Growth and micromorphology of stcaric acid crystals grown by solvent evaporation method has been studied. The cffect of the solvent and the rate of evaporation of the solvent on the growth micromorphology has been investigated. The formation of spherulitic growth features, rhombic platelets of B-and C forms having growth spirals associated wii,h solution channels and twinned crystals involving B-B, C-C, and B-C forms is observed. The complexity of the twins involving the B-and C forms is discussed.
iritroduetioiiCharacterization of the growth of long chain organic molecular crystals can be understood t o a certain extent from similar studies on hydrocarbon molecules having a simpler structure such as n-alkanes etc. Fatty acids and fatty alcohols also play a n important role in such studies, as these molecules have a different niolecular species at one end of the molecular chain compared t o the n-alkanes. The growth and niicroniorphology of these materials has been the study since a long time (e. g. MULLER; AMELINCKX ; VERMA ; DANIEL; BOISTELLE ; SATO 1977). This article reports a systematic study on the crystallization of stearic acid employing different solvents. Certain aspects related t o spherulitic growth and the formation of twinned crystals is considered.
Experinleiit a1Stcaric acid (99% pure) obtained from Loba Chemicals, India is used as the starting matcrial. Crystallization is carried out by solvent evaporation method. The solvents employed are (i) acetom, (ii) benzene, (iii) toluene and (iv) xylene. Characteristics of growth is investigated at different levels of supersaturation and growth rates. The rate of evaporation of the solvent is varied over wide limits i.e., 4 x -0.1 cm3 . min-'. Growth at high-and low levels of supersaturation is characterized by dendritic, spherulitic growth forms in addition t o lozenge shaped platelets and thin platelets 52
Observations and discussion
The mode of plastic deformation of CaCO3 and NaNO3 crystals under concentrated loads is investigated as a function of temperature. At room temperature CaCO3 undergoes plastic deformation by twinning on (011) planes at both, low and high loads whereas NaNO3 deforms by glide at low loads and at high loads both, the glide and twinning processes operate. At higher temperatures both, NaNO3 (T > 100 °C) and CaCO3 (T > 300 °C) exhibit plasticflow by glide at low loads; at high loads both, glide and twinning occur in CaCO3, whereas glide is the dominant mode of deformation in NaNO3 even at higher loads. The effect of adsorbate on microhardness of these materials is considered. The effect of adsorbates on microhardness value may be due to a weakening or strengthening of surface and near surface bonds.
Is0 -epit axial Growth of n -Oct acosane Cry st als Iso-epitaxial(epi1ayer)growth of n-octarosanc crysi als is reported. The niorphology of the epilaycrs is i n the form of triangular growth islands with or without truncature. Epilayer growth precedes spiral growth mechanism which occurs at medium and low supersaturations, respectively. The occurrence of triangular and truncated rhombic platelets is found to be a inanifestation of growth a t medium supersaturations.
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