Some Physical Properties of High-Density Thorium Dioxide

The values for a number of physical properties are reported for a very high density form of thorium dioxide. When specimens of a mixture of 99½% ThO² and ½% CaO, by weight, were hydrostatically pressed at 30,000 lb. per sq. in. and heat-treated for 1 hour at 1800°C., they attained 99.0% of theoretical density. All the test specimens were extremely brittle. Physical-property values determined at room tempera- ture were the following: lattice constant; bulk and theoretical (X-ray) densities; compressive and impact strengths; Knoop hardness; modulus of rupture and Young's modulus, determined by a static method; Young's modulus and the shear modulus, determined by a dynamic method; Poisson's ratio and the bulk modulus, calculated from the dynamic-test data; and the velocity of sound through the material. The properties determined at elevated temperatures were the following : linear thermal expansion modulus of rupture and Young's modulus, determined by a static method; Young's modulus and the shear modulus, determined by a dynamic method; and Poisson's ratio, calculated from the elevated-temperature dynamic-test data. "Martin's diameter" grain counts were taken for the material both before and after heat-treatment.     

Flexural Strength of Specimens Prepared from Several Uranium Dioxide Powders; Its Dependence on Porosity and Grain Size and the Influence of Additions of Titania

Flexural strengths of specimens prepared from four uranium dioxide powders were determined at room temperature and at 1000°C. The relation of the strength (S) to porosity (P) and to grain size (G) could be represented by the expression S = kG^−ae^−bP , where k, a , and b are empirical constants which differed with test temperature but did not differ for the different urania powders used. Additions of titania were very effective in promoting sintering and additions of 0.50 or 0.75% by weight markedly increased the strength of the specimens.     

TEXTURAL PARAMETERS IN COMPRESSION TESTING OF A GEL MADE FROM FRESH AND FROZEN FISH MINCE

The relation between deformability modulus and yield stress is evaluated in compression testing of a model product made from fresh and frozen stored mince of cod. The experiments were performed with a compression rate of 120 mm/min. Preliminary experiments showed decreasing values of yield stress when compression rates were below 50 mm/min. Two moduli were calculated from the slope of the compression curve; α₁, initially (small deformations) and α₂ in a linear part of the curve shortly before rupture of the gel. α₂ was linearly related to yield stress in gels of different water content, and in gels made from fresh and frozen raw material. α₁ showed different relations to yield stress depending on quality of the raw material.     

Dependence of Mechanical Strength of Brittle Polycrystalline Specimens on Porosity and Grain Size

An empirical equation form, approximating the apparent dependence of the strength of brittle polycrystalline specimens on the combined effect of porosity and grain size, has been developed from concepts and data in the literature. The form is shown to be applicable to data for thoria and chromium carbide specimens.     

Physical Characteristics of Titanium Carbide Type Cermets at Elevated Temperatures

The principal purpose of this investigation was to determine the creep behavior and strength at 1200° to 1850°F. of cermets which may be used in the high-temperature areas of aircraft. Initially a series of bending tests was made on variations of Kennametal 150-type Kentanium containing from 5 to 30% nickel binder. The 5, 15, and 20% compositions were the strongest and the most creep resistant. Because of the need for both thermal and mechanical shock resistance, tensile creep tests were then made on K150-type Kentanium compositions containing 20, 25, and 30% nickel binder. A limited number of tests also were made on Kennametal composition K162B and on Firth Sterling composition FS-27. The cermet K162B was the most creep resistant and the strongest. Linear thermal expansion determinations were made on Kennametal compositions K138A, K138, K151, and K151A. Their coefficients of expansion between room temperature and 1205°C. ranged from 8.1 × 10⁻⁶ to 8.6 × 10⁻⁶ per °C. Metallo-graphic examinations were made of all the tensile-tested specimens; in general, the test strains were too small to cause any noticeable deformation or changes in microstructure.     

Heat Transfer Between Moving Beds of Solids and a Transverse Finned Tube

Vie objective of the research reported in this article was to measure the rate of heat transfer between a transverse finned tube and a slowly moving bed of particles. Linear velocities of the moving bed of solids ranged from 0.0004 to 0.025 m/s. Three different particulate materials of various sizes were investigated, namely, polyethylene, silica sand, and copper. The experiments were conducted under steady-state conditions.

The following empirical equation for prediction of the heat transfer coefficient between the moving bed of particles and the transverse finned tube was developed employing dimensional analysis and nonlinear regression: This equation should be applied only within the range of the parameters for which it is derived.     

Functional Correlation of Surface Temperature and Flow Velocity on Fouling of Cooling-Tower Water

Experimental fouling data have been analyzed on the basis of the change in overall heal transfer coefficient of the fouling test section. It is assumed that thermal hydraulic conditions in the test section remain reasonably constant for the duration of a fouling test. The model ofTaborek et al.|I| is used, and two parameters,/8,. and Rf?, that can be determined for each fouling test are derived by regression analysis. The parameter Rf? contains all the factors that influence fouling, while 1/ ?_c, contains shear stress, deposit thickness, and bonding strength of the deposit. The parameter R?is the asymptotic fouling resistance and ? is the lime constant of the fouling resistance-time curve. These parameters were determined as a function of surface temperature. Limited data were available to indicate the effect of velocity on the parameters. The parameters 1/8, and R? may be used to predict the history of fouling in a heat exchanger. Until more.data are obtained and analyzed in this fashion, the values of 1/ ?_c. and R? obtained in this paper should be applied at conditions for which the fouling data were obtained. A numerical example is presented.