19 results on '"Ronald S. Gordon"'
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2. Creep of Polycrystalline MgO-FeO-Fe2O3 Solid Solutions
- Author
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Ronald S. Gordon, J. D. Hodge, Robert A. Giddings, and R. T. Tremper
- Subjects
Materials science ,Creep ,Dopant ,Diffusion ,Metallurgy ,Materials Chemistry ,Ceramics and Composites ,Analytical chemistry ,Lattice diffusion coefficient ,Diffusion creep ,Activation energy ,Crystallite ,Grain size - Abstract
Steady-state creep experiments were performed on hot-pressed polycrystalline MgO doped with Fe. Dead-load 4-point bend creep tests were conducted at stresses of 26 to 270 kg/cm2, at temperatures of 1250° to 1450°C, in O2 partial pressures of 1 to 10−9 atm, on specimens with grain sizes of 10 to 65 μm. Viscous steady-state creep was always observed when the grain size was stable. Experiments at variable PO2's and temperatures were used to identify regimes of high (117 ± 10 kcal/mol) and low (81 ± 5 kcal/mol) activation energy. In the latter, creep rates were nearly independent of Fe dopant concentration and PO2, whereas in the former creep rates were enhanced by increasing PO2's and Fe dopant levels. The high- and low-activation-energy regimes were interpreted as diffusional creep controlled primarily by Mg lattice diffusion and O grain-boundary diffusion, respectively. more...
- Published
- 1974
- Full Text
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Catalog
3. Transient Creep in Fe-Doped Polycrystalline MgO
- Author
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G. R. Terwilliger and Ronald S. Gordon
- Subjects
Stress (mechanics) ,Materials science ,Creep ,Fe doped ,Metallurgy ,Materials Chemistry ,Ceramics and Composites ,Thermodynamics ,Transient (oscillation) ,Crystallite ,Strain rate ,Grain size ,Exponential function - Abstract
The transient creep rate in polycrystalline Fe-doped MgO (grain size 4 to 19 μm) follows the exponential time relation The initial strain rate, , depends linearly on stress, and the relaxation time, τ, is thermally activated. Two mechanisms for the transient were considered, i.e. (1) viscous grain-boundary sliding with elastic accommodation and (2) transient diffusional creep. Although the results are not conclusive, transient diffusional creep appears to be the most promising mechanism. more...
- Published
- 1972
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4. Grain Size Distributions and Grain Growth in MgO and MgO-Fe2O3Solid Solutions
- Author
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Ronald S. Gordon and D. D. Marchant
- Subjects
Grain growth ,Chord (geometry) ,Materials science ,Materials Chemistry ,Ceramics and Composites ,Analytical chemistry ,Mineralogy ,Grain boundary ,Standard deviation ,Grain size ,Solid solution - Abstract
The Cahn-Fullman method was used to determine three-dimensional grain size distributions from experimentally measured two-dimensional chord distributions in high-purity MgO and magnesiowustite (0.10 and 0.48 wt% Fe2O3). Using the standard deviation of the three-dimensional distributions, the constant which relates average three- and two-dimensional grain sizes was evaluated by the procedure of Mendelson. The characteristics of the grain size distributions were correlated with steady state, abnormal, and terminal grain growth in MgO and magnesiowustite from 1300° to 1500°C. The distribution parameters were particularly useful in characterizing anomalous (i.e. abnormal and terminal) grain growth behavior. more...
- Published
- 1972
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5. Creep of Polycrystalline MgO and MgO-Fe2O3Solid Solutions at High Temperatures
- Author
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H. K. Bowen, Ronald S. Gordon, and G. R. Terwilliger
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Grain growth ,Materials science ,Creep ,Metallurgy ,Materials Chemistry ,Ceramics and Composites ,Lattice diffusion coefficient ,Diffusion creep ,Grain boundary ,Crystallite ,Strain rate ,Composite material ,Grain size - Abstract
Polycrystalline MgO and MgO-Fe2O3 solid solutions (0.10 to 8.08 wt% Fe2O3) were fabricated to almost theoretical density by vacuum hot-pressing. Specimens were creep-tested in air under four-point dead-load conditions between 1000° and 1400°C at stresses between 50 and 550 kg/cm2. Steady-state creep was never achieved in the experiments, which sometimes lasted more than 50 h. The strain rate vs time (t) data were described by an equation of the form =c1/(t+C2)p, which is consistent with the assumptions that creep occurs at least in part by a “viscous” mechanism and that grain growth occurs simultaneously. Doping MgO with Fe2O3 enhanced the viscous contributions to creep and inhibited the nonviscous ones. Creep rates in these specimens increased with increasing Fe2O3 additions. The occurrence of simultaneous grain growth during the high-temperature creep of magnesiowustite (i.e. MgO-Fe2O3 solid solutions) was used in establishing the strain rate vs grain size dependence. The results of this study are consistent with a transition between grain boundary and lattice diffusion mechanisms as the grain size increases (4 to 44 μan). The creep of polycrystalline MgO is a mixed process in that viscous and nonviscous (dislocation) contributions are present. more...
- Published
- 1970
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6. Mass Transport in the Diffusional Creep of Ionic Solids
- Author
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Ronald S. Gordon
- Subjects
Coble creep ,Materials science ,Lattice diffusion coefficient ,Diffusion creep ,Ionic bonding ,Thermodynamics ,Grain size ,Condensed Matter::Materials Science ,Crystallography ,Creep ,Condensed Matter::Superconductivity ,Physics::Atomic and Molecular Clusters ,Materials Chemistry ,Ceramics and Composites ,Grain boundary ,Crystallite - Abstract
A mass transport equation which takes into account parallel diffusion paths for both anions and cations was derived and applied to the diffusional creep of polycrystalline ionic solids. From the results of the analysis, several limiting conditions were found for grain-boundary- and lattice-diffusion-controlled kinetics. These conditions depend on temperature, grain size, and type and concentration of cation impurities. Examples of these limiting situations are given for the creep of polycrystalline Fe-doped MgO and transition-metal-doped Al2O3. Summary A mass transport equation which takes into account parallel diffusion paths for anions and cations was derived and applied to the diffusional creep of polycrystalline ionic solids. The effect of grain size and cation impurities of variable valence in solid solution on the relative contributions of lattice and grain-boundary diffusion of different ionic species in polycrystalline MgO and Al2O3 was examined. Depending on the temperature, grain size, impurity level, and O2 partial pressure, several limiting conditions were found: Limit I: At very small grain sizes and reasonably small cation lattice diffusivities the creep rate will be controlled by the slower-moving ion in the grain-boundary regions (i.e. Coble creep). Limit II: For intermediate grain sizes and cation lattice diffusivities the creep rate will be controlled by cation lattice diffusion when anion transport is significantly faster near grain boundaries than in the lattice (i.e. Nabarro-Herring creep). Limit III: For an appropriate combination of large grain size and high cation lattice diffusivity the creep rate will be controlled by anion boundary diffusion (i.e. Coble creep). Well-defined examples of limits I and II have been observed in the creep of Fe-doped polycrystalline MgO, and tentative evidence exists for limit III. Most results of studies of creep in polycrystalline Al2O3 (doped and undoped) fall within limit II, with some overlap with limit III. The model developed in the present work explains much of the data in the literature in which creep rates correspond to cation lattice mobilities. It is concluded that in the creep of polycrystalline ionic solids anion transport near grain boundaries is rapid and can, in some circumstances, be rate-controlling. It should also be possible to apply this model to sintering and thermal-grooving data for such systems, particularly for Al2O3, in which cation lattice diffusion is frequently observed to be rate-controlling.32 more...
- Published
- 1973
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7. Effect of Oxygen Partial Pressure on the Creep of Polycrystalline Al2O3 Doped with Cr, Fe, or Ti
- Author
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G. W. Hollenberg and Ronald S. Gordon
- Subjects
Materials science ,Creep ,Impurity ,Metallurgy ,Doping ,Materials Chemistry ,Ceramics and Composites ,Analytical chemistry ,Lattice diffusion coefficient ,Partial pressure ,Crystallite ,Grain size ,Solid solution - Abstract
Steady-state creep was studied in hot-forged polycrystalline Al2O3 (3 to 42 μm) of nearly theoretical density doped with≤1 cation % of Fe, Ti, or Cr. Tests were conducted at stresses between 10 and 550 kg/cm2 at 1375° to 1525°C under O2 partial pressures of 0.88 to 10−10 atm. Except in the 10-μm Fe-doped material tested at very small stresses, slightly nonviscous creep behavior was generally observed. The effects of Po2 on the creep rate indicated that increased concentration of a divalent (Fe2+) or quadrivalent (Ti4+) impurity in solid solution enhances the creep rate of polycrystalline Al2O3. The activation energies for the creep of Fe- and Ti-doped Al2O3 samples (148 and 145 kcal/mol, respectively) were significantly higher than that for Cr-doped material (114 kcal/mol). Taking into account the effects of Po2, temperature, and grain size, it was concluded that the steady-state creep of transition-metal-doped Al2O3 is controlled by cation lattice diffusion. more...
- Published
- 1973
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8. Calculation of Stresses and Strains in Four-Point Bending Creep Tests
- Author
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G. W. Hollenberg, Ronald S. Gordon, and G. R. Terwilliger
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Materials science ,Grain size ,Physics::Geophysics ,Elastic collision ,Creep ,Deflection (engineering) ,Condensed Matter::Superconductivity ,visual_art ,Materials Chemistry ,Ceramics and Composites ,Exponent ,Forensic engineering ,visual_art.visual_art_medium ,Stress relaxation ,Ceramic ,Fiber strain ,Composite material - Abstract
An analysis of strains and stresses in four-point bending creep tests in the limit of small beam deflections resulted in a general equation which relates the load-point deflection, the applied load, the creep exponent (N), and the geometrical parameters of the loading system. Measurements of load-point deflection rates, which are experimentally easy to accomplish in ceramic systems, vs the applied load lead to the direct determination of the creep exponent and the creep compliance in a steady-state creep test. The creep compliance is a function of the temperature, grain size, and all other factors except stress. The elastic equation relating the load-point deflection and the outer fiber strain is strictly valid for viscous creep and approximately valid for nonviscous creep (i.e. N>1) if the ratio of the distance between the support points to the distance between the load points is not very large. more...
- Published
- 1971
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9. Activation Energies in the Diffusional Creep of Polycrystalline Ceramics
- Author
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J. D. Hodge, Ronald S. Gordon, and P. A. Lessing
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Materials science ,Metallurgy ,Thermodynamics ,Activation energy ,Atmospheric temperature range ,Grain size ,Ion ,Creep ,Condensed Matter::Superconductivity ,visual_art ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Grain boundary ,Ceramic ,Crystallite - Abstract
A mixed diffusional creep mechanism in a polycrystalline ceramic can cause the apparent activation energy to vary with temperature and grain size. For mechanisms involving parallel transport paths for the same ion (e.g., cation lattice and grain-boundary diffusion), the process with the lowest activation energy will be dominant (i.e., rate-limiting) at low temperatures and the process with the highest activation energy will dominate at high temperatures. However, for mechanisms involving coupled and parallel diffusional steps (e.g., cation lattice and anion grain-boundary diffusion), the process with the lowest activation energy will be dominant at high temperatures whereas the high-activation-energy process will dominate at low temperatures. Examples of these effects are presented for the diffusional creep of polycrystalline MgO and Al/sub 2/O/sub 3/ doped with Fe. Variations in creep activation energy with grain size and temperature are only significant when the difference in activation energies for the competing processes is significant and the temperature range investigated is large. more...
- Published
- 1977
- Full Text
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10. Resistivity-Microstructure Relations in Lithia-Stabilized Polycrystalline beta'-Alumina
- Author
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Ronald S. Gordon, Anil V. Virkar, and Gerald R. Miller
- Subjects
Materials science ,Sodium ,Analytical chemistry ,Mineralogy ,chemistry.chemical_element ,Microstructure ,Grain size ,Ion ,chemistry ,Electrical resistivity and conductivity ,Lithia ,Materials Chemistry ,Ceramics and Composites ,Grain boundary ,Crystallite - Abstract
The sodium ion resistivity of lithia-stabilized polycrystalline β”-alumina was measured as a function of temperature for fine-grained and coarse-grained specimens with a chemical composition of 8.80 Na20-0.75 Li2O-90.45 A12O3 (wt%). A model is presented which explains the dependence of sodium ion resistivity on grain size. Using the model the activation energy was determined for the transport of sodium ions across a grain boundary in this form of sodium β”-alumina. more...
- Published
- 1978
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11. Creep of Doped Polycrystalline Magnesium and Aluminum Oxides
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Yasuro Ikuma and Ronald S. Gordon
- Subjects
Materials science ,Metallurgy ,Lattice diffusion coefficient ,Grain size ,Condensed Matter::Materials Science ,Creep ,Deformation mechanism ,Condensed Matter::Superconductivity ,visual_art ,visual_art.visual_art_medium ,Grain boundary diffusion coefficient ,Grain boundary ,Ceramic ,Crystallite - Abstract
It is well known that under conditions of small stress, fine grain size and enhanced lattice and/or grain boundary diffusion polycrystalline ceramics will deform at elevated temperatures by one or more diffusional creep mechanisms.[1–9] In this paper creep deformation maps will be utilized to illustrate the role of soluble (aliovalent) dopants, grain size, and oxygen fugacity on the relative contributions of (1) lattice diffusion, (2) grain boundary diffusion, (3) interfacial defect reactions at grain boundaries, and (4) power law or dislocation deformation mechanisms on the creep deformation of polycrystalline magnesium and aluminum oxides. more...
- Published
- 1984
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12. ChemInform Abstract: FRACTURE PROPERTIES OF POLYCRYSTALLINE LITHIA-STABILIZED β′′-ALUMINA
- Author
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Ronald S. Gordon and Anil V. Virkar
- Subjects
Flexural strength ,Chemistry ,Lithia ,Perpendicular ,Fracture (geology) ,General Medicine ,Crystallite ,Composite material ,Grain size - Abstract
The critical stress-intensity factor, K1C, and the fracture strength, σf, have been investigated on both hot-pressed and sintered lithia-stabilized β”-alumina. The hot-pressed material possessed a strong preferred orientation with many of the basal planes aligned perpendicular to the direction of hot-pressing. Both K1C and σf were found to be orientation-dependent. Two regimes of fracture were identified. In fine-grained material ( more...
- Published
- 1977
- Full Text
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13. ChemInform Abstract: CREEP OF POLYCRYSTALLINE MGO-FEO-FE2O3 SOLID SOLUTIONS
- Author
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J. D. Hodge, Ronald S. Gordon, Robert A. Giddings, and R. T. Tremper
- Subjects
Dopant ,Creep ,Chemistry ,Diffusion ,Analytical chemistry ,Lattice diffusion coefficient ,General Medicine ,Activation energy ,Crystallite ,Grain size ,Solid solution - Abstract
Steady-state creep experiments were performed on hot-pressed polycrystalline MgO doped with Fe. Dead-load 4-point bend creep tests were conducted at stresses of 26 to 270 kg/cm2, at temperatures of 1250° to 1450°C, in O2 partial pressures of 1 to 10−9 atm, on specimens with grain sizes of 10 to 65 μm. Viscous steady-state creep was always observed when the grain size was stable. Experiments at variable PO2's and temperatures were used to identify regimes of high (117 ± 10 kcal/mol) and low (81 ± 5 kcal/mol) activation energy. In the latter, creep rates were nearly independent of Fe dopant concentration and PO2, whereas in the former creep rates were enhanced by increasing PO2's and Fe dopant levels. The high- and low-activation-energy regimes were interpreted as diffusional creep controlled primarily by Mg lattice diffusion and O grain-boundary diffusion, respectively. more...
- Published
- 1975
- Full Text
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14. Microstructural Control During Sintering of β″-Alumina Compositions Through Ceramic Processing Modification
- Author
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Ronald S. Gordon, Arun D. Jatkar, Anil V. Virkar, and Ivan B. Cutler
- Subjects
Crystal ,Grain growth ,Materials science ,Chemical engineering ,Precipitation (chemistry) ,Impurity ,visual_art ,Volume fraction ,visual_art.visual_art_medium ,Sintering ,Ceramic ,Grain size - Abstract
The exaggerated grain growth during high temperature (1585° – 1600°C) sintering of Li2O-stabilized β″-alumina compositions is essentially a process or very rapid growth of stabilized 3″ nuclei to large dimensions (>100 µm) while the matrix remains extremely fine-grained (< 3 µm). The final grain size is therefore inversely proportional to the cube root of the volume fraction originally occupied by these nuclei~1 Such a relationship was reported by Cutler in the case of seeded alpha alumina powders and more recently by Lacour and Paulus3 in the case of barrium-hexaferrite. The occurrence of an exaggerated grain growth during sintering of ceramics has been shown to depend on the flux-growth mechanism wherein a film or channel of liquid phase surrounds the growing nuclei. The growth of nuclei to large dimensions takes place by the solution of surrounding fine grains in the liquid and their precipitation on the growing crystal surface. While Cooy4 and Stuijts5 reported accidental impurities as the cause of liquid phase formation, Lacour and Paulus3 showed that local inhomogenities can also give rise to a liquid phase responsible for the flux growth. more...
- Published
- 1978
- Full Text
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15. ChemInform Abstract: RESISTIVITY-MICROSTRUCTURE RELATIONS IN LITHIA-STABILIZED POLYCRYSTALLINE β′-ALUMINA
- Author
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Gerald R. Miller, Ronald S. Gordon, and Anil V. Virkar
- Subjects
chemistry ,Electrical resistivity and conductivity ,Sodium ,Lithia ,Analytical chemistry ,chemistry.chemical_element ,Grain boundary ,General Medicine ,Activation energy ,Crystallite ,Grain size ,Ion - Abstract
The sodium ion resistivity of lithia-stabilized polycrystalline β”-alumina was measured as a function of temperature for fine-grained and coarse-grained specimens with a chemical composition of 8.80 Na20-0.75 Li2O-90.45 A12O3 (wt%). A model is presented which explains the dependence of sodium ion resistivity on grain size. Using the model the activation energy was determined for the transport of sodium ions across a grain boundary in this form of sodium β”-alumina. more...
- Published
- 1978
- Full Text
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16. Impurity and Grain Size Effects on the Creep of Polycrystalline Magnesia and Alumina
- Author
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Ronald S. Gordon and Paul A. Lessing
- Subjects
Condensed Matter::Materials Science ,Materials science ,Deformation mechanism ,Creep ,Impurity ,Condensed Matter::Superconductivity ,Metallurgy ,Grain boundary diffusion coefficient ,Grain boundary ,Crystallite ,Composite material ,Grain size ,Solid solution - Abstract
Steady state, constant load, creep experiments have been conducted on pure and doped, polycrystalline magnesium and aluminum oxides to determine: 1) the effect of solid solution impurities (e.g. Fe, Cr, Ti) on deformation mechanisms, particularly as they relate to the concentration of lattice defects 2) the effects of impurities, atmosphere, and grain size on the relative contribution to viscous deformation of lattice and grain boundary diffusion of both cationic and anionic species 3) the relative roles of viscous and non-viscous deformation mechanisms. more...
- Published
- 1975
- Full Text
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17. ChemInform Abstract: RELATIVE EFFECTS OF PHASE CONVERSION AND GRAIN SIZE ON SODIUM ION CONDUCTION IN POLYCRYSTALLINE, LITHIA-STABILIZED β′-ALUMINA
- Author
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G. E. Youngblood, G. R. Miller, and Ronald S. Gordon
- Subjects
chemistry ,Phase conversion ,Sodium ,Lithia ,Analytical chemistry ,chemistry.chemical_element ,General Medicine ,Crystallite ,Thermal conduction ,Grain size - Published
- 1978
- Full Text
- View/download PDF
18. COMPARISON BETWEEN HIGH TEMPERATURE DEAD-LOAD CREEP AND STRESS-RELAXATION DEFORMATION IN IRON-DOPED POLYCRYSTALLINE ALUMINUM AND MAGNESIUM OXIDES
- Author
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Yasuro Ikuma, Dinesh K. Shetty, and Ronald S. Gordon
- Subjects
Materials science ,Magnesium ,Metallurgy ,technology, industry, and agriculture ,Diffusion creep ,chemistry.chemical_element ,Activation energy ,Grain size ,Condensed Matter::Materials Science ,Structural load ,Creep ,chemistry ,Condensed Matter::Superconductivity ,Stress relaxation ,Grain boundary diffusion coefficient ,Composite material - Abstract
The high temperature deformation of iron-doped polycrystalline aluminum and magnesium oxides was studied by stress relaxation and dead-load creep. Linear and non-linear anelastic effects, which are important in stress relaxation, can lead to significant differences in apparent creep rates and strain rate-stress relationships which are inferred from dead-load creep and stress relaxation data. In the low stress regime, the effects of the major variables, such as temperature and grain size, are similar for both modes of deformation and are consistent with diffusional creep controlled by various combinations of lattice and grain boundary diffusion. In the non-viscous deformation of magnesium oxide, dead-load creep and stress relaxation testing yielded similar results in terms of the grain size effect and activation energy for deformation. However, in the case of iron-doped aluminum oxide, the stress relaxation is apparently athermal and strongly influenced by non-linear anelasticity. more...
19. Relative Effects of Phase Conversion and Grain Size on Sodium Ion Conduction in Polycrystalline, Lithia-Stabilized beta-Alumina
- Author
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G. R. Miller, G. E. Youngblood, and Ronald S. Gordon
- Subjects
Materials science ,chemistry ,Chemical engineering ,Phase conversion ,Sodium ,Lithia ,Materials Chemistry ,Ceramics and Composites ,chemistry.chemical_element ,Crystallite ,Thermal conduction ,Grain size - Published
- 1978
- Full Text
- View/download PDF
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