New-generation refractory concretes. Interrelation between structure formation and strengthening

A thermodynamic approach is used to consider the general regularities of structure formation in binding systems used in the technologies of new refractory concretes. The fundamental distinction in both the mechanism of structure formation and the kinetics of strengthening among different types of binding systems is determined by their colloidal-chemical activity. The main regularities of structure formation and strengthening of systems without chemical reactions are considered for clays and highly concentrated binder suspensions, and these regularities for systems with chemical reactions are considered for the binder system of low-cement refractory concretes. The importance of microsilica additions in concrete technologies is shown. Translated from Ogneupory, No. 3, pp. 2–8, March, 1995.     

New-generation refractory concretes. Thermal processes,structure and high-temperature properties

Regularities of the processes of drying and heat treatment (firing) of new refractory concretes (ceramic concretes, low-cement refractory concretes, etc.) are considered. The conditions for the appearance of the effect of their explosive cracking (destruction) in drying are analyzed. Changes in the porous structure and some characteristics of the concretes (porosity, strength, shrinkage, expansion) are considered as functions of the temperature of their preliminary treatment. Regularities in the formation of the zonal structure and the stress state in use of refractory concretes are described. Data on the thermal conductivity and thermal expansion of refractory concretes of the Al₂O₃-SiO₂ system are presented for a wide temperature range.Translated from Ogneupory, No. 6, pp. 5–12, June, 1995.     

贯穿于物理化学热力学教学中的普遍化公式

本文从化学热力学全局的观点出发,提出了一个能够概括目前物理化学热力学中全部影响化学势因素的普遍化公式:dμ=-SdT VdP RT(d ln XA) σdA Adσ,并列举了每一步演化过程中的一些应用实例,得出了物理化学教材中全部热力学公式,如克拉伯龙方程、凝固点下降、范特霍夫渗透压公式、开尔文公式、吉布斯等温吸附方程式.这个公式将物理化学的热力学内容有机地结合在一起.     

Development of high-alumina ceramic concrete based on a composite binder

Information is provided for preparing high-alumina ceramic concretes based on a combined silicate-phosphate binder. Features are revealed for structure formation of the ceramic concrete developed during hardening, drying and firing; probable chemical reactions that occur are indicated.     

A review of the contributions of P. Raj Bishnoi to chemical engineering

This paper provides a review of Professor Bishnoi's research contributions in the broad discipline of chemical engineering. Prof. Bishnoi has been a dedicated mentor, collaborator, innovator, and outstanding researcher. He has had a most productive and illustrious career, spanning more than four decades in both academia and industry. He is among the top 50 most-published authors of the The Canadian Journal of Chemical Engineering. He initiated a most successful and renowned research group at the University of Calgary, which was dedicated to the understanding of thermodynamics and kinetics related to the formation and decomposition of gas hydrates as well as the chemical engineering process design and simulation. As a tribute to Prof. Bishnoi's numerous scientific and engineering contributions and innovations, this review highlights his academic and research accomplishments, which included the training of several doctoral degree students, master's degree students, and postdoctoral scholars and research associates. In this paper, we have divided Prof. Bishnoi's research contributions into three broad areas, namely, chemical thermodynamics of hydrocarbon systems, process development and simulation, and thermodynamics and kinetics of the formation and decomposition of gas hydrates.     

Thermodynamic analysis of structural transformations in solidifying systems

Structural transformations in solidifying binder systems are considered in the context of the thermodynamics of irreversible processes. It is shown that the coagulation-condensation structure emerging in the binder system in the period of hydratation acceleration is a dissipative structure. The emergence of instability in the binder system is accompanied by the development of oscillation phenomena, and the formation of a dissipative structure corresponds to an autowave process in the form of a standing electromagnetic wave. The structure formation schemes proposed in the paper make it possible to realize deliberate selection of external technological actions on binder systems. Translated from Steklo i Keramika, No. 6, pp. 11 – 14, June, 1998.     

Mathematical modelling of structure formation during combustion synthesis of advanced materials

The synthesis of advanced materials by a wave of heterogeneous combustion propagating through a charge mixture, or the so-called self-propagating high-temperature synthesis (SHS) has many potential advantages over conventional techniques of synthesis. Because of high heating rates, steep temperature and concentration gradients, and fast accomplishment of reactions, the mechanisms of physical, chemical and structural transformations in the SHS wave are intricate and often not known. Further understanding of interaction mechanisms in SHS waves, relating the process parameters to structure and properties of the target material, and the application of SHS to producing final articles necessitates developing mathematical models for SHS-related phenomena.Various aspects of mathematical modelling of SHS are discussed in this paper. They include the analysis of novel factors influencing the structure formation, viz. the heating-to-reaction and mass transfer-to-reaction time ratios, autocatalysis and intrinsic stochasticity, which are unnoticed in traditional synthesis methods. The application of chemical thermodynamics and combustion theory to modelling SHS processes is outlined. Novel mathematical models are developed for SHS on condensed systems, which involve stochastic effects and autocatalysis. New models for solid-gas systems are worked out, which include the reaction kinetics and mass transfer of a gaseous reactant and permit predicting the structure formation pattern in the SHS wave. Application of mathematical modelling to producing porous final articles by means of SHS is discussed.     

分子筛上甲醇转化过程的热力学和拓扑结构

现代新型煤化工是我国当今基础有机化学工业发展的新亮点,也是世界化工界的又一次革命。煤制化学品路线经历气化、变换、甲醇合成、甲醇制烃类等过程,其中,最为重要的是分子筛上甲醇转化的过程。本文综述了分子筛上甲醇转化的相关研究,一方面从ZSM-5上甲醇转化的生成烃池及烯烃的热力学机制和产物分布出发,介绍了多甲基苯生成烯烃热力学平衡模型和其中的芳烃池生成烯烃热力学机制,另一方面,介绍了基于Ising模型的分子筛离散拓扑结构模型。利用分子筛孔道堵塞与围棋中“气”的有无的类似性,能够很好地再现SAPO-34上的相变失活现象和不均匀的积炭分布现象。以模型为指导,介绍了一些分子筛多级结构构筑的工作,这些工作很好地提升了催化剂选择性和寿命。这些概念对于准确理解甲醇在分子筛上的反应与失活机制、产品分布及提高选择性有指导意义。     

ASR pessimum behaviour of siliceous limestone aggregates

Siliceous limestone aggregates have “pessimum” behaviours similar to those observed for pure siliceous aggregates such as flint or opal. For high alkali contents concretes based on fine and coarse reactive siliceous limestone aggregates swell less than concretes based on fine reactive siliceous limestone aggregates and non-reactive coarse aggregates. The reduction of the swelling is more significant for a “micritic” limestone containing highly reactive free silica than for a “sparitic” limestone containing less reactive free silica. The consumption of a part of the alkalis by non-expansive processes such as chemical sorption on silanol sites of reactive silica and pozzolanic C-S-H is expected to explain the reduction of the swelling.     

Mathematical Modeling of the Combustion of an Overfueled Aluminum–Air Mixture Based on the Nonequilibrium Thermodynamics of the Process

This paper presents the results of mathematical modeling of the combustion of flow of a multifractional suspension of an aluminum powder in air taking into account the nonequilibrium nature of the process. The calculations were performed for air-to-fuel ratios α = 0.1–0.5. Time dependences of thermodynamic parameters, the completeness of metal particle combustion, and the relative residence time of the fractions in the flow were obtained. The adequacy of the nonequilibrium model for describing thermodynamic processes was validated by comparing with the equilibrium model for time tending to ∞. The necessity of taking into account the formation of Al₂O suboxide present in the range of the air-to-fuel ratio is analyzed and proved. The need to include nitriding reactions in the mathematical modeling for 0.1 ≤ α < 0.4 is shown by comparing the results of calculations based on equilibrium and nonequilibrium thermodynamics.     

The potential for nondestructive testing of refractories

Conclusions Nondestructive physical methods of testing are suitable for assessing the quality of refractories in mass production; they can replace and (or) complement destructive methods. It is necessary to define a system of physical parameters that are adequate for assessing quality [15] — strength, porosity, thermal-shock resistance, apparent density, permeability, and resistance to crushing. Other possibilities for the use of these methods consist in detecting internal faults, determining the degree of wear, the thickness of the structure, the resistance of guncreted sections of a lining in operation, and determining the moment of completion of the formation of refractories and the setting of refractory concretes.Translated from Ogneupory, No. 2, pp. 21–23, February, 1992.     

A new approach for modeling of multicomponent gas hydrate formation

Several models have been proposed to investigate the kinetics of gas hydrate formation. The main differences between the proposed models are the definition of the driving force, thermodynamics approach and the number of resistances to study the gas consumption by the hydrate phase. This paper concentrates on gas hydrate formation from multicomponent mixture, which has not been much studied before. In the present research, chemical potential has been considered as the driving force and, consequently, a new resistance coefficient was introduced. A complete discussion and reasonable assumptions has been provided to support this modelling.     

Thermodynamics of wax formation in the fischer-tropsch synthesis products

A new method is suggested for calculating the thermodynamic equilibrium in a multicomponent multiphase system without chemical reactions. This method is based on ideas of statistical physics and non-equilibrium thermodynamics and includes numerical minimization of the Gibbs energy of the complex system. Component concentrations and the physically realizable roots of the equation of state are calculated as the steady state solutions of the set of ordinary differential equations that is implied by the procedure of seeking the probability maximum for the realization of the equilibrium distribution. The approach developed here is used to calculate the equilibrium distribution of the concentrations of vaporous, liquid, and solid substances in the Fischer-Tropsch synthesis products. A thermodynamic model of the formation of solid paraffins from the synthesis products is presented. The calculation of the properties of pure substances and liquid and gaseous products is based on the Lee-Kesler equation of state. The wax formation thermodynamics is considered in the regular solid solution approximation (Hildebrand-Scott model) and in the solid solution approximation taking into account the nonideality of the system (NRTL model). The calculated mass fractions of vaporous, liquid, and solid synthesis products are presented as a function of temperature for different values of the chain propagation constant.     

Sustainable development and its implications for chemical engineering

Sustainable development presents us all with the challenge of living in ways which are compatible with the long-term constraints imposed by the finite carrying capacity of the closed system which is Planet Earth. The chemical engineering approach to the management of complex systems involving material and energy flows will be essential in meeting the challenge. System-based tools for environmental management already embody chemical engineering principles, albeit applied to broader systems than those which chemical engineering conventionally covers. Clean technology is an approach to process selection, design and operation which combines conventional chemical engineering with some of these system-based environmental management tools; it represents an interesting new direction in the application of chemical engineering to develop more sustainable processes. Less conventional applications of chemical engineering lie in public sector decisions, using the approach known as post-normal science. These applications require chemical engineers to take on a significantly different role, using their professional expertise to work with people from other disciplines and with the lay public. The contribution of chemical engineering to the formation of UK energy policy provides an example of the importance of this role. Recognising the role of engineers as agents of social change implies the need for a different set of skills, which just might make the profession more attractive to potential new recruits.     

Distribution of the trace elements As,Cu, Ni,Be, and Sb in the combustion products of near-Moscow coals

The distribution processes of the trace elements As, Cu, Ni, Be, and Sb as the constituents of near-Moscow coal in the flow of coal combustion products with the excess oxidant (air) ratio α = 1.25 along the line of the P-59 boiler at the Ryazanskaya Thermal Power Plant was studied by simulation. The model proposed previously for the conversion of trace elements in the combustion of near-Moscow coals based on a complex approach combining the capabilities of geochemistry, chemical thermodynamics, phase analysis, and chemical kinetics was used with consideration for experimental data.     

Correlation between water permeability of latex-modified concrete (LMC) and water diffusion coefficient of latex film

Cement-based materials are generally known as weak materials in flexure and tension in comparison with compression. Polymers are used in cement-based materials to improve their flexural and tensile behaviors. The composite is called as polymer-modified concrete/mortar. Furthermore, polymers decrease permeability of water into cementitious matrices. Polymers are usually used as admixtures in concretes in form of latexes. Latexes are water-based polymers, which are consistent with water-based concrete matrices. On this basis, these kinds of products are called latex-modified concretes (LMCs). However, it has been found that chemical composition, particle size distribution, molecular weight, physical/mechanical properties of latexes affect performance of modified concretes. In this investigation, six latexes in three categories (acrylic, SBR and polyvinyl acetate) were used as concrete admixtures. They were characterized for chemical composition (by FTIR analysis), minimum film formation temperature, pH, glass transition temperature (T _g), particle size and particle size distribution to evaluate the effect of each property on LMC performance. Due to the formation of latex film in the microcracks and pores of concrete microstructure, it was suggested that diffusion of water into films controls permeability of whole concrete structures. On this basis, the diffusion coefficient of the latex films subjected to water was measured using a new method (continuous FTIR analysis). Capillary water absorption test was performed on concrete specimens to verify validity of the suggestion. It was found that there is a correlation between capillary water absorption of LMCs and water diffusion coefficient of latex films.     

高炉煤气洗涤水锌垢的热力学分析及处理技术

针对天津铁厂高炉煤气洗涤水系统容易形成锌垢的问题,从热力学角度,利用有关热力学原理和数据,进行了化学热力学分析,从理论上找出洗涤水系统的锌垢成因.采用复配絮凝剂和复合水质稳定剂进行了试验,研究出鲻适合于高炉煤气洗涤水系统的锌垢去除新技术.试验结果表明,新型的水质稳定剂完全达到了良好的处理效果.     

Explanatory Paper on Modern Theory Theory of Dyeing

A clearer appreciation of the significance of the conventional standard affinity of dyeing (–μo)can be obtained if the nature of the driving forces behind dyeing in simple, model dyeing systems is analysed. It is then seen that the standard affinity of dyeing is the driving force behind dyeing in a particularly well–defined model of the dyeing system, at a particular stage of dyeing. The simple assumption that the rate of dyeing is directly proportional to the magnitude of the driving force behind dyeing provides a unifying link between the thermodynamics and the kinetics of dyeing and is consistent with modern theories of nonequilibrium thermodynamics. The extension of these ideas to an analysis of the nature of the driving forces in systems in which the rate of dyeing is determined by diffusion processes within the fibre produces a rather surprising result that reveals the true complexity of the concept of ‘affinity’ in dyeing.     

Was leistet die statistische Thermodynamik für den Verfahrens-Ingenieur?

What does statistical thermodynamics do for the chemical engineer? Statistical thermodynamics introduces molecular properties of a particular system into model equations for the thermodynamic functions of fluid mixtures. It thus contributes to the prediction, extrapolation or estimation of fluid properties, in particular phase and reaction equilibria, which are fundamental to numerous processes in thermochemical engineering. For systems of small, rigid molecules, as frequently encountered in natural gas and refrigeration applications, this method has reached a high level that is beginning to be introduced into industrial practice. For systems of complicated organic molecules, models from molecular thermodynamics have firmly established themselves in industrial applications.