bluuebunny/crossref_metadata_2025 huggingface dataset:
DIFFICULTIES IN FIRING DECORATED WHITEWARE*
Authors: Robson J T.
Published: July 2010

Some of the problems cncountered in firing decorated whiteware are discussed. Both commercial and laboratory tests were conducted t o show the cause of difficultie and thrir prevention The subjects discussed are (1) “spit‐out” or blistered glaze, (2) prevention of craxd or duntcd glaze, (3) firing of selenium red overglaze, and (4) prevention of specks m decorating or overglazing one‐fired whiteware.
THE RELEASE OF STRAIN IN GLASS*
Authors: Bailey James , Sharp Donald E.
Published: July 2010

Measurements of strain release1 showed that check results were obtained only when the previous history of the samples was the same. Moreover, if. was found that the release of strain was more rapid a t first than could be accounted for by the equation of Adams and Williamson.

This paper discusses the effect of previous history on the measurements, describes an improved device for loading the specimens, and suggests a logarithmic equation which, in general, fits the observations better than that of Adams and Williamson. Tests of the equation are made both on data obtained from the modified apparatus described and on the data of Adams and Williamson. I t is indicated that the Adams and Williamson equation gives too long an annealing time at higher temperatures and too short an annealing time at lower temperatures.

It appears that the rate of release of strain depends on power of the strain which varies from unity at high temperatures where the glass is a viscous fluid to a higher power at. low temperatures where the release of strain is elastico‐viscous in character. With a single specimen at any fixed temperature in the annealing range, however, it appears that the release of strain in various parts of the specimen takes place at a rate which is proportional to the strain, but that the rate undergoes continnal change with time.
WATER MOVEMENT IN STIFF‐MUD WARE AND ITS RELATION TO DRYING*
Authors: Lovejoy Ellis
Published: July 2010

Stiff‐mud test bars were dried from one surface, and the rate of water loss was determined by frequent weighings. The plotted curves indicate an end point in the water movement with a loss of around 60% of the total water, This loss was checked by soluble salts in the clay and alkalinity tests at intervals.
AN X‐RAY STUDY OF THE TOUGHNESS OF PAVING BRICK*
Authors: Stong Guy E.
Published: July 2010

X‐ray diffraction photographs of paving brick were compared with those of pure materials.

The most important result obtained in this work is the discovery of a line in the X‐ray diffraction pattern of paving brick which is characteristic of high‐grade shale paving brick. This line, produced by an undetermined crystal, is more intense in the tougher than in the weaker brick. The line falls at 2.03 + 0.01 Ångström units.

A further result of this investigation is the proof that cristobalite, mullite, sillimanite, alumina, and cyanite are not present in the paving brick studied. This also shows that mullite is not produced in ceramic materials at the relatively low temperature at which paving brick are fired.
CONSTITUTION AND MICROHARDNESS OF FUSED CORUNDUM ABRASIVES*
Authors: Schrewelius Nils G.
Published: July 2010

Abstract

By means of X‐ray crystallographic studies it has been proved that fused corundum abrasives are mainly α‐Al2O3 or a solid solution of 10.6 mol.% Ti2O3 in alumina. In addition, the following crystalline impurities forming a matrix have been identified: a calcium titano‐aluminate with variable composition CaO.[6(Al, Ti)2O3], spinel (MgO.‐Al2O3), Na2O.11Al2O3, quartz, rutile, and an iron‐silicon‐titanium alloy.

Knoop microhardness numbers and dimensions of the unit cell of the corundum lattice have been determined and correlated with the chemical composition of various corundum abrasives. It has been found that the formation of a solid solution of Ti2O3 in Al2O3 is followed by a decrease of the microhardness of the corundum phase from about 2100 for the pure alumina to about 1940 for the solid solution. The latter has been found in all commercial corundum abrasives containing more than 1.5% TiO2, the former in all white titanium‐free samples. In making fused corundum blocks in large experimental electrical arc furnaces from various low‐grade bauxites and coke, the corundum obtained contained only about 1% TiO2, minute changes in the furnacing effecting the formation of the pure and hard corundum or the softer solid solution.
Phase Relationships in the System Zirconia—Ceria
Authors: DUWEZ POL , ODELL FRANCIS
Published: July 2010

The phase relationships in the system zirconia‐ceria were investigated by X‐ray diffraction and dilatometric methods. The specimens were prepared by mixing and compacting the oxide powders and firing at 2000°C. At 2000°C. zirconia and ceria are miscible in each other from about 24 to 100 mole % ceria. The range of solid solubility decreases markedly with temperature, so that near 1000°C. the solubility of zirconia in ceria is only about 10 mole %. The addition of 0 to 1.5 mole % ceria lowers the temperature at which zirconia transforms from the tetragonal to the monoclinic form. Near 15%, therefore, this temperature is below room temperature and zirconia is stabilized. On the basis of these results, a tentative phase diagram of the system zirconia‐ceria is presented. Experiments also have been conducted with zirconia containing 13.8 mole % magnesia (stabilized zirconia). In this case the solubility between stabilized zirconia and ceria is complete at high temperature (2000°C.). At lower temperature, however, the solid solution breaks down and a two‐phase region appears in the center of the diagram.
Phase Equilibria in the System BaO–TiO2
Authors: RASE D. E. , ROY RUSTUM
Published: July 2010

The system BaO‐TiO2 was investigated using quenching, strip‐furnace, and thermal techniques. Five compounds were found to exist in the system: Ba2TiO4, BaTiO3, BaTi2O5, BaTi3O7, and BaTi4O9. Of these, only barium metatitanate (BaTiO3) melts congruently (at 1618°C.). The dititanate melts incongruently at 1322° C. to yield BaTiO3 and liquid; the trititanate melts at 1357°C. to yield BaTi4O9 and liquid; the tetra‐titanate melts to TiO2 and liquid at 1428° C. The nature of melting of the orthotitanate could not be determined accurately because of the high temperature involved and the rapid reaction with platinum. The two eutectics in the system occur between Ba2TiO4 and BaTiO3 at 1563°C. and between BaTi2O5 and BaTi3O7 at 1317°C. The temperature of the cubic‐hexagonal transition in barium metatitanate was determined as 1460°C. and the transition has been shown to be reversible. The transition temperature is raised sharply by the addition of a small percentage of TiO2 although the extent of solid solution is quite limited. Some applications to the manufacture of titanate bodies and to the growth of single crystals of barium metatitanate are discussed.
New Data on Thermal Decomposition of Kaolinite and Halloysite
Authors: ROY RUSTUM , ROY DELLA M. , FRANCIS E. E.
Published: July 2010

Using single‐crystal electron diffraction data it has been possible to demonstrate more directly the existence of considerable order in dehydroxylated kaolinite and halloysite. The two‐dimensional (a‐b) plane structure of dehydroxylated kaolinite is very similar to that of kaolinite. This phase, appropriately described by the term “metakaolinite,” decomposes first at about 825°C., γ‐Al2O3 being the chief crystalline product. In the case of halloysite the γ‐Al2O3 appears first at about 650°C. The products observed on the dehydroxylation of kaolinite depend to a large extent on the particle size of the sample used. Electron microscope studies of dehydroxylated material and the same material treated under very mild hydrothermal conditions show that the main phenomena accompanying dehydroxylation apparently are disalignment along the c‐axis, the appearance of discontinuities in the sheets themselves (not visible directly in the crude image of the electron microscope), and the reduction of the effective particle size. The cause of the exothermic peak cannot be the formation of γ‐Al2O3 but is assigned to the formation of mullite which is not necessarily detected in an X‐ray powder pattern.
Properties of Si3N4 Produced by Nitriding Slip‐Cast Si Containing Si3N4 Grog Additions
Authors: Williams RobertM. , Ezis Andre , Caverly John C. , Onoda G.Y.
Published: July 2010

The properties of Si3N4 compositions produced by nitriding slip‐cast Si bodies containing up to 16% Si3N4 grog were determined. The introduction of grog consistently lowered the densities, the room‐ and high‐temperature strengths, and the resistance to oxidation. The open structure of the grog‐containing mixes favored low‐temperature gas‐phase reactions leading to α‐Si3N4 formation. In higher‐density compositions containing predominantly Si, gas‐liquid‐solid reactions at higher temperatures produced a relatively greater content of the β phase.
Comparison of Short‐Term Leaching in Both Radiation‐Damaged and Annealed Nuclear Waste Glasses
Authors: Wald John W. , Roberts Frank P. , LACKEY W.J.
Published: July 2010

Curium‐doped simulated nuclear waste glasses that received a cumulative α‐recoil dose of 9×1024α decays/m3 were leach‐tested under static conditions in deionized water at 90°C for 14 d. Test results indicate a diflerence of less than a factor of two between annealed and (saturation) radiation‐damaged glass in the release of 244Cm, glass‐forming constituents, and simulated waste products.
New Sodium Borate Glasses
Authors: Kasper JamesE. , Feller StevenA. , Sumcad GustavoL. , Boyd D.C.
Published: July 2010

The glass‐forming regions for the sodium borate system were determined using a roller‐quencher. The new regions are R=0 to 0.8 and R=1.2 to 4.9for samples prepared from sodium carbonate (where R=mol% Na2O/mol% B2O3). Above R=2.0 retention of‘C02 occurs. Quantitative measures of CO2 retention as a function of R are reported. The results using sodium carbonate extend by a considerable amount the limits reported by Imaoka and are comparable to the recent data of Ota and Soga.
Crack‐Growth Resistance of Microcracking Brittle Materials
Authors: EVANS A.G. , FABER K.T.
Published: July 2010

A mechanics model of microcrack toughening is presented. The model predicts the magnitude of microcrack toughening as well as the existence of R ‐curve effects. The toughening is predicated on both the elastic modulus diminution in the microcrack process zone and the dilatation induced by microcracking. The modulus effect is relatively small and process‐zone‐size‐independent. The dilatational effect is potentially more substantial, as well as being the primary source of the R curve. The dilatational contribution is also zone‐size‐dependent. The analysis demonstrates that microcrack toughening is less potent than transformation toughening.
The Formation of Magnesium Oxychloride Phases in the Systems MgO‐MgCl2‐H2O and NaOH‐MgCl2‐H2O
Authors: BILINSKI HALKA , MATKOVIĆ BORIS , MAŽURANIĆ CARMEN , ŽUNIĆ TONCCI BALIĆ
Published: July 2010

The reactions leading to the formation of crystalline Mg3(OH)5Cl·4H2O (phase 5), Mg2(OH)3,Cl·4H2O (phase 3), and Mg(OH)2 are compared for the systems MgO‐MgCl2‐H2O and NaOH‐MgCl2‐H2O. The crystalline phases were determined by X‐ray diffraction analysis. The concentration of the total magnesium and chloride in the solution and the pH of the solution determine the reaction product(s) in both systems. The influence of MgO reactivity and the molar ratio of reactants on the formation and stability of reaction products is discussed and the mechanism of the formation of phases 3 and 5 is explained. In the system MgO‐MgCl2‐H2O, MgO serves only to increase the concentration of total magnesium and the pH of the MgCl2 solution.
Effect of Glass‐Transition Temperature of Polyethylene Glycol‐Plasticized Polyvinyl Alcohol on Granule Compaction
Authors: NIES C. W. , MESSING G. L.
Published: July 2010

The glass‐transition temperature (Tg) is a fundamental property of all organic binders, It is illustrated with polyethylene glycol (PEG)‐plasticized polyvinyl alcohol (PVA) binder systems that densification is enhanced when the binder Tg, is below the pressing temperature. This is a result of the increased deformability of the binder system and the decrease in the granule strength. Because of the reduction in the binder film strength with increasing PEG content, increasing the PEG content to lower the binder Tg, results in reductions in the compact green strength.
Multiaxial Loading Fracture of Al2O3 Tubes: I, Experiments
Authors: STOUT M.G. , PETROVIC J.J.
Published: July 2010

Alumina thin‐walled tubes were fractured in axial tension, hoop tension, balanced biaxial tension, balanced tension‐compression, and pure torsion using an electrohydraulic mechanical testing apparatus. A slight anisotropy in the axial and hoop uniaxial strengths indicated that the predominant defects were axially oriented, and probably fabrication‐related as opposed to machining flaws. A 10% weakening was observed in balanced biaxial tension as compared to uniaxial tension, whereas strength was insensitive to a balanced tension‐compression stress state. The strength in pure torsion was 16% higher than the axial strength. Stress state results suggest a weakening due to in‐flaw plane tensile stresses and more complex fracture‐initiation phenomena for stresses not oriented perpendicular to the dominant defects.
Phase Equilibria in the System La2O3‐P2O5
Authors: PARK HEE DONG , KREIDLER ERIC R.
Published: July 2010

Subsolidus phase equilibria in the system La2O3‐P2O5 were established. The system contains six intermediate compounds having molar La2O3:P2O5 ratios of 3:1,7:3,1:1,1:2,1:3, and 1:5. It was found that the 3:1 compound has a phase transformation at 935°C. The 1:2 compound decomposes to a mixture of 1:1 and 1:3 at 755°C. The 1:3 compound melts incongruently to 1:1 and liquid at 1235°C and the 1:5 compound melts congruently at 1095°C. None of the lanthanum phosphates have lower temperature limits of stability.
Solubility of Metals in Substoichiometric TiC1‐x
Authors: KERANS R. J. , MAZDIYASNI K. S. , RUH R. , LIPSITT H. A.
Published: July 2010

Twenty‐one elements were screened for solubility in selected titanium‐carbide compositions at 1600°C. Tin, lead, and aluminum were found to dissolve to an appreciable extent only in carbide compositions very near the titanium‐titanium carbide phase boundary. Small additions of Sn caused a substantial shift in this boundary in the direction of reduced carbon content, accompanied by reduced microhardness, indicating reduced flow stress. The degree of solubility of the alloying additions and/or excess Ti in the carbide is lower at T<1400°C, as evidenced by the appearance of fine metallic precipitates on aging or slow cooling. However, a single‐phase alloyed carbide can be retained by quenching. In contrast, the solubility of Cr in TiC was found to decrease with decreasing carbon content, and the flow stress, as indicated by microhardness, to increase with increasing Cr content.
Effect of Step Size in Incremental Loading Tests on Glass Specimens
Authors: DAVIS M. W. , MOULD R. E.
Published: July 2010

When incremental loading tests are used to determine the strength of glass, preexisting flaws can grow subcritically during the loading history prior to the stress level, causing failure. Calculations have been performed using linear elastic fracture mechanics (LEFM) to predict the effect of the step size on the strength value obtained in such an incremental test. The theory showed step size to have a small, predictable effect on the average strength values determined by an incremental test. The results obtained permit taking this effect into consideration when utilizing such tests. Experimental verification of the theoretical approach was obtained by predicting and measuring the time‐to‐failure during the final load increment at which fracture occurred on actual tests.
Formation of Calcium Hydroxide from Aqueous Suspensions of Tricalcium Silicate
Authors: WU ZHAO‐QI , YOUNG J. FRANCIS
Published: July 2010

The release of Ca2+ and OH” from tricalcium silicate into the aqueous phase was monitored over the first few hours. The solution becomes supersaturated with respect to pure calcium hydroxide with the maximum activity product being about 3.5 times greater than the solubility product. Evidence is presented in support of “silicate poisoning” of calcium hydroxide nuclei. The addition of soluble salts changes the time at which maximum supersaturation is attained but not its magnitude. The analytical data are compared with the rate of heat released from companion pastes.
Heat Capacity of Sodium Silicate Liquids
Authors: Richet Pascal , Bottinga Yan , Tequi Christophe
Published: July 2010

Drop calorimetry measurements for four Na20‐Si02 liquids indicate that, to within ±0.5%, the heat capacities are temperature‐independent between 900 and 1800 K and additive functions of composition for liquids containing from 50 to 100 mol% Si02. In this composition interval, the partial molar heat capacities of Si02 and Na20 are 81.37 and 100.6 J /mole‐K, respectively.
Internal Friction in Metaphosphate Glasses
Authors: Suzuki Suguru , Takahashi Minoru , Kobayashi Taneo , Sakamura Hlroyasu
Published: July 2010

The internal friction of metaphosphate glasses was measured as a function of temperature by a free torsional vibration method. In the high‐temperature region metaphosphate glasses (MO/P2O5=l)for which M=Ca, Sr, or Ba exhibit high‐temperature peaks in plots of internal friction vs temperature, whereas for M =Mg or Zn this peak is missing.
The Effect of Stoichiometry on Mechanical Properties of Boron Carbide
Authors: Niihara Koichi , Nakahira Atsushi , Hirai Toshio
Published: July 2010

The mechanical properties of chemically vapor‐deposited boron carbides (B4C) with varied B/C ratios were investigated as a function of composition. The maximum hardness, H, and fracture toughness, K1c, were observed at an almost stoichiometric composition. For nonstoichiometric B4C (B/C>4), H and K1c decreased with increasing B content, suggesting that excess B diminishes the bond strength in the B4C structure. The decrease in H and K1C at B /C <4 was attributed to free C in the microstructure.
A Simple Calculation of Process‐Zone Toughening by Microcracking
Authors: Clarke D.R.
Published: July 2010

The method introduced by Evans and colleagues to calculate transformation toughening resulting from a dilatant transformation is extended, using the Eshelby “equivalent inclusion” approach, to treat the case of toughening resulting from microcracking.
Bubble Formation in Oxide Scales on SiC
Authors: Mieskowski Diane M. , Mitchell T. E. , Heuer A. H.
Published: July 2010

The oxidation ofa‐SiC single crystals and sintered α‐ and β‐SiC polycrystals has been investigated at elevated temperatures. Bubble formation is commonly observed in oxide scales on polycrystalline SiC but is rarely found on single‐crystal scales; bubbles result from the preferential oxidation of C inclusions, which are abundant in SiC polycrystals. The absence of bubbles on single crystals in fact implies that diffusion of the gaseous species formed on oxidation, CO (or possibly SiO), controls the rate of oxidation of SiC.
Vibrational Spectroscopy of Pb/Mn/Ga Fluoride Glasses
Authors: BENDOW BERNARD , BANERJEE PRANAB K. , MITRA SHASHANKA S. , JACOBONI CHARLES , DEPAPE ROBERT
Published: July 2010

Measurements of polarized Raman scattering and fundamental ir reflectivity in Pb /Mn /Ga fluoride glasses are reported. The spectra are similar overall to those of fluorozirconates, displaying two main bands in both Raman and ir, with the higher‐frequency Raman band being relatively narrow and highly polarized.
Preparation of High‐Strength Calcium Phosphate Glass‐Ceramics by Unidirectional Crystallization
Authors: ABE YOSHIHIRO , KASUGA TOSHIHIRO , HOSONO HIDEO , DE GROOT K.
Published: July 2010

Unidirectionally crystallized CaO‐P2O5 glass‐ceramics were produced by reheating glass rods between 450° and 580°C (glass transition temperature ∼500°C) under a temperature gradient of 30°C/cm. These glass‐ceramics exhibit high bending strength (∼650MN/m2) and toughness. Sample preparation is described and compared with conventional unidirectional solidification of melts. The characteristic mechanical properties are discussed in terms of the texture of the glass‐ceramics.
Creep Analysis of Bend Specimens Subject to Tensile Cracking
Authors: VENKATESWARAN ANURADHA , HASSELMAN D. P. H.
Published: July 2010

Expressions are derived which permit the analysis of creep data, obtained in bending, for poly crystalline ceramics subject to tensile cracking. A numerical example based on literature data indicates that by considering the effect of cracks much better agreement is obtained between diffusion coefficients inferred from the creep data and those obtained by direct diffusion measurements.
Controlled Crystallization of Amorphous Si3N4by Ti and CI Additives
Authors: NOBUGAI KOHJI , YABE SHIGEKI , KANAMARU FUMIKAZU
Published: July 2010

Thin films of amorphous Si3N4 were prepared by the rf‐sputtering method, and the effects of titanium and chlorine additives on its crystallization were examined. When Ti‐doped amorphous Si3N4 was heated, TiN precipitated at >1100°C; the TiN precipitates promoted the conversion of amorphous Si3N4 to β‐Si3N4. Chlorine led to preferential conversion of amorphous Si3N4 to α‐Si3N4.
Hot‐Pressing of High‐Purity Magnesium Oxide
Authors: VIEIRA J.M. , BROOK R.J.
Published: July 2010

High‐purity magnesium oxide powder was prepared by eon‐trolled decomposition of magnesium chloride hexahydrate. The MgO was hot‐pressed between 1720 and 2170 K and at pressures from 4.4 to 31 MPa. At 1873 K, the densification rates measured at fixed values of density were proportional to the power n= 3 of the applied pressure, this being consistent with a mechanism of dislocation creep. It was also observed that the density was proportional to the logarithm of time in this range of temperature and pressure. Given the theoretically expected lack of dependence of the dislocation creep rate on grain size, the proportionality between the density and the logarithm of time cannot be explained as a consequence of grain growth during densification.
Diphasic Xerogels, A New Class of Materials: Phases in the System Al2o3‐Sio2
Authors: HOFFMAN DAVID W. , ROY RUSTUM , KOMARNENI SRIDHAR
Published: July 2010

Two series of xerogels (desiccated hydrogels), one consisting of single phases and the other of two phases, were prepared from organic and inorganic precursors in the system Al2o3‐Sio2. The effect of these nanostructural differences in the xerogel powders on the energy content and behavior on heating were studied using DTA, powder X‐ray diffraction, and ultrafast heating on a strip furnace. The results demonstrate that diphasic xerogels are substantially different materials from single‐phase xerogels of the same composition.
Oxidation and Diffusion in Selected Pitch‐Bonded Magnesia Refractories
Authors: BREZNY RASTO , SEMLER CHARLES E.
Published: July 2010

A conventional and an improved (Mg‐containing) BOF refractory, of commercial pitch‐bonded magnesia type, were evaluated to determine their Mg diffusion and carbon oxidation characteristics. MgO dense‐zone formation was characterized experimentally for various firing times at 1650°C, from which Mg diffusion coefficients in the range 1.4x10‐9 to 8.13x10‐10cm2/s were determined. The data indicate that the Mg diffusion in the system is of the extrinsic type, controlled by the impurities in the MgO, such as Al3+, Fe3+, and Cr3+. The effects of Mg vaporization and MgO condensation, preceding dense‐zone formation, were observed to initiate at 1200°C. The dense‐zone thickness and the amount of unoxidized carbon were greatest for the Mg‐containing refractory.
Use of the Adam‐Gibbs Equation in the Analysis of Structural Relaxation
Authors: SCHERER GEORGE W.
Published: July 2010

Narayanaswamy's model of structural relaxation has been shown to provide an excellent description of the behavior of a variety of glasses. In the standard formulation, the relaxation time, τ is represented by the Arrhenius equation, with the activation energy partitioned between the temperature and Active temperature. That form for τ is successful, but lacks theoretical justification. In this paper, the Adam‐Gibbs equation is shown to describe accurately both τ and the viscosity of NBS 710 (alkali lime silicate) glass. This equation is expected to be accurate over a wider range of temperature and Active temperature than the Arrhenius equation.
CO2‐Catalyzed Surface Area and Porosity Changes in High‐Surface‐Area CaO Aggregates
Authors: BERUTO DARIO , BARCO LUIGI , SEARCY ALAN W.
Published: July 2010

The changes in surface area and mesoporosity in aggregates of ∼0.01 μm cross‐section CaO particles when heated in CO2at 686°C were determined from N2 adsorption isotherms. Initially, the surface area decreases rapidly with little change in porosity. When the surface area has decreased below ∼90 m2/g, surface area and porosity variations become consistent with expectations for coarsening by grain‐boundary or bulk diffusion. The initial rapid decrease in surface area must result from CO2‐catalyzed surface diffusion, but the data suggest that surface diffusion is not rate‐limiting. The rate‐limiting step may be reaction of CO2 to form surface CO32‐ ions or decomposition of these ions to O2‐ ions and CO2 gas.
Step‐Heating Technique for Thermal Diffusivity Measurements of Large‐Grained Heterogeneous Materials
Authors: Bittle R. R. , Taylor R. E.
Published: July 2010

The laser‐flash technique for thermal diffusivity determinations was modified to handle thicker samples (up to 1.3 cm). The modification consisted of substituting an ir source for the laser and using step heating. Thus measurements can be made on representative samples of large‐grained heterogeneous materials. Experimental measurements were made on a carbon magnesite brick, and the concept was verified using finite‐element models.
Directional Solidification of (Ti, Zr) Carbide‐(Ti, Zr) Diboride Eutectics
Authors: SORRELL C.C. , BERATAN H.R. , BRADT R.C. , STUBICAN V.S.
Published: July 2010

Crystallographic and microstructural features of the directionally solidified ZrC‐ZrB2, ZrC‐TiB2, and TiC‐TiB2 eutectics were studied. Growth directions were the [011] for the cubic carbide phases and the [01.0] for the hexagonal diborides, yielding an interfacial plane for the lamellar eutectics of (111)cubic parallel to (00.1)hexagonal. The ZrC‐ZrB2 and TiC‐TiB2 each exhibited regular lamellar growth, whereas the ZrC‐TiB2 had a Chinese script‐type of microstructure. A λ2R= constant growth law was followed where the constants are (2.57 plusmn; 0.63) × 10‐18 m3/s for the ZrC‐ZrB2, (3.97 ± 0.60) × 10−18 m3/s for the TiC‐TiB2, and (2.74 ± 0.68) ± 10‐17 m3/s for the ZrC‐TiB2.
Reaction of Sodium with Ionic Conductors Containing P‐O Bonds at Elevated Temperatures
Authors: TENNENHOUSE G. J. , CROSBIE GARY M.
Published: July 2010

Sodium phosphate and a series of compounds containing Na, Zr, Si, P, and O were found to react with sodium at 380°C. The reaction products formed phosphine on hydrolysis. On the basis of these reactions and some thermodynamic calculations, it is not likely that any materials containing P‐O bonds will be stable to sodium at the temperatures required for the Na‐S battery or Na heat engine operation.
Surface Analytical Study of Synroc Subjected to Hydrothermal Attack
Authors: MYHRA S. , ATKINSON A. , RIVIÈRE J. C. , SAVAGE D.
Published: July 2010

Specimens of the ceramic Synroc, both with (Synroc C) and without the addition of a simulated nuclear waste (Synroc B), were subjected to hydrothermal attack. The near‐surface regions, both before and after attack, were characterized using X‐ray photoelectron spectroscopy, Auger electron spectroscopy, and scanning electron microscopy. Ion‐beam erosion was used in conjunction with these surface analysis techniques to obtain information from below the original surface. It was found that hydrothermal attack led to the formation of a modified layer extending to a maximum depth of ∼200 nm after 25 days at 350°C. Within this modified layer, the abundances and chemical states of the elements were different from those in the unattacked Synroc. The changes which were observed can be explained qualitatively by postulating that selective dissolution (e.g., for Ca and Ba), hydration (e.g., for Al and Fe), recrystallization (e.g., for Ti and Zr), and reaction with Co2 dissolved in the liquid phase (e.g., to form CaCO3) are all taking place.
Quantitative Electron Energy‐Loss Measurements on the System ZrO2‐CaO
Authors: STENTON NICOLA , NOTIS MICHAEL R. , WILLIAMS DAVID B.
Published: July 2010

The accuracy of present EELS quantification procedures has been assessed using a directionally solidified eutectic in the system ZrO2‐CaO. In the present study, Ca/O ratios were determined under various operating and analysis conditions and showed good agreement with values calculated from the stoichiometry. Systematic errors in the EELS data were attributed to difficulties in fitting the Ca edge, due to the proximity of other edges in the spectrum, highlighting one of the major problems associated with analysis of multicomponent systems. In addition, sharp discontinuities in the Ca/O ratio were observed when profiling across lamellar interfaces, indicating that EELS shows good sensitivity to abrupt changes in composition and has potential for quantitative light element analysis.
Microstructural Changes in Hot Isostatically Pressed Alumina‐Glass Composites
Authors: Kwon Oh‐Hun , Messing Gary L.
Published: July 2010

Alumina‐glass composites with a small amount of a continuous glassy phase and closed pores were prepared and isostatically hot‐pressed under varied conditions. Induced macropore structure showed partiallcomplete pore filling with glass and some evidence of pore collapsing. Pore filling was achieved by viscous from of the glass from the grain boundary to the macropores, which causes a simultaneous localized rearrangement of the alumina grain structure.
Viscosities, Glass Transition Temperatures, and Microhardness of Y‐Si‐A1‐O‐N Glasses
Authors: Hampshire Stuart , Drew Robin A. L. , Jack Kenneth H.
Published: July 2010

Y‐Si‐A1‐O‐N glasses containing up to 15 at.% nitrogen were prepared. Comparisons of properties of glasses with the same cation composition but with varying N:O ratios show that glass transition temperature, viscosity, and microhardness all increase with increasing nitrogen content.
Hot Isostatic Processing of Shocked Si3N4 Powder
Authors: Sōmiya Shigeyuki , Yoshimura Masahiro , Fujiwara Shutaro , Kondo Ken‐Ichi , Sawaoka Akira , Haitori Takeo , Mohri Jun‐Ichi , Araki Masatada
Published: July 2010

To enhance the sinter ability of Si3N4, powders mixed with 0, 2, and 5 wt% Y2O3 were explosively shock‐treated. Compacts of these powders were encapsulated in 96% silica glass containers and isostatically hot‐pressed. The shocked Si3N4 with 5 wt% Y2O3 was pressed to a density of 3.09 g/cm3 (95.4% of theoretical) at 1400°C under 430 MPa for 3 h, whereas the unshocked material attained only 82.4% of theoretical density under the same hot isostatic pressing conditions.
Silicon Nitride Based Ceramic Nanocomposites
Authors: Pan Xiaoqing , Mayer Joachim , Rühle Manfred , Niihara Koichi
Published: July 2010

Nanocomposites (Si3N4/SiC) were studied by combined high‐resolution transmission electron microscopy and electron energy‐loss spectroscopic imaging (ESI) techniques. In ESI micrographs three types of crystalline grains were distinguished: Si3N4 matrix grains (0.5 μΩ), nanosized SiC particles (<100 nm) embedded in the Si3N4, and large SiC particles (100–200 nm) at grain boundary regions (intergranular particles). Amorphous films were found both at Si3N4 grain boundaries and at phase boundaries between Si3N4 and SiC. The Si3N4 grain boundary film thickness varied from 1 to 2. 5 nm. Two kinds of embedded SiC particles were observed: type A has a special orientation with respect to the matrix, and type B possesses a random orientation with respect to the matrix. The surfaces of type B particles are completely covered by an amorphous phase. The existence of the amorphous film between the matrix and the particles of type A depends on the lattice mismatch across the interface. The mechanisms of nucleation and growth of Ω‐Si3N4 grains are discussed on the basis of these experimental results.
Effect of Phase Transformation on the Sintering of Lead Barium Metaniobate Solid Solutions
Authors: Kimura Toshio , Kuroda Yukinori , Lee Ho Sung
Published: July 2010

The densiflcation behavior and microstructure development were examined for Pb1‐xBaxNb2O6(x = 0.0, 0.15, and 0.30) with the low‐temperature rhombohedral form. The rhombohedral form transformed to the high‐temperature tetragonal form during sintering. The phase transformation increased the rate of grain growth, which influenced the microstructure development and densiflcation. The densiflcation proceeded partly before the phase transformation occurred, and the microstructure changed by the sequential formation of necks, chainlike grains, and equiaxed grains. The microstructure just after the phase transformation was determined by the microstructure just before the phase transformation. The chainlike and equiaxed grains changed to elongated and large equiaxed grains, respectively. Pore shape also changed.
Oxidation Behavior of MuIlite‐Coated SiC and SiC/SiC Composites under Thermal Cycling between Room Temperature and 1200°‐1400°C
Authors: Lee Kang N. , Miller Robert A.
Published: July 2010

Refractory oxide barrier coatings are a promising approach for improving the environmental durability of silicon‐based ceramics in severe environments. The oxidation durability of a newly developed fully crystalline mullite coating on SiC and SiC/SiC composites was investigated under thermal cycling between room temperature and 1200°‐1400°C with a higher frequency (1‐ or 2‐h) and a lower frequency (20‐h) cycling for times up to 1200 h. The new mullite coating exhibited significantly improved adherence and resistance to cracking when compared to conventional mullite coatings. Current issues include oxidation of SiC‐based substrates, void formation at the coating/substrate interface, and cracking in the coating through the thickness.
Crack Suppression in Strongly Bonded Homogeneous/Heterogeneous Laminates: A Study on Glass/Glass‐Ceramic Bilayers
Authors: Wuttiphan Sataporn , Lawn Brian R. , Padture Nitin P.
Published: July 2010

A study is made of a glass/glass‐ceramic bilayer as a model homogeneous/heterogeneous laminate. The underlying objective is microstructural design of ceramic layer systems with optimum mechanical properties, alternating hard layers, for wear resistance, with tough layers, for fracture resistance. Mica flakes in the glass‐ceramic layer inhibit the propagation of well‐developed intrusive cracks, by bridging; these same flakes render the structure susceptible to distributed damage, by providing discrete weakness at the microstructural level. A major distinguishing feature of the bilayer design is the incorporation of a strong interface, so that cracks are inhibited by the underlayer rather than deflected between the layers. Vickers and Hertzian indentation tests on specimen cross sections demonstrate the capacity of the glass‐ceramic layer to arrest radial and cone cracks penetrating from the adjacent glass layer. Additional Hertzian tests on the outer surfaces of glass layers in a coating/substrate configuration show diffuse damage accumulation in the glass‐ceramic substrate layers. This diffuse damage absorbs energy and shields cone cracks in the glass from the applied loading. Implications concerening the design of damage‐tolerant laminate structures are discussed.
Arrest of Fatigue Cracks in Transformation‐Toughened Ceramics
Authors: Møller Carsten V , Karihaloo Bhushan L.
Published: July 2010

A theoretical model based on the theory of complex potentials and dislocation formalism is used to simulate fatigue crack growth in a transformation‐toughened ceramic. The effective stress‐intensity factor is calculated during crack growth, because it is believed to determine the crack‐growth rate similar to the Paris‐type growth law. For certain combinations of transformation strength and load, the effective stress‐intensity factor decreases to zero, indicating crack arrest. A detailed parametric study of this phenomenon reveals that the applied load and minimum transformation strength parameter necessary to cause crack arrest are linearly related, independent of initial crack length. This suggests that a threshold stress similar to the endurance limit in the conventional stress/life (S/N) approach should be used instead of the threshold stress‐intensity factor in the design of transformation‐toughened ceramics against fatigue.
Strength and Microstructure of Silicon Nitride Ceramics Brazed with Nickel‐Chromium‐Silicon Alloys
Authors: Hadian Ali Mohammad , Drew Robin A. L.
Published: July 2010

Joining of sintered Si3N4 was performed using a high‐temperature brazing technique. Ni‐based brazing alloys having the same Ni:Cr ratio as AWS BNi‐5 (Ni·18Cr·19Si (at. %)) but different Si content were used as the brazing filler metals. Joining experiments were performed at 1220°C under a N2 partial pressure of 15 Pa for different times between 5 to 15 min. The highest room‐temperature four‐point bend strength of the joints was 115 MPa, whereas 220 MPa was achieved when the joints were tested at 900°C. The high strength of the experimental joints was attributed to the reduction in residual stresses and formation of a CrN reaction layer at the ceramic/filler metal interface.
The System HfO2‐Y2O3‐Er2O3
Authors: Andrievskaya Elena R. , Lopato Lidia M. , Smirnov Vasily P.
Published: July 2010

A mathematical model of the liquidus surface based on a reduced polynomial method was proposed for the system HfO2‐Y2O3‐Er2O3. The results of calculations according to this model agree fairly well with the experimental data. Phase equilibria in the system HfO2‐Y2O3‐Er2O3 were studied on melted (as‐cast) and annealed samples using X‐ray diffraction (at room and high temperatures) and micro‐structural and petrographic analyses. The crystallization paths in the system HfO2‐Y2O3‐Er2O3 were established. The system HfO2‐Y2O3‐Er2O3 is characterized by the formation of extended solid solutions based on the fluorite‐type (F) form of HfO2 and cubic (C) and hexagonal (H) forms of Y2O3 and Er2O3. The boundary curves of these solid solutions have the minima at 2370°C (15. 5 mol% HfO2, 49. 5 mol% Y2O3) and 2360°C (10. 5 mol% HfO2, 45. 5 mol% Y2O3). No compounds were found to exist in the system investigated.
Homogeneity Region and Thermal Stability of Neodymium‐Doped α‐Sialon Ceramics
Authors: Shen Zhijian , Ekström Thommy , Nygren Mats
Published: July 2010

Dense sialon ceramics along the tie line between Si3N4 and Nd2O3·9AlN were prepared by hot‐pressing at 1800°C. The materials were subsequently heat‐treated in the temperature range 1300–1750°C and cooled either by turning off the furnace (yielding a cooling rate (Tcool) of ∼50°C/min) or quenching (Tcool≥ 400°C/min). It was found necessary to use the quenching technique to reveal the true phase relationships at high temperature, and it was established that single‐phase α‐sialon forms for 0.30 x 0. 51 in the formula NdxSi12–4SxAl4.5xO1. 5x, N16–1.5x. The α‐sialon is stable only at temperatures above 1650°C, and it transforms at lower temperatures by two slightly different diffusion‐controlled processes. Firstly, an α‐sialon phase with lower Nd content is formed together with an Al‐containing Nd‐melilite phase, and upon prolonged heat treatment thus‐formed α‐sialon decomposes to the more stable β‐sialon and either the melilite phase or a new phase of the composition NdAl(Si6‐zAlz)N10‐zOz. Nd‐doped α‐sialon ceramics containing no crystalline intergranular phase show very high hardness (HV10 = 22. 5 GPa) and a fracture toughness (Klc= 4.4 MPa·m1/2) at room temperature. The presence of the melilite phase, which easily formed when slow cooling rates were applied or by post‐heat‐treatment, reduced both the fracture toughness and hardness of the materials.
Advances in the Grinding Efficiency of Sintered Alumina Abrasives
Authors: Krell Andreas , Blank Paul , Wagner Eckhard , Bartels Günter
Published: July 2010

The study relates the grinding power of different grades of sintered alumina abrasives to their microstructures and to basic mechanical properties in comparison with conventionally fused electrocorundum and with an electrofused alumina/ zirconia eutectic. Contrary to the traditional approach of the Battelle test, the fracture toughness KIc of individual grains is measured by a quantitative indentation analysis. Compared with fused corundum, sintered alumina grits exhibit an increased toughness and grinding efficiency, but the further increase of KIc in the eutectic does not improve the grinding performance. The key parameter for grinding is the inherent hardness of the abrasive. The elimination of flaws by a new approach results in a strong increase in the grinding power of sintered alumina abrasives.
Hydrothermal Synthesis of Cerium(IV) Oxide
Authors: Hirano Masanori , Kato Etsuro
Published: July 2010

CeO2 powders have been prepared from cerium(III) nitrate, cerium(IV) sulfate, and cerium(IV) ammonium sulfate under hydrothermal conditions at 120° to 200°C for 5 to 40 h. The effects of the starting cerium compounds, hydrothermal treatment temperature, and the concentration of the solutions on the crystal growth of CeO2 were investigated. CeO2 powders hydrothermally synthesized at 180°C for 5 h from cerium(IV) salts had very fine particle sizes (30 Å); on the other hand, the powder from the cerium(III) salt had a relatively coarse particle size (160 Å). Although the crystallite size of the powder synthesized from the cerium(IV) compounds depended on the treatment temperature, that from the cerium(III) compound was insensitive to the treatment temperature. The mechanisms for the growth of CeO2 particles under hydrothermal conditions are discussed.
Thermal Decomposition of Alkoxides in an Inert Organic Solvent: Novel Method for the Synthesis of Homogeneous Mullite Precursor
Authors: Inoue Masashi , Kominami Hiroshi , Inui Tomoyuki
Published: July 2010

Thermal decomposition of a mixture of aluminum iso‐propoxide and tetraethoxysilane (Al/Si = 3) in toluene at 300°C was examined. The reaction completely proceeded and yielded an amorphous product. The DTA profile of the product showed a sharp peak at ∼1000°C which was associated with crystallization of mullite and a small amount of the spinel phase. The mullite prepared by calcination of the product at 1300°C was composed of micro‐crystals having an average diameter of 30 nm and had a large surface area of 41 m2g.
Compressive Properties of Yttrium Oxide
Authors: Ünal Özer , Akinc Mufit
Published: July 2010

Compressive properties of polycrystalline yttrium oxide (Y2O3) were studied by slow‐strain‐rate experiments (ε= 5.7 × 10–6 s−1) between room temperature and 1600°C. It was shown that Y2O3 fails in a brittle manner up to 1000°C, and at 1200°C and above plastic deformation becomes dominant. Plastic deformation of Y2O3 takes place exclusively by dislocation motion. Maximum stress, yield stress, and elastic modulus decrease with increasing temperature, although the decrease at temperatures above 1000°C is much more pronounced.
Aluminum K‐Edge Absorption (XANES) Studies of Noncrystalline Mullite Precursors
Authors: Küper Gerhild , Peitz Bettina , Winter Ines , Hormes Josef , Schneider Hartmut , Schmücker Martin , Voll Dietmar , Hoffbauer Wilfried
Published: July 2010

Noncrystalline aluminum silicate precursors MP1 and MP3 with different ratios of Al in tetrahedral ([4]A1), pentahedral ([5]A1), and octahedral ([6]A1) position were prepared from aluminum sec‐butylate and tetraethoxysilane (Al/Si ratio: 3/1) making use of a slow and rapid hydrolysis process, respectively. The MP2 precursor was synthesized from aluminum sec‐butylate and silicon tetrachloride (Al/Si ratio: 4/1) by rapid hydrolysis. All aluminum silicate gels were heat‐treated to temperatures just prior to crystallization to mullite and γ‐Al2O3, respectively (MP1 and MP3: 800°C; MP2: 300°C). Al K near‐edge absorption spectra (XANES) of the mullite precursors and of several suitable crystalline reference materials were measured using monochromatic synchrotron radiation. The reference XANES spectra yielded a linear correlation between the energy position of the first inflection point of the white lines and the frequency of sixfold‐coordinated Al ([6]A1) in the samples. A similar though less straightforward correlation seems to hold also for the white line intensities. From these findings, the actual [61]A1 frequencies for the mullite precursors under investigation were derived to be <10% (MP1), =30% (MP3), and =60% (MP2). The [6]A1 frequency distribution in the mullite precursors displays a trend similar to that determined by 27A1 NMR spectroscopy.
Freeform Fabrication of Ceramics via Stereolithography
Authors: Griffith Michelle L. , Halloran John W.
Published: July 2010

Ceramic green bodies can be created using stereolithography methods where a ceramic suspension consisting of 0.40–0.55 volume fraction ceramic powder is dispersed within an ultraviolet‐curable solution. Three ceramic materials were investigated: silica for investment casting purposes, and alumina and silicon nitride for structural parts. After mixing the powders in the curable solution, the ceramic suspension is photocured, layer by layer, fabricating a three‐dimensional ceramic green body. Subsequent binder removal results in a sintered ceramic part. Three‐dimensional objects have been fabricated from a 0.50 volume fraction silica suspension.
Change in Refractive Index of a Borosilicate Glass Fiber Annealed Below the Glass Transformation Temperature
Authors: Kang Seunggu , Lin Hongy , Day Delbert E.
Published: July 2010

Glass fibers pulled from multihole bushings can have a slight difference in thermal history that causes a distribution in the refractive index that can be narrowed by annealing the fibers. The kinetics for the initial stage change in refractive index for fiber annealed between 300° and 500°C are best described by a second‐order reaction with an activation energy of 120° 17 kj/mol. The improved uniformity in refractive index for annealed fibers is indicated by a decrease in the half‐height width of the optical transmission versus temperature curve for glass fiber immersed in a liquid. The standard deviation in the refractive index of glass fibers with a bimodal distribution in diameter decreases from 8 × 10‐4≤0.0002 to 4 × 10‐4 0.0002 after the fibers are annealed at 400°C for 1 h.
Ferroelastic Properties of Lead Zirconate Titanate Ceramics
Authors: Schäufele Ansgar B. , Heinz Härdtl Karl
Published: July 2010

To increase the reliability of multilayer actuators, calculation of the mechanical stress inside the device during operation is important. This paper shows that the small‐signal value of the elastic constant s is not sufficient to describe the complicated behavior of lead zirconate titanate (PZT) ceramics. Therefore, compressive strain and depolarization have been measured as a function of large‐signal stress applied parallel to the poling direction. The nonlinear dependence of the strain and depolarization can clearly be explained by domain processes. Soft and hard PZT ceramics have been investigated. In hard PZT, domain switching appears at higher stresses than in soft PZT. Moreover, in hard PZT, the domains partly switch back during unloading. The critical stress (coercive stress) necessary for a domain‐switching process shows a dependence on the Zr:Ti ratio that is quite similar to the dependence of the electric coercive field. The influence of an electric field applied parallel to the poling direction and superimposed on the compression experiment also has been examined. The coercive stress depends linearly on the electric field. The linear coefficient of this relation is given by the ratio of depolarization to compressive strain caused by domain switching.