Ceramic Properties of Samarium Oxide and Gadolinium Oxide; X-Ray Studies of Other Rare-Earth Oxides and Some Compounds

Samarium oxide forms a ceramic of medium strength and density (6.0) when it is fired at 1300°C. When it is fired at 1500°C., its density is increased to 7.4 but it loses its stability toward boiling water. X-ray data are given concerning the structure of the oxide as received and at 1300°C. and of the reaction product of Sm203 with water. Gadolinium oxide forms a ceramic of somewhat higher density (7.0) at 1300° than does Sm₂O₃; at 1500°C. its density is slightly higher (7.6) whereas its stability toward water is unchanged. Data concerning both oxides include density, shrinkage, moduli of elasticity and of rupture, linear thermal expansion, differential thermal analysis, and specific heat as well as X-ray data. Results are given of a brief survey of the reaction products obtained when Sm₂O₃ and Gd₂O₃ are heated at 1500°C. in equimolecular quantities with Al₂O₃, BaO, CaO, CdO, Fe₂O₃, HfO₂, MgO, SO₂, SrO, ThO₂, and ZrO₂. X-ray data for the following rare-earth oxides as received and after calcination at 1400°C. are given: ceria, praseodymia, neodymia, europia, dysprosia, holmia, erbia, thulia, and ytterbia.     

Some Kinetic Considerations Regarding the Double-Torsion Specimen

In the double-torsion specimen, crack velocity is a function of the shear wave velocity. At a constant load above the critical load required for crack propagation, crack velocity asymptotically approaches a constant value which is proportional to the shear wave velocity and is dependent on specimen geometry and load. The maximum possible crack velocity under a constant load is proportional to the shear wave velocity multiplied by the ratio of the specimen thickness to its width. For the case of constant deflection with an initial load greater than the critical load, crack velocity goes through a maximum and arrests, for a sufficiently long specimen. Testing-machine compliance increases the length that such a crack will attain before arrest. The load required for rapid crack propagation is only slightly greater than the critical load; stable crack growth in the absence of stress corrosion guarantees an accurate determination of the fracture energy.     

Analysis and Design of a Viscous-Flow Cooler

A hot stream of a very viscous fluid, such as a polymer, may be cooled in a heal exchanger consisting of multiple parallel passages. However, if a quite uniform temperature distribution is desired in the exit stream, the fluid flowing through each of the passages must be cooled to very nearly the same temperature. An analytical treatment of heat transfer and pressure drop in viscous flow between parallel plates during cooling reveals the operating conditions and passage geometry required to achieve this goal. Solution of the equation obtained depends only on the physical properties of the fluid and the cooler geometry. Non-Newtonian behavior of the fluid is approximated by a power-law function. A unique type of heat exchanger was designed on the basis of this analysis.     

Diffusion Sintering: I, Initial Stage Sintering Models and Their Application to Shrinkage of Powder Compacts

Consideration is given to several geometrical models that contribute to shrinkage. Various shapes of particles, vacancy sinks, and diffusion paths are described as they affect sintering shrinkage. These simplified models are extended to compacts of nonuniform particles so that much of the kinetics of sintering of a substance can be determined by measuring shrinkage rates of powder compacts. A nonideal compact may sinter as though it had once been an ideal compact after a specific amount of shrinkage has occurred. This shrinkage is characteristic of the particular compact and its origin and is independent of temperature.     

Effect of Tumbling and Tumbling Temperature on Total Aerobic Plate Counts (Incubated at 25°C) and Quality of Boneless, Cured Hams

The effects of intermittent tumbling (up to 18 hr) and processing temperature (25°C or 3°C) on internal temperature and exudate total aerobic plate counts incubated at 25°C (ATPC) in boneless, cured hams were determined. The design used 80 hams in five replicates involving four treatment groups (tumbled at 25°C tumbled at 0°C, control held at 25°C and control held at 0°C). The significant (P < 0.01) tumbling effect on the rise in internal ham temperature occurred after 3 hr, but only accounted for a difference of 1.26°C-1.32°C, independent of processing temperature. While tumbling significantly improved the cooked yield by 3.45%, processing at 25°C rather than at 0°C resulted in a significant (P<0.05) yield reduction of 2.15% after 9 hr of processing. The exudate ATPC was significantly (P<0.01) reduced after 18 hr of tumbling.     

Ceramic Properties of Europium Oxide

Europium oxide of 99.7% purity was compacted into small bars and pellets which were fired at temperatures from 1050° to 1700°C. for 2 to 120 hours in atmospheres that were oxidizing, mildly reducing (open furnace), or strongly reducing. It was found that (1) europium oxide compacts fired in oxygen for 2 hours at 1500°C. bad attained a density of 90% of theoretical and were stable in boiling water, (2) compacts fired under mildly reducing conditions at 1500°C. for 2 hours had attained a density of 84% of theoretical and disintegrated in boiling water, and (3) those fired similarly in a hydrogen atmosphere began to fuse at 1500°C. The linear thermal expansion of the compacts fired at 1500°C. in the open furnace was 10.5 x 10^-6in. perin. per°C. between 0° and 1000 °C. and their molar specific heat between 0° and 800°C. was 33.3 cal. Careful investigation of the structural changes occurring in europium oxide with rising temperature revealed that (1) the low-temperature (body-centered cubic) form inverts slowly to the high-temperature form at approximately 1050°C., (2) the high-temperature form has monoclinic symmetry, and (3) it does not revert readily to the cubic form; its theoretical density was calculated to be 8.18 gm. per cm.³.