FI93347B - High temperature-resistant refractory fibre which has an improved resistance to shrinking - Google Patents

Abstract

A composition for producing a refractory fibre which tolerates high temperatures and alkalis. The composition of the mixture by weight is 46 - 52% silicon dioxide, 32 - 38% aluminium oxide and 13 - 18% zirconium oxide, and the ratio between the silicon dioxide and the zirconium oxide is within the range 2.6 - 3.8. The maximum functional temperature of these fibres is within the range 1400 degree C (2550 degree F) - 1455 degree C (2650 degree F), and their shrinkage resistance is better than that of corresponding commercially available refractory fibres within the same functional range. <IMAGE>

Description

93347

The invention relates to a high-temperature refractory fiber, which has improved shrinkage resistance. Högtemperaturbeständig eldfast fiber, somhar förbättrad motständ av krympning 5 (separated by application 845077, requested from 20.12.1984). The invention also relates to use of fibers.

BACKGROUND AND SUMMARY OF THE INVENTION To date, most of the work in developing synthetic inorganic fiber, which is suitable for use in reinforcing cement-type matrices, has been accomplished in the field of glass fibers. As the word is used herein, the term "glass" means not only the glassy or non-crystalline structure of the resulting fiber, but also a mixture containing one or more fluxes, which is generally an alkali metal oxide. The function of these fluxes is to reduce the melting temperature of the mixture, which makes the mixture more fibrous by methods such as continuous drawing and fiber formation by rotation (pressing through holes in a rotating disk). At the same time, however, these fluxes tend to reduce. the chemical inertness of the fiber and its operating temperature. In applications where both chemical and temperature resistance are required (e.g., in the reinforcement of a cementitious product of heat treatment), glass-30 fibers containing alkali metal oxide fluxes may lose 35% or more of their tensile strength with this consequent reduction in reinforcement efficiency in the cement matrix. This results in a decrease in the fracture modulus of the resulting fiber / cement product (i.e., a direct decrease in strength in this reinforced product).

It should be noted that the high temperatures (150 ° C-600 ° C) involved in curing processes not only accelerate the chemical combination of silica and lime and the evaporation of organic fiber and excess 35 2 93347 water, as intended, but also accelerate other chemical reactions such as reinforcing fibers in this matrix from alkaline or acid etching. As a result, a fiber that may be chemically resistant to an alkaline situation and can withstand a temperature of 260 ° C (500 ° F) outside of this situation may still not be able to tolerate the combination of these conditions.

Zirconium oxide (ZrO 2) has been widely used as an additive in glass alloys as a means to increase its alkali resistance. In this regard, 10, for example, U.S. Patents 3,859,106; 3,966,481; 4,036,654; 4330628. In addition, zirconia alone or as the predominant component has been used to form refractory alloys at relatively high operating temperatures. In this regard, reference should be made to U.S. Patents 2,873,197; 2,919,944; 3,035,929; 3,754,950; 3,793,041; 15 4,053,321 and 4,119,472. However, as stated earlier, the suitability of one component for chemical and temperature resistance, independently of the other, still does not guarantee that the mixture in which this component is used will have the necessary combined chemical and thermal resistance. The simultaneous combination of a chemical and a thermal effect can create a highly corrosive situation. In fact, it was precisely the zirconia-containing, seemingly alkali-tolerant glass that just proved unsatisfactory for this purpose. Further studies carried out to carry out the present invention proved this by showing that not all blend compositions of the components used to make these fibers provide the desired thermal tolerance.

The fiber of the invention is characterized in that said fiber in pulp or felt form has improved shrinkage resistance of less than 11.5% after exposure to temperatures up to 1482 ° C (2700 ° F) for about four hours to form a refractory fiber composition. weight:

SiO2 46-52% 35 Äl203 32-38%

ZrO 2 13-18% n 3,93347 and wherein the ratio of silica to zirconia is in the range 2.6-3.8.

In researching the range of silica / alumina / zirconia fibers in search of substances with a specific combination of properties 5 chemical and thermal resistance, Applicants have invented a refractory fiber composition that produces a fiber that is slightly less chemically resistant but significantly more temperature tolerant. A number of previously known fibers have been sized by manufacturers to range from 1425 ° C (2600 ° F). Comparative experiments on shrinkage performed compared to these competing fibers show that the fibers of this invention are more temperature tolerant. In addition, this composition provides a higher amount of melt per the same amount of energy input, as well as a higher percentage of recovered fibers per batch of molten weight of batch than that obtained with conventional alumina / silica refractory melts.

These and also other features, advantages and features of the present invention can be better understood by reading the detailed description below.

Description of the drawings

Figure 1 is a triaxial drawing showing the amounts of silica, alumina-1'din and zirconia for the chemically and thermally resistant fibers of this invention. The points marked Z1-Z12 and B1-B7 are actual test melt cases and P1 and P2 are two production experiments.

Fig. 2 is a three-axis diagram illustrating the composition of a high temperature refractory fiber according to the present invention.

Figure 3 is an enlargement of a portion of the triaxial diagram of Figure 2 showing the region in question, as well as a series of production trials 35 for this high temperature composition.

4,93347

Detailed description of preferred embodiments

Fiber-reinforced cement-type products with a calcium silicate matrix are manufactured for a number of commercial applications that require thermal tolerance and structural strength.

One such high density calcium silicate product is marketed under the tradename MARINITE, manufactured by Manville Building Materials Corporation. One use for MARINITE is in the manufacture of molds for casting molten metals. At one time, these cement-10 type sheets were reinforced using amosite asbestos as fibers (cf. U.S. Patents 2,326,516 and 2,326,517). The health problems, both real and imagined, associated with asbestos fibers have led to the study of other fibers as suitable replacement reinforcing fibers for calcium silicate matrices. Suitable compositions using up to 40% by weight of wollastonite fibers and up to 15% by weight of the sheet of alkali-resistant glass fibers were developed from the mid to late 1970s (cf. U.S. Patents 4,111,712 and 4,128,434).

The use of these AR (AR - alkali tolerant) glass fibers with an average fiber diameter of 12 (or 20) microns

necessary to incorporate 5% of the amount of organic fiber material of the pulp as a facilitator of the treatment in order to improve the formability of the slurry mixture, to slow down the drying and to provide a high strength. Curing of these plates requires • 25 autoclaving (steam curing at 165 ° C).

(330 ° F) and 7 aty (100 psi)) to accelerate the silica / calcium hydroxide reaction. In addition, the organic fiber must be burned using a heat treatment of 290 ° C, 480 ° C or 600 ° C. The commercially available alkali-resistant (AR) glass used to reinforce these sheets has a composition of SiO 2 to 61%, ZrO 2 to 10.5%, Na 2 O to 14.5%, K 2 O to 2.5%, CaO to 5% , TiO 2 - 6.0%. The experiments showed that after curing, these sheets reinforced with AR glass fibers retained in some cases less than 70% of their fracture modulus and / or their specific strength (fracture modulus compared to a density of 35 square MR / D2). Such results showed breakage of some of the fibrous reinforcing components of the fibers, and further analyzes showed that it was AR glass that had failed. Chemically resistant refractory fiber was thus sought as a substitute for this AR glass.

5 Initially, four compositions (Z1-Z4) were experimentally tested (compare Figure 1) in search of a fiber with the desired properties. Formulation of the compositions was planned and the components were added in the desired proportions to a 90 cm (3 ft) and 48 cm (19 inch) deep test melter. The compositions of matter were electrically melted with the melt stream 10 coming out through the nozzle orifice and hitting a pair of spinning devices with a diameter of 20 cm, which rotate at 12,000 rpm.

This produces fibers that are typically 2-7 microns in diameter, 1-25 cm (h-10 inches) in length (5-8 cm average), and had varying grain contents (typically 35-45%). These fibers were collected and analyzed to confirm the composition and 1 gram samples of these different fibers were boiled in 0.1 N NaOH solution for one hour, dried and weighed to determine the percentage weight loss. The results of these experiments are shown in Table I.

20

TABLE I

Composition (% by weight) 25 Fiber identification SiO 2 Al 2 O 3 ZrO 2 SiO 2 / Al 2 O 3% by weight loss Z1 50.0 43.0 6.7 1.16 8.2 Z2 47.3 40.1 12.2 1.17 4.6 Z3 50.1 34.6 15.0 1.45 3.3 30 Z4 59.1 25.9 14.6 2.28 2.2 1300 ° C Std RF 53.8 46.0 - 1.19 7, 8 In addition, thermal tests were carried out on these fibers to identify those candidates with the best refractory properties. The pulp was vacuum formed into a felt for each composition tested. Certain sections of these fibrous felt samples were accurately measured, placed in a refractory oven for a specified time and at a specified temperature, allowed to cool, and then remeasured. These results are shown in Table II and in addition the pour rate (i.e., defibering rate), average fiber diameter, and melt fraction are included. These shrinkage rates are lower than for the production felt because the felting has removed some of the shrinkage of the clearance spaces that occurs with the production materials (i.e., these test samples have higher than normal densities).

10

TABLE II

1300 ° C Std 1425 ° C STD * Z1 Z2 Z3 Z4

Pouring rate 15 (kg per hour) - - - - 544 249 420 454

Average fiber diameter (microns) 2.8 3.5 1.9 2.4 3.7 4.7

Grain content (%) 40-45 40-45 48.6 41.5 30.4 40.1

Linear shrinkage 20 (%) a. 1300 ° C - 112 hours 3.7 - - 3.2 2.7 2.2 b. 1425 ° C - 24 hours - - 3.15 4.15 3.5 2.3 4.15 c. 1425 ° C - 125 hours - 3.70 4.2 3.5 2.3 4.25 d. 1480 ° C - 24 hours - - 6.1 7.3 6.8 3.2 9.2 e.

1480 ° C - 125 hours - - 10.1 8.0 7.6 3.7 This fiber composition is disclosed and claimed in U.S. Patent 3,444,137 and has a composition of 40-60% silica, 35-55% alumina and 1-8% chromium oxide. The specific fibers used in these experiments contained 43.5% silica, 55% alumina and 1.5% chromium oxide.

The results of these experiments show that Z3 had the best thermal performance and acceptable alkali resistance, while * 35 Z4 had the best alkali resistance and acceptable (disregarding the 1480 ° C reading) thermal behavior. It was now decided that the type of fibers should be further investigated in order to optimize the thermal behavior based on the Z3 composition.

It was now believed that the addition of alumina and / or zirconia to the Z3 composition would improve fire resistance.

Accordingly, a set of fibers (B1-B7) was produced based on the composition of Z3 using said 90 cm (3 ft) test melter according to the procedures outlined above. These compositions are shown in the triaxial diagram of Figure 1. These fibers were then subjected to a series of alt-10 temperatures at different times in a refractory furnace to determine the refractory. The results of these experiments and the compositions of substances B1-B7 are shown in Table III.

TABLE III

15 Z3 B1 B2 B3 B4 B5 B6 B7

Components (% by weight)

SiO 2 50.1 31.3 38.9 38.3 35.3 27.6 34.1 27.6 20 Al 2 O 3 34.6 53.2 45.5 41.3 48.2 53.1 55.0 58 4

ZrO 2 15.0 15.3 15.2 20.2 16.2 19.1 10.6 13.7

SiO 2 / Al 2 O 3 1.45 0.59 0.85 0.93 0.73 0.52 0.62 0.47

SiO 2 / ZrO 2 3.34 2.046 2.559 1.896 2.179 1.445 3.217 2.015 Temperature / time Linear shrinkage (%) '25 1200 ° C / 24 h 1.94 2.72 - 2.92 3.01 3.52 2, 83 1300 ° C / 24 h 2.47 2.83 - 2.63 2.80 4.50 2.20 1424 ° C / 48 t 2.94 2.94 - - 2.90 3, 64 4.69 3.23 1480 ° C / 24 h 3.42 4.07 5.94 6.34 4.79 4.22 3.68 3.06 1480 ° C / 100 t 4.7 5.1 10 4.9.6 7.1 4.8 6.8 3.9 30 1480 ° C / 260 t 5.4 6.0 14.5 12.7 9.3 5.2 8.8 4.9 1535 ° C / 24 t +50.0 13.8 19.4 19.6 20.0 14.2 19.3 10.5

Although these experiments succeeded in providing a fiber with approximately 10% shrinkage at 1538 ° C (2800 ° F) as opposed to 35 50+% with Z3, these experiments did not result in the formation of a commercially good fiber. First, all of these high alumina 8,93347 compositions (B1-B7) were significantly more difficult to fiberize than substance Z3. Second, all of these fibers exhibited a low degree of thermal stability at temperatures above 1093 ° C (2000 ° F). Fibers B1, B5, and B7 migrated away from the vitreous and lost fiber-5 character at temperatures between 1050-1300 ° C (2000-2400 ° F). Such behavior precludes their use as insulation, high temperature reinforcing fiber, or in any other industrial use. The deterioration in the quality of fibers B2, B3, B4, and B6 was less severe, but these fibers still have a linear shrinkage rate of 8-15% for 10 hours 260 hours after exposure to 1482 ° C (2700 ° F). Such high shrinkage rates also make these fibers unacceptable for any commercial application.

It should also be noted that none of these fibers (B2, B3, B4, and B6) were able to provide samples with less than 5.0% linear shrinkage after 100 hours of exposure to 1480 ° C (2700 ° F). In order for a fiber to be acceptable for a given operating temperature, this type of fiber (i.e., felted) should have no more than 5% linear shrinkage after 100 hours when warm. This ensures that a given fiber is not exposed to unacceptable amounts of shrinkage (i.e., in excess of 12%) when repeatedly cycled up to its operating temperature throughout its life. When fiber samples are collected in normal production use and knitted into felt instead of being compressed into felt, the amounts of shrinkage observed in this type of experiment are more similar to the maximum amounts of shrinkage desired during use.

Production experiments were performed with different ranges of chemical compositions to determine which of the compositions 1) formed into 30 very fibrous; 2) formed fibers with an acceptable level of shrinkage, and 3) possibly production results that are comparable to those achieved in test smelting. During these production experiments, the benefits of these zirconia-containing compositions became apparent. In a stabilized melter of the same structure as previously used for silica / alumina melts (with both overhead and bottom inlet electrodes), the composition of 9,93347 ci zirconia produced lower melt content and less reject-5 ran felt).

Samples of these different felt compositions were chemically analyzed and tested for shrinkage, as before. The amount of linear shrinkage is a phenomenon according to time and temperature. Accordingly, although this fiber was likely to be designated for use in the 1400-1455 ° C (2550-2650 ° F) range, the samples were placed in an oven at 1482 ° C (2700 ° F) for four hours to 1) accelerate the experiments, thereby reducing that time. , which was necessary both 2) to ensure that the blanket is able to withstand limited exposure to peak temperatures-15 above those recommended for use without marking catastrophic failure. The results of these experiments are shown in Table IIIA.

10,93347 TABLE IIIA% by weight 5 (1482 ° C 4h) Sample No. SiO 2 Al 2 O 3 ZrO 2 SiO 2 / ZrO 2% linear ratio shrinkage 1 53.1 45.8 0.4 132.75 15.6 2 51.9 42.5 4.6 11.282 14.6 10 3 50.0 44.3 5.3 9.434 14.9 4 51.7 42.1 5.4 9.57 13.3 5 49.0 38.9 11.2 4.375 12 , 1 6 48.0 38.2 13.2 3.636 9.2 7 49.2 36.4 13.8 3.565 8.2 15 8 54.7 30.3 14.1 3.879 12.9 9 49.4 35 .0 14.5 3.407 11.3 10 50.2 34.1 14.7 3.415 9.7 11 51.9 32.9 14.7 3.531 9.1 12 49.7 34.7 15.0 3.313 6, 8 20 13 49.7 34.8 15.0 3.313 8.2 14 47.6 37.3 15.2 3.132 10.9 15 49.3 34.6 15.3 3.222 9.7 16 46.0 37, 3 15.3 3.007 9.0 17 46.4 37.2 15.4 3.013 8.1 ;;; * 25 ie 46.2 37.0 15.5 2.98 6.8 19 46.2 37.3 15.6 2.961 7.2 20 50.1 32.0 17.4 2.879 7.6 21 49.3 32.4 17.4 2.833 7.4 22 47.2 34.4 17.5 2.697 8.6 30 23 47.4 33.9 17.6 2.693 6.0 24 47.4 34.2 17.7 2.678 7.2 25 48.0 33.2 17.8 2.697 7.3 26 47.7 33.4 17.8 2.680 7.2

II

35 11 93347 For these tests, an acceptable level of shrinkage is defined as 11.5%. Although this may appear to be an unreasonably high amount of shrinkage, it should be remembered that the amount of shrinkage has been intentionally exaggerated by exposing these samples to 5 temperatures (1480 ° C to 2700 ° F) that exceed this recommended operating temperature (1400-1455 ° C to 2550 ° F). 2650 ° F). Second, a significant portion of the felt made using this composition enters the insulation modules, which are of the type described in U.S. Patent 4,001,996. In such a modular structure, there is less shrinkage in the felt 10 because only a small portion of its surface is exposed to the temperature inside the furnace. In addition, most of any gap is filled, which may result from such shrinkage as the compressed modules expand.

Table IIIA shows that the fiber-producing compositions with an acceptable level of shrinkage have the following configurations: SiO 2 ranging from 46.0 to 52%, Al 2 O 3 ranging from 32 to 38%, and ZrO 2 ranging from 13 to 18% (all percentages are by weight). A further limitation for this set of compositions is that the ratio of silica to zirconia appears to be significant and should not exceed 3.8. In the defined range of zirconia (13-18%) in Table III, the SiO 2 / ZrO 2 ratio has a minimum value of 2.6. Within this set, a more preferred composition (based on shrinkage amounts) is SiO 2 between 46.4-50.1%, Al 2 O 3 between 32-37.3%. 25 ZrO 2 between 15-18% and SiO 2 / ZrO 2 ratio between 2.6-3.32.

The results from Table IIIA are shown graphically in Figure 2, where the set of compositions is shown in solid form. Figure 3 is an enlargement of a portion of the triaxial diagram of Figure 2 (shown in broken lines) to allow a clearer view of the illustrated compositions. Even in the enlarged view of Figure 2, the two sample points (samples 13 and 19) were too close to the other compositions to be presented as distinct points.

35 Both fiber in its pulp form and felt can be used up to 1426 ° C (2600 ° F). In order to compare this fiber with other fibers, 12,93347 having a nominal value of 1426 ° C (2600 ° F), felt samples of the indicated fibers (with a composition of 49.7% SiO 2, 34.7% Al 2 O 3 and 15.0% ZrO 2) were tested for shrinkage. testing them in a test of side-by-side furnaces, comparing them with 1) a commercially available 5 refractory fiber felt having a composition of Al 2 O 3 - 54%, SiO 2 --46%, and b) a commercially available refractory fiber felt which has been heat treated (i.e., pre-shrunk); ) and wherein the composition is 51% alumina, 49% silica, and c) 10 felts of commercially available refractory fibers having a composition of SiO 2 to 51.6%, Al 2 O 3 to 47.7%, wherein the felt is subsequently surface treated h % with chromium oxide.

The strips of the samples of these four felts were tested for shrinkage in the same manner as in previous experiments. Measured pieces of felt were placed in an oven at 1400 ° C (2550 ° F) and re-measured after 25, 50 and 75 hours each, and the percentage shrinkage was calculated by dividing the change in length by the original length and multiplying the result by 100. Due to the relatively small change in the amount of shrinkage between the 50 and 75 hour measurements, 20 experiments were then performed at 1426 ° C (2600 ° F) and 1482 ° C (2700 ° F), continuing for only 50 hours. The results of these experiments are shown in Table 1IIB.

TABLE IIIB

..25% linear shrinkage «4 Sample 25 h 50 h 75 h 25 h 50 h 25 h 50 h

Fiber shown 3.0 3.1 3.1 3.2 3.2 5.7 5.7 54/46 Composition 4.2 4.9 5.0 5.0 5.7 4.8 5.7 30 51 / 49 composition 3.4 3.6 3.6 4.6 4.6 6.7 6.9

Chromium-treated 3.6 3.9 4.0 4.1 4.3 10.5 11.2 These experiments show the superiority of the fiber presented over these three other commercially available fibers. Taken in conjunction with the difficulties of fiber formation when using high alumina compositions, the problems associated with <II; For treatment with 13,93347 chromium oxide, with the above improvements in pour rate and fiber recovery compared to other silica / alumina melts, the high temperature composition of this invention is clearly superior to other known refractory fiber compositions.

To confirm the experiments, product fiber was prepared in a full size melter, substance P1 based on sample Z3. The composition was slightly changed from the composition of sample Z3 to determine what effects the changes in composition might have on the properties of the fibers. 3240 kg of P1 material were produced as fibers with a design composition of 49% SiO2, 37% Al2O3 and 14% ZrO2. The melt was prepared in a top electrode, open top melter, generally of the type described in U.S. Patent 3,983,309.

Substance P1 has a melt boundary temperature of 1760 ° C and was fiberized at an average melt rate of 491 kg / hr using 800 kW of power to provide a flow temperature of 1840 ° C. Although the actual fiber-20 composition for P1 varied significantly from the intended composition, analysis of some of the fibers produced showed the following composition: 49.2% SiO 2, 36.5% Al 2 O 3, and 13.6% ZrO 2. This composition is satisfactorily comparable to the original Z3 fiber, which had a composition of 50.1 / 34.6 / 15.0. The two compositions differed by only 0.9 / 1.9 / 1.4% from each other. Still, the linear shrinkage of P1 samples ranged from 7.0 to 9.6 after only 24 hours of exposure to 1480 ° C. This suggests that the Z3 composition must be adjusted very precisely (+ - 1%) in order to produce an acceptable 1480 ° C fiber.

30

Various changes, alternatives, and variations will become apparent upon reading the foregoing explanatory text. For example, it may be considered to add up to 2.5% chromium oxide to Z3, which may be advantageous in improving fire resistance. Also, although only one method of defibering has been described, this refractory fiber may be formed using any other commercial method, such as blowing to mention an example. Accordingly, it is intended that all such changes, alternatives, and variations as fall within the scope of the appended claims should be construed as forming part of the present invention.

5 ♦ il,

Claims (5)

1. Fire phase high temperature fiber, characterized in that said fiber in pulp or felt form has an improved, below 11.5%, shrinkage resistance after being exposed to temperatures up to 1482 ° C (2700 ° F) for about 4 hours. hours, so that the composition of the refractory fiber consists in weight percentages of: SiO 2 46-52% Al 2 O 3 32-38% ZrO 2 13-18% and where the silica / zirconia ratio is within the range 2.6-3.8. 2. High temperature refractory refractory according to claim 1, characterized in that it contains in weight percentages most advantageous: SiO2 46.4-50.1% Al2 O3 32.0-37.3% ZrO2 is 15.0-18.0% and the SiO2 / ZrO2 ratio is 2.6-3.32. 3. The use of fibers having a composition in weight percentages: ..:: 25 SiO2 46-52% Al2 O3 32-38% ZrO2 13-18% 30 and where the silica / zirconia ratio is in the range 2.6-3.8 of refractory high temperature pulp or felt refractory fibers, which have an improved, below 11.5%, shrinkage resistance after being exposed to temperatures up to 1482 ° C (2700 ° F) for about 4 hours. 35 93347 Use of refractory high temperature fibers according to claim 1 having the following composition in weight percentages: SiO 2 46.4-50.1% Al2 O3 32.0-37.3% ZrO2 15.0-18.0% and the ratio SiO2 / ZrO2 is 2.6-3.32. 10 «li