Structural studies of odd-nylon crystals grown from solution

Lamellar crystals of nylons 5, 9 and 13 in-structure were grown from solution and systematically studied by electron microscopy and X-rays. Electron diffraction showed that they all consist of a twinned structure with hydrogen bonds running parallel to the long dimension of the crystals. Polyethylene decoration of such crystals revealed folding sectorization only in the case of nylon 9. Diffraction data from films both uniaxially and biaxially oriented were used to propose a unifying model for the-structure of odd nylons based on the antiparallel model given by Tadokoro. In this model successive sheets are progressively sheared along the chain axis by approximately twice the interatomic height. Such a model is able to account well for most of the structural observations we have made on solution grown crystals.     

Growth and characterization of gel grown pure and mixed iron-manganese levo-tartrate crystals

Several applications of iron tartrate and manganese tartrate compounds are reported in the literature. In the present investigation, we have grown pure and mixed iron (II)-manganese levo-tartrate crystals by single diffusion gel growth technique. Crystals with spherulitic morphology were harvested. The colouration of the crystals changed from black to pinkish brown upon increasing the content of manganese in the crystals. The crystals were characterized by FTIR spectroscopy, powder XRD, TGA, VSM and dielectric study. Crystal structures of different mixed crystals were studied. From TGA it was observed that on heating the hydrated crystals became anhydrous and then converted into oxides. Paramagnetic nature of the crystals was revealed from VSM study. The variation of the dielectric constant with frequency was studied. The results are discussed.     

Structure of nylon 7 solution grown crystals

Single crystals of nylon 7 prepared by crystallization from glycerine were studied by both X-rays and electron microscopy. Electron diffraction proved that they consist of a twinned layered-structure with hydrogen bonds running parallel to their long dimension. Polyethylene decoration of such crystals showed that they are subdivided in folding domains so that both chain folding and hydrogen bonding take place along the same crystallographical planes.     

Growth of anthraquinone crystals by gel aided solution technique and their characterization

Anthraquinone, an oxidation product of anthracene, has been grown by gel aided solution technique employing sodium metasilicate. Needle shaped crystals were obtained in 0–5% (w/v) solution of anthraquinone for pH 5-5. The grown crystals were characterized by optical microscopy, SEM, IR, UV and XRD.     

Growth,characterization and dielectric property studies of gel grown barium succinate single crystals

. Single crystals of barium succinate (BaC4H4O4) were grown in silica gel medium using controlled chemical reaction method. Plate-like single crystals of size up to 3 × 2 × 0·2 mm³ was obtained. Single crystal X-ray diffraction (XRD) studies confirmed that structure of the title compound is tetragonal. Powder X-ray diffraction (PXRD) pattern of the grown crystal and the Fourier transform infrared (FT–IR) spectrum in the range 400–4000 cm^–1 are recorded. The vibrational bands corresponding to different functional groups are assigned. Thermal stability of the grown crystals is confirmed by differential scanning calorimetry (DSC). Dielectric constant and dielectric loss have been calculated and discussed as a function of frequency at different temperatures.     

Growth and characterization of AgTlSe crystals

Good quality single crystals of silver thallium selenide (AgT1Se) up to the size of 15 mm diameter and 15.0 cm length were grown from the melt by the Bridgman-Stockbarger technique. The purification of the source materials minimized the surface voids and compositional inhomogeneities, and enhanced the optical quality of the crystals. The effect of annealing on the optical transmittance was studied for a crystal of 6 mm thickness. Lattice parameters were also determined. The values are in good agreement with literature values for crystals with orthorhombic symmetry.     

Growth and micro-topographical studies of gel grown cholesterol crystals

Cholesterol (C₂₇H₄₆O) is the most abundant and best-known steroid in the animal kingdom. The in vitro crystallization of this important biomaterial has been attempted by few researchers. Here we are reporting crystallization of pure cholesterol monohydrate crystals in gel medium. It is found that the morphology of the crystals depends on various parameters. The effect of solvent has been studied in detail. The different morphologies observed are fibrous, needle, platelet, dendrite etc. Micro topographical studies have been made and it is found that the crystals grow, at least in the last stage, by spreading of layers. However, at initial stage microcrystals formed and developed into dendrite or needle forms. These one-dimensional crystals developed into platelets and finally thickened. Further studies reveal that micro impurities play a vital role in the development of these crystals as seen by dissolution figures on the crystals. These crystals are characterized by using the XRD and IR spectroscopic methods.     

Growth and characterization of hydrothermally-grown zeolite crystals

Studies on hydrothermal synthesis of zeolite crystals, in Na₂O-Al₂O₃-SiO₂-H₂O system, are reported. Experimental procedure and growth parameters are briefly described. Cube-like and rod-like crystals (called VSZ-1 and VSZ-2) are illustrated. It is established that VSZ-1 crystals are metastable, while VSZ-2 crystals are stable. Crystallanity of these two samples is established. Observations and results of characterization of these two varieties by TEM, SEM, electron microprobe and infrared methods are described, illustrated and interpreted. The role of Si/Al ratio is explained.     

Growth and characterization of III-N bulk crystals

Hexagonal BN crystals were grown from solution by application of a thermal gradient. The solvent used to dissolve the source was optimized by changing the ratio of components to have the lowest melting point. The investigation of adding a third component demonstrated further reduction of the melting point with BN as an additive. A solution was created with enhanced properties allowing the growth of BN. BN was grown on a PBN seed at T _g = 900 °C and P = 0.2 MPa for approximately 65 h. The BN crystals were found to be embedded in a solvent matrix, as determined by EDS. In addition, GaN crystals were grown in a modified solution at T _g = 800 °C and P = 0.2 MPa. Raman spectroscopy verified wurtzite GaN structure with good crystallinity. The successful growth of BN and GaN from solution suggests this to be a method of choice for growth of the III-Ns, and may prove to be a viable alternative to current costly wafer production techniques.     

Fibers and square sapphire shaped single crystals grown from the melt and optical characterization

The micro-pulling down technique has been used to grow fibers (? = 1 mm) and square (2 × 2 mm²) sapphire shaped single crystals with controlled sizes. The hot zone construction and fiber pulling conditions have been optimized. As a result, growth of transparent and homogeneous sapphire shaped crystals has been performed. The crystals have been grown under 1 bar of argon atmosphere with pulling rate varied in the range of 0.5–3 mm/min. 100% of the melt has been continually transformed into crystalline sapphire with empty crucible at the end of the growth operation. The as grown crystals show high chemical homogeneities and good optical properties.     

Growth and characterization of vacuum sublimed PbTe crystals

Abstract

PbTe crystals have been grown by a closed‐tube vacuum sublimation technique. Steps in the preparation of the crystals include (i) purification of the starting materials, (ii) synthesis and purification of the PbTe, and (iii) growth of PbTe crystals. This paper describes the optimum growth conditions and some investigations on the physical properties of the grown crystals.     

Growth of LiNaSO4 single crystals from a solution of stoichiometric pH value

Single crystals of LiNaSO₄ were grown without adjusting the pH value of equimolar aqueous solution containing Li₂SO₄·H₂O and NaHSO₄ at 30°C. As-grown crystals were characterized using X-ray, IR, Raman and other crystal perfection studies such as chemical etching, scanning electron micrograph and microhardness measurements. Atomic absorption technique was adopted to verify the composition of Li⁺ and Na⁺ ion content and these were found to be consistent with the desired composition to within ± 6 mol%.     

Growth and characterization of hydroxyapatite crystals by hydrothermal method

Hydroxyapatite crystals were grown by hydrothermal method using dicalcium phosphate dihydrate crystals as a starting material. The grown crystals were found to be free from carbonate inclusion. Two distinct morphologies were obtained by following two different growth methods. Controlled slow growth process and rapid growth process results in hexagonal and whisker like morphologies.     

Growth and characterization of nonlinear optical diglycinehydrobromide single crystals

Diglycinehydrobromide (DGHB) a semi-organic nonlinear optical material with the molecular formula C₄H₁₁N₂O₄⁺Br⁻ has been synthesized at ambient temperature. Chemical composition of the synthesized material was confirmed by CHN analysis. Functional groups present in the sample were identified by FT-IR and Raman spectral analysis. Bulk single crystals of DGHB were grown by slow evaporation method at constant temperature. Powder X-ray diffraction pattern of the grown DGHB has been indexed. Unit cell parameters of the grown DGHB crystals were determined. Thermal stability of DGHB was determined from TGA/DTA and DSC response curves. Mechanical hardness of the grown crystal DGHB was determined and Vickers hardness number was calculated. The optical transparency and the lower cutoff of UV transmission were identified from the recorded UV-vis-IR spectrum of DGHB. The Kurtz powder second harmonic generation test shows that the crystal is a potential candidate for optical second harmonic generation.     

Growth, characterization and optical quality of CaF2 single crystals grown by the temperature gradient technique

The CaF₂ single crystals with diameters up to 200 mm were successfully grown by modified temperature gradient technique (TGT), which are suitable for application as optical elements in the ultraviolet range. The optimizations of various growth parameters were systematically studied. Properties of as-grown CaF₂ crystals were characterized by the nature of inclusions, dislocations, crystallinity, and impurities contents. The results showed that the dislocations and multinucleation were mostly constrained in the conical part of the crystals with the cylindrical parts having the best crystalline quality and lowest impurity contents. The high optical quality of TGT-grown CaF₂ single crystals was also confirmed to have excellent optical transmission in 190-2500 nm and refractive index homogeneity.     

Controlled preparation of hollow zinc oxide microspheres from aqueous solution using hexamethylenetetramine and cysteine

Zinc oxide particles were synthesized by precipitation from an aqueous solution of zinc nitrate tetrahydrate, R-(+)-cysteine and hexamethylenetetramine (HMTA, urotropine). Hollow microspheres of ZnO-cysteine hybrid material with a diameter of ca. 1 μm and a wall thickness ca. 50 nm were obtained. After heating up to 850 °C pure ZnO microspheres of roughly the same size were formed. The particles were characterized by XRD, SEM, FT-IR and TGA.