Acidic refractories

Acid refractory materials include fireclays, flint clays, china clays (kaolins), silica, flint, chalcedony, ganister and titanium dioxide. 

Acid refractories Basic refractories Neutral refractories Rarer... 

Chemical inertness This attribute implies immunity of a given refractory in a given application to any sort of chemical reaction. It should not, for instance, form fusible products with slags, fuel ashes and furnace gases. The condition inside most furnaces is usually either acidic or basic, and on this basis an acid refractory is prohibited from coming into physical contact with alkaline materials, or vice versa. 

Acid refractory furnace linings, 12 300 Acid resistant nanofiltration membranes, 21 635t... 

Marler, D.O. (1993) Catalysts bound with low acidity refractory oxide. US Patent 5,182,242. 

Refractories can be classified as acidic or basic, depending on the properties of the oxides in question. A basic refractory must not be used in contact with acid, and an acidic refractory must not be used in contact with a base. Classify magnesia and silica as acidic or basic refractories. 

A more complete approach is shown in Fig. 2, with details on other aggregated organics (surfactants, phenols, etc.), evolution factors (chemical and physico-chemical reactions) and residual by-products (organic acids, refractory organics, etc.). 

Acidic refractories (e.g. silica, fire, clay etc.) These are used in areas where slag and atmosphere are acidic. They are stable to acids but attacked by alkalis. Aluminium-silicate refractories These refractories vary widely in their physical, chemical and mineralogical characteristics depending on the nature and proportion of silica and alumina present on them. 

Acid Open-hearth Furnace. An open-hearth FURNACE (q.v.) used in the refining of hematite iron little such iron is now made. The particular feature is that the hearth is made of acid refractories - silica bricks covered with a fritted layer of silica sand. 

Acid Refractory Material. General term for those types of refractory material that contain a high proportion of silica, e.g. silica refractories (> 92% Si02) and siliceous refractories (78-93% Si02). 

ANSI standards cover a variety of prodncts, materials, and equipment that is used both in highly specialized fields and in nearly all other areas of modern life. ANSI publishes standards on ceramic tiles, chemical process equipment, home appliances, electronics equipment, motion picture film and equipment, acids, refractory materials, oil burners, office machines and supplies, hospital supplies, and combustion engines. 

In the case of refractory materials made of oxide ingredients, the reactions are mainly an acid-base ones in materials based on SiC and Si3N4, oxidation-reduction reactions also take place. In general, the intensity and rate of the acid-base reactions is highest when one of the substances involved is acidic and the other basic. The rate decreases when the acidity or basicity of the substances is similar. This is illustrated in the example in Table 2.5, in which shown is the dissolution rate of an acidic refractory material in a molten basic FeO. 

Acid refractories react with basic slags. Therefore, they are not useful in basic conditions but are used imder acidic conditions. In these refractories, Si02 is the basic constituent. Examples are silica, fireclay series with 30%-42% AI2O3, sillimanite, and andalusite with about 60% AI2O3. 

The first fundamental principle is that acid refractories tend to resist acid slags better than basic slags and, conversely, basic refractories tend to resist basic slags better than acid slags. The definitions of acidity and basicity in room-temperature solution chemistry and of refractory chemistry at elevated temperature have a key difference. 

This leads to the observation that acid refractories are more compatible with acid slags, that is, acid materials experience less corrosion loss against acid slags as compared to basic slags. In a like manner, basic refractories are more compatible with basic slags than with acid slags. 

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