Process for producing sintered magnesia

Details Process for producing sintered magnesia Process for producing sintered magnesia

1993-03-05

1994-09-06

Derrington, James

Plastic and nonmetallic article shaping or treating: processes

Including step of generating heat by friction

264 56, 264117, C04B 3504

Patent

active

053445996

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a process for producing coarse-grained sintered magnesia, starting from a pulverulent magnesium oxide, converting this into green compacts and subjecting the green compacts to sinterfiring at high temperature.
To obtain the desired high-temperature strength in sintered magnesia products, it is necessary to achieve a sufficiently high density of the sintered magnesia, which is usually abbreviated to "sinter". As a rule, an apparent density of the sintered magnesia of 3.3 g/cm.sup.3 is regarded as a minimum value, but the aim is to reach apparent densities above 3.4 g/cm.sup.3. In order to meet this aim, the green compacts which are to be subjected to the sintering treatment at high temperature, at which deadburning of the material takes place, must already have a sufficiently high density of at least about 1.7 g/cm.sup.3, but preferably more than 2.3 g/cm.sup.3, and a structure which tends to give considerable compaction on mild firing. To form such green compacts, magnesium oxide has hitherto been compacted by means of mechanical presses, so-called briquetting roller presses having in particular been used for this compaction. However, the use of mechanical presses for the formation of green compacts of a density which meets the abovementioned demands, requires a relatively large investment expense and, in operation, the consumption of considerable quantities of energy, because very high forces must be applied for compacting the pulverulent magnesium oxide. In spite of the application of high forces, however, a relatively large proportion of the green compacts provided by the presses has an unduly low mechanical strength. Such green compacts disintegrate during the manipulation which follows pressing and, for reprocessing the material which was contained in these green compacts, this material must be screened off and subjected to repeated pressing, which results in a considerable increase in the energy consumption required for pressing and a corresponding decrease in the production output of the presses, since, in fact, a considerable part of the magnesium oxide to be processed must be compacted several times.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process of the type described at the outset, which allows the production of sufficiently dense-fired coarse-grained sintered magnesia at substantially lower investment and operating energy costs than the abovementioned known technology. The process according to the invention, of the type described at the outset, is characterised in that the green compacts, which are subjected to sinter-firing, are formed from an active, reactive pulverulent magnesium oxide of a grain size of <0.15 mm by pelletising on a granulating disc at a material throughput of less than 250 kg of MgO/m.sup.2 of disc area and per hour. Such a reactive magnesium oxide is, for example, "caustic"-burnt magnesia.
Preferably, ground caustic magnesium oxide, which has a grain size distribution in which 90% of the material is smaller than 0.1 mm, is converted into the green compacts. This is also particularly advantageous from an economic aspect, because caustic magnesium oxide of this grain size can as a rule be made available at favourable conditions.
The abovementioned objective can be well met by the design, according to the invention, of a process of the type here under discussion. The pelletising on a granulating disc can be carried out at a relatively low drive power and allows the formation of green compacts having a sufficiently high density, as mentioned above, while maintaining the indicated conditions.
It may be mentioned here that the use of pelletising for coarsening the grain of fine-grained substances is known in various fields of technology such as, for example, in the treatment of cement raw meal or in the treatment of fine-grained iron ores. Usually, in these known technologies where provision is made for pelletising, the material throughput provided with the use of granulating discs

REFERENCES:
patent: 2579886 (1951-12-01), Vettel
patent: 4003736 (1977-01-01), Kreiger
Robert H. Perry, Chemical Engineers' Handbook, 5th Edition, McGraw-Hill Book Company, New York, 1973, pp. 8-61 thru 8-63.

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