Types of refractories

it is useful to know about the refractories.

1. TYPES OF REFRACTORIES Patel Roma Sem :3 Roll no. 14 Department of materials science

2. Types of refractories On the basis of chemical nature: 1)Acid refractories 2)Basic refractories 3)Neutral refractories Based on fusion temperature: Normal refractory: fusion temperature of 1580 ~ 1780 °C (e.g. Fire clay) High refractory: fusion temperature of 1780 ~ 2000 °C (e.g. Chromite ) Super refractory: fusion temperature of > 2000 °C (e.g. Zirconia ) Based on method of manufacture Dry press process Fused cast Hand molded Formed (normal, fired or chemically bonded) Un-formed (monolithic-plastic, ramming and gunning mass, castables , mortars, dry vibrating cements.) Un-formed dry refractories .

3. CLASSIFICATION OF REFRACTORIES BASED ON CHEMICAL NATURE Acidic refractories: Acidic refractories consist of mostly acidic materials. They are generally affected by basic materials. They includes substances such as silica, alumina and fireclay brick refractories .

4. Continued….. Basic Refractories : they are stable to alkaline materials but could not react with acids. Magnesia(MgO) is a very common example. other examples includes dolomites and crome-magnesia.

5. Continued……. Neutral refractories : they are used in areas where slag and atmosphere are either acidic or basic. Common example of these materials are cromia ( Cr₂O ₃) carbon and alumina.

6. FIRE CLAY BRICK REFRACTORIES fireclay refractories are classified , depending on their alumina content and degree of firing. These are divide into 4 categories

7. PROPERTY AND APPLICATIONS PROPERTY: Increasing the content of alumina; this also increases the compressive strength and resistance to high temperature, having fusion point higher than 1600◦C. APPLICATION: There uses are in blast furnace tops and lining , open hearth steel furnaces, lime kilns, cement kilns, alumina melting furnaces forge furnaces, pottery kilns and domestic firebricks.

8. SILICA BRICK REFRACTORIES Silica brick is a refractory material containing 93% SiO ₂. Raw materials is used quartz , quartzite and sand stone.

9. PROPERTIES AND APPLICATIONS PROPERTY : Do not shrink at high temperature , are resistant to thermal shocks from 600◦C up to melting point, and are highly resistant to attack by iron oxide and acid slag . APPLICATIONS : Their special importance in steel industries. They are also widely used in gas retorts , coke ovens and glass melting tank furnaces. Superduty silica bricks can be used at temperature up to 1700◦C.

10. MAGNESITE BRICKS REFRACTORIES Magnesite refrectories are chemically basic materials, containing at least 85% magnesium oxide. These are made from naturally occurring magnesite ( MgCO ₃) and silica ( SiO ₂). There are two types of magnesite bricks: (A) Burned magnesite bricks (B) Fused magnesite bricks

11. PROPERTIES AND APPLICATIONS PROPERTY : Good high temperature performance, strong slag resistance APPLICATIONS : Used in construction of basic open hearth furnaces, steel converter, lime kilns, glass tank regenerators, lining furnaces in which copper, lead, tin are refind.

12. MULLITE REFRACTORIES Mullite refractories usually have a mullite content of 80% or more. They are mainly made by calcining sillimanite , so that the terms mullite refractory and sillimanite refractory are often interchangeable.

13. PROPERTIES In refractories of high mullite content the ceramic bond of regular fireclay refractories is replaced by a crystalline bond, thus increasing their refractoriesness under load. Sillimanite refractories have a refractoriness ranging from 1950-1920◦C and refractoriness under load ranging from 1590-1700◦C. High temperature properties with improved thermal shock and thermal stress resistance owing to the low thermal expansion, good strength and interlocking gain structure.

14. APPLICATIONS There are used in hot zones of cement kilns and in certain ceramic kilns. important sillimanite products include pyrometer tubes and crucibles for making optical glass.

15. CROME AND CROME MAGNESITE REFRACTORIES Crome magnesite refractories in which crome predominates are neutral, and those in which magnesite predominates are basic. crome magnesite refractories made from a mixture of cromite and roasted magnesite . The refractoriness of such products is about 2000◦C. and higher, depending on the purity of the raw material.

16. PROPERTIES AND APPLICATIONS PROPERTY : Stronger thermal resistance, higher bulk density, good performance under high temperature APPLICATION : In furnaces where more than one type of refractories are used, neutral bricks play vital role of keeping acid and basic refractories out of direct contact with each other and also used in furnaces handing copper , aluminium and lead. In cement rotary kilns , glass kilns regenerators, electric arc furnaces, non ferrous metal furnaces.

17. CARBIDE REFRACTORIES The more important of the refractory carbide are carbides of silicon and boron. SiC refractories are produced from crystalline SiC , carborundum , which is graded to required size fractions, mixed with suitable bonding agent, and then shaped, dried and fired. Four major types of bonding have been used, nitride silicon Self bonding Bonding with refractory clay Silicon

18. Continued……… silicon carbide have superior refractoriness under load, high density, abrasion resistance, high chemical resistance. slowly oxidize to silica when heated in air at temperature 1000◦C. Boron carbide are made from high purity boron carbide powders. the method used is either hot pressing followed by firing to produced a self bonded material, or mixing with sodium silicate, boric oxide, and other silicates as a bonding agent and then firing to produce a ceramic bond.

19. PROPERTIES AND APPLICATION PROPERTY: high refractoriness, low thermal expansion, good resistance to thermal shock, ability to conduct electricity to a certain extent, outstanding hardness , loose abrasive APPLICATION: used as refractory ingredient for many kinds of refractories bodies.

20. HEAT INSULATING REFRACTORIES To optimize the energy use and to prevent its escape into the embience , special materials called insulating refractories necessary. The function of insulating refractory is to reduce the rate of heat flow through the walls of furnaces. Insulation is affected by providing a layer of material having low heat conductivity , which means heat does not readily pass through them.

21. APPLICATIONS Refractories to be used mainly as heat insulators are produced as lightweight highly porous bodies having a large number of extremely small pores most of which are sealed. they are used as an insulating backing to more slag and abrasion resistant bricks. refractories are used to store and transfer heat, as in exchangers, they are made as dense as possible to obtain high heat capacity.

22. REFERENCES Science of engineering materials(vol.2) by MANAS CHANDA WIKIPEDIA