Large size zirconia ceramic and method for manufacturing the same

Abstract

The present application relates to a kind of large size zirconia ceramic and its preparation method, the zirconia ceramic includes by percentage by weight, including 91-95% of monoclinic zirconia, 0-1% of lanthanum trioxide, 3-8% of magnesium calcium sand, preparation process uses wet ball milling process, powder after ball milling dry is pressed into shape under 120-180MPa, after being fired at 1600-1700 ℃, large size zirconia ceramic is obtained.The present application utilizes MgO and CaO in natural magnesium calcium sand to stabilize zirconia, the micro-impurities in magnesium calcium sand are in liquid phase at high temperature, can promote sintering, reduce firing temperature;And a small amount of liquid phase relieves thermal stress at high temperature, prevent large size zirconia ceramic cracking, improve yield.In addition, magnesium calcium sand hydration generates a small amount of Mg (OH) 2 And Ca (OH) 2 Play the role of binding, need not to add binder separately.The zirconia ceramic prepared by the method has the advantages of low energy consumption, low cost and volume stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of refractory materials, and particularly relates to a large-size zirconia ceramic and a preparation method thereof. BACKGROUND

[0002] In the steel smelting process, the slide nozzle is an important key functional element for continuous casting, is a flow control system of molten steel, and accurately controls the flow of molten steel from a ladle to a tundish and from the tundish to a crystallizer. In recent years, China has focused on the smelting of high-quality steel, but the smelting of high-quality steel seriously erodes refractory materials, for example, when casting calcium-treated steel, calcium vapor in the steel is extremely easy to react with Al2O3 and SiO2 in the slide plate to generate low-melting-point phases (2CaO•Al2O3•SiO2 (1539℃) and 12CaO•7Al2O3 (1392℃)), which are seriously damaged by the scouring of molten steel. Therefore, the service life of the commonly used aluminum-carbon and aluminum-zirconium-carbon slide plates is very low due to the erosion of calcium vapor, and there is a safety hazard of leakage of molten steel. The magnesium-carbon slide plate has excellent corrosion resistance, but the magnesium sand has a large thermal expansion coefficient, which causes the magnesium-carbon slide plate to have poor thermal shock resistance, and cracks or even cracks are easily generated under the strong impact of high-temperature molten steel, which not only has a low service life, but also has a safety hazard. The slide plate for casting calcium-treated steel is currently facing great challenges.

[0003] Zirconia material has a high melting point and excellent calcium vapor corrosion resistance, and is an ideal material for smelting calcium-treated steel. At present, a zirconia ring or a zirconia plate with a large size is used to prepare a slide plate for casting calcium-treated steel. However, zirconia will undergo a monoclinic phase to tetragonal and cubic phase transition at high temperatures, and the phase transition is accompanied by a volume effect, which causes cracks in zirconia products. At present, high-purity oxides such as MgO, CaO and lanthanum trioxide are used as stabilizers to partially stabilize zirconia. For small-size zirconia products, the method of using partially stabilized zirconia can reduce or even eliminate the cracking of products caused by phase transition. However, for large-size zirconia rings or zirconia plates, thermal stress is generated due to uneven temperature of different parts of the product during high-temperature sintering. In addition, the volume effect of the phase transition of zirconia also causes cracks or even cracks in the sintered zirconia ring or zirconia plate, resulting in a low yield.

[0004] In addition, the stabilizers used at present are all high-purity oxides, which are not only expensive, but also make the sintering temperature of zirconia products above 1700℃, resulting in high energy consumption and long production cycle. The low yield of zirconia rings or zirconia plates and the high sintering temperature result in high prices of the products, which limits their large-scale application and further affects the smelting of high-quality steel. Therefore, the preparation of large-size zirconia ceramics with low cost and stability is urgently needed. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of large-size zirconia ceramic, which is prepared by using low-cost natural raw material of magnesia-calcia sand and trace lanthanum trioxide as stabilizer. The technical innovation lies in that: MgO and CaO in the natural magnesia-calcia sand are used to stabilize zirconia, and the trace impurities in the magnesia-calcia sand are in liquid phase at high temperature, which can promote sintering and reduce the sintering temperature; and a small amount of liquid phase can relieve thermal stress at high temperature, prevent large-size zirconia ceramic from cracking, and improve the yield. In addition, the hydration of the magnesia-calcia sand generates a small amount of Mg(OH)2 and Ca(OH)2 to play a binding role, and no additional binder is needed. The zirconia ceramic prepared by the method has the advantages of low energy consumption, low cost, and volume stability.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is:

[0007] A large-size zirconia ceramic, comprising, in terms of weight percentage, 91-95% of monoclinic zirconia, 0-1% of lanthanum trioxide, and 3-8% of magnesia-calcia sand.

[0008] The zirconia ceramic prepared by the present application has a plate-like structure, with a length of more than 200 mm, a width of more than 100 mm, and a thickness of about 18-20 mm.

[0009] Further, the particle size of the monoclinic zirconia is ≤0.044 mm, the particle size of the lanthanum trioxide is ≤0.075 mm, and the particle size of the magnesia-calcia sand is ≤0.075 mm.

[0010] Further, in the chemical composition of the monoclinic zirconia, ZrO2 is >99.5wt%.

[0011] Further, in the chemical composition of the lanthanum trioxide, La2O3 is >99.9wt%.

[0012] Further, in the chemical composition of the magnesia-calcia sand, the content of MgO is 60-66wt%, the content of CaO is 31-35wt%, the content of SiO2 is ≤1.5wt%, the content of Al2O3 is ≤1.2wt%, and the content of Fe2O3 is ≤1.5wt%.

[0013] The preparation method of the large-size zirconia ceramic of the present application comprises the following steps:

[0014] (1) The monoclinic zirconia, lanthanum trioxide, and magnesia-calcia sand are weighed according to the proportion, and uniformly mixed in a planetary ball mill by using water as the ball milling medium through a wet ball milling process;

[0015] (2) After ball milling, the powder is dried and crushed, and then sieved;

[0016] (3) The powder obtained above is pressed into a green body under a pressure of 120-180MPa;

[0017] (4) Put the green body into a drying oven;

[0018] (5) Put the dried green body into an electric furnace for calcination, the heating rate is 1-10℃ / min, the calcination temperature is 1600-1700℃, and the holding time is 1-5h.

[0019] Further, the wet ball milling process is that the rotation speed of the ball mill is 250-300r / min, and the ball milling time is 12-24h.

[0020] Further, the drying in step (2) is at 100-110℃ for 6-12h.

[0021] Further, the drying temperature in step (4) is 100-120℃, and the drying time is 12-24h. Beneficial effects

[0022] 1. The present application uses magnesium calcium sand as a stabilizer, and uses MgO and CaO in natural magnesium calcium sand to stabilize zirconia. The micro-impurities in the magnesium calcium sand are in liquid phase at high temperature, which can promote sintering and reduce the firing temperature.

[0023] 2. The present application uses the small amount of liquid phase generated at high temperature to relieve thermal stress and prevent large-size zirconia ceramic from cracking, thereby improving the yield.

[0024] 3. The present application uses the hydration of natural magnesium calcium sand to generate a small amount of Mg(OH)2 and Ca(OH)2 to play a binding role, without adding a separate binder

[0025] 4. The zirconia ceramic prepared by the present application has the advantages of low energy consumption, low cost, and volume stability. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 a The scanning electron microscope image of the cross section of the zirconia ceramic prepared in Example 3 of the present application;

[0027] Figure 1 b The EDS energy spectrum of the cross section of the zirconia ceramic prepared in Example 3 of the present application;

[0028] Figure 2 The scanning electron microscope image of the polished surface of the zirconia ceramic prepared in Example 3 of the present application. IMPLEMENTATION

[0029] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] In the following examples, the MgO content of the magnesium calcium sand is 63.8wt%, the CaO content is 32.2wt%, the SiO2 content is 1.5wt%, the Al2O3 content is 1.2wt%, and the Fe2O3 content is 1.3wt%. Example 1

[0031] A large-size zirconia ceramic includes, by weight percentage, monoclinic zirconia powder 93%, lanthanum oxide 0.5%, and magnesium calcium sand 6.5%;

[0032] A preparation method thereof includes the following steps:

[0033] (1) The monoclinic zirconia, lanthanum oxide, and magnesium calcium sand are weighed according to the proportion, uniformly mixed in a planetary ball mill using a wet ball milling process, the rotation speed of the ball mill is 280r / min, and the ball milling time is 12h;

[0034] (2) After the ball milling is completed, the powder is dried at 105℃ for 12h, crushed, and sieved;

[0035] (3) The powder obtained above is pressed into a green body under a pressure of 150MPa;

[0036] (4) The green body is placed in a drying box, the drying temperature is 110℃, and the drying time is 12h;

[0037] (5) The dried green body is placed in an electric furnace for calcination, the temperature is kept at 1650℃ for 3h, the heating rate is 5℃ / min at 0-1000℃, the heating rate is 3℃ / min at 1000-1400℃, and the heating rate is 2℃ / min at 1400-1650℃.

[0038] (6) The calcined green body is tested for the cold modulus of rupture, elastic modulus, and thermal shock stability according to the national standards GB / T 3001-2007, GB / T 30758-2014, and the metallurgical standard YB / T 376.2-1995.

[0039] The prepared zirconia ceramic has a plate structure with a length of 400mm, a width of 200mm, and a thickness of 20mm.

[0040] The cold modulus of rupture of the product obtained in this example is 67.7MPa, the elastic modulus is 9.5GPa, the thermal shock strength retention rate is 77.1%, 100 green bodies are fired at one time, 98 finished products are obtained, and the finished product rate reaches 98%. Example 2

[0041] A large-size zirconia ceramic includes, by weight percentage, monoclinic zirconia powder 93%, lanthanum oxide 0.5%, and magnesium calcium sand 6.5%;

[0042] The preparation method comprises the following steps:

[0043] (1) monoclinal zirconia, lanthanum trioxide and magnesia calcia sand are weighed according to proportions, and are uniformly mixed in a planetary ball mill by adopting a wet ball milling process, the rotation speed of the ball mill is 280 r / min, and the ball milling time is 12 h;

[0044] (2) after the ball milling is completed, the powder is dried at 105 DEG C for 12 h, and is crushed and sieved;

[0045] (3) the powder obtained above is pressed into a green body under 150 MPa;

[0046] (4) the green body is placed into a drying box, the drying temperature is 110 DEG C, and the drying time is 12 h;

[0047] (5) the dried green body is placed into an electric furnace for calcination, the temperature is kept at 1650 DEG C for 3 h, the temperature rising rate is 5 DEG C / min at 0-1000 DEG C, the temperature rising rate is 3 DEG C / min at 1000 DEG C-1400 DEG C, and the temperature rising rate is 2 DEG C / min at 1400 DEG C-1650 DEG C.

[0048] (6) the calcined green body is detected according to the national standard GB / T 3001-2007, GB / T 30758-2014 and the metallurgical standard YB / T 376.2-1995 to detect the cold modulus of rupture, the elastic modulus and the thermal shock stability of the sample.

[0049] The prepared zirconia ceramic has a plate structure, the length is 500 mm, the width is 150 mm, and the thickness is 18 mm.

[0050] The cold modulus of rupture of the product obtained in the embodiment is 72.7 MPa, the elastic modulus is 10.2 GPa, the thermal shock strength retention rate is 78.7%, 100 green bodies are fired at one time, 97 finished products are obtained, and the finished product rate reaches 97%. Example 3

[0051] A large-size zirconia ceramic comprises, in percentage by weight, 92% of monoclinal zirconia powder, 0.5% of lanthanum trioxide and 7.5% of magnesia calcia sand.

[0052] The preparation method comprises the following steps:

[0053] (1) monoclinal zirconia, lanthanum trioxide and magnesia calcia sand are weighed according to proportions, and are uniformly mixed in a planetary ball mill by adopting a wet ball milling process, the rotation speed of the ball mill is 280 r / min, and the ball milling time is 12 h;

[0054] (2) after the ball milling is completed, the powder is dried at 105 DEG C for 12 h, and is crushed and sieved;

[0055] (3) Press the powder obtained above at 150 MPa to obtain a blank;

[0056] (4) Place the green body in a drying oven at 110°C for 12 hours.

[0057] (5) Place the dried blank into an electric furnace and calcine it at 1650℃ for 3 hours. The heating rate is 5℃ / min for 0-1000℃, 3℃ / min for 1000℃-1400℃, and 2℃ / min for 1400℃-1650℃.

[0058] (6) The room temperature flexural strength, elastic modulus and thermal shock stability of the fired blanks were tested according to national standards GB / T 3001-2007, GB / T 30758-2014 and metallurgical standard YB / T 376.2-1995.

[0059] The product obtained in this embodiment has a room temperature flexural strength of 75.1 MPa, an elastic modulus of 10.4 GPa, and a thermal shock strength retention rate of 74.8%. 100 pieces were fired at once, and 98 pieces were finished products, with a yield rate of 98%.

[0060] The prepared zirconia ceramic has a plate-like structure with a length of 450 mm, a width of 200 mm, and a thickness of 20 mm.

[0061] Please refer to Figure 1, which shows the scanning electron microscope (SEM) image and EDS spectrum of the cross-section of the zirconia ceramic prepared in Example 3 of this invention. As can be seen from Figure 1, the zirconia ceramic has well-developed and tightly bonded internal grains. The EDS spectrum shows that the grain surface contains Zr, Mg, and Ca elements, indicating that MgO and CaO in the magnesium calcium sand dissolved into the ZrO2 grains at high temperature, promoting the development and growth of ZrO2 grains.

[0062] Please see Figure 2 This is a scanning electron microscope (SEM) image of the zirconia ceramic surface prepared in Example 3 of this invention after polishing. Figure 2 It can be seen that the sintering of zirconia ceramics is dense with fewer and smaller pores. This is because the micro-impurities in the magnesium calcium sand are in the liquid phase at high temperatures, which promotes the sintering of zirconia ceramics and improves their strength. Example 4

[0063] The invention is basically the same as Example 1, except that: a large-size zirconia ceramic, by weight percentage, comprises 91% monoclinic zirconia powder, 1% lanthanum trioxide, and 8% magnesium calcium sand.

[0064] The fired green body is respectively tested for the cold modulus of rupture, elastic modulus and thermal shock stability according to the national standards GB / T 3001-2007, GB / T 30758-2014 and the metallurgical standard YB / T 376.2-1995.

[0065] The prepared zirconia ceramic has a plate structure with a length of 350 mm, a width of 260 mm and a thickness of 18 mm.

[0066] The cold modulus of rupture of the product obtained in the example is 76.5 MPa, the elastic modulus is 10.5 GPa, and the thermal shock strength retention rate is 70.2%. One hundred are fired at one time, and 99 are finished products, with a finished product rate of 99%. Example 5

[0067] The difference between the example 5 and the example 1 is that the large-size zirconia ceramic comprises, by weight percentage, 95% of monoclinic zirconia powder, 0% of lanthanum trioxide and 5% of magnesium-calcium sand.

[0068] The fired green body is respectively tested for the cold modulus of rupture, elastic modulus and thermal shock stability according to the national standards GB / T 3001-2007, GB / T 30758-2014 and the metallurgical standard YB / T 376.2-1995.

[0069] The prepared zirconia ceramic has a plate structure with a length of 300 mm, a width of 160 mm and a thickness of 19 mm.

[0070] The cold modulus of rupture of the product obtained in the example is 60.1 MPa, the elastic modulus is 8.4 GPa, and the thermal shock strength retention rate is 67.8%. One hundred are fired at one time, and 95 are finished products, with a finished product rate of 95%. Comparative Example 1

[0071] The difference between the example 5 and the example 1 is that the large-size zirconia ceramic comprises, by weight percentage, 95% of monoclinic zirconia powder, 0% of lanthanum trioxide and 5% of magnesium-calcium sand.

[0072] The fired green body is respectively tested for the cold modulus of rupture, elastic modulus and thermal shock stability according to the national standards GB / T 3001-2007, GB / T 30758-2014 and the metallurgical standard YB / T 376.2-1995.

[0073] The prepared zirconia ceramic has a plate structure with a length of 300 mm, a width of 160 mm and a thickness of 19 mm.

[0074] The product obtained in the example has a room temperature bending strength of 25.6 MPa, an elastic modulus of 3.7 GPa, and a thermal shock strength retention rate of 34.6%. 100 products are fired at one time, and 56 finished products are obtained, with a finished product rate of 56%.

[0075] As can be seen from Comparative Example 1, the performance and finished product rate of the product can be effectively improved by using the magnesium-calcium sand to partially replace or completely replace the lanthanum trioxide, as compared with Example 5, the room temperature bending strength of the product is increased by 135%, the elastic modulus is increased by 127%, the thermal shock strength retention rate is increased by 96%, and the finished product rate is increased by 70%. It can be seen that the magnesium-calcium sand can form stable calcium oxide and magnesium oxide compounds at high temperatures, which is beneficial to the sintering process of the zirconia ceramic and improves the mechanical properties and high temperature resistance of the material.

[0076] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A large size zirconia ceramic, characterized by: According to the percentage by weight, including 91-95% of monoclinic zirconium oxide, 0.5-1% of lanthanum trioxide, 3-8% of magnesium calcium sand; the zirconium oxide ceramic is plate structure, the length is greater than 200mm, the width is greater than 100mm, and the thickness is 18-20mm; in the chemical composition of the magnesium calcium sand, the content of MgO is 60-66wt%, the content of CaO is 31-35wt%, SiO2≤1.5wt%, Al2O3≤1.2wt%, Fe2O3≤1.5wt%; The preparation method thereof comprises the following steps: (1) the monoclinic zirconium oxide, lanthanum trioxide and magnesium calcium sand are weighed according to the proportion, water is used as the ball milling medium, and the wet ball milling process is adopted to uniformly mix in the planetary ball mill; (2) after the ball milling is completed, the powder is dried, crushed and sieved; (3) the powder obtained above is pressed into a green body under 120-180MPa; (4) the green body is placed into a drying box; (5) the dried green body is placed into an electric furnace for calcination, the heating rate is 1-10℃ / min, the calcination temperature is 1600-1700℃, and the holding time is 1-5h.

2. A large size zirconia ceramic according to claim 1, characterized in that: The particle size of the monoclinic zirconium oxide is ≤0.044mm, the particle size of the lanthanum trioxide is ≤0.075mm, and the particle size of the magnesium calcium sand is ≤0.075mm.

3. A large size zirconia ceramic according to claim 1, characterized by: In the chemical composition of the monoclinic zirconium oxide, ZrO2>99.5wt%.

4. A large size zirconia ceramic according to claim 1, characterized by: In the chemical composition of the lanthanum trioxide, La2O3>99.9wt%.

5. A large size zirconia ceramic according to claim 1, characterized by: The wet ball milling process is that the rotation speed of the ball mill is 250-300r / min, and the ball milling time is 12-24h.

6. A large size zirconia ceramic according to claim 1, characterized by: In the step (2), the drying is carried out at 100-110℃ for 6-12h.

7. A large size zirconia ceramic according to claim 1, characterized by: In the step (4), the drying temperature is 100-120℃, and the drying time is 12-24h.

Images