Effect of electric field on the growth of barium molybdate crystals in silica gel

The growth of BaMoO₄ crystals in silica gel under the influence of an externally applied uniform electric field is studied. The habit changes resulting from different growth parameters are reported. Crystals up to 4.0 mm×1.2 mm×0.9 mm were obtained under field. The morphology of some crystals is examined by optical and scanning electron microscopy.     

Growth of lanthanum tartrate crystals in silica gel

The spherulitic, dendritic and single-crystal growth of hydrated lanthanum tartrate by controlled diffusion in silica gels is reported. The influence of growth parameters, e.g. reactant concentrations, gel pH, gel ageing, on the size and nucleation density of crystals has been studied. Operative mechanisms of crystallization, results of growth kinetics and morphology of crystals are discussed. The adsorption property of the gel is found to play a vital role during the crystallization of lanthanum tartrate crystals, Parabolic kinetics, characteristic of a one-dimensional diffusion-controlled process, for single crystals is observed to be obeyed in case of variation of upper reactant concentration.     

Growth of Mixed Rare Earth Tartrate Crystals (Y(1-x)Sm_x)_2(C_4H_4O_6)_3·zH_2O from Silica Gels

Experiments performed on the grwth of mixed crystals of rare earth tartrates (Y1-xSmx)2 (C4H4O6)3.zH2O (0≤x≤1) from silica gels at 35~40℃ and 25~30℃ employing single-diffusion technique. are discussed. The crystals maintain spherulitic morphology, irrespective of the value of x, concentration of upper and lower reactants, gel pH, gel age and gel temperature. Formation Of Liesegang rings in this system is a temperature dependent phenomenon. It is shown that with the increase of the value of x the system passes from Liesegangring phenomenon to singlezone phenomenon. Operative mechanism of crystallization in the higher (35~40℃) and lower temperature ranges (25~30℃) is explained. Seeded growth experiments indicate the possibility of increasing the size of the spherulites in the gel medium     

Controlled nucleation and growth kinetics of lead nitrate phosphate in silica hydrogel and characterization of grown crystals

Lead nitrate phosphate (LNP) single crystals were grown in silica hydrogel at an ambient temperature employing various nucleation control methods. The effect of concentration of feed solution, gel density, gel pH, ageing of gels and temperature on reduction of nucleation centres is reported. Kinetic studies of the nucleation and growth of LNP crystals and dentrites were studied. The crystals are characterized by X-ray diffraction, density measurements, magnetic susceptibility, mechanical strength measurements and dissolution behaviour.     

In vitro studies of calcium mixed minerals growth in different growth faces and semiconductor laser induced suppression of nuclei strategy

Kidney stone consists of various organic, inorganic and semi organic compounds. Mineral oxalate monohydrate and di-hydrate are the main organic constituents of kidney stones. However, mechanisms leading to the formation of mineral oxalate kidney stones are not clearly understood. The effect of some urinary stone constituents such as ammonium oxalate, calcium citrate, proteins and trace elements were reported by us. The calcium magnesium hydrogen phosphate (CaMHP) crystals were grown in SMS gel medium which provides the necessary kidney stimuli growth medium. The growth processes were done by single diffusion method for different physical and chemical parameters. The pH range in which HPO₄²⁻ ions dominates were considered which in turn is necessary for the growth of CaMHP crystals. In the present study, calcium magnesium hydrogen phosphate (CaMHP) crystals are grown in three different growth faces to attain the total nucleation reduction. As an extension of this research, many characterization studies have been carried out like XRD, FTIR, TGA, SEM and etching and the results are reported.     

Nucleation and growth of CdC2O4·3H2O single crystals in silica gels

As part of our work on growth of cadmium oxalate single crystals in gels, we describe here variation of nucleation density and growth of these crystals as a function of concentration of feed solution, gel ageing, gel density, gel pH and intermediate neutral gel column. While high density and high pH gels have been found to produce opaque crystals, good quality transparent single crystals have been obtained in low density and low pH gels. It was observed that the intermediate neutral gel column and gel ageing considerably reduced the number of nucleation sites and increased the size of the crystals without affecting their quality. By concentration programming the size of the crystals increased.     

Growth and characterization of calcium pyrophosphate dihydrate grown in silica gel

Calcium pyrophosphate dihydrate crystals, which are responsible for various arthritic diseases, were grown in sodium metasilicate gel. Variations in gel density, pH value and concentration of the reactants were found to have profound effect on the growth of the crystals. The grown crystals were characterized using IR, XRD, TGA and optical microscopy.     

Nucleation and growth of potassium dihydrogen phosphate crystals in silica gels

Kinetic studies on nucleation and growth of potassium dihydrogen phosphate crystals in silica gels show that the rate-determining process for the growth of these crystals in silica gels is diffusion. Morphology, microhardness and perfection of gel grown crystals are also reported.     

Growth and characterization of barium copper oxalate single crystals in gels

Barium copper oxalate was grown in silica hydrogel at ambient temperature. The effect of various parameters like gel pH, gel density, gel aging and concentrations of reactants on the growth of these crystals was studied. The crystals grown were characterized by chemical analysis, X-ray powder diffractometry, infrared spectroscopy, thermogravimetric and differential thermal analysis. The results of these observations are described and discussed.     

Growth of strontium tartrate tetrahydrate single crystals in silica gels

Growth of single crystals of strontium tartrate tetrahydrate by controlled diffusion in silica gels has been narrated. In the field of material science, there is always a keen and competitive race to grow perfect single crystals with sufficient purity and perfection. Successful attempts to larger as well as more perfect crystals of SrTr are described in this paper and thus probably the largest (about 2 in. across) ever grown size of gel-grown products is reported here. The effect of several parameters, e.g. crystallization apparatus, environmental temperature, reactant concentration, gel density, gel-ageing and gel pH, on the size, quality and morphology of the crystals has also been studied.     

Growth features of ammonium hydrogen<Emphasis Type="Italic">d</Emphasis>-tartrate single crystals

Ammonium hydrogend-tartrate (d-AHT) single crystals were grown in silica gel. The growth features of these crystals with variation of parameters like specific gravity of the gel, gel pH, acid concentrations, concentration of the feed solution and gel age were studied in detail.     

In vitro studies on crystallization of SeMHP and strategies for nucleation reduction

Naturally many types of crystals grow in our human body. Especially different crystals or minerals are deposited in human urinary tracts. These crystals are named as octacalcium phosphate (OCP), calcium hydrogen phosphate (CHP), hydroxyapatite (HAP), magnesium hydrogen phosphate (MHP) etc. The SeMg-HPO₄ crystals are also known as Selenio-Newberryite crystals. The main reasons for the formation of crystals are due to the increased concentration of magnesium and phosphate ions in the human urine. In the present study, SeMHP crystals are grown in silica gel medium at various concentrations and different pH values in sun light medium and laser exposed medium. It has been observed that the nucleation rate was partially and completely reduced in sunlight and laser exposed medium, respectively. During the growth period, Liesegang rings were observed. Characteristic studies of SeMHP crystals such as FTIR, AAS, SEM, XRD, TGA/DTA and etching were done. The results are compared with the reported values and discussed in detail.     

Formation mechanism of zirconia nano-particles containing pores prepared via sol–gel-hydrothermal method

Zirconia single crystal nano-particles containing pores were prepared by a sol–gel-hydrothermal method. The unique character of the particles is that some irregular pores are embedded within the single crystals. The results of XRD, TEM and FT-IR show that the gaseous hydrolysates of the superstoichiometric urotropine are the origin of the pores. The gel structure and the hydrothermal treatment are the required conditions resulting in the pores in crystals. The formation mechanism was proposed: zirconia gel was formed after the reaction of ZrOCl₂ with urotropine. The superstoichiometric urotropine was dissolved and distributed uniformly in the gel. The small pores were generated because gaseous hydrolysates of urotropine were constrained in the gel during the hydrothermal treatment. During the process of the amorphous gel transferred into the crystals, some of the pores coarsened with the crystals growth. Big pores disappeared due to the break of the crystals. And only the small pores were remained in the interior of crystals, which could hardly be eliminated by the subsequent crystal growth if the calcination temperature is below 550 °C. Thus, the zirconia nano-particles containing pores were generated.     

Growth of single crystals of bismuth sulpho chloride in gel

Single crystals of the sparingly soluble compound, BiSCl have been grown in sodium silicate gel using straight tube and U-tube methods. Thiourea and bismuth trioxide dissolved in 10 N HCl are used as the reactants. The optimum conditions for growth of this crystal have been determined by studying the effect of the concentrations of the inner and outer reactants and that of the gel density. Single crystals of BiSCl upto 10 mm in size have been grown in a period of 20 to 25 days. The crystals grown have been identified as BiSCl by X-ray diffraction analysis.     

Growth and study of mixed crystals of Ca-Cd iodate

Mixed crystals of calcium-cadmium iodate were grown by a simple gel technique using diffusion method. The optimum conditions were established by varying various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of reactants etc. Crystals having different morphologies and habits were obtained. Prismatic, dendritic crystals of calcium-cadmium iodate and prismatic needle shaped, hopper crystals of mixed iodate were obtained. Some of them were transparent, some transluscent and a few others were opaque. The crystals were characterized using FT-IR, EDAX, XRD, TGA and DTA.     

Thermal,FT-IR and dielectric studies of gel grown sodium oxalate single crystals

Oxalic acid metabolism is important in humans, animals and plants. The effect of oxalic acid sodium salt is widely studied in living body. The growth of sodium oxalate single crystals by gel growth is reported, which can be used to mimic the growth of crystals in vivo. The grown single crystals are colourless, transparent and prismatic. The crystals have been characterized by thermogravimetric analysis, FT-IR spectroscopy and dielectric response at various frequencies of applied field. The crystals become anhydrous at 129·3°C. Coats and Redfern relation is applied to evaluate the kinetic and thermodynamic parameters of dehydration. The dielectric study suggests very less variation of dielectric constant with frequency of applied field in the range of 1 kHz-1 MHz. The nature of variation of imaginary part of complex permittivity, dielectric loss and a.c. resistivity with applied frequency has been reported.     

Growth of BaMoO4 and BaCO3 crystals in silica gel media

Barium molybdate, BaMoO₄, and barium carbonate, BaCO₃, crystals have been grown in sodium metasilicate gels. The influence of concentration of reactant solutions and pH of gels on the nucleation and growth, and on the penetration depth of the growth front of BaMoO₄ crystals in the test tubes were primarily studied. Combinations of pH 6 gel mixture with the 0.4 m and 0.6 m supernatant BaCl₂ and Na₂MoO₄ solutions resulted in the best size of crystals, inter-crystalline separation and clarity of the gel media. Two best test tube experimental combinations of hybrid growth were repeated in the U-shaped glass tubes to obtain further information. Depending on the growth sites in the tubes, different morphologies of the crystals were observed. The bulk morphologies of these crystals were studied by scanning electron microscopy. Growth of BaCO₃ crystals was performed only as exploratory work in the test tubes.At Universidad Central de Venzuela only.     

Growth of single crystals of some complex salts in silica gels

Single crystals of ammonium nickel sulphate, potassium nickel sulphate, ammonium alum and potassium alum are grown in sodium-metasilicate gels. The method of gel preparation and growth procedure are described. Both single diffusion and double diffusion methods are used. Studies on nucleation and characterisation of crystals are also reported. Crystals grown are illustrated.     

Study of gel grown mixed crystals of Ba<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>(IO<Subscript>3</Subscript>)<Subscript>4</Subscript>

The growth of mixed crystals of Ba _x Ca_1−x (IO₃)₄ were carried out with simple gel method. The effect of various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of reactants on the growth was studied. Crystals having different morphologies and habits were obtained. The grown crystals were characterized by XRD, FT-IR, EDAX, TGA, DTA and DSC.     

Growth and study of some gel grown group II single crystals of iodate

Single crystals of calcium iodate and barium iodate were grown by simple gel technique by single diffusion method. The optimum conditions were established by varying various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of the reactants etc. Crystals having different morphologies and habits were obtained. Prismatic, dendritic crystals of barium iodate and prismatic, needle shaped, hopper crystals of calcium iodate were obtained. Some of them were transparent, some transluscent, and few others were opaque. Both the crystals were studied using XRD, FT-IR, and thermal analysis. The crystals were doped by iron impurity. The effect of doping was studied using IR spectroscopy and thermal analysis.