JP4190678B2 - Purification method of gallium - Google Patents
Purification method of gallium Download PDFInfo
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- JP4190678B2 JP4190678B2 JP30417799A JP30417799A JP4190678B2 JP 4190678 B2 JP4190678 B2 JP 4190678B2 JP 30417799 A JP30417799 A JP 30417799A JP 30417799 A JP30417799 A JP 30417799A JP 4190678 B2 JP4190678 B2 JP 4190678B2
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- gallium
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【0001】
【発明の属する技術分野】
本発明は、真空加熱を利用したガリウムの精製方法、特にガリウムを半導体原料として使用可能な99.9999%以上の純度に精製するガリウムの精製方法に関するものである。
【0002】
【従来の技術】
ガリウムは、GaAsやGaPなどの化合物半導体結晶あるいはGaPやGaAsなどの液相エピタキシャル成長の用途で、99.9999%以上の純度が要求されている。
ガリウムは、ボーキサイトからアルミナを製造する際のバイヤー液か、または閃亜鉛鉱の亜鉛蒸留のレトルト残渣もしくは亜鉛ばい焼鉱の硫酸浸出残渣から酸化ガリウムを副生成物として回収し、この回収された酸化ガリウムを苛性ソーダ液に溶解した後、電解採取によって98〜99%の低純度ガリウムとして生産される。この低純度ガリウムは、さらに真空加熱精製、酸洗浄、再結晶の工程を組み合わせて精製し、99.9999%以上に高純度化されている。
【0003】
一方、ガリウムを含有するスクラップとして、GaAsあるいはGaP単結晶の端面カット部分、破損ウエハー、切断屑、ラッピング屑、気相エピタキシャル成長工程での排出ガス、液相エピタキシャル成長工程での使用済ガリウム、さらに回路形成後のウエハーの破損物などがある。
これらのガリウムスクラップは真空加熱精製、電解精製、酸洗浄、さらには再結晶の精製工程を単独あるいは組み合わせて高純度化され、再び化合物半導体結晶や液相エピタキシャル成長用原料に使用される。
【0004】
電解採取もしくは電解精製は、酸化ガリウムもしくは水酸化ガリウムを苛性ソーダ水溶液に溶解した液を電解液とし、白金、カーボンまたはステンレスを電極とする電解により陰極にガリウムを析出させ回収する方法である。電解液中のガリウム濃度は30%以下、水酸化ナトリウム濃度は30〜50%で、最大2000A/m2 の電流密度で電解する。
【0005】
電解採取は、原料である酸化ガリウムまたは水酸化ガリウムからガリウムを電析するのが主目的で、その純度は99%が限界である。電解精製は、より高い純度の99.99%を得る目的で行われる。電解採取または電解精製でHg、Al、Zn、Pbなどの低減が可能であるが、電解液の付着や巻き込み、さらに電解条件の精密制御が困難なため大きな純度向上を期待することはできず、得られるガリウムの純度は99.99%が上限とされている。
【0006】
真空加熱精製は、蒸気圧の差を利用してガリウムよりも蒸気圧の高い不純物を蒸発除去する方法である。金属ガリウムを1.3×10-3Pa以下の真空度で1000℃以上の温度に加熱し、蒸気圧の高い不純物であるHg、Znなどは1ppm以下まで低減させることが可能である。しかし、ガリウムと蒸気圧差の小さい不純物の場合には、さらに高温まで加熱するため容器から不純物が混入し易く、あるいはガリウムの蒸発による損失を招来する。さらに不純物が金属間化合物を形成している場合には、数ppmより低い値にすることは難しい。
【0007】
酸洗浄は、溶融状態のガリウムを塩酸、硝酸、あるいはこれらの混酸に接触させることによりイオン化傾向の大きな不純物を酸に溶出させ、純度を高くする方法である。0.001〜0.1mol/dm3 に希釈した酸とガリウムとを攪拌などで接触させて含有される不純物の溶出を促進する。攪拌は、強力なほど接触が増加するため短時間で精製効果が得られる。この方法ではCa、Zn、Cdなどの低減が可能である。
【0008】
しかし、強力な攪拌を続けると、酸溶液は黒色の懸濁液となる。懸濁液中の黒色物質はガリウム微粒子とその表面に生成したガリウム酸化物もしくは水酸化物皮膜からなり、酸溶性である。ガリウム微粒子の表面上のガリウム酸化物あるいは水酸化物皮膜に不純物が濃縮されており、純度の高いガリウムを得るためには、このガリウム微粒子を完全に分離する必要がある。また、収率向上のためには分離したガリウム微粒子の回収を行う必要があり、生産性を上げるうえで欠点となっている。
【0009】
再結晶は、ガリウム融液から結晶を晶出させる際に偏析係数の差を利用して融液中に不純物を濃縮し、固化部分の純度を高くする方法である。再結晶の手法には、一方向凝固、ゾーンメルティング、単結晶成長がある。
一方向凝固は、ボート等の容器に入れた溶融ガリウムを一端からゆっくり冷却、固化してゆき、融液中に不純物を濃縮する方法である。不純物の偏析には、冷却速度が影響し、冷却速度が遅いほど精製効率が上昇する。しかし、冷却速度を遅くすると生産性が低下するためコスト上昇を引き起こす。
【0010】
ゾーンメルティングは、多数回の一方向凝固を一回の操作で連続的に行う方法であるため一方向凝固の生産性の低さを改善できるが、一方向凝固と同様に処理量が多くなると制御が難しく、生産性の大幅な改善には至っていない。
そのため再結晶は、最終の精製工程として真空加熱精製、電解精製、酸洗浄で除去され難い不純物の低減に使われるが生産性が悪い欠点がある。再結晶で精製対象になる主な元素としては、鉛、インジウムなどが挙げられる。
【0011】
99.99%程度の低純度ガリウムや液晶エピタキシャル成長からのスクラップに対しては、一般に真空加熱精製、酸洗浄、および再結晶により純度アップすることで最終的に純度99.9999%以上のガリウムが得られている。
【0012】
【発明が解決しようとする課題】
従来のガリウムの精製方法では、ガリウムに含有される不純物の種類と量に応じ、上記各種の方法を組み合わせることでガリウムの高純度化が行われてきた。このように不純物の性状に最適な精製工程を多数組み合わせるという手法が用いられていたので、従来のガリウム精製方法は工程が多く、極めて煩雑であった。特に、鉛などの不純物は真空加熱や酸洗浄では除去され難く、一般に再結晶法により除去が行われてきたが、生産性が低いためコストが高くなっていた。
【0013】
本発明は、鉛などの不純物を再結晶法を用いずに除去することができ、生産性が高く、半導体原料として使用可能な純度99.9999%以上のガリウムを低コストで得ることのできるガリウムの精製方法を提供することを目的とする。
【0014】
【課題を解決するための手段】
本発明のガリウムの精製方法では、ガリウムに亜鉛を添加してアルゴンまたは窒素雰囲気中で420〜910℃に加熱保持し、次に真空に引きながら800〜1000℃で加熱した後、ろ過することにより上記課題を解決している。
亜鉛はガリウム中の不純物と共沸混合物を形成すると考えられ、鉛のような高沸点金属を本来の沸点より低温で蒸発除去することが可能となる。
【0015】
ガリウムは石英容器に入れ、そこに亜鉛を添加する。亜鉛は粒状が扱い易く、粒径は10μm〜5mmが適当である。亜鉛添加量は、ガリウム仕込み量と不純物濃度に依存するが、一般的には全不純物量の50〜200倍が良い。この範囲より少な過ぎると除去効率が低下し、除去のために長時間を要するかあるいは攪拌強度を上げる必要がある。また、この範囲より多いと亜鉛の除去に長時間を要することになる。
【0016】
次に、石英容器を電気炉に設置し、炉内をアルゴンまたは窒素で置換した後、目標の420〜910℃に加熱保持する。ガリウムと亜鉛は溶融するので、不純物と亜鉛の接触を効率的に起こさせるために混合攪拌を行う。
炉内をアルゴンまたは窒素で置換するのは、亜鉛、ガリウムの酸化を防止するためである。一般的に、酸化は雰囲気中の水分に依存するため、炉本体およびヒーターの耐酸化性が十分であるならば脱湿した空気でもよい。アルゴンまたは窒素は、昇温過程から加熱保持の間、500〜1000ml/minで導入するのが適当であるが、炉の大きさやガリウムの充填量を勘案して調節、制御する。
【0017】
加熱保持温度は420〜910℃に設定するが、加熱保持温度が420℃より低い場合、亜鉛は固体であるため不純物との拡散反応速度が遅く、また910℃より高い場合、亜鉛の蒸発速度が速いためガリウムから排出されてしまい、いずれの場合においても精製効果は期待できない。また、加熱保持時間は通常1〜5時間とするが、不純物の含有量およびガリウムの仕込み量に合わせてコントロールする必要がある。
【0018】
攪拌方法は、ガス吹き込み攪拌、インペラ攪拌などが適当であるが、攪拌によってガリウム飛沫が発生するような激しいものであってはならない。攪拌時間は、炉の昇温過程から真空加熱終了まで連続して行うことが好ましい。攪拌時間が短い場合は、亜鉛が不純物と接触する確率が少なくなり、次工程の真空加熱では亜鉛や不純物の蒸発を遅延するため十分な精製効果が期待できない。
【0019】
亜鉛は、炉の昇温とともにガリウム中に徐々に溶解し、攪拌によって均一な溶融物になり、ガリウム中の鉛と共沸混合物になると予想される。
亜鉛を添加したガリウムを420〜910℃に加熱保持した後、アルゴンまたは窒素の導入を止め、炉を真空に引きながら800〜1000℃で1〜5時間加熱すると亜鉛と同時に鉛が蒸発する。真空度は0.13Paが適当であるが、これに限られるものではない。真空度を上げれば不純物は蒸発分離され易いが、ガリウムの蒸発損失も多くなる。真空度が低ければ不純物の除去が不十分である。
【0020】
ガリウムの沸点が2403℃であるのに対し、鉛の沸点は1750℃、亜鉛の沸点は907℃である。鉛を通常の真空加熱で蒸発除去する場合には、ガリウムの蒸発損失が多くなるが、亜鉛を添加することで鉛と亜鉛の共沸混合物が形成され、ほぼ亜鉛の沸点で蒸発が進行すると考えられる。過剰な亜鉛は真空加熱で蒸発除去できガリウムから容易に分離可能である。
【0021】
ガリウムは炉内で30〜80℃まで冷却後、ろ布で吸引ろ過し、残留亜鉛の結晶粒およびガリウム表面に浮遊する酸化物皮膜を除去する。ろ布はポリエステルもしくはポリプロピレン製の不織布を使用し、ろ過速度を調節しつつろ過するのが適当である。吸引ろ過する場合の真空ポンプは,汚染を防ぐためダイヤフラム式ポンプを利用することが好ましい。ただし、ろ過器材はガリウム中の微粒子を捕捉分離できればこれらに限らない。
【0022】
以上の操作で通常、再結晶法を利用してきた鉛などの不純物除去を真空加熱精製法で行えるため生産性の向上が実現できる。
【0023】
【発明の実施の形態】
ガリウム(Ga99.999%以上、Pb10ppm未満)は、電気ヒーターもしくは赤外線ランプを使用し、30℃以上の温度に加熱し溶融する。
ガリウムを石英容器に入れ、さらにガリウム1kgに対し0.4gの亜鉛(平均粒径0.1mm)を添加する。石英容器を外部加熱式の真空加熱炉内に設置した後、石英製インペラーをガリウムに挿入する。石英製インペラーは真空用軸受けを介して炉本体の外部に設置した電動モーターによって回転させる。回転速度は6〜10rpmが適当であるが、これに限定されるものではない。
【0024】
真空加熱炉を油回転真空ポンプによりゆっくり0.13Paまで減圧した後、1000ml/min程度で窒素を導入し、ガス置換を行う。真空加熱炉内が大気圧になった時リーク弁を開き、引続き窒素をフローする。
次に、真空加熱炉を420〜910℃まで10℃/minで昇温し、2h加熱保持する。昇温速度と加熱保持時間と不純物量とガリウム仕込み量に合わせて任意に変更しなければならない。その後リーク弁を閉じ、真空加熱炉内を0.13Paまで油回転真空ポンプで減圧しながら10℃/minで800〜1000℃に加熱温度を調節し、2h加熱保持する。亜鉛及び鉛は蒸気となり、真空加熱炉内に設置した水冷冷却板に凝集する。
【0025】
加熱終了後、炉冷し、ガリウム融液温度が50℃になったのを確認して、真空加熱炉を開扉し、石英容器を取り出し、ろ布としてポリプロピレン製の不織布を接着固定したブフナーロートを使用し、吸引ろ過する。
【0026】
【実施例】
〔実施例1〕
ガリウム(Ga99.999%以上、Pb5.7ppm)は、赤外線ランプを使用し、加熱し溶融する。
ガリウム5kgを石英容器に入れ、さらに亜鉛(平均粒径0.1mm)2gを添加する。石英容器を外部加熱式の真空加熱炉内に設置した後、石英製インペラーをガリウムに挿入する。石英製インペラーの回転速度は6rpmとする。
【0027】
真空加熱炉を油回転真空ポンプで緩速に0.13Paまで減圧した後、1000ml/minで窒素を導入し、ガス置換を行う。真空加熱炉内が大気圧になった時リーク弁を開き、引続き窒素をフローする。
次に、真空加熱炉を800℃まで10℃/minで昇温し、2h加熱保持する。
【0028】
その後リーク弁を閉じ、真空加熱炉内を0.13Paまで油回転真空ポンプで減圧しながら10℃/minで1000℃に加熱し、その温度を2h保持する。亜鉛及び鉛は蒸気となり、真空加熱炉内に設置した水冷冷却板に凝集する。
加熱終了後、炉冷し、ガリウム融液温度が50℃になったのを確認して、真空加熱炉を開扉し、石英容器を取り出し、ろ布としてポリプロピレン製の不織布を接着固定したブフナーロートを使用し、吸引ろ過した。
【0029】
ろ過回収した精製ガリウム中のPb濃度をグロー放電質量分析計で測定したところ0.01ppmであった。ガリウムの回収率は99.5%であった。
〔実施例2〕
真空加熱に入る前の窒素雰囲気下での加熱を450℃とする以外、実施例1と同様に操作した。
【0030】
ろ過回収した精製ガリウム中のPb濃度をグロー放電質量分析計で測定したところ0.03ppmであった。ガリウムの回収率は99.6%であった。
〔実施例3〕
真空加熱時の温度を800℃とする以外、実施例2と同様に操作した。
ろ過回収した精製ガリウム中のPb濃度をグロー放電質量分析計で測定したところ0.02ppmであった。ガリウムの回収率は99.8%であった。
【0031】
【発明の効果】
本発明のガリウムの精製方法よれば、一般的に再結晶法によって除去されていた鉛などの不純物を真空加熱精製法で除去することができ、半導体原料として使用可能な純度99.9999%以上のガリウムの生産性が向上し、コスト低減が可能となる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gallium purification method utilizing vacuum heating, and more particularly to a gallium purification method for purifying gallium to a purity of 99.9999% or higher that can be used as a semiconductor raw material.
[0002]
[Prior art]
Gallium is required to have a purity of 99.9999% or higher in a compound semiconductor crystal such as GaAs or GaP or liquid phase epitaxial growth such as GaP or GaAs.
Gallium oxide is recovered as a by-product from the buyer's liquid used in the production of alumina from bauxite, or from the retort residue of zinc distillate zinc distillate or the sulfuric acid leaching residue of zinc roasting ore. After gallium is dissolved in caustic soda solution, it is produced as 98-99% low-purity gallium by electrowinning. The low-purity gallium is further purified by a combination of vacuum heating purification, acid washing, and recrystallization steps, and is highly purified to 99.9999% or more.
[0003]
On the other hand, as scrap containing gallium, GaAs or GaP single crystal end cut part, damaged wafer, cutting waste, lapping waste, exhaust gas in vapor phase epitaxial growth process, used gallium in liquid phase epitaxial growth process, and circuit formation There are damaged wafers later.
These gallium scraps are refined by vacuum heating purification, electrolytic purification, acid cleaning, and recrystallization purification processes alone or in combination, and are used again as compound semiconductor crystals and raw materials for liquid phase epitaxial growth.
[0004]
Electrowinning or electrolytic purification is a method of collecting and collecting gallium on the cathode by electrolysis using platinum, carbon, or stainless steel as an electrode, with a solution obtained by dissolving gallium oxide or gallium hydroxide in an aqueous caustic soda solution. Electrolysis is performed at a current density of 2000 A / m 2 at a maximum with a gallium concentration of 30% or less and a sodium hydroxide concentration of 30-50% in the electrolytic solution.
[0005]
The main purpose of electrowinning is to deposit gallium from gallium oxide or gallium hydroxide as a raw material, and its purity is limited to 99%. Electrolytic purification is performed for the purpose of obtaining a higher purity of 99.99%. Although it is possible to reduce Hg, Al, Zn, Pb, etc. by electrolytic collection or electrolytic refining, it is difficult to expect large improvement in purity because it is difficult to attach and entrain electrolyte, and to precisely control the electrolysis conditions. The upper limit of the purity of the gallium obtained is 99.99%.
[0006]
The vacuum heating purification is a method of evaporating and removing impurities having a higher vapor pressure than gallium using a difference in vapor pressure. Metallic gallium is heated to a temperature of 1000 ° C. or higher with a vacuum of 1.3 × 10 −3 Pa or lower, and Hg, Zn, and the like, which have high vapor pressure, can be reduced to 1 ppm or lower. However, in the case of an impurity having a small vapor pressure difference from gallium, the impurity is easily mixed from the container because it is heated to a higher temperature, or a loss due to evaporation of gallium is caused. Further, when impurities form an intermetallic compound, it is difficult to make the value lower than several ppm.
[0007]
The acid cleaning is a method in which molten gallium is brought into contact with hydrochloric acid, nitric acid, or a mixed acid thereof to elute impurities having a large ionization tendency into the acid, thereby increasing the purity. The elution of impurities contained is promoted by bringing the acid diluted to 0.001 to 0.1 mol / dm 3 into contact with gallium by stirring or the like. As the stirring becomes stronger, the contact increases, so that a purification effect can be obtained in a short time. This method can reduce Ca, Zn, Cd, and the like.
[0008]
However, if intense stirring is continued, the acid solution becomes a black suspension. The black substance in the suspension is composed of gallium fine particles and a gallium oxide or hydroxide film formed on the surface thereof, and is acid-soluble. Impurities are concentrated in the gallium oxide or hydroxide film on the surface of the gallium fine particles, and in order to obtain high purity gallium, it is necessary to completely separate the gallium fine particles. Further, in order to improve the yield, it is necessary to collect the separated gallium fine particles, which is a drawback in increasing productivity.
[0009]
Recrystallization is a method of increasing the purity of the solidified portion by concentrating impurities in the melt using the difference in segregation coefficients when crystallizing crystals from the gallium melt. Recrystallization methods include unidirectional solidification, zone melting, and single crystal growth.
Unidirectional solidification is a method of concentrating impurities in a melt by slowly cooling and solidifying molten gallium in a vessel such as a boat from one end. Impurity segregation is affected by the cooling rate, and the slower the cooling rate, the higher the purification efficiency. However, if the cooling rate is slowed, the productivity is lowered, which causes an increase in cost.
[0010]
Zone melting is a method in which a large number of unidirectional solidifications are continuously performed in a single operation, so that the low productivity of unidirectional solidification can be improved. It is difficult to control and has not led to a significant improvement in productivity.
Therefore, recrystallization is used as a final purification step to reduce impurities that are difficult to be removed by vacuum heating purification, electrolytic purification, and acid cleaning, but has a disadvantage of poor productivity. Examples of main elements to be purified by recrystallization include lead and indium.
[0011]
For low purity gallium of about 99.99% and scrap from liquid crystal epitaxial growth, generally gallium with a purity of 99.9999% or higher is finally obtained by increasing the purity by vacuum heating purification, acid cleaning, and recrystallization. It has been.
[0012]
[Problems to be solved by the invention]
In conventional gallium purification methods, gallium has been highly purified by combining the various methods described above according to the type and amount of impurities contained in gallium. As described above, since a method of combining many purification steps optimal for the properties of impurities has been used, the conventional gallium purification method has many steps and is extremely complicated. In particular, impurities such as lead are difficult to remove by vacuum heating or acid cleaning, and are generally removed by a recrystallization method, but the cost is high due to low productivity.
[0013]
The present invention can remove impurities such as lead without using a recrystallization method, has high productivity, and can obtain gallium having a purity of 99.9999% or more that can be used as a semiconductor raw material at low cost. An object of the present invention is to provide a purification method.
[0014]
[Means for Solving the Problems]
In the method for purifying gallium of the present invention, zinc is added to gallium, heated and held at 420 to 910 ° C. in an argon or nitrogen atmosphere, then heated at 800 to 1000 ° C. while being evacuated, and then filtered. The above problems are solved.
Zinc is considered to form an azeotrope with impurities in gallium, and it becomes possible to evaporate and remove a high boiling point metal such as lead at a temperature lower than the original boiling point.
[0015]
Gallium is put in a quartz container and zinc is added thereto. Zinc is easy to handle in a granular form, and a suitable particle size is 10 μm to 5 mm. The amount of zinc added depends on the amount of gallium charged and the impurity concentration, but is generally 50 to 200 times the total amount of impurities. If it is less than this range, the removal efficiency is lowered, and it takes a long time for removal or it is necessary to increase the stirring strength. Moreover, when it exceeds this range, it takes a long time to remove zinc.
[0016]
Next, the quartz container is placed in an electric furnace, and the inside of the furnace is replaced with argon or nitrogen, and then heated and held at a target of 420 to 910 ° C. Since gallium and zinc are melted, mixing and stirring are performed in order to efficiently bring the impurities into contact with zinc.
The reason for replacing the inside of the furnace with argon or nitrogen is to prevent oxidation of zinc and gallium. In general, since oxidation depends on moisture in the atmosphere, dehumidified air may be used if the oxidation resistance of the furnace body and the heater is sufficient. Argon or nitrogen is suitably introduced at a rate of 500 to 1000 ml / min during the heating and holding period, but is adjusted and controlled in consideration of the size of the furnace and the gallium filling amount.
[0017]
The heating and holding temperature is set to 420 to 910 ° C. When the heating and holding temperature is lower than 420 ° C, the diffusion reaction rate with impurities is slow because zinc is a solid, and when it is higher than 910 ° C, the evaporation rate of zinc is low. Since it is fast, it is discharged from gallium, and in any case, no purification effect can be expected. The heating and holding time is usually 1 to 5 hours, but it is necessary to control it in accordance with the content of impurities and the amount of gallium charged.
[0018]
As the stirring method, gas blowing stirring, impeller stirring and the like are appropriate, but the stirring method should not be so intense that gallium droplets are generated by stirring. The stirring time is preferably continuously performed from the temperature raising process of the furnace to the end of the vacuum heating. When the stirring time is short, the probability that zinc contacts with impurities decreases, and the vacuum heating in the next step delays evaporation of zinc and impurities, so that a sufficient purification effect cannot be expected.
[0019]
It is expected that zinc will gradually dissolve in gallium as the furnace heats up and will become a homogeneous melt by stirring and an azeotrope with lead in gallium.
After the gallium to which zinc is added is heated and held at 420 to 910 ° C., the introduction of argon or nitrogen is stopped, and when the furnace is evacuated and heated at 800 to 1000 ° C. for 1 to 5 hours, lead evaporates simultaneously with zinc. The degree of vacuum is suitably 0.13 Pa, but is not limited thereto. If the degree of vacuum is increased, impurities are easily evaporated and separated, but the evaporation loss of gallium increases. If the degree of vacuum is low, the removal of impurities is insufficient.
[0020]
The boiling point of gallium is 2403 ° C., whereas the boiling point of lead is 1750 ° C. and the boiling point of zinc is 907 ° C. When lead is removed by evaporation under normal vacuum heating, the evaporation loss of gallium increases. However, the addition of zinc forms an azeotrope of lead and zinc, and the evaporation proceeds almost at the boiling point of zinc. It is done. Excess zinc can be removed by evaporation by vacuum heating and easily separated from gallium.
[0021]
Gallium is cooled to 30 to 80 ° C. in a furnace and then suction filtered with a filter cloth to remove residual zinc crystal grains and oxide film floating on the gallium surface. It is appropriate to use a non-woven fabric made of polyester or polypropylene as the filter cloth and to filter while adjusting the filtration speed. As the vacuum pump for suction filtration, it is preferable to use a diaphragm pump in order to prevent contamination. However, the filter material is not limited to these as long as the fine particles in gallium can be captured and separated.
[0022]
With the above operation, it is possible to remove impurities such as lead, which have normally used the recrystallization method, by the vacuum heating purification method, thereby improving productivity.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Gallium (Ga 99.999% or more, Pb less than 10 ppm) is melted by heating to a temperature of 30 ° C. or higher using an electric heater or an infrared lamp.
Gallium is put in a quartz container, and 0.4 g of zinc (average particle size: 0.1 mm) is added to 1 kg of gallium. After the quartz container is installed in an external heating type vacuum heating furnace, a quartz impeller is inserted into gallium. The quartz impeller is rotated by an electric motor installed outside the furnace body through a vacuum bearing. The rotation speed is suitably 6 to 10 rpm, but is not limited thereto.
[0024]
The vacuum heating furnace is slowly depressurized to 0.13 Pa with an oil rotary vacuum pump, and then nitrogen is introduced at about 1000 ml / min to perform gas replacement. When the inside of the vacuum furnace reaches atmospheric pressure, the leak valve is opened and nitrogen is continuously flowed.
Next, the temperature of the vacuum heating furnace is increased from 420 to 910 ° C. at 10 ° C./min, and heated for 2 hours. It must be arbitrarily changed according to the heating rate, the heating and holding time, the amount of impurities, and the amount of gallium charged. Then, the leak valve is closed, the heating temperature is adjusted to 800 to 1000 ° C. at 10 ° C./min while reducing the pressure in the vacuum heating furnace to 0.13 Pa with an oil rotary vacuum pump, and the heating is maintained for 2 hours. Zinc and lead become steam and aggregate on a water-cooled cooling plate installed in the vacuum heating furnace.
[0025]
After the heating, the furnace was cooled, and it was confirmed that the temperature of the gallium melt reached 50 ° C., the vacuum heating furnace was opened, the quartz container was taken out, and a Buchner funnel with a polypropylene non-woven fabric bonded and fixed as a filter cloth And suction filtered.
[0026]
【Example】
[Example 1]
Gallium (Ga 99.999% or more, Pb 5.7 ppm) is melted by heating using an infrared lamp.
5 kg of gallium is put in a quartz container, and further 2 g of zinc (average particle size 0.1 mm) is added. After the quartz container is installed in an external heating type vacuum heating furnace, a quartz impeller is inserted into gallium. The rotation speed of the quartz impeller is 6 rpm.
[0027]
After the vacuum heating furnace is slowly depressurized to 0.13 Pa with an oil rotary vacuum pump, nitrogen is introduced at 1000 ml / min to perform gas replacement. When the inside of the vacuum furnace reaches atmospheric pressure, the leak valve is opened and nitrogen is continuously flowed.
Next, the vacuum heating furnace is heated up to 800 ° C. at a rate of 10 ° C./min, and heated for 2 hours.
[0028]
Thereafter, the leak valve is closed, and the inside of the vacuum heating furnace is heated to 1000 ° C. at 10 ° C./min while reducing the pressure to 0.13 Pa with an oil rotary vacuum pump, and the temperature is maintained for 2 hours. Zinc and lead become steam and aggregate on a water-cooled cooling plate installed in the vacuum heating furnace.
After the heating, the furnace was cooled, and it was confirmed that the temperature of the gallium melt reached 50 ° C., the vacuum heating furnace was opened, the quartz container was taken out, and a Buchner funnel with a polypropylene non-woven fabric bonded and fixed as a filter cloth And suction filtered.
[0029]
The Pb concentration in the purified gallium collected by filtration was measured with a glow discharge mass spectrometer and found to be 0.01 ppm. The recovery rate of gallium was 99.5%.
[Example 2]
The same operation as in Example 1 was performed except that heating in a nitrogen atmosphere before entering vacuum heating was set to 450 ° C.
[0030]
The Pb concentration in the purified gallium collected by filtration was measured with a glow discharge mass spectrometer and found to be 0.03 ppm. The recovery rate of gallium was 99.6%.
Example 3
The same operation as in Example 2 was performed except that the temperature during vacuum heating was 800 ° C.
The Pb concentration in the purified gallium collected by filtration was measured with a glow discharge mass spectrometer and found to be 0.02 ppm. The recovery rate of gallium was 99.8%.
[0031]
【The invention's effect】
According to the gallium purification method of the present invention, impurities such as lead that have been generally removed by the recrystallization method can be removed by a vacuum heating purification method, and a purity of 99.9999% or more that can be used as a semiconductor raw material. The productivity of gallium is improved and the cost can be reduced.
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