GB2147893A

GB2147893A - Method of manufacturing refractory bodies or compositions

Info

Publication number: GB2147893A
Application number: GB08425807A
Authority: GB
Inventors: Naresh Bikash Dasgupta; Hermann Leupold
Original assignee: Didier Werke AG
Current assignee: Didier Werke AG
Priority date: 1983-10-13
Filing date: 1984-10-12
Publication date: 1985-05-22
Also published as: GB8425807D0; ES8600177A1; ES536688A0; BE900761A; FR2553404A1

Abstract

A method of manufacturing refractory bodies or compositions includes forming a starting mixture containing one or more of an aluminosilicate, aluminium oxide, silicon dioxide, zirconium silicate and silicon carbide, and further containing a bonding agent, and adding thereto 0.5 to 40% by weight barium sulphate, and 3 to 25 parts by weight calcium fluoride, with respect to 100 parts by weight of the added barium sulphate. The mixture is fired at a 1100 DEG to 1600 DEG C and during the firing Celsian (BaO. Al2O 3.2 SiO2) is formed. The refractories may be used as bricks or ramming or casting mixtures e.g. in lining blast furnaces, metal-melting furnaces, rotary cement furnaces, refuse incineration furnaces, or regenerator checkers for glass bath furnaces.

Description

SPECIFICATION Method of manufacturing refractory bodies or compositions.

The present invention relates to a method of manufacturing refractory bodies or compositions, particularly for use in lining furnaces or metallurgical vessels, and to bodies and compositions made by such methods.

Chemically bonding compositions with a high alumina content based on bauxite and the use of such compositions for moulding bodies for lining aluminium melt installations are known from German Patent No. 2842 176 of the present applicants. Such compositions may be manufactured with an addition of 3 to 30% by weight, fine grained barium sulphate. Furthermore, refractory bodies based on aluminium oxide or aluminosilicates for lining aluminium melt furnaces are known from German Patent No. 2835934 which contain 0.5 to 30% by weight barium sulphate and a phosphate bonder.Ceramic compositions with Celsian (BaO.A1203.2 SiO2) are known from German Patent No. 536779. It is an object of the present invention to provide a method of manufacturing refractory moulded bodies or compositions of the type in which Celsian is formed during firing but which requires a lower firing temperature and in which the resulting bodies or compositions have improved properties with regard to their cold compression strength and corrosion resistance.

Surprisingly, it has now been found that by an addition of calcium fluoride to the starting mixture advantageous properties can be achieved.

According to the present invention, there is provided a method of manufacturing refractory bodies or compositions including forming a starting mixture containing one or more of an aluminosilicate, aluminium oxide, silicon dioxide, zirconium silicate and silicon carbide, the said material or materials containing Awl203 and SiO2, and the mixture also containing a bonding agent adding 0.5 to 40% by weight barium sulphate with respect to the starting mixture, and 3 to 25 parts by weight calcium fluoride, with respect to 100 parts by weight of the added barium sulphate, and firing the mixture at 1100 to 1 600"C, whereby Celsian ( Ba O.AI203.2SiO2) is formed during the firing. It will be appreciated that the precise order in which the components are added is not of importance.

The barium sulphate is preferably added to the dry starting mixture in an amount of 0.5 to 30, preferably 5 to 20% by weight. The barium sulphate may be naturally contaiminated with calcium fluoride and if this contamination is within the ratio given above, then the two components may be added simultaneously, but if less calcium fluoride is present, then additional calcium fluoride may be also added.

It is preferred that 6 to 14 parts by weight calcium fluoride, with respect to 100 parts by weight of the barium sulphate, is added to the starting mixture.

If the starting mixture is based on aluminium oxide silicates or Bauxite, it is preferably fired at 1100 to 1450 C whilst it the starting mixture is based on aluminium oxide, e.g. Corundum, or zirconium oxide, it is preferably fired at 1200 to 1600"C, and if it is based on silicon dioxide or silicon carbide, then it is preferably fired at 1200 to 1 5500C.

In a preferred form of the invention, the starting mixture contains 90 to 98% by weight Bauxite, 2 to 10% by weight calcined alumina, and the bonding agent comprises phosphoric acid and monaluminium phosphate.

The base or starting materials for the method in accordance with the invention are aluminium oxide, aluminosilicates, silicon carbide, zirconium silicate and silicon dioxide. This means that suitable mixtures of these base materials corresponding to the general expert knowledge in the field of refractories can be used.

Aluminium oxide can be used in the form of sintered corundum, calcined bauxite with 4 to 7% by weight SiO2 and in a small amount calcined aluminium oxide. The term aluminosilicate is to be understood as including the aluminosilicates commonly used in the refractory field, in particular sintered Mullite, Sillimanite or Andalusite, kaolin fire clay, refractory fire clay and refractory clays. The silicon dioxide can be a refractory Quartzite and in particular a comminuted fine grained vitreous silica.

The term refractory body is to be understood as including all conventional moulded bodies, in particular bricks. The terms refractory composition includes compositions in various different forms, e.g. ramming compositions or casting compositions and also includes so-called dry compositions, i.e. compositions which are delivered to the user dry and are prepared by the user for processing by the addition of an appropriate quantity of water.

The term barium sulphate is to be understood as including not only chemically prepared barium sulphate, such as precipitated barium sulphate, but also Barite occurring in nature. Such Barite can of course contain the usual impurities provided these to not cause problems in the finished product.

Celsian (BaOA1203.2 SiO2) is produced when the mixture is fired at 1100 to 1600"C from the barium sulphate added to the starting mixture and the components Awl203 and SiO2 which are present in sufficient quantity. The formation of the Celsian can be checked by X-ray examination. In order to achieve as complete a formation of Celsian as possible and also good properties of the fired bodies or compositions, the firing should preferably occur in the temperature ranges referred to above.The Al203 and SiO2 necessary for the formation of the Celsian in addition to the component BaO produced from the barium sulphate should be provided in the manufacture of the refractory bodies or compositions by materials containing fine grained Al203 and/or Six2. Suitable materials are fine grained corundum, calcined alumina, refractory clay, fine grained aluminosilicates, fine grained Quartz material and pyrogenic silicic acid. In the reaction of the fine grained components with one another Celsian is formed in the matrix of the bodies and compositions which takes part in the formation of the ceramic bonds and the development of the strength of the body or composition.

The calcium fluoride which is added in accordance with the invention to the starting mixture can be chemically prepared calcium fluoride or natural fluorite and the latter can also contain the usual impurities.

Certain naturally occurring barium sulphates are already contaminated with calcium fluoride. If these barium sulphates contain 3 to 25 parts by weight, calcium fluoride as an impurity to 100 parts by weight barium sulphate they are very suitable for use in the present invention. If the calcium fluoride content of the barium sulphate is too low it is possible additionally to add the necessary quantities of pure calcium fluoride or fluorite to the starting mixture in order to achieve the ratio of calcium fluoride to barium sulphate which is necessary in accordance with the invention.

The base materials may be used in the usual grain size distributions, e.g. with a grain distribution up to 3mm with 20% by weight below 0.09mm,15% by weight from 0.09 to 0.5mm,20% by weight from 0.5 to 1 mm and 45% by weight from 1 to 3mm. It is however also possible depending on the type of the base materials and the intended use of the refractory moulded body or composition, to use more finely grained mixtures with an upper grain size of e.g. 0.2mm. The barium sulphate and the calcium fluoride are however advantageously used in the form of dust, i.e. with a particle size below 0.09mm and preferably below 0.04mm.The materials containing Al203 and/or SiO2 which react with the BaO component to form Ceisian should also preferably be used in a grain size below 0.09mm and more preferably below 0.04mm. The amount of the latter fine grained materials follows from the stoichiometric composition of the Celsian and the base material and may be easily established for each composition by a few experiments on the Celsian content of the fired composition which may be determined by X-rays. The role of the base material, as regards the formation of Celsian, is that e.g. with a base material such as fire clay and Quartz material the Al203 and/or SiO2 content of larger grain size is involved in the reaction in the formation of Celsian by virtue of the firing.

In the manufacture of the bodies and compositions in accordance with the invention, conventional inorganic bonding agents can be used, such as sodium phosphate, sodium polyphosphate, monoaluminium phosphate, sodium silicate and also organic bonding agents, such as methylcellulose, sulphite waste, synthetic resin bonder and tarpitch. Since monoaluminium phosphate may be obtained in dry solid form it is particularly suitable in the manufacture of dry compositions since these otherwise may not have an adequate storage life. When using organic bonding agents there is no danger of a premature setting of the compositions. If the compositions are delivered in the damp state, i.e. water has already been added it can be advantageous to add a fungicide inhibiting the formation of mould.

The invention embraces also bodies and compositions made by a method of the type described above and intermediate compositions prior to firing which may occur when the composition is first used as, for instance, a furnace lining.

Such bodies or compositions have a high resistance to attack by molten metals and/or slags and to attack by infiltrating corrosive gases and alkaline salts. When using bodies or compositions in accordance with the invention based on aluminium oxide and aluminosilicates an improved durability and practically no infiltration by metals and slags was detected experimentally with aluminium melt furnaces. The bodies or compositons are also usable with advantage in the lining of rotary tubular cement furnaces, refuse incineration furnaces, in the regenerator of glass both furnaces and in blast furnaces.

The invention will be described in more detail with reference to the following examples: The essential composition of the refractory granular materials used in the starting mixture are set forth in Table 1.

In the examples of Table 2 and 4 a Barite dust with no calcium fluoride content was used containing about 88% by weight BaSO4 and 12% by weight SiO2. In addition a Barite dust containing calcium fluoride (designated barium sulphate (F) in Tables 2 and 4) with about 81% by weight BaSO4,12% by weight CaF2, 6% by weight SiO2, and a calcium fluoride was used.

Moulded bodies were produced from the mixtures by pressing with pressues of about 80 to 100 N/mm2 and these were fired after drying. With the mixtures including tar or bonding pitch as bonding agent the moulded bodies were tempered in a known manner at 350"C. In these moulded bodies Celsian was first formed in the refractory lining when the latter was used operationally and the appropriate temperature reached.

The refractory bodies based on calcined Bauxite of Examples 1 to 3 (Tables 2 and 3) achieved a high cold compression strength of 200 to 290 N/mm2 after the firing at 1300,1400 and 1450"C respectively. By comparison, in Examples 4 and 5 without calcium fluoride in addition to the barium sulphate a cold compression strength of only at most 80 N/mm2 was reached after firing at 1400DC.

The bodies on aluminium oxide or Bauxite contain Corundum, Celsian and Mullite as mineral phases after the firing. The mineral phases are given for some examples in Table 3 in a shortened form; K=Corundum, C=Celsian, M=Mullite and in the order of reducing content. Examples 1,2, and 3 show that with increasing firing temperature and with increasing addition of barium sulphate the proportion of Mullite decreases to the benefit of Celsian. With a further increased firing temperature, e.g. to 1500 C, the Celsian content decreases in bodies based on Bauxite since Celsian is then transformed to an increasing extent into the glassy bonding phase.

The bodies fired at 1400 or 14500C in Examples 2 are particularly suitable for use in the lining of blast furnaces due to their good CO resistance (examination at 600 C/100 h in a CO gas current).

The refractory bodies in accordance with the invention based on fire clay (Example 8) achieved a cold compression strength of 1 20N/mm2 after firing at 1 200"C. These bricks were characterised by a good alkali resistance to potassium carbonate in a crucible experiment for 5 hours at 11 00"C. They also proved to be very resistant to corrosion and infiltration by an aggressive aluminum melt (aluminium/silicon/zinc alloy) in a crucible experiment at 800C for 72 hours.

A fire clay composition is shown in Example 9 which is storable by virtue of the use of the dry bonding agent which can be made processible by the addition of water.

In Examples 10 and 11 using Andalusite in the starting mixture (Table 3) the possibility of using calcium fluoride in addition to barium sulphate or of calcium fluoride-containing barium sulphate in accordance with the invention is shown. The compositions of Examples 9,10, 11 are not fired during their initial manufacture but are fired when they are first used.

Examples 12 to 17 (Table 4) use vitreous silica, silicon carbide, zirconium silicate and the components of Al203 (calcined Al203) and SiO2 (pyrogenic SiO2) are present or added in sufficient quantity for the formation of Celsian.

TABLE 1: Awl203 Si02 ZrO2 Ti02 FeO3 (wit.%) Bauxite ca. 90 ca. 6 2.5-3 1.5-2 Corundum ca. 99 below 0.5 0.1 Andalusite ca. 60 39 ca. 1 Fire clay 48 48 2.0 1 Calcined Al203 99 below 0.5 0.1 Silicon carbide (99 % SiC) 1.8 0.6 0.2 Zirconium silicate 0.2 34 65 Vitreous Silica 1.3 98 0.3 TABLE 2 Wt.% 1 2 3 4 5 6 7 8 9 10 11 Corundum 0-3 mm 80 90 Bauxite, calcined 0-3 mm 95 95 95 95 95 Andalusite 0-3 mm 15 5 100 100 Fire clay 0-3 mm 100 100 Calcined Al2-O3 5 5 5 5 5 5 5 Barium sulphate + 10 + 10 + 20 + 10 + 10 + 10 Barium sulphate (F) + 5 + 20 + 10 + 10 + 10 Calcium fluoride + 12 + 1 + 1 + 1.2 Monoaluminium phosphate, solid + 0.5 + 0.5 + 0.5 + 0.5 + 0.5 + 1.5 + 1.5 + 0.5 + 4 Phosphoric acid (80% by Vol.) + 3.0 + 3.0 + 3.0 + 3.0 + 3.0 + 2.0 + 2.0 + 3.0 Soot + 4 + 4 Bonding pitch (softening point 60-65 C + 4 + 4 Water 1300 1300 1450 1400 1300 1480 1480 1200 Firing C 1400 1400 1400 TABLE 3: Properties 1 1 2 2 3 4 5 5 6 7 (Example with:) Barium sulphate (F) +wt.% 5 5 10 10 20 10 10 Barium sulphate %wt.% 10 20 20 Firing C 1300 1400 1300 1400 1450 1400 1300 1400 1480 1480 Gross density g/cm 2.98 2.97 3.03 3.08 3.00 2.97 2.84 2.82 3.07 3.15 Cold compression strength N/mm 260 215 240 290 200 80 40 55 250 295 Pressure refractoriness 1400 1630 ta-Value C (measured in accordance with D1N 51064 Mineral (Corundum, Celsian, Mullite) K,C,M K,C,M,K,C, Trace M K,C K,C,M K,C TABLE 4: : Wt.% 12 13 14 15 16 17 Quartz material 0-3.5 mm 95 95 Zirconium silicate 0-0.5 mm 92 92 Silicon carbide 0-3 mm 92 92 Calcined Al2O3 5 5 5 5 5 5 Pyrogenic SiO2 3 3 3 3 Barium sulphate + 10 + 10 + 10 Barium sulphate (F) + 10 + 10 + 10 Calcium fluoride + 1 + 1 + 1 Monoaluminium phosphate + 1 + 1 + 2 + 1 + 2 + 3 Phosphate acid (80% by Vol.) + 4 + 4 + 2 + 4 + 2 + 1 Sulphite waste, dry + 0.5 + 0.5 + 0.5 + 0.5 Firing C 1400 1400 1450 1450 1360 1360

Claims

1. A method of maufacturing refractory bodies or compositions including forming a starting mixture containing one or more of an aluminosilicate, aluminium oxide, silicon dioxide, zirconium silicate and silicon carbide, Al203 and SiO2 and the mixture also containing a bonding agent, adding 0.5 to 40% by weight barium sulphate with respect to the starting mixture, and 3 to 25 parts by weight calcium fluoride, with respect to 100 parts by weight of the added barium sulphate, and firing the mixture at 100 to 16009C whereby Celsian (BaO.A1203.2 SiO2) is formed during the firing.

2. A method as claimed in Claim 1 in which barium sulphate is added to the starting mixture in an amount of 5 to 20% by weight.

3. A method as claimed in Claim 1 in which a barium sulphate contaminated with calcium fluoride within the ratio given in Claim 1 is added to the starting mixture.

4. A method as claimed in Claims 1 or 2 in which 6 to 14 parts by weight calcium fluoride, with respect to 100 parts by weight of the added barium sulphate, is added to the starting mixture.

5. A method as claimed in Clain 1 in which the starting mixture is based on aluminium oxide silicates and bauxite and is fired at 1100 to 1450"C.

6. A method as claimed in Claim 1 in which the starting mixture is based on corundum and zirconium oxide and is fired at 1200 to 1600"C.

7. A method as claimed in Claim 1 in which the starting mixture is based on silicon dioxide and silicon carbide and is fired at 1200 to 1550"C.

8. A method as claimed in Claim 1 in which the starting mixture contains 90 to 98% by weight bauxite, 2 to 10% by weight calcined alumina and the bonding agent comprises phosphoric acid and monoaluminium phosphate.

9. A method of manufacturing refractory bodies or compositions substantially as specifically herein described with reference to any one of the accompanying examples.

10. A refractory body or composition manufactured by a method as claimed in any one of the preceding claims.

11. The use of a body or composition as claimed in Claim 10 for lining a metallurgical furnace or ladle.

12. The use of a body or composition as claimed in Claim 10 for the refractory lining of a blast furnace.

13. A composition comprising a mixture of one or more of a n an aluminosilicate oxide, silicon dioxide, zirconium silicate and silicon carbide, the said material or materials containing AL203 and SiO2, a bonding agent, 0.5 to 40% by weight barium sulphate and 3 to 25 parts by weight calcium fluoride, with respect to 100 parts by weight of the barium sulphate, whereby when the composition is fired celsian is formed.