This site makes use of cookies necessary for the operation and useful for the purposes described in the cookie policy. If you want to learn more, see the cookie policy. By closing this banner, scrolling this page, clicking on a link or continuing navigation in any other way, you consent to the use of cookies.
In the welding process large amounts of waste are discarded. This waste is usually deposited in landfills. This paper reports on the incorporation of the welding flux slag waste into clay bricks for civil construction. The waste was characterized with respect to crystalline phases present, chemical composition, morphology, and particle size. Clay-waste powder mixtures containing up to 10-wt. % of welding flux slag waste were prepared, pressed and fired at temperatures between 850 oC and 1050 oC. The effects of the waste incorporation and firing temperature on properties such as linear shrinkage, water absorption, apparent density, and flexural strength have been determined. The microstructure of the fired pieces was evaluated by SEM. The results showed that the waste incorporated pieces fulfill the specifications required for use in clay bricks at all firing temperatures.
In the production of ceramic tiles, composition of body and firing conditions determine the phase transformations and in turn affect the final properties of the product. Thus, selection of relevant raw materials and characterisation of their individual physico-mechanical and chemical characteristics are very important. In this study, sintering behaviour of a model double-fired ceramic wall tile body, mainly consisting of a sandy clay, was investigated. Further formulations were also prepared containing the sandy clay and increasing amount of calcite and were compared with a commercial formulation. Raw materials were characterized using XRF and XRD. In order to study the thermal properties of the developed formulations, TGA/DTG measurements were carried out. The sintering behaviour was evaluated using a double-beam optical non-contact dilatometer. XRD was also used to analyse the phases before and after firing. Microstructural and microchemical characteristics of the fired formulations were observed using scanning electron microscopy (SEM). Finally, the physical, mechanical and colour properties of the formulations, such as water absorption, linear firing shrinkage, bulk density, breaking strength and chromatic coordinates, were measured. The results showed that it was possible to develop wall tile formulations only by appropriate mixture of sandy clay and calcite and obtain suitable technological properties.
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.
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 bi-axial 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.
This paper deals mainly with the materials and processes associated with structuration of LTCC (Low Temperature Cofired Ceramics) in fabrication of micro/meso scale devices, including sensors, actuators and micro fluidic structures. LTCC, which is traditionally seen as a packaging material or substrate for Multi Chip Packaging Modules, is projected as an advantageous alternative to many of the technologies and processes used for various sensor and micro/meso device fabrication, which is a technology yet to be mastered in terms of processes. A roadmap for the fabrication process is drawn in detail, while the description of the devices is limited to the extent of providing the reader with sufficient information of the final structural details that have to be met. Issues in structuration like sagging, delamination, swelling, etc. are discussed. Graphite based sacrificial pastes (GB) are taken as the main structuration material, where the selection of the sacrificial material is the key to good structuration.
Glass-ceramic materials with brown, yellow-green and green-brown color and marble-like 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 hydro-purification 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 Xray phase analysis.
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.
This paper reviews a new, low-temperature process for soldering and brazing ceramics to metals that is based on the use of reactive multilayer foils as a local heat source. The reactive foils range in thickness from 40μ m to 100μ m and contain many nanoscale layers that alternate between materials with large heats of mixing, such as Al and Ni. By inserting a free-standing foil between two solder (or braze) layers and two components, heat generated by the reaction of the foil melts the solder (or braze) and consequently bonds the components. The use of reactive foils eliminates the need for a furnace, and dramatically reduces the heating of the components being bonded. Thus ceramics and metals can be joined over large areas without the damaging thermal stresses that are typically encountered when cooling in furnace soldering or brazing operations. This paper draws on earlier work to review the bonding process and its application to a variety of ceramic-metal systems. Predictions of thermal profiles during bonding and the resulting residual stresses are described and compared with results for conventional soldering or brazing processes. The microstructure, uniformity, and physical properties of the reactive foil bonds are reviewed as well, using several different ceramic-metal systems as examples.
The aim of this study is to determine the properties of metarhyolites from Ilgin-Konya (Turkey) area and to decide whether or not metarhyolites are suitable as a flux agent for porcelain stoneware tile production. For this aim, the chemical and mineralogical properties of metarhyolite were determined by chemical analyses, XRD and SEM studies. Starting from the reference mix composition, different amounts 4, 8, 12 and 16 wt.% of potassium feldspar were replaced with the same amounts of metarhyolite. All the samples were fired under industrial conditions at 1200 °C for 49 min. The physical and mechanical properties of the fired porcelain stoneware bodies such as water absorption, linear shrinkage, bulk density and fired flexural strength were measured. Fired bodies were subjected to colour measurements and X-ray diffraction (XRD). The results indicate the possible use of metarhyolite as an effective fluxing agent in porcelain tile bodies.
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 2 mass % 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.
Frost resistance of roofing tiles is of both practical and scientific interest, especially since the frost action mechanisms are still not well understood. Textural characteristics and low temperature dilatometrical behavior (from -40 to +40 °C) of clay roofing tiles are correlated with the type of frost damage identified by the standard procedure, EN 539-2, method C, giving the insight into the dominant frost action mechanism (mechanism of closed container, hydraulic pressure, and the ice lens mechanism). The samples of clay roofing tiles from the same batch were fired in laboratory conditions at different temperatures (920, 970, 995, 1015, 1055 and 1085 °C) and in the industrial plant (1100 °C). Based on the mentioned correlations, the change of the dominant frost action mechanism is explained by porous structure differentiation with the temperature, from a closed container at lower to micro ice lens formation at higher temperatures, with the hydraulic pressure mechanism contributing considerably in all the temperatures. The obtained correlations are of specific importance in taking fast and right corrective measures in a defined production line in order to improve the frost resistance characteristics of the final product.
In the pseudo ternary MgO-Si3N4-Al2O3 system at 1800 °C the occurrence of liquid phase is limited to areas near the MgO-Si3N4 line, close to Si3N4. The area near the MgO-Al2O3 line is interesting from the point of view of refractory materials. The results of investigations into the properties and microstructure of magnesia-spinel materials with oxynitride and nitride matrix obtained by sintering are presented. The materials with a matrix composed of AlN polytypoids were characterized by very high refractoriness under load (RUL) in reducing conditions (T0.6>1700 °C) and relatively high RUL in air (min T0.5>1620 °C). The TG curves showed that the oxidation course was similar to and depended on the composition and mixture of samples. A very good correlation was found between the calculated values of Rst coefficient and resistance to thermal shocks sustained by the cylinders subjected to sudden heating up to 950 °C and cooling.
Address
Links
Information