Crystal growth under the combined effect of gravity and magnetic field

#The present invention relates to the growth of crystals from solution under an applied magnetic field.

#The preparation of high purity crystals is of interest in a range of scientific and industrial applications; however, macroscopic and microscopic fluctuations of composition which commonly occur in solution, make it a challenge to obtain high quality crystals.

#There has been considerable investigation of the effect of magnetic field on crystal growth. Several reports suggest that a magnetic field affects the growth of crystals from an aqueous solution. Thus, application of a magnetic field decreases the growth rate of ammonium dihydrogen phosphate (Zizic et al. J Crystal Growth 54:439 (1981)) and Rochelle salts (Mitrovic et al. Appl. Phys. A 51:374 (1990)). On the other hand, application of a magnetic field increases the growth rate of Fe(NH.sub.4).sub.2 (SO.sub.2).sub.2 (M. Schieber J Crystal Growth 1:131 (1967). Other studies have reported an effect of a magnetic field on phase composition in polytypic crystals (B. P. J. Prezedmojski Crystal Res. & Technol. 17:759 (1982)). In all these studies, very high magnetic field strengths in the order of 5000-20,000 Gauss (0.5-2.0 T) were applied. The effect of weak magnetic fields on crystal growth from aqueous solutions has not been investigated.

#The invention is described with reference to the Figures which are provided for the purposes of illustration only and in which:

#FIG. 1 is an illustration of the combined effect of the earth's magnetic field and gravity on negatively and positively charged ions;

#FIG. 2 is a photograph of crystals grown under nearly zero effective magnetic field;

#According to the invention, crystals are grown in a solution while the solution is exposed to a weak magnetic field. The magnetic field in preferably in the range of one to ten times the strength of the earth's background magnetic field, or geomagnetic field. Since the earth's magnetic field is approximately 0.5 Gauss, the present invention calls for application of a magnetic field that is in the range of about 0.5 to 100 Gauss, and preferably about 0.5 to 25 Gauss and most preferably about 0.5 to 5 Gauss. Magnetic field strengths of about 0.5-5 Gauss were found to have significant effects on non-saturated ionic solutions. It is contemplated that super-saturated solutions may require somewhat stronger magnetic fields, e.g. up to about 100 Gauss, because ion cross-field diffusion can be large in super-saturated solutions.

#"Earth's magnetic field" or "geomagnetic field", as those terms are used herein means the magnetic field experienced by a body at its particular location on the earth's surface. The magnetic field varies in strength and in orientation over the surface of the earth. There is a vector component to the field. At the equator the geomagnetic field is substantially parallel to the earth's surface. At the poles, the field is substantially perpendicular to the earth's surface, In the intervening regions, the field has both a horizontal and vertical components.

#Because the vertical component of the earth's magnetic field will result in a cross product of zero, the present invention is concerned with a horizonal component of the earth's magnetic field, which strength varies with location on the earth's surface. The horizontal component of the earth's magnetic field is defined by the equation, B=0.5 cos .theta..sub.G, where .theta. is the dip angle. Thus, at the equator, the horizontal component is equivalent to the earth's magnetic field (cos .theta.=1), whereas at the poles, the horizontal component of the earth's magnetic field is near zero (cos .theta.=0).