Materials

Spray CVD for Making Solar-Cell Absorber Layers

Spray CVD combines the advantages of metalorganic CVD and spray pyrolysis. Spray chemical vapor deposition (spray CVD) processes of a special type have been investigated for use in making CuInS2 absorber layers of thin-film solar photovoltaic cells from either of two subclasses of precursor compounds: [(PBu3) 2Cu(SEt)2In(SEt)2] or [(PPh3)2Cu(SEt)2 In(SEt)2] . CuInS2 is a member of the class of chalcopyrite semiconductors described in the immediately preceding article. [(PBu3)2Cu(SEt)2In(SEt)2] and [(PPh3)2 Cu(SEt)2In(SEt)2] are members of the class of single-source precursors also described in the preceding article.

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Improved Single-Source Precursors for Solar-Cell Absorbers

Deposition properties and final compositions can be tailored. Improved single-source precursor compounds have been invented for use in spray chemical vapor deposition (spray CVD) of chalcopyrite semiconductor absorber layers of thin-film solar photovoltaic cells. The semiconductors in question are denoted by the general formula CuInxGa1–xSySe2–y, where x≤1 and y≤2. These semiconductors have been investigated intensively for use in solar cells because they exhibit longterm stability and a high degree of tolerance of radiation, and their bandgaps correlate well with the maximum photon power density in the solar spectrum. In addition, through selection of the proportions of Ga versus In and S versus Se, the bandgap of CuInxGa1–xSySe2–y can be tailored to a value between 1.0 and 2.4 eV, thus making it possible to fabricate cells containing high and/or graded bandgaps.

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Glass/BNNT Composite for Sealing Solid Oxide Fuel Cells

Boron nitride nanotubes contribute to strength and fracture toughness. A material consisting of a barium calcium aluminosilicate glass reinforced with 4 weight percent of boron nitride nanotubes (BNNTs) has shown promise for use as a sealant in planar solid oxide fuel cells (SOFCs). The composition of the glass in question in mole percentages is 35BaO + 15CaO + 5Al2O3 + 10B2O3 + 35SiO2. The glass was formulated to have physical and chemical properties suitable for use as a planar- SOFC sealant, but has been found to be deficient in one aspect: it is susceptible to cracking during thermal cycling of the fuel cells. The goal in formulating the glass/BNNT composite material was to (1) retain the physical and chemical advantages that led to the prior selection of the barium calcium aluminosilicate glass as the sealant while (2) increasing strength and fracture toughness so as to reduce the tendency toward cracking.

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Separating Ethanol From Water Via Differential Miscibility

Alcohol for combustion could be purified more economically. The differential miscibility of castor oil in ethanol and water would be exploited to separate ethanol from water, according to a proposal. Burning the separated ethanol would produce more energy than would be consumed in the separation process. In contrast, the separation of a small amount of ethanol (actually an ethanol/water solution poor in ethanol) from water by the conventional process of distillation requires more energy than can be produced by burning the resulting distillate. As in the process described in the preceding article, "Separating Ethanol From Water Via Differential Solubility" (LAR-14894), the proposed alcohol/water separation process could be exploited industrially to produce clean fuel from fermented vegetable matter.

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Multilayer Impregnated Fibrous Thermal Insulation Tiles

Temperature rises are limited by transpiration cooling. The term “secondary polymer layered impregnated tile” (“SPLIT”) denotes a type of ablative composite-material thermal- insulation tiles having engineered, spatially non-uniform compositions. The term “secondary” refers to the fact that each tile contains at least two polymer layers wherein endothermic reactions absorb considerable amounts of heat, thereby helping to prevent overheating of an underlying structure. These tiles were invented to afford lighter-weight alternatives to the reusable thermal-insulation materials heretofore variously used or considered for use in protecting the space shuttles and other spacecraft from intense atmospheric- entry heating. Tiles of this type could also be useful on Earth as relatively lightweight components of fire-retardant structures.

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Multifunctional, High-Temperature Nanocomposites

Electrical and thermal conductivities increase with proportions of nanotubes. In experiments conducted as part of a continuing effort to incorporate multifunctionality into advanced composite materials, blends of multi-walled carbon nanotubes and a resin denoted “PETI-330” (wherein “PETI” is an abbreviation for “phenylethynyl- terminated imide”) were prepared, characterized, and fabricated into moldings. PETI-330 was selected as the matrix resin in these experiments because of its low melt viscosity (<10 poise at a temperature of 280 °C), excellent melt stability (lifetime >2 hours at 280 °C), and high temperature performance (>1,000 hours at 288 °C). The multi-walled carbon nanotubes (MWCNTs), obtained from the University of Kentucky, were selected because of their electrical and thermal conductivity and their small diameters. The purpose of these experiments was to determine the combination of thermal, electrical, and mechanical properties achievable while still maintaining melt processability.

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Increasing Durability of Flame-Sprayed Strain Gauges

Low-oxygen heat treatments and internal platinum oxygen-diffusion barriers extend lifetimes. Thermally sprayed dielectric ceramic coatings are the primary means of attaching strain and temperature gauges to hot-section rotating parts of turbine engines. As hot-section temperatures increase, lifetimes of installed gauges decrease, and seldom exceed one hour above 2,000 °F ( ≈1,100 °C). Advanced engine components are expected to operate at temperatures approaching 2,200 °F ( ≈1,200 °C), and the required high-temperature lifetime is 10 hours minimum.

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