JPH0152325B2 - - Google Patents
Info
- Publication number
- JPH0152325B2 JPH0152325B2 JP56126634A JP12663481A JPH0152325B2 JP H0152325 B2 JPH0152325 B2 JP H0152325B2 JP 56126634 A JP56126634 A JP 56126634A JP 12663481 A JP12663481 A JP 12663481A JP H0152325 B2 JPH0152325 B2 JP H0152325B2
- Authority
- JP
- Japan
- Prior art keywords
- silicon carbide
- weight
- nitrogen
- sintering
- sic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims description 119
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 83
- 229910010271 silicon carbide Inorganic materials 0.000 claims description 72
- 239000013078 crystal Substances 0.000 claims description 45
- 238000005245 sintering Methods 0.000 claims description 39
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 34
- 238000010438 heat treatment Methods 0.000 claims description 32
- 229910052757 nitrogen Inorganic materials 0.000 claims description 32
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 30
- 238000006243 chemical reaction Methods 0.000 claims description 28
- 238000004519 manufacturing process Methods 0.000 claims description 25
- 229910052799 carbon Inorganic materials 0.000 claims description 22
- 239000002994 raw material Substances 0.000 claims description 22
- 239000007789 gas Substances 0.000 claims description 15
- 239000000377 silicon dioxide Substances 0.000 claims description 15
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 11
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 11
- 239000001301 oxygen Substances 0.000 claims description 11
- 229910052760 oxygen Inorganic materials 0.000 claims description 11
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 10
- 239000012535 impurity Substances 0.000 claims description 8
- 239000000843 powder Substances 0.000 claims description 7
- 229910052783 alkali metal Inorganic materials 0.000 claims description 5
- 150000001340 alkali metals Chemical class 0.000 claims description 5
- 229910052784 alkaline earth metal Inorganic materials 0.000 claims description 5
- 150000001342 alkaline earth metals Chemical class 0.000 claims description 5
- 229910052782 aluminium Inorganic materials 0.000 claims description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 5
- 229910052742 iron Inorganic materials 0.000 claims description 5
- 239000008187 granular material Substances 0.000 claims description 2
- 229910001873 dinitrogen Inorganic materials 0.000 description 19
- 238000000034 method Methods 0.000 description 16
- 239000002245 particle Substances 0.000 description 14
- 229910002804 graphite Inorganic materials 0.000 description 9
- 239000010439 graphite Substances 0.000 description 9
- 239000000654 additive Substances 0.000 description 8
- 239000000203 mixture Substances 0.000 description 6
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 5
- 229910052796 boron Inorganic materials 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 5
- 238000001816 cooling Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 230000000704 physical effect Effects 0.000 description 5
- 239000007858 starting material Substances 0.000 description 5
- 230000009466 transformation Effects 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 230000000996 additive effect Effects 0.000 description 4
- 238000001272 pressureless sintering Methods 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 210000003739 neck Anatomy 0.000 description 3
- 229910052580 B4C Inorganic materials 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- INAHAJYZKVIDIZ-UHFFFAOYSA-N boron carbide Chemical compound B12B3B4C32B41 INAHAJYZKVIDIZ-UHFFFAOYSA-N 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 238000013001 point bending Methods 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 238000001878 scanning electron micrograph Methods 0.000 description 2
- 235000012239 silicon dioxide Nutrition 0.000 description 2
- -1 silicon halide Chemical class 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 238000005979 thermal decomposition reaction Methods 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- HZAXFHJVJLSVMW-UHFFFAOYSA-N 2-Aminoethan-1-ol Chemical compound NCCO HZAXFHJVJLSVMW-UHFFFAOYSA-N 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 241000872198 Serjania polyphylla Species 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000006061 abrasive grain Substances 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 238000010306 acid treatment Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 229920002301 cellulose acetate Polymers 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000007872 degassing Methods 0.000 description 1
- 238000000280 densification Methods 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 238000004108 freeze drying Methods 0.000 description 1
- 238000010574 gas phase reaction Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 239000011812 mixed powder Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 229920001558 organosilicon polymer Polymers 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000011224 oxide ceramic Substances 0.000 description 1
- 229910052574 oxide ceramic Inorganic materials 0.000 description 1
- 239000002006 petroleum coke Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 239000011863 silicon-based powder Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000009423 ventilation Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Ceramic Products (AREA)
- Carbon And Carbon Compounds (AREA)
Description
本発明は、高密度でかつ高強度の炭化珪素焼結
体を製造するに適した炭化珪素粉末およびその製
造方法に関し、特に本発明は、窒素を含有する焼
結用炭化珪素粉末およびその製造方法に関する。
炭化珪素は、極めて優れた化学的および物理的
性質を有しており、特に高密度の焼結体はガスタ
ービン部品、高温熱交換器のような苛酷な条件下
で使用される高温構造材の如き用途に対して好適
な材料である。
従来、炭化珪素の焼結方法としては加圧焼結法
および反応焼結法が広く知られている。しかしな
がら前者の加圧焼結法によれば、複雑な形状の焼
結体を製造し難く、生産性もあがらない欠点が、
一方後者の反応焼結法によれば高強度の焼結体を
得難く、しかも遊離珪素を多量に含有するため高
温域における使用が困難である欠点があつた。
また、酸化物セラミツクスを製造するのに一般
的に行なわれている無加圧焼結法すなわち常温で
成形した生成形体を無加圧下で焼結する方法を炭
化珪素の焼結に用いることはこれまで困難である
とされていたが、最近になつて炭化珪素、ホウ素
含有添加剤および炭素質添加剤から成る混合粉末
を成形し、不活性雰囲気中で焼結する無加圧結結
方法が報告されている。
ところで、炭化珪素はその結晶型が数多く知ら
れており、従来六方晶系のα型と立方晶系のβ型
との2種類に大別されている。このうち前者のα
型には高温例えば2000℃以上でも安定な4H、6H
型等の高温安定タイプの炭化珪素と1500℃以下で
不安定な2H型炭化珪素とが知られている。
従来、炭化珪素の無加圧焼結方法の出発原料と
しては、例えば、特開昭53−84013号公報によれ
ばアチエソン法の炉において最も普通に製造され
る炭化珪素を粉砕し、粒度分級して得られる高温
安定タイプのα型炭化珪素の粉末が使用されてい
るが、前記高温安定タイプのα型炭化珪素は焼結
に際して結晶型の変態転移を伴わず、焼結速度が
遅いため、高密度の焼結体を得ようとすると焼結
温度を高めて焼結する必要があり、さらに高温安
定タイプのα型炭化珪素を出発原料として得られ
る焼結体は異方性のない擬球状の比較的粗大な結
晶粒よりなる構造となるため高強度の焼結体を得
ることは困難であつた。
これに対し、特開昭50−160200号公報によれば
ハロゲン化珪素および炭化水素よりプラズマジエ
ツト反応によつて製造されるサブミクロン粒度の
β型炭化珪素粉末が、また特開昭54−67599号公
報によれば有機珪素高分子化合物を熱分解して得
られる高純度のβ型炭化珪素粉末の製造方法が開
示されている。さらに本発明者等は特公昭55−
40527号公報にシリカと炭素とを出発原料とする
主としてβ型結晶よりなる炭化珪素の製造方法を
提案した。しかしながら、前記諸公報記載のβ型
結晶よりなる炭化珪素粉末を無加圧焼結用の出発
原料とすると焼結に際してSiCの熱分解による気
相が生成し、この気相を介して焼結が進行するた
め、α型結晶よりなる結晶粒が急速に成長し粗大
な板状結晶が生成して焼結体の高密度化が阻害さ
れる欠点があつた。
上述の如く従来知られた炭化珪素粉末を使用し
て高密度でかつ高強度の炭化珪素無加圧焼結体を
製造することは困難であつた。
本発明は、無加圧焼結体を製造するに極めて適
した炭化珪素粉末およびその製造方法を提供する
ことを目的とするものである。
本発明によれば、0.015〜0.20重量%の窒素お
よび0.01〜1.0重量%の酸素を含有し、残部がSiC
と不可避的不純物よりなり、前記SiCのうち少な
くとも80重量%がβ型結晶よりなるSiCであり、
かつ比表面積が5〜50m2/gである焼結用炭化珪
素粉末およびその製造方法を提供することによつ
て前記目的を達成することができる。
次に本発明を詳細に説明する。
従来、焼結体製造用原料としての炭化珪素粉末
は、炭素含有添加剤およびホウ素含有添加剤等の
焼結助剤以外の不純物含有量のなるべく少ない高
純度の炭化珪素粉末が有利であると考えられてお
り、窒素を比較的多量に含有させた炭化珪素粉末
が焼結体製造用原料として適していることは知ら
れていなかつた。
本発明者は、β型結晶を主体とする炭化珪素粉
末を製造するに際し、反応炉中に窒素ガスを装入
して窒素を含有させた炭化珪素粉末を調製し、前
記炭化珪素粉末を焼結体製造用原料として使用し
たところ、従来、焼結体製造用原料として良好で
あるとは推測だにされなかつたところの前記窒素
を含有する炭化珪素粉末が焼結特性に優れ、しか
も該粉末を使用して製造された焼結体は窒素含有
量の少ない従来のβ型結晶を主体とする炭化珪素
粉末を使用して製造された焼結体に比較して極め
て優れた特性を有していることを新規に知見し
た。
すなわち、0.015〜0.20重量%の窒素および0.01
〜1.0重量%の酸素を含有し、残部がSiCと不可避
的不純物よりなり、前記SiCのうち少なくとも80
重量%がβ型結晶よりなるSiCであり、かつ比表
面積が5〜50m2/gである焼結用炭化珪素粉末を
使用することにより、焼結時における炭化珪素の
熱分解反応を抑制してβ型結晶のα型晶への相変
態を適正化し、かつ相変態に伴う粗大な板状結晶
の生成を防止することができ、高密度で均一な微
細構造を有する高強度焼結体を得ることができ
る。
本発明によれば、炭化珪素粉末は0.015〜0.20
重量%の窒素および0.01〜1.0重量%の酸素を含
有し、残部がSiCと不可避的不純物よりなること
が必要である。
前記窒素の含有量を0.015〜0.20重量%の範囲
内に限定する理由は0.15重量%より少ないとβ型
結晶のα型結晶への相変態を適正化する作用が充
分に発揮されず、α型化に伴つてα型結晶の粗大
な板状結晶が焼結初期に生成し、焼成収縮を妨害
するため高密度でかつ均一な微細構造を有する焼
結体を得ることが困難であり、一方0.20重量%よ
りも多いとSiC中のβ型結晶が著しく安定化さ
れ、焼結時におけるSiCの拡散が抑制されるた
め、焼結時の焼成収縮が生起し難く、高密度の焼
結体を得ることが困難となるからであり、0.03〜
0.10重量%の範囲でさらに好適な結果が得られ
る。
次に前記酸素の含有量を0.01〜1.0重量%の範
囲内に限定する理由を述べる。前記炭化珪素粉末
に含有される酸素は焼結助剤として添加された炭
素と焼結時に反応し、次式に示される如き機構で
除去される。
SiO2+C→SiO+CO ………(1)
SiO+2C→SiC+CO ………(2)
したがつて、前記酸素が1.0重量%よりも多量
に存在すると炭素質添加剤を多量に使用しなけれ
ばならないばかりでなく、COガスが大量に発生
するため焼結時にガス抜きの必要が生じる等焼結
が困難になるばかりでなく、また高密度の焼結体
を得ることが困難になるからである。一方前記酸
素量が0.01重量%よりも少ない炭化珪素粉末は例
えば弗酸と硝酸の混酸で処理することによつて得
ることができるが、このようにして得た高純度の
炭化珪素粉末は極めて活性であり、空気雰囲気中
で乾燥したりすると常温でも容易に酸化してしま
うため、酸素量を低く維持するには酸処理後の雰
囲気を例えば非酸化性に保持しなければならず実
用的でないからであり、前記炭化珪素粉末中に含
有される酸素量は0.03〜0.4重量%の範囲内とす
ることが比較的容易であり、しかも焼結用原料と
して適している。
前記炭化珪素粉末を構成するSiCは少なくとも
80重量%がβ型結晶よりなるSiCであることが必
要な理由について次に述べる。
通常β型結晶を主体とする炭化珪素に混在する
結晶はβ型結晶より低温域で安定な2H型結晶あ
るいはβ型結晶より高温域で安定な4H、6H型等
のα型結晶である。前記2H型炭化珪素は通常の
焼結反応の生じる温度域において極めて不安定で
あり、焼結に際して異常粒成長の原因となり易い
し、一方4H、6H型の高温域で安定なα型炭化珪
素を含有すると焼結中にβ型結晶からα型結晶へ
の相変態が促進され、α型化に伴つてα型炭化珪
素の粗大な板状結晶が生成し、焼結収縮を妨害す
るため高密度でかつ均一な微細構造を有する高強
度の焼結体を得ることが困難である。したがつ
て、本発明の目的とする高強度の焼結体を得るに
は炭化珪素粉末を構成するSiCは少なくとも80重
量%がβ型結晶よりなるSiCであることが必要で
あり、なかでも90重量%以上がβ型結晶よりなる
SiCであることがより好適である。
本発明によれば、本発明の炭化珪素粉末に含有
される不可避的不純物のうち主体をなすものは.
01〜3.0重量%の遊離炭素、0.5重量%以下のアル
ミニウム、0.01〜0.5重量%の鉄、0.01〜0.5重量
%のアルカリ金属およびアルカリ土類金属であ
る。
前記不可避的不純物の含有量を前記範囲内とす
ることが好ましい理由は、遊離炭素は炭素質添加
剤としての作用効果を有するが、前記範囲よりも
多量に含有すると焼結時に焼結を著しく阻害し、
また焼結体内の介在物相が増加し、焼結体の物性
特に強度を著しく低下させるからであり、アルミ
ニウムは焼結体中に板状結晶を生成させる効果を
有するため、前記範囲よりも多量に含有すると高
密度の焼結体を得ることが困難になり、鉄やアル
カリ金属およびアルカリ土類金属は前記範囲より
も多量に含有すると焼結体の物性を著しく劣化さ
せるからである。
本発明によれば、高密度の焼結体を得る上で焼
結が開始される際に炭化珪素粉末粒子相互の接触
部に生起する焼結開始結合点すなわちネツクを均
一に発生させることが重要であり、前記炭化珪素
粉末の比表面積は5〜50m2/gの範囲内とするこ
とが必要である。前記比表面積を5〜50m2/gの
範囲内に限定する理由は、前記比表面積が5m2/
gより小さいと焼結開始時に形成されるネツクの
発生箇所が少なく焼結時における収縮が不均一と
なるため、本発明の目的とする高い密度と強度と
を有する焼結体を得ることが困難であるし、一方
50m2/gより大きな比表面積を有する炭化珪素粉
末はネツクの発生箇所も多く焼結体にも優れてい
ると考えられるが、このような炭化珪素粉末は入
手することが困難で、例え入手できたとしても極
めて高価となり実用的でないからであり、15〜35
m2/gの範囲内でより好適な結果が得られる。
次に本発明の炭化珪素粉末の製造方法について
説明する。
本発明の炭化珪素は、金属シリコンを炭素粉末
の混合物を加熱する方法、ハロゲン化珪素と炭化
水素のような混合ガスを気相反応させる方法によ
つて製造することもできるが、これらの方法によ
つて製造される炭化珪素はコストが非常に高い。
本発明の窒素を0.015〜0.20重量%含有し、全
SiCのうち少なくとも80重量%がβ型結晶よりな
るSiCである炭化珪素は、シリカ粉末と炭素粉末
とを混合して粒状に成形せしめた原料を間接加熱
炉へ装入し、炉内の反応温度を1700〜2150℃の範
囲内でかつ窒素分圧を5〜200mmHgの範囲内に維
持しながら加熱することによつて製造することが
できる。
前記炉内の窒素分圧を5〜200mmHgの範囲内に
限定する理由は、炉内の窒素分圧が5mmHgより
低いと本発明の目的とする窒素含有量の炭化珪素
を製造することができないばかりでなく、SiC生
成反応時に結晶粒が粗大化し易く微細な炭化珪素
粉末を製造することが困難となり、一方200mmHg
より高いと炭化珪素粉末に含有される窒素量が著
しく多くなり、本発明の目的とする窒素含有量の
範囲内とすることが困難となるばかりでなく、
SiC生成反応が著しく抑制されるため炭化珪素を
効率よく製造することが困難になるからである。
また前記反応温度を1700〜2150℃の範囲内に限
定する理由は、本発明によれば前述の如く炉内の
窒素分圧を比較的高く維持することにより、SiC
生成反応が抑制されるため、1700℃より低いと
SiC生成反応が著しく遅く効率的にSiCを製造す
ることが困難であり、一方2150℃より高いと生成
する炭化珪素の殆どがα型結晶よりなる炭化珪素
に結晶変態するため、焼結体製造用原料として適
したβ型結晶よりなるSiCを少なくとも80重量%
含有する炭化珪素を製造することが困難であるか
らである。
本発明によれば、シリカと炭素とのC/SiO2
モル比が3.2〜5.0の範囲内の原料を下部に窒素ガ
スの装入手段を有する竪型の間接加熱炉へ装入
し、前記間接加熱炉内を自重降下させつつSiC生
成反応を生起させるに際し、前記装入手段より装
入された窒素ガスと向流接触させることが好まし
い。
シリカと炭素とから生成される炭化珪素の反応
式は一般に下記式(3)で示されている。
SiO2+3C→SiC+2CO ………(3)
しかしながら、実際の主体をなす生成機構は前
記式(1)の反応によつて生成されるSiOガスが前記
式(2)にしたがつて炭素と反応することにより炭化
珪素が生成されることが知られている。
ところで、本発明によれば炉内の窒素分圧が5
〜200mmHgの範囲内に維持される。前記炉内の窒
素は前記式(2)の反応を抑制し、炉内におけるSiO
ガス量を増加させる作用効果を有する。前記SiO
ガス量が増加すると、予熱帯において下記式(4)、
(5)、(6)に従つて生成するSiO2、Si、SiC、C等の
混合した析出物量が増大し、炭化珪素を連続的に
製造する上で重要な原料の円滑な自重降下を阻害
するため、長期間の安定した連続操業が困難とな
る。
2SiO→SiO2+Si ………(4)
SiO+CO→SiO2+C ………(5)
3SiO+CO→2SiO2+SiC ………(6)
したがつて、本発明によれば、原料中の炭素量
を増加して前記式(2)の生起する箇所を増加させる
ことが望ましく、前記C/SiO2モル比を3.2〜5.0
の範囲内とすることが好ましい。その理由は前記
C/SiO2モル比が3.2より低いと前述の如くに原
料の円滑な自重降下を長期間にわたつて維持する
ことが難しく、他方5.0より高いと反応に寄与し
ない炭素を高温に加熱するために熱効率が低くな
り、また炭素原料に要する費用が増加するので経
済的でないからである。
なお、前記予熱帯における析出物の影響を少な
くすることを目的として、第1図に示す如き予熱
帯を形成する筒の任意の位置より上部の内部水平
断面積を加熱帯の内部水平断面積よりも大きく形
成された竪型の間接加熱炉を使用することも有利
である。
さらに、前記欠点を解決する上で、シリカの平
均粒径を75〜250μmの範囲内となし、かつシリ
カと炭素の平均粒径の関係を下記式(7)を満足する
ように調整し、
Y≦8.5×10-2RX+3.1×104/T ………(7)
前記式(1)と(2)との反応速度を好適な範囲内に維
持することが有利である。
なお、上記式中Xははシリカの平均粒径(μ
m)、Yは炭素の平均粒径(μm)、Tは反応温度
(〓)、Rは出発原料中のシリカと炭素のC/
SiO2モル比である。
また、本発明において下部に窒素ガスの装入手
段を有する竪型の間接加熱炉の上部より原料を装
入し、加熱炉内を自重降下させつつSiC生成反応
を生起させるに際し、前記装入手段より装入され
た窒素ガスと向流接触させることが好ましい。な
ぜならば、シリカと炭素とからなるSiC生成反応
は前記式(3)に示した如くであり、反応に伴つて大
量のCOガスが生成するため炉の上部より窒素ガ
スを装入すると窒素ガスはCOガスとともに排出
されてしまい、効率的に窒素ガスを装入物と接触
させることが困難であり、また加熱炉内における
窒素分圧の制御も極めて困難となるからである。
本発明によれば、0.015〜0.20重量%の窒素を
含有し、SiCのうち少なくとも80重量%がβ型結
晶よりなる炭化珪素を製造するには炉内の窒素分
圧と反応温度とを下記の関係式(8)を満足する範囲
内とすることが有利である。
3.3×10-4T2−1.35T+1384≦PN2≦8.5
×10-4T2−3.46T+3593 ………(8)
なお、上記式中PN2は炉内の窒素分圧(mm
Hg)、Tは反応温度(〓)である。
次に、本発明の方法において使用することので
きる竪型の間接加熱炉の一例を図面を参照しなが
ら説明する。
本発明の方法で使用することのできる間接加熱
炉は、第1図に示す如く原料装入口1と予熱帯2
と加熱帯3と冷却帯4と密閉自在の生成物排出口
5とを有し、それらが縦方向にそれぞれ連接され
てなる反応容器6であつて、前記加熱帯を形成す
る筒7は黒鉛製であり、加熱帯の装入物を間接電
気加熱する手段8,9を具備し、前記反応容器下
部の冷却帯には窒素ガスの装入口10が設けられ
たものである。
前記反応容器6は間接加熱炉の中心部に設置さ
れ、間接加熱手段8,9は黒鉛製発熱体8と前記
発熱体の外側に近接して設けられた黒鉛製反射筒
9からなり、前記黒鉛製反射筒の外側に炭素ある
いは黒鉛質微粉よりなる断熱層11が設けられて
いる。前記加熱帯を形成する筒と黒鉛製反射筒に
囲まれた空間内には非酸化性ガス封入口12より
例えばアルゴン、ヘリウム、窒素、一酸化炭素、
水素、その他の非酸化性ガスが封入され、空気の
侵入による黒鉛製発熱体の酸化消耗が防止され
る。
次に、本発明の炭化珪素粉末を使用する焼結体
の製造方法の一例について説明する。
本発明の炭化珪素粉末を使用する焼結体は、本
発明の炭化珪素粉末100重量部に対し、ホウ素含
有量に換算して0.1〜3.0重量部のホウ素含有添加
剤と固定炭素含有量に換算して0.1〜3.0重量部の
炭素質添加剤とを添加して均質混合し、前記均質
混合した混合物を任意の形状の生成形体に成形し
た後、前記生成形体をアルゴン、ヘリウム、ネオ
ン、クリプトン、キセノン、水素のなかから選択
されるいずれか少なくとも1種からなるガス雰囲
気中で2050〜2250℃で焼結することにより製造す
ることができる。
尚、窒素含有量の少ないβ型炭化珪素粉末を用
いて焼結体を製造する際に、その雰囲気を窒素ガ
ス雰囲気とすることにより窒素を含有する焼結体
を造ることのできることが知られているが、かゝ
る方法によると焼結体中に固溶した窒素濃度分布
が不均一であるため、焼結体は均一性に欠けその
用途が制限される。
以下、本発明の実施例について説明する。
実施例 1
平均粒径が153μmのシリカ粉末(SiO2=99.7重
量%)100重量部、平均粒径が29μmの石油コー
クス粉(C=98.7重量%)76重量部および平均粒
径が43μmの高ピツチ粉(C=50.4重量%)7重
量部を配合し、縦型スクリユー混合機にて10分間
混合した。前記配合原料にCMC0.5%水溶液をス
プレーしながらパン型造粒機を用いて成形し、篩
とバーグリズリーで整粒した後、バンド型通気乾
燥機に入れて150℃の熱風で90分間乾燥して平均
粒径が10.5mm、嵩比重が0.60g/cm3、C/SiO2モ
ル比が4.0の成形原料を得た。
この成形原料を第1図に示した如き構造でかつ
第1表に示した仕様の間接加熱炉の上部より装入
し、前記装入された原料を連続的に自重降下させ
て、黒鉛製筒の外壁温度が2150℃に制御された加
熱帯内に至らせ、前記加熱帯内で水平方向に間接
電気加熱して約1時間SiC生成反応を行なわせた
後、冷却帯に自重降下させ、排出口より反応生成
物を連続的に排出させた。
The present invention relates to a silicon carbide powder suitable for producing a high-density and high-strength silicon carbide sintered body, and a method for producing the same.In particular, the present invention relates to a silicon carbide powder for sintering containing nitrogen and a method for producing the same. Regarding. Silicon carbide has extremely excellent chemical and physical properties, and its high-density sintered body is particularly useful for high-temperature structural materials used under harsh conditions such as gas turbine parts and high-temperature heat exchangers. This material is suitable for such uses. Conventionally, pressure sintering methods and reaction sintering methods are widely known as methods for sintering silicon carbide. However, according to the former pressure sintering method, it is difficult to manufacture sintered bodies with complicated shapes, and the productivity does not increase.
On the other hand, the latter reactive sintering method has the disadvantage that it is difficult to obtain a sintered body with high strength, and furthermore, it contains a large amount of free silicon, making it difficult to use in a high temperature range. In addition, the pressureless sintering method, which is commonly used to produce oxide ceramics, in which the formed body is molded at room temperature and sintered under no pressure, is not used for sintering silicon carbide. Although it was thought to be difficult until now, a pressureless sintering method has recently been reported in which a mixed powder consisting of silicon carbide, boron-containing additives, and carbonaceous additives is compacted and sintered in an inert atmosphere. has been done. Incidentally, silicon carbide is known to have many crystal forms, and has conventionally been roughly classified into two types: hexagonal α type and cubic β type. Of these, the former α
The mold has 4H and 6H, which are stable even at high temperatures such as 2000℃ or higher.
Two types of silicon carbide are known: silicon carbide that is stable at high temperatures such as molds, and 2H type silicon carbide that is unstable at temperatures below 1500°C. Conventionally, as a starting material for the pressureless sintering method of silicon carbide, for example, according to Japanese Patent Application Laid-Open No. 53-84013, silicon carbide, which is most commonly produced in a furnace of the Acheson process, is crushed and subjected to particle size classification. High-temperature-stable α-type silicon carbide powder obtained by In order to obtain a dense sintered body, it is necessary to increase the sintering temperature, and the sintered body obtained using high-temperature stable α-type silicon carbide as a starting material has a pseudospherical shape with no anisotropy. Since the structure consists of relatively coarse crystal grains, it has been difficult to obtain a high-strength sintered body. On the other hand, according to JP-A-50-160200, β-type silicon carbide powder with submicron particle size is produced from silicon halide and hydrocarbon by plasma jet reaction, and JP-A-54-67599 According to the publication, a method for producing high purity β-type silicon carbide powder obtained by thermally decomposing an organic silicon polymer compound is disclosed. Furthermore, the inventors of the present invention
In Japanese Patent No. 40527, we proposed a method for producing silicon carbide mainly consisting of β-type crystals using silica and carbon as starting materials. However, if silicon carbide powder consisting of β-type crystals described in the above-mentioned publications is used as a starting material for pressureless sintering, a gas phase will be generated due to thermal decomposition of SiC during sintering, and sintering will occur through this gas phase. As the sintering progresses, crystal grains made of α-type crystals grow rapidly and coarse plate-like crystals are formed, which has the drawback of hindering the densification of the sintered body. As mentioned above, it has been difficult to produce a pressureless sintered body of high density and high strength silicon carbide using conventionally known silicon carbide powder. An object of the present invention is to provide a silicon carbide powder that is extremely suitable for producing a pressureless sintered body and a method for producing the same. According to the present invention, it contains 0.015-0.20% by weight of nitrogen and 0.01-1.0% by weight of oxygen, with the balance being SiC.
and unavoidable impurities, and at least 80% by weight of the SiC is SiC consisting of β-type crystals,
The above object can be achieved by providing a sintering silicon carbide powder having a specific surface area of 5 to 50 m 2 /g and a method for producing the same. Next, the present invention will be explained in detail. Conventionally, it has been thought that high-purity silicon carbide powder containing as few impurities as possible other than sintering aids such as carbon-containing additives and boron-containing additives is advantageous as a raw material for producing sintered bodies. However, it was not known that silicon carbide powder containing a relatively large amount of nitrogen is suitable as a raw material for producing a sintered body. When producing silicon carbide powder mainly composed of β-type crystals, the inventor charged nitrogen gas into a reaction furnace to prepare nitrogen-containing silicon carbide powder, and sintered the silicon carbide powder. When used as a raw material for manufacturing a sintered body, it was found that the nitrogen-containing silicon carbide powder, which had not previously been considered to be good as a raw material for manufacturing a sintered body, had excellent sintering properties. The sintered body manufactured using this method has extremely superior properties compared to the sintered body manufactured using conventional silicon carbide powder mainly composed of β-type crystals with low nitrogen content. I discovered something new. i.e. 0.015-0.20 wt% nitrogen and 0.01
Contains ~1.0% by weight of oxygen, with the remainder consisting of SiC and unavoidable impurities, and at least 80% of the SiC
By using silicon carbide powder for sintering that is SiC consisting of β-type crystals in weight% and has a specific surface area of 5 to 50 m 2 /g, the thermal decomposition reaction of silicon carbide during sintering can be suppressed. It is possible to optimize the phase transformation of β-type crystals to α-type crystals, and prevent the formation of coarse plate-like crystals due to phase transformation, thereby obtaining a high-strength sintered body with a high density and uniform microstructure. be able to. According to the present invention, the silicon carbide powder is 0.015-0.20
It is necessary to contain % by weight of nitrogen and 0.01-1.0% by weight of oxygen, with the remainder consisting of SiC and unavoidable impurities. The reason for limiting the nitrogen content to within the range of 0.015 to 0.20% by weight is that if it is less than 0.15% by weight, the effect of optimizing the phase transformation of β-type crystals to α-type crystals will not be sufficiently exerted, Coarse plate-shaped crystals of α-type crystals are formed in the initial stage of sintering, and as a result, it is difficult to obtain a sintered body with a high density and uniform microstructure because it interferes with firing shrinkage. When the amount is more than 1% by weight, the β-type crystals in SiC are significantly stabilized, and the diffusion of SiC during sintering is suppressed, making it difficult for sintering shrinkage to occur during sintering, resulting in a high-density sintered body. This is because it becomes difficult to
Even better results are obtained in the range of 0.10% by weight. Next, the reason for limiting the oxygen content to within the range of 0.01 to 1.0% by weight will be described. Oxygen contained in the silicon carbide powder reacts with carbon added as a sintering aid during sintering, and is removed by a mechanism as shown in the following equation. SiO 2 +C→SiO+CO……(1) SiO+2C→SiC+CO……(2) Therefore, if the oxygen is present in an amount greater than 1.0% by weight, a large amount of carbonaceous additive must be used. Moreover, a large amount of CO gas is generated, which not only makes sintering difficult, such as the necessity of degassing during sintering, but also makes it difficult to obtain a high-density sintered body. On the other hand, silicon carbide powder with an oxygen content of less than 0.01% by weight can be obtained, for example, by treatment with a mixed acid of hydrofluoric acid and nitric acid, but the highly purified silicon carbide powder obtained in this way is extremely active. However, if it is dried in an air atmosphere, it will easily oxidize even at room temperature, so in order to maintain a low oxygen content, the atmosphere after acid treatment must be kept non-oxidizing, which is not practical. Therefore, it is relatively easy to set the amount of oxygen contained in the silicon carbide powder within the range of 0.03 to 0.4% by weight, and it is suitable as a raw material for sintering. SiC constituting the silicon carbide powder is at least
The reason why it is necessary to use SiC with 80% by weight of β-type crystals will be described below. Usually, the crystals mixed in silicon carbide, which mainly consists of β-type crystals, are 2H-type crystals, which are more stable at lower temperatures than β-type crystals, or α-type crystals, such as 4H and 6H types, which are more stable at higher temperatures than β-type crystals. The 2H type silicon carbide is extremely unstable in the temperature range where normal sintering reactions occur, and tends to cause abnormal grain growth during sintering.On the other hand, the 4H and 6H types, which are stable in the high temperature range, are If it is contained, the phase transformation from β-type crystal to α-type crystal is promoted during sintering, and coarse plate-like crystals of α-type silicon carbide are generated as the α-type crystal changes, which hinders sintering shrinkage and increases the density. It is difficult to obtain a high-strength sintered body having a large and uniform microstructure. Therefore, in order to obtain a high-strength sintered body, which is the object of the present invention, it is necessary that at least 80% by weight of the SiC constituting the silicon carbide powder be SiC consisting of β-type crystals, and especially 90% by weight of SiC. At least % by weight consists of β-type crystals
More preferably, it is SiC. According to the present invention, the main constituents of the inevitable impurities contained in the silicon carbide powder of the present invention are:
01-3.0% by weight free carbon, 0.5% by weight or less aluminum, 0.01-0.5% by weight iron, 0.01-0.5% by weight alkali metals and alkaline earth metals. The reason why it is preferable to keep the content of the unavoidable impurities within the above range is because free carbon has the effect of functioning as a carbonaceous additive, but if it is contained in an amount larger than the above range, it will significantly inhibit sintering. death,
In addition, the inclusion phase in the sintered body increases, which significantly reduces the physical properties, especially the strength, of the sintered body.Aluminum has the effect of generating plate crystals in the sintered body, so the amount of aluminum in the sintered body is larger than the above range. This is because if the iron, alkali metal, or alkaline earth metal is contained in an amount greater than the above range, it will be difficult to obtain a high-density sintered body, and if the iron, alkali metal, or alkaline earth metal is contained in an amount greater than the above range, the physical properties of the sintered body will be significantly deteriorated. According to the present invention, in order to obtain a high-density sintered body, it is important to uniformly generate sintering initiation bonding points, that is, necks, which occur at the mutual contact areas of silicon carbide powder particles when sintering starts. The specific surface area of the silicon carbide powder must be within the range of 5 to 50 m 2 /g. The reason why the specific surface area is limited to a range of 5 to 50 m 2 /g is that the specific surface area is 5 m 2 /g.
If it is smaller than g, there will be fewer areas where necks are formed at the start of sintering, and shrinkage during sintering will be uneven, making it difficult to obtain a sintered body with the high density and strength that is the objective of the present invention. On the other hand,
Silicon carbide powder with a specific surface area larger than 50 m 2 /g is considered to be excellent in forming a sintered body because it has a large number of areas where there are necks, but it is difficult to obtain such silicon carbide powder, and even if it is not available, Even if it were, it would be extremely expensive and impractical;
More suitable results are obtained within the range of m 2 /g. Next, a method for producing silicon carbide powder of the present invention will be explained. The silicon carbide of the present invention can also be produced by heating a mixture of carbon powder with metallic silicon, or by causing a gas phase reaction between silicon halide and a mixed gas such as a hydrocarbon; The silicon carbide thus produced is very expensive. Contains 0.015 to 0.20% by weight of nitrogen of the present invention, and
Silicon carbide, which is SiC in which at least 80% by weight of SiC is composed of β-type crystals, is produced by charging a raw material made by mixing silica powder and carbon powder into granules and charging it into an indirect heating furnace. It can be produced by heating at a temperature of 1,700 to 2,150°C while maintaining a nitrogen partial pressure within a range of 5 to 200 mmHg. The reason why the nitrogen partial pressure in the furnace is limited to a range of 5 to 200 mmHg is that if the nitrogen partial pressure in the furnace is lower than 5 mmHg, silicon carbide with the nitrogen content targeted by the present invention cannot be produced. However, the crystal grains tend to become coarse during the SiC production reaction, making it difficult to produce fine silicon carbide powder.
If it is higher, the amount of nitrogen contained in the silicon carbide powder will increase significantly, and it will not only be difficult to keep the nitrogen content within the range targeted by the present invention, but also
This is because the SiC production reaction is significantly suppressed, making it difficult to efficiently produce silicon carbide. Furthermore, the reason why the reaction temperature is limited to a range of 1700 to 2150°C is that according to the present invention, as mentioned above, by maintaining the nitrogen partial pressure in the furnace relatively high, SiC
If the temperature is lower than 1700℃, the production reaction will be suppressed.
The SiC production reaction is extremely slow and it is difficult to efficiently produce SiC, and on the other hand, if the temperature is higher than 2150°C, most of the silicon carbide produced undergoes crystal transformation to silicon carbide consisting of α-type crystals, so it is difficult to produce SiC efficiently. At least 80% by weight of SiC consisting of β-type crystals suitable as a raw material
This is because it is difficult to manufacture the silicon carbide contained therein. According to the present invention, C/SiO 2 of silica and carbon
When charging raw materials with a molar ratio within the range of 3.2 to 5.0 into a vertical indirect heating furnace having nitrogen gas charging means at the bottom and causing a SiC production reaction while lowering the interior of the indirect heating furnace by its own weight. , it is preferable to bring the nitrogen gas into countercurrent contact with the nitrogen gas charged from the charging means. The reaction formula of silicon carbide produced from silica and carbon is generally shown by the following formula (3). SiO 2 +3C→SiC+2CO……(3) However, the actual main generation mechanism is that SiO gas generated by the reaction of formula (1) above reacts with carbon according to formula (2) above. It is known that silicon carbide is produced by this process. By the way, according to the present invention, the nitrogen partial pressure in the furnace is 5
Maintained within ~200mmHg. Nitrogen in the furnace suppresses the reaction of formula (2), and the SiO
It has the effect of increasing the amount of gas. The SiO
As the gas amount increases, the following equation (4) in the preheating zone
The amount of mixed precipitates of SiO 2 , Si, SiC, C, etc. generated according to (5) and (6) increases, which impedes the smooth fall of the raw material, which is important in the continuous production of silicon carbide. This makes stable continuous operation over a long period of time difficult. 2SiO→SiO 2 +Si……(4) SiO+CO→SiO 2 +C……(5) 3SiO+CO→2SiO 2 +SiC……(6) Therefore, according to the present invention, the amount of carbon in the raw material is increased. It is desirable to increase the number of locations where the above formula (2) occurs by increasing the C/SiO 2 molar ratio from 3.2 to 5.0.
It is preferable to set it within the range of. The reason for this is that if the C/SiO 2 molar ratio is lower than 3.2, it is difficult to maintain the smooth weight fall of the raw material over a long period of time, as mentioned above, and on the other hand, if it is higher than 5.0, carbon that does not contribute to the reaction is heated to high temperatures. This is because the thermal efficiency decreases due to heating, and the cost required for the carbon raw material increases, so it is not economical. In addition, for the purpose of reducing the influence of precipitates in the preheating zone, the internal horizontal cross-sectional area of the upper part of the cylinder forming the preheating zone, as shown in Fig. 1, is calculated from the internal horizontal cross-sectional area of the heating zone. It is also advantageous to use a large vertical indirect heating furnace. Furthermore, in order to solve the above drawbacks, the average particle size of silica is set within the range of 75 to 250 μm, and the relationship between the average particle sizes of silica and carbon is adjusted so as to satisfy the following formula (7), Y ≦8.5×10 −2 RX+3.1×10 4 /T (7) It is advantageous to maintain the reaction rate between formulas (1) and (2) above within a suitable range. In the above formula, X is the average particle size of silica (μ
m), Y is the average particle diameter of carbon (μm), T is the reaction temperature (〓), and R is the C/C of silica and carbon in the starting materials.
SiO2 molar ratio. In addition, in the present invention, when charging raw materials from the upper part of a vertical indirect heating furnace having nitrogen gas charging means at the bottom and causing the SiC production reaction while lowering the inside of the heating furnace by its own weight, the charging means It is preferable to bring the nitrogen gas into countercurrent contact with the introduced nitrogen gas. This is because the SiC production reaction consisting of silica and carbon is as shown in equation (3) above, and a large amount of CO gas is produced as a result of the reaction, so when nitrogen gas is charged from the top of the furnace, the nitrogen gas is This is because the nitrogen gas is discharged together with the CO gas, making it difficult to efficiently bring the nitrogen gas into contact with the charge, and also making it extremely difficult to control the nitrogen partial pressure in the heating furnace. According to the present invention, in order to produce silicon carbide containing 0.015 to 0.20% by weight of nitrogen and in which at least 80% by weight of SiC is β-type crystal, the nitrogen partial pressure in the furnace and the reaction temperature are set as follows. It is advantageous to set the value within a range that satisfies relational expression (8). 3.3×10 -4 T 2 −1.35T+1384≦PN 2 ≦8.5×10 -4 T 2 −3.46T+3593 ………(8) In the above formula, PN 2 is the nitrogen partial pressure in the furnace
Hg), T is the reaction temperature (〓). Next, an example of a vertical indirect heating furnace that can be used in the method of the present invention will be described with reference to the drawings. The indirect heating furnace that can be used in the method of the present invention has a raw material charging port 1 and a preheating zone 2 as shown in FIG.
A reaction vessel 6 has a heating zone 3, a cooling zone 4, and a sealable product discharge port 5, which are connected in the vertical direction, and a cylinder 7 forming the heating zone is made of graphite. It is equipped with means 8 and 9 for indirectly electrically heating the charge in the heating zone, and a nitrogen gas charging port 10 is provided in the cooling zone at the bottom of the reaction vessel. The reaction vessel 6 is installed in the center of the indirect heating furnace, and the indirect heating means 8 and 9 are composed of a graphite heating element 8 and a graphite reflector tube 9 provided close to the outside of the heating element. A heat insulating layer 11 made of carbon or graphite fine powder is provided on the outside of the reflective cylinder. In the space surrounded by the cylinder forming the heating zone and the graphite reflector cylinder, for example, argon, helium, nitrogen, carbon monoxide,
Hydrogen and other non-oxidizing gases are sealed to prevent the graphite heating element from being consumed by oxidation due to air intrusion. Next, an example of a method for manufacturing a sintered body using the silicon carbide powder of the present invention will be described. A sintered body using the silicon carbide powder of the present invention has a boron-containing additive of 0.1 to 3.0 parts by weight in terms of boron content and fixed carbon content in terms of boron content of 100 parts by weight of the silicon carbide powder of the present invention. 0.1 to 3.0 parts by weight of a carbonaceous additive are added thereto and mixed homogeneously, and the homogeneously mixed mixture is formed into a formed body of any desired shape. It can be produced by sintering at 2050 to 2250°C in a gas atmosphere consisting of at least one selected from xenon and hydrogen. It is known that when producing a sintered body using β-type silicon carbide powder with a low nitrogen content, it is possible to create a sintered body containing nitrogen by setting the atmosphere to a nitrogen gas atmosphere. However, according to such a method, the nitrogen concentration distribution dissolved in the solid solution in the sintered body is non-uniform, so the sintered body lacks uniformity and its uses are limited. Examples of the present invention will be described below. Example 1 100 parts by weight of silica powder (SiO 2 = 99.7% by weight) with an average particle size of 153 μm, 76 parts by weight of petroleum coke powder (C = 98.7% by weight) with an average particle size of 29 μm, and silica powder with an average particle size of 43 μm 7 parts by weight of pitchch powder (C=50.4% by weight) was blended and mixed for 10 minutes using a vertical screw mixer. While spraying a 0.5% CMC aqueous solution onto the above-mentioned blended raw materials, the mixture is molded using a pan-type granulator, sized using a sieve and a burr grizzly, and then placed in a band-type ventilation dryer and dried with hot air at 150°C for 90 minutes. A molding raw material having an average particle diameter of 10.5 mm, a bulk specific gravity of 0.60 g/cm 3 and a C/SiO 2 molar ratio of 4.0 was obtained. This forming raw material is charged from the upper part of an indirect heating furnace having the structure shown in Fig. 1 and the specifications shown in Table 1, and the charged raw material is continuously lowered under its own weight to form a graphite cylinder. The temperature of the outer wall of the sample was controlled to 2150°C in a heating zone, and the SiC production reaction was carried out for about 1 hour by indirect electrical heating in the horizontal direction within the heating zone, and then lowered under its own weight into a cooling zone and discharged. The reaction product was continuously discharged from the outlet.
【表】【table】
【表】
前記炉内の窒素分圧は冷却帯に設けられた窒素
ガス装入口より窒素ガスを装入することによつて
制御し、100〜130mgHgの範囲内に維持した。
得られた反応生成物より遊離炭素及びSiO2を
除去精製したところ、窒素を0.06重量%含有し、
全SiCのうち88重量%がβ型結晶よりなる炭化珪
素粉末が得られた。
前記炭化珪素粉末をさらに粒度分級し、7μm
以上の粗粒を除去した。前記粒度分級した炭化珪
素粉末の特性は第2表に示した。
前記炭化珪素粉末98.7と市販の200メツシユ炭
化ホウ素粒を粉砕、粒度分級して比表面積を24.3
m2/gに調製した炭化ホウ素粉末1.3gと比表面
積123m2/gのカーボンブラツク1.5gとの混合物
に対し、水280mlと酢酸セルロース1.0gとモノエ
タノールアミン0.3gとを添加し、ボールミルに
て分散処理を行つた後、凍結乾燥を行つた。
この乾燥混合物から適量を採取し、金属製押し
型を用いて0.15t/cm2の圧力で円盤状に仮成形し
た。次にアイソスタテイツクプレス機を用いて
2.0t/cm2の圧力で成形した。前記生成形体との密
度は1.86g/cm3であることが認められた。
前記生成形体をタンマン型焼結炉に装入し、ア
ルゴンガス気流中で最高温度2100℃で30分間保持
することにより焼結させた。
得られた焼結体は3.05g/cm3の密度を有し、第
2図の走査型電子顕著鏡写真(750倍)に示した
如く約3〜7μmの均一な結晶粒よりなる微細構
造を有していることがわかつた。この焼結体を3
×3×30mmの棒状に加工し、最終的に3μmのダ
イヤモンド砥粒で研磨仕上げし、スパン20mm、ク
ロスヘツドスピード0.5mm/minの条件で3点曲
げ強度を測定したところ64Kg/mm2の平均強度を有
していた。
比較例 1
実施例1と同様の製造方法であるが、反応炉内
へ窒素ガスを送入することなく炭化珪素を製造し
た。反応炉内の窒素ガス分圧は0〜3mmHgであ
つた。得られた炭化珪素粉末の物性を第2表に示
す。この炭化珪素粉末を使用して実施例1と同様
の操作で焼結体を得た。
得られた焼結体の密度は2.83g/cm3と低く、ま
た3点曲げ強度も常温で48Kg/mm2の平均強度であ
つた。この焼結体は第3図の走査型電子顕微鏡写
真(750倍)に示した如く、粗大な板状結晶を含
んだ構造であつた。
実施例2、比較例2
実施例1と同様の製造方法であるが、炉内の窒
素ガス分圧および反応温度を変えて炭化珪素を製
造し、第2表に示した如くの物性を有する炭化珪
素粉末を得た。この炭化珪素粉末を使用して実施
例1と同様の操作で焼結体を得た。
得られた焼結体の物性を実施例1に示した方法
と同様の方法で測定し、その結果を第2表に示
す。[Table] The nitrogen partial pressure in the furnace was controlled by charging nitrogen gas from a nitrogen gas charging port provided in the cooling zone, and was maintained within the range of 100 to 130 mgHg. When the obtained reaction product was purified to remove free carbon and SiO2 , it contained 0.06% by weight of nitrogen,
A silicon carbide powder was obtained in which 88% by weight of the total SiC was composed of β-type crystals. The silicon carbide powder was further classified to a particle size of 7 μm.
The above coarse particles were removed. The characteristics of the silicon carbide powder subjected to particle size classification are shown in Table 2. The silicon carbide powder 98.7 and commercially available 200 mesh boron carbide particles were crushed and classified to have a specific surface area of 24.3.
To a mixture of 1.3 g of boron carbide powder prepared to m 2 /g and 1.5 g of carbon black with a specific surface area of 123 m 2 /g, 280 ml of water, 1.0 g of cellulose acetate, and 0.3 g of monoethanolamine were added, and the mixture was placed in a ball mill. After performing a dispersion treatment, freeze-drying was performed. An appropriate amount was taken from this dry mixture and temporarily formed into a disk shape using a metal mold at a pressure of 0.15 t/cm 2 . Next, using an isostatic press machine
It was molded at a pressure of 2.0t/cm 2 . The density of the resulting form was found to be 1.86 g/cm 3 . The formed body was placed in a Tammann type sintering furnace and sintered by holding it at a maximum temperature of 2100° C. for 30 minutes in an argon gas flow. The obtained sintered body had a density of 3.05 g/cm 3 and had a microstructure consisting of uniform crystal grains of about 3 to 7 μm, as shown in the scanning electron mirror photograph (750x magnification) in Figure 2. I found out that I have it. This sintered body is 3
It was processed into a rod shape of ×3 × 30mm, and finally polished with 3μm diamond abrasive grains.The three-point bending strength was measured under the conditions of a span of 20mm and a crosshead speed of 0.5mm/min, and the average was 64Kg/ mm2 . It had strength. Comparative Example 1 Silicon carbide was produced using the same manufacturing method as in Example 1, but without introducing nitrogen gas into the reactor. The nitrogen gas partial pressure in the reactor was 0 to 3 mmHg. Table 2 shows the physical properties of the obtained silicon carbide powder. Using this silicon carbide powder, a sintered body was obtained in the same manner as in Example 1. The density of the obtained sintered body was as low as 2.83 g/cm 3 , and the average three-point bending strength was 48 Kg/mm 2 at room temperature. This sintered body had a structure containing coarse plate-like crystals, as shown in the scanning electron micrograph (750x magnification) in Figure 3. Example 2, Comparative Example 2 Silicon carbide was produced using the same manufacturing method as in Example 1, but by changing the partial pressure of nitrogen gas in the furnace and the reaction temperature. Silicon powder was obtained. Using this silicon carbide powder, a sintered body was obtained in the same manner as in Example 1. The physical properties of the obtained sintered body were measured by the same method as shown in Example 1, and the results are shown in Table 2.
【表】【table】
【表】
第2表に示した如く、比較例2の窒素含有量の
多い炭化珪素炭化粉末を使用して得られた焼結体
は焼結収縮が劣化しており、2.90g/cm3と低密度
であつた。
以上述べた如く、本発明によれば、極めて微細
で均一な結晶構造よりなる炭化珪素焼結体を製造
することのできる炭化珪素微粉を安価にかつ容易
に供給でき、産業上に寄与する効果は極めて大き
い。[Table] As shown in Table 2, the sintered body obtained using the silicon carbide powder with a high nitrogen content of Comparative Example 2 had deteriorated sintering shrinkage of 2.90 g/ cm3 . It was low density. As described above, according to the present invention, it is possible to inexpensively and easily supply silicon carbide fine powder capable of producing a silicon carbide sintered body having an extremely fine and uniform crystal structure, and the effects contributing to industry are Extremely large.
第1図は、本発明の実施例および比較例におい
て炭化珪素を製造するのに使用した竪型連続製造
装置の縦断面図、第2図は実施例1に記載の焼結
体の走査型電子顕微鏡写真(750倍)、第3図は比
較例1に記載の焼結体の走査型電子顕微鏡写真
(750倍)である。
1……原料装入口、2……予熱帯、3……加熱
帯、4……冷却帯、5……生成物排出口、6……
反応容器、7……加熱帯を形成する筒、8……黒
鉛製発熱体、9……黒鉛製反射筒、10……窒素
ガス装入口、11……断熱層、12……非酸化性
ガス封入口、13……案内電極、14……可とう
導体、15……ブスバー、16……測温パイプ、
17……外殻、18……耐火煉瓦、20……排気
ダクト、19……原料ホツパー。
FIG. 1 is a longitudinal cross-sectional view of a vertical continuous manufacturing apparatus used to manufacture silicon carbide in Examples and Comparative Examples of the present invention, and FIG. Micrograph (750x) FIG. 3 is a scanning electron micrograph (750x) of the sintered body described in Comparative Example 1. 1... Raw material charging port, 2... Pre-preparation zone, 3... Heating zone, 4... Cooling zone, 5... Product discharge port, 6...
Reaction container, 7...Cylinder forming a heating zone, 8...Graphite heating element, 9...Graphite reflector tube, 10...Nitrogen gas charging port, 11...Insulating layer, 12...Non-oxidizing gas Sealing port, 13... Guide electrode, 14... Flexible conductor, 15... Bus bar, 16... Temperature measuring pipe,
17... Outer shell, 18... Firebrick, 20... Exhaust duct, 19... Raw material hopper.
Claims (1)
量%の酸素を含有し、不純物として、0.01〜3.0
重量%の遊離炭素、0.5重量%以下のアルミニウ
ム、0.01〜0.5重量%の鉄および0.01〜0.5重量%
のアルカリ金属、アルカリ土類金属を含有し、そ
して残部のSiCは、少なくともその80重量%がβ
型結晶よりなるものであつて、比表面積が5〜50
m2/gである焼結用炭化珪素粉末。 2 シリカ粉末と炭素粉末とを、シリカと炭素と
のモル比C/SiO2が3.2〜5.0となるような範囲内
で混合し、その後粒状に成形せしめてなる原料
を、間接加熱炉内の窒素ガス雰囲気のその中に装
入し、炉内の反応温度を1700〜2150℃の範囲内に
保持すると同時に窒素分圧を5〜200mmHgの範囲
内に維持しながら加熱することにより、 0.015〜0.20重量%の窒素および0.01〜1.0重量
%の酸素を含有し、不純物として、0.01〜3.0重
量%の遊離炭素、0.5重量%以下のアルミニウム、
0.01〜0.5重量%の鉄および0.01〜0.5重量%のア
ルカリ金属、アルカリ土類金属を含有し、そして
残部のSiCは、少なくともその80重量%がβ型結
晶よりなるものであつて、比表面積が5〜50m2/
gである焼結用炭化珪素粉末の製造方法。[Claims] 1 Contains 0.015 to 0.20% by weight of nitrogen and 0.01 to 1.0% by weight of oxygen, and contains 0.01 to 3.0% by weight of impurities.
wt% free carbon, 0.5 wt% or less aluminum, 0.01-0.5 wt% iron and 0.01-0.5 wt%
of alkali metals and alkaline earth metals, and the remaining SiC is at least 80% by weight of β
It is made of type crystal and has a specific surface area of 5 to 50
m 2 /g of silicon carbide powder for sintering. 2 Silica powder and carbon powder are mixed in such a range that the molar ratio C/SiO 2 of silica to carbon is 3.2 to 5.0, and then the raw material is formed into granules, and the raw material is heated with nitrogen in an indirect heating furnace. By charging it into a gas atmosphere and heating it while maintaining the reaction temperature in the furnace within the range of 1700 to 2150°C and at the same time maintaining the nitrogen partial pressure within the range of 5 to 200 mmHg, 0.015 to 0.20 weight % nitrogen and 0.01-1.0 wt% oxygen, as impurities, 0.01-3.0 wt% free carbon, not more than 0.5 wt% aluminum,
The SiC contains 0.01 to 0.5% by weight of iron and 0.01 to 0.5% by weight of alkali metals and alkaline earth metals, and the remaining SiC is composed of at least 80% by weight of β-type crystals and has a specific surface area of 5~ 50m2 /
A method for producing silicon carbide powder for sintering, which is g.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP56126634A JPS5832007A (en) | 1981-08-14 | 1981-08-14 | Silicon carbide powder for sintering use and its preparation |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP56126634A JPS5832007A (en) | 1981-08-14 | 1981-08-14 | Silicon carbide powder for sintering use and its preparation |
Publications (2)
Publication Number | Publication Date |
---|---|
JPS5832007A JPS5832007A (en) | 1983-02-24 |
JPH0152325B2 true JPH0152325B2 (en) | 1989-11-08 |
Family
ID=14940043
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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JP56126634A Granted JPS5832007A (en) | 1981-08-14 | 1981-08-14 | Silicon carbide powder for sintering use and its preparation |
Country Status (1)
Country | Link |
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JP (1) | JPS5832007A (en) |
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JP6304477B2 (en) * | 2013-09-04 | 2018-04-04 | 太平洋セメント株式会社 | Silicon carbide powder and method for producing the same |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS54134100A (en) * | 1978-04-11 | 1979-10-18 | Toshiba Ceramics Co | Manufacture of beta type silicon carbide powder |
JPS5684310A (en) * | 1979-12-14 | 1981-07-09 | Hiroshige Suzuki | Manufacture of betaatype silicon carbide |
-
1981
- 1981-08-14 JP JP56126634A patent/JPS5832007A/en active Granted
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS54134100A (en) * | 1978-04-11 | 1979-10-18 | Toshiba Ceramics Co | Manufacture of beta type silicon carbide powder |
JPS5684310A (en) * | 1979-12-14 | 1981-07-09 | Hiroshige Suzuki | Manufacture of betaatype silicon carbide |
Also Published As
Publication number | Publication date |
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JPS5832007A (en) | 1983-02-24 |
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