Clay-based mullite was prepared for insulating substrate applications. The clay and reactive alumina are the starting materials for the stoichiometric mullite prepared by reaction sintering at 1600 °C/3 h. MgO and boehmite were added as sintering aid to improve the density and decrease the sintering temperature. The properties of the sintered bodies, such as thermal, electrical and mechanical properties of the sintered samples were studied. The boehmite (5.0 wt.%) substituted for reactive alumina mixture showed higher density (96% theoretical density). Clay and reactive alumina completely reacted at 1600 °C and formed mullite phase. Samples with 3.0 wt.% MgO addition showed the presence of secondary phases such as α-alumina and spinel. The mullite crystals formed are needle-shaped with rectangular faces. The MgO (3.0 wt.%) addition slightly decreased the thermal expansion. Dielectric constant values are almost same for the samples with boehmite or MgO addition. © 2003 Elsevier B.V. All rights reserved.

M. Balasubramanian

Department of Metallurgical and Materials Engineering

Alumina

Permittivity

Sintering

stoichiometry

Thermal expansion

MULLITE PHASE

Clay Minerals

Aluminum oxide

CLAY MINERAL

Electronic equipment

Insulation

PORCELLANITE

SINTER

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Applied Clay Science

Porous mullite with interlocked needle shape microstructure was developed from China clay and aluminium fluoride trihydrate (AlF3·3H2O). The effects of various parameters like sintering temperature, sintering time and the amount of AlF3·3H2O on the phase evolution, microstructure and porosity have been studied. Quantitative analysis of mullite was carried out using X-ray diffraction combined with Rietveld-RIR method (Internal standard method). Porous mullite ceramics with 62% open porosity have been prepared at a relatively lower temperature of 1400 °C. The results show that the nucleation of mullite can be achieved from 700 °C onwards using hydrated aluminium fluoride without the formation of intermediate topaz crystals. The high amount of water vapour produced within the system during the in-situ reaction has a crucial role in deciding the reaction mechanism. © 2018 Elsevier Ltd

Journal of the European Ceramic Society

Characteristics of porous mullite developed from clay and AlF3·3H2O

The sintered mullite is produced commercially, using clay and alumina as the source materials. South India has an abundant quantity of high aluminous clay. The present article reports the results of the mullitisation behavior of three south Indian clays (Neyveli, Panruti and Udayarpalayam clays) and three different alumina sources, (reactive alumina, gibbsite and boehmite) to produce stoichiometric mullite. The raw materials as per the stochiometric composition were weighed and wet milled in a planetary ball mill. The dried and powdered materials were passed through 75 μm sieve, then uniaxially pressed at 50 kN to make bars, and finally the specimens were sintered at 1600 °C for 3 h under normal atmospheric condition. By reaction-sintering the clay-alumina mixture reacts to form mullite. Physical characterization such as bulk density and water absorption and the mechanical properties, like flexural strength of sintered specimens were also carried out. The Neyveli-reactive alumina mixture showed high density (2.71 g cm-3) and high strength (82 MPa). The impure Udayarpalayam clay-reactive alumina mixture shows high strength (87 MPa), but low density (2.65 g cm-3). Microstructural studies on sintered and polished samples and X-ray diffraction studies on sintered specimens are carried out to estimate the mullitisation behavior of individual clays. Among the three clays and the three alumina sources, Neyveli clay and reactive alumina mixture gave the maximum mullitisation. The specimens with bohemite exhibited poor mechanical properties as well as poor physical properties. © 2002 Elsevier Science Ltd and Techna S.r.l. All rights reserved.

Ceramics International

Mullitisation behaviour of south Indian clays

Plastic aluminous clays are abundantly available in Tamilnadu. However, at present the utilization of these clays is very low due to lack of detailed characterization. In the present work, the green and fired characteristics of clays obtained from three different locations in Tamilnadu (Udayarpalayam, Panruti and Neyveli) have been investigated to assess their potential use as raw materials. Physical properties, plasticity index, particle size analysis, chemical analysis, X-ray diffraction and thermal analysis of these clays have been carried out. Physical properties such as density, bending strength, X-ray diffraction and scanning electron microscopy of the fired samples have also been carried out. The properties of the above three clays are compared with each other. The results show that these clays are plastic in nature containing a moderate amount of impurities with high alumina content. © 2002 Taylor and Francis Group, LLC.

Transactions of the Indian Ceramic Society

Characterization of aluminous clays from tamilnadu

ChemInform

ChemInform Abstract: Mullite for Structural, Electronic, and Optical Applications

Journal	Data powered by TypesetApplied Clay Science
Publisher	Data powered by TypesetElsevier BV
ISSN	01691317
Open Access	No