Year 2008, Volume 28

Abstract

Rice husk is an agricultural waste, generated by the rice producing countries, mainly being utilized as cattle feed and cheap source of fuel for the boilers of rice mills. Ash generated after burning is regarded as a waste which contains >80% silica and some free carbon. Acid resistance characteristics of silica enable the possibility of the use of rice husk ash for the development of acid resistant ceramic products. Acid resistant porous ceramic pots are useful for electroplating industries. The present study was planned to develop slip cast acid resistant porous ceramic pots using a mix of rice husk ash as the main raw material and clay. Three different compositions were tried with rice husk ash content in the range of 50-70 wt%. Sintering was carried out in the temperature range of 1150-1200 °C. Final products were characterized by various physical, mechanical, phase content and acid resistant properties.

Abstract

The ceramic cutting tool requirements for metal machining are reviewed, taking into account the trends in industry towards dry high-speed cutting and the need for tools with complex geometry. The emphasis will be on bulk materials rather than on coatings and most attention will be devoted to machining of iron-based alloys (steels). In the development of new tool materials, special attention should be given to the chemical matching of tool and workpiece material at elevated temperatures. The chemical compatibility of the tool-workpiece combination can be investigated by means of static interaction couples at elevated temperatures, which have been exposed for times long enough to be able to characterise the interaction layer. Complementary to the experimental investigation, the chemical compatibility of tool and workpiece materials can be predicted from thermodynamic equilibrium solubility calculations of tool materials in a selected workpiece material. Taking into account the mechanical properties needed, new ZrO₂-based composites were defined based on the thermodynamically estimated chemical stability. The selection, development and proof testing of the new ZrO₂-based composites is highlighted and their wear behaviour and performance in high speed dry turning of construction steel is compared with that of state-of-the-art cutting tool materials.

Abstract

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 °C 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.

Abstract

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.

Abstract

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 production of vitreous porcelain tiles through beneficiation.

Abstract

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 pseudo-industrial surrounding with multiparameter analysis. The clustering of AE data corrupted by noise was successfully achieved by the k-means method.

Abstract

This paper provides an evaluation of commercial castable refractories by the crucible corrosion test for possible use in secondary lead smelting short rotary furnace; one mullite-zirconia fused grain and two alumina-chrome based on white and brown fused alumina were compared to five commercial burned magnesia-chromite bricks. All products were supplied by refractory Brazilian manufacturers. After the corrosion tests, the slag penetration area of the samples was measured and the refractory-slag castables interface was analyzed by Scanning Electron Microscopy (SEM), Energy Dispersive Analysis (EDS) and X-Ray diffractometry. The performance of the castables was not higher than the standards burned magnesia-chromite bricks normally used in this application. Nevertheless the good slag attack resistance of alumina-chrome castable based on white fused alumina shows the use castable refractory to be very promising.

Abstract

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, microwave-coupling 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.

Abstract

Different versions of thermoelectric unicouples composed of p-type Ca₃Co₄O₉ (Co-349) and n-type LaNiO₃ (Ni-113) or CaMnO₃ (Mn-113) bulk materials were prepared. In the unicouples p- and n-type legs were connected with Ag electrodes using Ag paste including various oxide powders with various ratios. For the Co-349/Ni-113 unicouples, maximum output power (Pmax ) reaches 177mW at a hot side temperature (T_H ) of 1073K and a temperature differential (ΔT) between T_H and cold side temperature of 500K at 6wt% of Co-349 powder. On the other hand, the lowest internal resistance (RI ) is observed in a Co-349/ Mn-113 unicouple prepared using Ag paste including 3wt% of Mn-113 powder. Thermoelectric modules consisting of 8 pairs of oxide legs were fabricated using the same method with the unicouples. The open circuit voltage (V_O) and P_max increase with increasing T_H and reach 0.392 V and 0.314 W, and 0.911 V and 0.233 W at a T_H of 1273 K in air for the Co-349/Ni-113 and Co-349/Mn-113 modules, respectively.