Mixture of chemicals for forming a refractory composition

Details Mixture of chemicals for forming a refractory composition Mixture of chemicals for forming a refractory composition

1996-09-10

1999-08-24

Bell, Mark L.

Compositions: ceramic

Ceramic compositions

Carbide or oxycarbide containing

501 961, 501108, 501120, 501121, 501123, 501125, 501127, 501133, C04B 3503, C04B 35101, C04B 3516, C04B 3544

Patent

active

059424532

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention concerns a mixture of chemical substances for forming a refractory composition that takes the form either of blocks or moulded parts or of refractory coatings, in particular a pulverulent mixture, comprising a charge of refractory particles, metallic particles and particles containing a metal peroxide.
More specifically, it concerns a mixture of inert refractory particles and of chemical substances which, by oxidation or decomposition, can form a mixed oxide in an exothermic manner, where said mixed oxide constitutes a binding phase for the charge of refractory particles.


BACKGROUND OF THE INVENTION

For the purpose of manufacturing refractory materials, Belgian patent 871.496 shows the use of oxides, oxidisable elements such as metals, and oxidising compounds, in particular metal peroxides with a particle size between 50 and 300 microns.
Similarly, in UK patent 2.213.812 with the same object, oxidising agents are used with an average particle size less than 200 microns and a maximum particle size of 500 microns, such as higher oxides, nitrates, perhalogenates or peroxides. Such peroxides are also mentioned in German patent application 4.221.480, as substances which can decompose.
Further, international patent application PCT/BE92/00012, submitted by the same applicant as for the present patent application, describes mixtures containing peroxides which enable refractory mixed oxides to be formed which play the role of a binding phase for refractory particles.


SUMMARY OF THE INVENTION

One of the essential aims of the present invention is to propose a mixture of chemical substances of the type mentioned above, offering significantly higher safety of use compared with the known mixtures of chemical substances.
Indeed, the combination of reducing agents, such as metallic elements, and oxidising agents, such as peroxides, can pose problems of stability and of controlling the reactions at various stages of production of the above-mentioned refractory composition.
For example, right from the preparation of the mixture of metallic particles and particles containing metal peroxide, forming the reducing and oxidising agents, it is necessary to avoid the presence of any compound which could trigger a violent catalytic reaction.
Further, when the pulverulent mixture thus obtained is suspended in a carrier gas for spraying, excessive transport speeds can also give rise to uncontrollable or even explosive decomposition.
Finally, during spraying, there is a risk of the combustion front propagating upstream towards the fuel source.
The mixture of chemical substances according to the invention is characterised by the fact that the particles containing metal peroxide have a calcium peroxide content of at most 75% by weight and preferably at most 65% by weight, a magnesium peroxide content of at most 30% by weight, a barium peroxide content of at most 92% by weight and/or strontium peroxide of at most 90% by weight.
The invention also concerns a refractory composition obtained from the above-mentioned mixture.
This composition comprises a charge of refractory particles immersed in a binding phase containing at least 20% and preferably more than 50% of at least one refractory mixed oxide with at least two different metals, said binder having a melting point lower than the refractory charge.
The invention further concerns a process for preparing a refractory composition by the application of the above-mentioned mixture.
According to this process, refractory oxides of different metals are first formed by oxidation reactions and/or decomposition reactions of chemical starter substances. These refractory oxides are formed in ratios such that, subsequently, a mixed refractory oxide is formed by reaction between at least 50% of said nascent refractory oxides, where said mixed refractory oxide is thermodynamically stable under the conditions of this reaction. The type and quantity of the chemical reagents are chosen such that said reactions are exothermic and lead to the formation o

REFERENCES:
patent: 5221647 (1993-06-01), Hida et al.
Sax et al., Hawley's Condensed Chemical Dictionary, pp. 120, 121, 207, 722 & 1099, 1984.
Encyclopedia of Chemical Technology, Third Edition, pp. 1-6, 1982.
Encyclopedia of Chemical Technology, Fourth Edition, pp. 202-210, 1996.

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