No abstract

No abstract

C i n flowing dry hydrogen. Homogeneous fuel pellets with densities in e x c e s s of 97 per cent of theoretical were obtained for property studies. of the UO2-5O mole per cent Z r 0 2 composition was found considerably lower than that of UO, but higher than that of ZrOp. roughly paralleled that of pu.re U 0 2 at a slightly higher value, over the temperature range measured. Electrical resistivity decreased with increasing temperature, a s is typical of a ceramic material. In t e s t s of UO2-2O to 50 mole per cent Z r 0 2 compositions, in general, both room-temperature and high-pressure hardness values increased a s the ZrOz content increased. Homogeneous UO2-5O mole per cent ZrO, pellets were more resistant to cracking under thermal cycling than were inhomogeneous pellets of the same composition. Phase relationships in the UOp-ZrOp s y s t e m up to 50 mole per cent ZrOq were evaluated to determine a s a function of temperature the equilibrium phases present and the solubility limits of Z r 0 2 in UOz. At 1000 C or above it was found that, at low ZrOp contents, a singlephase face-centered-cubic solid-solution regior) i s present. A t Zr02 contents greater than 13.5 mole per cent a two-phase face centered cubic-face centered tetragonal region e x i s t s at 1000 C.

T h e repDr1 ral

Before aluminum alloys are welded, they are usually subjected to some kind of surface treatment. This may involve machining, solvent degreasing, chemical cleaning, anodizing, etc. Storage time until welding often means exposure to a variety of environmental conditions.It has long been known that weld quality depends on the condition of the surface. A systematic program was started in our laboratory (ref. 1) to investigate and characterize surfaces and the associated weld-defect potential as a function of different treatments. The characterization of surfaces includes topography, metallography, quantitative and qualitative determination of adsorption of contaminants, and the nature of the oxide layer by electron microscopy. The electron replication studies are reported herein.