JPS5820904B2 - Thank you for your understanding. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for sintering dense chromium oxide, particularly to a method for producing a dense chromium oxide sintered body used as a glass refractory.

Conventionally, when sintering a chromium oxide molded body, it has been known that it is relatively easy to sinter it in an atmosphere with low oxygen partial pressure, such as in a hydrogen stream or vacuum, or to densify it by hot pressing. It is being

Namely, Mr. Ownby and Mr. Jungquist (J, ofAm-C) in the Journal of the Ceramic Society of America.
er-8oc, Vol, 55, A9 p, 4
33-436.

(1972), it was fired at 1600°C in a low oxygen partial pressure atmosphere with Co/CO2 gas, and the density was 99.4% of the theoretical density.
However, when fired in air, only about 65% of the theoretical density was obtained.

This situation is clearly understood from the measured physical properties of chromium oxide bricks, which are commercially available as glass refractories, as shown in Table 1 below.

The commercially available chromium oxide refractories shown in Table 1 contain 1 to 4% Ti02, and it is generally known that the addition of Ti02 is effective for densification of Cr2O3. .

Since such dense chromium oxide sintered bodies have low air permeability, they are suitable for use as bricks in glass melting furnaces and the like to adjust the atmosphere, and there is a demand for good quality products.

However, as mentioned above, when sintering a chromium oxide compact with a low oxygen partial pressure, it is troublesome to create an atmosphere with a low oxygen partial pressure, and in some cases, it is difficult to create an atmosphere with a low oxygen partial pressure. It was difficult to form a stable structure.

In view of these shortcomings in the conventional methods for producing dense sintered bodies, the present invention has researched methods to eliminate these shortcomings, and as a result of various studies, has discovered the method for producing dense chromium oxide sintered bodies of the present invention. This is what we provide.

The object of the present invention is to provide a method for obtaining dense chromium oxide sintered bodies such as bricks of various shapes by sintering in air without using a low oxygen partial pressure atmosphere as in the conventional method.

That is, in the present invention, Nb2O5 or/and Ta2O is added to 100 parts by weight of fine chromium oxide powder as a raw material.

By adding 0.5 to 3 parts by weight and a small amount of a binder, and further adding up to 1 part by weight of boron oxide, the mixture is mixed, water is added, pressure molded, dried, and then baked. This is a method for producing a dense chromium oxide sintered body having a specific gravity of 4.1 or more.

(Hereinafter, parts are expressed as parts by weight).

According to the method of the present invention, it is possible to obtain a sintered body having a bulk specific gravity equal to or higher than that of existing commercially available chromium oxide sintered bodies for glass refractories, or by using a special isostatic method or slip casting method. This is an excellent method that allows for easy sintering in air using a normal press molding method without bending.

Of course, a dense sintered body can be obtained by molding the raw material composition of the present invention by a slip casting method or an isostatic method, and this method is also included in the method of the present invention.

In one example of the present invention, a small amount of a binder such as clay is added to and mixed with a normal finely powdered chromium oxide raw material, water is added, and the product is shaped, dried thoroughly, and fired at 1600°C.

Commercially available chromium oxide refractories contain 1.4% (wt%) TiO2, and chromium oxide (Cr20
It was also recognized in the research conducted by the present inventors that the addition of T t 02 is effective for densification in 3).

However, the present inventors discovered that 1 of chromium oxide (Cr203)
It has been found that the addition of 0.5 to 3 parts of Nb2O5 or/and Ta205 to 00 parts of TiO2 is more effective than that of TiO2.

The inventor further found that for 100 parts of Cr2O3, Nb2O
By roughly adding 1 part by weight or less of B2O3 to 0.5 to 3 parts of 5 or/and Ta205, densification is further promoted and a sintered body with a maximum bulk specific gravity of 4.62 can be obtained. did it.

In this way, the present invention sinters chromium oxide molded bodies under normal air pressure, whereas conventionally chromium oxide molded bodies were sintered in a special atmosphere with no oxygen partial pressure or a special atmosphere with extremely low oxygen partial pressure. As a result, it has a bulk specific gravity of 4.62, which is close to the theoretical fine dust.
We have succeeded in producing a chromium oxide sintered body with extremely high density.

Therefore, it becomes possible to manufacture a dense and uniform chromium oxide sintered body that is inexpensive, reliable, extremely easy to operate, and greatly contributes to the refractory industry.

Next, the present invention will be further explained with reference to Examples.

Example 1 Chromium oxide, Nb2O5 and Ta205 used as raw materials
Others such as columbite and boric acid containing

After thoroughly grinding these raw materials, blend them as shown in Table 3.
After dry mixing, add a small amount of water to 150kg/cr? Press molding was carried out at a pressure of t.

Table 4 shows the measured physical properties of the sintered body obtained by drying the molded body and firing it at 1600° C. for 30 minutes.

Tables 3 and 4 are summarized to show the relationship between chromium oxide (Nb
Figures 1 and 2 show the relationship between the addition percentage of 2O5+Ta205), the addition amount of B2O3, and the bulk specific gravity of the sintered body, and Figure 1 shows the effect of addition of B2030 to 0.3%.

a-curve-(Nb205+Ta205) addition amount 1.3
7% b-curve = (Nb20.+Ta203) addition amount 2.
05% C-curve = (Nb205 + Ta205) Addition amount 0.60% d-line - Bulk specific gravity 4.1 Limiting line The numbers on each curve in both figures are the sample numbers in Tables 3 and 4. This corresponds to

The e-curve in Figure 2 shows the amount of B2O3 added in the a-curve changed to 1.0%;
This is a curve showing the optimum addition amount.

From these results, the effect of Nb2O5 + Ta205 gives the maximum bulk specific gravity when 1.37 parts are added to 100 parts of chromium oxide, and the effect decreases if the amount is more or less than this, and the lower limit is approximately 0. .5 parts, with an upper limit of approximately 3 parts.

The bulk specific gravity of the sintered compact targeted by the present inventors is approximately 4.
1 or higher, it showed excellent compactness, which was shown by the d-line.

In these cases, B2O3 exhibits its effect as shown in FIG. 1 even when added in an extremely small amount, and the increase in bulk specific gravity shows a sharp curve starting from 0%.

As is clear from Figure 2, this upper limit is 1.0%, which is 0.
．． The maximum is around 4%, but even at 0%, a specific gravity of 4.27 can be obtained.

Example 2 Using the raw materials used in the above-mentioned sister example 1, a dish-shaped brick-shaped molded body was produced in the same manner using a raw material composition of A6 at a molding pressure of 200 kg/i.

After drying, the temperature was raised to 1600° C. at a rate of 10° C./min, maintained at 1600° C. for 1 hour, and then cooled in a furnace. Table 5 shows the custom-made sintered bodies obtained.

It was an excellent dense sintered body with a bulk specific gravity of 4.58.

These examples use columbite as a raw material for Nb2q and Ta205, but pure Nb205Ta
Since 205 does not contain any impurities, it goes without saying that a chromium oxide sintered body of higher quality can be obtained.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams illustrating the measured values of Example 1, and show the relationship with the bulk specific gravity of the sintered body of the three-component system of Cr205-Nb2O5+Ta205-B2O3. Each curve is expressed as a percentage relative to 100 parts of chromium oxide. a-curve = (Nb20., +Ta203) addition amount 1
．． 37% b-curve = (Nb205 + Ta203) addition amount 2.05% C-curve = (Nb205 + Ta203) addition amount 0.60% d-line = bulk specific gravity 4.1 limiting line e-curve - B2030 to 1 of the a-curve .0% addition curve.

Claims (1)

[Claims] 1 Nb2 per 100 parts by weight of raw material chromium oxide fine powder
Add 0.5 to 3 parts by weight of O5 or/and T a 205 and a small amount of binder, and further add 1 part by weight or less of boron oxide, mix, add moisture, pressure mold, dry, and then , bulk specific gravity 4 characterized by firing
．． A method for producing one or more dense chromium oxide sintered bodies.