Method for producing quartz glass crucible
A method of producing a quartz glass crucible by arc melting a quartz powder molded product loaded on the inner side of a mold while performing vacuum suction, includes initiating the melting of quartz powder from the rim edge of a quartz powder molded product, subsequently lowering the arc electrode or raising the mold to heat and melt the sections on the downside of the rim edge. The method is preferably carried out such that the inner surface of the crucible is sealed within a time corresponding to 10% of the total arc time starting from the initiation of arc melting, and the seal thickness is 3 mm or less. The quartz glass crucible thus produced is useful for the pulling up of silicon single crystals and has a uniform glass layer with fewer internal bubbles.
1. A method for producing a quartz glass crucible, the method comprising melting a quartz powder molded product loaded on the inner side of a mold, through arc discharge from an arc electrode, while performing vacuum suction, wherein the melting of quartz powder is initiated from a rim edge of the quartz powder molded product, and after the quartz powder at the rim edge is melted, heating is performed from a wall section of the quartz powder molded product to a bight section and a bottom section of the quartz powder molded product in order, to thereby seal the entire surface of the inner side of the quartz powder molded product,
wherein:
at the time point of initiating melting of the rim edge of the quartz powder molded product, the lower end of the electrode is disposed at a position higher than the rim edge of the quartz powder molded product by 20 to 150% of a bore diameter of the quartz glass crucible to be produced, as the distance along the axial direction of the mold;
the time period from the time point of initiating melting the rim edge to the time point of sealing of the entire surface of the inner side of the quartz powder molded product, is 0.01% or more and 10% or less of a total arc time, the total arc time being a time from the time point of initiating melting the rim edge to the time point of completing arc discharge, and
the molten thickness of the quartz powder molded product from the time point of initiating melting the rim edge to the time point of sealing of the entire surface of the inner side of the quartz powder molded product, is 0.05 mm or more and 3 mm or less.
2. The method for producing a quartz glass crucible according to claim 1 , wherein sealing the entire surface of the inner side of the quartz powder molded product, the lower end of the electrode is disposed at a position lower than the rim edge of the quartz powder molded product by 30 to 40% of the bore diameter of the quartz glass crucible to be produced, as the distance along the axial direction of the mold.
3. The method for producing a quartz glass crucible according to claim 1 , wherein the amount of relative displacement of the electrode and the mold along the axial direction from the time point of initiating melting of the rim edge to the time point of completing the formation of a seal layer, is 0 to 100% of the bore diameter of the quartz glass crucible to be produced.
4. The method for producing a quartz glass crucible according to claim 1 , further comprising, after producing the quartz glass crucible, a heating process for degassing the gas in air bubbles of the quartz glass layer.
5. The method for producing a quartz glass crucible according to claim 4 , wherein the heating process involves heating the quartz glass crucible obtained after the arc melting process, in a furnace at 1600 to 2500° C. for 0.2 to 2.0 hours.