JP2004176144A - Magnesium oxide for separation agent for annealing - Google Patents
Magnesium oxide for separation agent for annealing Download PDFInfo
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Abstract
Description
【0001】
【発明の属する技術分野】
本発明は、フォルステライト被膜形成能に優れた焼鈍分離剤用酸化マグネシウムに関し、特に酸化マグネシウム中に含有されるホウ素の形態とその量を制御した酸化マグネシウムに関する。
【0002】
【特許文献1】
特許第2650817号明細書
【特許文献2】
特開平11−269555号公報
【特許文献3】
特許第2665451号明細書
【特許文献4】
特許第1740962号明細書
【特許文献5】
特許第2690841号明細書
【特許文献6】
特許第3043975号明細書
【特許文献7】
特開平10−88244号公報
【0003】
【従来の技術】
変圧器や発電機に使用される方向性電磁鋼板は、一般に、約3%のケイ素を含有するケイ素鋼を熱間圧延し、次いで最終板厚に冷間圧延し、その後脱炭焼鈍(一次再結晶焼鈍)、仕上げ焼鈍を経て製造している。このとき、電磁鋼板に絶縁性を付与する目的で、脱炭焼鈍後、鋼板表面に酸化マグネシウムを含むスラリー(焼鈍分離剤)を塗布し、乾燥させ、コイル状に巻取り、次いで最終の仕上げ焼鈍を行っている。脱炭焼鈍では、鋼板中のケイ素と酸素が反応して、鋼板表面に酸化ケイ素(SiO2)被膜を形成する。次いで、仕上げ焼鈍では、このSiO2被膜とスラリー中の酸化マグネシウム(MgO)とが反応して、絶縁性に優れたフォルステライト(Mg2SiO4)被膜を鋼板表面に形成する(2MgO+SiO2→Mg2SiO4)。このフォルステライト被膜を、通常グラス被膜ともいう。このフォルステライト被膜形成においては、酸化マグネシウムの性状、特性が影響すると考えられている。フォルステライト被膜は、鋼板に絶縁性を付与することに加えて、鋼板との熱膨張率の差異により鋼板表面に張力を付与することにより、方向性電磁鋼板の鉄損を低減し磁気特性を向上させると考えられている。
【0004】
したがって、方向性電磁鋼板の製造においては、フォルステライト被膜は極めて重要な役割を果たしており、この被膜を形成する酸化マグネシウムの特性が、方向性電磁鋼板の磁気特性に、直接影響を及ぼすと考えられている。
【0005】
焼鈍分離剤としての酸化マグネシウムの特性を判断する一つの評価値として、酸化マグネシウム粒子とクエン酸との反応活性度(Citric Acid Activity、以下、CAAと略す)が着目されており、CAA分布を制御することで、焼鈍分離剤性能を向上させる研究がされている。
【0006】
例えば、CAA分布の広いアルカリ土類金属を得るために、焼成条件を変化させてCAAの平均値が異なる焼成品を得たのち、これらを配合する製造方法、又は焼成温度を段階的に上昇させてCAAの平均値が異なる焼成品を得る製造方法がある(特許文献1〜3参照)。しかし、いずれもフォルステライトの生成量及び被膜の均一度は低く、焼鈍分離剤としての性能は不充分である。
【0007】
一方、酸化マグネシウム中に微量に含まれる不純物量を制御することで、酸化マグネシウムの焼鈍分離剤性能を向上させる提案がされている。特に、ホウ素(B)のフォルステライト被膜形成促進効果が期待されている。
【0008】
酸化カルシウム(CaO)量とB量を特定した焼鈍分離剤用酸化マグネシウムが知られている(特許文献4参照)。また、塩素(Cl)量とB量を特定した焼鈍分離剤用酸化マグネシウムが知られている(特許文献5参照)。また、CaO、SO3、ハロゲン、B量を特定し、加えて、その他の諸物性を特定した焼鈍分離剤用酸化マグネシウムが知られている(特許文献6参照)。更に、Bを含む多くの物性値を制御した焼鈍分離剤用酸化マグネシウムが知られている(特許文献7参照)。この様に、Bの含有量を含めた複数の物性値を制御し、Bのフォルステライト形成促進効果を安定させる試みがなされているが、いずれもフォルステライトの生成量及び被膜性能の点から充分な結果は未だ得られていない。
【0009】
【発明が解決しようとする課題】
本発明の目的は、フォルステライト(グラス被膜)形成に非常に優れた焼鈍分離剤用酸化マグネシウムを、安定的にかつ確実に提供することである。さらに、本発明の焼鈍分離剤用酸化マグネシウムを使用して、優れた磁気特性を有する方向性電磁鋼板を提供することである。
【0010】
【課題を解決するための手段】
本発明の発明者らは、上記の課題を解決するため、鋭意検討した結果、酸化マグネシウム中に含有されるホウ素の形態に着目し、この形態及びその量を制御することで、安定したグラス被膜形成が可能な焼鈍分離剤用酸化マグネシウム及びその利用を見出したものである。
【0011】
すなわち本発明の酸化マグネシウムは、ホウ素を含有する焼鈍分離剤用酸化マグネシウムであって、該酸化マグネシウム中に含有されるホウ素中の三配位ホウ素の比率が、55〜70%であることを特徴とする焼鈍分離剤用酸化マグネシウムである。
【0012】
【発明の実施の形態】
【0013】
本発明において、三配位ホウ素(以下「三配位B」という)とは、中心原子となって配位化合物を構成するホウ素であり、かつ配位子を3個有するホウ素をいう。
【0014】
ここで、三配位Bの存在量は、Bの形態を核磁気共鳴(B−NMR)スペクトルのフーリエ変換分析法で決定し、算出することができる。
【0015】
11B−NMR分析は、Chemagnetics社製CMX−300を用い、室温で、測定対象の核種11Bを、観測周波数96.326403MHzにてDD−MAS(Dipole Decoupling−Magic Angle Spinning)法で行った。パルス強度の設定は固体の無水ホウ酸を測定して行い、調整は、11Bのm=−1/2⇔m=1/2の遷移によるピークが、パルス幅4.5μs以下ではベースラインに対してy軸の正方向に観察されるように位相を設定し、その後パルス幅を長くして、9μsでベースラインに対するピーク強度の平均が0となるように設定した。次に測定は、パルス幅1.5μs、観測幅200kHz、観測ポイント4096点、観測繰り返し時間5.0秒、試料回転数5.0kHz、化学シフト基準は、飽和ホウ酸水溶液を用い、外部基準を19.49ppmで行った。
【0016】
図1には、このようにして得られた本発明の酸化マグネシウムについてのB−NMRスペクトルを示す。なお、本図のB−NMRスペクトルは、ゼーマン分裂により遷移したもののうち、m=1/2⇔m=−1/2遷移の情報であり、横軸は化学シフトδ〔ppm〕、縦軸は強度で示している。
【0017】
図1におけるB−NMRスペクトルには、3個のピークが重なって現れている。中央ピークは、B原子核の周辺に4つの原子核が配位した四配位Bであり、その両側に現れた2個のショルダーピークは、B原子核周辺に3つの原子核が配位した三配位Bである。三配位Bは、B原子核近傍に電場勾配を有するため、四極分裂して、四配位Bピークの両側に観察されている。このような配位の異なる2種のBの存在を、本発明では、以下の方法で簡易的に評価した。
【0018】
B−NMRスペクトルにおいて、中央ピーク6〜−4ppm範囲を四配位Bと、ショルダーピーク22〜6ppm及び−4〜−20ppmの範囲を三配位Bと定義し、積分法で算出した面積を積分値とする。次に、これらの積分値を用いて、次式を用いて三配位ホウ素の比率を算出した。
三配位Bの比率〔%〕
=三配位Bの積分値/(三配位Bの積分値+四配位Bの積分値)×100
【0019】
次に、ホウ素(B)中の三配位Bの比率の好ましい範囲は、以下のようにして求めた。ここでB含有量は、試料を酸に溶解し、ICP発光分光分析により求めた数値である。
【0020】
まず、製造条件、焼成条件を変えて製造した複数個の酸化マグネシウム(以下「MgO」という)について、B含有量及び上記の方法により算出した三配位Bの比率を表1に示す。これらの焼成品を、表2に示す配合で混合し、表3に示す特性を有する試料酸化MgOを得た。表1、表3には、後述する測定方法で測定したCAA値も併せて示す。これらの試料MgOにおける三配位Bの比率とフォルステライト生成率の関係を図2に示す。
【0021】
【表1】
【0022】
【表2】
【0023】
【表3】
【0024】
図2において、三配位Bの比率とフォルステライト生成率の関係は、大きく3つのグループに分類できる。第1は、三配位Bの比率が55〜70%でフォルステライトの生成量が90%以上を示すグループ、第2は、三配位Bの比率が55〜70%であるにもかかわらずフォルステライトの生成量が70〜87%のグループ、そして第3は、三配位Bの比率が55%未満でフォルステライトの生成量が90%未満を示すグループである。ここで、第1と第2のグループの相違は、表3によると、後者のB含有量が、0.034質量%、0.185質量%、0.195質量%であるのに対し、前者が概略0.04〜0.15質量%である点にある。
【0025】
したがって、フォルステライトの生成率90%以上を満たすためには、三配位Bの比率は55%〜70%であることが必要であり、好ましくは57〜65%である。三配位Bの比率がこの範囲にあり、かつB含有量が、0.04〜0.15質量%の範囲、より好ましくは0.05〜0.12質量%の範囲、特に好ましくは0.06〜0.10質量%の範囲にあると、90%以上のフォルステライト生成率が安定して得られることがわかる。なお、フォルステライトの生成量が90%を基準値としたが、これは、この基準値を満たすことができれば、MgO粒子とシリカを主成分とする鋼板表面上の皮膜との固相反応性が優れ、密着性の良好なフォルステライト皮膜が形成し得るからである。
【0026】
次に、このような好ましい範囲の三配位B量を有するMgOは、以下の方法で製造することができる。
【0027】
MgO自体は、公知の一般的な方法を用いて製造することができる。すなわち、原料として塩化マグネシウムを用い、塩化マグネシウム含有水溶液に、水酸化カルシウム、水酸化ナトリウム、水酸化カリウム等のアルカリ性水溶液(スラリー)を添加し反応させて水酸化マグネシウムを生成し、これを焼成して得ることができる。また、塩化マグネシウム含有水溶液からアマン法又はマグネサイト焼成によって得たMgO、またはマグネサイトを焼成して得たMgOを再水和した水酸化マグネシウムを焼成して得ることもできる。
【0028】
水酸化マグネシウムの焼成は、ろ過、水洗、乾燥したのち、例えば直接式連続型加熱炉で焼成してMgOを生成し、次いでMgOを粉砕し、粒径を制御して、焼鈍分離剤用酸化マグネシウムを製造する。ここで、直接式連続型加熱炉とは、被加熱体を直接、バーナー等で連続的に加熱する加熱炉をいい、例えば、ロータリーキルン等が挙げられる。なお、水酸化マグネシウムを焼成する条件は、1073〜1473Kで600〜7200秒の条件で行うことが好ましい。
【0029】
またMgOに含有させるB量の調整は、例えば塩化マグネシウム水溶液にホウ酸、ホウ酸ナトリウム、ホウ酸カリウム、ホウ酸カルシウム、ホウ酸リチウム、ホウ酸アンモニウム、酸化ホウ素等のB化合物を添加する方法、MgOを水和する際にこれらのB化合物を添加する方法、水酸化マグネシウムとB化合物を予め混合して焼成する方法、などにより制御することができる。一方、B量が過剰な場合には、洗浄等により除去することができる。
【0030】
次に、表1を参照すると、高温で焼成するほど、また焼成時間を長時間化するほど、MgO中の三配位Bの比率が増大する。したがって、焼成温度と焼成時間を適正化することで、単一の製造(焼成)条件で製造したMgOのみを用いて、三配位Bの比率55%以上を満たすことができる(表3、試料3参照)。しかしながら、高温で焼成した酸化マグネシウムは、CAA活性度が低下する傾向にあるので、上記した好ましい焼成条件の範囲内で、異なる条件で焼成して三配位B量が異なるMgOを予め製造しておき、三配位Bの比率が上記の範囲内になるようにこれらを混合することが好ましい。
【0031】
このようにして三配位B量、及び好ましくはB含有量が本発明の範囲にあるMgOは、CAA40%が100〜200秒にあり、かつCAA70%が200〜2000秒の範囲にあり、反応活性度が適切な範囲のMgOを得ることができる。
【0032】
なおCAAの測定は、以下の様にして行った。
(1)300mlビーカーに、0.4Nのクエン酸溶液を100ml取り、次いで1%フェノールフタレイン指示薬を2ml添加し、マグネチックスターラーを備えた恒温槽で295.15±0.3Kに保つ。
(2)反応率40%の場合はMgO2.00×10−3kgを、反応率70%の場合はMgO1.14×10−3kgを投入し、投入と同時に時間測定を開始する。。
(3)投入から5秒後に、撹拌を開始する(回転数:400rpm)。
(4)終点は、液の色が桃色となる点とし、投入から終点までの所要時間を、CAAとした。
【0033】
なお、焼鈍分離剤用MgOには、例えば、特許第2690841号明細書に記載のMg、Ca、Cu、Fe、Zn、Mn、Zr、Co、Ni、Al、Sn、V等の塩素化合物など、フォルステライト被膜形成のための、公知の反応補助剤、インヒビター補助剤、張力付与型絶縁被膜添加剤を添加することもできる。
【0034】
方向性電磁鋼板用焼鈍分離剤及び方向性電磁鋼板は下記の方法で製造することができる。方向性電磁鋼板はSi2.5〜4.5%を含有するケイ素鋼スラブを熱間圧延し、酸洗後に冷間圧延又は中間焼鈍をはさむ2回冷間圧延を行って、所定の板厚とする。次に、冷間圧延したコイルを923〜1173Kの湿潤水素雰囲気中で脱炭を兼ねた再結晶焼鈍を行い、このとき鋼板表面にシリカ(SiO2)を主成分とする酸化被膜が形成する。この鋼板上に、上記方法で製造した本発明のMgOを水に均一に分散させた水スラリーを、ロールコーティング又はスプレーを用いて連続的に塗布し、約573Kで乾燥させる。こうして処理された鋼板コイルを、例えば、1473Kで20時間の最終仕上げ焼鈍を行って、鋼板表面にフォルステライト(Mg2SiO4)を形成し、これが絶縁被膜とともに、鋼板表面に張力を付与して、方向性電磁鋼板の鉄損値を向上させることができる。
【0035】
【実施例】
下記の実施例により本発明を詳細に説明するが、これらの実施例は本発明をいかなる意味においても制限するものではない。
【0036】
実施例1
濃度2.0mol・kg−1の塩化マグネシウム溶液に対し、ホウ酸をBに換算して0.0184質量%、水酸化カルシウムスラリーを、得られるMgOの濃度が1.2mol・kg−1となるように添加した。この混合溶液を、343Kで2時間反応させ、ろ過、水洗、乾燥して、水酸化マグネシウムを製造した。この水酸化マグネシウムを、ロータリーキルンを用いて、1303Kで、20分間焼成し、次いで、粉砕して、MgOを得た。得られたMgOの三配位B比率、B量、CAA40%及びCAA70%を測定し、結果を、表4に示した。
【0037】
実施例2
ロータリーキルンを用いて、マグネサイトを1373Kで1時間焼成し、MgOを製造した。このMgOを、スラリー中のMgOの濃度が2mol・kg−1となるように、水に投入し、MgOに対して、2.8質量%のホウ酸ナトリウムを添加し、363Kで2時間反応させ、水酸化マグネシウムを製造した。更に、ロータリーキルンを用いて、1173Kで30分間、及び、1373Kで30分間、それぞれ焼成したのち、粉砕し、焼成度の異なるMgOを製造した。それぞれの三配位比率は、49.8%、68.5%であった。またB量は、0.076質量%、0.077質量%であった。その後、三配位B比率、B量が、本発明の範囲に入るように、2種類のMgOを、混合比率55:45で混合して、実施例2のMgO粒子を得た。得られたMgOの三配位B比率、B量、CAA40%及びCAA70%を測定し、結果を、表4に示した。
【0038】
実施例3
アマン法により得られたMgOを、スラリー中のMgOの濃度が3mol・kg−1となるように、水に投入し、MgOに対して、3.8質量%のホウ酸を添加し、353Kで2時間反応させて、水酸化マグネシウムを製造した。次いで、ロータリーキルンを用いて、1073Kで1時間、1323Kで20分間、1473Kで30分間、それぞれ焼成したのち、粉砕し、焼成度の異なるMgOを製造した。それぞれの三配位比率は、47.0質量%、60.5質量%、75.8質量%であった。またB量は、0.09、0.092、0.093であった。その後、三配位B比率、B量が、本発明の範囲にはいるように、3種類のMgOを、混合比率40:25:35で混合して、実施例3のMgOを得た。得られたMgOの三配位B比率、B量、CAA40%及びCAA70%を測定し、結果を、表4に示した。
【0039】
比較例1
実施例1と同一条件で製造した水酸化マグネシウムを、ロータリーキルンを用いて、1223Kで1時間焼成し、粉砕して比較例1のMgOを得た。得られたMgOの三配位B比率、B量、CAA40%及びCAA70%を測定し、結果を、表4に示した。
【0040】
比較例2
実施例2と同一条件で製造した水酸化マグネシウムを、ロータリーキルンを用いて、1073Kで1時間、1173Kで2時間、1273Kで2時間、それぞれ焼成したのち、粉砕し、焼成度の異なるMgOを製造した。それぞれの三配位比率は、46.6質量%、50.1質量%、54.3質量%であった。またB量は、0.062、0.064、0.066であった。その後、3種類のMgOを、混合比率30:30:40で混合して、比較例2のMgOを得た。得られたMgOの三配位B比率、B量、CAA40%及びCAA70%を測定し、結果を、表4に示した。
【0041】
【表4】
【0042】
表4から明らかなように、実施例1〜3は、三配位B比率が55%以上を満たした。比較例1及び2は、三配位B比率が、下限を下回った。
【0043】
次に、これらのMgOについて、フォルステライト被膜の形成挙動を調査した。フォルステライトの形成は、2MgO+SiO2→Mg2SiO4の固相反応に従って起こると考えられることから、実施例、比較例のMgO粉末とSiO2を、モル比で2:1になるように調合した混合物を用いて、圧力50MPaで、直径15×10−3m、高さ15×10−3mに成形し、これを窒素雰囲気中で、1473Kで4時間焼成した。この焼成温度は、方向性電磁鋼板上でSiO2とMgOを含むスラリーとが反応する仕上げ焼鈍温度に相当している。こうして得られた焼結体中のMg2SiO4生成量を、X線回折により定量分析した。結果を表5に示す。
【0044】
【表5】
【0045】
表5から明らかなように、実施例1〜3は、フォルステライトの生成量が90%を超えている。一方、比較例1及び2は、フォルステライト形成が90%を下回り、充分ではない。
【0046】
次に、ケイ素鋼板上にMgOを塗布して、フォルステライトの被膜特性を調査した。供試鋼は、質量%で、C:0.058%、Si:2.8%、Mn:0.06%、Al:0.026%、S:0.024%、N:0.0050%、残部は不可避的な不純物とFeよりなる方向性電磁鋼板用のケイ素鋼スラブを、公知の方法で熱間圧延、酸洗、冷間圧延を行って、最終板厚0.23×10−3mとし、更に、窒素25%+水素75%の湿潤雰囲気中で脱炭焼鈍した鋼板である。
【0047】
この鋼板に対し、本発明のMgO又は比較例のMgOをスラリー状にして、乾燥後の重量で12×10−3kg・m−2になるように鋼板に塗布し、乾燥後1473K、20時間の最終仕上げ焼鈍を行った。鋼板上のフォルステライト被膜の形成状況を表6に示す。
【0048】
【表6】
【0049】
表6から明らかなように、実施例1〜3のMgOから形成したフォルステライト被膜は、均一で充分な厚みを有し、かつ被膜の密着性に優れていることを確認している。その一方、比較例の被膜は、均一であっても薄く、密着性にも劣っていた。
【0050】
【発明の効果】
以上述べたように、本発明は、MgO中のホウ素の形態を制御したことにより、フォルステライト(グラス被膜)形成に非常に優れた焼鈍分離剤用MgOを安定して、かつ確実に提供することができる。また、本発明のMgOを用いて処理して得ることができる方向性電磁鋼板は、方向性電磁鋼板として充分な磁気特性を有するものである。
【図面の簡単な説明】
【図1】本発明の酸化マグネシウムについてのB−NMRスペクトルである。
【図2】試料MgOにおける三配位Bの比率とフォルステライト生成率の関係図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to magnesium oxide for an annealing separator having excellent forsterite film forming ability, and more particularly to a magnesium oxide in which the form and amount of boron contained in magnesium oxide are controlled.
[0002]
[Patent Document 1]
Patent No. 2650817 [Patent Document 2]
JP-A-11-269555 [Patent Document 3]
Japanese Patent No. 2665451 [Patent Document 4]
Patent No. 1740962 [Patent Document 5]
Patent No. 2690841 [Patent Document 6]
Patent No. 3043975 [Patent Document 7]
JP-A-10-88244
[Prior art]
Grain-oriented electrical steel sheets used in transformers and generators are generally formed by hot-rolling silicon steel containing about 3% silicon, then cold-rolling to a final thickness, and then decarburizing annealing (primary re-heating). (Crystal annealing) and finish annealing. At this time, for the purpose of imparting insulation to the magnetic steel sheet, after decarburizing annealing, a slurry containing magnesium oxide (annealing separating agent) is applied to the surface of the steel sheet, dried, wound into a coil, and then subjected to final finish annealing. It is carried out. In the decarburizing annealing, silicon in the steel sheet reacts with oxygen to form a silicon oxide (SiO 2 ) coating on the steel sheet surface. Next, in the finish annealing, the SiO 2 film reacts with magnesium oxide (MgO) in the slurry to form a forsterite (Mg 2 SiO 4 ) film having excellent insulation properties on the steel sheet surface (2MgO + SiO 2 → Mg). 2 SiO 4 ). This forsterite film is usually called a glass film. It is considered that the properties and properties of magnesium oxide influence the formation of the forsterite film. The forsterite coating not only imparts insulation to the steel sheet, but also applies tension to the steel sheet surface due to the difference in the coefficient of thermal expansion from the steel sheet, thereby reducing iron loss and improving magnetic properties of grain-oriented electrical steel sheets. It is thought to be.
[0004]
Therefore, in the production of grain-oriented electrical steel sheets, the forsterite film plays an extremely important role, and the properties of magnesium oxide forming this film are thought to directly affect the magnetic properties of grain-oriented electrical steel sheets. ing.
[0005]
As one evaluation value for judging the characteristics of magnesium oxide as an annealing separator, a reaction activity (Citric Acid Activity, hereinafter abbreviated as CAA) between magnesium oxide particles and citric acid is focused on, and the CAA distribution is controlled. Research has been conducted to improve the performance of the annealing separator.
[0006]
For example, in order to obtain an alkaline earth metal having a wide distribution of CAA, after obtaining baked products having different average values of CAA by changing calcination conditions, the production method of blending them, or the calcination temperature is increased stepwise. There is a manufacturing method for obtaining fired products having different CAA average values (see
[0007]
On the other hand, it has been proposed to improve the performance of an annealing separator for magnesium oxide by controlling the amount of impurities contained in a trace amount in magnesium oxide. In particular, boron (B) is expected to have a forsterite film formation promoting effect.
[0008]
A magnesium oxide for an annealing separating agent having a specified amount of calcium oxide (CaO) and an amount of B is known (see Patent Document 4). Further, magnesium oxide for an annealing separator having a specified amount of chlorine (Cl) and amount of B is known (see Patent Document 5). In addition, a magnesium oxide for an annealing separator in which the amounts of CaO, SO 3 , halogen, and B are specified, and in addition, other physical properties are specified, is known (see Patent Document 6). Further, there is known a magnesium oxide for an annealing separator in which many physical properties including B are controlled (see Patent Document 7). As described above, attempts have been made to stabilize the forsterite formation promoting effect of B by controlling a plurality of physical properties including the content of B, but all of them are sufficient in terms of the amount of forsterite produced and the film performance. No results have yet been obtained.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide a stable and reliable magnesium oxide for an annealing separator which is very excellent in forming forsterite (glass film). Another object of the present invention is to provide a grain-oriented electrical steel sheet having excellent magnetic properties by using the magnesium oxide for an annealing separator of the present invention.
[0010]
[Means for Solving the Problems]
The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, focused on the form of boron contained in magnesium oxide, and by controlling this form and the amount thereof, a stable glass coating was obtained. A magnesium oxide for an annealing separator which can be formed and its use have been found.
[0011]
That is, the magnesium oxide of the present invention is a magnesium oxide for an annealing separator containing boron, wherein the ratio of three-coordinate boron in the boron contained in the magnesium oxide is 55 to 70%. Magnesium oxide for an annealing separator.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
[0013]
In the present invention, the three-coordinate boron (hereinafter, referred to as “three-coordinate B”) is boron that constitutes a coordination compound as a central atom and refers to boron having three ligands.
[0014]
Here, the abundance of the three-coordinate B can be calculated by determining the form of B by a Fourier transform analysis of a nuclear magnetic resonance (B-NMR) spectrum.
[0015]
The 11 B-NMR analysis was performed on the nuclide 11 B to be measured at room temperature by a DD-MAS (Dipole Decoupling-Magic Angle Spinning) method using CMX-300 manufactured by Chemmagnetics at room temperature at an observation frequency of 96.326403 MHz. Setting pulse intensity is performed by measuring the boric anhydride solid, adjustment, 11 peaks due transitions m = -1 / 2⇔m = 1/ 2 and B, the baseline in the following pulse width 4.5μs On the other hand, the phase was set so as to be observed in the positive direction of the y-axis, and then the pulse width was increased so that the average of the peak intensity with respect to the baseline became 0 in 9 μs. Next, the measurement was performed with a pulse width of 1.5 μs, an observation width of 200 kHz, 4096 observation points, an observation repetition time of 5.0 seconds, a sample rotation speed of 5.0 kHz, and a chemical shift standard using a saturated boric acid aqueous solution. Performed at 19.49 ppm.
[0016]
FIG. 1 shows a B-NMR spectrum of the magnesium oxide of the present invention thus obtained. In addition, the B-NMR spectrum in this figure is information on the transition of m = 1 / 2⇔m = − の う ち among the transitions due to Zeeman splitting, the horizontal axis is the chemical shift δ [ppm], and the vertical axis is the Indicated by strength.
[0017]
In the B-NMR spectrum in FIG. 1, three peaks appear overlapping. The central peak is a four-coordinate B in which four nuclei are coordinated around the B nucleus, and the two shoulder peaks appearing on both sides are three-coordinate B in which three nuclei are coordinated around the B nucleus. It is. Tricoordinate B has an electric field gradient near the B nucleus, so it is quadrupolar and observed on both sides of the tetracoordinate B peak. In the present invention, the existence of two kinds of B having different coordinations was simply evaluated by the following method.
[0018]
In the B-NMR spectrum, the range of the central peak of 6 to -4 ppm is defined as tetracoordinate B, and the ranges of the shoulder peaks of 22 to 6 ppm and -4 to -20 ppm are defined as tricoordinate B, and the area calculated by the integration method is integrated. Value. Next, using these integral values, the ratio of three-coordinate boron was calculated using the following equation.
Tricoordinate B ratio [%]
= Integrated value of three-coordinate B / (integral value of three-coordinate B + integral value of four-coordinate B) × 100
[0019]
Next, a preferable range of the ratio of the three coordinate B in boron (B) was determined as follows. Here, the B content is a numerical value obtained by dissolving a sample in an acid and performing ICP emission spectroscopy.
[0020]
First, for a plurality of magnesium oxides (hereinafter referred to as “MgO”) manufactured under different manufacturing conditions and firing conditions, the B content and the ratio of three-coordinate B calculated by the above method are shown in Table 1. These calcined products were mixed in the composition shown in Table 2 to obtain a sample MgO having the properties shown in Table 3. Tables 1 and 3 also show CAA values measured by a measurement method described later. FIG. 2 shows the relationship between the ratio of tricoordination B and the forsterite generation rate in these sample MgOs.
[0021]
[Table 1]
[0022]
[Table 2]
[0023]
[Table 3]
[0024]
In FIG. 2, the relationship between the ratio of tricoordination B and the forsterite generation rate can be roughly classified into three groups. The first is a group in which the proportion of tricoordinate B is 55 to 70% and the amount of forsterite is 90% or more, and the second is the group in which the proportion of tricoordinate B is 55 to 70%. The third group is a group in which the amount of forsterite produced is 70 to 87%, and the third is a group in which the proportion of tricoordinate B is less than 55% and the amount of forsterite produced is less than 90%. Here, the difference between the first and second groups is that according to Table 3, the B content of the latter is 0.034% by mass, 0.185% by mass, and 0.195% by mass, whereas the B content of the latter is 0.034% by mass, 0.185% by mass, and 0.195% by mass. Is about 0.04 to 0.15% by mass.
[0025]
Therefore, in order to satisfy the formation rate of forsterite of 90% or more, the proportion of the three-coordinate B needs to be 55% to 70%, and preferably 57% to 65%. The ratio of tricoordinate B is in this range, and the B content is in the range of 0.04 to 0.15% by mass, more preferably in the range of 0.05 to 0.12% by mass, and particularly preferably 0.1 to 0.1% by mass. It is understood that when the content is in the range of 06 to 0.10% by mass, a forsterite generation rate of 90% or more can be stably obtained. The reference value was 90% forsterite generation. If this reference value could be satisfied, the solid-state reactivity between the MgO particles and the coating on the steel sheet surface containing silica as a main component was determined. This is because a forsterite film having excellent and good adhesion can be formed.
[0026]
Next, MgO having such a preferred range of tricoordinate B content can be produced by the following method.
[0027]
MgO itself can be manufactured using a known general method. That is, magnesium chloride is used as a raw material, and an alkaline aqueous solution (slurry) such as calcium hydroxide, sodium hydroxide, or potassium hydroxide is added to a magnesium chloride-containing aqueous solution and reacted to produce magnesium hydroxide, which is then calcined. Can be obtained. Alternatively, MgO obtained from the aqueous solution containing magnesium chloride by the Aman method or magnesite firing or magnesium hydroxide obtained by rehydrating MgO obtained by firing magnesite can be fired.
[0028]
After calcination of magnesium hydroxide, filtration, washing with water, and drying, for example, calcination in a direct type continuous heating furnace to produce MgO, then pulverizing MgO, controlling the particle size, magnesium oxide for an annealing separator To manufacture. Here, the direct type continuous heating furnace refers to a heating furnace that continuously heats the object to be heated directly by a burner or the like, and includes, for example, a rotary kiln. The firing of magnesium hydroxide is preferably performed at 1073 to 1473K for 600 to 7200 seconds.
[0029]
Adjustment of the amount of B contained in MgO is, for example, a method of adding a B compound such as boric acid, sodium borate, potassium borate, calcium borate, lithium borate, ammonium borate, boron oxide to an aqueous magnesium chloride solution, It can be controlled by a method of adding these B compounds when hydrating MgO, a method of mixing magnesium hydroxide and the B compound in advance, and firing. On the other hand, when the amount of B is excessive, it can be removed by washing or the like.
[0030]
Next, referring to Table 1, the ratio of the three-coordinate B in MgO increases as the firing is performed at a higher temperature and as the firing time is lengthened. Therefore, by optimizing the firing temperature and the firing time, it is possible to satisfy the ratio of three-coordinate B of 55% or more using only MgO manufactured under a single manufacturing (sintering) condition (Table 3, sample 3). However, magnesium oxide calcined at a high temperature tends to have reduced CAA activity. Therefore, within the range of the preferable calcining conditions described above, MgO calcined under different conditions to previously produce MgO having a different amount of three-coordinate B is prepared. It is preferable to mix them so that the ratio of tricoordination B is within the above range.
[0031]
Thus, MgO having a tricoordinate B content, and preferably a B content within the range of the present invention, has a CAA of 40% in a range of 100 to 200 seconds and a CAA of 70% in a range of 200 to 2,000 seconds. MgO having an appropriate activity can be obtained.
[0032]
The measurement of CAA was performed as follows.
(1) In a 300 ml beaker, take 100 ml of 0.4N citric acid solution, then add 2 ml of 1% phenolphthalein indicator, and keep it at 295.15 ± 0.3 K in a thermostat equipped with a magnetic stirrer.
(2) When the conversion is 40%, 2.00 × 10 −3 kg of MgO is charged, and when the conversion is 70%, 1.14 × 10 −3 kg of MgO is charged, and time measurement is started simultaneously with the charging. .
(3) After 5 seconds from the introduction, stirring is started (rotation speed: 400 rpm).
(4) The end point was a point at which the color of the liquid turned pink, and the time required from the introduction to the end point was CAA.
[0033]
In addition, for MgO for the annealing separator, for example, chlorine compounds such as Mg, Ca, Cu, Fe, Zn, Mn, Zr, Co, Ni, Al, Sn, and V described in Japanese Patent No. 2690841, Known reaction auxiliaries, inhibitor auxiliaries, and tension imparting type insulating coating additives for forming a forsterite film can also be added.
[0034]
The annealing separator for grain-oriented electrical steel sheets and grain-oriented electrical steel sheets can be produced by the following method. The grain-oriented electrical steel sheet is obtained by hot rolling a silicon steel slab containing 2.5 to 4.5% of Si, cold-rolling after pickling, and cold rolling twice with intermediate annealing to obtain a predetermined thickness. I do. Next, the cold-rolled coil is subjected to recrystallization annealing combined with decarburization in a wet hydrogen atmosphere of 923 to 1173 K. At this time, an oxide film containing silica (SiO 2 ) as a main component is formed on the steel sheet surface. A water slurry obtained by uniformly dispersing the MgO of the present invention produced by the above method in water is continuously applied on the steel plate by using roll coating or spraying, and dried at about 573K. The steel sheet coil thus treated is subjected to, for example, a final finish annealing at 1473 K for 20 hours to form forsterite (Mg 2 SiO 4 ) on the steel sheet surface, which, together with the insulating coating, applies tension to the steel sheet surface. In addition, the iron loss value of the grain-oriented electrical steel sheet can be improved.
[0035]
【Example】
The following examples illustrate the invention in detail, but do not limit the invention in any way.
[0036]
Example 1
With respect to a magnesium chloride solution having a concentration of 2.0 mol · kg −1 , boric acid is converted to 0.0184 mass% in terms of B, and a calcium hydroxide slurry is obtained, resulting in a concentration of MgO of 1.2 mol · kg −1. Was added as follows. The mixed solution was reacted at 343K for 2 hours, filtered, washed with water, and dried to produce magnesium hydroxide. The magnesium hydroxide was baked at 1303 K for 20 minutes using a rotary kiln, and then pulverized to obtain MgO. The tricoordination B ratio, B amount,
[0037]
Example 2
Using a rotary kiln, magnesite was fired at 1373K for 1 hour to produce MgO. This MgO is added to water so that the concentration of MgO in the slurry is 2 mol · kg −1 , 2.8% by mass of sodium borate is added to MgO, and the mixture is reacted at 363 K for 2 hours. To produce magnesium hydroxide. Further, using a rotary kiln, firing was performed at 1173K for 30 minutes and at 1373K for 30 minutes, respectively, and then pulverized to produce MgO having different firing degrees. The respective three coordination ratios were 49.8% and 68.5%. The B content was 0.076% by mass and 0.077% by mass. Thereafter, two types of MgO were mixed at a mixing ratio of 55:45 so that the three-coordinate B ratio and the B amount were within the range of the present invention, to obtain MgO particles of Example 2. The tricoordination B ratio, B amount,
[0038]
Example 3
MgO obtained by the Aman method was charged into water so that the concentration of MgO in the slurry was 3 mol · kg −1, and 3.8% by mass of boric acid was added to MgO, and the pressure was increased to 353K. The reaction was performed for 2 hours to produce magnesium hydroxide. Next, using a rotary kiln, firing was performed at 1073K for 1 hour, at 1323K for 20 minutes, and at 1473K for 30 minutes, and then pulverized to produce MgO having different firing degrees. The respective three coordination ratios were 47.0% by mass, 60.5% by mass, and 75.8% by mass. The B content was 0.09, 0.092, and 0.093. Thereafter, three types of MgO were mixed at a mixing ratio of 40:25:35 so that the three-coordinate B ratio and the B amount were within the range of the present invention, to obtain MgO of Example 3. The tricoordination B ratio, B amount,
[0039]
Comparative Example 1
Magnesium hydroxide produced under the same conditions as in Example 1 was calcined at 1223 K for 1 hour using a rotary kiln and pulverized to obtain MgO of Comparative Example 1. The tricoordination B ratio, B amount,
[0040]
Comparative Example 2
Magnesium hydroxide produced under the same conditions as in Example 2 was calcined using a rotary kiln for 1 hour at 1073K, 2 hours at 1173K, and 2 hours at 1273K, and then pulverized to produce MgO having different degrees of calcining. . The respective three coordination ratios were 46.6% by mass, 50.1% by mass, and 54.3% by mass. The B content was 0.062, 0.064, and 0.066. Thereafter, three types of MgO were mixed at a mixing ratio of 30:30:40 to obtain MgO of Comparative Example 2. The tricoordination B ratio, B amount,
[0041]
[Table 4]
[0042]
As is clear from Table 4, in Examples 1 to 3, the three-coordinate B ratio satisfied 55% or more. In Comparative Examples 1 and 2, the three-coordinate B ratio was lower than the lower limit.
[0043]
Next, the formation behavior of the forsterite film was investigated for these MgOs. Since it is considered that the formation of forsterite occurs according to the solid-phase reaction of 2MgO + SiO 2 → Mg 2 SiO 4 , the MgO powders of Examples and Comparative Examples and SiO 2 were prepared in a molar ratio of 2: 1. The mixture was molded at a pressure of 50 MPa at a diameter of 15 × 10 −3 m and a height of 15 × 10 −3 m, and fired at 1473 K for 4 hours in a nitrogen atmosphere. This firing temperature corresponds to the finish annealing temperature at which the SiO 2 and the slurry containing MgO react on the grain-oriented electrical steel sheet. The amount of Mg 2 SiO 4 produced in the sintered body thus obtained was quantitatively analyzed by X-ray diffraction. Table 5 shows the results.
[0044]
[Table 5]
[0045]
As is clear from Table 5, in Examples 1 to 3, the production amount of forsterite exceeds 90%. On the other hand, in Comparative Examples 1 and 2, forsterite formation was less than 90%, which was not sufficient.
[0046]
Next, MgO was applied on a silicon steel plate, and the film properties of forsterite were investigated. The test steel was, in mass%, C: 0.058%, Si: 2.8%, Mn: 0.06%, Al: 0.026%, S: 0.024%, N: 0.0050%. The remainder is subjected to hot rolling, pickling, and cold rolling of a silicon steel slab for a grain-oriented electrical steel sheet composed of inevitable impurities and Fe by a known method, so that the final sheet thickness is 0.23 × 10 −3. m and decarburized and annealed in a humid atmosphere of 25% nitrogen + 75% hydrogen.
[0047]
To this steel sheet, MgO of the present invention or MgO of the comparative example was made into a slurry state, applied to a steel sheet so as to have a weight after drying of 12 × 10 −3 kg · m −2 , and dried at 1473 K for 20 hours. Was subjected to final finish annealing. Table 6 shows the state of formation of the forsterite film on the steel sheet.
[0048]
[Table 6]
[0049]
As is clear from Table 6, it was confirmed that the forsterite films formed from MgO of Examples 1 to 3 had a uniform and sufficient thickness, and were excellent in the adhesion of the films. On the other hand, the coating of the comparative example was uniform and thin, and was poor in adhesion.
[0050]
【The invention's effect】
As described above, the present invention stably and surely provides MgO for an annealing separator excellent in forsterite (glass film) formation by controlling the form of boron in MgO. Can be. The grain-oriented electrical steel sheet obtainable by treating with MgO of the present invention has sufficient magnetic properties as a grain-oriented electrical steel sheet.
[Brief description of the drawings]
FIG. 1 is a B-NMR spectrum of the magnesium oxide of the present invention.
FIG. 2 is a graph showing the relationship between the ratio of tricoordination B and the forsterite generation rate in a sample MgO.
Claims (5)
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JP2008260668A (en) * | 2007-04-13 | 2008-10-30 | Jfe Steel Kk | Magnesia for annealing separating agent and manufacture method of grain oriented magnetic steel sheet |
JP2017128772A (en) * | 2016-01-21 | 2017-07-27 | Jfeスチール株式会社 | Powder for annealing separation agent, production of the powder, and directive magnetic steel sheet |
JP2017128773A (en) * | 2016-01-21 | 2017-07-27 | Jfeスチール株式会社 | Powder for annealing separator, manufacturing method therefor and oriented electromagnetic steel sheet |
JP2017179459A (en) * | 2016-03-30 | 2017-10-05 | タテホ化学工業株式会社 | Annealing separation agent magnesium oxide and grain oriented silicon steel sheet |
WO2017169851A1 (en) * | 2016-03-30 | 2017-10-05 | タテホ化学工業株式会社 | Magnesium oxide for annealing separators, and grain-oriented magnetic steel sheet |
RU2719845C1 (en) * | 2016-03-30 | 2020-04-23 | Татехо Кемикал Индастриз Ко., Лтд. | Magnesium oxide for annealing separators and anisotropic electrotechnical sheet steel |
US11566297B2 (en) | 2016-03-30 | 2023-01-31 | Tateho Chemical Industries Co., Ltd. | Magnesium oxide for annealing separators, and grain-oriented magnetic steel sheet |
JP2020015982A (en) * | 2019-09-04 | 2020-01-30 | Jfeスチール株式会社 | Manufacturing method of powder for annealing separation agent |
EP4206136A4 (en) * | 2020-08-28 | 2024-02-28 | Jfe Steel Corp | Powder for annealing separator, method for producing same, and method for producing grain-oriented electrical steel sheet |
WO2024048721A1 (en) * | 2022-08-31 | 2024-03-07 | 日本製鉄株式会社 | Mixed powder, mgo particles, method for producing grain-oriented electrical steel sheet, method for producing mgo particles, and method for producing mixed powder |
WO2024048751A1 (en) * | 2022-08-31 | 2024-03-07 | 日本製鉄株式会社 | Mixed powder, mgo particles, method for producing grain-oriented electrical steel sheet, method for producing mgo particles, and method for producing mixed powder |
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