found that the dose of radiation of 25 kGy is sufficient for complete sterilization of the product. This radiation dose improves the mechanical properties of the material and thermal stability. On the other hand, the dose of 25 kGy does not affect the morphology of the exposed sample and has small effect on the color change.

Polymethyl methacrylate (PMMA) is a polymer material widely used in dental applications due to its excellent biocompatibility, stable physicochemical properties, easy manipulation, and low cost. The combination of biocompatible polymers and ceramics has great potential for the development of materials in the dental industry with improved mechanical properties. The addition of Al2O3 nanoparticles to PMMA can significantly improve its compressive and flexural strengths and wear resistance. Since this material is used in dental applications, it requires a high degree of product sterility. This can easily be achieved with gamma radiation treatment. Gamma radiation not only ensures the sterility of the product but can also affects changes in numerous material properties. The aim of this paper is to determine the influence of different doses of gamma radiation on the microbiological purity and changes in the mechanical and thermal properties of the PMMA/Al2O3 composite as well as the microstructural and color changes. It was found that the dose of radiation of 25 kGy is sufficient for complete sterilization of the product. This radiation dose improves the mechanical properties of the material and thermal stability. On the other hand, the dose of 25 kGy does not affect the morphology of the exposed sample and has small effect on the color change.

I nanocompositi di gomma mostrano generalmente una scarsa conduttività termica, che può essere parzialmente migliorata dall'aggiunta di riempitivi termicamente conduttivi, ad esempio grafite, nerofumo, fibre di carbonio, particelle di ceramica o di metallo. Per raggiungere questo obiettivo sono in genere necessari concentrazioni di riempimento elevate; tuttavia, ciò altera notevolmente il comportamento meccanico e la densità di reticolazione dei materiali finali. Inoltre, i sistemi di riempimento attualmente impiegati non sono in grado di soddisfare contemporaneamente i requisiti chiave di elevata conducibilità termica e prestazioni meccaniche. In questo contesto, l'attività di ricerca del dottorato mira a progettare nuovi riempitivi adatti allo sviluppo di nanocompositi di gomma con elevata conducibilità termica e prestazioni meccaniche soddisfacenti. Sarà condotta un'indagine su diversi nano-riempitivi termicamente conduttivi, studiando in profondità le correlazioni tra struttura, morfologia, dispersione e distribuzione delle nanoparticelle nella matrice polimerica e proprietà finali dei compositi. Le migliori formulazioni verranno selezionate ed eventualmente scalate al fine di fornire reali applicazioni tecnologiche., Rubber nanocomposites generally exhibit poor thermal conductivity, which has been partially enhanced by the addition of thermally conductive fillers, i.e. graphite, carbon black, carbon fibres, ceramic or metal particles. High filler loadings are typically necessary to achieve this target; however, this dramatically alters the mechanical behaviour and the cross-linking density of the final materials. Further, the filler systems currently employed are not able to fulfil the key requirements of high thermal conductivity and remarkable performances, simultaneously. In this context, the PhD research activity aims at design novel fillers suitable for developing rubber nanocomposites with high thermal conductivity and satisfactory mechanical performances. A survey of different conductive nanofillers will be carried out, by investigating in depth the correlations between nanoparticles structure, morphology, dispersion and distribution in the polymer matrix, and final composites properties. The best formulations will be selected and possibly up-scaled in order to provide real technological applications.

Polymethyl methacrylate (PMMA) is a polymer material widely used in dental applications due to its excellent biocompatibility, stable physicochemical properties, easy manipulation, and low cost. The combination of biocompatible polymers and ceramics has great potential for the development of materials in the dental industry with improved mechanical properties. The addition of Al2O3 nanoparticles to PMMA can significantly improve its compressive and flexural strengths and wear resistance. Since this material is used in dental applications, it requires a high degree of product sterility. This can easily be achieved with gamma radiation treatment. Gamma radiation not only ensures the sterility of the product but can also affects changes in numerous material properties. The aim of this paper is to determine the influence of different doses of gamma radiation on the microbiological purity and changes in the mechanical and thermal properties of the PMMA/Al2O3 composite as well as the microstructural and color changes. It was found that the dose of radiation of 25 kGy is sufficient for complete sterilization of the product. This radiation dose improves the mechanical properties of the material and thermal stability. On the other hand, the dose of 25 kGy does not affect the morphology of the exposed sample and has small effect on the color change.

Energy transition has brought widespread attentions to the concept of coupled utilization of the geothermal and solar energy. This paper provides an integrated assessment on developing a nanofluid geothermal-photovoltaic hybrid system that addresses the multi-objective optimization and multi-criteria evaluation difficulties. The coupling system design and dispatch are optimized by considering the multiple objectives from the microscopic particles to the system. The life cycle cost, levelized cost of energy, levelized cost of heat, and the irreversibility are introduced in the optimization stage. The optimization parameters include the pipe arrangement, type of nanoparticles, and the concentration of the nanoparticles in nanofluids. A combined analysis including the energy, exergy, economy, and the environment is proposed to evaluate the various objectives and cases. The results show that the combination of 2% Al2O3 nanofluid and spiral pipe has the optimum performance. The monocrystalline solar panels with the nanofluids-aided heat pump create the least CO2 emissions (550 kg/year), the least LCOE (198.18 $), and the highest exergy efficiency. However, the LCOH (211.78 $/MWh) is still much high. Only when the electricity cost is higher than 0.11$/kWh, the proposed coupling system would show competitiveness. In summary, these results effectively prove the robustness and superiority of the hybrid system.

A novel and simple electrochemical sensor for the determination of gallic acid is presented. The alumina sample was characterized by X-ray diffraction, FTIR, and particle size distribution analysis. The carbon paste electrode was modified with alumina and used as a sensor. The performances of the sensor were assessed by cyclic voltammetry and square-wave voltammetry techniques. The oxidation of gallic acid on alumina-modified carbon paste electrode was an irreversible diffusion-controlled process. The linear relationship of peak current and concentration was obtained for the concentration range of 1.4 to 115 µM with the limit of detection of 0.8 µM. The sensor’s ability to test gallic aid in real systems was successfully tested in wine samples.

The preparation of a transparent ultra-fine-grained doped ceramics requires a homogeneous dopant distribution in a matrix. In the present work, two thermodynamical phenomena allowing the preparation of such ceramics (the dissolution of the dopant and the formation of undesirable secondary phases) were experimentally and theoretically studied. A general thermodynamic-kinetic model was developed for dopant dissolution, which was verified for the experimental conditions used in this work. The model and experiment showed that Mn3O4 dopant with overall concentration of 1 at.% and particle size of 50 nm is dissolved and homogenized in a fine-grained alumina matrix within less than one hour at a temperature of 1220 °C. For the purposes of the study of the formation of undesired secondary phase, the phase diagram of the Al2O3-Mn3O4 system was calculated using the CALPHAD approach. Detailed STEM observations combined with EDX and EELS chemical analyses showed that the data used for the calculation of the phase diagram need some modifications because they overestimate the solubility of Mn in the alumina and underestimate the solubility of Mn in the MnAl2O4 spinel.

Blast-furnace slag is one of the main by-products produced in the process of blast-furnace iron-making. Its metallurgical properties have an important impact on the smooth operation and long life of blast furnaces. In this paper, the activity of MgO in a CaO-SiO2-MgO-Al2O3 quaternary slag system was measured using the reference-slag method at 1 773–1 873 K. The effects of temperature on MgO activity and the activity coefficient of Mg in Sn of the CaO-SiO2-MgO-Al2O3 quaternary slag system were discussed. The results showed that when w(MgO)/w(Al2O3) = 0.40, B(w(CaO)/w(SiO2)) = 1.30 and w(Al2O3) = (12 %; 15 %; 18 %; 20 %), the activity of the MgO and the activity coefficient of the Mg in Sn increased with increasing temperature. With increasing temperature, the grooves in the SiO4 tetrahedral structure at wavenumbers of 800–1 200 cm–1 gradually became shallow and flat, indicating that the complex silicate structure synthesised in the form of SiO2 decreased and the activity of the MgO increased. According to the CaF2-MgO binary phase diagram, the dissolution enthalpy of MgO was calculated to be –16.409 kJ/mol. (Authors.), Blast-furnace slag is one of the main by-products produced in the process of blast-furnace iron-making. Its metallurgical properties have an important impact on the smooth operation and long life of blast furnaces. In this paper, the activity of MgO in a CaO-SiO2-MgO-Al2O3 quaternary slag system was measured using the reference-slag method at 1 773–1 873 K. The effects of temperature on MgO activity and the activity coefficient of Mg in Sn of the CaO-SiO2-MgO-Al2O3 quaternary slag system were discussed. The results showed that when w(MgO)/w(Al2O3) = 0.40, B(w(CaO)/w(SiO2)) = 1.30 and w(Al2O3) = (12 %; 15 %; 18 %; 20 %), the activity of the MgO and the activity coefficient of the Mg in Sn increased with increasing temperature. With increasing temperature, the grooves in the SiO4 tetrahedral structure at wavenumbers of 800–1 200 cm–1 gradually became shallow and flat, indicating that the complex silicate structure synthesised in the form of SiO2 decreased and the activity of the MgO increased. According to the CaF2-MgO binary phase diagram, the dissolution enthalpy of MgO was calculated to be –16.409 kJ/mol. (Authors.)

In recent years, many researchers have attempted to model the solidification process of nano-reinforced materials. In the present document, the effect on the heterogeneous solidification regime of the different sizes, shapes, and chemical compositions of nanometric ceramic particles in an AlSi10MnMg alloy is studied. This article develops a mathematical model to predict the solidification behavior of a general nano-reinforced alloy, then validates the results using experimental techniques. The main objective of the model is to minimize the costly and time-consuming experimental process of fabricating nano-reinforced alloys. The proposed model predicts the critical Gibbs energy and the critical radius required for nucleation in the heterogeneous solidification regime. Conversely, the experimental part focuses on understanding the solidification process from the differential thermal analysis (DTA) of the solidification curves. It was concluded that if subcooling is involved, cubic and pyramidal particles work better as nucleating particles in the studied alloy.

Este trabajo tiene como objetivo principal la caracterización del comportamiento mecánico de una muela de alúmina vitrificada. Nace de la necesidad por parte de los fabricantes de muelas abrasivas de obtener información que permita identificar los fenómenos de desgaste predominantes que suponen el desgaste prematuro de la herramienta durante el proceso de rectificado. Para la caracterización del material se realiza una serie de ensayos experimentales de flexión a 3 puntos. Se realiza, además, la simulación de un modelo computacional con el fin de caracterizar otras tipologías de muela sin la necesidad de llevar a cabo ensayos experimentales como los realizados. Se lleva a cabo un análisis visual a nivel microscópico de la fractura de las probetas de alúmina vitrificada ensayada con el fin de estudiar los fenómenos de desgaste predominantes., Lan honen helburu nagusia alumina beiraztatuzko harri baten portaera mekanikoa ezaugarritzea da. Harri urratzaileen fabrikatzaileek informazioa lortzeko duten beharretik sortzen da, artezketa-prozesuan erremintaren higadura goiztiarra dakarten higadura- fenomeno nagusiak identifikatzeko, eta, beraz, kostu gehigarria. Material konposatuen karakterizazio mekanikoari eta artezketa-prozesuaren modelizazioari dagokion bibliografia ondo aztertu ondoren, lanaren metodologia eta prozedura diseinatu eta egin da. Harri urratzaileen karakterizazio mekanikoa egingo da 3 puntuko flexio-saiakuntzaren bidez. Prismatikoak diren probetak aztertzen dira, eta horien konposizioa alumina beiraztatuzko harri urratzaile batena da. 2 ale urratzaile mota aztertzen dira, konbentzionalak edo polikristalinoak eta monokristalistak, harri urratzailearen propietate mekanikoetan kristal-egituraren eragina lortzeko. Azpimarratu behar da karakterizazio mekaniko hori esperimentalki zein zenbakizko simulazioaren bidez egiten dela, harri urratzaileko materialaren propietate mekanikoak zehaztu ahal izateko, etorkizunean harri-konposizio mota bakoitza esperimentalki entseatu behar izan gabe, eta zenbakizko simulazioa nahikoa izanik. Horrek harrien konfigurazio berriak prest jartzeko kostuak merkatzen ditu. Gainera, saiakuntza esperimentalen sentsorizazioa egiten da, indarra eta desplazamendua neurtuz, horietatik abiatuta hausturaren tentsioaren balioa eta materialaren modulu elastikoa lortzeko eta egitura kristalografiko motak harriaren portaera mekanikoan duen eragina aztertzeko. Bestalde, esperimentalki entseatutako probeten laginak hartzen dira eta Ikerketa Zerbitzu Orokorretako (SGIKER) espektroskopia akoplatuen laborategi berezira eramaten dira (LASPEA). Bertan, haustura-aurpegiaren ikuskapen bisuala egiten da, SEM irudiak hartuz eta EDAX analisia eginez. Horrela, maila mikroskopikoan aztertzen dira materialaren haustura nagusitzen eta errazten duten higadura-fenomenoak, bai eta horien konposizioare, The objective of this work is the characterization of the vitrified alumina grinding wheel mechanical behavior. It arises from the need of grinding wheel manufacturers to obtain information to identify the predominant wear phenomena. This information may allow to reduce the tool premature wear during the grinding process and, therefore, to reduce this additional cost. Initially, an exhaustive analysis of the state of the art in relation to the composite materials mechanical characterization and the grinding process modeling is carried out. The grinding wheels mechanical behavior characterization by performing flexural tests is obtained from of the 3-point bending test. Prismatic specimens of vitrified alumina are analyzed. Two types of abrasive grains are tested, conventional or polycrystalline and monocrystalline, in order to obtain the influence of the crystalline structure on the grinding wheel mechanical properties. This mechanical characterization is carried out both experimentally and numerically, in order to be able to determine the grinding wheel mechanical properties without having to experimentally test each type of wheel composition in the future, being sufficient its numerical simulation. This reduces the costs for the development of new wheel configurations. In addition, the sensorization of the experimental tests is carried out, measuring force and displacement, to obtain from them the value of the fracture stress and the elastic modulus of the material and to study the influence of the crystallographic structure type on the grinding wheel mechanical behavior. On the other hand, samples of the experimentally tested specimens are taken to the singular laboratory of coupled multispectroscopy (LASPEA) of the General Research Services (SGIKER). There, a visual inspection of the fracture face is carried out by SEM and EDAX analysis. In this way, the wear phenomena that predominate and favor the fracture of the material, as well as the influence of its compo

The aim of this study is development and characterization of the novel Zn-Mn/Al2O3 composite coatings. The coatings were electrodeposited with constant current density on steel, from chloride solution, without any commercial additives. The Zn−Mn alloy coatings that show high corrosion resistance, may be used in future as an alternative to cadmium coatings. However, the pure Zn and Zn alloy coatings are characterized with poor mechanical properties. Therefore, in this work the alumina particles were incorporated into the Zn-Mn matrix, and the hardness and corrosion resistance of the obtained composite coatings were tested. The mechanical and ultrasound agitation were used to achieve good dispersion of plating solution and homogeneous co-deposition of second phase. The goal was to examine the effect of the agitation type in bath, on the attributes of the deposited composite coatings. The incorporation of Al2O3 particles was enhanced when the mechanical agitation of the solution was applied. However, in case that this agitation method was used, the agglomeration of the alumina particles occurred. In contrast, when an ultrasonic agitation of the plating solution was applied, the uniform distribution of the alumina particles could be achieved. The presence of particles in the matrix, along with applied ultrasound, resulted in grain refinement and homogeneous microstructure. The Al2O3 nanoparticles incorporated in Zn-Mn alloy matrix, resulted in a significant increment in the indentation hardness and a modest increase in the coating corrosion resistance. However, the coating hardness increased with alumina addition, only in case when an ultrasonic agitation of the electrodeposition solution was used.

Pt-supported catalysts are widely used industrially for hydrogenation reactions. However, the kinetics of hydrogen activation, a critical step for any hydrogenation reaction, is still not well understood on supported Pt surfaces. Recent studies had shown that activity and selectivity vary with Pt nuclearity for the acetylene semihydrogenation reaction, increasing in activity and decreasing in selectivity while increasing the particle size from single atoms (SA) to sub-nanoclusters to nanoparticles (NP), attributing the cause of these differences on activities to the activity of H2 activation in the H/D isotopic exchange reaction. In this work, the kinetics of H2 is studied by performing the H2-D2 isotopic exchange reaction on Pt-supported catalysts with different nuclearity to extract the activation barriers and pre-exponential factors for dissociating adsorption and associative desorption (Eads, Edes, and vads, vdes respectively) from the microkinetic model derived from the Bonhoeffer Farkas mechanism, this to perform a more in-depth analysis regarding the differences in activity when comparing the H2 adsorption energy (Eads+ = Eads-Edes) and frequency factors as a function of nuclearity. Experiments were carried out in a quartz tubular fixed bed reactor coupled with a Mass Spectrometer to analyze the product gas by carrying out both, an integral analysis (from 0 to equilibrium conversion) by performing light-off experiments and differential analysis (low conversions) by performing Arrhenius experiments in the low and high coverage regions.

In recent years, many researchers have attempted to model the solidification process of nano-reinforced materials. In the present document, the effect on the heterogeneous solidification regime of the different sizes, shapes, and chemical compositions of nanometric ceramic particles in an AlSi10MnMg alloy is studied. This article develops a mathematical model to predict the solidification behavior of a general nano-reinforced alloy, then validates the results using experimental techniques. The main objective of the model is to minimize the costly and time-consuming experimental process of fabricating nano-reinforced alloys. The proposed model predicts the critical Gibbs energy and the critical radius required for nucleation in the heterogeneous solidification regime. Conversely, the experimental part focuses on understanding the solidification process from the differential thermal analysis (DTA) of the solidification curves. It was concluded that if subcooling is involved, cubic and pyramidal particles work better as nucleating particles in the studied alloy.

This paper scrutinizes the nonlinear multibubble model with considering bubble-bubble (BB) interaction in Cu−Al2O3/water hybrid nanofluid over the vapour bubble radius in Newtonian mediums. Firstly, we present the derivation of the extended Rayleigh-Plesset (ERP) equation of multibubble under the effect of BB interaction in hybrid nanofluids based on the Navier-Stokes equation. The model is formulated by the continuity equation, the ERP in the hybrid nanofluids and the relations of thermophysical features in mono and hybrid nanofluids. The ERP equation is transformed into an ordinary differential equation using the non-dimensions variables methodology, which is then solved analytically using the modified Plesset-Zwick method. In addition, the current model presents the influence of BB interactions on growth process of multibubble in Cu−Al2O3/H2O hybrid nanofluids. As a result, the impact of increasing of the number of bubbles “n” and BB interactions in a hybrid nanofluid, at n=1,2,3 on the growth process are investigated. Moreover, it is found that the growth process of multibubble dynamics in hybrid nanofluid increases when the distance between BB interaction and volume concentration decrease. The growth of multibubble dynamics in Cu−Al2O3/water hybrid nanofluid is less than in the cases of water-base fluid and Al2O3/water nanofluids. Additionally, vapour bubble radii in the current study give a good agreement and lower behavior if compared with the prior investigations. © 2022

Bauxite residue, also known as red mud (RM), from alumina production is the most promising technogenic material for the production of scandium (Sc) and other rare earth elements (REEs). Conveniently, RM is processed by using a strong acid (pH < 2.5), which lead to co‐dissolution of iron and other undesirable major components. In this work, for the first time, the possibility of selective extraction of scandium from red mud by using highly diluted acid (pH > 4) in the presence of MgSO4 was shown. The effect of temperature (40–80 °C), time (0–60 min), pH (2–5), and the MgSO4 concentration (12–36 g L−1) on Sc extraction efficiency was evaluated. It was shown that Sc extraction was higher than 63% even at a pH of 4, at 80 °C, after 1 h, while more than 80% could be extracted at a pH of 2. Iron extraction reduced from 7.7 to 0.03% by increasing the pH from 2 to 4. The kinetics study using the shrinking core model (SCM) has shown that diffusion through a product layer is a rate‐limiting stage of the process at high temperatures (>60 °C) and low pH (<3), whereas, at lower temperatures and higher pH values, the leaching rate is limited by diffusion through the liquid film. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

The preparation of a transparent ultra-fine-grained doped ceramics requires a homogeneous dopant distribution in a matrix. In the present work, two thermodynamical phenomena allowing the preparation of such ceramics (the dissolution of the dopant and the formation of undesirable secondary phases) were experimentally and theoretically studied. A general thermodynamic-kinetic model was developed for dopant dissolution, which was verified for the experimental conditions used in this work. The model and experiment showed that Mn3O4 dopant with overall concentration of 1 at.% and particle size of 50 nm is dissolved and homogenized in a fine-grained alumina matrix within less than one hour at a temperature of 1220 °C. For the purposes of the study of the formation of undesired secondary phase, the phase diagram of the Al2O3-Mn3O4 system was calculated using the CALPHAD approach. Detailed STEM observations combined with EDX and EELS chemical analyses showed that the data used for the calculation of the phase diagram need some modifications because they overestimate the solubility of Mn in the alumina and underestimate the solubility of Mn in the MnAl2O4 spinel.

The preparation of a transparent ultra-fine-grained doped ceramics requires a homogeneous dopant distribution in a matrix. In the present work, two thermodynamical phenomena allowing the preparation of such ceramics (the dissolution of the dopant and the formation of undesirable secondary phases) were experimentally and theoretically studied. A general thermodynamic-kinetic model was developed for dopant dissolution, which was verified for the experimental conditions used in this work. The model and experiment showed that Mn3O4 dopant with overall concentration of 1 at.% and particle size of 50 nm is dissolved and homogenized in a fine-grained alumina matrix within less than one hour at a temperature of 1220 °C. For the purposes of the study of the formation of undesired secondary phase, the phase diagram of the Al2O3-Mn3O4 system was calculated using the CALPHAD approach. Detailed STEM observations combined with EDX and EELS chemical analyses showed that the data used for the calculation of the phase diagram need some modifications because they overestimate the solubility of Mn in the alumina and underestimate the solubility of Mn in the MnAl2O4 spinel.

In this work, a procedure for fabricating porous alumina with the use of a carbon sacrificial template has been tested in order to optimize the fabrication of porous structures mimicking the porosity and mechanical properties of the human cortical bone. Two different sources of sacrificial carbon were used and compared, and different sintering and calcination routes were considered. The porosity of the alumina structures studied by Hg porosimetry revealed that the amount of porosity and the size and shape of the pores are still below the required values, although some acicular pores were clearly observed by SEM. Moreover, measured mechanical properties (Young’s modulus) remained below that of the bone, suggesting the need for further consolidation treatments. In summary, these encouraging results drive the optimization of future fabrication routes.

For decades, enormous investigation effort has been devoted to the fabrication of new ceramic matrix composites with enhanced mechanical properties. One of the most explored strategies is the addition of carbon allotropic phases such as carbon nanotubes, graphene, and carbon nanofibers due to their outstanding properties. In this review, the main fabrication protocols considered for the synthesis of the ceramic composites based on alumina and zirconia are shown, and their mechanical properties and the changes achieved by the addition of carbon allotropes are presented and discussed. Under particular circumstances, significant improvements in properties such as fracture toughness and wear at low temperature, or creep behavior and superplasticity at high temperature have been accomplished. Nevertheless, some critical aspects such as the homogenization of the carbon allotropes within the matrix are still lacking consolidated responses, which suggest that the potentialities of this reinforcing strategy have not yet been completely exploited. In summary, this work collects the fabrication strategies, major results, and main controversies of two decades of scientific research on the improvement of the fabrication methods and mechanical properties of ceramic matrix composites.

El desenvolupament de la tècnica de fabricació additiva (AM) ha suposat una millora en la qualitat i la complexitat de les impressions en 3D. Un dels seus principals beneficis és el poc temps i consum energètic que requereix aquesta tècnica. A més a més de la gran varietat de materials imprimibles que hi ha al mercat i la seva accessibilitat. D'aquesta manera, la fabricació additiva ha suposat un punt d'inflexió pels materials ceràmics, que destaquen per les seves propietats físiques i mecàniques, ja que permet la seva producció amb costos molt inferiors comparats amb les tecnologies convencionals. Un dels materials més utilitzats com a catalitzador és la a-Al2O3. Els dissenys que s’apliquen actualment mitjançant mètodes convencionals no permeten millorar la seva eficiència en la conversió dels productes químics. És per aquest motiu, que la impressió 3D, concretament la coneguda com a Direct Ink Writing, es perfila com una tècnica candidata per tal d’aconseguir dissenyar catalitzadors amb geometries més complexes que millorin el seu rendiment. Aquest encara pot incrementar-se més amb l’aplicació de recobriments, com és el cas de la g-Al2O3. En aquest sentit, aquest treball té com a primer objectiu aconseguir dissenyar un model que permeti obtenir mostres impreses amb les dimensions que es requereixen i determinar la temperatura de sinterització que permeti un millor comportament pel que fa a la contracció de les mostres, duresa i rugositat. El segon objectiu està relacionat amb l’aplicació d’un recobriment de a-Al2O3 a mostres impreses d’g-Al2O3. En aquest cas, el treball pretén avaluar quins són els factors que més influeixen en l’adhesió del recobriment al substrat i la temperatura de sinterització. Per fer-ho es tindran en compte: el temps d’immersió i temperatura de sinterització de les mostres recobertes., El desarrollo de la técnica de fabricación aditiva (AM) ha supuesto una mejora en la calidad y complejidad de las impresiones en 3D. Uno de sus principales beneficios es el poco tiempo y consumo energético que requiere esta técnica. Además de la gran variedad de materiales imprimibles que existen en el mercado y su accesibilidad. De esta forma, la fabricación aditiva ha supuesto un punto de inflexión por los materiales cerámicos, que destacan por sus propiedades físicas y mecánicas, ya que permite su producción con costes muy inferiores comparados con las tecnologías convencionales. Uno de los materiales más utilizados como catalizador es la a-Al2O3. Los diseños que se aplican actualmente mediante métodos convencionales no permiten mejorar su eficiencia en la conversión de productos químicos. Por este motivo, la impresión 3D, concretamente la conocida como Direct Ink Writing, se perfila como una técnica candidata para conseguir diseñar catalizadores con geometrías más complejas que mejoren su rendimiento. Éste todavía puede incrementarse más con la aplicación de recubrimientos, como es el caso de la g-Al2O3. En este sentido, este trabajo tiene como primer objetivo conseguir diseñar un modelo que permita obtener muestras impresas con las dimensiones requeridas y determinar la temperatura de sinterización que permita un mejor comportamiento en cuanto a la contracción de las muestras, dureza y rugosidad . El segundo objetivo está relacionado con la aplicación de un recubrimiento de a-Al2O3 en muestras impresas de g-Al2O3. En este caso, el trabajo pretende evaluar cuáles son los factores que más influyen en la adhesión del recubrimiento en el sustrato y la temperatura de sinterización. Para ello se tendrán en cuenta: el tiempo de inmersión y temperatura de sinterización de las muestras recubiertas., The development of the additive manufacturing (AM) technique has led to an improvement in the quality and complexity of 3D prints. One of its main benefits is the low time and energy consumption required by this technique. In addition to the wide variety of printable materials available on the market and their accessibility. Thus, additive manufacturing has been a turning point for ceramic materials, which stand out for their physical and mechanical properties, since they can be produced at much lower costs compared to conventional technologies. One of the most widely used materials as a catalyst is a-Al2O3. The designs currently applied by conventional methods do not allow improving its efficiency in chemical conversion. For this reason, 3D printing, specifically that known as Direct Ink Writing, is emerging as a candidate technique for designing catalysts with more complex geometries that improve their performance. This can be further increased with the application of coatings, as in the case of g-Al2O3. In this sense, the first objective of this work is to design a model that allows to obtain printed samples with the required dimensions and to determine the sintering temperature that allows a better performance in terms of sample shrinkage, hardness and roughness. The second objective is related to the application of a-Al2O3 coating on g-Al2O3 printed samples. In this case, the work aims to evaluate which are the factors that most influence the adhesion of the coating on the substrate and the sintering temperature. For this purpose, the immersion time and sintering temperature of the coated samples will be taken into account.