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At least 19 records

Evaluation of a metering, mixing, and dispensing system for mixing polysulfide adhesive

Tests were performed to evaluate whether a metered mixing system can mix PR-1221 polysulfide adhesive as well as or better than batch-mixed adhesive; also, to evaluate the quality of meter-mixed PR-1860 and PS-875 polysulfide adhesives. These adhesives are candidate replacements for PR-1221 which will not be manufactured in the future. The following material properties were evaluated: peel strength, specific gravity and adhesive components of mixed adhesives, Shore A hardness, tensile adhesion strength, and flow rate. Finally, a visual test called the butterfly test was performed to observe for bubbles and unmixed adhesive. The results of these tests are reported and discussed.

Evans, Kurt B.↗

Crystal growth of sulfide materials from alkali polysulfide liquids

The fluids experiment system was designed for low temperature solution growth, nominally aqueous solution growth. The alkali polysulfides, compositions in the systems Na2S-S and K2S-S form liquids in the temperature range of 190 C to 400 C. These can be used as solvents for other important classes of materials such as transition metal and other sulfides which are not soluble in aqueous media. Among these materials are luminescent and electroluminescent crystals whose physical properties are sensitive functions of crystal perfection and which could, therefore, serve as test materials for perfection improvement under microgravity conditions.

White, W. B.↗

Flight 20 (STS-45) polysulfide gas path investigation

This report documents the results of the investigation into causes of gas paths on the 20A and 20B case-to-nozzle joints on STS-42. The investigation was conducted by the Investigation Board appointed by the senior vice president and general manager of Space Operations, Mr. R. E. Lindstrom, on 7 Feb. 1992. The probability of gas path occurrence in the nozzle-to-case-joint polysulfide had been identified during joint redesign. However, actual flight gas path incidence has been limited to RSRM-11 and the 20A and 20B segments. The blow-by condition on the 20A segment was a first time occurrence which was a special concern. The investigation covered all technical aspects associated with the gas path and blow-by conditions: materials and processing history, design requirements and as-built compliance to the design, thermal and structural analyses, computer modeling, and laboratory experimentation with the materials involved. The investigation was coordinated with Mr. Ken Jones at NASA Marshall in bi-weekly teleconferences. The Board also supported Dr. James C. Blair's independent NASA investigation team by providing copies of collected data, conducting requested analyses, and supporting several all-day teleconferences to provide understanding and resolve issues. The Dr. Blair support requirement was successfully concluded on 4 Mar. 1992.

Bjorkman, Rey C.↗

Coating processes for increasing the moisture resistance of polyurethane baffle material

An investigation was conducted with the objective to improve the hydrolytic stability of reticulated polyurethane baffle material. This material is used in fuel tanks of aircraft and ground vehicles. The most commonly used foam of this type is hydrolytically unstable. Potential moisture barrier coatings which were evaluated include Parylene, epoxy-polysulfide, polyether based polyurethanes, polysulfides, polyolefin rubbers, and several other materials. Parylene coatings of at least 0.2 mil were found to provide the greatest improvement in hydrolytic stability.

Bilow, N.↗

Solid-state battery designed for electric aviation

The demand for higher energy density batteries increases as the demand for portable electronic devices and electric automotive increases, as well as a variety of other applications requiring substantially higher power and energy than attainable with current lithium-ion capabilities which includes the areas of high performance vehicles, military applications, and electric aviation. However, the improvement of energy density is insufficient alone for enabling electric aviation when considering the high flammability and risk of thermal runaway inherent in current state-of-the-art liquid electrolytes. The development of high energy, high power, and safe batteries are required to enable hybrid and fully electric aircraft. Next generation chemistries such as lithium-sulfur provide high theoretical specific energy density suitable for electric aviation without as strict of volumetric requirements observed in the automotive industry. However, due to the phase transition during discharge where sulfur generates a series of soluble intermediate polysulfides, which are lost to the liquid electrolyte, cause detrimental side effects, and severely limit cycle life battery performance is severely reduced. Additionally, the low electrical conductivity of sulfur requires a large amount of inactive carbon dramatically increasing parasitic mass. The dissolution issue make sulfur a desirable candidate to pair with a solid-state electrolyte in order to avoid polysulfide dissolution and shuttling. In addition, inorganic solid-electrolytes have low flammability providing the improved safety required. Combining this chemistry with a solid-state electrolyte provides a path for achieving the energy and safety required for electric aviation. The development of scalable thin solid-state electrolytes paired with lithium-sulfur chemistry will be discussed and how their development will aid in enabling a unique application.

Donald A. Dornbusch↗

Producibility of potting compounds

Effect of environmental temperatures and relative humidities on curing times of polyurethane and polysulfide potting compounds

HUMIDITY MEASUREMENT↗

An intumescent coating for improved fuel fire protection of heat sensitive articles.

Intumescent coating compositions have been prepared using the ammonium salt of 4-nitroaniline-2-sulfonic acid and a copolymer of polysulfide-epoxy resin as the binder, into which have been dispersed various fillers. The fillers used in the study were low density microballoons for density control and fibers for controlled intumescence on contoured substrates. The filler effect on the thermal-physical efficiency of coatings has been measured. The coating utilizing short length silica fibers has been shown to have superior mechanical, environmental, and thermal properties. The coating applied to the exterior of loaded weapons has increased the time-to-detonation from three minutes for the unprotected weapon to 10-13 minutes.

Sawko, P. M.↗

Adhesive bonding and the use of corrosion resistant primers

The use of an anti-corrosive primer has been shown to be essential to assure survival of a bonded structure in a hostile environment, particularly if a stress is to be applied to the adhesively bonded joint during the environmental exposure. For example, the Lockheed L-1011 TriStar assembly, after exhaustive evaluation tests specifies use of chromate filled inhibitive polysulfide sealants, and use of corrosion inhibiting adhesive primers prior to structural bonding with film adhesive.

Hockridge, R. R.↗

Infrared spectroscopy of Comet Kohoutek

Interferometry observations from 90-in. and 61-in. telescopes tracking the Comet Kohoutek are summarized. Laboratory reflection studies of ices potentially useful for future cometary work were conducted. The frosts studied included: H2O, CO2 NH3, H2S, CH4, NH4HS, and ammonia polysulfide. The frost spectra show remarkable changes with the temperatures, particularly in the case of hydrogen sulfide. Additional analysis found the variation in the H2S ice spectrum to be due to a phase change from a low temperature tetragonal unit cube to a higher temperature face-centered cubic structure. The spectra data indicate that if frost spectra are required for comparison with observed cometary or planetary absorption, the temperature of the frost must be matched.

Fink, U.↗

Photoelectrochemical cells - Conversion of intense optical energy

Conversion of optical energy to chemical energy and/or electrical energy using wet photoelectrochemical cells is described. Emphasis is on (1) the photoelectrolysis of H2O to H2 and O2 using cells having n-type semiconductor photoelectrodes fabricated from TiO2, SnO2, SrTiO3, KTaO3, and KTa(0.77)Nb(0.23)O3, and (2) the conversion of light to electrical energy using CdSe- and CdS-based cells with polysulfide electrolytes.

Wrighton, M. S.↗

Fire protection covering for small diameter missiles

Flexible intumescent protection sheeting of unusually uniform thickness were prepared from epoxy-polysulfide compositions, containing microfibers and the ammonium salt of 1,4-nitroaniline-2-sulfonic acid, as disclosed in U.S. Pat. No. 3,663,464, except that an ammonium salt particle size in the order of 5 to 8 microns and a fiber size of about 1/128th inch in length and 3 to 5 microns in diameter were found critical to obtain the required density of 1.46 to 1.50 g/cc. The insulation sheeting was prepared by a continuous process involving vacuum mixing, calendering, and curing under very strict conditions which depend to some extent upon the thickness of the sheet produced.

Riccitiello, S. R.↗

Compatibility of elastomers in alternate jet fuels

The compatibility of elastomeric compositions of known resistance to aircraft fuels was tested for potential use in Jet A type fuels obtainable from alternate sources, such as coal. Since such fuels were not available at the time, synthetic alternate fuels were prepared by adding tetralin to a petroleum based Jet A type fuel to simulate coal derived fuels which are expected to contain higher amounts of aromatic and hydroaromatic hydrocarbons. The elastomeric compounds tested were based on butadiene-acrylonitrile rubber, a castable Thiokol polysulfide rubber, and a castable fluorosilicone rubber. Batches of various cross-link densities of these rubbers were made and their chemical stress relaxation behavior in fuel, air, and nitrogen, their swelling properties, and response to mechanical testing were determined.

Kalfayan, S. H.↗

Improved and lower cost sealing of aerospace structure

An improved sealing method has been developed for the exposed metal fastener surfaces of the Solid Rocket Booster vehicle for the Space Shuttle launch system. The method employs properly sized flexible plastic caps filled with catalyzed polysulfide sealant, frozen and stored. At the time of use, the caps and sealant are thawed and positioned on the fasteners. The sealant covers the exposed portion of the fastener and prevents salt water damage. The method is one of high reliability with low installation and inspection costs.

Angeloni, D. J.↗

Development and evaluation of an ablative closeout material for solid rocket booster thermal protection system

A trowellable closeout/repair material designated as MTA-2 was developed and evaluated for use on the Solid Rocket Booster. This material is composed of an epoxy-polysulfide binder and is highly filled with phenolic microballoons for density control and ablative performance. Mechanical property testing and thermal testing were performed in a wind tunnel to simulate the combined Solid Rocket Booster trajectory aeroshear and heating environments. The material is characterized by excellent thermal performance and was used extensively on the Space Shuttle STS-1 and STS-2 flight hardware.

Patterson, W. J.↗

Microstructure of the combustion zone: Thin-binder AP-polymer sandwiches

Experimental results are summarized for systematic quench-burning tests on ammonium perchlorate-HC binder sandwiches with binder thicknesses in the range 10 - 150 microns. Tests included three binders (polysulfide, polybutadiene-acrylonitrile, and hydroxy terminated polybutadiene), and pressures from 1.4 to 14 MPa. In addition, deflagration limits were determined in terms of binder thickness and pressure. Results are discussed in terms of a qualitative theory of sandwich burning consolidated from various sources. Some aspects of the observed results are explained only speculatively.

Price, E. W.↗

Phototrophic bacteria and their role in the biogeochemical sulfur cycle

An essential step that cannot be bypassed in the biogeochemical cycle of sulfur today is dissimilatory sulfate reduction by anaerobic bacteria. The enormous amounts of sulfides produced by these are oxidized again either anaerobically by phototrophic bacteria or aerobically by thiobacilli and large chemotrophic bacteria (Beggiatoa, Thiovulum, etc.). Phototrophic bacteria use sulfide, sulfur, thiosulfate, and sulfite as electron donors for photosynthesis. The most obvious intermediate in their oxidative sulfur metabolism is a long chain polysulfide that appears as so called sulfur globules either inside (Chromatiaceae) or outside (Ectothiorhodospiraceae, Chlorobiaceae, and some of the Rhodospirillaceae) the cells. The assimilation of sulfur compounds in phototrophic bacteria is in principle identical with that of nonphototrophic bacteria. However, the Chlorobiaceae and some of the Chromatiaceae and Rhodospirillaceae, unable to reduce sulfate, rely upon reduced sulfur for biosynthetic purposes.

Trueper, H. G.↗