Knudsen measurements of the sublimation of manganese /II/ telluride
Knudsen effusion measurements of stoichiometric MnTe sublimation at high temperature and low pressure
Sadeek, H.↗
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Results for “sublimation”
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Effects of sublimation on silicon-germanium RTG performance
Performance of silicon-germanium thermoelement in RTG with sublimation at high operating temperatures
Source record↗
Effect of sublimation on the behavior of cryodeposits
Calculation of rates of energy loss due to sublimation for water, carbon dioxide, argon, krypton, xenon, and oxygen
Campbell, J. P.↗
Shape evolution of a subliming surface subjected to unsteady spatially nonuniform heat flux
Two dimensional unsteady heat conduction in solid with subliming surface, replacing original boundary value problem by ordinary integrodifferential equation
Charwat, A. F.↗
Subliming nuclear microthruster and its space applications
Subliming nuclear microthrustor design with Monte Carlo study of rarefied gas nozzle flow, noting application to spin stabilization
Choong, P. T.↗
Access to uncombined titanium through an inhibiting film in sublimation pumping of deuterium.
In principle, titanium bulk sublimator pumping should be ideal for removing large quantities of deuterium from a vacuum system. In practice, much of the deposited titanium remains uncombined and is wasted. We have demonstrated, through a series of experiments, that it is possible (by the addition of a thin layer of titanium to an apparently occluded surface) to gain access to previously deposited sublayers of uncombined titanium in spite of the presence of an inhibiting film (such as an oxide) on the surface.
Steinberg, R.↗
Analysis of sublimation-cooled coated mirrors in convective and radiative environments.
Analytical solutions were obtained for the thermal response of a transpiration- or sublimation-cooled spherical mirror coating exposed to convective and radiative heating. The solutions allow unlimited spectral detail to be accounted for. Results indicate that transpiration-cooled thick coatings (1 cm) may withstand up to 10 kW/sq cm on a steady basis without excessive temperature rise for quartzlike materials with an internal absorption coefficient of 0.01 per cm. On a transient basis, fluxes up to 20 kW/sq cm can be accommodated for a second (cW laser exposure time), 4 kW/sq cm for 5 sec (planetary entry heating time), and of the order of MW/sq cm for millisecond times (short-duration laser bursts) without transpiration cooling for a material with an absorption coefficient of 0.1 per cm. Proportionately higher fluxes can be accommodated with lower absorption coefficients. Thermal stresses produced by the heat pulse are found to be high but within the strength of the materials. The regime in which meaningful solutions may be obtained is mapped in detail.
Howe, J. T.↗
Thermal shielding by subliming volume reflectors in convective and intense radiative environments.
The behavior of dielectric materials having densely packed internal scattering centers subject to extreme convective and radiative environments is analyzed. Experiments have shown that these materials act as volume reflectors of incident radiation even when the exposed surface is being eroded by thermochemical ablation. The analysis was applied to interpret experiments of subliming Teflon models exposed to combined radiative and convective fluxes up to 1.7 kW/sq cm for several seconds. Results show that, although the exposed surface receded at an apparently steady rate, the internal temperature climbed continually, due to internal absorption of radiation and would have caused failure internally if the test duration were extended a few seconds. Thus, performance is time-limited by the internal absorption coefficient. Results were obtained for larger configurations and other materials. Typically, Teflon shells may withstand radiant fluxes up to 20 kW/sq cm for about 5 sec and fritted quartz up to 50 kW/sq cm for about 8 sec (corresponding to the Jupiter entry).
Howe, J. T.↗
Modeling sublimation of a charring ablator
The Hertz-Knudsen analysis is shown to accurately predict the sublimation rate from a charring ablator. Porosity is shown to have a significant effect on the surface temperature. The predominant carbon species found in the vapor is C3, which agrees well with the results of previous investigations.
Balhoff, J. F.↗
Knudsen measurements of the sublimation and the heat of formation of GeSe
Knudsen effusion studies of the sublimation of polycrystalline GeSe have been performed employing mass spectrometry. The results demonstrate that GeSe vaporizes congruently under present experimental conditions according to the reaction: GeSe(s) yields GeSe(g). The mean values for the third-law heat and second-law entropy of reaction based on direct mass-loss data are 42.0 + or - 1.5 kcal/mole and 42.3 + or - 1.6 eu respectively. From these data the standard heat of formation was calculated to be -10.1 + or - 2.0 kcal/mole, and the standard absolute entropy was determined to be 16.9 + or - 2.0 eu.
Wiedemeier, H.↗
Sublimation behavior of silicon nitride /Si3N4/ coated silicon germanium /SiGe/ unicouples
For the Multi-Hundred Watt (MHW) Radioisotope Thermoelectric Generator (RTG), the silicon germanium unicouples are coated with silicon nitride to minimize degradation mechanisms which are directly attributable to material sublimation effects. A program is under way to determine the effective vapor suppression of this coating as a function of temperature and gas environment. The results of weight loss experiments, using Si3N4 coated hot shoes (SiMo), operating over a temperature range from 900 C to 1200 C, are analyzed and discussed. These experiments were conducted both in high vacuum and at different pressures of carbon monoxide (CO) to determine its effect on the coating. Although the results show a favorable vapor suppression at all operating temperatures, the pressure of the CO and the thickness of the coating have a decided effect on the useful lifetime of the coating.
Stapfer, G.↗
The sublimation kinetics of GeSe single crystals
The sublimation kinetics of (001) oriented GeSe single crystal platelets was studied by high-temperature mass spectroscopy, quantitative vacuum microbalance techniques, and hot stage optical microscopy. For a mean experimental temperature of 563 K, the activation enthalpy and entropy are found to equal 32.3 kcal/mole and 19.1 eu, respectively. The vaporization coefficient is less than unity for the range of test temperatures, and decreases with increasing temperature. The combined experimental data are correlated by means of a multistep surface adsorption mechanism.
Irene, E. A.↗
The source of sublimates on the Apollo 15 green and Apollo 17 orange glass samples
Elemental analyses of the thin film of micromounds which coat the surfaces of Apollo 15 green glass and Apollo 17 orange glass are reported. It is thought that Zn, Ga, Pb, Cu, Tl, S, F, and Cl condensed as a sublimate on the outside surface of these glass particles in lava fountains about 3.4 and 3.6 b.y. ago (Apollos 15 and 17, respectively). The heavy metals enriched in these samples may have been mobilized in a halide- and sulfide-rich vapor, while the source of these elements and of the glass may be a sulfide- and halide-rich pyroxenite inside the moon. The isotopic composition of lead on the surface of individual particles was determined, and the composition is considered with respect to the evolution of the source region. The lead on the surfaces is similar to lead that has been mixed into other soils and breccias at nearby sites.
Meyer, C., Jr.↗
Transformation of Polar Ice Sublimate Residue into Martian Circumpolar Sand
The experimental demonstration that a credible Martian sand may be formed from dust-bearing ice provides a new set of possible explanations for some of the observed Martian aeolian landforms. It is hypothesized that a light-weight fluffy rind is formed on the polar caps. This could provide material easily entrainable by Martian winds, which generally blow equatorward from the poles. These winds would peel the fluffy rind from the surface of the sublimating summer polar caps and from the equatorward slopes of the polar troughs. These pieces of material would then be rolled into lumps (of high sailarea/mass ratio) by the wind. They would become pigmented as they saltate across the surface, perhaps gathering carbonaceous meteoritic dust or other impurities on their surfaces, or through chemical reactions with the ice-free environment away from their point of origin. Once they became trapped in topographic wind shadows, they would form dune structures because they are hydraulically equivalent to sand particles.
Saunders, R. S.↗
Onset of sublimation in comet P/Halley (1982i)
The first direct evidence for the onset of sublimation of a comet nucleus is reported. Emission due to CN observed in spectra of the comet P/Halley provides evidence for the development of the gas coma. Broad-band photometric observations of the comet indicate that the dust coma developed near a preperihelion heliocentric distance r of about 6 AU. Rates of gas production and brightening for the comet have been derived at r of 4-6 AU. The mean preperihelion nuclear magnitude derived for the comet was used to calculate an effective radius of the nucleus, which for plausible values of the geometric albedo lies in the range 1-4 km.
Wyckoff, S.↗
Solid sulfur in vacuum: Sublimation effects on surface microtexture, color and spectral reflectance, and applications to planetary surfaces
A form of sulfur that is white at room temperature and very fluffy in texture has been found in laboratory experiments on the effects of vacuum sublimation (evaporation) on solid sulfur. This work is an outgrowth of proton sputtering experiments on sulfur directed toward understanding Jovian magnetospheric effects on the surface of Io. Fluffy white sulfur is formed on the surface of solid yellow, tan, or brown sulfur melt freezes in vacuum by differential (fractional) evaporation of two or more sulfur molecular species present in the original sulfur; S(8) ring sulfur is thought to be the dominant sublimination phase lost to the vacuum sink, and polymeric chain sulfur S(u) the dominant residual phase that remains in place, forming the residual fluffy surface layer. The reflectance spectrum of the original sulfur surface is greaty modified by formation of the fluffy layer: the blue absorption band-edge and shoulder move 0.05 to 0.06 microns toward shorter wavelengths resulting in a permanent increase in reflectivity near 0.42 to 0.46 microns; the UV reflectivity below 0.40 microns is reduced. This form of sulfur should exist in large quantity on the surface of Io, especially in hotspot regions if there is solid free sulfur there that has solidified from a melt. Its color and spectra will indicate relative crystallization age on a scale of days to months and/or surface temperature distribution history.
Nash, D. B.↗
Dust clouds around red giant stars - Evidence of sublimating comet disks?
The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated.
Matese, John J.↗
Sublimating icy planetesimals as the source of nucleation seeds for grain condensation in classical novae
The problem of grain nucleation during novae outbursts is a major obstacle to our understanding of dust formation in these systems. How nucleation seeds can form in the hostile post-outburst environment remains an unresolved matter. It is suggested that the material for seeding the condensation of ejecta outflow is stored in a primordial disk of icy planetesimals surrounding the system. Evidence is presented that the requisite number of nucleation seeds can be released by sublimation of the planetesimals during outbursts.
Matese, John J.↗