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Critical superconducting-transition temperature of 107.2 K observed in specimen made by annealing glass of composition Bi1.5Pb0.5Sr2Ca2Cu3Ox for 243 h at 840 degrees C. PbO found to lower melting temperature and viscosity of glass, possibly by acting as fluxing agent. Suggested partial substitution of lead into bismuth oxide planes of crystalline phase having Tc of 110 K stabilizes this phase and facilitates formation of it.
Easily processed liquid resins of low dielectric constants and high glass transition temperatures are useful for the manufacture of certain composite electronic boards. That combination of properties is difficult to acquire when dielectric constants are below 2.5, glass transition temperatures are above 200 C and processability is of conventional practicality. A recently issued patent (US 4,981,941 of 1 Jan. 1991) teaches practical materials and is the culmination of 23 years of research and effort and 15 patents owned by the Navy in the field of fluorinated resins of several classes. In addition to high fluorine content, practical utility was emphasized.
This final report details the work performed under this delivery order from April 1991 through April 1992. The currently available capabilities for integrated optical performance modeling at MSFC for large and complex systems such as AXAF were investigated. The Integrated Structural Modeling (ISM) program developed by Boeing for the U.S. Air Force was obtained and installed on two DECstations 5000 at MSFC. The structural, thermal and optical analysis programs available in ISM were evaluated. As part of the optomechanical engineering activities, technical support was provided in the design of support structure, mirror assembly, filter wheel assembly and material selection for the Solar X-ray Imager (SXI) program. As part of the fabrication activities, a large number of zerodur glass samples were prepared in different sizes and shapes for acid etching, coating and polishing experiments to characterize the subsurface damage and stresses produced by the grinding and polishing operations. Various optical components for AXAF video microscope and the x-ray test facility were also fabricated. A number of glass fabrication and test instruments such as a scatter plate interferometer, a gravity feed saw and some phenolic cutting blades were fabricated, integrated and tested.
At the highest temperatures of extraction, trapped Martian atmospheric CO2 is released. For this component, delta C-13 rises to +27 percent (compared to +15 percent previously). Because of the possibilities that C-13 rich atmospheric CO2 is released along with C-13 depleted crustal carbon, the highest delta C-13 value measured represents a lower limit to the true isotopic composition of the atmospheric species. Thus, the new delta C-13 determination is considered to best represent Martian atmospheric CO2. Based on a delta C-13 of +27 percent, and a release temperature of 1000-1200 C, the new analysis shows the glass to contain 2.4 ppm C as CO2, compared to 5.5 ppm C previously. Thus, it would seem that trapped CO2 is distributed rather unevenly throughout the glass.
A laboratory experiment is described that shows students the different strengths and fracture toughnesses between tempered and untempered glass. This paper also describes how glass is tempered and the materials science aspects of the process.
A suite of 365 Apollo 15 green-glass particles was analyzed by INAA and then described petrographically so that comparisons between composition and physical characteristics could be made. Nonuniform compositional distributions of crystalline and elongate particles were evident, although differences in the distribution of volatile-element coatings and extent of particle breakage were not as striking. A binomial evaluation of these textures on an intergroup basis supports the previously proposed hypothesis that the green-glass groups formed during discrete eruptive events because the groups that were defined compositionally also show significant differences in the average texture and structure of particles. Furthermore, in at least one case (Group D), intragroup differences in the distribution of vitrophyric and vitric particles were apparent. An extension of previous models for pyroclastic volcanism suggests that this feature may indicate that a systematic change in the composition of ejecta occurred as eruption progressed.
The occurrence and chemical compositions of some uncommon yellow to yellowish orange glasses associated with KREEP basalt fragments in Apollo 15 solids of possibly pyroclastic origins are discussed. The glasses show compositional variations that are compatible with igneous fractionation trends. A scenario is described in which late-stage KREEP basalt magmas erupted violently enough to fragment and incorporate previously crystallized basalts and deposited pyroclastic material on the moon.
A test program was conducted at the NASA/Johnson Space Center (JSC) concerning hypervelocity impact damage in fused silica glass. The objectives of this test program were: to expand the penetration equation data base in the velocity range between 2 and 8 km/s; to determine how much strength remains in a glass pane that has sustained known impact damage; and to develop a relationship between crater measurements and residual strength predictions that can be utilized in the Space Shuttle and Space Station programs. The results and conclusions of the residual strength testing are discussed below. Detailed discussion of the penetration equation studies will follow in future presentations.
A SrO-Al2O3 - 2SrO2 (SAS) glass ceramic matrix is reinforced with CVD SiC continuous fibers. This material is prepared by casting a slurry of SAS glass powder into tapes. Mats of continuous CVD-SiC fibers are alternately stacked with the matrix tapes. This tape-mat stack is warm-pressed to produce a 'green' composite. Organic constituents are burned out of the 'green' composite, and the remaining interim material is hot pressed.
Glass fiber has been produced from two lunar soil simulants. These two materials simulate lunar mare soil and lunar highland soil compositions, respectively. Short fibers containing recrystallized areas were produced from the as-received simulants. Doping the highland simulant with 8 weight percent B2-O3 yielded a material which could be spun continuously. The effects of lunar gravity on glass fiber formation were studied utilizing NASA's KC-135 aircraft. Gravity was found to play a major role in final fiber diameter.
A slurry of BSAS glass powders is cast into tapes which are cut to predetermined sizes. Mats of continuous chemical vapor deposition (CVD)-SiC fibers are alternately stacked with these matrix tapes. This tape-mat stack is warm-pressed to produce a 'green' composite which is heated to burn out organic constituents. The remaining interim material is then hot-pressed to form a BSAS glass-ceramic fiber-reinforced composite.
The effects of a 5.8-y exposure to low-earth-orbit environment upon the mechanical properties of five commercial glasses and a low-expansion-coefficient glass-ceramic have been examined. The radiation components of the earth-orbit environment did not degrade the mechanical strength of the samples examined within the limits of experimental error. Statistical problems arising from the low frequency of micrometeorite or space debris impacts upon the samples precluded statistically valid measurement of impacted sample strengths. Upper bounds for the magnitude of the impact event damage upon the strengths for impacted samples have been determined.
The damage that accompanies flexural deformation of a unidirectional glass fiber composite of polyphenylene sulfide was examined by AE and SEM. These complementary techniques were used to identify damage mechanisms at the microscale and correlate them with the macroscopic stress state in four-point bending. The flexural stress-strain curve was nominally linear to about 1.0 percent strain, but the onset of damage detectable by AE occurred at 0.3 percent strain. Two peaks in the AE amplitude distribution were observed at 35 dB and 60 dB. Low-amplitude events were detected along the entire length of the specimen, and correlation with direct observations of damage made by deforming the composite on the SEM stage suggested that these events arose from matrix cracking and fiber debonding concentrated at flaws on the composite. High amplitude events occurred primarily in the region of highest flexural stress between the inner loading points. They were attributed to fracture of glass fibers on the tension side and surface damage on the compressive side.
Experimental observations of the interaction behavior of cracks between two adjacent indents were made using an indentation technique in soda-lime glass. It was specifically demonstrated how one indent crack initiates and propagates in the vicinity of another indent crack. Several types of crack interactions were examined by changing the orientation and distance of one indent relative to the other. It was found that the residual stress field produced by elastic/plastic indentation has a significant influence on controlling the mode of crack interaction. The interaction of an indent crack with a free surface was also investigated for glass and ceramic specimens.
Fourteen adhesives used to bond a glass-fabric-reinforced phenolic resin laminate to steel were tested in order to determine their shear strengths at temperatures from 75 F to 500 F. Fabrication methods were varied to evaluate the effect of placing cloth between the facing surfaces to maintain a uniform bond-line thickness. One glass-fabric supported phenolic adhesive was found to have a shear strength of 3,400 psi at 300 F and over 1,000 psi at 500 F. Strength and fabrication data are tabulated for all adhesives tested.
The commercial application of Indium Phosphide solar cells in practical space missions is crucially dependent upon achieving a major cost reduction which could be offered by heteroepitaxy on cheaper, more rugged substrates. Furthermore, significant mass reduction, compatibility with mechanically stacked multijunction cells, and elimination of the current loss through glue discoloration, is possible in III-V solar cells by the development of ultrathin, directly glassed cells. The progress of a UK collaborative program to develop high efficiency, homojunction InP solar cells, grown by MOCVD on Si substrates, is described. Results of homoepitaxial cells (is greater than 17 percent 1 Sun AM0) are presented, together with progress in achieving low dislocation density heteroepitaxy. Also, progress in a UK program to develop ultrathin directly-glassed GaAs cells is described. Ultrathin (5 micron) GaAs cells, with 1 Sun AM0 efficiencies up to 19.1 percent, are presented, together with progress in achieving a direct (adhesive-less) bond between the cell and coverglass. Consequential development to, for example, cell grids, are also discussed.
Maturity, which is a measure of the time lunar soils have been in the upper approximately 1 mm of the surface, is correlated with changes in the soils' optical properties. Mature soil is darker and somewhat redder than immature soil of the same composition, and features in the reflectance spectrum become more subdued with increasing maturity. The maturation process also involves accumulation of agglutinitic glass and submicroscopic metallic iron particles. We have produced submicrometer iron metal blebs on the surface and within glass and mineral grains by the method of high-temperature reduction. This technique has permitted the determination of optical changes in samples much simpler than lunar soil, and offers a useful tool with which to investigate the maturation process.
Produced by shock experiments impact melts of albite, jadeite, and Pyrex glass demonstrate a loss of both Na and Al relative to Si, which can be due to selective vaporization. It is suggested that the high volatility of Al is related to volatility of a Na-Al compound of proposed NaAlO2 composition. The similar loss of Al and Na seems to be possible during tektite-forming processes. A degree of selective vaporization and modification of a melt chemical composition during impact processes is still poorly understood. The selective vaporization of some elements has been shown by shock experiments. The vaporization and condensation processes can take place in the lunar regolith. On this basis, there are hypotheses explaining differentiation of planetary bodies through the impact vaporization. On the other hand, studies of tektites, impact glasses, and lunar soils show that bulk compositions of impact melts are not modified significantly. In order to estimate degree of the vaporization during shock fusion, chemical compositions of experimentally produced impact melts were studied. We chose Al-containing compositions, because a high volatilization of Al during unequlibrated evaporization had been demonstrated.