Alumina base refractories
Introduction of refractory and its types:
According to May Metals, today these materials are widely used as a protective coating for surfaces exposed to high temperatures or molten materials, not only in metallurgical and ceramic industries such as iron and steel, non-ferrous metals, casting, coking, etc. are used in chemical industries, power plants, nuclear industries and aerospace industries. The global production of these materials is estimated at two million tons annually.
According to the definition, refractory products are non-metallic ceramic materials whose melting temperature (melting temperature: the final temperature at which the tip of the cone made of the mentioned material (Zecker cone) contacts the plate held by it and other standard ceramic cones) is higher than C is 1500°. The main condition for a product to be considered refractory is to have compounds with a high melting point such as oxides, carbides, nitrides, broides, silicides and carbon/graphite. For the mass production of refractory materials, SiO2, Al2O3, MgO, CaO, Cr2O3 and ZrO3 oxides are usually present. . These materials do not have eutectics at low degrees.
Mechanical stability, resistance to corrosion at high temperatures (materials for the inner walls of furnaces and melters), high thermal resistance (materials for the outer walls of furnaces and melters) and sufficient resistance to thermal shocks (for all these products) are other conditions. Refractory products are of interest.
Non-flammable uses
The approximate share of each of the basic industries in the consumption of refractory products is:
70% in iron and steel production, 3% in non-ferrous metals production, 8% in cement production, 8% in ceramic production industries, 8% in glass production industries, 4% in chemical industries and 6% in other uses.
Classification of refractory materials
Classification based on traditional criteria: acidic-alkaline-neutral, shaped refractory materials (refractory bricks) – shapeless (refractory masses) and dense with less than 45% porosity and light with more than 45% porosity
The current classification is based on the EN12475 standard (parts 1-4, 1998 edition) of the European Union
A) Dense shaped materials
A-1- Alumina silica bricks
A-2- Alkaline bricks with less than 7% carbon residue
A-3- Alkaline bricks with 7% to 30% carbon residue
A-4- Special products
b) Dense shapeless materials
c) insulating materials
Compositions, properties and applications of silica-alumina refractories
Silica (93% ≤ SiO2), siliceous (93% > SiO2 ≥ 85%), low alumina refractory soil (85% > SiO2 and 30% > Al2O3≥ %), refractory soil (45% > Al2O3 ≥ 30%), High alumina (45% ≤ Al2O3)
raw materials, quartzite, clays, kyanite (other Al2SiO2 minerals) and mullite
Al2O3-SiO2 two-phase diagram (with special attention to mullite) and SiO2-CaO
High sensitivity to heat and the behavior of different phases of SiO2 at high temperatures
Silica refractories – rapid softening at a hot point and very good resistance to thermal shock (due to low thermal expansion between 600 and 1500 degrees Celsius, but phase changes are observed at temperatures above this thermal range)
Chamotte refractories – wide softening temperature range
Compositions, properties and uses of alkaline refractories
Magnesia (80% ≤ MgO), magnesia-doloma, dolomite, lime, magnesia-spinel, magnesia-chromite, forsterite, chromite, magnesia-zirconia, magnesia-zirconia-silica
Raw materials from magnesite and other carbonates, sea water
binary phase diagrams MgO-CaO, SiO2-CaO, SiO2- MgO, Al2O3-MgO, Fe2SiO4 – Mg2SiO4, FeO – CaO, FeO-MgO, Fe2O3-CaO, Fe2O3-MgO, ternary phase diagram SiO2- MgO- CaO (with Paying special attention to monticelite, mervinite and dicalcium silicate)
Magnesian refractories – excellent stability at high temperatures (no phase changes in MgO) but low thermal resistance (due to high thermal expansion)
Has environmental and health issues related to refractories with chromite
Other refractory products and special applications
Melt cast refractory products (improved corrosion resistance due to their closed pores)
Zircon (ZrSiO4), zirconia (cubic crystals, fully stable, or a mixture of cubic and monoclinic or weakly tetragonal crystals, locally stabilized with MgO or CaO) and AZS refractories (molten casting SiO2 – ZrO – Al2O3, for fiberglass corrosive melting)
SiC refractories (excellent resistance to thermal shocks due to low thermal expansion and high thermal conductivity)
Expensive Si3N4 and cheap Sialon refractories (with excellent resistance to thermal shocks)
Pure carbon refractories (can only be used in regeneration environments)
Oxide-carbon compounds (oxide: resistance to oxidation, graphite: thermal conductivity, low wettability and resistance to metal slag)
pure oxide refractories such as Al2O3 or ZrO (limited and expensive applications)
Highly porous refractories for thermal insulation purposes
Whiskers (single crystal) and fibers (amorphous or polycrystalline) for thermal insulation purposes.
