Attempts to gain a better understanding of the reactive species in the sodium-sulfur battery system developed at Ford Motor Co. have led us to reexamine the sodium-sulfur phase diagram published by Pearson and Robinson in 1930. A modified phase diagram was constructed based on dta studies. In addition, dta revealed that when a mixture of Ña2S and NajSj or Ña2S4 and S8 is heated, a reaction takes place around the melting point of sulfur, with the formation of the pentasulfide, Na2Ss, as the initial step. Unless the sulfur:sodium ratio in the mixture is 5:2 or higher, further interaction between the sulfides can be observed by dta, until at equilibrium only those species are observed corresponding to the given stoichiometric Na:S ratio. The highest sulfide is Na2Ss, whereas the trisulfide, Na2S3, does not exist at the melting point, and the mixture with the same stoichiometry was found to be a 1:1 Na2S2-Na2S4 eutectic.
The polysulfides of potassium-K2S2, K2S3, K2S4, K2S5, and K2S6-are all known and well-characterized compounds. In the case of the analogous sodium compounds, only the disulfide, tetrasulfide, and pentasulfide are reported in the literature, whereas reports pertaining to the existence and isolation of the trisulfide, Na2S3, have been disputed. Past efforts to synthesize Na2S3 have always yielded the 1:1 eutectic Na2S2-Na2S4. A novel method to synthesize the sodium polysulfides in liquid ammonia, based on the reaction scheme 2NaCl + K2SX -+ 2KC4 + Na2Sx {x = 3, 5, 6), is described, yielding Na2S3 and Na3S5, but not Na2S6. The results of ESCA (electron spectroscopy for chemical analysis) applied to the polysulfides are discussed. The density and surface tension of molten Na2S4 and Na2S5 were determined at various temperatures.
Measurements of the residual stress in polysilicon films made by Low Pressure Chemical Vapor Deposition (LPCVD) at different deposition pressures and temperatures are reported.The stress behavior of phosphorus (P)-ion implanted/annealed polysilicon films is also reported.Within the temperature range of deposition, 580 'C to 650 0 C, the stress vs deposition temperature plot exhibits a transition region in which the stress of the film changes from highly compressive to highly tensile and back to highly compressive as the deposition temperature increases.This behavior was observed in films that were made by the LPCVD process at reduced pressures of 210 and 320 mTORR.At deposition temperatures below 590 °C the deposit is predominantly amorphous, and the film is highly compressive; at temperatures above 610 UC (110) oriented polycrystalline silicon is formed exhibiting high compressive residual stress.
This report documents a portion of the results of the project entitled "Direct-Hydrogen-Fueled Proton-Exchange-Membrane Fuel Cell System for Transportation Applications" performed by Ford Motor Company, under contract DE-AC02-94CE50389. The project objective was to design, fabricate, and test a 50-kW direct hydrogen fueled proton exchange membrane (PEM) fuel cell system including onboard hydrogen storage, efficient lightweight fuel cell, gas management system, and complete system controls that can be economically mass produced and comply with all safety, environmental, and consumer requirements for vehicle applications for the 21 st century. Specifically, this report presents conceptual designs for a batteryaugmented fuel cell-powered vehicle based on three different vehicle classes, namely, small car, mid-size car, and full-size van.Dr. Djong-Gie Oei, project manager at Ford, prepared the report with contributions from Ford staff, namely, James Adams, Alan Kinnelly, Georgianna Purnell, Ron Sims, Mark Sulek, and David Wernette. Brian James, Franklin Lomax, George Baum, C. E. (Sandy) Thomas, and Ira Kuhn, all from Directed Technologies, Inc., also contributed to the report. AbstractIn partial fulfillment of the U.S. Department of Energy Contract No. DE-AC02-94CE50389, "Direct Hydrogen-Fueled Proton-Exchange-Membrane (PEM) Fuel Cell System for Transportation Applications", this conceptual vehicle design report addresses the design and packaging of battery augmented fuel cell powertrain vehicles. This report supplements the "Conceptual Vehicle Design Report -Pure Fuel Cell Powertrain Vehicle" and includes a cost study of the fuel cell power system. The three classes of vehicles considered in this design and packaging exercise are the same vehicle classes that were studied in the previous report: the Aspire, representing the small vehicle class; the A N (Aluminum Intensive Vehicle) Sable, representing the mid-size vehicle; and the E-150 Econoline, representing the van-size class. A preliminary PEM fuel cell power system manufacturing cost study is also presented.As in the case of the previous report concerning the "Pure Fuel Cell Powertrain Vehicle", the same assumptions are made for the fuel cell power system. These assumptions are fuel cell system power densities of 0.33 kWkg and 0.33 kW/l, platinum catalyst loading of less than or equal to 0.25 mg/crn2 total, and hydrogen tanks containing compressed gaseous hydrogen under 340 atm (5000 psia) pressure. The batteries considered for power augmentation of the fuel cell vehicle are based on the Ford Hybrid Electric Vehicle (HEV) program. These are state-of-the-art high power lead acid batteries with power densities ranging from 0.8 kW/kg to 2 kW/kg.The results reported here show that battery augmentation provides the fuel cell vehicle with a power source to meet instant high power demand for acceleration and start-up. Trade-offs between battery weight, volume and cost and fuel cell weight, volume and cost are carefully considered and discussed. Based on the assumpt...
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