Production of High Purity Metals: A Review on Zone Refining Process

Purification is a primary application of zone melting, in which the improvement of efficiency, production yield and minimum achievable impurity level are always the research focus due to the increasing demand for high purity metals. This paper has systematically outlined the whole development of related research on zone refining of metals including basic theories, variants of zone refining, parametric optimization, numerical models, and high purity analytical methods. The collection of this information could be of good value to improve the refining efficiency and the production of high purity metals by zone refining.

Structural and Optical Properties of Triglycine Sulfate Single Crystals Doped with Potassium Bromide

Triglycine sulfate crystal and potassium bromide doped triglycine sulfate crystals were grown from aqueous solution by slow evaporation method. Energy dispersive X-ray analysis identifies the elements present in the crystal. The Fourier Transform Infrared spectroscopy has been recorded in the range 400 to 4000 cm-1 and the functional groups of the grown crystals have been identified. The structural studies on the grown crystals were carried out by X-ray diffraction analysis technique and found that the grown crystal crystallizes in monoclinic structure. The lattice cell parameters of pure Triglycine sulfate are a = 9.6010 ?, b = 12.5600 ?, c = 5.4500 ?. Ultraviolet-Visible spectra show that the grown crystals have wide optical transparency in the entire visible region.

High Purity Germanium, a Review on Principle Theories and Technical Production Methodologies

Since the early 1950’s the use of Germanium has been continuously growing as new applications are being developed. Its first commercial usage as the main material, from which the semiconductors were made, was later replaced by Silicon. The applications were then shifted to a key component in fiber optics, infrared night vision devices and space solar cells, as well as a polymerization catalyst for polyethylene terephthalate (PET). With the advance development in new technologies, the attentions have been brought back to Germanium due to its excellent semiconductor properties. New applications on the field of high efficiency solar cells, SiGe based chips, LED technologies, etc., are being developed and show a great potential. According to DERA (Deutsche Rohstoffagentur/German Mineral Resources Agency), the demand for Ge will grow considerably by 2030, pushed mostly by the increase in the fiber optics market and advanced materials sector [1]. Therefore, this paper focuses on an overview of the production chain of Germanium, especially from its concentrate up to the single crystal growth of its valuable ultra-pure metallic form to be used in high technological applications.

Reaction Rate Models for the Thermal Decomposition of Ibuprofen Crystals

Kinetics of the decomposition of racemic ibuprofen crystals were studied by non-isothermal analysis. Thermogravimetric analysis revealed that ibuprofen is thermally stable up to 152.6°C and the initial loss of mass was due to evaporation only. Activation energy, pre-exponential factor, activation entropy and Gibbs free energy for the decomposition of ibuprofen were determined using the integral method of Coats-Redfern (CR). Geometrical contraction models were found to be the best fits. The Arrheinus equation for the thermal decomposition of ibuprofen is k = (1.1 × 107) e–79125/RT sec–1.

Optical and Dielectric Studies on L-Valinium Picrate Single Crystal

Single crystals of L-Valinium picrate were grown from aqueous solution by slow evaporation technique. Single crystal X-ray diffraction analysis reveals that the crystal belongs to monoclinic system. The optical transmission study reveals the transparency of the crystal in the entire visible region and the cut off wave length has been found to be 470 nm. The optical band gap is found to be 2.55 eV. The transmittance of L-Valinium picrate crystal has been used to calculate the refractive index (n), the extinction coefficient (K) and both the real (εr) and imaginary (εi) components of the dielectric constant as functions of wavelength. Low dielectric loss at high frequency region is indicative of enhanced optical quality with lesser defects. Photoconductivity measurements carried out on the grown crystal reveal the negative photoconducting nature.

Decomposition of Solutions in Front of the Interface Induced by Directional Crystallization

Here we show the results of experimental observation of decomposition of the solution components into the neighboring cells. The liquid solution under crystallization first gets into the unstable state and then decomposes. The decomposition result is fixed in the solid phase as inhomogeneous component distribution. Our experimental results enable to argue that the eutectic pattern forms due to interface instability and spinodal decomposition of non-equilibrium solution forming in front of the interface.

The Oleic Acid Composition Effect on the Carboxymethyl Cellulose Based Biopolymer Electrolyte

Biopolymer electrolyte based on carboxymethyl cellulose has been prepared by doping with different concentration of oleic acid via solution casting technique. Fourier Transform Infrared spectroscopy was used to study the complexation between the salt and polymer. New peak was observed at 1710, 2850, 2920 cm-1. X-ray diffraction study reveals the amorphous nature of the biopolymer electrolyte. Impedance study shows the highest ionic conductivity, σ, was found to be 2.11 × 10-5 S·cm-1 at room temperature (303 K) for sample containing 20 wt.% of oleic acid and the biopolymer electrolyte obeys Arrhenius behaviour.

Recrystallization Kinetics and Microstructure Evolution of Annealed Cold-Drawn Low-Carbon Steel

The recrystallization behavior of cold-drawn 0.12 wt% C steel during annealing at temperatures 600°C and 650°C was investigated. Hardness tests were used to characterize the recrystallization kinetics. The micrographs of the steel were obtained using optical microscopy (OM) to characterize the grain microstructure of the non-treated and the annealed steel samples. Annihilation of dislocation defects occur within the soaking time of 5 - 10 minutes for all the deformed steel after annealing at 650°C. Specifically at 5 minutes soaking time the grains elongation is still observed indicating that reformation of grains is not taking place but recovery of the deformed grains. At the 10 minutes annealing time, new grains are observed to begin and full recrystallization is achieved at 15 minutes annealing time. At annealing time between 20 - 25 minutes, grains coarsening are observed indicating the onset of grain growth. The hardness of the material reduces with increasing annealing temperature for all the degree of cold drawn deformation. On the basis of the experimentally obtained hardness values, recrystallization increases with increasing degree of cold drawn deformation for the annealed steel. Recovery process was found to prolong in the 20% cold drawn steel as compared to the 55% cold drawn steel. The prolong recovery process is due to reduction in the driving force. Full recrystallization of the annealed steel is achieved at different soaking time depending on the degree of the cold drawn steel.

Continuous Melt Suspension Crystallization of Phosphoric Acid

A continuous melt suspension crystallization process has been presented for the purification of the phosphoric acid in this study, which is performed in the cascade of a mixed suspension mixed product removal (MSMPR) crystallizer and a gravity wash column for the subsequent solid-liquid separation. Dynamic behavior in the crystallizer and role of reflux ration on the purification efficiency of column are studied in detail. A reasonable steady state with respect to the liquid phase is achieved after 2 to 3 hrs, which is followed by a solid-phase steady state in terms of the slurry density after 4 hrs. Reflux ratio is the effective parameter for separation and purification by the crystallization equipment from the influences of reflux ratio on the purity of product, the number of theoretical plates and the stability of the operations.

Effect of BaTiO₃Nanoparticle on Electro-Optical Properties of Polymer Dispersed Liquid Crystal Displays

Ferro nematic suspensions are the prominent materials to enhance the electro optical performance of liquid crystal displays. Electro optical properties of polymer dispersed liquid crystal (PDLC) display with the introduction of Barium Titanate nanoparticles have been investigated in this article and it is shown that there is a considerable enhancement in electro-optical response of the displays. The nanoparticles lower the switch-on electric field and thereby increase the optical transmission at certain voltages of the displays. The electro-optical characteristics of the PDLC cells were investigated with a He-Ne laser followed by MatLab calculations.

Crystal Growth and Nucleation in Glasses in the Lithium Silicate System

The crystal growth and nucleation in glasses in the lithium silicate system have been investigated. Phase separation in ultimately homogenized glasses of the lithium silicate system xLi2O·(100 ﹣ x)SiO2 (where x = 23.4, 26.0, 29.1, and 33.5 mol% Li2O) has been studied. The glasses of these compositions have been homogenized using the previously established special temperature-time conditions, which make it possible to provide a maximum dehydration and removal of bubbles from the glass melt. The parameters of nucleation and growth of phase separated in homogeneities and homogeneous crystal nucleation have been determined. The absolute values of the stationary nucleation rates Ist of lithium disilicate crystals in the 23.4Li2O·76.6SiO2, 26Li2O·74SiO2 and 29.1Li2O·70.9SiO2 glasses with the compositions lying in the metastable phase separation region have been compared with the corresponding rates Ist for the glass of the stoichiometric lithium disilicate composition 33.51Li2O·66.5SiO2. It has been found that the crystal growth rate has a tendency toward a monotonic increase with an increase in the temperature, whereas the dependences of the crystal growth rate on the time of low temperature heat treatment exhibit an oscillatory behavior with a monotonic decrease in the absolute value of oscillations. The character of crystallization in glasses with the compositions lying in the phase separation region of the Li2O-SiO2 system is compared with that in the glass of the stoichiometric lithium disilicate composition. The conclusion has been made that the phase separation weakly affects the nucleation parameters of the lithium disilicate and has a strong effect on the crystal growth.

Volume and Surface Nucleation of Crystals in Glass Based on Blast-Furnace Slag

Using differential thermal analysis, X-ray phase analysis, electron microscopy, and optical microscopy, the nucleation of crystals in glass obtained by blending metallurgical slag with silicon dioxide has been studied. The type of crystallization (homogeneous or heterogeneous, volume or surface) is revealed for each of nine compositions of synthesized glass. It is shown that the first crystalline phase in a volume crystallizing glass is perovskite (CaO·TiO2);in this phase a nucleation of the main phase occurs: melilite (solid solution of gehlenite 2CaO·Al2O3·SiO2 in akermanite 2CaO·MgO·2SiO2). The fundamental characteristics of homogeneous (for a catalizing phase, perovskite) and heterogeneous (for a catalyzed phase, melilite) of crystallization are determined: the steady state nucleation rate Ist, time of unsteady state nucleation τ, crystal growth rate U, and activation energy of frictional flow. The temperature dependences of Ist, τ, and U are obtained. The kinetics of the crystallization of glass is studied and the rates of the surface crystal growth are determined in the glass of nine compositions. The influence of grinding the particles of the original glass on the sequence of deposition of the crystalline phases was studied. Practical recommendations are presented for the use of blast-furnace slag as a raw material for the synthesis of glass and their further utilization.

First-Eutectic Features of Polar Metals in Double Systems

It is known that the dense part of any liquid metal consists of ramified clusters of almost regular tetrahedrons (triangular pyramids with atoms in their vertexes) that are connected into chains by faces. Any metal additive as a second component of liquid alloy can be both beyond these clusters as separated atoms and into them as inherent clusters. The liquid-metal alloy transfers into the second state, at the first eutectic of the solvent. This polymorphic transition of liquid matrix is discovered in the systems, Pb-K and Na-Pb, by molecular-dynamic simulating their microstructure and in experiments on scattering slow neutrons by these alloys of different compositions. In the first system, the obtained results identify both the homogeneous alloy at low concentrations of potassium in liquid lead and the alloy clustering, (Pb4K)n, at potassium concentrations following the eutectic, Pb0.91K0.09. In the second one at the concentrations of lead more than 2%, just the second state is discovered with the clusters, (Na4Pb)n. One can expect the same polymorphic transition in the eutectic, Na0.93Tl0.07, with the micro-inhomogeneity, (Na6Tl)n, and with the melting point of 64 C. This eutectic maintained by the oxygen-free technology and enriched by the isotope, 205Tl, can become the best coolant for fast nuclear reactors due to the depressed chemical activity of sodium and composition stability.

Systematic Relationship between Sr Content and the Lattice Constants in Sr Substituted Hydroxyapatite Thin Films

To increase the biocompatibility of hydroxyapatite (HA), Ca10(PO4)6(OH)2, the Sr substitution of Ca into the HA structure was effected to yield Ca10-xSrx(PO4)6(OH)2(Sr-HA). For medical and dental applications, it is important that Sr-HA is prepared as a thin film so that the Sr fully substitutes the Ca sites in the HA structure and does not form segregated impurities consisting of Sr compounds. If the segregated Sr forms different amounts of different impurities, the dissolution of the Sr into the living body will not be reproducible across different samples. To confirm the Sr substitution into the Ca site in the HA structure, the systematic variation in the lattice constants of the Sr-HA with Sr content was evaluated as the first step. The a- and c-axis lengths were found to exhibit a linear relationship with the Sr content for six samples with different Sr contents, indicating that the prepared Sr-HA thin films likely possessed partial Sr substitution into the Ca sites of the HA structure. This result is an important first step in the accurate evaluation of the biological effects of Sr-HA thin films.

Direct Process to Prepare Crystallized Freestanding Membranes of Hydroxyapatite Using Sacrificial Layer of Barium-Compounds

Freestanding membrane (FSM) of hydroxyapatite (HA) is a thin sheet of pure HA without any supporting substrates. Our original preparation process of FSM of HA had three steps: The first was the deposition of HA layer on sacrificial layer of solvent-soluble materials, the second was separation of FSM of HA by means of dissolution of sacrificial layer, and the third was post-annealing to crystallize FSM of HA. To date, the post-annealing process was a serious bottleneck of productivity owing to its too long time. In this short report, we proposed a novel sacrificial layer, heatproof and water-soluble Ba-compound, which makes the direct deposition of crystallized HA possible due to its heatproof property because the problem on the original process was that the previous sacrificial layers have no heatproof property and HA layer should be deposited as amorphous. We can deposit the Ba-compound sacrificial layer only in 1 hour followed with the direct deposition of crystallized HA layer, substituting the 20 hours of post-annealing. The FSM of HA was separated successfully from the substrate by means of dissolution of Ba-compound with water. Our novel process can shrink the process time by 19 hours.

Studies on Nano Crystalline Ceramic Superconductor LaZrYBaCa₂Cu₃O₁₁at Three Different Temperatures

The high temperature superconductors are ceramic materials with layers of Copper-oxide spaced by layers containing Barium and other atoms. The Yttrium compound is somewhat unique in that it has a regular crystal structure while the Lanthanum version is classified as a solid solution. The Yttrium compound is often called the 1-2-3 superconductor because of the ratios of its constituents. Lanthanum Zirconium Yttrium Barium Calcium Copper Oxide (LaZrYBaCaCuO) was prepared by the usual solid state reaction method. In order to show the viability of the proposed method, super-conducting powder was prepared in special furnace. The sample was analyzed by X-ray Diffraction (XRD), Particle size determination, SEM and EDX. The comparison of XRD results with JCPDS files confirmed the orthorhombic structure of the sample with a ≠ b ≠ c and α = β = γ = 90°. Scanning Electron Microscopy (SEM) studies revealed that its particle size is in the nanometer range. It also confirmed the calculated value of particle size from Debye Scherrer’s formula. EDX spectrum shows the elements of the sample. X-ray instrumental peak broadening analysis was used to evaluate the size and lattice strain by the Williamson-Hall Plot method.

Crystallization in the Three-Component Systems Rb₂SO_4-MSO_4-H₂O (M = Mg, Co, Ni, Cu, Zn) at 298 K

The crystallization in the three-component systems Rb2SO4-MSO4-H2O (M = Mg, Co, Ni, Cu, Zn) is studied by the method of isothermal decrease of supersaturation. It has been established that isostructural double compounds, Rb2M(SO4)2·6H2O (M = Mg, Co, Ni, Cu, Zn), , crystallize from the ternary solutions within wide concentration ranges. The infrared spectra are discussed with respect to the normal vibrations of the sulfate ions and water molecules. The unit-cell group theoretical treatment of the double salts is presented. The extent of energetic distortions of guest ions (about 2 mol%) matrix-isolated in the respective selenates, (M' = K, Rb,;M" = Mg, Co, Ni, Cu, Zn), is commented.

Theoretical Model of Diffraction Line Profiles as Combinations of Gaussian and Cauchy Distributions

Previously we derived equations determining line broadening in ax-ray diffraction profile due to stacking faults. Here, we will consider line broadening due to particle size and strain which are the other factors affecting line broadening in a diffraction profile. When line broadening in a diffraction profile is due to particle size and strain, the theoretical model of the sample under study is either a Gaussian or a Cauchy function or a combination of these functions, e.g. Voigt and Pseudovoigt functions. Although the overall nature of these functions can be determined by Mitra’s R(x) test and the Pearson and Hartley x?test, details of a predicted model will be lacking. Development of a mathematical model to predict various parameters before embarking upon the actual experiment would enable correction of significant sources of error prior to calculations. Therefore, in this study, predictors of integral width, Fourier Transform, Second and Fourth Moment and Fourth Cumulant of samples represented by Gauss, Cauchy, Voigt and Pseudovoigt functions have been worked out. An additional parameter, the coefficient of excess, which is the ratio of the Fourth Moment to three times the square of the Second Moment, has been proposed. For a Gaussian profile the coefficient of excess is one, whereas for Cauchy distributions, it is a function of the lattice variable. This parameter can also be used for determining the type of distribution present in aggregates of distorted crystallites. Programs used to define the crystal structure of materials need to take this parameter into consideration.

Au Nanoparticle Formation from Amorphous Au/Si Multilayer

By direct observations of transmission electron microscopy (TEM), irreversible morphological transformations of as-deposited amorphous Au/Si multilayer (a-Au/a-Si) were observed on heating. The well arrayed sequence of the multilayer changed to zigzag layered structure at 478 K (=Tzig). Finally, the zigzag structure transformed to Au nanoparticles at 508 K. The distribution of the Au nanoparticles was random within the thin film. In situ X-ray diffraction during heating can clarify partial crystallization Si (c-Si) in the multilayer at 450 K (= ), which corresponds to metal induced crystallization (MIC) from amorphous Si (a-Si) accompanying by Au diffusion. On further heating, a-Au started to crystallize at around 480 K (=Tc) and gradually grew up to 3.2 nm in radius, although the volume of c-Si was almost constant. Continuous heating caused crystal Au (c-Au) melting into liquid AuSi (l-AuSi) at 600 K (= ), which was lower than bulk eutectic temperature ( ). Due to the AuSi eutectic effect, reversible phase transition between liquid and solid occurred once temperature is larger than . Proportionally to the maximum temperatures at each cycles (673, 873 and 1073 K), both and Au crystallization temperature approaches to . Using a thermodynamic theory of the nanoparticle formation in the eutectic system, the relationship between and the nanoparticle size is explained.

Ceramic Nanocrystalline Superconductor Gadolinium Barium Copper Oxide (GdBaCuO) at Different Treating Temperatures

With the discovery of high-TC superconducting materials like Yttrium Barium Cupric Oxide, Bismuth Strontium Calcium Copper Oxide and Thallium Calcium Barium Copper Oxide, tremendous interest has developed over the past two years in understanding these materials as well as utilizing them in a variety of applications. The thin films of these materials are expected to play an important role in the area of microelectronics, especially for interconnects in integrated circuits, Josephson junctions, magnetic field sensors and optical detectors. Here, the authors designed a new nanocrystalline ceramic type II high-TC superconductor, Gadolinium Barium Copper Oxide (GdBaCuO/GBCO). The GBCO perovskite phase structure was prepared by the conventional solid state thermochemical reaction technique involving mixing, milling, calcination and sintering. In GBCO system, the method for controlling microstructure and superconducting state is related to oxygen content consideration because small changes in oxygen concentration can often?lead to huge change in Tc. In order to show the viability of the proposed method, super-conducting powder was prepared in special furnace. The sample was analyzed by X-Ray Diffraction (XRD), an indispensible non-destructive tool for structural materials characterization and quality control which makes use of the Debye-Scherrer method. The comparison of XRD results with JCPDS files confirmed the orthorhombic structure of the sample. Micro-structural features are studied using Scanning Electron Microscopy (SEM) which revealed that its particle size is in the nanometer range. It also confirmed the calculated value of particle size from Debye Scherrer’s formula. EDX plot shows the presence of all the constituents. X-ray instrumental peak broadening analysis was used to evaluate the size and lattice strain by the Williamson-Hall Plot method.