Zircon (ZrSiO4) belongs to quadratic system, the theoretical composition is ZrO2 67.2% and SiO2 32.8%, which is the only compound in the ZrO2-SiO2 binary system. Zircon has the following characteristics:
a. Small thermal expansion rate
b. High load softening temperature
c. The thermal conductivity decreases with the increase of temperature
Dense zircon bricks produced by spray granulation, isostatic pressing and high temperature firing processes are the key construction material of fiber glass furnace. It is used for tank wall, tank bottom paving and sub layer at melting and working end area, since its contact with glass liquid, the corrosion resistance is a very important index for dense zircon bricks. In this case, we do one testing to check the corrosion resistance of dense zircon brick as follows:
1. The performance indexes of zircon brick we used in the testing
Chemical composition %
ZrO2 65. 59
Al2O3 0. 80
Fe2O3 0. 805
Others 1.605
Apparent porosity/ % 0.5
Density/(g•cm3 ) 4.40
CCS/ Mpa 425
Coefficient of thermal expansion/（19 ~1500℃）/ [ × 10-6•K-1 ] 4.23
Thermal expansion/（1500 ℃）% 0.63
SiO2 Al2O3 MgO CaO Na2O K2O igloss
67. 85 18. 80 0. 05 3. 74 0. 39 0. 14 6. 23
3. Make sample from zircon brick as size Φ130x400 mm
Test temperature: 1500℃±10℃
Add fiber glass each 3 hours; totally add fiber glass 40 kgs
Image of Corrosion resistance testing furnace we used
Image of section of dense zircon brick after testing
Image of microstructure of dense zircon brick after testing.
From the image of microstructure of glass adhesion and reaction layer, it can be seen that the glass adhesion layer is mainly glass phase, which is uniform amorphous and has no grain precipitation. Energy spectrum analysis shows that the ZrO2 content in the glass attachment layer is 2.96%, which proves that a small amount of zircon is dissolved in the glass solution. The interface between molten glass and refractory is relatively smooth, and only a small amount of particles are melted. The glass phase in the pores of the sample in the reaction layer contains 27.49% of ZrO2, and no other compounds are generated, which proves that the reaction is mainly the dissolution of zircon in the liquid glass.
From the image of microstructure of permeable layer, it can be seen that there is a certain amount of glass phase in the pores of the permeable layer, which is mainly caused by the infiltration of glass into the brick along the channel between grains in the brick.
After that, we do chemical composition analyze of different parts of the sample (results listed below), from the difference of content of CaO that 0.41% at 2mm from contact face and 0% at 4 mm from contact face, we concluded that the penetration depth of glass is about 3 mm.
|
parts |
chemical composition % |
||||
|
Al2O3 |
SiO2 |
CaO |
ZrO2 |
others |
|
|
Surface mixed with glass |
19.58 |
61.64 |
14.15 |
2.96 |
1. 67 |
|
Contact face |
2.16 |
31.95 |
1.14 |
64.04 |
0.71 |
|
2 mm from contact face |
1.98 |
31.22 |
0.41 |
65.38 |
1.01 |
|
4 mm from contact face |
1.98 |
31.16 |
0 |
65.74 |
1.12 |
a. The scouring of glass on the brick surface,
b. The diffusion and penetration of glass into the brick through open pores,
c. The direct dissolution of brick surface under scouring.
Therefore, the corrosion of zircon in fiber glass is directly dissolved, and the glass will not cause stones. The thickness of the measured sample has no obvious change after the test, and the penetration depth is only 3 mm. As our experience, the corrosion resistance of dense zircon brick used in fiber glass furnace are much better than the testing results in lab, usually the penetration depth is 15~20 mm after 6 months operation.
