Papers by Author: His Hsin Chien

Abstract: There are growing varieties of glasses available on the market for the manufacture of molded optical lenses. A glass with a low transition temperature (Tg) has the advantage of extending the service life of molding dies. However, most of the low Tg glasses have a high content of alkali metal oxides and tend to induce severe glass sticking problems. This has made the molding process of these kinds of glasses very difficult indeed. The low Tg glasses normally demonstrate poor chemical durability and scratch resistance. As a result, the yields of fabricating the glass-preforms are frequently rather low. This research tried depositing a very thin layer of aluminum oxide on various glass-preforms by a water based sol-gel process. A high temperature glass wetting experiment was carried out to investigate the high temperature interfacial reaction between the coated glass gobs and stainless steel substrate. It was found that when the uncoated glass-preforms were brought into contact with stainless steel, the contact angle decreased with increasing heating temperature and duration. Owing to the severe interfacial chemical reaction, the originally transparent glass gradually turned translucent. In the case of Al2O3 coated glass-preforms, the variation of the contact angles was very limited, which presented no sticking and no wetting behavior. No reaction products could be detected on the contact area after the wetting test. The optical transmission of those lenses molded from the coated glass-preforms exhibited no or very little changes after the molding process.

Abstract: The glass molding process provides great potential for mass production of precise glass optical components at low cost. The key issue for achieving a low production cost is to extend the service life of the expensive mold inserts. The precious metal based alloy is one of the coating materials for the molds which provides excellent glass anti-sticking results. However, the inter-diffusion between the WC/Co mold materials and precious metal coatings will deteriorate the coatings which needs to be resolved. It is essentially to deposit an interlayer as the diffusion barrier to improve the inter-diffusion problem. A thin layer of TaN was deposited on the WC/Co substrate as the diffusion barrier using a magnetron sputtering system, and followed by the deposition of Pt-Ir layer as the protective layer. Low Tg Glass gobs (L-BAL 42) were placed on the coated substrate to investigate inter-diffusion between the substrate and coating at high temperature. The surface interaction between the glass gobs and protective coatings was also examined. The obtained TaN and Pt-Ir multilayer had a dense nano-crystalline structure. High temperature wetting tests showed that the TaN film could effectively resist the cobalt and tungsten diffusion into the precious metal protective layer and, as a result, minimized the possibility of oxidation and interaction between glass and protective coating. The coated substrates retained a good surface finish and the glass gobs stayed fully transparent after 6 hours reaction test at 700°C.

Abstract: . Glass molding process is considered to have a great potential for the mass production of optical components with lower cost. Up to now, the service life of molding dies is still not satisfied. This study mainly focuses on the development of sol-gel derived Al2O3 coatings in order to extend the service life of glass molding dies. High temperature glass wetting experiment was carried out to investigate the high temperature interfacial reaction between the coatings and glass gobs. The 304 stainless steel were used as the substrate materials. The sol-gel coated Al2O3 was selected as the protective coating. OHARA L-BAL42 glass gobs were chosen as the test materials. It can be observed that very severe interfacial reaction occurs between stainless steel and glass at high temperature. The contact angle dramatically decreases from initial and then gradually approaches 25° at 825°C after 2 minutes holding time. The severe interface chemical reaction also results in the loss of transparency in glass appearance. The reaction products such as Zn and Ba are mainly from glass material. For the case of Al2O3 coated substrate, the variation of the contact angles varied from 152 to 138°, presents anti-sticking or non wetting behavior. There are no reaction products can be found on the glass contacted area after wetting test.