JOURNAL OF MATERIALS SCIENCE LETTERS 11 (1992) 535-537 Morphological and X-ray characterization studies of gel-grown Newberyite M. DEEPA, K. RAJENDRA BABU, V. K. VAIDYAN Department of Physics, University of Kerala, Thiruvananthapuram, 695 581, India Y. M. FAZIL MARICKAR Department of Surgery, Medical College, 695 011, India Newberyite or magnesium hydrogen phosphate tri- hydrate (MgHPOa-3H20) is a naturally occurring rare mineral and it was first identified as a new species in Skipton Caves, Victoria, Australia. The occurrence of Newberyite in the human urinary calculi has been reported by several workers [1], and in 1956 it was first identified as a crystalline component of a kidney stone. The crystal structure of Newberyite was worked out by Sutor [2]. The structure of pure synthetic crystals of Newberyite is orthorhombic with unit-cell dimensions a = 1.0215 nm, b = 1.0681 nm and c = 1.0014 nm [3]. In this study the growth and morphology of Newberyite crystals grown in silica gel at room temperature in the initial pH range 5.5-8 were investigated. The addition of citric acid and tartaric acid in the control solution showed an inhibitory effect on the growth of the crystal with a change in the morphology. The grown crystals are characterized using infrared spectroscopy, X-ray diffractometry (XRD) and opt- ical micrography. The most common gel used for crystal growth experiments is the silica gel obtained by neutraliza- tion of sodium metasilicate. The gelling process is quickly achieved in a narrow pH range of 5.5-8, the gel density varying between 1.02 and 1.09. The growth experiments were carried out in standard Hane's tubes using sodium metasilicate solution of specific gravity 1.02-1.09. The pH of 20 ml sodium metasilicate solution was adjusted to 7 by titration with 3 M acetic acid and 10 ml 1 M magnesium acetate, and the mixture was allowed to gel in a test tube. 10ml 0.5 M ammonium dihydrogen ortho- phosphate solution was then placed over the per- fectly set gel. Very clear crystals of Newberyite appeared below the gel surface and well inside the gel column. The crystals attained an optimum size of 3 mm within 3 weeks after placing ammonium dihydrogen orthophosphate solution over the gel. In the course of the experiments it was noted that the number of crystals always diminished with increasing distance from the gel interface. In these regions the diffusion gradients were different from those near the interface, and this is believed to be the principle explanation for the observed crystal distribution [4]. Experiments were conducted for various values of specific gravity of sodium metasilicate solution, and concentrations of magnesium acetate solution and 0261-8028 ©1992 Chapman & Hall ammonium dihydrogen orthophosphate solution. It is conjectured that a critical value exists for the density of silicate solution and concentration of top and bottom nutrient which will yield best-quality crystals of optimum size. The critical values obtained were 1.03 g cm -3 for the density of the sodium silicate solution, 1 M magnesium acetate solution and 0.5 M ammonium dihydrogen orthophosphate solution. Different concentrations of citric acid and tartaric acid dopants were added to the control solution to study the effect of dopants. Infrared spectroscopy, XRD and optical microscopy were used for characterization of doped and undoped Newberyite crystals. FeKo~ radiation was used for XRD studies in the range 20 = 0-1000. The infrared spectra of the samples were taken in the range 400-4000 cm -1 . 80: 60 / E L E u °i ° z :Q 1 < 20 0 0. 5 1.0 1.5 Molarity of dopant Figure1 Plot of molarityof dopant against nucleationtime and crystal size for (a) citric acid-doped crystal and (b) tartaric acid-dopedcrystal. 535