Showing papers in "Journal of the American Ceramic Society in 1988"
TL;DR: In this paper, the stability of α-Al2O3 suspensions with Na+ salt of poly(methacrylic acid) (PMAA-Na) polyelectrolyte was studied as a function of pH.
Abstract: Stability of aqueous α-Al2O3 suspensions with Na+ salt of poly(methacrylic acid) (PMAA-Na) polyelectrolyte was studied as a function of pH. At a given pH, the transition from the flocculated to the dispersed state corresponded to the adsorption saturation limit of the powders by the PMAA. As the pH was decreased, the adsorption saturation limit increased until insolubility and charge neutralization of the PMAA was approached. The critical amount of PMAA required to achieve stability is outlined in a stability map.
566 citations
TL;DR: In this article, the effect of crystal anisotropy on the formation of grain-boundary microcracks is analyzed, by considering a planar array of hexagonal grains as a model of a polycrystalline ceramic.
Abstract: The effect of crystal anisotropy on the formation of grain-boundary microcracks is analyzed, by considering a planar array of hexagonal grains as a model of a polycrystalline ceramic. The stress singularities at triple-grain junctions are analyzed by an asymptotic method as well as by a numerical solution, and the critical size of a grain-boundary defect is investigated by a crack analysis. It is found that elastic anisot-ropies can significantly increase the stress levels near triple points, which results in a smaller critical grain size for microcracking.
558 citations
TL;DR: In this article, the authors analyzed the toughening behavior of a bridging zone immediately behind the crack tip of a SiC-whisker-reinforced ceramics.
Abstract: The toughening behavior of whisker-reinforced ceramics is analyzed in terms of a whisker bridging zone immediately behind the crack tip. This approach is consistent with microscopy observations which reveal that intact bridging whiskers exist behind the crack tip as a result of debonding of the whisker-matrix interface. The theoretical results based on both the stress intensity and the energy change introduced by bridging whiskers reveal the dependence of toughening upon the composition and matrix, interface, and whisker properties. Furthermore, the analytical models of whisker bridging accompanied by very limited pullout accurately describe experimental observations of the toughening behavior in several SiC-whisker-reinforced ceramics. Such analytical descriptions also indicate that increases in whisker size and strength and modification of interface properties will result in further increases in toughness by whisker reinforcement.
519 citations
TL;DR: In this paper, the stability and rheology of aqueous α-Al2O3 suspensions with poly(methacrylic acid) and poly(acrylic acids) polyelectrolytes were studied as a function of pH, solids loading, and molecular weight.
Abstract: Stability and rheology of aqueous α-Al2O3 suspensions with poly(methacrylic acid) and poly(acrylic acid) polyelectrolytes were studied as a function of pH, solids loading, and molecular weight. Past work has found polyelectrolyte-stabilized suspensions to be fairly pH independent at low (e.g., 20 vol%) solids loadings. However, we now show that the effective pH range to provide dispersed and fluid suspensions narrows as the concentration of solids increases as related to interparticle forces. At high solids levels, the presence of excess polymer in solution has detrimental effects on stability, which increases as the molecular weight increases. Finally, with knowledge of these concepts, highly concentrated fluid suspensions of 60 vol% Al2O3 (>85 wt%) with submicrometer-size particles have been processed. Higher consolidated densities and reduced sintering temperatures are attained when compared with more conventional processing techniques.
448 citations
TL;DR: In this paper, straight-through precracks were introduced into rectangular beams of several ceramic materials to evaluate the fracture toughness of these materials and gave Kic values almost constant over wide ranges of the pop-in precrack length and the loading rate of the three-point bend test.
Abstract: As a substitute for the fatigue-cracked-beam method prescribed in ASTM E399 A2, a recently devised precracking method was applied to the evaluation of fracture toughness of ceramic materials. Straight-through precracks proved to be easily introduced into rectangular beams of several ceramic materials. This method gives Kic values almost identical with those of the fatigue-cracked-beam method. The Kic values are almost constant over wide ranges of the pop-in precrack length and the loading rate of the three-point bend test. The test can be easily performed even at elevated temperatures although its validity should be further examined.
354 citations
TL;DR: In this paper, a mixture of mixed solutions of yttrium(III) and cerium (III) salts under similar experimental conditions yielded composite spherical particles of basic carbonate and rod-like particles of ammine carbonate.
Abstract: Colloidal dispersions of uniform spherical particles of yttrium basic carbonate and rodlike particles of yttrium ammine carbonate were prepared by aging at elevated temperatures yttrium salt solutions in the presence of urea. Different composition and morphology were achieved by altering the aging temperature and time. Coprecipitation in mixed solutions of yttrium(III) and cerium(III) salts under similar experimental conditions yielded composite spherical particles of basic carbonate. The content of the two metals in the solids followed closely the initial composition of the reacting solutions. On calcination all prepared solids converted to their corresponding oxides while retaining their particle morphology. The so-prepared powders were characterized by various techniques.
221 citations
TL;DR: The 27Al and 29Si NMR signal analysis of samples heated above 400°C demonstrates that the tetrahedral sheet of kaolinite begins to break down near 600°C and continues to do so to 900°C as discussed by the authors.
Abstract: The 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS-NMR) study of the kaolinite-mullite transformation has shown the presence of Al in tetra- and pentacoordination in dehydroxylated kaolinite. The 29Si NMR signal analysis of samples heated above 400°C demonstrates that the tetrahedral sheet of kaolinite begins to break down near 600°C and continues to do so to 900°C. From the 27Al NMR signal evolution, it can be deduced that the exothermic peak at 980°C in DTA curves is associated with the modification of the coordination of Al, which changes from the tetra- or pentacoordination to the more stable octahedral coordination. Heating the sample at 880°C for 36 h produces the same transformation in the coordination of Al ions and the elimination of the exothermic peak at 980°C in the DTA diagram. After this transformation, all spectra show two tetrahedral lines characteristic of mullite, indicating that nuclei of mullite with low crystallinity are generated during the exothermic process which are not detected by XRD. At higher temperatures tetrahedral NMR peaks increase in intensity, yielding, at 1200°C, the 3:2 mullite NMR spectrum.
216 citations
TL;DR: In this article, phase relationships in the SiC-AlN pseudobinary system were determined by analytical electron microscopy of local equilibria among adjacent phases in hot-pressed samples and in diffusion couples.
Abstract: Phase relationships in the SiC-AlN system were determined by analytical electron microscopy of local equilibria among adjacent phases in hot-pressed samples and in diffusion couples. At 2100° to 2300°C, a 4H–2H equilibrium exists, the 4H field extending from ∼2 mol% AlN to an upper limit of 11 to 14 mol% AlN. The wurtzite-type 2H (δ) solid solution extends from an impurity-sensitive lower limit of 17 to 24 mol% AlN up to 100 mol% AlN. Semiquantitative Auger electron spectroscopy and energy dispersive X-ray spectroscopy ultrathin-window detector measurements confirmed the assumption that the solid solutions have the general formula (SiC)1-x(AlN)x and belong to the SiC-AlN pseudobinary system. The existence of a miscibility gap below 1950°C was confirmed, but its limits were not determined accurately. A faulted metastable cubic phase, β′, exists below ∼2000°C and contains up to ∼4 mol% AlN. The transformations into the stable a structures occur through diffusion-controlled stacking rearrangements.
191 citations
TL;DR: In this article, the authors studied the deformation of tetragonal zirconia polycrystals by inducing volumetric and shear deformation under compression and bending between the burst temperature of martensite (monoclinic) formation (Mb) and burst temperature (Ab) of austenite (tetragonal) formation and found that yield stress has a strong, positive pressure and temperature sensitivity but is strain-rate sensitive only in the last stage of deformation.
Abstract: Transformation plasticity in CeO2-stabilized tetragonal zirconia polycrystals due to the tetragonal-to-monoclinic transformation was studied by inducing volumetric and shear deformation under compression and bending between the burst temperature of martensite (monoclinic) formation (Mb) and the burst temperature of austenite (tetragonal) formation (Ab). The stress-strain curve features a load drop, a perfect plastic regime, and an extended strain-hardening regime before the exhaustion of transformation. Macroscopic shear bands formed in the perfect plastic regime. The yield stress has a strong, positive pressure and temperature sensitivity but is strain-rate sensitive only in the last stage of deformation. These results are rationalized in terms of stress assistance to the transformation which, in a homogeneous tetragonal polycrystal, may propagate autocatalytically. Autocatalysis can be impeded by a second phase, such as monoclinic ZrO2 or Al2O3, and is suppressed at higher temperature. Flow localization is found to precede and precipitate crack formation. As a result, the actual fracture energy is much less than the total plastic work. The implications of stress-assisted, autocatalytic transformation on strength and toughness are explored.
187 citations
TL;DR: In this paper, the electrical conductivity and thermopower of cubic Mn3O4 were measured in the temperature range 920° to 1530°C, and the concentrations of Mn4+ and Mn3+ were governed by the disproportionation equilibrium 2Mnoct3+⇄MNOct4++ Mnoct2+.
Abstract: The electrical conductivity and thermopower of Mn3O4 were measured in the temperature range 920° to 1530°C. Electrical conduction in cubic Mn3O4 is explained by the small polaron hopping of electron holes between Mn4+ and Mn3+ on octahedral sites. The concentrations of Mn4+ and Mn3+ are governed by the disproportionation equilibrium 2Mnoct3+⇄Mnoct4++ Mnoct2+. This model also explains the electrical behavior of NiMn2O4 and CuMn2O4.
173 citations
TL;DR: In this paper, the sessile-drop method has been used to determine the Wettability of silica by gold, silicon, and lead by using an empirical equation which takes into account both metal-oxygen and metal-oxide chemical bonds.
Abstract: Wettability of silica by gold, silicon, and lead has been determined by the sessile-drop method. The contact angle, θ, and the work of adhesion, W, have been found to be 143° and 227 mJ·m−2 for gold at 1353 K, 87° and 869 mJ·m−2 for silicon at 1723 K, and 120° and 203 mJ·m−2 for lead at 1000 K. Thermodynamic adhesion between silica and nonreactive pure metals has been analyzed using models for metal-oxide bonds. Models based on the assumption that only van der Waals interactions and/or metal-oxygen chemical bonds exist at the metal-oxide interface are unsuited for explaining the relative variations in the W values. A valid model can be accomplished by using an empirical equation which takes into account both metal-oxygen and metal-oxide chemical bonds. It appears that chemical bonds exist at the interface even for nonreactive metal-ionocovalent oxide systems.
NEC1
TL;DR: In this paper, the effect of several additives, such as CaC2, CaO, Y2O3, and C, on thermal conductivity of hot-pressed AlN ceramics was investigated.
Abstract: The effect of several additives, such as CaC2, CaO, Y2O3, and C, on thermal conductivity of hot-pressed AlN ceramics was investigated. The addition of CaC2 reductant was found to be useful for achieving high thermal conductivity of 180 W/(m·K) at room temperature. The characterization of AlN ceramics with CaC2 additive was performed by chemical analysis of Ca, C, and O and microstructural analysis using transmission electron microscopes equipped with an energy-dispersive X-ray analyzer and an electron energy loss spectrometer. The major influence on high thermal conductivity is the disappearance of a thermal barrier caused by oxygen impurities at the grain boundary.
TL;DR: In this paper, a shear-lag analysis is presented for estimating sliding friction stress at fiber-matrix interfaces in ceramic matrix composites using the single-fiber push-out test.
Abstract: A shear-lag analysis is presented for estimating sliding friction stress at fiber-matrix interfaces in ceramic-matrix composites using the single-fiber push-out test. The analysis includes an approximate correction for the increased interfacial compression and, therefore, the interfacial friction stress arising from the transverse (Poisson) expansion of the fibers subjected to the compressive load. An exponential decrease of the interfacial shear stress along the fiber length is predicted. This result is similar to the results of a finite-element analysis reported in the literature. The analysis also provides a basis for the experimental determination of a coefficient of interfacial friction (μ) and a residual interfacial compression (σ0). It is shown that the sliding friction stress (τf=μσ0) can be overestimated if the transverse expansion of the fibers is not taken into account.
TL;DR: In this article, the sintering behavior of compacts constituted of monodispersed agglomerates was evaluated, and changes in macroscopic dimensions were correlated with changes in particle microstructure and chemistry.
Abstract: Monosized titania particles (∼0.35-μ diameter) prepared by controlled hydrolysis of titanium tetraethoxide in ethanol were found to be porous agglomerates of ∼6-nm primary particles. The sintering behavior of compacts constituted of monodispersed agglomerates was evaluated, and changes in macroscopic dimensions were correlated with changes in particle microstructure and chemistry. The total volume shrinkage during sintering was ≥87%. Five contributions to the total shrinkage and the temperature ranges for the associated processes were identified: removal of chemisorbed water (from ambient to 250°C), crystallization to anatase (between 250° to 425°C), intra-agglomerate densification (425° to 800°C), conversion of anatase to rutile (600° to 800°C), and inter-agglomerate densification (>800°C). Approximately one-half the compact shrinkage was the result of agglomerate substructure changes. Studies of the agglomerate structural evolution indicated the intra-agglomerate densification and crystallite growth rates are the secondary factors, after compact packing, that influenced microstructure development.
TL;DR: In this paper, the elastic constants of yttria-stabilized zirconia were measured for a range of materials which vary from a mixture of monoclinic, tetragonal, and cubic to those which are fully cubic.
Abstract: Results are presented for the measured single-crystal elastic constants of yttria-stabilized zirconia, for yttria contents of 1.7 to 20 mol%. The results cover a range of materials which vary from a mixture of monoclinic, tetragonal, and cubic to those which are fully cubic. These single-crystal measurements are used to calculate the bounds on the elastic moduli for polycrystalline materials. Comments are made on the elastic anisotropy of zirconia relative to a number of other single-crystal ceramics, with graphical comparisons of the anisotropy of Young's moduli of these ceramics.
TL;DR: The formation of mullite in diphasic aluminosilicate gels of stoichiometric composition was studied by quantitative X-ray diffraction (QXRD) and electron microscopy (AEM and SEM) as mentioned in this paper.
Abstract: The formation of mullite in diphasic aluminosilicate gels of stoichiometric composition was studied by quantitative X-ray diffraction (QXRD) and electron microscopy (AEM and SEM). The transformation is preceded by an incubation time which is apparently an activated process with an activation energy of 236 ± 15 kcal/(g·mol) (∼987 ± 63 kJ/(g·mol)). Microscopic observations show that mullitization occurs via nucleation and growth as a mechanism either interface-controlled or controlled by short-range diffusion near the interface. The kinetic time exponent (n), determined by microstructural and QXRD observations, is close to 1.3. The transformation kinetics involve a nearly constant nucleus density, and time-dependent growth rate for nearly spherical grains. A linear time-temperature-transformation diagram is observed.
TL;DR: Preparation de poudres ultrafines et quasispheriques de ferrites NiFe 2 O 4, ZnFe 2O 4, Ni x Zn 1−x Fe 2O4, Mn 0,5 Zn 0, 5 Fe 2 O4 and CoFe 2 o 4 dans des conditions hydrothermales moderees par precipitation de nitrates metalliques avec de l'ammoniaque.
Abstract: Preparation de poudres ultrafines et quasispheriques de ferrites NiFe 2 O 4 , ZnFe 2 O 4 , Ni x Zn 1−x Fe 2 O 4 , Mn 0,5 Zn 0,5 Fe 2 O 4 et CoFe 2 O 4 dans des conditions hydrothermales moderees par precipitation de nitrates metalliques avec de l'ammoniaque. Ces poudres sont frittees a 1000°C sans additif avec obtention d'une densite proche de la densite theorique
TL;DR: In this article, the analytical function of crack extension to a fractional power is used to represent the fracture resistance of a vitreous-bonded 96% alumina ceramic.
Abstract: The analytical function of crack extension to a fractional power is used to represent the fracture resistance of a vitreous-bonded 96% alumina ceramic. A varying flaw size, controlled by Vickers indentation loading between 3 and 300 N, was placed on the prospective tensile surfaces of four-point bend specimens, previously polished and annealed. The lengths of surface cracks were measured by optical microscopy. Straight lines were fitted to the logarithmic functions of observed bending strength versus indentation load in two series of experiments: (I) including the residual stress due to indentation and (II) having the residual stress annealed out at an elevated temperature. Within the precision of measurement these lines have the same slope, being about 32% less than the -1/3 slope which a fracture toughness independent of crack extension would indicate. Considering the criteria for crack extension and specimen failure, the fracture mechanics equations were solved for the conditions of the two series of experiments. Approximately the same values of fracture toughness, rising as a function of indentation flaw size, were obtained from both series of experiments.
TL;DR: In this article, reaction curves were obtained at various temperatures and concentrations for the formation of BaTiO3 from particulate titania in Ba(OH)2 solution and the measured activation energy was 105.5 kJ/mol.
Abstract: Reaction curves were obtained at various temperatures and concentrations for the formation of BaTiO3 from particulate titania in Ba(OH)2 solution. Kinetic analyses were performed by constructing mathematical models which took into account the particle size distribution of the reactant titania for both the topochemically-rate-controlled and the diffusion-rate-controlled reactions. At [Ba(OH)2] > ca. 0.1M the rate-controlling step is the Ba reaction with TiO2 at the interface. The measured activation energy is 105.5 kJ/mol. The rates are independent of Ba(OH)2 concentration, indicating that the TiO2 interface is saturated. At [Ba(OH)2] < ca. 0.1M the rate-determining step shifts to diffusion through the product BaTiO3 layer, the rates are concentration dependent, and the BaTiO3 particle sizes are inversely proportional to the Ba(OH)2 concentrations used.
TL;DR: In this paper, the electrical conductivity and thermoelectric power of single-crystalline Ba0.03Sr0.97TiO3 were measured over a wide temperature (800° to 1100°C) and oxygen partial pressure (105 to 10-15 Pa) range.
Abstract: The electrical conductivity and thermoelectric power of single-crystalline Ba0.03Sr0.97TiO3 were measured over a wide temperature (800° to 1100°C) and oxygen partial pressure (105 to 10-15 Pa) range. Our experimental data, like those of previous workers on nominally undoped BaTiO3 or SrTiO3, support a defect model based on doubly ionized oxygen vacancies, electrons, holes, and accidental acceptor impurities. The simultaneous measurement of electrical conductivity and thermoelectric power, together with precise experimental data obtained with an advanced thermoectric power measurement technique, enabled us to determine for the first time reliable values for the preexponential factors and the activation energies which characterize the defect equilibrium constants. These calculated values, together with the defect model, were found to give an excellent fit to the experimental data, and were used to generate the boundaries, in Po2-1/T space, of the various defect regimes.
TL;DR: In this paper, a series of magnesia-partially-stabilized zirconia ceramics with varying degrees of transformation toughening were measured for the growth of surface cracks.
Abstract: Crack growth resistance curves (R curves) for the growth of surface cracks have been measured in a series of magnesia-partially-stabilized zirconia ceramics with varying degrees of transformation toughening. The shapes of the R curves are correlated with strength-toughness relations and the predictions of fracture mechanics analysis of transformation toughening. Results support a previous hypothesis that the peak in the strength-toughness relation is associated with a decreasing slope of the R curve with increasing steady-state toughness. The role of microstructural influences due to localized regions of transformation on crack growth is assessed, and the relation between reversible and irreversible transformation and toughness is examined.
TL;DR: In this paper, a shape memory effect was demonstrated by first deforming a CeO2-stabilized tetragonal zirconia polycrystal (Ce-TZP) between the Mb and As temperatures and then recovering the shape change by heating above Ab.
Abstract: A macroscopic shape memory effect is demonstrated by first deforming a CeO2-stabilized tetragonal zirconia polycrystal (Ce-TZP) between the Mb and As temperatures and then recovering the shape change by heating above Ab. Shape changes effected above Ab are immediately recoverable during unloading, giving rise to a pseudoelastic behavior. Deformation texture is reversible when the shape strain recovers. Both Mb and Ab, along with the associated temperature range for these effects, are depressed to lower temperatures by grain refinement. Prior deformation widens the gap between the transformation temperatures. These observations demonstrate that the shape accommodation in Ce-TZP arises from twinning and elastic distortions. The operation of pseudoelasticity and shape memory effect is rationalized in terms of martensitic nucleation statistics, the stability of thermoelastic martensite, and internal stresses at the martensitic interface. The implications on transformation plasticity and transformation toughening are explored.
TL;DR: In this paper, a generic approach is presented for a wide range of composite systems based on particulate and whisker SiC reinforcement in combination with CaSiO3, SrSiO 3, and strontium feldspar matrices.
Abstract: Melt infiltration offers an alternative route to the synthesis of fully dense ceramic matrix composites. Necessary conditions with respect to chemical reactivity, melt viscosity, and wetting must be satisfied. Other properties of the reinforcement and matrix constituents must also be considered. With these restrictions this generic approach is applicable to a wide range of composite systems. Preliminary structure and property results are presented for the representative systems based on particulate and whisker SiC reinforcement in combination with CaSiO3, SrSiO3, and strontium feldspar matrices.
TL;DR: In this article, the authors discuss the effect of hydration dans l'eau, en presence d'additifs et dans un broyeur a boulets.
Abstract: L'etude se fait conjointement par RMN a angle magique et a polarisation croisee. On etudie l'hydratation dans l'eau, en presence d'additifs et dans un broyeur a boulets
TL;DR: In this paper, the grain size in partially sintered compacts of alumina was measured as a function of density, and the grain growth behavior fell into two distinct regions: the porosity remained interconnected, grain growth was negligible; when the continuous pore network collapsed into isolated pores, grains grew rapidly.
Abstract: When the grain size in partially sintered compacts of alumina was measured as a function of density, we found that the grain-growth behavior fell into two distinct regions. In the region where the porosity remained interconnected, grain growth was negligible; when the continuous pore network collapsed into isolated pores, grains grew rapidly. The transition in grain-growth behavior was observed at approximately 90% of theoretical density. A simple phenomenological method for obtaining the transition in grain growth is suggested. It is based on the idea that an abrupt increase in grain size should be accompanied by a significant decrease in the rate of sintering since the sintering rate changes as the third or fourth power of the grain size. The method consists of fitting the sintering data to an exponential function. The transition then appears as a change in the time constant for the exponential. The low rate of grain growth in the region where the pores are interconnected contradicts earlier work in the literature where significant grain growth during intermediate-stage sintering has been reported. This difference is explained in terms of the homogeneity of packing of our powder compacts, which were prepared by colloidal processing.
TL;DR: In this article, the creep behavior of reaction-bonded silicon carbide was characterized at a temperature of 1300°C and the authors found that the creep rate in tension was at least 20 times higher than that obtained in compression.
Abstract: The creep behavior of a commercial grade of reaction-bonded silicon carbide was characterized at a temperature of 1300°C. Creep occurred more easily in tension than in compression. At a given applied stress, the steady-state creep rate in tension was found to be at least 20 times that obtained in compression. In both tension and compression, the stress exponent for steadystate creep was found to increase with increasing applied stresses. At low applied stresses, the stress exponent was ∼4, suggesting some kind of dislocation mechanism operating in the two-phase composite. At high stresses, the stress exponent was ∼11 in tension. The increase in the stress exponent was attributed to damage accumulation in the form of cavities. An effective threshold stress for cavitation of less than 100 MPa was suggested. In compression, the cause of the increase of stress exponent with stress cannot be attributed to cavitation.
TL;DR: In this paper, the R-curve behavior of an isotropic polycrystalline graphite is characterized by rapidly increasing values at the initial stage of crack extension (Δa≤1 to 2 mm) followed by a steady-state plateaulike region and then a distinct decrease when the primary crack tip approaches the end surface of the test specimen.
Abstract: The contributions of nonlinear fracture processes both in the microcracking frontal process zone and in the following wake region and of grain bridging to crack-growth resistance parameters are discussed in terms of the R-curve behavior of an isotropic polycrystalline graphite. The R-curve behavior of the graphite is characterized by rapidly increasing values at the initial stage of crack extension (Δa≤1 to 2 mm) followed by a steady-state plateaulike region and then a distinct decrease when the primary crack tip approaches the end surface of the test specimen. Scanning electron microscopy of fracture mechanics specimens revealed a dominant role of grain bridging in the following wake regions on the rising R-curve behavior and confirmed the significant size effect of the large-scale microcracking process zone on the falling R-curve behavior. The stress-derived fracture toughness (KR) and the energy fracture toughness (Rc) are discussed in relation to the micro-cracking residual strain.
TL;DR: Etude de l'influence du pH des solutions aqueuses dans lequelles sont trempees les fibres ainsi que l''influence de la presence ou non d'un revetement sur leur comportement de fatigue statique.
Abstract: Etude de l'influence du pH des solutions aqueuses dans lequelles sont trempees les fibres ainsi que l'influence de la presence ou non d'un revetement sur leur comportement de fatigue statique
TL;DR: A fine-sized (∼0.1 μm), agglomerate-free Al2O3 dispersion was used to prepare homogeneous green bodies with ∼69% relative density and ∼10-nm median pore radius as mentioned in this paper.
Abstract: A fine-sized (∼0.1 μm), agglomerate-free Al2O3 dispersion was used to prepare homogeneous green bodies with ∼69% relative density and ∼10-nm median pore radius. Samples could be sintered at 1150°C to a relative density >99.5% and an average grain size of 0.25 μm.
TL;DR: In this paper, several potential alternative transformation tougheners to zirconia have been identified on the basis of crystallographic considerations and experimental observations, and the relative effects of volume change, X-ray unit-cell shape change, and macroscopic shape change on the mechanical properties of a composite ceramic can be investigated.
Abstract: Several new potential alternative transformation tougheners to zirconia have been identified on the basis of crystallographic considerations and experimental observations Examples can be found in ceramics, minerals, and components of glass and of cement The displacive transformations exhibit martensitic characteristics of dusting or self-disintegration, and a critical particle size effect operates Large positive volume changes (< 12%) accompany the transformations on cooling, in the lanthanide sesquioxides (Ln2O3), dicalcium silicate (Ca2SiO4), and nickel sulfide (NiS) High Ms temperatures (<2000°C) in the Ln2O3 compounds also suggest the possibility of high-temperature transformation toughening Detrimental negative volume changes are seen in composites with enstatite (MgO · SiO2) and the lanthanide borates (LnBO3) The relative effects of volume change, X-ray unit-cell shape change, and the (martensitic) macroscopic shape change on the mechanical properties of a composite ceramic can thus be investigated