The Technology Study Of Optical Engineered Stress Profile(ESP) Glass

Silicate glass plays an important role in the national economy in various fields. The brittleness makes its actual fracture strength much lower than the its theoretical strength. Although the traditional tempering technology has improved its actual strength greatly improved, but in some special fields which has very high request to the concentration of the fracture. The Engineered Stress Profile(ESP) glass provides a very good research direction for solving this kind of problems. The most prominent process is the method named,two-step ion exchange at low temperature method..In this paper, two-step ion exchange at low temperature method was used to enhance the 1.1mm thickness ultra-thin aluminum sodium silicate glass for the preparation of ESP glass. The microstructure of ion exchanged glassed were mainly investigated by EPMA, and the surface stress, bending strength, microhardness and transmittance test were used to characterize the property of the glasses. By changing the process parameters, effect of one-step ion exchange process parameters on the properties of glass, differences between glass properties of the glasses prepared by two-step ion-exchange method and one-step method and effect of first step parameters on the properties of ESP glasses were studied. The results of the study show that:1) When the original glasses were under one-step ion exchange method,time and temperature remarkably affected the strength and the Weibull modulus. When the exchange time is more than 12 h, with the increase of time, the bending strength decreases gradually, Weibull modulus increased first and then decreased; with the increase of temperature, the bending strength and Weibull modulus increased first and then decreased. When the time was 40 hours and temperature was 450 ?,the Weibull modulus reached its highest point, 35.82, when the bending strength was 397.72 MPa. By Fick's second law, the diffusion coefficient of K+ at 450 ? was calculated to be 1.102×10-14m2/s, using the Boltzmann-Matano method, the diffusion coefficient of K+ at 450 ? was calculated to be 2.92 ×10-14m2/s.2) When the original glasses were under two-steps ion exchange method, the second step ion exchange time significantly affected the Weibull modulus of glass. The second step medium was the mixture of NaNO3 and KNO3, the ratio of NaNO3 to KNO3 was 3/7. Along with the extension of the second step switching time, the bending strength and Weibull modulus increased first and then decreased and when the second step ion exchange time is 30 min, they all reached the maximum value, the bending strength was 421.67 MPa, the Weibull modulus reached 48.97. And it proved that the mechanism of Weibull module to improve the ESP glass: K+ concentration peak position moves inside with the second step ion exchange time increases, and Na+ concentration moves inside by diffusion, and then surface stress gradient increases, the maximum stress move to the internal side. As a result, cracks stop to expand or expand steadily within the stable extention region, resulting the enhancement of the concentration of the fracture.3) In this paper, the ESP glass' crack resistant ability was studied under the condition of on load and without load. The ratio of crack depth and crack half length a/c of ESP glass was even lower than the one-step ion exchange glass, indicating high stress gradient forming in ESP glass, the stress distribution of the glass had the very big enhancement in the crack resistant ability of the glass on the depth direction. The glass prefabricated crack by using microhardness tester, and then use bending strength test, ESP glass showed high crack resistance in the stress conditions. The calculation of the micro crack strength showed that compared to single step method, ESP glass had a higher anti crack ability without external force.4) When the original glasses were under two-steps ion exchange method, the first step exchange temperature time and temperature determined the bending strength of ESP glass, and decided the second exchange time step to obtain high modulus Weibull. Comparison of K+ concentration peak's moving speed to the internal glass draw the conclusion: the appropriate first step temperature and longer first step time with some short second step time will obtain ESP glass with high Weibull modulus.5) In this paper, seven groups of process parameters for preparing ESP glass with Weibull modulus greater than 40 were put forward through the experiment, suitable for preparation of mechanical sensitive glass.Trough the transmittance test, ESP glass transmittance was about 84%, which proved it has optical properties, showed these glass can be called Optical Engineered Stress Profile glass.