GB2206110A

GB2206110A - Manufacturing fired, refractory magnesia bricks

Info

Publication number: GB2206110A
Application number: GB08812938A
Authority: GB
Inventors: Thomas Weichert
Original assignee: Didier Werke AG
Current assignee: Didier Werke AG
Priority date: 1987-06-20
Filing date: 1988-06-01
Publication date: 1988-12-29
Anticipated expiration: 2008-06-01
Also published as: AT394038B; GR880100300A; DE3720460A1; GB8812938D0; GR1000325B; GB2206110B; IT8804834A0; FR2616778B1; DE3720460C2; FR2616778A1; IT1221387B; ATA129088A

Description

j 2206110 1 MANUFACTURING FIRED, REFRACTORY MAGNESIA BRICKS The invention

relates to a method of manufacturing fired, refractory magnesia bricks based on sintered magnesia and finely divided zirconium silicate of the. type which have a low porosity and a forsteritic matrix.

DE-B 1471232 discloses refractory shaped bodies on the basis of magnesite - zirconium silicate with good constancy of volume, low porosity (open porosity less than 16 vol.%) and low permeability for use as the thermal store of glass tank furnaces. Such bodies should exhibit no tendency to cracking under changes in temperature which occur periodically and a good strength at high temperatures. When manufacturing these shaped bodies one starts with a composition of 60 to 90% MgO in the form of sintered magnesia and 40 to 10% Zr02S'02 in the form of zirconium silicate, with the zirconium silicate being wholly present in a grain size of less than 0.21 mm and a sufficient amount of the sintered magnesia having a grain size of less than 0.21 mm. The zirconium silicate and the fine grained sintered magnesia are preferably present with a grain size of less than 0.15 mm. After firing, the shaped body is petrographically characterised by a texture with coarse Periclase grains bonded by a matrix of Forsterite (2 MgOSi02), and by deposits of stabilised zirconium oxide distributed in the matrix. The resulting shaped bodies are, howevert not entirely satisfactory in all cases as regards constancy of volume on firing anrI resistance to changes in temperature at high temperatures, particularly if a high proportion of zirconium silicate is used.

2 It is an object of the present invention to improve a magnesia brick of the type referred to above as regards its properties, particularly such as porosity, resistance to changes in temperature and chemical attack by gases and vapours, e.g. when constituting part of the chamber grid of a glass tank furnace.

According to the present invention there is provided a method of manufacturing R fired, refractory brick with a forsteritic matrix, which includes forming a mixture of 10 to 20 wt.% zirconium silicate with a grain size of less than 0.1 mm, 5 to 20 wt.% zirconium silicate with a grain size of 0.1 to 0.5 mm, the total amount of zirconium silicate constituting 15 to 30% by weight of the mixture, sintered magnesia with a grain size of less than 0.1 mm in an amount corresponding to 0.4 to 1 times, preferably 0.5 to 0.7 times, the amount of the zirconium silicate with a grain size of 0.1 to 0.5 mm, the remainder constituting substantially sintered magnesia with a grain size of 0.1 to 4 mm, the amounts being in each case with respect to the starting mixture of sintered magnesia and zirconium silicate, mixing the mixture with a bonding agent, pressing it into a brick-shaped body, drying it and then firing it.

By virtue of the additional use of a certain proportion of zirconium silicate in the mixture with a grain size above 0.1 mm and up to 0.5 mm, a surprising improvement in the properties of the brick is achieved, in particular an improvement in its resistance to changes in temperature.

The zirconium silicate with the grain size of 0.1 to 0.5 mm is preferably divided into two grain size ranges, with 50 to 70 wt.% zirconium silicate with a , 1 4 ip 3 grain size of 0.1 to 0.2 mm and 30 to 50 wtA zirconium silicate with a grain size of 0.2 to 0.5 mm.

The amount of the sintered magnesia with a grain size of less than 0.1 mm is selected in accordance with the amount of the zirconium silicate with a grain size of 0.1 to 0.5 mm. This results in the desired advantageous result and the formation of the desired mineral phases on firing of the bricks being achieved in a particularly reliable manner.

It is preferred that the mixture contains a total of 15 to 25 wtA zirconium silicate and sintered magnesia together with a grain size of less than 0.1 mm. It is also preferred that the mixture contains at least 60 wtA sintered magnesia with a grain size of 0.1 to 4 mm.

- Sintered magnesia which has a low content of CaO, A1203 and Fe203 and a high bulk density is advantageous in order to obtain a good strength at high temperatures, a low porosity and a matrix comprising substantially only Forsterite (2 MgOOSi02) and zirconium oxide (Zr02) in addition to the grains of Periclase (MgO). It is thus preferred that the sintered magnesia comprises at least 94 wtA Mgo, at most 2 wtA CaO, at most 0.5 wt.% Fe203 and A1203 together and has a bulk density of at least 3.25 g/cm3.

The zirconium silicate can be of generally conventional type with 65 to 68% Zr02 and 31 to 33% Si02. (The proportion.of Hf02 in an amount of about 2 wtA is included in the proportion of Zr02).

The method in accordance with the invention will be described in more detail below by reference to Examples 1 to 6 and comparative Examples 7 and 8 in the following Table.

4 In the Examples a sintered magnesia and a zirconium silicate of the following compositions (amount in percentages by weight) were used:

Sintered ca.95 magnesle Zirconium silicate Mgo CaO Si02 Zr02 A1203 Fe203 +Hf02 1.5 3.5-4 31.5 67.3 0.60 0.05 Bulk density g/CM3 3.35 About 2.5 litres 50% sulphite lve was added to 100 kg of the dry mixtures of sintered magnesia and zirconium silicate which were then pressed with a pressure of 1000 kp/cm2 into brick-shaped bodies, dried and then fired at a temperature of 1500 to 16000C.

v 1 2 3 4 5 6 7 8 Wt. % Sintered magnesia 2-4 mm 32 30 32 32 30 32 35 33 0.1-2 mm 50 46 40 32 30 35 45 42 -0.1mm 3 4 3 6 10 3 -- 5 Zirconium silicate 0.2-0.5mm 2 3 2 7 9 2 0.1-0.2mm 3 4 3 8 11 3 -0.1mm 10 13 20 15 10 25 20 20 Total Zirconium silicate Firing 20 25 30 30 30 20 20 behaviour A linear 0 +1 +2 0 -0.5 Bulk density 3.10 3.05 3.05 3.08 3.10 g/CM3 open porosity volA 14.0 17.0 18.0 15.5 14.5 Co ld compression strength N/mm2 90 60 50 70 100 11 6 1 2 3 4 5 6 7 8 1 Hot bending strength N/mm 2; 14000C 9.0 8.0 6.5 6.5 10.5 Refractoriness under load ta, Oc DIN 51064 1740 1730 1730 17401730 Changes in temperature DIN 51068, Part 2 > 30 > 30 > 30 25 17 Mgo wt.% 76 71 67 ZrO 13.5 16 19 2+ wt.% Hf02 Si02 wt'% 9 11 Q 76 13.5 12 9 i> 7 Examples 1 to 6 in accordance with the invention are arranged in the Table with an increasing proportion of zirconium silicate in the mixture. With a higher Zr02 content of the magnesia bricks the resistance to chemical attack by gases or vapours basically increases.

The fired brick-shaped bodies have a texture with coarse Periclase grains, a matrix of Forsterite (2 M90S'02) and cubically stabilised zirconium oxide (Zr02) and, particularly with the mixtures with a higher proportion of zirconium silicate, a border of Forsterite and stabilised zirconium oxide surrounding the Periclase grains. There is no zirconium silicate not converted by reaction with magnesia. Example 2 shows a magnesia brick produced from a mixture with 20 wtA zirconium silicate, which has a good constancy of volume on firing and particularly a high resistance to changes in temperature compared to comparative Examples 7 and 8. In Examples 3 and 4 with more than 20 wtA zirconium silicate in the starting mixture a high resistance to change in, temperature is also achieved with values of the constancy of volume on firing which are still acceptable and an increased porosity. In mixtures 4 and 5 there is a high proportion of coarse- grained zirconium silicate and a correspondingly high proportion of fine- grained sintered magnesia. By contrast, in mixture 6 the proportions of coarsegrained zirconium silicate-and fine-grained sintered magnesia are relatively low.

8

Claims

1. A method of manufacturing a fired, refractory brick with a forsteritic matrix, which includes forming a mixture of 10 to 20 wtA zirconium silicate with a grain size of less than 0.1 mm, 5 to 20 wtA zirconium silicate with a grain size of 0.1 to 0.5 mm, the total amount of zirconium silicate constituting 15 to.30% by weight of the mixture, sintered magnesia with a grain size of less than 0.1 mm in an amount corresponding to 0.4 to 1 times the amount of the zirconium silicate with a grain size of 0.1 to 0.5 nnL, the, remainder constituting substantially sintered magnesia with a grain size of 0.1 to 4 mm, the amounts being in each case with respect to the,starting mixture of sintered magnesia and zirconium silicate, mixing the mixture with a bonding agent, pressing it into a brick-shaped bodvi drying it and then firing it.

2. A method as claimed in claim 1, in which the sintered magnesia with a grain size of less than 0.1 mm 20 is present in an amount corresponding to 0.5 to 0.7 times the amount of the zirconium silicate with a grain size of 0.1 to 0.5 mm.

3. A method as claimed in claim 1 or claim 2 in which the zirconium silicate with a grain size of 0.1 to 0.5 mm comprises 50 to 70 wtA zirconium silicate with a grain size of 0.1 to 0.2 mm and 30 to 50 wtA zirconium silicate with a grain size of 0.2 to 0.5 mm.

4. A method as claimed in claim 1 or claim 2 or claim 3 in which the mixture contains 15 to 25 wtA zirconium 1 Z v 9 silicate and sintered magnesia together with a grain size of less than 0. 1 mm.

5. A method as claimed in any one of the preceding claims in which the mixture contains at least 60 wtA sintered magnesia with a grain size of 0. 1 to 4 mm.

6. A method as claimed in any one of the preceding claims in which the sintered magnesia which is used in 10 the mixture comprises at least 94 wtA Mgo, at most 2 wtA CaO, at most 0.5 wtA Fe203 and A1203 together and 3 has a bulk density of at least 3.25 g/cm

7. A method of manufacturing a fired, refractory brick with a forsteritic matrix substantially as specifically herein described with reference to any one of Examples 1 to 6.

8. A fired. refractory brick with a forsteritic matrix manufactured by a method as claimed in any one of the preceding claims.

11 Published 1988 at The Patent office, State louse, 66.171 High Holborn, London WC1R 4TP. Purther copies may be obtained from The Patent OMCC, Sales Branch, St Mary Gray. Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1187.