Showing papers on "Directional solidification published in 1979"

Solar-grade silicon by directional solidification in carbon crucibles

Abstract: Directional solidification of silicon in carbon crucibles was achieved by using two variations of the Bridgman-Stockbarger method. One was a static technique wherein liquid silicon in a carbon crucible was positioned in a tamperature gradient of about 35°C/cm, with the highest temperature at the top of the crucible. Solidification was achieved by lowering the system temperature at a rate of 4-5°C/min. The second technique entailed lowering a silicon-loaded carbon crucible through a fixed-rf coil at a rate of 0.55 cm/min. Crack-free silicon was produced by both methods. The equilibrium grain structure was initiated by nucleation at the crucible walls, with surviving grains tending to grow in alignment with the temperature gradient to produce an axially columnar grain structure of mainly 〈110〉 orientation. The average grain diameter was 0.11 cm; a typical length was 0.7 cm. Solar cells made with this material gave an AMI conversion efficiency of 11.5%.

Alumina shell molds used for investment casting in directional solidification of eutectic superalloys

Abstract: An alumina investment casting mold has a microstructure characterized by the porous nature of the interconnecting alumina grains which is indicative of alumina-silica molds fired in a reducing atmosphere to remove the silica.

Minimization of strain in single crystals

Abstract: Single crystals are conveniently produced by directional solidification of a liquid body under a pressurized atmosphere and, preferably, under a liquid encapsulating layer to minimize loss due to volatilization. Such production entails a concern for internal stress in a grown crystal in the interest of minimization of breakage of wafers cut from a crystal. According to the invention, minimization of stress is accomplished by a post-growth annealing step during which pressure is reduced substantially, preferably to a pressure which does not exceed 50% of a pressure at which a constituent of the liquid body volatilizes, while substantially maintaining the temperature of the annealing step. The method may be applied for producing single crystals of semiconductor materials as may be used as device substrates. In particular, the method is beneficial for producing high-quality doped or undoped InP, GaP and GaAs single crystals.

Synthesis and crystal growth of CdGeP2

Abstract: A technique has been developed for growing single crystals of the chalcopyrite nonlinear optical material CdGeP2 that are of sufficient size (centimeter dimensions), electrical resistivity and optical quality to permit measuring the electrooptic coefficients The horizontal gradient-freeze method is used for directional solidification of near- stoichiometric melts synthesized in a two-zone furnace by direct reaction of the elements sealed in fused-silica ampoules The ingots (∼ 120 g) prepared in this manner are polycrystalline and therefore severely cracked due to anisotropic thermal contraction, but these ingots have yielded uncracked single crystals up to 6 cm3 in volume Samples from these crystals have been used for the first measurements of the electrooptic coefficients of CdGeP2, as well as for the measurement of the thermal expansion coefficients and infrared transmission

Rate controlled directional solidification method and article made by this method

Abstract: An improved method of directional solidification is provided by varying the rate of withdrawal of a casting from the hot zone of a solidification furnace according to the sense of change of the perimeter to area ratio of the casting. The rates are varied to achieve desired microstructure and resultant properties in the casting. Also, the rate of withdrawal is varied according to controlled and predetermined relationships to cause the solidification interface to move through a transition section connecting sections of differing perimeter to area ratios in a manner which produces a desired microstructure in a first, transition, and second sections.

Silicon coating of ceramic substrates for low cost solar cell applications

Abstract: Mullite ceramic substrates were coated with silicon using a unique method of growth designed to produce low-cost material suitable for terrestial based solar cell applications. Pieces of mullite were carbon coated on one side and then dipped into molten silicon. The silicon wet the mullite only where the carbon was applied. Directional solidification occurs upon withdrawal. The film thicknesses were reasonably uniform over the area and could be controlled by varying the melt temperature and withdrawal rate, with higher temperatures and faster pull rates giving thinner films. Typical thicknesses of dip coated layers ranged between 20 and 150ym. The layers consist of large elongated grains aligned in the direction of withdrawal. The mullite substrates are slowly dissolved by the molten silicon resulting in some contamination of the silicon layers upon solidification. Glassy carboncoatings were found to be essentially impervious to the molten silicon and prevented dissolution of the substrate even after one hour of immersion. Cells of 1 cm2 active area having JSC

Austenitic stainless steel casting and manufacture thereof

Abstract: PURPOSE:To make it possible to easily perform supersonic flaw detection of a cast material by cooling the material with a suitable temp. gradient to carry out directional solidification so that the structure has regularity to grow the crystals to [100] orientation.

SIMS Identification of Impurity Segregation to Grain Boundaries in Cast Multigrained Silicon

Abstract: The application of secondary ion mass spectroscopy (SIMS) and complementary Auger electron spectroscopy (AES) to the comparative compositional analysis of grain and grain boundary regions in multigrained silicon is presented. The method incorporates in-situ ultrahigh vacuum fracturing of the material with the surface sensitive analytical techniques to delineate differences in elemental composition and chemistry between the inter- and intra-grain region. By this analysis, the first direct physical evidence for the localization of impurities at the grain boundaries in silicon grown by casting [1] and the related directional solidification technique [2] is provided.

Development of Mullite Substrates and Containers

Abstract: The mullite-molten silicon interaction was evaluated through fabrication of a series of bodies made with variations in density, alumina-silica ratio, and glass-crystalline ratio. The materials were tested in a sessile drop technique. None of the variations stood up to extended exposure to molten silicon sufficiently to be recommended as a container material. However, directional solidification experiments suggest that, under proper conditions, contamination of the silicon by mullite containers can be minimized. To improve an already good thermal expansion match between mullite and silicon, compositional variations were studied. Altering of the alumina-silica ratio was determined to give a continuously varying thermal expansion. A standard mullite composition was selected and substrates 40 x 4 x .040 inches were fabricated. Slotted substrates of various configurations and various compositions were also fabricated.

Fabrication of superconducting wire composites by directional solidification

Abstract: Progress is reported for a program to develop a new process for producing composite Nb/sub 3/Sn/Cu superconducting wires and evaluating their critical current densities and the stress dependence of their critical currents. The process involves directional solidification of Cu--Nb or Cu--Nb--Sn alloys. (SDF)