Chemical composition of refractories
Chemical composition of refractories
The chemical composition of refractories is one of the most basic characteristics of refractories. In general, the chemical composition of refractories is divided into two parts according to their composition (content) and their action: (1) the basic component, the principal component, which plays a decisive role in its properties; (2) a small number of subordinate components-by-components, which are accompanied by impurities in the raw materials or added in order to achieve a certain purpose in the process of production (additions). The chemical composition of refractories is divided into two parts according to the composition (content) and its action: (1) the basic component, the principal component, which plays a decisive role in its properties; (2) a small number of subordinate components.
1.1 Principal components
The principal component is the refractory matrix in the refractory, and it is the characteristic basis of the refractory. Its properties and quantity play a decisive role in the properties of materials. The principal component can be oxide or non-oxide. Therefore, refractories can be composed of refractory oxides, refractory oxides and carbon or other non-oxides, or all refractory non-oxides. Oxide refractories can be divided into acid, neutral and alkaline according to the properties of principal component oxides.
Acid refractory. the material contains a considerable amount of free sio2. the most acidic refractory is siliceous refractory, consisting of almost 94% to 97% free sio2. the content of free sio2 in clay refractory is relatively small and is weakly acidic. The semi-silicon refractory is in the process.
Neutral refractory. High aluminum refractories (the mass fraction of Al2O3 is more than 45%) are acid-oriented and neutral refractories, and chromium refractories are alkali-oriented and neutral refractories.
Alkaline refractories contain a considerable amount of MgO and CaO. Magnesia and dolomite refractories are strongly alkaline, magnesia-chromium and forsterite refractories and spinel refractories belong to weak alkaline refractories.
This classification is of great significance for understanding the chemical properties of refractories and judging the chemical interaction between refractories and contacts in the process of use.
1.2 impurity composition
Most of the raw materials of refractories are natural minerals, so they often contain a certain amount of impurities in refractories. These impurities will reduce some properties of refractories, for example, the principal components of magnesia refractories are MgO, other oxides such as silicon oxide, iron oxide and so on. The more impurities are, the more liquid phase is formed at high temperature.
The impurity composition in refractories directly affects the high temperature properties of refractories, such as refractory degree, load deformation temperature, corrosion resistance, high temperature strength and so on. The advantage is that impurities can reduce the firing temperature of the product and promote the sintering of the product.
1.3 add ingredients
In the production or use of refractories, especially amorphous refractories, a small amount of additives are added to improve the physical properties, molding or construction properties (operational properties) and performance of refractories. The addition of additives varies according to their properties and functions, and is a few to a few percent of the total composition of refractories.
The additives are divided into the following methods according to their purpose and function:
The rheological property can be changed, including water reducing agent (dispersing agent), plasticizer, gelling agent, breaker, etc.;
Adjust the rate of condensation hardening: including coagulant promoter, retarder, etc.
Adjust the internal tissue structure: including foaming agent (air entraining), defoamer, anti-shrinkage agent, expansion agent and so on;
Include material construction performance category: including inhibitor (anti-expansion agent), storage agent, antifreeze, etc.
Improve performance: including sintering aid, mineralizer, quick drying agent, stabilizer, etc.
These additions, with the exception of those that can be burned, remain in the chemical composition of the material.
By chemical composition analysis, the purity and characteristics of the product or raw material can be judged according to the type and quantity of the composition. The mineral composition and other related properties of the product can be roughly estimated by means of the relevant phase diagram.