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A comparative research between the technical properties of a typical porcelain composition manufactured from bone ash according to English traditional composition and a hard porcelain was made. The influence of quartz addition on final strength was also studied. Chemical and mineralogical composition of the glass and crystalline phase were analyzed by SEM and XRD. The results revealed that compared to traditional porcelains it is more difficult to sinter bone china in fast firing cycle, due to its shorter firing range. The higher mechanical strength of bone china is dependent on the presence of quartz and its particle size.
The possibility of utilizing Indian clays in vitreous porcelain tile production with a view to replace imported Ukrainian clays in the composition was assessed. A “Beneficiated clay Blend(BCB) was prepared by blending of selected five different Indian clays. The crude blend was beneficiated through two different integrated techniques utilizing levigation and hydrocyclone classification. The prepared BCB’s were characterized and incorporated singularly (35 wt%) in a standard vitreous porcelain tile composition. Their effect on technological properties with emphasis on colour indices were studied. Hydrocyclone classification of clays resulted in kaolinite enrichment at the expense of free silica and other impurities. The vitrification parameters of hydrocyclone beneficiated BCB containing bodies conformed to W.A.% ≤ 0.08, B.D. ≥ 2.2 g. cm-3, fired MOR ≥ 47 Mpa, as per IS 15622 : 2006 specification for pressed ceramic tiles with water absorption E ≤ 0.08%. The unfired and fired modulus of rupture and CIE whiteness were found superior to that of Ukrainian clay (20-25 wt%) containing bodies. The research established the possibility of replacement of Ukrainian clays by Indian clays in prodction of vitreous porcelain tiles through beneficiation.
The mineralogical composition and technological characteristics of an industrial red clay mixed with 3%, 6%, 9%, 12% and 15% of carbonates, respectively, have been studied. The added components were samples from two limestones and two dolomites from carbonate formations of Kozani area, NW Macedonia, Greece and one magnesite from Gerakini formation of Chalkidiki peninsula, N Greece. After firing them at 1150 ºC for one hour, the addition of 3% of limestone gave better properties compared to the reference clay. Porosity and water absorption followed the same trend, with the limestone containing specimens giving the lowest values and the dolomite ones the highest. The highest values of compressive strength are given with the limestone addition and the lowest ones with the dolomite addition. Limestone addition favours the formation of diopside, whereas dolomite contributes to the formation of augite. High amounts of magnesite addition assist the formation of forsterite.
Acoustic Emission (AE) can be used to discriminate the different types of damage occurring in a constrained material. However, in industrial surrounding the main problem associated with data analysis is the discrimination between the noises and the acoustic emission signals. The goal of our paper was to differentiate between air flow and AE signals produced by the material during thermal shock of a refractory material in a pseudoindustrial surrounding with multiparameter analysis. The clustering of AE data corrupted by noise was successfully achieved by the k-means method.
Slag penetration into a magnesia refractory castable was investigated by the crucible test method. A synthetic calcium aluminate slag system has been used to corrode a commercial magnesia mix refractory for 1, 2, 3, 4, 5 and 6 h at 1450 °C and 1600 °C. It has been shown that the penetration rate was controlled by a diffusion mechanism at 1450 °C, capillaries being the main channels of initial slag penetration into the refractory. In the penetration process, calcium silicate was formed on the surfaces of MgO grains, and around them by reaction between the grain boundary and mayenite, as a main phase of slag with a low melting point. Dissolution of the refractory components in the slag supported the penetration process at 1600 °C. In this case, dissolution of the refractory components in the slag not only makes new open channels, but also changes the local slag composition, resulting in a decrease of viscosity and an increase of surface tension of the slag.
Production scale inert atmosphere microwave sintering has not been successful yet, mainly because of lack of suitable equipment. For sintering in air microwave furnaces are available at different industrial scale, e.g., gas-microwave hybrid heated batch kilns or microwave “adiabatic casket” tunnel kiln1. Inert atmosphere furnaces require vacuum and gastight coupling of microwave energy. In the State of the Art technology, microwavecoupling windows represent a heat sink inside the sintering furnace. Although, radiation heat loss at temperatures >1600°C can be reduced by using a thermally insulating casket inside the microwave furnace, heat loss and temperature gradients caused by the microwave transparent windows are still not acceptable. Therefore, a new concept was developed assisted heating in inert atmosphere sintering furnaces, enabling high power microwave coupling by means of high temperature resistant antennas2. This paper presents microwave sintering results of commercial powder metallurgical (PM)-parts, details of the antenna system and the processing technology.
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