JPS60260410A - Manufacture of beta-sialon powder - Google Patents

Abstract

PURPOSE:To manufacture easily high purity beta-sialon powder by adding a dispersant and a pH adjusting liq. to silica powder, alumina powder and powder of a substance contg. carbon, mixing them to prepare a slurry, drying the slurry, and calcining it in a flow of gaseous nitrogen. CONSTITUTION:The dispersant and a pH adjusting liq. are added to high purity silica powder of <=about 3mum average particle size, high purity alumina powder of <=about 3mum average particle size and powder of a substance contg. carbon such as carbon black of <=about 1mum average particle size, and they are mixed to prepare a slurry. Ammonium oxalate or the like is used as the dispersant by about 1.0-6.0wt% of the total amount of the silica and alumina powders. An aqueous ammonia soln. is used as the pH adjusting liq. to adjust the slurry to about 8.0-9.5pH. The prepd. slurry is dried and calcined at about 1,350-1,500 deg.C in a flow of gaseous nitrogen for about 0.2-20hr to form beta-sialon.

Description

[Detailed description of the invention] The present invention relates to a novel method for producing β-sialon powder.

βsialon has the general formula S + a z A Z z O
It is represented by □Ng-= (O<Z≦4.2), and is a solid solution of β-type silicon nitride (β-8i3N, ) substituted with At and O. Since β-sialon has high oxidation resistance at high temperatures and excellent corrosion resistance against molten metals, etc., it is useful as a raw material for various refractories. Furthermore, because of its high strength and hardness at high temperatures, β-SiAlON sintered bodies are attracting attention for use in various engine parts and cutting tools.

Conventional methods for producing β-SiAlON powder include: 1) Dry mixing carbon powder with clay powder mainly composed of natural silica-alumina minerals, such as olinite, and then firing it in a nitrogen stream; 2) Silica AA gold metal dry mixing 1- Then firing in a nitrogen stream; 3) Wet mixing silica-alumina coprecipitate obtained by hydrolyzing silicon alkoxide and aluminum alkoxide with an organic solvent and carbon powder. There is a method in which the material is then dried and fired in a nitrogen stream. The common disadvantage of 1) and 2) of these conventional methods is that the raw materials are dry mixed, so even if mixing is performed for a long time, the dispersion state is incomplete and the reaction is not uniform during the subsequent firing process. If this process is not carried out, unreacted oxides, aluminum nitride, and silicon nitride remain or are generated, making it impossible to obtain highly pure β-sialon. A further drawback of 1) is that since natural clay powder is used as a starting material, alkali metals are inevitably mixed in, making the purity of the β-sialon powder even worse. In addition, method 3) uses forced wet stirring and can obtain β-sialon with higher purity than the first two methods, but has the drawback that the raw materials used are extremely expensive and it is difficult to industrialize.

The present inventors conducted intensive research to solve the drawbacks of the conventional method described above, and found that high-purity β-SiAlON powder can be easily produced by adding and mixing a dispersant and a Pl-1 adjustment liquid to the raw materials and reducing agent used. The present invention was completed based on the knowledge that it could be manufactured in a number of ways.

That is, in the present invention, a slurry obtained by adding and mixing a dispersant and a pH adjusting liquid to silica powder, alumina powder, and carbon-containing substance powder is dried and then smelted in a nitrogen stream to produce β-sialon powder. The gist of this is to

The feature of the present invention is that a slurry obtained by adding carbon-containing substance powder as a reducing agent to the starting materials of silica powder and alumina powder,
By mixing and stirring the dispersant and pH adjustment liquid, the secondary particles of each starting material and reducing agent can be dispersed almost to the state of primary particles, resulting in an extremely uniform M1 agglomerate with extremely high purity. The β-sialon powder is crushed.

The present invention will be explained in detail below.

The dispersing agent used in the present invention to obtain the slurry is water.

The dispersant used in the present invention is a7-■-nium oxalate, a nonionic surfactant. The former acts mainly on silica powder and alumina powder, and the latter acts on carbon-containing substance powder, respectively, to lower the tension and promote dispersion. I don't know much about the mechanism. As a dispersant for inorganic powders, oxalic acid, potassium oxalate, puttrium hexanotalinoate, etc. are commonly used, but when these alkali metal compounds are used, these metals are Since it remains in the powder, it is preferable to use oxalic acid in the present invention.1
Nonionic surfactants include higher alcohol ethylene oxide adducts that do not decompose with alkali,
Examples include polyethylene glycol-based adducts such as alkyl funol ethylene oxide adducts and polypropylene glycol ethylene oxide adducts.

For ammonium oxalate, the amount of dispersant used is 11 (preferably 11) for the total of silica powder and alumina powder.
or 0.3% by weight or more, and for nonionic surfactants, 0) weight N% or more in the carbon-containing material powder.
It's Hi. A more preferable range is 1.0 to 6.0% by weight for the former and 0.2 to 2.0% by weight fTtφ for the latter. If the amount used is less than 0.3% by weight or less than 0.1 weight 5'r4, the dispersion effect will be small.

On the other hand, even if more than 6.0% by weight of ammonium phosphate is used, no further dispersion effect is observed, so it is uneconomical to add it in excess.
．． If it is used in excess of 0% by weight, the amount of entrained air will be excessive, and the distance between raw material particles will become large, and some raw materials will not be able to react, and the raw materials will remain in the unreacted 11 fired product, resulting in bf-4.
+-<tc.

Ammonia water is used as the pl-1 adjustment liquid.fl-1
Add so that the pH of the slurry is in the range of 8.0 to 9.5. Although ammonia water itself has a dispersion effect, the dispersion of the powder can be stably maintained by setting the aqueous ammonia to the above-mentioned pl-1 range. Therefore, 1) When outside the II region, the powder of raw materials, reducing agents, etc. collects in St, +5. In addition, especially in the case of pflll, Q and above, it becomes concentrated and the dispersion deteriorates significantly. I) In accordance with 11, alkali metal compounds cannot be used as in the case of the dispersant described above.

As the material 1 used in the present invention, Noriyoku Powder Q1 white carbonate, commercially available /'lika such as licagel is used, and the average particle size rJ 311 m, Lzo 1 is preferred. If it is larger than that, it will remain as an unreacted substance in the obtained β→Noia 11 powder, so IT: 4 L
<No.

Like silica powder, it is desirable that alumina powder be of high purity. In particular, high-purity alumina synthesized by a gas phase method is most suitable.
Oxide Cl is mentioned.

The average particle diameter of the alumina powder is also preferably 3 μm or less; if it is larger than that, it remains unreacted in the fired product, which is not preferred.

Carbon-containing substances are added as reducing agents for the above two raw materials, and include amorphous carbon powders such as furnace black, acetylene blank, and lamp black, as well as organic compounds that decompose and generate free carbon when heated in a reducing atmosphere. Powders can be used, such as powders of phenolic resins, urea resins, and epoxy resins. The average particle size of the above carbon black is 1μIll
Below, it is preferable that the organic compound powder has an average particle size of 10 μm or less, but if the average particle size is larger than that, the reducing effect is insufficient and the raw material remains in the undecomposed it β sialon powder, which is not preferable. .

The composition of the two raw materials is as follows: βsialon is 5i6-2A t
z Oz N8- z structure T O < Z ≦4.2
(7) Since it is a continuous solid solution in the range °, it is carried out so that it falls within that range. That is, when the two raw materials are blended, Si
/At atomic ratio is 0.45 to 5.5 (theoretical amount is 0.429
~6. (+), 5in2, At20B No E Nil ratio display fd”0.9 <, 5i02/At203≦11
Blend so that Preferably 1.0≦5i02
There are 7Az203<, 10 te. The above molar ratio is 0.9
If it is less than that, impurities such as aluminum nitride will be produced in the fired product, which is not good. On the other hand, if it exceeds J1, silicon nitride will be generated quickly, which is also not preferable.

Theoretically, the amount of carbon-containing material to be blended should be such that the amount of carbon contained therein reduces the total amount of the two raw materials, but in reality, it is added a little more than the equivalent amount. However, even if the total amount is the same, S i02 /kl-
If the 20s (molar ratio) is different, the amount of carbon used will also be different. For example, in the case of 5lo2/A t 2'Os (molar ratio)-1, the amount of carbon is 21 to 2 with respect to the total ht.
When the weight is 5 and the molar ratio is 4 (31 to 34 weight), and when the weight and molar ratio is 10, the preferable amount is 35 to 38 weight. If much more than the amount is added, the reaction will proceed too much and 1'5R-
It is not preferable to use an excessive amount because it tends to produce a fired product containing many impurities such as Sialon and requires an oxidation treatment step for the remaining excess carbon, which causes economic disadvantage. Note that when using organic compound powder as the carbon-containing substance, the amount to be blended may be determined by considering the amount of carbon contained therein.

Next, the method for producing β-sialon powder of the present invention will be described.

The mixing order, addition, and mixing method of the raw materials may be any known method, and conventional equipment may be used. -! Since dispersants and pH adjustment liquids are used only in small quantities, various methods are used depending on the case, such as dissolving them in water before adding them to the raw materials and carbon-containing substance powder, and mixing them. There is no difference in the dispersion effect depending on the method.

The resulting slurry may be removed after dehydration and drying.
Alternatively, it may be dehydrated to some extent, then kneaded in a wet state (or granulated several times), and then dried. The obtained dried product was heated in a nitrogen or ammonia stream at 1350~
When baked at 150° C. for 0.2 to 20 hours, β-sialon is generated. If the firing temperature is 1000° C. or higher, it is difficult to control the reductive nitriding reaction and aluminum nitride and other impurities are generated, and if the firing temperature is 1350° C. or lower, β-sialon is insufficiently generated.

According to the method of the present invention explained above, the raw material and the carbon-containing substance powder are sufficiently dispersed and mixed, so that
Unlike conventional methods, there is no unreacted material left behind or aluminum nitride produced, which reduces purity.
Pure β-sialon powder is obtained.

Next, the present invention will be explained by examples.

Examples 1-5. Comparative Examples 1 and 2 Various experiments regarding the effects of dispersants were conducted using the following raw materials and carbon-containing substance powders.

1 Silica powder White carbon Manufactured by Nippon Aerosil Co., Ltd. 1'-AERO] L-380J Average particle size 3. Qmμ 2 Alumina powder Aluminum oxide Made by Nippon Aerosil Co., Ltd. I Aluminum Oxide CJ average particle size 2Tada reagent) 25mμ 4 Dispersant i. /Ammonium oxalate (first class reagent) b.
Polyethylene glycol alkyl ether 1-Neogen ET 135J manufactured by Daiichi Yakuhin Kogyo Co., Ltd. c. Sodium oxalate (first class reagent) 2. Sodium hexametaphosphate (first class reagent) 5, p
H Adjustment Solution To the total amount of 100 parts by weight of ammonia water silica powder, 100 parts by weight of alumina powder, and 40 parts by weight of carbon-containing substance, add 4 times the amount of water to make a slurry, and then make a slurry as shown in Table 1. A dispersant was added to each, and a pH adjustment solution was used to prepare a slurry with pi (9, Q). After centrifugal dehydration, this slurry was granulated to about 6 fin diameters and dried at about 90°C. The granules were placed in a graphite crucible and fired at 1450°C for 6 hours in an electric furnace with a nitrogen flow of 509 cc/min.
3.

After the obtained fired product was cooled to room temperature 1, it was subjected to X-ray diffraction, and the confirmed minerals are shown in Table 2 VC.

The obtained results show that when the dispersant of the present invention is used, there is no residual unreacted raw material or generation of other compounds, and ammonium oxalate triO, 3ilI+i, nonionic surfactant 60.1 It was found that adding a weight of 1:1 or more is effective. 2 (Full white hereafter) ゛ Examples 6 to 8. Comparative Examples 3 to 5 The pH of the slurry was varied by varying the amount of ammonia water, and experiments were conducted using the raw materials and carbon-containing powder of Example 1 except for dispersants C and 2, and following the same operating procedure. went. At that time, for comparison, a case where no ammonia water was added and a case where caustic soda was used were also conducted, and the obtained results are shown in Table 3. As a result, the slurry p
It was confirmed that pure β-sialon was obtained only in this example, in which H was controlled to 8.0 to 9.5 using aqueous ammonia.

(Margin below)

Claims (1)

[Claims] Silica powder, alumina powder and carbon honorable material powder,
It is characterized by adding and mixing a dispersing agent and a pH adjusting liquid, drying the slurry, and then firing it in a nitrogen stream.
Method for producing β-sialon powder