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Transient one dimensional heat transfer analysis demonstrating infiltrant melting effect on self heat-retarding porous metal composite during surface melt layer formation
Passivation phenomena were observed upon cathodic and anodic polarization of the Al electrode in AlCl3-KCl-NaCl melts between 100 and 160 C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and 1/sq root of 2 pi (rps). Upon cathodic polarization dentrite formation occurs at the Al electrode. The activation overvoltage in AlCl3-KCl-NaCl (57.5-12.5-20 mol%) was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/cm2 at 130 C and a double layer capacity of 40 plus or minus 10 microfarad/cm2 were measured.
Passivation phenomena have been observed upon cathodic and anodic polarization of the Al electrode in AlCl3-KCl-NaCl melts between 100 and 160 C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and omega to the minus 1/2 power. Upon cathodic polarization, dendrite formation occurs at the Al electrode. The activation overvoltage in AlCl3-KCl-NaCl was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/sq cm at 130 C and a double layer capacity of 40 plus or minus 10 microfarad/sq cm were measured.
Discussion of a problem encountered in the processing of viscoelastic materials that is caused by the presence of a hydrodynamic instability in the extrusion of polymer melts. The importance of the so-called Weissenberg number in determining the onset of the melt fracture is examined using classical linearized hydrodynamic stability analysis. It is shown that the simple shearing flow of a viscoelastic fluid becomes unstable at a critical value of the Weissenberg number. Implications for the extrusion processing of polymers are reviewed.
A direct-current arc in argon at atmospheric pressure was used to determine effective work functions of refractory metals, including tantalum, tungsten, molybdenum, and niobium. The procedure is experimentally advantageous, because surface cleanliness of the specimen is not critical, high vacuum is not required, and the anode-cathode spacing is not critical. The experimental procedure involves striking an arc to a metal wire cathode to form a melted ball having an emitting area defined by its diameter. The literature melting point of the metal is taken as the emitting temperature. By using these parameters and the known arc current, effective work functions were calculated from the Richardson-Dushman equation. The calculated work functions agree with recommended handbook values to within about 0.1 V and have typical repeatabilities of 0.02 V.
Information developed to characterize flight and ground based samples from the metals melting experiment is detailed in this report. Included are the characteristics determined by nondestructive examination, visual observation, metallographic examination and posttest measurements. Comparisons of the flight and ground based discs showed that an electron beam heat source can be used successfully in zero gravity for cutting, welding, or melting. Few differences were observed that could be attributed to the absence of gravity in these operations.
The pertinent factors in levitation heating and melting of tungsten are discussed. The benefits to be derived from conducting purification processes in space environments are analyzed. It was determined that the following advantages would be realized: (1) crucibleless heating and melting, (2) vacuum and/or inert gas purification, and (3) control of grain size through supercooling.
A description is given of the methods used to arc-melt and to homogenize near-stoichiometric ZrC and ZrC-boron alloys, giving attention to the oxygen contamination problem. The starting material for the carbide preparation was ZrC powder with an average particle size of 4.6 micron. Pellets weighing approximately 3 g each were prepared at room temperature from the powder by the use of an isostatic press operated at 50,000 psi. These pellets were individually melted in an arc furnace containing a static atmosphere of purified argon. A graphite resistance furnace was used for the homogenization process.
Characterizations of flight and ground based samples from the metals melting experiment are detailed. The characteristics were determined by nondestructive investigation, visual observation, metallographic examination, and post-test measurements. Comparisons of the flight and ground based discs showed that an electron beam heat source can be used in zero gravity for cutting, welding, or melting.
Microscopic and chemical evidence are presented to support the contention that shock-generated incipient grain-boundary melting of plagioclase occurred in an anorthositic lunar rock and that shock-generated plagioclase liquid was present along grain boundaries during post-shock adiabatic expansion in a fragment of anorthositic breccia. The first contention is supported by microtextural relationships in the rock, the composition of its metal particles (most iron with some cobalt and less nickel), and glass inclusions with vapor bubbles. The second contention is supported by angular irregular voids in the fragment as well as the occurrence of oriented glass filaments in some of the voids. It is shown that shock-generation of 'cataclastic anorthosite' and high-temperature plagioclase liquids can explain the exceptionally young lead and argon ages of the anorthositic rock. The results of the breccia study indicate that shock lithification of plagioclase-rich particulate material from the highland regolith is due to grain-boundary melting of plagioclase.
We present evidence to support the hypothesis that the fine-grained, basaltic-textured portions of rocks 60618 and 65785 were produced by impact melting of the coarse-grained spinel-olivine anorthosite (60618) and spinel troctolite (65785) portions, coupled with admixture of approximately 33% and 63%, respectively, material of alkalic high-alumina basalt (KREEP) composition. The abundance of impact-modified rocks at the Apollo 16 site with compositional similarities to the impact melts reported here, suggests that the relations observed in these rocks are indicative of widespread impact mixing with KREEP in rocks of the lunar highlands.
The purpose of experiment MA-060 was to investigate quantitatively the effects of near-zero gravity conditions on crystal growth and dopant segregation during directional solidification from the melt. Gallium-doped germanium single crystals were successfully grown from the melt with simultaneous interface demarcation during the Apollo Soyuz Test Project mission. The analysis of the experimental data indicates striking differences of dopant segregation and growth behavior in the presence and absence of gravity. The results obtained are believed to have far-reaching implications on materials processing under zero-gravity conditions and on the theory of crystal growth and segregation in general.
A biased random walk, Monte Carlo procedure is used to study the melting transition in small clusters of N atoms. Results show an abrupt change in physical properties near melting, but there is no evidence that the transition is either first or second order; rather the transition is more gradual.
Experiments were performed determining the distribution of chromium between olivine, pyroxenes, and melt at oxygen fugacity values near those of lunar rocks for a wide range of bulk compositions. The range of values of D-Cr (wt% of Cr2O3 in crystals/Cr2O3 in melt) is 0.6-1.3 for olivine and 1.6-3.5 for pyroxene; this ratio shows no obvious dependence on any experimental parameter.
The early intense bombardment of the moon has not necessarily gardened most of the crust to more than a few kilometers depth. Deep crustal material sampled by the largest impacts is most likely to be preserved as melt-rock deposits on or near the rims of mare basins. The Apollo 17 melt-rock boulders and the matrices of the Apollo 15 'black-and-white' rocks (15445, 15455) are considered the most likely of all lunar samples to represent deep crustal material. These samples have the composition of low-K Fra Mauro (LKFM) basalt. A two- or three-layer crustal model is proposed, in which a layer of anorthositic gabbro, which forms most of the exposed surface of the lunar highlands, is underlain by a layer of LKFM basalt. If the Apollo 15 and 17 heat-flow measurements are representative of the mean lunar heat flow, they constrain the LKFM layer to be no more than 20 km thick.
The reported investigation was conducted in connection with the desirability to obtain information regarding the response of a solidified planetary surface to the primary impact of a meteoroid whose dimensions are small compared to that of the planet. The investigation is an extension of studies conducted by Ahrens and O'Keefe (1977) concerned with a calculation via finite-difference techniques of the entire flow field, the energy partitioning, and the quantity of melt and vapor produced upon impact of an iron object on a gabbroic anorthosite half-space at 15 km/sec. The assumptions used in these calculations are summarized. Calculations based on an equation of state for the low- and high-pressure mineral assemblage of gabbroic anorthosite, initial density 2.94 g/cu cm are considered. An algorithm is formulated for the description of the phase transformation upon shock loading. It is shown that the relative volume of melt and the equivalent volume of shock-induced vapor is proportional to the meteoroid kinetic energy (at high speeds) using the similarity scaling of projectile and target properties as suggested by Dienes and Walsh (1970).
Primary silicate melt inclusions in ilmenite crystals in seven mare basalt samples were analyzed by electron microprobe, and analyses were made of their host and associated phases. Two distinct and restricted chemical composition ranges are drawn: high-K and low-K. The high-K samples are nearly identical with the granitic residual liquid, averaging a weight percentage of 6.27% K20, 76.3% SiO2, plus 82% normative quartz and orthoclase. It is noted that no low-K melt was found as a re-entrant or interstitial inclusion in any sample; only as isolated inclusions in illmenite.
Equilibrium crystallization sequences are determined in melting experiments in vacuum at Fe saturation on synthetic mare basalt compositions 70215 and 15318 Red Glass (both high-Ti) as well as 15555-15016 (low-Ti). The experiments confirm that much of the chemical variation within both the high- and low-Ti suites is controlled by near-surface fractionation processes, although the two suites cannot be related by such mechanisms. The components and crystallization products of the liquidus at various temperatures and pressures are reported. Mare basalt petrogenesis is interpreted in terms of high-pressure equilibria at Fe saturation; it is suggested that low-Ti basalts represent partial melts of a differentiated olivine-pyroxenite lunar mantle at 240 km or deeper, while cumulus clinopyroxene in the source is responsible for their REE characteristics. The formation of high-Ti basalts is considered.