Volume 4, Issue 3
May 1982, pages 1-373
pp 1- May 1982
pp 193-206 May 1982
Vapour phase crystal growth experiments performed in the Skylab and ASTP missions are reviewed. The basic vapour phase crystal growth technique is described and effect of gravity is discussed. The multipurpose furnace specially designed to carry out various experiments in flight conditions is described. Ge Se, Ge Te and GeS as well as ternary GeSe0·99 Te0·01 and GeS0·98 Se0·02 crystals have been grown in space showing improvement over similarly grown crystals on ground as determined by x-ray diffraction, chomical homogeneity and surface morphology studies. Mass flux rates under microgravity conditions have been found to be up to 10 times larger than expected indicating need for better theoretical and experimental understanding of the effect of gravity on crystal growth.
pp 207-228 May 1982
A review of experiments on crystal growth from melt in nearly zero gravity environments in space is given. The review includes experiments from skylab and ASTP missions. The results discussed are morphological observations, melt interfaee observations, dopant segregation, alloy solidification and containerless experiments.
pp 229-245 May 1982
The growth of large and perfect single crystals are now of considerable interest because of their increasing scientific and industrial importance. Any imperfection in the crystal causes malfunctioning, rapid aging, low reliability and low yield in manufacture. Due to the availability of earth orbiting spaceships, there is a possibility of growing these crystals with high purity. In this review paper, the author discusses mainly the growth of crystals under microgravity conditions (in spaceships) and their basic principles and also their relative merits.
pp 247-259 May 1982
Defect-free eutectic components are favoured for certain applications in view of their improved performance and/or better stability. Eutectics produced even under best conditions possible on earth have some microstructural defects. Unavoidable density driven convectional currents in liquid are considered as a major cause for the production of these defects. Intensity of such convectional currents proportionally reduces with gravity. Therefore the defect density in the eutectics is expected to be very low when processed under microgravity conditions. The advantages and limitations of processing under microgravity conditions are examined. The potential of newly developed ‘skin technology’ for processing eutectic components in space is considered.
pp 261-266 May 1982
Possible experiments in space on ceramics, composites and inorganic glasses are listed. Advantages in processing these materials under microgravity conditions, anticipated effects and likely problems are discussed. Theoretical conclusions and experimental results to date are reviewed. It is suggested that experiments on metallic glasses in space could prove to be rewarding.
pp 267-282 May 1982
The paper surveys the available literature on the direct influence of microgravity on diffusion in liquid metals, rate of solidification, growth of dendrites, undercooling of liquid metals and alloys and monotectic solidification. Agreement between theoretical predictions and experimental observations is discussed critically and areas requiring further study are highlighted.
pp 283-288 May 1982
The paper discusses the potential effects of space environment on solidification; reviews the previous solidification experiments in space and suggests new-experiments. The proposed experiments in space include (a) breakdown of planar interfaces in transparent systems, (b) thermal perturbations ahead of interfaces, (c) dendrite spacings, (d) fragmentation of dendrites and their transport, (e) solute concentration profiles in castings, (f) maximum undercoolings in alloy melts under containerless conditions; ultrafine structures produced on freezing of highly under-cooled melts, (g) preparation of wires and ribbons from alloys; solidification in ultrathin films and (h) dendritic shrinkage.
pp 289-295 May 1982
Recent developments in fabrication of cast metal ceramic particle composites by liquid metallurgy techniques are outlined. Difficulties encountered in preparing cast composites in the ground environment (including non-uniform distribution and agglomeration of dispersed particles and relatively poor bonding between dispersoids and matrix) and how these can be overcome in a microgravity environment have been discussed. This paper also reviews experiments performed by various space agencies including NASA and ESA on fabrication of composites in space. Some new experiments concerning fabrication of cast composites like dispersion of submicron ceramic particles in molten metals, preparation of cermets with very large volume fractions of ceramic particles and dispersion of flake-type ceramic particles to achieve grain refinement have been proposed.
pp 297-316 May 1982
In view of the interesting possibilities of controlling surface tension-driven convection, anticipated in space experiments involving fluid interfaces, the problem of the stability of a thin horizontal fluid layer subjected to rotation about a vertical axis, when the thermal (or concentration) gradient is not uniform is examined by linear stability analysis. Attention is focussed on the situation where the critical Marangoni number is greater than that for the case of uniform thermal gradient and the convection is not, in general, maintained. The case of adiabatic boundary condition is examined because it brings out the effect of surface tension at the free surfaces and allows a simple application of the Galerkin technique, which gives useful results. Numerical results are obtained for special cases and some general conclusions about the destabilizing effects of various basic temperature profiles and the stabilizing effect of coriolis force are presented. The results indicate that the most destabilizing temperature gradient is one for which the temperature gradient is a step function of the depth. Increase in Taylor number and the inverted parabolic basic temperature profile suppress the onset of convection.
pp 317-319 May 1982
In the case of animal systems, gravity probably plays an important role only during early development; this has to do with the determination of embryonic polarity. At other times in the life of an animal, gravity is a hindrance. If animals are to be sent into space, it is clearly necessary to study the effect of zerog on their physiology and behaviour. This apart, there seems to be no basis for thinking that biological experiments conducted in outer space might yield interesting insights into how living systems work.
pp 321-339 May 1982
In this paper, an attempt has been made to summarise the essential elements of a space vehicle design. After giving an overview of the methodology of spacecraft sizing and configuration, a brief outline of the technical considerations related to the design of different subsystems of the vehicle has been presented. The essential aspects related to manned systems are also discussed. The article concludes with the identification of some of the important payload interfaces, that are relevant to the design of material processing experiments in space.
pp 341-346 May 1982
The capabilities of Indian sounding rockets for conducting material science experiments are briefly described in this paper.
pp 347-356 May 1982
The “Laboratoire d’Etude de la solidification” (L.E.S.) in Grenoble is currently in charge of a significant number of various space experiments. They are 13 for the time being belonging to 7 programmes in cooperation with 5 international or national space agencies. It stands to reason that these 13 projects are not concerned with 13 entirely different problems. The six scientific problems that L.E.S. is trying to solve by operating in space conditions were not introduced as new activities, but rather as the best solution to solve many problems that were encountered in the frame of the classical ground-based research activity of this Laboratory. They are: (i) Thermomigration studies in liquid alloys (Sn +εX), (ii) Nucleation of eutectics (Ag-Ge, Au-Si). (iii) Unidirectional solidification of eutectics (Al-Al Cu, Al-Al Ni, Ag-Ge). (iv) Unidirectional solidification of solid solutions (Ge-Si, Al-·Cu, Sn-·Pb, Bi-·Sn, Ge +ε·Ga). (v) Unidirectional solidification of emulsions (Al-In). (vi) Unidirectional solidification of foams (Al-Zn).
Amongst these thirteen projects, three will use or have used rockets, three have used the Salyut-6 equipments, one will be operated as an automatic experiment aboard the Space Transportation System (the Space Shuttle), and the six remaining ones will be realized aboard the European Spacelab. Eleven experiments will use common facilities, one of those the low gradient heating facility (LGHF), being built in Grenoble: this equipment will be used by us in three experiments of the F.S.L.P. (first spacelab payload) and by two other European investigators.
pp 357-368 May 1982
The present overview will take into account both the qualities and the defects of the past programmes, and of the present hardware development studies and will try to define what will be the future interest of those rockets activities when compared with the manned spacecraft systems such as Spacelab, or with the automatic stations such as the ones that will be launched by the new Ariane system.
pp 369-373 May 1982
Volume 42 | Issue 6
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