A. Paul

Effect of thermal stabilization on redox equilibria and colour of glass

Abstract Oxidation-reduction equilibria in glass forming melts change with temperature, fugacity of oxygen, concentration of the redox ion and chemical composition of the melt. Near the glass transition temperature the rate of diffusion of oxygen into the melt is slow and no significant change of oxidation state takes place with conventional rates of cooling. However, if more than one redox oxide is present then during cooling the melt, mutual interaction takes place causing changes in the oxidation state and colour of the glass; the extent of the interaction depends upon the rate of cooling. Rate of cooling of the melt vis-a-vis “Fictive Temperature” also affects the coordination equilibria of some transition metal ions and thus causes a change of colour of the glass. Mutual interaction of manganese-arsenic in a silicate glass is discussed.

Oxidation-reduction equilibrium in glass

Abstract The effect of temperature, oxygen fugacity, and melt composition on the oxidation-reduction equilibrium in glass forming melts has been discussed. The thermodynamics of mutual oxidation-reduction in glass, and the effect of heat treatment at lower temperatures has also been described.

Relative role of Al2O3 and PbO in binary and ternary phosphate glasses

Etude des verres suivants: KH 2 PO 4 , PbO-P 2 O 5 , Al 2 O 3 -P 2 O 5 et K 2 O-Al 2 O 3 -P 2 O 5

Lithium conducting glassy solid electrolytes in the LiFLi2 OAl(PO3)3 system

Abstract Electrolytic properties of lithium ion conducting glasses in the system LiF-Li 2 O-A1(PO 3 ) 3 have been investigated. Complex plane impedance analysis has been carried out using different electrode materials like silver, graphite and lithium. The interface resistance is much smaller for the lithium electrode compared to the electrolyte resistance. Ion migration in the bulk of the electrolyte gives rise to a nearly perfect semicircle in the impedance plot and a relaxation peak in the modulus spectrum. Wagners polarization technique has been used to measure the electronic conductivity of the glasses which is found to be negligible compared to the total conductivity and arises mainly from n-type conduction. Lithium ion transport number is found to be greater than 0.999. Cells using these electrolytes produce open circuit voltages which are very close to the theoretical values.

Equilibrium thermodynamics of nonstoichiometry in ZnO and aluminium doping of ZnO using aluminium chloride

A critical assessment of nonstoichiometry that can occur in zinc oxide at various temperatures and oxygen pressures has been made using the concepts of equilibrium thermodynamics. The feasibility of producing transparent conducting films of aluminium-doped zinc oxide by spray pyrolysis of organo-zinc salt solution containing aluminium chloride is also discussed.

Effect of interface on the mechanical behaviour of glass bead-filled PVC

The surface of glass beads of average particle size 100μm was modified (a) by incorporating extra hydroxyl groups by chemcial treatment, and (b) by applying a thin coating of polymethacrylic acid (PMA) on the glass surface. The corresponding chemical changes were investigated using infrared spectroscopy. The tensile behaviour of a glass bead-filled PVC composite prepared with surface-modified glass beads, showed the following effects: (a) hydroxyl groups incorporated on to the glass surface did not affect the glass-PVC interface and hence did not change the tensile behaviour of the composite; (b) PMA coating on the glass surface caused improvement in the tensile behaviour in the low strain region and deterioration in the high region. An SEM study of the fractured surface suggested debonding at the glass-PVC interface in the first case, and failure of the PVC-PMA interface in the second case.

Ionic conductivity in the system Li9−4xZrx[PO4]3

Lithium ion conductors of composition Li9−4xZrx〈PO4〉3 (0.0 < x < 2.0) have been prepared by the conventional solid state reaction and also by a wet chemical method. X-ray diffraction patterns reveal identical crystallographic morphology for the compounds prepared by the two methods. However, they can be prepared and sintered at much lower temperatures by the wet chemical method. Their conductivities are also higher. Compared to pure Li3PO4, one of the end member of the series, the conductivity increases sharply with substitution of lithium by zirconium. The highest conductivity has been obtained in the composition Li1.8Zr1.8〈PO4〉3 (x = 1.8), prepared by the wet chemical method. The conductivity value of 10−3 ω−1 cm−1 is obtained at around 225°C with an activation energy of about 0.5 eV.

Quenched glasses in the system LiFLi2OAl(Po3)3

Abstract A simple and rapid quenching apparatus has been designed and fabricated. The limit of glass formation in the system LiFLi 2 OAl(PO 3 ) 3 could be expanded by rapid quenching with this arrangement. The electrical conductivity of rapidly quenched glasses derived from complex impedance/admittance analysis are higher and the activation energy are lower compared to conventionally prepared glasses of corresponding chemical compositions. Annealing of the “as quenched” glasses causes considerable reduction in conductivity.

Correlation between chemical corrosion and structural variations in fibrous tremolite

An understanding of the correlation between the durability under different corroding conditions and the corresponding structural variations of silicates, is highly essential for their proper utilization in modern technology. To achieve this, a sample of fibrous chain silicate (tremolite) was subjected to various mechanical and chemical treatments and the resulting samples were analysed by X-ray diffraction, differential thermal analysis, scanning electron microscopy, and infrared spectroscopy. Several interesting results on chemical corrosion have been obtained. Attempts have been made to establish a correlation between these results with the X-ray diffraction data.

Alkaline durability of glass fibre containing SiO2, PbO and Al2O3

In the process of developing an alkali-resistant glass composition to be used as reinforcing fibres with cement, a glass in the system SiO2-PbO- Al2O3-R2O (R = an alkali metal) was adopted after some trials. The glass composition which possesses low melting point (1350° C), fair alkaline resistance (particularly in the long term) and appears to have satisfactory fibrilizing qualities, has the composition: SiO2 = 34%, PbO = 59%, Al2O3 = 3%, K2O= 3.5% and Na2O = 0.5% (wt%). The alkaline durability of the glass fibres (coated and uncoated) was studied at pH 9, 10, 11 and 12. There was no significant difference in the amount of extraction of the constituents in the leaching solution at pH 9 and 10. At pH 11 and 12 the amount of extraction value of the constituents initially increased up to seven days and thereafter no significant increase could be detected. The thermodynamic stability of the different oxides under present investigation (SiO2, Al2O3, PbO) in aqueous solutions at different pH values has been discussed with standard thermochemical data and it has been shown that alkaline durability of the glass fibres can be satisfactorily correlated with thermodynamic predictions. There is a lower value in the extraction of the constituents in the case of coated fibres, than those of uncoated fibres. An epoxy resin with a cycloaliphatic diamine improves alkaline durability.