| Phosphate glasses have drawn much attentions as promising candidates for low melting sealing glasses and found wide applications as resistive or conductive pastes, sealing or coating frits for electronic components, adhesives for metal materials and ceramic, due to their low glass transition temperature, appropriate thermal expansion coefficient and low viscosity. However, the low chemical resistance and moisture degradation of these glasses limited their commercial exploitation in engineering applications. In recent years, much interests have focused on improving the chemical durability of phosphate glasses through introducing glass former and modifier such as Fe2O3, MoO3, CuO, Cr2O3, SrO, etc., in to P2O5 glass network.In this paper, ZnO-B2O3-P2O5-RnOm (RnOm=Li2O, Al2O3, Na20) quaternary system glasses were prepared through the melting quenching method. Various factors which effect on physical properties were investigated, including thermal expansion coefficient (a), weight loss percentage (WL), glass density (p), volume resistivity (Rv), dielectric constant (ε) and fluxion property. The ZnO-B2O3-P2O5-RnOm glass was characterized by infrared spectra (IR), Raman spectra, nuclear magnetic resonance (NMR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopic (EDS) and differential thermal analysis (DTA). In addition, the structural influence of manganese and iron ions on the ZnO-B2O3-P2O5-RnOm glass network with a gradual increase in the concentration of MnO2 and Fe2O3 was investigated through the spectroscopic and chemical durability studies. Such studies will pave the way for assessing the water resistance character of the phosphate glasses.Firstly, the glass forming region in the ZnO-B2O3-P2O5-RnOm quaternary system has been determined. It was observed that the glass forming region crosses the entire quaternary system with 30 to 50 mol% P2O5. The IR band around 1440 cm-1, which dues to the Vas(B-O-B) vibrations of bridging oxygen atoms, increased in intensity with increasing B2O3 content, while the vs(P-O-P) vibration around 760 cm-1 disappears, indicating the formation of P-O-B linkages. The resulting XRD patterns indicated that the major crystalline phase changes from Zn2P2O7 to BPO4 as the B2O3 substitution increases from 0-20 mol% to 30-40 mol%. It is well known that the crystalline BPO4 and AIPO4 are interconnected with PO4-BO4 tetrahedra and PO4-AlO4 tetrahedra networks which are similar to SiO2. Therefore, it can be supposed that the glasses contain P-O-B and P-O-Al linkages within their structural networks. The values of Tg shifted monotonously to higher temperature with increasing B2O3 content, whereas the value of Tg rose abruptly at small additions of P2O5 and reached a maximum at about 40～45 mol% P2O5 in the glasses. The observed increasing Tg values indicates the enlarged cross-link density of various structural groups and low closeness of packing in the network of the glasses. The variations of a shifted monotonously to lower values with increasing B2O3 contents, whereas the value of a abruptly increased at 30 mol% additions of P2O5 and reached a maximum at about 43 mol% additions of P2O5 in the series A glass. The water durability of these glasses was found to be sensitive to the glass composition. It can be seen clearly that the glasses whose P2O5 content is less than 35 mol% and B2O3 content is less than 10 mol% exibited much better water durability (less weight loss percentage), which decreased with the increasing amount of P2O5 and B2O3. It was found that the WL abruptly increased at about 30 mol% additions of P2O5 and reached a maximum at about 40 mol% additions of P2O5. The controlled release mechanism of the phosphate glass was studied in detail. The results showed that the etch pits forming stage and etch pits stable stage appear in the dissolution process of the phosphate glasses.These two stages were in good consistence with that of the weight loss of the phosphate glasses. The p of the glasses decreased linearly with the increasing P2O5 contents, whereas it nonlinearly decreased with increasing B2O3 contents from 0 to 40 mol%. Obviously, the decrease was mainly due to the much higher mass molar weight of P2O5 and B2O3 than that of ZnO.Secondly, we have investigated the structural influence of MnO2 on the ZnO-B2O3-P2O5-RnOm glass network with the gradual increase in the concentration of MnO2.The analysis indicated that when the concentration of MnO2 is up to 3 mol%, manganese ions mostly exist in Mn2+ state, occupy networks forming positions with MnO4 structural units and increase the rigidity of the glass network. When the MnO2 content is beyond 3 mol%, these ions mostly act as network modifiers positions and strengthen the glass network. The values of Tg decreased firstly and then increased with the increasing MnO2 content from 440℃to 408℃. A new crystallization peak was presented in the DTA curves and shifted to a lower temperature for the glass sample containing≥1 mol% MnO2. The resulting XRD patterns indicated the major crystalline phase of Zn2P2O7 changes weakly with the substitution of different amount MnO2. Zn2P2O7 and BPO4 were precipitated in the glasses when heated at low temperature. However, the increased heating temperature initialed the reduction of BPO4 phase and the enhancement of MnPO4 phase. XRD results revealed that the MnPO4 phase could reacted to moisture in the atmosphere, and the reaction products of Mn2P2O7 distributed on the surface of the heated glasses and formed a water resistance layer, which could greatly inhance the water durability. SEM and EDS analysis showed that some particles with irregular layer shape had grown to a uniform phase, whereas other particles formed rod-like crystals. Values of a decreased between 0 and 3 mol% additions of MnO2, a minimum at about 3 mol% additions of MnO2 and then increased with further additions. The p of the glasses increased between 0 and 3 mol% additions of MnO2, a maximum at about 3 mol% additions of MnO2 and then decreased with further addition. These changes due to manganese ions participated in the glass network with different structural units. The weight loss was related to MnO2 concentration and lower ZnO concentration leaded to better water durability. The WL (0≤t≤10) was similar to that of the relative thermal expansion coefficient. Mn3+ provided a stronger crosslink between the phosphate tetrahedra. The interlinkage of highly dissolvable P-O nonbridging oxygens by Mn3+ and the replacement of easily hydrated phosphate chains by corrosion resistant P-O-Mn bonds improved the durability of the glass samples undoubtedly. Thus the glass containing MnO2 had better water durability. The Rv of the glasses decreased and the fluxion property of the glasses increased with the increased temperature, whereas the s of the glasses decreased between 0 and 3mol% addtions of MnO2 and reached a minimum at about 3 mol% additions of MnO2 and then increased with further additions.Thirdly, we investigated the structural influence of iron ions on B2O3-P2O5-RnOm glass network with a gradual increase in the concentration of through spectroscopic and chemical durability studies. The physical properties coupled with infrared spectroscopic and XRD indicated that the iron ions (when present in the concentration range,0～2 mol%) exist mostly in trivalent state and occupy both tetrahedral and octahedral substitutional positions and were found to inhance the rigidity of the glass network. However, in the concentration range of 2-5 mol%, the iron ions in the glass networks were in Fe2+ state, occupying predominantly octahedral positions and were acting as modifiers. The XRD results revealed that the small amount of Fe2O3 (1 mol%) was effective to promote the appearance of BPO4 crystal, while more amount of Fe2O3 (3-5 mol%) was effective to suppress the formation of BPO4 and Zn2P2O7 crystal. The SEM pictures showed an increasing crystalline with the increasing concentration of Fe2O3 up to 5 mol%, and some particles with irregular layer shape had grown to quite big uniform phase, whereas other particles formed rod-like crystals. A much more internal defect was observed in the sample F0, whereas these defect decreased with the increasing Fe2O3 content. The crystalline phase changed in compact zone at about 3-5 mol% additions of Fe2O3 in the glasses. EDS analysis showed that the dark gray regions labeled as "c" have higher Fe content and might reveal to contain more P-O-Fe bonds, whereas the light gray regions labeled as "a" have lower Fe content and might reveal to contain less P-O-Fe bonds. The values of Tg decreased firstly and then increased with the increasing Fe2O3 content. A new crystallization peak was presented in the DTA curves and shifted to a lower temperature for the glass sample containing≥1 mol% Fe2O3. The a and p vary in opposite way for the glass. The WL was similar to that of the relative a. The values of a decreased between 0 and 2 mol% additions of Fe2O3, reached a minimum at about 2 mol% additions of Fe2O3 and then increased with further additions. The p increased between 0 and 2 mol% additions of Fe2O3, reached a maximum at about 2 mol% additions of Fe2O3 and then decreased with further additions. These changes might be attributed to iron ions participated in the glass network with different structural units. The Rv of the glasses decreased and the fluxion property of the glasses increased with increasing of the temperature, whereas theεof the glasses decreased between 0 and 2 mol% additions of Fe2O3, reached a minimum at about 2mol% additions of Fe2O3 and then increased with further additions.Finally, the spectroscopic properties of nano-aluminum oxide instead of aluminum hydroxide in the glass system were systematically investigated. SEM analysis showed that aluminum ions could react to P2O5, and the reaction products of AIPO4 could improve the machinable property obviously. Aluminum ions failed to participate into the glass network with P-O-Al structural units. Therefore, the absorption peak at 1640 cm-1 which was assigned to the Vas(Al-H-Al) vibrations of bridging hydrogen atoms disappears. XRD results revealed that the major crystalline phase of Zn2P2O7 changes weakly, but the structure of boronphosphate became distinctly which might reveal to contain more P-O-B bonds with the substitution of A1(OH)3 for nano-aluminum. The values of Tg and Tcl decreased obviously and a new crystallization peak was presented in the DTA curves in the sample N1. The a, p, s, WL values and the fluxion property increased, whereas the Rv value of the sample N1 glasses decreased with the increasing of the temperature.Based on the structure and crystallization analysis of ZnO-B2O3-P2O5-RnOm glass, effects of P2O5, B2O3 and additive oxides (including MnO2, Fe2O3, nano-aluminum oxide) on sealing properties, especially chemical stability of lead free sealing glass were investigated. The results indicated that doped MnO2, Fe2O3 and nano-aluminum oxide in the phosphate glasses had protection functions for sealing properties. The results of chemical durability measurements together with spectroscopic properties might also throw some light on the coordination of the polyhedral of manganese and iron ions, which dissolved in phosphate glass matrix even in very small quantities and could greatly increase the chemical durability and reduce the corrosion rate in aqueous environments. Furthermore, the effects of nano-aluminum oxide on the structure and properties of the glass were discussed in the glass systems. The crystallization course and mechanism were discussed, which could provide certain theory reference value for practice producing and glass seals to glass, ceramic and metal.
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