CN117550617B - Technology for preparing mullite by taking coal-series kaolinite as raw material - Google Patents
Technology for preparing mullite by taking coal-series kaolinite as raw material Download PDFInfo
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- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 title claims abstract description 91
- 229910052863 mullite Inorganic materials 0.000 title claims abstract description 91
- NLYAJNPCOHFWQQ-UHFFFAOYSA-N kaolin Chemical compound O.O.O=[Al]O[Si](=O)O[Si](=O)O[Al]=O NLYAJNPCOHFWQQ-UHFFFAOYSA-N 0.000 title claims abstract description 51
- 229910052622 kaolinite Inorganic materials 0.000 title claims abstract description 35
- 239000002994 raw material Substances 0.000 title claims abstract description 25
- 238000005516 engineering process Methods 0.000 title description 6
- 238000005245 sintering Methods 0.000 claims abstract description 72
- 239000000843 powder Substances 0.000 claims abstract description 69
- 239000004576 sand Substances 0.000 claims abstract description 41
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 claims abstract description 32
- 238000000034 method Methods 0.000 claims abstract description 21
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 21
- 238000000227 grinding Methods 0.000 claims abstract description 20
- 238000001354 calcination Methods 0.000 claims abstract description 17
- 229910052845 zircon Inorganic materials 0.000 claims abstract description 17
- GFQYVLUOOAAOGM-UHFFFAOYSA-N zirconium(iv) silicate Chemical compound [Zr+4].[O-][Si]([O-])([O-])[O-] GFQYVLUOOAAOGM-UHFFFAOYSA-N 0.000 claims abstract description 17
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 16
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 16
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 16
- 229910052573 porcelain Inorganic materials 0.000 claims abstract description 16
- 239000004575 stone Substances 0.000 claims abstract description 16
- 238000001035 drying Methods 0.000 claims abstract description 15
- 238000000498 ball milling Methods 0.000 claims abstract description 13
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 11
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 11
- 238000004519 manufacturing process Methods 0.000 claims abstract description 8
- 238000002156 mixing Methods 0.000 claims abstract description 7
- 238000001816 cooling Methods 0.000 claims abstract description 6
- 238000007873 sieving Methods 0.000 claims abstract description 5
- DLHONNLASJQAHX-UHFFFAOYSA-N aluminum;potassium;oxygen(2-);silicon(4+) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[Al+3].[Si+4].[Si+4].[Si+4].[K+] DLHONNLASJQAHX-UHFFFAOYSA-N 0.000 claims description 63
- 229910052500 inorganic mineral Inorganic materials 0.000 claims description 54
- 239000011707 mineral Substances 0.000 claims description 54
- 230000008569 process Effects 0.000 claims description 16
- 238000005530 etching Methods 0.000 claims description 13
- 239000003245 coal Substances 0.000 claims description 11
- 238000004137 mechanical activation Methods 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 10
- 239000012670 alkaline solution Substances 0.000 claims description 6
- 238000012216 screening Methods 0.000 claims description 6
- 230000003213 activating effect Effects 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 5
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 3
- 239000011435 rock Substances 0.000 claims 2
- 239000005995 Aluminium silicate Substances 0.000 abstract description 16
- 235000012211 aluminium silicate Nutrition 0.000 abstract description 16
- 230000015572 biosynthetic process Effects 0.000 abstract description 6
- 238000003889 chemical engineering Methods 0.000 abstract description 2
- 239000012847 fine chemical Substances 0.000 abstract description 2
- 238000007254 oxidation reaction Methods 0.000 abstract description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 40
- 230000000052 comparative effect Effects 0.000 description 21
- 239000000047 product Substances 0.000 description 13
- 239000002245 particle Substances 0.000 description 12
- 239000013078 crystal Substances 0.000 description 7
- 239000012535 impurity Substances 0.000 description 7
- 230000000694 effects Effects 0.000 description 6
- 239000007791 liquid phase Substances 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
- 238000009792 diffusion process Methods 0.000 description 5
- 238000002844 melting Methods 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 239000012071 phase Substances 0.000 description 5
- 238000012545 processing Methods 0.000 description 4
- 230000001737 promoting effect Effects 0.000 description 4
- 230000009471 action Effects 0.000 description 3
- 238000005266 casting Methods 0.000 description 3
- 229910052906 cristobalite Inorganic materials 0.000 description 3
- 230000005496 eutectics Effects 0.000 description 3
- 238000010304 firing Methods 0.000 description 3
- 238000005495 investment casting Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 229910018068 Li 2 O Inorganic materials 0.000 description 2
- 239000012752 auxiliary agent Substances 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052593 corundum Inorganic materials 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 239000012467 final product Substances 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 230000002401 inhibitory effect Effects 0.000 description 2
- 229910001416 lithium ion Inorganic materials 0.000 description 2
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 description 2
- 239000000347 magnesium hydroxide Substances 0.000 description 2
- 229910001862 magnesium hydroxide Inorganic materials 0.000 description 2
- 238000003801 milling Methods 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- -1 oxygen ions Chemical class 0.000 description 2
- 239000010453 quartz Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 239000000377 silicon dioxide Substances 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- 230000003746 surface roughness Effects 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 229910021532 Calcite Inorganic materials 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 235000006481 Colocasia esculenta Nutrition 0.000 description 1
- 240000004270 Colocasia esculenta var. antiquorum Species 0.000 description 1
- 229910004742 Na2 O Inorganic materials 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- UQZIWOQVLUASCR-UHFFFAOYSA-N alumane;titanium Chemical compound [AlH3].[Ti] UQZIWOQVLUASCR-UHFFFAOYSA-N 0.000 description 1
- 229910000323 aluminium silicate Inorganic materials 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000010431 corundum Substances 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 238000006253 efflorescence Methods 0.000 description 1
- 230000003628 erosive effect Effects 0.000 description 1
- 239000010433 feldspar Substances 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000003837 high-temperature calcination Methods 0.000 description 1
- 150000004677 hydrates Chemical class 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 239000000395 magnesium oxide Substances 0.000 description 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 1
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- MKTRXTLKNXLULX-UHFFFAOYSA-P pentacalcium;dioxido(oxo)silane;hydron;tetrahydrate Chemical compound [H+].[H+].O.O.O.O.[Ca+2].[Ca+2].[Ca+2].[Ca+2].[Ca+2].[O-][Si]([O-])=O.[O-][Si]([O-])=O.[O-][Si]([O-])=O.[O-][Si]([O-])=O.[O-][Si]([O-])=O.[O-][Si]([O-])=O MKTRXTLKNXLULX-UHFFFAOYSA-P 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 206010037844 rash Diseases 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 229910021646 siderite Inorganic materials 0.000 description 1
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 238000003746 solid phase reaction Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
- 229910001845 yogo sapphire Inorganic materials 0.000 description 1
Abstract
The invention discloses a process for preparing mullite by taking coal-series kaolinite as a raw material, which belongs to the technical field of fine chemical engineering, wherein the coal-series kaolinite is crushed and screened into sand, then the sand is put into a ball mill, zirconia balls and water as grinding media are added, ball milling is carried out at room temperature, drying is carried out, and a pretreated kaolinite powder is obtained through sieving; mixing pretreated kaolin powder and an aluminum source according to the alumina content of 45% in mullite, adding sintering aids of lithium porcelain stone and zircon sand, grinding for 3-5 hours at room temperature, drying, pre-calcining for 1-2 hours in a tunnel kiln at 1000-1100 ℃, sintering for 16-18 hours at 1380-1450 ℃, naturally cooling, and taking out to obtain mullite. According to the method, coal-series kaolinite is used as a raw material to prepare mullite, firstly, the coal-series kaolinite is crushed, sieved and ball-milled to obtain kaolinite powder, then the kaolinite powder is sintered and synthesized with aluminum source industrial alumina at high temperature, the oxidation reaction of aluminum provides energy for the formation of alpha-Al 2O3 phase, and then alpha-Al 2O3 reacts with the kaolinite to form mullite.
Description
Technical Field
The invention belongs to the technical field of fine chemical engineering, and particularly relates to a process for preparing mullite by taking coal-series kaolinite as a raw material.
Background
The type of the North-Huai coal series kaolinite ore deposit belongs to a sedimentary type, is produced in a ancient world two-fold system and is 2.5 hundred million years away from the present day, is associated with a coal bed, the range is basically consistent with the coal bed, the occurrence depth is 200 meters, the layer thickness is about 4 meters, the ore body is stable, and the reserve of 3.4 hundred million tons is ascertained in a sluice ore zone.
The crude ore has the advantages of high purity, good crystallization order degree, uneasy efflorescence and the like, the kaolinite content is more than 95 percent, and the SiO 2/Al2O3 molar ratio is close to the theoretical value of 2.0; the ore has stable content of beneficial components A1 2O3、SiO2 and the like, small change, lower content of Na and K and lower content of siderite which are main harmful substances, and is particularly suitable for producing fine casting sand powder and refractory raw materials.
The mullite precision casting sand and powder products adopt an original complete processing technology of breaking before burning: dynamic calcination technology in rotary kiln makes crystal phase development perfect and balanced, and sand-shaped edges and corners 'passivated'; impurity precipitation and aggregation after high-temperature calcination of fine sand, impurity reduction and quality improvement after high-field strength impurity removal; the strong air flow blowing technology is used for stripping the powder in the sand; the full-flow ceramic lining powder preparation and grading technology not only improves the quality of powder products, but also ensures that the particle size distribution is more suitable for proportioning with silica sol.
The mullite precision casting sand and powder product has the characteristics of high refractoriness, small expansion coefficient, strong chemical erosion resistance, high softening point under load and the like, and is widely suitable for investment precision casting of carbon steel, stainless steel, heat-resistant steel, aluminum titanium and other alloys. The prepared fine casting mould shell has high strength, good air permeability, good shell collapsibility after casting, no deformation, no shrinkage and high smoothness.
However, the prior art adopts high-temperature sintered coal-series kaolinite to prepare mullite, and has the defects of high sintering temperature, low volume density and low purity of mullite.
Disclosure of Invention
The invention aims to provide a process for preparing mullite by taking coal-based kaolinite as a raw material, which aims to solve the problems of high sintering temperature and low volume density and low purity of mullite in the process of preparing mullite by sintering coal-based kaolinite at high temperature.
The aim of the invention can be achieved by the following technical scheme:
(1) Pretreatment of coal-series kaolin:
Crushing and screening coal-series kaolin into sand materials with 10-80 meshes, putting the sand materials into a ball mill, adding grinding media zirconia balls and water (the ratio of water to sand materials is 2:1), ball milling for 3-5 hours at room temperature at 200-300rmp, drying at 140-160 ℃, and screening the sand materials with 300 meshes to obtain pretreated coal-series kaolin;
(2) Mechanical activation of potassium feldspar mineral powder:
Adding potassium feldspar mineral powder, water and zirconia balls into a ball mill, and mechanically activating for 2-3 hours at a rotating speed of 500-800rpm, wherein the mass ratio of the zirconia balls to the potassium feldspar mineral powder is 1:100, and the mass ratio of the potassium feldspar mineral powder to the water is 10:1, obtaining mechanically activated potassium feldspar mineral powder;
Alkaline etching of potassium feldspar mineral powder:
adding alkaline solution (0.5-1 mol/L potassium hydroxide solution or magnesium hydroxide solution) into 2-4 parts by weight of mechanically activated potassium feldspar mineral powder at a ratio of 1:10, and performing alkaline etching treatment for 2-4 hours at 180-190 ℃ and pH value of 11-12 to obtain alkaline etched potassium feldspar mineral powder;
(3) And (3) two-step calcination:
Mixing 100-150 parts by weight of pretreated coal kaolin and aluminum source industrial alumina according to the alumina content of 45% in mullite, adding alkaline etched potassium feldspar powder obtained in the step (2) and 1-2 parts by weight of sintering aid (such as lithium porcelain stone, zircon sand and the like), grinding for 3-5 hours at 200-300rpm at room temperature, drying at 100-120 ℃, applying 100MPa pressure to process into a block shape, sintering in a reducing atmosphere, heating at a rate of 10 ℃/min, pre-calcining in a tunnel kiln at 1000-1100 ℃ for 1-2 hours, sintering at 1380-1450 ℃ for 16-18 hours, and taking out after natural cooling to obtain mullite.
The invention has the beneficial effects that:
(1) According to the method, coal-series kaolinite is used as a raw material to prepare mullite, firstly, the coal-series kaolinite is crushed, sieved and ball-milled to obtain kaolinite powder, then the kaolinite powder is sintered and synthesized with aluminum source industrial alumina at high temperature, the oxidation reaction of aluminum provides energy for the formation of alpha-Al 2O3 phase, and then alpha-Al 2O3 reacts with the kaolinite to form mullite.
(2) Potassium feldspar plays an important role in sintering mullite. Before firing, the potassium feldspar can play a role of barren raw materials, reduce the drying shrinkage and deformation of the green body, improve the drying performance and shorten the drying time. Meanwhile, in the sintering process, the potassium feldspar can be used as a flux, so that the sintering temperature is reduced, and quartz and kaolin are promoted to be melted. These molten components diffuse into each other in the liquid phase, thereby accelerating the formation of mullite. In addition, the formed feldspar glass body can be filled between mullite grains of the blank body, so that the blank body is compact, gaps are reduced, and the mechanical strength and the dielectric property are improved.
The mechanical activation of potassium feldspar mineral powder can reduce the sintering temperature of mullite: the mechanical activation process of the potassium feldspar mineral powder mainly involves the changes of the characteristics of particle size distribution, specific surface area, surface roughness, particle morphology and the like. Specifically, the mechanical activation can increase the specific surface area and the surface roughness of the potassium feldspar mineral powder, so that the interaction between the potassium feldspar mineral powder and other materials is improved, and the efficiency of the potassium feldspar mineral powder in the sintering process is improved.
Alkaline etching of potassium feldspar can reduce the sintering temperature of mullite: the potassium feldspar is hydrothermally etched under alkaline conditions to form minerals such as layered aluminosilicate, wherein the main products include tobermorite, hydrocalumite and calcite. These newly formed minerals act as low melting point fluxes, lowering the firing temperature and thus promoting mullite formation. In addition, the formation of the new phases can also fill gaps in the green body, so that the compactness of the green body is improved, and the mechanical strength and dielectric property of the green body are further improved.
The principle of reducing the mullite calcination temperature by the potassium feldspar is as follows: k 2 O in the potassium feldspar can react with Al 2O3 in the mullite at high temperature to generate fusible KAlO 2, so that the firing temperature of the mullite is reduced.
(3) The sintering aid is an effective method for reducing the sintering temperature of mullite, and can promote the diffusion and movement among particles, thereby reducing the sintering temperature and improving the volume density of mullite. For mullite, it is difficult to sinter because of the low diffusion rates of Si 4+ and Al 3+ ions at their grain boundaries. In order to reduce the sintering temperature of the mullite, lithium porcelain stone and zircon sand are added into the mullite as sintering aids.
The principle of the lithium porcelain stone for reducing the sintering temperature of mullite is as follows: k 2O、Na2 O and a small amount of Li 2 O are introduced into the lithium porcelain stone, and Li ions belong to inert gas ions, form asymmetric centers in the structure at high temperature, polarize oxygen ions, and play a role in reducing and destroying silicon oxygen bonds (O/Si), so that a small amount of Li 2 O introduced into the lithium porcelain stone can play a role in high Wen Churong and accelerating high-temperature liquid phase formation at high temperature, and the sintering temperature of mullite is reduced.
The zircon sand can be used as a sintering aid to reduce the sintering temperature of mullite, and can be subjected to substitution reaction with Al 3+ in mullite solid solution to cause mullite crystals to generate lattice distortion, activate lattices or form a low-temperature liquid phase, so that the diffusion coefficient is improved, and the sintering temperature of mullite is reduced. In addition, zircon sand can also generate a liquid phase, and the surface wetting force and the surface tension of the liquid phase enable solid phase particles to be close to and fill pores, so that more liquid phase can accelerate sintering, and the sintering temperature is reduced.
(4) The sintering aid lithium porcelain stone and zircon sand can increase the volume density of the sintered mullite and reduce the apparent porosity:
The manner in which magnesium oxide increases the bulk density of sintered mullite: promoting the sintering process: the addition of a proper amount of lithium porcelain stone can promote the combination among particles in the sintering process and improve the density and strength of the sintered product. Improving the crystal structure: the lithium porcelain stone can promote the melting and recrystallization of particles in the sintering process, improve the crystal structure and grain boundary property of the sintered product, and further improve the performance of the sintered product.
The lithium porcelain stone reduces the apparent porosity of the sintered mullite by its effect of promoting sintering and inhibiting the generation of pores. Promoting sintering: li ions belong to inert gas ions, form asymmetric centers in the structure at high temperature, polarize oxygen ions, play a role in reducing and destroying silicon oxygen bonds (O/Si), generate eutectic with low melting point and promote the sintering of mullite. This helps to reduce the porosity in the sintered mullite and reduce apparent porosity. Inhibiting the generation of air holes: the lithium porcelain stone can react with moisture or other volatile substances in the sintering raw materials to generate corresponding oxides or hydrates, so that the escape of the volatile substances in the sintering process is reduced, and the generation of pores is inhibited.
Zircon sand can increase the bulk density of sintered mullite in a number of ways. Firstly, zircon sand can be used as a sintering aid to react with Al 2O3 in mullite to generate eutectic matters with low melting point so as to promote the sintering of the mullite. This helps to increase the bulk density of the mullite. Second, the high density and stability of the zircon sand itself also helps to increase the bulk density of the sintered mullite. The addition of zircon sand can make the internal structure of sintered mullite more compact, reduce air holes and cracks and further raise its volume density.
The principle of reducing the apparent porosity of the sintered mullite by zircon sand is as follows: zircon sand reacts with alumina in mullite at high temperature to generate eutectic with lower melting point, so as to promote the sintering of the mullite. This helps to reduce the porosity in the sintered mullite and thus reduce its apparent porosity.
(5) The reduction of the particle size of the powder mainly occurs at the initial stage of ball milling, and as the ball milling time increases, the fine particles are agglomerated. As the milling time increases, the morphology of the particles changes from irregular to spherical. The crystal structure of the raw material is changed along with the increase of the ball milling time, and the kaolin is firstly peeled off along the layered structure, and the crystal structure of the kaolin is destroyed until the kaolin becomes an amorphous state.
The pre-grinding has a significant effect on the purity of the sintered mullite. Specifically, after the raw materials are ground, the crystal structure of the raw materials can be improved, which is helpful for improving the purity of the sintered mullite. The internal structure of the raw material particles is optimized after mechanical activation, so that the activity of the raw material is improved, and the solid-phase reaction and sintering of mullite are facilitated.
The effect of pre-grinding on sintered mullite purity is mainly manifested in several aspects:
grinding can refine raw material particles, increase specific surface area, promote mass transfer and diffusion, and thereby accelerate sintering process. The thinned particles are easier to contact atoms or molecules, promote the reaction, and help to improve the purity and crystallinity of the mullite.
The grinding can remove impurities and inclusion in the raw materials, and improve the purity of the raw materials, thereby influencing the purity of the final sintered mullite.
(6) The pre-calcination and then sintering process has a significant effect on the purity of mullite, and the pre-calcination process can help reduce impurities in the raw materials, thereby improving the purity of the final product. During the pre-calcination and re-sintering process, the diffusion and bonding between the grains can be more sufficient, which is helpful for forming a dense mullite material. During the pre-calcination stage, impurities and part of the minerals in the kaolin may decompose or volatilize at lower temperatures, which helps to increase the purity of the final product. In the sintering stage, the non-decomposed minerals and residual impurities can be further reacted or removed, so that the purity of the product is further improved.
The initial raw materials are pre-calcined to form a mixture of Al 2O3-SiO2 with higher activity and transitional corundum, quartz and cristobalite phases, and the phases are more easily reacted to form mullite during high-temperature sintering.
Detailed Description
The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
(1) Pretreatment of coal-series kaolin:
Crushing and screening coal-series kaolinite into 10-mesh sand, putting the sand into a ball mill, adding grinding media zirconia balls and water (the ratio of water to sand is 2:1), ball milling for 3 hours at room temperature at 200rmp, drying at 140 ℃, and sieving with a 300-mesh sieve to obtain pretreated coal-series kaolinite;
(2) Mechanical activation of potassium feldspar mineral powder:
adding potassium feldspar mineral powder, water and zirconia balls into a ball mill, and mechanically activating for 2 hours at a rotating speed of 500rpm, wherein the mass ratio of the zirconia balls to the potassium feldspar mineral powder is 1:100, and the mass ratio of the potassium feldspar mineral powder to the water is 10:1, obtaining mechanically activated potassium feldspar mineral powder;
Alkaline etching of potassium feldspar mineral powder:
Adding alkaline solution (0.5 mol/L potassium hydroxide solution) into 2 parts by weight of mechanically activated potassium feldspar mineral powder at a ratio of 1:10, and performing alkaline etching treatment for 2 hours at 180 ℃ under the condition of pH 11 to obtain alkaline etched potassium feldspar mineral powder;
(3) And (3) two-step calcination:
Mixing 100 parts by weight of pretreated coal-series kaolin and aluminum source industrial alumina according to the alumina content of 45% in mullite, adding alkaline etched potassium feldspar powder obtained in the step (2) and 1 part by weight of sintering aid (such as lithium porcelain stone, zircon sand and the like), grinding for 3 hours at room temperature at 200rpm, drying at 100 ℃, applying 100MPa pressure, processing into blocks, sintering in a reducing atmosphere, heating at a rate of 10 ℃/min, pre-calcining for 1 hour in a tunnel kiln at 1000 ℃, sintering for 10 hours at 1410 ℃, naturally cooling, and taking out to obtain mullite.
Example 2
(1) Pretreatment of coal-series kaolin:
Crushing and screening coal-series kaolinite into sand with 80 meshes, putting the sand into a ball mill, adding grinding media zirconia balls and water (the ratio of water to sand is 2:1), ball milling for 5 hours at room temperature at 300rmp, drying at 160 ℃, and sieving with a 300-mesh sieve to obtain pretreated coal-series kaolinite;
(2) Mechanical activation of potassium feldspar mineral powder:
Adding potassium feldspar mineral powder, water and zirconia balls into a ball mill, and mechanically activating for 3 hours at a rotating speed of 800rpm, wherein the mass ratio of the zirconia balls to the potassium feldspar mineral powder is 1:100, and the mass ratio of the potassium feldspar mineral powder to the water is 10:1, obtaining mechanically activated potassium feldspar mineral powder;
Alkaline etching of potassium feldspar mineral powder:
Adding an alkaline solution (1 mol/L magnesium hydroxide solution) into 4 parts by weight of mechanically activated potassium feldspar mineral powder at a ratio of 1:10, and performing alkaline etching treatment for 4 hours at 190 ℃ and pH 12 to obtain alkaline etched potassium feldspar mineral powder;
(3) And (3) two-step calcination:
Mixing 150 parts by weight of pretreated coal-series kaolin and aluminum source industrial alumina according to the alumina content of 45% in mullite, adding alkaline etched potassium feldspar powder obtained in the step (2) and 2 parts by weight of sintering aid (such as lithium porcelain stone, zircon sand and the like), grinding for 5 hours at room temperature at 300rpm, drying at 120 ℃, applying 100MPa pressure, processing into blocks, sintering in a reducing atmosphere, heating at a rate of 10 ℃/min, pre-calcining for 2 hours in a tunnel kiln at 1100 ℃, sintering for 16 hours at 1410 ℃, naturally cooling, and taking out to obtain mullite.
Example 3
(1) Pretreatment of coal-series kaolin:
Crushing and screening coal-series kaolinite into sand with the size of 50 meshes, putting the sand into a ball mill, adding grinding media zirconia balls and water (the proportion of water to sand is 2:1), ball milling for 4 hours at the room temperature at the temperature of 250rmp, drying at the temperature of 150 ℃, and sieving the sand with a 300-mesh sieve to obtain pretreated coal-series kaolinite;
(2) Mechanical activation of potassium feldspar mineral powder:
adding potassium feldspar mineral powder, water and zirconia balls into a ball mill, and mechanically activating for 2.5 hours at a rotating speed of 600rpm, wherein the mass ratio of the zirconia balls to the potassium feldspar mineral powder is 1:100, and the mass ratio of the potassium feldspar mineral powder to the water is 10:1, obtaining mechanically activated potassium feldspar mineral powder;
Alkaline etching of potassium feldspar mineral powder:
Adding an alkaline solution (0.7 mol/L potassium hydroxide solution) into 3 parts by weight of mechanically activated potassium feldspar mineral powder at a ratio of 1:10, and performing alkaline etching treatment for 3 hours at 185 ℃ and pH value of 11.5 to obtain alkaline etched potassium feldspar mineral powder;
(3) And (3) two-step calcination:
mixing 120 parts by weight of pretreated coal-series kaolin and aluminum source industrial alumina according to the alumina content of 45% in mullite, adding alkaline etched potassium feldspar powder obtained in the step (2) and 1.5 parts by weight of sintering aid (such as lithium porcelain stone, zircon sand and the like), grinding for 4 hours at room temperature at 250rpm, drying at 110 ℃, applying 100MPa pressure, processing into blocks, sintering in a reducing atmosphere, heating at a rate of 10 ℃/min, pre-calcining for 1.5 hours in a 1050 ℃ tunnel kiln, sintering for 12 hours at 1410 ℃, naturally cooling, and taking out to obtain mullite.
The potassium feldspar mineral powder reduces the sintering temperature of mullite: comparative examples 1 to 3
Comparative example 1
Compared with example 3, the potassium feldspar mineral powder is not added, and the rest steps are the same.
Comparative example 2
Compared with example 3, the potassium feldspar mineral powder is not subjected to mechanical activation treatment, and the rest steps are the same.
Comparative example 3
Compared with example 3, the potassium feldspar mineral powder is not subjected to alkaline etching treatment, and the rest steps are the same.
The sintering aid can reduce sintering temperature, increase bulk density and reduce apparent porosity, and comparative examples 4-6:
comparative example 4
In comparison with example 3, no sintering aid was added, and the rest of the steps were the same.
Comparative example 5
Compared with example 3, only the lithium porcelain stone is added, and the rest steps are the same.
Comparative example 6
In comparison with example 3, only zircon sand was added, and the other steps were the same.
Influence of milling time on mullite purity: comparative examples 7 to 9
Comparative example 7
In comparison with example 3, no grinding was carried out after addition of the sintering aid, and the rest of the steps were the same.
Comparative example 8
Compared with example 3, the sintering aid was added and grinding was carried out for 2 hours, and the other steps were the same.
Comparative example 9
Compared with example 3, the sintering aid was added and grinding was carried out for 6 hours, and the other steps were the same.
The mullite prepared in examples 1 to 3 and comparative examples 1 to 9 of the present invention were subjected to performance tests according to the standards of mullite (YB/T5267-2013, YB/T5267-2005) and the test results are shown in tables 1 and 2:
TABLE 1
TABLE 2
As can be seen from tables 1 and 2, the mullite prepared according to the scheme described in examples 1-3 has properties that meet the specification of M45-1 in the standard, and each property is superior to grade 1.
In comparative example 1, since potassium feldspar powder was not added, the sintering temperature could not be lowered, and at the same sintering temperature as in example 3, the properties of the obtained mullite became poor, and the requirement of the M45-2 secondary product in the standard was not satisfied.
In comparative examples 2 to 3, the mechanical activation treatment or the alkaline etching treatment is carried out on the potassium feldspar mineral powder alone, and compared with example 3, the physical and chemical properties of the obtained mullite are poor, and each property still meets the requirements of M45-2 secondary products in the standard.
Compared with the comparative example 4 and the example 3, the properties of the obtained mullite are all poor without adding sintering auxiliary agents, and the requirements of M45-2 secondary products in the standard are not met.
Compared with the embodiment 3, the comparative examples 5-6 only add one sintering aid, the physical and chemical properties of the obtained mullite are poor, and each property still meets the requirements of M45-2 secondary products in the standard.
Compared with the comparative example 7 and the example 3, the performance of the mullite obtained by ball milling is poor after adding the sintering aid, and the mullite does not meet the requirements of the M45-2 grade in the standard.
Compared with the comparative example 8 and the example 3, the mullite obtained by ball milling for 2 hours after adding the sintering aid has various properties meeting the requirements of an M45-2 secondary product in the standard.
Compared with the comparative example 9 and the example 3, the sintering auxiliary agent is added and ball milling is carried out for 6 hours, the ball milling time is too long, and the excessive abrasion of raw materials can be caused, so that the purity of the sintered mullite is affected, compared with the mullite of the comparative example 8, the purity of the mullite is reduced, and the other indexes meet the requirements of the M45-2 grade in the standard.
It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (5)
1. The process for preparing mullite by taking coal-based kaolinite as a raw material is characterized by comprising the following steps of:
(1) Alkaline etching of potassium feldspar mineral powder:
adding alkaline solution into 2-4 parts by weight of mechanically activated potassium feldspar mineral powder in a ratio of 1:10, and performing alkaline etching treatment for 2-4 hours at 180-190 ℃ and pH 11-12 to obtain alkaline etched potassium feldspar mineral powder;
(2) And (3) two-step calcination:
mixing 100-150 parts by weight of pretreated coal-series kaolinite rock and an aluminum source according to the standard, adding the alkaline etched potassium feldspar powder obtained in the step (1) and 1-2 parts by weight of sintering aid, grinding for 3-5 hours at room temperature, drying at 100-120 ℃, applying 100MPa pressure to process the mixture into blocks, sintering in a reducing atmosphere, pre-calcining for 1-2 hours in a tunnel kiln at 1000-1100 ℃, sintering for 16-18 hours at 1380-1450 ℃, and taking out the mixture after natural cooling to obtain mullite;
The aluminum source is industrial alumina, and the mixing of the alumina according to the standard means that the alumina content in the mullite is 45%;
the sintering aid is lithium porcelain stone, zircon sand and other materials.
2. The process for preparing mullite by using coal-based kaolinite as raw material as claimed in claim 1, wherein the mechanical activation of potassium feldspar mineral powder is characterized in that:
Adding potassium feldspar mineral powder, water and zirconia balls into a ball mill, and mechanically activating for 2-3 hours at a rotating speed of 500-800rpm to obtain mechanically activated potassium feldspar mineral powder;
the mass ratio of the zirconia balls to the potassium feldspar mineral powder is 1:100, and the mass ratio of the potassium feldspar mineral powder to the water is 10:1.
3. The process for preparing mullite according to claim 1, wherein the alkaline solution is a potassium hydroxide solution of 0.5-1 mol/L.
4. The process for preparing mullite by using coal-based kaolinite as raw material as claimed in claim 1, wherein the pretreatment of the coal-based kaolinite is as follows:
Crushing and screening coal-series kaolinite rock into sand materials with 10-80 meshes, putting the sand materials into a ball mill, and adding grinding media zirconia balls and water, wherein the proportion of the water to the sand materials is 2:1, ball milling for 3-5 hours at room temperature of 200-300rmp, drying at 140-160 ℃, and sieving with a 300-mesh sieve to obtain the pretreated coal-series kaolinite.
5. The process for preparing mullite by using coal-based kaolinite as raw material as claimed in claim 1, wherein the grinding rate is 200-300rpm and the heating rate is 10 ℃/min during sintering.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102674381A (en) * | 2012-05-22 | 2012-09-19 | 中国地质大学（北京） | Method for preparing nano mullite powder from coal-based kaolin |
| CN106745124A (en) * | 2016-12-08 | 2017-05-31 | 湖南先导电子陶瓷科技产业园发展有限公司 | A kind of technique that aluminium hydroxide and concrete admixture are produced from Coaseries kaolin |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102674381A (en) * | 2012-05-22 | 2012-09-19 | 中国地质大学（北京） | Method for preparing nano mullite powder from coal-based kaolin |
| CN106745124A (en) * | 2016-12-08 | 2017-05-31 | 湖南先导电子陶瓷科技产业园发展有限公司 | A kind of technique that aluminium hydroxide and concrete admixture are produced from Coaseries kaolin |
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