13.0 Refractory and Refractory materials

 

Refractory and Refractory materials

A suitable selection of the refractory lining material for a furnace can only be made with an accurate knowledge of the chemical and physical properties of the refractories and refractory materials, and of the stresses of the materials during service. There are four types of stresses which refractories face during their period of service. These are given below:

Thermal – The important properties for thermal stresses are pyrometric cone equivalent (PCE), refractoriness under load (RUL), Thermal expansion under load (creep), hot modulus of rupture, thermal expansion, reheat change (after-shrinkage and after-expansion) and thermal shock resistance.

Thermo-technical – The important properties for thermo-technical stresses are thermal conductivity, specific heat, bulk density, melting point, thermal capacity and temperature conductivity.

Mechanical – The important properties for mechanical stresses are cold modulus of rupture and deformation modulus, crushing strength, abrasion resistance, porosity and density.

Chemical – The important properties for chemical stresses are chemical composition, mineralogical composition and crystal formation, pore size distribution and types of pores, gas permeability and resistance to slag, glass melts, gases and vapors.

	Refractories are classified in multiple ways, based on:
	Based on	Type	Composition	Properties	Application
1	Chemical composition
	Acidic refractories	Silica refractories	93% silicon oxide (SiO2).	They are acidic, have high resistance to thermal shock, flux and slag resistance, and high spalling resistance	iron and steel industry as furnace materials
		Zirconia refractories	zirconium oxide (ZrO2).	low thermal conductivity, are not easily wetted by molten glass and have low reactivity with molten glass	Glass furnaces , high temperature construction materials
		Aluminosilicate refractories	alumina (Al2O3) and silica (SiO2)	semiacidic, fireclay composite, or high alumina content composite
	Basic refractories	Magnesite refractories	≥ 85% magnesium oxide (MgO).	high slag resistance to lime and iron-rich slags, strong abrasion and corrosion resistance, and high refractoriness under load	metallurgical furnaces
		Dolomite refractories	calcium magnesium carbonate		converter and refining furnaces
		Magnesia-chrome refractories	magnesium oxide (MgO) and chromium oxide (Cr2O3)	high refractoriness and have a high tolerance for corrosive environments
	Neutral refractories	Carbon graphite refractories	carbon	high refractoriness allow them excellent thermal stability and resistance to slags	highly reducing environments
		Chromite refractories	sintered magnesia and chromia	They have constant volume at high temperatures, high refractoriness, and high resistance to slags
		Alumina refractories	≥ 50% alumina (Al2O3)
2	Fusion temperature (melting point)
	Normal refractories	Fire clay		fusion temperature of 1580 ~ 1780 °C
	High refractories	Chromite		fusion temperature of 1780 ~ 2000 °C
	Super refractories	Zirconia		fusion temperature of > 2000 °C
3	Refractoriness	Refractoriness is the property of a refractory's multiphase to reach a specific softening degree at high temperature without load, and is measured with a pyrometric cone equivalent (PCE) test
	Super duty			PCE value of 33–38
	High duty			PCE value of 30–33
	Intermediate duty			PCE value of 28–30
	Low duty			PCE value of 19–28
4	Thermal conductivity
	Conducting		SiC and ZrC
	Nonconducting		silica and alumina
	Insulating		calcium silicate materials, kaolin, and zirconia.
		Heat-resistant			≤ 1100 ºC
		Refractory			≤ 1400 ºC
		High refractory			≤ 1700 ºC
		Ultra-high refractory			≤ 2000 ºC
5	Method of manufacture
	Dry press process
	Fused Cast
	Hand molded
	Formed	Normal bonded
		Fired bonded
		Chemically bonded
	Unformed	Monolithic-plastic
		Ramming
		Gunning mass
		Castable
		Mortars
		Dry vibrating cement
	Unformed Dry refractories
	Refractory Materials And Their Applications
1	Fired Refractory Products	refractory materials obtained by kneading, molding, drying and high-temperature firing of granular and powdery refractory raw materials and binders
2	Non Fired Refractory Products	refractory materials that are made of granular, powdered refractory materials and suitable binders but are directly used without being fired
3	Special Refractory	refractory material with special properties made of one or more of high melting point oxides, refractory non-oxides and carbon
4	Monolithic Refractory (Bulk Refractory Or Refractory Concrete)	refractory materials with a reasonable gradation of granular, powdery refractory raw materials, binders, and various admixtures that are not fired at high temperatures, and are used directly after mixing, molding and grilling material
5	Functional Refractory Materials	fired or non-fired refractory materials that are mixed with granulated and powdered refractory raw materials and binders to form a certain shape and have specific smelting applications.
6	Clay Bricks	Clay bricks are aluminum silicate refractory materials composed of mullite, glass phase, and cristobalite with an AL203 content of 30% to 48%			used in masonry blast furnaces, hot blast stoves, glass kilns, rotary kilns, etc
7	High Alumina Bricks			High alumina bricks refer to refractory materials with an AL3 content of more than 48%, mainly composed of corundum, mullite, and glass.	used in the metallurgy industry to build the plug and nozzle of a blast furnace, hot air furnace, electric furnace roof, steel drum, and pouring system, etc.
8	Silicon Bricks			The Si02 content of silicon brick is more than 93%, which is mainly composed of phosphor quartz, cristobalite, residual quartz, and glass	used to build the partition walls of the coking oven carbonization and combustion chambers, open-hearth heat storage chambers, high-temperature bearing parts of hot blast stoves, and vaults of other high-temperature kilns
9	Magnesium Bricks			alkaline refractory materials made from sintered magnesia or fused magnesia as raw materials, which are press-molded and sintered.	Magnesium bricks are mainly used in open-hearth furnaces, electric furnaces, and mixed iron furnaces.
10	Corundum Bricks			alumina content ≥90% and corundum as the main phase	used in blast furnaces, hot blast stoves, refining outside the furnace, and sliding nozzles.
11	Ramming Material			The ramming material refers to a bulk material formed by a strong ramming method, which is composed of a certain size of refractory material, a binder, and an additive	used for the overall lining of various industrial furnaces, such as open-hearth furnace bottom, electric furnace bottom, induction furnace lining, ladle lining, tapping trough, etc.
12	Plastic Refractory			Plastic refractories are amorphous refractory materials that have good plasticity over a long period of time. It is composed of a certain grade of refractory, binder, plasticizer, water and admixture.	used in various heating furnaces, soaking furnaces, annealing furnaces, and sintering furnaces.
13	Casting Material			The casting material is a kind of refractory with good fluidity, suitable for pouring molding. It is a mixture of aggregate, powder, cement, admixture and so on.	used in various industrial furnaces. It is the most widely used monolithic refractory material.