JP3942245B2 - Method for producing silicon nitride powder granules - Google Patents

Description

【００２６】
【表２】

【００２７】
実施例２
焼結助剤としてイットリア粉末、アルミナ粉末及びマグネシア粉末を各々５重量部、２重量部及び３重量部を添加したこと以外は、実施例１と同様の方法でスラリーの調製及び噴霧造粒乾燥を行った。表３にスラリー条件及びスプレードライヤー条件を示す。なお、実験９と参照実験５については焼結助剤をイットリア粉末５重量部、ＭｇＡｌ_２Ｏ_４粉末４重量部に変更して行った。
【００２８】
得られた顆粒について、焼成温度を１６８０℃にしたこと以外は、実施例１と同様にしてΔＳ、焼結体特性を評価し、表４の結果を得た。表４の結果より、マグネシア系酸化物を含有する焼結助剤を用いると、さらに高強度で高信頼性の焼結体が得られた。
【００２９】
【表３】

【００３０】
【表４】

【００３１】
参考例１
９０μｍのフルイに通した実験１及び参照実験１で得た窒化珪素顆粒について、各々ＣＩＰ圧１０ＭＰａ、３０ＭＰａ、５０ＭＰａ、１５０ＭＰａ、２７０ＭＰａ及び３００ＭＰａでＣＩＰ成形し、実施例１と同様に全細孔比表面積値を測定した。それらの結果を表５に示す。表５より、全細孔比表面積値は、成形圧が１０〜５０ＭＰａの範囲では成形圧の増加と共にかなり増加したが、成形圧が１５０〜３００ＭＰａの範囲では成形圧を上げてもほとんど増加していない。これらの結果から、本発明のように、異なる圧力で成形されたＣＩＰ成形体の全細孔比表面積値に基づいて窒化珪素粉末顆粒を特定するに際しては、全細孔比表面積がもっとも変化しやすい１０〜５００ＭＰａの成形圧にあって、成形中期の成形圧として３０ＭＰａを、また成形終期の成形圧として２７０ＭＰａを代表させることは妥当であることが示された。
【００３２】
【表５】

【００３３】
【発明の効果】
本発明によれば、高強度でワイブル係数の高い、高信頼性の焼結体を得ることのできる窒化珪素粉末顆粒を容易に製造することができる。 [0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing silicon nitride powder granules for press molding, CIP molding and the like .
[0002]
[Prior art]
Engineering ceramics sintered body various mechanical parts, but are expected to automobile parts, etc., large variations in the strength as compared with the metal material, have a problem of poor reliability. Among them, sintered silicon nitride is excellent in heat resistance, bending strength, and toughness, and is expected to be put to practical use .
[0003]
The cause of the low reliability of the sintered ceramics is the various defects present in the sintered body. Taking silicon nitride as an example , before the development of high-purity and fine silicon nitride powder, impurities and coarse particles were developed. Silicon nitride particles were mainly the source of destruction. When high-purity and fine silicon nitride powder is used, aggregated particles and pores are mainly the source of destruction, and when the aggregated particles and pores become large, the sintered body not only has low strength but also has high strength. Variations increase. Since the formation of such agglomerated particles and pores is strongly influenced by the characteristics of the granules adjusted for molding, studies have been made on reducing defects by controlling the fracture strength of the granules and controlling the aggregation state.
[0004]
For example, a method for reducing the fracture strength of granules (J. Ceram. Soc., Japan 103 [10] 1037-1040 (1995)), a method for reducing variations in granule fracture strength (Japanese Patent Laid-Open No. 9-25171), or a slurry A method (J. Am. Ceram. Soc., 79 [4] 843-848 (1996)) that suppresses aggregation of granules by controlling conditions has been proposed.
[0005]
The evaluation of the obtained granule is generally performed by measuring the bulk specific gravity and angle of repose, or measuring the breaking strength of the green molded body as described above. It was not a method to evaluate . Evaluation if the molding pressure is high pressure Ri SEM observation main der of the molded body fracture, but can be evaluated destruction state of the granule, have yet before digitizing.
[0006]
[Problems to be solved by the invention]
As described above, in order to obtain a reliable engineering ceramic sintered body, it must prevent coarse defects become fracture source. However, with the proposed method, it is possible to evaluate a certain amount of defects derived from the granules and suppress the generation of defects based on the evaluation, but it is difficult to obtain a bending strength with high strength and little variation. Needed an improvement. That is, there was no medium pressure ~ overall molded body information of a high pressure, such as a problem in actual molding.
[ 0007 ]
The present invention has been made in view of the above, the result of examining the bending strength of the relationship of the characteristics after the sintering of the silicon nitride powder granules, Oite the Middle to late during molding, as measured with a mercury porosimeter When the granulated product is granulated so that the change in the total pore specific surface area of the molded product is small, the silicon nitride sintered body produced using the granulated product has few rough air holes and high bending strength. Further, it was found that the variation in bending strength is reduced , and the present invention has been achieved .
[0008]
[Means for solving problems]
The present invention includes a silicon nitride powder, an organic binder, a slurry comprising water, a two-fluid nozzle type using a spray dryer when performing spray granulation drying, the solid content of the slurries 50 wt% or more the outlet temperature of the spray dryer you, characterized in that the 50 ° C. or more, in the manufacturing method of the change rate ΔS 2.5% or less is silicon nitride powder granules of the total pore specific surface area defined below is there. In the present invention, it is preferable that the slurry further contains a magnesia-based oxide.
[Definition of change rate ΔS of total pore specific surface area value]
A CIP compact is molded at a pressure of 30 MPa using silicon nitride powder granules passed through a 90 μm sieve. The total pore specific surface area value (Sa) is measured with a mercury porosimeter using 1-5 μm powder obtained by pulverizing this. The total pore specific surface area value (Sb) of the CIP compact is measured in the same manner except that the pressure is 270 MPa. From these values, the rate of change ΔS of the total pore specific surface area value is calculated by the formula: ΔS (%) = (Sb−Sa) × 100 / Sb.
[ 0009 ]
DETAILED DESCRIPTION OF THE INVENTION
The silicon nitride powder granules produced by the present invention have a specific value when a CIP compact is molded at a specific pressure and the total pore specific surface area value is measured. That is, when a molded body having a CIP pressure of 30 MPa and a molded body having a CIP pressure of 270 MPa were molded and the total pore specific surface area values (Sa) and (Sb) were measured, ΔS (%) = (Sb -Sa) × 100 / Sb, in 2.5% change rate ΔS of the total pore specific surface area represented less, preferably 2.0% or less, more preferably be 1.5% or less . ΔS is larger than 2.5%, still disintegration of the granules is not sufficient, because there are still a number of closed pores and large pore size in the molded product, Re this also remains after sintering, a large pore size Becomes a source of fracture, and the bending strength decreases . Na us, [Delta] S from the relationship of the measurement error in the present invention may also be a negative value.
[0010]
The total pore specific surface area value is measured by a mercury porosimeter. Mercury porosimeters are devices that are generally commercially available and that press-fit mercury with a large surface tension into a molded body and determine the pore size distribution from the relationship between the pressure and the pore size. From this pore size distribution, the total surface area calculated assuming that the pore size is a cylinder is the total pore specific surface area, depending on the presence of closed pores within and between the granules, the total pore volume, the size of the pore diameter, This total pore specific surface area is determined.
[0011]
In the present invention, the evaluation of the silicon nitride powder granules was performed by measuring the total pore specific surface area values for the compacts formed by CIP molding at molding pressures of 30 MPa and 270 MPa, and comparing the values as follows. It is. That is, first, to the molding pressure was 30MPa, the total pore specific surface area of the shaped body is most easily varied between 10 to 500, in terms of examining the change of the total pore specific surface area of the granules, 10～60MPa Corresponds to the above-mentioned mid-stage molding , but the specific surface area of the total pore changes due to the cause not depending on the measurement error even within this pressure range (see Reference Example 1), and the identification becomes insufficient. Therefore, the pressure was set to 30 MPa near the center of 10 to 60 MPa. On the other hand, the molding pressure was set to 270 MPa. 100 to 500 MPa corresponds to the final stage of molding with a general high molding pressure, and the total pore specific surface area value does not change within this range ( In consideration of the possibility that the identification would still be insufficient, the pressure was set to 270 MPa near the center of 100 to 500 MPa.
[ 0012 ]
The reason why the total pore specific surface area of the molded body is most likely to change when the molding pressure is 10 to 500 MPa is as follows. As a result of evaluating various granules, in the range of molding pressure lower than 10 MPa, when the molding pressure is increased, the contact between the granules proceeds and the total pore volume is reduced, but the closed pores are reduced or the pore diameter is reduced. Although the total pore specific surface area greatly increases, the pore specific surface area value of the molded body in this region is merely the rearrangement of the granules, and there is little change in the pores themselves within the granules, Inappropriate for evaluation. That is, the pressure is too low. Further, when the molding pressure is higher than 60 MPa, it is a transition region to a high pressure, and even in a granule in which coarse defects remain, the disintegration within and between the granules proceeds considerably, so that the total pore specific surface area value (Sb) The difference between and becomes too small, making determination difficult.
[0013]
On the other hand, at a high molding pressure of 100 MPa or more, the closed pores have already almost disappeared, the pore diameter has been reduced to some extent, and the total pore volume is also reduced. The surface area does not increase. In other words, the increase in the total pore specific surface area occurs due to the disappearance of closed pores due to the collapse of the granule or the refinement of the pore diameter, so that the total pore specific surface area closer to the high-pressure molded body at the end of molding can be obtained in the middle stage of molding. With such a granule, a sintered body having truly small defects can be obtained in subsequent molding and sintering. Therefore, the high molding pressure for the evaluation of the granules, Ru required der at least 100 MPa. Becomes high pressure Furthermore, in the above ultra-high pressure 500 MPa, from the pores decrease of the molded article, since the transgranular fracture of the inorganic powder particles, selectively generate, are unsuitable as the evaluation of the granules.
[ 0014 ]
The reason why the molded body for evaluating the silicon nitride powder granules was made into a CIP molded body was that uniform pressure could be obtained, so that more accurate data could be obtained, and the molded body was broken in a mortar and sieved. The reason why the grain size of 1 to 5 mm was evaluated was that stable data was obtained .
[ 0015 ]
In the production method of the present invention, after preparing a slurry containing silicon nitride powder , an organic binder , and water and optionally containing a magnesia-based oxide, spray granulation drying is performed with a spray dryer. A ball mill or the like is used for the preparation of the slurry .
[ 0016 ]
The silicon nitride powder is not particularly limited, but the particle size distribution is preferably as narrow as possible, and the 10% volume fraction diameter is preferably 0.2 μm or more and the 90% volume fraction diameter is preferably 3 μm or less. The reason is that if the particle size distribution is wide, the resulting granules tend to be heterogeneous and ΔS tends to increase. The silicon nitride powder in the present invention, rather than simply refers only silicon nitride powder, alumina, sintering aids, or hardness, such as rare earth oxides, thermally conductive, SiC for improving the electrical properties, BN, TiN, etc. Including those containing composite additives. As the sintering aid, the one containing the MgO-based oxide aid can be fired at a low temperature and the sintered body structure becomes finer, so that the defect size reduction effect of the present invention becomes remarkable and higher. Strength is obtained.
[0017]
There is no restriction | limiting in particular as an organic binder, For example, a wax + stearic acid type | system | group (For example, the product made by Chukyo Yushi: Celna WF-610), a poval type (for example, made by Chukyo Yushi: Celna WF-804) etc. can be used. If the slurry does not contain an organic binder, ΔS exceeds 2.5% (see Reference Experiment 3 ).
[ 0018 ]
In the present invention, a two-fluid nozzle is used in order to obtain a soft granule having a relatively small granule size by using a spray dryer because the shape of the granule is spherical, it is easy to obtain a uniform particle size, and continuous production is possible. expression of the spray dryer by chromatography (eg if Yamato scientific Co., Ltd. Pal piston mini spray -GA-31 type) to spray granulation drying the slurry using. The slurry compatible with the spray dryer chromatography is at least 50% by weight solids concentration of the slurry is preferred, the amount of the organic binder is relatively large to the extent shown in the Examples 1, or those reasonably hard prone are preferred. If the granules deviate from this condition, the closed pores are less than the low molding pressure, but because of the softness, the granules collapse too quickly and the pressure transmission into the molded body becomes insufficient. Therefore, the remaining granules between pores to a high pressure, [Delta] S is thus E This 2.5%. For example, prior art granules with low granule breaking strength fall into this category. It should be noted that the mixing time of the organic binder is preferably long, and at least 10 hours or more is necessary. If it is shorter than that, a high-strength sintered body cannot be obtained after all.
[ 0019 ]
For even conditions of the spray dryer, it is necessary to soften it difficult conditions, the inlet temperature is preferably at least 0.99 ° C., the outlet temperature is required at least 50 ° C. or higher. It is also important operational factor Ass Pireta attraction, fines Ri remaining when the suction force of the aspirator is less than before and after 85%, delta S exceeds 2.5%.
[ 0020 ]
As in the present invention, a slurry containing a silicon nitride powder, an organic binder, and water and having a solid content concentration of 50% by weight or more is selected using a two-fluid nozzle spray dryer within an outlet temperature range of 50 ° C. or more. and, to produce the silicon nitride powder granules delta S is 2.5% or less are not in the prior art. Incidentally, in order to produce a sintered body with silicon nitride powder granules produced in the present invention, mold, pressureless sintering through forming such CIP, by sintering in a conventional manner, such as gas pressure sintering That's fine.
[ 0021 ]
【Example】
Example 1
Burned into 91 parts by weight of silicon nitride powder (specific surface area 11 m ² / g, oxygen content 1.2 wt%, average particle diameter 0.6 μm, volume fraction 10% diameter 0.25 μm, volume fraction 90% diameter 1.2 μm) As a binder, 5 parts by weight of yttria powder and 4 parts by weight of alumina powder were added, and a slurry having a solid content concentration shown in Table 1 was prepared using distilled water. Furthermore, after adding 2 wt% of a polycarboxylic acid-based peptizer (manufactured by Chukyo Yushi: Celna D-735) to the raw material powder and mixing for 6 hours with a ball mill, wax + stearic acid-based binder A (manufactured by Chukyo Yushi) : Selna WF-610) and Povar binder B (manufactured by Chukyo Yushi Co., Ltd .: Selna WF-804) are added to the raw material powder in the amount shown in Table 1 and remixed for 14 hours in a ball mill Did. The obtained slurry is spray -granulated and dried under the conditions shown in Table 1 using a two-fluid nozzle spray dryer (Palpis Mini Spray-GA-31 manufactured by Yamato Kagaku Co., Ltd.), and granules of silicon nitride powder are obtained. Got.
[ 0022 ]
The obtained granule was passed through a 90 μm sieve, and a part thereof was subjected to CIP molding at 30 MPa and 270 MPa. Each obtained compact was roughly crushed in a mortar to give a size of 1 to 5 mm . The total pore specific surface area values (Sa) and (Sb) of the coarsely crushed product were measured with a mercury porosimeter (trade name Pore Sizer 9310) manufactured by Shimadzu Corporation, and ΔS was obtained using Equation 1. The obtained ΔS is shown in Table 2.
[ 0023 ]
The granules passed through the 90 μm sieve were subjected to 10 MPa press molding with a 54 × 9 mm size mold, and then 270 MPa CIP molding. The compact was subjected to atmospheric pressure sintering in a nitrogen atmosphere at a maximum temperature of 1750 ° C. and a holding time of 8 hours, and the obtained sintered body was subjected to a four-point bending strength test according to JIS-R1601 at n = 10. . Table 2 shows the obtained bending strength and Weibull coefficient.
[ 0024 ]
From the results shown in Tables 1 and 2, a slurry containing silicon nitride powder, an organic binder and water and having a solid content concentration of 50% by weight or more is used in a range where the outlet temperature is 50 ° C. or more using a two-fluid nozzle type spray dryer. The silicon nitride powder granules having a ΔS of 2.5% or less can be produced by selecting and spraying and drying in the above, and the sintered body using the same has a four-point bending strength of 1200 MPa or more, The Weibull coefficient was 20 or more .
[0025]
[Table 1]

[0026]
[Table 2]

[ 0027 ]
Example 2
The slurry was prepared and spray granulated and dried in the same manner as in Example 1 except that 5 parts by weight, 2 parts by weight and 3 parts by weight of yttria powder, alumina powder and magnesia powder were added as sintering aids, respectively. went. Table 3 shows slurry conditions and spray dryer conditions. In Experiment 9 and Reference Experiment 5 , the sintering aid was changed to 5 parts by weight of yttria powder and ₄ parts by weight of MgAl ₂ O ₄ powder.
[ 0028 ]
About the obtained granule, (DELTA) S and a sintered compact characteristic were evaluated like Example 1 except having made the calcination temperature into 1680 degreeC, and the result of Table 4 was obtained. From the results shown in Table 4, when a sintering aid containing a magnesia-based oxide was used, a sintered body with higher strength and higher reliability was obtained.
[ 0029 ]
[Table 3]

[ 0030 ]
[Table 4]

[ 0031 ]
Reference example 1
The silicon nitride granules obtained in Experiment 1 and Reference Experiment 1 that were passed through a 90 μm sieve were CIP molded at CIP pressures of 10 MPa, 30 MPa, 50 MPa, 150 MPa, 270 MPa, and 300 MPa, respectively. The value was measured. The results are shown in Table 5. From Table 5, the total pore specific surface area, although molding pressure is in the range of 10~50MPa increased becomes whether to increase co the molding pressure in the range of the molding pressure is 1 50～300MPa raising the molding pressure Mohoton etc. do not increase. From these results, when specifying the silicon nitride powder granules based on the total pore specific surface area values of the CIP compacts molded at different pressures as in the present invention, the total pore specific surface area is most likely to change. In the molding pressure of 10 to 500 MPa, it was shown that it is appropriate to represent 30 MPa as the molding pressure at the middle of molding and 270 MPa as the molding pressure at the end of molding.
[ 0032 ]
[Table 5]

[ 0033 ]
【The invention's effect】
By the present invention lever, high Weibull modulus high strength, the silicon nitride powder granules can be obtained a highly reliable sintered product can be produced easily.

Claims (2)

And a silicon nitride powder, an organic binder, a slurry comprising water, a two-fluid nozzle type using a spray dryer when performing spray granulation drying, the solid content of the slurries 50 wt% or more, of the spray dryer the outlet temperature you characterized in that the 50 ° C. or higher, the manufacturing method of the silicon nitride powder granules is change rate ΔS of the total pore specific surface area of 2.5% or less, which is defined below.
[Definition of change rate ΔS of total pore specific surface area value]
A CIP compact is molded at a pressure of 30 MPa using silicon nitride powder granules passed through a 90 μm sieve. The total pore specific surface area value (Sa) is measured with a mercury porosimeter using 1-5 μm powder obtained by pulverizing this. The total pore specific surface area value (Sb) of the CIP compact is measured in the same manner except that the pressure is 270 MPa. From these values, the rate of change ΔS of the total pore specific surface area value is calculated by the formula: ΔS (%) = (Sb−Sa) × 100 / Sb. The method for producing a silicon nitride powder granule according to claim 1, wherein the slurry further contains a magnesia-based oxide.