JPH11263663A - Production of refractory for gas blowing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a refractory for gas blowing excellent in a function to prevent bubbling defect at a low cost. SOLUTION: A refractory raw material using 65-80 wt.% alumina particle and 15-30 wt.% unstabilized zirconia particle having 0.3-2 mm particle diameter as aggregate raw materials and the balance at least one kind of a fine powdery raw material selected from the group composed of silica fine powder, alumina fine powder, clay fine powder and chromium oxide fine powder is prepared. A sintered compact having zirconia particle, around which fine cracks are generated, is obtained by adding a binder into the refractory raw material, kneading, forming into a prescribed shape and firing in the atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a refractory for gas injection, and more particularly, to a porous plug used for stirring molten steel, cleaning molten steel, and the like. The present invention relates to a refractory for gas injection and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, argon gas or the like has been blown into molten steel through a breathable refractory disposed at the bottom of a ladle.
The so-called ladle refining for stirring the molten steel, making the molten steel temperature uniform, dispersing the alloy components evenly, and removing and floating the nonmetallic inclusions, etc., has been frequently performed. This gas-impermeable breathable refractory placed at the bottom of the ladle is called a "porous plug". In general, a spherically-granulated alumina raw material or a massive alumina raw material is used as a main aggregate, and fine powders of alumina, silica, viscoel, etc. are added and kneaded to form a predetermined shape. It is manufactured by firing inside.

[0003] The performance required of this gas-injecting refractory is that the gas-injecting characteristics are stable even when the use conditions change, and that the service life is long. The most important performance is the stability of the gas blowing characteristics. that is,
If the gas blowing characteristics are deteriorated during use, so-called bubbling defects occur, and as a result, the quality of the steel is reduced, or the operation is seriously affected by replacing molten steel.

[0004] The bubbling defect does not always occur when a specific gas-injecting refractory is used, but occurs irregularly under various conditions. Ladle refining methods using refractories for gas injection include CAS treatment, LF treatment, and the like.
As in the S treatment, the number of gas blows, hot water time, additive alloy type,
A processing method in which operating conditions such as molten steel temperature fluctuate greatly has a high probability of occurrence of bubbling failure.

Generally, there are two types of bubbling defects.

[0006] The first form is caused by the infiltration of molten steel and slag into a refractory for gas injection. In this case, the outflow (blowing) of the gas itself stops, or the flow rate of the blown gas becomes smaller than the reference value.

In the second embodiment, gas is leaked through cracks generated in a reinforcing refractory (outer ring) mounted on the outer peripheral surface of the gas-injecting refractory. In this case, the flow rate of the gas to be blown has reached the reference value, but the gas is not released through the gas blowing refractory, so that desired functions such as stirring of molten steel cannot be performed. As a result, the desired treatment cannot be performed on the molten steel portion from which the slag has been removed (referred to as “bow”).

[0008] Of these two forms, the first form has a higher probability of occurrence, so that measures to prevent bubbling defects of that form are more strongly required.

[0009] Bubbling failure of the first embodiment is caused by the infiltration of molten steel and slag at the tip of a refractory for gas injection to form an infiltration layer, and the infiltration layer hinders gas blowing. Is known. Therefore, in order to prevent the bubbling defect of the first embodiment, it is only necessary to prevent infiltration of molten steel and slag, and for that purpose, it is conceivable to reduce the pore diameter to suppress the infiltration of steel and slag itself. However, if so, the required flow rate of the gas cannot be secured.

For these reasons, it is difficult to prevent infiltration of molten steel and slag by controlling the pore diameter, and it is necessary to prevent bubbling defects by other methods.

Japanese Utility Model Publication No. Hei 6-38107 discloses a "porous plug characterized in that a porous joint layer is provided between the plug body and the sleeve, and the air permeability thereof is lower than that of the plug body." Is disclosed.

In this conventional porous plug, the plug main body (that is, the gas blowing refractory) is supported by the sleeve (that is, the outer ring) via the joint layer. If the infiltration layer of molten steel and slag is formed at the tip of the plug body during use, gas will not be released from the plug body, but will instead be released from the joint layer, which is less permeable than the plug body.

When gas is released from the joint layer into the molten steel,
The molten steel in the vicinity of the joint layer is agitated, and the flow of the molten steel becomes violent, so that the joint layer melts. As a result, a gap is formed between the plug body and the joint layer. Molten steel enters the gap and erodes the vicinity of the joint between the plug body and the infiltration layer. The infiltration layer is easily peeled from the plug main body due to the erosion, and thus easily peels off from the plug main body by the pressure of the blowing gas, and the ventilation of the plug main body is restored. Thus, bubbling defects can be prevented.

Japanese Utility Model Application Laid-Open No. 62-70158 discloses that "a plurality of thin-layered voids having the same flat area or gradually decreasing from the used surface to the non-used surface are provided in the center portion of the plug body. Are provided in parallel with the use surface and in multiple stages. "

In this conventional porous plug, the infiltration layer formed in the plug main body can be easily peeled off by the thin layer gap provided in the plug main body (ie, the gas blowing refractory). Therefore, ventilation of the plug body is restored during use, and defective bubbling is prevented.

[0016]

However, the conventional porous plug has the following problems.

In the porous plug disclosed in Japanese Utility Model Publication No. 6-38107, in order to release gas from the joint layer, the pores inside the joint layer need to be open pores and the pores must communicate with each other. is there. However, the publication only discloses that the joint layer is made of fire-resistant mortar, but does not show a specific method of forming the pores.

In actual use, pressure from molten steel several meters high filled in the ladle is applied to the gas discharge surface at the tip of the plug body (refractory for gas injection). However, the publication also does not describe what air permeability can be released from the joint layer under such circumstances.

Therefore, it must be said that the practical use of the porous plug disclosed in Japanese Utility Model Publication No. 6-38107 is extremely difficult.

Even if gas is released from the joint layer by any method, a large amount of time is required for erosion generated in the joint layer to reach the inside of the plug body (gas-blown refractory). It is presumed that considerable time is required until the ventilation can be restored. Thus, the actual fairness 6-3
The porous plug disclosed in Japanese Patent Application Laid-Open No. 8107 has a problem that a sufficient function of preventing bubbling failure cannot be obtained.

In the porous plug disclosed in Japanese Utility Model Laid-Open Publication No. 62-70158, a plurality of flammable substances are formed at regular intervals during molding in order to provide a thin-layered space inside the plug body (refractory for gas injection). It is necessary to fill while filling, and to burn off the combustible substance in the firing step. However, such a work itself is not only extremely poor in productivity, but also causes a problem that the production cost is increased because the yield is reduced due to cracks generated from voids during firing.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a gas-injecting refractory which can produce a gas-injecting refractory excellent in preventing bubbling defects at low cost.

[0023]

(1) The method for producing a refractory for gas injection according to the present invention is characterized in that alumina particles 65 to 8 are used.
0 wt% and 15 to 30 wt% of unstable zirconia particles having a particle size of 0.3 to 2 mm are used as an aggregate raw material, and the balance is at least one selected from the group consisting of silica fine powder, alumina fine powder, clay fine powder and chromium oxide fine powder. A step of producing a refractory raw material as a fine powder raw material, a step of adding and kneading a binder to the refractory raw material to produce a molded body raw material, and forming the molded body raw material into a predetermined shape to obtain a molded body Process and
Firing the molded body in the air to obtain a sintered body having fine cracks formed around the zirconia particles.

(2) In the method for producing a refractory for gas injection according to the present invention, alumina particles 65 to 65 are used as aggregate raw materials.
Unstable zirconia particles having a particle size of 0.3 to 2 mm and 15 to 30 wt% are used in addition to 80 wt%. Unstabilized zirconia has the property of abnormal expansion and contraction at temperatures around 1000 ° C. Therefore, due to the difference in the coefficient of thermal expansion from alumina particles, fine cracks are formed around the zirconia particles inside the sintered body during the firing step. (Hereinafter, referred to as microcracks). The microcracks have a function of easily peeling off the infiltration layer of molten steel and slag formed on the surface of the refractory for gas injection according to the present invention.

That is, if the infiltration layer of molten steel or slag is formed on the surface of the refractory for gas injection according to the present invention during use, the permeability of the refractory is impaired, and as a result, the gas inside the refractory is reduced. Pressure rises. Microcracks grow by this gas pressure. In particular, the gas tends to accumulate in the vicinity of the infiltration layer that is preventing air permeability, so that micro cracks grow significantly. For this reason, in the vicinity of the infiltration layer, the mechanical strength of the refractory deteriorates extremely, and the infiltration layer peels off when the mechanical strength cannot withstand the gas pressure.

The ventilation is restored by the peeling of the infiltration layer in this way. Even if the infiltration layer is formed again, the process from the growth of microcracks to the peeling of the infiltration layer is repeated, so that stable air permeability is always secured, and poor bubbling can be prevented.

In the refractory for gas injection according to the present invention, the growth of the microcracks is directly related to the deterioration of the air permeability due to the formation of the infiltration layer, and the growth of the microcracks follows the progress of the deterioration of the air permeability. proceed. Therefore, the time from the formation of the infiltration layer to the separation can be shortened. For this reason, the ventilation is quickly restored, and an excellent function of preventing poor bubbling is obtained.

Further, since a complicated structure such as the technique disclosed in Japanese Utility Model Application Laid-Open No. 62-70158 is not required, the manufacturing cost can be reduced.

(3) The compounding amount of the zirconia particles is
The content is preferably in the range of 15 to 30% by weight of the refractory raw material. If the addition amount of the zirconia particles is less than 15 wt%, the zirconia particles have a large specific gravity and a low dispersibility as compared with the alumina particles, and are not well dispersed in the structure of the sintered body. The infiltration layer is not sufficiently stripped.

On the other hand, the amount of zirconia particles added is 30 wt.
%, The microcracks are excessively generated in the structure of the sintered body, resulting in a decrease in mechanical strength. Therefore, damage due to wear caused by contact with the molten steel flow increases. Also,
The zirconia raw material has a large specific gravity, which deteriorates the handling property, and the raw material price is high, so that the production cost increases. By setting the content to 30% by weight or less, they can be reduced to a practically acceptable level.

The preferred range of the particle size of the zirconia particles is 0.3 to 2 mm. If the particle size of the zirconia raw material is less than 0.3 mm, the pore size of the sintered body (refractory) becomes too small, and it becomes difficult to secure a required gas flow rate. On the other hand, if it exceeds 2 mm, the voids formed by the constituent particles of the aggregate become excessive, so that the infiltration of molten steel and slag becomes easy, and as a result,
The infiltration layer becomes thick, and it becomes difficult to peel off due to the pressure of the excessively blown gas.

As the zirconia particles, unstabilized zirconia particles are used. Generally, zirconia raw materials include unstabilized zirconia, partially stabilized zirconia, and stabilized zirconia due to the difference in crystal form. In order to effectively generate microcracks due to the difference in thermal expansion between zirconia particles and alumina particles, it is necessary that the difference between the amounts of thermal expansion is sufficiently large. For this reason, unstabilized zirconia particles having a monoclinic crystal structure in which abnormal expansion and contraction occur due to phase transformation of the crystal are used.

(4) The reason why alumina particles are used in addition to the unstabilized zirconia particles as the raw material for the aggregate is that alumina particles have an excellent balance between corrosion resistance and spall resistance.

The type of the alumina particles used is not particularly limited, and any of an electrofused alumina raw material, a sintered alumina raw material, a spherical alumina raw material and the like may be used.

(5) The portion other than the aggregate raw material, that is, the remaining portion, is at least one fine powder raw material selected from the group consisting of silica fine powder, alumina fine powder, clay fine powder, and chromium oxide fine powder.

The silica fine powder, alumina fine powder and clay fine powder have an action of promoting sintering. Clay fines also have the effect of imparting plasticity to refractories. The chromium oxide fine powder has an effect of making it difficult to wet the molten steel and improving the infiltration resistance, so that it is possible to prevent the formation of an infiltration layer, and it is effective in preventing poor bubbling.

The alumina fine powder is preferably spherical particles having a particle diameter of 0.3 to 1 mm. If the particle size is less than 0.3, the pore size distribution becomes small and the required gas flow rate cannot be secured. On the other hand, if the particle size exceeds 1 mm, the pore size distribution becomes large and the infiltration layer becomes thick, and as a result, the infiltration layer does not peel off.

The use of alumina fine powder in the form of spherical particles is excellent in packing property and sharp in pore size distribution as compared with agglomerated particles. Therefore, it is necessary to improve the balance between securing gas flow and suppressing infiltration of molten steel. Because it can be.

(6) Any binder can be used as the binder. For example, lignin, an aluminum phosphate aqueous solution and the like are suitable.

(7) The molding step is not particularly limited. For example, a uniaxial pressing type molding process such as a hydraulic press or a friction press is suitable.

(8) The baking step is performed in the air because controlling the baking atmosphere significantly increases equipment costs and running costs, and particularly because the main raw materials used are oxides, Because there is no need to control the

In the firing step, the firing temperature is set so that a sintered body having appropriate fine cracks formed around the zirconia particles is obtained. A preferred temperature range is 1500-1850 ° C. If the temperature is lower than 1500 ° C., the sintering of the particles does not proceed sufficiently, and the required strength cannot be obtained. On the other hand, if the temperature exceeds 1850 ° C., oversintering occurs, the strength becomes too high, and the spall resistance decreases.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on specific examples.

Example 1 As an aggregate raw material, a particle size of 0.5 was used.
16% by weight of a single component zirconia (unstabilized zirconia) containing no stabilizer of 2 mm and 75% by weight of alumina spherical particles having a particle diameter of 0.3 to 1 mm are blended, and further 3% by weight of alumina fine powder and 2% by weight of silica fine powder
%, Viscous powder 2 wt%, and chromium oxide fine powder 2 wt%
Was added to produce a refractory raw material. Next, an appropriate amount of an organic binder (binder) (for example, lignin) was added to the refractory raw material, and the mixture was kneaded using a wet pan to produce a molded body raw material. Thereafter, the raw material of the compact was formed into a predetermined shape and dried to prepare a compact. Finally, the molded body was fired at 1700 ° C. in the air to obtain a refractory for gas injection according to the present invention.

A cylindrical test piece having a diameter of 50 mm and a height of 50 mm was prepared from the refractory for gas injection thus obtained, and the apparent porosity, compressive strength and air permeability were measured. As a result, the apparent porosity was 25.8%, the compressive strength was 65.2 MPa, and the air permeability was 1.69 cm ³ · cm /
cm ² · sec · cmH ₂ O.

Further, as an actual machine test, the refractory for gas injection obtained in this manner was attached to a 250-ton ladle, and then the CAS treatment was carried out to confirm the presence or absence of gas blowing failure and the number of usable times. As a result, no bubbling defects occurred, and wear was small, so that it was used ten times.

(Example 2) Unstabilized zirconia particles 20 wt%, alumina spherical particles 72 wt%, alumina fine powder 3 wt%, silica fine powder 2 wt%, viscous fine powder 1 w
A refractory for gas injection was produced under the same conditions as in Example 1 except that the content was changed to t% and chromium oxide fine powder was 2 wt%.

From this refractory, a diameter of 50
A cylindrical test piece having a size of 50 mm × height of 50 mm was prepared, and apparent porosity, compressive strength, and air permeability were measured. The apparent porosity was 25.2%, the compressive strength was 67.5 MPa,
The air permeability is 1.61 cm ³ · cm / cm ² · sec · cmH
₂ O, equivalent to Example 1.

Using the produced gas-injecting refractory, an actual machine test was conducted in the same manner as in Example 1. As a result, no bubbling defect occurred and the device was used 11 times.

(Example 3) Without adding clay fine powder, the mixing ratio was unstabilized zirconia particles 28 wt%, alumina spherical particles 66 wt%, alumina fine powder 3 wt%, silica fine powder 1 wt%, and chromium oxide fine powder 2 wt%. A refractory for gas injection was produced under the same conditions as in Example 1 except that the refractory was used.

From this refractory, a diameter of 50
When an apparent porosity, compressive strength and air permeability were measured after preparing a cylindrical test piece having a size of 50 mm × height of 50 mm, the apparent porosity was 24.6%, the compressive strength was 71.1 MPa,
The air permeability is 1.50 cm ³ · cm / cm ² · sec · cmH
₂ O, equivalent to Example 1.

Using the produced gas-injecting refractory, an actual machine test was conducted in the same manner as in Example 1. As a result, no bubbling defect occurred and the device was used ten times.

(Example 4) Without adding clay fine powder, the mixing ratio was 25 wt% of zirconia particles and 6 of alumina spherical particles.
8 wt%, alumina fine powder 3 wt%, silica fine powder 2 wt
% And chromium oxide fine powder of 2 wt%, a refractory for gas injection was produced under the same conditions as in Example 1.

From this refractory, a diameter of 50
When a cylindrical test piece having a size of 50 mm × height of 50 mm was prepared and the apparent porosity, compressive strength and air permeability were measured, the apparent porosity was 24.9%, the compressive strength was 69.4 MPa,
The air permeability is 1.56 cm ³ · cm / cm ² · sec · cmH
₂ O, equivalent to Example 1.

An actual machine test similar to that of Example 1 was performed using the produced gas-injecting refractory. As a result, no bubbling defect occurred and the device was used 11 times.

(Comparative Example 1) The blending ratio of unstabilized zirconia particles was reduced to 10% by weight, and alumina spherical particles 79% by weight.
%, Alumina fine powder 4 wt%, silica fine powder 3 wt%, viscous fine powder 2 wt%, and chromium oxide fine powder 2 wt%, and a refractory for gas injection was produced under the same conditions as in Example 1.

From this refractory, a diameter of 50
When a cylindrical test piece having a size of 50 mm × height of 50 mm was prepared and the apparent porosity, compressive strength and air permeability were measured, the apparent porosity was 26.1%, the compressive strength was 61.5 MPa,
The air permeability is 1.73 cm ³ · cm / cm ² · sec · cmH
₂ O.

An actual machine test similar to that of Example 1 was conducted using the produced gas-injecting refractory. As a result, bubbling failure occurred and the use was stopped three times. This is presumed to be because the mixing ratio of the zirconia particles was less than 15 wt%, the microcracks did not sufficiently develop, and the effect of peeling the infiltration layer was not sufficiently obtained.

Comparative Example 2 Example 4 was repeated except that the blending ratio of the zirconia particles was increased to 35 wt% and the alumina spherical particles were 59 wt%, alumina fine powder 3 wt%, silica fine powder 1 wt%, and chromium oxide fine powder 2 wt%. A refractory for gas injection was manufactured under the same conditions.

From this refractory, a diameter of 50
When a cylindrical test piece having a height of 50 mm and a height of 50 mm was prepared and the apparent porosity, compressive strength and air permeability were measured, the apparent porosity was 24.5%, the compressive strength was 57.3 MPa,
The air permeability is 1.51 cm ³ · cm / cm ² · sec · cmH
₂ O.

The compressive strength is lower than that of Example 4. This is because the mixing ratio of the unstabilized zirconia particles is 30.
It is presumed that, by exceeding wt%, microcracks were excessively generated.

An actual machine test similar to that of Example 1 was carried out using the produced gas-injecting refractory. As a result, no bubbling defect occurred, but the strength was low, and the damage due to abrasion was large, so that it could be used only seven times. Did not.

(Comparative Example 3) The particle size of the unstable zirconia particles was increased from more than 2 mm to 3 mm or less, and the mixing ratio was 20 wt% of the unstabilized zirconia particles and the alumina spherical particles 74.
A refractory for gas injection was produced under the same conditions as in Example 2 except that wt%, alumina fine powder 3 wt%, clay fine powder 1 wt%, and chromium oxide fine powder 2 wt%, and silica fine powder was not added.

From this refractory material, a diameter of 50
When a cylindrical test piece having a size of 50 mm × height of 50 mm was prepared and the apparent porosity, compressive strength and air permeability were measured, the apparent porosity was 28.6%, the compressive strength was 53.8 MPa,
The air permeability is 2.03 cm ³ · cm / cm ² · sec · cmH
₂ O.

As compared with Example 2, the apparent porosity and air permeability are higher, and the compressive strength is lower. This is presumed to be due to the fact that the zirconia particles had a particle size of more than 2 mm, which increased the voids between the aggregate constituent particles.

An actual machine test similar to that of Example 1 was performed using the produced gas-injecting refractory. As a result, bubbling defects occurred and the refractory could be used only four times. It is presumed that the infiltration layer became thick and did not peel off due to the expansion of the voids between the aggregate constituent particles.

(Comparative Example 4) The particle size of the unstable zirconia particles was reduced to 0.25 mm or less, and the mixing ratio was 20 wt% of the unstabilized zirconia particles and 69 wt% of the alumina spherical particles.
%, Alumina fine powder 4 wt%, silica fine powder 3 wt%, clay fine powder 2 wt%, and chromium oxide fine powder 2 wt%, and a refractory for gas injection was produced under substantially the same conditions as in Example 2.

For this refractory, a cylindrical test piece having a diameter of 50 mm and a height of 50 mm was prepared in the same manner as in Example 1, and the apparent porosity, compressive strength and air permeability were measured. 2%, compressive strength 80.6M
Pa, air permeability is 1.06 cm ³ · cm / cm ² · sec ·
cmH ₂ O.

As compared with Example 2, the compressive strength was higher and the apparent porosity and air permeability were lower. This is presumably because the zirconia particles had a particle size of less than 0.25 mm, and the structure of the refractory became dense.

Further, the air permeability was too low, and the actual machine test was not completed.

Comparative Example 5 A refractory for gas injection was produced under the same conditions as in Example 2 except that partially stabilized zirconia particles having a particle size of 0.5 to 2 mm were used instead of the unstable zirconia particles. From this refractory, a cylindrical test piece having a diameter of 50 mm and a height of 50 mm was prepared in the same manner as in Example 1, and the apparent porosity, compressive strength and air permeability were measured. The apparent porosity was 24.9%, and the compressed porosity was 24.9%. Strength is 69.6M
Pa, air permeability is 1.59cm ³ · cm / cm ² · sec ·
cmH ₂ O.

An actual machine test similar to that of Example 1 was performed using the produced gas-injecting refractory. As a result, a bubbling defect occurred and the refractory could be used only five times. It is presumed that the use of the partially stabilized zirconia particles did not sufficiently generate microcracks and did not peel off the infiltration layer.

Comparative Example 6 A refractory for gas injection was produced under the same conditions as in Example 2 except that stabilized zirconia particles having a particle size of 0.5 to 2 mm were used instead of the unstable zirconia particles.

From this refractory, a diameter of 50
When a cylindrical test piece having a size of 50 mm × height of 50 mm was prepared and the apparent porosity, compressive strength and air permeability were measured, the apparent porosity was 24.7%, the compressive strength was 70.9 MPa,
The air permeability is 1.58 cm ³ · cm / cm ² · sec · cmH
₂ O.

An actual machine test similar to that of Example 1 was conducted using the produced gas-injecting refractory. As a result, bubbling defects occurred and the refractory could be used only four times. It is presumed that microcracks did not occur due to the use of the stabilized zirconia particles, and the infiltration layer did not peel off during use.

The above Examples 1 to 4 and Comparative Examples 1 to 6 are shown in Table 1 below.

[0077]

[Table 1]

[0078]

As described above, according to the method for manufacturing a gas injection refractory of the present invention, a gas injection refractory excellent in the function of preventing bubbling defects can be manufactured at low cost.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Morita Osamu 1 Minamito, Ogakie-cho, Kariya-shi, Aichi Prefecture Toshiba Cellular Co., Ltd. Lamix Corporation Kariya Factory

Claims (2)

[Claims] 1. An unstable zirconia particle having a particle size of 0.3 to 2 mm and a particle size of 0.3 to 2 mm.
% As a raw material of an aggregate, and a process of producing a refractory raw material using at least one fine powder raw material selected from the group consisting of silica fine powder, alumina fine powder, clay fine powder and chromium oxide fine powder, A step of adding and kneading a binder to form a raw material of a molded body; a step of forming the raw material of the molded body into a predetermined shape to obtain a molded body; and a step of firing the molded body in the air to surround the zirconia particles. Obtaining a sintered body in which fine cracks are formed in the refractory for gas injection. 2. The method according to claim 1, wherein the alumina fine powder has a particle size of 0.3 to 1 mm.
The method for producing a refractory for gas injection according to claim 1, wherein the refractory is a spherical particle.