JP2545238B2 - PH-adjustable refractory fine powder for castable refractories - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a refractory fine powder blended with a castable refractory.

[Prior Art] In recent years, a castable refractory has been developed which uses a small amount of alumina cement and uses refractory fine powder as a binder, and is widely used in various kilns due to its excellent properties.

However, as the refractory fine powder as a binder, mainly used is so-called silica flour, which is a by-product generated during the production of ferrocilicon, metallic silicon, and zirconia, but the flour is easy to absorb moisture and has a quality. Unstable, pH
The values of 2 to 10 greatly vary, and there is a problem that the curing time and pot life after hydro-kneading are unstable. This silica flower can avoid the above-mentioned phenomenon to some extent by using only those having a pH of about 2 to 4 in the summer, but it is difficult to secure a raw material having a limited pH because it is a by-product.

As one method of improving such problems, JP-A-61-158872 discloses that the pH of silica flour is adjusted to 3.5 to 8.5 before use. In this method, the pH is adjusted by mixing two or more types of silica flour and surface-treating the silica flour with an acid or an alkali. However, this requires that several types of silica flour with different pH be always provided, and Silica flour is so fine that it is difficult to mix it homogeneously. In addition, if the surface treated with acid or alkali is used immediately after preparation, there is no problem, but it changes with the passage of time and the secondary particles become difficult to be crushed.

[Problems to be Solved by the Invention] The present invention relates to a refractory fine powder of a castable refractory which uses a small amount of alumina cement and uses the refractory fine powder as a binder, and has an appropriate and stable pot life and curing time. The present invention provides a refractory fine powder which can be crushed by kneading in a short time while having a low hygroscopic property while being adjusted to a proper one.

[Means for Solving Problems] That is, the pH-adjustable refractory fine powder for castable refractory of the present invention is obtained by mixing and dispersing refractory fine powder (excluding silica flour) having an average particle diameter of 1 to 10 μm in an aqueous acid solution, It is an acidic fine powder obtained by drying.

The refractory fine powder used in the present invention is preferably neutral or acidic one such as alumina, mullite, titania or chromium oxide. The average particle size of such fine powder is 1-10μ
In terms of stability, it is preferable to use a processed product such as a sintered or electrofused product rather than a natural one. When the average particle size is 10 μm or more, the specific surface area becomes small and the amount of acid content supported per unit weight of the particle decreases, and as a result, a large amount of refractory fine powder is required to adjust to the predetermined pot life and curing time. It will adversely affect the composition and structure of refractories. The average particle size is 1 μm
Below, the agglomeration of secondary particles becomes strong and it becomes difficult to disintegrate during kneading.

The acid for adjusting the pH, phosphoric acid, inorganic acids such as boric acid, citric acid, oxalic acid, malic acid, ligninsulfonic acid, polyacrylic acid, any of these salts and organic acids such as gluconic acid Can be used.

Refractory fine powder A certain amount of acid solution and water are mixed to obtain a desired pH and adjusted to a slurry of a certain concentration by stirring with a disperser, stirrer, etc. until sufficiently dispersed, then , Spray dryer, band dryer,
The refractory fine powder adjusted to a desired pH is obtained by drying by a method such as vacuum drying.

[Example] (Example 1) The pH value of the alumina fine powder to be adjusted was set to 2.70.

1 kg of fused alumina fine powder having an average particle size of 5 μm, 50 g of a 85% phosphoric acid solution and 500 g of water were mixed and stirred with a stirrer until sufficiently dispersed. About 300 of this slurry
Spray drying was carried out at ℃ to obtain a pH-adjusted granulated powder. When the pH of this powder was measured at n = 10,
There is very little variation from 2.68 to 2.73, which is close to the set pH value.

(Example 2) The alumina fine powder obtained in Example 1 and silica flour whose pH value was adjusted to 2.70 by the same method for comparison were used for 1 week at a humidity of 55% and a temperature of 30 ° C, respectively. Weekly 4
The amount of moisture absorption after a lapse of weeks and the disintegration property and the curing time when this powder was compounded and used in a castable refractory were examined. Regarding the amount of moisture absorption, the results shown in Fig. 1 were obtained. The results shown in Table 1 were obtained for disintegration and the like.

[Effects of the Invention] As described above, in a castable refractory in which the amount of alumina cement is reduced and refractory fine powder is used as a binder, when the product of the present invention is used as a compound,
The refractory fine powder of the present invention has a considerably low hygroscopicity, is hard to congeal even after a lapse of time, and thus has good storage stability, and is crushed by kneading for a short time during use. In addition, by adjusting the pH of the refractory fine powder to a desired acid value, it is effective to adjust the pot life and curing time of the castable refractory material to an appropriate and stable one.

[Brief description of drawings]

The drawing is a graph showing changes in the amount of moisture absorption of the product of the present invention and the conventional product over time.

Claims (1)

(57) [Claims] 1. A pH control for a castable refractory characterized by acidic fine powder obtained by mixing and dispersing refractory fine powder (excluding silica flour) having an average particle diameter of 1 to 10 μm in an aqueous acid solution and then drying. Refractory fine powder.