Showing papers in "Journal of the American Ceramic Society in 2001"
TL;DR: In this paper, the pore formation mechanism was discussed in relation to the starting slurry concentration and sintering temperature, and pore structure was substantially affected by these effects.
Abstract: Porous ceramics with complex pore structure were synthesized by a freeze-dry process. Freezing-in of a water-based ceramics slurry was done while controlling the growth direction of the ice. Sublimation marks of the ice were generated by drying under reduced pressure. Porous ceramics having a complex pore structure were obtained by sintering the green body: aligned macroscopic open pores contained micropores in their internal walls. The pore structure was substantially affected by the starting slurry concentration and sintering temperature. The pore formation mechanism is discussed in relation to these effects.
395 citations
TL;DR: In this article, the electrical properties of two single phase, lanthanum-doped BaTiO3 compositions, x= 0.03 and x = 0.20, were investigated by impedance spectroscopy after heat treatment in oxygen, argon, and air at 1350°C.
Abstract: The electrical properties of two single-phase, lanthanum-doped BaTiO3 compositions, x= 0.03 and x= 0.20, in Ba1–xLaxTi1–x/4O3 were investigated by impedance spectroscopy after heat treatment in oxygen, argon, and air at 1350°C. Samples heated in oxygen were electrically insulating, whereas those heated in argon lost oxygen and were semiconducting at room temperature, irrespective of x. Samples heated in air showed intermediate electrical properties and also were electrically inhomogeneous; the two compositions showed different electrical behaviors, and a model for each, based on oxygen nonstoichiometry within the ceramics, is proposed. Oxygen deficiency in samples sintered in air was avoided by heating at 1200°C, instead of 1350°C. Alternatively, oxygen lost from ceramics heated in air at 1350°C was regained by postannealing in oxygen at 1350°C.
266 citations
TL;DR: In this article, the microstructural evolution of anatase-based commercial TiO2 powders, with an average size of 100 nm, at high temperatures was investigated using transmission electron microscopy analysis, and new information regarding the nature and mechanisms of this polymorphic reaction was revealed.
Abstract: Titania (TiO2) is an important electronic ceramic material for use in diverse applications such as gas sensors, catalysts, dielectrics, and ceramic membranes. TiO2 exists as several polymorphic phases, most commonly as rutile or anatase. This paper investigates the microstructural evolution of anatase-based commercial TiO2 powders, with an average size of 100 nm, at high temperatures. These powders transform to the rutile structure at 1000°C. The characteristics of the anatase-to-rutile transformation have been studied using transmission electron microscopy analysis, and new information regarding the nature and mechanisms of this polymorphic reaction has been revealed.
263 citations
TL;DR: Magnetoelectric laminate composites were constructed by stacking and bonding together a PZT disk and two layers of Terfenol-D disks with different directions of magnetostriction as mentioned in this paper.
Abstract: Magnetoelectric laminate composites of piezoelectric/magnetostrictive materials were prepared by stacking and bonding together a PZT disk and two layers of Terfenol-D disks with different directions of magnetostriction. These composites were studied to investigate (i) dependence on the magnetostriction direction of the Terfenol-D disk and (ii) dependence on the direction of the applied ac magnetic field. Three different types of assemblies were prepared by using two types of disks: one with magnetostriction along the radial direction, the other with magnetostriction along the thickness direction. The maximum magnetoelectric voltage coefficient (dE/dH) of 5.90 V/cm·Oe was obtained for a design where the composite was made by two Terfenol-D layers with a radial magnetostriction direction.
253 citations
TL;DR: Suspensions of fine alumina powder in a paraffin wax have been successfully formulated with viscosity values sufficiently low to allow ink-jet printing using a commercial printer as discussed by the authors.
Abstract: Suspensions of fine alumina powder in a paraffin wax have been successfully formulated with viscosity values sufficiently low to allow ink-jet printing using a commercial printer. A commercial-grade paraffin wax, with stearylamine and a polyester, were used as the dispersant system. Suspensions with powder loadings up to 40 vol% were passed through the ink-jet printer head. Unfired ceramic bodies with a feature size of <100 μm have been successfully fabricated with waxes that had a powder loading of 30 vol%. The influence of suspension fluid properties on the ink-jet printing process has been studied, and the importance of the acoustic resonance within the ink-jet printing apparatus has been demonstrated.
231 citations
TL;DR: In this article, the aging behavior of base-metal electrode materials above the temperature of the permittivity maximum (T M ), including the influence of the zirconium content and annealing conditions, is described for the first time.
Abstract: The purpose of the present investigation is to describe the influence of the processing parameters on the dielectric behavior of manganese-doped Ba(Ti 1-x Zr x )O 3 ceramics, particularly variations in the small-signal aging rate, temperature characteristic, and hysteresis. In this paper, the aging behavior of base-metal electrode materials above the temperature of the permittivity maximum (T M ), including the influence of the zirconium content and annealing conditions, is described for the first time. The aging rate at temperatures greater than T M decreases as the oxygen partial pressure increases during annealing and the zirconium content increases, whereas the aging rate exhibits a maximum at temperatures much less than T M . The behavior is explained in terms of a diffuse phase transition. Hysteresis-loop deformation is observed during aging.
185 citations
TL;DR: In this article, a multilayer ceramic capacitors that have been prepared from hydrothermal powders are preferentially collected at the inner electrodes, which results in “bloating,” cracks, and delamination.
Abstract: Hydrothermal powders of BaTiO3 and (Ba,Ca)(Ti,Zr)O3 contain large amounts of protons in the oxygen sublattice. The proton defects are compensated by vacancies on metal sites. When the powder is annealed, water is released and the point defects disappear in the temperature range of 100°–600°C. Metal and oxygen vacancies combine to small nanometer-sized intragranular pores. At temperatures of >800°C, the intragranular pores migrate to the grain boundaries and disappear. In multilayer ceramic capacitors that have been prepared from hydrothermal powders, the intragranular pores are preferentially collected at the inner electrodes, which results in “bloating,” cracks, and delamination.
181 citations
TL;DR: In this article, the Gibbs energy minimization (GEM) approach was applied to the available experimental solubility data at solid 0.8 < Ca/Si < 2.0 ± 0.3.
Abstract: Solubility in the fully hydrated CaO–SiO2–H2O system can be best described using two ideal C-S-H-(I) and C-S-H-(II) binary solid solution phases. The most recent structural ideas about the C-S-H gel permit one to write stoichiometries of polymerized C-S-H-(II) end-members as hydrated precursors of the stable tobermorite and jennite minerals in the form of 5Ca(OH)2·6SiO2·5H2O and 10Ca(OH)2·6SiO2·6H2O, respectively. For thermodynamic modeling purposes, it is more convenient to express the number of basic silica and portlandite units in these stoichiometries using the coefficients nSi and nCa. Thermodynamic solid-solution aqueous-solution equilibrium modeling by applying the Gibbs energy minimization (GEM) approach shows the best generic fits to the available experimental solubility data at solid 0.8 < Ca/Si < 2.0 if both stoichiometry and thermodynamic constants of the end-members are normalized to nSi= 1.0 ± 0.3. Recommended stoichiometries and thermodynamic data for the C-S-H end-members provide a reliable basis for the subsequent multicomponent extension of the ideal C-S-H solid solution model by incorporation of end-members for the (radio)toxic elements or trace metals.
169 citations
TL;DR: In this article, a nanograined 3 mol% Y2O3-doped ZrO2 powder was produced by hydrothermal precipitation from metal chlorides and urea sol followed by a washing-drying treatment and calcination.
Abstract: Nanosized tetragonal 3 mol% Y2O3-doped ZrO2 powder was produced by hydrothermal precipitation from metal chlorides and urea sol followed by a washing–drying treatment and calcination. The effects on powder properties of powder washing by water and ethanol with subsequent centrifuging, with possible deagglomeration using microtip ultrasonication, were experimentally shown. Ultrasonic irradiation induced pressure waves, which generated cavities that could violently collapse, producing intense stress. This induced stress was effective in minimizing secondary particle size, deagglomerating the powder, redispersing the ZrO2 after all the washing–centrifuging cycles, and minimizing mean aggregate size after final calcination. A uniformly aggregated tetragonal ZrO2 nanopowder with a mean secondary particle size of ∼45 nm and without hard agglomerates was prepared. The properties of the nanopowders produced by colloidal processing and CIP were studied. Determination of the best suspension parameters allowed for low-temperature sinterability, which resulted in a nanograined ∼95 nm ceramic.
164 citations
TL;DR: In this paper, the fracture strength of porous Al2O3-based porous ceramics fabricated from pure Al 2O3 powder and the mixtures with Al(OH)3 was investigated.
Abstract: The mechanical properties of Al2O3-based porous ceramics fabricated from pure Al2O3 powder and the mixtures with Al(OH)3 were investigated. The fracture strength of the porous Al2O3 specimens sintered from the mixture was substantially higher than that of the pure Al2O3 sintered specimens because of strong grain bonding that resulted from the fine Al2O3 grains produced by the decomposition of Al(OH)3. However, the elastic modulus of the porous Al2O3 specimens did not increase with the incorporation of Al(OH)3, so that the strain to failure of the porous Al2O3 ceramics increased considerably, especially in the specimens with high porosity, because of the unique pore structures related to the large original Al(OH)3 particles. Fracture toughness also increased with the addition of Al(OH)3 in the specimens with higher porosity. However, fracture toughness did not improve in the specimens with lower porosity because of the fracture-mode transition from intergranular, at higher porosity, to transgranular, at lower porosity.
163 citations
TL;DR: In this article, transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) were used to study the phase separation of stoichiometric SiO2 and SiC-based environments.
Abstract: SiCO glasses prepared from sol–gel precursors via pyrolysis in argon at temperatures ranging from 1000° to 1400°C were studied by transmission electron microscopy (TEM), in conjunction with electron energy-loss spectroscopy (EELS). EELS analysis showed that stoichiometric SiCO glass underwent phase separation, forming SiO2- and SiC-based environments. This process started at ∼1200°C. However, at temperatures >1300°C, precipitation of nanometer-sized SiC particles embedded in vitreous SiO2 was monitored by high-resolution TEM.
TL;DR: In this paper, a simple suspension chemistry (8-mol%-yttria-stabilized zirconia particles in acetic acid) yields films of similar quality to those from conventional approaches (such as electrochemical vapor deposition), but at potentially much less expense.
Abstract: Electrophoretic deposition (EPD) is used to produce zirconia electrolyte films for tubular solid oxide fuel cells. A simple suspension chemistry (8-mol%-yttria-stabilized zirconia particles in acetic acid) yields films of similar quality to those from conventional approaches (such as electrochemical vapor deposition), but at potentially much less expense. A key factor in obtaining high-density, adherent films via the EPD approach is the application of a thin fugitive phase (carbon in this study) on the porous, doped lanthanum manganite cathode tubes prior to zirconia deposition.
TL;DR: In this article, six sillenite compounds were synthesized to obtain ∼97% dense ceramics, and an analysis of their microwave dielectric properties, performed at ∼5.5 GHz, revealed a permittivity of ∼40 for all six compounds.
Abstract: Six sillenite compounds Bi12MO20-δ (M = Si, Ge, Ti, Pb, Mn, B1/2P1/2) were synthesized, and the resulting single-phase powders were then sintered to obtain ∼97% dense ceramics. An analysis of their microwave dielectric properties, performed at ∼5.5 GHz, revealed a permittivity of ∼40 for all six compounds. The temperature coefficient of resonant frequency was the lowest for the Pb analogue (−84 ppm/K) and was found to increase with increasing ionic radius of the B-site ion to a value of −20 ppm/K for the Bi12SiO20 and Bi12(B1/2P1/2)O20 compounds. The Q×f value is a maximum for Bi12SiO20 and Bi12GeO20 with 8100 and 7800 GHz, respectively. The dielectric properties of the sillenites have been correlated with the structure of the oxygen network of the sillenite crystal lattice. As a result of its low sintering temperature (850°C), chemical compatibility with silver, low dielectric losses, and temperature-stable permittivity, the Bi12SiO20 compound is a suitable material for applications in low-temperature cofiring ceramic (LTCC) technology.
TL;DR: In this paper, the thermal stability and spectroscopic properties of Er 2 O 3 -doped TeO 2 -GeO 2 −ZnO-Na 2 O-Y 2 O3 glasses for 1.5 μm fiber amplifiers were investigated.
Abstract: The thermal stability and spectroscopic properties of Er 2 O 3 -doped TeO 2 -GeO 2 -ZnO-Na 2 O-Y 2 O 3 glasses for 1.5 μm fiber amplifiers were investigated. The thermal stability of the 75TeO 2 .20ZnO. 5Na 2 O glass was improved by introducing GeO 2 and Y 2 O 3 . The radiative transition and the nonradiative transition have a dominant influence on the 4 I 13/2 level lifetime of Er 3+ in high- and low-GeO 2 regions, respectively. Adding Y 2 O 3 increases the 4 I 13/2 level lifetime of Er 3+ significantly. The Judd-Ofelt (J-O) parameter Ω 6 shows a strong correlation with the 1.5 μm emission bandwidth; and the larger the Ω 6 , the wider the bandwidth.
TL;DR: In this article, the effects on thermal conductivity of pores having these shapes and spatial arrangements are taken from the literature and combined with new results to provide descriptors of overall relationships between the relative density and pore morphology of a coating and its thermal conductivities.
Abstract: Thermal barrier coatings (TBCs) made by electron-beam physical vapor deposition (EB-PVD) exhibit a thermal conductivity strongly affected by a hierarchy of pores introduced during the deposition process. These pores are in the form of narrow gaps, aligned spheroids, and random spheres at specific sites within the coatings. Models for the effects on thermal conductivity of pores having these shapes and spatial arrangements are taken from the literature and combined with new results to provide descriptors of overall relationships between the relative density and pore morphology of a coating and its thermal conductivity. Correlations between conductivity and elastic modulus are also explored as a means for determining the viability of modulus measurements as a simple-to-use conductivity probe. For the types of pore commonly found in EB-PVD TBCs, there appears to be a tight correlation at typical porosity levels.
TL;DR: In this article, simple relations for the onset of competing brittle and quasi-plastic damage modes in Hertzian contact are presented, expressed in terms of well-documented material parameters, elastic modulus, toughness, and hardness, enabling a priori predictions for given ceramics and indenter radii.
Abstract: Simple relations for the onset of competing brittle and quasi-plastic damage modes in Hertzian contact are presented. The formulations are expressed in terms of well-documented material parameters, elastic modulus, toughness, and hardness, enabling a priori predictions for given ceramics and indenter radii. Data from a range of selected ceramic (and other) materials are used to demonstrate the applicability of the critical load relations, and to evaluate coefficients in these relations. The results confirm that quasi plasticity is highly competitive with fracture in ceramics, over a sphere radius range 1–10 mm. Implications concerning the brittleness of ceramics in the context of indentation size effects are discussed.
TL;DR: In this paper, the authors present results of molecular-dynamics simulations of the thermal conductivity, K, of ZrO{sub 2} and Ysub 2 O{sub 3}-stabilized Zr O{ sub 2} (YSZ), and find that the high-temeprature K is typical of a crystalline solid.
Abstract: The authors present results of molecular-dynamics simulations of the thermal conductivity, K, of ZrO{sub 2} and Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} (YSZ). For both pure ZrO{sub 2} and YSZ with low concentrations of Y{sub 2}O{sub 3}, they find that the high-temeprature K is typical of a crystalline solid, with the dominant mechanism being phonon-phonon scattering. With increasing Y{sub 2}O{sub 3} concentration, however, the mechanism changes to one more typical of an amorphous system. In particular, phononlike vibrational modes with well-defined wave vectors appear only at very low frequencies. As in amorphous materials, the vast majority of vibrational modes, while delocalized, do not propagate like ordinary phonon modes but transport energy in a diffusive manner. The authors also find that the few highest frequency modes are localized and do not contribute to K.
TL;DR: In this article, the influence of the size distribution of the cement particles on the induced autogenous deformation and stresses in cement pastes of identical water-to-cement ratios is examined for four different finenesses.
Abstract: The influence of cement particle-size distribution on autogenous strains and stresses in cement pastes of identical waterto-cement ratios is examined for cement powders of four different finenesses. Experimental measurements include chemical shrinkage, to quantify degree of hydration; internal relative humidity development; autogenous deformation; and eigenstress development, using a novel embedded spherical stress sensor. Because the latter three measurements are conducted under sealed conditions, whereas chemicalshrinkage measurements are made under “saturated” conditions, the National Institute of Standards and Technology cement hydration and microstructure development model is used to separate the effects of differences in hydration rates (kinetics) from those caused by the different initial spatial arrangement of the cement particles. The initial arrangement of the cement particles controls the initial pore-size distribution of the cement paste, which, in turn, regulates the magnitude of the induced autogenous shrinkage stresses produced by the water/air menisci in the air-filled pores formed throughout the hydration process. The experimental results indicate that a small autogenous expansion (probably the result of ettringite formation), as opposed to a shrinkage, may be produced and early age cracking possibly avoided through the use of coarser cements.
TL;DR: The temperature dependence of the viscosity and stress-relaxation kinetics of sol-gel-derived SiOC glasses that contain up to 14.5% carbon have been characterized in the temperature range of 1000°-1400°C as mentioned in this paper.
Abstract: The temperature dependence of the viscosity and stress-relaxation kinetics of sol–gel-derived SiOC glasses that contain up to 14 at.% carbon have been characterized in the temperature range of 1000°–1400°C. The viscosity, as determined from relaxation experiments, is in good agreement with the creep viscosity and is typically two orders of magnitude higher than the viscosity of vitreous silica. However, materials suffer from partial crystallization at >1150°C, and the precipitation of β-SiC nanocrystals induces a flow-hardening behavior and results in a dynamic increase in viscosity, especially at >1200°C and for glasses with a high carbon content.
TL;DR: In this paper, the thermal conductivity of Si3N4 powders with the concurrent addition of Yb2O3 and MgSiN2 were sintered at 1900°C for 2-48 h under 0.9 MPa nitrogen pressure.
Abstract: Si3N4 powders with the concurrent addition of Yb2O3 and MgSiN2 were sintered at 1900°C for 2–48 h under 0.9 MPa nitrogen pressure. Microstructure, lattice oxygen content, and thermal conductivity of the sintered specimens were evaluated and compared with Si3N4, Yb2O3, and MgO addition. MgSiN2 addition was effective for improving the thermal conductivity of Si3N4 ceramics, and a material with high thermal conductivity over 140 W·(m·K)−1 could be obtained. For both specimens, lattice oxygen content was decreased with sintering time. However, the thermal conductivity of the MgSiN2-doped specimen was slightly higher than the MgO-doped specimen with the same oxygen content.
TL;DR: The average barrier height measured was about 630 mV as mentioned in this paper, which is the same as the one measured in this paper, and a brick layer analysis of conventional impedance experiments yields satisfying estimates of the grain boundary properties.
Abstract: Microcontacts on adjacent grains of polycrystalline Fe-doped SrTiO3 samples have been used to locally investigate the properties of individual grain boundaries. Impedance spectroscopy was employed to separate bulk and grain boundary impedances. Experiments at about 30 different grain boundaries permit far-reaching conclusions on the distribution of grain boundary resistances, capacitances, and peak frequencies measured between adjacent grains. The rather narrow distribution of the grain boundary peak frequencies indicates a narrow distribution of grain boundary resistivities. All features (e.g., nonlinear current–voltage characteristics, grain boundary thickness, temperature dependence) are in accordance with the assumption of space charge depletion layers (double Schottky barriers) as the origin of the enhanced grain boundary resistivity. The average barrier height measured was about 630 mV. For comparison conventional (macroscopic) impedance measurements on a polycrystal were also performed and a brick layer model was used to extract effective properties. The reasonable agreement between these effective parameters and the average of the locally obtained parameters demonstrates that, in this case, a brick layer analysis of conventional impedance experiments yields satisfying estimates of the grain boundary properties.
TL;DR: In this article, Al 2 O 3 -based porous ceramics with high surface area were fabricated by adding Al(OH) 3 to the starting powder, followed by pressureless sintering at temperatures > 1100°C.
Abstract: Al 2 O 3 -based porous ceramics with high surface areas were fabricated by adding Al(OH) 3 to the starting powder, followed by pressureless sintering at temperatures >1100°C. Three types of starting powders were used in the present study: pure α-Al 2 O 3 , α-Al 2 O 3 + Al(OH) 3 , and α-Al 2 O 3 + ZrO 2 + Al(OH) 3 . The addition of Al(OH) 3 considerably increased the surface area of the porous Al 2 O 3 , and the addition of ZrO 2 further increased the surface area; a surface area as high as 36.39 m 2 /g was obtained, and the high surface area was retained at higher temperature. The pore size distribution of the specimens with high surface area was bimodal, with one peak at ∼100 nm and the other, which contributed most of the surface area, at ∼10 nm. X-ray analysis showed that in the sample with the fine pores and high surface area, there was θ-Al 2 O 3 phase produced by the decomposition of Al(OH) 3 , presumably because the phase transformation of θ-Al 2 O 3 to α-Al 2 O 3 was incomplete after low-temperature sintering. Moreover, the porous Al 2 O 3 with high surface area retained superior mechanical properties, attributed to the good sinterability of the fine α-Al 2 O 3 powder used in the present study. The sintered specimens could be large and designed to any shape, because pressureless sintering was used for fabrication. The present approach provides a new way of fabricating porous Al 2 O 3 ceramics that could be widely used as catalyst supports in industry, especially for high-temperature catalysis.
TL;DR: In this article, the magnitude of residual stresses in polycrystalline ceramics during processing was predicted using object oriented finite (OOF) element analysis and experimentally determined grain orientations.
Abstract: Microstructure-level residual stresses arise in polycrystalline ceramics during processing as a result of thermal expansion anisotropy and crystallographic disorientation across the grain boundaries. Depending upon the grain size, the magnitude of these stresses can be sufficiently high to cause spontaneous microcracking during the processing of these materials. They are also likely to affect where cracks initiate and propagate under macroscopic loading. The magnitudes of residual stresses in untextured and textured alumina samples were predicted using object oriented finite (OOF) element analysis and experimentally determined grain orientations. The crystallographic orientations were obtained by electron-backscattered diffraction (EBSD). The residual stresses were lower and the stress distributions were narrower in the textured samples compared to those in the untextured samples. Crack initiation and propagation were also simulated using the Griffith fracture criterion. The grain boundary to surface energy ratios required for computations were estimated using AFM groove measurements.
TL;DR: In this article, the temperature coefficient of the resonant frequency of complex perovskite (Pb 1-x Ca x )[Fe 0.5, 0.55; 0.0 ≤ y ≤ 1.0) was investigated, relative to the bond valence of the A- and B-site ions.
Abstract: The temperature coefficient of the resonant frequency (TCF) of complex perovskite (Pb 1-x Ca x )[Fe 0.5 (Nb 1-y Ta y ) 0.5 ]O 3 ceramics (x = 0.5, 0.55; 0.0 ≤ y ≤ 1.0) was investigated, relative to the bond valence of the A- and B-site ions in the ABO 3 perovskite structure (such as the barium-, strontium-, and calcium-based complex perovskites). The TCF of these complex perovskite compounds varied with the bond valence of the A- and B-sites and the tolerance factor (t) in the perovskite structure. In the tilted region (t < 1.0), the tilting of the oxygen octahedra increased and the TCF decreased, because of the increased bond valence of the B-site. Also, the dependence of TCF on the bond valence of the A-site was similar to its dependence on t.
TL;DR: In this paper, the microstructural evolution and dissolution phenomena in a Ti(C0.7N0.3)−WC−NbC−20Ni system were investigated.
Abstract: An investigation of the microstructural evolution and dissolution phenomena in a Ti(C0.7N0.3)–xWC–yNbC–20Ni system is reported. In Ti(C0.7N0.3)–yNbC–20Ni systems, a phase separation occurs between the Ti(CN) core and the (Ti,Nb)(CN) rim phases when the system contains >15 wt% NbC. This phase separation results from the increased misfit between the cores and the solid-solution rim phases with the addition of NbC. Based on data obtained from a previous study and compositional analyses of the rim structure of the Ti(C0.7N0.3)–yNbC–20Ni system, the average dissolution rates of WC and NbC appear to be approximately the same with respect to that of Ti(CN), under given sintering conditions (1510°C for 1 h). In addition, compositional changes in the rim structure of the Ti(C0.7N0.3)–xWC–yNbC–20Ni system are compared with those for a Ti(C0.7N0.3)–xWC–20Ni system to explain the effect of NbC on WC dissolution in the Ti(C0.7N0.3)–WC–NbC–Ni system. The presence of NbC in the Ti(C0.7N0.3)–xWC–20Ni system is found to suppress the dissolution of WC.
TL;DR: In this article, simple explicit relations for the onset of competing fracture modes in ceramic coatings on compliant substrates from Hertzian-like contacts are presented for a deleterious mode of radial cracking that initiates at the lower coating surface beneath the contact, in addition to traditional cone cracking and quasiplasticity in the near contact area.
Abstract: Simple explicit relations are presented for the onset of competing fracture modes in ceramic coatings on compliant substrates from Hertzian-like contacts. Special attention is given to a deleterious mode of radial cracking that initiates at the lower coating surface beneath the contact, in addition to traditional cone cracking and quasiplasticity in the near-contact area. The critical load relations are expressed in terms of well-documented material parameters (elastic modulus, toughness, hardness, and strength) and geometrical parameters (coating thickness and sphere radius). Data from selected glass, Al2O3 and ZrO2 coating materials on polycarbonate substrates are used to demonstrate the validity of the relations. The formulation provides a basis for designing ceramic coatings with optimum damage resistance.
TL;DR: Different ternary carbide phases were successfully synthesized in a self-sustaining regime as mentioned in this paper, and reaction conditions and X-ray diffraction patterns of different ternaries were presented.
Abstract: Different ternary carbide phases, namely Ti3AlC2, Ti3AlC, and Ti2AlC, were successfully synthesized in a self-sustaining regime. Direct reactions among elemental powders of titanium, aluminum, and carbon are strongly exothermic, and the resulting reaction products consist of binary carbides and they are partially molten. The use of TiAl, instead of elemental titanium and aluminum, significantly reduces the combustion temperature. As a result, ternary titanium aluminum carbide phases are formed. In addition, the combustion-synthesized products are not sintered and easy to deagglomerate. Reaction conditions and X-ray diffraction patterns of different ternary phases formed in a self-sustaining regime are presented.
TL;DR: In this article, the effect of the nitridation temperature and holding time on the powder properties is discussed, and it is shown that the synthesized TiN powders consisted of uniform spherical particles with an average diameter of ∼20 nm.
Abstract: Nanocrystalline TiN powder has been synthesized by the direct nitridation of nanocrystalline TiO2 powder. Powder XRD patterns indicated that the TiN nanocrystalline powder could be obtained by nitridation at 800°C for 5 h. TEM micrographs showed that the synthesized TiN powders consisted of uniform spherical particles with an average diameter of ∼20 nm. The effect of the nitridation temperature and holding time on the powder properties is discussed.
TL;DR: In this paper, a set of laboratory experiments has been developed to determine the nature and importance of the interaction between clay bodies and lead glazes during firing following different thermal paths (firing time and temperature, cooling rates) and using different glaze compositions and different clays.
Abstract: A set of laboratory experiments has been developed to determine the nature and importance of the interaction between clay bodies and lead glazes during firing following different thermal paths (firing time and temperature, cooling rates) and using different glaze compositions and different bodies (illitic, kaolinitic, and calcareous clays). It is shown that the interaction consists of a digestion/diffusion process. This process involves (i) decomposition of the phases forming the clay body (digestion), (ii) chemical diffusion of elements between clay body and glaze, and (iii) formation of a layer (interface between clay and glaze) of small K-Pb feldspar crystallites.
TL;DR: Lead niobium zirconate titanate (PNZT) pastes with tailored rheological properties have been developed for direct-write fabrication of thick-film capacitor elements in highly integrated, multifunctional electroceramic devices as discussed by the authors.
Abstract: Lead niobium zirconate titanate (PNZT) pastes with tailored rheological properties have been developed for direct-write fabrication of thick-film capacitor elements in highly integrated, multifunctional electroceramic devices. Such pastes exhibited pseudoplastic behavior with a low shear apparent viscosity of roughly 1 10 6 cP. On aging, the degree of shear thinning and the low shear apparent viscosity decreased. Pastes prepared from as-received powders attained printable, steady-state viscosities of 2 10 5 cP after 50 days of aging. In contrast, pastes prepared from dispersant-coated powders showed no measurable rheological changes after 1 day of aging. Square elements were patterned on dense alumina substrates or Teflon sheets. Leveling behavior as a function of time for single line prints, and the resulting surface topographies of dried PNZT films were measured by laser profilometry. PNZT layers sintered at varying temperatures between 950° and 1050°C fo r5hi neither air or a lead-rich atmosphere yielded porous microstructures as revealed by scanning electron microscopy (SEM). Such layers exhibited dielectric constants (K) of 1400 –1570 at 1 kHz with dissipation factors (D )o f less than 4.1%.