Growth and characterization of calcium hydrogen phosphate dihydrate crystals from single diffusion gel technique

Calcium hydrogen phosphate dihydrate (CaHPO₄·2H₂O, CHPD) a dissolved mineral in urine is known to cause renal or bladder stones in both human and animals. Growth of CHPD or brushite using sodium metasilicate gel techniques followed by light and polarizing microscopic studies revealed its structural and morphological details. Crystal identity by powder x‐ray diffraction confirmed the FT‐IR and FT‐Raman spectroscopic techniques as alternate methods for fast analysis of brushite crystals which could form as one type of renal stones. P‐O‐P asymmetric stretchings in both FT‐IR (987.2, 874.1 and 792 cm^‐1) and FT‐Raman (986.3 cm^‐1, 1057.6 cm^‐1 and 875.2 cm^‐1) were found as characteristics of brushite crystals. Differential Scanning Calorimetry (DSC) analysis revealed brushite crystallization purity using gel method by studying their endothermic peaks. This study incorporated a multidisciplinary approach in characterizing CHPD crystals grown in vitro to help formulate prevention or dissolution strategy in controlling urinary stone growth. Initial studies with 0.2 M citric acid ions as controlling agent in the nucleation of brushite crystals further support the presented approach. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of Struvite‐K crystals

Struvite‐K is the natural potassium equivalent to Struvite. Struvite‐K crystals were grown by single diffusion gel growth technique in silica hydro gel medium. Struvite‐K crystals with different morphologies having transparent to translucent diaphaneity were grown with different growth parameters. The phenomenon of Liesegang rings was also observed with some particular growth parameters. The crystals were characterized by powder XRD, FT‐IR, TGA and dielectric study. The powder XRD results of Struvite‐K confirmed the orthorhombic crystal structure. The FT‐IR spectrum proved the presence of water of hydration, metal – oxygen bond and P – O bond. The TGA, DSC and DTA were carried out simultaneously. It was found that crystals started dehydrating and decomposing from 75 °C and finally at 600 °C temperature it became 64.14% of the original weight and remained almost constant up to the end of analysis. From the thermo‐gravimetry, the numbers of the water molecules associated with the crystal were calculated and found to be 5. The kinetic and thermodynamic parameters of dehydration / decomposition process were calculated. The variation of dielectric constant with frequency of applied field was studied in the range from 400 Hz to 100 kHz, which exhibited the decreasing nature of the dielectric constant as frequency increased. The dielectric study showed that a.c. conductivity increased and consequently the a.c. resistivity decreased with the increase in frequency. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Understanding the growth mechanism of CuI crystals during gel growth experiments

Cuprous iodide crystals have been grown with decomplexation method in silica gel. Various crystal morphologies, such as polycrystalline aggregate, skeletal, dendrite, hopper crystals and regular tetrahedron crystals, were observed in different growth regions with an optical microscope. Their surfaces were photographed using a binocular metallographic microscope and the results were explained with the crystal growth mechanism which was determined by supersaturation. These observations support the general hypothesis that the concentration of reactant affects the relative growth rate by controlling the nucleation and diffusion. The mutual influence of the crystals grown in different regions was also discussed. Additionally, the suitable condition for getting regular tetrahedron crystals or large hopper crystals was obtained by changing the concentration of CuI·HI complex in the later period of crystal growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of Potassium Sulphate Crystals by Silica Gel Technique

Single and transparent crystals of potassium sulphate up to 30 × 3 × 3 mm in size have been grown by silica gel technique, using various methods (two-layers three-layers and hybrid gel technique) which are described. The effects of the three differents alcohols (used as top solutions) upon the quality and nucleation of crystals are also reported. The “growth and equilibrium” morphologies and microstructures of the habit faces are discussed.     

Investigation of growth kinetics and morphology of sodium fluorosilicate ice‐analogue crystals in solutions and gels

The effect of growth method (solution or gel growth) and growth conditions on the morphology of ice analogue crystals (sodium fluorosilicate) has been studied. Many habits typical for atmospheric ice crystals (hexagonal columns, plates, different types of stars or dendrites) were obtained during experiments. The dependence of growth rate of basal and prism faces of columnar crystals on supersaturation was measured for crystals growing by evaporation of solvent. The experiments establish evaporation rate and growth rate ranges at which appearance of certain types of crystals is most probable. The experiments have also shown that good quality sodium fluorosilicate crystals can be obtained in TMS gel. These crystals were significantly bigger than those obtained in solution. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An electrolytic method to grow copper dendrites and single crystals in gels

A new electrolytic method for the growth of any metallic crystal in gel by using gel as a medium for controlled growth, is reported. Different types of large dendrites and single crystals of copper were grown by electrolytic method in the gel medium. It is found that pH of the gel medium, the concentration of the supernatant solution, the current density and the electrode material used, have considerable influence on the habits of the dendrites and the single crystals thus grown. The surface features and morphology of crystals and dendrites were studied by optical and scanning electron microscopy. Compared to other conventional electrolytic growth techniques, the present method has a number of additional parameters that can be varied, and hence a more effective controlled growth of crystals is possible.     

Growth aspects of barium oxalate monohydrate single crystals in gel medium

Single crystals of barium oxalate monohydrate (BaC₂O₄.H₂O, BOM) were grown in pure form by controlled diffusion of Ba²⁺ using the gel technique at different temperatures. Starting from aqueous Ba²⁺ chloride (BaCl₂) and acetic acid (C₂H₂O₄) in gel, this method offers a low‐cost and an easiest alternative to other preparation methods for the production of barium oxalate bulky single crystals. The optimal conditions for the growth of BOM crystals in silica gel were found by investigating different growth parameters such as gel pH, gel aging and crystallization temperature. Irrespective of all such crystallization environments, growth rate of the crystals were initially less and then exhibited supersaturation effect leading to non‐linearity. Gel aging and temperature has profound effect on nucleation density that resulted less number of crystals of maximum size in the gel matrix. Perfect single crystals were grown on gels of higher pH. The macropore morphology and porosity was controlled by changing age of the gel. It has been found that temperature has a fabulous effect in controlling the nucleation density by altering the supersaturation conditions for the formation of critical nuclei. The entire growth kinetics informed that the grown crystals were derived by the one dimensional diffusion controlled process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A detailed study of gold single crystal growth in a silica gel

Gold single microcrystals have been fabricated by electrochemical growth in a silica gel. Structural characterization of the single crystals by backscatter electron diffraction showed a preferred orientation of Au (1 1 1) and a minor orientation of Au (1 0 0). In addition, the influence of additives on the nucleation and growth of gold microcrystals has been studied. It was found that the inclusion of chemical additives in the growth solutions altered the characteristics of the gold crystals. Possible mechanisms for nucleation and growth of these crystals are discussed.     

Effect of different solvents on the habit of meta‐nitroaniline single crystals

The habit of the organic non‐linear optical material meta‐nitroaniline (mNA) crystallized from different organic solvents such as acetone, benzene, ethyl acetate, n‐hexane, methanol and toluene were studied. Solubility of mNA in these solvents at various temperatures in the range between 288 and 323 K was determined by gravimetric method. Crystals were grown by restricted evaporation of solvents method. Solutions with different solvents having different chemical nature and polarity yielded crystals with different habits: one‐dimensional needles, two‐dimensional rhombic platelets and three‐dimensional octahedral. In addition, the mNA crystals show unidirectional growth behaviour along its polar [001] direction irrespective of the solvents used. All the grown crystals were found to be orthorhombic system with point group mm2 and space group Pbc2₁ which was confirmed by powder X‐ray diffraction study. Optical transmittance study showed that the grown mNA single crystals have optical transparency in the wavelength range between 430 and 1550 nm. SHG efficiency of the grown mNA crystal was 3 times grater than KDP. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization and Characterization of Calcium Phosphates: Brushite and Monetite

Spherulitic monetite (CaHPO₄) and brushite (CaHPO₄ · H₂O) of different morphologies which have close resemblance to those found in pathological joints, stones and dental calculi were crystallized in silica gel under acidic conditions. These crystals were characterized by x-ray powder diffraction, fourier transform infra-red, and thermogravimetric analyses. The molar ratios (Ca/P) were calculated from ICP analysis and found to be in agreement with the theoretical stoichiometric molar ratio. The microstructure of the spherulitic monetite crystals have been studied using scanning electron microscopy.     

Amorphous phase separation and crystallization in a lithium silicate glass prepared by the sol-gel method

A 10Li₂O---90SiO₂ (mol%) gel-glass has been prepared by using tetramethyl orthosilicate and lithium iso-propoxide as starting materials. The phase separation and crystallization behaviour was compared with the corresponding conventionally melted glass using DTA, X-ray diffraction and TEM. The same crystallization phase was found in both the gel glass and melted glass upon heating above 650°C. However, the rate of crystallization in the gel-glass was higher than in the melted glass. TEM revealed amorphous phase separation in the gel glass and melted glass. However, the morphologies were different, an interconnected microstructure being observed in the gel glass and a droplet structure in the melted glass. These differences can be partly attributed to differences in OH content. Other potential influencing factors are also considered. After 650°C for 2 h lithium disilicate crystals were observed in the volume of the gel glass by TEM. As the crystals grew they absorbed Li₂O from the surrounding lithia-rich amorphous phase so that silica-rich (lithia depleted) diffusion zones formed around them.     

Reducing Inversion Twinning in Single Crystal Growth of GaPO4

Gallium orthophosphate (GaPO₄) single crystals were grown by the reverse temperature gradient method from phosphoric acid solutions under hydrothermal conditions. Twins after (110) were studied by etching faces having been cut perpendicular to one of the twofold axes. Based on the determination of the twin boundary position as well as on the knowledge of the growth rates of different crystallographic forms, a few faces have been chosen to be quite promising for growing high‐quality GaPO₄ single crystals if they are offered at the referring seed crystal. From the characterization of the grown crystals conditions have been found, which may lead to the reduction of the inversion twin number during the growth process.     

In situ atomic force microscopy studies of surface morphology,growth kinetics,defect structure and dissolution in macromolecular crystallization

Surface morphologies of thaumatin, catalase, lysozyme and xylanase crystals were investigated using in situ atomic force microscopy. For thaumatin, lysozyme and xylanase crystals, growth steps having a height equal to the unit cell parameter were produced both by screw dislocations and two-dimensional nuclei. Growth of catalase crystals proceeded in alternating patterns exclusively by two-dimensional nucleation and the successive deposition of distinctive growth layers, each having a step height equal to half the unit cell parameter. The shapes of islands on successive layers were related by 2-fold rotation axes along the 〈0 0 1〉 direction. Experiments revealed that step bunching on crystalline surfaces occurred either due to two- or three-dimensional nucleation on the terraces of vicinal slopes or as a result of uneven step generation by complex dislocation sources. Growth kinetics for thaumatin and catalase crystals were investigated over wide supersaturation ranges. Strong directional kinetic anisotropy in the tangential step growth rates in different directions was seen. From the supersaturation dependencies of tangential step rates and the rates of two-dimensional nucleation, the kinetic coefficients of the steps and the surface free energy of the step edge were calculated. Adsorption of impurities which formed filaments on the surfaces of catalase and thaumatin crystals was recorded. Cessation of growth of xylanase and lysozyme crystals was also observed and appeared to be a consequence of the formation of dense impurity adsorption layers. Crystal growth resumed upon scarring of the impurity adsorption layer and clearing of the crystal surface with the AFM tip. Adsorption of three-dimensional clusters, which consequently developed into either properly aligned multilayer stacks or misaligned microcrystals was recorded. For catalase crystals, incorporation of misoriented microcrystals as large as 50×3×0.1 μm³ produced elastic deformations in growth layers of ≈0.6%, but did not result in the defect formation. Etching experiments on catalase crystals revealed high defect densities.     

Growth and characterization of 4‐(2‐hydroxyphenylamino)‐pent‐3‐en‐2‐one single crystals

4‐(2‐hydroxyphenylamino)‐pent‐3‐en‐2‐one (HPAP) was synthesized and single crystals were grown by the solution growth technique using methanol as a solvent. The crystals having orthorhombic symmetry were characterized by single crystal XRD, FTIR spectroscopy, NMR spectroscopy, TGA, DSC and dielectric studies. Very less variation in the value of dielectric constant is found for different frequencies of applied field. The crystals were exhibiting positive photoconductivity and poor NLO responses. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Yb∶YAl3(BO3)4晶体形貌与生长速度的关系

观察测量了不同生长速度(相应于不同降温速度)自发成核生长的Yb∶YAl3(BO3)4晶体形貌。粒度较大(>2mm)的晶体不管降温速度快慢形态都很简单,只发育六方柱｛1120｝和菱面体｛1011｝;粒度较小(<2mm)的晶体形态随降温速度增快而变复杂,发育一些罕见的高指数晶面。说明在生长速度较快的条件下,在晶体生长早期,一些高能面发育,在晶体生长后期已尖灭了,晶体生长的大部分时间是在低能面｛1120｝和｛1011｝上进行的。对比了不同生长条件下晶面的粗糙度,随着降温速度的增快,六方柱面｛1120｝和菱面体面｛1011｝由光滑变粗糙,顶面｛0001｝永远是粗糙的。从晶体结构上定性地探讨了3种晶面的杰克逊因子α及生长机理     

Vapor phase growth of alumina whiskers by hydrolysis of aluminum fluoride

The vapor phase growth of alumina whiskers by the hydrolysis of aluminium flouride has been studied at an elevated temperature. The product was obtained in various forms: wool-like whiskers, needle-like whiskers, jointed needle-like crystals which consisted of linked small single crystals, tightly coagulated powder or as thin film covering the substrate. Aluminium oxi-fluoride was suggested as the intermediate gaseous species in the formation of alumina. The relation between the growth mechanism and crystal morphologies was studied.     

自发形核生长的AlN单晶湿法腐蚀研究

采用湿法腐蚀工艺,使用熔融态KOH和NaOH作为腐蚀剂,对一种物理气相传输(PVT)自发形核新工艺在2100~2250 ℃条件下生长的AlN单晶进行了腐蚀实验.通过实验及扫描电子显微镜(SEM)结果分析,得到了典型的AlN单晶c面、r系列面及m面最佳的腐蚀工艺参数及腐蚀形貌.另外,基于腐蚀形貌分析,发现了采用该自发形核新工艺生长的AlN晶体某些独特习性并计算出AlN单晶腐蚀坑密度(EPD).     

Preparation of calcium carbonate crystals in the presence of trisodium citrate

The dumbbell‐like calcium carbonate (CaCO₃) crystals were synthesized in the presence of trisodium citrate. Different morphologies were obtained by changing the reaction temperature and the trisodium citrate concentration. The obtained samples were characterized by means of X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the morphology of CaCO₃ crystals was markedly affected by the reaction temperature and citrate anion concentration. The possible growth mechanism of CaCO₃ crystals was proposed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Direct melt crystal growth of isotactic polybutene‐1 trigonal phase

The morphology, crystalline structure and crystal growth kinetics of melt‐crystallized thin isotactic polybutene‐1 films have been studied with transmission electron microscopy, electron diffraction and optical microscopy. It is demonstrated that a bypass of tetragonal phase crystallization and direct melt crystal growth of the trigonal phase can be achieved via self‐seeding at atmospheric pressure using solution‐grown trigonal crystals as nuclei. Electron microscopy and optical microscopy observations show that melt‐crystallized isotactic polybutene‐1 single crystals of the trigonal phase have rounded or hexagonal morphologies around 75°C. The growth rate of trigonal crystals in the melt has been obtained by in‐situ optical microscopy. The growth rate of trigonal crystals in the melt is 1/100 and 1/1000 that of tetragonal crystals in the melt around 70 and 90°C, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)