WO2008005008A2

WO2008005008A2 - Inorganic fiber

Info

Publication number: WO2008005008A2
Application number: PCT/US2006/025840
Authority: WO
Inventors: Bruce K. Zoitos; Michael J. Andrejcak; Paul M. Boymel
Original assignee: Unifrax Corporation
Priority date: 2006-06-30
Filing date: 2006-06-30
Publication date: 2008-01-10
Also published as: AU2006345730A1; EP2038116A2; AU2006345730B2; JP5162584B2; BRPI0621848A2; JP2009542927A; EP2038116A4; CN101528623B; CN101528623A; MX2008016366A; WO2008005008A3

Abstract

Provided are inorganic fibers containing calcium and alumina as the major fiber components. Also provided are methods of preparing the inorganic fibers and of thermally insulating articles using thermal insulation comprising the inorganic fibers. The fibers are resistant to temperatures of 1100oC and greater, and are resistant to flux attack.

Description

INORGANIC FIBER

TECHMCAL FIELD

A high temperature resistant inorganic fiber useful as a thermal, electrical, or acoustical insulating material is provided, which has a use temperature of HOO⁰C or greater. The high temperature resistant inorganic fiber is easily manufacturable, exhibits low shrinkage after prolonged exposure to the use temperature, retains good mechanical strength after exposure to the use temperature, and is soluble in physiological fluids.

BACKGROUND

The insulation material industry has determined that it is desirable to utilize fibers in thermal and acoustical insulating applications, which are not durable in physiological fluids, that is, fiber compositions which exhibit a low biopersistence. While candidate materials have been proposed, the use temperature limit of these materials have not been high enough to accommodate many of the applications to which high temperature resistant fibers, including vitreous fibers and ceramic fibers, are applied. Many compositions within the synthetic vitreous fiber family of materials have been proposed which are non-durable or decomposable in a physiological medium.

The high temperature resistant fibers should also exhibit minimal linear shrinkage at expected exposure temperatures, and after prolonged or continuous exposure to the expected use temperatures, in order to provide effective thermal protection to the article being insulated. In addition to temperature resistance as expressed by shrinkage characteristics that are important in fibers that are used in insulation, it is also required that the fibers have mechanical strength characteristics during and following exposure to the use or service temperature, that will permit the fiber to maintain its structural integrity and insulating characteristics in use.

One characteristic of the mechanical integrity of a fiber is its after service friability. The more friable a fiber, that is, the more easily it is crushed or crumbled to a powder, the less mechanical integrity it possesses. In general, inorganic fibers that exhibit both high temperature resistance and non-durability in physiological fluids also exhibit a high degree of after service friability. This results in the fiber lacking the strength or mechanical integrity after exposure to the service temperature, to be able to provide the necessary structure to accomplish its insulating purpose.

Thus, it is still desirable to produce an improved inorganic fiber composition that is readily manufacturable from a fiberizable melt of desired ingredients, which exhibits low shrinkage during and after exposure to service temperatures of HOO⁰C or greater, which exhibits low brittleness after exposure to the expected use temperatures, and which maintains mechanical integrity after exposure to use temperatures of HOO⁰C or greater.

SUMMARY

A high temperature resistant inorganic fiber that is useful as a thermal, electrical or acoustical insulating material is provided. The inorganic fiber has a use temperature of HOO⁰C and greater. The high temperature resistant inorganic is fiber is easily manufacturable from a melt of fiber ingredients, exhibits low linear shrinkage, retains good mechanical strength and integrity after exposure to the use temperature, and yet is soluble in physiological fluids. At least 90 weight percent of the inorganic fiber comprises the fiberization product of greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina.

Also provided is a process for the production of an inorganic fiber, the process comprises forming a melt with ingredients comprising calcia and alumina, and producing fibers from the melt, wherein the ingredients comprise, in total, at least 90 weight percent of said ingredients comprise greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina.

A thermal insulation article is additionally provided, the thermal insulation article comprises inorganic fibers comprising a fiberization product, wherein at least 90 weight percent of the fiberization product comprises greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina.

A method of insulating an article is further provided, the method comprises disposing on, in, near or around the article, a thermal insulation material comprising inorganic fibers comprising a fiberization product, wherein at least 90 weight percent of the fiberization product comprises greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron micrograph of a calcium-aluminate fiber comprising the fiberization product of about 65 weight percent alumina and about 33 weight percent calcia. FIG. 2 is a scanning electron micrograph of a calcium-aluminate fiber comprising the fiberization product of about 55.8 weight percent alumina and about 42.1 weight percent calcia.

FIG. 3 is a scanning electron micrograph of a calcium-aluminate fiber comprising the fiberization product of about 43.5 weight percent alumina and about 53 weight percent calcia.

FIG. 4 is a viscosity vs. temperature curve for a calcium-aluminate fiber melt chemistry comprising about 55.8 weight percent alumina and about 42.1 weight percent calcia.

FIGS. 5A-5C are photographs of refractory ceramic fiber thermal insulation blankets after exposure to a Na∑O flux.

FIGS. 6A-6D are photographs of thermal insulation blankets comprising calcium-aluminate fibers after exposure to a Na2θ flux.

DETAILED DESCRIPTION

An inorganic fiber that is useful as a thermal, electrical, and acoustical insulation material is provided. The inorganic fiber has a continuous service or use temperature of 1100⁰C or greater. According to certain embodiments, the vitreous inorganic fiber has a continuous service or use temperature of 1260°C or greater.

The inorganic fiber is non-durable in physiological fluids. By "nondurable" 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. The inorganic vitreous fiber also exhibits a linear shrinkage, as determined by the test method described below, of less than about 5 percent in response to exposure to a use temperature of 126O⁰C for 24 hours. Thus, the inorganic fiber possesses a very low biopersistence in physiological fluids, and good linear shrinkage properties.

The low shrinkage, high temperature resistant inorganic fiber comprises the fiberization product of a melt containing calcia and alumina as the primary constituents. The inorganic fiber comprising the fiberization product of calcia and alumina is referred to as a "calcium-aluminate" fiber.

According to certain embodiments, at least 90 weight percent of the calcium-aluminate fiber comprises the fiberization product of greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina.

According to other embodiments, at least 90 weight percent of the calcium-aluminate fiber comprises the fiberization product of greater than 50 to about 60 weight percent calcia and from about 40 to less than 50 weight percent alumina.

According to further embodiments, at least 90 weight percent of the calcium-aluminate fiber comprises the fiberization product comprising greater than 50 to about 80 weight percent calcia and about 20 to less than 50 weight percent alumina.

According to further embodiments, at least 90 weight percent of the calcium-aluminate fiber comprises the fiberization product of about 60 to about 80 weight percent calcia and about 20 to about 40 weight percent alumina. According to further embodiments, at least 90 weight percent of the calcium-aluminate fiber comprises the fiberization product of greater than 50 to about 70 weight percent calcia and about 30 to less than 50 weight percent alumina.

The raw materials for the melt may be obtained from any suitable source capable of supplying the required chemistry and purity. Without limitation, suitable sources of calcium oxide include calcium-aluminate cement having a desired ratio of CaO/AkCb, lime, limestone, and quicklime. Without limitation, suitable sources of alumina are those having the required purity and which may be blended as needed with the CaO-bearing materials to achieve the desired chemistry.

In addition to calcia and alumina, the calcium-aluminate fiber may contain up to about 10 weight percent of impurities. Such impurities may include iron oxides. If iron oxide impurities are present in the fiberization melt from the starting raw materials, they are usually present in an amount of about 1 weight percent or less, calculated as Fe2θ3.

The impurities in the calcium-aluminate fiber may include up to 10 percent by weight of silica impurity, based on the total weight of the fiber. However, in certain embodiments the calcium-aluminate fibers may contain less than about 5 weight percent silica, or even as low as about 2 weight percent silica or less.

Linear shrinkage of an inorganic fiber is a good measure of a fiber's high temperature resistance or of its performance at a particular continuous service or use temperature. The calcium-aluminate fibers exhibit a linear shrinkage after exposure to a service temperature of 126O⁰C for 24 hours of 5 percent or less. Thus, the calcium-aluminate fibers are useful for thermal insulating applications at continuous service or operating temperatures of at least 126O⁰C or greater. Furthermore, it has been found that the calcium-aluminate fibers do not melt until they are exposed to a temperature of 132O⁰C or greater.

A method for preparing a low shrinkage, high temperature resistant, non- durable calcium-aluminate fiber having a use temperature of at least 1100°C or greater is also provided. The method of forming the calcium-aluminate fiber includes forming a material melt of ingredients comprising calcia and alumina, and forming fibers from the melt of ingredients. The calcium-aluminate fibers may be produced from the melt of ingredients by standard melt spinning or fiber blowing techniques.

According to certain embodiments, the method of forming the calcium- aluminate fiber includes forming a material melt of ingredients where at least 90 weight percent of the ingredients comprise, in total, greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina, and forming fibers from the melt of ingredients. It is understood that not each ingredient of the material melt must possess this calcia: alumina ratio, or any of the other calcia: alumina ratios described herein. Rather, the total amount of calcia and alumina contained in the material melt of ingredients comprises this ratio, or any of the calcia: alumina ratios described herein. Thus, in this embodiment, and the embodiments that follow, each ingredient need not have calcia and alumina in the disclosed ranges, but that total of such ingredients should comprise the disclosed ranges.

According to other embodiments, the method of forming the calcium- aluminate fiber includes forming a material melt of ingredients where at least 90 weight percent of the ingredients comprise, in total, greater than 50 to about 60 weight percent calcia and from about 40 to less than 50 weight percent alumina, and forming fibers from the melt of ingredients. According to other embodiments, the method of forming the calcium- aluminate fiber includes forming a material melt of ingredients where at least 90 weight percent of the ingredients comprise, in total, about greater than 50 to about 80 weight percent calcia and about 20 to less than 50 weight percent alumina.

According to other embodiments, the method of forming the calcium- aluminate fiber includes forming a material melt of ingredients where at least 90 weight percent of the ingredients comprise, in total, about 60 to about 80 weight percent calcia and about 20 to about 40 weight percent alumina.

According to other embodiments, the method of forming the calcium- aluminate fiber includes forming a material melt of ingredients where at least 90 weight percent of the ingredient comprise, in total, greater than 50 to about 70 weight percent calcia and about 30 to less than 50 weight percent alumina.

The viscosity of the material melt of ingredients may optionally be controlled by the presence of viscosity modifiers, in an amount sufficient to provide the fiberization required for the desired applications. The viscosity modifiers may be present in the raw materials which supply the main components of the melt, or may, at least in part, be separately added. Desired particle size of the raw materials is determined by furnacing conditions, including furnace size, pour rate, melt temperature, residence time, and the like.

As described above, the calcium-aluminate fiber may be prepared by fiber blowing or fiber spinning techniques. A suitable fiber blowing technique includes the steps of mixing the starting raw materials containing calcia and alumina together to form a material mixture of ingredients, introducing the material mixture of ingredients into a suitable vessel or container, melting the material mixture of ingredients for discharge through a suitable nozzle, and blowing a high pressure gas onto the discharged flow of molten material mixture of ingredients to form the calcium-aluminate fibers.

A suitable fiber spinning technique includes the steps of mixing the starting raw materials containing calcia and alumina together to form a material mixture of ingredients, introducing the material mixture of ingredients into a suitable vessel or container, melting the material mixture of ingredients for discharge through a suitable nozzle onto spinning wheels. The molten stream then cascades over the wheels, coating the wheels and being thrown off through centripetal forces, thereby forming fibers.

A method of insulating an article using a thermal insulation material containing the calcium-aluminate fibers is also provided. The method of insulating an article includes disposing on, in, near, or around the article to be insulated, a thermal insulation material that contains calcium-aluminate fibers. The calcium-aluminate fibers included in the thermal insulation material are those in which at least 90 weight percent of the fiber comprises the fiberization product of greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina.

According to certain embodiments, the calcium-aluminate fibers included in the thermal insulation material are those fibers in which at least 90 weight percent of the fiber comprises the fiberization product of greater than 50 to about 60 weight percent calcia and from about 40 to less than 50 weight percent alumina.

According to certain embodiments, the calcium-aluminate fibers included in the thermal insulation material are those fibers in which at least 90 weight percent of the fiber comprises the fiberization product comprising about greater than 50 to about 80 weight percent calcia and about 20 to less than 50 weight percent alumina.

According to certain embodiments, the calcium-aluminate fibers included in the thermal insulation material are those fibers in which at least 90 weight percent of the fiber comprises the fiberization product of about 60 to about 80 weight percent calcia and about 20 to about 40 weight percent alumina.

According to certain embodiments, the calcium-aluminate fibers included in the thermal insulation material are those fibers in which at least 90 weight percent of the fiber comprises the fiberization product of greater than 50 to about 70 weight percent calcia and about 30 to less than 50 weight percent alumina.

Thermal insulation containing the calcium-aluminate fibers may be utilized in thermal insulation applications as a replacement for standard mineral wool or alumino-silicate refractory ceramic fiber. Thermal insulation material containing the calcium-aluminate fibers may be utilized for thermal insulation applications that require resistance of HOO⁰C or greater. Moreover, thermal insulation material containing the calcium-aluminate fibers may be utilized for thermal insulation applications that require resistance up to about 126O⁰C. Without limitation, thermal insulation containing the calcium-aluminate fibers may be utilized to thermally insulate heating vessels, such as furnaces, in the chemical processing, petroleum processing, ceramic processing, glass processing, metals production and processing industries, or in the automotive, aerospace, appliance, and fire protection industries.

The calcium-aluminate fibers may be provided in the form of bulk fibers. Additionally, the calcium-aluminate fibers may be incorporated into a wide variety of acoustical, electrical, or thermal insulation articles or products. Without limitation, for example, the calcium-aluminate fibers may be processed into high temperature resistant fiber containing blankets, including needled and stitched blankets, boards, braids, cloths, expanding papers, non-expanding papers, fabrics, felts, cast shapes, modules, bonded modules, mats, packings, ropes, tapes, sleeving, vacuum cast shapes, woven textiles, workable compositions, including high temperature resistant caulks, cements, coatings, mortars, pumpable compositions, putties, and moldable compositions.

EXAMPLES

The following examples are set forth to further describe certain properties of illustrative embodiments of the calcium-aluminate fibers.

However, the examples should not be construed as limiting the fiber, the fiber containing articles, or the processes of making or using them as thermal insulation in any manner.

The flux resistance of the calcium-aluminate fibers was evaluated. The term "fluxing" describes a reaction in which a relatively minor component (the flux) acts to drastically lower the melting point of a second material. The fluxing process can significantly compromise the integrity of a thermal insulation material. In the context of high temperature resistant insulation applications, such as, for example, kiln insulation applications, a flux may be present in the fuel that is used to fire the kiln. Two common fluxes encountered in high temperature resistant kiln insulation applications are Na2θ and KiO, which are very damaging to refractory ceramic fiber. If Na.0 and K2O are present in a sufficient concentration and come into contact with the refractory ceramic fiber, it will cause the refractory ceramic fiber to melt, thereby compromising the integrity of the insulation material. The flux test is designed to test the aggressiveness of an impurity (the flux) toward the fiber at elevated temperatures. Briefly, a 1 gram sample of a powdered flux is piled in a 1 square inch area on the surface of fiber blanket. The assembly is then heated to 126O⁰C (or the desired test temperature) and held for 24 hours. Following the heating, the flux attack on the blanket is determined by visual inspection. Fluxing attack results in melting of the fiber which is in contact with the fluxing agent. The degree of attack can be assess by the amount of fiber which is melted. The results of the flux testing is reported in Table I:

Table I

Comparative Examples Cl and C2 represent commercially available alumina-zirconia-silica fiber blanket, and Comparative Example C3 represents a commercially available alumino-silicate ceramic fiber blanket. The results indicate that the commercially available alumina-zirconia-silica and alumino- silicate blankets were attacked by the Na2θ flux, thereby compromising the integrity of the insulation. In the case of the fiber refractory ceramic fiber material blankets of the comparative examples, the 1 square inch of blanket which had been in contact with the flux had melted. In stark contrast to the refractory ceramic fiber material of the comparative examples, no flux attack was observed for insulation blankets manufactured from the calcium-aluminate fibers.

The inorganic fiber compositions, method for producing the inorganic fiber composition, the various inorganic fiber containing articles, and method of insulating articles are not limited to the embodiments described above, but include all variations, modifications, and equivalent embodiments. The embodiments that are disclosed separately are not necessarily in the alternative, as the various embodiments of the invention may be combined to provide the desired characteristics. Therefore, the inorganic fiber, fiber containing articles, and methods for preparing the fiber and using the fiber as thermal insulation should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the attached claims.

Claims

WE CLAIM:

1. An inorganic fiber, wherein at least 90 weight percent of said fiber comprises the fiberization product of greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina.

2. The inorganic fiber of claim 1, wherein at least 90 weight percent of said fiber comprises the fiberization product of greater than 50 to about 60 weight percent calcia and from about 40 to less than 50 weight percent alumina.

3. The inorganic fiber of claim 1, wherein at least 90 weight percent of said fiber comprises the fiberization product of about greater than 50 to about 80 weight percent calcia and about 20 to less than 50 weight percent alumina.

4. The inorganic fiber of claim 1 , wherein at least 90 weight percent of said fiber comprises the fiberization product of about 60 to about 80 weight percent calcia and about 20 to about 40 weight percent alumina.

5. The inorganic fiber of claim 1, wherein at least 90 weight percent of said fiber comprises the fiberization product of greater than 50 to about 70 weight percent calcia and about 30 to less than 50 weight percent alumina.

6. The inorganic fiber of claim 1, containing about 10 weight percent or less silica.

7. The inorganic fiber of claim 1, containing about 5 weight percent or less silica.

8. The inorganic fiber of claim 1, containing about 2 weight percent or less silica.

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

10. The inorganic fiber of claim 1, containing about 1 weight percent or less iron oxide, calculated as Fe2θ3.

11. The inorganic fiber of claim 1 , having a continuous use temperature of at least HOO⁰C.

12. An inorganic fiber containing thermal insulation article selected comprising at least one of bulk fiber, blankets, needled blankets, papers, felts, cast shapes, vacuum cast forms, or compositions, wherein said inorganic fiber containing article comprises the inorganic fiber of claim 1.

13. A method for producing an inorganic fiber comprising: forming a melt with ingredients comprising calcia and alumina, wherein at least 90 weight percent of said ingredients comprise, in total, greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina; and producing fibers from the melt.

14. The method of claim 13, wherein at least 90 weight percent of said ingredients comprise, in total, from greater than 50 to about 60 weight percent calcia and from about 40 to less than 50 weight percent alumina.

15. The method of claim 13, wherein at least 90 weight percent of said ingredients comprise, in total, about greater than 50 to about 80 weight percent calcia and about 20 to less than 50 weight percent alumina.

16. The method of claim 13, wherein at least 90 weight percent of said ingredients comprise, in total, about 60 to about 80 weight percent calcia and about 20 to about 40 weight percent alumina.

17. The method of claim 13, wherein at least 90 weight percent of said ingredients comprise, in total, greater than 50 to about 70 weight percent calcia and about 30 to less than 50 weight percent alumina.

18. The method of claim 13, wherein said producing the fibers from the melt comprises one of (i) spinning the fibers from the melt or (ii) blowing the fibers from the melt.

19. A method of insulating an article comprising disposing on, in, near or around the article, a thermal insulation material comprising inorganic fibers comprising a fiberization product, wherein at least 90 weight percent of the fiberization product comprises greater than 50 weight percent calcia and greater than 0 to less than 50 weight percent alumina.

20. The method of claim 19, wherein at least 90 weight percent of the fiberization product comprises greater than 50 to about 60 weight percent calcia and from about 40 to less than 50 weight percent alumina.

21. The method of claim 19, wherein at least 90 weight percent of the fiberization product comprises about greater than 50 to about 80 weight percent calcia and about 20 to less than 50 weight percent alumina.

22. The method of claim 19, wherein at least 90 weight percent of the fiberization product comprises about 60 to about 80 weight percent calcia and about 20 to about 40 weight percent alumina.

23. The method of claim 19, wherein at least 90 weight percent of the fiberization product comprises greater than 50 to about 70 weight percent calcia and about 30 to less than 50 weight percent alumina.