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Nanocrystalline mullite has been synthesized by sintering of absorbed monophasic aluminosilicate precursors into cotton wool and filter paper cellulosic structures. Effects of molybdenum and tungsten doping on template mediated mullite at 1200°C and 1400°C have been investigated using differential thermal analysis ( DTA), X-ray diffraction analysis ( XRD), Fourier transform infrared spectroscopy ( FTIR) and field emission scanning electron micrographs ( FESEM). Microstructures of the sintered samples revealed successful replication of cellulosic structure with the formation of dense mullite phases having grain diameter in the range of 50-80 nm. Strong photoluminescence emissions in the UV and visible regions result from the oxygen vacancies and Al-O bonds present in mullite structures. [ABSTRACT FROM AUTHOR]

Ceramic aerogels are attractive for their promising applications in thermal insulation, ultrafiltration, catalysis, and many other areas, owing to their high porosity, low density, high specific surface area, low thermal conductivity, and thermal stability. However, the practical applications of conventional ceramic aerogels are usually impeded by brittleness. Resilient ceramic aerogels overcame the brittleness of conventional ceramic aerogels and realized reversible compressibility, but they usually show brittleness under tensile stress and limited load‐bearing ability. In this short review paper, we reviewed the strategies to modify the mechanical properties of resilient ceramic aerogel. These strategies were achieved through tuning the deformation and moving ability of the nanowire building blocks and the deformation resistance provided by the aerogel architecture. Perspectives for further modifying the mechanical properties of resilient ceramic aerogel are also discussed. [ABSTRACT FROM AUTHOR]

In this paper, synthesis and sintering of MAX phases in the Zr–Al–C system is described. Different mixtures of initial Zr/Al/C and Zr/Al/ZrC powders were used to synthesize the MAX phases of Zr2AlC and Zr3AlC2 compositions by a combined method (high‐temperature sintering followed by spark plasma sintering [SPS]). The highest content of the Zr3AlC2 MAX‐phase was obtained using initial Zr/Al/ZrC powders in a component ratio of 1:1.5:2—51.1 vol.%. The optimal temperature for the synthesis of a material based on the Zr2AlC MAX phase is 1525°C, and a material based on Zr3AlC2 is 1575°C. During subsequent SPS at a temperature of 1500°C, a pressure of 50 MPa, within 5 min, it was obtained a material containing up to 71.1 vol.% Zr3AlC2. The relative density of the samples synthesized and consolidated by the SPS method reaches 98.9%. The structure of the obtained synthesized MAX materials includes elongated grains of the composition Zr2AlC and Zr3AlC2, which determines their high strength. The influence of the sintering time and temperature on the formation of the MAX phase of Zr3AlC2 from the initial powders of Zr/Al/ZrC is shown. Zirconium carbide, as an intermediate phase, is always present in the final products. Due to the large evaporation of aluminum, the ZrAl2 phase is also present in the synthesis products. An excess of aluminum contributes to the greatest formation of the Zr2AlC and Zr3AlC2 phases during the combined synthesis. [ABSTRACT FROM AUTHOR]

A novel class of preceramic paper may serve as a preform to manufacture lightweight as well as multilayer ceramic products. In this article, we discuss the formation, microstructure, and properties of preceramic papers and their conversion into ceramic materials. Oxide as well nonoxide ceramics were processed into single-sheet, corrugated structures, and multilayer ceramics. A high filler loading and uniform distribution of ceramic fillers involves control of colloidal surface interaction including electrostatic, electrosteric, and mechanical retention. Sintering of an oxide-loaded preceramic paper in air results in highly porous products, with the porosity shape and distribution templated by the pulp fiber used in papermaking. In the case of carbide-loaded paper, dense composite materials are obtained by reactive infiltration processing. Anisotropic properties of machine-fabricated preceramic paper and bonding interfaces in multilayer stacks give rise to anisotropic mechanical properties of the resulting ceramic composites. Noncatastrophic failure was observed when tensile loading stress was applied parallel to the interfaces (in-plane loading). Applying well-established paper processing technologies, including laminated object manufacturing, ceramic structures of complex shape and size can easily be processed, offering a high potential for economical manufacturing. [ABSTRACT FROM AUTHOR]

The brittleness of Si3N4 ceramics has always limited its wide application. In this paper, Si3N4 ceramics were prepared based on foam. Combining the unique honeycomb structure of the ceramic foams and the self‐toughening mechanism of Si3N4, the strengthening and toughening of Si3N4 ceramics can be further achieved by adjusting the microstructure of Si3N4 ceramic foams. The powder particles are self‐assembled by particle‐stabilized foaming to form a foam body with a honeycomb structure. It was pretreated at different temperatures (1450–1750°C). The microstructure evolution of foamed ceramics at different pretreatment temperatures and the conversion rate of α‐Si3N4 to β‐Si3N4 at different pretreatment temperatures were explored. Then the foamed ceramics with different microstructures are hot‐press sintered to prepare Si3N4 dense ceramics. The effects of different microstructures of foamed ceramics on the strength and toughness of Si3N4 ceramics were analyzed. The experimental results show that the relative density of Si3N4 ceramics prepared at a particle pretreatment temperature of 1500°C is 97.8%, and its flexural strength and fracture toughness are relatively the highest, which are 1089 ± 60 MPa and 12.9 ± 1.3 MPa m1/2, respectively. Compared with the traditional powder hot‐pressing sintering, the improvement is 21% and 33%, respectively. It is shown that this method of preparing Si3N4 ceramics based on foam has the potential to strengthen and toughen Si3N4 ceramics. [ABSTRACT FROM AUTHOR]

This paper investigates the phase evolution and pulverization mechanism of a self‐pulverizing carbonatable clinker (SPCC) with a variety of raw material compositions. The particle size, mineral phases, and microstructure of SPCC, produced by sintering at 1400°C for 3 h, were systematically studied by laser particle size testing, XRD/QXRD and SEM/EDS. Results show that clinkers sintered by raw materials with low‐Ca/low‐Al (Ca/Si < 1.6; Al2O3 < 10 wt.%) or high‐Ca/medium‐Al (Ca/Si > 2.6; Al2O3 ≈ 10 wt.%) are non‐pulverized after cooling. The mineral phases of C2AS, CA, and C12A7 are considered to facilitate clinker pulverization at low γ‐C2S contents. With the increase of Al2O3 content in raw materials, SPCC is refined in particle size, accompanied by the significant decrease in the content of calcium silicates. Based on the results, guidelines for producing SPCC are proposed. [ABSTRACT FROM AUTHOR]

This paper introduces a new method for adjusting the particle size of ZrO2 powder through the electric field effect of tourmaline. The 3 mol% yttria‐stabilized ZrO2 (3YSZ) powder was prepared by using ZrOCl2∙8H2O, YCl3∙6H2O, NaOH, and nano‐tourmaline powder as raw materials through direct precipitation. The powder was characterized with thermogravimetric‐differential scanning calorimeter, X‐ray diffraction, Brunauere‐Emmette‐Teller, Fourier transform infrared, scanning electron microscope, and transmission electron microscope, and the mechanism of tourmaline in the process of powder preparation was also discussed. Findings demonstrate that the electric field generated by spontaneous polarization of tourmaline can control the size of ZrO2 crystal grains, improve the dispersibility of the powder, and promote the stability of ZrO2 in the tetragonal phase. When the electric intensity of tourmaline is 9.02 × 106 V/m, and the addition amount is 2.5 vol%, tourmaline/3YSZ powders are mainly tetragonal phase, and the grain size is the smallest, with an average crystallite size of 19 nm. Then the mechanical properties of tourmaline/3YSZ ceramics were tested. Compared with 3YSZ ceramics without tourmaline, the flexural strength and fracture toughness were improved by 39.5% and 35.8%. [ABSTRACT FROM AUTHOR]

Glass‐ceramics from the studied system are able to precipitate a crystalline phase with an anomalous and low coefficient of thermal expansion. Besides the crystalline phase called LEAZit (Low Expansion Alkaline Earth Zinc Silicate), other phases appear within those glass‐ceramics. In order to understand the thermal expansion behavior of the whole material, the phase content has to be known as a function of the composition and the chosen heat treatment. In this paper, a glass with the molar composition 5 BaO · 12 SrO · 35 ZnO · 46.2 SiO2 · 1.5 Sb2O3 · 0.3 Ag is studied using X‐ray tomography. With this method, the phase content can be studied in detail together with the microstructure. An ex‐situ workflow was used to study one and the same sample after different heat treatments, which makes it possible to characterize the structures (crystalline phase, residual matrix, and porosity) inside the sample in a nondestructive way. The size of the different phases was characterized with a strut thickness analysis of the three‐dimensional datasets. The tomographic results are supported by results from X‐ray diffraction as well as scanning electron microscopy in combination with elemental analysis. [ABSTRACT FROM AUTHOR]

It is thought that the sintering of high‐entropy (HE) ceramics is generally more difficult when compared to that of the corresponding single‐component ceramics. In this paper, we report a novel approach to densify the HE carbide ceramics at relatively low temperatures with a small amount of silicon. Reactive spark plasma sintering (SPS) was used to densify the ceramics using powders of HE carbide and silicon as starting materials. Dense ceramics can be obtained at 1600 ‐1700°C. X‐ray diffraction analysis reveals that only non‐stoichiometric HE carbide phase with carbon vacancy and SiC phase exist in the obtained ceramics. The in‐situ formed SiC phase inherits the morphology of the starting silicon powder owing to the slower diffusion of silicon atoms compared to that of the carbon atoms in HE carbide phase. The mechanical properties of the prepared ceramics were preliminarily studied. [ABSTRACT FROM AUTHOR]

In this paper, we report the synthesis and characterization of composites of bioplastics (Poly‐lactic Acid (PLA), Polyhydroxyalkaonate (PHA), and PLA‐PHA blends) filled with dried grains with solubles (DDGS) and hydroxyapatite (HAP) by using a solvent casting process. Detailed microstructural, thermal, and mechanical characterization is presented in the text. At low concentrations of HAP (5–10 vol%) and DDGS (5–31 vol%) additions, the bioplastic films had mechanical integrity, but the ultimate tensile strength (UTS) decreased after the addition of DDGS and HAP reinforcements due to poor adhesion between the bioplastics and fillers. In the intermediate concentration, pre‐pregnated chips of DDGS (31–51 vol%)‐bioplastics and HAP (30–50 vol%)‐bioplastics with dichloromethane (DCM) were partially dried and then hot‐pressed to produce bulk samples (HPC‐process). The addition of bioplastics improved the plasticity of DDGS‐bioplastics composites. The HAP‐bioplastics composites showed polymer dependent response, for example the ultimate compressive strength (UCS) of 50%HAP‐PLA, and 30%HAP‐PLA were 77.6 ± 10.2 and 97.7 ± 5.9 MPa, respectively which are comparable to bone. The DDGS additions increased the hydrophilicity of PLA, PHA, and PLA‐PHA blend. For comparison, HAP increased the hydrophilicity of PHA and PLA‐PHA blends. At higher concentration (bioplastics with 70 vol% HAP additions), the films converted into microencapsulated HAP particles with bioplastics by a simple milling process thus eliminating the need for emulsions and/or surfactants during the microencapsulation process. [ABSTRACT FROM AUTHOR]

In this paper, the effect of phase transformation on microstructure evolution and mechanical behaviors of mullite fibers was well investigated from 1100 to 1300°C. In such a narrow temperature range, the microstructure and mechanical properties showed great changes, which were significant to be studied. The temperature of the alumina phase transformation started at below 1100°C. The main phases in fibers were γ‐Al2O3 and δ‐Al2O3 with amorphous SiO2 at 1150°C. The stable α‐Al2O3 formed at 1200°C. Then the mullite phase reaction occurred. As the alumina phase reaction took place, the tensile strength increased with the increasing temperature. In particular, the filaments achieved the highest strength at 1150°C with 1.98 ± 0.17 GPa, and the Young's modulus was 163.08 ± 4.69 GPa, showing excellent mechanical performance. After 1200°C, the mullite phase reaction went on with the crystallization of orthorhombic mullite. The density of surface defects increased rapidly due to thermal grooving, which led to mechanical properties degrade sharply. The strength at 1200°C was 1.01 ± 0.15 GPa with a strength retention of 63.13%, and the Young's modulus was 184.14 ± 10.36 GPa. While at 1300°C, the tensile strength was 0.64 ± 0.14 GPa with a strength retention of only 40.00%. [ABSTRACT FROM AUTHOR]

This paper reports on an investigation into the pore structure characteristics of MgO–SiO2 binders. Paste specimens were prepared using two MgO/SiO2 ratios (1 and 1.5), two silica sources (Silica fume‐SF and Metakaolin‐MK), two water to binder ratios (0.5 and 0.6) and compared to a portland cement (PC) control mix. Mercury intrusion porosimetry was used to understand the evolution of pore structural features of the binder with hydration period. A continued reduction in porosity and refinement of pores was observed with the progress in hydration irrespective of the type of the silica source or the initial MgO/SiO2 ratio. The MgO–MK mixes exhibited a finer and denser microstructure as compared to the equivalent MgO–SF mixes. The formation of hydrotalcite in addition to M‐S‐H in MgO–MK mixes was postulated to be the primary reason for the difference in microstructural characteristics, compared to MgO–SF mixes. The space‐filling capacity of hydration products of MgO–MK binder was found to be better than PC. [ABSTRACT FROM AUTHOR]

Extinction ratio (ER) is one of the important parameters to characterize the polarization‐maintaining (PM) performance of the fiber. In this paper, we report the preparation and properties of a novel chalcogenide microstructure fiber with a high ER. We fabricate a preform using a peeled‐off extrusion method. The core and cladding material of the fiber are Ge9As23Se68 and Ge10As22Se68. The preform was drawn into a fiber with an average ER of −17.08 dB. The loss of the fiber is less than 2 dB over 5.20–8.55 μm, and the minimum loss of the fiber is 0.57 dB/m at 6.2 μm. Moreover, a flat mid‐infrared supercontinuum spectrum spanning from 1.53 to 12.50 μm is generated by pumping an 18‐cm‐long PM fiber for the first time. [ABSTRACT FROM AUTHOR]

In this paper, C/SiC‐diamond composites were obtained by chemical vapor infiltration (CVI) and reactive melt infiltration (RMI), and the effects of phenolic resin contents on the microstructures and properties of as‐obtained C/SiC‐diamond composites were studied. The results suggested a significant influence of phenolic resin contents on the pore structure of the composites before reactive melt infiltration (RMI), as well as phase composition and density of the matrix after RMI. The mechanical properties of composites were shown to correlate with the threshold effect of phenolic resin. Sample R5 prepared with high phenolic resin contents displayed significantly declined mechanical properties. On the other hand, adjustment of the phenolic resin content yielded samples with maximum room temperature thermal conductivity reaching 14.75 W/(m·K). The theoretical thermal conductivity of the composites calculated by the Hasselman‐Johnson (H‐J) theoretical model was estimated to 24.52 W/(m·K). Overall, the increase in phenolic resin content led to unreacted diamond‐C regions and the formation of substantial porosity. These features reduced the thermal conductivity of the resulting C/SiC‐diamond composites. [ABSTRACT FROM AUTHOR]

Magnesium potassium phosphate cement (MKPC) is a class of chemically bonded ceramic for special engineering applications. The selection of mass ratios of MgO‐to‐KH2PO4 (M/P) and water‐to‐cement (W/C) is an important aspect for formulating MKPC paste. This paper analyzed the stoichiometry of the primary reaction of MKPC and investigated the effect of W/C (0.14–0.40) on paste microstructure and properties at different M/P (1.5–4). At high M/P, low W/C was sufficient to complete the hydration of KH2PO4 and higher W/C yielded looser microstructure, dictating that properties of high M/P pastes were monotonic functions of W/C. However, a clear W/C threshold effect was found in medium M/P pastes at both micro‐ and macro‐levels. Low W/C below stoichiometric value suppressed the formation of K‐struvite and favored the presence of an amorphous phase, leading to intense early shrinkage, low early compressive strength, and poor long‐term water resistance. The increase in W/C above stoichiometric value resulted in the segregation of excess water and thus to porous structure, with detrimental effects on dimensional stability and strength. The micro–macro analysis highlighted the importance of stoichiometric water amount in the optimal design of MKPC. [ABSTRACT FROM AUTHOR]

Barium cerate (BaCeO3) is one of the possible additions to bulk YBa2Cu3O7 single‐grain superconductors to suppress the growth of Y2BaCuO5 (Y211) particles. This paper investigates the synthesis of barium cerate powder and its use in YBa2Cu3O7 bulk superconductors. Crystalline barium cerate was synthesized by solid‐state reaction, by co‐precipitation of oxalates and by sol‐gel method. Final calcination was held in air or in vacuum. It is shown that the most efficient in refining Y211 is nanocrystalline barium cerate prepared by sol‐gel method calcined in vacuum. The effective refinement of Y211 particles occurred over the entire interval of nanocrystalline BaCeO3 addition from 0.38 to 1.90 wt%. The optimal concentration of nanosize barium cerate was determined, microstructure and superconducting properties were characterized. The effect of Y211 content on trapped field in YBCO bulks with addition of nanocrystalline barium cerate is shown. [ABSTRACT FROM AUTHOR]

Long‐term chemical durability of borosilicate glasses that makes them a widely accepted form of nuclear waste disposal is achieved through the formation of a porous aluminosilicate gel layer that provides passivity and limits the transport of water to the reaction front. Detailed understanding of the porous silicate gel layer is thus critical in elucidating the corrosion mechanism of these glasses and to design of new glass composition for waste immobilization and other applications. In this paper, we use the diffuse charge reactive potential to generate porous aluminosilicate glass structures with compositions equivalent to the gel layers formed at the glass‐water interface with an aim to understand the processing condition on the microstructure and atomic structure of these systems. We demonstrate the use of the charge scaling techniques is an effective approach to generate these porous structures with controllable pore mophologies. After initial validation of the potentials and calcium aluminosilicate glass structures using neutron diffraction, we created gel structures with compositions similar to well‐known model nuclear waste borosilicate glasses. The porosities and the pore size distribution bear a strong correlation to the processing temperature, as well as to the local atomic structure. Thus, by controlling the processing parameters, the generated porous structures can be customized to closely resemble gel structures due to borosilicate glass corrosion. These results provide insights of the micro‐ and atomic structure features of the porous aluminosilicate glasses and on the optimal procedure to generate porous structures that can be comparable to experimentally observed gel layer structures thus to elaborate on the correlations between the structure and phenomena in glass‐water interactions. [ABSTRACT FROM AUTHOR]

In zirconia‐based shape memory ceramics (SMCs), cracking during the martensitic transformation can be avoided in structures that reduce the relative presence of grain boundaries where high levels of transformation mismatch stress develop. This approach has been well established in single crystals, but only for sample sizes below about 5 microns. In this paper, we extend the strategy of eliminating grain boundaries to bulk specimen scales by fabricating mm‐scale single crystal SMCs via cold crucible induction melting. For 1.5 and 2.0 mol% Y2O3‐ZrO2, we study the cyclic martensitic transformation of both single crystal and polycrystal structures. Whereas single crystals have very repeatable transformation behavior in terms of hysteresis and strain amplitude, polycrystals degrade dramatically as they accumulate cracking damage with repeated cycling. As the polycrystal evolves from a pellet to granular packing of loose single crystals/grains, the energy dissipation converges with that of the single‐crystal structure, and the energy spent on cracking throughout that process is captured by calorimetry analysis. These results verify that grain boundaries play a key role in damage evolution during martensitic transformation and that microstructural control can extend the size‐scale of viable single crystal or oligocrystal SMCs from the micro‐ to the millimeter scale. [ABSTRACT FROM AUTHOR]

A theoretical and experimental approach was applied to investigate phase relations in a system containing calcium carbonate and different ammonium phosphate solutions. Using laboratory experiments and thermodynamic modeling, this paper provides an insight into the formation of stable phase assemblages in the calcium carbonate and mono‐, di‐, triammonium phosphate aqueous system. Focus is placed on the morphological and mineralogical characterization and thermodynamic calculation of calcium phosphates precipitating due to the reaction between the calcium carbonate and ammonium phosphate solutions. Correlations between the formed stable calcium phosphate phases and the ammonium phosphate precursors are provided. Advantages and limitations of various analytical and modeling techniques used in this study such as geochemical equilibrium‐based modeling, X‐ray diffraction, scanning electron microscopy, and thermal analysis, are critically evaluated. Additionally, possible impacts of the ammonium phosphate solution type on the kinetics of phase transformations are discussed. [ABSTRACT FROM AUTHOR]

Fifty years have elapsed from the moment the first light transmitting ceramic-based commercial item--a sodium vapor-based street lamp component--reached the market. This paper intends to be a brief chronicle (albeit not a chronology) of this first half century of translucent and transparent ceramic history. The main ceramic materials now available in a transparent state are presented and their main applications are described. Applications range from aerospace and relativistic optics to medical care, supermarket shopping, and modern warfare. Light transmitting ceramics usable as laser gain-media, armor windows, IR domes, phosphors, scintillators, and electro-optical components have been developed. The principal achievements this research produced are discussed. Processing strategies for full densification have been devised and quantitative relationships were established between different microstructural features such as amount and size distribution of porosity or level of birefringence, and the level of electromagnetic radiation attenuation they cause. Future prospects list ends the paper. [ABSTRACT FROM AUTHOR]

This paper investigated the hydration and formation of the AH3 phase in three structural modifications of ye'elimite (namely, ss‐ye'elimite, Sr‐ye'elimite, and Ba‐ye'elimite). Three structural modifications of ye'elimite were synthesized, and their reactions with water were studied. The similarities and differences of the microstructure of the final AH3 phase formed during the hydration of different structural modifications of ye'elimite were investigated using a multitechnique approach. The crystal structure of three structural modifications of ye'elimite had an important influence on the kinetics of the reaction. The AH3 phases formed from ss‐ and Sr‐ye'elimite pastes were nanocrystalline, whereas the AH3 phases formed in Ba‐ye'elimite pastes were microcrystalline. The distinct microstructures of the AH3 phase in three structural modifications of ye'elimite had been investigated by the amount, composition, and crystal size of the AH3 phase. [ABSTRACT FROM AUTHOR]

Nonisothermal glass molding has recently become a promising technology solution for the cost‐efficient production of complex precision glass optical components. During the molding process, the glass temperature and its temperature distribution have crucial effects on the accuracy of molded optics. In nonisothermal molding, the glass temperature is greatly influenced by thermal contact conductance because there is a large temperature difference between the glass and mold parts. Though widely agreed to be varied during the molding process, the contact conductance was usually assumed as constant coefficients in most early works without sufficient experimental justifications. This paper presents an experiment approach to determine the thermal contact coefficient derived from transient temperature measurements by using infrared thermographic camera. The transient method demonstrates a beneficially short processing time and the adequate measurement at desirable molding temperature without glass sticking. Particularly, this method promises the avoidance of the overestimated contact coefficients derived from steady‐state approach due to the viscoelastic deformation of glass during the inevitably long period of holding force. Based on this method, the dependency of thermal contact conductance on mold surface roughness, contact pressure, and interfacial temperature ranging from slightly below‐to‐above glass transition temperature was investigated. The results reveal the dominance of interfacial temperature on the contact conductance while the linear pressure‐dependent conductance with an identical slope observed for all roughness and mold temperatures. The accurate determination of the contact heat transfer coefficients will eventually improve the predictions of the form accuracy, the optical properties, and possible defects such as chill ripples or glass breakage of molded lenses by the nonisothermal glass molding process. [ABSTRACT FROM AUTHOR]

Field‐assisted processing techniques can enhance the kinetics of powder synthesis, accelerate sintering processes, and drive phase transformations at significantly lower temperatures compared to conventional methods. However, the exact nature of this nonthermal interaction between field and matter remains vastly speculative. A 2‐day workshop on "Electromagnetic Effects in Materials Synthesis" was organized at Carnegie Mellon University (Pittsburgh, USA) in June 2017, jointly sponsored by the U.S. National Science Foundation and the U.S. Office of Naval Research. This workshop gathered the scientific community working on field‐assisted techniques of materials processing. Inspired by the discussions held at the workshop, this paper summarizes the advancements to date and opens scientific questions and research opportunities in the three major field‐assisted sintering techniques (laser, microwave, and flash sintering). Significant challenges remain in (a) experimental design, measurements, and computational simulations to distinguish the nonthermal effects of the externally applied fields from conventional thermal phenomena; and (b) identifying fundamental mechanisms behind low temperature, nonthermal effects that produce phase transitions and microstructural evolution in materials under externally applied fields. We also present the recent developments in multiscale characterization techniques and the theory and modeling efforts, which aim to tackle the aforementioned grand multidisciplinary challenges facing researchers. [ABSTRACT FROM AUTHOR]

In 1969, M.I. Mendelson published a paper in the Journal of the American Ceramic Society that introduced a proportionality constant of 1.558 for estimating the average 3D grain size from the mean 2D lineal intercept under the assumption of lognormally distributed grains. Recent simulations by the authors revealed that the lognormal parameterization in the original work actually calculates the median grain size instead of the mean. The relationship between the mean caliper diameter and mean lineal intercept was found to be 1.60 when using common parameterizations. In addition, it is demonstrated through simulations that the correct proportionality constant can range from 1.776 to below unity depending on a material's grain size dispersion, such that 1.60 should only be used as a crude approximation. [ABSTRACT FROM AUTHOR]

Abstract: The ceramic sanitary‐ware market generates large amounts of waste, both during the production process and due to construction and demolition practices. In this paper, the effect of different amounts and calcium sources (calcium hydroxide Ca(OH)2, calcium aluminate cement CAC, Portland cement PC) on the alkaline activation of ceramic sanitary‐ware waste (CSW) was assessed. Blended samples were activated with NaOH and sodium silicate solutions and cured for 3 and 7 days at 65°C. The maximum amount of calcium source‐type added to the system varied according to its influence on the compactability of the mortars.CSW was physico‐chemically characterized and the compressive strength development of activated samples was assessed on the mortars. The nature of the reaction products was analyzed in pastes, by X‐ray diffraction, thermogravimetric analysis, infrared spectroscopy and microscopic studies. The results show a great positive influence with the addition of moderate amounts of Ca(OH)2, PC and CAC on the mechanical properties. Among the typical hydrates usually observed in plain water‐hydrated PC or CAC, only AH3 and a small amount of C3AH6 were identified in the alkali‐activated CSW/CAC blended pastes, which indicates that Al and Ca from PC, CAC and Ca(OH)2 are taken up in the newly formed (N,C)‐A‐S‐H or C‐A‐S‐H gels. [ABSTRACT FROM AUTHOR]

In this paper, the Li2/3(1− x)Sn1/3(1− x)Mg xO (LSM xO) ceramic systems were prepared by solid-state reaction using novel atmosphere-controlled sintering ( x = 0-4/7). Pure Li2SnO3 was observed for x = 0, the Li2Mg3SnO6 and Li2SnO3 coexisted for x = 1/7, and the coexistence of three kinds of phases was detected for x = 1/5 and 1/4, including Li4MgSn2O7 impurity phase. Pure Li2Mg3SnO6-like phase with cubic rock salt structure in Fm-3 m space group was obtained in the range of 1/3-4/7. All samples showed well-dense and smooth microstructures. The microwave dielectric properties highly depended on the phase composition, bond valence, FWHM of Raman spectrum, Raman shift, average grain sizes, and octahedral distortion. The LSM xO ceramics sintered at 1250°C for 5 hours possessed excellent comprehensive properties of εr = 15.43, Q×f = 80 902 GHz and τ f = +5.61 ppm/°C for x = 1/7. Typically, the LSM xO ceramics sintered at 1350°C for 5 hours showed a maximum Q × f of 168 330 GHz for x = 1/2. [ABSTRACT FROM AUTHOR]

Ho:Lu3Al5O12(Lu AG) transparent ceramics are potential 2 μm eye-safe laser materials. Polycrystalline 0.8 at.% Ho:Lu AG ceramics with high optical quality were successfully fabricated by solid-state reactive sintering of high-purity oxide powders. The microstructure, the optical transmission, the spectrum characteristic, and the laser performance were investigated in this paper. The average grain size of Ho:Lu AG ceramics vacuum sintered at 1830°C for 30 hour is about 14 μm. The in-line transmittance of the sample is measured to be 81.7% and 82.0% at 1000 and 2250 nm, respectively. The absorption and the emission cross sections are calculated to be 0.88 × 10−20 cm2 at 1906 nm and 1.26 × 10−20 cm2 at 2094 nm. Using a thulium-doped yttrium-lithium-fluoride (Tm: YLF) laser with the central wavelength of 1907.5 nm as the pump source, 2.67 W continuous wave ( CW) laser operation at 2100.74 nm was obtained with a slope efficiency of 26.5%. The beam quality factor M2 was calculated to be 1.1, which indicated nearly diffraction-limited beam propagation and the laser was the fundamental TEM00 Gaussian mode. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) ceramics have been widely used in industry due to its high thermal conductivity. Understanding the relations between the microstructure and the thermal conductivity of SiC ceramics is critical for improving the efficiency of heat removal in heat sink applications. In this paper, a multiscale model is proposed to predict the thermal conductivity of SiC ceramics by bridging atomistic simulations and continuum model via a materials genome model. Interatomic potentials are developed using ab initio calculations to achieve more accurate molecular dynamics ( MD) simulations. Interfacial thermal conductivities with various additive compositions are predicted by nonequilibrium MD simulations. A homogenized materials genome model with the calculated interfacial thermal properties is used in a continuum model to predict the effective thermal conductivity of SiC ceramics. The effects of grain size, additive compositions, and temperature are also studied. The good agreement found between prediction results and experimental measurements validates the capabilities of the proposed multiscale genome model in understanding and improving the thermal transport characteristics of SiC ceramics. [ABSTRACT FROM AUTHOR]

Recently developed techniques to measure the structure of interfacial networks in three dimensions have the potential to revolutionize our ability to control the microstructures of polycrystals and interface-dominated materials properties. This paper reviews recent findings from two- and three-dimensional orientation mapping studies. The observations confirm a strong inverse correlation between the relative energies of grain boundaries and the frequency with which they occur in microstructures. The observations also show that during microstructure evolution, relatively higher energy grain boundaries are more likely to be shrinking while lower energy interfaces are more likely to be growing. These processes can lead to a steady-state distribution of grain boundaries that is influenced as much by the relative grain-boundary energies as by the exact processing conditions. Recent findings and emerging opportunities for grain-boundary characterization are reviewed in the final section of the paper. [ABSTRACT FROM AUTHOR]

This paper reports recent theoretical perspectives and experimental results on microstructural evolution during sintering in terms of the interface structure, which is either rough (atomically disordered) or faceted (atomically ordered). The paper presents theoretical predictions and calculations of grain growth during liquid-phase sintering based on crystal growth theories. It is shown that various types of grain growth behavior, which may be normal, abnormal, or stagnant, can appear as a result of the coupling effects of the maximum driving force for growth and the critical driving force for appreciable growth. The predictions are also shown to be valid in the case of solid-state sintering. A number of experimental observations showing the effect of some critical processing parameters have been found to be in excellent agreement with the predictions. Principles of microstructure development (grain growth control) during sintering are suggested. In addition, the effect of the interface structure on densification is briefly described and discussed. [ABSTRACT FROM AUTHOR]

This paper deals with the critical aspects of sintering of crystallizable glass+ceramic system, which is a critical part of low-temperature-cofired ceramics (LTCC) process. Densification studies clearly revealed the influence of filler's nature especially at lower glass contents (≤70 vol%) and lower sintering temperatures. In this temperature range, marked improvement in density was observed in the order cordierite>fused silica>mullite>alumina. The decisive role played by wetting of glass on filler has been demonstrated using heating microscopy and wetting studies. However, densification was not influenced by the nature of filler at higher glass contents (>70 vol%) and at higher sintering temperatures. This is because in this range of glass content viscous flow of glass dominates the wetting behavior. This paper brings out the salient features responsible for the sintering behavior of anorthite glass+ceramic LTCC composition. [ABSTRACT FROM AUTHOR]

This paper reports ionic conductivity of yttria-stabilized zirconia (YSZ)–Al2O3 composite membranes. The tape cast specimens were subjected to binder burnout (500°C) and sintering (1550°C) processes to obtain 200–300 μm thick membranes. The ionic conductivity and microstructure of the membranes were characterized and are discussed in this paper. The ionic conductivity of the composite specimens was enhanced and was correlated with the number of charge carrier and their mobility. The solubility of Al2O3 in YSZ was minimal and nanosize Al2O3 of the batch sintered into microsize and existed as a distinct phase. The scanning electron microscopy micrographs revealed that YSZ and Al2O3 grains were strained. [ABSTRACT FROM AUTHOR]

This paper describes the evolution of a sol–gel-derived PbZr xTi1− xO3 film microstructure and ferroelectricity as a function of thickness in the 0.2–1.2 μm range. In particular, we concentrate on the pyrochlore (Py) content in the film studied by the quantitative analysis of HRSEM images and corresponding ferroelectric properties. We have found that the Py content decreases with increasing thickness and have explained this phenomenon by a different extent of lead loss during processing. The ferroelectric hysteresis and fatigue of the films are correlated with the Py content. This paper shows that the Py presence in the film is responsible for the thickness-dependence of the coercive field. [ABSTRACT FROM AUTHOR]

Fabrication of microstructures has been the subject of considerable attention in recent years. Techniques such as surface silicon micromachining and bulk silicon etch have emerged as practical methods for thin microstructures and processes such as LIGA (an acronym for the German words for lithography, electrodeposition, and molding) are being used to produce high aspect ratio structures from a limited set of electroformable metals and polymers. As microsystem technologies and application prospects continue to grow, it is of interest and much practical value to expand the material choices for LIGA-scale micros structures to ceramics and a broader class of metals. To this end, this paper investigates a new technique for the fabrication of high aspect ratio ceramic or metal microparts. This technique is based on capillary-driven microcasting and curing of an epoxy- based metallic or ceramic nanoparticulate slurry into a sacrificial plastic mold produced by microinjection molding. The cured preform is subsequently heated to remove the organic phase and to sinter the particulate ceramic or metallic phase. The fabrication process is discussed in the paper along with illustration of example microparts produced using the process. A theoretical model of the fluid flow during the microcasting process is developed and validated with experimental data from the fabrication of rectangular rib sections. [ABSTRACT FROM AUTHOR]

This paper reports on the influence of rapid rate sintering (RRS) on densification and microstructure evolution of yttria transparent ceramics by using vacuum sintering. The presence of temperature gradient has been confirmed during the RRS process. The higher the heating rate (HR), the larger the temperature gradient in the samples would be. By using RRS, e.g., HR = 40°C/min, the samples could be densified very fast to a relative density of 99.6%. However, these samples could not be further densified, due to the presence of difference in densification caused by a heating rate-induced temperature gradient. By using a two-step RRS with an intermediate-temperature thermal treatment, this problem has been successfully addressed. The intermediate-temperature treatment allowed for the particle neck growth, so that effective thermal conductivity of the compacts was increased greatly. Therefore, the temperature gradient and differentiate densification were effectively prevented. Samples sintered using the two-step RRS process could be fully densified and excellent in-line optical transmittance was achieved. It is believed this strategy is applicable to other transparent ceramics, as well as other engineering ceramics. [ABSTRACT FROM AUTHOR]

Despite technological improvements in its production process, the sanitary ware industry inevitably generates a certain volume of discards, products whose quality is not up to standard. The present paper is the first to scientifically explore clay-based sanitary ware waste ( SW) with a view to its valorization as an addition in the design of new, more environmentally friendly cements. The focus is on characterization of the waste and its pozzolanicity, as well as the structural and microstructural changes taking place in the pozzolan/Ca( OH)2 system in the first 90 d of reaction. The findings show that pozzolanicity in clay-based waste is comparable to the activity observed in silica fume (SF) and higher than that found in other clay-based materials and fly ash (FA). The microstructural study of the clay-based waste/Ca( OH)2 system, in turn, reveals that the proportion of C-S-H gels rises with hydration time. These gels are characterized by long mean chain lengths (MCL) and low Ca/Si ratios. The intrinsic characteristics of this thermally activated clay-based waste qualify it as a type Q pozzolans as defined in the European cement standards, making it apt for use in the manufacture of CEM II, IV, and V cements. [ABSTRACT FROM AUTHOR]

This paper investigates the effective steady-state creep response of porous Ni-YSZ composites used in solid oxide fuel cell applications by numerical homogenization based on three-dimensional microstructural reconstructions and steady-state creep properties of the constituent phases. The Ni phase is found to carry insignificant stress in the composite and has a negligible role in the effective creep behavior. Thus, when determining effective creep, porous Ni-YSZ composites can be regarded as porous YSZ in which the Ni phase is counted as additional porosity. The stress exponents of porous YSZ are the same as that of dense YSZ, but the effective creep rate increases by a factor of 8-10 due to porosity. The relationship of creep rate and volume fraction of YSZ computed by numerical homogenization is underestimated by most existing analytical models. The Ramakrishnan-Arunchalam creep model provides the closest approximation among all analytical models. [ABSTRACT FROM AUTHOR]

In this paper the dielectric properties of crack-free, Bi12 Si O20 thin films were investigated. The films were prepared on Pt/ TiO2/ SiO2/ Si and corundum substrates using the sol-gel method. The formation of a pure Bi12 SiO20 phase was observed at a temperature of 700°C. The Bi12 SiO20 thin films, heat treated at 700°C for 1 h, had a dense microstructure with an average roughness ( Ra) of 50 nm. The dielectric properties of the film were characterized by using both low- and microwave-frequency measurement techniques. The low-frequency measurements were conducted with a parallel capacitor configuration. The dielectric constant and dielectric losses were 44 and 7.5 × 10−3, respectively. The thin-film dielectric properties at the microwave frequency were measured using the split-post, dielectric resonator method (15 GHz) and the planar capacitor configuration (1-5 GHz). The dielectric constant and the dielectric losses measured at 15 GHz were 40 and 17 × 10−3, respectively, while the dielectric constant and the dielectric losses measured with the planar capacitor configuration were 39 and 65 × 10−3, respectively. [ABSTRACT FROM AUTHOR]

In March 2012, a group of researchers met to discuss emerging topics in ceramic science and to identify grand challenges in the field. By the end of the workshop, the group reached a consensus on eight challenges for the future:-understanding rare events in ceramic microstructures, understanding the phase-like behavior of interfaces, predicting and controlling heterogeneous microstructures with unprecedented functionalities, controlling the properties of oxide electronics, understanding defects in the vicinity of interfaces, controlling ceramics far from equilibrium, accelerating the development of new ceramic materials, and harnessing order within disorder in glasses. This paper reports the outcomes of the workshop and provides descriptions of these challenges. [ABSTRACT FROM AUTHOR]

Despite the omnipresence of clay brick as construction material since thousands of years, fundamental knowledge about the link between composition, microstructure, and mechanical performance is still scarce. In this paper, we use a variety of advanced techniques of experimental mechanics and material characterization for extruded clay brick for masonry, that range from scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy, mercury intrusion porosimetry, to instrumented nanoindentation and macroscopic strength and durability tests. We find that extruded clay brick possesses a hierarchical microstructure: depending on the firing temperature, a 'glassy' matrix phase, which manifests itself at submicrometer scales in form of neo-crystals of mullite, spinel-type phase, and other accessory minerals, forms either a granular or a continuum matrix phase that hosts at submillimeter scale the porosity. This porous composite forms the backbone for macroscopic material performance of extruded brick, including anisotropic strength, elasticity, and water absorption behavior. [ABSTRACT FROM AUTHOR]

Porous lead zirconate titanate (PZT) ceramics are of great interest for hydrophones and medical imaging applications. The 0-3 type and 3-3 type porous PZT ceramics have been extensively discussed these years but the 1-3 type PZT ceramics have seldom been reported. This paper describes the fabrication process to obtain such 1-3 type porous PZT ceramics with one-dimensional pore channels by using tert-butyl alcohol-based directional freeze-casting method, and presents analysis of both microstructure and functional properties. The 1-3 type porous PZT ceramics with porosity ranging from 28.1%to 68.7%were fabricated by adjusting initial solid loading. With the increase of porosity, relative permittivity (er) decreased slightly and longitude piezoelectric coefficient (d33) exhibited only a small decline, which could be attributed to the special 1-3 type porous structure. The resultant samples with 61.3% porosity possessed a high value of hydrostatic figure of merit, >100 times higher than that of dense materials. The acoustic impedance (Z) showed a linear dependence on porosity with the lowest magnitude reaching 1.3 MRayls (106 kg · (m2 · s)-1), matching very well with biological tissue or water. [ABSTRACT FROM AUTHOR]

The base-metal electrode multilayer ceramic capacitors for future application require much thinner dielectric layers (<1 μm). Therefore, the grain size and uniformity of dielectric ceramics should be effectively controlled. In this paper, a two-step sintering (TSS) method has been utilized to prepare the ultrafine-grained X7R BaTiO3 ceramics in reducing atmosphere with the average grain size below 200 nm. And the influence of TSS schedule on the microstructure (such as bulk density, grain size) and dielectric properties is discussed in detail. Furthermore, the development of core-shell structure and corresponding temperature coefficient of capacitance characteristics during the intermediate stage of TSS process has been systematically investigated. [ABSTRACT FROM AUTHOR]

Previous literatures have all emphasized that the successful control of microstructure homogeneity of ZTA (ZrO2 toughened Al2O3) composites can only be achieved provided that the ZrO2 particles are homogeneously distributed and the volume content exceeds 5 vol%. In this paper, we report our strategy to incorporate fine-sized ZrO2 into Al2O3 by infiltrating presintered alumina compact using zirconium ion-containing solution and then in situ precipitation with ammonia solution. Homogeneous microstructure without AGG can be achieved in the prepared composite at a lower ZrO2 content (2.3 vol%). Such a result might be attributed to the excellent homogeneous distribution of finesized incorporated ZrO2 particles in Al2O3 matrix. [ABSTRACT FROM AUTHOR]

This paper discusses the results of tests conducted to ascertain at high temperatures the mechanical behavior of cements whose most prominent characteristic is the absence or near absence of Portland cement in their composition. More specifically, it reports on the study of three binders: (a) Portland cement (control); (b) 100% sodium silicate-activated fly ash; and (c) a blend of 70% ash+30% clinker activated with solid-state activators (solid sodium silicate+Na2CO3). Two types of tests were conducted: (i) tests to determine the mechanical strength and fracture toughness of the three materials between 25° and 600°C and (ii) postthermal treatment tests to evaluate the residual strength after 1 h of exposure to temperatures ranging from 200° to 1000°C. XRD and SEM techniques were also deployed to track the mineralogical and microstructural variations in the materials as a result of such an exposure. The findings showed that a pseudo-viscous phase is generated in alkaline cements at around 600°C that would explain the decline in strength observed when specimens were loaded at increasing temperatures. This phase and its subsequent recrystallization into new phases (nepheline, albite, and gehlenite) were also responsible for the high-residual mechanical strength values observed in these materials after exposure to high temperatures and subsequent cooling but absent in OPC. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of dewatering on the strength and microstructure of mortars manufactured from Portland cement, hydrated calcium lime (CL90), and natural hydraulic limes of classification 2, 3.5, and 5 with binder/aggregate/water ratios of 1:2:0.78. Dewatering was achieved by placing the mortars on a high porosity brick. Dewatered and nondewatered specimens were exposed to an atmosphere containing 400 ppm carbon dioxide with a relative humidity of 65%, at 20°C for periods of 14, 28, and 56 days. Following hardening for these periods, compressive strengths were compared with evaluate the mechanical performance. The structural morphology of the samples was determined using scanning electron microscopy and chemical composition by Raman spectroscopy. Results showed CL90 mortars are unaffected by dewatering. However, dewatering resulted in an increase in the compressive strength for the hydraulic limes and cement mortars tested. [ABSTRACT FROM AUTHOR]

The high-density tungsten bronze Sr2NaNb5O15 ceramics without abnormal grain growth were successfully synthesized by a two-step solid-state reaction method in this work. The phase evolution and reaction mechanism in SrNb2O6 and NaNbO3 solid solutions were analyzed by X-ray diffraction and differential scanning calorimetry. The results showed that the Sr2NaNb5O15 phase could exist stably in the temperature range of 1100°–1360°C, and would be decomposed to SrNb2O6 and NaNbO3 phases at temperatures above 1360°C. It was also found that the sintering temperature could significantly affect the density, microstructure, and electric properties of Sr2NaNb5O15 ceramics. When the sintering temperature was 1340°C, the ceramic with a near-theoretical density and a uniform and fine-grained microstructure was obtained, exhibiting outstanding electrical properties: ℇm=2210, tan δ=0.023, Tc=280°C, Pr=11.71 μC/cm2, and Ec=16.15 kV/cm. Further increasing the temperature to 1360°C led to the existence of some molten areas and cracks on the surface of ceramics obtained, which could significantly deteriorate the electric properties. In addition, no abnormal large grains (>50 μm) could be found in the system and the reason was also discussed in this paper. [ABSTRACT FROM AUTHOR]

Nanoparticles offer many advantages in the manufacture of ceramic products concerning processing and final properties, but are still difficult to process, and not all ceramic powder compositions can be obtained commercially like, e.g., α-alumina. In this paper, the production of α-alumina nanosized particles with a median size <60 nm by a wet grinding process in a highly concentrated suspension of up to 49 wt% solid content starting from a commercial microsized powder is presented. Furthermore, the subsequent direct processing of these suspensions to ceramic green tapes via tape casting is performed. The effect of nanosized α-Al2O3 powders on the viscosity of slurries, the casting process, binder burnout, and sintering behavior is characterized. Flat and crack-free sintered substrates with a density >95%TD, a submicrometer microstructure, and a translucent appearance could be obtained. A decrease of the sintering temperature, an improvement of the mechanical strength, and a lower surface roughness were achieved through the use of nanoparticles compared with particles in the micrometer size range. [ABSTRACT FROM AUTHOR]

In this paper, Co2O3-added-85(Bi1/2Na1/2)TiO3–12(Bi1/2K1/2)TiO3–3BaTiO3 (BNKB) lead-free piezoceramics were fabricated by the conventional solid oxide routine. By the use of X-ray photonic spectra, X-ray diffraction, and scanning electronic microscope, the valence state of Co cations, lattice distortion, and microstructures were investigated. It is revealed that the Co2O3 addition affects the concentration of Co3+ cations and changes the tetragonality c/ a of the perovskite lattice. The variation in tetragonality and microstructure, combined with the acceptor doping behavior of Co2O3, play a determinant role in the depolarization temperature Td, mechanical quality factor Qm, and other electrical properties of the ceramics. The Td is elevated to 157°C for 0.5 mol% Co2O3 addition; and the Qm reaches a maximum of 626 at 1.5 mol% Co2O3 addition, which is in the highest flight compared with other BNKB ceramics reported until now. [ABSTRACT FROM AUTHOR]

A review of the densification mechanisms and the microstructural development for transparent spinel made by free sintering and by hot pressing is given. The paper is divided into two main parts. The first part considers spinel without any sintering additives because there still is some controversy concerning the role of cation stoichiometry on sintering and grain growth. The second part discusses the role of the classic sintering aid, LiF, in processing transparent spinel. LiF is shown to have multiple behaviors: (1) it initially wets spinel and forms a liquid phase at relatively low temperatures, which affects early-stage densification and also grain growth; (2) upon cooling from intermediate temperatures, or even from higher temperatures if microstructure evolution (e.g., formation of closed porosity) prevents volatization, the LiF-containing liquid dewets and resides in isolated pockets; (3) LiF alters the cation stoichiometry, thereby enhancing diffusion via an increase in the concentration of oxygen vacancies; this affects both the densification rate and grain growth; and (4) it reacts with impurities in the system, thereby acting as a cleanser. For the production of transparent spinel, it is critical that LiF or associated reaction products not be retained as a secondary phase. [ABSTRACT FROM AUTHOR]

Structural ceramics, including ultrahigh-temperature ceramics such as zirconium diboride (ZrB2) and hafnium diboride (HfB2), are brittle and sensitive to flaws. As a result, the structural integrity of this ceramic component may be affected seriously. In this paper, a novelty technique namely preoxidation was proposed to overcome this problem. A ZrB2-based composite containing 20 vol% SiC whisker was produced by hot pressing. The composite was preoxidized at temperatures of 800° and 1200°C for various times ranging from 10 to 180 min in air. The flexural strength and microstructure of specimens were investigated systematically under each preoxidation condition. The strength was improved after preoxidation, with a maximum increase of strength (15%) for samples after preoxidizing at 800°C for 180 min. Microstructure analysis suggested that the increase in strength was due to the self-crack-healing behavior of the composite by surface oxide glass, such as B2O3-, SiO2-rich liquids, and borosilicate glass. However, oxide evaporation and formation of gas (i.e., B2O3 and CO) were found to be detrimental to for the crack-healing ability. Oxidation behavior during the preoxidation process followed parabolic-law kinetics. [ABSTRACT FROM AUTHOR]