Effect Of Fining Agents On Structure And Property Of Pyrex Flat Glass

Pyrex glass is a kind of borosilicate which contains above 78% SiO₂ and 13% B2O3. It was invented and granted patent by Sullivan in 1915, researcher of Corning Inc. America. Pyrex flat glass, produced based on floating technology, has a lot of advantages, such as high thermal shock resistance, good chemical resistance, excellent transmissivity, fine level surface, low thermal expansion coefficient and various thickness-standards, therefore it is widely used in plane display(for example LCD), biologic DNA CMOS chip, photoelectric cell, superior quality bulletproof glass and fireproof glass, etc.Pyrex glass is hard to satisfy float-shaping technics because of special technical characteristics (high melting temperature, hard to fining, boron volatilization, layering and phase separation). Now, only Schott Inc. of Germany can produce Pyrex flat glass, while it is a gap in our country. As Pyrex glass is hard to fining, there will be many bubbles in glass, which are considered as serious defects of flat glass and can induce negative effects on properties of glass, such as optical uniformity, mechanical strength, etc. Therefore, it is very important to research fining of Pyrex flat glass.In this essay, starting from preparation processes of Pyrex glass, the characteristics of melting Pyrex glass with crucible in lab were researched, and the optimal composition of glass and proper melting system were determined. The topic of this paper was about fining of Pyrex flat glass. Little NaCl, CeO₂, La₂O₃ and K₂H₂Sb₂O₇.4H₂O were chosen as fining agents. The optimal kind of fining agent and content were determined by comparison with the fining effects. The study suggested that using single fining agent couldn't satisfy the fining require of Pyrex flat glass. When rare earth oxide was compounded with NaCl used as fining agents, the fining effect, apparent quality and transmissivity could be greatly improved. This was because rare earth oxide was mainly used to eliminate fmeseeds while the function of NaCl was to remove bubbles. However, K₂H₂Sb₂O₇.4H₂O was found unfit for finingof Pyrex glass.Furtherly, FTIR and TEM measurements were adopted to research the influence of fining agents on the microstructure of Pyrex glass. By FTIR, it was found that in Pyrex glass, [SiO4], [BO4] and [A1O4] formed the frame structure together. As [BO4] is negatively charged, it needs [BO3] to isolate and there were borate group in the structure of glass. The addition of fining agents didn't induce the change of glass structure. This is because FTIR of inorganic glass is mainly determined by the network-structure while not extra-network ions. The remaining Cl" and rare earth ions were located in the interstices of network, while antimony ions formed the (SbaOg) " rings in the structure. By TEM, a small amount of crystals were observed due to phase separation existed on the slight local area of Pyrex glass. Under higher powerful microscopes, many particles, which were similar to "tiny crystal" were observed. Their diameters were about 3^-10nm, which resulted in the un-homogenizing of chemistry and structure. It was suggested that fining agents had no direct influence on the microstructure of glass, as the "tiny crystals" were similar in all kinds of glasses.In this essay, effects of kinds of fining agents on comprehension properties such as density, U-V transmissivity and dielectric were furtherly researched. The densities of Pyrex glass were found between 2.32 and 2.35g/cnr1 and the visible transmissivities varied between 90.8% and 92%. That was to say, fining agents had less influence on them. But they had obvious effect on dielectric constant and dielectric loss of glass. The change of dielectric property had great relativity with the change of inner structure of glass, concentration of mobile ions, concentration of non-bridging oxygens and concentration of apt-to-polarization ion when kinds of fining agents were added.