摘要:

Synthetic aluminum oxide crystals were irradiated with fast neutrons to a dose of 1.8 × 1020nvt and examined by. transmission electron microscopy. As‐irradiated crystals contained damage on a fine scale, revealed by diffraction contrast, and showed a 28% increase in Knoop diamond hardness compared with unirradiated material. Annealing above 600° C decreased the hardness and caused the small defect clusters to grow, forming dislocation loops on [100] planes with 1/3(101) Burgers vectors. High temperature annealing caused the loops to interact to give dislocation segments. These tended to align with the (100) and (1120) directions, and some of them had 1/3(101) Burgers vectors. Grown‐in dislocations also began to climb but showed evidence of impurity pinning. Isolated platelike precipitates on [101]planes were observed in samples annealed at high temperatures. Possible effects of the observed damage on physical properties are considered; there is qualitative agreement between predictions and existing

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12630.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Phase relations in the system U‐C‐O‐N at 1700°C were established at nitrogen levels up to an atomic ratio N: C 1:3 by microstructural and X‐ray analyses of sintered powder compacts. The extent of the solid‐solution field of uranium oxycarbonitride was established on the ternary plane U‐C0.75No.0.25‐O. The maximum solubility of oxygen in the solid solution is 14 at.%, corresponding to a composition U0.50C0.27O0.14N0.09compared to 17 at.% on the U‐C‐O plane. Nine other phase fields were established on the U‐C‐O C0.75N0.25‐O plane, all of which contain a uranium oxycarbonitride solid‐solution phase and a gaseous phase of CO and N.2. Equilibrium pressure varies from about 0.01 torr in phase fields containing free uranium to about 200 torr in the field containing solid solution +“UC2” (oxy‐gen‐containing dicarbide) + C + UO2. Lattice parameters of the solid‐solution phase were determined. A field containing solid solution and UzC3 exists to about 3.5 at.% O and 2 at.% N at the hyperstoichiometric boundary of the solid‐solution field. An isothermal phase diagram for the low‐nitrogen

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12631.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Mixtures of PbO and silicic acid were fired at 710°, 820°, and 910°C for periods up to 1000 hr in air. At each temperature cristobalite and tridymite crystallized rapidly, with the greatest development in samples with compositions of 1 mole PbO to 50 and 60 moles SO2. At 820° and 91O°C tridymite continued to crystallize at the expense of cristobalite. At 710°C quartz formed, after a nucleation time of approximately 200 hr, at the expense of cristobalite and tridymite. The equilibrium assemblages were cristobalite and tridymite at 820° and 910°C and quartz and PbSiO2at 710°C. The results are interpreted in terms of the tentative phase relations outlined by Holmquist for the high‐silica regions of binary silicate systems. Phase development curves and lattice parameter measurements characterize the initially formed cristobalite as a metastable solid solution containing approximately 2 mole % PbO. Equilibrium was approached by exsolution of PbO from the cristobalite

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12632.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The structural, dielectric, and piezoelectric properties of the solid solution (Na1‐x,Lix,)NbO2were studied. Solid solution ceramics withxvalues up to 0.14 occur as a single phase. The phase diagram from 0° to 600°C is given. The low‐temperature phase has a perovskite pseudo‐monoclinic structure and inverts to a pseudotetragonal structure at a temperature that decreases with increasingx.The high‐temperature phase is pseudocubic, and the minimum transition temperature from the pseudotetragonal to the pseudocubic structure is 350° C nearx= 0.04. Anomalies in the dielectric constant vs. temperature curve agree well with the transition temperatures, although no anomaly was observed at the temperature of transition from the pseudotetragonal to the pseudocubic phase whenxwas less than 0.06. Lithium ions in the system facilitate the transformation from the antiferro‐electric to the ferroelectric state produced by applying an electric field. A new ferroelectric phase becomes stable whenxis greater than 0.07. Poled ferroelectric specimens had a planar coupling coefficient of 0.232, a dielectric constant of 220, and a frequency constant of 3352 kc‐mm. The piezoelectric properties disappear not at the transition temperature but at the temperature at which strain exhibits an anomaly whenxis greater than 0.07. A perovskite phase with a pseudorhombohedral subcell exists as an intermediate phase forxgreater than 0.10, the exact value depending on the preparation method. The phase can be easily converted to pseudomonoclinic when the ceramic is fired at 1

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12633.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The wettability of sapphire single crystals by liquid copper which contained oxygen added as cupric oxide was investigated using the sessile drop technique in vacuum at 1230°C. Additions of cupric oxide to copper, varying from 1 to 72% of copper weight, resulted in rapid chemical reaction at the solid‐liquid interface with a significant reduction of the contact angle, the final value being dependent on the oxygen in the system. In all cases the interfacial product was CuAlO2. A linear relation between the fourth power of the basal radius of the molten drop and the amount of oxygen present was observed. The initial stage of the reaction could be explained by the formation of a Cu2O layer at the interface, followed by reaction between Cu2O and Al2O3to form CuAl

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12634.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Vapor deposition was used to obtain homogeneous glass films of several BaO‐SiO2compositions in the region of the metastable miscibility gap. The films were electron‐beam heated in the electron microscope, and the phase separation process was observed. At low BaO contents, separation was characterized by the appearance of discrete, amorphous, second‐phase particles. For compositions near the center of the miscibility gap, separation resulted in two continuously interconnected phases similar to those in the corresponding bulk glasses. In the thinnest of these films, the process proceeded by the coalescence of isolated particles into the interconnected second‐phase submicrostructure. At high BaO contents, rapid crystallization of the films prevented study of the separation process. Two processes which could lead to coalescence of discrete second‐phase particles into an interconnected submicrostructure are discussed. It is suggested that coalescence may occur when either of these processes results in the particles approaching within some small distance of each other. It is indicated that under appropriate conditions, this requirement may be satisfied by either process. These conclusions, together with the present observations of BaO‐SO2thin films and those previously reported for bulk samples, indicate that observations of final phase‐separated morphologies are inadequate for specifying the processes by which those morph

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12635.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The diffusion of oxygen in monocrystalline ScaO3, YzO3, Dy,O2, HosO3, Er2O3, Tm2O2, and Lu2O3was measured by a thermobalance technique. The reoxidation of partially reduced crystals of these materials was treated as a diffusion‐controlled process with a moving boundary. Large diffusion coefficients and fairly low activation energies were found for this process, in agreement with a proposed migration mechanism which involves the inherently defective anion sublattice of these material

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12636.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Several new compounds with the formula AB2S4were synthesized. Pressure‐induced polymorphism of the sulfospinels was investigated. The only spinels which transformed to the NiAs derivatives were those in which the A and B cations had unfilleddorbitals. Pressure‐temperature phase relations were investigated for a series of sulfochromites. At 600°C the transformation pressure decreased in the order MnCr2S4, FeCr2S4= CoCr2S4, NiCr2S4(an NiAs structure atP= 1 atm). Sulfospinels which produced new high‐pressure phases were NiRh2S4, FeYb2S4, CrIn2, NiIn2S4, CoIn2S4, and M

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12637.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Synthetic β‐Spodumene and several β‐Spodumene‐silica solid solutions were prepared, and their thermal expansion behavior was studied using high‐temperature X‐ray diffraction techniques. Data indicate that all β‐Spodumenes are characterized by a pronounced anisotropy of thermal expansion much the same as that of the silica polymorph keatite. Anisotropy increases slightly and the volume expansion decreases as the compositions become richer in SiO2. Specimens with more than 80.8 wt% SiO2at 130O°C and 1 atm contain P‐cristobalite along with β‐Spodumene. The lattice parameters of β‐Spodumene compositions throughout the solid solution range were determined. The structural aspects of the anisotropy of thermal

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12638.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Simple (100) tilt, twist, and double‐tilt bicrystals of NaCl, grown by the Kyropoulos technique from melts of high‐purity NaCl, alone and with controlled impurity additions, were examined for mechanical strength and structure of the grain boundaries. Grain boundary fracture strengths, measured in three‐point bending, showed that high‐purity bicrystals with simple tilt orientations were stronger than those with simple twist at high mismatch angles (37° to 45°). The results did not show a functional dependence of strength on angle of mismatch in either tilt or twist bicrystals. Pips observed on parted grain boundaries of high‐purity NaCl (100] twist and double‐tilt bicrystals were believed to represent regions of continuity across the boundary. This feature was rare in similar‐purity NaCl (100) tilt bicrystals. Separate additions of 100 ppm SiO2, CaCl2, FeCls, and KCl to the melt had no apparent effect on the character of the grain boundary. However, an addition of 1000 ppm CaCl2nearly doubled the strength of a (1001) 30° twist bicrystal, whereas the same addition weakened a (100) 45° tilt bicrystal. Sodium chloride (100) tilt grain boundaries, examined in situ under dark‐field illumination, showed randomly distributed spots, believed to be impurity segregations, with their maximum density at the boundary. The spot densities increased with increasing tilt angle for angles of 15° and greater. The spots were not observed in the low‐angle tilt boundaries (<15°) and were seen only in intermittent clusters in the few tw

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb12639.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY