JPH07315913A - Magnesia refractory brick - Google Patents

Abstract

PURPOSE:To provide a magnesia refractory brick excellent in corrosion resistance and spalling property and containing no chromium oxide. CONSTITUTION:The magnesia refractory brick contains a magnesia clinker as a main component, which mainly contains 10-79wt.% magnesia clinker containing MgO and Al2O3 as main structural components or containing MgO, Al2O3 and SiO2 as main structural components and having spinel phase or spinel phase and forsterite phase of the structural components present in the grain boundary of MgO and the balance magnesia. Then, pores distribute in the refractory structure to mitigate the stress caused by thermal shock and as a result, thermal spalling resistance is improved. And since spinel phase and forsterite phase are present in the refractory structure, the penetration of a slag is prevented and corrosion resistance and structural spalling resistance are increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromium oxide-free magnesia refractory brick having excellent corrosion resistance and spalling resistance.

[0002]

2. Description of the Related Art Magnesia refractory bricks are used in large amounts as refractory linings for metal refining vessels because they have a high melting point and excellent erosion resistance to basic slag generated during metal refining. However, despite the above-mentioned features, magnesia refractory bricks are inferior in heat-resistant spalling resistance and structural spalling resistance, and a container lined with magnesia refractory bricks has a short life. Structural spalling is a phenomenon in which an altered part having a significantly different structure from that of the original part is generated by slag infiltration, and this altered part peels from the original part due to a rapid rise or fall in temperature during container use. Is. Therefore, as a measure for preventing the exfoliation of such magnesia refractory bricks, it has been considered to combine magnesia and phosphorous graphite as a material or combine magnesia and chromite. Further, as a measure for improving the corrosion resistance and the spalling resistance, in JP-A-4-187560, the magnesia clinker which is the main component is MgO and Al ₂
O ₃ as a main constituent, or MgO, Al ₂ O ₃ and SiO ₂ as main constituents,
Moreover, a magnesia refractory brick to which a chromium oxide component is added by using a magnesia clinker in which a spinel phase or a spinel phase and a forsterite phase due to these constituents exist at the grain boundary of MgO has been reported.

On the other hand, considering the present situation where various environmental problems and their countermeasures are being discussed from a global perspective, particularly in magnesia-chromic refractory bricks used in vacuum degassing equipment and rotary kilns for cement. The presence of chromium oxide is considered a problem, and a magnesia refractory brick containing no chromium oxide is desired. That is, C
r is stable as long as it has a trivalent form, but when the content of alkali and alkaline earth is high, hexavalent chromium is generated under conditions such as a temperature of 1000 ° C or higher and an oxidizing atmosphere. It is a toxic substance specified by law.

[0004]

The combination of magnesia and phosphorous graphite prevents the penetration of slag and improves the structural spalling resistance, but there is a problem that graphite is easily oxidized. In addition, depending on the type of molten metal in contact with the container, carbon contamination may not be allowed, and the use of graphite is also a problem. On the other hand, the combination of magnesia and chrome-based raw materials has improved corrosion resistance and structural spalling resistance compared to magnesia-based refractory bricks, but the penetration of slag from the operating surface is still large. It had the problem of suffering from static spalling damage. The present invention solves the above-mentioned problems and provides a magnesia refractory brick which is excellent in corrosion resistance, has heat resistant spalling resistance and structural spalling resistance, and does not contain chromium oxide.

[0005]

In order to achieve the above object, the present invention has MgO and Al ₂ O ₃ as main constituents, or MgO, Al ₂ O ₃ and SiO ₂
A magnesia clinker having as main constituents, and a spinel phase or a spinel phase and a forsterite phase due to these constituents exist at the MgO grain boundary (hereinafter, simply referred to as "SF magnesia clinker"): Provided is a magnesia refractory brick characterized by mainly containing a magnesia clinker containing 10 to 79 wt% and the balance being MgO as a main component.

The present invention will be described in detail below. The SF magnesia clinker according to the present invention comprises MgO, Al
₂ O ₃ as a main constituent or MgO, Al ₂ O ₃
And SiO ₂ as its main constituents. The preferred composition of these constituents is Mg based on the total weight of [MgO + Al ₂ O ₃ ] and [MgO + Al ₂ O ₃ + SiO ₂ ].
O is 80 wt% or more, and Al ₂ O ₃ and SiO ₂ are each 20 wt% or less. More preferably, MgO:
85 wt% or more, Al ₂ O ₃ : 15 wt% or less, Si
O ₂ : 5 wt% or less. In particular, if the amount of SiO ₂ is too large, the hot strength and corrosion resistance of the SF magnesia clinker tend to decrease, which is not preferable.

M used for the SF magnesia clinker
Examples of the gO raw material include ordinary magnesia clinker, naturally occurring magnesite, magnesium hydroxide, magnesium hydroxide, magnesium oxide obtained by calcining naturally occurring magnesite, and magnesium salts. As such MgO raw material, it is desirable to use a high-purity MgO component of 99% or more. If the amount of impurities is large, a low-melt material is likely to be generated, which leads to deterioration of corrosion resistance, which is not preferable.

Examples of the Al ₂ O ₃ raw material include alumina clinker, aluminum oxide, aluminum hydroxide, naturally occurring bauxite, shale shale and its fired products, and aluminum salts. Examples of the SiO ₂ raw material include crystalline silica such as natural quartz and diatomaceous earth, amorphous silica such as sodium silicate and silica flour, and micro silica. As with the MgO raw material, it is desirable that the Al ₂ O ₃ raw material and the SiO ₂ raw material also have high purity with few impurities. These MgO raw materials, Al ₂ O ₃ raw materials and S
In addition to the iO ₂ raw material, SF magnesia clinker containing CaO, Fe ₂ O ₃ or the like within a range not impairing spalling resistance, corrosion resistance and the like can also be used in the present invention.

The SF magnesia clinker in which the spinel phase or the spinel phase and the forsterite phase exist in the MgO grain boundary is produced by mixing the above-mentioned raw materials and then firing in a rotary kiln or a tunnel kiln.
In particular, the SF magnesia clinker used in the present invention, in the process of this firing, Al ₂ O ₃ and Si
O ₂ reacts with MgO to generate spinel (MgO.
Al ₂ O ₃ ) and forsterite (2MgO.SiO)
₂ ) must have been generated. for that reason,
The firing temperature is preferably 1500 ° C. or higher, 16
It is more preferable that the temperature is 00 ° C. or higher. If the firing temperature is too low, the formation of spinel and forsterite will not be sufficient.

When spinel and forsterite are produced, voids are formed in the regions occupied by Al ₂ O ₃ and SiO ₂ , and the SF magnesia clinker having pores is obtained. The size of the pores depends on the particle diameters of the Al ₂ O ₃ raw material and the SiO ₂ raw material, and the larger these particle diameters, the larger the pores can be obtained. However, if it is too large, spinels and forsterites are locally generated, and cracks are likely to occur due to the accompanying expansion.
Therefore, the grain size of the Al ₂ O ₃ raw material and the SiO ₂ raw material is preferably 2 mm or less. A normal magnesia clinker has pores having a diameter in the range of 20 to 30 μm, but large pores can be generated by using Al ₂ O ₃ raw material and SiO ₂ raw material having large particle diameters. The larger the pores, the more contributes to the improvement of the spalling resistance, which will be described later. However, if the pores are too large, the penetration of foreign components is promoted and the corrosion resistance is lowered. Therefore, the pore diameter is preferably 50 to 2000 μm.

The magnesia refractory brick according to the present invention is made of a refractory raw material containing an SF magnesia clinker in which the spinel phase or the spinel phase and the forsterite phase are present in the MgO grain boundaries as described above. Then, the SF magnesia clinker is crushed, the compounding material and the binder are appropriately mixed, kneaded and molded, dried, and fired. Firing temperature is 1750 ° C
The above is preferable. The reason is that at a high temperature of 1750 ° C. or higher, the periphery of the refractory constituent particles is melted and a direct bond is formed between the particles, and the formation of the direct bond strengthens the structure of the refractory brick. be able to. Here, the mixing ratio of the SF magnesia clinker in which the spinel phase or the spinel phase and the forsterite phase exist in the MgO grain boundary is 10
It is limited to the range of ~ 79 wt%. If it is less than 10 wt%, spalling resistance cannot be obtained due to the effect of the voids formed in the SF magnesia clinker, and conversely 79 wt%
This is because if it exceeds, the number of voids will increase, which will help the penetration of foreign components and reduce the corrosion resistance.

In the magnesia refractory brick according to the present invention, as a refractory raw material, a spinel phase or a spinel phase and a forsterite phase exist in the grain boundary of MgO.
In addition to the magnesia clinker, the rest is magnesia clinker containing MgO as a main component. It is desirable to use a high-purity magnesia clinker having a MgO component of 99% or more. As a specific example, the MgO raw material mentioned in the production of the SF magnesia clinker can be used. Since the magnesia clinker has a high melting point, its addition provides further corrosion resistance. In order to improve the bondability between the magnesia clinker and the SF magnesia clinker, it is possible to add Al ₂ O ₃ and SiO ₂ to the extent that spalling resistance and corrosion resistance are not impaired.

[0013]

[Function] One of the components constituting the SF magnesia clinker
Part of Al₂O₃And SiO ₂At least one of
Species burned in the manufacturing process of SF magnesia clinker
Spinel together with MgO, which is the main component of the composition at the stage of formation
And forsterite are formed (following formula), MgO + Al₂O₃→ MgO ・ Al₂O₃... 2MgO + SiO₂→ 2MgO ・ SiO₂... Presence of slag in the grain boundary of refractory constituent particles
It At the same time, Al₂O₃And SiO₂The area occupied by
Pores are formed in the area. Therefore, SF mag after manufacturing
With the Nessia clinker, the space around the uniformly distributed pores is
Surrounded by pinel phase and forsterite phase, MgO
(Periclase) Grain boundary in spinel phase and false
It will take the form in which the tellite phase is filled and present.

[0014]

EXAMPLES Examples of the present invention and comparative examples will be described below. Table 1 shows examples of the present invention, comparative examples and test results thereof.

[0015]

[Table 1]

In each example, 2 wt% of a phenol resin as a binder is externally added to and mixed with a refractory material and a compounding material at a compounding ratio (wt%) shown in Table 1, and after kneading with a fret mill, a friction press is used. It was pressure-molded into an ordinary refractory brick. The obtained molded body was appropriately dried and then fired in a tunnel kiln at 1750 ° C. for 7 hours to obtain a test brick. Using the test bricks thus obtained, the physical properties and characteristics shown in Table 1 were evaluated. The test items and measurement methods are as follows. Bulk specific gravity, apparent porosity; ordinary refractory test method (JIS
It was measured according to R2205).

Spalling resistance; 55 from the test brick
Cut out a 55 x 230 mm prismatic test piece,
One side is placed in an electric furnace kept at 1400 ° C. and kept for 15 minutes. Then, the sample was taken out of the furnace and the thermal shock by a heating-cooling cycle of forced air cooling at room temperature for 15 minutes was repeated, and the number of thermal shocks until peeling was evaluated. The spalling resistance is better when the number of thermal shocks before the peeling is large.

Corrosion resistance: Evaluated by the amount of erosion and the slag penetration thickness. That is, a plurality of trapezoidal columnar test pieces were cut out from a test brick, lined in a drum, and while rotating the drum, an oxygen-propane flame was blown in the axial direction of the drum to heat it to 1700 ° C. While maintaining the temperature at 1700 ° C, steel and slag (having a CaO to SiO ₂ ratio of 3: 1) were added as an erosion agent at a ratio of 7: 3, and 3
Erosion was performed for 0 minutes. After discharging the erosion agent, forced air cooling with pressurized air was performed for 20 minutes. The operation from heating by the gas flame to forced air cooling was repeated 5 times. Then, the test piece was cut, and the melt loss amount and the slag permeation thickness were measured by the average value of each part of each test piece.

As is clear from the results of measurement of physical properties shown in Table 1, in Examples 1 to 7, penetration of slag was suppressed and structural spalling resistance was increased, and heat resistant spalling was improved. It can be seen that the spalling resistance and the corrosion resistance, including the properties, complement each other, and the durability based on both characteristics is improved. In particular, regarding corrosion resistance, even if either the melt loss amount or the slag infiltration thickness is a good result, a good operating state in the actual furnace cannot be obtained, and the melt loss amount and the slag infiltration thickness are in equilibrium physical property values. In view of the fact that showing the fact that the durability of refractory bricks is improved,
The thing of Examples 1-7 of this invention is suitable.

In Comparative Example 1, the proportion of SF magnesia clinker A in which the spinel phase is present in the MgO grain boundaries is too high, and the corrosion resistance is inferior to that of Example 1. In Comparative Example 2, conversely, the mixing ratio of the SF magnesia clinker A in which the spinel phase is present in the MgO grain boundaries is small, and both spalling resistance and corrosion resistance are poor.

Comparative Example 3 is a conventional magnesia refractory brick that does not use a magnesia clinker in which a spinel phase or a spinel phase and a forsterite phase are present in MgO grain boundaries, and Comparative Example 4 is a conventional magnesia containing chromium oxide. -Chromic refractory brick. Both do not use the magnesia clinker in which the spinel phase or the spinel phase and the forsterite phase of the present invention are present in the MgO grain boundaries, so that the penetration of slag is larger than that of the examples and the spalling resistance is poor, and particularly The permeation thickness is 28 mm and 33 mm, which are poor.

[0022]

EFFECTS OF THE INVENTION By using such an SF magnesia clinker, the magnesia refractory brick of the present invention has pores distributed in the brick structure, thereby alleviating stress due to thermal shock. As a result, the heat resistant spalling property is improved. Further, since the spinel phase and the forsterite phase are present in the brick structure, penetration of slag is suppressed, structural spalling resistance is increased, and addition of a magnesia clinker containing MgO as a main component also increases corrosion resistance. Therefore, it is suitable for an inner lining material such as a metal refining container that requires particularly excellent heat-resistant spalling resistance and structural spalling resistance. Furthermore, since the magnesia refractory brick according to the present invention is manufactured using a magnesia clinker, the manufacturing cost is low. Further, the mixing ratio of Al ₂ O ₃ and SiO ₂ can be arbitrarily selected so as not to impair the corrosion resistance and the spalling resistance, and it becomes possible to provide a magnesia refractory brick having desired characteristics.

Claims (1)

[Claims] 1. A composition comprising MgO and Al ₂ O ₃ as main constituents, or MgO, Al ₂ O ₃ and SiO ₂ as main constituents, and a spinel phase formed by these constituents or Magnesia clinker in which spinel phase and forsterite phase are present in the grain boundary of MgO: 10-79 wt%, and the balance is a magnesia clinker mainly composed of MgO. .