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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Reinvestigation of the olivine-spinel transformation in Ni2SiO4 and the incongruent melting of Ni2SiO4 olivine

The olivine-spinel transformation and the melting behavior of Ni2SiO4 were investigated over the PT ranges of 20-40 kbar, 650-1200 C, and 5-13 kbar, 1600-1700 C, respectively. It was confirmed that Ni2SiO4 olivine melts incongruently at high pressures and that it is a stable phase until melting occurs. The PT slope of the incongruent melting curve is approximately 105 bars/deg. The olivine-spinel transformation curve was shown to be a reversible univariant curve, and could be expressed by the linear equation P(bars) equals 23,300 + 11.8 x T(deg C). The transformation curve determined by Akimoto et al. (1965) is nearly parallel to that of the present work, but lies at pressures about 12% lower.

Ma, C.-B.↗
NASA NTRS1976

M551 metals melting experiment

The Metals Melting Skylab Experiment consisted of selectively melting, in sequence, three rotating discs made of aluminum alloy, stainless steel, and tantalum alloy. For comparison, three other discs of the same three materials were similarly melted or welded on the ground. The power source of the melting was an electron beam unit. Results are presented which support the concept that the major difference between ground base and Skylab samples (i.e., large elongated grains in ground base samples versus nearly equiaxed and equal sized grains in Skylab samples) can be explained on the basis of constitutional supercooling, and not on the basis of surface phenomena. Microstructural observations on the weld samples and present explanations for some of these observations are examined. In particular, ripples and their implications to weld solidification were studied. Evidence of pronounced copper segregation in the Skylab A1 weld samples, and the tantalum samples studied, indicates a weld microhardness (and hence strength) that is uniformly higher than the ground base results, which is in agreement with previous predictions. Photographs are shown of the microstructure of the various alloys.

Li, C. H.↗
NASA NTRS1976

Metal melting, joining, and alloying under weightlessness

During the Skylab mission experiments were conducted concerning the influence of weightlessness on molten metals and the solidification process. It was found that the absence of gravity-induced thermal convection and sedimentation modified the properties of the bulk melt. A metals melting experiment was conducted to study the behavior of metal melted by an electron beam and to evaluate the feasibility of joining metals in space. An exothermic brazing experiment investigated the spreading, mixing, and capillary flow of molten braze material. The containerless melting and solidification of small samples of several metals was studied in another experiment. A description is also given of a study of the directional solidification of solid solution alloys.

Snyder, R. S.↗
NASA NTRS1977

The Apollo 17 'melt sheet' - Chemistry, age and Rb/Sr systematics

Major, minor, and trace-element compositions, age data, and Rb/Sr systematics of Apollo 17 boulders have been compiled, and additional analyses performed on a norite breccia clast (77215) included in the Apollo 17, Station 7 boulder. The Apollo 17 boulders are found to be identical or nearly so in major, minor, and trace-element composition, suggesting that they all originated as an impact melt analogous to melt sheets found in larger terrestrial craters. The matrix dates (Ar-40/Ar-39) and Rb/Sr systematics available suggest that this impact melt formed by a single impact about 4 billion years ago. This impact excavated, shocked, brecciated, and melted norites, norite cumulates, and possibly anorthositic gabbros and dunites about 4.4 billion years old. The impact was likely a major one, possibly the Serenitatis basin-forming event.

Winzer, S. R.↗
NASA NTRS1978

The thermal history of the Manicouagan impact melt sheet, Quebec

Calculations for the heat transfer between superheated silicate melt and evenly dispersed 1-mm cold clasts indicate that most of the thermal gradients are smoothed out in 100 s and that the rate of equilibrium is sufficiently high so that clasts whose dissolution in the melt is slow may be preserved. The calculations also show the extent to which cold debris and clasts are melted. Calculations for cooling of the 200-m-thick melt sheet at Manicouagan suggest that complete crystallization takes 35 years at 10 m from the edge and 1600 years at the center.

Onorato, P. I. K.↗
NASA NTRS1977

Examination of the liquid line of descent of mare basalts in light of data from melt inclusions in olivine

Data on 226 melt inclusions and their host olivines (173 new analyses) are presented and interpreted in terms of general liquid lines of descent and olivine fractionation. The melt inclusions in olivine along with those in ilmenite and late-stage mesostasis in mare basalts define a complex trend. The trend is complicated by the effects of ilmenite, plagioclase, and pyroxene fractionation within the melt inclusions in olivine, the fact that most of the basalts were multiply saturated during olivine fractionation, and the phenomenon of late-stage silicate immiscibility. It is suggested that the first two factors can account for the observed marked divergence of the melt inclusion data from simple early olivine fractionation trends. The elimination of the effects of daughter mineral fractionation by homogenization experiments is considered.

Weiblen, P. W.↗
NASA NTRS1977

Compositional variation in late-stage differentiates in mare lavas, as indicated by silicate melt inclusions

Questions regarding an interpretation of data from silicate melt inclusions are considered, taking into account the fragmental nature of the record, the possible effects of cooling rate on late-stage melt composition, and the crystallization of the trapped melt. New data related to 484 new analyses are provided in a separate table. Textural and mineralogical features and bulk chemical composition for an overall characterization of late-stage differentiates are discussed. A description is presented of a grouping and recognition of rock types on the basis of late-stage inclusion analyses. Attention is given to the bimodality of potassium values and the delineation of differentiation trends. It is found that many of the problems in interpretation and much of the scatter found in the composition of silicate melt inclusions in lunar samples can be attributed to the incomplete nature of the record and to crystallization after trapping.

Roedder, E.↗
NASA NTRS1977

Experimental melting relations of 63545, 76015, and 76055

The experiments discussed were conducted for the purpose of placing additional constraints on the origin of lunar highlands noritic compositions. The sample 63545 represents a fine-grained, crystalline melt rock consisting of pink spinel, plagioclase, divine, interstitial glass, minor oxides, and metal. According to Chao (1973), 76055 is an olivine-bearing micronorite hornfels with abundant xenocrysts and xenoliths. The sample 76015 is a vesicular, poikilitic impact melt with a homogeneous matrix. The obtained experimental melting relations of 63545, 76055, and 76015, are examined, taking into account experimental petrology and trace element chemistry of mare basalts. It is concluded that the studied compositions do not represent magmas derived by partial melting of either cosmic or differentiated source regions at any pressure in the moon. Presently available information would seem to favor an origin by impact-fusion of several highlands components.

Delano, J. W.↗
NASA NTRS1975

Magma genesis by in situ melting within the lunar crust

Blue-gray breccia 73217 represents a brecciated and partially melted assemblage of plutonic rock fragments. The textural and chemical evidence leads to the conclusion that the melt was generated within the lunar crust and that subsequent cooling and crystallization occurred prior to the transportation of this rock to the surface. The melt generated in this fashion, by in situ melting at depth, of moderately Mg-rich rocks, produced a liquid enriched in Fe, Ti, K, and P which could produce sodic ferrogabbro and granitic rocks similar to the light portion of 12013, but not KREEP.

Crawford, M. L.↗
NASA NTRS1978

Melt inclusions in Luna 24 soil fragments

Optical examinations of 28 slides of Luna 24 soil fragments revealed melt inclusions in grains of olivine, plagioclase, spinel, and ilmenite as well as interstitial inclusions. In contrast with Apollo samples, the Luna 24 samples contain sulfide melt inclusions, which indicates that saturation with respect to an iron sulfide melt took place throughout much of the crystallization history, even while olivine was crystallizing. The Luna 24 silicate-melt inclusions have recorded a more extensive differentiation toward higher iron magmas than have the Apollo inclusions, but they have also recorded some inexplicably low aluminum values.

Roedder, W.↗
NASA NTRS1979

The solubility of carbon monoxide in silicate melts at high pressures and its effect on silicate phase relations

Autoradiographic analysis and gas chromatography were used to measure the solubility in silicate melts of CO-CO2 vapors (30 to 40% CO by thermodynamic calculation) in equilibrium with graphite at temperatures up to 1700 deg C and pressures to 30 kbar. At near-liquidus temperatures CO-CO2 vapors were found to be slightly more soluble than CO2 alone. As a result of the apparently negative temperature dependence of CO solubility, the solubility of CO-CO2 at superliquidus temperatures is less than that of CO2. Melting points of two silicates were depressed more by CO than by CO2. Phase boundary orientations suggest that CO/CO + CO2 is greater in the liquid than in the vapor. The effect of the presence of CO on periodotite phase relations was investigated, and it was found that melts containing both CO and CO2 are nearly as polymerized as those containing only CO2. These results suggest that crystallization processes in planetary interiors can be expected to be about the same, whether the melts contain CO2 alone or CO2 and CO.

Eggler, D. H.↗
NASA NTRS1978

Nucleation and growth of plagioclase and the development of textures in a high-alumina basaltic melt

Detailed experiments on the nucleation and growth of plagioclase from an igneous melt are carried out to characterize the magma prior to cooling. It is shown that the nature of the melt directly preceding cooling has a strong effect on texture development, regardless of the origin of the melt. The number, size, and shape of the crystals present in a melt upon extrusion can have a drastic effect on the final textures present in the resulting rocks. Conditions necessary for the formation of poikilitic, intersertal, and porphyritic textures in basaltic rocks are defined.

Nabelek, P. I.↗
NASA NTRS1978

Dynamic crystallization and kinetic melting of the lunar soil

Dynamic crystallization and kinetic melting tests have been conducted for a lunar soil that resembles the bulk composition of the matrices of melt-rock breccias. The melting tests indicate that plagioclase and olivine can exist for finite times above their equilibrium liquidus temperatures; within 20-30 C below its liquidus temperature the sample is choked with crystals. A range of textures from radiate to porphyritic pyroxene-plagioclase granophyric to subophitic to intergranular to intersertal to very fine-grained poikilitic is found in the dynamic crystallization experiments. The number of nuclei, as deduced from the textures, increases as the melting temperature deceases from above the liquidus to below.

Lofgren, G. E.↗
NASA NTRS1979

Negative pressures and melting point depression in oxide-coated liquid metal droplets

Negative pressures and melting point depression in oxide-coated liquid metal droplets are studied. The calculation presented show the existence of large negative pressures when the oxide coating is thick enough. The change in the melting point caused by these negative pressures should be considered in studies of homogeneous crystal nucleation. Furthermore, since the negative pressure raises the entropy of the melt, it increases the entropy loss at the crystal-melt interface; the resulting increase of the surface tension could have a large effect on the homogeneous nucleation frequency.

Spaepen, F.↗
NASA NTRS1981

The nature of melt process changes in microgravity

The effects on melt impurities of the lack of buoyancy-driven convection in melts and the gas phase are outlined. Probable effects noted are: retardation of convective flow by a thin adsorbed impurity layer because of surface tension gradients (Marangoni flow); changes in the transport of volatile impurities to the melt surface and the consequent reduction of evaporation; and the change in dependence of evaporation rates on pressure due to the absence of convective flow in the gas next to the melt.

Wilcox, W.↗
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

Apollo 17 impact melts and their relation to the Serenitatis basin

Regional geologic relations are seen as suggesting that the distribution of highland landforms is not consistent with their derivation from a single impact event but is consistent with multiple events involving both distant basins and smaller, local craters. Thus the highland samples collected at the Apollo 17 landing site may not consist solely of Serenitatis basin ejecta but probably include both exotic ejecta and reworked local material. On the basis of these observations, it is suggested that the Apollo 17 highland melt breccias are not all derived from the Serenitatis basin impact; that is, the aphanitic melt rocks may be either other basin or local crater ejecta. It is thought that if the melt rocks collected at Apollo 17 are all derived from the same impact, the significant chemical and petrographic differences between the rocks may require modification of current models for impact melt petrogenesis.

Spudis, P. D.↗
NASA NTRS1983

Measured thermal diffusivity of Hg(1-x)Cd(x)Te solids and melts

The thermal diffusivity of Hg(1-x)Cd(x)Te melts is found to rise rapidly with temperature to values characteristic of metals. Solid and melt diffusivities for values of x from 0 to 0.3 and over a temperature range from 150 to 900 C have been determined by the laser flash method of Parker, Taylor, and Cowan. The diffusivity decreases from a maximum at x = 0 in both the solid and the liquid, with the values observed at x = 0.3 being about 40 percent of those for x = 0. The solid diffusivity for x = 0 is 1.7 sq mm/s at 150 C, decreasing to 0.7 sq mm/s at the melting point. The x = 0 liquid diffusivity increases from 0.7 sq mm/s at the melting point to 3.5 sq mm/s at 900 C.

Holland, L. R.↗