JPH0229615B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to heat-resistant inorganic fibers. The most common type of heat-resistant inorganic fiber is what is usually called ceramic fiber, which is made of alumina and silica, has a glassy quality, and has an average diameter of about 3 μm. In recent years, energy saving measures have been taken in various industrial furnaces due to the need to save oil, and the adoption of ceramic fibers for furnace walls has rapidly become widespread and has achieved corresponding results. It is also true that accidents have occurred in furnace walls using ceramic fibers, such as delamination, opening of joints and cracks, and partial or complete collapse of furnace walls and ceilings. Looking into the cause of these accidents, we found that the heat resistance of the ceramic fiber products used did not reach the level required by the environmental conditions in which they were used; in other words, the usage conditions were not suitable for ceramic fibers. The conclusion has often been that it is too harsh. Ceramic fiber is a glassy material, so when heated, it transforms into a more stable crystal structure.
As a result, the fibers shrink and their strength deteriorates, causing shrinkage and a decrease in elasticity of the ceramic fiber product, which is an aggregate of these fibers. There are many publications and documents regarding this phenomenon, but the most representative ones are Leonard E. Olds and William C.
Miller, John M. Pallo, “Hish Temperature
Alumina−Silicate Fibers Stabilized with
_{Cr2O3 Ceramic} Bulletin, 59 , 7, 739-741
(1980). Olds et al. conducted a comparison between a conventional alumina-siliceous ceramic fiber and a ceramic fiber containing 3 to 4% chromia (chromia stabilized ceramic fiber), and investigated the deterioration of the ceramic fiber and the stabilizing effect of chromia. and its effects were clarified. As a result, we discovered the remarkable fact that the effect of chromia is not to delay or prevent fiber crystallization, but to prevent sintering that occurs at the contact points between fibers, which was previously thought. The theory that crystallization causes the deterioration of fibers and their aggregates has been overturned. However, although the chromia-containing alumina-silica ceramic fiber tested by Olds et al. had better heat resistance than the conventional alumina-silica fiber, it still satisfies the severe usage conditions required today. It is difficult to say that it is something that can be adapted. Therefore, today, crystalline fibers made by a completely different method have no choice but to be used where necessary, even though they are expensive. This product is composed of microcrystals, such as those manufactured by Imperial Chemical of the UK.
Industries Ltd.'s alumina fiber called "Safil" and the applicant's company's mullite fiber called "Fibermux". Figure 1 shows the thermal expansion and contraction rates (fiber length line change rate) of these chromia-containing ceramic fiber B and mullite crystalline fiber C in comparison with alumina-siliceous ceramic fiber A. .
In this experiment, a weight was hung from the end of each fiber to keep it vertical, and the temperature was raised at a heating rate of 3°C/min to measure the expansion or contraction rate of each fiber. It is something. As is clear from FIG. 1, both the alumina-siliceous ceramic fiber and the chromia-containing ceramic fiber undergo rapid fiber shrinkage at around 950°C. In contrast, 1000 for mullite crystalline fiber.
℃, there is almost no expansion or contraction, and at 1400℃ it is approximately
It has expanded by 3.3%. In order to investigate the cause of shrinkage in alumina-siliceous ceramic fibers, the inventors conducted numerous experiments.
As a result, it was recognized that this is closely related to the crystallization of mullite crystals, and it was concluded that any composition that causes the crystallization of mullite would not be able to prevent the rapid shrinkage of fibers at 950℃. . Therefore, the inventors conducted further research, and first, they focused on the fact that silica glass has less decrease in viscosity at high temperatures and is more stable than other heat-resistant glasses. As a result of repeated experiments, we discovered that a raw material with a basic composition in which oxides of metals belonging to Groups 5 to 8 of the fourth period of the periodic table were blended with the quartz glass was equivalent to or better than the conventional one. It has been found that the above heat-resistant fibers can be obtained. Furthermore, it was confirmed that by using the above raw materials, the same process and equipment as used for manufacturing conventional ceramic fibers could be used, and this invention was finally completed. That is, this invention can be applied to V, Fe, Co, Ni, Cr, Mn.
4 to 30 mol% of one or more oxides of
70-90 mol% silica, CaO, MgO, _TiO2 ,
It is a heat-resistant inorganic fiber containing 0 to 26 mol% of one or more types of Al ₂ O ₃ and having a uniform glassy appearance throughout. This invention will be explained below. The basic ingredients of the present invention are silica and a metal belonging to Group 4 or Group 4 of the periodic table, namely V,
These are oxides of Cr, Mn, Fe, Co, and Ni (hereinafter referred to as metal oxides). By mixing 4 to 30 mol% of this metal oxide with silica, the heat resistance of the fibers is greatly improved and the molten silica is given electrical conductivity. That is, silica has a large electrical resistance even in a molten state, but by blending the metal oxide with it, it can be imparted with electrical conductivity and can be easily melted in an electric furnace. When silica is less than 70 mol%, the amount of metal oxide and the third component described below increases, and conversely, the amount of silica decreases, resulting in a decrease in the stability of the glass and the tendency for metal oxide crystals to crystallize. As a result, a large amount of shots are produced and the yield of fibers is reduced. Also, heat resistance becomes poor. On the other hand, if the silica content exceeds 90 mol%, the viscosity of the melt increases and the melt cannot flow out from the electric furnace. In the fiber obtained by the present invention, at room temperature or before it is heated, most of the metal oxides constitute one component of glass or are in a state of being fused in quartz glass,
Only a small amount exists as a solid phase. Therefore, there is no problem in adding a third component to the raw material which serves to stabilize the glass without significantly impeding the heat resistance of the glass made of metal oxide and silica. Such third components include calcia (CaO), magnesia (MgO),
There are one type or a combination of two or more of titania (TiO ₂ ) and alumina (Al ₂ O ₃ ), and when these are used with the amounts of metal oxide and silica within the above-regulated ranges, appropriate effects can be obtained. demonstrate. The above raw material mixture is made into fibers in exactly the same manner as in the production of conventional ceramic fibers. That is, raw materials are melted in an electric furnace having a structure as disclosed in U.S. Pat. The material is then blown away with air or steam to form fibers. The structure of the present invention is as described above, and the obtained ceramic fiber is either a conventional alumina-silica ceramic fiber or an alumina-silica fiber containing chromia as a raw material as disclosed in U.S. Pat. No. 3,449,137. The heat resistance was clearly improved compared to high-quality ceramic fiber. The tests used by the present inventor to confirm the effects of the present invention include a simple heat resistance test using a cigarette lighter, measurement of the fiber length change rate, and a blanket linear shrinkage test. First, a simple heat resistance test using a cigarette lighter involves bringing heat-resistant fibers directly close to the flame of a cigarette lighter. By this test, all the conventional alumina-silica ceramic fibers shrink from the ends and become invisible, so that the superiority or inferiority of the products of the present invention and the conventional products can be easily determined by this test. The next measurement of changes in fiber length involves measuring the expansion and contraction of a single fiber while heating it. In order to keep the fibers vertical, fibers with shots attached to their ends are selected and used as weights.Fibers without shots are coated with coating cement by suspending fine ceramic fiber powder in coiled silica liquid. A drop of was applied to the tip and dried. Finally, to measure the linear shrinkage rate of the blanket product, some of the fiber samples were stirred in water to remove most of the shots, and then formed into a blanket using a conventional method, and the linear shrinkage rate was measured. The present invention will be further explained by showing examples below. Example 1 (When chromia is used as the metal oxide) As raw materials, the silica source is Australian Fremantle silica sand, the chromia is Aecrox-R (trade name) manufactured by Pfzer-Quigley, and the alumina is A- manufactured by Sumitomo Chemical. 21 (trade name), and other commercially available industrial chemicals were used. The above raw materials are melted in an electric furnace with a tap width of 25 mm,
While the electric furnace was tilted and the melt gradually flowed out, it was blown away with compressed air using a nozzle shown in US Pat. No. 3,426,324 to form fibers. The compressed air was 750Kg/cm ² and the capacity was 10m ³ /min. The fibers were collected in a collection room surrounded by metal. The amount of fiber shots was relatively small, and as a result of X-ray diffraction analysis, no crystalline material was observed. Take a part of the fiber and bring it close to the flame of a cigarette gas lighter.If there is no visible shrinkage even in the flame, it is rated as "excellent."Slight shrinkage is observed, but it is better than conventional ceramic fiber. However, those that were recognized to have a significantly lower level of severity were rated "good." In addition, the softening temperature, blanket shrinkage rate, etc. were also measured and the results are shown in Table 1. The measurement results of the rate of change in fiber length are shown in FIGS. 2A to 2K.

【table】

[Table] Example 2 (When the metal oxides are chromia and iron oxide) Chromium ore from India was used as the metal oxide. The chemical analysis values were as follows.

[Table] Other than this, fibers were made in the same manner as in Example 1.
The test was conducted in the same manner as in Example 1. The results are shown in the table below.

[Table] The measurement results of the fiber length change rate are shown in Figure 3 a to h. Example 4 (In the case of other metal oxides) Examples 1 and 2 using cobalt oxide, vanadium pentoxide, nickel oxide, and iron oxide as metal oxides
conducted a similar experiment. The results are shown in Table 4. Incidentally, No. 5 and No. 6 contained silica which was not within the scope of the present invention and were shown as comparative examples. Moreover, these fiber length change rates are shown in FIG.

【table】 [Brief explanation of drawings]

Figure 1 is a diagram showing the rate of change in fiber length (%) with respect to temperature change for alumina-siliceous ceramic fiber A, chromia stabilized ceramic fiber B, and mullite crystalline ceramic fiber C; Figures 2 A to K; Figures 3 a to h are graphs showing the fiber length change rate (%) with respect to temperature changes for ceramic fibers according to the present invention. FIG. 2 is a diagram showing the percentage change in fiber length with respect to temperature change of ceramic fiber. The above E and F are diagrams showing the fiber length change rate with respect to temperature change of the ceramic fiber shown as a comparative example of the present invention.

Claims (1)

[Claims] 1 4 to 30 mol% of one or more oxides of V, Fe, Co, Ni, Cr, Mn, 70 to 90% of silica
1. A heat-resistant inorganic fiber containing 0 to 26 mol % of one or more of CaO, MgO, TiO ₂ , and Al ₂ O ₃ by mol %, and having a uniform glassy appearance as a whole.