Patent ID: 9637405
Date: 2017-05-02
CPC Classifications: C03B,C30B,G01N,G02B,Y02P

Claim:
1. An evaluation method of silica powder for forming a bubble-free layer of a vitreous silica crucible for pulling of a silicon single crystal, comprising: a process of measuring a porosity between silica particles in the silica powder before melting the silica powder; a process of melting the silica powder; a process of measuring a bubble content rate of a vitreous silica block obtained by cooling to harden the melted silica powder; a process of calculating a contraction index representing a contraction degree before and after melting the silicon powder by comparing the bubble content rate of the vitreous silica with the porosity of the silica powder; and a process of evaluating the silica powder by judging whether the contraction index is within a predetermined range.