High Quality Zircon Bricks Production Study

With the rapid development of the glass industry, a series of advanced measures such as large-scale glass melting furnaces and new melting and energy-saving technologies have also put forward higher requirements for refractory materials, high quality and good stability. The demand for bricks (containing more than 65% of zirconium) has also increased sharply. At present, there is no industry standard for zircon bricks provided in the domestic market, and the product performance varies greatly, and the effect of use is very different.

zircon brick

The performance indicators of the representative zircon bricks produced in china and western countries for glass kilns are as shown in Table 1. The chemical composition of various zircon bricks is not much different. It is known that the main crystal phase is zircon crystal phase. Mainly, the performance index is related to the structure of the brick. The performance difference mainly comes from the aggregate. The preparation of high-quality brick becomes the key. A good sintered and dense structure aggregate must be used. Generally, a coarse particle with a particle size greater than 3 mm is required to improve thermal shock resistance and other performace of zirconia brick in high-temperature.

Table 1 Zircon brick properties

 

ZS65-1

ZS65-2

ZS65-3

ZS65-4

ZrO2

65.21

65.2

64.37

65.11

SiO2

32.25

32.13

33.1

32.43

Al2O3

1.38

0.95

2.1

0.75

Fe2O3

0.16

0.15

0.12

0.14

TiO2

0.62

0.73

0.2

0.14

CaO

0.07

-

0.06

-

MgO

0.03

-

0.04

-

R2O

0.08

-

-

-

Density/g.cm3

3.75

3.8

3.2

3.6

AP/ %

17

17

21

21

CCS. Mpa

98

101

110

90

R.U.L/

1650

1700

1580

1610

Refractoriness/

1830

1830

1830

1830

Linear Change/ %

0.03

0.04

0.11

0.05

The crushed raw materials are made into blanks and then sintered, crushed and sieved to obtain ideal granular bricks. Generally, the forming of the Zircon brick adopts machine pressing, casting and isostatic pressing method. Based on the above three kinds of sintering methods to make each brick, further research on the use of melting and casting method to prepare bricks is discussed.

Table 2  Zircon properties analysis under different forming method

 

 

Isostatic Pressing

Slurry Casting

Machine Pressing

Melting & Casting

chemical
 composition

ZrO2

64.49

62.59

65.66

67.3

SiO2

35.47

37.06

34.38

32.21

Al2O3

-

0

-

-

Fe2O3

0

0.42

0

-

TiO2

0.09

0

-

0.54

CaO

-

0

-

0.51

Combine Part
chemical
 composition

ZrO2

61.03

59.71

65.65

95.99

SiO2

37.24

36.65

33.92

3.27

Al2O3

-

1.65

-

0.65

Fe2O3

0.96

1.22

0.11

0

TiO2

0.8

0.81

0.34

0

CaO

-

0

-

0.1

Choose 4 methods to prepare bricks with basically the same chemical composition, fire them at the same temperature to produce samples of different densities (including fused-cast samples), and immerse them in an alkali-free glass solution for 50 hours at 1500 ℃. The degree of infestation is shown in Table 4. It can be seen from Table 4 that the apparent porosity is reduced and the water absorption is low, and its corrosion resistance is significantly better than that of the green body with high apparent porosity.

Table 3 Corrosion difference of Zircon Brick

 

Density/g.cm3

AP/ %

Water absorption
%

Corrosion Depth
mm

Machine Pressing

3.65

10.53

2.88

3.67

Isostatic Pressing

4.03

4

1.01

3.14

Slurry Casting

3.89

7.91

2.03

3.35

Melting & Casting

4.2

3.4

0.51

2.87

First of all, it is necessary to consider making the chemical composition and physical properties of the brick reach the expected technical indicators, and at the same time have good performance. In addition to meeting the above technical requirements, it is also necessary to take into account the ease of production. When ensuring the amount of zirconium, consider the sintering temperature. Impact. In order to reduce the firing temperature and not reduce the technical indicators (practicality and corrosion resistance) of the bricks, in the batching process, as little as possible or not use minerals that affect the performance of the bricks. Compared with alkali, alkaline earth metal oxides and mineralizers such as yttrium oxide and manganese oxide, titanium oxide can promote sintering as a mineralizer, but it is less resistant to the corrosion of bricks than alkali and alkaline earth metal oxides.

The particle size of zircon is related to its decomposition rate. The determination of the particle size should not only conform to the principle of close packing, but also have enough ingredients to improve the cohesiveness and sinterability of the ingredients. The particle size range of 10-3.5 mm is 2 % -5%, 3.5-14 mm is 43%-53%, 3.5-1.4 mm is 15%, <10 um is 27%-42%.


Through experiments, several binding agents such as pulp waste liquid, water glass, dextrin and AST were compared and studied, and sucrose was selected as the binding agent. The prepared material is mixed with a wheel-mill mixer, and mineralizer, water and organic binder are added at the same time, and it is required to be fully mixed and evenly mixed. The trapped material was formed by a friction brick press for 24 hours, the bulk ratio of the material was 1: 1.25, the sample was dried at 110 ℃, and the kiln moisture was controlled below 1%. Body strength after drying 7-15Mpa


The firing process of zircon bricks is similar to the firing process of general refractory materials, as shown in Figure 2. The firing temperature is between 1500 and 1700 ℃, the zircon bricks begin to shrink at 1300 and 1400 ℃, and the sintering starts at 1 The shrinkage is the most severe at 4K and 1500 ℃, and the shrinkage is very small after 1 600 ℃, and the sintering is terminated. Therefore, when firing, the temperature should be increased slowly at 13 K and 1500 ℃, and the highest firing temperature can be set at about 1600 ℃. If the amount of impurities is small, or the amount of mineralizer added is small, the firing temperature can be increased by 1650, 1700 ℃.


Table 4 Zircon brick Linear shrinkage curve

zircon brick curve

Comprehensive analysis of the developed samples and the determination of the production process. The aggregate samples made by the press blanks have bulk densities of 3.58 and 3.67 g/cm3, apparent porosity of 20% and 23%, and RUL. The temperature is lower than 1600℃; the aggregate sample prepared by isostatic pressing and mud casting method has a body density of 377 and 3.85 g/cm3, and the apparent porosity is all <18%, and the RUL > 1700℃; The sample is made of aggregate made by the melting and casting method, and its body density is 3,87 and 4.0 g/cm3, the apparent porosity is <16%, and the RUL is between 1570 and 1630 ℃ but the melting and casting method Higher cost and difficulty in controlling fusion. Among the aggregate samples prepared by the above three methods, the creep values ​​of the aggregate samples prepared by isostatic pressing and mud grouting method at 1500 ℃ for 50 h are all 0.2% of the 4 kinds of brick production processes, the mud pouring method and the isostatic pressing method can meet the technical requirements of practical applications. The mud pouring method is mature, skilled in operation and easy to master. However, isostatic pressing has a large one-time investment and high technical difficulty. It takes a long time to master the operation. Therefore, it is more economical and reasonable to use the slurry casting method to produce machine-pressed zircon bricks.

After researching and experimenting with the optimization method, the formula and process route in the experiment were determined. The overall test results of the sample are as follows: chemical composition: ZrO2 content 65.28%; bulk density, 3.77 g/cm; apparent porosity, 16. 3%; normal temperature compressive strength 109 MPa; load softening temperature (TO.6) 1700 ℃; reheating shrinkage 1 600 ℃ × 4 h, 0.03%, thermal shock resistance greater than 10 times. The products are listed in Table 5 Performance comparison with foreign products used in several domestic and foreign kinescope glass bulb kilns.

Table 5 Comparison chart of Zircon bricks from different manufacturers

 

ZrO2

SiO2

Density
/g.cm3

AP/ %

CCS. Mpa

R.U.L/

TZB-1

64.84

32.04

3.69

20

86.4

1540

ZS65A

65.13

32.21

3.75

17.5

102

1700

ZS65J

65.2

32.13

3.8

17.2

100.9

1700

ZIR-B

65.7

32.11

3.73

20

49

1570

ZBK-L

65.15

32.85

3.67

20

96.3

1630

TZB-2

64.84

31.69

3.64

21

117

1700

It can be seen from Chart 5 that the performance of the developed and produced ZS65AK and ZS65J Zircon Bricks has reached the international advanced level. ZS65J model Zircon Silicate Brick was produced by Zhengzhou Shennan Refractory Co.,ltd