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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Performance of silicon solar cells fabricated from multiple Czochralski ingots grown by using a single crucible

Results on the performance of solar cells fabricated on wafers from multiple silicon ingots of large diameter, grown by using a single crucible and a sequential melt replenishment Czochralski (CZO) technique are presented. Samples were analyzed for resistivity, dislocation density and impurity content. Solar cells were fabricated from the seed, center and tang end of each ingot to evaluate the growth reproducibility and material quality. The cell efficiency within a given wafer varies by no more than plus or minus 5% of the average value. A small but consistent decrease in the cell efficiency is observed from the first to the fourth ingot grown from a single crucible. This decrease may be related to an increase in impurity content or dislocation density or a combination of both. The efficiency of the cells fabricated from the tang end of the fourth ingot is about 10% lower than that of the control cell. An impurity effects model is employed to correlate this decrease in efficiency with the impurity build-up in the residual melt.

Kachare, A. H.↗
NASA NTRS1981

Development of advanced Czochralski Growth Process to produce low cost 150 KG silicon ingots from a single crucible for technology readiness

The goals in this program for advanced czochralski growth process to produce low cost 150 kg silicon ingots from a single crucible for technology readiness are outlined. To provide a modified CG2000 crystal power capable of pulling a minimum of five crystals, each of approximately 30 kg in weight, 150 mm diameter from a single crucible with periodic melt replenishment. Crystals to have: resistivity of 1 to 3 ohm cm, p-type; dislocation density below 1- to the 6th power per cm; orientation (100); after growth yield of greater than 90%. Growth throughput of greater than 2.5 kg per hour of machine operation using a radiation shield. Prototype equipment suitable for use as a production facility. The overall cost goal is $.70 per peak watt by 1986. To accomplish these goals, the modified CG2000 grower and development program includes: (1) increased automation with a microprocessor based control system; (2) sensors development which will increase the capability of the automatic controls system, and provide technology transfer of the developed systems.

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NASA NTRS1982

Continuous Czochralski growth. Development of advanced Czochralski growth process to produce low cost 150 kg silicon ingots from a single crucible for technology readiness

The improvement of growth rates using radiation shielding and investigation of the crucible melt interaction for improved yields were emphasized. Growth runs were performed from both 15 and 16 inch diameter crucibles, producing 30 and 37 kg ingots respectively. Efforts to increase the growth rate of 150 mm diameter ingots were limited by temperature instabilities believed to be caused by undesirable thermal convections in the larger melts. The radiation shield improved the growth rate somewhat, but the thermal instability was still evident, leading to nonround ingots and loss of dislocation-free structure. A 38 kg crystal was grown to demonstrate the feasibility of producing 150 kg with four growth cycles. After the grower construction phase, the Hamco microprocessor control system was interfaced to the growth facility, including the sensor for automatic control of seeding temperature, and the sensor for automatic shouldering. Efforts focused upon optimization of the seeding, necking, and shoulder growth automation programs.

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NASA NTRS1985

Thermal Shock-Resistant Composite Crucible

Heating rates of 350 degrees F per minute have not caused cracking. Surrounding inner crucible is annulus of loosely packed alumina powder, which serves as compressible insulating material. Second annulus consisting of section of fused-quartz tubing surrounds and retains alumina powder. Quartz tube held in place by refractory cement helps to contain alumina powder. Small holes in upper ring of cement allow alumina powder to outgas during operation in vacuum. Originally intended for use in Chill Block Melt Spinning (CBMS) apparatus, crucible adaptable to other operations involving rapid self-induction heating of metallic charges.

Geringer, H. J.↗
NASA NTRS1992

The effect of axial crucible rotation on microstructural uniformity during horizontal directional solidification

The effects on microstructure of crucible orientation with respect to the earth's gravitational vector, g, during directional solidification of low-volume fraction copper and aluminum, Pb-Cu, and Sn-Al alloys are examined. It is demonstrated that horizontal alignment (i.e. perpendicular to g) in combination with axial rotation of the crucible during growth is sufficient to negate factors which initiate macrosegregation, e.g. density gradients attributed to temperature and/or compositional differences, and promotes a uniform microstructure.

Grugel, R. N.↗
NASA NTRS1958

Boron and Zirconium from Crucible Refractories in a Complex Heat-Resistant Alloy

In a laboratory study of the factors involved in the influence of induction vacuum melting on 55ni-20cr-15co-4mo-3ti-3al heat resistant alloy, it was found that the major factor was the type of ceramic used as the crucible. The study concluded that trace amounts of boron or zirconium derived from reaction of the melt with the crucible refactories improved creep-rupture properties at 1,600 degrees F. Boron was most effective and, in addition, markedly improved hot-workability.

Decker, R F↗
NASA NTRS1982

Crucible Grows Wide Silicon Ribbon

Inexpensive manufacture of solar cells may require quality silicon ribbon crystals. One way to produce them is by growing wide dendritic webs, which can be very long and have high structural perfection. Dendrites grow from supercooled melt, so width of ribbon depends on how wide a region of supercooled molten silicon can be maintained in crucible. Elongated geometry of suscepter/crucible/lid assembly allows molten silicon to supercool over a wider region -- a necessary condition for the growth of wide dendritic crystal ribbon.

Seidensticker, R.↗
NASA NTRS1982

The redox potential of boron nitride and implications for its use as a crucible material in experimental petrology

The suitability of boron nitride for use as a crucible material in silicate and oxygen-bearing metal sulfide systems has been investigated. Boron nitride is unsatisfactory for use with many silicate systems because its presence in combination with a source of oxygen establishes the oxygen fugacity at values below that of the assemblage quartz + fayalite + iron, reducing transition metal ions such as Ni(2+) and Fe(2+) to the metallic state. B2O3, resulting from the oxidation of BN, acts as a flux to promote formation of melt.

Wendlandt, R. F.↗
NASA NTRS1983

Gas-Bearing Crucible for Shot Tower

Device protects molten drops from contamination and distortion. Gas flowing through levitator tube levitates small balls while they melt. Gas heated by filament extending through center of tube. Gas bearing crucible on tube has concave configuration to hold single relatively large ball or many recesses to hold many small balls. By time spheres reach foam, they are cooled sufficiently by radiation to retain their shape.

Youngberg, C. L.↗
NASA NTRS1984

Cold-Crucible Premelter for Silicon

System allows replenishment of silicon melt in crystal puller. Cold crucible consists of water-cooled, silver plated boat in 500kHz field. Induced secondary currents cause preheated chunks of silicon to melt. Magnetic repulsion between current in silicon and in boat prevents silicon from touching boat. Used for crystal growth of other materials sufficiently conductive and difficult to keep free of contamination by container walls at temmperature of operation.

Lane, R. L.↗
NASA NTRS1985

Melt Stirring by Horizontal Crucible Vibration

Horizontal vibration suggested as technique for more effective stirring of melts in crystal-growth apparatus. Vibrational technique may replace accelerated crucible rotation. Potential superiority of vibrational technique shown by preliminary experiments in which ink stirred into water.

Wolf, M. F.↗
NASA NTRS1986

Crystal-Growing Crucible To Suppress Convection

Platform under growth region stabilizes melt for more uniform crystal growth. In new crucible, platform just below growth interface so melt is too shallow to support convection. Critical depth for onset of pertinent instability calculated from heat flux through surface of melt, volume coefficient of thermal expansion, thermal conductivity, thermal diffusivity, and kinematic viscosity.

Richter, R.↗
NASA NTRS1998

A Study of Undercooling Behavior Of Immiscible Metal Alloys in the Absence of Crucible-Induced Nucleation

The purpose of this study is to investigate the question: Would eliminating the crucible eliminate the wall-induced nucleation of one of the liquid phases in an immiscible alloy and result in undercooling of the liquid into the metastable region thereby producing significant differences in the separation process and the microstructure upon solidification. Another primary objective of this research is to study systems with a metastable miscibility gap and to directly determine the metastable liquid miscibility gap by undercooling experiments. Nucleation and growth of droplets in these undercooled metallic liquid-liquid mixtures is also being studied. Results of this investigation indicate that containerless processing of immiscibles may not promote the undercooling of the single-phase liquid into the metastable region. Although no recalescence event was observed for this liquid-liquid transition, undercooling did occur across the miscibility gap for the solidification of the Ti phase that eventually separated.

Robinson, Michael B.↗
NASA NTRS1981

Development of Advanced Czochralski Growth Process to produce low cost 150 KG silicon ingots from a single crucible for technology readiness

The modified CG2000 crystal grower construction, installation, and machine check-out was completed. The process development check-out proceeded with several dry runs and one growth run. Several machine calibrations and functional problems were discovered and corrected. Several exhaust gas analysis system alternatives were evaluated and an integrated system approved and ordered. A contract presentation was made at the Project Integration Meeting at JPL, including cost-projections using contract projected throughput and machine parameters. Several growth runs on a development CG200 RC grower show that complete neck, crown, and body automated growth can be achieved with only one operator input. Work continued for melt level, melt temperature, and diameter sensor development.

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NASA NTRS1981

Development of advanced Czochralski growth process to produce low cost 150 kg silicon ingots from a single crucible for technology readiness

The process development continued, with a total of nine crystal growth runs. One of these was a 150 kg run of 5 crystals of approximately 30 kg each. Several machine and process problems were corrected and the 150 kg run was as successful as previous long runs on CG2000 RC's. The accelerated recharge and growth will be attempted when the development program resumes at full capacity in FY '82. The automation controls (Automatic Grower Light Computer System) were integrated to the seed dip temperature, shoulder, and diameter sensors on the CG2000 RC development grower. Test growths included four crystals, which were grown by the computer/sensor system from seed dip through tail off. This system will be integrated on the Mod CG2000 grower during the next quarter. The analytical task included the completion and preliminary testing of the gas chromatograph portion of the Furnace Atmosphere Analysis System. The system can detect CO concentrations and will be expanded to oxygen and water analysis in FY '82.

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