FR2531423A1 - COMPOSITION OF REFRACTORY MORTAR - Google Patents

Abstract

THE COMPOSITION IS ESSENTIALLY COMPOSED OF A MIXTURE OF 75 TO 95 BY WEIGHT OF COINS OF CHROMIUM MAGNESIA OXIDE; 1 TO 10 BY WEIGHT OF A PULVERULENT REFRACTORY PLASTICIZER CHOSEN BETWEEN FIGULIN CLAY, BENTONITE, KAOLIN AND THEIR MIXTURES; FROM 6 TO 12 BY WEIGHT OF A SOURCE OF FINELY DIVIDED CHROMIUM OXIDE; AND 0 TO 5 BY WEIGHT OF A FINELY DIVIDED MAGNESIS SOURCE INTO PARTICLES

Description

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  The present invention relates, in general, to refractory products and, more particularly, it has

  for object a composition of refractory mortar.

  To the knowledge of the Applicant, the most relevant prior art S is represented by United States patents NO 2 406 909 issued on September 3, 1946, in the name of RA SCHOENLAUB, n 3 285 762, issued on November 15, 1966 , in the name of 0 M WICKEN and NO 3 868 261 issued on February 25, 1975, 'in the name of N CASSENS Jr et ai and the French utility certificate NO 2 478 621, deposited on March 2, 1981, in the name of OSTERREICHISCHAMERIKANISCHE MAGNESIT

AKTIENGESELLSCHAFT AT.

  The use of refractory mortars in the cons-

  furnace and hearth lining truction and the like is well known The refractory bricks and mortars used in such applications are exposed not only to molten metal, but also to extremely corrosive vapors and slag Slag rich in silica, such as , for example, western coal slag

  -20 American, are particularly corrosive.

  The refractory bricks having the composition described in the French utility certificate N O 2 478 621 are particularly useful for the lining of hearths exposed to slag rich in silica These bricks

  refractories are composed of chromium-ma-

  co-fused genesis, comprising a certain quantity of relatively fine grains which are shaped to the desired shape, at ambient temperature, and agglomerated at 1 7500 C. This certificate of utility teaches, for example, that a mixture of co-fused grains of chromium and magnesia oxide having the indicated particle size, was mixed with residual sulphite liquor and water, formed into a brick and calcined at 17500 C under reducing conditions

to agglomerate the grains.

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  2 3 Mg O Particle size 6 12 mm 1.5 6 mm 20 less than 1.5 mm less than 0.12 mm The certificate of utility also suggests that the same particle size mixtures can be used as mortar for the meeting bricks thus formed This prior document is interesting in that it teaches the use of a mortar composed of grains or particles

  of co-fused chromium-magnesia oxide spinel Cepen-

  when used as a mortar and subjected to it

  heat treatment, chromium-ma-

  co-fused genesis create a link between the bricks by

  agglomeration Such is not the case according to the invention -

  A refractory mortar of general application is described by Wicken, this mortar being composed of a major quantity of iron oxide, extinguished magnesite calcined and ground in a ball mill, hydrated sodium silicate

  water soluble, usually figulin clay as plastic

  reliable and an effective amount of an organic plasticizer such as corn starch To this mixture of powdery solids, a sufficient amount of water is added to give it a consistency such that it can be spread with a trowel. mortar is used in the usual way The Wicken patent is interesting, in order to appreciate the present invention, in the sense that both of them use

  figulin clay and organic plasticizers.

  The Schoenlaub patent teaches a composition of relatively plastic basic refractory materials, usable as mortar, and which is made of 81% Mg O, 8% Ca O, 4% Si O 2, 2% Cr 0, 2% Ai O and 0, 5% BO Interest

2 '2 3 0, 2 3'

  major of this prior document is its general teaching of the use of plasticizing agents such as water-soluble starch, figulin clay, plastic refractory clays and bentonite which are materials which can

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  be incorporated into the mortar composition according to the invention. The Cassen et al patent describes a refractory mortar composition composed of chromium-magesia grains having a particular particle size distribution, fine Cr 203, dextrin and methylcellulose Chrome-magnesia grains according to the Cassen patent and al are made by agglomeration of chromium and magnesia ore and therefore the grains themselves are made up of agglomerated particles of chromium oxide and magnesia This is different from the present invention o the grains are made of co-fused chromium magnesia and The interest of the Cassen et al patent, vis-à-vis the invention, basically lies in its teaching of the use of chromium oxide as an additive to oxide grains.

  chromium-magnesia agglomerates and in the use of materials

  organic rials, such as dextrin and methylcellulo-

  se. The present invention relates to a refractory mortar

  particularly suitable for joining refractory bricks

  silices based on chromium-magnesia oxide spinel, as described in the French utility certificate no. 2 478 621, this mortar offering great resistance to corrosion by slags rich in silica * The mortar composition according to invention is preferably as close to that of bricks as possible The co-fused grains of chromium oxide and magnesia are necessary to form mortar joints having optimal resistance to corrosion and -to maintain volume stability in use , the particle size of the grains should be fine to allow the realization of very thin joints The spinel grains of chromium oxide and co-fused magnesia represent from 75 to 95% by weight of the dry mortar mixture with a preferred particle size ranging from 44 microns and less to 250 microns and less to be able to make the joints of minimum thickness Larger grains can be used but, as indicated above, these coarse-grained mortars ns are generally less useful Although there are no rigid standards to be observed in the

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  chromium oxide / magnesia ratio in co-melting grains-

  born, the ideal composition is rather on the side rich in chromium oxide of the composition of spinel chromium oxide-magnesia which will contain approximately 79% by weight of chromium oxide and approximately 21% by weight of magnesia. The grain is bonded with a combination of 1 to 10% by weight of a powdery refractory plasticizer and 6 to 12% by weight of a source of chromium oxide in fine particles, alone or in combination with up to 5% by weight of a source of magnesia in fine particles The powders of chromium oxide and of chromium oxide / magnesia, are really the main binding ingredients but the refractory plasticizers really contribute to the ceramic bond of the chromium magnesia oxide grains. in addition, the refractory plasticizer acts naturally as a plasticizer as is well known to those skilled in the art. The refractory plasticizing agents which are preferred are figulin clay, bentonite> kaolin and, in particular, a mixture of 2 to 6. % by weight of figulin clay and 1 to 3% by weight of bentonite When such a bonding combination is mixed -with the fused chromemagnesia and calcined grains, which is generally carried out when the newly furnished hearth is all umé for the first time, the fine particles of chromium oxide and magnesia react to form, in situ, a microcrystalline matrix of spinel essentially formed of chromium oxide and magnesia, or a microcrystalline matrix of chromium oxide when only chromium oxide has been used as the main grain binder Chromium oxide powder should have an average particle size of about 1 micron or less and magnesia is more effective when its size particle average is 30 microns or less Although sources of chromium oxide and magnesia are not critical, they must be rich in these materials; for example, periclase is a good source of magnesia and the

  green chromium, a suitable source of chromium oxide.

  The preceding refractory mixture is made plastic and spreadable with a trowel or applicable in the form of a

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  coating by mixing with an appropriate amount of water and an organic plasticizing agent Normally, the organic plasticizing agent is used in an amount of approximately 2%

  weight of the combined weights of all refractory powders

  res; however, the presence of organic material is not absolutely necessary The amount of water added is that which gives the mixture the desired consistency If the mortar must be spread with a trowel, the mixture must be relatively thick and, therefore, we will add about 40 to 45% by weight of water relative to the total weight of all refractory materials On the other hand, if the mortar is to be applied to the bricks by soaking or spraying, a greater amount of water will be added such by

  example, 50% of the total weight of the refractory mixture.

  There are a large number of organic materials which can act as organic plasticizers, for example, natural gums, alginates, waxes, alcohols, cellulose, lignin and fats; the preferred organic plasticizer is methylcellulose used in an amount of about 2% by weight relative to the total weight of the

inorganic materials.

  A preferred mortar mixture was prepared by mixing the following refractory materials in the weight percentages shown

MATERIALS PERCENTAGE PONDERAL

  grain of co-fused chromium and magnesia oxide (74 microns and less) 85 clay powdery figulin 3 powdery bentonite 2 chromium oxide (1 micron and less) 8 periclase (30 microns and less) 2 To the powder mixture is added 0, 1% of a 400 centipoise solution of methyl cellulose and approximately 50% of water, these weight percentages being based on the total weight of the refractory powders The resulting mortar mixture

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  is of a consistency suitable for soaking and, after calcination, the mortar shows practically no shrinkage since the shrinkage which would be caused by the loss of water and methyl cellulose is essentially compensated by the increase in volume produced by the reaction between chromium oxide and periclase forming the spinel chromium-magnesia oxide Refractory bricks such as those described in the French utility certificate 2 478 621 are soaked in mortar and assembled to fill an oven The heat of furnace causes the mortar to harden in situ. A mortar mixture can be prepared with a trowel by mixing the following materials in the quantities indicated below:

MATERIALS BY WEIGHT

  grain of co-fused chromium and magnesia oxide (216 microns and less) 425 powdery figulin clay 15 powdery bentonite 10 chromium oxide (1 micron and less) 40 calcined magnesia (44 microns and less) 10 methyl cellulose 0.5 water 225 The resulting mortar mixture has a smooth and smooth consistency and it is easily spread with a trowel on refractory bricks The bricks have been pressed together on site to produce a joint as thin as possible After calcination, the bond between the mortar

  hardened and the bricks is excellent.

  It is understood that the present invention is not limited to the embodiments described which have not been described.

as examples.

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Claims (6)

  1 refractory mortar composition, characterized in that it essentially consists of a mixture of 75 to 95% by weight of chromium-magnesia oxide grains co-fused; 1 to 10% by weight of a powdery refractory plasticizer chosen from figulin clay, bentonite, kaolin and their mixtures; from 6 to 12% by weight of a source of chromium oxide finely divided into particles; and 0 to 5% by weight of a source of magnesia finely divided into particles.   2 Composition of refractory mortar according to the claim   cation 1, characterized in that said co-fused grain has a particle size between 44 microns or less and 250 microns or less, said source of chromium oxide having an average particle size of about 1 micron or less and said source of magnesia with particle size   average of about 30 microns or less.   3 Composition of refractory mortar according to the claim   cation 2, characterized in that said plasticizer refracts   Silent powder consists of an amount of up to 2 to 6% by weight of figulin clay and from 1 to 3% in weight of bentonite.   4 Composition of refractory mortar according to the claim   cation 3, "characterized in that said oxide grain of-   confused chromium magnesia and the combination of the sources of chromium oxide and magnesia are each composed of approximately 75% by weight of chromium oxide and 21% by weight of magnesia.   5 Composition of refractory mortar according to the claim   cation 4, characterized in that said co-fused grain represents 85% by weight of said mortar and has a particle size of 74 microns or less; in that said refractory plasticizer consists of an amount up to 3% by weight of figulin clay and 2% by weight of bentonite; and in that the source of chromium oxide is green chromium and represents an amount of 8% by weight while the source of magnesia is periclase   representing an amount of 2% by weight.   6 Composition of refractory mortar according to one   any of claims 1 to 5, characterized in that   that it contains from O to 2% of an organic plasticizing agent and from 40 to 50% of water, these percentages being expressed relative to the total weight of said refractory mortar composition.