Issue No. 1

Abstract

Textured samples cut from a vacuum extruded blank (50 wt.% kaolin, 25 wt.% feldspar and 25 wt.% quartz) were studied by a radiointroscopic method based on propagation of plane-polarized electromagnetic wave through a dry green sample as well as through the fired sample. The method is suitable for mapping the texture of large extruded ceramic blanks. A spiral character of the texture in the green hollow blank was revealed which has been found preserved even after high temperature firing.

Abstract

The paper deal with the suitability of Sardinian clays in mixture for ceramics craft, using statistical model based on multiple regression of their main parameter. The study consist in two part: the first is the characterization of the local material and the comparison with the common material used by potters, and coming from national market. The second part is the realization of a statistical design model based on measured data, useful for the prevision of technological property of the final ceramics product from clays pre-firing characteristics. In particular, the model from the particle size distribution (PSD), the chemical composition, the Atterberg limits can predict the Loss off Ignition (LoI), the Water Absorption (WA), the Linear Firing Shrinkage (LFS) and the Dilatometry (DIL) of ceramics fired between temperature from 800 ° to 1200 °C. The model is obtained with multivariate analysis (correlation and cluster analysis), and it is tested in a preliminary application.

Abstract

Five glasses were prepared from wastes of Saudi basalt-glass cullet. Sequential additions of glass cullet wastes were experimented up to 50% to basalt wastes. Crystallization of such glasses gave major Al-rich augite Ca (Mg,Fe,Al)(Si,Al)₂O₆ - augite Ca (Fe,Mg) Si₂O₆ with little spinel Mg(Al,Fe)₂O₄ phase, however, decrease of spinel contents took place with the dilution of basalt with glass cullet. Bulk crystalline microstructures were developed in all the glass-ceramic samples, however, relatively coarsening in texture took place with increasing the glass cullet wastes. The coefficient of thermal expansion was between 55-73 x 10^-7 °C^-1 for the glasses and 69-82 x 10^-7 °C^-1 for the glass-ceramic samples. The micorhardness values of glass-ceramic samples were between 7257-8862 MPa.

Abstract

The effects of nepheline tailing and ZnO on the physical, mechanical, microstructure and dielectric properties were investigated. Specimens fired at 1125 °C from batches containing 40 mass % nepheline tailing (product nepheline syenite beneficiation process) and 2mass% ZnO showed a maximum MOR of 44.81 Mpa. The main phases recorded were quartz, cristobalite, albite, hematite and gahnite. The dielectric constant (ε’ ) and dielectric loss (ε”) of ceramic bodies based on nepheline syenite tailing and clay as well as with 2 and 5% Zn were determined at temperatures between (25 to 275 °C) and over a wide range of frequency between 100 Hz and 1MHz. It was found that both ε’ and ε” showed increase with rise in temperature and fall in frequency. On the other hand, both ε’ and ε” showed a decrease on the addition of zinc oxide, attributed to the presence of gahnite (ZnAl₂O₄), which significantly enhanced their dielectric properties.

Abstract

Three bauxite samples (BX3, BX5 and BX8) of high alumina content from the region of Haleo-Danielle, Minim-Martap in Cameroon were characterized thermally at temperatures between 1000 °C and 1600 °C with the objective to study their suitability for dense refractory materials. The water absorption, porosity, linear shrinkage, flexural strength and bulk density were assessed. At 1600 °C, BX3 and BX5 presented high densification (bulk density of 3.4 g/cm3) with low porosity (7%) with a bi-axial bending strength of 75 and 41MPa respectively. On the contrary at the same temperature, BX8 presented 31.5% porosity, bulk density of 2.54 g/cm3 and biaxial bending strength of 55MPa. The low content in iron and titanium oxides give BX8 a clear grey color at 1600 °C. BX3 and BX5 presented an average linear shrinkage of about 27% while that of BX8 was only 13% at 1600 °C.

Abstract

Having undertaken studies into a lightweight and highly efficient superconducting transformer for rolling stock, we developed a prototype with a primary winding, four secondary windings and a tertiary winding using Bi-2223 high temperature superconducting wire. Its primary voltage is 25kV, which is widely adopted as the catenary voltage on the world’s high-speed lines. We adopted liquid nitrogen cooling, the weight being 1.71t excluding the refrigerator. The maximum output available to maintain superconductivity is 3.5MVA. We also introduce railways in Japan.

Abstract

Glass-ceramic materials with brown, yellowgreen and green-brown color and marblelike structure were obtained using a glass composition based on bulgarite and corrected by introduction of a waste product, i.e. exhausted guard layer from the diesel fraction hydropurification facility of Lukoil Neftochim Bourgas Co. The main phase observed was parawollastonite (β -CaSiO₃) with crystal sizes from 100 to 200 μ m. On the basis of the measured physico-mechanical and chemical properties, it was proved that the introduction of 7-10% guard layer did not significantly affect the glass-ceramic properties but only their appearance. A two-stage synthesis method was used. The coloring and characteristic color coefficients were determined by a computer program according to the sRGB system. Bulgarite from the quarry “Bulgarovo” and the main phases in the obtained glass-ceramic materials were characterized by X-ray phase analysis.