A brief description of various kinds of alumina
A variety of aluminum oxide also known as special alumina, non-metallurgical aluminum oxide or chemical aluminum oxide, aluminum oxide and aluminum hydroxide differentiated products or extension products.According to its chemical composition, crystal structure, particle size, purity, hardness, sintering degree, etc., can be divided into more than 300 varieties.The nature of many varieties of alumina is very different, some can be as hard as sapphire, some can be as soft as talcum powder;Some have an apparent density of more than 3,200kg /m, while others have a density of less than 3.2kg/m.Some inert insoluble substances, but some can be soluble in acid and base, with significant activity;Some fluids can be like sand sieving, but some are viscous or even thixotropic colloid and can not be filtered;Some crystal structure and crystal diameter of a wide range of variation, some are amorphous;Some have high adsorption capacity, some have no adsorption capacity;Some are active catalysts and some are inert.However, a common feature of all varieties of alumina, in any form, is that they are eventually converted to alpha alumina if heated for a long time at very high temperatures.Various kinds of alumina are widely used in chemistry, medicine, catalyst, rubber, plastic, papermaking, filler, pigment and other fields.With the development of science and technology and the application of new materials, the market of multi-variety alumina is becoming wider and wider.
Ii. Classification of various kinds of alumina
(I) Multiple varieties of aluminum hydroxide
1.Classification of multiple varieties of aluminum hydroxide:
(1) Ordinary filler aluminum hydroxide, D50 =50 m,70 m;
(2) Fine alumina hydroxide powder, D50 ≤20 m;
(3) Aluminum hydroxide micro powder (ultrafine aluminum hydroxide), D50 ≤1 m;
(4) Dry white aluminum hydroxide, whiteness ≥93%;
(5) High white aluminum hydroxide (artificial agate and artificial marble stuffing), whiteness ≥95%;
(6) Low alkali (sodium) aluminum hydroxide, Na2O+K2O≤0.10%;
(7) Low iron aluminum hydroxide, Fe2O3≤0.005%;
(8) Quasi-thin bauxite, with a crystal type of? -alooh as a monohydrous bauxite of 1-2 crystalline waters;
(9) Aluminum hydroxide gel, crystal al2O3.NH2O, the main phase is amorphous crystal type.
2.USES of various kinds of aluminum hydroxide:
(1) Used as a flame retardant
Aluminum hydroxide is an ideal flame retardant filler for plastics, rubber and other organic polymers and textiles.The synthetic materials with aluminum hydroxide as filler are: polyester, epoxy, phenolic, polypropylene, polyethylene, polyvinyl chloride, butyraldehyde rubber, neoprene, silicone rubber and advanced fire retardant coating, fire carpet, fire canvas, fire conveyor belt and so on.Because aluminum hydroxide is white powder, its physical properties and chemical properties are relatively stable under normal conditions, no moisture absorption, no color change, non-toxic harmless no smell, particle size can be processed as needed production.When the heating temperature exceeds 200℃, aluminum hydroxide begins to absorb heat and decompose, releasing three crystal water. The higher the temperature is, the faster the decomposition speed will be, thus inhibiting the rise of polymer temperature and playing the role of cooling, flame retardation and fire suppression.
(2) Used as filling material for artificial agate stone and artificial marble
With aluminum hydroxide and unsaturated polyester resin or methacrylate resin can produce artificial marble and agate decorative materials and sanitary ware.Because aluminum hydroxide has a refractive index (1.57) that is very close to that of polyester resin, artificial products are provided with a translucent and satisfactory brightness, and different colors can be added to design various patterns and specifications.The product also has the characteristics of high grade, light weight, no radiation, no brittle, easy cutting, etc., and has been widely used at present.
(3) Used as papermaking filler
Aluminum hydroxide is mainly used as surface coating, filler and non-combustible paper in papermaking production.High white ultrafine aluminum hydroxide is characterized by high whiteness, fine particle size, uniform distribution, and linear crystal shape, etc. It can replace titanium white powder on the premise of not reducing paper whiteness and opacity, save paper cost, improve paper gloss, and improve printing performance.
(4) Used as filling in toothpaste
Aluminum hydroxide has mild friction characteristics and belongs to the neutral material, filling in toothpaste as a friction agent can effectively remove the dirt on the teeth and gums without damage.The particle size of aluminum hydroxide used as the filling material of toothpaste is generally D50 ≤7 m, and the alkali addition must be < 0.01%.
(5) Used as pharmaceutical raw materials
One of the main components of gastric medicine is aluminum hydroxide, which can neutralize gastric acid and is a good raw material for making gastric medicine.
(6) As chemical raw materials
Because aluminum hydroxide is amphoteric compound, it can be quickly dissolved in strong acid or alkali, so it has become the raw material for many aluminum salts.Such as aluminum sulfate and alum is the product of aluminum hydroxide to react with sulfuric acid and its salts, polyaluminium chloride is a product of aluminum hydroxide to react with hydrochloric acid, aluminum fluoride is the product of aluminum hydroxide to react and hydrofluoric acid, etc., with the aluminum hydroxide (or sodium aluminate solution) as raw materials, can produce 3 a, 4 a, 5 a 13 x molecular sieve, 10 x, and Y type molecular sieves.
(2) Activated alumina
There are eight crystalline types of alumina:,,,,,, and.By heating and dehydrating aluminum hydroxide at different temperatures, different crystal types of aluminum oxide can be obtained. However, if it is roasted at a temperature above 1200℃, other crystal types of aluminum oxide will eventually be converted into -alumina.Alpha – alumina is called high – temperature alumina, also known as inert alumina, the other seven crystal alumina is called low – temperature alumina, also known as activated alumina.
As a hydrate of alumina, the mechanism and specific process of phase transition are also very different due to the difference in roasting temperature, roasting time and the complementarity of the hydrate.When aluminum hydroxide is rapidly dehydrated at 400-600 ℃, due to water removal, its crystal set disintegrates, crystal surface becomes loose, and many pores and cracks are formed, thus resulting in a sharp increase in specific surface area.The alumina with reasonable pore structure, larger pore volume and higher specific surface area has a high activity. The catalyst or catalyst carrier produced by it can be used for perfume, hydrocarbon cracking or synthesis, dehydration, oxidation, dehydrogenation, hydrogenation, reforming, desulfurization, dechloritization, defluorination and so on.Activated alumina can also be rolled into balls or squeezed into strips as a desiccant and hygroscopic agent for liquids and gases, used for refrigeration, air separation drying, instrument wind drying and selective adsorption of trace elements or trace pollutants in industrial processes.In addition, has a strong adhesion, is the raw material for the manufacture of fire-clay refractory materials.
(3) Inert alumina
Inert aluminum oxide is also called high temperature aluminum oxide, aluminum hydroxide or other crystalline aluminum oxide formed by 1200℃ or so high temperature roasting -crystalline aluminum oxide.As a metal oxide, alpha – alumina has good physical and chemical properties. It has great intermolecular cohesion, compact and perfect crystallization, and can withstand various chemical changes.At the same time, alpha-alumina also has the advantages of high melting point (2050℃), high hardness, good insulation performance, high mechanical strength, good abrasion resistance, and high heat resistance and heat resistance impact strength, so it is widely used in the following aspects:
1.refractory
Due to its high melting point, excellent mechanical properties and corrosion resistance at high temperatures, alpha-alumina is used to produce various refractory materials, such as mullite and alumina refractory bricks, corundum refractory bricks and corundum products, as well as amorphous refractory castables.
2.High alumina ceramics
As a result of the volume density of -alumina is large, can form a compact sintered body, and wear resistance and high mechanical strength, so it is suitable for the production of wear-resistant porcelain, such as grinding with a variety of porcelain ball, sandblast nozzle, water brush, etc., but also because of its good heat resistance, thermal impact strength, suitable for the production of ceramic tools.Due to its high temperature insulation performance, low sodium -alumina is suitable for the production of spark plugs and insulators for high temperature electrical appliances, thin film integrated electric subgrade board, standard parts and other high-frequency insulation porcelain.Alpha-alumina is widely used in the production of architectural ceramics, industrial ceramics, electronic electrical ceramics, sanitary ware and living ceramics, as well as process ceramics, such as ceramic bricks made of alpha-alumina, ceramic floors, ceramic rolling rods, ceramic pumps, ceramic filters, etc.
3.Abrasive material (abrasion resistant material)
Because of its high hardness, alpha – alumina can be used as grinding materials, grinding materials and wear – resistant materials.If it can be used as steel, nonferrous metal, plastic, wood or wood fiber and all kinds of rock (including jade) grinding and polishing materials, can make grinding wheel, turning tool and other cutting tools, can be used in the composite wood floor surface wear layer and some equipment or metal products surface wear layer.
(4) High purity ultrafine alumina
High-purity ultrafine aluminum oxide is refers to the content of AL2O3 > 99.99%, granularity < 1 mu m high purity superfine alumina powder, it is mainly used for transparent alumina sintering, fluorescent carrier, high pressure sodium lamp, high-grade physical and chemical equipment, artificial bone, semiconductor substrate substrate (C), the recording tape filling material, super filter medium, high-grade abrasive materials, special ceramics, cutting tools, high purity crucible, around the axis, bombarding target, furnace tube, packaging materials, single crystal materials, artificial stones, etc.;It can improve the compactness, finish, cold and hot fatigue, fracture toughness and creep resistance of ceramics.It can improve the wear resistance of molecular products, used for plastic, rubber reinforcement and toughening, wear resistant, high temperature resistant coating fillers and advanced cosmetic fillers;At the same time, it is also used as catalyst and catalyst carrier in the petrochemical and fertilizer industries, laser technology as raw material for laser neodymium glass and ruby laser materials, as advanced insulation materials in the power industry, aerospace industry, as surface treatment for aerospace aircraft, rockets and artificial satellites, etc.With the progress of society and the development of science and technology, the application field of high purity and ultra-fine alumina is also expanding, and the market prospect is very promising.
(5) Corundum
The naturally occurring -type alumina crystal is called corundum, which often has different colors due to different impurities. It has glass or diamond luster, with a density of 3.9-4.1g /cm3 and a hardness of 8.8.Natural corundum is also called precious stone. Those with a small amount of chromium oxide in the crystal are ruby, those with a small amount of iron and titanium impurities are sapphire, and those with a small amount of iron and cobalt impurities are emerald.
The output of natural corundum in nature is very small, and it is mostly used for decoration. The corundum used for industrial raw materials is artificially made.There are two kinds of artificial corundum: fused corundum and sintered corundum.There are mainly the following varieties:
1.Fused corundum
Fused alumina mainly consists of white fused alumina and brown fused alumina.
Fused white corundum is made from industrial alumina and smelted in an arc furnace at a high temperature above 2000℃.It has the characteristics of high whiteness, high purity, high hardness, excellent self-sharpness, strong grinding force, low heat, corrosion resistance, high temperature resistance, good thermal stability and so on.It can be used for making advanced grinding and polishing materials, grinding tools made from it, grinding high carbon steel and stainless steel;It is also widely used in the production of high-grade refractory and precision casting mold, used to make special ceramics and military, electronic and other high-tech materials;Corundum produced from high purity ultrafine alumina can also be used as artificial gems.
Brown corundum, also known as emery, is made of bauxite, anthracite and scrap iron by smelting at a high temperature above 2000℃ in an electric furnace. Its color is brown.
Brown corundum is characterized by moderate hardness, high pile density, good crystallization, low linear expansion coefficient, good toughness and corrosion resistance, etc. It is widely used in sandblasting materials, abrasives, fillers, filtration media, cutting materials, refractories, abrasives and ceramics.
2.Sintered corundum
Sintered corundum based on industrial or high purity alumina bauxite ore as raw material, made by fine grinding material ball or body, in 1750-1900 ℃ high temperature sintering, and it has a big secret, low porosity, grain with high intensity, excellent thermal shock resistance at high temperature and slag erosion resistance, widely used for making refractory and abrasive abrasive.
3.Tabular corundum
The plate corundum is a kind of aluminum oxide powder with high purity, which is first grinded, pelleted and dried and calcined at the high temperature of 1850-1950℃. It is formed with a well-developed plate and flake crystal structure with large grain size. It is an ideal refractory material with high purity, good volume stability, small shrinkage after refiring and strong thermal shock resistance.Plate corundum is mainly produced by sintering, but also by electric melting.
6) aluminium salts
Aluminum salts refer to compounds of aluminum. Only a few commonly used aluminum salts are described here.
1.Aluminum sulfate
Aluminum sulfate has aluminum sulfate and polyaluminum sulfate, aluminum ammonium sulfate (ammonium alum), aluminum sulfate potassium (alum or potassium alum), generally with sulfuric acid and aluminum hydroxide or bauxite, kaolin, fly ash and other aluminum minerals reaction production.Aluminum sulfate is mainly used as industrial reagent, flocculant, water treatment agent, papermaking, etc., and also used in the production of other aluminum-containing chemical products.Polyaluminum sulfate is mainly used for surface water treatment;Alum can be used as leavening agent, neutralizing agent and water precipitant for food.Alum is used in traditional Chinese medicine and baking powder. It is also used in paper making, painting and as a waterproofing agent.
2.Aluminium chloride
Aluminum chloride and polyaluminum chloride (aluminum sol) are used in the carbonate of aluminum, which is generally prepared by the reaction of hydrochloric acid with metallic aluminum, aluminum hydroxide or aluminum-containing minerals.Aluminum chloride and polyaluminum chloride are a kind of water purifier with low price and good effect, and can also be used as paper sizing, sugar refining, casting molding, cloth anti-wrinkle, catalyst carrier, binder, pharmaceutical refining, cement quick-setting, cosmetic raw materials, etc.
3.Aluminum fluoride and sodium fluoride
Aluminium fluoride and sodium fluoaluminate are two main fluoride salts.Aluminum fluoride is mainly used as an adjustment agent in electrolytic aluminum refining medium. It is a white powder with needle-like crystallization.The production process of aluminum fluoride has wet method and dry method. Due to the requirements of environmental protection, the wet method is basically eliminated and the dry method is widely used for production.The process flow of dry production of aluminum fluoride includes circulating fluidized bed process of Luqi Company in Germany, multi-layer fluidized bed process of Booth company in Switzerland and HF synthesis ALF3 process of internal and external heat furnaces of Pincnair company in France.The dry process is to produce calcium sulfate (gypsum) and HF gas by the reaction of fluorite and sulfuric acid, and then to produce aluminum fluoride by the reaction of HF gas and aluminum hydroxide after dehydration.When the phosphate fertilizer plant by-product of fluorosilicic acid production of aluminum fluoride, the Austrian Linz company’s wet process process, the first meet the requirements of fluorosilicic acid solution preheating, and then in the stirred tank with aluminum hydroxide (or bauxite slurry) at a certain temperature reaction, aluminum fluoride and silica (precipitation);Also can first use ammonia water and fluorosilicic acid reaction, the formation of ammonium fluoride and silica gel (precipitation), then with ammonium fluoride solution and aluminum hydroxide under a certain temperature and pressure reaction, the formation of aluminum fluoride.
Sodium fluoroaluminate (also known as cryolite) is a complex fluoride, usually a gray white crystalline particles or powder, mainly used in electrolytic aluminum as a solvent.The production process of sodium fluoroaluminate mainly includes soda fluoroaluminate method, which firstly reacts with hydrofluoric acid and aluminum hydroxide to produce fluoroaluminate, and then reacts with soda to synthesize sodium fluoroaluminate (cryolite).
4.Other aluminum salt
Aluminum nitrate can be used as a catalyst for organic synthesis, mordant in the printing and dyeing industry, leather finishing agent, etc., usually made by reacting aluminum or aluminum hydroxide with nitric acid.
Aluminum phosphate can be used as fumigating insecticide. It is generally prepared by burning mixed aluminum powder and red phosphorus.
The molecular sieves of aluminum phosphate series have high ion exchange capacity and catalytic activity and were prepared by the reaction of aluminum hydroxide and phosphoric acid.
Aluminum dihydrogen tripolyphosphate can be used as anticorrosive pigment, adsorbent (deodorant), ethylene to ethanol catalyst, generally from metal aluminum or aluminum hydroxide reaction with phosphoric acid.
Ultrafine aluminum silicate is amorphous super white powder with excellent suspension and pure white appearance. It is widely used in coating, leather, printing and dyeing, printing ink, paper making, plastic, rubber and other aspects in combination with other pigments (titanium white powder).Crystalline aluminum silicate can be used as catalyst for methanol gas phase dehydration to produce dimethyl ether.Ordinary aluminum silicate can be used as insulation material.Aluminum silicate is generally prepared by reaction of water glass with aluminum sulfate.
Aluminum borate crystal can be used as plastic, metal, ceramic reinforcement materials, generally with aluminum oxide and boron or boron oxide mixed, after the high temperature melting contact made, can also be water vapor into the gas state of aluminum fluoride and boron oxide, aluminum borate crystal made.
(vii) other multi-varieties of alumina and related extension products
The other variety of alumina still has carbonated aluminium, aluminium oxide fibre, aluminium oxide film, SB powder, in addition aluminium gallium alloy shot, trimethyl-aluminium and other organic aluminium are also the product with higher technical content.Alumina fiber consists of -Al2O3 single crystal fiber, -Al2O3 long fiber, -Al2O3 short fiber, which is mainly used as metal, plastic, rubber, ceramic reinforcement material, refractory insulation material and refractory material for rocket launch trajectory, oil-water emulsion, oil-water mixture and glue liquid separation and filtration material, and also used as catalyst carrier for hydrocarbon transformation.SB powder is the raw material for hydrogenation catalyst and other high grade catalysts.Alumina and hydrogen are formed by strong reaction of aluminum-gallium alloy pellets in water, which is an ideal hydrogen production process for future hydrogen-powered vehicles.Trimethyl aluminum is used as olefin polymerization catalyst, rocket fuel and raw material to make trimethyl gallium.
Bauxite ore can be used to produce refractory materials, water treatment flocculants, oil field fracturing proppants, brown corundum and high alumina cement, calcium aluminate powder or calcium aluminate cement, etc., and aluminum-silicon alloy can also be produced by electric heating method.
The red mud produced by alumina can be used as desulfurizer and soil improvement agent for coal-fired power plants. After the removal of sodium, it can be used to produce cement, wall materials, ceramsite, etc. From the red mud can also be used to extract iron ore powder, rare scandium, bismuth and other precious metals.
The intermediate products of aluminum oxide, liquid sodium aluminate and solid sodium aluminate (sintered clinker), can be used as concrete accelerator or used in the production of accelerator;Gallium, vanadium and other precious metals can be recovered and extracted from the intermediate mother liquor produced by alumina.
Post time: Sep-15-2020