JPS6016866A - Graphite-containing refractories - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a refractory having extremely excellent corrosion resistance as a refractory for a kiln.

At present, typical kilns for desulfurization, dephosphorization, and desiliconization of hot metal use a ladle and a mixing wheel.

The case where a pig iron mixer car is used will be explained below, but the pig iron mixer car has conventionally been used as a conveyor container for hot metal.

However, recently, treatment agents such as Na, Co, and OaO (CaF2) are injected into the kiln through a lance pipe for desulfurization, dephosphorization, and desiliconization, and the furnace is used as a smelting furnace. Therefore, it has become impossible to obtain a stable furnace life with conventional refractories such as waxite, high-grade clay, and high-alumina bricks.

For this purpose, carphone-containing refractories such as alumina-carphone materials and non-magnetic carbon materials have been developed and applied. In other words, alumina (Al2O
,), magnesia ('go), spiru (MgO
- A.J. 203) can be mentioned. However, in order to exhibit the corrosion resistance of the surface-coated material in relation to /θθ, it is necessary to suppress the inclusion of impurities as much as possible, and it is particularly desirable not to include impurities in the IJ section. However, refractories based on alumina, Mag Z, shea, and spinel are very susceptible to thermal spalling under conditions of hot metal pretreatment operations.

That is, cracks occur on the surface due to temperature changes and thermal stress during use, resulting in peeling! It has the disadvantage that the phenomenon is likely to occur. For example, alumina has a hot linear expansion coefficient of /θoo°C and θ. High ff6% and thermal conductivity of 1000℃
"Wmhr℃" is relatively small. This is because the characteristic values inside the refractory differ greatly between the working surface and the back during use, and therefore the generated thermal stress is large and thermal spalling is likely to occur. Graphite is used to improve the thermal spalling properties of various types of materials.That is, graphite is added in the usual form, but the coefficient of hot linear expansion of graphite is about half that of alumina, and the thermal conductivity is 20 times that of alumina. It has extremely high and excellent heat spalling resistance.

In this way, unfired refractories are used that are based on refractory materials such as alumina, magnesia, and spinel, and have graphite added thereto to improve heat spalling resistance.

However, graphite inherently has extremely poor corrosion resistance against soda-based fluxes, etc., and the quality of refractories deteriorates due to oxidation of the stale graphite.

For example, in alumina-carbon refractories, the matrix portion is worn out in advance, resulting in a decrease in corrosion resistance. For these reasons, it has been concluded that the amount of graphite involved in reducing corrosion resistance should be minimized as much as possible.

However, in order to suppress thermal spalling by adding conventional graphite, the following problems occur when the amount of graphite added decreases, and the cause was determined by detailed analysis of used refractories.

In other words, the decrease in the amount of graphite added is due to the non-uniform distribution of graphite within the structure of the refractory, and during use, the alumina grains without graphite are directly bonded to each other due to the influence of heat reception, and the alumina grains on the refractory structure are bonded directly. It was found that the effect of suppressing thermal spalling was not sufficient due to the formation of an integrated structure of HjIJ.

As a countermeasure to this problem, we discovered that by peeling commercially available laminated graphite into thin layers and adding the thin layers, it was possible to uniformly disperse the graphite.

In this case, the particle size of graphite can be determined by the specific surface area.

Specific surface @tsOθcm2/, when using the above, 5
It is possible to provide sufficient thermal spalling properties with a carbon blending ratio of -25% by weight.

As mentioned above, the specific surface area of graphite is limited to /S(:l(7-4 or more) because the ideal shape of graphite is to make the Q axis as thin as possible, and it is better for the a@B axis to be as long as possible.

Therefore, it is not appropriate to control by particle size, but it is better to control by specific surface area.

Next, adjust the amount to 5-. The reason why it is limited to 25% by weight is that if graphite exceeds 25% by weight, refractory materials such as alumina and magnesia that are involved in corrosion resistance decrease, and the corrosion resistance of the entire refractory decreases.

In addition, if the amount is less than 5% by weight, the effect of suppressing thermal spalling cannot be obtained. The fireproof materials of the present invention include conventional metal materials such as alumina, spinel, magnesia, silicon carbide, AJ, AJ-Fe, and silicon nitride. After kneading and molding the refractory aggregate containing 5 to 25% by weight of scaly graphite with a specific surface area of 7 g 00 cm"7 or more, using refractory material of , drying (unfired)
Alternatively, it is fired after drying.

Example/Example/-/-/-5 and Comparative Examples/-6 to/- obtained by kneading and drying at the blending ratio shown in Table 1
1. Line the erosion testing apparatus shown in FIG. In Fig. 7, A is the unfired refractories of Examples and Comparative Examples, and B is
indicates slag, and C indicates oxygen-propane combustion gas.

FIG. 2 is a cross-sectional view taken along line M-11 in FIG. 1, where A indicates the unfired refractories of Examples and Comparative Examples, and B indicates slag.

The test conditions for thermal spalling and corrosion resistance tests using an erosion testing device are Na2O/EliO! expressed as oxides.
= Using a slag with a composition of j/! ; Heated at 00°C for 5 hours. , the rotation speed of the device is λ-rpm
It is. The test results are shown in Table 1 and Figure 3. FIG. 3 shows the corrosion state of the cut surface when the sample was cut at I-1 in FIG. 2, and from this it can be seen that the corrosion resistance was better as the amount of graphite was reduced. It can be seen that the comparative sample had a large amount of erosion and thermal spalling cracks, and it was found that the amount of graphite added should preferably be in the range of 5 to 25%.

EXAMPLE An actual furnace test unfired refractory was prepared using the compounding ratios shown in Table 2, and actual operation was carried out in a 250 ton pig iron mixed car slag line. The operation is a desulfurization operation using OaO-based treated materials.

As shown in Table 2, the obtained results showed that the corrosion resistance was about 20% superior to Comparative Example λ-+ (conventional product), and there was no thermal spalling or peeling damage due to thermal stress.

[Brief explanation of the drawing]

Figure 1 is an erosion test device, Figure 2 is a cross-sectional view taken along I-4 in Figure 1, and Figure 3 is a cross-sectional view taken along II-x in Figure 2 of the sample after the erosion test. It is a figure showing the state of erosion of the cut surface. In the diagram: A... (Example or Comparative Example) Refractory B... Slag C... Oxygen-propane combustion gas patent applicant Shinagawa Shiro Brick Co., Ltd.

Claims (1)

[Claims] 5 to 2 pieces of scaly graphite with a specific surface area of 7300 am'/1 or more
A graphite-containing refractory, characterized in that a refractory aggregate containing 5% by weight is kneaded, molded, dried, or fired after drying.