Evaluation of Selected Chemical Processes for Production of Low-cost Silicon, Phase 3

The construction of the 50 MT Si/year experimental process system development unit was deferred until FY 1980, and the fluidized bed, zinc vaporizer, by-product condenser, and electrolytic cell were combined with auxiliary units, capable of supporting 8-hour batchwise operation, to form the process development unit (PDU), which is scheduled to be in operation by October 1, 1979. The design of the PDU and objectives of its operation are discussed. Experimental program support activities described relate to: (1) a wetted-wall condensor; (2) fluidized-bed modeling; (3) zinc chloride electrolysis; and (4) zinc vaporizer

Evaluation of selected chemical processes for production of low-cost silicon, phase 3

A Process Development Unit (PDU), which consisted of the four major units of the process, was designed, installed, and experimentally operated. The PDU was sized to 50MT/Yr. The deposition took place in a fluidized bed reactor. As a consequences of the experiments, improvements in the design an operation of these units were undertaken and their experimental limitations were partially established. A parallel program of experimental work demonstrated that Zinc can be vaporized for introduction into the fluidized bed reactor, by direct induction-coupled r.f. energy. Residual zinc in the product can be removed by heat treatment below the melting point of silicon. Current efficiencies of 94 percent and above, and power efficiencies around 40 percent are achievable in the laboratory-scale electrolysis of ZnCl2

Evaluation of selected chemical processes for production of low-cost silicon

Plant construction costs and manufacturing costs were estimated for the production of solar-grade silicon by the reduction of silicon tetrachloride in a fluidized bed of seed particles, and several modifications of the iodide process using either thermal decomposition on heated filaments (rods) or hydrogen reduction in a fluidized bed of seed particles. Energy consumption data for the zinc reduction process and each of the iodide process options are given and all appear to be acceptable from the standpoint of energy pay back. Information is presented on the experimental zinc reduction of SiCl4 and electrolytic recovery of zinc from ZnCl2. All of the experimental work performed thus far has supported the initial assumption as to technical feasibility of producing semiconductor silicon by the zinc reduction or iodide processes proposed. The results of a more thorough thermodynamic evaluation of the iodination of silicon oxide/carbon mixtures are presented which explain apparent inconsistencies in an earlier cursory examination of the system

Evaluation of selected chemical processes for production of low-cost silicon, phase 2

Potential designs for an integrated fluidized-bed reactor/zinc vaporizer/SiCl4 preheater unit are being considered and heat-transfer calculations have been initiated on versions of the zinc vaporizer section. Estimates of the cost of the silicon prepared in the experimental facility have been made for projected capacities of 25, 50, 75, and 100 metric ton of silicon. A 35 percent saving is obtained in going from 25 metric ton/year to the 50 metric ton/year level. This analysis, coupled with the recognition that use of two reactors in the 50 metric ton/year version allows for continued operation (at reduced capacity) with one reactor shut down, has resulted in a recommendation for adoption of an experimental facility capacity of 50 metric ton/year or greater. At this stage, the change to a larger size facility would not increase the design costs appreciably. In the experimental support program, the effects of seed bed particle size and depth were studied, and operation of the miniplant with a new zinc vaporizer was initiated, revealing the need for modification of the latter

LSA silicon material task closed-cycle process development

The initial effort on feasibility of the closed cycle process was begun with the design of the two major items of untested equipment, the silicon tetrachloride by product converter and the rotary drum reactor for deposition of silicon from trichlorosilane. The design criteria of the initial laboratory equipment included consideration of the reaction chemistry, thermodynamics, and other technical factors. Design and construction of the laboratory equipment was completed. Preliminary silicon tetrachloride conversion experiments confirmed the expected high yield of trichlorosilane, up to 98 percent of theoretical conversion. A preliminary solar-grade polysilicon cost estimate, including capital costs considered extremely conservative, of $6.91/kg supports the potential of this approach to achieve the cost goal. The closed cycle process appears to have a very likely potential to achieve LSA goals

Development of a chromium-thoria alloy

Low temperature ductility and high temperature strength of pure chromium and chromium-thoria alloy prepared from vapor deposited powder

Evaluation of selected chemical processes for production of low-cost silicon phase 2. silicon material task, low-cost silicon solar array project

Progress from October 1, 1977, through December 31, 1977, is reported in the design of the 50 MT/year experimental facility for the preparation of high purity silicon by the zinc vapor reduction of silicon tetrachloride in a fluidized bed of seed particles to form a free flowing granular product

ALUMINA COATING OF UOsup2sup 2 SHOT BY HYDROLYSIS OF ALUMINUM CHLORIDE VAPOR

Uniform, dense coatings of alumina about 5 to 150 mu thick were applied to uranium dioxide particles 44 to 350 mu in diameter by hydrolysis of aluminum chloride vapor in a fluidized bed of the particles at 1830 deg F. The coated particles were resistant to nitric acid leaching, to oxidation in 1830 deg F air, and to thermal cycling from 6OO to 2500 deg F. After low neutron exposures, the coated particles showed excellent fission-gas retention at temperatures up to 2400 deg F in inert gas. Although not optimized in the study, the coating process appears to have commercial feasibility. (auth

Evaluation of Selected Chemical Processes for Production of Low-cost Silicon, Phase 3

The construction and operation of an experimental process system development unit (EPSDU) for the production of granular semiconductor grade silicon by the zinc vapor reduction of silicon tetrachloride in a fluidized bed of seed particles is presented. The construction of the process development unit (PDU) is reported. The PDU consists of four critical units of the EPSDU: the fluidized bed reactor, the reactor by product condenser, the zinc vaporizer, and the electrolytic cell. An experimental wetted wall condenser and its operation are described. Procedures are established for safe handling of SiCl4 leaks and spills from the EPSDU and PDU

FLUIDIZED-BED COATING OF UOsub2sub 2 POWDER WITH NIOBIUM AND OTHER ELEMENTS

The chemical vapor deposition of niobium, molybdenum, tungsten, chnomium, carbcn, and niobium--vanadium alloys in a fluidized bed of UO/sub 2/ powder particles wss used to provide uniform, dense, nonporous coatings on the individual particles. in the case of niobium, which received major attention, hydrogen reduction of niobium pentachloride vapor was used as the vapor- deposition reaction. The most serious problem was that of maintaining bed fluidity aad avoiding agglomeration. This problem was overcome to permit routine operation of the coating equipment. In the entire program of 68 experimental runs, only 1.1 per cent of the product was lost by agglomeration. In routine operation, this loss should be even lower. (auth