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Permeation of high density gases and propellant vapors through laminated Teflon expulsion bladders
Dispersion /peak broadening/ in gel chromatography measured with nonporous and porous column packings, suggesting diffusion controlled separation with linear permeation isotherm
Elimination of permeation and bubble formation in Apollo RCS positive expulsion tankage
The permeation of benzene and acetone vapors through sulfur-cured natural rubber was studied by the time-lag method. The zero concentration diffusion coefficient, was obtained by the early-time method. The Frisch time lag equation was utilized to estimate both the solubility coefficient and the additional parameter required to define the concentration-dependence of the diffusion coefficient. This form of concentration dependence was manifested by the corresponding permeability coefficient values. At low entering penetrant pressure where the transport coefficients are constant, indirect evidence was obtained that zero diffusion coefficient is the mechanically correct diffusion coefficient. The solubility coefficient values calculated for benzene vapor in natural rubber are in reasonable agreement with published equilibrium sorption data for a similar rubber compound. At higher entering penetrant pressures, average diffusion coefficients obtained at steady state tended to be larger than the corresponding average diffusion coefficients derived from the time-lags.
The susceptibility of adhesive-sealed ceramic packages to moisture permeation was investigated. The two adhesives, Ablebond 789-1 and Epo-Tek H77, were evaluated as package sealants. These adhesives were previously selected as the most promising candidates for this application from a group of ten adhesives. Ceramic packages sealed with these adhesives were exposed to temperature-humidity conditions of 25 C/98 percent RH, 50 C/60 percent RH, 50 C/98 percent RH, and 85 C/85 percent RH and their moisture contents using were monitored solid state moisture sensors sealed inside them. Five packages were tested at each of these exposures - two ceramic packages sealed with each of the two adhesives and one seam-sealed gold-plated Kovar package. This latter package was included to serve as a control. The results showed that the adhesive-sealed packages were not hermetic to moisture. The rates at which moisture entered the packages increased with the severity of the exposure environments (i.e., higher temperatures and higher moisture vapor pressures) with greater dependence on temperature than on moisture vapor pressure.
Gel-permeation chromatography was used to analyze C-ether lubricant formulations from high-temperature bearing tests and from micro-oxidation tests. Three mu-styragel columns (one 500 and two 100 A) and a tetrahydrofuran mobile phase were found to adequately separate the C-ether degradation products. The micro-oxidation tests yielded degradation results qualitatively similar to those observed from the bearing tests. Micro-oxidation tests conducted in air yielded more degradation than did tests in nitrogen. No great differences were observed between the thermal-oxidative stabilities of the two C-ether formulations or between the catalytic degradation activities of silver and M-50 steel. C-ether formulation I did yield more degradation than did formulation II in 111- and 25-hour bearing tests, respectively.
Permeation of liquid through polymer sheets retarded by including in polymer solute for excluded liquid. Long-term or steady state permeability not reduced by solute inclusions.
The permeation of high purity, large grain Ag membranes by oxygen has been studied over the temperature range 400 to 800 C. The permeability was found to be quite linear and repeatable, but the magnitude was 3.2 times smaller than that determined by past research. Since previous investigators studied substantially less pure Ag and conducted experiments within much poorer vacuum environments (which indicates that their grain boundary density was much greater), the data presented here suggest oxygen transport through the membrane is primarily by grain boundary diffusion. The diffusivity measurements were found to exhibit two distinct linear regions, one above and one below a critical temperature of 630 C. The high-temperature data have an activation energy (11.1 kcal/mole) similar to that reported by others, but the low-temperature data have a higher activation energy (15.3 kcal/mole), which can be explained by impurity trapping in the grain boundaries. Vacuum desorption of the oxygen-saturated Ag was found to occur at a threshold of 630 C, which is consistent with the onset of increased mobility within the grain boundaries.
Water vapor in working fluid equilibrates with permeability-reducing oxides in metal parts. Report describes study of effects of water on permeation of heater-head tubes by hydrogen in Stirling engine. Experiments performed to determine minimum concentration of oxygen and/or oxygen-bearing gas maintaining oxide coverage adequate for low permeability. Tests showed 750 ppm or more of water effective in maintaining stable, low permeability.
The design criteria for heterogeneous chemical reactions in liquid/liquid systems formally correspond to those of classical physical extraction. More complex models are presented which describe the material exchange at the individual droplets in an extraction with chemical reaction and in liquid membrane permeation.
During the development of an atomic oxygen beam generator for laboratory simulation of the atmospheric conditions in low earth orbit, a new technique for performing electron stimulated desorption (ESD) in a continuous manner has been developed. In this technique, oxygen permeates through an Ag membrane at elevated temperature thereby providing a continuous supply of oxygen atoms to the 1000-A ZrO2 coating at the vacuum interface. ESD then results in a large peak of neutral O2 molecules which ultimately decay into steady-state desorption. The ESD signal is linear with respect to primary beam flux (0.035 O2 molecules per electron at a primary beam energy of 1 keV) but nonlinear with respect to primary beam energy.
Technique for generating supply of highly pure O2 from CO2 developed. First, atomic oxygen at useful partial pressure generated by glow-discharge dissociation of CO2. Atomic oxygen formed in vicinity of hot silver membrane and permeates through membrane to downstream region, where thermally recombined into O2 and pumped away to storage tank. Pure oxygen stored suitable for human consumption and other uses. Originally developed to convert Martian atmosphere of CO2 to O2 for astronaut consumption. Other potential applications include purification of atmospheres in Space Shuttle and Space Station Freedom. Byproduct CO must be handled by other techniques.
Hydrogen permeation measurements have been conducted for the Incoloy 909 Ni-Fe-Co superalloy via the 'membrane' technique, in which the gaseous hydrogen at the entrance of a thin membrane is transposed through the bulk to the exit side of the membrane, at 400-810 C; the pressure range explored was 2.7 x 10 exp 3 to 1.3 x 10 exp 5 N/sq m. The lattice hydrogen solubility of Incoloy 909 is found to be only weakly temperature-dependent. These results are compared with those obtained for Incoloy 903.
Oxygen can be extracted from carbon dioxide via thermal dissociation at elevated temperatures. However, temperatures in excess of 1000 K are needed to effect significant levels of dissociation. The experiments reported here have examined the feasibility of using a glow-discharge in low-pressure carbon dioxide to produce increased atomic oxygen yields at lower temperatures (on the order of 800 K). The experiments have shown that when silver membranes are used simultaneously as anodes for the glow discharge and as permeable membranes for oxygen separation, oxygen yields which are comparable to the permeation rates for pure oxygen, can be produced. Since the silver membrane can be employed as the electrode interface between Mars atmosphere and a stabilized-zirconia electrochemical pump, glow-discharge enhancement can be considered as a complementary technology which can be used with the zirconia-based oxygen extraction systems described previously by others. Not only can glow-discharge be used to increase oxygen yields at lowered temperatures, but it can also be considered as a possible way to avoid filtration and compression of Mars atmosphere, since the glow-discharge can be sustained in Mars ambient pressures.
Extraction of oxygen from Martian atmosphere and compression of lunar oxygen can utilize stabilized zirconia electrochemical pumps. Silver membranes can be used as electrodes to increase oxygen yield at relatively low temperatures. This study has investigated oxygen permeation through Ag 0.05Zr membranes with glow-discharge assisted disassociation. Data show that the overall process is controlled by bulk diffusion but the slow dissociative adsorption onto the surface limited the overall transport substantially. With glow-discharge assisted dissociation, an order of magnitude increase in oxygen throughput can be produced at relatively low temperatures (450-550C).
The permeation of a mixture of CH4 and CO2 (97% CH4 and 3% CO2) saturated with water vapour through Tefzel has been studied at 950 C and 25 and 50 bars. Tefzel is the Du Pont trademark of an ETFE (ethylenetetrafluorethylene) which is a copolymer of ethylene and tetrafluorethylene. This material might be used as inner plastic lining of flexible pipes. For methane and carbon dioxide, the permeability of Tefzel is higher than the deplasticized PVDF (Polyvinylidenefluoride), but lower than the plasticized PVDF. For water, the situation seems to be the other way round; Tefzel has a lower permeability than deplasticized PVDF. Whether the permeability tests on Tefzel at higher temperatures and pressures will be pursued or not, will be considered by the steering committee of the CAPP project in May.
A Method is described for determining the molecular weight distribution of fluorinated polymers by gel permeation chromatography. Porous silica-packed columns are used with Freon 113 as the chromatographic solvent. Fluoroether oligomers are used for column calibration in the molecular weight range of 1400 to 12000.
This report contains the results of a fifteen month analytical and experimental study of the leakage rate of the pressurant gases (N2, He) and the propellant vapors (N2O4,N2H4) through bladder structures consisting of two layers of Teflon separated by a metallic foil diffusion barrier containing microscopic or larger holes. Results were obtained for the steady state leakage rate through circular holes and long rectangular openings in the barrier for arbitrary thicknesses of the two Teflon layers. The effect of hole shape and relative hole position on the leakage rate were studied. The transient problem was analyzed and it was shown that steady state calculations are adequate for estimating the leakage rate. A computer program entitled "Diffusion Analyzer Program" was developed to calculate the leakage rate, both transient and steady state. Finally, the analytical results were compared to experimentally determined values of the leakage rate through a model laminated bladder structure. The results of the analysis are in good agreement with experiment. The experimental effort (Part II of the Bladder Permeation Program) measured the solubility, diffusion coefficient and permeability of helium, nitrogen and nitrogen tetroxide vapor through Teflon TFE and FEP membranes. Data were obtained in the temperature range of 25 to 100 C at pressures ranging from near vacuum to about 20 atmospheres. Results of the experimental effort were compared with the limited data previously reported. As a verification to the applicability of results to actual bladder systems, counter diffusion tests were performed with a laminated sample containing aluminum foil with a selected group of holes.