S.M. Salman

Crystallization characteristics of some lithia calcia magnesia borosilicate glasses

Abstract The crystallization process of the glasses based on the lithium-borosilicate system containing CaO and/or MgO has been investigated by X-ray diffractometry, DTA and scanning electron microscopy (SEM). Lithium metasilicate was formed as a major phase constituent during the crystallization of the glasses. However, lithium disilicate and α-quartz were crystallized as well. On the addition of CaO at the expense of B2O3, calcium silicate (wollastonite) and calcium borate were crystallized together with varieties of lithium borate phases including lithium diborate, lithium tetraborate and lithium pyroborate, which were mostly formed as functions of the CaO B 2 O 3 and Li 2 O B 2 O 3 ratios in the glasses, as well as the heat treatment applied. Pyroxene phase of diopsidic [CaMgSi2O6] type was also formed due to the replacement of CaO and MgO instead of B2O3 and Li2O, respectively. The role played by the glass oxide constituents in determining the crystallization characteristics of the glasses, as well as the conditions at which the crystallized phase assemblages were formed, are discussed.

Contribution of germanium dioxide to the thermal expansion characteristics of some borosilicate glasses and their corresponding glass-ceramics

The thermal expansion characteristics of some lithium aluminium germanium borosilicate glasses and their crystalline solids have been investigated. The base glass composition was modified by partial replacement of germanium dioxide instead of silica. In some cases, however, TiO2 was also added to some selected glasses as a nucleation catalyst. Slight increase in the thermal expansion coefficient (α) values of the glasses and corresponding slight decrease in both transition (Tg) and softening (Ts) temperatures are detected by GeO2/SiO2 replacements, however, the reverse results were recorded by TiO2 addition. The obtained data were correlated to the local structure changes induced by GeO2 or TiO2 and their contributions to the thermal expansion property of the glasses. On the crystallization, the expansivity of the glasses was markedly changed. It was greatly affected by crystallization of GeO2-containing phases and aluminosilicate solid solutions together with the TiO2-containing phases formed. The results obtained were explained in relation to the nature, composition and concentration of all phases formed in the glass-ceramics including a residual glass matrix.

Chemical stability of some manganese glass-ceramics

The chemical durability of some selected glass-ceramic materials based on the Li2O(MnO,CaO)MgOAl2O3SiO2 glass composition has been determined using the HCl/powder test. The leachability of the glass ceramic was gradually increased by replacing MgO with MnO, while it was decreased by adding MnO instead of CaO. Calcium oxide had a retarding effect on the durability of the material when it was added instead of MgO and/or MnO. The durability of the material was markedly improved by addition of A12O3 in place of Li2O. The leaching values were found to be dependent mainly on the proportion of the glass oxide constituents, i.e., the MgOMnO, CaOMnO and Li2OAl2O3 ratios in the nominal glass compositions. The results were correlated to different views concerning the effect of various ions on the rate of interdiffusion between the glass-ceramic materials and the leaching solution, the types and proportions of the crystalline phases developed, and the residual glass phase.

Characterization of glass-ceramic corrosion and durability

Abstract The chemical durability of some selected glass-ceramic materials based on the Li 2 O- (MnO, CaO)MgOAl 2 O 3 SiO 2 glass composition, has been determined by HCl, using the powder test. The leachability of the glass-ceramic was gradually increased by replacing MgO with MnO, while it was decreased by addition of MnO instead of CaO. Calcium oxide had a retarding effect on the durability of the material when it was added instead of MgO and/or MnO. However, on the addition of Al 2 O 3 in replacing Li 2 O, the durability of the material was markedly improved. The leaching data were found to be dependent mainly on the proportion of the glass oxide constituents i.e. MgO/MnO, CaO/MnO and Li 2 O/Al 2 O 3 ratios present in the glasses. The results were correlated to different views concerning the effect of various ions on the rate of interdiffusion between the crystalline-glass materials and leaching solution, the type, and proportions of the crystalline phases developed in glass-ceramics and residual glass phase.

Contribution of manganese oxide to the thermal expansion of some silicate glasses and their crystalline solids

Abstract The thermal expansion characteristics of some lithium silicate materials containing various MnO/CaO and MnO/MgO ratios together, in some cases, with Al2O3/Li2O replacement have been examined. The coefficients of thermal expansion were determined at different temperatures to detect the local structure changes induced by MnO, and its contribution with CaO and MgO to the thermal expansion of both glass and crystalline solids. The addition of MnO replacing CaO decreases the thermal expansion of the glasses, while MnO/MgO replacement increases this property. A large, abrupt decrease in the expansion coefficient of the glasses was observed following Al2O3/Li2O replacement. On crystallisation, the expansivity of the glasses was markedly changed. It was greatly affected by crystallization of various Mn-silicate varieties and/or aluminosilicate solid solutions. Correlation between the expansion data and the contribution of the incorporated cations in the glass structure as well as the crystal phase composition of the crystalline solids are discussed.

Crystallization characteristics of iron-containing spodumene-diopside glasses

Abstract The crystallization characteristics of glasses based on a stoichiometric spodumene (LiAlSi2O6)-diopside (CaMgSi2O6) composition with addition of Fe2O3 replacing Al2O3 are described. The effects of compositional variation due to the Al2O3/Fe2O3 replacement and thermal treatment on the nature, type and stability fields of crystallizing phases as well as the resulting microstructure are traced by DTA, X-ray diffraction (XRD) and scanning electron microscopy (SEM). In most cases, intense uniform bulk crystallization with fine-grained microstructure were achieved on increase of iron oxide at the expense of alumina. The crystallizing phases, β-eucryptite solid solution (ss), β-spodumene ss, varieties of pyroxene solid solution of diopside, hedenbergite and augite nature are mostly formed together, in some cases, with α-quartz, lithium silicates, lithium ferrate (LiFeO2) and iron oxide. The type, stability and compatibility of the crystallized phases are discussed in relation to the compositional variation of the glass and thermal treatment.

The Role of GeO2 and In2O3 in the Glass-Ceramic Formation and Microstructure of Lithium Alumino-Silicate Glasses

The crystallization characteristics of the glasses based on the Li2O–Al2O3–SiO2 system have been investigated. The base glass composition was modified by partial replacement of GeO2 for SiO2 and In2O3 for Al2O3. The effect of the compositional variation on the crystallization products of the glasses and the type of the solid solution (ss) phases formed as well as the resulting microstructure were traced by differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). A decrease in the endothermic and exothermic temperatures was detected by the replacement processes. β -spodumene ss, β -eucryptite ss, lithium meta- and di-silicate, lithium aluminum germanate and two forms of indium-containing phases (LiInSi2O6 & In2Si2O7 phases) were mostly developed in the crystallized glasses. The objective of the present work is to understand the role of the glass oxide constituents in determining the type of the crystalline phases formed, their solid solution formed and the microstructure of the resultant glass-ceramic materials.

Contribution of Al2O3 to crystallization characteristics of some lithia manganese calcia magnesia silicate glasses

Abstract The effect of thermal treatment on the crystallization characteristics and phase composition of lithia aluminosilicate glasses with additional constituents of some divalent oxides were examined by DTA, X-ray analysis and microscopy. On partial Al 2 O 3 /Li 2 O replacement, lithia aluminosilicate (β-eucryptite and/or β-spodumene) solid solutions were formed at the expense of lithium silicate phases. The progress of β-eucryptite and/or β-spodumene crystallization was accelerated with the addition of Al 2 O 3 instead of Li 2 O. The stability field of β-eucryptite was shifted to higher temperature if the Al 2 O 3 /Li 2 O ratio exceeded unity. In the presence of mixed divalent cations like Mn 2+ , Ca 2+ and/or Mg 2+ , varieties of pyroxene solid solutions, Mn-containing phases and anorthite were crystallized. The formation of various solid solution phases and their stoichiometric composition were greatly related to the Al 2 O 3 /Li 2 O and/or the divalent oxide ratios in the glass as well as the conditions of thermal treatment.

Crystallization Characteristics of Lithium Calcium Gallium Aluminium Borosilicate Glasses

The crystallization processes of lithium calcium gallium borosilicate glass containing Al 2 O 3 have been followed by X-ray diffractometry (XRD), differential thermal analysis (DTA) and scanning electron microscope (SEM). Lithium gallium silicate - LiGaSiO 4 phase was formed as a major constituent during the crystallization of the base glass. Solid solutions of lithium aluminosilicate and lithium aluminium gallium silicate - LiAl 0.5 Ga 0.5 SiO 4 phases were mostly formed as a function of Al 2 O 3 /Ga 2 O 3 ratios in the glasses. Varieties of lithium borate phases including Li 2 B 4 O 7 , α-Li 4 B 2 O 5 , Li 3 BO 3 , β-LiBO 2 and LiB 3 O 5 phases were detected together with lithium metasilicate and lithium disilicate. Different calcium bearing phases including wollastonite - CaSiO 3 , calcium borosilicate - Ca 2 B 2 SiO 7 , larnite - Ca 2 SiO 4 , rankinite - Ca 3 Si 2 O 7 , and calcium borate - CaB 2 O 4 were mainly detected as a function of heat-treatment in the CaO-containing samples. The role played by the glass oxide constituents in determining the crystallization characteristics and the nature of the crystal phases formed in the glasses are discussed.