Composition, structure, and properties of iron-rich nontronites of different origins

The composition, structure, and properties of smectites of different origins have been studied by X-ray diffraction, IR spectroscopy, scanning electron microscopy, and microprobe analysis. The results showed that nontronites of different origins differ in composition, properties, morphology, and IR spectroscopic characteristics. Depending on the degree of structural order and the negative charge of iron-silicate layers in nontronites, the shift of the 001 reflection to smaller angles as a result of impregnation with ethylene glycol (this shift is characteristic of the smectite group) occurs differently. The calculated values of the parameter b (from 9.11 to 9.14Å) are valid for the extreme terms of dioctahedral smectite representatives: nontronites.     

Development and properties of a glass made from MSWI bottom ash

A uniform shiny black-coloured glass was obtained using bottom ash produced by a Portuguese municipal solid waste incinerator (MSWI). The bottom ash was the single batch material used in the formation of the glass, which was obtained by vitrification of the solid waste at 1400 °C for 2 h. Under these conditions, a homogeneous melt with an appropriate viscosity to be shaped was obtained, indicating the suitability of this waste material to be employed in the development of vitreous products. The characterization of the resulting glass was performed in order to assess its structural, physical, mechanical, thermal and chemical features. The glass had a density of 2.69 g cm⁻³, a hardness of 5.5 GPa, a fracture strength of 75 MPa, a thermal expansion coefficient of 9.5 × 10⁻⁶ °C⁻¹ and it exhibited a very good chemical stability. In summary, the MSWI bottom ash glass has good mechanical and chemical properties and may, therefore, be used in several applications, particularly as a construction material.     

Crystallochemical characteristics of alkali calcium silicates from charoitites

The characteristic features of the crystal structures of alkali calcium silicates from various deposits are considered. The structures of these minerals, which were established by single-crystal X-ray diffraction methods, are described as the combinations of large construction modules, including the alternating layers of alkali cations and tubular silicate radicals (in canasite, frankamenite, miserite, and agrellite) and bent ribbons linked through hydrogen bonds in the layers (in tinaksite and tokkoite). The incorporation of impurities and the different ways of ordering them have different effects on the structures of these minerals and give rise to the formation of superstructures accompanied by a change of the space group (frankamenite-canasite), leading, in turn, to different mutual arrangements of the layers of silicate tubes and the formation of pseudopolytypes (agrellites), structure deformation, and changes in the unit-cell parameters (tinaksite-tokkoite).     

Kinetic characteristics of the crystallization from model solutions of blood plasma

Crystallography Reports - The kinetic regularities of crystallization (growth order and constants) in a model solution of blood plasma have been investigated. The particular order and...     

Influence of deposition conditions for bottom cell on micromorph tandem device performance

We have realized micromorph tandem solar cells on Asahi U-type TCO-covered glass substrates. The intrinsic layers of both amorphous top cell and microcrystalline bottom cell are grown by very high frequency plasma enhanced chemical vapour deposition (VHF-PECVD) at 100 MHz at low substrate temperature (150 °C). For the bottom cell different growth regimes have been explored by changing both chamber pressure and plasma power. The effect of the structural composition of the microcrystalline absorber layer on the electrical parameters of the device has been investigated. High short circuit current density and constant FF in a wide silane concentration range are obtained when using large power to pressure ratio (0.5 W/Pa). However, low open circuit voltage is generally found in this regime. The largest V_OC values are found at 67 Pa and power to pressure ratio of 0.3 W/Pa, where the highest efficiency (11.1%) is reached. An evaluation of device stability has been done by exposing the tandem solar cells to white light (AM 1.5-like spectrum) for 200 h.     

Flow characteristics and spinnability of sols prepared from silicon alkoxide solution

Structural evolution of the solution of tetraethoxysilane hydrolyzed with [H₂O]/[Si(OC₂H₅)₄] = 2 under acidic condition has been investigated by rheological measurements. It was found that the solution behaves as a Newtonian liquid up to a highly viscous state and shows spinnability before gelation when the evaporation of the solvent is allowed during gelation reaction. On the other hand, the solution behaved as a non-Newtonian liquid in the viscous state, showing no spinnability when the evaporation of the solvent was not allowed during the reaction. It was indicated from the Casson plots that the spinnable solution prepared in the open system has no yield stress up to highly viscous states, whereas the non-spinnable solution prepared in the closed system has a yield stress at viscous states. It was proposed that the increase in viscosity of the open system solution is attributable to the concentration of the sol particles whereas that of the closed system solution is attributable to the formation of the three dimensional network in the solution.     

Rapid growth of KDP crystals in the coniform bottom device and their characterization

The coniform bottom device was designed and used in the rapid growth process of KDP crystal. A seed support rack was also designed to be used in rapid growth of KDP crystal to avoid spontaneous nucleation on the interface of seed crystal and rack. The KDP crystals were fast grown at the growth rate of up to 25 mm/day. The optical scatter centers in KDP crystals were observed and their transmissions of different parts were measured. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mass fractal characteristics of sonogels prepared from sonohydrolysis of tetraethoxysilane with additions of dimethylformamide

Wet silica gels with ∼1.4 × 10⁻³ mol SiO₂/cm³ and ∼90 vol.% liquid phase were prepared from the sonohydrolysis of tetraethoxysilane (TEOS) with different additions of dimethylformamide (DMF). Aerogels were obtained by CO₂ supercritical extraction. The samples were studied mainly by small-angle X-ray scattering (SAXS) and nitrogen adsorption. Wet gels exhibit a mass fractal structure with fractal dimension D increasing from 2.23 to 2.35 and characteristic length ξ decreasing from ∼9.4 nm to ∼5.1 nm, as the DMF/TEOS molar ratio is increased from 0 to 4. The supercritical process apparently eliminates some porosity, shortening the fractality domain in the mesopore region and developing an apparent surface/mass fractal (with correlated mass fractal dimension D_m ∼ 2.6 and surface fractal dimension D_s ∼ 2.3) in the micropore region. The fundamental role of the DMF addition on the structure of the aerogels is to diminish the porosity and the pore mean size, without, however, modify substantially the specific surface area and the average size of the silica particle of the solid network.     

Structural characteristics of multicomponent GaAs-InxGa1-x As system from double-crystal X-ray diffractometry data

The article continues a series of publications on the technologically important multilayer In_xGa_1-x As-GaAs/GaAs system with the 3-, 6-, and 9 nm-thick layers (quantum wells). The collimation system of the incident beam is improved. The dimensions of quantum wells and the interfaces between these wells are determined. The qualitative picture of quantum well “spreading” is described. The experimental diffraction reflection curves are measured from three different parts of the specimen. Their analysis shows how homogeneous the structure grown is.     

The effect of crucible bottom deformation on the quality of Nd:GGG crystals grown by Czochralski method

In this paper, we report the growth of neodymium doped Gadolinium Gallium Garnet (Nd: GGG) crystal using Czochralski (CZ) method, and study the effects of crucible bottom deformation and thermal insulator thickness on the growth process and crystal quality. Garnet structure and <111> crystallography orientation of the crystal were confirmed by the X‐Ray diffraction (XRD) analysis. Macroscopic defects, residual stresses, quality, and homogeneity of the crystals were investigated by means of parallel plane polariscope and laser fizeau interferometer respectively and the results compared together. Experimental observations show that the crucible bottom deformation from flat to convex, and decreasing the thickness of zirconia insulator under the crucible result in the formation of lateral cores and increasing the crystal inhomogeneity and tensions, leading to the decrease of the crystal quality. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transient analysis of the cooling process and influence of bottom insulation on the stress in the multicrystalline silicon ingot

Directional solidification is one of the most popular techniques for massive production of multicrystalline silicon. After growth and annealing, the ingot is cooled down by a designed cooling process, which is initialized by descending bottom insulation, and then is controlled both by power ramp‐down rate and by motion of the bottom insulation. Thermal stress is piled up during cooling, and associated crystal defects, such as dislocation and micro‐cracks, may generate and propagate in the ingot. In the paper, transient modeling is applied to study the effect of bottom insulation on the cooling process. Temperature, velocity and thermal stress fields are obtained with linear, parabolic and sinusoidal motions of the insulation. The measured and predicted temperatures at two points of the ingot are found consistent. Distributions of von Mises stress in the ingot at different cooling time are obtained, and the maximum von Mises stresses are presented as a function of the cooling time. Specifically, dislocation‐free regions, evaluated by the critical resolved shear stress model, at certain cooling time, and area fractions of the regions as a function of the cooling time are proposed. The linear motion is further discussed with different moving rates, considering its wide applications in the current industry and convenient realization in control.     

Characterization of interface states at Ni/n-Si Schottky barriers from I – V characteristics

Experiments were performed on Ni/n-Si(111) Schottky diodes fabricated by the thermal vacuum deposition of nickel on n/n⁺ Si epitaxial wafer at ˜ 10⁻⁵ torr pressure. The non-equilibrium occupation functions of the interface states were studied using the Shockley-Read-Hall (SRH) theory and considering the charge exchange between metal and interface states. Interface states density was determined from (I - V) characteristics using metal-interfacial layer-semiconductor (MIS) structure. The density was found to be in the range of 10¹² eV⁻¹ cm⁻² with a broad peak in the band gap of Si at about 0.554 eV below the conduction band edge.     

Textural and adsorption characteristics of carbon xerogel adsorbents for removal of Cu (II) ions from aqueous solution

Resorcinol–formaldehyde (RF) carbon xerogels were synthesized using different resorcinol/sodium carbonate catalyst molar ratios (R/C = 50, 200, 500 and 1000) and heat treatment temperatures (HTT = 500, 600 and 700) under no external gas flow. The carbon adsorbents were extensively characterized by CHO content, FTIR, TEM and nitrogen adsorption isotherm at 77 K. The effect of R/C, HTT and oxygen content on the development of porosity within carbons was studied. Also, the adsorption capacity of these adsorbents was investigated by the removal of copper (II) ions from aqueous solution using single bottle test. The produced carbon xerogels exhibit a micro-mesopore character, but with different extents depending on the mechanism of porosity generation in relation to R/C, HTT and oxygen functional groups. Results show that the optimum conditions to obtain porous carbon xerogels were the highest R/C = 500–1000 in combination with carbonization preferably at 600 or 700 °C. Single bottle removal of Cu (II) ions indicated the developed carbons with appreciable capacity (q_u = 32–130 mg/g) which are controlled by the surface area and surface chemical nature (acidic O-functional groups). Finally, the present investigation provides a new, nanoporous type of porous carbon adsorbents with high adsorption capacity for removal of heavy metals from wastewater media.     

Polarisation characteristics of visible VCSELs

Vertical cavity surface emitting lasers (VCSELs) based on InGaP lase in the visible close to 650 nm. The polarisation characteristics of these devices are unlike other VCSELs in that they are stable and reproducible and show no switching with increased current. We describe the polarisation characteristics for such devices where the structures were grown on different orientation wafers. We show that polarisation selectivity increases directly with the degree of spontaneous ordering in the InGaP quantum wells, but not with the wafer offset angle.     

Influence of the crucible bottom shape on the heat transport and fluid flow during the seeding process of oxide Czochralski crystal growth

For the seeding process of oxide Czochralski crystal growth, influence of the crucible bottom shape on the heat generation, temperature and flow field of the system and the seed‐melt interface shape have been studied numerically using the finite element method. The configuration usually used in a real Czochralski crystal growth process consists of a crucible, active afterheater, induction coil with two parts, insulation, melt, gas and seed crystal. At first, the volumetric distribution of heat inside the metal crucible and afterheater inducted by the RF‐coil was calculated. Using this heat generation in the crucible wall as a source the fluid flow and temperature field of the entire system as well as the seed‐melt interface shape were determined. We have considered two cases, flat and rounded crucible bottom shape. It was observed that using a crucible with a rounded bottom has several advantages such as: (i) The position of the heat generation maximum at the crucible side wall moves upwards, compared to the flat bottom shape. (ii) The location of the temperature maximum at the crucible side wall rises and as a result the temperature gradient along the melt surface increases. (iii) The streamlines of the melt flow are parallel to the crucible bottom and have a curved shape which is similar to the rounded bottom shape. These important features lead to increasing thermal convection in the system and influence the velocity field in the melt and gas domain which help preventing some serious growth problems such as spiral growth. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical characteristics of float glass surfaces

The regions near the top and bottom surfaces of float glass are chemically different from the bulk glass composition. In addition to the presence of tin oxide at the bottom surface and to a lesser extent at the top surface, differences are found in SiO₂, Na₂O, CaO, SO₃ and Fe₂O₃. The concentrations of Na₂O, CaO and SO₃ are lower at the top surface than in the bulk glass, while SiO₂ is higher. In the case of tin at the bottom surface and iron at both top and bottom surfaces, the components exist in complex concentration gradients. In addition, there are variations in oxidation state for tin, iron and sulfur. Tin appears to exist in both stannous and stannic states near the bottom surface. So far it has been found that iron at the top surface and sulfur at the bottom are largely in reduced states. Some consequences of these effects have been observed in physical and chemical behavior of the surface.     

Thermodynamic characteristics of Ti-based glass-forming alloys

Based on thermodynamic characteristics of the stable metallic liquid at melting temperature and the supercooled liquid, the present work calculated the mixing enthalpy ΔH^mix, the mixing entropy ΔS^mix and the Gibbs free energy difference between the supercooled liquid and the resulting crystalline phases ΔG of typical Ti-based amorphous alloys. The results show that for the case of larger ΔS^mix, moderate ΔH^mix for the stable liquid and smaller ΔG for the supercooled liquid, Ti-based alloys tend to achieve high glass-forming ability (GFA). A new parameter, β, defined as (T_g ? T_k)/(T_l ? T_g), has been introduced to evaluate the GFA of Ti-based bulk amorphous alloys (wherein T_g, T_l, and T_k represent the glass transition temperature, the liquidus temperature, and the Kauzmann temperature, respectively). Experimental data imply that the larger the β, the better the GFA for Ti-based amorphous alloys.     

Composition and morphological characteristics of sialoliths

Sialolithiasis refers to pathological minerilazation in the salivary glands and ducts. Aiming to a better understanding of the formation phenomena, structural and morphological analysis of a relatively large ensemble of sialoliths extracted from 22 patients via sielendoscopy was performed. Characterization methods, including Fourier Transform Infrared (FTIR) Spectroscopy, X‐Ray Diffraction, Raman spectroscopy and Scanning Electron Microscopy (SEM), showed that the large majority of 90% of sialoliths were composed of carbonate apatite as the inorganic phase, while SEM imaging revealed the presence of bacteria in 13 cases. Furthermore, carbonate apatite crystals in the form of parallel or randomly oriented sheets were observed and in some cases rhombohedral calcite‐type nanocrystals were detected. The present findings may contribute to a better understanding of the formation mechanisms in vivo and and contribute to the treatment of sialolithiasis.     

Structure characteristics of disordered zirconium hydroxoxides

The structural characteristics of low-temperature zirconium hydroxoxide and zirconium dioxide obtained from zirconyl nitrate and treated at 383 and 653 K have been studied by the X-ray method of distribution of radial electron density. It is shown that the low-temperature hydroxide contains a ～10 to 15-Å nucleus of the crystalline phase with a structure of short-range order similar to the short-range order in ZrO₂. An increase in treatment temperature of zirconium hydroxide results in the formation of a mixture of cubic and monoclinic zirconium dioxide with a particle size of ～60 Å.     

MOMBE growth characteristics of antimonide compounds

This paper describes the MOMBE (metalorganic molecular beam epitaxy) growth characteristics of antimonide compounds using TMIn (trimethylindium), TEGa (triethylgallium) and TIBAl (triisobutylaluminium) as group III sources, and As₄, Sb₄, TEAs (triethylarsine) and TESb (triethylstibine) as group V sources. Large differences in the growth characteristics of GaAs and GaSb MOMBE are observed. These are explained, using a theoretical consideration of the growth mechanism, by the difference in the effective surface coverage of excess As and Sb atoms during the growth. The use of TEAs and TESb instead of As₄ and Sb₄ alters the growth rate variation of both GaAs and GaSb with substrate temperature (T_sub), which results from the interaction of alkyl Ga species with the alkyl radicals coming from the thermally cracked TEAs and TESb. The alkyl exchange reaction process is observed in the growth of AlGaSb using TIBAl and TEGa, where the incorporation rate of Al is suppressed by the coexistence of TEGa on the growth surface, in the low T_sub region. This is caused by the formation of an ethyl-Al bond which is stronger than the isobutyl-Al bond. The composition and the growth rate variations of InGaSb with T_sub are similar to those of InGaAs, which are closely related to the MOMBE growth process and are quite different from those of MBE (molecular beam epitaxy) and MOVPE (metalorganic vapor phase epitaxy) growth. In the MOMBE growth of InAsSb and GaAsSb using TEAs and TESb, the composition variation with T_sub is weaker than that of MBE. This is a superior point of MOMBE growth for the composition control. The electrical and optical properties of MOMBE grown films as well as the quantum well structures are also described.