TW202140371A - Silicon nitride powder, and method for producing silicon nitride sintered body - Google Patents

Abstract

One aspect of the invention provides a silicon nitride powder containing silicon nitride primary particles, wherein in a distribution curve of the volume-based particle diameter measured using a laser diffraction and scattering method, if the particle diameters when the cumulative value reaches 10% and 90% of the total from the small particle diameter side are deemed D10 and D90 respectively, then the difference between D90 and D10 is 5.5 [mu]m or less.

Description

Silicon nitride powder and manufacturing method of silicon nitride sintered body

This disclosure relates to a manufacturing method of silicon nitride powder and a silicon nitride sintered body.

Silicon nitride is a material with excellent strength, hardness, toughness, heat resistance, corrosion resistance, and thermal shock resistance, so it is used in various industrial parts such as die-casting equipment and melting furnaces, and automotive parts. In addition, because silicon nitride has excellent mechanical properties at high temperatures, it has been studied to use it in gas turbine parts that require high-temperature strength and high-temperature creep characteristics.

For silicon nitride sintered bodies, further improvements in thermal conductivity and mechanical properties are required. For example, Patent Document 1 discloses a silicon nitride sintered body characterized by a thermal conductivity of 100 to 300 W/(m･K) at room temperature and a three-point bending strength of 600 to 1500 MPa at room temperature. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP 2004-262756 A

[The problem to be solved by the invention]

An object of the present disclosure is to provide silicon nitride powder capable of producing a sintered body with excellent bending strength. Another object of the present disclosure is to provide a method for manufacturing a silicon nitride sintered body with excellent bending strength. [Means to solve the problem]

One aspect of the present disclosure is to provide a silicon nitride powder, which contains primary particles of silicon nitride, and the distribution curve of the volume-based particle size measured by the laser diffraction scattering method starts with a small particle size. When the particle diameters when the cumulative value reaches 10% and 90% of the total are set to D10 and D90, respectively, the difference between D90 and D10 is 5.5 μm or less.

Since the above-mentioned silicon nitride powder has the difference between D90 and D10 (D90-D10) being a predetermined value or less, it is possible to prepare a compact (uncalcined) having a narrower particle size distribution and a denser structure. The silicon nitride sintered body obtained by calcining the above-mentioned molded body has suppressed generation of voids and the like, and has excellent bending strength.

The D50 of the above-mentioned silicon nitride may be 1.5 μm or less. If the upper limit of D50 falls within the above range, the silicon nitride powder will have a moderate particle size distribution, so the packing density of the primary particles can be improved.

The D90 of the above-mentioned silicon nitride powder may be 6.0 μm or less. If the upper limit of D90 falls within the above range, the ratio of coarse particles can be sufficiently reduced, and the decrease in the density of the sintered body can be more sufficiently suppressed. In addition, the operability will be more excellent.

The BET specific surface area of the above-mentioned silicon nitride powder may not reach 9.0 m ² /g.

One aspect of the present disclosure is to provide a method for manufacturing a silicon nitride sintered body, which has the steps of forming and calcining the sintering raw material containing the above-mentioned silicon nitride powder.

Since the method for manufacturing the silicon nitride sintered body uses the sintering raw material containing the silicon nitride powder, the obtained silicon nitride sintered body can exhibit excellent bending strength. [Effects of the invention]

According to the present disclosure, it is possible to provide silicon nitride powder capable of producing a sintered body with excellent bending strength. According to the present disclosure, it is possible to provide a method for producing a silicon nitride sintered body with excellent bending strength.

Hereinafter, the embodiment of the present disclosure will be described. However, the following embodiments are examples for explaining the present disclosure, and do not mean that the present disclosure is limited by the following content.

Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. The content of each component in the composition, when there is a majority of substances equivalent to each component in the composition, unless otherwise specified, refers to the total amount of the plurality of substances present in the composition. The "steps" in this manual can refer to mutually independent steps or steps that are performed simultaneously.

One embodiment of silicon nitride powder contains primary particles of silicon nitride, and in the distribution curve of the volume-based particle size measured by the laser diffraction scattering method, the cumulative value starting from the small particle size reaches all When the particle diameters at 10% and 90% are D10 and D90, respectively, the difference between D90 and D10 is 5.5 μm or less.

The upper limit of the difference between D90 and D10 (D90-D10) is 5.5 μm or less, for example, 5.4 μm or less, 5.2 μm or less, 5.0 μm or less, 4.8 μm or less, or 4.6 μm or less. If the upper limit of the above difference falls within the above range, the molded body prepared by compression molding of the silicon nitride powder can have a denser structure, so that the generation of voids during sintering can be more suppressed. That is, the bending strength of the obtained silicon nitride sintered body can be more improved. The lower limit of the difference between D90 and D10 can be, for example, 3.0 μm or more, 3.2 μm or more, or 3.4 μm or more. If the lower limit of the above difference falls within the above range, since the silicon nitride powder will have an appropriate particle size distribution, the packing density of the primary particles can be more improved. The above difference can be adjusted within the above range, for example, it can be 3.0 to 5.5 μm, 3.2 to 5.4 μm, or 3.4 to 4.6 μm. The above-mentioned difference can be controlled by adjusting the pulverization conditions of the silicon nitride powder at the time of manufacturing, and the like.

The upper limit of D90 of the silicon nitride powder may be 6.0 μm or less, 5.8 μm or less, 5.6 μm or less, 5.4 μm or less, or 5.2 μm or less, for example. If the upper limit of D90 falls within the above range, the ratio of coarse particles can be sufficiently reduced, and the decrease in the density of the sintered body can be more sufficiently suppressed. The lower limit of D90 may be 3.5 μm or more, 3.7 μm or more, 3.9 μm or more, or 4.0 μm or more, for example. D90 can be adjusted within the above range, for example, it can be 3.5 to 6.0 μm, or 4.0 to 5.2 μm. The D90 of the silicon nitride powder can be controlled, for example, by adjusting the crushing conditions during the production of the silicon nitride powder.

The upper limit of D50 of the silicon nitride powder may be 1.5 μm or less, or 1.4 μm or less, for example. If the upper limit of D50 falls within the above range, the strength of the silicon nitride sintered body can be more improved. The lower limit of D50 of the silicon nitride powder may be 1.1 μm or more, or 1.2 μm or more, for example. The D50 of the silicon nitride powder can be adjusted within the above range, for example, it can be 1.1~1.5μm, or 1.2~1.4μm.

In this manual, D10, D50, and D90 respectively represent the volume-based particle size distribution curve measured by the laser diffraction scattering method. The cumulative value starting from the small particle size reaches 10%, 50%, and The particle size at 90%. The laser analysis scattering method can be measured according to the method described in JIS Z 8825:2013 "particle size analysis-laser diffraction scattering method". For the measurement, a laser diffraction scattering method particle size distribution measuring device (manufactured by Beckman Coulter, trade name: LS-13 320) or the like can be used. In addition, D50 is also called the median particle size, which refers to the average particle size of silicon nitride powder.

The silicon nitride powder BET specific surface area, for example, the upper limit may be less than 9.0m ² /g,8.8m ² / g or less, 8.6m ² / g or less, or 8.5m ² / g or less. The silicon nitride powder BET specific surface area, for example, the lower limit may be 5.0m ² / g or more, 5.1m ² / g or more, 5.2m ² / g or more, 5.3m ² / g or more, 5.4m ² / g or more, 5.5m ² /g or more, 6.0m ² /g or more, or 7.0m ² /g or more. The BET specific surface area of the silicon nitride powder can be adjusted within the above range, for example, it can be 5.0~9.0m ² /g, or 5.5~8.5m ² /g, or 7.0~8.5m ² /g. The BET specific surface area of the silicon nitride powder can be controlled, for example, by adjusting the pulverization conditions during the production of the silicon nitride powder.

The BET specific surface area in this manual follows the method described in JIS Z 8830:2013 "Powder (solid) specific surface area measurement method using gas adsorption", using nitrogen and the value measured by the BET one-point method.

The upper limit of the amount of surface oxygen of silicon nitride may be 2.0% by mass or less, 1.5% by mass or less, or 1.3% by mass or less, for example. If the upper limit of the amount of surface oxygen of silicon nitride falls within the above range, the grain boundary phases in the production of silicon nitride sintered bodies can be more sufficiently reduced. The lower limit of the surface oxygen content of silicon nitride can be, for example, 0.20 mass% or more, 0.30 mass% or more, 0.35 mass% or more, 0.40 mass% or more, 0.45 mass% or more, 0.60 mass% or more, 0.80 mass% or more, or 1.0% by mass or more. If the lower limit of the amount of surface oxygen of silicon nitride falls within the above range, the growth of crystal grains during calcination of silicon nitride can be promoted, and the bending strength of the silicon nitride sintered body can be improved. The surface oxygen content of silicon nitride can be adjusted within the above range, for example, it can be 0.20~2.0% by mass, 0.20~1.5% by mass, or 1.0~1.5% by mass. The amount of surface oxygen of silicon nitride can be controlled, for example, by adjusting the composition of the gas environment in the calcination step in the production of silicon nitride powder, as well as the calcination temperature and calcination time.

The "surface oxygen content" in this manual refers to the value obtained by the following procedure. The oxygen and nitrogen analyzer is used to analyze the oxygen and nitrogen content of silicon nitride powder. In a helium atmosphere, the sample for measurement is heated from 20°C to 2000°C at a temperature increase rate of 8°C/sec. The infrared absorption method is used to detect the oxygen that desorbs as the temperature rises. As soon as the temperature rises, the oxygen bonded to the surface of the silicon nitride powder will escape. If it is heated further and the temperature reaches around 1400°C, silicon nitride will begin to decompose. The start of the decomposition of silicon nitride can be confirmed by starting to detect nitrogen. If silicon nitride starts to decompose, oxygen in the silicon nitride powder will escape. Therefore, the oxygen system desorbed at this stage corresponds to the amount of internal oxygen, so the amount of oxygen detected and quantified before the detection of nitrogen is taken as the amount of surface oxygen.

The above-mentioned silicon nitride powder can be produced, for example, by the following method. An embodiment of the method for manufacturing silicon nitride powder has the following steps: calcining the silicon powder in a gas atmosphere containing nitrogen and at least one selected from the group consisting of hydrogen and ammonia to obtain a calcined product The step (hereinafter, also referred to as the calcination step); the step of dry pulverizing the above-mentioned calcined product to obtain a pulverized product (hereinafter, also referred to as the pulverization step); the step of subjecting the above-mentioned pulverized product to dry classification (hereinafter, also referred to as the pulverization step) Grading steps).

As for silicon powder, silicon powder with a low oxygen concentration can be used. The upper limit of the oxygen concentration of the silicon powder may be 0.40% by mass or less, 0.30% by mass or less, or 0.20% by mass or less, for example. If the oxygen concentration of the silicon powder falls within the above range, the amount of oxygen in the obtained silicon nitride powder can be further reduced. The lower limit of the oxygen concentration of the silicon powder can be, for example, 0.10% by mass or more, or 0.15% by mass or more. The oxygen concentration of the silicon powder can be adjusted within the above range, for example, it can be 0.10~0.40% by mass.

The oxygen concentration of silicon powder in this manual refers to the value measured by infrared absorption method.

Commercially available silicon powder can be used, or another preparation can be used. When the oxygen concentration of the silicon powder is high, for example, a pretreatment solution containing hydrofluoric acid can be used to reduce the amount of oxygen bonded to the silicon powder. For example, the above-mentioned manufacturing method of silicon nitride powder may further have a pretreatment step of using a pretreatment liquid containing hydrofluoric acid to pretreat the silicon powder and obtain a silicon powder with an oxygen concentration of 0.40% by mass or less.

The pretreatment liquid contains hydrofluoric acid, but may be a mixed acid with acids such as hydrochloric acid, or may be composed of hydrofluoric acid alone. The temperature of the pretreatment liquid in the pretreatment step can be, for example, 40 to 80°C. In addition, the time for bringing the pretreatment liquid into contact with the silicon powder can be, for example, 1 to 10 hours.

In the calcining step, the silicon powder is calcined in a mixed gas environment containing nitrogen and at least one selected from the group consisting of hydrogen and ammonia to obtain a calcined product containing silicon nitride. Based on the entire mixed gas environment, the total content of hydrogen and ammonia in the mixed gas environment may be, for example, 10-40% by volume. The calcination temperature can be, for example, 1100 to 1450°C, or 1200 to 1400°C. The calcination time can be 30 to 100 hours, for example.

In the pulverization step, the above-mentioned calcined product obtained in the calcination step is pulverized by a dry method to obtain a pulverized product. In the method for producing silicon nitride powder of this embodiment, the pulverization step includes two steps of ball mill pulverization and vibration mill pulverization. The calcined product is pulverized and the particle size is adjusted, thereby facilitating the control of the subsequent classification step. When the calcined product including the silicon nitride obtained in the calcining step is in the shape of a block or an ingot, the effect of the pulverization step is more significant.

Each pulverization can be divided into multiple stages such as coarse pulverization and fine pulverization. The pulverization step is performed as a dry pulverization step.

The filling rate of the ball to the container in the ball milling step can be adjusted according to the target particle size distribution of the silicon nitride powder. The lower limit of the filling rate of the balls to the container is based on the volume of the container, and may be, for example, 40% by volume or more, 45% by volume or more, 50% by volume or more, or 60% by volume or more. Regarding the upper limit of the filling rate of the balls to the container, based on the volume of the container, for example, it may be 70% by volume or less, or 65% by volume or less.

The lower limit of the time (pulverization time) of the pulverization process in the ball mill pulverization step may be, for example, 5 hours or more, 6 hours or more, 7 hours or more, or 8 hours or more. If the lower limit of the pulverization time falls within the above range, the pulverized product can be made sufficiently fine, and the pulverization efficiency when further pulverized by a dry method can be improved. The upper limit of the time of the pulverization treatment in the ball mill pulverization step may be, for example, 15 hours or less, 14 hours or less, 13 hours or less, or 12 hours or less. If the upper limit of the pulverization time falls within the above range, the calcined product can be sufficiently pulverized and excessive pulverization can be prevented. The pulverization time can be adjusted within the above range, for example, it can be 5 to 15 hours, or 8 to 12 hours.

The pulverization step is followed by the ball mill pulverization step to further pulverize the above-mentioned calcined product through a vibration milling pulverization step. The filling rate of the ball to the container in the vibration grinding and crushing step can be adjusted according to the target particle size distribution of the silicon nitride powder. The lower limit of the filling rate of the balls to the container is based on the volume of the container, and may be, for example, 50% by volume or more, 55% by volume or more, or 60% by volume or more. The upper limit of the filling rate of the balls to the container is based on the volume of the container, for example, it may be 80% by volume or less, or 75% by volume or less.

The lower limit of the time (grinding time) of the grinding treatment in the vibration grinding and grinding step can be, for example, 8 hours or more, 9 hours or more, 10 hours or more, or 12 hours or more. If the lower limit of the pulverization time falls within the above range, the pulverized product can be made sufficiently fine, and the processing efficiency of the classification step can be improved. The upper limit of the time of the grinding treatment in the vibration grinding and grinding step can be, for example, 20 hours or less, 19 hours or less, 18 hours or less, or 17 hours or less. If the upper limit of the pulverization time falls within the above range, the calcined product can be sufficiently pulverized, and excessive pulverization can also be prevented. The pulverization time can be adjusted within the above range, for example, it can be 8-20 hours, or 12-17 hours.

In the classification step, the above-mentioned pulverized product prepared through the pulverization step is then classified by a dry method to prepare silicon nitride powder having a desired particle size distribution. For example, coarse powder can be removed to adjust the D90 of silicon nitride powder. Dry classification can be performed by, for example, airflow classification. The air flow classifier can perform classification using, for example, a swirling air flow or the like. The primary gas pressure (inlet pressure) may be 0.2 to 0.8 MPa, or 0.3 to 0.7 MPa, for example.

The silicon nitride powder obtained by the above-mentioned manufacturing method has excellent sinterability. That is, the above-mentioned silicon nitride powder can be ideally used as a sintered body raw material.

One embodiment of the method of manufacturing a silicon nitride sintered body includes a step of forming and firing the sintering raw material containing the above-mentioned silicon nitride powder.

The sintering raw material may contain an oxide-based sintering aid in addition to the silicon nitride powder. Examples of oxide-based sintering aids include Y ₂ O ₃ , MgO, Al ₂ O ₃ and the like. The content of the oxide-based sintering aid in the sintering raw material can be, for example, 3-10% by mass.

In the above step, the sintering raw material is pressurized at a molding pressure of, for example, 3.0 to 30.0 MPa to obtain a molded body. The molded body can be produced by uniaxial pressing, or can be produced by CIP. In addition, it may be calcined while forming by hot pressing. The calcination of the formed body can be carried out in a passive gas environment such as nitrogen or argon. The pressure during calcination can be 0.7~1.0MPa. The calcination temperature can be 1860~2100℃, or 1880~2000℃. The calcination time of the calcination temperature can be 6-20 hours, or 8-16 hours. The rate of temperature increase up to the calcination temperature can be, for example, 1.0 to 10.0°C/hour.

The obtained silicon nitride sintered body exhibits excellent flexural strength because the grain boundary phase is reduced and the structure is dense.

The bending strength of the silicon nitride sintered body can be set to, for example, 550 MPa or more, 600 MPa or more, or 650 MPa or more at room temperature. The flexural strength of the silicon nitride sintered body in this specification refers to the 3-point flexural strength measured at room temperature after making a test piece for strength measurement in accordance with JIS R 1601:2008.

Above, several embodiments have been described, but the present disclosure is not limited to the above-mentioned embodiments at all. In addition, the descriptions of the above-mentioned embodiments can be mutually adopted. [Example]

Hereinafter, the present disclosure will be described in more detail with reference to Examples and Comparative Examples. However, the present disclosure is not limited by the following embodiments.

(Example 1) <Preparation of silicon nitride powder> A commercially available silicon powder (specific surface area: 3.0m ² /g) was immersed in a mixed acid containing hydrogen chloride and hydrogen fluoride adjusted to a temperature of 60°C and maintained at 60°C, Treat it 2 hours before applying. The above-mentioned mixed acid is obtained by mixing commercially available hydrochloric acid (concentration: 35% by mass) and hydrofluoric acid (concentration: 55% by mass) in a mass ratio of 10:1. After that, the silicon powder is taken out from the mixed acid, washed with water, and dried in a nitrogen atmosphere. The oxygen concentration of the silicon powder after drying was 0.4% by mass. The oxygen concentration is measured by infrared absorption method.

Use the dried silicon powder to make a molded body (bulk density: 1.4g/cm ³ ). The obtained molded body was statically placed in an electric furnace and calcined at 1400° C. for 60 hours to produce a calcined body containing silicon nitride. Regarding the gas environment during calcination, a mixed gas of nitrogen and hydrogen is supplied (a mixed gas _{produced by mixing N 2} and H ₂ in a standard state in a volume ratio of 80:20). After coarsely pulverizing the obtained calcined body, it is dry pulverized with a ball mill. For ball milling, the filling rate of the ball to the container is set to 60% by volume, and the crushing time is set to 8 hours. Dry pulverization by vibration milling, the filling rate of the balls to the container is set to 70% by volume, and the pulverization time is set to 15 hours.

The silicon nitride powder obtained by dry pulverization was classified under the condition of a primary gas pressure of 0.4 MPa to obtain silicon nitride powder.

<Evaluation of silicon nitride powder: measurement of D10, D50, and D90> Measure D10, D50, and D90 of silicon nitride powder by laser analysis and scattering method according to the method described in JIS Z 8825:2013 "Particle size analysis-Laser diffraction scattering method". The measurement system used a laser diffraction scattering method particle size distribution measuring device (manufactured by Beckman Coulter, trade name: LS-13 320).

<Evaluation of silicon nitride powder: measurement of BET specific surface area> The BET specific surface area is measured by the BET one-point method in accordance with JIS Z 8803:2013 and using nitrogen. The results are shown in Table 1.

＜Evaluation of silicon nitride powder: measurement of surface oxygen content＞ The surface oxygen content was measured using an oxygen/nitrogen simultaneous analysis device (manufactured by Horiba, Ltd., device name: EMGA-920). Specifically, by heating the silicon nitride powder from 20°C to 2000°C at a temperature increase rate of 8°C/sec in a helium atmosphere, the amount of oxygen before nitrogen is detected is quantified for measurement.

[Production of silicon nitride sintered body] Weigh 90 parts by mass of the prepared silicon nitride powder, _{5 parts by mass of Y 2} O _{3 powder with an average particle size of 1.5 μm, and Yb 2} O _{3 with} an average particle size of 1.2 μm 5 parts by mass of the powder was put in a container, methanol was added, and the mixture was wet-mixed for 4 hours. After that, the mixed powder (calcined raw material) obtained by drying was molded into a mold at a pressure of 10 MPa, and then cold-isolated (CIP) molded at a pressure of 25 MPa. The obtained molded body and the filler powder composed of a mixed powder of silicon nitride powder and BN powder were set in a carbon crucible and calcined at a temperature of 1900°C for 12 hours in a nitrogen pressurized atmosphere of 1 MPa to produce nitrogen. Silica sintered body.

＜Measurement and evaluation of bending strength of silicon nitride sintered body＞ According to JIS R1601:2008, a test piece for strength measurement was made from a silicon nitride sintered body, and the three-point bending strength at room temperature was measured. Evaluate from the measurement results based on the benchmarks. The results are shown in Table 1. In addition, the measurement results of the bending strength in Table 1 are expressed as relative values obtained using the silicon nitride sintered body prepared in Comparative Example 1 described later as a reference. A: The bending strength (relative value) is 1.10 or more. B: The bending strength (relative value) is 1.05 or more and less than 1.10. C: The bending strength (relative value) is less than 1.05.

(Example 2) Except for changing the vibration milling conditions of dry milling to the conditions described in Table 1, the same procedure as in Example 1 was carried out to prepare silicon nitride powder. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 3) Except that the ball mill grinding conditions of dry grinding were changed to the conditions described in Table 1, the same procedure as in Example 1 was carried out to prepare silicon nitride powder. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative example 1) Except for changing the conditions of the dry classification to the conditions described in Table 1, the same procedure as in Example 1 was carried out to prepare silicon nitride powder. The obtained silicon nitride powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Table 1] Example 1 Example 2 Example 3 Comparative example 1 Conditions for dry pulverization (ball mill pulverization) Ball filling rate [vol%] 60 60 60 60 Crushing time [hour] 8 8 5 8 Dry grinding conditions (vibration grinding and grinding) Ball filling rate [vol%] 70 70 70 70 Crushing time [hour] 15 10 15 15 Dry classification conditions Inlet pressure [MPa] 0.4 0.4 0.4 0.1 Silicon Nitride Powder D90[μm] 5.0 5.4 5.5 6.6 D10[μm] 0.47 0.48 0.48 0.53 D50[μm] 1.34 1.41 1.42 1.52 D90-D10[μm] 4.5 4.9 5.0 6.1 BET specific surface area [m ² /g] 7.7 7.5 7.5 6.9 Surface oxygen content [mass%] 1.1 1.0 1.0 0.9 Silicon nitride sintered body Bending strength [relative value] 1.11 1.07 1.06 1.00 Evaluation A B B C [Industrial Utilization]

According to the present disclosure, it is possible to provide silicon nitride powder capable of producing a sintered body with excellent bending strength. According to the present disclosure, it is possible to provide a method for producing a silicon nitride sintered body with excellent bending strength.

Claims (5)

A kind of silicon nitride powder, Containing primary particles of silicon nitride, In the volume-based particle size distribution curve measured by the laser diffraction scattering method, when the cumulative value from the small particle size reaches 10% and 90% of all the particle sizes as D10 and D90, D90 and D90 The difference of D10 is 5.5 μm or less. Such as the silicon nitride powder of claim 1, wherein D50 is 1.5 μm or less. Such as the silicon nitride powder of claim 1 or 2, wherein D90 is less than 6.0 μm. Such as the silicon nitride powder of claim 1 or 2, wherein the BET specific surface area is less than 9.0 m ² /g. A method for manufacturing a silicon nitride sintered body has the steps of forming and calcining a sintering raw material containing the silicon nitride powder according to any one of claims 1 to 4.