Hot corrosivity of coal gasification products on gas turbine alloys. Summary report, 15 April 1978-15 November 1979

The results of this investigation have produced mechanisms for the hot corrosion of a number of pure metals and alloys in the types of atmospheres likely to be obtained in turbines using coal conversion products as fuel. The results of these mechanistic studies suggest the following conclusions regarding application of alloys in these situations: (1) Simple Cr/sub 2/O/sub 3/-forming alloys of both Co and Ni have good hot corrosion resistance to most of the deposits likely to form in turbines burning coal conversion products with the exception of deposits containing considerable amounts of chlorides. (2) The presence of carbide phases is detrimental to the hot corrosion resistance of both Ni and Co alloys. (3) The complex alloy compositions characteristic of superalloys result in susceptibility to hot corrosion, the extent of which is sensitive to salt composition, particularly for Ni-base alloys. (4) Conclusion 3 suggests that uncoated alloys will not be able to provide the require combination of corrosion resistance and high-temperature strength for any of the components in turbines running on coal gas. (5) Several alloys including Co-18Cr-6Al-1Hf, Co-27Cr, Co-20Ni-27Cr, Ni-50Cr, and Fe-18Cr-6Al-Hf have corrosion resistance for use as coatings and claddings at high temperatures (900 to 1000/sup 0/C). (6) The problem of low temperature hot corrosion (700 to 800/sup 0/C) must still be investigated for the types of deposits likely to form in coal fired systems before selection of reliable coatings can be made

SOLUBILITY OF HYDROGEN IN THE 50 WEIGHT PERCENT URANIUM-ZIRCONIUM ALLOY. Scientific Paper 100FF1010-P1

The reaction of He with the epsilon phase of the 50 wt. % U--Zr alloy is studied using a sensitive vacuum microbalance apparatus to prepare the alloys, a sensitive McLeod gage to measure the dissociation pressures, and x-ray diffraction analyses to determine the phases present in the alloy. Although the reaction of H/sub 2/ with the alloy is very rapid at 100 deg C for oxide free surfaces, homogenization is very slow. Hydrogen alloys are prepared in the composition range of U/sub 0.28/Zr/sub 0.72/H/sub 0.0007/to U/sub 0.28/Zr/sub 0. 72/H/sub 0.121/ and the dissociation pressure measurements determined in the temperature range of 300 to 600 deg C. Due to the slow processes of homogenization, the hydride ZrH/sub 1.2/ is not readily precipitated below 400 deg C. On heating to 525 deg C and cooling, the hydride is readily formed for compositions of U/sub 0.28/Zr/sub0.72/H/sub 0.035/ and higher. For lower H/sub 2/ compositions, the hydride is not found in the x-ray diffraction patterns on heating these compositions to 525 deg C and cooling. It is suggested that small hydride nuclei are formed which are not observable by x-ray diffraction methods. Due to a slow rate of metallic diffusion, these nuclei cannot grow. The solubility of H/sub 2/ in the alloy is determined to be approximately 0.02 at.% at 500 deg C. This is a smaller value than that found for pure Zr. However, the heat of solution of hydride is +8,900 plus or minus 1,000 calories per gram atom and compares with a value of +8,600 calories per gram atom found for Zr. A transformation of the epsilon to gamma phase of the alloy is found near 550 deg C. (auth

THE REACTION OF HYDROGEN WITH A 50 WEIGHT PERCENT ALLOY OF URANIUM AND ZIRCONIUM BETWEEN 542 C AND 798 C. Research Report 100FF1010-R1

Hydrogen sorption isotherms have been measured between 542 and 798 deg C at pressures of 0.001 to 70 cm of Hg. The isotherms give the terminal solubility of S in the initial alloy phases and the limiting compositions of new phases containing H/sub 2/. Values for the heat of solution of H/sub 2/ at all concentrations are presented. A comparison of the data with that of the H-- Zr system indicates that, above a minimum H/sub 2/concentration, the alloy breaks down to give V and Zr. The alloy then behaves, to some extent, as the H--Zr system modified by the presence of U. X-ray diffraction studies give support to this interpretation (auth

OXIDATION OF TUNGSTEN AND TUNGSTEN BASED ALLOYS

The results of studies related to the oxidation of tungsten and its alloys are presented. The pressure of WO/sub 3/ polymers over WO/sub 2/ was measured in a tungsten Knudsen cell andd found to agree with measurements in a platinum cell. Literature data for WO/sub 2/ and WO/sub 3/ were combined with vapor pressures determined to give thermodynamic values for W/sub 18/O/sub 49/and W/sub 20/O/sub 58/. Tungsten oxidation rates were measured from 800 to 1700 deg C and in pressures of oxygen between 2 x l0/sup -1/ and 10/sup -2/ atmospheres. The effects of oxygen pressure indicate that the rate may be governed by oxygen dissociating to atoms in the reacting surface. The oxidation rate is demonstrated to be independent of the oxide evaporation rate. All of the evidence indicates that if an oxide barrier layer is present at temperatures above 800 deg C it must be very thin. Studies on the oxidation of tantalum tungsten alloys between 800 and l200 deg C indicate that the 50-50 alloy has the greatest oxidation resistance, oxidizing at a rate as much as l0 times slower than tungsten alone. (auth