BORON AND BORATES: EXTRACTION, PROCESSING AND APPLICATIONS

The potential of the Barker lattice theory for interpreting thermodynamic properties of mixtures of non-electrolytes is discussed. The basics of this theory and a short survey of the results of its application to hydrocarbon systems found in the literature are presented. Further development and results of adaptation of the theory for oxide melts modeling are reviewed and the occurring difficulties are sorted out. Based on the computational results for MO-B2O3-SiO2 melts a proposal is made to improve consistency of the modeling by devising a more sophisticated set of lattice parameters. Introduction of additional 'virtual' components in the model allows to take into account four-coordinated boron and some other structural features of the melts. This idea was tested for the melts in the PbO-SiO2 and PbO-B2O3 systems using experimental values of the component activities obtained by high temperature mass spectrometric method.

In this study, production of sub-micron sized boron carbide powders via self-propagating high temperature synthesis were investigated by igniting of stoichiometric mixture of B2O3, C and Mg powders and with the addition of different percentages of NaCl as SHS diluents. The SHS reactions were realized in a MgO-lined crucible in inert argon atmosphere and reaction was initiated by W (tungsten) wire coil. The selective leaching was carried out after SHS reaction. The addition of NaCl reduced the particle size of the final product by reducing the adiabatic temperatures of the SHS reaction. The samples were investigated by using XRD, chemical analysis and SEM techniques during different stages of production.

The general lattice theory of the associated solutions was used for modeling of thermodynamic properties such as component activities, chemical potentials of components and Gibbs energies of borosilicate glass-forming melts containing PbO. Experimental data on thermodynamic functions in these melts obtained by the Knudsen effusion mass spectrometric method in the temperature range 1000-1300 K were used for these purposes. The agreement between calculated and experimental values of thermodynamic properties in the frame of the 15 % of the middle relative accuracy was illustrated. Based on this approach the relative numbers of bonds of various types when the second coordination sphere was taken into consideration were calculated. The correlation between the level of deviations from the ideality of thermodynamic functions in the ternary and corresponding binary melts studied and the changes of the relative numbers of these bonds as the function of concentration were shown. Information on the structural description of the melts in ternary PbO-B2O3-SiO2 and corresponding binary systems obtained as the result of modeling using general lattice theory of associated solutions was confirmed by the result of the direct experimental studies of these glasses by X-ray scattering method at large angles.

Boron carbide (B4C) is one of the hardest materials known, behind cubic boron nitride and diamond, used in tank armor, bulletproof vests, nuclear plant, and numerous industrial applications. Commercially it is produced by carbothermal reduction process using boric acid and coke at a high temperature in a resistance heating furnace. The process is inefficient in terms of production as only 15% of total charge gets converted into useful product. No published attempt has been made to optimise this process either mathematically or physically. This process has been modelled mathematically. A few experiments have been performed on a laboratory scale hot model. Model’s predictions are validated against experiments and initially it is found that the match is poor. This led us to think to find out the uncertainties associated with either the experiments or modeling. It is found that porosity can affect the simulation results significantly. Therefore, experiments were performed to measure the porosity of the mixture/product at various temperatures. Similarly, significant inaccuracies are found in temperature measurements, thermal conductivity of coke, etc. After incorporation of the above corrections a good match is found between the computed and experimental results. This gives a fine example that how a mathematical model can be used to improve the physical model. The process has been optimized mathematically.

Monocrystals of barium borate low-temperature modification are important material of non-linear optics and are used for transformation of laser rays frequancy in visible and UV-regions [1]. Many multicomponent systems are tested as the solvents to grow its crystals. System Li, K, Na//BO2,Cl, WO4 with compounds D1=2Na2WO4 x (NaCl)2 and D2=Li2WO4 x K2WO4 consists of 9 pentatops with the eutectics: (LiBO2)2-Na2WO4-D2-(KCl)2-K2WO4, (LiBO2)2-(NaBO2)2-(KCl)2-(KBO2)2-K2WO4, (LiBO2)2-(NaBO2)2-Na2WO4-(KCl)2-K2WO4, (LiBO2)2-(NaBO2)2-D1-Na2WO4-(KCl)2, (LiBO2)2-(NaCl)2-(NaBO2)2-D1-(KCl)2, (LiBO2)2-Li2WO4-Na2WO4-D2-(KCl)2, (LiBO2)2-Li2WO4-D1-Na2WO4-(KCl)2, (LiBO2)2-Li2WO4-(NaCl)2-D1-(KCl)2, (LiCl)2-(LiBO2)2-Li2WO4-(NaCl)2-(KCl)2. System Li, K//BO2,Cl, SO4,NO3 with a compound D=Li2SO4 x K2SO4 has 5 pentatops and system К, Li//Cl, SО4,WО4,ВО2 with compounds D1=Li2WO4 x K2WO4, D2=Li2SO4 x K2SO4 consists of 6 4-dimensional simplexes. There are some unresolved problems with polyhedration of the reciprocal salt systems. One of them is the existance of inner point within the simplex. This type of inner point is a ternary hetero-compound Ba2Na3(B3O6)2F, or 3Ba(BO2)2 x BaF2 x 3(NaBO2)2, or 4Ba(BO2)2 x (NaF)2 x 2(NaBO2)2, or 24Ba(BO2)2 x 4BaF2 x 18(NaBO2)2 x 3(NaF)2, in the system Ba, Na//BO2,F [2]. These problems have been overcome in our software, based by polyhedration algorithms of n-component system: 1) to represent n-component system as a graph, to record the adjacency list of the adjacency matrix zero elements, to multiply the adjacency list elements accounting the absorption law, to fulfill inversion; 2) to connect local mass-centric coordinates Х(x1,…xm) of subsystems in common concentrate space of the system Z(z1,…zn) by matrix equations as Z=KX, where K is the matrix (mxn) and Z-coordinates of the subsystem tops are placed in its columns; 3) to verify polyhedration results (number and dimension of simplexes) by special formulas connecting with them initial data (adjacency matrix), taking into account, that: - any point G belongs to the subsystem K at condition of 0 < xi < 1 for all matrix equation G=KX solutions xi; - polyhedration with solid solutions requires additive virtual diagonals; - polyhedration with inner isolated points is fulfilled in two stages: Without inner points at first and then micro-complexes with inner points only; 1. Mokhosoev M. V., Alekseev F. P., Lutsyk V. I. State Diagrams of Molybdate and Tungstate Systems, Novosibirsk, Nauka, 1978 (in Russian). 2. T. B. Bekker, A. E. Kokh, N. G. Kononova, et al, Crystal Growth Design, 9 (2009) 4060.

In this study, production of boron containing advanced ceramic powders (B4C, ZrB2, TiB2) and effects of the production parameters on the final products were carried out via self propagating high temperature synthesis method which is one of the highly productive and economically reasonable method for the metallurgical areas. The experimental studies were applied in two stages, SHS process and the following HCl leaching. In the SHS experiments, B4C, ZrB2, TiB2 powders productions were studied by using different amounts of a mixture of boron trioxide and reducing Mg powders with C, ZrO2 or TiO2 powders. In the leaching step, the SHS product was leached in a HCl solution to eliminate the magnesium containing phases. Different amounts of HCl concentrations, leaching temperature and leaching duration were tried in the leaching step. After solid/liquid separation, the filter cakes were characterized by X-ray diffractometer and SEM, and spent solutions were analyzed by ICP technique.

The relaxation of the light scattered intensity in the lithium borate melts containing 1.6 mol % Li2O subjected to a temperature gradient has been investigated. It was observed that the during relaxation process the intensity enhanced and finally reached the stationary value. It was found that in this stationary state the magnitude of the scattered intensity was proportional to the square of the temperature gradient subjected to the sample. The enhancement of scattered intensity is connected with arising of the non-equilibrium concentration fluctuations produced by a temperature gradient. Based on the measured the time-dependence of a scattered intensity the mass diffusion coefficient D is calculated for the temperature interval from 4070C to 4550C.

Study of high temperature behaviour of ternary borosilicate melts has the great importance for the development of the modern material science as well as for various technologies such as for the incorporation of nuclear wastes, for obtaining metals from slags in metallurgy, for preparation the special glasses: - with low melting point; - with high refractive index; - with high dispersion coefficient; - with high radiotransparency; - with the effective absorbtion of the slow neutrons. Information on the vaporization processes and thermodynamic properties of ternary borosilicate systems containing Na2O, Cs2O, Rb2O, MgO, CaO, SrO, BaO and GeO2, obtained by high temperature mass spectrometric method in the temperature range 1100-2000 K was discussed. Various types of vapour species were found over ternary borosilicate melts studied such as the associated, dissociated and polymerized products of vaporization. It was shown that the content of vapour over these systems was in agreement with the composition of the gaseous phase over the corresponding binary systems. The regularities of the vaporization of corresponding binary and ternary systems according to the position of oxide modifier in the Periodic table of atoms were also illustrated and discussed from the point of view of the acid-base concept. Results on determination of thermodynamic functions in ternary borosilicate silicate systems mentioned were considered taking into account the main requirements for the confirmation of their reliability. Thermodynamic functions of these systems such as activities and chemical potentials of components as well as the Gibbs energies showed various signs of the deviations from the ideal behaviour. The general lattice theory of associated solutions was used for the prediction and the calculation of these thermodynamic properties of ternary borosilicate melts studied. Based on this theory the correlation between thermodynamic functions obtained in the systems studied and the number of various types of bonds formed in these melts was illustrated. Using this approach the different levels of deviation from the ideality in the melts studied were clarified.

This paper deals with the numerical analysis of a quasistatic contact problem with friction between an elastic body and a rigid obstacle and with the numerical modelling material damage. The body is assumed to be viscoelastic with long memory. The contact is frictional and is modeled with a version of normal compliance condition and the Coulomb's law of dry friction, including the development of material damage, caused by opening and growth of micro-craks and micro-cavities, which results from internal compression or tension. Material damage, which results from tension or compression, is taken into account in the constitutive law. The modelling material damage is introduced by the damage field and was motivated by the evolution of damage in structures. The damage field varies between one and zero at each point in body. The effective functioning and safety of a mechanical system may be deteriorated by this decrease as the material undergoes damage. The variational form of this problem is a coupled system which consists of a first-kind variational inequality for the displacement field and a linear parabolic variational equation for the evolution of damage field. The discrete scheme of the coupled system is introduced based on the finite element method to approximate the spatial variable and an Euler scheme to discretize the time derivative. The algorithm used is an iterative-alternative. The novelty of this work is the proposed numerical algorithm, and its implementations for a numerical simulation of the model.

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