Zirconia electrode bricks and their preparation methods and applications

Abstract

The present invention belongs to the technical field of refractory materials, and particularly relates to a zirconia-based electrode brick and its preparation method and application. The zirconia-based electrode brick is obtained by wet grinding a powder material and an organic binder to obtain a slurry, spray granulating the slurry to obtain a granulated powder, isostatically pressing the granulated powder to obtain a green body, and sintering the green body to obtain the electrode brick. The powder material comprises raw materials in the following weight percentages: zirconia powder of grade 65, 10% - 40%; zirconia powder of grade 66, 59.3% - 89.6%; titanium dioxide, 0.4% - 0.7%. The present invention greatly improves the high-temperature resistivity and high-temperature stability, and has a long service life. The present invention also provides its preparation method and application in a glass melting furnace.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractory materials, and particularly relates to a zirconia electrode brick, a preparation method thereof, and an application thereof. Background Art

[0002] The energy-saving and consumption-reducing technologies for industrial furnaces such as high-power "fire-electricity" composite melting and all-electric melting in glass melting furnaces have developed rapidly. The all-electric glass melting furnace is mainly heated by electric energy. The current in the heating electrode causes the temperature of the electrode brick to rise, and the flow rate of the glass liquid to accelerate, resulting in severe erosion around the electrode holes of ordinary dense zirconia bricks, increasing the stones in the glass liquid, affecting the quality of the glass, and seriously affecting the service life of the all-electric glass melting furnace.

[0003] Chinese Utility Model Patent Authorization Publication No. CN207002556U proposes an electrode layer brick for an all-electric glass melting furnace. By adding a more erosion-resistant fused high-zirconia brick as the inner lining at the severely eroded electrode hole part, the erosion resistance of the electrode hole part of the electrode layer brick is improved, the service life of the all-electric glass melting furnace is extended, and the quality of the glass liquid is improved. However, the price of this electrode layer brick is high, the intensity of the staff during masonry is high, and the operation difficulty is relatively large.

[0004] In the 6th issue of the 31st volume of "Shandong Ceramics", "Development and Application of High-Resistance Cast Zirconia Corundum Bricks", through reasonable design of the chemical composition of the fused zirconia corundum brick, controlling its composition to meet the requirements of fused zirconia corundum refractory products for glass melting furnaces, a high-resistance and erosion-resistant fused zirconia corundum brick was developed. The high-temperature resistivity of the fused zirconia corundum brick at 1600 °C was increased from about 80 Ω·cm to 250 Ω·cm, and the actual erosion situation of the furnace was greatly improved, but the high-temperature resistivity was still relatively low.

[0005] In Chinese Patent Application Publication Nos. CN108727019A, CN116986897A, CN102007089A, and US Patent Publication No. US5124287A, the zirconia brick was improved in thermal shock stability and erosion resistance by adding ZrO 2 、ZA、MgO, etc. However, the added ZrO 2 component is conductive, and this type of thermal shock-resistant zirconia brick cannot be used in the electrode part.

[0006] Chinese Patent Application Publication Nos. CN111039682A, CN105060902A, CN102036934A, CN101851107A, CN107117963A, and CN102584286A mainly propose technical solutions to improve the creep rate of zirconia or zirconia composite overflow bricks.

[0007] Chinese invention patent application publication numbers CN106116571A and CN106518107A disclose methods for preparing high-purity dense zircon bricks or layered high-purity zircon refractory materials using quartz powder and zirconium oxide powder.

[0008] Chinese invention patent application publication number CN105272187A proposes a method for preparing zircon ceramics, with zircon as the matrix. The sintering aid in the technical solution is composed of 5% magnesium oxide, 1% yttrium oxide, and 4% titanium dioxide, which account for 5% of the mass of zircon. The high proportion of the additives magnesium oxide and titanium dioxide results in poor volume stability of the ceramic at high temperatures.

[0009] In summary, ordinary zircon bricks have the following problems: low high-temperature resistivity. Due to the heating effect of the current in the electrode on the brick, the temperature of the electrode brick increases and the glass erosion around the electrode hole intensifies, causing abnormal erosion of the electrode brick; ordinary zircon bricks decompose at 1600°C or higher temperatures, resulting in volume expansion and loose structure, which seriously affects the service life of the electrode brick. Summary of the invention

[0010] In order to solve the above technical problems, the present invention provides a zircon electrode brick, which greatly improves high temperature resistivity and high temperature stability and has a long service life. The present invention also provides a preparation method and application of the zircon electrode brick in a glass melting furnace.

[0011] The zircon electrode brick of the present invention is obtained by wet grinding powder and organic binder to obtain slurry, spray granulation of the slurry to obtain granulated powder, isostatic pressing of the granulated powder to obtain green body, and sintering of the green body to obtain the electrode brick, wherein the powder includes the following raw materials in percentage by weight:

[0012] 65 grade zircon powder, 10%-40%;

[0013] Grade 66 zircon powder, 59.3%-89.6%;

[0014] Titanium dioxide, 0.4%-0.7%;

[0015] Chemical composition of 65 grade zircon powder in mass percentage: SiO 2 <34%, 0.3%<Al 2 O 3 <1.0%, 0.1%<Fe 2 O 3 <0.2%, ZrO 2 >65%; preferably, 0.6%<Al in 65-grade zircon powder 2 O 3 The mass percentage of Al in 65 grade zircon powder is less than 1.0%, and the particle size is ≤320 mesh. 2 O 3When it is less than 0.6%, it is beneficial to increase the high-temperature resistivity of the product, but the heating permanent linear change rate at 1700 °C for 24 h is relatively high; in the zircon powder of grade 65, Al 2 O 3 When it is higher than 1.0%, the bulk density of the product is low.

[0016] The chemical composition of the zircon powder of grade 66 is calculated by mass percentage: SiO 2 <34%, Al 2 O 3 <0.3%, Fe 2 O 3 <0.1%, ZrO 2 >65.7%; preferably, in the zircon powder of grade 66, the mass percentage of Al 2 O 3 is less than 0.2%, the mass percentage of Fe 2 O 3 is less than 0.05%, and the particle size is ≤ 320 mesh. When the mass percentage of Al 2 O 3 in the zircon powder of grade 66 is less than 0.3%, it is beneficial to increase the resistivity of the product. Especially when the mass percentage of Al 2 O 3 in the zircon powder of grade 66 is less than 0.2%, the high-temperature resistivity of the product is the highest, the bulk density is high, but the heating permanent linear change rate at 1700 °C for 24 h is only reduced by about 30% compared with the prior art.

[0017] Preferably, the titanium dioxide is of rutile type, the chemical composition TiO 2 >98.5%, and the particle size is ≤ 320 mesh. When the addition amount of titanium dioxide is < 0.4%, the bulk density is relatively low, which is beneficial to increasing the high-temperature resistivity of the product, but the heating permanent linear change rate at 1700 °C for 24 h is high and the high-temperature stability is poor; when the addition amount of titanium dioxide is > 0.7%, for example, adding 1.0% of titanium dioxide, it is not beneficial to both increasing the high-temperature resistivity of the product and the high-temperature stability at 1700 °C for 24 h.

[0018] The wet grinding step is: wet grind the zircon powder of grade 65, titanium dioxide, and organic binder first, and then add the zircon powder of grade 66 to continue wet grinding to obtain a slurry.

[0019] Preferably, the organic binder is one or both of carboxymethyl cellulose and polyvinyl alcohol, and the addition amount is 1.5% - 3.0% of the mass of the powder material.

[0020] The preparation method of the zirconia electrode brick described in the present invention includes the following steps:

[0021] (1) Wet grind 65-grade zircon powder, titanium white powder, and organic binder for the first step for 10 - 30 min until the particle size reaches 4 - 8 μm; then add 66-grade zircon powder and conduct the second step of wet grinding for 20 - 40 min until the particle size reaches 5 - 9 μm to obtain a compound material slurry.

[0022] The specific steps of step (1) are as follows: Add zirconia balls, water, 65-grade zircon powder, titanium white powder, and organic binder into a ball mill for the first step of wet grinding. The grinding time is 10 - 30 min until the particle size reaches 4 - 8 μm; then add 66-grade zircon powder into the ball mill for the second step of wet grinding. The grinding time is 20 - 40 min until the particle size reaches 5 - 9 μm to form a compound material slurry.

[0023] In step (1), the mass ratio of zirconia balls, the total mass of powder materials and organic binder, and water is 2:2:1.

[0024] (2) Spray granulate the compound material slurry to form granulated powder, and isostatically press the granulated powder to obtain a green body.

[0025] (3) Dry and sinter the green body to obtain the product. The green body can be dried naturally or using equipment. In the case of natural drying, it takes several days, preferably 1 - 3 d.

[0026] The function of wet grinding is to adjust the particle size of zircon particles and make the titanium white powder, organic binder, and zircon particles evenly distributed. The present invention finds that the wet grinding sequence of raw materials affects the high-temperature resistivity and the high-temperature stability of the brick. Grinding 66-grade zircon powder first, or grinding 65-grade and 66-grade zircon powders simultaneously, or grinding 65-grade and 66-grade zircon powders separately and then mixing them are all unfavorable to the high-temperature resistivity. In the present invention, first wet grind 65-grade zircon powder, and then add 66-grade zircon powder to continue wet grinding, then the high-temperature resistivity of the brick is significantly improved. This is because the impurity components Al 2 O 3 , Fe 2 O 3 , TiO 2 have changes in particle size and distribution state in different grinding environments. The impurity components on the grain boundaries after firing are more stable when grinding 65-grade zircon powder first. Therefore, the resistivity and stability of the electrode brick at high temperatures are improved.

[0027] Preferably, the isostatic pressure is 120 - 180 MPa.

[0028] Preferably, the sintering temperature is 1520 - 1560 °C, the holding time for sintering is 36 - 72 h, and the heating rate for sintering is 3 - 5 °C / h.

[0029] Application of zirconia electrode bricks in glass furnaces. The apparent porosity of the electrode bricks is ≤ 1.0%, the bulk density is ≥ 4.40 g / cm 3 , the permanent linear change rate after heating at 1700 °C for 24 h is ≤ 6%, and the high-temperature resistivity at 1600 °C is ≥ 1000 Ω·cm.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The present invention uses grade 65 and grade 66 zircon powder in combination, grinds them step by step and then fires them. The high-temperature resistivity of the obtained products is 4 times higher than that of the high-resistance and erosion-resistant fused zirconia corundum bricks in the prior art, and 40% higher than that of ordinary zircon bricks; the high high-temperature resistivity can play an insulating role, reduce the heating effect of the current in the electrode on the bricks, slow down the glass erosion around the electrode holes, and at the same time reduce the heat loss of the electrode bricks;

[0032] 2. It is found in the present invention that when the addition amount of titanium dioxide is in the range of 0.4% - 0.7%, the permanent linear change rate of the obtained products after heating at 1700 °C for 24 h is reduced by about 50% compared with the zircon bricks with a titanium dioxide addition amount of 1.0% or 0.3% in the prior art; the zirconia electrode bricks have high high-temperature stability, and the volume expansion and structural loosening phenomena caused by zircon decomposition are weakened, which can effectively improve the service life of the electrode bricks.

[0033] 3. The products obtained in the present invention do not require the electrode layer brick technology, are easy to operate and have the advantage of low cost;

[0034] 4. The preparation method of the present invention is simple, feasible, scientific and reasonable, and is convenient for large-scale industrial production. Specific embodiments

[0035] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0036] In actual operation, a temperature control with a fluctuation temperature difference of 2 °C is allowed. All raw materials used in the examples are commercially available unless otherwise specified.

[0037] Among them, the titanium dioxide is rutile type, and the chemical components of the raw materials are shown in Table 1 below.

[0038] Table 1 Chemical composition table of raw materials

[0039]

[0040] The preparation method of the zirconia electrode bricks described above includes the following steps:

[0041] (1) Add zirconia balls, water, grade 65 zircon sand powder, titanium dioxide, and organic binder into a ball mill for the first step of wet grinding; then add grade 66 zircon sand powder into the ball mill for the second step of wet grinding to form a batch slurry. Among them, the mass ratio of zirconia balls, the total mass of powder and organic binder, and water is 2:2:1;

[0042] (2) Spray granulate the batch slurry to form granulated powder, and isostatically press the granulated powder to obtain a green body. The length of the green body is 800 mm, the thickness is 500 mm, and the width is 600 mm;

[0043] (3) Naturally dry and sinter the green body to obtain the product.

[0044] Examples 1-9 and Comparative Examples 1, 2, 5, and 6 were prepared by the above method.

[0045] The difference between Comparative Example 3 and the above preparation method is that in step (1), zirconia balls, water, grade 65 zircon sand powder I, grade 66 zircon sand powder I, titanium dioxide, and organic binder were added into the ball mill for the first step of wet grinding, and then the second step of wet grinding was directly carried out to form a batch slurry without adding grade 66 zircon sand powder.

[0046] The difference between Comparative Example 4 and the above preparation method is that in step (1), grade 66 zircon sand powder I was placed in the first step of wet grinding, and grade 65 zircon sand powder I was placed in the second step of wet grinding.

[0047] The specific raw material dosages and preparation process parameters of Examples 1-9 and Comparative Examples 1-6 are shown in Table 2. Among them, the data corresponding to grade 65 zircon sand powder I, grade 65 zircon sand powder II, grade 66 zircon sand powder I, grade 66 zircon sand powder II, titanium dioxide, and organic binder are all mass percentages of the powder; the particle sizes were all measured by a laser particle size analyzer. Here, the particle size refers to the median diameter. The median diameter is the particle diameter corresponding to when the cumulative particle size distribution percentage of the sample reaches 50%. Its physical meaning is that 50% of the particles are larger than it and 50% of the particles are smaller than it, but it does not involve the aspect ratio of the particles.

[0048] Table 2 Raw material dosages and process parameters of Examples 1-9 and Comparative Examples 1-6

[0049]

[0050] Performance test

[0051] After the obtained electrode bricks were cooled to room temperature with the furnace, samples were cut to detect the bulk density, apparent porosity, compressive strength, high-temperature resistivity at 1600 °C, and heating permanent linear change rate at 1700 °C for 24 h. The obtained results are shown in Table 3.

[0052] Among them, the bulk density and porosity were measured according to the test methods for bulk density, apparent porosity and true porosity of dense shaped refractory products in GB / T 2997-2015.

[0053] The chemical composition was measured according to "Refractory materials - Chemical analysis by X-ray fluorescence spectrometry - Fusion-cast bead method" in GB-T21114-2019.

[0054] The high-temperature resistivity was measured according to the test method for high-temperature resistivity of fine ceramic thermoelectric materials in JISR1650-2002. For JISR1612-2010, the direct current four-terminal method was adopted, the specimen size was Φ3 - 5 mm, and the length was 15 - 20 mm.

[0055] The heating permanent linear change was measured according to the test method for heating permanent linear change of refractory materials in GB-T5988-2007: the specimen size was 50 mm × 50 mm × 10 mm, the test condition was 1700 °C × 24 h, the heating rate was 100 °C / h, and the heating permanent linear change was expressed by dividing the percentage of volume change after test heating by 3.

[0056] Table 3 Test results of physical and chemical indexes of Examples 1-9 and Comparative Examples 1-6

[0057]

[0058] Compared with Example 6, Comparative Example 1 used a single type of grade 65 zircon powder Ⅰ, the apparent porosity reached 5.5%, and the bulk density was only 4.02 g / cm 3 , although the high-temperature resistivity of the material reached 930 Ω·cm at 1600 °C, the heating permanent linear change rate at 1700 °C for 24 h was 10.5%, and it could not be used for a long time at high temperature.

[0059] Compared with Example 6, Comparative Example 2 used a single type of grade 66 zircon powder Ⅰ, and the apparent porosity and bulk density were comparable to those of Example 6. However, the high-temperature resistivity of Example 6 at 1600 °C was 40% higher than that of Comparative Example 2, and the heating permanent linear change rate at 1700 °C for 24 h was 72% lower than that of Comparative Example 2, showing high resistance and high volume stability.

[0060] Compared with Example 4, in Comparative Example 3, zircon powder Ⅰ of grade 65 and zircon powder Ⅰ of grade 66 were added simultaneously and ground together. The apparent porosity and bulk density of Example 4 and Comparative Example 3 were comparable, but the high-temperature resistivity of Example 4 at 1600 °C was 94% higher than that of Comparative Example 3, and the heating permanent linear change rate of Example 4 at 1700 °C for 24 h was 77% lower than that of Comparative Example 3. Compared with Comparative Example 3, Example 4 had significant changes in both the high-temperature resistivity at 1600 °C and the permanent linear change rate at 1700 °C for 24 h, showing high resistance and high volume stability. It indicates that co-grinding the two zircon powder raw materials will have an adverse effect on the high-temperature resistivity at 1600 °C and the high-temperature stability at 1700 °C, especially having a greater impact on the high-temperature resistivity.

[0061] Compared with Example 5, in Comparative Example 4, zircon powder Ⅰ of grade 66 was first ground in the first-step wet grinding, and then zircon powder Ⅰ of grade 65 was added in the second-step wet grinding for co-grinding. The apparent porosity and bulk density of Example 5 and Comparative Example 4 were comparable, but the high-temperature resistivity of Example 5 at 1600 °C was 49% higher than that of Comparative Example 4, and the heating permanent linear change rate of Example 5 at 1700 °C for 24 h was 68% lower than that of Comparative Example 4. Compared with Comparative Example 4, Example 5 had significant changes in both the high-temperature resistivity at 1600 °C and the permanent linear change rate at 1700 °C for 24 h; it shows that first grinding zircon powder Ⅰ of grade 66 and then adding zircon powder Ⅰ of grade 65 for co-grinding will also have an adverse effect on the high-temperature resistivity at 1600 °C and the high-temperature stability at 1700 °C, especially having a greater impact on the high-temperature stability at 1700 °C.

[0062] Compared with Example 1, the content of titanium dioxide used in Comparative Example 5 was 0.3%, its apparent porosity reached 5.0%, and its bulk density was only 4.10 g / cm 3 , although the high-temperature resistivity of the material at 1600 °C reached 950 Ω·cm, the heating permanent linear change rate at 1700 °C for 24 h was 9.7%, about 5 times that of Example 1, and the high-temperature volume stability was poor.

[0063] Compared with Example 2, the content of titanium dioxide used in Comparative Example 6 was 0.8%. The apparent porosity and bulk density of the two were comparable, but the high-temperature resistivity of Comparative Example 6 at 1600 °C was about 29% lower than that of Example 2, and the heating permanent linear change rate at 1700 °C for 24 h of Comparative Example 6 was about 4.5 times that of Example 2.

[0064] Comparative Examples 5 and 6 show that when the content of titanium dioxide in the powder is less than 0.3%, it will have a greater adverse effect on the high-temperature stability of the product at 1700 °C. When the content of titanium dioxide in the powder exceeds 0.7%, it will have an adverse effect on both the high-temperature resistivity of the product at 1600 °C and the high-temperature stability at 1700 °C.

[0065] In summary, when preparing zirconia-based electrode bricks by using the preparation method of the present invention, they have high high-temperature resistivity and high high-temperature volume stability, can reduce the heating effect of the current in the electrode on the bricks, lower the heat loss and erosion phenomenon of the electrode bricks, and can effectively improve the service life of the electrode bricks.

Claims

1. A zircon electrode brick, characterized in that: The powder and the organic binder are wet-grinded to obtain a slurry, the slurry is spray-granulated to obtain a granulated powder, the granulated powder is isostatically pressed to obtain a green body, and the green body is sintered to obtain the electrode brick, wherein the powder includes the following raw materials in percentage by weight: 65 grade zircon powder, 10%-40%; Grade 66 zircon powder, 59.3%-89.6%; Titanium dioxide, 0.4%-0.7%; The chemical composition of 65-grade zircon powder is calculated by mass percentage: SiO2<34%, 0.3%<Al2O3<1.0%, 0.1%<Fe2O3<0.2%, ZrO2>65%; The chemical composition of 66-grade zircon powder is calculated by mass percentage: SiO2<34%, Al2O3<0.3%, Fe2O3<0.1%, ZrO2>65.7%; The wet grinding steps are as follows: firstly wet-grind the 65-grade zircon powder, titanium dioxide, and organic binder, and then add the 66-grade zircon powder and continue wet-grinding to obtain a slurry.

2. The zircon electrode brick according to claim 1, characterized in that: The mass percentage of Al2O3 in grade 65 zircon powder is 0.6%<1.0%, and the particle size is ≤320 mesh.

3. The zircon electrode brick according to claim 1, characterized in that: The mass percentage of Al2O3 in grade 66 zircon powder is less than 0.2%, the mass percentage of Fe2O3 is less than 0.05%, and the particle size is ≤320 mesh.

4. The zircon electrode brick according to claim 1, characterized in that: Titanium dioxide is rutile type, the mass percentage of TiO2 is greater than 98.5%, and the particle size is ≤320 mesh.

5. The zircon electrode brick according to claim 1, characterized in that: The organic binder is one or two of carboxymethyl cellulose and polyvinyl alcohol, and the added amount is 1.5%-3.0% of the powder mass.

6. A method for preparing a zircon electrode brick according to any one of claims 1 to 5, characterized in that: The steps include: (1) Wet-grinding grade 65 zircon powder, titanium dioxide, and an organic binder to a particle size of 4-8 μm in the first step; then adding grade 66 zircon powder, and wet-grinding to a particle size of 5-9 μm in the second step to obtain a batch slurry; (2) spray granulating the batch slurry to form granulated powder, and isostatically pressing the granulated powder to obtain a green body; (3) Drying and sintering the green body.

7. The method for preparing zircon electrode brick according to claim 6, characterized in that: The isostatic pressure is 120-180MPa.

8. The method for preparing zircon electrode brick according to claim 6, characterized in that: The sintering temperature is 1520-1560°C, and the sintering holding time is 36-72h.

9. The method for preparing zircon electrode brick according to claim 6, characterized in that: In step (1), the first step wet grinding time is 10-30 min, and the second step wet grinding time is 20-40 min.

10. Use of the zircon electrode brick according to any one of claims 1 to 5 in a glass melting furnace, characterized in that: The apparent porosity of the electrode brick is ≤1.0%, and the volume density is ≥4.40g / cm 3 , the heating permanent line change rate at 1700℃ for 24h is ≤6%, and the high temperature resistivity at 1600℃ is ≥1000Ω·cm.

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