Abstract
The main objective of this thesis is to study the structure and properties of ternary sodium copper phosphate (P2O5-Na2O- CuO) glass system in a systematic manner, in order to develop low melting lead-free phosphate glasses. Ternary P2O5-Na2O-CuO glasses can be prepared in air at 750 ~ 1100 °C. The glass formation region is P2O5 > 40; Na2O < 60 and CuO < 50 mol%, expect for the composition 40P2O5-10Na2O-50CuO. The glasses formed more favorably with a higher P2O5 content. Glasses with a glass transition temperature (Tg) below 420 °C, a glass softening temperature (Td) below 450 °C, a thermal expansion coefficient of 99 ~ 258E-7/°C (50 ~ 200°C), and a dissolution rate in 30 °C deionized water at the order of ~1E-7g/cm2-min can be obtained. The dissolution rate of this glass system is 3 ~ 4 order lower than the binary sodium phosphate glasses (P2O5-Na2O).The properties of this glass system are strongly composition dependent. Substitution of CuO for Na2O increases density, hardness, Tg and Td, while decreases thermal expansion coefficient of the glasses. Besides, the chemical durability of the glasses was improved. In the glass system with 40 mol% P2O5, there are two glassy states co-existing, leading to some abnormal behavior in this glass system. The higher Tg phase has longer phosphate chain length, and the lower Tg phase has shorter phosphate chain length.The conductivity is dependent on the composition of the glasses. The dc conduction activation energy increases with CuO content (number of Na+ charge carrier decreased) as CuO < 20 mol% (glasses with 50 and 60 mol% P2O5) or CuO < 30 mol% (glasses with 40 mol% P2O5), depicting an ionic conduction behavior. As CuO > 20 mol% (glasses with 50 and 60 mol% P2O5) or CuO > 30 mol% (glasses with 40 mol% P2O5), the dc conduction activation energy decreases with increasing CuO content, depicting polaron conduction behavior. The ac conductivity of the glasses with high CuO content can be described by the polaron hopping over barrier model (HOB).The structure of the glasses was examined by Fourier trans -formed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). O1s XPS confirms the formation of P-O-Cu bonds in the glass network. In the glass systems with 50 and 60 mol% P2O5, the fraction of P-O-Cu bond, which replaces P-O..Na+ bond while doesn't disrupt the P-O-P bond, increases with increasing CuO content. Thus, the crosslink density and strength of the glass network increase, leading to enhanced chemical durability and increased Tg of the glasses. In the glass system with 40 mol% P2O5, the formation of P-O-Cu bonds replaces P-O..Na+ bond and shortens the phosphate chain length of the glasses by disrupting P-O-P bonds.The structure and properties of P2O5-Na2O-CuO glasses vary with melting time and atmosphere. [Cu2+] in the glasses increases with longer melting time and partial pressure of oxygen. When the [Cu2+] is increased, the chain structure will be tighter leading to increased Tg and chemical durability of the glasses.