JP2006248876A - High density powder compact, its sintered compact and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slurry suitable for cast molding, its manufacturing method, a high density powder compact manufactured by using the slurry and a high density sintered compact with low shrinkage. <P>SOLUTION: In the method for manufacturing the slurry by mixing raw material powders and a solvent, a raw material slurry having low viscosity and low thixotropy is prepared by adopting wet jet mill processing without the use of a grinding medium. The homogeneous and high density powder compact is molded by the cast molding of the slurry. A method for manufacturing a high density sintered compact with low shrinkage at sintering by sintering the molded product and the sintered product are provided. The high density sintered compact with low shrinkage has a relative density of 98% or more and a shrinkage factor at sintering of 13% or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a slurry suitable for casting, a production method thereof, a high-density molded body using the slurry, and a sintered body thereof. More specifically, the present invention relates to a low-viscosity / low-pressure produced by a wet jet mill process. The present invention relates to a slurry having thixotropy, a high-density molded body produced by casting this, and a high-density low-shrinkage sintered body obtained by sintering the slurry. With the development of industrial technology in recent years, the present invention, for example, in the fields of architecture, automobiles, electronic equipment, etc. It was developed to realize near net shaping by increasing the density and accuracy. The present invention makes it possible to provide sintered parts with high yield, high dimensional accuracy, high density, and high accuracy in technical fields such as fine ceramic products.

  Conventionally, in the production of powder molded bodies and sintered bodies by casting molding, the powder sintering process in which raw powder is molded into a predetermined shape and the powder molded body is sintered to produce a product is complicated. Since it has the merit of being efficient and inexpensive, it is widely used in various industrial fields. In the powder sintering process, the quality, shape, and accuracy of the product obtained are greatly affected by the powder compact before sintering. For example, when the density of the compact is low, the shrinkage of the sample during sintering becomes large, and it becomes difficult to control the shape and accuracy of the product. Moreover, the quality of a product may be reduced remarkably by the space | gap in a molded object remaining. When the density of the powder compact is uneven, there is a difference in the shrinkage rate depending on the location, causing a problem that the powder shrinks unevenly during sintering and cracks occur. Therefore, in order to obtain a good product, it is extremely important to produce a powder compact having a high density and a uniform density distribution.

  There are many methods for forming a powder compact, and broadly divided into two types: a dry process and a wet process. Examples of the dry process include pressing, extruding, rolling, and the like that apply high temperature and high pressure to the raw material powder. Since these methods require high temperatures and high pressures, the size of the apparatus increases and the cost increases. In addition, the refinement of raw material powder has been progressing due to the higher functionality and higher performance of the demands for materials and components in accordance with the recent development of industrial technology, but in the dry process, workability is improved by making the raw material powder finer. Problems such as reduction, increased risk, and deterioration of the work environment occur. On the other hand, the wet process includes a slurry casting process in which a raw material powder is mixed with a solvent to prepare a slurry and cast into a porous mold, and an injection process in which the mold is injected at a high pressure. The injection process requires high pressure and therefore costs as much as the dry process, whereas the mud casting process does not require specially expensive equipment. Furthermore, the mud casting process is a method suitable for high-mix low-volume production of complex shapes because it can produce a compact body having a relatively large complex shape at a high density.

  However, in recent years, there is an increasing expectation for net shaping to produce more complex parts with higher precision, and further densification of the mud cast molding is required. As a method for further increasing the density of the cast molded body, there are a method resulting from a molding process and a method resulting from a slurry used for molding. Examples of methods resulting from the molding process include pressure casting (see Patent Document 1) in which an external force is applied during molding, centrifugal casting in which centrifugal force is applied, and vibration casting in which vibration is applied (see Patent Document 2). However, each process such as pressure casting, centrifugal casting, and vibration casting requires a pressurizing device, a centrifugal device, and a vibration device, so that the size of the device is increased, and the mold and the device are heavily consumed. Have Furthermore, the density is not so high.

  As a method resulting from the slurry used for molding, a method of increasing the particle size distribution width of the raw material powder (for example, see Patent Document 3), a method of adjusting the solvent, pH, and dispersant of the slurry (for example, Patent Document) 4)). By increasing the particle size distribution of the raw material powder, it is possible to increase the density of the compact, but sintering proceeds in such a way that large particles absorb small particles, resulting in abnormal grain growth during sintering. The quality of the aggregate is reduced. On the other hand, in the method of adjusting the solvent and pH of the slurry, a slight density increase effect is obtained. This is partly due to viscosity increase and particle re-aggregation in the slurry preparation process. As a method of preparing a slurry by mixing raw material powder and a solvent, a ball mill using a grinding medium called a media is often used. However, when a ball mill is used, the crystal and surface structure of the raw material powder are damaged due to the collision of a medium having a large mass, and the raw material powder is re-agglomerated due to an increase in surface energy. Such reaggregation of the raw material powder is known to cause an increase in slurry viscosity and an increase in thixotropy. Slurries containing high viscosity, high thixotropy and / or agglomerated particles impede densification and homogenization of the molded body during slurry casting. When such a low density, non-homogeneous shaped body is sintered, degreased, or sintered, only a low density, non-homogeneous sintered body can be obtained, and inconveniences such as deformation and cracking occur during sintering.

  Furthermore, media abrasion powder is mixed into the material as impurities due to collision between the media. If the mixing amount is large, the amount becomes 1 wt%, and such impurities interfere with sintering and cause deterioration of characteristics of the obtained product. The conventional slurry preparation method mainly uses this grinding medium type, but there are other preparation methods such as a stirring type, a powder type, and an ultrasonic type. However, in any of the methods, damage to the raw material powder surface or re-aggregation due to excessive energy is an unavoidable problem, and not a few impurities are mixed. Furthermore, all the conventional slurry preparation methods have problems in terms of economy and environment, such as requiring several hours to several days for the treatment.

  On the other hand, regarding the wet jet mill process employed in the present invention, there have been several reports so far, but its application field is mainly related to food (for example, see Patent Document 5). In addition, there are examples applied to ceramic powder, metal powder, and the like (see, for example, Patent Document 6), but all of them are focused on miniaturizing the raw material powder. In fact, no consideration is given to the molding method using the slurry produced by the provided wet jet mill, the molded body, and the sintered body.

JP-A-8-99306 JP-A-2-141455 JP 2000-128625 A JP-A-3-169506 Japanese Patent Laid-Open No. 11-113544 JP-A-11-147714

  Under such circumstances, the present inventors can solve the problems of the prior art in view of the prior art, and, for example, in the production of fine ceramic materials, As a result of intensive research aimed at developing a new technology that makes it possible to achieve high functionality and near net shape by manufacturing as a sintered body with high density and high precision, It has been found that the intended purpose can be achieved by using the produced low-viscosity and low-thixotropic slurry, and the present invention has been completed.

  It is an object of the present invention to provide a high-density powder molded body and a high-density low-shrinkage powder sintered body that enable high reliability, high functionality, and near-net shape of various members, and a manufacturing process thereof. Is. It is another object of the present invention to provide a slurry having low viscosity and low thixotropy used for producing those products. Another object of the present invention is to provide a method for producing a low-viscosity and low-thixotropic slurry capable of obtaining a high-density powder compact and a high-density low-shrinkage powder sintered body by a wet jet mill process. Is. Another object of the present invention is to provide a method for producing a fine powder crushed to primary particles, in which the crystal structure and surface structure of the raw material powder are not damaged and the surface energy is not increased. To do. A further object of the present invention is to provide a new casting technique useful for producing, for example, fine ceramic parts.

The present invention for solving the above-described problems comprises the following technical means.
(1) A slurry having a low viscosity and a low thixotropy and having a viscosity of 40 mPa · s or less and a change in viscosity per unit time of 10 mPa · s / h or less.
(2) The slurry according to (1) above, wherein the concentration of the raw material powder in the slurry is in the range of 10 to 60 vol%.
(3) The slurry according to (1) above, wherein the powder in the slurry retains the original crystallinity and surface structure without breaking the surface state before dispersion.
(4) The powder is pulverized into primary particles, (1) the original crystallinity and surface structure are maintained without breaking the surface state, and (2) the powder is dispersed in a solvent. The powder is characterized in that the viscosity of the slurry is 40 mPa · s or less and the amount of change in viscosity per unit time is 10 mPa · s / h or less.
(5) A high density molded body of the slurry according to any one of (1) to (3), wherein the relative density is 65 to 75%.
(6) A sintered compact of the molded product according to (5) above, having a linear shrinkage rate of 13% or less and a relative density of 98% or more.
(7) A method for producing a slurry having a viscosity of 40 mPa · s or less and a unit time variation of viscosity of 10 mPa · s / h or less, comprising a step of mixing and crushing by a wet jet mill treatment. A method for producing a slurry.
(8) The wet jet mill process forms the raw material powder and solvent into a slurry, and pumps the slurry at a high pressure to a nozzle arranged in a sealed state in a pressure-resistant vessel so that the opposing flow of the slurry collides and joins each other. The manufacturing method of the slurry as described in said (7) which is a wet jet mill process which mixes, disperses, and crushes the raw material powder in a slurry by making it.
(9) The manufacturing method of the slurry as described in said (7) in which raw material powder exists in the range of 10-60 vol% with respect to the total amount of raw material powder and a solvent.
(10) The method for producing a slurry according to (7), wherein the wet jet mill treatment is performed under a treatment pressure of 10 MPa or more.
(11) A method for producing a high-density molded body, comprising producing a high-density molded body by casting the slurry according to any one of (1) to (3) above into a mold.
(12) The method for producing a high-density molded body according to (11), wherein the relative density of the molded body is 65 to 75%.
(13) The slurry according to any one of (1) to (3) above is cast into a mold and solidified to produce a high-density molded body, and the molded body is sintered to obtain a sintered body. A method for producing a high-density, low-shrinkage sintered body, characterized by being produced.
(14) The method for producing a high-density, low-shrinkage sintered body according to (13), wherein the linear shrinkage rate is 13% or less and the relative density is 98% or more.

Next, the present invention will be described in more detail.
The present invention provides a slurry having a viscosity of 40 mPa · s or less and / or a change in viscosity per unit time of 10 mPa · s / h or less, and a relative density obtained by casting the slurry of 65% to 75%. High-density powder compacts (hereinafter also referred to as compacts) in the range of 10%, and high-density low-shrinkage having a relative density of 98% or more and a linear shrinkage ratio of 13% or less obtained by sintering the compacts. It is characterized by a powder sintered body. Further, the present invention is characterized by a powder produced through a mixing and pulverization process by a wet jet mill, without damaging the surface structure, and pulverized to primary particles. A method for producing the slurry having a mixing and crushing step by a jet mill, and preferably, as the wet jet mill treatment step, the slurry is pumped at a high pressure to a nozzle disposed in a sealed state in a pressure vessel. It has a feature in a method of manufacturing a slurry by adopting a step of colliding / merging opposite flow of the slurry with each other.

  As described above, the present invention employs a slurry preparation method that does not use a pulverizing medium such as a medium, thereby containing a powder pulverized to a primary particle size or close to the primary particle size, and having low viscosity and low thixotropy. The slurry which has property is manufactured. The slurry of the present invention contains a powder having the original crystallinity and surface structure that is crushed into primary particles and the surface state before dispersion is not broken. Based on these characteristics, a slurry suitable for casting is formed that has low viscosity and does not exhibit thixotropic properties. Further, in the present invention, the slurry is made into a high-density powder molded body by casting and sintered, so that the linear shrinkage rate during sintering is 13% or less, and the relative density after firing is 98%. The high-density sintered body as described above is produced.

  The slurry of the present invention has a viscosity of 40 mPa · s or less and a change in viscosity per unit time of 10 mPa · s / h or less. When the viscosity of the slurry is 40 mPa · s or more, it is not preferable because the rearrangement of particles at the time of casting is hindered and the relative density of the molded body is lowered. In addition, when the amount of change in viscosity per unit time is 10 mPa · s / h or more, the reaggregation property is increased and the relative density of the molded body is lowered, which is not preferable. Regarding the change in the viscosity of the slurry of the present invention, for example, as shown in FIG. 1, even after 3 hours, the viscosity is almost the same as that immediately after the production, and almost no increase in viscosity is observed. The slurry of the present invention is preferably produced by a wet jet mill process. In the slurry, the powder is almost pulverized into primary particles, and the original crystallinity and surface state are preserved without breaking the surface state before dispersion. On the other hand, as shown in FIG. 5, the viscosity of a slurry manufactured by a slurry manufacturing method using a pulverizing medium such as a medium, for example, a pulverizing / dispersing process using a ball mill, rapidly increases. Such an increase in viscosity is caused by the re-aggregation of the powder due to the damage of the crystallinity and surface structure of the raw material powder due to the collision of the medium having a large weight and the increase of the surface energy.

  As the raw material powder, metal powder, intermetallic compound powder, ceramic powder such as oxide, carbide, and nitride, or mixed powders thereof are used, and there are no particular restrictions as long as they can be cast by moulding. Preferably, aluminum oxide, TiAl intermetallic compound, zirconium oxide, barium titanate, silicon carbide, silicon nitride, aluminum nitride, etc. are preferably used. About the particle size of these raw material powders, when the slurry is used, if the viscosity is 40 mPa · s or less and the amount of change in viscosity per unit time satisfies the condition of 10 mPa · s / h or less, Although there is no restriction | limiting in particular, The thing with an average particle diameter of 50-1000 nm is used suitably.

  As for the solvent, those conventionally used such as water, alcohols, ketones, oils, and amines can be used as they are in the present invention, and there is no particular limitation. Preferably, water (distilled water, ion exchange water, tap water, industrial water, etc.) is used from the viewpoint of environmental load.

  The suitable density | concentration of the raw material powder contained in a slurry is the range of 10-60 vol%. If it is 10 vol% or less, a high-density molded article cannot be obtained, and if it is 60 vol% or more, a fluid slurry capable of wet jet milling cannot be produced. Preferably, a slurry containing the raw material powder in the range of 20 to 50 vol% is used. Moreover, as long as the effects of the present invention are not impaired, known additives such as ammonium polyacrylate and ammonium polycarboxylate are used in addition to the raw material powder in order to improve the properties of the obtained molded body or sintered body. A polymer additive such as salt or polyethyleneimine may be blended in the slurry.

  The powder contained in the slurry of the present invention maintains the original crystallinity and surface structure without breaking the surface state before the treatment, is crushed into primary particles, and 10 in a solvent. It is a novel powder having the respective characteristics that the viscosity of the slurry dispersed in the range of ˜60 vol% is 40 mPa · s or less and the change amount of the viscosity per unit time is 10 mPa · s / h or less.

  As for the surface state of the powder of the present invention, the results of infrared spectroscopic analysis of the three types of alumina powders produced in Examples 1 and 2 and Comparative Example 3 of the present invention and the particle surface of the raw material alumina powder. In contrast, the alumina powder of the present invention shows the same surface state as the raw material alumina powder. On the other hand, it can be seen from the result of infrared spectroscopic analysis that the surface state of the alumina powder produced by the ball mill of Comparative Example 3 is changed (see FIG. 5). As for the particle size of the powder, the present invention shows an average particle size value of 582 nm and the comparative example is 570 nm, respectively, which is almost the same as 500 nm of the raw material alumina. It can be seen that it has been crushed. The powder of the present invention is a powder that is crushed into almost primary particles that retain the original crystallinity and surface structure without breaking the surface state of the raw material powder before processing.

  In order to produce the slurry of the present invention, it is important to prepare a mixture of the raw material powder and the solvent, and mix and pulverize the mixture by wet jet mill treatment, which enables the low viscosity and low thixotropic properties described above. A slurry is produced. Further, in the present invention, a powder in which the surface state of the powder before the wet jet mill treatment is not broken by the treatment and the original crystallinity and the surface structure are maintained and pulverized into primary particles can be obtained.

  In order to produce a slurry having a viscosity of 40 mPa · s or less and a change in viscosity per unit time of 10 mPa · s / h or less, a wet jet mill is used. The wet jet mill does not use a pulverization medium, and the processing solution is made to flow at a high speed by any method, and the turbulent flow, shear flow generated by collision between the processing liquids and / or the processing liquid and the flow path wall and the high speed flow, and A type that effectively utilizes the cavitation effect and mixes, disperses, and disintegrates the object to be processed in the processing solution is preferably used. A preferable processing pressure for more effectively exerting the effects of mixing, dispersion and crushing by such a wet jet mill is about 10 MPa or more, more preferably about 50 MPa or more, and further preferably about 100 MPa or more. In this wet jet mill process, the number of treatments is not particularly limited, and the treatment can be repeated many times until a slurry having desired characteristics is obtained. Usually, the treatment is performed 1 to 10 times. Is called.

  Next, the wet jet mill will be described. The wet jet mill used in the present invention generates a high-speed flow by an arbitrary method, causes a collision between liquids or a liquid and a flow path wall, and causes a high-speed flow. This wet jet mill is a generic term for equipment that has the function of effectively emulsifying, dispersing, and mixing by effectively utilizing the turbulent flow, shearing, and cavitation effects that occur and atomizing the workpiece. As a high-pressure homogenizer, specifically, a method in which a liquid to be treated is injected from a nozzle by a plunger pump or a rotary pump and collides with a fixed plate at a high speed, and a method in which the liquids to be treated collide with each other There is. When the liquid to be treated passes through the flow path at high speed or while colliding, the dispersoid contained in the fluid to be treated is subjected to turbulent flow and shearing and is crushed and immediately after the collision. When released under reduced pressure, a cavitation effect occurs, and the dispersoid in the liquid to be treated is remarkably atomized due to an impact caused by sudden pressure release.

  As such a wet jet mill, for example, a type that uses a high-speed jet by a valve plate that is commercially available as a “high-pressure homogenizer”, a type that collides at high speed in a flow path formed in a slit shape, and a 90 ° phase shift A type that causes high-speed collisions within each flow channel that communicates with each other, a type that generates multiple collisions between fluids within the same nozzle, a type that causes collisions by jetting from opposing orifices into a non-spherical structure room, Or the type etc. which collide a liquid phase jet flow at high speed are mentioned.

  Each of these wet jet mills has some difference in mixing, dispersion, and crushing effect depending on the characteristics of each device type. However, a dispersion device such as a conventional media medium type disperser as described above was used. Compared to the case, a stable slurry can be obtained with remarkably high efficiency. Therefore, the type of the wet jet mill used in the present invention is not particularly limited, but the method of causing high-speed slurry to collide from the front is desirably the most desirable.

  The mud casting mold can be used as long as it has water absorption, such as a plaster mold and a resin mold, and is not particularly limited, and can be appropriately selected from known porous molds. As for the casting method, for example, known casting methods such as waste mud casting, solid casting, vibration casting, pressure casting, reduced pressure casting, and centrifugal casting can be employed, and the casting method is not particularly limited.

  The powder compact produced by casting using the slurry of the present invention is a compact having a homogeneous structure with a relative density of 65 to 75%. This formed body is then subjected to a sintering step and sintered to produce a sintered body. In the present invention, the firing method is not particularly limited, and various sintering furnaces, sintering atmospheres, sintering temperatures and times, and the like can be selected according to the raw material powder. By the above method, a slurry having a viscosity of 40 mPa · s or less and a unit time variation of viscosity of 10 mPa · s / h or less is produced, and a high-density powder molded body and a high-density low-shrinkage powder sintered body are produced. Is done.

  As described above, when the slurry of the present invention is molded by a wet molding process represented by casting molding, centrifugal molding, etc., it is possible to form a high-density powder molded body having a relative density of 65 to 75%. Moreover, as shown in FIG. 3, this compact | molding | casting forms the uniform filling state of a powder. By sintering this homogeneous and high-density powder compact, a sintered compact having a relative density of 98% or more can be produced. Further, in the process of manufacturing the sintered body by heating the powder compact at a high temperature, the linear shrinkage rate of the sintered body can be suppressed to 13% or less. As described above, according to the present invention, the shape and accuracy of the product can be accurately controlled, so that the net shape can be realized and the quality of the product can be remarkably improved. It is clear that the linear shrinkage rate during sintering of the sintered body of the present invention is small by comparing the shrinkage state of the sintered body in the example of the present invention shown in FIG. 4 and the comparative example.

  According to the present invention, (1) a low-viscosity and low-thixotropic slurry capable of producing a high-density, homogeneous sintered body can be obtained. (2) Applying a wet jet mill, A method of producing a thixotropic slurry suitable for casting molding can be provided. (3) A high-density powder molded body is produced by casting molding, and a high-density, high-precision sintered body is produced by sintering. (4) Since it is possible to manufacture sintered bodies with small shrinkage during sintering, metal, intermetallic compounds, ceramics and their composite materials, high performance products, and near net shape (5) The slurry can be produced and casted on both sides by a shorter time and / or energy saving compared to the conventional process. (6) A slurry having low viscosity and low thixotropy. Over the casting process other than a wet process, for example, application to an ink-jet method is expected, the effect is exhibited that.

  EXAMPLES Next, although this invention is demonstrated concretely based on an Example, this invention is not limited at all by the following Example. In the following Examples, the raw material powder was mixed with a solvent, and this was wet-jet milled to produce a slurry. Using this slurry, waste mud casting using a gypsum mold was performed to produce a molded body. The molded body was dried at room temperature and then sintered at a predetermined temperature, atmosphere, and time to obtain a sintered body.

  Aluminum oxide powder (alumina powder: average primary particle diameter of about 500 nm) is used as a raw material powder, distilled water is used as a solvent, and weighed and mixed so that the alumina concentration is 30 vol%. A jet mill treatment was performed to prepare a slurry. Using this slurry, casting was performed to obtain a molded body. Then, it was set as the sintered compact by sintering at 1600 degreeC in air | atmosphere.

  The change over time in the viscosity of the slurry after the wet jet mill treatment was measured using a viscometer, and it was 6.1 mPa · s, and the viscosity did not change at all during the measurement for 3 hours (see FIG. 1). . The average particle size of the alumina particles after the wet jet mill treatment was crushed to almost primary particles at 582 nm, and the surface state was almost the same as the raw material powder (see FIG. 2). That is, a slurry can be produced with a powder whose surface state of the powder particles is not broken, and furthermore, since the surface energy is small, the reaggregation property, that is, thixotropy property is low. The relative density of the molded body was 67.0%, and a uniform filling state was obtained (see FIG. 3). The relative density of the sintered body was 98.5%, and the linear shrinkage rate was 11.5% (see FIG. 4a).

  Alumina powder and distilled water were weighed and mixed at the same mixing ratio as in Example 1, and wet-jet mill treatment was performed under conditions of 200 MPa · 5 times to obtain a slurry. Thereafter, casting and sintering were performed in the same manner as in Example 1. The slurry viscosity after the treatment was 6.3 mPa · s, and no change in viscosity with time was observed (see FIG. 1). The average particle size after the wet jet mill treatment was 558 nm, and the surface state thereof was almost the same as that of the raw material powder as in Example 1 (see FIG. 2). The relative density of the molded body and the relative density of the sintered body were 67.6% and 98.6%, respectively, and the linear shrinkage rate was 11.7% (see FIG. 4b).

  A mixture obtained by weighing and mixing alumina powder and distilled water at the same mixing ratio as in Example 1 was subjected to a wet jet mill treatment under the conditions of 100 MPa · one time to obtain a slurry. Thereafter, casting and sintering were performed in the same manner as in Example 1. The slurry viscosity after the treatment was 6.8 mPa · s, and no change in viscosity with time was observed. The relative density of the molded body and the relative density of the sintered body were 65.7% and 99.1%, respectively, and the linear shrinkage rate was 12.5%.

  Alumina powder and distilled water were weighed and mixed so that the alumina concentration was 50 vol%, and wet jet mill treatment, casting and sintering were performed under the same conditions as in Example 1. The slurry viscosity after the treatment was constant at 38.4 mPa · s. The relative densities of the molded body and the sintered body were 72.8% and 99.5%, respectively, and the linear shrinkage rate was 9.9%.

  Using ethanol as the solvent, wet jet milling, casting, and sintering were performed in the same manner as in Example 1. The viscosity of the slurry was constant at 7.2 mPa · s. The relative density of the molded body and the relative density of the sintered body were 66.8% and 98.9%, respectively, and the linear shrinkage rate was 12.0%.

  TiAl intermetallic compound powder was used as a raw material powder, and after wet wet milling and casting under the same conditions as in Example 1, sintering was performed at 1400 ° C. in vacuum. The slurry viscosity was constant at 8.2 mPa · s, the relative density of the compact and the relative density of the sintered body were 68.1% and 99.3%, respectively, and the linear shrinkage rate was 11.6%. .

Comparative Example 1
A mixture of alumina powder and distilled water in the same ratio as in Example 1 was subjected to a wet jet mill treatment under conditions of 5 MPa · 1 time to produce a slurry. Thereafter, casting and sintering were performed under the same conditions as in Example 1. The viscosity of the slurry after the wet jet mill treatment was constant at 7.2 mPa · s. Since the jet mill treatment pressure was low and sufficient mixing, dispersion and crushing effects could not be obtained, the relative density of the molded product showed a low value of 61.2%. The relative density of the sintered body was a good value of 98.1%, but the linear shrinkage rate was a high value of 14.6% because the relative density of the molded body was low.

Comparative Example 2
Weighing and mixing were performed so that the concentration of the alumina powder was 5 vol%, and wet jet milling, casting and sintering were performed in the same manner as in Example 1. Since the slurry concentration was low, the viscosity was constant at a low value of 2.3 mPa · s, but the relative density of the molded body was as low as 63.1%. The relative density of the sintered body was 98.4%, and the linear shrinkage rate was 13.5%.

Comparative Example 3
When weighed and mixed so that the alumina powder concentration was 70 vol%, the mixture did not have fluidity and could not be subjected to wet jet milling.

Comparative Example 4
In the same manner as in Example 1, the slurry prepared so that the alumina powder concentration was 30 vol% was treated in a conventional ball mill for 24 hours to prepare a slurry. Thereafter, casting and sintering were performed under the same conditions as in Example 1. Due to excessive energy application due to ball milling, re-agglomeration of alumina powder occurs, and the slurry viscosity immediately after processing is a slightly high value of 29.7 mPa · s. After that, an increase in viscosity of about 120 mPa · s is shown in 1 hour. (See FIG. 5). The average particle size of the alumina particles after the ball mill treatment was 570 nm, and the particles were almost pulverized to primary particles. Moreover, the increase in the hydroxyl group of the surface considered to be the surface damaged by the excess energy by a ball mill was observed (refer the arrow in FIG. 2). Thus, since the slurry has high viscosity and high thixotropy, that is, re-aggregation property, the relative density of the molded body showed a low value of 57.4%. The relative density of the sintered body was a good value of 99.0%, but the linear shrinkage rate was as high as 16.8% because the relative density of the molded body was low (see FIG. 4c).

  As described above in detail, the present invention relates to a slurry suitable for casting, a method for producing the same, a high-density powder molded body produced using the slurry, and a high-density low-shrinkable powder sintered body. According to the present invention, a slurry having a low viscosity and a low thixotropy produced by a wet jet mill process, a high-density powder molded body produced by casting the slurry, and obtained by sintering the slurry. A high-density low-shrinkage powder sintered body can be provided. In the present invention, since the linear shrinkage rate of the sintered body during sintering can be reduced to 13% or less, it can greatly contribute to high reliability, high performance, and near net shape of various members. Further, in the present invention, since the relative density of the molded body can be increased, the sintering temperature and the sintering time can be reduced, and the environmental load reduction and cost reduction of the powder sintering process are expected. Is done. Furthermore, the slurry having low viscosity and low thixotropy of the present invention is expected to be applied to processes other than casting, for example, inkjet.

The viscosity of the alumina slurry after a wet jet mill process is shown. The solid line is the viscosity of the slurry of Example 1, and the dotted line is the viscosity of the slurry of Example 2. The infrared spectroscopy analysis result of an alumina powder is shown. a, b, c, and d are the results of the raw material powder, Comparative Example 4, Example 1 and Example 2, respectively. The fracture surface of the molded object of Example 1 is shown. a, b, and c correspond to the upper part, the center part, and the lower part of the molded body, respectively. The appearance of the sample after sintering is shown. The dotted line indicates the sample size before sintering. a, b, and c are the samples of Examples 1 and 2 and Comparative Example 4, respectively. The viscosity of the alumina slurry after a ball mill process (comparative example 4) is shown.

Claims (14)

  A slurry having a low viscosity and a low thixotropic property, having a viscosity of 40 mPa · s or less and a change in viscosity per unit time of 10 mPa · s / h or less.   The slurry according to claim 1, wherein the concentration of the raw material powder in the slurry is in the range of 10 to 60 vol%.   The slurry according to claim 1, wherein the powder in the slurry retains the original crystallinity and surface structure without breaking the surface state before dispersion.   It is a powder crushed into primary particles, (1) the original crystallinity and surface structure are maintained without breaking the surface state, and (2) the slurry in which the powder is dispersed in a solvent. A powder having a viscosity of 40 mPa · s or less and a change in viscosity per unit time of 10 mPa · s / h or less.   4. A high density molded body according to any one of claims 1 to 3, wherein the relative density is 65 to 75%.   6. A sintered compact of a compact according to claim 5, wherein the linear shrinkage rate is 13% or less and the relative density is 98% or more.   A method for producing a slurry having a viscosity of 40 mPa · s or less and a unit time variation of viscosity of 10 mPa · s / h or less, comprising a step of mixing and crushing by a wet jet mill treatment. Manufacturing method.   The wet jet mill process is a process in which the raw material powder and the solvent are made into a slurry, and the slurry is pumped at a high pressure to a nozzle arranged in a sealed state in a pressure vessel, and the opposing flows of the slurry collide and merge with each other. The method for producing a slurry according to claim 7, which is a wet jet mill treatment in which the raw material powder in the slurry is mixed, dispersed, and pulverized.   The manufacturing method of the slurry of Claim 7 which has raw material powder in the range of 10-60 vol% with respect to the total amount of raw material powder and a solvent.   The method for producing a slurry according to claim 7, wherein the wet jet mill treatment is performed under a treatment pressure of 10 MPa or more.   A method for producing a high-density molded body, comprising producing a high-density molded body by casting the slurry according to any one of claims 1 to 3 into a mold.   The method for producing a high-density molded body according to claim 11, wherein the relative density of the molded body is 65 to 75%.   A slurry according to any one of claims 1 to 3 is cast into a mold and solidified to produce a high-density molded body, and the molded body is sintered to produce a sintered body. A method for producing a high-density, low-shrinkage sintered body.   The method for producing a high-density, low-shrinkage sintered body according to claim 13, wherein the linear shrinkage ratio is 13% or less and the relative density is 98% or more.