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Summary of the current state of knowledge about the thermodynamic properties of liquid metals, including heats of fusion and heat capacities. A table is presented of consistent thermodynamic data for liquid metals, including estimates for the many high-melting transition metals which have not yet been studied, based on new levitation data and on periodic table correlations.
Concept utilizes porous metal or nonmetal matrix containing liquid metal in porous structure and confines liquid metal to contact area between rotor and brush by capillary forces. System may also be used to lubricate bearing systems.
The design of a single axis orientation mechanism for solar arrays on high power synchronous satellites is studied primarily with respect to providing 116 liquid metal slip rings for reduced friction and improved electrical characteristics. Designs and tradeoff studies for the slip rings and other components are presented. An assembly containing 33 slip rings of three design approaches was designed, fabricated, and vacuum tested to 30 amperes and 30,000 volts. Containment of the liquid metal gallium in large diameter slip rings was difficult. A design approach is presented which is expected to provide improved retention of the liquid metal.
In an effort to reduce structural weight while maintaining structural integrity on the space shuttle and other proposed space vehicles, various composite materials are being evaluated to determine their applicability and reliability in load carrying situations. While most of the composites being considered for structural components are of the metal-metal type, there are some applications for which metal-epoxy composites are proposed. An approximate method is presented to analyze plane stress orthotropic linear viscoelastic problems under isothermal conditions. A computer program which is based on the method was used to solve a simple uniaxial creep problem for a Maxwell type material. This solution is presented and compared with the analytical solution.
Sliding friction experiments were conducted with copper, nickel, iron, and cobalt sliding on themselves in air and argon. The resulting wear surfaces were examined with X-ray analysis to determine if surface texturing had occurred as a result of sliding. Results of the investigation indicate that, for the face-centered-cubic metals copper and nickel, a (111) texture develops with the (111) planes tilted 10 deg in the direction of sliding. The body-centered-cubic metal iron exhibited a (110) texture with the (100) direction oriented in the direction of sliding. It also exhibited a 10 deg tilt in the direction of sliding. The environment influenced the results in that the degree of texture observed in argon was less than that seen in air for iron. No texturing was observed for the close-packed-hexagonal metal cobalt. Recrystallization was observed with copper as a result of sliding.
A compilation of eutectics and melting-point minima for binary combinations of metals having vapor pressures below 10 to the minus 10th power torr at 1500 degrees K and .00005 torr at 2000 degree K is presented. These compositions and others near them on their phase diagrams are potential special brazing fillers for refractory metals. Some possible problems and advantages for fusion bonds of such mixtures are indicated. Evaluations of brazing fillers containing refractory metals are reported.
A liquid metal slip ring/solar orientation mechanism was designed and a model tested. This was a follow-up of previous efforts for the development of a gallium liquid metal slip ring in which the major problem was the formation and ejection of debris. A number of slip ring design approaches were studied. The probe design concept was fully implemented with detail drawings and a model was successfully tested for dielectric strength, shock vibration, acceleration and operation. The conclusions are that a gallium liquid metal slip ring/solar orientation mechanism is feasible and that the problem of debris formation and ejection has been successfully solved.
The measurement of infrared frequencies of metal-oxygen species which could be formed in the matrix and to investigate with an oxygen-18 enrichment study the controversy on the vibrational assignments for the suboxide. Several new molecules, Al3O2, Ga3O, In3O, In4O2, IntaO, IntaO2, and In2WO4, were found by mass spectrometric sampling to exist in extremely minor concentrations in the vapor phase. The latter three species were formed by reaction with the crucible materials and were unimportant for an infrared analysis. The infrared spectroscopic measurements were obtained by the matrix isolation technique of molecular beam sampling. The MO2 species were formed by direct reaction between metal and O2 in the matrix. A C2v structure and an O-M-O bond angle near 40 deg was favored for these molecules by analogy with a similar investigation of the alkali metals. The vibrational frequencies which were determined are given.
A survey of the literature through 1969 shows an almost total lack of experimental emissivity data for metals in the liquid state. The emissivities for several transition metals and various other metals and compounds in the liquid state at their fusion temperatures have been determined. The technique used involves electromagnetic levitation-induction heating of the materials in an inert atmosphere. The brightness temperature of the liquid phase of the material is measured as the material is heated through fusion. Given a reliable value of the fusion temperature, which is available for most pure substances, one may readily calculate an emissivity for the liquid phase at the fusion temperatures. Even in cases where melting points are poorly known, the brightness temperatures are unique parameters, independent of the temperature scale and measured for a chemically defined system at a fixed point. Better emissivities may be recalculated as better melting point data become available.
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.
Metal smeared into grooves of serial numbers by grinding or filing can be cleaned out by process called cavitation. Ultrasonic vibrator generates very high frequency vibrations in water which create millions of microscopic bubbles. Cavitation bubbles impact metal surface at thousands of pounds per square inch pressure. Metal particles filling grooves are broken away.
A theory is developed for the compressibility and transport properties of liquid metallic hydrogen, near to its melting point and under high pressure. The interionic force law is assumed to be of the screened Coulomb type, because hydrogen has no core electrons. The random phase approximation is used to obtain the structure factor S(k) of the system in terms of the Fourier transform of this force law. The long wavelenth limit of the structure factor S(o) is related to the compressibility, which is much lower than that of alkali metals at their melting points. The diffusion constant at the melting point is obtained in terms of the Debye frequency, using a frequency spectrum analogous with the phonon spectrum of a solid. A similar argument is used to obtain the combined shear and bulk viscosities, but these depend also on S(o). The transport coefficients are found to be about the same size as those of alkali metals at their melting points.
The packaging of metal wool for reusable thermal heat shields applied to aerodynamic and other surfaces for the space shuttle was analyzed and designed, and samples were fabricated and experimentally studied. Parametric trends were prepared for selected configurations. An all-metal thermally efficient, reliable, reusable and producible heat shield system was designed and structurally tested for use on spacecraft aerodynamic surfaces where temperatures do not exceed 810 K. Stainless steel sheet, primarily for structure and secondarily in the transverse plane for thermal expansion, was shown to accommodate thermal expansion in all directions when restrained at the edges and heated to 1360 K. Aerodynamic loads of 0.35 x 1000,000 newtons/sq meter, and higher, may be easily accepted by structures of this design. Seven all-metal thermal protection specimens, 12.7 cm square and 2.5 cm thick were fabricated and are being experimentally evaluated at simulated shuttle entry conditions in an arc jet facility.
Crack propagation is discussed for metals with liquid metal in the crack space. The change in electrochemical potential of an electron in a metal due to changes in stress level along the crack surface was investigated along with the change in local chemistry, and interfacial energy due to atomic redistribution in the liquid. Coupled elastic-elastrostatic equations, stress effects on electron energy states, and crack propagation via surface roughening are discussed.
The results of research to identify the cavitation erosion damage mechanisms at the microscopic level for three metals (aluminum, stainless steel, and titanium) representing a range of properties and microstructure are presented. The metals were exposed to cavitation generated in distilled water by a 20-kHz ultrasonic facility operating at a vibration amplitude of 2 mils. Representative properties of the metals and experimental details are summarized. Replicas of the eroded surfaces of the specimens obtained periodically during exposure were examined with a transmission electron microscope to follow progression of the erosion damage and identify dominant erosion mechanisms as a function of exposure time. Eroded surfaces of selected specimens were also examined with a scanning electron microscope to assist in the interpretation.
The mechanical properties of multipass high-strength steel weld metals depend upon several factors, among the most important being: (1) The interaction between the alloy composition and weld metal cooling rate which determines the as-deposited microstructure; and (2) the thermal effects of subsequent passes on each underlying pass which alter the original microstructure. The bulk properties of a multipass weld are therefore governed by both the initial microstructure of each weld pass and its subsequent thermal history. Data obtained for a high strength low alloy steel weld metal confirmed that a simple correlation exists between mechanical properties and welding conditions if the latter are in turn correlated as weld cooling rate.
An analytical method is developed for determining heat transfer by impinging liquid-metal slot jets. The method involves mapping the jet flow region, which is bounded by free streamlines, into a potential plane where it becomes a uniform flow in a channel of constant width. The energy equation is transformed into potential plane coordinates and is solved in the channel flow region. Conformal mapping is then used to transform the solution back into the physical plane and obtain the desired heat-transfer characteristics. The analysis given here determines the heat-transfer characteristics for two parallel liquid-metal slot jets impinging normally against a uniformly heated flat plate. The liquid-metal assumptions are made that the jets are inviscid and that molecular conduction is dominating heat diffusion. Wall temperature distributions along the heated plate are obtained as a function of spacing between the jets and the jet Peclet number.
We show that the characteristic features of lunar glass welded aggregates including their irregular shapes, vesicularity, and content of submicron Fe metal in the welding glass can be explained by a model in which they are predominantly formed by micrometeorite impacts into the solar wind saturated topmost surface of the regolith. The Fe metal is reduced from silicates by the solar wind gases. Other possible mechanisms of Fe metal formation are discussed and shown to play at most minor roles. It is shown that surface tension forces control vesicularity and that the low gravity and high vacuum conditions prevailing on the moon are unimportant. Consequences of this surface tension control to possible lunar eruptive volcanism and to the Ar-40/Ar-39 dating of impact events are discussed.