ON THE SHRINKAGE OF MAGNESIA WHICH TAKES PLACE IN ITS DEAD-BURNING
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A magnesite produced at Byakkozan in South Manchuria was fired to 600, 1100, 1500, and 1800°C. Then X-ray diffraction patterns of the products were compared one another by powder method. On the other hand, the effect of various fluxes on the fire shrinkage of pure magnesia or on its dead-burning behavior was compared by continuously measuring the linear change of dry pressed columnar test pieces, 2cm. wide, 1.5cm. thick, and 5cm. high, when they were heated in an cryptol furnace up to 1800°C, and also by tracing the change of the rate of shrinking with the rise of temperature.The results of the experiments may be abridged as follows:(1) Thermal dissociation of the magnesite was started at about 400°C and was nearly completed at 620°. Diffraction patterns of the magnesite which were fired to the four temperatures mentioned above were perfectly same. In other words, magnesite seems to produce periclase as soon as it dissociates.(2) The rate of shrinkage of the test piece made of c. p. magnesia rose suddenly at about 1290° and attained its maximum value at 1385°, arriving at a nearly constant value at 1670°.(3) Each of SiO2, Al2O3, Fe2O3, Cr2O3, and Mn2O3 accelerated the shrinkage of magnesia, though the effcct was not so intense as for natural magnesite. A secondary shrinkage occurred with Al2O3 and Cr2O3, namely the rate of shrinkage rose again at about 1470° with Al2O3, and at about 1450° with Cr2O3. The other fluxes showed similar but less distinct tendencies. The effect of FeS2 and PbSO4 was not so intense as expected.(4) The test pieces with 2% NaCl began to shrink at about 600° and completed the first shrinkage at a temperature a little over 1000°. Thus NaCl seems to encourage the shrinkage at comparatively low temperatures.(5) The effect of precipitated CaF2 was most remarkable. On its addition, the rate of shrinkage increased suddenly at about 900°, reached its maximum value at 1140°, and was reduced to almost zero at 1540°, the temperature for the maximum rate of shrinkage having been lowered by about 150°C. The effect of BaF2 was also marked though weaker than the former.
- 公益社団法人 日本セラミックス協会の論文
公益社団法人 日本セラミックス協会 | 論文
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