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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Thermal barrier coatings - Burner rig hot corrosion test results

A Mach 0.3 burner rig test program was conducted to examine the sensitivity of thermal barrier coatings to Na- and V-contaminated combustion gases simulating potential utility gas turbine environments. Coating life of the standard ZrO2-12Y2O3/Ni-16.2Cr-5.6Al-0.6Y (composition in wt %) NASA thermal barrier coating system which was developed for aircraft gas turbines was significantly reduced in such environments. Two thermal barrier coating systems, Ca2SiO4/Ni-16.2Cr-5.6Al-0.6Y and ZrO2-8Y2O3/Ni-16.4Cr-5.1Al-0.15Y and a less insulative cermet coating system, 50 vol % MgO-50 vol % Ni-19.6Cr-17.1Al-0.97Y/Ni-16.2Cr-5.6Al-0.6Y, were identified as having much improved corrosion resistance compared to the standard coating.

Hodge, P. E.↗
NASA NTRS1980

Adherence of ion beam sputter deposited metal films on H-13 steel

An electron bombardment argon ion source sputter deposited 17 metals and metal oxides on H-13 steel. The films ranged 1 to 8 micrometers in thickness and their adherence was generally greater than the capacity of the measuring device; adherence quality depended on proper precleaning of the substrate before deposition. N2 or air was introduced for correct stoichiometry in metallic compounds. Au, Ag, MgO, and Ta5Si3 films 8 microns thick have bond strength equal to 1 micron coatings; the bond strength of pure metallic films up to 5 microns thick was greater than the epoxy to film bond (8000 psi). The results of exposures of coated material to temperatures up to 700 C are presented.

Mirtich, M. J.↗
NASA NTRS1980

Chemical composition of earth, Venus, and Mercury

Model compositions of the earth, Venus, and Mercury are calculated from the premise that planets and chondrites underwent four identical fractionation processes in the solar nebula. Because elements of similar properties stay together in these processes, five constraints suffice to define the composition of a planet: mass of the core, abundance of U, and the ratios K/U, TI/U, and FeO/(FeO + MgO). Complete abundance tables, and normative mineralogies, are given for all three planets. A review of available data shows only a few gross trends for the inner planets: FeO decreases with heliocentric distance, whereas volatiles are depleted and refractories are enriched in the smaller planets.

Morgan, J. W.↗
NASA NTRS1981

Chondrules in H3 chondrites - Textures, compositions and origins

Compositional and textural variations among chondrules in unequilibrated (type 3) H-group chondrites are examined in order to determine possible relations between chondrule compositions and textures. Bulk compositions of polished thin sections of 90 individual chondrules and 16 compound chondrule sets from the Sharps, Tieschitz and Bremervorde chondrites were measured by broad-beam electron probe analyses; the chondrules were also classified petrographically as barred olivine, porphyritic olivine, porphyritic pyroxene, barred pyroxene, radiating pyroxene or fine-grained. The mean compositions of each type are found to be distinct as verified by discriminant analysis, despite a large scatter, with the olivine-rich chondrules characterized by low SiO2 and high FeO and MgO contents, greater concentrations of TiO2, Al2O3, Na2O and K2O, and lower Cr2O3 and MnO relative to pyroxene-rich chondrules. Data suggest that composition, together with cooling rate, has played a conspicuous role in producing observed chrondrule textures, and are consistent with chondrule formation from mixtures of differing fractions of high-, intermediate- and low-temperature nebular condensates that underwent melting in space.

Lux, G.↗
NASA NTRS1980

Thermal barrier coatings for superalloys

The current status of ceramic thermal barrier coatings for protection of turbine airfoil components is reviewed. Test results for an early duplex coating system ZrO2-12% Y2O3/Ni-16% Cr-6% Al-0.6% Y, improved system ZrO2-8% Y2O3/Ni-17% Cr-5% Al-0.35% Y, and air/fuel impurity tolerant systems based on ZrO2-8% Y2O3, 2CaO-SiO2, and a MgO-NiCrAlY cermet are discussed. Preliminary test results at 800 C for a graded ZrO2-8% Y2O3/Ni-20% Cr-11% Al-0.4% Y coating system show that the coating can survive at least 500 hr in the presence of 50 ppm V plus other fuel contaminants and additives.

Miller, R. A.↗
NASA NTRS1981

Review of NASA progress in thermal barrier coatings for stationary gas turbines

Ceramic thermal barrier coatings for industrial/utility gas turbines were investigated. In burner rig tests of a zirconia yttria/nickel chromium aluminum yttrium ZrO2-12w/0Y2O3/NiCrAlY coating system on air cooled superalloy specimens, ceramic coating life (spallation) was sensitive to Na and V concentration in the fuel. The locations of coating spallation correspond to areas where combustion products were predicted to condense. Three new thermal barrier coating systems were identified. These are based on calcium silicate, ZrO2-8w/0Y2O3, and a MgO-NiCrAlY cermet. The spall resistance can be increased by reducing the ceramic layer thickness from 0.038 to 0.013 cm and by the use of more oxidation/corrosion resistant bond coats.

Hodge, P. E.↗
NASA NTRS1981

Thermal shock resistance of silicon oxynitride

The thermal shock resistance of Si2N2O refractory material was studied. The thermal expansion coeff. is 3.55x10 to the -6th power at 20 to 800 C and 2.86x10 to the -6th power m/m/deg at 20 to 200 C. The breaking loads are high at high stress. Young's modulus E and the shear modulus G decrease linearly with increasing porosity. For dense material E sub o approx. = 216,500 N/mm2 and G approx = 90,600 N/mm2. The Vickers hardness of the dense material is comparable to that of sapphire. The results on thermal shock show that R, the breaking load, stays constant for T T sub c, the first cracks appear and R decreases sharply for T=T sub c. As the severity of the thermal shock is increased at T T sub c, a small no. of new, large-size cracks appears. The shock's cumulative effect is negligible, and repeated shocks do not change the cracks. The low values of the thermal expansion coefficient and Young's modulus and the high tension breaking load are considered. Sintered Si2N2O with 5% MgO shows excellent cracking resistance under thermal shock.

Glandus, J. C.↗
NASA NTRS1974

High modulus invert analog glass compositions containing beryllia

Glass compositions having a Young's modulus of at least 15 million psi and a specific modulus of at least 110 million inches consisting essentially of, in mols, 10-45% SiO2, 2-15% Li2O, 3-34% BeO, 12-36% of at least one bivalent oxide selected from the group consisting of CaO, ZnO, MgO and CuO, 10-39% of at least one trivalent oxide selected from the group consisting of Al2O3, B2O3, La2O3, Y2O3 and the mixed rare earth oxides, the total number of said bivalent and trivalent oxides being at least three, and up to 10% of a tetravalent oxide selected from the group consisting of ZrO2, TiO2 and CeO2.

Bacon, J. F.↗
NASA NTRS1974

Non-toxic invert analog glass compositions of high modulus

Glass compositions having a Young's modulus of at least 15 million psi are described. They and a specific modulus of at least 110 million inches consist essentially of, in mols, 15 to 40% SiO2, 6 to 15% Li2O, 24 to 45% of at least two bivalent oxides selected from the group consisting of Ca, NzO, MgO and CuO; 13 to 39% of at least two trivalent oxides selected from the group consisting of Al2O3, Fe2O3, B2O3, La2O3, and Y2O3 and up to 15% of one or more tetravelent oxides selected from the group consisting of ZrO2, TiO2 and CeO2. The high modulus, low density glass compositions contain no toxic elements. The composition, glass density, Young's modulus, and specific modulus for 28 representative glasses are presented. The fiber modulus of five glasses are given.

Bacon, J. F.↗
NASA NTRS1976

High modulus rare earth and beryllium containing silicate glass compositions

Glass compositions having a Young's modulus of at least 16 million psi and a specific modulus of at least 110 million inches consisting essentially of approximately, by weight, 20 to 43% SiO2, 8 to 21% Al2O3, 4 to 10% BeO, 27 to 58% of at least one oxide selected from a first group consisting of Y2O3, La2O3, Nd2O3, Ce2O3, Ce2O3, and the mixed rare earth oxides, and 3 to 12% of at least one oxide selected from a second group consisting of MgO, ZrO2, ZnO and CaO are described. The molar ratio of BeO to the total content of the first group oxides is from 1.0 to 3.0.

Bacon, J. F.↗
NASA NTRS1980

Predictions of mineral assemblages in planetary interiors

It is shown that mineral compatibilities in the model system CaO-MgO-Al2O3-SiO2 can be applied to deduce the mineral assemblages expected in planetary interiors and their variation with depth. In general, the available estimates of bulk composition of the terrestrial planets suggest that the terrestrial planets can be divided into two groups based on their predicted mineral assemblages. The terrestrial, Venusian, and lunar bulk compositions are expected to display the following sequence of mineral assemblages with increasing pressure: plagioclase lherzolite, spinel lherzolite, and garnet lherzolite. The sequences expected in Martian and Mercurian are different: spinel-plagioclase wehrlite, spinel lherzolite, and spinel-garnet wehrlite. These assemblages have a major influence on the compositions of liquids produced by melting of these planetary interiors, on the solidus temperatures, and thus on the nature of planetary differentiation and the types of magmas extruded at planetary surfaces.

Stolper, E.↗
NASA NTRS1982

Compositional variation in the Hadley Apennine region

Orbital geochemical data in the Hadley Apennine region are related to typical rock compositions and used in determining the distribution of soils derived from the rock types found in this region. Orbital XRF Mg/Si and Al/Si intensities are the orbital data that are used primarily. These data are corrected for spurious interorbit variation using a modification of a previously developed method. The corrected values are than converted to % MgO and % Al2O3, respectively, from theoretical considerations, and as such are compared with similar concentrations for typical lunar rocks and soils of the Apollo 15 landing site. The relationship of the XRF values to Fe, Ti, and Th concentrations, derived from gamma-ray observations, is also considered. It is established that the orbital geochemistry data for this region are consistent with the presence of a mixture of ANT suite and Fra Mauro basalt components frequently dominated by a KREEP basalt component toward the west and by a mafic pyroclastic component toward the east.

Clark, P. E.↗
NASA NTRS1982

Preliminary modeling of high pressure partial melting - Implications for early lunar differentiation

A quantitative model is presented for equilibrium crystallization of lunar magmas at high pressure, which, viewed in reverse, is equivalent to equilibrium partial melting. Data are extrapolated from simple systems, mare basalt systems, and from experiments on terrestrial compositions. Liquidus phase equilibria in a portion of the CaO-MgO-Al2O3-SiO2 system serve as a guide for predicting phase equilibria in the natural system. High pressure partial melting sequences are calculated for several proposed whole moon compositions at nominal pressure of 10 and 20 kb. Results show that compositions with chondritic Ca/Al have quite different melting paths from those with subchondritic Ca/Al, and as a result the types of magmas produced are quite different. If the moon possesses a chondritic Ca/Al ratio, models which rely on small degrees of partial melting to produce the early lunar magnetism are suspect.

Longhi, J.↗
NASA NTRS1981

Influence of CO2 on melting of model granulite facies assemblages - A model for the genesis of charnockites

It is shown that partial melting studies at crustal pressures in SiO2-rich portions of the system KAlSiO4-Mg2SiO2-H2O-CO2 can be used in modeling the anatectic origin of charnockites. The univariant reaction phlogopite + sanidine + quartz + vapor = enstatite + liquid yields an SiO2-rich melt (granite analog) at 3 kbar; the vapor composition at the solidus is buffered to high H2O contents by virtue of the coexistence of phlogopite with its breakdown products. With higher pressures (8 and 15 kbar), the fluid phase is buffered to higher CO2 contents and the melt composition becomes enriched in K2O and MgO (charnockite analog). Melting relations are controlled through the expansion of the quartz liquidus field relative to the enstatite and sanidine fields with increasing pressure. It is noted that partial melts generated at the base of the crust in the presence of CO2-rich fluid will be of an alkaline nature and will crystallize enstatite at lower pressures. CO2-saturated melting of similar SiO2-rich bulk compositions (phlogopite-absent) through the reaction enstatite + sanidine + quartz + CO2 - liquid occurs at temperatures above 1000 C to about 15 kbar.

Wendlandt, R. F.↗
NASA NTRS1982

Ceramic thermal barrier coatings for gas turbine engines

The results of studies concerning the high temperature corrosion resistance of ZrO2-Y2O3, ZrO2-MgO, and Ca2SiO4 plasma-sprayed coatings, which may be used as gas turbine engine thermal barriers, are reported. The coatings were evaluated in atmospheric burner rig and pressurized passage tests, using GT No. 2 fuel in pure form and with sodium, sulfur and vanadium corrosive impurities doping. It is found that, while the coatings performed well in both pressurized passage and burner rig tests with pure fuel chemical reactions between the ceramic coatings and combustion gases/condensates resulted in coating degradation with impure fuels. Chemical reactions between the ceramic coatings and vanadium compounds played a critical role in coating degradation.

Bratton, R. J.↗
NASA NTRS1982

A new LL3 chondrite, Allan Hills A79003, and observations on matrices in ordinary chondrites

Allan Hills A79003 is an LL3 chondrite with a petrologic subtype of 3.4 + or - 0.2. Contrary to previous suggestions, it is not paired with other Allan Hills specimens. It contains haxonite, (Fe,Ni)23C6; shock-melted, 'fizzed' metal-troilite intergrowths; and translucent, glassy-looking Huss matrix (fine-grained, Fe-rich silicate matrix), in addition to the normal opaque and recrystallized varieties of Huss matrix. Some chondrules are partly coated with opaque matrix, others with translucent matrix. Translucent matrix is more uniform in composition and contains less S, CaO and FeO and more MgO than the opaque variety. Both kinds of matrix rimmed chondrules before consolidation of the meteorite.

Scott, E. R. D.↗
NASA NTRS1982

Mechanisms of devitrification of grain boundary glassy phases in Si3N4 materials

Changes in the grain boundary (g.b.) phases of Si3N4 are analyzed, the effects of composition and thermal history on devitrification of the g.b. phases are determined, devitrification of the g.b. phases of Si3N are related to mechanical behavior and oxidation sensitivity of the material. The phase relationships that occur within the grain boundaries of Si3N4 containing various densification aids are reviewed. Comparisons of the effects of MgO, Y2O3, CeO2, and Y2O3 + AL2O3 are made in terms of the phase equilibria of the Si3N4 + SiO2 + additive compositional system. Two new equilibrium phase diagrams for the Si3N4-SiO2 and Y2O3 and Si3N4-SiO2-Ce2O3 systems are preented. The effects of Y2O3 vs CeO2 densification aids on the fracture surfaces of Si3N4 are compared. Auger electron spectroscopy shows that both oxides are concentrated within the fracture surface. Scanning electron microscopy shows evidence that Si3N4 with CeO2 formed an intergranular structure of fine grained oxynitride reaction products, as predicted by phase quilibria, whereas the Y2O3 containing sample shows evidence of an intergranular glassy phase.

Hench, L. L.↗
NASA NTRS1982

Theoretical prediction of phase relationships in planetary mantles

Thermodynamic and phase equilibrium data are used to generate an internally consistent set of enthalpies and entropies for important components of the CaO-MgO-Al2O3-SiO2 (CMAS) system in silica-undersaturated compositions. The addition of Na and Fe(2+) to the CMAS system produces shifts in the plagioclase, spinel and garnet stability fields. While the Morgan and Anders (1979) model Martian composition has stability fields of plagioclase and garnet lherzolite, and a small spinel lherzolite field at temperatures below 900 C, the Martian mantle composition of McGetchin and Smyth (1978) would not contain orthopyroxene, and a low pressure assemblage of plagioclase-spinel wehrlite would be replaced by garnet-spinel wehrlite at higher pressure. In both cases, the Fe-Mg ratio would be substantially greater than that found in primitive terrestrial basalts.

Wood, B. J.↗