Search

ispartof: Procedia CIRP vol:113 pages:576-581 status: Published online

Functionally graded materials (FGM) present enormous potential to combine materials with distinct mechanical and thermal properties in a component via a compositional gradient throughout the body. In the present work, step graded Al2O3/NbC composites were assessed in order to obtain a FGM with high hardness and good fracture toughness. Step graded uniaxially pressed cylinders were consolidated by Spark plasma sintering (SPS) into fully dense (>99% TD) crack-free graded bodies. The designed gradient was successfully maintained after sintering and, due to the high density of FGMs, it was possible to obtain a high hardness up to 25.1 GPa and a good fracture toughness of ~5 MPa m1/2.

Mould casting and sacrificial templating techniques, common in bioceramic technology, were employed to process porous TaCx ultra-high temperature ceramics intended as novel target materials for isotope separation on-line (ISOL) facilities, aiming primarily at the production of medical radioisotopes. A feedstock of Ta4AlC3 MAX phase powder, polyamide spheres and wax was used to obtain different porous TaCx grades with bimodal pore size distributions. The ‘green’ bodies underwent de-binding and vacuum annealing to decompose the MAX phase, whereas a reference material was also produced from commercial TaC powders. The thermal stability of the porous TaCx ceramics was assessed at ISOL-relevant conditions by heating in high vacuum up to 2200 °C. The MAX phase-derived TaCx porous ceramics evolved from biphasic TaCx/α-Ta2C to single-phase TaCx at higher temperatures, due to carbon incorporation. The porous TaCx microstructure was stable at 2200 °C with a specific surface area stabilizing at ∼0.25 m2/g and thermal conductivity of 1−4 W/m K.

Directionally solidified B4C–NbB2-SiC ternary composites were prepared by a floating zone method based on crucible-free zone melting of compacted powders. The ternary eutectic composition of B4C–15NbB2–35SiC (mol.%) was characterized by a boron carbide matrix, directionally reinforced by lamella-type NbB2 and SiC phases. NbB2 and SiC inclusions about 1−2 μm in thickness were uniformly dispersed in B4C matrix of B4C–NbB2–SiC eutectic composite. The Vickers hardness and indentation fracture toughness of the B4C–NbB2–SiC ternary eutectic were 35.8 GPa and 6.4 MPa m1/2, respectively.

Objectives: New strategies for implant surface functionalization in the prevention of peri-implantitis while not compromising osseointegration are currently explored. The aim of this in vivo study was to assess the osseointegration of a titanium-silica composite implant, previously shown to enable controlled release of therapeutic concentrations of chlorhexidine, in the Göttingen mini-pig oral model. Material and methods: Three implant groups were designed: macroporous titanium implants (Ti-Porous); macroporous titanium implants infiltrated with mesoporous silica (Ti-Porous + SiO2 ); and conventional titanium implants (Ti-control). Mandibular last premolar and first molar teeth were extracted bilaterally and implants were installed. After 1 month healing, the bone in contact with the implant and the bone regeneration in the peri-implant gap was evaluated histomorphometrically. Results: Bone-to-implant contact and peri-implant bone volume for Ti-Porous versus Ti-Porous + SiO2 implants did not differ significantly, but were significantly higher in the Ti-Control group compared with Ti-Porous + SiO2 implants. Functionalization of titanium implants via infiltration of a SiO2 phase into the titanium macropores does not seem to inhibit implant osseointegration. Yet, the importance of the implant macro-design, in particular the screw thread design in a marginal gap implant surgery set-up, was emphasized by the outstanding results of the Ti-Control implant. Conclusions: Next-generation implants made of macroporous Ti infiltrated with mesoporous SiO2 do not seem to compromise the osseointegration process. Such implant functionalization may be promising for the prevention and treatment of peri-implantitis given the evidenced potential of mesoporous SiO2 for controlled drug release. ispartof: Clinical and Experimental Dental Research vol:7 issue:4 ispartof: location:United States status: published

The in-situ exothermic reactions between ZrC0.8, B4C and Si have assisted densification and allowed to obtain fully dense ZrB2-31 wt.%SiC ultra-high temperature ceramics within 6 min at 1750 °C. The use of zirconium carbide instead of metallic zirconium in the green body obviated the possibility of in-situ SHS process and allowed to apply the pressure at low temperatures. The latter provided a first densification stage just above 1050 °C. A slight carbon excess was created in the green body to preserve the carbon nanotubes. The developed reactive hot pressing route (1830 °C, 3 min, 30 MPa) has been successfully used to obtain ZrB2-SiC ceramics containing 8 vol.% of multi-wall carbon nanotubes (MW-CNT). The carbon nanotubes survived the thermal cycle and could be clearly observed in the sintered ceramics. The CNT addition improved the fracture toughness of the composite from 4.3 MPa m1/2 for ZrB2-31 wt.%SiC to 6.8 MPa m1/2 for ZrB2-29 wt.%SiC-CNT.

ispartof: MATERIALS CHARACTERIZATION vol:187 status: published

TaC ceramics with 0-0.237 wt% B addition were prepared by hot pressing. The effect of B addition on the phase constitution, interfacial chemistry/bonding and mechanical properties of the TaC ceramics were investigated. Upon B addition, the elimination of O impurity and segregation of B at grain boundaries were evidenced, accompanied by an increase in bonding strength of the TaC grains, to result in a fracture mode change from intergranular to transgranular and a reduced fracture toughness. Addition of excessive B resulted in the formation of TaB2 and C within TaC ceramics. Further, TaC-TaB2-SiC composites were prepared by Si addition. Coherent bonding between TaB2 and TaC was preserved in the TaC-TaB2-SiC composites, and residual stresses due to thermal expansion mismatch of the different phases increased flexural strength and fracture toughness of the composites.

This work investigates the compatibility of Zr2AlC MAX phase-based ceramics with liquid LBE, and proposes a mechanism to explain the observed local Zr2AlC/LBE interaction. The ceramics were exposed to oxygen-poor (C-O Funding Agencies|European Atomic Energy Communitys (Euratom) Seventh Framework Programme FP7/2007-2013 [604862]; Euratom research and training programme 2014-2018 [740415]; SCK CEN Academy for Nuclear Science and Technology (Belgium); Hercules Foundation [AKUL/1319]; MYRRHA project (SCK CEN, Belgium)

The current research explores the influence of multi-asperity abrasive particles engagement on multiphase materials. WC-Co (WC-15.6% Co) and NbC-cermet (NbC-12% Ni–10% Mo2C) hard materials were tested using a scale down single point scratch tester. Multi-asperity scratch patterns were produced by implying multiple scratches on hardmetal surface by parallel and repeated sliding. Superimposition of interactions has been implemented to study the damage evaluation of close-up parallel scratches. The abrasive particle characteristics such as size and apex angle were replicated by the diamond indenter and their influence with different applied loads [1–20 N] and sliding speeds [0.2–5 mm/s] were studied. NbC-cermet and WC-Co show a decrease in friction coefficient by 20–46% and 11–30% respectively, while the indenter tip radius changes from 200 μm to 25 μm under the same operating conditions. The wear micro-mechanism mainly changes from plastic deformation to fracture when the load and tip radius is increased. An extensive comparative study shows NbC-cermet prematurely experiences fracture dominated failure than its reference WC-Co. Moreover, tip size defect from indenter curvature geometry greatly affects the mean apex angle.

A porous pre-sintered hexagonal boron nitride powder compact was recently developed as target for the production of intense 11C beams for Positron Emission Tomography-aided hadron therapy. In a previous study, this target has been characterized regarding its operational limitations. In this work, microstructural characterization with respect to the target's grain size, porosity and pore structure, and a dedicated fractional release study from activated targets, i.e. how much 11C is extracted by a short heat treatment, is presented. Corresponding results include an average grain size of approximately 1.7(1) μm, total and open porosity of 40(5) and 21(7)%, respectively, which is mostly composed of pores with sizes ranging from 120 to 470 nm. From the measured release fraction the order of magnitude of carbon's diffusion coefficient D(1500 °C) = 10−15 − 10−14 cm2 s−1 in porous boron nitride, and a 11C extraction efficiency of about 10% at 1500 °C target temperature were estimated.

The thermal expansion of polycrystalline LaB6–MeB2 ceramic composites (where Me denotes Ti, Zr, Hf) has been studied experimentally within the temperature range from 20 °C to 1500 °C. These ceramic composites were obtained by crucible-free float zone melting method. The first temperature interval with a negative thermal elongation (NTE) (~1000–1100 °C) coincided in the LaB6–MeB2 composites and LaB6 hexaboride and was associated with La–La atomic bond softening. The hierarchy of the interatomic Me–Me–B–B bonds in the LaB6–MeB2 composite compounds, their interface and residual stresses in the LaB6 matrix and the MeB2 reinforcing phase were identified to be the source of such phenomenon. The strong covalent component of interatomic bonds compresses the crystal lattice of the composites after softening ionic and metallic components and removing residual stresses. The composites exhibited several additional NTE intervals at a higher temperature (~1000–1250°С) which were associated with the of interatomic bonds softening in the TiB2, HfB2, ZrB2 reinforcing fibers. NTE intervals determines transition of the deformation mechanism of composites from low-temperature to high-temperature one. Insignificant plasticity and brittle fracture in the area of low-temperature deformation is replaced with an increase in both plasticity and strength with temperature rise.

Dental pieces are subjected to constant friction due to grinding during mastication and mouth disorders such as bruxism. Therefore, wear resistance of Y-TZP materials used for dental prostheses must be investigated. In this work, the influence of humidity and low temperature hydrothermal degradation (LTD) in 3Y-TZP ceramics subjected to fretting has been evaluated. A 100% r.h. reduces the effects of wear due to the lubricative effect of water, compared to those at ambient r.h. COF, wear volume and damage are considerably lowered at a r.h. of 100%. Exposure to degradation conditions for 25 h increased the vulnerability to wear damage of LAVA grade Y-TZP sintered at 1400 °C since the critical grain size of 300 nm was exceeded.

Quasi phase-pure (>98 wt %) MAX phase solid solution ceramics with the (Zr,Ti)2(Al0.5,Sn0.5)C stoichiometry and variable Zr/Ti ratios were synthesized by both reactive hot pressing and pressureless sintering of ZrH2, TiH2, Al, Sn, and C powder mixtures. The influence of the different processing parameters, such as applied pressure and sintering atmosphere, on phase purity and microstructure of the produced ceramics was investigated. The addition of Sn to the (Zr,Ti)2AlC system was the key to achieve phase purity. Its effect on the crystal structure of a 211-type MAX phase was assessed by calculating the distortions of the octahedral M6C and trigonal M6A prisms due to steric effects. The M6A prismatic distortion values were found to be smaller in Sn-containing double solid solutions than in the (Zr,Ti)2AlC MAX phases. The coefficients of thermal expansion along the ⟨ a⟩ and ⟨ c⟩ directions were measured by means of Rietveld refinement of high-temperature synchrotron X-ray diffraction data of (Zr1- x,Ti x)2(Al0.5,Sn0.5)C MAX phase solid solutions with x = 0, 0.3, 0.7, and 1. The thermal expansion coefficient data of the Ti2(Al0.5,Sn0.5)C solid solution were compared with those of the Ti2AlC and Ti2SnC ternary compounds. The thermal expansion anisotropy increased in the (Zr,Ti)2(Al0.5,Sn0.5)C double solid solution MAX phases as compared to the Zr2(Al0.5,Sn0.5)C and Ti2(Al0.5,Sn0.5)C end-members. ispartof: INORGANIC CHEMISTRY vol:58 issue:10 pages:6669-6683 ispartof: location:United States status: published

© 2019, The Minerals, Metals & Materials Society. A convenient recycling loop is one of the key factors that will help to implement the thorium-based nuclear fuel cycle in the future. Herein, a study is presented concerning the recycling loop of thoria production scrap using dissolution with trifluoromethanesulfonic (triflic) acid and recovery by precipitation with oxalic acid. The kinetics of thoria powders and pellet dissolution was assessed and compared with the THOREX process. The effect of the triflic acid concentration on the recovery yield of thorium during oxalate precipitation was examined, as well as the behavior of radium during this reaction. Finally, the effect of the triflic acid concentration on the recovered thoria morphology was investigated. The triflic acid has minimal effect on the recovery yield during oxalate precipitation even in the case of high acid concentrations. In general, the solubility of radium(II) oxalate is higher than for thorium(IV) and has a maximum at a triflic acid solution of 4 M. An interesting observation was that a stable dihydrate of thorium(IV) oxalate is formed in solution of high triflic acid concentration. It might be explained by the hygroscopic medium during precipitation of the oxalate. All above mentioned observations confirm the benefits of usage of the triflic acid-based closed recycling loop for thorium dioxide-based nuclear fuel. ispartof: JOURNAL OF SUSTAINABLE METALLURGY vol:5 issue:1 pages:118-126 status: published

The possibility of additive manufacturing of ceramics has been reported widely in scientific literature. This study investigates the potential of direct inkjet printing or material jetting of 3Y-TZP ceramics by assessing the microstructure and mechanical properties of the sintered printed parts. The technique allows to print in layers of 10.5 μm, with an as-printed green density of 58 % and nearly fully sintered density of 6.03 ± 0.1 g/cm3 (99.7 % TD). The dimensions of the green and sintered parts were highly accurate but showed an anisotropic roughness in function of the building direction, mainly due to the support structures. The biaxial bending and 4-point bending strength of the sintered material was found to be substantially higher in the XY direction than in the building (Z) direction. SEM and X-Ray computed tomography revealed the presence of delamination cracks, agglomerates and spherical pores, which were identified as fracture origins on fractured surfaces. ispartof: Journal of The European Ceramic Society vol:41 issue:10 pages:5292-5306 status: Published online

Wear resistance is a fundamental property which defines the lifetime of cutting tools, but the investigation of wear performance of alternative hard materials for traditional WC-Co composites are recent. The present work evaluated the pin-on-disk wear behavior and mechanical properties, i.e., hardness and fracture toughness of spark plasma sintered Al2O3 matrix composites with additions of 5, 15, 25 or 30%wt of niobium carbide NbC. The wear resistance was observed to increase as a function of the NbC content, even though the hardness reached a plateau at 25%wt NbC. The composite behavior was compared to that of other alumina composite tool materials proving to be a promising material for applications such as ceramic cutting tools. The composition A95N5 presented the best combination of values of wear rate: 8.9 mm3/N.m, hardness equal to (17.36±1.72) GPa and fracture toughness of (3.2±0.6) MPa. m1/2.

Laser surface texturing is widely explored for modifying the surface topography of various materials and thereby tuning their optical, tribological, biological, and other surface properties. In dentistry, improved osseointegration has been observed with laser textured titanium dental implants in clinical trials. Due to several limitations of titanium materials, dental implants made of zirconia-based ceramics are now considered as one of the best alternatives. Laser surface texturing of zirconia dental implants is therefore attracting increasing attention. However, due to the brittle nature of zirconia, as well as the metastable tetragonal ZrO2 phase, laser texturing in the case of zirconia is more challenging than in the case of titanium. Understanding these challenges requires different fields of expertise, including laser engineering, materials science, and dentistry. Even though much progress was made within each field of expertise, a comprehensive analysis of all the related factors is still missing. This review paper provides thus an overview of the common challenges and current status on the use of lasers for surface texturing of zirconia-based ceramics for dental applications, including texturing of zirconia implants for improving osseointegration, texturing of zirconia abutments for reducing peri-implant inflammation, and texturing of zirconia restorations for improving restoration retention by bonding. ispartof: Materials Science & Engineering C-Materials For Biological Applications vol:123 ispartof: location:Netherlands status: Published online

TaCx (x = 0.5, 0.55, 0.6, 0.7) ceramics with 20 mol% Fe, Co or Ni addition were prepared by hot pressing TaC and Ta powder mixtures at 1800 °C. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, X-ray energy dispersive spectroscopy and selected area electron diffraction were used to investigate the constituent phases and microstructures of the composites. Vickers hardness, flexural strength and fracture toughness were measured. Intermetallic compounds Fe7Ta3, Co2Ta and Ni3Ta were formed due to reactions of Fe, Co and Ni with Ta. The remaining TaC and Ta reacted to form hexagonal Ta2C, rhombohedral ζ-Ta4C3-z or cubic TaCy depending on the overall C:Ta ratios. The microstructure of the TaC0.5–20 mol% Fe, Co, Ni compositions (where C:Ta = 0.5) were composed of intermetallics and fine anisotropic Ta2C and ζ-Ta4C3-z grains. As the C:Ta ratio increased to 0.55–0.7, the ζ-Ta4C3-z and TaCy grains were enlarged in size and equiaxed in the TaC0.55-, TaC0.6-, and TaC0.7–20 mol% Fe, Co, Ni compositions. Addition of Ni instead of Fe and Co benefitted to refine microstructures of the composites. The TaC0.5–20 mol% Fe, Co, Ni compositions had good flexural strength (580-650 MPa) and fracture toughness (9.3–9.5 MPa·m1/2) due to growth of fine lamellar grains, despite the high Ta2C content.

This work reports on sputter depositions carried out from a compound (Ti,Zr)(2)AlC target on Al2O3(0 0 0 1) substrates at temperatures ranging between 500 and 900 degrees C. Short deposition times yielded 30-40 nm-thick Al-containing (Ti,Zr)C films, whereas longer depositions yielded thicker films up to 90 nm which contained (Ti,Zr)C and intermetallics. At 900 degrees C, the longer depositions led to films that also consisted of solid solution MAX phases. Detailed transmission electron microscopy showed that both (Ti,Zr)(2)AlC and (Ti,Zr)(3)AlC2 solid solution MAX phases were formed. Moreover, this work discusses the growth mechanism of the thicker films, which started with the formation of the mixed (Ti,Zr)C carbide, followed by the nucleation and growth of aluminides, eventually leading to solid state diffusion of Al within the carbide, at the highest temperature (900 degrees C) to form the MAX phases. Funding Agencies|Swedish research council VR-RFISwedish Research Council [2017-00646_9]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [RIF14-0053]; Euratom research and training programme 2014-2018 [740415]; Stiftelsen Olle Engkvist ByggmastareSwedish Research Council [184-561]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [KAW 2015.0043]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-MatLiU) [2009 00971]; Research Foundation FlandersFWO [AKUL/1319]

In this work, the macrotexture of dense Zn produced by laser powder bed fusion (LPBF) was studied and the mechanical properties for different tensile bar orientations were measured. The compressive strength of LPBF Zn scaffolds with five different unit cells was measured for a relative density of 20-51%. In addition, the response of mesenchymal stem cells to the LPBF Zn scaffolds was studied. The elastic modulus and yield strength of dense LPBF Zn were 110.0 +/- 0.2 GPa and 78.0 +/- 0.4 MPa, respectively in the vertical and 81.0 +/- 0.4 GPa and 55.0 +/- 0.7 MPa in the horizontal direction. This could be explained by the preferential orientation of the < 0001 > direction in the building plane. For LPBF Zn scaffolds, the plateau stress for the different unit cells varied between 8 and 33 MPa for a 30% relative density. Calcein staining, lactate production and DNA measurements over a 13-day period showed that mesenchymal stem cell viability was low for Zn scaffolds. This work forms a basis for further research into the LPBF texture formation of metals with hexagonal crystal structure, guides implant designers in scaffold unit cell and relative density selection and motivates further research into the cytocompatibility of LPBF Zn., Statement of Significance, Laser powder bed fusion (LPBF) is a manufacturing technology which allows the seamless combination of porous and non-porous volumes in a metallic implant and is used in the orthopedic manufacturing industry today. The production of highly dense Zn with LPBF has been described earlier, but the mechanical properties of the resulting material have not been studied in detail yet. This study is the first to report on (i) the influence of different scanning strategies on the macrotexture of dense LPBF Zn and the resulting anisotropy of its mechanical properties, (ii) the relationship between the relative density and strength for LPBF Zn scaffolds with five different unit cells and (iii) the in vitro response of mesenchymal stem cells to these scaffolds. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

New bulk MAX phase-based ceramics were synthesized in the Ta-Hf-Al-C and Ta-Nb-Al-C systems. Specifically, (Ta1-x,Hf-x)(4)AlC3 and (Ta1-x,Nb-x)(4)AlC3 stoichiometries with x = 0.05, 0.1, 0.15, 0.2, 0.25 were targeted by reactive hot pressing of Ta2H, HfH2, NbH0.89, Al and C powder mixtures at 1550 degrees C in vacuum. The produced ceramics were characterized in terms of phase composition and microstructure by X-ray diffraction, scanning electron microscopy, electron probe microanalysis and scanning transmission electron microscopy. The investigation confirmed the existence of such M-site solid solutions with low solute concentrations, as predicted by first-principles calculations. These calculations also predicted a linear trend in lattice parameter evolution with increasing Hf concentration, in agreement with the experimental results. In order to increase the low phase purity of the produced ceramics, Sn was added to form (Ta1-x,Hf-x)(4)(Al-0.5,Sn-0.5)C-3 and (Ta1-x,Nb-x)(4)(Al-0.5,Sn-0.5)C-3 double solid solutions, thus resulting in a higher content of the 413 MAX phase compounds in the produced ceramics. Funding Agencies|SCK-CEN through the ISOL@MYRRHA project; Hercules Foundation [AKUL/1319]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation

Laser texturing of zirconia-alumina ceramics is a promising surface modification method for many applications, such as enhancing osseointegration of alumina toughened zirconia (ATZ) dental implants or improving friction behavior of zirconia toughened alumina (ZTA) hip replacement bearing components. The common problems in laser texturing of ATZ/ZTA ceramics are thermal cracking, low material removal rate (MRR), and laser-induced phase transformation (LIPT). Furthermore, the compositional variation of those ceramics will complicate these problems. In order to improve the manufacturing processability, ultrashort pulsed laser ablation behavior of ATZ/ZTA composites was investigated in this research. Single phase zirconia and alumina were found to have smaller MRRs than their composites, and this behavior was negatively correlated to the materials single-pulse laser ablation threshold. However, under multi-pulse laser irradiation, the ablation thresholds of all materials saturated to the same level, indicating that single phase materials were more sensitive to the incubation effect than their composites. This led to the MRRs of the single phase materials being reduced at larger scan speeds, while the MRRs of their composites remained independent of scan speed. It was also shown that single phase materials were less susceptible to thermal cracking than their composites under excessive heat accumulation. These results suggest that a lower scan speed is preferred for single phase materials in order to achieve a larger MRR, while a higher scan speed is beneficial for the composites for suppressing thermal cracking without compromising ablation efficiency. In addition, no LIPT was detected for zirconia dominated materials after laser ablation.

Guided by predictive theory, a new compound with chemical composition (Cr2/3Zr1/3)2AlC was synthesized by hot pressing of Cr, ZrH2, Al, and C mixtures at 1300 °C. The crystal structure is monoclinic of space group C2/c and displays in-plane chemical order in the metal layers, a so-called i-MAX phase. Quantitative chemical composition analyses confirmed that the primary phase had a (Cr2/3Zr1/3)2AlC stoichiometry, with secondary Cr2AlC, AlZrC2, and ZrC phases and a small amount of Al–Cr intermetallics. A theoretical evaluation of the (Cr2/3Zr1/3)2AlC magnetic structure was performed, indicating an antiferromagnetic ground state. Also (Cr2/3Hf1/3)2AlC, of the same structure, was predicted to be stable.

Thorium was precipitated homogeneously from a thorium nitrate solution by the thermal decomposition products of urea. The kinetics of the hydrolysis were studied at 90 and 100°C by pH measurement during the initial 5 h and the precipitation efficiencies of thorium and radium were measured over a 24 h period. Precipitation of the radium daughters was closely followed with the aim of co-precipitation of radium with thorium. The CO2 formed during urea decomposition dissolved in the solution, forming CO3 2− during the experiment upon reaching a sufficiently high pH level (>7). This allowed radium to co-precipitate partially, thus reducing the activity of the filtrate. After filtration or centrifugation, the precipitate is composed of nanocrystalline thorium dioxide (crystallite size ~10 nm), with weakly bound H2O and CO2.

This work studied the effect of adding 10 at% Fe, Co or Ni to M-Sn-C mixtures with M = Ti, Zr or Hf on MAX phases synthesis by reactive spark plasma sintering. Adding Fe, Co or Ni assisted the formation of 312 MAX phases, i.e., Ti3SnC2, Zr3SnC2 and Hf3SnC2, while their 211 counterparts Ti2SnC, Zr2SnC and Hf2SnC formed in the undoped M-Sn-C mixtures. The lattice parameters of the newly synthesized Zr3SnC2 and Hf3SnC2 MAX phases were determined by X-ray diffraction. Binary MC carbides were present in all ceramics, whereas the formation of intermetallics was largely determined by the selected additive. The effect of adding Fe, Co or Ni on the MAX phase crystal structure and the microstructure of the produced ceramics was investigated in greater detail for the case of M = Zr. A mechanism is herein proposed for the formation of M3SnC2 MAX phases.

We precipitated thorium in a two-step process with ammonia and carbonates. In contrast to single step ammonia or carbonate precipitation, the two-step process precipitates >99.9% of Th and removes >99.5% of Ra alongside. Filterability is strongly affected by pH variations in the ammonia step, and under well-controlled conditions, the precipitated ThO2 filters quickly and calcines to crystalline ThO2 at low temperatures. As-precipitated ThO2 contains significant quantities of adsorbed H2O and CO2, which are removed during calcination. The calcination temperature greatly affects the green density of produced pellets, but for all calcination temperatures investigated, the sintered densities are in excess of 96% with grain sizes within the range applied for nuclear fuels at 10–16 μm.

Thorium oxalate is easy to prepare, but the derived oxide powders retain the platelet morphology of the primary oxalate. This negatively impacts packing and sintering. If powder milling is to be avoided, powder synthesis needs to be optimized. That is the goal of this paper, where different precipitation strategies were used and their effect on powder characteristics and pellet synthesis was investigated. Oxalates prepared by adding a thorium nitrate solution to an oxalic acid solution proved most promising. Further optimizing of the calcination temperature revealed that with increasing calcination temperature the packing density improved significantly. This came at the cost of decreased early stage sintering and a higher frequency of end-capping during compaction. The calcination temperature at which the highest final density can be reached was dependent on the sintering cycle. Furthermore, the ThO2 powders had less surface area and thus adsorbed less gases during storage when calcined at higher temperatures.

Advanced biomaterials that are capable of guiding robust bone regeneration are highly demanded for translational therapy of bone defects or bone augmentation in clinics. One of the strategic approaches is to produce tissue engineering (TE) constructs that mediate bone regeneration by recapitulating the natural bone formation or healing process. In this study, we aimed at producing devitalized mineralized carriers with augmented bone forming capacity via a modified culture protocol (i.e., culture conditions with high calcium and/or phosphate concentrations) that first promotes cell growth and, subsequently, mineralized extracellular matrix (ECM) deposition by human periosteum-derived osteoprogenitor cells (hPDCs) on additive manufactured three-dimensional (3D) porous titanium (Ti)-based scaffolds. Qualitative and quantitative analysis was performed to characterize the physicochemical properties of the produced devitalized mineralized carriers, as well as their effects as carriers on in vitro cell growth and osteochondrogenic differentiation of hPDCs under a perfusion bioreactor culture set-up. The results showed that the modified culture protocol was useful to produce devitalized mineralized carriers with different amount, distribution, composition, and morphology of mineralized matrix that resembled hydroxyapatite, and exhibited different Ca2+ release kinetics, distinct human bone morphogenetic protein (hBMP)-2, human vascular endothelial growth factor (hVEGF) proteins, and collagen contents. The produced devitalized mineralized carriers supported 3D growth of hPDCs, with minor osteochondrogenic differentiation effects under the perfusion bioreactor culture condition. Subcutaneous implantation of hPDC-seeded devitalized mineralized carriers in athymic nude rats showed nearly five-fold augmentation in the ectopic bone-forming capacity, with no bone induction obtained for unseeded, devitalized mineralized carriers and plain Ti scaffolds. Implantation of devitalized mineralized carriers in critical-sized calvarial defects resulted in encouraging defect bridging as compared with limited defect bridging by plain Ti scaffolds or in empty defects. This defect bridging was not enhanced by implanting hPDC-seeded devitalized mineralized carriers. In conclusion, the investigated modified culture protocol was useful to produce devitalized mineralized carriers with augmented bone-forming capacity, which potentially could aid bone repair or augmentation in clinics.

[EN] The fretting wear behavior of self-mated Y-TZP dental materials obtained by non-conventional microwave and conventional sintering has been investigated. Two 3Y-TZP materials, a widely utilized commercial dental ceramic (LAVA) and a lab-prepared 3Y-TZP powder based equivalent have been assessed. Relative density and mechanical properties as well as the grain size variations upon sintering have been evaluated. After exposure to selected gross slip regime fretting wear conditions, the wear tracks have been characterized allowing the measurement of the coefficient of friction, track profiles, and pit features. The results indicate thaT microwave sintering results in a similar fretting wear behavior as observed for conventional sintered 3YTZP, since the measured volumetric wear loss is of a comparable order of magnitude. Regarding the influence of the grain size, the analysis revealed that a large grain size (>300 nm) results in an increased wear volume and that a higher resistance to fretting wear is constrained to a midrange particle size. Since the fracture toughness of all investigated ceramic grades was comparable, the influence of the fracture toughness could not be assessed. Abrasive grooving, delamination and microcracking have been identified as major wear mechanisms inside the wear tracks for both conventional and microwave sintered 3Y-TZP. In general, microwave sintering can provide 3Y-TZP dental materials with a comparable fretting wear resistance as that observed for conventional sintering using lower dwell sintering temperatures and a shorter processing time., Spanish Ministry of Economy and Competitiveness MINECO, Grant/Award Number: MAT2015-67586-C3-R; Generalitat Valenciana, Grant/Award Number: GRI-SOLIA/2013/035, GV/2014/009; MINECO, Grant/Award Number: IJCI-2014-19839.

We present here a study of the mechanical behavior of cellular Zn and Zn1.5Mg with densities between 11.9 and 24.5%, produced by replication processing using NaCl as a spaceholder. Cellular Zn and Zn1.5Mg deform homogeneously during quasi-static compression. The plateau stress scales with the relative density according to a power-law of exponent of 2.8 for both materials; recorded values are 6.0 ± 0.6 MPa for cellular Zn of relative density 24% and 10.0 ± 0.5 MPa for cellular Zn1.5Mg of relative density 23%. In ambient-temperature creep tests with loads up to 50% of the plateau stress, after more than 70 h deformation remains negligible (in the range of experimental error). This observation, coupled with other measured mechanical properties, indicates that replicated cellular Zn and Zn1.5Mg are viable materials in the context of their application as a low load-bearing implant material. ispartof: Materials Characterization vol:157 status: published

© 2019 The precursor of all-silica COK-14 zeolite (OKO topology) with interrupted framework was subjected to wet ball milling in the presence of aluminum isopropoxide. Alumination and particle size reduction of the zeolite crystals was combined in this way. Wet ball milling resulted in fragmentation of the platelet-shape COK-14 crystals while preserving crystallinity. 27 Al NMR spectroscopy of the fully condensed COK-14 zeolite, obtained by calcination of milled -COK-14 precursor, confirmed the incorporation of tetrahedrally coordinated Al atoms in the framework. The creation of Brønsted acid sites was confirmed by pyridine adsorption. Loaded with platinum, the sample showed ideal bifunctional catalytic behavior in hydroisomerization and hydrocracking of n-decane model alkane compound. Aluminum incorporation by milling is an alternative to the atomic layer deposition (ALD) process using trimethylaluminum and to thermal alumination. Wet ball milling in presence of aluminum isopropoxide shows great potential for making siliceous zeolites catalytically active. ispartof: Catalysis Today vol:334 pages:3-12 ispartof: location:BELGIUM, Univ Catholique Louvain, Louvain la Neuve status: published

OBJECTIVES: For the use of partially stabilized zirconia (PSZ) as high-translucent zirconia, the importance of cubic phase (c-ZrO2) is commonly emphasized without much attention for the remaining tetragonal phase (t-ZrO2). The aim is to understand whether the crystal structure and microstructure of t-ZrO2 have paramount influences on the properties of PSZ. METHODS: Two grades of 5mol% yttria-stabilized PSZ ceramics were prepared by different processing routes. A 5mol % yttria co-precipitated zirconia (T5Y) was compared with a 3 and 8mol% yttria-stabilized powder mixture grade with a bimodal grain size distribution (B5Y). The phase composition and lattice parameters were studied with x-ray diffraction (XRD) and Rietveld analysis. Mechanical properties were compared in terms of hardness, toughness and biaxial bending strength with Weibull analysis. Their translucency and aging stability were also characterized, and the microstructure before and after aging were followed by scanning electron microscopy (SEM). RESULTS: T5Y and B5Y having similar phase composition (about 40% t- and 60% c-ZrO2) showed the same basic properties (density, hardness and toughness), but the lattice parameters of t-ZrO2 and the concomitant microstructure were completely different. The t-ZrO2 phase in T5Y had a higher yttria content and a lower tetragonality (c/a) of 1.0126±0.0002, whereas the t-ZrO2 phase in B5Y was comparable to that in conventional 3Y-TZPs with a tetragonality of 1.0153±0.0002. Consequently, B5Y showed a lower strength with lower Weibull modulus, being less translucent and more aging susceptible as compared to T5Y. The translucency and aging susceptibility of B5Y were even comparable to those of conventional 3Y-TZP. SIGNIFICANCE: Not only the phase composition with high cubic phase content but also the lattice parameters and the yttria content in the remaining t-ZrO2 played a determinant role for PSZs to be used as 'high-translucent' zirconia. ispartof: DENTAL MATERIALS vol:36 issue:4 pages:491-500 ispartof: location:England status: published

The present work describes a synthesis route for bulk Ta4AlC3 MAX phase ceramics with high phase purity. Pressure assisted densification was achieved by both hot pressing and spark plasma sintering of tantalum hydride, aluminium and carbon powder mixtures in the 1200-1650{\deg}C range. The phases present and microstructures were characterized as a function of the sintering temperature by X-ray diffraction and scanning electron microscopy. High-purity alfa-Ta4AlC3 was obtained by hot pressing at 1500{\deg}C for 30 min at 30 MPa. The beta-Ta4AlC3 allotrope was observed in the samples produced by SPS. The elastic modulus, Vickers hardness, flexural strength and single-edge V-notch beam fracture toughness of the high-purity bulk sample were determined. The thermal decomposition of Ta4AlC3 into tantalum carbide and Al vapor in high vacuum at 1200{\deg}C and 1250{\deg}C was also investigated, as a possible processing route to produce porous tantalum carbide components., Comment: 16 pages, 9 figures, 3 tables

Selective laser melting of pure copper is challenging because of its high optical reflectivity and thermal conductivity. Accordingly, the surface of pure copper powder was modified by oxidation to enhance the optical absorption. The powder with improved optical absorption facilitated the production of crack‐free and dense copper parts at relatively lower laser energy density in both argon and nitrogen atmosphere. The microstructural analysis demonstrated the presence of stable melt tracks without obvious porosity. A very high electrical conductivity of ~89% of the international annealed copper standard, the hardness of ~93 HV, a tensile strength of ~270 MPa, and ductility of ~28% were achieved in the as‐built condition. ispartof: Material Design & Processing Communications status: accepted