Effective Reduction of Nickel Sulfide Stones in Heat-strenghtened and Tempered Glass

NiS stone can be effectively reduced in molten glass by addition of zinc (Zn) series compounds, that is, the zinc sulfate (ZnSO47H2O) or the zinc nitrate (Zn(NO3)26H2O) during glass batch-mixing process. Adjustment of oxidation-reduction condition and the addition of other compounds (e.g. metal oxides, iron-series compounds, or nitrates) are also effective about the reduction of the NiS stone.
Heat Soak Test (HST) cannot reduce very small-sized particle of crystalline NiS (less than 20 micrometer in diameter), according to statistical analysis of reliability of the HST and non-equilibrium phase analysis of the NiS to avoid spontaneous breakage. The following methods are very useful to avoid the spontaneous breakage.

1) Addition of the zinc series compounds in the molten glass can reduce small-sized NiS less than 20-micron meter in diameter, preferentially. This method is very effective and low cost performance for glass-making process. Zn component in the soda-lime-silicate glass can be easily detected by chemical analysis.

2) Adjustment of oxidation-reduction condition during glass making process avoids to form the NiS particles.

3) Perfect HST based on kinetics of phase transformation from alpha to beta phases of several types of nickel sulfides (e.g. NiS, Ni1-x
S, or Ni7S6, etc.), can break the glass products that include the crystalline NiS with beta-form, and effectively reduce the NiS in the glass.

Synthetic process combined with above methods and the analysis of reliability of the HST, can reduce most of the NiS particles in the heat-strengthened and tempered glass. We always can get the heat-strengthened and tempered glass with high quality and reliance.

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The Authors

Dr. Chihiro Sakai Nippon Sheet Glass Techno-Research Co., Ltd. Nippon Sheet Glass Techno-Research Co.,Ltd. My major is phase petrology, mineralogy and rock-forming mineralogy. I have get a dgree of doctor for phase petrology in Kyoto University, 1960. Now, I belong in the R&D and testing tection ( NSG Tec... Read more