Mullite needle-like

After 1200 °C oxidation (see Z-1200), there were large numbers ofwhite needlelike oxides of less than 1 pm in length on the surface of Zl-1200. Combining the EDS analysis and XRD result, we are convinced that the needle-like oxides should be mullite crystals which grew in amorphous Si02. Clearly, no oxide crystals were seen on the surface of Z2-1200, except for large numbers of white spots which should be mullite oxide as same as the needle-like crystals in Zl-1200. However, their size was smaller than that in Zl-1200. For Z3-1200, we can see that the surface of the specimen was oxidized considerably. Combining the element analysis with the result of XRD, we can conclude that the oxide is mullite. 

When the oxidation temperature was increased to 1400 ° C (Z-1400), the needlelike mullite crystals in Zl-1400 grew up to more than about 10 pm in length. In Z2-1400, the mullite showed two kinds of shapes, needle-like crystals and agglomerates. The needle-like crystals were same as those in Zl-1400, and the agglomerates were same as those in Z3-1400. The whole surface of Z3-1400 is covered with the scale consisting of agglomerates of mullite. 

Needle-like mullite particles are more attractive for applications like reinforcement in high temperature structural components. Needle-like mullite samples prepared from... 

Strength is due to the interlocking of long, needle-like crystals. Some authorities have stated that to get long crystals there mnst be present impurities which will promote then-growth, but a mullite body with short, interlocking crystals is more stable to load-deformation at high temperatures. 

Figure 3.31 Scanning electron microscopy images of porcelain-like stoneware, (a) Vitreous China ware from Sawankhalok, Thailand (15th century C.E.), showing primary platy mullite (Mu I), secondary needle-shaped mullite (Mu II), and a partially dissolved residual quartz grain (Qz)...

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