Spherical cristobalite powder for power device and preparation method of spherical cristobalite powder

Abstract

The invention discloses spherical cristobalite powder for a power device and a preparation method of the spherical cristobalite powder, and belongs to the technical field of nonmetallic mineral processing. Flame method spherical silica powder is selected as a raw material to be mixed with a mineralizing agent composed of fluorine salt substances, the mixture is sealed in a high-pressure reaction kettle to be subjected to heat treatment for a period of time, and a precursor obtained through heat treatment is subjected to high-temperature calcination to obtain the spherical cristobalite powder. According to the preparation process of the precursor, crystal lattices of amorphous flame melting method spherical silicon dioxide micro powder are pre-arranged to a certain extent, so that a cristobalite product has high purity and high cristobalite phase content, meanwhile, the phase transformation potential barrier when an amorphous phase is converted into a cristobalite phase is reduced, the temperature of high-temperature calcination is reduced, and the yield of the cristobalite product is improved. After the flame melting method spherical silicon dioxide micro powder raw material is converted from an amorphous phase to a cristobalite phase, the high sphericity degree can still be kept, and the thermal expansion requirement of a power device can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of non-metallic mineral processing, and in particular relates to spherical cristobalite powder for power devices and a preparation method thereof. Background Art

[0002] Quartz is a non-metallic mineral with abundant reserves, strong acid resistance and excellent electrical insulation. Cristobalite is a species in the quartz family of minerals. Compared with quartz, cristobalite has excellent optical properties, high reflectivity, high whiteness, low density and thermal shock resistance. It is widely used in electronic materials, precision casting and other fields.

[0003] Patent announcement number (CN108455617A) discloses a method for preparing spherical quartz, wherein spherical quartz powder and an isolating agent are mixed in a certain proportion, the mixed powder is placed in an electric furnace protected by an inert gas, and heated under certain heating conditions, and then the obtained powder is placed in an aerobic environment for calcination, and the calcined powder is cleaned and dried to obtain a spherical quartz product. The above technical scheme uses spherical quartz powder as a raw material, and a certain amount of graphite is wrapped as an isolating agent. The powder is calcined at high temperature in an atmosphere of protective gas such as N2, so that the original quartz phase is gradually converted into a cristobalite phase, and then the graphite as an isolating agent is removed by high temperature calcination under aerobic conditions. Since the surface of quartz softens and thus adheres during high-temperature phase change, the presence of the graphite isolating agent weakens the adhesion effect, and the spherical morphology can still be maintained during the phase change, and graphite is a good conductor of heat, and heat can be input more evenly during the phase change, so that the reaction is more complete;

[0004] The above technical solution uses graphite as an isolation agent and then needs to undergo a high-temperature phase change process under a N2 atmosphere. The materials and atmosphere resources used are relatively large, and high-temperature calcination is still required to remove the graphite after the phase change. The process steps are complicated and the energy consumption is relatively large.

[0005] Patent announcement number (CN106660813A) discloses a spherical crystalline silica particle and its manufacturing method which has high productivity and low manufacturing cost compared with the past, and has high thermal expansion coefficient, high thermal conductivity, high fluidity, high dispersibility, high filling property, low wear resistance, high purity, and can also be applied to the semiconductor field. A spherical crystalline silica particle, characterized in that it contains 400 to 5000 ppm of aluminum and contains more than 80% of the crystalline phase; the above technical scheme selects silica particles and a certain amount of aluminum to mix for hot spraying, and then performs high-temperature calcination at a certain temperature to perform the phase transformation of cristobalite, and the silica particles are mixed with an aluminum source and then hot sprayed, and the aluminum source is transformed into aluminum oxide at a high temperature, and the aluminum oxide can destroy the crystal structure of silica and activate the lattice, so that the phase transformation can be carried out at a lower temperature;

[0006] The above technical solution uses aluminum source and silica particles for thermal spraying. The supporting instruments for thermal spraying are expensive and the process is complicated, resulting in a high threshold that is not conducive to the development of the industry. Summary of the invention

[0007] Purpose of the invention: The purpose of the present invention is to provide a method for preparing spherical quartz powder for power devices, so as to solve the technical problems of more atmosphere and materials required when using graphite as an isolation agent and expensive thermal spraying supporting equipment.

[0008] The above technical objectives of the present invention are achieved through the following technical solutions: a spherical quartz powder for power devices and a preparation method thereof, characterized in that it comprises the following steps:

[0009] S1 Raw material pretreatment: flame fusion spherical silica powder is used as raw material, fluorine-containing salt substances are selected as mineralizer A, the mass fraction of mineralizer A and deionized water is 1%-10% of mineralizer B, and the mineralizer B and flame fusion spherical silica powder raw material are sealed into a high-pressure reactor in a mass ratio of 100:30-60.

[0010] Preparation of S2 precursor: Place the high-pressure reactor in a high-temperature device for heat treatment for a certain period of time. The heat treatment temperature is 150-250°C and the heat treatment time is 8-24h. Repeatedly wash with deionized water and then dry to obtain the precursor P.

[0011] S3 high temperature phase transition: The precursor P is placed in a high temperature device for high temperature calcination to complete the crystal phase transition, wherein the high temperature device is heated to 1100°C~1500°C at a heating rate of 5~10°C / min, the phase transition time is 2-12H, and the product is obtained after cooling.

[0012] S4 depolymerization: After depolymerization of the product obtained in S3, a spherical quartz product C with D50=20-50 μm and adjustable particle size is obtained.

[0013] Preferably, the mineralizer A is one or more combinations of fluoride-containing salt substances.

[0014] Preferably, the calcination temperature of S3 is 1200°C to 1400°C.

[0015] Compared with the prior art, the present invention has the following advantages: flame-melted spherical silicon micropowder is selected as a raw material and mixed with a mineralizer composed of fluoride salt substances, sealed in a high-pressure reactor for heat treatment for a period of time, and the precursor obtained by the heat treatment is calcined at high temperature. The preparation process of the precursor pre-arranges the lattice of amorphous flame-melted spherical silicon dioxide micropowder to a certain extent, so that the cristobalite product has the characteristics of a high cristobalite phase, and at the same time reduces the phase transition barrier when the amorphous phase is transformed into the cristobalite phase, so that the temperature of high-temperature calcination is reduced, and the flame-melted spherical silicon dioxide micropowder raw material can still maintain a high sphericity after the amorphous phase is transformed into the cristobalite phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The XRD pattern of the product C1 obtained in Example 1 of the present invention;

[0017] Figure 2 The SEM spectrum of C1 produced in Example 1 of the present invention;

[0018] Figure 3 The XRD pattern of product C2 obtained in Example 2 of the present invention;

[0019] Figure 4 This is the XRD pattern of product C4 obtained in Comparative Example 1 of the present invention;

[0020] Figure 5 It is the XRD spectrum of the product obtained in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0022] Embodiment 1:

[0023] In this embodiment, flame fusion spherical silica powder with D50 = 40 μm is selected as the raw material, magnesium fluoride is selected as the mineralizer A1, deionized water is added to prepare a mineralizer B1 with a mass fraction of 5%, the mineralizer B1 and the flame fusion spherical silica powder raw material are sealed in a high-pressure reactor according to a mass ratio of 100:50, the high-pressure reactor is placed in a hot air circulation oven at 200° C. for heat treatment for 10 hours, washed 8 times with deionized water and then dried to obtain a precursor P1;

[0024] The prepared precursor P1 was placed in a crucible for calcination at a maximum temperature of 1250°C, a heating rate of 8°C / min, and kept warm for 8 hours. The product C1 obtained after cooling was placed in a ball mill and ground to obtain product D1. After XRD, density and SEM tests on product D1, it was found that product D1 was spherical cristobalite with a cristobalite content of more than 99%.

[0025] Embodiment 2:

[0026] In this embodiment, flame fusion spherical silica powder with D50 = 25 μm is selected as the raw material, ammonium fluoride is selected as the mineralizer A2, deionized water is added to prepare a mineralizer B2 with a mass fraction of 8%, the mineralizer B2 and the flame fusion spherical silica powder raw material are sealed in a high-pressure reactor according to a mass ratio of 100:40, the high-pressure reactor is placed in a hot air circulation oven at 220° C. for heat treatment for 20 hours, washed with deionized water 6 times and then dried to obtain a precursor P2;

[0027] The prepared precursor P2 was placed in a crucible for calcination at a maximum calcination temperature of 1210°C, a heating rate of 5°C / min, and kept warm for 14 hours. The product C2 obtained after cooling was placed in a ball mill and ground to obtain product D2. After XRD, density and SEM tests on product D1, it was found that product D1 was spherical cristobalite with a cristobalite content of more than 99%.

[0028] Embodiment three:

[0029] In this embodiment, flame fusion spherical silica powder with D50 = 50 μm is selected as a raw material, a mixture of magnesium fluoride: ammonium fluoride in a mass ratio of 3:1 is selected as a mineralizer A3, deionized water is added to prepare a mineralizer B3 with a mass fraction of 3%, and the mineralizer B3 and the flame fusion spherical silica powder raw material are sealed in a high-pressure reactor according to a mass ratio of 100:35. The high-pressure reactor is placed in a hot air circulation oven at 240° C. for heat treatment for 12 hours, washed 8 times with deionized water, and then dried to obtain a precursor P3;

[0030] The prepared precursor P3 was placed in a crucible for calcination at a maximum temperature of 1300°C, a heating rate of 10°C / min, and kept warm for 10 hours. The product C3 obtained after cooling was placed in a ball mill and ground to obtain product D3.

[0031] Density and particle size data chart of the products C1 and C2 obtained according to Example 1, Example 2 and Example 3:

[0032]

[0033] Comparative Example 1:

[0034] Comparative Example 1 uses the same flame fusion method spherical silica powder as the raw material, mineralizer and phase transformation process as Example 1, except that the mineralizer is directly calcined after being mixed with the raw material;

[0035] Select flame fusion spherical silica powder with D50=40μm as raw material, select magnesium fluoride as mineralizer A4, add deionized water to make mineralizer B4 with a mass fraction of 5%, add mineralizer B4 and flame fusion spherical silica powder raw material in a mass ratio of 100:50 into a crucible for calcination, the maximum calcination temperature is 1250℃, the heating rate is 8℃ / min, and the temperature is kept for 8H. After cooling, the product C4 is obtained. The XRD spectrum of the obtained product C4 is as follows Figure 4 As shown, from the XRD pattern results, it can be concluded that most of the material remains in the amorphous phase.

[0036] Comparative Example 2:

[0037] Comparative Example 2 selects the same spherical silicon powder raw material, mineralizer, and precursor preparation process as Example 1, except that no high-temperature phase transformation process is performed after the precursor preparation. An XRD test is performed on the product obtained without the high-temperature phase transformation process. From the XRD test spectrum, most of the five items remain in an amorphous phase.

[0038] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention. These improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A spherical quartz powder for power devices and a preparation method thereof, characterized in that The steps include: S1 Raw material pretreatment: flame fusion spherical silica powder is used as raw material, fluorine-containing salt substances are selected as mineralizer A, mineralizer A is added with deionized water to prepare mineralizer B, mineralizer B and flame fusion spherical silica powder raw material are mixed according to mass ratio and sealed into a high-pressure reactor. Preparation of S2 precursor: Place the high-pressure reactor in a high-temperature device for heat treatment for a certain period of time, wash it repeatedly with deionized water, and then dry it to obtain the precursor P. S3 high temperature phase transition: The precursor P is placed in a high temperature device for high temperature calcination to complete the crystal phase transition, wherein the high temperature device is heated to 1100°C~1500°C at a heating rate of 5~10°C / min, the phase transition time is 2-12H, and the product is obtained after cooling. S4 depolymerization: After depolymerization of the product obtained in S3, a spherical quartz product C with D50=20-50 μm and adjustable particle size is obtained.

2. The method for preparing spherical cristobalite powder for power devices according to claim 1, characterized in that: The mineralizer A is one or more combinations of fluoride-containing salt substances.

3. The method for preparing spherical cristobalite powder for power devices according to claim 2, characterized in that: The mass fraction of the mineralizer A and deionized water is 1%-10% of the mineralizer B.

4. The method for preparing spherical cristobalite powder for power devices according to claim 2, characterized in that: The mineralizer B and the flame-processed spherical silica powder raw material are mixed in a mass ratio of 100:30-60.

5. The method for preparing spherical cristobalite powder for power devices according to claim 2, characterized in that: The heat treatment temperature of S2 is 150-250° C., and the heat treatment time is 8-24 hours.

6. The method for preparing spherical cristobalite powder for power devices according to claim 2, characterized in that: The calcination temperature of S3 is preferably 1200°C to 1400°C.

7. A spherical quartz powder for power devices, characterized in that: The cristobalite content is greater than 99%, D50 is 25-55 μm, and the morphology is spherical.

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