bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiotracer Study of the Preparation of High‐Purity Lanthanum Fluoride
Authors: Ewing Kenneth J. , Jaganathan James , Peitersen Laura , Aggarwal Ishwar D. , Sommers James A. , Fahey Jeff V.
Published: March 2005

The behavior of the impurities iron, cobalt, yttrium, and cerium is determined via radiotracer techniques for the preparation of high‐purity lanthanum fluoride. The behavior of nickel and copper during the coprecipitation of a lanthanum nitrate solution is determined by graphite furnace atomic absorption spectrometric (GFAAS) analysis. There is no commercially available radiotracer for neodymium, a key impurity associated with absorption losses in fluoride glasses. However, the chemical behavior of neodymium and that of yttrium are very similar and, therefore, it is resonable to assume that the behavior of yttrium throughout the processing is indicative of the behavior of neodymium. The concentrations of impurities in lanthanum nitrate, carbonate, and fluoride are estimated using the radiotracer and GFAAS data for each processing step. Results indicate that while high‐purity lanthanum carbonate can be prepared, any impurities present in the lanthanum carbonate will be carried quantitatively into lanthanum fluoride upon hydrofluorination. The data also indicate that lanthanum nitrate can be prepared in higher purity than lanthanum carbonate; however, lanthanum fluoride prepared from the nitrate forms a very wet precipitate which is extremely difficult to filter and dry. The presence of excess water in lanthanum fluoride results in high levels of oxide contamination in lanthanum fluoride as well as the fluoride glass. Preparation of low‐oxide lanthanum fluoride is required because high oxide levels in fluoride glasses cause increased scattering. Therefore, from a fluoride glass point of view, the preferred synthetic route for the preparation of high‐purity lanthanum fluoride is to first purify lanthanum nitrate, then convert this to the carbonate, which is then converted to lanthanum fluoride. The estimated impurity concentrations in lanthanum fluoride derived from lanthanum carbonate are as follows: Fe, 89 ng/g; Co, <3 ng/g; Ni, <12 ng/g; Cu, 6 ng/g; Y, 62 ng/g; Ce, 248 ng/g. The loss contributed to a ZBLAN fiber incorporating this lanthanum fluoride is calculated to be 0.082 dB/km; here the concentration of neodymium is assumed to be equal to that of yttrium. These data indicate that the lanthanum fluoride prepared by the current method will not meet the ultimate requirements for ultra‐low‐loss fluoride glasses.
Reactive Multicomponent Powder Mixtures Prepared by Microencapsulation: Pb(Mg1/3Nb2/3)O3 Synthesis
Authors: Mort Paul R , Riman Richard E.
Published: March 2005

Microencapsulation of ceramic powders using metalloorganic stearate soaps was investigated as an economical means to increase solid‐state reactivity of multicomponent mixtures. The specific system investigated was lead magnesium niobate (PMN); however, the process may be applicable to a wide range of other compositions. The physical and chemical characteristics of the unfired powder mixtures and reactivity during subsequent calcination were studied as a function of batch composition and mixing method. Batch composition was varied by molar substitution of magnesium stearate for magnesium carbonate. Mixing method was investigated by comparing a dry‐mixing technique developed for particle coating (mechanofusion) with conventional wet ball milling. Both mixing processes resulted in surface coating of the ceramic particles by the stearate soap. In addition, the mechanofusion process produced densely packed spherical granules of coated particles (multicored microcapsules) in the 50‐ to 200‐μm range. Solid‐state reactivity was measured in terms of perovskite phase yield, increased yields being indicative of a more reactive mixture. The highest perovskite yields (95 to 98 vol%) were achieved at 100 mol% substitution of magnesium stearate for magnesium carbonate, independent of mixing method. However, when magnesium stearate was only partially substituted for magnesium carbonate, the mechanofusion process produced consistently higher perovskite yields than did ball milling. Compared to conventional mixed‐oxide processing, the increased reactivity of the microencapsulated mixtures can be attributed to higher chemical activity of the metallo‐organic precursor, finer scale of mixing achieved by particle coating, and a further reduction in segregation scale due to the dense intragranule packing of multicore microcapsules.
Alkoxide‐Derived Titania Particles: Use of Electrolytes to Control Size and Agglomeration Levels
Authors: Look Jee Loon , Zukoski Charles F.
Published: March 2005

Methods of controlling the size and morphology of particles precipitated from the hydrolysis and condensation of tetraethyl orthotitanate (TEOT) in aqueous ethanol solutions through the addition of electrolytes are described. The precipitates display great sensitivity to agitation where, above a critical shear rate, agglomerated morphologies are observed. For reactions carried out at shear rates less than the critical value, narrow size distribution, spherical titania particles are formed under conditions where the particles have electrophoretic mobilities greater than 0.2 × 10−8 m2· V−1· s−1 for 0.05M < [TEOT] < 0.2M and 0.15M < H2O < 0.9M. Addition of HCl and NaCl to the precipitation solution increases particle charge and expands the TEOT, H2O concentration ranges where uniform particles are formed.
Crystallization Behavior of CaO–P2O5 Glass with TiO2, SiO2, and Al2O3 Additions
Authors: Nan Y. , Lee William E. , James Peter F.
Published: March 2005

TiO2 above 4 mol% is an effective nucleating agent for CaO–P2O5 glass which also contains substantial SiO2 and Al2O3 additions. Glass ceramics can be made from this glass using a single slow heating ramp with no need for a nucleating heat treatment step. Powder of this composition crystallizes rapidly to β‐Ca2P2O7, whereas bulk glass crystallizes from diphasic nuclei consisting of a central cubic Ca‐P‐Ti‐Si‐Al oxide phase surrounded by impure AlPO4 dendrites. Metastable calcium phosphate grows on the AlPO4 dendrites and later transforms to β‐Ca2P2O7.
Concentrations of Residual Carbonate Ions in the Bi‐Sr‐Ca‐Cu‐O Glasses
Authors: Lee Won‐Hyuk , Hosono Hideo , Abe Yoshihiro
Published: March 2005

It was found that the IR absorption bands appearing at 600 to 1600 cm−1, which had been previously assigned to the fundamental vibrations of [BiO3] or [BiO6] polyhedra, are due to residual carbonate ions (CO2−3) dissolved in Bi‐Sr‐Ca‐Cu‐O glasses. The concentrations of the remaining CO2−3 in the Bi2.2Sr2Ca1Cu2Ox glasses that melted at 1100° and 1400°C are 170 × 10−5 mol/cm3 (3.3 mol%) and 3.2 × 10−5 mol/cm3 (0.25 mol%), respectively. The apparent activation energy for the dissociation of the carbonates was approximately 220 kJ/mol. The CO2−3 content in the precursor glasses did not significantly affect the superconducting properties of the resulting glass–ceramics.
In Situ Ductile Toughening of Nb2Al by Combustion Synthesis
Authors: Bhattacharya Arun K.
Published: March 2005

Ductile toughening of niobium aluminide (Nb2Al) has been accomplished in situ while combustion synthesizing the compound from a mixture of Nb, Al, and 3 wt% B powders. An enhancement of the fracture toughness of the resulting Nb2Al has been shown to be primarily caused by the interaction of propagating cracks and cores of ductile Nb phases inside the partly combusted Nb powders.
X‐ray Powder Diffraction Structural Phase‐Transition Study of La(Cr1‐xMnx)O3 (x = 0 to 0.25) Using the Rietveld Method of Analysis
Authors: Howard Scott A. , Yau Jen‐Kuan , Anderson Harlan U.
Published: March 2005

The La(Cr1‐xMnx)O3 (x = 0 to 0.25) system exhibited a displacive phase transformation from an orthorhombic to a rhombohedral structure at temperatures ranging from about 256°C at x= 0 to 305°C at x= 0.25. The Rietveld method of X‐ray analysis was used to determine structural characteristics and to assay phase concentrations when multiple phases were present. Indications were that the Mn ions on the B site affected the transition temperature through an ionic size effect; i.e., Mn3+, with a larger ionic size than Cr3+, increased the transition temperature while the presence of the smaller Mn4+ ions reduced it. A hysteresis was also observed with respect to the phase transformation as a function of temperature. The phase transformation was associated with a change in the rotation of the oxygen octahedra from an antiphase to an in‐phase tilt sequence.
Measurement of Nonsymmetric Creep in Al2O3 with a Glass Phase
Authors: Fett Theo
Published: March 2005

To check the development of nonsymmetry in bending creep tests an Al2O3 ceramic containing a glass phase is investigated in interrupted creep tests. The symmetric part of the strain is measured by the deflection and the nonsymmetric part is obtained by length measurements between two Knoop indentations situated at the centerline of bending bars. It is observed that nonsymmetry in creep occurs not only in the secondary creep range but also in the primary range.
Simultaneous Thermogravimetry and Evolved‐Gas Analysis of YBa2Cu3O7 and LaBa2Cu3O7 Superconductors
Authors: Wada Takahiro , Yamauchi Hisao , Tanaka Shoji
Published: March 2005

Concurrent thermogravimetry (TG) and evolved‐gas analysis (EGA) were done for YBa2Cu3O7‐z and LaBa2Cu3‐O7‐z superconductors. The sample weights were monitored by thermobalance and the evolved O2 and CO2 species were monitored by quadruple mass spectrometer (QMS). No diffraction peak for the impurity phase containing a carbonate group was observed in the X‐ray diffraction patterns for these samples, but the release of CO2 was detected by EGA. CO2 gas began to evolve from YBa2Cu3O7‐z at 543°C and from LaBa2Cu3O7‐z at 692°C. Preparation of high‐quality YBa2Cu3O7‐z and LaBa2Cu3O7‐z superconductors is discussed on the basis of results of these thermal analyses.
Effect of Two‐Dimensional Pressure on the Permittivity of Fine‐ and Coarse‐Grained Barium Titanate
Authors: BUESSEM W. R. , CROSS L. E. , GOSWAMI A. K.
Published: March 2005

The effect of two‐dimensional pressure on the permittivity of fine‐and coarse‐grained ceramic BaTiO3 was investigated. It was shown that, unlike coarse‐grained (10μ or above) barium titanate, the permittivity of the fine‐grained (1μ mean) material increased with the increase in two‐dimensional compression perpendicular to the electrode, whereas for an intermediate grain size, the permittivity was almost independent of pressure. The apparent anomalous effect of the fine grain size on the pressure coefficient of permittivity was explained satisfactorily on the basis of an internal stress model using a modified Devonshire thermodynamic treatment.
Mechanical Behavior of a Laminar Ceramic/Fiber‐Reinforced Epoxy Composite
Authors: Folsom Craig A. , Zok Frank W. , Lange Fred F. , Marshall David B.
Published: March 2005

The mechanical properties of a noval laminar composite are investigated. The composite consists of dense alumina sheets bonded between sheets of a uniaxial carbon‐fiber‐reinforced epoxy tape. The behavior of the composite in both flexural and tensile loading is characterized and the results are related to the properties of the constituents. The role of the interlaminar interface in composite behavior is also examined. Implications for the design of laminar composites with complex shapes are briefly discussed.
Role of Crack‐Bridging Ligaments in the Cyclic Fatigue Behavior of Alumina
Authors: Guiu Frank , Li Ming , Reece Michael J.
Published: March 2005

The cyclic fatigue crack growth behavior in two aluminas with different grain sizes and purities has been investigated using tapered cantilever beam specimens. The curves of load–crack opening displacement revealed a hysteretic loss behavior, in both aluminas, produced by frictional forces generated in the crack wake. From measurements of the specimen complinces it is concluded that the fatigue cracks in these materials were strongly bridged by both “frictional” and “elastic” load‐bearing ligaments. It is shown that the “elastic” contribution to the total crack‐bridging force is far greater than that produced by fristional sliding ligaments. The results support the view that cyclic loads produce degradation of the strength of the bridging ligaments. The effect of grain size and compressive loads on the magnitude of the bridging forces is discussed.
Role of Si2N2O in the Passive Oxidation of Chemically‐Vapor‐Deposited Si3N4
Authors: Ogbuji Linus U. J. T.
Published: March 2005

The results of two‐step oxidation experiments on chemically‐vapor‐deposited Si3N4and SiC at 1350°C show that a correlation exists between the presence of a Si2N2O interphase and the strong oxidation resistance of Si3N4. During normal oxidation,kpfor SiC was 15 times higher than that for Si3N4, and the oxide scale on Si3N4was found by SEM and TEM to contain a prominent Si2N2O inner layer. However, when oxidized samples are annealed in Ar for 1.5 h at 1500°C and reoxidized at 1350°C as before, three things happen: the oxidationkpincreases over 55‐fold for Si3N4, and 3.5‐fold for SiC; the Si3N4and SiC oxidize with nearly equalkp's; and, most significant, the oxide scale on Si3N4is found to be lacking an inner Si2N2O layer. The implications of this correlation for the competing models of Si3N4oxidation are discussed.
Phase Equilibria in the System HfO2–Y2O3–CaO
Authors: Andrievskaya Elena R. , Lopato Lidiya M.
Published: March 2005

Phase equilibria in the system HfO2–Y2O3–CaO were studied in the temperature range 1250° to 2850°C by both experimental methods (X‐ray phase analysis at 20° to 2000°C, petrography, annealing and quenching, differential thermal analysis in He at temperatures to 2500°C, thermal analysis in air using a solar furnace at temperatures to 3000°C, and electron microprobe X‐ray analysis) and theoretical means (development of a mathematical model for the liquidus surface by means of the reduced polynomial method). Phase equilibria were determined by the structure of the restricting binary systems. No ternary compounds were found. The liquidus was characterized by the presence of six four‐phase, invariant equilibria. Solid solutions were based on monoclinic (M), tetragonal (T), and cubic (F) modifications of HfO2; C and H forms of Y2O3; CaO; and CaHfO3 that crystallized in two polymorphous modifications, namely, the cubic and rhombic perovskite‐type structure.
Tie Lines and Activities in the System CoO─MgO─SiO2 at 1373 K
Authors: Jacob K. T. , Mukhopadhyay Sukanya , Shukla A. K.
Published: March 2005

The tie lines between (CoXMg1−X)O solid solution with rock salt structure and orthosilicate solid solution (CoYMg1−Y)‐Si0.5O2, and between orthosilicate and metasilicate (CoZMg1‐Z)SiO3 crystalline solutions, have been determined experimentally at 1373 K. The compositions of coexisting phases have been determined by electron probe microanalysis (EPMA) and lattice parameter measurement on equilibrated samples. The metasilicate solid solution exists only for 0 > Z > 0.213. The activity of CoO in the rock salt solid solution was determined as a function of composition and temperature in the range of 1023 to 1373 K using a solid‐state galvanic cell:

Pt, (CoXMg1−X)O+Co|(Y2O3)ZrO2|Co+CoO, Pt

The free energy of mixing of (CoXMg1−X)O crystalline solution can be expressed by the equation

ΔGE=X(1 −X)[(6048 − 2.146T)X+ (8745 − 3.09T)(1 −X)] J·mol−1

The thermodynamic data for the rock salt phase is combined with information on interphase partitioning of Co and Mg to generate the mixing properties for the ortho‐ and metasilicate solid solutions. For the orthosilicate solution (CoYMg1 −Y)Si0.5O2 at 1373 K, the excess Gibbs free energy of mixing is given by the relation

ΔGE=Y(1 −Y)[2805Y+ 3261(1 −Y)] J·mol−1

For the metasilicate solution (CoZMg1 −Z)SiO3 at the same temperature, the excess free energy can be expressed by the relation

ΔGE=Z(1 −Z)[2570Z+ 3627(1 −Z)] J·mol−1
Crack Bridging by Inclined Fibers/Whiskers in Ceramic Composites
Authors: Cai Hongda , Faber K. T. , Fuller Edwin R.
Published: March 2005

Crack bridging by inclined fibers has been studied in a brittle fiber–brittle matrix model ceramic composite. Results of the fiber bridging force vs the crack opening displacement have been obtained for different fiber inclination angles using a fracture mechanics approach. Localized matrix cracking has been observed for inclined fibers and related to fiber inclination angle. The experimental results showing the influence of fiber inclination angle are discussed and compared with theoretical analyses to provide insight into crack bridging by inclined fibers/whiskers. Implications for toughening by whisker bridging are also discussed.
Homogeneous Mullite‐Forming Powders from Spray‐Drying Aqueous Solutions
Authors: Jaymes Isabelle , Douy André
Published: March 2005

A mullite precursor solution was made by hydrolyzing TEOS in a diluted aqueous solution of aluminum nitrate. This solution was spray‐dried at a relatively low temperature (200°C), producing a chemically homogeneous powder crystallizing completely into mullite at 975°C. By aging this solution at 100°C, a diphasic precursor sol made of colloidal silica and aluminum nitrate was made. The resulting spraydried powder was less homogeneous, crystallizing into mullite and spinel or only spinel. The aging by thermal treatment may thus be a way to control the heterogeneity of the powder.
Effect of the Melt Temperature on the Solidification Process of Liquid Garnets Ln3Al5O12 (Ln = Dy, Y, and Lu)
Authors: Gervais Monique , Le Floch Sylvie , Rifflet Jean Claude , Coutures Juliette , Coutures Jean Pierre
Published: March 2005

The solidification process of liquid garnets Ln3Al5O12 (Ln = Dy, Y, Lu) was probed by differential thermal analysis. A critical temperature Tclg was evidenced in the liquid. Cooling from temperatures under Tclg leads to the crystallization of the single garnet phase. Cooling from temperatures above Tclg leads to the solidification of a mixture of perovskite LnAlO3 and aluminum oxide α‐Al2O3. For Ln = Y, the results are in agreement with stable and metastable phase diagrams previously proposed. The YAIO3 melt was shown to display a critical temperature Tclp also. Its metastable solidification from temperatures above Tclp leads to the formation of the perovskite at around 1550°C.
Fiber Bundle Pushout: A Technique for the Measurement of Interfacial Sliding Properties
Authors: Mackin Thomas J. , Zok Frank W.
Published: March 2005

An experimental technique for the measurement of interfacial sliding properties in fiber‐reinforced materials is presented. The technique involves pushing a bundle of fibers simultaneously through a thin section of the composite. Using this technique, sample averages are immediately available, eliminating the need for repeated single‐fiber tests. The technique is particularly useful for composites that contain small‐diameter fibers. Salient features of the technique are demonstrated through tests on a CAS/SiC composite.
High‐Temperature Deformation and Microstructural Analysis for Silicon Nitride–Scandium (III) Oxide
Authors: Cheong Deock‐Soo , Sanders William A.
Published: March 2005

Limited past studies have indicated that Si3N4 doped with Sc2O3 may exhibit high‐temperature mechanical properties superior to Si3N4 systems with various other oxide sintering additives. High‐temperature deformation of this system was studied by characterizing the microstructures before and after deformation. It was found that elements of the additive, Sc and O, exist in small amounts at thin grain boundary layers and within secondary phases at triple and multiple grain boundary junctions. The secondary phase is devitrified as crystalline Sc2Si2O7. Deformation of the samples was dominated by cavitation rather than dislocation processes. Thus, the excellent deformation resistance of the samples at high temperature can be attributed to the high refractories and enhanced crystallization of a secondary phase.
Homogeneous Fabrication of Al2O3–ZrO2–SiC Whisker Composite by Surface‐Induced Coating
Authors: Jang Hyun M. , Moon Jong H. , Jang Cheol W.
Published: March 2005

Al2O3–ZrO2–SiC whisker composites were prepared by surface‐induced coating of the precursor for the ZrO2 phase on the kinetically stable colloid particles of Al2O3 and SiC whisker. The fabricated composites were characterized by a uniform spatial distribution of ZrO2 and SiC whisker phases throughout the Al2O3 matrix. The fracture toughness values of the Al2O3–15 vol% ZrO2–20 vol% SiC whisker composites (∼12 MPa.m1/2) are substantially greater than those of comparable Al2O3–SiC whisker composites, indicating that both the toughening resulting from the process zone mechanism and that caused by the reinforced SiC whiskers work simultaneously in hot‐pressed composites.
Effect of Temperature on Ostwald Ripening of Silver in Glass
Authors: Yata Kunio , Yamaguchi Takashi
Published: March 2005

The effect of temperature and volume fraction on the growth of silver particles in a lead borosilicate glass has been studied. The particle growth obeyed the Ostwald ripening theory and was controlled by diffusion. An anomaly of growth rate coefficient was observed around 700°C and explained in terms of the dissolution behavior of silver. Also, the solubility of silver in glass was evaluated from the normalized rate coefficient K using volume fraction of silver particles and viscosity of the glass.
Nitridation of Amorphous Silica with Ammonia
Authors: Sjöberg Jörgen , Pompe Robert
Published: March 2005

The reaction between amorphous silica and ammonia in the temperature range 200° to 1230°C has been investigated. The reaction process was monitored with respect to the nitrogen content of the reaction product, the specific surface area of the amorphous nitrided silica, and the decomposition of ammonia. A surface reaction was observed at temperatures between 300° and 500°C, but in agreement with other studies bulk reaction only occurred above 800°C, reaching its maximum rate at about 1000°C. It is suggested that the decomposition of ammonia, which also becomes important above 800°C, is essential for the bulk nitridation reaction. At temperatures above 1050°C the nitridation yield decreases, until gas‐phase reaction between SiO(g) and N2 or NH3 becomes dominant at 1230°C, leading to the formation of α‐Si3N4.
Photoelastic Measurement of Residual Thermomechanical Stress in SiC‐Reinforced Glass Composites
Authors: Krynicki Joseph W. , Nagle Dennis C. , Green Robert E.
Published: March 2005

Residual thermomechanical stresses in a Nicalon® SiC/7740 glass composite system were measured directly. Residual stresses for both single‐tow and two‐dimensional cloth‐reinforced samples were completely described via a digital microphotoelastic technique. Normal stresses approaching 4 MPa were observed in this composite system that had a thermal expansion coefficient mismatch of only 1.8%. The advantages of using this direct, full‐field technique over other theoretical and composite model approaches are also discussed.
Semiconductive Property and Impedance Spectra of Alumina–Silicon Carbide Whisker Composite
Authors: Zhang Jinsong , Huang Hua , Cao Lihua , Xia Fei , Li Guangqiang
Published: March 2005

The room‐ and high‐temperature resistances and impedance spectra of Al2O3–SiC(w) composites made by a sol–gel process were measured by the common dual‐electrode method and frequency response analysis. The experimental results show that the composites have semiconductive properties and that there is a dual nature of the inductive and capacitive reactance as the SiC(w) content becomes greater than a critical volume fraction.
Modification of Surface Texture by Grinding and Polishing Lead Zirconate Titanate Ceramics
Authors: Cheng Si , Lloyd Isabel K. , Kahn Manfred
Published: March 2005

Grinding and polishing affected the orientation of 90° domains at the surface of lead zirconate titanate (PZT) ceramics. This was quantified by using changes in the intensity ratio of the {002} and {200} X‐ray reflections. Grinding unpoled PZT with 600‐grit SiC paper gave X‐ray intensity ratios similar to those of poled material. This implies that 90° domain realignments had occurred in the near surface region probed by the X‐rays. Grinding poled samples with 600‐grit SiC further increased the X‐ray intensity ratio beyond that caused by poling, indicating that additional surface reorientation of 90° domains had occurred. The effects of diamond polishing depended on the size of the diamond particles. The use of 6‐μm diamond had no effect on the {002}/{200} intensity ratio of either poled or unpoled samples, while polishing with 15‐ or 45‐μm diamond significantly enhanced the 90° domain rotation. In unpoled samples, the increase in the X‐ray intensity ratio then approached that induced by poling or grinding with 600‐grit SiC paper. While the observed increase in X‐ray intensity ratio upon grinding is attributed to the rotation of 90° domains, the simultaneous formation of 180° domains appears to minimize or reduce the increase in electrical polarization.
Improvement of Mechanical Properties of Machinable Glass‐Ceramics through Postmachining Heat Treatments
Authors: Unuma Hidero , Miura Koh , Kodaira Kohei
Published: March 2005

A mica‐based machinable glass‐ceramic has been converted to a glass‐ceramic containing cordiertie and body‐centered cubic chondrodite through heat treatment at temperatures higher than that used for the crystallization of mica. The machinability is lost, microhardness increases, and the thermal expansion coefficient decreases with the change of the crystalline phase from mica to cordierite and chondrodite.
Deformation Twinning in Single‐Crystal Monoclinic Zirconia: A First Report
Authors: First Richard C. , Heuer Arthur H.
Published: March 2005

The hardness of single crystals of flux‐grown, untwinned monoclinic zirconia was determined using Knoop and Vickers microindenters. Significant hardness anisotropy existed on (100) and {110} faces, with a maximum Knoop hardness of ∼8 GPa, although large variance was observed between different batches of crystals. Extensive deformation twinning, primarily on {110}, but also on (001), accompanied microindentation at all temperatures between room temperature and 800°C.
FOURIER ANALYSIS OF X‐RAY PATTERNS OF VITREOUS SiO2 AND B2O3*
Authors: Warren B. E. , Krutter H. , Morningstar O.
Published: March 2005

The X‐ray scattering curves for vitreous SiO2 and B2O3 are obtained in a vacuum camera, using monochromatic Mo and Cu radiation. A Fourier analysis of the scattering curve gives directly a curve representing the distribution of neighboring atoms about any one atom. For SiO2, the distribution curve establishes difinitely the tetrahedral silicon‐oxygen network. The distribution curve for B2O3 indicates a triangular coördination, each boron surrounded by three oxygens, and each oxygen shared between two borons. The interatomic distances which are found are in good agreement with the values found in crystalline silicates and borates. The importance of the new Fourier method of analysis of glass diffraction patterns is emphasized by the fact that the distribution curves which are obtained are unique, no assumptions as to structure being involved.
Mullite/Alumina Particulate Composites by Infiltration Processing: IV, Residual Stress Profiles
Authors: Marple Basil R. , Green David J.
Published: March 2005

Residual stress profiles through mullite/alumina bodies prepared by an infiltration process were determined. In one approach, residual stress profiles were predicted by obtaining concentration profiles and treating the bodies as laminates. In a second approach, a strain gage technique in which part of the sample was ground away while recording the resulting strain was used. The results showed that residual compressive stresses existed in the surface region of all composite samples. The strain gage approach indicated values of surface compression in the range of 176 to 291 MPa, which were higher than those predicted using the laminate approach. The results were compared with changes in the mechanical properties and found to be consistent with the increases in the strength and indentation fracture toughness which resulted when mullite was added to alumina by the infiltration technique.
Time–Temperature–Transformation Diagrams with More than One Nose
Authors: Weinberg Michael C.
Published: March 2005

The structures of time–temperature–transformation diagrams of glasses which crystallize by combined homogeneous and heterogeneous crystallization mechanisms are examined. Considerations are given to the factors which might produce more than one extremum in such diagrams. Specific nucleation and growth models are used, and the influence of the parameters which appear in the nucleation and growth rate expressions upon the structure of the diagrams is evaluated.
Synthesis of Perovskite‐Type (La1−xSrx)MnO3 (O X 0.3) at Low Temperature
Authors: Taguchi Hideki , Matsuda Daisuke , Nagao Mahiko , Tanihata Kimiaki , Miyamoto Yoshinari
Published: March 2005

Perovskite‐type (La1‐xSrx)MnO3 (0 x 0.3) was synthesized through the sol–gel process at low temperature (400° to 500°C). Poly(acrylic acid) (PAA) was used to make a gel from an aqueous solution of lanthanum, strontium, and manganese nitrates. The particle‐diameter distribution of the manganites had a maximum value of 0.3 to 0.7 μm, and a specific surface area of about 17.5 to 23.5 m2/g.
Sol–Gel Synthesis of Cadmium Telluride‐Microcrystal‐Doped Silica Glasses
Authors: Nogami Masayuki , Nagasaka Katsumi , Suzuki Toshiharu
Published: March 2005

The sol–gel process has been applied to the preparation of small‐sized CdTe‐doped silica glasses. Gels synthesized by the hydrolysis of a complex solution of Si(OC2H5)4, Cd(CH3COO)2· 2H2O, and Te were heated from 350° to 600°C in a H2─N2 atmosphere to form fine cubic CdTe crystals. The size of CdTe crystals, determined from the line broadening of X‐ray diffraction pattern, increases from 4 to 9 nm in diameter with increasing heat‐treatment temperature. The optical absorption edge shifts to the higher‐energy side as the size of the CdTe crystals decreases. This phenomenon is interpreted in terms of a quantum confinement effect of electron and hole in the CdTe microcrystals.
Synthesis of Compositionally Homogeneous Sr(CuxZn1−x)1/2W1/2O3
Authors: Abe Yoshiyuki , Kakegawa Kazuyuki , Sasaki Yoshinori
Published: March 2005

A complex perovskite of Sr(CuxZn1‐x)1/2 W1/2O3 (SCZW) is synthesized by a new combination of wet and dry processess. Mixed oxides containing Cu2+ and Zn2+ (CZ) are prepared by the wet process (coprecipitate method). SCZW is obtained by the dry process (mixed‐oxide method) from a mixture of CZ, SrCO3, and WO3. SCZW has practically no compositional, unlike solid solutions prepared by the conventional dry method. The wet–dry process method is useful because the wet process is applied to only B‐site cations having the same valence.
Synthesis of Cubic Boron Nitride by Decomposition of Magnesium Boron Nitride
Authors: Nakano Satoshi , Ikawa Hiroyuki , Fukunaga Osamu
Published: March 2005

Cubic boron nitride (c‐BN) was synthesized by the decomposition of Mg3BN3 under high pressure and high temperature. The minimum pressure for c‐BN synthesis was 4 GPa, which was 1 GPa lower than that of the conventional catalytic process. The decomposition of Mg3BN3 was observed only when H2O was added. Therefore, the reaction was as follows: Mg3BN3+ 3H2O = 3MgO +c‐BN + 2NH3. The c‐BN crystals obtained were tetrahedron in shape and about 10 μm in diameter.
Heterogeneous Nucleation in the Intergranular Phase of a SiAlON
Authors: Szabó D. V. , Campbell G. H. , Brulely J. , Hoffmann M. J. , Rühle M.
Published: March 2005

A SiAlON ceramic with yttria as a sintering aid has been fabricated and subjected to a 1‐h heat treatment at 1150°C. Microstructural characterization by analytical electron microscopy and diffraction analysis indicates that the residual intergranular phase crystallizes into a metastable hexagonal phase (Y2SiAlO5N) and mullite. The mullite appears as a characteristically shaped precipitate forming with a definite orientation relationship on the (1010) facets of SiAlON grains. The absence of a residual amorphous film between the precipitate and the SiAlON indicates that the precipitation occurred in a heterogeneous manner on the surface of the SiAlON.
Grain Boundary Migration in Cubic Zirconia–Yttria Induced by Addition of Magnesia at Varying Concentrations
Authors: Jeong Jun‐Whan , Yoon Duk‐Yong , Lee Jeong‐Yong , Kim Doh‐Yeon
Published: March 2005

When partially sintered cubic ZrO2–10 mol% Y2O3 specimens are heat‐treated at 1500°C with powder mixtures of MgO and ZrO2–10Y2O3 at varying ratios, the grain boundaries migrate, leaving behind new solid solutions enriched with MgO but depleted of Y2O3. With increasing MgO content in the solute source powder, the average migration velocity increases, and the MgO content increases and the Y2O3 content decreases slightly in these new solid solutions. With increasing MgO content in the solute source, the grain boundaries tend to be corrugated and faceted. Migration reversal is also observed at the corrugated boundaries. These variations of the grain boundary migration behavior with the MgO content in the solute source are consistent with the diffusional coherency strain energy as the driving force for the migration.
Thermodynamics of the Y‐Ba‐Cu‐C‐O‐H System: Application to the Organometallic Chemical Vapor Deposition of the YBa2Cu3O7−x Phase
Authors: Vahlas Constantin , Besmann Theodore M.
Published: March 2005

A calculational thermodynamic investigation of the chemical vapor deposition (CVD) of YBa2Cu3O7−x from organometallic precursors has been performed, based on the minimization of the Gibbs energy of the Y‐Ba‐Cu‐C‐O‐H chemical system. Thermodynamic data for the participating compounds were selected after a critical assessment of the available thermochemical information and are self‐consistent with an accepted phase diagram. The results are presented in CVD diagrams which illustrate the influence of the most commonly used operating conditions of temperature, pressure, and initial gas composition on the formation of stable phases.
Influence of the Nonsingular Stress Terms on Small‐Scale Supercritical Transformation Toughness
Authors: Giannakopoulos Antonios E. , Olsson Mårten
Published: March 2005

In the present paper we examine the influence of the secondorder term of the asympotic stress solution for mode‐I, steady‐state, plane‐strain, quasi‐static crack growth in a supercritically trasforming material. It was found that the second‐order term can affect the toughness, not always in a positive way. The second‐order term includes the effects of the loading, of the overall geometry, and of the crack length. The findings can be used for the evaluation of the purely material resistance curves of small‐scale transforming ceramics, as well as for the toughness predictions of these materials. The results may be useful for unifying different test results, and for a better understanding of the strength‐toughness relation.
Measurement of Residual Stres in Injection‐Molded Ceramics
Authors: Kostić Branko , Zhang Tao , Evans Julian R. G.
Published: March 2005

This paper discribes the adaptation of the layer removal method for the measurement of residual stresses in the plane of a plate for a ceramic injection molding suspension. The latter contained 56 vol% alumina in a polypropylenebased organic vehicle. A strain gauge method was used to measure curvatures. The experimental precautions are discussed and the errors evaluated. The method is applied to conventional moldings made at high and low pressures, to annealed moldings, and to moldings made with a heated sprue.
Highly Reactive β‐Dicalcium Silicate: IV, Ball‐Milling and Static Hydration at Room Temperature
Authors: Ishida Hideki , Sasaki Kaori , Mizuno Akihiro , Okada Yoshihiko , Mitsuda Takeshi
Published: March 2005

The ball‐milling hydration of highly reactive β‐Ca2SiO4 synthesized from hillebrandite, Ca2(SiO3)(OH)2, was investigated and compared with its static hydration under a water/solid ratio of 10. In static hydration, the hydration is completed in 8 d to yield C‐S‐H with a Ca/Si ratio of 1.81 and Ca(OH)2. There is no major change after this period. In the case of ball milling, the hydration is completed in 2 d to yield C‐S‐H with Ca/Si = 1.81 and Ca(OH)2. After this, the two products react to form a C‐S‐H(II)‐like monophase hydrate having a Ca/Si ratio of 1.98. The morphology and structure of this hydrate are different from those of the earlier hydrate, and afwillite is not formed. 29Si MAS NMR measurements indicated the C‐S‐H to be a mixture of dimers and single‐chain structures. Dimeric species are the main species up to completion of the reaction, but polymerization progresses very rapidly after the completion.
Microstructural Characterization of Cofired Tungsten‐Metallized High‐Alumina Electronic Substrates
Authors: Behrens Gesa , Heuer Arthur H.
Published: March 2005

Microstructural characterization of a high‐Al2O3 substrate containing cofired thick‐film tungsten metallization, with particular emphasis on the metal/ceramic interface, was conducted. The substrate contained tabular Al2O3 grains surrounded by a continuous calcium magnesium aluminum silicate glass containing particles of monoclinic ZrO2 and reduced rutile (TiO2‐x). The metal/ceramic adhesion was caused by mechanical interlocking between the W and Al2O3 grains by the glass phase which penetrated the porous W layers during sintering; there was no interfacial reaction or diffusion zone. The mechanical properties of the W metallization did not limit interfacial strength. Heat treatments of the substrate at 1400 K in air and under vacuum resulted in the devitrification of the intergranular glass. The most abundant devitrification product was anorthite (CaAl2Si2O8), accompanied by magnesium aluminate titanate, magnesium aluminate spinel, α‐cristobalite (SiO2), and α‐cordierite (Mg2Al4Si5O18). In addition, small rutile particles precipitated within the Al2O3 grains.
Thermal Expansion of Silicon Carbide Monofilaments and Silicon Carbide–Borosilicate Composites
Authors: Elkind Alexander , Barsoum Michel , Kangutkar Pramod
Published: March 2005

The coefficient of thermal expansion (CTE) of a 140‐μm‐diameter SiC monofilament was determined to be 6.5 ± 0.5 × 10−60C−1 in the temperature range 25°–900°C. Heat treatment of the fibers at 1400°C for 90 min resulted in both an increase in the intensities of the SiC peaks and a reduction of their width, indicating some grain growth. Furthermore, heat treatment of the fibers for 2 h at 1600°C in vacuum reduced their CTE to 5.7 × 10−60C−1. The anomalously high CTE and its decrease upon heat treatment were attributed to the presence of a large fraction of the atoms in the boundaries between the nanometer β‐SiC grains. The thermal expansion coefficients of a series of SiC/borosilicate composites were measured as a function of fiber volume fraction in the temperature range 25°–500°C and found to follow the rule of mixtures.
Development of SiC‐Whisker‐Reinforced Lithium Aluminosilicate Matrix Composites by a Mixed Colloidal Processing Route
Authors: Jang Hyun M. , Kim Kwang S. , Jung Chang J.
Published: March 2005

Based on the surface properties of aqueous silica, boehmite, and SiC‐whisker dispersions, SiC‐whisker‐reinforced lithium aluminosilicate (LAS) matrix composites were fabricated by a mixed colloidal processing route. The composites were characterized by a uniform spatial distribution of SiC whiskers throughout the matrix. The fracture toughness increased from 1.3 MPa.m1/2 for the LAS specimen to 5.0 MPa.m1/2 for the hot‐pressed composite (950°C and 20 MPa for 20 min) containing 20 wt% SiC whisker. The increase in fracture toughness appears to result mainly from crack deflection and crack bridging by whiskers with some additional toughenings from load transfer and whisker pullout.
Lead Zirconate Titanate Films on Nickel–Titanium Shape Memory Alloys: SMARTIES
Authors: Chen Jayu , Xu Qi Chang , Blaszkiewicz Michael , Meyer Richard , Newnham Robert E.
Published: March 2005

Thin films of 52/48 PZT have been deposited on Ni–Ti shape memory alloys using a sol–gel spin‐on method. Micrometer‐thick PZT films adhere well to the alloy for strains as large as 0.4%, and they retain their ferroelectric properties during repeated cycling through the shape memory transformation.
Structural Ceramic Microlaminates by Electrophoretic Deposition
Authors: Sarkar Partho , Haung Xuening , Nicholson Patrick S.
Published: March 2005

Yttria‐stabilized zirconia (YSZ)/Al2O3 laminar microcomposites with a total of 80 layers, each as thin as ∼2 μm, were fabricated by electrophoretic deposition. Positively charged YSZ or Al2O3 powders were deposited on a cathode, layer by layer from 10 wt% solids/ethanol suspensions. The suspensions were characterized by their rate of deposition as a function of voltage. The deposited samples had a green density of ∼60% of theoretical. The microstructure of the sintered, theoretically dense samples was characterized by optical and electron microscopy, and microindentation was used to explore the mechanical properties.
Shear Thickening Creep in Superplastic Silicon Nitride
Authors: Chen I‐Wei , Hwang Shyh‐Lung
Published: March 2005

A novel shear‐thickening phenomenon has been observed in superplastic silicon nitrides compression tested between 1500° and 1600°C. Liquid‐enhanced creep of SiAlONs undergoes a transition from Newtonian behavior to shear‐thickening behavior at a characteristic stress, with the strain rate sensitivity increasing from unity to around 2. The transition stress is always around 20 MPa, even though the Newtonian flow stress is very sensitive to temperature, grain size, and phase composition. Rheopexic hysteresis, manifested as a slow stress relaxation to a steady‐state value after a strain rate decrease, was also observed in the shear‐thickening regime. We attribute the cause for shear thickening to a repulsive force between initially wetted SiAlON grains, which form a “dry” and “rigid” bridge in between when pressed above a characteristic stress, possibly due to the contact of the residue Stern layers on the opposing grain/liquid interfaces. A micromechanical model, which takes into account the stress variation among differently oriented grain boundaries, has been formulated to assess the effect of “rigid” grain boundaries. A continual stochastic rearrangement of grain configurations and a relatively thick Stern layer are suggested as the necessary prerequisites for shear thickening in liquid‐enhanced creep.
Convergent Beam Electron Diffraction Analysis of Lattice Shifts in Aluminum Nitride
Authors: Callahan Daniel L. , Thomas Gareth
Published: March 2005

Changes in lattice parameter in high‐purity polycrystalline (2Hδ) aluminum nitride due to oxygen contamination have been examined by convergent beam electron diffraction. The operative lattice distortion was determined by computer simulation to be a continuous increase in c/a ratio commensurate with constant volume as impurity concentration increases and a fine break in hexagonal symmetry. These results are consistent with the distortions associated with planar polytypoid structures at higher oxygen levels.
Damage‐Resistant SiC–AlN Layered Composites with Surface Compressive Stresses
Authors: Sathyamoorthy Rengaswamy , Virkar Anil V. , Cutler Raymond A.
Published: March 2005

Three‐layer samples in the SiC‐AlN system with outer layers richer in SiC, as well as monolithic samples of uniform composition, were fabricated by hot‐pressing. The strain gage technique, previously described, was used to estimate residual compressive stress in the outer layers developed because of the difference in coefficients of thermal expansion between inner and outer layers. Bar‐shaped samples were indented using a Vickers indenter under loads as high as 20 kg (196 N) on outer layers and were fractured in three‐point bending. Three‐layer samples with outer layers under compression exhibited increased resistance to the contact‐induced damage in comparison to the monoclinic samples.
SiC‐Whisker‐Reinforced Glass‐Ceramic Composites: Interfaces and Properties
Authors: Brennan John J. , Nutt Steven R.
Published: March 2005

Different types of SiC whiskers were incorporated into lithium aluminosilicate (LAS) and calcium aluminosilicate (CAS) glass‐ceramic matrices. Interfaces in these composites were characterized using Auger spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and the observations were correlated with measurements of fracture toughness and strength. The chemistry and morphology of the resulting interfaces affected the composite strength and toughness and controlled the mode of crack propagation. Certain types of SiC whiskers were characterized by a carbon‐rich near‐surface chemistry that became more carbon rich after composite fabrication. In these materials, the flexural strength at 20°C increased by up to 400% and the fracture toughness increased by up to 500%. Crack propagation modes were characterized by crack deflection, whisker–matrix debonding, and crack bridging. In contrast, SiC whiskers with stoichiometric near‐surface chemistry generally did not form carbon‐rich interfaces during composite fabrication, resulting in composites with low strength and fracture toughness.
Theoretical Process Development for Freeze‐Drying Spray‐Frozen Aerosols
Authors: McGrath Patrick J. , Laine Richard M.
Published: March 2005

Freeze‐dry processing was investigated as a means of producing homogeneous multicomponent preceramic powders. A general procedure was developed for synthesizing homogeneous multicomponent powders by spray freezing and subsequent freeze‐drying. Uniform particle morphology and high chemical homogeneity were used as criteria for powder quality. Methods of controlling powder morphology and sources of chemical segregation within the powder processing scheme were determined and classical transport phenomena models were constructed in order to define operating parameters required to meet powder quality specifications.
Ultimate Strengths of Partially Stabilized Zirconia Ceramics
Authors: Stump David M.
Published: March 2005

Previous results for ultimate tensile fracture strengths of partially stabilized zirconia (PSZ) containing preexisting finite cracks are reformulated in terms of a new transformation‐strengthening parameter. This allows a simplified method for estimating the strengths of bulk PSZ containing arbitrarysized, preexisting critical cracks.
Peculiar Morphology in Some Phase‐Separated Multicomponent Silicate Glasses
Authors: Taylor Peter
Published: March 2005

Several researchers have reported the formation of convoluted, silica‐rich, dispersed‐phase particles during amorphous phase separation in some glass‐forming silicate systems. These appear to be analogous to crystalline growth instabilities such as dendritic, fingered, and cellular structures that can arise during diffusion‐controlled solidification in undercooled systems.
Effects of In Vitro Aging of Magnesia‐Stabilized Zirconia
Authors: Drummond James L.
Published: March 2005

The intent of this project was to evaluate any changes in the flexure strength of magnesia‐partially‐stabilized zirconia when aged in distilled water for time periods of 6, 12, and 18 mos. The aging conditions were autoclaved specimens in air (AA) or distilled water (AW) and nonautoclaved specimens in distilled water (NW) at stressing rates of 10.0, 1.0, or 0.1 mm/min. The statistical analysis showed no significant difference between the aging times. The aging‐time data were then pooled and a statistical analysis run between the different aging conditions (AA, AW, and NW) and stressing rates. The specimens tested in air were significantly stronger than those tested in water autoclaved or nonautoclaved. For the pooled data, all stressing rates were statistically significant from each other.