Theme: Silicates in a liquid condition. The theory of a structure of liquids. Features of structure silicate fusion

1. Silicates in a liquid condition.

2. Hypothesis of a structure of a liquid.

3. Feature of structure silicate melt.

Quasi-crystalline - deformed crystal

Cybotaxic group - strongly deformed deformed structure of crystals

As is known, key operation in manufacture silicate and other refractory materials is the high-temperature processing, during which the initial firm substances can completely (technology flown down, enamels, glaze, molten of cements, refractory, abrasive) or partially to pass in fusion (portland cement clinker, aluminous cement, porcelain, faience, fire clay both dinas refractory and e. c.). Knowledge of a nature fusion silicate and their properties therefore is rather important.

Melting - process of transition of substance of a firm condition in liquid, made under action of temperature. Melting of crystal substances is phase transformation caused spasmodic change of their internal structure and physics-chemical properties, connected to it.

Besides structure on a structure fusion, in particular on structure of particles, of which they consist, the large influence is rendered by(with) temperature. Agrees

О. V. Mazurin, kinds of structural transformations in fusions, the temperatures, occurring at change, are reduced to the following basic types:

1. Temperature fluctuation of density.

2. Change of coordination.

3. Education and dissociation of structural complexes.

At manufacturing the majority silicate of products (glass, ceramics, cement clinker) during them burn occurs private(individual) or even complete melting of a material. The properties formed thus of a liquid phase are rendered by(with) the extremely large influence on technological process of manufacture and on final properties of ready production. Now is established, that between a structure of substances which are taking place in crystal, liquid or glass-like a condition, are available not only various, but also essential similarities. Basically there are three hypotheses of a structure of a liquid. The greatest recognition was received by(with) models of a structure of liquids offered in different years Bernal, E.Yu. Fraenkel and G. Stuart. Agrees Bernal, offered a hypothesis without defects of a liquid, the liquid has structure poorly distinguished from geometry of a crystal, from which she is received. The model of a structure of a liquid offered Fraenkel, is called quasi-crystalline. According to this model is especial nearby of temperature crystallization is considered(examined) as the deformed crystal, in which the distant order is lost, but is saved near.

According to the theory " cluster or cybotactic grouping " in a liquid there are units named cybotactic by groups representing pseudo-crystal educations, which structure comes nearer to a structure of the appropriate crystals allocated from a liquid at crystallization. The structure cybotactic of groups can be considered(examined) as the strongly deformed deformed structure of crystals. Cybotactic of group are mobile, dynamic units, which collapse at movement and are created again. These groups are divided(shared) by areas of a chaotic arrangement of particles, however of sharp transitions between areas with partially ordered and disorder. This hypothesis in comparison with other hypotheses now has the greatest recognition.

Structure fusion silicate.

High temperature melting silicate (is usual from 500 0С up to 2000 0С) puts significant obstacles to research of their structure in molten a condition. To number of the most important properties silicate fusion, connected with their structure and investigated with sufficient completeness concern: viscosity, superficial tension and density.

Viscosity silicate fusion.

Viscosity of substance in particular silicate fusion is understood as property of substance to render resistance mainly of one parts of a liquid concerning others. The existing methods of measurement of viscosity of glasses can be divided(shared) into 2 kinds:

1) Methods of definition of viscosity in rather low temperatures:

а) Method of a stretching of a string;

б) Method of a deflection of a string;

в) Method wrench of a core.

2) Method of definition of viscosity at high temperatures:

а) Method of a falling ball;

б) Method of rotating cylinders.

The role fusion by manufacture silicate of materials is rather various. Determining meaning(importance) have the properties silicate fusion for technology of a glass - product of cooling fusion without them crystallization. The vast role fusion and for technology of various materials received by them crystallization (fused refractory, cements, abrasive, monocrystals various thallic oxide, chalcogenides, halogenide and т is abundantly clear. д.). At the same time it is necessary to note and that large meaning(importance), which belongs fusion in technology of a number(line) of the basic multitonnage products silicate of technology, where they are that environment, in which there are many reactions of education of chemical connections determining at the end properties of ready products. The liquid phase in many respects defines(determines) also processes of sintering, т. е. Condensation of a material at burn many silicate of products.

It is possible to result many examples from various areas of technology silicate, which well illustrate a role fusion in technology silicates.

1. At baking portland cement clinker in rotating furnaces a liquid phase appearing in a zone of sintering, completely

Supervises process of formation main cement of a mineral - tricalium silicate с - alite ЗСаО · SiO₂.

2. By manufacture of one of most important fire-resistant

Materials - dinas the liquid phase also plays determining role. dinas - acid refractory, on structure approximately on 90 % (mass).

Consisting from SiO₂ and 10 % (mass). СаО. In the phase attitude(relation) is submitted basically tridymite.

3. By manufacture of porcelain the basic phase component of this material - mullite is formed by dissolution of quartz and products of decomposition kaolinite in feldspathic fusion.

Thus, nature and the properties fusion, raw materials, formed at high-temperature processing, by manufacture various silicate of materials, have huge practical meaning(importance), enabling a choice of optimum parameters of technological process and reception of materials with the beforehand given properties.

Questions:

What factors define(determine) absolute meaning(importance) of temperature melting of crystal substances?

Describe essence of existing modelling representations about a structure of liquids and, in particular, structure silicate fusion.

How influence temperature and structure silicate fusion their viscosity?

What defines(determines) size of a superficial tension and moistening ability fusion?

How it is possible to classify oxides on their influence on a superficial tension?

In what parameter and how it is possible to characterize moistening ability fusion?

Result examples of a role of a liquid phase by manufacture silicate of materials.

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