Browsing by Author "Tezuka, N"

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    In situ neutron diffraction investigation on the phase transformation sequence of kaolinite and halloysite to mullite
    (Elsevier B. V., 2006-11-15) Tezuka, N; Low, IM; Davies, IJ; Prior, MJ; Studer, AJ
    “Kaolin” is a major raw material for the fabrication of conventional ceramics. In this work the authors have investigated the thermal phase transformation of mullite from two different types of kaolin (kaolinite and halloysite), with or without alumina matrix constraint, during heating up to 1500 °C and then cooling using in situ neutron diffraction. Mullitization was initiated upon heating to 1200 °C for all specimens and followed spinel formation at 1100 °C. Above this temperature, however, evolution of the main phases, i.e., mullite, cristobalite and corundum, was influenced by the presence of impurities, initial type of silica, and alumina constraint. The relative amount of mullite was largest for the pure kaolinite specimen, particularly during heating, and this was attributed to the presence of a glassy phase. However, kaolinite with alumina suppressed the crystallization of cristobalite from the glassy phase upon cooling due to a reaction between alumina and amorphous silica, consequently resulting in an amount of mullite as for the pure kaolinite specimen (approximately 65 wt%). Halloysite was less active in terms of mullitization due to the lower level of initial impurities and greater amount of cristobalite, particularly for the alumina-constrained specimen. However, the final amount of mullite derived from the pure halloysite specimen was similar to that as from the kaolinite specimen. Crown Copyright © 2006 Published by Elsevier B.V.
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    In situ neutron diffraction study on the effect of aluminium fluoride on phase transformation of mullite from alumina/clay
    (John Wiley & Sons Inc, 2007-09-16) Tezuka, N; Low, IM; Davies, IJ; Alecu, I; Stead, R; Avdeev, M; Mehrtens, EG; Latella, BA
    The effect of aluminium fluoride (AIF3) on the phase transformation sequence of mullite (3AI2032Si02) from two different types of kaolin (kaolinite and halloysite) (AI2Si20s(OH)4-2H20) within an alumina (A1203) matrix for a temperature range of 20 - 1500 C was investigated using in situ neutron diffraction. Samples containing a mixture of A1F3 (0 - 5 wt%), AI203 and kaolin were heated up to 1500 C and then furnace cooled. During the heating procedure, one hour neutron diffraction scans were conducted at 600, 900, 1100, 1200, 1300 and 1400 C, followed by six consecutive one hour scans at 1500 C and finally a one hour scan at room temperature upon cooling. The diffraction patterns collected between 1100 and 1500 C were analyzed by Rietveld analysis. The observed phase transformations exhibited a typical sequence found inclay/alumina ceramics. Corundum, mullite and cristobalite were observed. A common feature among the specimens containing different amounts of AIF3 and kaolin was that the content of corundum decreased as the amount of mullite increased, whilst the cristobalite content tended to peak near the temperature where the amounts of corundum and mullite were approximately equal. The mullitization temperature was reduced as the AIF3 content increased for both kaolinite and halloysite. The presence of AIF3 appeared to reduce the onset temperature for mullite nucleation, which is at a much lower temperature compared to that of grain growth. However, AIF3 also seemed to lower densification. Likewise mechanical properties of the resulting specimens were determined. © MS&T07
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    In-situ neutron diffraction investigation on the phase transformation sequence of kaolinite and halloysite to mullite
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Tezuka, N; Low, IM; Davies, IJ; Prior, MJ; Studer, AJ
    “Kaolin” is a major raw material for the fabrication of conventional ceramics. Whilst kaolin has been thoroughly studied in the past decades with regards to its application as conventional ceramics there has been renewed interests in the conversion of kaolin to mullite (3Al2O3,2SiO2) with purpose of furthering the understanding of processing advanced ceramics with high strength, toughness, and thermal stability. One of the advantages of kaolin as a starting material is the needle-like morphology of mullite that is obtained by the transformation sequence at elevated temperature: kaolin —> metakaolin —> Al-Si spinel —> primary mullite (2Al203.SiO2) —> secondary mullite (3Al2O3.2SiO2). The ratio of Al203/SiO2 in mullite is considered to change by the replacement of Al and Si atoms in the tetrahedral positions. However, the in-situ transformation of primary to a secondary mullite has not been investigated in detail. This paper investigates the thermal phase transformation of mullite from two different types of kaolin (kaolinite and halloysite) with or without AIZO3 matrix constraint through the heating and cooling process by in-situ neutron diffraction. The effects of starting materials and heat treatment on the mullitisation process, especially in terms of primary —> secondary mullite evolution, are highlighted and discussed. © 2005 The Authors