FUNDAMENTALS OF DIFFUSIONAL BONDING--III. Third Annual Progress Report for June 30, 1957 to June 30, 1958

An investigation has been begun of interdiffusion in the aluminum- uranium system and of the effects thereon of applied pressure. In confirmation of the results of other investigations, it has been found that UAl/sub 3/ layer growth is accelerated by increasing applied pressure. The growth kinetics are characterized by a transient'' period, during which growth occurs non- parabolically, which is followed by a steady state'' period of parabolic growth. Interesting correlations are shown to exist between annealing time, annealing temperature, and applied pressure on the one hand, and the nature and distribution of structural defects in the UAl/sub 3/ diffusion zone. (auth

FUNDAMENTALS OF DIFFUSIONAL BONDING--IV. Fourth Annual Progress Report for July 1, 1958 through June 30, 1959

Investigatlon of interdiffusion in the aluminumuranium system and of the effects of applied pressure on such systems was about completed. The growth kinetics of the UAl/sub 3/ phase were determined at 400 to 600 C and at pressures of 1 1/4, 5, and 10 tsi. The origin of the macroscopic defects occurring in the UAl/sub 3/ layer during interdiffusion was clarified. The solubility range of UAl/sub 3/ was determined by a nuclear track emulsion technique to be about 2.6 at.% uranium. Exploratory runs were made with incremental diffusion couples of aluminum vs. UAl/sub 3/ and of UAl/sub 3/ vs. uranium disks to determine the growth rates of the UAl/sub 4/ and UAl/sub 2/ phases. A theoretical estimate was made of the importance of pressure-induced shifts in equilibrium concentrations in intermetallic layer growth in the aluminum-uranium and aluminum-nickel systems. (For preceding period see SEP- 251.) (auth

FUNDAMENTALS OF DIFFUSIONAL BONDING--II. Second Annual Progress Report, June 30, 1956 to June 30, 1957

The study of the kinetics of layer growth in the aluminum -- nickel system and the effect thereon of applied pressure has been continued. Additional information has been obtained about the growth of the beta phase, and a method was developed whereby the kinetics of growth of the beta phase could be investigated. The implications of Vasileff's equations which provide the solution for interdiffusion in a three-phase two-component system have been examined semi-analytically, and quantitative insight has been gained into the kdnetics of interface movement. Finally, an investigation of the kinetics of interface movement and layer growth has been begun on systems which have less complicated phase equilibrium relationships than those existing in the aluminum -- nickel system. (auth

DIMENSIONAL INSTABILITY OF URANIUM--II. Second Annual Progress Report, January 1, 1956 to June 30, 1957

The mechanism of dimensional instability of irradiated uranium is under investigation. In order to confirm an assumption of the diffusion theory, the magnitude of diffusion anisotropy in alpha-uranium single crystals is being determined by measurement of the diffusion coefficients along the principal directions. Progress made in working out procedures for the preparation of uranium single crystals, preparation of the diffusion couples, measurement of valid concentration-penetration data in very thin diffusion zones by sectioning, and measurement of surface concentrations by means of nuclear tracking emudsions is discussed. Also, in-pile experiments are being designed to further clarify the nature of growth under irradiation. (auth

THE SELF-DIFFUSION OF NIOBIUM--II. Second Annual Progress Report, July 1, 1957 to June 30, 1958

The self-diffusion coefficient of niobium was measured as a function of temperature. Procedures were developed for the preparation of NbCl/sub 5/ from a solution of radioactive Nb/sup 95/ in oxalic acid, and the subsequent vapor plating of a radioactive metallic layer from this volatile compound. Initial measurements made at 2000 and 1800 deg C yield values for the self-diffusion coefficient of 3.2 x 10/sup -9/ cm/sup 2/sec and 1.7 x 10/sup 10/ cm/sup 2/sec, respectively. (auth

FUNDAMENTALS OF SINTERING--II. Second Annual Progress Report, June 30, 1956 to June 30, 1957

Rates of spheroidization and densification of gold and of nickel wire compacts were measured as a function of time, temperature, and wire size. The necks joining the sintered particles were found to grow proportionally to the one- fifth root of time. The value of the coefficient of self-difiusion calculated from the sintering rate is of the sane order of magnitude as that obtained by ordinary tracer techniques but with a somewhat higher activation energy. These results are entirely consistent with those predicted by the Kuczyrski diffusional theory of sintering, as is the effect of wire size on sintering rate. The experiments did not reveal a clear effect of grain boundaries on sintering rates. This may be due to a relatively slow densification of the nickel wire compacts at even 0.98 of the absolute melting point, which obscured the effect of grain growth on sintering rate. (auth

FUNDAMENTALS OF SINTERING--III. Third Annual Progress Report for June 30, 1957 to June 30, 1958

The influence of the presence of grain boundaries on the rates of sintering of nickel, copper and iron wire wound compacts was studied. In iron compacts sintered in the alpha range, surface diffusion appears predominant and no grain boundary effect is therefore expected or evident. On the other hand, sintering of copper and of nickel compacts at temperatures close to their respective melting points apparently occurs by volume diffusion but with varying grain boundary effects. Neck growth in both materials appears entirely unaffected by the presence or absence of grain boundaries. Void shrinkage was found to be sharply inhibited in nickel samples from which grain boundaries had been deliberately eliminated, but no definite effect was noticed in copper, in apparent contradiction to previous results. (auth

DIMENSIONAL INSTABILITY OF URANIUM--III. Third Annual Progress Report for June 30, 1957 to June 30, 1958

The mechanism of dimensional instability of uramium is under investigation. Ih order to confirm an assumption of the diffusion theory, the magnitude of diffusion anisatropy in alpha-uranium single crystuls is being determincd by measurement of the self-diffusion coefficients along principal crystullographic directions. lnitial measurements have yielded values of 5 x 10/ sup -15/ cm/sup 2//sec along the (010! and 4 x 10/sup -15/ cm/sup 2/ sec along the (OOl!. These values are being rechecked. in addition, in- -pile experiments designed to further clarify the effect of grain size on growth under irradiation have been initiated. (For preceding period see SEP-246.) (auth

THE SELF-DIFFUSION OF NIOBIUM--I. First Annual Progress Report, January 1, 1956 to June 30, 1957

The measurement of the self-diffusion coefficient of niobium as a function of temperature has been undertaken. It is planned to prepare the diffusion couples by the deposition of Nb/sup 95/ onto the surfaces of niobium discs from the Nb/sup 95/Cl/sub 5/ vapor phase and to anneal the couples in the temperature range 1600 deg to 2000 deg K. Details are given of the construction of the vapor deposition apparatus and of the preparation of Nb/sup 95/Cl/sub 5/ from the oxalate form in which the isotope is received. Preliminary measurements of the diffusion coefficient in a Nb-8 wt.% Ti alloy and In a Nb-1.4 wt.% V alloy indicate that the diffusion coefficient in the former is approximately 10/sup -9/ cm/sup 2//sec at 1600 deg C and is approximately 8 x 10/sup -11/ cm/sup 2//sec in the latter at 1400 deg C. (auth