Preparation method of mullite whisker precursor non-pressure molding one-time sintering light heat insulation ceramic

Abstract

The invention relates to a preparation method of mullite whisker precursor pressureless forming one-time sintering light heat insulation ceramic, which comprises the following steps: mixing nano aluminum sol, nano silicon sol and water according to a certain proportion, adding ammonium molybdate tetrahydrate, and uniformly stirring to prepare a whisker growth precursor; and drying in a drying oven, grinding into a solid powdery product in a mortar, filling an aluminum oxide mold with the solid powdery product, carrying out non-pressure compaction, carrying out high-temperature calcination in a furnace, cooling, taking out, and demolding to obtain the lightweight porous ceramic block prepared by in-situ growth of the mullite whiskers. The preparation method has the advantages that the preparation process is easy to operate, green and free of pollution, renewable materials are used as raw materials, and the requirements for environmental protection and sustainable development are met; the morphology and components of the porous light heat-insulating block can be accurately controlled, and the porous light heat-insulating block has better stability under a high-temperature condition; the prepared porous light heat-insulating ceramic block has high compressive strength which is concentrated at 4.15-4.57 MPa, and is light, the density is concentrated at 0.65-0.75 g / cm < 3 >, the porosity can reach 76.3-79.4%, and the load of the whole structure can be reduced. After the ceramic block is exposed for 1800-2000 seconds at 1250-1350 DEG C, the back temperature of the ceramic block is 290-300 DEG C, and the ceramic block has excellent heat insulation performance.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal insulation materials, and in particular relates to a method for preparing a mullite whisker precursor through pressureless molding and one-time sintering of lightweight thermal insulation ceramics. Background Art

[0002] With the increasing demand for high-temperature thermal insulation materials in the construction, metallurgy, chemical industry and other industries, traditional thermal insulation materials such as graphite and asbestos have problems such as heavy weight, high thermal conductivity and poor heat resistance, and can no longer meet the demand for high-performance thermal insulation materials in industrial production.

[0003] As a new type of thermal insulation material, lightweight thermal insulation ceramics have attracted widespread attention due to their light weight, low thermal conductivity, and good heat resistance. They can be used for thermal insulation of high-temperature equipment, effectively reducing heat loss, improving the energy efficiency and stability of equipment, and can also help improve the thermal insulation performance of buildings, reduce energy consumption, and improve the comfort of buildings. In the aviation field, the thermal insulation performance of materials is very high. The low thermal conductivity and high temperature resistance of lightweight thermal insulation ceramics make them an ideal choice for engine thermal insulation materials. It can effectively reduce the heat loss of engine components and improve engine efficiency. Its excellent thermal insulation performance can help reduce the temperature difference between the inside and outside of the aircraft, which helps save the energy consumption of the aircraft.

[0004] Traditional thermal insulation ceramic preparation processes include foam template method, foaming agent method, molding method, gel injection molding method, etc. Among them, the foam template method requires a large amount of foam templates, which will produce a large amount of waste during the production process, causing a certain burden on the environment; the foaming agent required by the foaming agent method will affect the density and mechanical properties of ceramic products and reduce their quality; the mold needs to be processed during the preparation process of the molding method, and the production cost is relatively high; the gel template used in the gel injection molding method is complicated to prepare and has a long production cycle. Common lightweight thermal insulation ceramics include foam glass ceramics, polystyrene boards, rock wool boards, perlite boards, etc. Foam glass ceramics have a high cost and a relatively fragile structure; polystyrene boards have high flammability and are easily corroded by ultraviolet rays and oxides; rock wool boards are easy to absorb water in a humid environment, affecting their thermal insulation effect; perlite boards are brittle and easily damaged by external forces. Therefore, there is an urgent need for a new preparation method that can achieve green environmental protection, simple production process, and improve product stability, thereby improving the performance and production efficiency of thermal insulation materials. Summary of the invention

[0005] In order to solve the above problems, the object of the present invention is to provide a method for preparing a lightweight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor.

[0006] In order to achieve the above object, the method for preparing a lightweight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor provided by the present invention comprises the following steps performed in sequence:

[0007] (1) Weigh nano-aluminum sol, nano-silica sol and ammonium molybdate in a mass ratio of 38-42:9-12:0.4-1.6.

[0008] (2) Mix the weighed aluminum sol and silica sol with water accounting for 15-25% of the total mass of the solution, and mix them evenly in a stirrer.

[0009] (3) adding the weighed ammonium molybdate to the liquid prepared in step (2), stirring continuously for 10-30 minutes, and obtaining a colloidal mullite whisker growth precursor cream.

[0010] (4) placing the whisker growth precursor cream prepared in step (3) in an oven, drying at 75-85° C. for 12-18 h, taking it out and grinding it in a mortar into a powder product with a particle size of 300-340 mesh;

[0011] (5) The solid powder product is filled in an alumina mold and compacted without pressure, and the temperature is increased to 1200-1400°C at a heating rate of 4-6°C / min. After being kept at this temperature for 60-180 minutes, the temperature is lowered along with the furnace, and after it cools to room temperature, it is taken out from the furnace and demolded to obtain a porous lightweight insulating ceramic block prepared by in-situ growth of mullite whiskers.

[0012] Preferably, the solid content of the nano aluminum sol in step (1) is 14-16%.

[0013] Preferably, the solid content of the nano-silica sol in step (1) is 23-25%.

[0014] Preferably, the ammonium molybdate tetrahydrate powder in step (1) is analytically pure, with a purity higher than 99.1%.

[0015] Preferably, the control of the stirring speed in steps (2) and (3) is critical, and the stirring speed should be ensured to be between 100 and 300 rpm.

[0016] Preferably, the order of adding the raw materials in steps (1), (2), and (3) is to first mix and stir the aluminum sol and the silica sol; after stirring for 2-5 minutes, add water to the solution and continue stirring; after stirring for 7-10 minutes, add ammonium molybdate tetrahydrate to the solution.

[0017] Preferably, in step (5), the solid powder product is filled into the alumina mold by means of pressureless vibration compaction, and vibration is used without applying excessive pressure, so that the product is closely arranged under the action of its own weight and naturally formed in the mold.

[0018] The method for preparing a lightweight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor provided by the present invention has the following beneficial effects.

[0019] 1. The preparation process is simple, green and pollution-free, and uses renewable materials as raw materials, which meets the requirements of environmental protection and sustainable development.

[0020] 2. By optimizing the growth conditions and processes, the morphology and composition of the lightweight porous thermal insulation ceramic block can be precisely controlled. It has good stability under high temperature conditions and is not easy to deform or degrade.

[0021] 3. The prepared lightweight porous ceramic block has a high compressive strength, with the highest concentration of 4.15-4.57MPa; it is also relatively light, with a density of 0.65-0.75g / cm 3 The porosity can reach 76.3-79.4%, which is beneficial to reduce the load of the overall structure; the specific strength is 5533.34-6093.33N·m / kg, with excellent mechanical properties.

[0022] 4. The prepared lightweight porous ceramic block has excellent thermal insulation effect, which can effectively prevent heat from propagating into the material. The temperature difference between the front and back sides of the sample can reach up to 1000-1100℃ stably. The internal heat conduction ability is weak, and the external heat source is not easy to conduct through the sample to the other side. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD analysis spectrum of the mullite whisker precursor prepared in Example 1, which is a lightweight thermal insulation ceramic that is sintered once by pressureless molding.

[0024] Figure 2 This is the FTIR spectrum of the mullite whisker precursor prepared in Example 1, which is a lightweight thermal insulation ceramic that is sintered once by pressureless molding.

[0025] Figure 3 This is a scanning electron microscope photograph of the mullite whisker precursor prepared in Example 1, which is a lightweight thermal insulation ceramic that is sintered once by pressureless molding.

[0026] Figure 4 This is the compression curve of the mullite whisker precursor prepared in Example 1, which is a lightweight thermal insulation ceramic that is sintered once by pressureless molding.

[0027] Figure 5 This is the thermal insulation curve of the lightweight thermal insulation ceramic prepared in Example 1 by pressureless molding and one-time sintering of the mullite whisker precursor.

[0028] Figure 6 This is the thermal expansion curve of the lightweight thermal insulation ceramic prepared in Example 1 by pressureless molding and one-time sintering of the mullite whisker precursor. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments.

[0030] Example 1

[0031] The method for preparing a lightweight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor provided in this embodiment comprises the following steps performed in sequence:

[0032] (1) Nano-aluminum sol, nano-silica sol and ammonium molybdate were weighed in a mass ratio of 40:9.1:0.41.

[0033] (2) The weighed aluminum sol and silica sol are mixed with water accounting for 20% of the total mass of the solution, and the mixture is placed in a stirrer and mixed evenly.

[0034] (3) adding the weighed ammonium molybdate to the liquid prepared in step (2), stirring continuously for 30 minutes, and obtaining a colloidal mullite whisker growth precursor cream.

[0035] (4) placing the whisker growth precursor cream prepared in step (3) in an oven, drying at 80° C. for 16 h, taking it out and grinding it in a mortar into a powder product with a particle size of 320 mesh;

[0036] (5) The solid powder product is filled in an alumina mold and compacted without pressure, and the temperature is increased to 1300°C at a heating rate of 5°C / min. After being kept at this temperature for 180 minutes, the temperature is cooled along with the furnace. After the temperature drops to room temperature, the product is taken out of the furnace and demolded to obtain a porous lightweight insulating ceramic block prepared by in-situ growth of mullite whiskers.

[0037] Example 2

[0038] The method for preparing lightweight thermal insulation ceramics by non-pressure forming and one-time sintering of a mullite whisker precursor provided in this embodiment includes the following steps performed in sequence.

[0039] (1) Nano-aluminum sol, nano-silica sol and ammonium molybdate were weighed in a mass ratio of 38:9:0.4.

[0040] (2) The weighed aluminum sol and silica sol are mixed with water accounting for 15% of the total mass of the solution, and the mixture is placed in a stirrer and mixed evenly.

[0041] (3) adding the weighed ammonium molybdate to the liquid prepared in step (2), stirring continuously for 10 minutes, and obtaining a colloidal mullite whisker growth precursor cream.

[0042] (4) placing the whisker growth precursor cream prepared in step (3) in an oven, drying at 75° C. for 12 h, taking it out and grinding it in a mortar into a powder product with a particle size of 300 mesh;

[0043] (5) The solid powder product is filled in an alumina mold and compacted without pressure, and the temperature is increased to 1200°C at a heating rate of 4°C / min. After being kept at this temperature for 60 minutes, the temperature is decreased along with the furnace. After the temperature drops to room temperature, the product is taken out from the furnace and demolded to obtain a porous lightweight insulating ceramic block prepared by in-situ growth of mullite whiskers.

[0044] Example 3

[0045] The method for preparing a lightweight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor provided in this embodiment comprises the following steps performed in sequence:

[0046] (1) Weigh nano-aluminum sol, nano-silica sol and ammonium molybdate in a mass ratio of 42:12:1.6.

[0047] (2) The weighed aluminum sol and silica sol are mixed with water accounting for 25% of the total mass of the solution, and the mixture is placed in a stirrer and mixed evenly.

[0048] (3) adding the weighed ammonium molybdate to the liquid prepared in step (2), stirring continuously for 20 minutes, and obtaining a colloidal mullite whisker growth precursor cream.

[0049] (4) placing the whisker growth precursor cream prepared in step (3) in an oven, drying at 85° C. for 18 h, taking it out and grinding it in a mortar into a powder product with a particle size of 340 mesh;

[0050] (5) The solid powder product is filled in an alumina mold and compacted without pressure, and the temperature is increased to 1400°C at a heating rate of 6°C / min. After being kept at this temperature for 120 minutes, the temperature is cooled along with the furnace. After the temperature drops to room temperature, the product is taken out of the furnace and demolded to obtain a porous lightweight insulating ceramic block prepared by in-situ growth of mullite whiskers.

[0051] Example 4

[0052] The method for preparing a lightweight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor provided in this embodiment comprises the following steps performed in sequence:

[0053] (1) Nano-aluminum sol, nano-silica sol and ammonium molybdate were weighed in a mass ratio of 41:10.12:1.21.

[0054] (2) The weighed aluminum sol and silica sol are mixed with water accounting for 22% of the total mass of the solution, and the mixture is placed in a stirrer and mixed evenly.

[0055] (3) adding the weighed ammonium molybdate to the liquid prepared in step (2), stirring continuously for 15 minutes, and obtaining a colloidal mullite whisker growth precursor cream.

[0056] (4) placing the whisker growth precursor cream prepared in step (3) in an oven, drying at 78° C. for 15 h, taking it out and grinding it in a mortar into a powder product with a particle size of 310 mesh;

[0057] (5) The solid powder product is filled in an alumina mold and compacted without pressure, and the temperature is increased to 1250°C at a heating rate of 5°C / min. After being kept at this temperature for 80 minutes, the temperature is cooled along with the furnace. After the temperature drops to room temperature, the product is taken out of the furnace and demolded to obtain a porous lightweight insulating ceramic block prepared by in-situ growth of mullite whiskers.

[0058] The mullite whisker precursor in-situ growth pressureless molding one-time sintering lightweight thermal insulation ceramic provided by the present invention is prepared with nano aluminum sol as aluminum source, nano silica sol as silicon source, and ammonium molybdate tetrahydrate as flux. Ammonium molybdate can decompose to generate molybdenum oxide at high temperature, and at the same time produce liquid phase as flux, which is beneficial to promote the dissolution and crystallization reaction of aluminum source, silicon source and other substances. In this process, the presence of liquid phase can provide a better medium environment and promote the radial growth of whiskers; needle-shaped mullite whiskers grow in a staggered arrangement, the pore size between whiskers is relatively large and uniform, and the overlap and locking between whiskers increase the compressive strength of the block and reduce the density, thereby obtaining a lightweight thermal insulation ceramic material with excellent performance.

[0059] In order to verify the effect of the method for preparing lightweight thermal insulation ceramics by pressureless molding and one-time sintering of mullite whisker precursors provided in the above embodiment, the inventors conducted the following experiments:

[0060] (1) Prepare a mullite whisker precursor non-pressure-molded, one-time sintered lightweight thermal insulation ceramic according to the method of Example 1, and prepare samples required for composition analysis, density and porosity analysis, infrared spectrum analysis, surface morphology analysis, mechanical property analysis, thermal insulation performance analysis, and thermal expansion performance analysis. Among them, the size of the thermal insulation ceramic for the compression test is 16 mm in diameter and 16 mm in height. The size of the sample for thermal insulation performance analysis is 40 mm in diameter and 15 mm in thickness. The size for thermal expansion performance analysis is 6 mm in diameter and 5 mm in height.

[0061] (2) Composition analysis: The composition of the mullite whisker precursor pressureless forming and once sintered lightweight thermal insulation ceramic prepared in Example 1 was analyzed using an XRD tester (D / Max 2500v / PC, Rigaku, Japan). The XRD spectrum is as follows: Figure 1 shown.

[0062] Depend on Figure 1 It can be seen that in the crystal phase shown by the XRD spectrum, the mullite phase Al6Si2O 13 The proportion is the largest, which can reach 92%, indicating that the lightweight thermal insulation ceramics prepared by this preparation method inherit the original excellent properties of mullite materials, and on this basis, the characteristics brought by the fibrous structure are added.

[0063] (3) Density and porosity analysis: The density and porosity of the mullite whisker precursor pressureless forming and one-time sintering lightweight thermal insulation ceramic prepared in Example 1 above were analyzed using the density calculation formula and the total porosity calculation formula.

[0064] The calculation formula of total porosity is: porosity = 1-actual density / theoretical density. The actual density of the sample can be obtained by direct measurement. The mass of the ceramic block is measured by an electronic balance to be 3.54g. The diameter and height of the ceramic block are measured by a vernier caliper to be 16mm and 16mm, respectively. The actual density can be obtained by the density calculation formula to be 0.75g / cm 3 The theoretical density is the standard mullite theoretical density (3.16g / cm 3 ), the total porosity formula can be used to calculate that the maximum porosity of the prepared sample ceramic block is as high as 79.4%.

[0065] (4) Infrared spectrum analysis: Molecular bonding analysis of the mullite whisker precursor pressureless forming and one-time sintering lightweight thermal insulation ceramic prepared in Example 1 was performed using infrared spectroscopy (Nicolet, Waliham, USA). Figure 2 is the infrared spectrum of the prepared sample.

[0066] Depend on Figure 2 It can be seen that in the high frequency region (2000cm -1 -2500cm -1 ) has no obvious absorption band. In the mid-frequency region (1000cm -1 -2000cm -1 ) has a sharp band, which is caused by the asymmetric stretching vibration of Si-O-Si. -1 -1000cm- 1 )’s spectral bands are mainly caused by the vibration of Al-O and Si-O.

[0067] (5) Surface morphology analysis: The microscopic morphology of the mullite whisker precursor pressureless formed and once sintered lightweight thermal insulation ceramic prepared in Example 1 was observed using a scanning electron microscope (Hitachi, Tokyo, Japan). Figure 3 shown.

[0068] Depend on Figure 3 It can be seen that the surface of lightweight thermal insulation ceramics is densely arranged, and the whiskers are evenly distributed in the matrix, without local density being too high or too low. The whiskers are mostly short and thick needle-like structures, growing in a staggered arrangement, overlapping and locking with each other, and arranged closely, without obvious bumps or irregular shapes. The length is about 40-70μm, the diameter is about 5-9μm, and the aspect ratio is about 4.44-14.

[0069] (6) Mechanical properties analysis: The performance characteristics of the mullite whisker precursor pressureless molding and one-time sintering lightweight thermal insulation ceramics prepared in Example 1 under pressure were analyzed using a microcomputer-controlled electronic universal testing machine (CMT4504, Meters, China). Figure 4 is the compressive strength curve of the prepared samples.

[0070] Depend on Figure 4 It can be seen that the maximum compressive strength of the prepared porous lightweight thermal insulation ceramic block can reach 4.57MPa. The density of the ceramic block can be calculated using the density formula to be 0.75g / cm 3 , using the specific strength calculation formula, the maximum compressive specific strength is 6093.33N·m / kg.

[0071] (7) Analysis of thermal insulation performance: A butane flame spray gun was used to spray a flame of 1300°C on the front of the mullite whisker precursor pressureless forming and one-time sintering lightweight thermal insulation ceramic block prepared in Example 1. A multi-channel temperature inspection instrument (JK4000, Jinke, China) was used to analyze the ability of the mullite whisker precursor pressureless forming and one-time sintering lightweight thermal insulation ceramic prepared in Example 1 to resist heat conduction. Figure 5 is the thermal conductivity curve of the prepared sample.

[0072] Depend on Figure 5 It can be seen that the initial back surface temperature of the sample rises rapidly with the increase of flame spraying time, reaching 300°C after 300s, and then the temperature curve tends to be flat. The spraying time lasts for 1800s, and the back surface temperature of the sample remains stable. The temperature difference between the front and back sides can reach 1000°C, and the thermal insulation performance is relatively excellent.

[0073] (8) Thermal expansion performance analysis: A microcomputer horizontal dilatometer (HPY-3, Beijing Hengjiu, China) was used to characterize the physical properties of the linear expansion and contraction of the mullite whisker precursor pressureless molding and once-sintered lightweight thermal insulation ceramics prepared in Example 1 when the temperature changes. Figure 6 is the thermal expansion coefficient curve of the prepared sample.

[0074] Depend on Figure 6 It can be seen that the thermal expansion coefficient of the prepared porous lightweight thermal insulation ceramic block increases with the increase of temperature. When the temperature rises from room temperature to 250℃, the thermal expansion coefficient increases rapidly and the volume expands sharply. At 250-1400℃, the expansion rate tends to be flat, and the volume remains basically unchanged. The thermal expansion coefficient can reach up to 4.32×10 -6 k -1 .

Claims

1. A method for preparing a lightweight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor, characterized in that: The preparation method comprises the following steps performed in sequence: (1) Weigh nano-aluminum sol, nano-silica sol and ammonium molybdate in a mass ratio of 38-42:9-12:0.4-1.

6. (2) Mix the weighed aluminum sol and silica sol with water accounting for 15-25% of the total mass of the solution, and mix them evenly in a stirrer. (3) adding the weighed ammonium molybdate to the liquid prepared in step (2), stirring continuously for 10-30 minutes, and obtaining a colloidal mullite whisker growth precursor cream. (4) placing the whisker growth precursor cream prepared in step (3) in an oven, drying at 75-85° C. for 12-18 h, taking it out and grinding it in a mortar into a powder product with a particle size of 300-340 mesh; (5) The solid powder product is filled in an alumina mold and compacted without pressure, and the temperature is increased to 1200-1400°C at a heating rate of 4-6°C / min. After being kept at this temperature for 60-180 minutes, the temperature is lowered along with the furnace, and after it cools to room temperature, it is taken out from the furnace and demolded to obtain a porous lightweight insulating ceramic block prepared by in-situ growth of mullite whiskers.

2. The method for preparing a lightweight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor according to claim 1, characterized in that: The solid content of the nano aluminum sol in step (1) is 14-16%.

3. The method for preparing a light-weight thermal insulating ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor according to claim 1, characterized in that: The solid content of the nano-silica sol in step (1) is 23-25%.

4. The method for preparing a light-weight thermal insulating ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor according to claim 1, characterized in that: The ammonium molybdate tetrahydrate powder in step (1) is analytically pure, with a purity higher than 99.1%.

5. The method for preparing a light-weight thermal insulating ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor according to claim 1, characterized in that: The control of stirring speed in steps (2) and (3) is critical, and the stirring speed should be kept between 100 and 300 rpm.

6. The method for preparing a lightweight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor according to claim 1, characterized in that: The order of adding the raw materials in steps (1), (2) and (3) is to first mix and stir the aluminum sol and the silica sol; after stirring for 2-5 minutes, add water to the solution and continue stirring; after stirring for 7-10 minutes, add ammonium molybdate tetrahydrate to the solution.

7. The method for preparing a light-weight thermal insulation ceramic by non-pressure forming and one-time sintering of a mullite whisker precursor according to claim 1, characterized in that: In step (5), the solid powder product is filled into the alumina mold by means of pressureless vibration compaction, and vibration is used without applying excessive pressure, so that the product is closely arranged under the action of its own weight and naturally formed in the mold.

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