Inorganic fiber with improved shrinkage and strength

Abstract

An inorganic fiber containing silica and magnesia as the major fiber components which further includes an intended strontium oxide additive to improve the thermal stability of the fiber. The inorganic fiber exhibits good thermal performance at 1260 C. and greater for 24 hours or more, retains mechanical integrity after exposure to the use temperature, and exhibits low biopersistence in physiological fluids. Also provided are thermal insulation product forms, methods of preparing the inorganic fiber and of thermally insulating articles using thermal insulation prepared from a plurality of the inorganic fibers.

Claims

1. An inorganic fiber comprising the fiberization product of about 65 to about 86 weight percent silica, about 14 to about 35 weight percent magnesia, less than 0.4 weight percent calcia, and greater than 0 to less than 0.5 weight percent strontium oxide, wherein said inorganic fiber exhibits and low biopersistence in physiological saline, low shrinkage and good mechanical strength at temperatures of 1260 C. and greater.

2. The inorganic fiber of claim 1, wherein said fiberization product further comprises a viscosity modifier.

3. The inorganic fiber of claim 1, wherein said viscosity modifier is selected from the group consisting of alumina, boria, and mixtures thereof.

4. The inorganic fiber of claim 1, wherein said viscosity modifier comprises alumina.

5. The inorganic fiber of claim 1 further comprising greater than 0 to about 11 weight percent zirconia.

6. The inorganic fiber of claim 1 containing 1 weight percent or less iron oxide, measured as Fe.sub.2O.sub.3.

7. The inorganic fiber of claim 1 containing substantially no alkali metal oxide.

8. The inorganic fiber of claim 1, wherein said inorganic fiber has an average diameter of greater than 2 microns.

9. The inorganic fiber of claim 1, wherein said fiber exhibits a shrinkage of about 10% or less at 1260 C. for 24 hours.

10. The inorganic fiber of claim 1, wherein said fiber exhibits a shrinkage of about 5% or less at 1260 C. for 24 hours.

11. The inorganic fiber of claim 1, wherein said fiber exhibits a shrinkage of about 10% or less at 1400 C. for 24 hours.

12. The inorganic fiber of claim 1, wherein said fiber exhibits a shrinkage of about 5% or less at 1400 C. for 24 hours.

13. The inorganic fiber of claim 1, comprising the fiberization product of about 65 to about 86 weight percent silica, about 14 to about 35 weight percent magnesia, and greater than 0 to less than 0.4 weight percent strontium oxide.

14. The inorganic fiber of claim 1, comprising the fiberization product of about 65 to about 86 weight percent silica, about 14 to about 35 weight percent magnesia, and greater than 0 to less than 0.3 weight percent strontium oxide.

15. The inorganic fiber of claim 1, comprising the fiberization product of about 65 to about 86 weight percent silica, about 14 to about 35 weight percent magnesia, and greater than 0 to less than 0.2 weight percent strontium oxide.

16. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 70 to about 80 weight percent silica, about 15 to about 30 weight percent magnesia, and greater than 0 to less than 0.5 weight percent strontium oxide.

17. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 72 to about 80 weight percent silica, about 20 to about 28 weight percent magnesia, and greater than 0 to less than 0.5 weight percent strontium oxide.

18. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 72 to about 80 weight percent silica, about 20 to about 28 weight percent magnesia, and greater than 0 to less than 0.4 weight percent strontium oxide.

19. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 72 to about 80 weight percent silica, about 20 to about 28 weight percent magnesia, and greater than 0 to less than 0.3 weight percent strontium oxide.

20. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 72 to about 80 weight percent silica, about 20 to about 28 weight percent magnesia, and greater than 0 to less than 0.2 weight percent strontium oxide.

21. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 72 to about 86 weight percent silica, about 14 to about 28 weight percent magnesia, and greater than 0 to less than 0.5 weight percent strontium oxide.

22. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 72 to about 86 weight percent silica, about 14 to about 28 weight percent magnesia, and greater than 0 to less than 0.4 weight percent strontium oxide.

23. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 72 to about 86 weight percent silica, about 14 to about 28 weight percent magnesia, and greater than 0 to less than 0.3 weight percent strontium oxide.

24. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 72 to about 86 weight percent silica, about 14 to about 28 weight percent magnesia, and greater than 0 to less than 0.2 weight percent strontium oxide.

25. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 75 to about 80 weight percent silica, about 20 to about 25 weight percent magnesia, and greater than 0 to less than 0.5 weight percent strontium oxide.

26. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 75 to about 80 weight percent silica, about 20 to about 25 weight percent magnesia, and greater than 0 to less than 0.4 weight percent strontium oxide.

27. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 75 to about 80 weight percent silica, about 20 to about 25 weight percent magnesia, and greater than 0 to less than 0.3 weight percent strontium oxide.

28. The inorganic fiber of claim 1, wherein said inorganic fiber comprises the fiberization product of about 75 to about 80 weight percent silica, about 20 to about 25 weight percent magnesia, and greater than 0 to less than 0.2 weight percent strontium oxide.

29. A method for preparing the inorganic fiber exhibiting low biopersistence in physiological saline, low shrinkage, and good mechanical strength comprising: forming a melt with ingredients comprising of 65 to 86 weight percent silica, 14 to 35 weight percent magnesia, less than 0.4 weight percent calcia, greater than 0 to less than 0.5 weight percent strontium oxide, 0 to 11 weight percent zirconia, and optionally a viscosity modifier; and producing fibers from the melt.

30. A method of insulating an article, including disposing on, in, near or around the article, a thermal insulation material, said insulation material comprising the fiberization product of 65 to 86 weight percent silica, 14 to 35 weight percent magnesia, less than 0.4 weight percent calcia, greater than 0 to less than 0.5 weight percent strontium oxide, 0 to 11 weight percent zirconia, and optionally a viscosity modifier.

31. An inorganic fiber containing article comprising at least one of bulk fiber, blankets, blocks, boards, caulking compositions, cement compositions, coatings, felts, mats, moldable compositions, modules, papers, pumpable compositions, putty compositions, sheets, tamping mixtures, vacuum cast shapes, vacuum cast forms, or woven textiles, braids, cloths, fabrics, ropes, tapes, sleeving, wicking, said fiber containing article comprising the fiberization product of claim 1.

Description

EXAMPLES

(1) The following examples are set forth to describe illustrative embodiments of the magnesium-silicate fibers containing strontium oxide addition in further detail and to illustrate the methods of preparing the inorganic fibers, preparing thermal insulating articles containing the fibers and using the fibers as thermal insulation. However, the examples should not be construed as limiting the fiber, the fiber containing articles, or the processes of making or using the fibers as thermal insulation in any manner.

(2) Linear Shrinkage

(3) A shrinkage pad was prepared by needling a fiber mat using a bank of felting needles. A 3 inch5 inch test piece was cut from the pad and was used in the shrinkage testing. The length and width of the test pad was carefully measured. The test pad was then placed into a furnace and brought to a temperature of 1400 C. for 24 hours. After heating for 24 hours, the test pad was removed from the test furnace and cooled. After cooling, the length and width of the test pad were measured again. The linear shrinkage of the test pad was determined by comparing the before and after dimensional measurements.

(4) A second shrinkage pad was prepared in a manner similar to that disclosed for the first shrinkage pad. However, the second shrinkage pad was placed in a furnace and brought to a temperature of 1260 C. for 24 hours. After heating for 24 hours, the test pad was removed from the test furnace and cooled. After cooling, the length and width of the test pad were measured again. The linear shrinkage of the test pad was determined by comparing the before and after dimensional measurements.

(5) Compression Recovery

(6) The ability of the inorganic fibers to retain mechanical strength after exposure to a use temperature was evaluated by a compression recovery test. Compression recovery is a measure of the mechanical performance of an inorganic fiber in response to the exposure of the fiber to a desired use temperature for a given period of time. Compression recovery is measured by firing test pads manufactured from the inorganic fiber material to the test temperature for the selected period of time. The fired test pads are thereafter compressed to half of their original thickness and allowed to rebound. The amount of rebound is measured as percent recovery of the compressed thickness of the pad. Compression recovery was measured after exposure to use temperatures of 1260 C. for 24 hours, and 1400 C. for 24 hours. According to certain illustrative embodiments, the test pads manufactured from the inorganic fibers exhibit a compression recovery of at least 10 percent.

(7) Fiber Dissolution

(8) The inorganic fiber is non-durable or non-biopersistent in physiological fluids. By non-durable or non-biopersistent in physiological fluids it is meant that the inorganic fiber at least partially dissolves or decomposes in such fluids, such as simulated lung fluid, during in vitro tests described herein.

(9) The biopersistence test measures the rate at which mass is lost from the fiber (ng/cm.sup.2-hr) under conditions which simulate the temperature and chemical conditions found in the human lung. In particular, the fibers exhibit low biopersistence in Simulated Lung Fluid at a pH of 7.4.

(10) To measure the dissolution rate of fibers in simulated lung fluid, approximately 0.1 g of fiber is placed into a 50 ml centrifuge tube containing simulated lung fluid which has been warmed to 37 C. This is then placed into a shaking incubator for 6 hours and agitated at 100 cycles per minute. At the conclusion of the test, the tube is centrifuged and the solution is poured into a 60 ml syringe. The solution is then forced through a 0.45 m filter to remove any particulate and tested for glass constituents using Inductively Coupled Plasma Spectroscopy analysis. This test may be conducted using either a near-neutral pH solution or an acidic solution. Although no specific dissolution rate standards exist, fibers with dissolution values in excess of 100 ng/cm2 hr are considered indicative of a non-biopersistent fiber.

(11) Table I shows fiber melt chemistries for various comparative and inventive fiber samples.

(12) TABLE-US-00001 TABLE I SiO.sub.2 MgO Al.sub.20.sub.3 CaO Fe.sub.20.sub.3 SrO Sample wt % wt % wt % wt % wt % wt % C1 55 0 45 0 0 0 C2 78 20 1.4 0.39 0.17 0 3 77.89 19.61 1.4 0.14 0.12 0.80 4 77.89 19.61 1.4 0.14 0.12 0.80 5 78.24 18.27 1.35 0.14 0.09 1.85 6 78.24 18.27 1.35 0.14 0.09 1.85 7 76.96 19.82 1.3 0.15 0.09 1.16 8 77.69 18.41 1.23 0.18 0.09 2.07 9 77.09 20.26 1.11 0.16 0.08 1.31 10 75.41 20.65 1.06 0.17 0.09 2.68 11 79.8 15.70 1.01 0.21 0.14 2.6

(13) Table II shows the results for shrinkage, compressive strength, compression recovery, and solubility for the fibers of Table I.

(14) TABLE-US-00002 TABLE II Compress Compress Compress Compress Diameter Shrinkage Strength Recovery Shrinkage Strength Recovery K ng/ Mean m 1260 C. % 1260 C. psi 1260 C. % 1400 C. 1400 C. psi 1400 C. % cm2 hr C1 4.7 11.7 49.7 9.9 15.7 31.1 0 C2 8.5 8.2 15.8 9.2 3.2 3.7 260 3 4.1 4.5 10.8 43.6 4.7 9.5 27.6 1024 4 2.4 10.1 17.5 45.5 10.3 11.5 33.5 5 3.3 6 14.5 53.9 7.1 5.2 20.1 773 6 5.2 6.1 7.7 47.8 5.2 2.2 16.3 7 6.3 4.7 6.2 40.2 7 2.0 17.7 924 8 7.8 3 5.4 37.3 4.1 0.9 4.4 596 9 4.15 4.4 9.9 46.8 4.5 4.5 14.4 1068 10 4.48 3.3 7.5 30.6 4.3 1.5 4.5 716 11 4.3 5.6 10.1 32.8 6.4 2.6 6.9 747

(15) As shown in Table II above, magnesium-silicate fiber samples which included a strontium oxide addition exhibited excellent linear shrinkage values. At 1260 C., magnesium-silicate fiber samples with a 0.8% strontium oxide addition exhibit improved shrinkage, and similar compressive strength and compressive recovery properties as a refractory ceramic fiber (RCF). At 1400 C., the magnesium-silicate fibers with 0.8% strontium oxide exhibit improved shrinkage and similar compressive recovery as an RCF. The shrinkage results for inventive example 4 of Table II are considered to be within experimental error. However, the RCF fails to dissolve in physiological fluid. In contrast, the magnesium-silicate fiber sample dissolved in simulated lung fluid at a rate of 1024 ng/cm.sup.2 hr.

(16) Also shown in Table II, magnesium-silicate fiber samples with a strontium oxide addition compare favorably to ISOFRAX fibers. At 1260 C., magnesium-silicate fiber samples with a 0.8% strontium oxide addition exhibit improved shrinkage, improved compressive strength, and improved compressive recovery properties as ISOFRAX fibers. At 1400 C., the magnesium-silicate fibers with 0.8% strontium oxide exhibit improved shrinkage, improved compressive strength, and improved compressive recovery properties as ISOFRAX fibers. Further, the magnesium-silicate fibers with 0.8% strontium oxide additions were nearly four times more soluble (1024 ng/cm.sup.2 hr vs. 260 ng/cm.sup.2 hr) as the ISOFRAX fibers.

(17) Also shown in Table II are the results for the testing of magnesium-silicate fiber samples with 1.9% strontium oxide additions. At 1260 C., magnesium-silicate fiber samples with a 1.9% strontium oxide addition exhibit improved shrinkage, similar compressive strength, and improved compressive recovery (53.9% vs. 49.7%) properties as a refractory ceramic fiber (RCF). At 1400 C., the magnesium-silicate fibers with 1.9% strontium oxide exhibit improved shrinkage and similar compressive recovery properties as an RCF. The RCF fails to dissolve in simulated lung fluid, but the magnesium-silicate fibers exhibit a solubility of 773 ng/cm.sup.2 hr in simulated lung fluid.

(18) Also shown in Table II are the results for testing magnesium-silicate fiber samples with a 1.9% strontium oxide addition as compared to ISOFRAX fibers. At 1260 C., magnesium-silicate fiber samples with a 1.9% strontium oxide addition exhibit improved shrinkage, improved compressive strength, and improved compressive recovery properties as ISOFRAX fibers. At 1400 C., the magnesium-silicate fibers with 1.9% strontium oxide exhibit improved shrinkage, improved compressive strength, and improved compressive recovery properties as ISOFRAX fibers. Further, the magnesium-silicate fibers with 1.9% strontium oxide additions were nearly three times more soluble (773 ng/cm.sup.2 hr vs. 260 ng/cm.sup.2 hr) as the ISOFRAX fibers.

(19) The magnesium-silicate fibers with strontium oxide additions exhibit lower shrinkage than current commercial fibers following exposure to temperatures up to 1400 C. The magnesium-silicate fibers with strontium oxide additions also retain equivalent, or superior mechanical properties following exposure to temperatures up to 1400 C. when compared to existing commercial fibers.

(20) The present fiber composition exhibits lower shrinkage compared to standard RCF and higher fired strength measured by overall resiliency following compression after exposures to temperatures of 1260 C. and 1400 C. The improved inorganic fiber composition may exhibit superior performance to higher temperatures, possibly up to 1500 C.

(21) While the inorganic fiber, thermal insulation, methods of preparing the inorganic fiber, and method of insulating articles using the thermal insulation have been described in connection with various embodiments, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiments for performing the same function. Furthermore, the various illustrative embodiments may be combined to produce the desired results. Therefore, the inorganic fiber, thermal insulation, methods of preparing the inorganic fiber, and method of insulating articles using the thermal insulation should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims. It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described hereinabove. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.