Crystal Growth In Microgravity Research Articles

Multi-user facility for protein crystal growth in microgravity: results from PCAM and DCAM

Multi-user facility for protein crystal growth in microgravity: results from PCAM and DCAM

Magnetic damping of buoyant convection during semiconductor crystal growth in microgravity. Continuous random g-jitters

This paper treats the buoyant convection of a liquid metal in a circular cylinder with a uniform, steady, axial magnetic field and with the random residual accelerations encountered on earth-orbiting vehicles. The objective is to model the magnetic damping of the melt motion during semiconductor crystal growth by the Bridgman process in space. For a typical process with a magnetic flux density of 0.2 T, the convective heat transfer and the nonlinear inertial effects are negligible, so that the governing equations are linear. Therefore, for residual accelerations or ‘‘g-jitters’’ whose directions are random functions of time, the buoyant convection is given by a superposition of the convections for two unidirectional accelerations: an axial acceleration which is parallel to the cylinder’s axis and a transverse acceleration which is perpendicular to this axis. Similarly, the response to accelerations whose amplitudes are random functions of time is given by a Fourier-transform superposition of the buoyant convections for sinusoidally periodic accelerations for all frequencies. Since the temperature gradient in the Bridgman process is primarily axial, the magnitude of the three-dimensional buoyant convection for the transverse acceleration is much larger than the magnitude of the axisymmetric convection for the axial acceleration. At a low frequency, only the magnetic damping limits the magnitude of the buoyant convection. As the frequency is increased, linear inertial effects augment the magnetic damping, so that the magnitude of the convection decreases, and its phase shifts to a quarter-period lag after the acceleration.

Recent results and new hardware developments for protein crystal growth in microgravity

Protein crystal growth experiments have been performed on 16 space shuttle missions since April 1985. The initial experiments used vapor diffusion crystallization techniques similar to those used in laboratories for earth-based experiments. More recent experiments have assessed temperature-induced crystallization as an alternative method for growing high quality protein crystals in microgravity. Results from both vapor-diffusion and temperature-induced crystallization experiments indicate that protein crystals grown in microgravity may be larger, display more uniform morphologies, and yield diffraction data to significantly higher resolutions than the best crystals of these proteins grown on earth.

Numerical simulation of non-Navier-Stokes fluid-dynamics in vapour crystal growth

In recent theoretical developments, non-linear irreversible thermodynamic effects, like Burnètt stresses and slip boundary conditions, have been recognized as playing an important role under typical conditions encountered during vapour crystal growth in microgravity, and new classes of convection and flow regimes have been identified via a rigourous non-dimensional order of magnitude analysis. In this paper we present a numerical quantitative analysis of these regimes for geometrical configurations of interest in vapour crystal growth. The results are presented for different combinations of the non-dimensional characteristic parameters, ranging from microgravity to earth environment conditions. In each case we give isotherms, stream lines and velocity profiles, and compare the results with the corresponding solution of the Navier-Stokes approximation.

微小重力での結晶成長

微小重力での結晶成長

Erratum: Protein Crystal Growth in Microgravity

The report "Protein crystal growth in microgravity" by L. J. DeLucas et al . (3 Nov. 1989, p. 651) contained a typographical error regarding the B values of space- and Earth-growth crystals. The last sentence of the first paragraph on page 652 should have read, "The slopes of these plots are directly related to the difference in overall B values for two different crystals, b (Earth-grown) and a (space-grown)."

Surface tension of Pb 0.8Sn 0.2Te melt and the effect of Marangoni convection in microgravity crystal growth

The surface tension of Pb 0.8Sn 0.2Te melt is determined to be γ = (230±10)−0.17( T− T liq) mN/m using the sessile drop technique between 900 and 1030°C. The Marangoni convective flow rate at the free melt surface estimated from the measured temperature coefficient of the surface tension can be expected to be about 4 orders greater than the PbTeSnTe mutual diffusion rate. Therefore, for diffusion-controlled steady-state growth in space, a free melt surface should be avoided during Pb 1− x Sn x Te crystal growth.

Crystal growth in a low gravity environment

Crystal growth in microgravity possesses several distinct technological advantages over earth-bound processes; containerless handling and reduction of density gradient driven as well as sedimentation flows. Experiments performed in space to date have been basically reproductions of processes currently used on earth and the results have clarified our understanding of crystal growth dynamics. In addition, both unresolved problems and areas requiring further study on earth have been identified. Future work in space processing of materials must address these areas of study as soon as possible if the full potential of a space environment to develop new techniques and materials is to be realized.

Thermocapillary convection in microgravity crystal growth melts of indium-antimonide

Thermocapillary convection in microgravity crystal growth melts of indium-antimonide

Thermocapillary convection in microgravity crystal growth melts of indium-antimonide

Results of two recent crystal growth experiments conducted aboard Skylab are analyzed for thermoconvective aspects. Theoretical temperature and velocity profiles in the crystal melts are predicted via computer modeling. These results are compared with experimental data obtained from Skylab investigators. From theoretical considerations, both indium-antimonide experiments should have exhibited substantial thermocapillary convection, but did not due to probable oxide film interference and/or opposing solutal effects.