Heat soak test (HST) with high reliability

Dr. Chihiro Sakai, Nippon Sheet Glass Techno-Research Co.,Ltd. and Masashi Kikuta, Nippon Sheet Glass Co.Ltd.

HST (Heat Soak Test) is very useful to avoid spontaneous breakage of tempered glass. Most of spontaneous breakages are caused by the volume expansion (e.g. about 4% expansion as described by Swain [1]) of Nickel Sulfide (NiS) with phase transformation from unstable alpha to stable beta form.

Sometimes, the maximum glass temperature condition of HST has been carried out at higher temperature than 260 degree Centigrade as recommended by Kasper ([2], [3] and [4]). But, the crystalline NiS with excess sulfur content (NixSy: x from stable beta to stable alpha at 282 degree Centigrade. It forms the eutectic mineral which includes some crystalline phases such as Ni3S2, Ni7S6, NiS, Ni0.96S (Ni1-xS), and Ni2S3. Therefore, higher temperature HST than 282 degree Centigrade has some risks that the NiS including high content of sulphur component in the grain causes
to transform already stable beta-NiS to alpha.

On the basis of the binary phase diagram about Ni and S components by Kullerud ([5]), the suitable temperature condition of HST is less than 260 degree. We will describe the
appropriateness of 260 degree HST, based on several experimental results such as high-temperature microscope observation, differential thermal analysis (DTA), and X-ray Diffraction (XRD) measurements under high temperature conditions.

Full-text Article [156 KB]

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
	Mr. Masashi Kikuta Nippon Sheet Glass Co., Ltd. Read more