JP2007099562A - Air permeable refractory and method of producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide air permeable refractory containing no Cr<SB>2</SB>O<SB>3</SB>having excellent corrosion resistance, thermal shock resistance and capable of replacing air permeable refractory containing Cr<SB>2</SB>O<SB>3</SB>. <P>SOLUTION: The air permeable refractory having pores 3 for passing a gas comprises: a spinel type mineral 6 comprising Al<SB>2</SB>O<SB>3</SB>and NiO; and zirconia-mullite formed by dispersing ZrO<SB>2</SB>7 in mullite 4 in a crosslinking part 1 between coarse grains 2, 2 of main aggregate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a breathable refractory used mainly for blowing gas into a molten metal such as molten steel and a method for producing the same.

  In the refining process or continuous casting process of molten metal such as molten steel, gas is often blown into the molten metal for various purposes, such as refining of molten metal, stirring, elimination of slag, and the like.

  Breathable refractories used for such use include, in addition to breathability for gas blowing, chemical resistance to reaction with FeO, etc., that is, corrosion resistance, thermal shock resistance to withstand rapid thermal shocks or large temperature gradients, etc. It is necessary to have

Conventionally, in use conditions that require particularly high corrosion resistance and thermal shock resistance, many refractories containing Cr ₂ O ₃ have been used. This is because when Cr ₂ O ₃ is added to the Al ₂ O ₃ system, effects such as an increase in melting point, improvement in corrosion resistance, and improvement in thermal shock resistance are obtained due to the formation of a solid solution.

However, Cr ₂ O ₃ containing refractories, since the under certain conditions may produce harmful hexavalent chromium, in recent years environmental issues have been greatly closeup, to refractories without Cr ₂ O ₃ content Conversion has become necessary.

As an alternative to a Cr ₂ O ₃ -containing refractory, for example, Patent Document 1 discloses a spinel made of nickel-containing material such as nickel oxide and Al ₂ O ₃ as an amorphous refractory for lining such as a garbage incinerator. It is disclosed that a refractory containing a mineral composition in the form is effective in improving corrosion resistance and the like. However, this is mainly for the purpose of improving corrosion resistance on the premise of a dense structure, and breathing resistance for gas blowing that requires high thermal shock resistance as well as corrosion resistance while assuming constant breathability. The product is not practical because of its low thermal shock resistance.

  Patent Document 2 discloses an amorphous refractory material obtained by adding partially stabilized zirconia to a nickel-containing material such as nickel oxide as a means for improving the spalling resistance (thermal shock resistance).

  However, this is also intended to improve the spalling resistance on the premise of a dense structure, and stress is obtained by utilizing the property that partially stabilized zirconia that exists independently in the fine grain region transforms against impact. It is intended to improve the spalling resistance by absorbing. Therefore, when it is applied to a breathable refractory for gas blowing that requires high thermal shock resistance as well as corrosion resistance, assuming a certain breathability, the structure of the bridging part that connects the aggregates is a binding force Is not practical because of weakness and insufficient thermal shock resistance.

Thus, in the breathable refractories, particularly the porous breathable refractories for gas blowing, a refractory substitute for Cr ₂ O ₃ has not been put into practical use.
JP 2002-241173 A JP 2003-183082 A

An object of the present invention is to provide excellent corrosion resistance and thermal shock resistance, which can be substituted in the gas-permeable fireproof material which Cr ₂ O ₃ content, to provide a gas-permeable fireproof material that does not Cr ₂ O ₃ content is there.

The breathable refractory of the present invention is a breathable refractory having pores for allowing a gas to pass through, and a spinel type composed of Al ₂ O ₃ and NiO at a bridging portion between coarse refractory raw materials as a main aggregate. It contains a mineral and zirconia-mullite in which ZrO ₂ is dispersed in mullite.

Further, the method for producing a breathable refractory according to the present invention is a method for producing a breathable refractory having pores for allowing gas to pass therethrough, and Al ₂ O ₃ around a coarse refractory raw material as a main aggregate. Main particles and NiO source particles, or spinel-type particles composed of Al ₂ O ₃ and NiO, and zirconia-mullite particles in which ZrO ₂ is dispersed in mullite, and then firing, A cross-linked portion between coarse refractory raw materials as an aggregate is characterized by containing a spinel mineral composed of Al ₂ O ₃ and NiO and zirconia-mullite.

FIG. 1 shows a structure diagram centering on a cross-linked portion of the breathable refractory of the present invention. As shown in the figure, the bridging portion 1 between the coarse particles 2 and 2 as the main aggregate is formed on the base portion 4 centered on Al ₂ O ₃ —SiO-based minerals such as mullite and the like, and Al ₂ O ₃ grains 5 It exhibits a structure in which spinel-type mineral 6 composed of Al ₂ O ₃ and NiO and ZrO ₂ 7 are dispersed. There are also pores 3 between the coarse particles 2 and 2 as the main aggregate.

A refractory containing a spinel mineral made of Al ₂ O ₃ and NiO is excellent in corrosion resistance against FeO, slag, and the like. In order to improve the strength and thermal shock resistance as a breathable refractory while utilizing this corrosion resistance, in the present invention, in the bridging portion between coarse refractory raw materials that become the skeleton of the main aggregate, that is, the refractory, Al _A spinel mineral composed of ₂ O ₃ and NiO is included. This bridging portion supports the main aggregate and serves as the basis of strength as a structure. Moreover, this bridge | crosslinking part is also a part which contacts FeO, slag, etc. primarily from the request | requirement of air permeability ensuring. Therefore, it is effective to have a high proportion of spinel mineral made of Al ₂ O ₃ and NiO having excellent corrosion resistance in this portion.

In order to contain the spinel mineral composed of Al ₂ O ₃ and NiO in the cross-linked portion between the main aggregates, corundum fine particles as the Al ₂ O ₃ source and nickel oxide fine particles as the NiO source are used as raw materials. A method of generating a spinel-type mineral in the firing step, using a raw material already in the form of a spinel-type mineral, or the like can be employed. In this two-component system, _Al 2 _{O 3} molar ratio of NiO is from about 1: to produce a stable spinel-type minerals even at high temperatures in the area _Al 2 _{O 3} is often from 1, _Al 2 _{O 3} source In addition, it is preferable that the molar ratio (Al ₂ O ₃ / NiO) of Al ₂ O ₃ and NiO in the fine particles as the NiO source is about 1 or more, that is, the mass ratio is about 1.4 or more.

In this case, to obtain equivalent or characteristics to those _Cr 2 _{O 3} content in _Al 2 _{O 3} system, the content of NiO _is, Cr ₂ when using _Cr 2 _{O 3} in Al 2 _{O 3} system It is preferable not to fall below an amount corresponding to one half of the O ₃ content. That is, in order to obtain characteristics corresponding to the case where the content of Cr ₂ O ₃ is 2% by mass, the content of NiO in the refractory raw material including the main aggregate should not be less than 1% by mass. It is preferable to do.

However, if only the spinel-type mineral composed of Al ₂ O ₃ and NiO is contained in the bridge portion between the main aggregates, the stress relaxation function of the bridge portion is insufficient and it is difficult to ensure sufficient thermal shock resistance. It is. Therefore, in the present invention, zirconia-mullite is further contained in the cross-linked portion.

Zirconia-mullite is obtained by dispersing ZrO ₂ in mullite (3Al ₂ O ₃ .2SiO ₂ ). In the present invention, zirconia is used to contain zirconia-mullite in a cross-linked portion between main aggregates. - fine mullite, for example, a SiO ₂ minutes contained therein and zircon _(ZrO 2 · SiO ₂₎ were mixed calcined alumina in the amount to be converted mullite _{(3Al 2 O 3 · 2SiO 2} ), the arc electric After melting in a furnace, it can be obtained by pulverizing into a granular or powdery form (zirconia-mullite obtained by this method is referred to as “electrofused zirconia-mullite”).

Zirconia-mullite is a refractory raw material that combines the corrosion resistance of ZrO ₂ and the thermal shock resistance of mullite. The chemical composition is about 37% by mass of ZrO ₂ , about 45% by mass of Al ₂ O _{3 and} about 18% by mass of SiO ₂ , and monoclinic ZrO ₂ is present in mullite. And it has an integral structure with few grain boundaries. Under high temperature, Al ₂ O ₃ , SiO ₂ , and ZrO ₂ constituting mullite melt and become viscous, and ZrO ₂ also exerts a reinforcing function. Even if zirconia-mullite fine particles, Al ₂ O ₃ fine particles, and NiO fine particles coexist in the fine particle region, the spinel mineral of Al ₂ O ₃ —NiO is selectively generated. This zirconia-mullite part is a SiO ₂ melt in which mullite is thermally dissociated, a SiO ₂ —Al ₂ O ₃ melt that incorporates other constituent materials such as clay and impurities, and a low melt that involves impurities. In addition, Al ₂ O ₃ fine particles and Al ₂ O ₃ —NiO spinel minerals are taken into a viscous state in which they are dispersed, forming a support / bonding part between the main aggregates as a breathable refractory .

  Since the crosslinked portion in such a viscous state is rich in strength and toughness and has the ability to deform, stress can be relaxed without destroying the crosslinked portion. The breathable refractory is exposed to a high temperature in the vicinity of the surface in contact with the molten steel, while the back side is lower in temperature than the surface in contact with the molten steel due to the cooling effect of the passing gas, and the temperature gradient is large. This viscous cross-linked portion is particularly effective in relieving the stress caused by such a thermal gradient of the breathable refractory, the stress caused by thermal shock received during steel receiving, during rapid cooling after use, and the like.

Furthermore, this cross-linked portion in a viscous state contributes to an improvement in corrosion resistance. When FeO, slag, or the like comes into contact with this portion, those components are taken in or melted down with a reaction such as low melt formation. In the present invention, as described above, the Al ₂ O ₃ —NiO-based spinel-type mineral having particularly excellent corrosion resistance is contained in this portion, so that the melting loss can be suppressed while suppressing the decrease in viscosity.

  In addition, this brittle part in the viscous state is deformed by the pressure and generated stress by the molten steel head near the molten steel contact surface, and part of the main aggregate also moves, forming a state close to the coating. The pores near the molten steel contact surface of the breathable refractory are closed or reduced. As a result, at the end of the gas blowing process, molten steel or slag penetrates deeply into the back side of the refractory due to molten steel head pressure, capillary action, etc., blocking the pores that are open for ventilation, impairing the ventilation characteristics To suppress the melting or erosion of deep tissue.

  By such an action, the refractory for ventilation of the present invention can obtain high corrosion resistance, high thermal shock resistance, high infiltration resistance, high ventilation stability, and the like.

As described above, the technique using the zirconia-mullite of the present invention uses ZrO ₂ as partially stabilized zirconia as shown in Patent Document 2 and uses its own stress relaxation function as a single structure. It is completely different from technology in its technical idea and operation.

According to the present invention, in a breathable refractory for gas blowing or the like, its corrosion resistance, thermal shock resistance, infiltration resistance and the like can be improved, and it can be replaced with a breathable refractory containing Cr ₂ O _{3. A} breathable refractory containing no ₂ O ₃ can be obtained.

In the present invention, Al ₂ O ₃ source particles and NiO source particles, or Al used to form a structure containing a spinel mineral composed of Al ₂ O ₃ and NiO and zirconia-mullite in the cross-linked portion between the main aggregates in the present invention Each of the spinel-type fine particles composed of ₂ O ₃ and NiO and the zirconia-mullite fine particles have the composition and structure as described above during the production of a refractory having a step of firing at about 1600 ° C. to about 1800 ° C. Therefore, 0.2 mm or less is preferable and 0.1 mm or less is more preferable. When it exceeds 0.2 mm, a sufficient bonded state cannot be obtained, the strength as a refractory structure is inferior, and sufficient thermal shock resistance and corrosion resistance cannot be obtained. In the case of 0.1 mm or less, the sintering rate and the melting rate can be further increased, and a more uniform and integrated state can be achieved.

The blending amount of these fine particles is 7% by mass to 12% by mass of Al ₂ O ₃ source fine particles and 1% by mass of NiO source fine particles when the total amount of the refractory raw materials including the main aggregate is 100% by mass. % To 6% by mass, or in the case of spinel-type fine particles composed of Al ₂ O ₃ and NiO instead of 2% to 12% by mass, and zirconia-mullite fine particles are preferably 1% by mass to 10% by mass. preferable.

If the spinel-type fine particles composed of Al ₂ O ₃ and NiO are less than 2% by mass, the corrosion resistance and thermal shock resistance are not sufficient, and if it exceeds 12% by mass, the corrosion resistance and thermal shock resistance tend to decrease.

The Al ₂ O ₃ source fine particles and the NiO source fine particles need to determine their blending amounts from this viewpoint. That is, when the Al ₂ O ₃ source fine particle exceeds 12% by mass and the NiO source fine particle is less than 1% by mass, a spinel mineral composed of Al ₂ O ₃ —NiO contributing to corrosion resistance, thermal shock resistance and the like is obtained. When the Al ₂ O ₃ source fine particles are less than 7% by mass and the NiO source fine particles are more than 6% by mass, NiO is saturated and partially present alone, etc. Thermal shock resistance and the like tend to decrease.

When the zirconia-mullite fine particle is less than 1% by mass, the stress relaxation function is small and sufficient thermal shock resistance cannot be obtained. When it exceeds 10% by mass, the SiO ₂ component is relatively increased, and the corrosion resistance tends to be lowered.

Moreover, each mixing ratio of these three raw materials in these fine particles is about 35 to about 60% by mass of the Al ₂ O ₃ component raw material when the total amount of the fine particles of only these three raw materials is 100% by mass, NiO The component raw material is about 5 to about 35% by mass (about 10 to about 60% by mass in the case of a spinel mineral raw material made of Al ₂ O ₃ —NiO), and the zirconia-mullite raw material is about 5 to about 50% by mass. However, it is preferable for obtaining a structure of the crosslinked portion having a suitable balance of corrosion resistance, thermal shock resistance, infiltration resistance, and the like in the crosslinked portion. However, these blending ratios are preferably changed in accordance with fluctuations in operating conditions such as steel type, molten steel temperature, treatment time, gas flow rate, erosive components such as slag, and amounts. That is, when the corrosion resistance is enhanced, the proportions of Al ₂ O ₃ and NiO components are increased, and when the thermal shock resistance and infiltration resistance are enhanced, the zirconia-mullite raw material is increased.

As the refractory raw material of coarse grains as the main aggregate, Al ₂ O ₃ , Al ₂ O ₃ —MgO based compound, MgO—SiO ₂ based compound, ZrO ₂ , MgO—ZrO ₂ based compound, ZrO ₂ —SiO ₂ based Can be used for breathable refractories such as compounds, Al ₂ O ₃ —SiO ₂ compounds, Al ₂ O ₃ —NiO compounds, or a mixture of these compounds with MgO added Refractory raw materials can be used.

Among these, it is preferable to obtain a bond such as sintering in at least a part of the contact portion with the fine particle portion in order to ensure or improve the strength and thermal shock resistance as the refractory structure. ₂ O ₃ electrofused or sintered alumina, Al ₂ O ₃ —SiO ₂ compound mullite, sillimanite and other synthetic or natural raw materials, Al ₂ O ₃ —MgO compound spinel, Al ₂ O ₃ —NiO compound Spinel or the like is preferable.

  The grain size of these coarse grains is preferably about 0.2 mm or more and 2 mm or less, and the optimum value should be selected within this range depending on various operating conditions such as the composition of the molten metal to be used, temperature, pressure, gas flow rate, etc. Is preferred. In the case of gas blowing in a general molten steel ladle, about 0.2 mm or more and 1 mm or less is more preferable in order to optimize the balance with the size of the gap for ventilation. If it exceeds 2 mm, the bonding portion between the coarse particles and the fine particles decreases, and the thermal expansion amount of the coarse particles starts to affect the fine particle portions, which may destroy the fine particle portions, resulting in a decrease in strength and thermal shock resistance. Is likely to occur.

  The ratio between the coarse particles as the main aggregate and the fine particles constituting the crosslinked portion is preferably 60% by mass or more and 90% by mass or less of the coarse particles, and 10% by mass or more and 40% by mass or less of the fine particles. The mass ratio is more preferably about coarse particles 7: fine particles 3 to coarse particles 8: fine particles 2.

When the coarse particles are less than 60% by mass and the fine particles are more than 40% by mass, the refractory structure becomes dense, the air permeability is lowered, and the corrosion resistance and the wear resistance tend to be lowered. On the other hand, when the coarse particles exceed 90% by mass and the fine particles are less than 10% by mass, the refractory structure becomes too coarse, and the cross-linked structure by the fine particle part that bears the bonding function is too little, and the strength and heat resistance Causes a drop in impact. In addition, the amount of Al ₂ O ₃ —NiO-based spinel minerals excellent in corrosion resistance and thermal shock resistance decreases, and corrosion resistance and wear resistance equivalent to Cr ₂ O ₃ -containing refractories cannot be obtained.

  In the method for producing a breathable refractory according to the present invention, first, a liquid binder or a liquid containing a binder is added to a coarse refractory raw material as a main aggregate and kneaded, and then a fine refractory raw material is added. It is preferable to add and knead further. That is, a kneading method that obtains a form in which the fine refractory raw material is uniformly present on the surface of the coarse refractory raw material is preferable.

  As this liquid binder or a liquid containing a binder, organic or natural pastes such as starch, dextrin, gum arabic, molasses, methylcellulose, polyvinyl alcohol, lignin sulfonate, vinyl acetate emulsion, Acrylates, etc.), synthetic resins (phenolic resins, epoxy resins, acrylic resins, pitches, etc.), inorganic materials, silicates, phosphates, etc. can be used. These water-soluble ones can be used as an aqueous solution. In order to increase these plasticity and adhesiveness, it is also possible to add clay, silica flour or the like within about 5% by mass.

  The kneaded product thus obtained is molded into a predetermined shape by a method such as pressing, flow, or vibration, and after drying, preferably fired at 1600 ° C. or higher to obtain the desired breathable refractory. Can do. This breathable refractory can be used as a part of other refractories, bonded, etc., covered with a metal case to prevent gas leakage or reinforce depending on the usage conditions and shape, gas introduction It can also be used with installation of pipes for use.

Table 1 shows the blending ratio of the refractory raw materials in the breathable refractories of each example and the test results.

  First, phenol resin and clay were added as a liquid binder to the coarse refractory raw material as the main aggregate and kneaded with a mixer, and then the fine refractory raw material was added and further kneaded. Thereafter, it was formed into a large porous plug shape by a press machine, and baked at 1600 ° C. or higher after a drying process. The porous plug was cut into a test piece corresponding to each test.

  Each test method is as follows.

・ Corrosion resistance: Each test piece was installed so as to constitute the furnace wall in the rotary erosion test furnace, held at 1750 ° C for 30 minutes, then oxygen was blown with an oxygen lance, the damage dimension after the test was measured, and the erosion dimension Expressed as a percentage.

Infiltration resistance: A cubic test piece with a side of 30 mm was placed on the bottom of a high frequency furnace, immersed in molten steel at 1700 ° C. for 2 hours, and then the sample was cut to infiltrate the inner molten steel (mm )

Thermal shock resistance: The test piece of 40 × 40 × 160 mm was immersed in molten steel at 1600 ° C. for 3 minutes and air-cooled repeatedly, and expressed as the number of times the test piece was broken and peeled off.

-Air permeability: According to JISR2115.

-Apparent porosity: According to JISR2105.

-Compressive strength: According to JISR2106.

In Table 1, Examples 1-12 are breathable refractories that do not contain Cr ₂ O ₃ within the scope of the present invention, and Comparative Examples 1-3 are breathable refractories that do not contain Cr ₂ O ₃ outside the scope of the present invention. Material 1 and Reference Example 1 are breathable refractories containing Cr ₂ O ₃ .

As shown in Table 1, Examples 1 to 12 which do not contain Cr ₂ O ₃ of the present invention have corrosion resistance, wet resistance and thermal shock resistance as compared with Comparative Examples 1 to 3 which also do not contain Cr ₂ O _3. It has improved. Particularly, Example 2 in which the blending amount of Al ₂ O ₃ fine powder is 7 to 12% by mass, the blending amount of NiO fine powder is 1 to 6% by mass, and the blending amount of zirconia-mullite fine powder is 1 to 10% by mass. 5 and example 7 has the same or more properties and reference example 1 containing Cr ₂ O ₃ 2 wt%, it is quite possible alternative to the gas-permeable fireproof material containing Cr ₂ O _3.

  The present invention is a breathable refractory having a gas blowing function used for various molten steel and hot metal processing such as refining and homogenizing molten steel, for example, a porous plug, various nozzles for continuous casting, and a gas blowing portion at the tip of a stopper Widely available for etc.

It is a structure chart centering on the bridge | crosslinking part of the breathable refractory of this invention.

Explanation of symbols

1 Cross-linked part (part consisting of fine particles)
2 Coarse grain as main aggregate 3 Pore (space)
4 Base part of cross-linked part centered on Al ₂ O ₃ —SiO-based minerals such as mullite 5 Al ₂ O ₃ grains (corundum, indicated by “C” in FIG. 1)
6 Spinel-type mineral consisting of Al ₂ O ₃ and NiO (indicated as “S” in FIG. 1)
7 ZrO ₂ (indication of “Z” in FIG. 1)

Claims (2)

In a breathable refractory having pores for allowing gas to pass therethrough, a spinel mineral composed of Al ₂ O ₃ and NiO and ZrO ₂ in mullite at a bridging portion between coarse refractory raw materials as a main aggregate. Breathable refractory containing dispersed zirconia-mullite. In a method for producing a breathable refractory having pores for allowing gas to pass therethrough, Al ₂ O ₃ source fine particles and NiO source fine particles, or Al ₂ O ₃ around a coarse refractory raw material as a main aggregate And a zirconia-mullite fine particle in which ZrO ₂ is dispersed in mullite, followed by firing, thereby forming a bridging portion between the coarse refractory raw material as the main aggregate. spinel-type minerals and zirconia of Al ₂ O ₃ and NiO - method for producing breathable refractory to contain and mullite.