Energy is becoming more and more tight and environmental protection is becoming more and more stringent. As an indispensable part of high-temperature industry, refractory materials have put forward new requirements for some of its key properties, such as low thermal conductivity, high refractoriness, better volume stability, and better Thermal shock resistance, etc. In order to meet the needs of high-temperature kilns with lightweight structures.
In the Chinese market, light weight high alumina bricks, light weight mullite bricks, light weight clay bricks, light weight silica bricks, etc., prepared by the loss-of-ignition method or foaming method, have been widely used in the backing layer and insulation layer of industrial kilns ;but the working face bricks used in high temperature or ultra-high temperature industrial kilns are mainly alumina bubble brick.Alumina bubble bricks mainly use Alumina bubble as aggregates, which are combined with corundum and mullite.These bricks are characterized by relatively high bulk density and relatively large thermal conductivity. For reducing the weight of the kiln, energy saving and consumption reduction are unfavorable, but the strength is greater, and the high-temperature structural stability of the industrial kiln is better;Alumina light weight bricks usually use alumina fine powder to add poly light ball, sawdust, graphite, petroleum coke and other burning loss or sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecyl benzene sulfonate, dodecyl sulfate triethanolamine and other foaming agents are used to create pores to obtain low thermal conductivity. However, due to the large volume changes during the production process, they are usually used to produce large bodies and then processed to the required size.
In view of the above alumina bubble as closed pores and ablated foaming pores to produce thermal insulation materials, Chinese technicians combine the two modes to produce a smaller bulk density, better thermal insulation effect and a certain strength insulation materials.
A patent discloses a method for making alumina bubble bricks, using alumina bubble, Al2O3 micropowder, ρ-Al2O3 micropowder, silicon micropowder, and organic polymer powder such as distiller’s grains, starch, glucose, and dextrin as raw material, add water, stir evenly, cast and form, after demoulding and curing, sinter at a high temperature of 1600～1700℃; the volume density of the prepared alumina bubble products is 1.1～1.7g/cm3, and the compressive strength is 11 ～25Mpa. Because this technology uses casting, the molding efficiency is very low, and it is not suitable for large-scale production. At the same time, due to firing shrinkage, it cannot be molded into near-final size.
A patent discloses a method for making alumina bubble bricks. The alumina bubble are used as aggregates and the alumina micropowderr is used as the matrix. Water and foaming agent are added to the alumina micropowder and foamed by mixing.Add pores into the matrix of bubble bricks to obtain a porous matrix; use the organic monomer and crosslinking agent in the foamed slurry to undergo polymerization under the action of the initiator and catalyst to realize the solidification of the foamed slurry and leave it to stand for demoulding A green body composed of a porous matrix and hollow sphere aggregate is obtained. After drying and sintering, a lightweight alumina bubble insulation brick is obtained. The finished product has a density of 0.6 to 1.0 g/cm3 and a thermal conductivity of 0.36. ~ 0.83W/m ·k. The disadvantages of this product are that the slurry is cured and demoulded, and the molding efficiency is low. At the same time, the strength of the product is low, the size shrinks too much during the firing process, and the product yield is low.
A patent discloses a method for making alumina bubble bricks. The alumina bubble is used as the aggregate, and the porous matrix is calcium hexaaluminate made of alumina and calcium oxide at high temperature. Mix alumina mircopowder and calcium aluminate cement, add pore-forming agent polystyrene balls, dispersant, water and alumina bubble, stir and mix to obtain a mixed slurry, pour it into the mold and release it after solidification, and dry and fire it the alumina bubble heat insulation product is obtained. The product has a bulk density of 0.6 to 1.16g/cm3, a thermal conductivity of 0.265 to 0.464W/m·k, and a compressive strength of 4.83 to 13.42Mpa. The process is complicated, the slurry is solidified and demolded, the molding efficiency is low, the near-final size molding cannot be performed, the strength is limited, and the application range is limited.
In order to solve the above technical problems, the purpose of the present invention is to provide a method for preparing alumina bubble bricks by using a pore former.
The present invention adopts the following technical solutions to accomplish the above-mentioned purpose:
A method for preparing alumina bubble bricks by using a pore-forming agent. The raw material composition and mass percentage of alumina bubble bricks are:
Alumina bubble, 3～0.2mm, 40～55%, Al2O3 content is greater than 99%;
Al2O3 micropowder, less than 325 mesh, 20-40%, Al2O3 content greater than 99%;
Silicon micropowder, less than 325 mesh, 1～4%, SiO2 content greater than 96%;
Fine clay powder, less than 325 mesh, 10-25%, the content of Al2O3 after ignition of the fine clay powder is greater than 45%;
The method for preparing alumina bubble bricks with pore formers is: pre-mixing three kinds of fine powders of Al2O3 powder, fine clay powder, and fine silicon powder as the matrix part; using silica sol solution to fully carry out the spherical pore-forming agent of 50～150um stir to make the silica sol solution fully wet and adhere to the surface of the spherical pore former; then mix and granulate the mixed powder of the three kinds of micropowders as the matrix and the spherical pore former with the silica sol solution attached to the mixed powder. The coating particles of spherical pore-forming agent; then the alumina bubble and the binder are fully mixed, then the coating particles are added and mixed again, and finally the shaped products of various required sizes are made by the vibration pressure method, after 100～120℃ drying, heat preservation at 1600-1700°C for 5-8 hours and firing to obtain alumina bubble bricks.
The added amount of spherical pore-forming agent is 6-15% of the total weight of the three mixed powders of Al2O3 powder, clay powder, and silicon powder.
The amount of silica sol added is 5 to 13% of the total weight of the three mixed powders of Al2O3 powder, clay powder, and silicon powder;
The amount of binder added is 2 to 4% of the weight of the alumina bubble.
The spherical pore former is any one of PS and PMMA, or any combination of the two.
The present invention proposes a method for making alumina bubble bricks using a pore former. Three spherical pore formers of different sizes are used to create 50um, 100um, and 150um pores in the matrix of the alumina bubble brick. On the one hand, the closed pores of the alumina bubble with the smallest particle size of 0.2mm form a structure with continuous pore size distribution, which reduces the bulk density of the brick and increases the thermal insulation performance of the brick; a pore former with a minimum of 50um can also avoid smaller size pores appear in the matrix structure, so that the sintered continuous structure of the matrix phase will not be interrupted by too many small pores; in addition, most of the pores formed are spherical pores, and the spherical arched structure of the matrix also enhances its bonding. Ensure the high strength of the brick; Figure 1 and Figure 2 shows the microstructure of the alumina bubble brick.
The invention uses silica sol solution for granulation and packaging. When the granulator is ablated at 400°C, the matrix powder infiltrated by the silica sol forms a spherical shell on the periphery of the circular cavity after the granulator is burned, which can prevent the size of the green body. Deformation; as the temperature continues to rise, silica fine powder, silica powder and silica sol decomposed silica and alumina powder react to form a certain amount of mullite binding phase, the reaction of mullite is a slight expansion Reaction can avoid changes in product size.
Compared with traditional alumina bubble thermal insulation products made by this method, the bulk density can be reduced from the original 1.4～1.7g/cm3 to 0.8～1 .0g/cm3, the thermal conductivity is reduced from the original 0.76～1.13W/m·k to 0.38～0.54W/m·k, and the compressive strength is 15～27Mpa; because the newly prepared alumina heat insulation products mainly The crystal phases are corundum phase and mullite phase, which also have the characteristics of good high temperature creep resistance and excellent thermal shock resistance.
The method has a simple process, and the used pore former is a mature product on the market, which is convenient for large-scale production.
Description of the drawings
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Figure 1
Figure 2
Figure 1 is a 15 times magnified microstructure diagram of alumina bubble bricks;
Figure 2 is a microstructure diagram of alumina bubble bricks magnified by 100 times.
In the picture: 1. The pores left by the pore former, 2. The corundum-mullite binding phase, 3. The alumina bubble.
Detailed ways
The present invention will be described in combination with specific embodiments:
Example one:
A method for making alumina bubble bricks by using a pore former: first mix 36% Al2O3 micropowder, 10% clay fine powder, and 2% silica micropowder in advance to serve as the matrix mixed powder;
Spherical PS is selected as the pore former. The three sizes and the addition ratio are 50um, 33%; 100um, 35%; 150um, 32%; the added amount is 6% of the weight of the mixed powder and the added amount is the weight of the mixed powder. The 7% silica sol solution of 7% is thoroughly mixed and moistened, and then the mixed powder is added for wrapping and granulation;
Mix 52% alumina bubble and 3% of the weight of the alumina bubble with a CMC:PVA=1:5 aqueous solution, then add the finished coating particles to mix, and prepare each by vibration and pressure. A shaped product of the required size is dried at 120°C and kept at 1650°C for 8 hours and fired.
At the same time, a comparative example is also used in this embodiment. The comparative example is the scheme in CN20111036367.6 "A method for preparing alumina bubble heat insulation refractory material": 65% alumina bubble , 15% alumina bubble , 15% Clay, 20% Al2O3 micropowder, 2% dextrin, 8% water are fully mixed, pressed and shaken for molding, dried at 100°C for 30 hours, and heated at 1650°C for 8 hours.
The bulk density of the alumina bubble bricks obtained in this embodiment is 0.9g/cm3, the thermal conductivity is 0.42W/m·k, the compressive strength is 15Mpa, and the alumina bubble bricks are 15 times magnified The microstructure diagram and the 100 times magnified microstructure diagram are shown in Figure 1 and Figure 2, respectively. The alumina bubble bricks obtained in the comparative example have a bulk density of 1.3 to 1.5 g/cm3, a thermal conductivity of 0.5 to 0.6 W/m·k, and a compressive strength of 9 to 10 Mpa.
Example two:
A method of making alumina bubble bricks by using a pore former; firstly mix 20% Al2O3 micropowder, 24% clay fine powder, and 1% silica micropowder in advance to serve as the matrix mixed powder;
Spherical PMMA is selected as the pore-forming agent. The three sizes and the addition ratio are 50um, 30%; 100um, 40%; 150um, 30%; the added amount is 15% of the weight of the mixed powder and the added amount is the weight of the mixed powder The 11% silica sol solution is fully mixed and wetted, and then the mixed powder is added to wrap and granulate;
Mix 55% alumina bubble and 2.5% of the weight of the alumina bubble with CMC:PVA=1:1 aqueous solution, then add the finished coating particles to mix, and prepare each by vibrating pressure. Kinds of shaped products of the required size are dried at 115°C and kept at 1700°C for 6 hours;
At the same time, a comparative example is also used in this embodiment. The comparative example is in the patent CN 201110023753.0 "A kind of aluminum oxide hollow sphere lightweight insulation brick and its preparation method". The scheme: 45-50% alumina bubble s are used. , 37～43% Al2O3 micropowder, 7～12% ρ-Al2O3 micropowder, 4～5% silicon micropowder, and 10～15% starch and 23-27% water of the external mixture, stir evenly, and cast into shape. After demoulding and curing, it is fired at a high temperature of 1650～1700℃ for 3～6 hours.
The alumina bubble brick obtained in this embodiment has a bulk density of 0.85 g/cm3, a thermal conductivity of 0.45 W/m·k, and a compressive strength of 25 Mpa. It is molded at one time, and the firing size remains unchanged. The alumina bubble bricks obtained in the comparative example have a bulk density of 1.2～1.6g/cm3, a thermal conductivity of 0.22～0.60W/m·k, and a compressive strength of 15～25Mpa. Pouring molding has very low molding efficiency and is not suitable for large-scale production. At the same time, due to firing shrinkage, it cannot be molded to near-final size.
Example three:
A method for making alumina bubble bricks by using a pore former; firstly, 31% Al2O3 micropowder, 18% clay fine powder, 4% silica micropowder are pre-mixed and used as the matrix mixed powder;
Spherical PS is selected as the pore former: PMMA=1:1, three sizes and the addition ratio are 50um, 25%; 100um, 40%; 150um, 35%; the addition amount is 11% of the weight of the mixed powder. Add a 9% silica sol solution of the weight of the mixed powder to fully mix and wet, and then add the mixed powder to wrap and granulate;
Mix 47% of the alumina bubbles and 4% of the PVA aqueous solution of the weight of the alumina bubbles, and then add the finished coating particles to mix, and use vibration pressure to prepare various desired sizes. The product is dried at 110°C and kept at 1680°C for 7 hours and fired;
At the same time, a comparative example is also used in this embodiment. The comparative example is the solution in the patent CN201410434384. 8 "a method for preparing a lightweight alumina hollow spherical heat insulation product": 5000g alumina micropowder, 750g water, 100g Sodium hexametaphosphate, 250g acrylamide AM, 50g methylenebisacrylamide MBAM, tetramethylethylenediamine TEMED are ball milled and mixed to obtain a slurry, then 50g sodium lauryl sulfate is added, stirred and foamed to obtain a foamed material Then add 5000g of alumina bubble s and 50g of ammonium persulfate to the foamed slurry for injection molding. After leaving the mold, a green body composed of porous matrix and hollow sphere aggregates is obtained, which is dried at 1600°C for 6 hours and sintered. , To obtain lightweight alumina bubble insulation bricks.
The alumina bubble brick obtained in this embodiment has a bulk density of 1.0 g/cm3, a thermal conductivity of 0.54 W/m·k, and a compressive strength of 20 Mpa. The volume density of the alumina bubble brick obtained in the comparative example is 1.0g/cm3, and the heat conduction
The coefficient is 0.83W/m·k, the strength is low, the process is complicated, and the shrinkage rate is too large during the sintering process and it is easy to crack.
Example four:
A method of making alumina bubble bricks by using a pore former; firstly mix 33% Al2O3 micropowder, 20% clay fine powder, and 3% silica micropowder in advance to serve as the matrix mixed powder;
The pore former is made of spherical PS: PMMA=1:2, three sizes and the addition ratio are 50um, 35%; 100um, 35%; 150um, 30%. Add 13% of the weight of the mixed powder with a pore-forming agent and add 5% of the weight of the mixed powder with a silica sol solution to fully mix and wet, and then add the mixed powder to wrap and granulate;
Mix 44% alumina bubble and 2% of the weight of the alumina bubble with CMC:PVA=2:1 aqueous solution, then add the finished coating particles to mix, and prepare each by vibrating pressure. A shaped product of the required size is dried at 105°C and kept at 1630°C for 5 hours and fired;
At the same time, a comparative example is also used in this embodiment. The comparative example is the scheme in the patent CN201510981871. 0 "a method for preparing a lightweight high-strength alumina hollow sphere product": weighing 1000 g of alumina powder and 388 g of aluminate calcium cement, 64 g of polystyrene balls, 20 g of polyethylene glycol-based polymer FS10 and 270 g of water were stirred and mixed for 20 minutes to obtain a slurry. Add 1388g of alumina bubble to the slurry, stir and mix to obtain a mixed slurry, pour it into a mold and release it after solidification, dry and fire at 1550°C to obtain an alumina hollow sphere insulation product.
The alumina bubble brick obtained in this embodiment has a bulk density of 0.8 g/cm3, a thermal conductivity of 0.38 W/m·k, a compressive strength of 15 Mpa, and a one-time compression molding with high molding efficiency. The volume density of the alumina bubble brick obtained in the comparative example is 1.0g/cm3, the thermal conductivity is 0.43W/m·k, and the compressive strength is 12Mpa. The process is complicated, the slurry is solidified and demoulded, and the molding efficiency is low. , Can not be molded into near-final size, the strength is limited, and the scope of use is limited.
Example five:
A method for makingalumina bubble bricks by using a pore former. First, pre-mix three kinds of fine powders: 34% Al2O3 powder, 25% clay fine powder, and 1% silicon powder as the matrix mixed powder;
The pore former is made of spherical PS: PMMA=3:1, three sizes and the addition ratio are 50um, 30%; 100um, 45%; 150um, 25%. Add 8% of the weight of the mixed powder of the pore-forming agent and the added amount of 13% of the weight of the mixed powder with a silica sol solution to fully mix and wet, and then add the mixed powder to wrap and granulate.
Mix 40% of thealumina bubble and the 3.5% CMC aqueous solution that is the weight of the alumina bubble , and then add the finished coating particles to mix, and use vibration pressure to prepare various sizes. The shaped products are dried at 100°C and kept at 1600°C for 8 hours.
At the same time, a comparative example is also used in this example. The comparative example is "Refractory Materials" 1997, 31 (5) 284-285 "Development of high thermal shock resistance alumina bubble bricks". The scheme and: alumina The hollow sphere is aggregate, the binder and part of the clay are slurried as the binder, Al2O3 micropowder, sillimanite powder and part of the clay powder are pre-mixed as a matrix. After uniform mixing, they are vibrated and pressed for molding, dried at 120°C, and dried at 1620°C for 8 hours firing.
bubble brick obtained in this embodiment has a bulk density of 1.0 g/cm3, a thermal conductivity of 0.54 W/m·k, and a compressive strength of 27 Mpa. The alumina bubble brick obtained in the comparative example has a bulk density of 1.29 g/cm3 and a compressive strength of 11.9Mpa.
