MARITIME GAS-COOLED REACTOR PROGRAM. REACTOR MATERIALS COMPATIBILITY WITH IMPURITIES IN HELIUM

Results are presented of an investigation to determine the maximum permissible partial pressure of carbon dioxide that could be tolerated in the Maritime Gas Cooled Reactor system without oxidizing and embrittling niobium and its alloys, and to screen the heat-resistant nickel- and iron-base alloys for resistance to oxidation and carburization by hydrogen, carbon dioxide, and carbon monoxide. The effect of hydrogen additions on carburization of heatresisting alloys and on the decomposition of carbon monoxide was also studied along with the cataltic effects of heat-resisting alloys on disproportionation of carbon monoxide. (J.R.D.

In vitro and in vivo studies on biocompatibility of carbon fibres

In the present study we focused on the in vitro and in vivo evaluation of two types of carbon fibres (CFs): hydroxyapatite modified carbon fibres and porous carbon fibres. Porous CFs used as scaffold for tissues regeneration could simultaneously serve as a support for drug delivery or biologically active agents which would stimulate the tissue growth; while addition of nanohydroxyapatite to CFs precursor can modify their biological properties (such as bioactivity) without subsequent surface modifications, making the process cost and time effective. Presented results indicated that fibre modification with HAp promoted formation of apatite on the fibre surface during incubation in simulated body fluid. The materials biocompatibility was determined by culturing human osteoblast-like cells of the line MG 63 in contact with both types of CFs. Both tested materials gave good support to adhesion and growth of bone-derived cells. Materials were implanted into the skeletal rat muscle and a comparative analysis of tissue reaction to the presence of the two types of CFs was done. Activities of marker metabolic enzymes: cytochrome c oxidase (CCO) and acid phosphatase were examined to estimate the effect of implants on the metabolic state of surrounding tissues. Presented results evidence the biocompatibility of porous CFs and activity that stimulates the growth of connective tissues. In case of CFs modified with hydroxyapatite the time of inflammatory reaction was shorter than in case of traditional CFs

The Mechanism of the Martensite Burst Transformation in Single Crystals of Iron Containing 31.7 Per Cent Nickel

The martensite burst transformation was studied in single crystals of iron containing 31.7% nickel. It was found that the morphology of the transformation was greatly simplified in crystals that had heen strained plastically prior to transformation. This simplification made possible detaiied crystallographic studies of the morphology of the transformation. These studies showed that the autocatalysis responsible for the burst transformation had its origin in a mechanical stimulation (coupling) between certain variants of the habit plane that were geometrically oriented such that the stress induced by transformation on one aided transformation on the others. In both strained and unstrained crystals, the most effective mechanical autocatalysis was observed to be between groups of four nearly parallel pianes whose poles clustered about common ( 110) directions. In the transformation of strained crystals, the operation of certain of these groups was favored. These were the groups whose planes were nearly perpendicular to the active slip plane, but did not include the group whose poles clustered about the Burger's vector of the active slip system. This behavior was taken to be a consequence of the anisotropic substructure introduced during deformation. Because of the enhanced transformation by certain groups in strained crystals, the frequency of secondary coupling was low, and the regions of the crystals that were transformed through the operation of a single group of four variants of the habit plane were large This effect was responsible for the simplification of the morphology produced in the burst transformation of strained crystals. (auth

EVALUATION OF (Th,U)Csub2sub 2, CARBON-COATED (Th,U)Csub2sub 2 PARTICLES, AND CARBON COATINGS

Thorium and uranium carbide nuclear fuel particles were evaluated by metallographic and x-ray diffraction techniques. Techniques were developed to etch the polished surface of Th--U carbide to reveal the grain structure. In addition, techniques to determine particle density and coating thickness were developed. Comparison of the data indicates that the use of spherical particles allowed for more precise determination of the coating thickness, density, and strength of coatings. Strength of individual particles was about 700 to 1300 g per particle. A large scatter in crushing-strength values was observed when individual particles were crushed. Consequently, a relative crushingstrength test was developed for comparing coating strength: loads were applied to a column of particles in stepped increments, and broken coatings were detected by observing a weight gain in moist air from hydrolysis of the Th--U carbides. A correlation of relative crushing strength and coating thickness was obtained. The crystal structure of the C coatings was found to depend on the temperature of deposition in the range from 1400 to 2400 deg C; the twodimensional structure became more defined with increasing deposition temperatures. Subsequent annealing at 2400 deg C of the coatings deposited at 1400 deg C and at 2200 to 2400 deg C produced graphitization, whereas those deposited at 1800 to 2000 deg C retained their two-dimensional character. Macrostructure of the coatings as revealed by metallographic techniques showed a concentric shell-like structure in the 1400 deg C deposits and mottled or conical structure in the 1800 deg C deposits. Annealing to higher temperatures did not alter the general appearance of either macrostructure. (auth