Modified closed-cell expanded perlite and preparation method thereof

Abstract

The invention relates to modified closed-cell expanded perlite and a preparation method thereof, and the expanded perlite is prepared by the following steps: (1) preheating and drying: preheating and drying a perlite raw material at the temperature of 300-450 DEG C for 5-30 minutes to obtain the perlite raw material with the bound water content of 1.5-3%; (2) preliminary puffing: pre-puffing for 5-10 seconds at the temperature of 800-900 DEG C; (3) cooling the preliminarily-expanded expanded perlite to normal temperature, spraying a certain amount of water glass solution on the surface of the expanded perlite, then spraying an aluminum sulfate solution, and continuously stirring for a period of time; the continuous stirring time is 5-10 minutes; and (4) carrying out secondary puffing at 1100-1150 DEG C for 2-10 seconds to obtain the closed-cell expanded perlite.

Description

Technical Field

[0001] The present invention relates to a modified closed-cell expanded perlite and a preparation method thereof, and specifically discloses that during the roasting process, sodium silicate and aluminum sulfate are used for coating, so as to obtain a closed-cell expanded perlite that can be prepared by gas furnace expansion and has excellent strength and waterproofness. Background Art

[0002] Perlite is a kind of acidic lava ejected by volcanoes and is a vitreous rock formed by rapid cooling. It is named because of its pearl crack structure. Expanded perlite is a porous mineral obtained by high-temperature expansion of perlite ore sand, and has excellent properties such as light weight, heat preservation, cold preservation, adsorption, sound insulation, non-combustibility, non-toxicity, and stable chemical properties. Due to different processes and heating temperatures during the firing of perlite ore sand, the expansion ratio is different, and the properties of the generated products are also different, which can be divided into open-cell expanded perlite, closed-cell expanded perlite, and vitrified microspheres.

[0003] However, compared with expanded vermiculite, an inorganic fireproof filler mainly used in high-end fireproof materials, different types of expanded perlite have the following disadvantages: 1. The compressive strength is relatively low, its texture is brittle, and the particle structure is easy to break. When under long-term pressure or external force, the particles may be crushed, resulting in a decrease in structural stability. The expanded vermiculite with a flaky structure has better flexibility and compressive resistance and is not easy to collapse under long-term load; 2. The water absorption rate is higher. Expanded perlite is all or partially an open-cell structure and the surface of the structure is a strongly polar functional group, making it have extremely strong water absorption. The water absorption rate can reach 2-4 times its own weight. After water absorption, the thermal conductivity coefficient increases significantly, and at the same time, the strength is low and it is easy to break, resulting in a significant decrease in the fireproof and heat preservation performance. Although many experts in the industry have tried to coat and modify open-cell expanded perlite with inorganic materials such as water glass or organic materials such as VAE emulsion, the waterproofness has been improved to some extent, but the fragile coating layer has a very limited effect on improving the strength of perlite, and many coatings are absorbed into the pores of expanded perlite, which not only causes waste of the coating material, increases the cost, but also blocks the pores and affects the thermal conductivity coefficient of perlite.

[0004] Compared with open-cell expanded perlite, the water absorption rate and compressive strength of closed-cell expanded perlite (partially open-cell) and vitrified microspheres have been significantly improved, but there are also obvious problems. First of all, both closed-cell expanded perlite and vitrified microspheres are produced by precisely controlling the gradient heating and residence time of raw ore sand to melt the product surface and seal the pores, which requires very strict temperature control of the production process, and low-cost gas furnaces cannot meet the requirements. Since electric furnaces have higher temperature control advantages compared to gas furnaces, in current actual production, both closed-cell expanded perlite and vitrified microspheres must be produced using electric furnaces, and their costs are much higher compared to the gas furnaces used for open-cell expanded perlite. Secondly, the low closed-cell rate of closed-cell expanded perlite has always been a difficult problem in the industry. The closed-cell rate obtained by general processes is only close to 60%. Although some literature claims to exceed 70% or even more than 80%, in industry technical discussions and actual sold products, industry experts have a consensus that it is difficult for the closed-cell rate of mass-produced closed-cell expanded perlite to exceed 70%, and the performance of different batches is unstable. Relatively speaking, vitrified microspheres have a higher closed-cell rate and better performance, but the production of vitrified microspheres has high requirements for raw materials and can only use pitchstone in perlite. The output is low, the process is complex, and the cost is high. Therefore, the price of vitrified microspheres once reached about 2-3 times that of closed-cell expanded perlite. In addition, there are also problems of low expansion ratio and large bulk density in the production of closed-cell expanded perlite and vitrified microspheres using electric furnaces.

[0005] All in all, the main market of expanded perlite is occupied by low-cost open-cell expanded perlite and high-performance but high-cost vitrified microspheres, and closed-cell expanded perlite cannot be recognized by the market. Therefore, developing a closed-cell expanded perlite with improved compressive strength, water absorption rate, expansion ratio, and bulk density using a gas furnace for expansion has become the focus of the industry's common concern. Summary of the Invention

[0006] The purpose of the present invention is to provide a modified closed-cell expanded perlite and its preparation method, which is characterized by the following steps: 1. Preheating and drying Preheat and dry the perlite raw material at a temperature of 300-450°C for a holding time of 5-30 minutes to obtain a perlite raw material with a combined water moisture content of 1.5-3%.

[0007] 2. Preliminary expansion Pre-expand at a temperature of 800-900°C for 5-10 seconds using a rotary furnace.

[0008] 3. Spraying coating Cool the preliminarily expanded expanded perlite to room temperature, first spray a certain amount of water glass solution on its surface, then spray aluminum sulfate solution, and continuously stir for a period of time; the continuous stirring time is 5-10 minutes; 4. Secondary expansion At 1100 - 1150 °C for 2 - 10 seconds to obtain closed-cell expanded perlite; a gas jet expansion furnace or a vertical expansion furnace is used for secondary expansion.

[0009] For the said closed-cell expanded perlite, the bulk density (Kg / m 3 ³) is 40 - 150, the thermal conductivity (at 25 °C) (w / (m*K)) is 0.035 - 0.048, the water absorption rate (for 24 h, %) is 15 - 35, the cylinder compressive strength / kPa is 150 - 220, and the volume floating rate ≥ 85%; the closed-cell rate ≥ 85%.

[0010] In the preheating and drying process of step 1, further, the preheating temperature is 400 - 450 °C, and the heat preservation time is 8 - 10 minutes; further, the preheating and drying are carried out in a rotary kiln or a vertical preheater; Further, before preheating and drying, natural perlite ore is selected and crushed and screened, divided into coarse crushing and fine crushing, and the water content is 2 - 6%; The particle size of the fine-crushed perlite is 20 - 325 mesh (45μm - 850μm), preferably 40 - 200 mesh (75μm - 425μm); The inventor also found that when applied to fireproof materials such as coatings and perlite boards, if the expanded perlite prepared by grading the raw materials has better heat insulation effect. Through a large number of experimental studies, the preferred ratio is: the mass ratio of perlite ore with particle sizes of (40 - 60 mesh):(80 - 120 mesh):(140 - 200 mesh) is (1 - 3):(4 - 6):(2 - 4).

[0011] In the preliminary expansion process of step 2, it is preferably pre-expanded at a temperature of 850 °C, and the further time is 8 - 10 seconds In the process of spraying coating in step 3, further, the water glass solution contains 10 - 20 wt% of water glass; further, in the aluminum sulfate solution, it contains 10 - 20 wt% of aluminum sulfate; further, based on the mass of the raw material substances in the reaction, the mass ratio of water glass, aluminum sulfate, and pre-expanded perlite is: (4 - 5):(3.2 - 3.6):(72 - 152). In the theoretical reaction, the molar ratio of water glass to aluminum sulfate should be 3:1, and the mass ratio is about 107:100. In actual technical development, it is found that water glass needs to be added slightly more. This may be because in the prior spraying of the water glass solution, part of the water glass is adsorbed into the pores of the pre-expanded perlite and does not participate in the subsequent reaction with aluminum sulfate.

[0012] In the secondary expansion process of step 4, the expansion temperature is 1100 °C and the time is 3 - 5 seconds to obtain closed-cell expanded perlite; Technical effects In view of the problems of existing closed-cell expanded perlite, such as the low closed-cell rate of the gas furnace and the need for an electric heating expansion furnace with precise temperature control, and the complex process and high cost, the present invention uses aluminum sulfate and sodium silicate to coat the pre-expanded perlite and then performs secondary expansion. Through the special pre-coating process, expanded perlite with a high closed-cell rate is prepared using a gas furnace. At the same time, the special pretreatment process also reduces the expansion temperature, greatly shortens the high-temperature expansion time, and significantly reduces the production cost and improves the production efficiency.

[0013] After secondary expansion, the surface of the expanded perlite is covered with a gray coating layer. The inventor speculates that its main components are albite, nepheline, etc. This should be due to the double decomposition reaction of aluminum sulfate and sodium silicate on the surface of the pre-expanded perlite, generating aluminum silicate and sodium sulfate. Among them, a small part of the aluminum silicate may also exist in the form of a composite colloid precipitate of aluminum hydroxide and silicic acid and / or a precipitate of aluminum silicate. Under the condition of 1100-1150 degrees Celsius, it is obtained by the reaction of aluminum silicate, sodium sulfate with SiO2, Al2O3, etc. in the perlite. Among them, sodium sulfate may undergo a decomposition reaction. Relatively speaking, vitrified microspheres and traditional closed-cell perlite require a longer time and temperature to sufficiently soften and melt the perlite on the surface to form a vitreous layer on the perlite surface. Currently, the expansion temperature of the traditional process is 1250-1300 °C, and the time is at least 5-20 seconds, or up to 2-5 minutes.

[0014] In the expansion stage of the process of the present invention, due to the adoption of the pre-coating technology, precise temperature control and long-time expansion are not required. Therefore, gas furnaces can be used for all equipment, instead of electric furnaces with high construction costs and operating costs. Since the equipment for the closed-cell expanded perlite and the open-cell expanded perlite of the invention is compatible, the production line for open-cell expanded perlite can be directly used to produce closed-cell expanded perlite, which not only reduces the cost but also avoids the trouble of technological transformation of the production line.

[0015] Due to the adoption of the pre-coating technology, the closed-cell rate of the closed-cell expanded perlite of the present invention exceeds the mainstream closed-cell expanded perlite products with a closed-cell rate of 50-70% in the current market, reaching more than 90%, which is close to the closed-cell rate of vitrified microspheres. However, the cost is significantly lower than that of vitrified microspheres, and the raw material requirements are much lower than those of vitrified microspheres.

[0016] The albite, nepheline, etc. on the surface coating, due to their dense crystal structure and low surface energy, not only have high strength but also excellent waterproof performance, which significantly improves the cylinder compressive strength and waterproof performance of the expanded perlite.

[0017] In addition, compared with the current finished products of spraying inorganic waterproof materials such as silica sol or water glass or organic waterproof materials such as VAE emulsion and polyurethane on closed-cell or open-cell expanded perlite, the coating material of the present invention is added during the preparation process of expanded perlite and reacts in-situ to generate a dense coating layer of albite and nepheline. It not only has a high closed-cell rate, but also has high strength and excellent waterproof performance. At the same time, the coating before the finished product reduces the phenomenon that the coating material is adsorbed into the pores, not only reducing the usage amount of the coating material, but also avoiding the filling of the pores of expanded perlite by the coating material and reducing its heat insulation and fireproof performance.

[0018] In addition, the inventors also found that in the process of spraying sodium silicate and aluminum sulfate solutions after pre-expansion using perlite ore raw materials with different mesh number combinations, the coating effect of the above composite solution is significantly higher than that of perlite ore with a single mesh number. This may be because fewer voids in perlite are beneficial for the composite solution to coat on the surface of perlite. Secondly, the closed-cell expanded perlite products with different mesh number combinations also achieved better heat insulation and fireproof effects. This may be because the closed-cell expanded perlite with different particle sizes reduces the stacking voids and prevents the formation of microscopic thermal bridges, significantly improving the heat insulation and fireproof effects of closed-cell expanded perlite. Examples

[0019] Example 1 Preparation of Closed-Cell Expanded Perlite A Select perlite ore with mesh numbers (40 - 60 mesh): (80 - 120 mesh): (140 - 200 mesh) respectively, with a mass ratio of 2:5:3, and stir and mix them. Preheat and dry the perlite at a temperature of 400 °C for a holding time of 10 minutes to obtain perlite ore with a combined water moisture content of less than 2%; perform preliminary expansion at a temperature of 850 °C for 8 seconds; cool the preliminarily expanded expanded perlite to room temperature, then first spray sodium silicate with a concentration of 15 wt% on its surface, and then spray aluminum sulfate with a concentration of 10 wt%. Based on the mass of the reaction raw materials, the mass ratio of sodium silicate, aluminum sulfate, and pre-expanded perlite is: 4.5:3.5:92, and continuously stir for 7 minutes; perform secondary expansion on the coated pre-expanded perlite at 1100 °C for 4 seconds to obtain closed-cell expanded perlite A.

[0020] Example 2 Preparation of Closed-Cell Expanded Perlite B Select perlite ore with a mesh size of 80 - 120 meshes, preheat and dry the perlite at a temperature of 400 °C for 10 minutes to obtain perlite ore with a combined water moisture content of less than 2%; perform preliminary expansion at a temperature of 850 °C for 8 seconds; cool the preliminarily expanded expanded perlite to room temperature, then first spray sodium silicate with a concentration of 15 wt% on its surface, and then spray aluminum sulfate with a concentration of 10 wt%. Based on the mass of the raw materials for the reaction, the mass ratio of sodium silicate, aluminum sulfate, and pre-expanded perlite is: 4.5:3.5:92, and continuously stir for 7 minutes; subject the pre-expanded perlite treated by coating to secondary expansion at 1100 °C for 4 seconds to obtain closed-cell expanded perlite B.

[0021] Comparative Example 3 Preparation of Closed-Cell Expanded Perlite C In the process stage of spraying the coating, only spray sodium silicate with a concentration of 15 wt%. The mass ratio of sodium silicate to pre-expanded perlite is: 8:92. Other processes are the same as those in Example 1 to obtain closed-cell expanded perlite C.

[0022] Comparative Example 4 Preparation of Closed-Cell Expanded Perlite D In the process stage of spraying the coating, only spray aluminum sulfate solution with a concentration of 10 wt%. The mass ratio of aluminum sulfate to pre-expanded perlite is: 8:92. Other processes are the same as those in Example 1 to obtain closed-cell expanded perlite D.

[0023] Comparative Example 5 Preparation of Closed-Cell Expanded Perlite E Omit the process of spraying the coating, cool the pre-expanded perlite to room temperature and then perform secondary high-temperature expansion. Other processes are the same as those in Step 1 to obtain closed-cell expanded perlite E.

[0024] Refer to the standard JC / T 1042 - 2007 "Expanded Glass Microspheres" to test the bulk density, cylinder compressive strength, thermal conductivity, volume water absorption rate, volume floating rate, and closed-cell rate of the closed-cell expanded perlite prepared in the examples. The results are as follows: Closed-cell expanded perlite A Closed-cell expanded perlite B Closed-cell expanded perlite C Closed-cell expanded perlite D Closed-cell expanded perlite E Bulk density (Kg / m3) 98 92 91 86 80 Cylinder compressive strength / kPa 212 195 35 32 34 Thermal conductivity (W / (m*K)) at 25℃ 0.038 0.040 0.042 0.048 0.045 Volume water absorption rate (24h, %) 18% 25% 38% 45% 51% Volume floating rate 90% 85% 63% 55% 42% Closed-cell ratio 92% 87% 60% 54% 40% As can be seen from the above table, the expanded perlite in-situ modified with the mixed coating material of aluminum sulfate and sodium silicate has obvious improvements in terms of cylinder compressive strength, thermal conductivity, closed-cell rate and water absorption compared with the single-component modified or conventional unmodified expanded perlite. In contrast, when sodium silicate or aluminum sulfate is used alone for coating, the cylinder compressive strength of expanded perlite is not significantly increased and its water absorption is not significantly reduced at the same time. This is probably because when sodium silicate and aluminum sulfate are coated on the surface of perlite alone, they are still in solution and cannot form a network-like colloid covering layer. A large amount of them will enter the pores of perlite and a continuous covering layer cannot be obtained. At the same time, we also note that generally speaking, there is a positive correlation between bulk density and thermal conductivity. The bulk density of the present invention is slightly higher than that of the unmodified expanded perlite, but its thermal conductivity is better because the closed-cell rate of the present invention is high and the vast majority are closed pores. Although the bulk density is slightly inferior, the thermal conductivity is better instead.

Claims

1. A preparation method of modified closed-cell expanded perlite, characterized in that, The closed-cell expanded perlite is prepared by the following steps: (1) Preheating and drying: The perlite raw material is preheated and dried at a temperature of 300 - 450°C for a holding time of 5 - 30 minutes to obtain a perlite raw material with a combined water moisture content of 1.5 - 3%; (2) Preliminary expansion: Pre-expand at a temperature of 800 - 900°C for 5 - 10 seconds; (3) Cool the preliminarily expanded expanded perlite to room temperature. First, spray a certain amount of sodium silicate solution on its surface, then spray aluminum sulfate solution, and continuously stir for a period of time; the continuous stirring time is 5 - 10 minutes; (4) Secondary expansion: At 1100 - 1150°C for 2 - 10 seconds to obtain closed-cell expanded perlite; The closed-cell expanded perlite has a bulk density of 40 - 150 Kg / m 3 , a thermal conductivity (at 25°C) (w / (m*K)) of 0.035 - 0.048, a water absorption rate (for 24 hours) of 15 - 35%, a cylinder compressive strength of 150 - 220 kPa, a volume floating rate ≥ 85%; and a closed-cell rate ≥ 85%.

2. The preparation method according to claim 1, characterized in that, In the preheating and drying process of step (1), the preheating temperature is 400 - 450°C and the holding time is 8 - 10 minutes.

3. The preparation method according to claim 1, characterized in that, In the preheating and drying process of step (1), the preheating and drying are carried out in a rotary kiln or a vertical preheater.

4. The preparation method according to claim 1, characterized in that, Before preheating and drying, natural perlite ore is selected and subjected to crushing and screening, divided into coarse crushing and fine crushing, to obtain perlite with a moisture content of 2 - 6%.

5. The preparation method according to claim 4, characterized in that, The particle size of the finely crushed perlite is 20 - 325 mesh.

6. The preparation method according to claim 1, characterized in that, In the preliminary expansion process of step (2), it is preferably pre-expanded at a temperature of 850°C for a further time of 8 - 10 seconds.

7. The preparation method according to claim 1, characterized in that, In the process of spraying coating in step (3), the sodium silicate solution contains 10 - 20 wt% of sodium silicate; in the aluminum sulfate solution, it contains 10 - 20 wt% of aluminum sulfate.

8. The preparation method according to claim 1, characterized in that, In the process of spraying coating in step (3), the mass ratio of sodium silicate, aluminum sulfate, and pre-expanded perlite is: (4 - 5) : (3.2 - 3.6) : (72 - 152).

9. The preparation method according to claim 1, characterized in that, In the secondary expansion process of step (4), the expansion temperature is 1100°C and the time is 3 - 5 seconds to obtain closed-cell expanded perlite.

10. A modified closed-cell expanded perlite, prepared by the preparation method according to any one of claims 1 - 9.