Cordierite phase

Fig. 10 Time-resolved XRD (panel A) and QEXAFS (panel B) data showing the thermally induced formation of a crystalline cordierite phase from Mg-exchanged zeolite B. This transformation takes place via an intermediate amorphous phase as is clearly visible in the XRD data.

Cordierite insulator has the formula 2Mg0-2Al203-5Si02. A variety of fluxes are used in its manufacture. The cordierite phase develops as prismatic habit crystals. These are again bonded with a glassy phase. In addition, some mullite, corundum, spinel, forsterite, or enstatite (Mg0-Si02) phases may also be seen. 

The modification of cordierite with manganese oxide (only up to substitution degree x=0.5) additionally promotes cordierite phase formation as presented in Table 1. A shift of diffraction peaks corresponding to the increase of cordierite unit cell volume was found (Figure 1) for these samples due to the possible isomorphic substitution of Mg ions by Mn ions having larger ionic radious [7],... 

Also at 1000 °C, spinel formed and was a major phase at 1100 °C. Cristobalite began forming at about 900 °C and became a major phase by 1100 °C. Minor, weak X-ray reflections at 1000 °C also suggested cordierite and diopside (clinopyroxene), but both of these were uncertain and disappeared by 1100 °C. 

Cordierite synthesis method based on mechanical activation of mixtures of hydrated oxides of calcium, aluminium and silicon, as well as natural hydrated compounds (talc, kaolinite and gibbsite), has been developed in [2, 3]. Mechanical activation of these mixtures does not lead to the formation of new phases but provides good mixing at the cluster level giving aggregates that form cordierite during the subsequent thermal treatment. 

In industry, cordierite is usually obtained by calcination of the mixtures containing talc, kaolinite and silica at 1300-1450°C for 20-60 h. The product contains the impurity phases spinel, mullite, clinoenstatite, etc., that worsen the exploitation characteristics of cordierite. Since the mentioned minerals contain structural water, chemical interaction between them during mechanical activation can be considered from the viewpoint of soft mechanochemical synthesis. Mechanical activation of this mixture does simplifies the interaction between its components. It is sufficient to heat this mixture for 2 h at a temperature of 1260°C to obtain practically homogeneous cordierite without impurity phases (Fig. 7.2) [2-9]. 

There has been a considerable effort in the physics and chemistry communities to use INS methods to study magnetic dynamics, which can often be described as spin waves. Measurements of spin wave dispersion curves can provide information about the interactions between atomic magnetic moments, the so-called exchange interactions. There have been comparatively few INS measurements on magnetic minerals. INS methods have been used to produce spin wave dispersion curves for hematite. Crystal field magnetic transitions in cobalt bearing cordierite, and spinel phases have also been studied by INS. ... 

FIGURE 13.2 Scaiming electron micrographs of fractnre snrfaces of cordierite composition gels sintered at 1300°C for 2 h (a) nanocomposite and (b) homogeneons (single phase). (Reprinted with permission from Kazakos, A.M., Komameni, S., and Roy, R., J. Mater. Res., 5, 1095, 1990.)... 

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