M. S. Joshi

Nucleation in supersaturated potassium dihydrogen orthophosphate solutions

Abstract Rates of nucleation in supersaturated aqueous solutions of potassium dihydrogen orthophosphate (KDP) as indicated by the induction period were measured. Effects of supersaturation, temperature and agitation of the solution on the nucleation rate are reported. Nucleation rate increases with increase in supersaturation, temperature and agitation. Results were analysed in accordance with classical nucleation theory. The interfacial energy for growth of KDP crystals in the temperature range 30 to 45°C shows a decrease with the increase in temperature ranging from 2.4 erg/cm2 at 30°C to 1.8 erg/cm2 at 45°C.

Effect of supersaturation and fluid shear on the habit and homogeneity of potassium dihydrogen phosphate crystals

Abstract Potassium dihydrogen phosphate crystals are grown from aqueous solutions at a constant temperature (30 ± 0.5 °C) and at different supersaturations lying between 3.7 x 10-2 and 35 x 10-2. The dependence of the habit, homogeneity and structural perfection of these crystals on supersaturation and fluid shear has been studied. The variation in the habit, homogeneity and structural perfection with respect to supersaturation and the system of growth has been attributed to the difference in the relative growth rates along different directions, the formation of inclusions and the occurence of complex nucleation processes.

Microtopographical studies of first order prism faces of synthetic quartz

Abstract Surface structures of first order prism faces of synthetic quartz, grown on different types of seed crystals, are studied using optical techniques. Oriented hexagonal growth pyramids, which are so commonly found on such faces, are illustrated. Oriented, pentagonal elevations, observed on hexagonal growth pyramids, are described. Origin of growth islands is explained. Rows of growth hillocks on opposite faces are illustrated and are attributed to growth along the edges of the seed plate. It is proposed that the first order prism faces of synthetic quartz grow mainly by two-dimensional nucleation process due to spreading and piling up of hexagonal growth layers.

Growth of fibrous sodium aluminosilicate crystals in silica gel

Abstract Following Charnells method, the synthesis of fibrous sodium aluminosilicate crystals in silica gel is briefly desctibed. Optimum conditions to secure good crystals are discussed. Influence of pH, temperature and concentration of the reactants on the quality, growth rate and number of fibrous crystals is assessed. Different stages of growth are illustrated. Also described are the methods (X-ray powder analysis, electron microprobe analysis and infra-red spectral studies) for identification of synthesized crystals. It is established that the fibrous crystals reported here are a kind of zeolite.

The growth mechanism of apophyllite crystals studied by surface microstructures

Abstract It is proposed that apophyllite crystals grow mainly by two-dimensional nucleation process. Main growth takes place on the ‘a’ (100) faces by spreading and piling up of hexagonal growth ayers. ‘p’ (111) faces develop by independent growth in the form of triangular growth sheets. Growth rate on ‘p’ faces is greater than that of ‘a’ faces. Occasionally ‘a’ faces seem to grow by piling up of elliptical growth layers. Observations of hexagonal and elliptical growth pyramids on ‘a’ faces, oval shaped, hexagonal and rhombus shaped natural etch pits on ‘a’ faces, triangular natural etch pits on ‘p’ faces etc. reported, here, endorse the proposed mechanism of growth of apophyllite crystals.

Studies on microhardness of quenched mesolite crystals

Observations and results on studies of the microhardness of {1 0 1} and {1 0 ¯1} faces of natural mesolite crystals are illustrated and explained. Variations in Vickers hardness number (VHN) with temperature of quenching and also with the applied load are discussed.

Microtopographical studies of prism faces of potassium dihydrogen phosphate crystals

Surface structures on prism faces of potassium dihydrogen phosphate crystals grown from aqueous solutions and also by gel method are described and illustrated. Density of growth centres increases as the supersaturation of the mother liquor is increased. Gel grown crystals predominantly show rectangular growth hillocks on their prism faces. In the needle shaped crystals further nucleation extends predominantly along theC axis than at right angles to it. Influence of misoriented guest microcrystals on the growth of the prism faces is described.

Dislocations and their spatial configuration in amethyst crystals

Etch patterns produced on habit rhombohedral faces and rhombohedral cleavages of amethyst crystals are described and illustrated. Fidelity of etchants used is assessed. Also described are paired pits produced on match cleavages etched with the same or different etchants. By prolonged etching experiments it is established that the dislocations penetrate into the body of the crystal. Spatial distribution of dislocation in the body of the crystal is worked out. Uniformly spaced etch pits in an array observed on match cleavages (etched with different etchants) are attributed to low-angle tilt boundaries.

Synthesis and characterization of mordenite crystals

The hydrothermal synthesis of large port mordenite crystals and experimental observations are reported. Unit cell parameters are estimated asa = 18·142,b = 20·328 andc = 7·508 Å. Prismatic and prismatic pyramidal mordenite crystals are illustrated. The average particle size computed was 8–20µ. Adsorption capacities of synthesized mordenite crystals are 13·4% for water, 9·9% for methanol and 5·8% for benzene by weight.