JP4927292B2 - Alumina ceramics with excellent wear and corrosion resistance - Google Patents

Alumina ceramics with excellent wear and corrosion resistance Download PDF

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JP4927292B2
JP4927292B2 JP2002124672A JP2002124672A JP4927292B2 JP 4927292 B2 JP4927292 B2 JP 4927292B2 JP 2002124672 A JP2002124672 A JP 2002124672A JP 2002124672 A JP2002124672 A JP 2002124672A JP 4927292 B2 JP4927292 B2 JP 4927292B2
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alumina
wear
corrosion resistance
particle size
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JP2003321270A (en
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宏司 大西
一代 乾
利夫 河波
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Nikkato Corp
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Nikkato Corp
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Description

【0001】
【発明の属する技術分野】
本発明は、耐摩耗性および耐食性を有するアルミナ質セラミックス、特に、耐摩耗性部材材料として有用な耐摩耗性および耐食性を有するアルミナ質セラミックスに関するものである。
【0002】
【従来の技術】
セラミックスは、金属と比べて耐摩耗性および耐食性に優れたものであり、従来、金属が使用されていた耐摩耗部材として、セラミックスが使用されている。この様な耐摩耗部材として用いるセラミックスとしては、アルミナ、ジルコニア、窒化珪素、炭化珪素等が使用されているが、その中でもアルミナは硬度が高く、耐食性に優れ、他のセラミックスに比べて安価であることから広く使用されるようになってきた。しかしながら、従来の耐摩耗性アルミナセラミックスとしては、アルミナ含有量が90〜92重量%程度のものが主として用いられているが、不純物を多く含有するために、アルミナ結晶以外にガラス相や第2相を多く含むものとなり、高温下あるいは腐食雰囲気中などにおける使用では粒界のガラス相が腐食されて摩耗特性が大幅に低下することから、このような条件下では耐摩耗性部材として満足して使用することはできなかった。
そこで、例えば、特開昭62−187157号公報に示されているように、アルミナ含有量を99.9%以上とすることで、ガラス相等のアルミナ結晶以外の第2相量をほとんど含有しない高強度、高硬度としたアルミナ質セラミックスが開発されているが、高純度のアルミナ原料を使用するため、その精製精度を上げる必要からコストが非常に高くなるという問題点を有している。
また、従来のアルミナ質セラミックスでは、Alの含有量が99%以上になると焼結助剤その他の添加剤の量が制限されるため、焼結性が低下するため高温で焼成しなければならず、そのために結晶粒径が大きくなり、また焼成温度によっては結晶粒径分布が広くなりやすく、充分な耐摩耗性が得られないという問題点があった。
【0003】
【発明が解決しようとする課題】
本発明者等は、特にその精製精度を上げることなく、安価な原料を用いて優れた耐摩耗性と耐食性を有するアルミナ質セラミックスを提供することを目的とする。
【0004】
【課題を解決するための手段】
本発明者は、上記した如き従来技術の問題点に鑑みて、安価な原料を用いて優れた耐摩耗性と耐食性を有するアルミナ質セラミックスを得るべく鋭意研究を重ねてきた。その結果、アルミナ質セラミックスにおいて、焼結助剤の組成を一定の範囲にすると共に、その焼結助剤を均一に混合・分散することで、焼結性を向上させ、且つ、微細構造が均一な焼結体を得ることができ、焼結体の結晶粒径および密度を一定の範囲の値となるように制御されたアルミナ質セラミックスは、極めて優れた耐摩耗性だけでなく耐食性をも有するものとなることを見出し、ここに本発明を完成するに至った。
【0005】
本発明の第1は、純度が99.7%以上、比表面積が3m /g以上、平均粒径2μm以下のアルミナ原料を使用し、平均粒径0.3〜0.7μmの微粉末を所定形状に成形して大気中1350〜1650℃で焼成することを特徴とする、主としてAlからなり、SiO20〜90重量%、MgO0〜70重量%およびCaO10〜80重量%の三成分からなる焼結助剤の各成分を合計量として0.2〜0.8重量%含有し、残部として実質的に不可避的不純物が0.3重量%以下である、平均結晶粒径0.5〜5.0μmで結晶粒径の最大値が15μm以下、かさ密度3.70g/cm以上、鏡面仕上げ面での欠陥量が5%以下、粉砕用ボールとしての摩耗率が0.2%/h以下の耐摩耗性および耐食性を有するアルミナ質セラミックスに関する。
本発明の第2は、前記不可避的不純物として含まれるアルカリ金属酸化物が0.1重量%以下、TiOが0.05重量%以下であることを特徴とする請求項1に記載の耐摩耗性および耐食性を有するアルミナ質セラミックスに関する。
【0006】
即ち、本発明は、SiO20〜90重量%、MgO0〜70重量%およびCaO10〜80重量%の三成分からなる焼結助剤を用いることによって、焼結性が向上し、粒成長の抑制、結晶粒径の均一性が達成される。また、アルミナ結晶粒界強度を高めることができるため、靱性の向上にも効果がある。使用する焼結助剤は上記組成のSiO、MgOおよびCaOの三成分からなることが必要であり、組成割合がこの範囲から外れると焼結性が低下したり、異常粒成長を起こしやすく、また焼結体中にアルミナ以外の結晶やガラス相が多く生成して、硬さ、強度、靱性等の低下による耐摩耗性の低下や耐食性の劣化をきたすので好ましくない。この組成割合は、好ましくはSiO25〜85量%、MgO0〜60重量%およびCaO15〜75重量%、より好ましくはSiO30〜80量%、MgO0〜50重量%およびCaO20〜70重量%である。
【0007】
得られる焼結体中では前記焼結助剤の各成分を前記した組成比率の範囲内で含有すると共に、各成分の合計量が焼結体中0.2〜0.8重量%であることが必要である。この合計量が0.2重量%未満の場合には、焼結性が悪くなり、欠陥量が増え、硬さ、強度等が低下するので好ましくなく、0.8重量%を越えると、アルミナ結晶以外の結晶やガラス相が多く生成するので好ましくない。
【0008】
アルミナ質セラミックスの原料には通常、不可避的不純物、例えば、Fe、NaO、KOおよびTiO等が含まれるが、不可避的不純物のうちアルカリ金属酸化物およびTiOはガラス相や第2相を生成したり異常粒成長をきたすので、不可避的不純物の含有量が可能な限り少ないものを使用する必要があり、焼結体中の不可避的不純物は0.3重量%以下、好ましくは0.1重量%以下である。特に、NaOおよびKOはSiO等と容易にガラス相を形成するため、アルカリ金属酸化物の含有量は0.1重量%以下、好ましくは0.08重量%以下、より好ましくは0.05%以下に、またTiOは結晶成長を促進させたり異常粒成長の原因となることから、その含有量は0.05重量%以下、好ましくは0.02重量%以下、より好ましくは0.01重量%以下になるように原料を選択して配合される。
【0009】
焼結体の平均結晶粒径は0.5〜5.0μmである。本発明は結晶粒径を小さくかつ均一にすることによって耐摩耗性に優れたアルミナセラミックスが得られることが明らかで、0.8〜3.0μmが好ましい。平均結晶粒径が0.5μmを下回る場合は、靱性の低下が起こり結果的に耐摩耗性の低下につながり、また耐食性も低下するため好ましくない。また、平均結晶粒径が5.0μmを越えると硬さが低下し、また、大きい結晶粒子より摩耗が優先的に起こり、粒離脱摩耗による損耗が大きくなり耐摩耗性の低下をきたすため好ましくない。また、耐チッピング性が問題となる場合には耐摩耗性とのバランスを考慮して0.5〜5.0μmの範囲内で適宜設定すればよい。また、焼結体を構成する結晶粒子の最大径が15μmを越える場合には結晶粒径分布が広く、硬度の低下が起こり、その結果、耐摩耗性の低下につながるので好ましくなく、最大径が15μm以下、より好ましくは10μm以下が好適である。
本発明の平均結晶粒径は焼結体を鏡面仕上げし、これを熱エッチングし、走査電子顕微鏡にて視野に結晶が100個以上観察できる倍率で観察して写真撮影し、その写真からインターセプト法により10点平均から求める。算出式としてはD=1.5×L/n〔D:平均結晶粒径(μm)、L:測定長さ(μm)、n:長さLあたりの結晶数〕を用いる。最大径は100個の粒子のうち最も大きい粒子の長径とする。
【0010】
かさ密度を3.70g/cm以上としたのは、かさ密度が3.70g/cm未満の場合、焼結度が不十分であると共に欠陥となるポアーが多く存在することになり、強度、硬度および靱性の低下を引き起こすだけでなく、このポアーが起点となって摩耗を促進するので好ましくない。かさ密度はより好ましくは3.80g/cm以上とする。
【0011】
また、かさ密度が所定の範囲であってもかさ密度に現れない欠陥が存在する場合があり、その欠陥量は、セラミックスの耐摩耗性に非常に大きな影響を与えるため、鏡面仕上げ面での欠陥量は5%以下が好ましい。これは、欠陥量が5%を越えるとこれらの欠陥が摩耗の起点となって摩耗が促進され、耐摩耗性の低下を招くと同時に耐衝撃強度の低下が起こるので好ましくなく、また、耐食性の低下をきたすからである。この欠陥量は、好ましくは3%以下、より好ましくは2%以下が好適である。
本発明において、セラミックスの欠陥量とは、平面研削盤を用いてセラミックスを下記条件により研削加工した後、研磨加工して鏡面仕上げし、その鏡面仕上げした面(通常500倍)を走査電子顕微鏡で写真撮影を行い、その写真を画像解析にて欠陥部分と欠陥でない部分とを二値化により分離して、その欠陥部分が画像全体に占める面積の割合、即ち、面積率(%)をいう。この欠陥部分には、気孔だけでなく、焼結体の研削および研磨加工して鏡面仕上げする際に発生する脱粒の後、および焼結体のかさ密度値に影響を与えないレベルの欠陥も含まれる。
【0012】
前記鏡面仕上げは、平面研削盤とレジンボンドタイプのダイヤモンド砥石を用い、まず、粒度#140のダイヤモンド砥石で、その砥石の周速を1500m/sec、切り込み深さを8μm、被研削物であるセラミックス(以下、ワークという。)の左右の送り速度(以下、ワーク速度という。)を17m/secとして約80μm研削した後、切込みを止めて砥石を5往復させ、次に砥石を#400のダイヤモンド砥石に取り替え、周速1500m/sec、切込み深さを5μm、ワーク送り13m/secの条件下で約50μm研削した後、切込みを止めて砥石を10往復させ、更に砥石を#600のダイヤモンド砥石に取り替え、周速1500m/sec、切込み深さを2μm、ワーク送り10m/secの条件下で約20〜30μm研削した後、切込みを止めて砥石を15往復させることにより研削を行い、その後、研削加工したセラミックスの研削面に、40μmのダイヤモンド砥粒を埋め込んだダイヤモンドパッドを2.6kgf/cmで加圧して3分研磨し、更に6μmのダイヤモンド砥粒で2.6kgf/cmに加圧して5分研磨した後、3μmのダイヤモンド砥粒で2.6kgf/cmに加圧して15分間研磨し、最後に1μmのダイヤモンド砥粒で1.3kgf/cmに加圧して5分研磨することにより行う。
【0013】
本発明の試料の粉砕用ボールとしての摩耗率は0.2%/h以下である。摩耗率がこれ以上になると粉砕用ボール等粉砕用部材として用いた場合、被粉砕物への摩耗粉混入量が増加し得られた焼結体特性に問題が生じる危険性があるため好ましくない。また、ベアリングあるいは半導体用部材などの耐摩耗部材として用いた場合にも、上記摩耗率を超えると使用中に摩耗が大きくなり装置に支障をきたす可能性があるため好ましくない。
本発明における粉砕用ボールとしての摩耗率は以下に示す測定方法により求めた摩耗率が0.2%/h以下であると定義する。粉砕機として三井三池製アトライター(MA−01S)を用い、容量650mlのアルミナ製〔純度99.9%、(株)ニッカトー製SSA−999W〕タンク中にボール表面をバレル研磨したφ2mmの粉砕用ボールを400ml投入し、更に平均粒子径10μm、比表面積1.2m/gのアルミナ粉末200gおよび水200mlを入れてジルコニア製〔(株)ニッカトー製YTZ〕アームにて回転数400rpmで24時間摩耗テストし、下式により摩耗率を求める。
摩耗率={〔(Wb−Wa)/Wb〕×100}/24
(Wa:テスト後のボール重量 Wb:テスト前のボール重量)
【0014】
また、本発明は、前記アルミナ質セラミックスの焼結性の向上、強度および靱性を一段と向上させると共に、その微細構造組織をより均一化するため、前記成分組成からなる基本組成物100重量部に対してZrOを15重量部以下、好ましくは10重量部以下、より好ましくは8重量部以下含有させることができる。
その添加量が基本組成物100重量部に対して15重量部を越えると、硬度の低下を生じ、特に安定化剤の添加されていないZrO粉体を用いると焼結体に単斜晶系ジルコニアが存在しやすくなり、マイクロクラックの発生が起こって耐摩耗性の低下につながるので好ましくない。
この場合、添加するZrO原料はその平均粒子径が1.0μm以下のものを使用するのが好適である。これはZrO原料の平均粒子径が1.0μmを越えると、焼結体に単斜晶系ジルコニアが存在しやすくなり、マイクロクラックの発生が起こって耐摩耗性、耐衝撃性の低下につながるので好ましくない。
また、ZrO原料としては、希土類元素酸化物等の安定化剤を固溶させたものを用いることもできる。この場合、希土類元素酸化物、例えばYを安定化剤として含むZrO原料の場合、Yの含有量は5モル%以下のものを使用するのが好ましく、これによりジルコニアの応力誘起変態効果により靱性の向上を図ることができる。
【0015】
更に本発明は原料粉末を所定の割合で配合し、その混合物を平均粒径0.3〜0.7μm、比表面積5〜14m/gに粉砕し、得られた粉末を所定形状に成形し、大気中1350〜1650℃で焼成することにより、優れた耐摩耗性および耐食性を有するアルミナ質セラミックスからなる成形物を提供することができる。粉砕後の粒度が0.3μm以下であると成形性が低下し、その結果、焼結体中に欠陥が多く含有し耐摩耗性および耐食性の低下をもたらすので好ましくない。また、0.7μmを越えると焼結性の低下をもたらし、焼結体に欠陥を生じやすいため好ましくない。粉砕後の平均粒径は0.3〜0.5μm、比表面積は7〜12m/gがより好ましい。また、焼成温度としては1400〜1600℃がより好ましい。
【0016】
本発明の耐摩耗性および耐食性を有するアルミナ質セラミックスは以下に示す方法で製造できる。アルミナ原料はアルミナ純度が99.7%以上、比表面積が3m/g以上、平均粒径2μm以下の原料を使用する。使用するアルミナ原料は明礬法から作られた原料でも良いが、バイヤー法アルミナ原料を使用することが好ましく、安価に作ることができる。
焼結助剤の原料としては平均粒径0.5μm以下、純度98%以上のMgOおよびCaO原料もしくは水酸化物、炭酸化物の塩を使用することが可能である。SiOは珪石、石英をはじめシリカゾル、エチルシリケート等の塩も使用でき、更にはカオリン等の粘土鉱物を用いても良い。これら原料を所定量アルミナ原料に添加し粉砕・混合・分散しても良いが、MgO、CaOおよびSiO原料を先に混合し、次いで熱処理することによって、更に均一に分散することが可能となり、焼結性の向上、結晶粒径の微細化および組織の均一化がはかれ、より耐摩耗性にすぐれた焼結体を得ることができる。
熱処理した焼結助剤を用いる場合は、MgO、CaOおよびSiO原料を所定量になるよう水もしくは有機溶媒中で湿式によってポットミル、アトリッションミル等の粉砕機で粉砕、混合し、900℃〜1300℃にて熱処理することによって熱処理した焼結助剤を作製する。900℃以下では熱処理の効果が現れず、アルミナ原料に助剤原料を単体で添加した場合と大差が見られない。また、1300℃を越えた場合には熱処理した焼結助剤の結合が強固で、助剤として添加した場合に粉砕・分散が充分に行えないため好ましくなく、1000℃から1200℃で加熱処理することがより好ましい。
【0017】
アルミナ原料に所定のMgO、CaO、SiOおよびZrO量となるように、上記熱処理した焼結助剤あるいは各焼結助剤原料と必要に応じZrO原料を添加し、水もしくは有機溶媒中で湿式によってポットミル、アトリッションミル等の粉砕機で粉砕、混合、分散する。得られた粉体の平均粒径は0.3〜0.7μm以下、比表面積は5〜14m/gにする必要がある。得られたスラリーにバインダーとしてポリビニルアルコール(PVA)、アクリル樹脂およびパラフィンワックスエマルジョン等を添加してスプレードライヤーにて乾燥・造粒して成形用粉体とする。次いでこの粉体を用いてセラミックスの製造における常法に従って金型プレス、冷間静水圧成形(CIP)等により所定の形状に成形する。これらの成形方法以外に鋳込み成形、押出成形、射出成形、造粒成形等の成形方法によっても成形できる。得られた成形体を1350℃〜1650℃、好ましくは1400℃〜1600℃の温度で焼成し耐摩耗性および耐食性アルミナ質セラミックスとする。
【0018】
本発明の耐摩耗性アルミナセラミックスは、耐摩耗性および耐食性に優れるため、粉砕用メディア、ケージミル用部材、内張材、粉砕用容器、ノズル、ローラ、ゲージ、ベアリング(軸受部品)および半導体用治具等の耐摩耗部材として最適である。
【0019】
【実施例】
以下に実施例を挙げて本発明を説明するが、本発明はこれにより何ら限定するものではない。
【0020】
実施例1
各原料を表1に示す組成の焼結体が得られるように配合し、得られた混合物を92%アルミナ製〔(株)ニッカトー製HD〕ポットミル(内容積7.2リットル)とφ10mmの92%アルミナ製〔(株)ニッカトー製HD−11〕ボールを用いて濃度50%で24〜72時間湿式粉砕し、表2に示す平均粒径を有し比表面積が5m/g以上の微粉末を含むスラリーを得た。得られたスラリーにポリビニルアルコール水溶液を3〜5重量%バインダとして添加して、粘度を300cps以下に調整し、これをスプレードライヤーにて乾燥・造粒し成形用粉体を得た。続いてこの粉体を造粒成形にて球状に成形し、1300℃〜1700℃で焼成して、φ2mmのボールとし、次いでこのボールの表面をバレル研磨して粉砕用ボールとした。また、耐食性評価のため、成形用粉体をCIP1tonf/cm成形し、粉砕用ボールと同様に焼成して10×10×3mmの焼結体を作製し、鏡面仕上げして評価用サンプルとした。
【0021】
アルミナ原料としては、試料No.17、18は平均粒径が2μm、比表面積3m/g、純度99.7%のバイヤー法により作製されたローソーダアルミナ原料を、それ以外の試料は平均粒径1μm、比表面積5m/g、純度99.8%のリアクティブアルミナ原料を用いた。
助剤原料としては、MgOおよびCaOの原料として純度99.5%の炭酸塩を使用し、SiOの原料としては珪石を使用した。更に、ZrOの原料としては試料No.3,4および14については平均粒径1.0μm、比表面積12m/g、純度99.9%の二酸化ジルコニウムを用い、試料No.2についてはYを3.0モル%含有する平均粒径0.5μm、比表面積15m/gの二酸化ジルコニウムを用いた。
【0022】
試料No.2、7〜9、13〜16および21については、配合した助剤原料をポットミルで24時間湿式混合し、乾燥後900℃〜1300℃で熱処理した後、上記アルミナ原料と配合し、試料No.2および14については更にZrO原料を配合した。また、試料No.3および4については助剤原料とアルミナ原料およびZrO原料を配合した。これら配合した原料をポットミルで所定の粒度となるように湿式粉砕を行い、次いでPVAを加えた後、スプレードライヤーにて乾燥・造粒し成形用粉体を得た。続いてこの粉体を造粒成形にて球状に成形し、1300℃〜1700℃で焼成して、φ2mmのボールとし、次いでこのボールの表面をバレル研磨して粉砕用ボールとした。また、耐食性評価のため、成形用粉体をCIP1tonf/cm成形し、粉砕用ボールと同様に焼成して10×10×3mmの焼結体を作製し、鏡面仕上げして評価用サンプルとした。
【0023】
得られた粉砕用ボールを下記の測定方法により摩耗率を求めた。粉砕機として三井三池製アトライター(MA−01S)を用い、容量650mlのアルミナ製〔純度99.9%、(株)ニッカトー製SSA−999W〕タンク中にボール表面をバレル研磨したφ2mmの粉砕用ボールを400ml投入し、更に平均粒子径10μm、比表面積1.2m/gのアルミナ粉末200gおよび水200mlを入れてジルコニア製〔(株)ニッカトー製YTZ〕アームにて回転数400rpmで24時間摩耗テストし、下式により摩耗率を求める。
摩耗率={〔(Wb−Wa)/Wb〕×100}/24
(Wa:テスト後のボール重量 Wb:テスト前のボール重量)
また、これら試料の耐食性は下記の方法で評価した。鏡面仕上げを行った10×10×3mmのサンプルを容量70mlの圧力分解容器に入れ、30mlのHSO溶液(濃度20%)中で150℃−48h保持し、サンプルの表面積に対する重量減で評価した。これらの結果を、粉砕用ボールのかさ密度、結晶粒径、欠陥量、並びに粉砕粉体の平均粒径および焼成温度と共に表2に示す。
【0024】
【表1】

Figure 0004927292
【0025】
【表2】
Figure 0004927292
【0026】
表1中のZrO量はアルミナ、焼結助剤および不可避的不純物からなる基本組成物100重量部に対する添加量(重量部)で示してある。表2中の耐食性評価結果はAが0.24mg/cm/day以下で優秀、Bが2.4mg/cm/day以下で良好、Cが7.2mg/cm/day以下で十分、Dが24mg/cm/day以下で劣ることを示す。また、表1および表2中の試料No.1〜10の焼結体は本発明の条件を満足するものであり、試料No.11〜22は本発明において規定する条件を少なくとも1つを満たしていない本発明の範囲外のものである。
本発明の試料の摩耗率は0.2%/h以下とすぐれた摩耗特性を示し、また耐食性にも非常にすぐれていた。
【0027】
【発明の効果】
本発明は、原料としてのアルミナの精製精度を特に高くする必要もなく、優れた耐摩耗性と耐食性を有するアルミナ質セラミックスを提供することができた。[0001]
BACKGROUND OF THE INVENTION
The present invention is alumina ceramics having abrasion resistance and corrosion resistance, and in particular relates to alumina ceramics having useful wear resistance and corrosion resistance as the wear resistant member material.
[0002]
[Prior art]
Ceramics are superior in wear resistance and corrosion resistance compared to metals, and ceramics are conventionally used as wear-resistant members for which metals have been used. As ceramics used as such wear-resistant members, alumina, zirconia, silicon nitride, silicon carbide, etc. are used. Among them, alumina has high hardness, excellent corrosion resistance, and is inexpensive compared to other ceramics. It has come to be widely used. However, as conventional wear-resistant alumina ceramics, those having an alumina content of about 90 to 92% by weight are mainly used. However, since they contain a large amount of impurities, in addition to alumina crystals, a glass phase or a second phase is used. When used at high temperatures or in corrosive atmospheres, the glassy phase at the grain boundaries is corroded and the wear characteristics are greatly reduced. I couldn't.
Therefore, for example, as disclosed in JP-A-62-187157, by setting the alumina content to 99.9% or more, a high amount of the second phase other than alumina crystals such as a glass phase is hardly contained. Alumina ceramics with high strength and high hardness have been developed. However, since a high-purity alumina raw material is used, there is a problem that the cost is very high because it is necessary to increase the purification accuracy.
Also, in the conventional alumina ceramics, if the content of Al 2 O 3 is 99% or more, the amount of sintering aid and other additives is limited, so that the sinterability is reduced, so it must be fired at a high temperature. For this reason, there is a problem that the crystal grain size becomes large, and the crystal grain size distribution tends to be widened depending on the firing temperature, so that sufficient wear resistance cannot be obtained.
[0003]
[Problems to be solved by the invention]
The present inventors have in particular without increasing the purification accuracy, and to provide a alumina ceramics having excellent wear resistance and corrosion resistance by using inexpensive raw materials.
[0004]
[Means for Solving the Problems]
In view of the problems of the prior art as described above, the present inventor has intensively studied to obtain an alumina ceramic having excellent wear resistance and corrosion resistance using an inexpensive raw material. As a result, in alumina ceramics, the composition of the sintering aid is kept within a certain range, and the sintering aid is uniformly mixed and dispersed to improve the sinterability and the microstructure is uniform. Alumina ceramics whose crystal grain size and density are controlled to be within a certain range can have not only extremely excellent wear resistance but also corrosion resistance. As a result, the present invention has been completed.
[0005]
The first of the present invention uses an alumina raw material having a purity of 99.7% or more, a specific surface area of 3 m 2 / g or more, and an average particle size of 2 μm or less, and a fine powder having an average particle size of 0.3 to 0.7 μm. It is mainly composed of Al 2 O 3 and is formed into a predetermined shape and fired at 1350 to 1650 ° C. in the atmosphere, and is composed of 20 to 90% by weight of SiO 2 , 0 to 70% by weight of MgO and 10 to 80% by weight of CaO. Each component of the sintering aid consisting of the components is contained in a total amount of 0.2 to 0.8% by weight, and the balance is substantially inevitable impurities of 0.3% by weight or less. the maximum value of the crystal grain size of 15μm or less in 5~5.0Myuemu, bulk density 3.70 g / cm 3 or more, defects of a mirror finished surface is less than 5%, the wear rate of the powder砕用ball 0.2 % / h or less alumina cell having abrasion resistance and corrosion resistance under It is about ramix.
The second aspect of the present invention is the wear resistance according to claim 1, wherein the alkali metal oxide contained as the inevitable impurities is 0.1% by weight or less and TiO 2 is 0.05% by weight or less. The present invention relates to an alumina ceramic having heat resistance and corrosion resistance.
[0006]
That is, in the present invention, by using a sintering aid composed of three components of SiO 2 20 to 90 wt%, MgO 0 to 70 wt% and CaO 10 to 80 wt%, the sinterability is improved and the grain growth is suppressed. Uniformity of the crystal grain size is achieved. Moreover, since the alumina grain boundary strength can be increased, it is effective in improving toughness. The sintering aid to be used is required to be composed of three components of SiO 2 , MgO and CaO having the above composition, and if the composition ratio is out of this range, the sinterability is lowered or abnormal grain growth is likely to occur. In addition, a large number of crystals and glass phases other than alumina are produced in the sintered body, which causes a decrease in wear resistance and corrosion resistance due to a decrease in hardness, strength, toughness, etc., which is not preferable. The composition ratio is preferably SiO 2 25 to 85 weight%, MgO0~60 wt% and CaO15~75 wt%, more preferably SiO 2 30 to 80 weight%, in MgO0~50% and CaO20~70 wt% is there.
[0007]
In the obtained sintered body, each component of the sintering aid is contained within the range of the composition ratio described above, and the total amount of each component is 0.2 to 0.8 % by weight in the sintered body. is required. If the total amount is less than 0.2 wt%, sinterability is deteriorated, increased amount of defects, hardness, it is not preferable because the strength and the like decreases, exceeds 0.8 wt%, alumina crystal Since many crystals and glass phases other than the above are generated, it is not preferable.
[0008]
The raw materials for alumina ceramics usually contain unavoidable impurities such as Fe 2 O 3 , Na 2 O, K 2 O and TiO 2, and among the unavoidable impurities, alkali metal oxides and TiO 2 are glass. It is necessary to use an inevitable impurity content that is as low as possible because it generates a phase or a second phase or causes abnormal grain growth, and the inevitable impurity in the sintered body is 0.3% by weight or less. The content is preferably 0.1% by weight or less. In particular, since Na 2 O and K 2 O easily form a glass phase with SiO 2 or the like, the content of the alkali metal oxide is 0.1% by weight or less, preferably 0.08% by weight or less, more preferably 0.05% or less, and since TiO 2 promotes crystal growth or causes abnormal grain growth, its content is 0.05% by weight or less, preferably 0.02% by weight or less, more preferably The raw materials are selected and blended so as to be 0.01% by weight or less.
[0009]
The average crystal grain size of the sintered body is 0.5 to 5.0 μm. In the present invention, it is clear that alumina ceramics excellent in wear resistance can be obtained by making the crystal grain size small and uniform, and 0.8 to 3.0 μm is preferable. When the average crystal grain size is less than 0.5 μm, the toughness is reduced, resulting in a decrease in wear resistance, and the corrosion resistance is also lowered. Further, when the average crystal grain size exceeds 5.0 μm, the hardness is decreased, and wear is preferentially performed over larger crystal grains, and wear due to grain detachment wear is increased, resulting in a decrease in wear resistance. . Further, when chipping resistance becomes a problem, it may be appropriately set within the range of 0.5 to 5.0 μm in consideration of the balance with wear resistance. In addition, when the maximum diameter of the crystal grains constituting the sintered body exceeds 15 μm, the crystal grain size distribution is wide and the hardness decreases, resulting in a decrease in wear resistance. It is preferably 15 μm or less, more preferably 10 μm or less.
The average crystal grain size of the present invention is that the sintered body is mirror-finished, thermally etched, photographed by observing with a scanning electron microscope at a magnification capable of observing 100 or more crystals in the field of view, and an intercept method from the photograph. From the average of 10 points. As a calculation formula, D = 1.5 × L / n [D: average crystal grain size (μm), L: measurement length (μm), n: number of crystals per length L] is used. The maximum diameter is the longest diameter of the largest particle among 100 particles.
[0010]
The bulk density was set to 3.70 g / cm 3 or more when the bulk density was less than 3.70 g / cm 3 and the degree of sintering was insufficient and many pores were present as defects. In addition to causing a decrease in hardness and toughness, this pore is the starting point and promotes wear. The bulk density is more preferably 3.80 g / cm 3 or more.
[0011]
In addition, there may be defects that do not appear in the bulk density even if the bulk density is within the specified range, and the amount of the defect has a very large effect on the wear resistance of the ceramics. The amount is preferably 5% or less. This is not preferable because if the amount of defects exceeds 5%, these defects become the starting point of wear, which promotes wear and causes a decrease in wear resistance and at the same time a decrease in impact strength. This is because it causes a decline. The amount of defects is preferably 3% or less, more preferably 2% or less.
In the present invention, the ceramic defect amount means that a ceramic is ground using a surface grinder under the following conditions, then polished and mirror-finished, and the mirror-finished surface (usually 500 times) is scanned with a scanning electron microscope. A photograph is taken, and a defective part and a non-defect part are separated by binarization by image analysis, and the ratio of the area occupied by the defective part in the entire image, that is, the area ratio (%). This defect includes not only pores but also defects that do not affect the bulk density value of the sintered body after grain removal that occurs when the sintered body is mirror-finished by grinding and polishing. It is.
[0012]
For the mirror finish, a surface grinder and a resin bond type diamond grindstone are used. First, a diamond grindstone with a grain size of # 140, the peripheral speed of the grindstone is 1500 m / sec, the cutting depth is 8 μm, and the ceramic to be ground. (Hereinafter referred to as workpiece) The left and right feed speed (hereinafter referred to as workpiece speed) is set at 17 m / sec and grinding is performed for about 80 μm, then the incision is stopped and the grindstone is reciprocated 5 times, and then the grindstone is # 400 diamond grindstone After grinding about 50 μm under the conditions of a peripheral speed of 1500 m / sec, a cutting depth of 5 μm, and a workpiece feed of 13 m / sec, the cutting was stopped and the grindstone was reciprocated 10 times. , Grinding about 20-30μm under conditions of peripheral speed 1500m / sec, cutting depth 2μm, workpiece feed 10m / sec And then performs grinding by 15 reciprocate grindstone stop notches, then, on the grinding surface of the grinding the ceramic, pressurizes the diamond pads embedded diamond abrasive grains 40μm at 2.6 kgf / cm 2 3 minutes polished, further after polishing 5 minutes pressurized to 2.6 kgf / cm 2 with diamond abrasive grains 6 [mu] m, and pressurized to 2.6 kgf / cm 2 at 3μm of diamond abrasive grains and polishing 15 min and finally And pressurizing to 1.3 kgf / cm 2 with 1 μm diamond abrasive and polishing for 5 minutes.
[0013]
The wear rate of the sample of the present invention as a grinding ball is 0.2% / h or less. When the wear rate is higher than this, when used as a pulverizing member such as a pulverizing ball, the amount of wear powder mixed into the material to be pulverized increases, which may cause a problem in the characteristics of the sintered body, which is not preferable. Further, even when used as a wear-resistant member such as a bearing or a semiconductor member, if the wear rate exceeds the above-mentioned wear rate, it is not preferable because wear may increase during use and the device may be hindered.
The wear rate as a grinding ball in the present invention is defined as the wear rate obtained by the measurement method shown below being 0.2% / h or less. Using a Mitsui Miike Attritor (MA-01S) as a pulverizer, 650ml alumina [purity 99.9%, Sica-Nisca SSA-999W] tank for ball diameter grinding for φ2mm 400 ml of balls were added, and 200 g of alumina powder having an average particle size of 10 μm and a specific surface area of 1.2 m 2 / g and 200 ml of water were put in, and worn for 24 hours at a rotation speed of 400 rpm with a zirconia [Nikkato YTZ] arm. Test and determine the wear rate according to the following formula.
Wear rate = {[(Wb−Wa) / Wb] × 100} / 24
(Wa: ball weight after test Wb: ball weight before test)
[0014]
In addition, the present invention further improves the sinterability, strength and toughness of the alumina ceramics, and makes the microstructure more uniform, in order to make 100 parts by weight of the basic composition comprising the above component composition. ZrO 2 can be contained in an amount of 15 parts by weight or less, preferably 10 parts by weight or less, more preferably 8 parts by weight or less.
When the added amount exceeds 15 parts by weight with respect to 100 parts by weight of the basic composition, the hardness is lowered. In particular, when ZrO 2 powder to which no stabilizer is added is used, the sintered body is monoclinic. Zirconia tends to be present, and microcracks are generated, which leads to a decrease in wear resistance.
In this case, it is preferable that the ZrO 2 raw material to be added has an average particle size of 1.0 μm or less. This is because when the average particle diameter of the ZrO 2 raw material exceeds 1.0 μm, monoclinic zirconia tends to exist in the sintered body, and microcracks occur, leading to a decrease in wear resistance and impact resistance. Therefore, it is not preferable.
Further, as the ZrO 2 raw material, a material in which a stabilizer such as a rare earth element oxide is dissolved can be used. In this case, in the case of a ZrO 2 raw material containing a rare earth element oxide, for example, Y 2 O 3 as a stabilizer, it is preferable to use a Y 2 O 3 content of 5 mol% or less. The toughness can be improved by the stress-induced transformation effect.
[0015]
In the present invention, the raw material powder is blended at a predetermined ratio, the mixture is pulverized to an average particle size of 0.3 to 0.7 μm and a specific surface area of 5 to 14 m 2 / g, and the obtained powder is molded into a predetermined shape. By firing at 1350 to 1650 ° C. in the atmosphere, a molded product made of an alumina ceramic having excellent wear resistance and corrosion resistance can be provided. If the particle size after pulverization is 0.3 μm or less, the moldability deteriorates. As a result, many defects are contained in the sintered body, resulting in a decrease in wear resistance and corrosion resistance. On the other hand, if it exceeds 0.7 μm, the sinterability is lowered and defects are likely to occur in the sintered body. More preferably, the average particle size after pulverization is 0.3 to 0.5 μm and the specific surface area is 7 to 12 m 2 / g. Moreover, as a calcination temperature, 1400-1600 degreeC is more preferable.
[0016]
The alumina ceramics having wear resistance and corrosion resistance of the present invention can be produced by the following method. As the alumina raw material, a raw material having an alumina purity of 99.7% or more, a specific surface area of 3 m 2 / g or more, and an average particle diameter of 2 μm or less is used. The alumina raw material to be used may be a raw material made from the alum method, but it is preferable to use a Bayer method alumina raw material, which can be made inexpensively.
As raw materials for the sintering aid, MgO and CaO raw materials or hydroxides and carbonate salts having an average particle size of 0.5 μm or less and a purity of 98% or more can be used. For SiO 2 , salts such as silica, quartz, silica sol, ethyl silicate and the like can be used, and further, clay minerals such as kaolin may be used. These raw materials may be added to a predetermined amount of alumina raw material and pulverized, mixed and dispersed, but by mixing the MgO, CaO and SiO 2 raw materials first and then heat-treating, it becomes possible to further uniformly disperse, Sinterability is improved, the crystal grain size is refined, and the structure is made uniform, so that a sintered body with higher wear resistance can be obtained.
When using the heat-treated sintering aid, MgO, CaO and SiO 2 raw materials are pulverized and mixed with a pulverizer such as a pot mill, an attrition mill or the like in water or an organic solvent so as to obtain a predetermined amount, and 900 ° C. A heat-treated sintering aid is produced by heat treatment at ˜1300 ° C. Below 900 ° C., the effect of heat treatment does not appear, and there is no significant difference from the case where the auxiliary material is added alone to the alumina material. If the temperature exceeds 1300 ° C., the bonding of the heat-treated sintering aid is strong, and when added as an aid, crushing and dispersion cannot be performed sufficiently, which is not preferable. Heat treatment is performed at 1000 ° C. to 1200 ° C. It is more preferable.
[0017]
Add the above-mentioned heat-treated sintering aid or each sintering aid raw material and, if necessary, ZrO 2 raw material in water or an organic solvent so that the alumina raw material has a predetermined amount of MgO, CaO, SiO 2 and ZrO 2. Then, it is pulverized, mixed and dispersed by a wet mill such as a pot mill or an attrition mill. The obtained powder must have an average particle size of 0.3 to 0.7 μm or less and a specific surface area of 5 to 14 m 2 / g. Polyvinyl alcohol (PVA), acrylic resin, paraffin wax emulsion and the like are added to the resulting slurry as a binder, dried and granulated with a spray dryer to obtain a molding powder. Next, this powder is molded into a predetermined shape by a die press, cold isostatic pressing (CIP) or the like according to a conventional method in the production of ceramics. In addition to these molding methods, molding can also be performed by molding methods such as cast molding, extrusion molding, injection molding, and granulation molding. The obtained molded body is fired at a temperature of 1350 ° C. to 1650 ° C., preferably 1400 ° C. to 1600 ° C., to obtain wear-resistant and corrosion-resistant alumina ceramics.
[0018]
Since the wear-resistant alumina ceramic of the present invention is excellent in wear resistance and corrosion resistance, grinding media, cage mill members, lining materials, grinding containers, nozzles, rollers, gauges, bearings (bearing parts) and semiconductor treatments are used. It is optimal as a wear-resistant member for tools.
[0019]
【Example】
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.
[0020]
Example 1
Each raw material was blended so that a sintered body having the composition shown in Table 1 was obtained. The obtained mixture was 92% alumina [Nikkato HD Co., Ltd.] pot mill (internal volume 7.2 liters) and φ10 mm 92 Fine powder having an average particle size shown in Table 2 and a specific surface area of 5 m 2 / g or more using a 50% alumina [HD-11 manufactured by Nikkato Co., Ltd.] ball for 24 to 72 hours. A slurry containing was obtained. A polyvinyl alcohol aqueous solution was added to the obtained slurry as a 3 to 5% by weight binder, the viscosity was adjusted to 300 cps or less, and this was dried and granulated with a spray dryer to obtain a molding powder. Subsequently, this powder was formed into a spherical shape by granulation molding, fired at 1300 ° C. to 1700 ° C. to form a φ2 mm ball, and then the surface of this ball was barrel-polished to obtain a grinding ball. Further, for corrosion resistance evaluation, the molding powder was formed into CIP1tonf / cm 3 , and fired in the same manner as the grinding ball to produce a 10 × 10 × 3 mm sintered body, which was mirror-finished to obtain a sample for evaluation. .
[0021]
As the alumina raw material, Sample No. 17 and 18 average particle size of 2 [mu] m, a specific surface area of 3m 2 / g, the low soda alumina raw material which is produced by a purity of 99.7% Bayer process, other samples average particle size 1 [mu] m, a specific surface area of 5 m 2 / g, Reactive alumina raw material having a purity of 99.8% was used.
As the auxiliary material, carbonate of 99.5% purity was used as the raw material for MgO and CaO, and silica was used as the raw material for SiO 2 . Further, as a raw material of ZrO 2 , sample No. For samples 3, 4 and 14, zirconium dioxide having an average particle size of 1.0 μm, a specific surface area of 12 m 2 / g and a purity of 99.9% was used. For No. 2, zirconium dioxide containing 3.0 mol% of Y 2 O 3 and having an average particle size of 0.5 μm and a specific surface area of 15 m 2 / g was used.
[0022]
Sample No. For Nos. 2, 7 to 9, 13 to 16 and 21, the blended auxiliary materials were wet mixed in a pot mill for 24 hours, dried and then heat treated at 900 ° C. to 1300 ° C., and then blended with the alumina raw material. For 2 and 14, a ZrO 2 raw material was further blended. Sample No. For 3 and 4, an auxiliary material, an alumina material, and a ZrO 2 material were blended. These blended raw materials were wet pulverized with a pot mill to a predetermined particle size, then PVA was added, and then dried and granulated with a spray dryer to obtain a molding powder. Subsequently, this powder was formed into a spherical shape by granulation molding, fired at 1300 ° C. to 1700 ° C. to form a φ2 mm ball, and then the surface of this ball was barrel-polished to obtain a grinding ball. Further, for corrosion resistance evaluation, the molding powder was formed into CIP1tonf / cm 3 , and fired in the same manner as the grinding ball to produce a 10 × 10 × 3 mm sintered body, which was mirror-finished to obtain a sample for evaluation. .
[0023]
The wear rate of the obtained ball for grinding was determined by the following measuring method. Using a Mitsui Miike Attritor (MA-01S) as a pulverizer, 650ml alumina [purity 99.9%, Sica-Nisca SSA-999W] tank for ball diameter grinding for φ2mm 400 ml of balls were added, and 200 g of alumina powder having an average particle size of 10 μm and a specific surface area of 1.2 m 2 / g and 200 ml of water were put in, and worn for 24 hours at a rotation speed of 400 rpm with a zirconia [Nikkato YTZ] arm. Test and determine the wear rate according to the following formula.
Wear rate = {[(Wb−Wa) / Wb] × 100} / 24
(Wa: ball weight after test Wb: ball weight before test)
Moreover, the corrosion resistance of these samples was evaluated by the following method. A 10 × 10 × 3 mm sample with a mirror finish is placed in a 70 ml capacity pressure decomposition vessel and held in 30 ml of H 2 SO 4 solution (concentration 20%) at 150 ° C. for 48 h, with a weight reduction relative to the surface area of the sample. evaluated. These results are shown in Table 2 together with the bulk density, crystal particle size, defect amount, and average particle size and firing temperature of the pulverized powder.
[0024]
[Table 1]
Figure 0004927292
[0025]
[Table 2]
Figure 0004927292
[0026]
The amount of ZrO 2 in Table 1 is shown as an addition amount (parts by weight) with respect to 100 parts by weight of the basic composition comprising alumina, a sintering aid and inevitable impurities. The corrosion resistance evaluation results in Table 2 are as follows. A is 0.24 mg / cm 3 / day or less, B is 2.4 mg / cm 3 / day or less, and C is 7.2 mg / cm 3 / day or less. It shows that D is inferior at 24 mg / cm 3 / day or less. Sample Nos. 1 and 2 in Tables 1 and 2 were used. The sintered bodies 1 to 10 satisfy the conditions of the present invention. 11 to 22 are outside the scope of the present invention which does not satisfy at least one of the conditions defined in the present invention.
The wear rate of the sample of the present invention showed excellent wear characteristics of 0.2% / h or less, and the corrosion resistance was also very good.
[0027]
【Effect of the invention】
The present invention is not in particular necessary to increase the purification accuracy of alumina as a raw material, it is possible to provide a alumina ceramics having excellent wear resistance and corrosion resistance.

Claims (2)

純度が99.7%以上、比表面積が3m /g以上、平均粒径2μm以下のアルミナ原料を使用し、平均粒径0.3〜0.7μmの微粉末を所定形状に成形して大気中1350〜1650℃で焼成することを特徴とする、主としてAlからなり、SiO20〜90重量%、MgO0〜70重量%およびCaO10〜80重量%の三成分からなる焼結助剤の各成分を合計量として0.2〜0.8重量%含有し、残部として実質的に不可避的不純物が0.3重量%以下である、平均結晶粒径0.5〜5.0μmで結晶粒径の最大値が15μm以下、かさ密度3.70g/cm以上、鏡面仕上げ面での欠陥量が5%以下、粉砕用ボールとしての摩耗率が0.2%/h以下の耐摩耗性および耐食性を有するアルミナ質セラミックス。 An alumina raw material having a purity of 99.7% or more, a specific surface area of 3 m 2 / g or more, and an average particle size of 2 μm or less is used, and a fine powder having an average particle size of 0.3 to 0.7 μm is formed into a predetermined shape and the atmosphere Sintering aid mainly composed of Al 2 O 3 and comprising three components of SiO 2 20 to 90 wt%, MgO 0 to 70 wt% and CaO 10 to 80 wt% , characterized by firing at 1350 to 1650 ° C. the components of the total amount contained 0.2 to 0.8% by weight, is 0.3 wt% or less substantially unavoidable impurities as the balance, crystals with an average crystal grain size 0.5~5.0μm the maximum value of the particle size of 15μm or less, a bulk density 3.70 g / cm 3 or more, defects of a mirror finished surface is less than 5%, the wear rate of the powder砕用ball 0.2% / h hereinafter resistant Alumina ceramics with wear and corrosion resistance. 前記不可避的不純物として含まれるアルカリ金属酸化物が0.1重量%以下、TiOが0.05重量%以下であることを特徴とする請求項1に記載の耐摩耗性および耐食性を有するアルミナ質セラミックス。The unavoidable alkali metal oxide contained as an impurity is 0.1 wt% or less, alumina having wear resistance and corrosion resistance according to claim 1, wherein the TiO 2 is 0.05 wt% or less Ceramics.
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