JP4557441B2

JP4557441B2 - Method and apparatus for refining quartz powder and quartz glass product

Info

Publication number: JP4557441B2
Application number: JP2001019768A
Authority: JP
Inventors: 正治石渡; 俊夫辻元
Original assignee: Japan Super Quartz Corp
Current assignee: Japan Super Quartz Corp
Priority date: 2000-03-17
Filing date: 2001-01-29
Publication date: 2010-10-06
Anticipated expiration: 2021-01-29
Also published as: JP2001328807A

Description

【０００１】
【発明の属する技術分野】
本発明は、石英粉末に含まれるアルカリ金属や鉄、銅などの不純物金属量を低減する精製方法と装置および精製した石英粉末を用いた製品に関する。より詳しくは、半導体工業用石英ガラス材料、シリコン引き上げ用石英ルツボ等の原料として用いられる天然石英粉末等の精製技術に関する。
【０００２】
【従来の技術】
天然石英には微量のアルカリ金属が含まれている。このアルカリ金属を含有する石英粉末を石英ガラスルツボ等の半導体工業用の熱処理部材等に使用すると部材の変形や失透を生じる。また、シリコン単結晶の引き上げに用いる石英ガラスルツボの場合には、ルツボに含まれるアルカリ金属によってシリコン単結晶が汚染される問題がある。そこで、天然石英等からアルカリ金属不純物を除去するために、(イ)電場を印加してアルカリ金属を陰極側に濃集させる方法や、(ロ)高温下で塩素含有ガス等を導入し、アルカリ金属を塩化物にして揮発除去する方法などの精製法が従来から知られている。
【０００３】
例えば、特開昭59-129421号公報、特開昭60-137892号公報、および特開平06-16494号公報には、石英インゴットないし石英ガラスルツボ製品に、１２００〜１３００℃の加熱下で、１０〜５０kvの直流を印加することにより、製品中のアルカリ金属イオンや銅イオンを移動させることが記載されている。しかし、これらの電解精製法はガラス製品に関するものであり、石英粉末についてそのまま適用するのは難しい。ガラス製品の場合は製品表面に電極を装着して通電することにより製品の一部にアルカリ金属を濃集させることができるが、石英粉末では粒子が流動化するので、石英粉末に通電してアルカリ金属を陰極側に濃集させても、通電後に石英粉末を取り出す際に、陰極側と陽極側の石英粉末が混じり合うと十分な精製効果は得られない。
【０００４】
一方、石英粉末については塩素含有ガス等を用いた精製方法が従来知られている。例えば、特開昭55-42267号公報、特開昭62-30632号公報、特開昭63-100038号公報には、天然石英粉末等を塩素含有ガス流中で加熱処理することにより、アルカリ金属等を塩化物にして揮発分離することが記載されている。これら従来の精製方法は、石英粉末に含まれるナトリウムやカリウムについてはある程度の効果が得られるが、リチウムについては十分な精製効果が得られない問題がある。
また、塩素ガスを用いるとその排ガス処理に手間がかかる欠点がある。
【０００５】
また、米国特許第4,956,069号公報には、石英粉末を装入した横型回転炉に、塩素含有ガスを導入すると共に電流を通じて石英粉末を精製する装置が記載されている。この精製装置では装置構成の安定化を図るために横型キルンを用い、キルンを回転して石英粉末を分散流動させて塩素含有ガスと接触させている。この機械的な回転機構のために装置が大型化する傾向があり、また、回転を妨げないように電極やガス流通の構造が回転軸の周囲に限定されるので装置構成が複雑になる。しかも、石英粉末とガスとの接触が必ずしも良好ではないために精製効果が良くない。さらに、この精製装置では石英粉末が回転されるので電極材が石英粉末によって削られ、これが石英粉末に混入して不純物となる問題がある。とくに電極材が炭化珪素(SiC)製であると、石英粉末に混入した炭化珪素が石英溶融時に気泡を生じてルツボの欠陥になる。また、本装置は塩素含有ガスを炉内に導入してアルカリ金属を塩化物にし、揮発除去しているが、排ガスの温度が適切に維持され通気が円滑でないと精製炉の排気口にアルカリ塩化物が凝縮して石英粉末に混入し不純物になる虞がある。
【０００６】
【発明が解決しようとする課題】
本発明は、従来の精製技術における上記問題を解決するものであり、石英粉末に含まれるアルカリ金属や銅、鉄などの不純物金属を簡単な構成で、しかも効率よく低減することができる精製技術を提供するものである。
【０００７】
【課題を解決するための手段】
すなわち本発明は、（１）陽極と陰極との間に石英ガラス製の隔壁を設けた精製容器を用い、隔壁の両側に装入した石英粉末に高温下で電場を形成し、石英粉末に含有されている不純物金属を陰極側に移動させることによって陽極側石英粉末の不純物金属量を低減することを特徴とする石英粉末の精製方法に関する。
【０００８】
本発明の上記精製方法は、好ましくは、（２）窒素ガス雰囲気下、空気雰囲気下、またはこれらに少量の水素ないし水を含む雰囲気下で、石英粉末の電解精製を行う方法、（３）精製容器内の石英粉末に、８００〜１３００℃の高温下で、５０V/cm以上の電場を形成することによって石英粉末の電解精製を行う精製方法（４）リチウム、カリウム、ナトリウム、銅、鉄の含有量をおのおの０.１ppm以下に低減する精製方法、（５）外筒の内側に内筒を有する二重管構造の石英ガラス製容器であって、外筒の周面と内筒の内側に電極を設けた精製容器を用い、外筒と内筒におのおの石英粉末を装入して精製する方法、（６）角形容器の両側に電極を有し、内部が隔壁で仕切られた石英ガラス製の精製容器を用いる精製方法を含む。
【０００９】
また、本発明は、（７）石英粉末を入れる精製容器と加熱手段とを備え、精製容器は外筒とその内側に内筒を有する二重管構造の石英ガラス製容器であって、外筒の周面と内筒の内側に電極を有し、さらに容器内部に通じる通気路が設けられていることを特徴とする石英粉末の精製装置、（８）角形の石英ガラス製精製容器と加熱手段とを備え、容器の両側には電極が設けられ、内部が隔壁で仕切られており、さらに容器内部に通じる通気路が設けられていることを特徴とする石英粉末の精製装置に関する。
【００１０】
さらに本発明は、（９）上記(1)〜(6)の何れかの方法によって精製された石英粉末によって製造された石英ガラス製品に関する。
【００１１】
【発明の実施の態様】
以下、本発明を実施態様に即して詳細に説明する。図１は本発明に係る縦型筒状装置の概略断面図、図２はその概略横断面図、図３、図４は本発明に係る他の装置構成例を示す概略縦断面図である。
【００１２】
( Ｉ ) 精製方法
図示するように、本発明の精製方法は、陽極と陰極を備え、両極の間に隔壁を設けた電解精製容器を用いる。この隔壁は石英粉末から放出されたアルカリ金属等の不純物金属イオンの移動が妨げられないように石英ガラスからなるものが好ましい。陽極と陰極および隔壁を有するものであれば精製容器の形状は限定されない。筒型でも良く、角型でも良い。精製容器の例としては、図１,２に示す筒状の縦型容器を用いることができる。この容器１０は外筒１１と内筒１２とからなる二重管の構造を有し、内筒１２が隔壁となり、外筒１１の下部内周を囲む帯状の陽極または陰極１３が設けられており、これと対になる棒状の電極１４が内筒１２の軸芯に設けられている。
【００１３】
精製容器の他の例は、図３に示すように、縦型の筒型容器３１の上端および下端に陽極３３または陰極３４を設け、この容器内部を上下に仕切る隔壁３２を設けたものでも良い。また、図４に示すように、角型容器４０の両側に陽極４１または陰極４２を設け、その間に隔壁４３を設けたものでも良い。陽極および陰極の材質はカーボンまたは白金が好ましい。外筒の電極や角型容器の電極は、石英ガラス質の容器を用いた場合、容器の外周に電極を密着して取り付けても良い。
電極を容器の外周に装着することにより、石英粉末の流動によって電極が磨耗するのを防止することができる。なお、石英ガラス製の容器の外周に電極を設けても、電極が密着して設けられていれば石英粉末に十分な電場をかけることができる。また、石英粉末全体に均一に電場が印加されるように、電極の少なくとも一方は面状に形成したものが良い。
【００１４】
電解容器の隔壁に密着するように陽極と陰極の間に石英粉末を充填し、高温下で、上記電極を通じて直流電圧を印加して石英粉末に高強度の電場をかける。具体的には、８００〜１３００℃の高温下で、５０V/cm以上、好ましくは１００V/cm以上、より好ましくは５００V/cm以上の電場を加える。通電時間は石英粉末の量に応じて調整すれば良い。なお、カーボン製の電極を用いる場合には、電極の酸化による劣化を防止するため容器を密閉型とし内部を窒素ガス雰囲気にするのが好ましい。アルゴンガスは放電を招きやすいので好ましくない。白金製電極等の場合には空気雰囲気で良く、容器内部を密閉しなくても良い。
【００１５】
なお、これらの窒素ガス雰囲気または空気雰囲気に、少量の水素または水を含有させることによって精製効果を高めることができる。添加量は雰囲気中の濃度で、水素の場合１〜５wt％、水(水蒸気)の場合５〜３０wt％が好ましい。
【００１６】
容器内の石英粉末に電場を加えると、石英粉末に含まれているアルカリ金属等の不純物金属がイオン化して陰極に引き寄せられる。隔壁は石英粉末と同様に石英ガラス製であるので陽極側の石英粉末に含まれる不純物金属イオンは隔壁を通過して陰極側に移動する。この結果、陽極側の石英粒子に含まれる不純物金属量が低減し、石英粉末を精製することができる。陰極側の石英粒子にはアルカリ金属等の不純物金属イオンが濃集するが、陽極側と陰極側とは隔壁によって仕切られているので、両方の石英粉末が混じることはなく、陽極側の精製石英粉末を陰極側の石英粉末と分離して回収することができる。なお、陰極側の石英粉末は再使用することができる。
【００１７】
このように、本発明の上記精製方法は、石英ガラス製の隔壁を介在させて石英粉末に電場を加えることにより、アルカリ金属等の不純物金属イオンがこの隔壁を通じて陰極側に移動するので、陽極側石英粉末の不純物金属量が低減し、優れた精製効果を得ることができ、かつ隔壁によって陽極側の精製石英粉末と陰極側の石英粉末とを分離して回収することができる。
【００１８】
なお、塩素ガス等を用いる従来の精製方法では特にリチウムの精製効果が低いが、本発明の精製方法によれば、アルカリ金属が電場の作用によってイオン化するのでリチウムについても良好な精製効果を得ることができる。具体的には、リチウム、カリウムおよびナトリウムを何れも０.１ppm以下、好ましくは０.０５ppm以下に低減することができる。従って、本発明の方法によって精製した石英粉末を用いることにより、アルカリ金属不純物が大幅に少ない石英ガラス製品を得ることができる。
【００１９】
(II) 精製装置
本発明に係る図１,図２の精製装置は、図示するように、石英粉末５０を入れる縦型容器１０とその加熱手段(図示省略)によって形成されている。容器１０は縦型の外筒１１と、その内側に一定間隔を保って設けた石英ガラス質の内筒１２とによって形成されており、この外筒１１と内筒１２からなる二重管構造を有している。外筒１１と内筒１２は石英ガラス製のものを用いることができる。石英ガラス製の外筒および内筒を用い、この外筒周壁と内筒内側におのおの電極を設けることにより、石英粉末全体に効果的に電場をかけることができる。具体的には、外筒１１の周面にはカーボン製の陽極１３が外筒の内周を巡って設けられており、一方、内筒１２の中央には棒状の陰極１４が設けられている。外筒１１および内筒１２の頭部にはおのおの蓋１５,１６が冠着し、内筒１２は倒れないように外筒１１の蓋１５によって支えられている。これら外筒１１および内筒１２の内部は蓋１５,１６によって密閉されている。この蓋１５,１６にはおのおの石英粉末を内部に供給する開口部２１,２２が設けられている。また、外筒１１の底部は通気性の床材１７によって形成されており、その下側に通気室１８が形成されている。通気室１８には通気路２０が接続しており、この通気路２０に対応して上記蓋１５には排気管路１９が接続している。なお、通気室１８を設けずに通気路２０を直接に外筒の底部に接続しても良い。
【００２０】
外筒１１および内筒１２の内部に石英粉末を陽極１３の高さに充填し、この石英粉末を充填した容器内部に、カーボン製電極を保護するために窒素ガスを導入し、外筒１１の周囲に配設したヒータ(図示省略)によって容器内部を８００〜１３００℃に加熱し、電極１３,１４を通じて石英粉末に５０V/cm以上、好ましくは５００V/cm以上の電場を加える。なお、白金製電極を用いた場合には容器内部に窒素ガスを導入する必要はない。
【００２１】
電場の作用により、外筒１１と内筒１２の間に充填されている石英粉末に含まれるアルカリ金属等の不純物金属はイオン化し、内筒１２を通過して陰極側に移動し内筒１２の内側に濃集する。この結果、外筒側の石英粒子の不純物金属量が低減する。精製後、蓋１５を外して外筒側の精製した石英粉末５０を取り出す。
一方、内筒１２の石英粉末５０は、引き続き内筒に充填したまま外筒側に新たな石英粉末を充填して電解精製を継続してもよく、あるいは内筒の石英粉末を取り出して新たな石英粉末と混合し、再利用しても良い。
【００２２】
図３に示す装置構成は、縦型容器３１の内部を隔壁３２で上下に仕切ったものであり、筒状容器３１の底部に陽極３４と排出口３５が設けられており、一方、容器３１の頭部には蓋３７が冠着し、この蓋３７に陰極３３が設けられている。
上記隔壁３２は石英ガラスによって形成されており容器内部に遊嵌されている。
なお、容器底部に陰極を設け頭部に陽極を設けても良い。
【００２３】
容器３１の蓋３７を開けて内部に石英粉末を頭部付近まで装入した後に、隔壁３２を石英粉末に載せ、さらにその上に石英粉末を入れて蓋３７を閉める。次いで、電極３３,３４を通じて電圧を印加し、石英粉末に電場を加える。この電場の作用により、陽極側の石英粉末のアルカリ金属量が低減する。通電停止後、排出口３５を開いて容器内部の石英粉末を取り出す。陽極側の精製された石英粉末５０が排出口３５から抜き出されるのに伴って隔壁３２が自重によって次第に下降し、精製石英粉末の排出終了と共に排出口３５を塞ぎ、陰極側の石英粉末が容器内部に残る。
【００２４】
図４の装置構成は、角型容器４０を用いたものであり、容器４０の両側面に陽極４１と陰極４２が設けられており、これらの間に石英ガラス質の隔壁４３が介設されている。容器４０の上面は蓋４４によって閉じられている。陽極４１と陰極４２および隔壁４３に接触するように容器内部に石英粉末５０を充填する。この石英粉末５０に電場を加えることにより、陽極側の石英粉末の不純物金属量を低減することができる。
【００２５】
(III) 精製例
図１,図２に示す装置構成の精製装置を用い、石英粉末２０kgを容器(外筒および内筒)に充填し、カーボン製電極を保護するため容器内部に窒素ガスを導入した後に１２００℃に加熱し、石英粉末に１５kvの直流電圧を６時間印加した。この電解精製後、石英粉末に含まれるリチウム、ナトリウム、カリウムの濃度を定量した。この結果を表１のNo.１に示した。処理前の石英粉末に比較して、外筒側の石英粉末(20kg)のアルカリ金属濃度は大幅に低減しており、特にリチウムは０.０１ppmと約１/２０に激減している。また、ナトリウム、カリウムの濃度も０.１ppm以下であり、優れた精製効果が得られた。一方、内筒側の石英粉末(20kg)のアルカリ金属量は増加しており、外筒側の石英粉末に含まれるアルカリ金属が内筒側の石英粉末に移動して濃集したことが分かる。
【００２６】
電圧の印加時間を３時間に変え、容器内の雰囲気を窒素ガス雰囲気(No.２)、水素２wt％混入した窒素ガス雰囲気(No.３)、水蒸気１５wt％を混入した窒素ガス雰囲気(No.４)に変えた以外は上記と同様にして石英粉末を電解精製した。この結果を表１に示した。この結果に示すように、窒素ガスに少量の水素または水蒸気を混入することによって、精製効果が大幅に向上することが確認された。すなわち、No.３〜４の精製時間はNo.１の１/２であるが、アルカリ金属、銅、鉄についてNo.１の場合を上回る除去効果を達成している。
【００２７】
【表１】

【００２８】
【発明の効果】
本発明の精製方法および精製装置によれば、石英粉末に含有されているアルカリ金属や銅、鉄などの不純物金属を簡単な構成で、しかも効率良く低減することができる。
【図面の簡単な説明】
【図１】本発明に係る型筒状装置の概略縦断面図
【図２】図１に示す装置の概略横断面図
【図３】本発明に係る他の装置構成例を示す概略縦断面図
【図４】本発明に係る他の装置構成例を示す概略縦断面図
【符号の説明】
１０−精製装置、１１−外筒、１２−内筒、１３−陽極、１４−陰極、
１５,１６−蓋、１7−床材、１８−通気室、１９−排気管路、２０−通気路、
２１,２２−開口部、３１−容器、３２−隔壁、３３−陰極、３４−陽極、
３５−排出口、３７−蓋、４０−容器、４１−陽極、４２−陰極、４３−隔壁、
４４−蓋[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a purification method and apparatus for reducing the amount of impurity metals such as alkali metals, iron, and copper contained in quartz powder, and a product using the purified quartz powder. More specifically, the present invention relates to a purification technology for natural quartz powder used as a raw material for quartz glass material for semiconductor industry, quartz crucible for pulling silicon, and the like.
[0002]
[Prior art]
Natural quartz contains trace amounts of alkali metals. When the quartz powder containing the alkali metal is used for a heat treatment member for semiconductor industry such as a quartz glass crucible, the member is deformed or devitrified. Further, in the case of a quartz glass crucible used for pulling up a silicon single crystal, there is a problem that the silicon single crystal is contaminated by an alkali metal contained in the crucible. Therefore, in order to remove alkali metal impurities from natural quartz or the like, (b) a method of applying an electric field to concentrate the alkali metal on the cathode side, or (b) introducing a chlorine-containing gas at a high temperature to 2. Description of the Related Art Purification methods such as a method of volatilizing and removing metals as chlorides are conventionally known.
[0003]
For example, JP-A-59-129421, JP-A-60-137892, and JP-A-06-16494 disclose that a quartz ingot or a quartz glass crucible product is heated at 1200 to 1300 ° C. under 10 ° C. It describes that alkali metal ions and copper ions in a product are moved by applying a direct current of ˜50 kv. However, these electrolytic purification methods are related to glass products and are difficult to apply as they are to quartz powder. In the case of glass products, it is possible to concentrate alkali metal in a part of the product by attaching an electrode to the surface of the product and energizing it. However, in quartz powder, particles are fluidized. Even if the metal is concentrated on the cathode side, a sufficient purification effect cannot be obtained if the quartz powder on the cathode side and the anode side are mixed when the quartz powder is taken out after energization.
[0004]
On the other hand, a purification method using a chlorine-containing gas or the like is conventionally known for quartz powder. For example, in Japanese Patent Laid-Open Nos. 55-42267, 62-30632, and 63-100038, a natural quartz powder or the like is heat-treated in a chlorine-containing gas stream to obtain an alkali metal. It is described that volatile separation is performed using chloride as a chloride. These conventional purification methods have a certain effect for sodium and potassium contained in the quartz powder, but have a problem that a sufficient purification effect cannot be obtained for lithium.
Further, when chlorine gas is used, there is a drawback that it takes time to treat the exhaust gas.
[0005]
US Pat. No. 4,956,069 describes an apparatus for introducing a chlorine-containing gas into a horizontal rotary furnace charged with quartz powder and purifying the quartz powder through an electric current. In this refining apparatus, a horizontal kiln is used to stabilize the structure of the apparatus, and the kiln is rotated to disperse and flow the quartz powder to contact the chlorine-containing gas. This mechanical rotation mechanism tends to increase the size of the apparatus, and the structure of the apparatus is complicated because the electrode and gas flow structure is limited to the periphery of the rotation axis so as not to prevent rotation. Moreover, since the contact between the quartz powder and the gas is not always good, the purification effect is not good. Further, in this refining apparatus, since the quartz powder is rotated, the electrode material is scraped by the quartz powder, which is mixed into the quartz powder and becomes an impurity. In particular, when the electrode material is made of silicon carbide (SiC), silicon carbide mixed in the quartz powder generates bubbles when the quartz is melted, resulting in a crucible defect. In addition, this equipment introduces chlorine-containing gas into the furnace to convert alkali metal into chloride and volatilizes and removes it. However, if the exhaust gas temperature is maintained properly and ventilation is not smooth, alkali chloride is introduced into the exhaust port of the purification furnace. There is a risk that the material will condense and mix into the quartz powder and become impurities.
[0006]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems in the conventional refining technology, and provides a refining technology that can reduce the impurity metals such as alkali metals, copper, and iron contained in the quartz powder with a simple structure and efficiently. It is to provide.
[0007]
[Means for Solving the Problems]
That is, the present invention (1) uses a purification vessel provided with a partition made of quartz glass between an anode and a cathode, forms an electric field at high temperature on the quartz powder charged on both sides of the partition, and is contained in the quartz powder. The present invention relates to a method for purifying quartz powder, characterized in that the amount of impurity metal in the anode-side quartz powder is reduced by moving the impurity metal that is applied to the cathode side.
[0008]
The above purification method of the present invention preferably comprises (2) a method of performing electrolytic purification of quartz powder in a nitrogen gas atmosphere, an air atmosphere, or an atmosphere containing a small amount of hydrogen or water, and (3) purification. A purification method for electrolytic purification of quartz powder by forming an electric field of 50 V / cm or higher on the quartz powder in the container at a high temperature of 800 to 1300 ° C. (4) Inclusion of lithium, potassium, sodium, copper and iron A purification method for reducing the amount to 0.1 ppm or less, (5) a quartz glass container having a double-pipe structure having an inner cylinder inside the outer cylinder, with electrodes on the outer surface of the outer cylinder and the inner cylinder (6) A quartz glass made of quartz glass having electrodes on both sides of a rectangular container and partitioned inside by a partition wall. A purification method using a purification vessel is included.
[0009]
The present invention also includes (7) a purification container for containing quartz powder and a heating means, wherein the purification container is a quartz glass container having a double-pipe structure having an outer cylinder and an inner cylinder inside thereof. A quartz powder refinement device, characterized in that an electrode is provided on the inner surface of the inner cylinder and the inner cylinder, and a ventilation passage leading to the interior of the vessel is provided, (8) a square quartz glass purification vessel and heating means And an electrode is provided on both sides of the container, the interior is partitioned by a partition wall, and an air passage leading to the interior of the container is further provided.
[0010]
Furthermore, the present invention relates to (9) a quartz glass product produced from the quartz powder purified by any one of the above methods (1) to (6).
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail according to embodiments. FIG. 1 is a schematic cross-sectional view of a vertical cylindrical device according to the present invention, FIG. 2 is a schematic cross-sectional view thereof, and FIGS. 3 and 4 are schematic vertical cross-sectional views showing other device configuration examples according to the present invention.
[0012]
( I ) Purification method As shown in the figure, the purification method of the present invention uses an electrolytic purification vessel provided with an anode and a cathode and provided with a partition wall between both electrodes. The partition walls are preferably made of quartz glass so that movement of impurity metal ions such as alkali metals released from the quartz powder is not hindered. The shape of the purification vessel is not limited as long as it has an anode, a cathode, and a partition. It may be cylindrical or square. As an example of the purification container, a cylindrical vertical container shown in FIGS. 1 and 2 can be used. The container 10 has a double tube structure composed of an outer cylinder 11 and an inner cylinder 12, the inner cylinder 12 serves as a partition, and a strip-like anode or cathode 13 surrounding the lower inner periphery of the outer cylinder 11 is provided. A rod-shaped electrode 14 which is paired with this is provided on the axial center of the inner cylinder 12.
[0013]
As shown in FIG. 3, another example of the purification container may be one in which an anode 33 or a cathode 34 is provided at the upper and lower ends of a vertical cylindrical container 31 and a partition wall 32 is provided to partition the inside of the container vertically. . Moreover, as shown in FIG. 4, the anode 41 or the cathode 42 may be provided on both sides of the rectangular container 40, and the partition wall 43 may be provided between them. The material of the anode and cathode is preferably carbon or platinum. When a quartz glassy container is used, the electrode of the outer cylinder or the electrode of the square container may be attached in close contact with the outer periphery of the container.
By mounting the electrode on the outer periphery of the container, it is possible to prevent the electrode from being worn by the flow of the quartz powder. Even if the electrode is provided on the outer periphery of the quartz glass container, a sufficient electric field can be applied to the quartz powder as long as the electrode is provided in close contact. Further, it is preferable that at least one of the electrodes is formed in a planar shape so that an electric field is uniformly applied to the entire quartz powder.
[0014]
A quartz powder is filled between the anode and the cathode so as to be in close contact with the partition wall of the electrolytic vessel, and a high-intensity electric field is applied to the quartz powder by applying a DC voltage through the electrode at a high temperature. Specifically, an electric field of 50 V / cm or higher, preferably 100 V / cm or higher, more preferably 500 V / cm or higher is applied at a high temperature of 800 to 1300 ° C. The energization time may be adjusted according to the amount of quartz powder. When a carbon electrode is used, it is preferable to use a sealed container and a nitrogen gas atmosphere inside to prevent deterioration of the electrode due to oxidation. Argon gas is not preferable because it easily causes discharge. In the case of a platinum electrode or the like, an air atmosphere may be used, and the inside of the container may not be sealed.
[0015]
The purification effect can be enhanced by adding a small amount of hydrogen or water to these nitrogen gas atmosphere or air atmosphere. The addition amount is a concentration in the atmosphere, preferably 1 to 5 wt% for hydrogen and 5 to 30 wt% for water (steam).
[0016]
When an electric field is applied to the quartz powder in the container, impurity metals such as alkali metals contained in the quartz powder are ionized and attracted to the cathode. Since the partition walls are made of quartz glass like the quartz powder, the impurity metal ions contained in the quartz powder on the anode side move to the cathode side through the partition walls. As a result, the amount of impurity metal contained in the quartz particles on the anode side is reduced, and the quartz powder can be purified. Impurity metal ions such as alkali metals are concentrated in the quartz particles on the cathode side, but since the anode side and the cathode side are separated by a partition wall, both quartz powders are not mixed, and the purified quartz on the anode side is not mixed. The powder can be recovered separately from the quartz powder on the cathode side. Note that the quartz powder on the cathode side can be reused.
[0017]
Thus, in the above purification method of the present invention, when an electric field is applied to the quartz powder through the quartz glass partition wall, impurity metal ions such as alkali metals move to the cathode side through the partition wall. The amount of impurity metal in the quartz powder is reduced, an excellent purification effect can be obtained, and the purified quartz powder on the anode side and the quartz powder on the cathode side can be separated and collected by the partition walls.
[0018]
Although the purification effect of lithium is particularly low in the conventional purification method using chlorine gas or the like, according to the purification method of the present invention, the alkali metal is ionized by the action of an electric field, so that a good purification effect can be obtained also for lithium. Can do. Specifically, lithium, potassium, and sodium can all be reduced to 0.1 ppm or less, preferably 0.05 ppm or less. Therefore, by using the quartz powder purified by the method of the present invention, it is possible to obtain a quartz glass product with significantly less alkali metal impurities.
[0019]
(II) Purification apparatus The purification apparatus of Figs. 1 and 2 according to the present invention is formed by a vertical container 10 containing quartz powder 50 and its heating means (not shown) as shown. . The container 10 is formed by a vertical outer cylinder 11 and a quartz vitreous inner cylinder 12 provided at a constant interval on the inner side thereof, and a double tube structure comprising the outer cylinder 11 and the inner cylinder 12 is formed. Have. As the outer cylinder 11 and the inner cylinder 12, those made of quartz glass can be used. By using an outer cylinder and an inner cylinder made of quartz glass and providing electrodes on the outer peripheral wall and the inner cylinder, an electric field can be effectively applied to the entire quartz powder. Specifically, a carbon anode 13 is provided around the inner circumference of the outer cylinder 11 on the peripheral surface of the outer cylinder 11, while a rod-like cathode 14 is provided in the center of the inner cylinder 12. . Lids 15 and 16 are respectively attached to the heads of the outer cylinder 11 and the inner cylinder 12, and the inner cylinder 12 is supported by the lid 15 of the outer cylinder 11 so as not to fall down. The insides of the outer cylinder 11 and the inner cylinder 12 are sealed with lids 15 and 16. The lids 15 and 16 are provided with openings 21 and 22 for supplying quartz powder therein. Further, the bottom of the outer cylinder 11 is formed by a breathable flooring 17, and a ventilation chamber 18 is formed on the lower side thereof. A ventilation path 20 is connected to the ventilation chamber 18, and an exhaust pipe 19 is connected to the lid 15 corresponding to the ventilation path 20. The ventilation path 20 may be directly connected to the bottom of the outer cylinder without providing the ventilation chamber 18.
[0020]
The outer cylinder 11 and the inner cylinder 12 are filled with quartz powder at the height of the anode 13, and nitrogen gas is introduced into the container filled with the quartz powder to protect the carbon electrode. The inside of the container is heated to 800 to 1300 ° C. by a heater (not shown) arranged around it, and an electric field of 50 V / cm or more, preferably 500 V / cm or more is applied to the quartz powder through the

electrodes

13 and 14. When a platinum electrode is used, it is not necessary to introduce nitrogen gas into the container.
[0021]
Due to the action of the electric field, the impurity metal such as alkali metal contained in the quartz powder filled between the outer cylinder 11 and the inner cylinder 12 is ionized, passes through the inner cylinder 12, moves to the cathode side, and moves to the inner cylinder 12. Concentrate on the inside. As a result, the amount of impurity metal in the quartz particles on the outer cylinder side is reduced. After purification, the lid 15 is removed and the purified quartz powder 50 on the outer cylinder side is taken out.
On the other hand, the quartz powder 50 in the inner cylinder 12 may continue to be subjected to electrolytic purification by filling the outer cylinder side with new quartz powder while the inner cylinder is still filled, or the quartz powder in the inner cylinder may be taken out and renewed. It may be mixed with quartz powder and reused.
[0022]
In the apparatus configuration shown in FIG. 3, the inside of the vertical container 31 is partitioned vertically by a partition wall 32, and an anode 34 and a discharge port 35 are provided at the bottom of the cylindrical container 31. A lid 37 is attached to the head, and a cathode 33 is provided on the lid 37.
The partition wall 32 is made of quartz glass and is loosely fitted inside the container.
A cathode may be provided at the bottom of the container, and an anode may be provided at the head.
[0023]
After opening the lid 37 of the container 31 and loading the quartz powder into the vicinity of the head, the partition wall 32 is placed on the quartz powder, and the quartz powder is further placed on the partition wall 32 and the lid 37 is closed. Next, a voltage is applied through the

electrodes

33 and 34 to apply an electric field to the quartz powder. By the action of this electric field, the amount of alkali metal in the quartz powder on the anode side is reduced. After stopping energization, the discharge port 35 is opened and the quartz powder inside the container is taken out. As the purified quartz powder 50 on the anode side is extracted from the discharge port 35, the partition wall 32 gradually descends due to its own weight, closes the discharge port 35 when the purified quartz powder is completely discharged, and the quartz powder on the cathode side becomes the container. Remains inside.
[0024]
The apparatus configuration of FIG. 4 uses a rectangular container 40, and an anode 41 and a cathode 42 are provided on both side surfaces of the container 40, and a quartz glassy partition wall 43 is interposed therebetween. Yes. The upper surface of the container 40 is closed by a lid 44. The container is filled with quartz powder 50 so as to be in contact with the anode 41, the cathode 42 and the partition wall 43. By applying an electric field to the quartz powder 50, the amount of impurity metal in the quartz powder on the anode side can be reduced.
[0025]
(III) Example of purification Using a purification apparatus having the configuration shown in Figs. 1 and 2, 20 kg of quartz powder is filled into a container (outer cylinder and inner cylinder), and inside the container to protect the carbon electrode. After introducing nitrogen gas, it was heated to 1200 ° C., and a DC voltage of 15 kv was applied to the quartz powder for 6 hours. After this electrolytic purification, the concentrations of lithium, sodium and potassium contained in the quartz powder were quantified. The results are shown as No. 1 in Table 1. Compared to the quartz powder before the treatment, the alkali metal concentration of the quartz powder (20 kg) on the outer cylinder side is greatly reduced, and in particular, lithium is drastically reduced to about 1/20 at 0.01 ppm. Further, the concentration of sodium and potassium was 0.1 ppm or less, and an excellent purification effect was obtained. On the other hand, it can be seen that the amount of alkali metal in the quartz powder on the inner cylinder side (20 kg) has increased, and the alkali metal contained in the quartz powder on the outer cylinder side has moved to the quartz powder on the inner cylinder side and concentrated.
[0026]
The voltage application time was changed to 3 hours, and the atmosphere inside the container was a nitrogen gas atmosphere (No. 2), a nitrogen gas atmosphere mixed with 2 wt% hydrogen (No. 3), and a nitrogen gas atmosphere mixed with 15 wt% water vapor (No. 2). The quartz powder was electrolytically purified in the same manner as described above except that it was changed to 4). The results are shown in Table 1. As shown in this result, it was confirmed that the purification effect was greatly improved by mixing a small amount of hydrogen or water vapor into the nitrogen gas. That is, the purification time of No. 3 to 4 is 1/2 of No. 1, but the removal effect exceeding the case of No. 1 is achieved for alkali metals, copper and iron.
[0027]
[Table 1]

[0028]
【The invention's effect】
According to the purification method and the purification apparatus of the present invention, it is possible to efficiently reduce alkali metals, impurity metals such as copper and iron contained in quartz powder with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view of a cylindrical apparatus according to the present invention. FIG. 2 is a schematic transverse sectional view of the apparatus shown in FIG. 1. FIG. 3 is a schematic longitudinal sectional view showing another apparatus configuration example according to the present invention. FIG. 4 is a schematic longitudinal sectional view showing another apparatus configuration example according to the present invention.
10-purifier, 11-outer cylinder, 12-inner cylinder, 13-anode, 14-cathode,
15, 16-lid, 17-floor, 18-ventilation chamber, 19-exhaust duct, 20-ventilation path,
21, 22-opening, 31-container, 32-partition wall, 33-cathode, 34-anode,
35- discharge port, 37- lid, 40- container, 41- anode, 42- cathode, 43- partition,
44-lid

Claims

Using a purification vessel with a quartz glass partition between the anode and cathode, an electric field is formed at high temperature on the quartz powder charged on both sides of the partition, and the impurity metal contained in the quartz powder is removed from the cathode side. A method for purifying quartz powder, characterized in that the amount of impurity metal in the anode-side quartz powder is reduced by moving to an anode.

The purification method according to claim 1, wherein the electrolytic purification of the quartz powder is performed in a nitrogen gas atmosphere, an air atmosphere, or an atmosphere containing a small amount of hydrogen or water.

The purification method according to claim 1 or 2, wherein the electrolytic purification of the quartz powder is performed by forming an electric field of 50 V / cm or more on the quartz powder in the purification container at a high temperature of 800 to 1300 ° C.

The method according to claim 1, 2 or 3, wherein the contents of lithium, potassium, sodium, copper and iron are reduced to 0.1 ppm or less.

A quartz glass container with a double-pipe structure having an inner cylinder inside the outer cylinder, using a refining container with electrodes provided on the outer surface of the outer cylinder and the inner cylinder, and the quartz in each of the outer cylinder and the inner cylinder The purification method according to claim 1, wherein the powder is purified by charging.

2. The purification method according to claim 1, wherein a purification vessel made of quartz glass having electrodes on both sides of the rectangular vessel and partitioned by a partition is used.

A purification container for containing quartz powder and a heating means are provided, and the purification container is a quartz glass container having a double tube structure having an outer cylinder and an inner cylinder inside thereof, and is provided on the outer surface of the outer cylinder and on the inner side of the inner cylinder. An apparatus for purifying quartz powder, comprising an electrode and further provided with a ventilation path leading to the inside of the container.

A rectangular quartz glass purification vessel and a heating means are provided, electrodes are provided on both sides of the vessel, the inside is partitioned by a partition wall, and an air passage leading to the inside of the vessel is further provided. Purification equipment for quartz powder.

A quartz glass product produced from the quartz powder purified by the method according to claim 1.