CN102584301A - Method for preparing zirconium oxide metering nozzle - Google Patents

Abstract

The invention discloses a method for preparing a zirconium oxide metering nozzle. The method comprises the following steps of: first, preparing ZrO2-Al2O3 composite powder; and then grading particle sizes of the zirconium oxide powder; grinding the zirconium oxide powder together with the ZrO2-Al2O3 composite powder for 24-48 h; and then adding ZrO2-Al2O3 gel, which accounts for 5-10% of the total amount of the material, to the mixed powder as a binder; carrying out isostatic press molding on the mixed powder; drying the mixed powder at 105+/-5 DEG C for 24 h; sintering the mixed powder at 1700-1720 DEG C in two steps, wherein the zirconium oxide content of the prepared zirconium oxide metering nozzle is that the ZrO2 content is 92+/-1% and the content of ZrO2 and Al2O3 is not less than 95%; the volume density is 4.45-4.55 g/cm3; and the cold compression strength is not less than 500 MPa. It is shown by the trial that the heat shock resistance stability reaches 22 times; and compared with the heat shock resistance stability of the traditional zirconium oxide metering nozzle, the heat shock resistance stability of the zirconium oxide metering nozzle obtained by the method disclosed by the invention is increased by three times; no rupture occurs in one hundred of upper nozzles; and within the casting period of 50 hours, the usage of lower nozzles can be reduced by 1/3.

Description

A kind of preparation method of zirconia sizing nozzle

technical field

The invention relates to the preparation of a device for controlling molten steel flow in a continuous casting tundish in the iron and steel metallurgy industry, in particular to a method for preparing a zirconia sizing nozzle with excellent thermal shock resistance stability.

Background technique

The sizing nozzle refers to a functional device made of high-temperature structural ceramics installed at the bottom of the continuous casting tundish. Its main function is that the static pressure of the molten steel in the tundish remains basically unchanged, the molten steel flows into the crystallizer through the sizing nozzle, and the crystallizer is cooled by a large flow of water to take away the heat released when the molten steel solidifies, so that the molten steel solidifies into a billet. Since the heat taken away by the water cooling of the mold is limited, the amount of molten steel flowing into the mold per unit time must be within a certain range. The larger the aperture of the sizing nozzle, the more the amount of molten steel flowing into the crystallizer per unit time. Select the appropriate aperture to make the tundish nozzle, which is the sizing nozzle. The main reason for the failure of the sizing nozzle is that the diameter is enlarged due to the erosion and erosion during the flow of molten steel, so that the heat released by the solidification of the molten steel flowing into the crystallizer is greater than the heat that can be taken away by the cooling water of the crystallizer, and it is withdrawn from use; the second is that When it is used for the first time, the temperature in contact with molten steel rises sharply, and it will be cracked and scrapped due to rapid cooling and rapid heating.

Composite sizing nozzle means that the nozzle is made of two parts of different materials compounded and inlaid. Generally, the outer part is made of lower-priced materials, and the part where the inner layer contacts the molten steel is made of higher-priced materials. Compared with the integral sizing nozzle, the main reason for compounding is to reduce production costs without affecting the service life.

The shape of the composite sizing nozzle has not changed much. Pore size is determined by the units used. The key to improving the service life is the improvement of the inner layer material of the inlay.

At present, the integral sizing nozzle produced at home and abroad is mostly made of zircon; the external material of the composite sizing nozzle is mostly high alumina, and the composite inner layer is made of zirconia, and its zirconia content (wt%) is generally 95%. About, the actual service life is about 10 hours. The main reasons for the short service life are poor corrosion resistance and rapid "diameter expansion". When in use, other elements in steel and slag form low-melting point oxides with zirconia, and the melting temperature decreases. At present, the firing temperature of the composite inner layer of the zirconia composite sizing nozzle in China is generally 1700-1720°C. In order to reduce the sintering temperature, a sintering agent is added during the preparation of the composite inner layer of the composite sizing nozzle. The added sintering agent is actually a low-melting substance. During the firing process, the sintering agent and zirconia form a low-melting phase, and the composite inner layer of the sizing nozzle forms a ceramic bond. In actual use, the thermal shock stability of the low-melt phase is poor, and it bursts at the start of pouring, so it can only be blocked, and then the tundish continues to operate under the condition of one less flow (four rheology and three flows). For four-flow tundishes, the output is only three-quarters of normal. The research on the damage mechanism of sizing nozzles shows that most of the nozzles that can be used normally have actually formed cracks of different degrees when starting pouring. The formation of bursting and cracks is the main factor affecting the service life of the sizing nozzle in addition to the erosion "diameter expansion".

At present, the tundish coating accounts for the largest proportion in the contract price per ton of steel for refractory materials used in tundishes, accounting for about 50%. With the digestion of imported technology and the improvement of raw material quality, the current service life of tundish coating has been developed from the original service life of 6-8 hours of silicon insulation board to the service life of 16-20 hours of wet coating materials, and then It has developed into a dry vibrating material with a service life of more than 30-40 hours, that is, the service life of the other materials in the tundish except for the sizing nozzle is more than 30-40 hours, and the service life is about 10 hours. The nozzle has become a bottleneck restricting the service life of the entire tundish.

In order to reduce the production cost per ton of steel in the tundish, a device is added to the part where the sizing nozzle of the tundish is used --- the quick change mechanism of the sizing nozzle of the tundish. The quick change mechanism of the sizing nozzle of the tundish is composed of two parts, and the two parts cooperate to control the flow of molten steel. The first part is a sizing nozzle embedded in the tundish, called the upper nozzle. The upper nozzle requires good quality and long service life. Closely matched with the upper nozzle is the lower nozzle (or called the lower slider), which can slide under the forceful push of the hydraulic device. After pouring, due to the flow control function of the upper nozzle, the first lower nozzle matched with it can be used for 6-8 hours, and then the hydraulic device is used to slide and push the second nozzle; so as to maintain the continuous flow of the entire tundish. Work more than 30 hours. The problem is that the service life of the upper nozzle determines the service life of the lower nozzle. When the upper nozzle bursts and bursts, the flow stops working; when the upper nozzle diameter expansion is small and the flow control ability is strong, the service life of the lower nozzle can reach 8 hours or even longer; when the upper nozzle diameter expansion is serious and the flow control ability is poor, The service life of the drain is only 2-4 hours. Therefore, it is the key to improve the overall service life of the tundish to study the upper nozzle with good corrosion resistance, thermal shock resistance and long service life. Of course, the development of single-component flow control and sizing nozzles with a service life of 30-40 hours can completely eliminate the quick-change mechanism.

Contents of the invention

The object of the present invention is to provide a method for preparing a zirconia sizing nozzle, and the zirconia sizing nozzle produced by the method has excellent thermal shock resistance stability.

In order to realize above-mentioned task, the present invention takes following technical solution:

A method for preparing a zirconia sizing nozzle, characterized in that it is carried out in accordance with the following steps:

1) Preparation of ZrO ₂ -Al ₂ O ₃ composite powder

Take ZrOCl ₂ .8H ₂ O: Al(NO ₃ ) ₃ .9H ₂ O=50～85:15～50 by weight percentage, prepare mother liquor, the concentration of mother liquor is 0.5-2.0Mol/L, add 1.2% of the total weight of materials to disperse agent, NH ₄ OH positive titration, stirring until pH = 7 ~ 10, to obtain a composite gel;

Aging the composite gel for 12h to 24h, vacuum suction filtration at -0.095MPa, washing with deionized water until no Cl ^- can be detected by silver nitrate;

Then react at 500°C for 2 hours, raise the temperature to 700°C, and react for 10 hours. After the reaction is completed, degumming is performed to obtain ZrO ₂ -Al ₂ O ₃ composite powder with ZrO ₂ =45±1%.

2) According to the mass ratio, take 93%-99% of zirconia powder and 1%-7% of ZrO ₂ -Al ₂ O ₃ composite powder composed of different average particle size gradations, grind together for 24h-48h, and then add the total amount of materials 5 %~10% ZrO ₂ -Al ₂ O ₃ gel as binder, isostatic pressing, and dried at 105±5°C for 24 hours;

3) Sintering in two steps under the condition of 1700℃～1720℃, first sintering at 1700℃ for 2 hours, then cooling down to below 1300℃ with the furnace to generate internal micro-cracks, then raising the temperature to 1720℃, sintering for 6h, and obtained Zirconia sizing nozzle.

The gradation of the zirconia powder with different average particle sizes is that 30% of the particles have a particle size of 0-3μm, 15% have a particle size of 5-15μm, and 55% have a particle size of 30-90μm.

The zirconia sizing nozzle prepared by the method of the present invention has a zirconia content of ZrO ₂ =92±1%, ZrO ₂ +Al ₂ O ₃ ≥ 95%, and a volume density of 4.45g/cm3～4.55g/cm3 , cold compressive strength ≥ 1000MPa, after the applicant's trial, the results show that the thermal shock resistance reaches 22 times (the known thermal shock resistance of zirconia sizing nozzle is 5-6 times), and the thermal shock resistance is stable The performance has been increased by three times, and none of the hundreds of upper nozzles burst, and the consumption of the lower nozzles can be reduced by one-third during the 50-hour pouring cycle.

Description of drawings

Fig. 1 is a flow chart of the preparation process of the zirconia composite sizing nozzle of the present invention.

Fig. 2 is a picture of the typical internal structure of the zirconia composite sizing nozzle of the present invention

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Detailed ways

The applicant has continuously undertaken the national scientific and technological research projects from the "Seventh Five-Tenth Five-Year Plan" to study ZrO ₂ -Al ₂ O ₃ materials. The research results prove that the corundum badley zircon eutectoid structure formed by ZrO ₂ -Al ₂ O ₃ in the ZrO ₂ -Al ₂ O ₃ material has much better corrosion resistance than single corundum phase or tetragonal zirconia phase. The main reason is that after ZrO ₂ and Al ₂ O ₃ form a corundum baddeleyite eutectoid structure, the ZrO ₂ crystal phase is uniformly dispersed in the corundum matrix, and the oxides in steel or slag interact with ZrO ₂ and Al ₂ O ₃ , ZrO ₂ , Al ₂ O ₃ are uniformly eroded by steel or slag at the same time, there is no problem that the corundum or zirconia crystal phase is eroded into the steel or slag after the bonding phase is eroded, and the service life is obviously prolonged. Due to the phase transformation and toughening effect of zirconia, the thermal shock resistance of ZrO ₂ -Al ₂ O ₃ material is significantly higher than that of single ZrO ₂ material.

The key to producing corundum badley zircon eutectoid fine crystal ceramic composite sizing nozzle is to produce ceramic raw materials with high corundum baddeley zircon eutectoid content and uniform distribution of ZrO ₂ and Al ₂ O ₃ . In order to realize the uniform distribution of ZrO ₂ and Al ₂ O ₃ at the molecular level, the preparation of ZrO ₂ -Al ₂ O ₃ composite superfine powder is the prerequisite for the preparation of products.

The applicant jointly undertakes the scientific and technological research project of Shaanxi Province "Research and Development of Corundum Baddeleyite Eutectoid Fine Crystalline Ceramics (No. 2003K07-G9)", the industrial research project of Xi'an City "Zirconium Oxide Composite Dispersed Corundum Phase Special High-temperature Ceramics (No. GG200347) "Research and Jinan City "Quancheng Scholars" construction project "ZrO2/Al2O3 composite material research and application in continuous casting functional materials" research results, using sol-gel method, complex precipitation method, carbon black wrapped combustion By controlling the relative content of soluble aluminum and zirconium salts, a preparation method of ZrO ₂ -Al ₂ O ₃ composite powder was found, that is, ZrOCl ₂ .8H ₂ O: Al(NO ₃ ) ₃ .9H ₂ O:= 50～85:15～50 to prepare the mother liquor, the concentration of the mother liquor is 0.5-2.0Mol/L, the optimal pH of the precipitation is 7-10, and the composite gel is prepared, and the composite gel is aged for 12-24h, and vacuum suction is filtered at -0.095MPa , washed with deionized water until no Cl ^- can be detected by silver nitrate; the process of washing and removing chlorine was optimized, and then reacted at 500°C for 2h, the temperature rose to 700°C, and reacted for 10h. 1-3μm, 5-15μm, 30-90μm different particle size distribution, ZrO ₂ -Al ₂ O ₃ composite powder with uniform chemical composition distribution. The ZrO ₂ -Al ₂ O ₃ composite powder can be used to prepare the ZrO ₂ -Al ₂ O ₃ long-life sizing nozzle, but the preparation cost is relatively high.

In view of the poor thermal shock stability of zirconia sizing nozzles, the inventors used zirconia powders of different proportions and different particle sizes to prepare modified zirconia sizing nozzles in combination with the prepared ZrO ₂ -Al ₂ O ₃ composite powder. Nozzle, its preparation process is shown in Figure 1. The principle is to use the high activity of ZrO ₂ -Al ₂ O ₃ composite powder to achieve the same sintering degree at the same sintering temperature with less or no sintering agent; to use the high activity of ZrO ₂ -Al ₂ O ₃ composite powder to achieve the same sintering shrinkage Great feature, co-grinding with zirconia raw materials, try to make ZrO ₂ -Al ₂ O ₃ composite powder evenly filled between zirconia particles, the sintering shrinkage of ZrO ₂ -Al ₂ O ₃ composite powder is much larger than that of zirconia particles in the sintering process The shrinkage of zirconia forms micropores, reduces the deformation constraint of zirconia particles when thermal stress is generated due to thermal shock, reduces the degree of deformation constraint of zirconia particles, and improves the thermal shock stability of zirconia sizing nozzles.

The following are examples given by the inventors.

Example 1:

Step 1, take ZrOCl ₂ .8H ₂ O: 70%, Al(NO ₃ ) ₃ .9H ₂ O: 30% by mass ratio, prepare mother liquor, add 1.2% dispersant (TH-908 ceramic dispersant), NH ₄ OH is positively titrated, stirred until PH = 7-10, the prepared gel is aged for 12-24h; -0.095MPa vacuum suction filtration, washed with deionized water until the silver nitrate cannot detect Cl ^- ; degumming after the reaction is completed, and then React at 500°C for 2 hours, raise the temperature to 700°C, and react for 10 hours to prepare ZrO ₂ -Al ₂ O ₃ composite powder with ZrO ₂ =45±1%;

Step 2, using iridium oxide or magnesia-stabilized zirconia as the raw material, the zirconia raw material accounts for 97% by weight, and the ZrO ₂ -Al ₂ O ₃ composite powder accounts for 3% by weight; wherein, the particle size composition of zirconia is 0- 3μm accounts for 30%, particle size 5-15μm accounts for 15%, 30-90μm accounts for 55%; the particle size composition of ZrO ₂ -Al ₂ O ₃ composite powder is 1-3μm;

Step 3: Grinding zirconia and ZrO ₂ -Al ₂ O ₃ composite powder for 24 hours, isostatic pressing, drying at 105±5°C for 24 hours; Sinter at 1700°C for 2 hours, then cool down to below 1300°C with the furnace to generate internal micro-cracks, then raise the temperature to 1720°C, and sinter for 6 hours to obtain a zirconia sizing nozzle. Its thermal shock stability reaches 22 times (the thermal shock resistance stability of the known zirconia sizing nozzle is 5-6 times), and the thermal shock resistance stability is increased by three times. There is no bursting of hundreds of nozzles, and it can be poured in 50 hours During the period, the lower slider usage was reduced by one-third.

Example 2:

Step 1, take ZrOCl ₂ .8H ₂ O:Al(NO ₃ ) ₃ .9H ₂ O=70:30 by weight percentage, prepare mother liquor, add dispersant (TH-908 ceramic dispersant) with a total weight of 1.2%, NH4(OH) positive titration, stirring until PH = 7-10, obtained gel, aging for 12h; vacuum suction filtration at -0.095MPa, washing with deionized water until silver nitrate can no longer detect ^Cl- ; degumming after the completion of the reaction, Then react at 500° C. for 2 hours, then raise the temperature to 700° C., react for 10 hours, degumming after the reaction is completed, and ZrO ₂ -Al ₂ O ₃ composite powder with ZrO ₂ =45±1% is obtained.

Zirconia stabilized with iridium oxide or magnesium oxide is used as raw material, zirconia raw material accounts for 94% by weight, ZrO ₂ -Al ₂ O ₃ composite powder accounts for 6% by weight, and the particle size composition of zirconia is 0-3μm. 30%, 15% with a particle size of 5-15μm, and 55% with a particle size of 30-90μm; the particle size composition of ZrO ₂ -Al ₂ O ₃ composite powder is 1-3μm;

Step 3: Mix zirconia and ZrO ₂ -Al ₂ O ₃ composite powder, co-mill for 48 hours, then add 10% ZrO ₂ -Al ₂ O ₃ gel as a binder, and perform isostatic pressing at 105±5°C Drying for 24 hours, firing in two steps at 1700°C to 1720°C, that is, first sintering at 1700°C for 2 hours, then cooling down to below 1300°C with the furnace to generate internal micro-cracks, then heating up to 1720°C, and sintering for 6 hours. Get zirconia sizing nozzle. Its thermal shock resistance reaches 26 times. Compared with the thermal shock resistance of the known zirconia sizing nozzle which is 5-6 times, the thermal shock resistance is more than three times higher, and there is no bursting of a hundred nozzles. , In the 50-hour pouring cycle, the amount of lower sliders has been reduced by more than one-third. Embodiment 2 index is better than embodiment 1.

Example 3:

The difference between this example and Example 1 is: 98% of zirconia powder is used, ZrO ₂ -Al ₂ O ₃ composite powder accounts for 2% by weight, and they are co-milled for 24 hours. The rest are the same as in Example 1. Zirconium sizing nozzle, its thermal shock resistance reaches 24 times. Compared with the thermal shock resistance of the known zirconia sizing nozzle which is 5-6 times, the thermal shock resistance stability is increased by three times, and there is no bursting of a hundred nozzles. reduced by a third.

The picture of the typical internal structure of the zirconia sizing nozzle prepared in the above examples is shown in Figure 2.

Claims (2)

1. a zirconia quality sizing nozzle preparation method, is characterized in that, carries out according to the following steps: 1) Preparation of ZrO ₂ -Al ₂ O ₃ composite powder Take ZrOCl ₂ .8H ₂ O: Al(NO ₃ ) ₃ .9H ₂ O = 50-85: 15-50 by weight percentage, prepare mother liquor, the concentration of mother liquor is 0.5-2.0Mol/L, add 1.2% of the total weight of materials Dispersant, NH4(OH) positive titration, stirring until pH = 7-10, to prepare a composite gel; Aging the composite gel for 12h to 24h, vacuum suction filtration at -0.095MPa, washing with deionized water until no Cl ^- can be detected by silver nitrate; degumming after the reaction is completed; Then react at 500°C for 2 hours, raise the temperature to 700°C, and react for 10 hours to obtain ZrO ₂ -Al ₂ O ₃ composite powder with ZrO ₂ =45±1%; 2) According to the mass ratio, take 93%-99% of zirconia powder and 1%-7% of ZrO ₂ -Al ₂ O ₃ composite powder with different average particle size gradations, grind together for 24h-48h, and then add the total amount of materials 5 %~10% ZrO ₂ -Al ₂ O ₃ gel as binder, isostatic pressing, and dried at 105±5°C for 24 hours; 3) Sintering in two steps under the condition of 1700℃～1720℃, first sintering at 1700℃ for 2 hours, then cooling down to below 1300℃ with the furnace to generate internal micro-cracks, then raising the temperature to 1720℃, sintering for 6h, and obtained Modified zirconia sizing nozzle. 2. The method according to claim 1, characterized in that, the gradation of the zirconia powders with different average particle sizes is that the particle size composition is 0 μm to 3 μm and accounts for 30%, and the particle size is 5 μm to 15 μm and accounts for 15%. , the particle size is 30μm ~ 90μm accounted for 55%.

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