Spray granulation process for high-purity ceramic material

Abstract

The invention provides a high-purity ceramic material spray granulation process which sequentially comprises the following process steps: a preheating step, a material preparation step and a granulation step, and further comprises a pre-spraying step: preparing pre-spraying slurry, pouring the pre-spraying slurry into a stirring barrel and starting the stirring barrel, starting an atomizing nozzle, adjusting the rotating speed of the atomizing nozzle in a reciprocating manner from high to low and from low to high, and ensuring that the pneumatic knocking hammer is not started, so that the pre-sprayed slurry can be attached to the inner surface of the granulation tower and is cured, and the components of the pre-sprayed slurry are contained in the range of the components contained in the product slurry; the pre-spraying step is arranged after the preheating step and before the material preparation step. According to the high-purity ceramic material spray granulation process, transformation of a common spray granulation tower is avoided, high-purity granulation can be achieved, and metal element pollution can be avoided to a great extent.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic material spray granulation, in particular to a high-purity ceramic material spray granulation process. Background Art

[0002] Spray granulation of ceramic materials is a common granulation technology, which is mainly used for the processing of ceramic powders. Specifically, this method is to mix the ceramic powder with an appropriate amount of binder, configure it into a slurry with a certain solid content, and then spray the slurry into the granulation tower through a sprayer for atomization. In this process, the atomized slurry forms very fine droplets, so its specific surface area is large, so that the water in the droplets evaporates quickly, the drying process ends quickly, and finally spherical particles with good fluidity are obtained.

[0003] Compared with general granulation methods, spray granulation has the advantages of fast granulation speed, good finished product quality, closed and continuous operation of the system, and easy operation. It is suitable for large-scale production. Moreover, since the material is heated for a short time during the spray granulation process, the temperature of the dried material is relatively low, which is suitable for the processing of heat-sensitive materials. Therefore, the resulting product has high purity.

[0004] However, since ceramic materials are non-metallic materials with excellent mechanical properties, they are often used in some metal-free environments, such as semiconductor manufacturing. In these application scenarios, the purity requirements for ceramic materials are very strict, especially the need to remove almost all metal elements, but spray granulation, like most granulation methods, requires the use of equipment such as spray granulation towers. During the granulation process, the slurry will inevitably contact metal parts and be mixed with metal elements, which usually requires specialized modifications to equipment such as spray granulation towers. Such modifications seem to be of limited difficulty, but in fact, during the spray granulation process, the equipment parts that the slurry may contact are very complicated, and the processing methods of different parts may be different, so the cost and modification risks are difficult to control. Summary of the invention

[0005] In view of the defects of the prior art, the technical problem to be solved by the present invention is to propose a high-purity ceramic material spray granulation process, which avoids the modification of ordinary spray granulation towers and can achieve high-purity granulation, thereby avoiding metal element pollution to a great extent.

[0006] In order to solve the above technical problems, the present invention proposes a high-purity ceramic material spray granulation process, comprising the following process steps in sequence:

[0007] Preheating step: preheating the granulation tower to ensure that the temperature inside the tower reaches the set temperature and maintains it; material preparation step: prepare product slurry, pour the product slurry into the stirring barrel, and turn on the stirring barrel; granulation step: turn on the atomizing nozzle and adjust the nozzle speed to appropriate parameters, turn on the pneumatic hammer, and turn on the peristaltic pump to feed; in addition, it also includes a pre-spraying step: prepare pre-spray slurry, pour the pre-spray slurry into the stirring barrel and turn on the stirring barrel, turn on the atomizing nozzle and reciprocately adjust the speed of the atomizing nozzle from high to low and from low to high, and ensure that the pneumatic hammer is not turned on, the pre-spray slurry can adhere to the inner surface of the granulation tower and solidify, and the components of the pre-spray slurry are included in the range of components contained in the product slurry; and the pre-spraying step is arranged after the preheating step and before the material preparation step.

[0008] Conventional granulation processes and equipment generally try to avoid the formation of material hanging on the wall during the granulation process to avoid the problem of raw material waste and difficulty in cleaning. For example, the Chinese utility model patent with application number 202022503201.7 and titled A spray drying granulation tower with anti-sticking inner wall proposes a granulation tower that uses a blower and a circular pipe to form an air curtain to blow the mist raw material away from the inner wall of the granulation tower, thereby improving production efficiency and reducing the number of cleaning times. In contrast, the technical problem to be solved by the present invention is to improve the purity of granulation to obtain high-purity ceramic materials and to avoid metal contamination of the raw materials by the granulation tower as much as possible. The material hanging on the wall during the granulation process happens to be the best isolation layer, which can effectively prevent the contact between the mist particles and the granulation tower during the granulation process.

[0009] Therefore, the technical solution controls the cyclic change of the rotation speed of the atomizing nozzle to change the distance of the mist particles being thrown out, so as to form a complete isolation layer inside the granulation tower as much as possible. Although controlling the feed speed and slurry viscosity can also affect the distance of the mist particles being thrown out, they are not as efficient and convenient as controlling the change in the rotation speed of the atomizing nozzle. At the same time, the pre-spraying is different from the ordinary granulation process. The present solution requires that the pneumatic hammer should not be turned on during the pre-spraying process, because the hammering will seriously damage the formation of the isolation layer. In addition, since the goal of the present solution is to obtain high-purity ceramic materials, the present solution limits the composition of the pre-spraying slurry to be included in the range of the composition contained in the product slurry to avoid the introduction of other impurities that affect the purity of the ceramic material.

[0010] Preferably, the pre-spraying slurry has the same composition as the product slurry, that is, both include the same high-purity ceramic powder and binder. The pre-spraying slurry has the same composition as the product slurry, which can ensure that no other impurities are generated during the pre-spraying process, ensure the high purity of the ceramic material, and avoid defects in the subsequent molding and sintering processes of the ceramic material.

[0011] Furthermore, the binder content in the pre-sprayed slurry is 2-3 times the binder content contained in the product slurry. In order to increase the viscosity of the mist particles to improve adhesion, the binder content in the pre-sprayed slurry is increased. However, considering that the particles formed by the pre-sprayed slurry may also be mixed into the final finished particles, it is necessary to control the binder content not to be too high, because too much binder will evaporate during the sintering process, and the original position will become a cavity. Part of these cavities will shrink during sintering but may not shrink completely, resulting in poor density of the final ceramic body. However, considering further that most of the particles formed by the pre-sprayed slurry are attached to the wall or discharged in advance, the number of particles that fall off is small, so the binder content can be slightly higher. Based on the above, this ratio was selected.

[0012] In addition, the temperature in the granulation tower in the pre-spraying step is 50-100°C lower than the temperature of the granulation tower in the granulation step. The purpose of the granulation process is to quickly dry the mist particles to obtain granulated powder, so the temperature of the granulation tower is relatively high. In this scheme, the mist particles are required to hang on the wall, and the temperature should be lowered. However, when the temperature is set to a low level, the fluidity of the mist particles on the tower wall is too high, and the hanging effect on the wall in the top area of ​​the granulation tower is poor, so the above temperature range is selected.

[0013] As another option, the binder in the product slurry is phenolic resin, and the pre-spray slurry is a phenolic resin solvent. Phenolic resin is a common binder for ceramic materials, which is often mixed with ceramic powder before granulation and removed by carbonization during the subsequent ceramic sintering process. The use of phenolic resin as the pre-spray slurry can fully utilize the viscosity of phenolic resin, improve the wall hanging efficiency, effectively shorten the time required for the pre-spray step, and will not introduce impurities into the high-purity ceramic material. Compared with other common resins, PVA, PVB, and PVP ceramic material binders, phenolic resin has higher mechanical strength and hardness, good wear resistance, and can still maintain good dimensional stability at high temperatures, which is particularly suitable for this process.

[0014] Furthermore, the temperature in the granulation tower in the pre-spraying step does not exceed 190°C, and the temperature in the granulation tower in the granulation step does not exceed 280°C. As an isolation layer, phenolic resin requires both certain toughness and certain hardness. Generally speaking, the higher the temperature, the lower the toughness and the higher the hardness of the phenolic resin. When the temperature is too high, it will become completely brittle and easy to peel off. Therefore, this temperature is selected during the pre-spraying process. In the granulation process, the higher the temperature, the higher the production efficiency. At this time, in order to consider the phenolic resin isolation layer, it is considered to improve the production efficiency by other parameters and reduce the temperature to a certain extent. Therefore, the above temperature is selected during the granulation process.

[0015] Furthermore, after the pre-spraying step is completed, the first hammering step is performed, and the first hammering step includes turning on the pneumatic hammer to collect waste at the discharge port of the granulation tower and remove it in time. Since phenolic resin is used as an isolation layer, it is found that blocky phenolic resin will peel off and mix into the granulation powder during the granulation process. Such granulation powder may cause subsequent firing defects. Therefore, before the formal granulation, the hammering function of the formal granulation is used to remove some phenolic resins that are not firmly solidified, so as to improve the purity of the granulation powder.

[0016] Furthermore, a supplementary spraying step is performed after the first hammering step, and the specific operation of the supplementary spraying step is the same as the pre-spraying step. After the first hammering step, exposed areas that cannot be completely covered by the isolation layer may appear on the inner wall of the granulation tower. At this time, the supplementary spraying operation can effectively solve this problem.

[0017] Furthermore, a second hammering step is performed after the supplementary spraying step, and the specific operation of the second hammering step is the same as the first hammering step. The second hammering step is still performed after the supplementary spraying, so that the excess phenolic resin can be shaken off, and at the same time, the probability of the exposed area on the inner wall of the granulation tower caused by the hammering is greatly reduced, thereby ensuring the isolation effect of the granulation tower and reducing the pollution of the granulation powder.

[0018] Furthermore, the duration of the supplementary spraying step is 1 / 3-1 / 2 of the duration of the preliminary spraying step. Since it is necessary to ensure that no exposed area appears on the inner wall of the granulation tower, the duration of the supplementary spraying cannot be too short, and it is more reasonable to select the above time.

[0019] In summary, such a high-purity ceramic material spray granulation process avoids the modification of ordinary spray granulation towers and can achieve high-purity granulation, which can avoid metal element pollution to a great extent. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0021] The present invention provides a high-purity ceramic material spray granulation process, comprising the following process steps in sequence:

[0022] Preheating step: preheat the granulation tower to ensure that the temperature inside the tower reaches the set temperature and maintains it;

[0023] Pre-spraying step: prepare pre-spraying slurry, pour the pre-spraying slurry into the mixing barrel and start the mixing barrel, turn on the atomizing nozzle and reciprocately adjust the speed of the atomizing nozzle from high to low and from low to high, and ensure that the pneumatic percussion hammer is not turned on, the pre-spraying slurry can adhere to the inner surface of the granulation tower and solidify, and the components of the pre-spraying slurry are included in the range of components contained in the product slurry;

[0024] Material preparation steps: prepare product slurry, pour the product slurry into the mixing barrel, and start the mixing barrel;

[0025] Granulation steps: turn on the atomizing nozzle and adjust the nozzle speed to the appropriate parameters, turn on the pneumatic hammer, and turn on the peristaltic pump to feed;

[0026] Conventional granulation processes and equipment generally try to avoid the formation of material hanging on the wall during the granulation process to avoid the problem of raw material waste and difficulty in cleaning. For example, the Chinese utility model patent with application number 202022503201.7 and titled A spray drying granulation tower with anti-sticking inner wall proposes a granulation tower that uses a blower and a circular pipe to form an air curtain to blow the mist raw material away from the inner wall of the granulation tower, thereby improving production efficiency and reducing the number of cleaning times. In contrast, the technical problem to be solved by the present invention is to improve the purity of granulation to obtain high-purity ceramic materials and to avoid metal contamination of the raw materials by the granulation tower as much as possible. The material hanging on the wall during the granulation process happens to be the best isolation layer, which can effectively prevent the contact between the mist particles and the granulation tower during the granulation process.

[0027] Therefore, the technical solution controls the cyclic change of the rotation speed of the atomizing nozzle to change the distance of the mist particles being thrown out, so as to form a complete isolation layer inside the granulation tower as much as possible. Although controlling the feed speed and slurry viscosity can also affect the distance of the mist particles being thrown out, they are not as efficient and convenient as controlling the change in the rotation speed of the atomizing nozzle. At the same time, the pre-spraying is different from the ordinary granulation process. The present solution requires that the pneumatic hammer should not be turned on during the pre-spraying process, because the hammering will seriously damage the formation of the isolation layer. In addition, since the goal of the present solution is to obtain high-purity ceramic materials, the present solution limits the composition of the pre-spraying slurry to be included in the range of the composition contained in the product slurry to avoid the introduction of other impurities that affect the purity of the ceramic material.

[0028] Specifically, regarding the selection of pre-spraying slurry and the corresponding process method, there are the following two embodiments:

[0029] First embodiment:

[0030] The pre-spraying slurry has the same composition as the product slurry, that is, both include the same high-purity ceramic powder and binder. The pre-spraying slurry has the same composition as the product slurry, which can ensure that no other impurities are generated during the pre-spraying process, ensure the high purity of the ceramic material, and avoid defects in the subsequent molding and sintering processes of the ceramic material.

[0031] Preferably, the binder content in the pre-sprayed slurry in this embodiment is 2-3 times the binder content contained in the product slurry. In order to increase the viscosity of the mist particles to improve adhesion, the binder content in the pre-sprayed slurry is selected to be increased, but considering that the particles formed by the pre-sprayed slurry may also be mixed into the final finished product particles, it is necessary to control the binder content not to be too high, because too much binder will volatilize during the sintering process, and the original position will become a cavity. Part of these cavities will shrink during sintering but may not shrink completely, resulting in poor density of the final ceramic body. However, considering further that most of the particles formed by the pre-sprayed slurry are hung on the wall or discharged in advance, the number of particles that fall off is small, so the binder content can be slightly higher. Based on the above, this ratio was selected.

[0032] In addition, the temperature in the granulation tower in the pre-spraying step is 50-100° C. lower than the temperature of the granulation tower in the granulation step. The purpose of the granulation process is to quickly dry the mist particles to obtain granulated powder, so the temperature of the granulation tower is relatively high. In this scheme, the mist particles are required to hang on the wall, and the temperature should be lowered. However, when the temperature is set to a low level, the fluidity of the mist particles on the tower wall is too high, and the hanging effect on the wall in the top area of ​​the granulation tower is poor, so the above temperature range is selected.

[0033] Second embodiment:

[0034] The binder in the product slurry is phenolic resin, and the pre-spray slurry is a phenolic resin solvent. Phenolic resin is a common binder for ceramic materials. It is often mixed with ceramic powder before granulation and removed by carbonization during the subsequent ceramic sintering process. The use of phenolic resin as the pre-spray slurry can make full use of the viscosity of phenolic resin, improve the wall hanging efficiency, effectively shorten the time required for the pre-spray step, and will not introduce impurities into the high-purity ceramic material. Compared with other common resins, PVA, PVB, and PVP ceramic material binders, phenolic resin has higher mechanical strength and hardness, good wear resistance, and can still maintain good dimensional stability at high temperatures, which is particularly suitable for this process.

[0035] In this embodiment, the temperature in the granulation tower in the pre-spraying step does not exceed 190°C, and the temperature in the granulation tower in the granulation step does not exceed 280°C. As an isolation layer, phenolic resin requires both certain toughness and certain hardness. Generally speaking, the higher the temperature, the lower the toughness and the higher the hardness of the phenolic resin. When the temperature is too high, it will become completely brittle and easy to peel off. Therefore, this temperature is selected during the pre-spraying process. In the granulation process, the higher the temperature, the higher the production efficiency. At this time, in order to consider the phenolic resin isolation layer, it is considered to improve the production efficiency by other parameters and reduce the temperature to a certain extent. Therefore, the above temperature is selected during the granulation process.

[0036] Preferably, the first hammering step is performed after the pre-spraying step is completed, and the first hammering step includes turning on the pneumatic hammer to collect waste at the discharge port of the granulation tower and remove it in time. Since phenolic resin is used as an isolation layer, it is found that blocky phenolic resin will peel off and mix into the granulation powder during the granulation process. Such granulation powder may cause subsequent firing defects. Therefore, before the formal granulation, the hammering function of the formal granulation is used to remove some phenolic resin that is not firmly solidified, so as to improve the purity of the granulation powder.

[0037] Furthermore, a supplementary spraying step is performed after the first hammering step, and the specific operation of the supplementary spraying step is the same as the pre-spraying step. After the first hammering step, exposed areas that cannot be completely covered by the isolation layer may appear on the inner wall of the granulation tower. At this time, the supplementary spraying operation can effectively solve this problem.

[0038] To further improve the isolation effect, a second hammering step is performed after the supplementary spraying step. The specific operation of the second hammering step is the same as the first hammering step. The second hammering step is still performed after the supplementary spraying, so that the excess phenolic resin can be shaken off. At the same time, the probability of the exposed area on the inner wall of the granulation tower caused by the hammering is greatly reduced, ensuring the isolation effect of the granulation tower while reducing the pollution of the granulation powder.

[0039] In terms of time, the duration of the supplementary spraying step in this embodiment is 1 / 3-1 / 2 of the duration of the preliminary spraying step. Since it is necessary to ensure that no exposed area appears on the inner wall of the granulation tower, the duration of the supplementary spraying cannot be too short, and it is more reasonable to choose the above time.

[0040] In summary, such a high-purity ceramic material spray granulation process avoids the modification of ordinary spray granulation towers and can achieve high-purity granulation, which can avoid metal element pollution to a great extent.

[0041] In short, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-purity ceramic material spray granulation process, comprising the following process steps in sequence: Preheating step: preheat the granulation tower to ensure that the temperature inside the tower reaches the set temperature and maintains it; Material preparation step: prepare product slurry, pour the product slurry into a mixing barrel, and start the mixing barrel; Granulation steps: turn on the atomizing nozzle and adjust the nozzle speed to the appropriate parameters, turn on the pneumatic hammer, and turn on the peristaltic pump to feed; Features: The method further comprises a pre-spraying step: preparing a pre-spraying slurry, pouring the pre-spraying slurry into the stirring barrel and turning on the stirring barrel, turning on the atomizing nozzle and reciprocatingly adjusting the rotation speed of the atomizing nozzle from high to low and from low to high, and ensuring that the pneumatic percussion hammer is not turned on, the pre-spraying slurry can adhere to the inner surface of the granulation tower and solidify, and the components of the pre-spraying slurry are included in the range of components contained in the product slurry; The pre-spraying step is arranged after the preheating step and before the material preparation step.

2. The high-purity ceramic material spray granulation process according to claim 1, characterized in that: The pre-spraying slurry has the same composition as the product slurry, that is, both include the same high-purity ceramic powder and binder.

3. The high-purity ceramic material spray granulation process according to claim 2, characterized in that: The binder content in the pre-sprayed slurry is 2-3 times the binder content contained in the product slurry.

4. The high-purity ceramic material spray granulation process according to claim 2, characterized in that: The temperature in the granulation tower in the pre-spraying step is 50-100° C. lower than the temperature in the granulation tower in the granulation step.

5. The high-purity ceramic material spray granulation process according to claim 1, characterized in that: The binder in the product slurry is phenolic resin, and the pre-sprayed slurry is phenolic resin solvent.

6. The high-purity ceramic material spray granulation process according to claim 5, characterized in that: The temperature in the granulation tower in the pre-spraying step does not exceed 190°C, and the temperature in the granulation tower in the granulation step does not exceed 280°C.

7. The high-purity ceramic material spray granulation process according to claim 6, characterized in that: After the pre-spraying step is completed, a first hammering step is performed, and the first hammering step includes turning on the pneumatic hammer to collect waste materials at the discharge port of the granulation tower and remove them in time.

8. The high-purity ceramic material spray granulation process according to claim 7, characterized in that: After the first hammering step, a supplementary spraying step is performed, and the specific operation of the supplementary spraying step is the same as that of the preliminary spraying step.

9. The high-purity ceramic material spray granulation process according to claim 8, characterized in that: The second hammering step is performed after the supplementary spraying step, and the specific operation of the second hammering step is the same as that of the first hammering step.

10. The high-purity ceramic material spray granulation process according to claim 9, characterized in that: The duration of the supplementary spraying step is 1 / 3-1 / 2 of that of the preliminary spraying step.