High-temperature thermal storage systems for advanced solar receivers materials selections

Advanced space power systems that use solar energy and Brayton or Stirling heat engines require thermal energy storage (TES) systems to operate continuously through periods of shade. The receiver storage units, key elements in both Brayton and Stirling systems, are designed to use the latent heat of fusion of phase-change materials (PCMs). The power systems under current consideration for near-future National Aeronautics and Space Administration space missions require working fluid temperatures in the 1100 to 1400 K range. The PCMs under current investigation that gave liquid temperatures within this range are the fluoride family of salts. However, these salts have low thermal conductivity, which causes large temperature gradients in the storage systems. Improvements can be obtained, however, with the use of thermal conductivity enhancements or metallic PCMs. In fact, if suitable containment materials can be found, the use of metallic PCMs would virtually eliminate the orbit associated temperature variations in TES systems. The high thermal conductivity and generally low volume change on melting of germanium and alloys based on silicon make them attractive for storage of thermal energy in space power systems. An approach to solving the containment problem, involving both chemical and physical compatibility, preparation of NiSi/NiSi2, and initial results for containment of germanium and NiSi/NiSi2, are presented

Development of surface treatments and alloy modifications for corrosion-resistant oxide scales

Alloys based on the long-range ordered system Fe{sub 3}Al are under development at Oak Ridge National Laboratory in support of coal conversion and combustion materials requirements. Of particular interest is the performance of these alloys in coal gasifiers involving product gases with relatively low oxygen activities and high sulfur activities. Using H{sub 2}S-H{sub 2}-H{sub 2}O gas mixtures, several experimental iron-aluminum alloys have been tested to assess the effects of aluminum concentration on oxidation-sulfidation response at 700 to 800{degree}C in a simulated gasifier environment. Metallographic and chemical analyses of the corrosion product scales and the underlying alloy were performed to determine the role of respective metallic elements on the sulfidation-oxidation processes. These results, together with thermogravimetric analyses, are discussed in terms of the apparent corrosion mechanisms and optimization of alloy composition for exposure to coal-derived environments. More recently, the corrosion performance of an Fe-28% Al-2% Cr alloy has been evaluated in gases produced by an operating gasifier. The reaction products and scale morphologies under actual service conditions were generally similar to the laboratory test results except for the presence of an ash deposit on the gasifier specimens. 2 refs., 7 figs., 4 tabs

AN EVALUATION OF ELECTRO-MACHINING FOR THE ANALYSIS OF METAL SURFACES

A procedure is described for the uniform removal of very thin sections of metal surfaces by electrolysis. Equipment requirements and the various parameters affecting operation are considered, and the results of applying the technique to studies of solid-state diffusion are discussed. The technique appears to offer considerable promise for evaluating chemical changes at metal surfaces which have taken place as a result of corrosion or diffusion processes. (auth

Alkali- Metal Corrosion of Refractory Metals

This report talks about the Alkali- Metal Corrosion of Refractory Metal

Corrosion of Fe-Cr-Mn alloys in thermally convective lithium

A series of austenitic Fe-Cr-Mn steels was exposed to circulating lithium at temperatures up to 500/sup 0/C. Two groups of the alloys, which contained 12 to 30 wt % Mn and 2 to 20 wt % Cr, were sequentially exposed for periods greater than 3000 h in a type 316 stainless steel thermal convection loop. Mass transfer of manganese caused very large weight losses from the steels containing 30 wt % Mn. However, the actual magnitude of corrosion losses for alloys containing 12 to 20 wt % Mn was difficult to establish due to competing surface reactions involving chromium

Attack of superheater tube alloys, coatings, and claddings by coal-ash corrosion

Twenty stainless steels, nickel alloys, claddings, and intermetallics have been evaluated for resistance to coal-ash attack. Six series of test conducted to determine effects of two gas and three ash compositions at 650 and 700C (1202 and 1292F) for times up to 800 hours

METALLOGRAPHIC EXAMINATION OF ORNL NO. 1, SHE NO. 2

Small Heat Exchanger ORNL No. I, type SHE No. 2, was removed from test stand B after 2071 hours of operation; 1041 hours were under 4 T conditions. The heat exchanger contatned 20 Inconel tubes having an outside diameter of 0.25 in. and a wall thickness of 0.025 in. The outside of these tubes was exposed to the fluoride mixture NaF contained NaK (44% Na--56% K). During o degradation t T conditions, the fluoride temperature entering the heat exchanger was 1310 tained F and on leaving was 1235 tained F. The temperature of the NaK entering the heat exchanger was 1050 tained F and at the exit was 1290 tained F. During isothermal operation, the temperature of both the NaK and fluoride circuits was 1300 tained F. Thirtysix termperature transitions from isothermal to o degradation t T conditions were made during the course of operation. An examination of the resistance heater used in conjunction with this heat exchanger also was made: the results are reported. (auth

Metallographic Examination of Cambridge Nos. 1 and 2 Metallography Report No. 267

The radiators designated Cambridge #1 and #2 were visually examined and modified before operation. The initial examination revealed poor quality braze joints at the top and bottom plates of Cambridge #1. However, the same plates of Cambridge #2 were adequately brazed. The copper core of the fins was exposed in many of the tube-to-fin joints on both radiators, indicating that the braze material had not covered the fin collars. Samples were removed from each radiator and examined for evidence of mass transfer. Samples were also removed from the air inlet and outlet banks of both radiators and examined for fin-to-tube integrity