GB2204573A

GB2204573A - Spinning solution for producing zirconia fibers

Info

Publication number: GB2204573A
Application number: GB08806928A
Authority: GB
Inventors: Masahiro Hayase; Tsunenobu Saeki; Hajime Asami; Hiroyuki Asakura
Original assignee: Shinagawa Refractories Co Ltd; Shinagawa Shiro Renga KK
Current assignee: Shinagawa Refractories Co Ltd; Shinagawa Shiro Renga KK
Priority date: 1987-03-31
Filing date: 1988-03-23
Publication date: 1988-11-16
Anticipated expiration: 2008-03-23
Also published as: GB2204573B; DE3810523C2; FR2613347B1; GB8806928D0; FR2613347A1; IT1219888B; DE3810523A1; IT8847790A0

Description

22 0 jC r7 9 U J ZIRCONIUM-CONTAINING AQUEOUS SOLUTION AND A PROCESS FOR

PRODUCING ZIRCONIA FIBERS is This invention relates to a zirconium-containing aqueous solution and a process for production thereof and more particularly, to a zirconium"containing aqueous solution which can be used as a spinning solution f rom which zirconia fibers are spun, as an impregnating solution for filling pores of ceramics and refractories with zirconia, or as a binder for ceramics and refractories. The present invention also relates to a process for producing zirconia fibers.

In recent years, refractory fibers such as alumina fibers, zirconia fibers and silica fibers have been developed as heat insulators for high temperatures, reinforcing agents in composite materialso, fillers and electrical insulators. These fibers have excellent characteristics at high temperatures, and therefore their uses such as that for heat insulators mentioned above as well as an extremely wide range of uses in many industrial fields and their development have been expectantly hoped for.

Of these refractory fibers, zirconia fibers are refractory fibers whoseF application in various fields is especially expected because zirconia fibers have a melting point (2,,600"C) much higher by far than other inorganic fibers, are chemically stable, have excellent corrosion resistance, have a low vapor pressure at a high temperature, and are not wetted by almost any molten metal or molten glass.

Heretofore, the refractory fibers have been produced by different methods depending on their types. For example, alumina-silica fibers (aluminum silicate fibers) are produced by a blowing method which comprises adding borate glass, zirconia, chromium oxide (III) or the like to a mixture of a kaolin calcinater an aluminaceous starting material, refractory clay, a siliceous starting material and the like, melting the resulting mixture in an electric furnace at a high temperature, causing the melt to f low out as a fine stream, and blowing it away with compressed air or vapor jet or by a spinning method wherein the melt is caused to flow down onto a high speed rotatable drum. However, such methods cannot produce zirconia fibers.

Fibers such as alumina fibers and zirconia fibers are produced by fiberizing a solution oi an aluminum salt such as aluminum chloride or aluminum acetate, or an aqueous solution of a zirconium salt as a starting material (a spinning solution), to form a fiber precursor, and firing the fiber precursor at a high temperature. Examples of processes, for producing refractory fibers involving the formation of this fiber precursor include a process for producing refractory V 1 1 fibers wherein a hollow rotatable disc having 0.3 to 1.5 millimeter holes is charged with a spinning solution and is rotated to obtain a fiber precursor,, and thereafter the fiber precursor is fired (U.S. Patent No. 4,277,269).

In another process for producing refractory fibers, a spinning solution is extruded through one or more openings in'to a stream of air having a component flowing at a high speed in the travel direction of the extruded spinning solution and having a relative humidity of at least 80% in order to obtain a fiber precursor, and thereafter the fiber precursor is fired (Japanese Patent Publication No. 36726/1980).

When zirconia fibers are produced by these processest an aqueous solution of a compound such as zirconium oxychloride, zirconyl sulfate, zirconyl nitrate, zirconyl acetate, or ammonium zirconyl carbonate can be used as the spinning solution. Of these, zirconium oxychloride is preferred because it is inexpensive, and zirconia is obtained in a relatively high yield.

Zirconium oxychloride can be used as a spinning solution from which zirconia fibers are produced, as an impregnating solution for filling pores of ceramics and refractories with zirconia, or as a binder for ceramics and refractories. r Zirconium oxychloride is represented by the chemical formula ZrOC128H20. (molecular weight: 321) This is zirconium oxychloride is heat treated to form zirconia Zr02. (molecular weight: 123) Accordingly, the yield of zirconia obtained by the heat treatment of zirconium oxychloride is about 38% by calculation on the basis of molecular weight conversion. However, the solubility of zirconium oxychloride in water is of the order of about 100 grams per 100 grams of water at 250C, and therefore the yield of zirconia is only about 19% even if a 50% aqueous solution, which is a saturated aqueous solution 10 of zirconium oxychloride, is used. The strength of zirconia fiber-s obtained from this spinning solution is low, and these zirconia fibers have not been produced commercially.

U.S. Patent No. 3,385,915 disclosei a:-process for producing zirconia fibers which comprises the steps of impregnating organic fibers with an aqueous solution of a zirconium metal saltr and firing the impregnated fibers. However, only refractory fibers which are easily broken to short fibers can be obtained because hollow pores. are generated therein, and the volume is changed due to burnoff of the organic fibers. Further, as stated in the case of the aqueous solution of zirconium oxychloride, the yield of zirconia from the impregnating aqueous solution of the zirconium metal salt is low, and therefore the strength of the resulting zirconia fibers is low.

1 An object of the present invention is to provide a zirconium-containing aqueous solution capable of forming zirconia in a high yield by heat treatment and a process for producing the same.

Another object of the present invention is to provide a process for producing zirconia fibers having excellent strength by using a spinning solution which produces a high yield of zirconia.

We have carried out various studies as a result of which, we have now found that while, in the process of con-centrating an aqueous solution of zirconium oxychloride by the evaporation of its water contentr zirconium oxychloride becomes supersaturated to deposit zirconium oxychloride crystals, a zirconium-containing aqueous solution obtained from the reaction product of an aqueous solution of zirconium oxychloride with aqueous hydrogen peroxide enhances the yield of zirconia from the zirconium-containing aqueous solution and maintains its liquid state. The objects of the present invention are achieved by such a zirconium-containing aqueous solution.

The process for producing a zirconium-containing aqueous solution of the present invention comprises the steps of adding aqueous hydrogen peroxide to an aqueous solution of zirconium oxychloride, reacting zirconium oxychloride with aqueous hydrogen peroxide upon heating, preferably at a temperature of from 3011C to 75"C, and optionally concentrating the reaction mixture by evaporating its water content after the reaction is completed.

A zirconium-containing aqueous solution which is another embodiment of the present invention comprises the reaction product pf an aqueous solution of zirconium oxychloride with aqueous hydrogen peroxide.

A process for producing zirconia. fibers according to the present invention comprises the steps of optionally concentrating the reaction product of an aqueous solution of zirconium oxychloride with aqueous hydrogen peroxide, preferably the reaction product obtained by the reaction of zirconium oxychloride with hydrogen peroxide at a temperature of from 3011C to 7511C, by evaporating its water content after the reaction is completed; cold spinning the resulting product to form a fiber precursor; and then firing said precursor.

It is believed that, while the mechanism of the reaction of the aqueous zirconium oxychloride solution with hydrogen peroxide, and the structure and composition of the product are not theoretically clear, a polymer of zirconium compound is formed by the reaction of zirconium oxychloride with hydrogen peroxide. This is presumed from the facts that: the solid matter obtained by drying the resulting solution is in the form of a transparent glass; functional groups other than 04 groups are not detected in its infrared absorption spectrum; mineral peaks appear in the X-ray diffraction pattern; and the 1 solid matter exhibits an amorphous pattern. This polymer of zirconium compound has a high content of zirconium, and therefore the use of such a polymer as a starting material for a spinning solution provides zirconium fibers having a high content of zirconia.

The present invention has the following features and advantages.

(a) Zirconium oxychloride which is a water-soluble zirconium salt is a compound represented by the chemical formula ZrOC12,8H20, and its molecular weight is 321.

Since the molecular weight of zirconia obtained by the heat treatment of this zirconium oxychloride is 123, the yield of zirconia from powdered zirconium oxychloride is about 38%. On the contrary. when a simple aqueous solution of zirconium oxychloride is usedr the yield of zirconia is about 50% of the yield of zirconia obtained by using the powdered zirconium oxychloride, i.e., only about 19% because the concentration of zirconium oxychloride of the saturated aqueous solution is of the order of 50%.

Howevery the zirconium-containing aqueous solution (the reaction product) used in the present invention can provide a yield of zirconia comparable to that of powdered zirconium oxychloride or a higher yield by heat treatment. In the present invention,! the zirconiumcontaining aqueous solution is used as a spinning is solution, and therefore the yield of zirconia is high and zirconia fibers having high strength are obtained.

(b) While it is possible to obtain a high yield of zirconia, the zirconium-containing aqueous solution of the present invention is a transparent and high viscosity solution and is effectively utilized as a spinning solution from which zirconia fibers are produced, as an impregnating solution for filling pores of articles such as ceramics, or as a binder.

(c) Since the yield of zirconia is high, zirconia fibers having high strength are obtained. The zirconiumcontaining aqueous solution is efficiently impregnated into pores of articles such as ceramics and thus can be used as a binder exhibiting strong bonding strength.

(d) The spinning solution used in the present invention, i.e., the aqueous solution of the reaction product of zirconium oxychloride with hydrogen peroxide is converted to a viscous solution exhibiting spinnability by enhancing the degree of concentration for evaporating its water content. Accordingly, it is unnecessary to add an organic sizing agent in order to impart spinnability.

(e) Since the reaction product is cold spun in the present invention, there is little restriction in the spinning method of forming the fiber pgecursor, and the reaction product can be spun -by various methods such as extrusion, centrifugal spinning and spraying.

The zirconium oxychloride used in the present invention is a compound represented by the chemical formula ZrOC128H20, and it may be in any form, i.e., powder or liquid. When powdered zirconium oxychloride is usedi it is desirable that it be throughly dissolved in water. This zirconium oxychlorlde may contain impurities usually contained in a commercially available material. The zirconium oxychloride is dissolved in water by a conventional method to prepare an aqueous solution thereof. While the concentration of zirconium oxychloride can be suitably varied according to the uses of a desired zirconium-containing aqueous solution, it is desirable to start from a saturated solutionp e.g.i a 50% solution at 25C from the standpoint of efficiency of the preparation of the solution.

Aqueous hydrogen peroxide which is added to the aqueous solution of zirconium oxychloride is an aqueous solution containing hydrogen peroxide, and for convenience a commercially available 30% aqueous solution can be used. The amount of hydrogen peroxide added is preferably from 0.1 to 10 molest more preferably from 0.5 to 5 moles per mole of zirconium oxychloride powder represented by the chemical formula Zr0C12.8H20' If the amount of hydrogen peroxide is less than,the lower limit, the reaction of zirconium oxychloride with hydrogen peroxide will be insufficient, and zirconium oxychloride -g- Z crystals will deposit during the concentration process, whereby a clear solution cannot be obtained. If the amount of hydrogen peroxide is more than the upper limit, the cost will be increased. 1 The preparation of the reaction product of the aqueous zirconium oxychloride solution with aqueous hydrogen peroxide is carried out by reacting zirconium oxychloride with hydrogen peroxide with heating. The reaction temperature is preferably from 300 to 750C, more preferably from 400 to 700C. If the reaction temperature is less than the lower limit, the reaction will take a long period of time from several days to several months. If the reaction temperature is more than the upper limit, crystalline zirconia submicron particles will deposit, and the resulting solution will become turbid.

The resulting reaction product is optionally concentrated by evaporating off its water content from the product. The yield of zirconia can be further enhanced by this concentration. Examples of such concentration operations include boiling and vacuum evaporation. In the present invention, the degree of concentration can be suitably selected depending on the spinning method. For exampler when the reaction product is to be spun by a centrifugal method or spraying method, a solution having a relatively low visco-tity is suitable. and therefore the degree of concentration is reduced. When the reaction product is to be spun by extrusion molding, a highly viscous solution is suitable, and therefore the degree of concentration is increased. When the reaction product is to be used as an impregnating solution for pores of refractories and ceramics,, a low viscous solution is suitable..

In preparing the viscous solution (the reaction product) for the formation of a fiber precursor, a viscosity modifier or diluent can be added in order to adjust the viscosity property (spinnability). Examples of such viscosity modifiers which can be used in the present invention are: synthetic polymeric materials such as polyethylene oxide, polyvinyl alcohol, and polyacrylic acid; cellulose derivatives such as methyl cellulose, carboxyethyl. cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose and cellulose phosphate; and animal and plant viscous materials such as starch and starch derivatives, pectin, sodium alginate and agar. The amount of the viscosity modifier or diluent added can be suitably varied depending on the desired fiber length and fiber diameter of the refractory fibers, i.e., desired viscosity.

Furtheri, in preparing the viscous solution of the present invention, various adjuvants can be added in order to impart a variety of characteristics to the fiber precursor and/or refractory fibers. Examples of such adjuvants which can be added are crystal stabilizers such as chlorides, sulfates and nitrates of magnesium, i R yttrium, calcium, samarium, cadmium, lanthanum and neodymium. The time of addition of the adjuvant is the same as the time of the preparation step of the viscous solution in the present invention or before or after the preparation step. The adjuvant is preferably added in the form of an aqueous solution.

A step of cold spinning the reaction product in the present invention to form a fiber precursor can he carried out by any conventional method. Examples of such methods include centrifugal spinning, extrusion and spraying.

The resulting fiber precursor is then fired by any conventional method to produce zirconia fibers.

EXAMPLES

While the present invention is illustrated more fully by the following examples and comparative examples, the present invention is not intended to be limited thereto. Quantities expressed hereinafter in "parts" and 11C are by weight.

Example 1

One hundred parts of zirconium oxychloride powder was dissolved in 100 parts of water to prepare an aqueous zirconium oxychloride solution having a concentration of 50%. Thirty parts of 35% aqueous hydrogen peroxide was added to 100 parts of the aqueous sqlutionf and the mixture was heated to 500C with stirring. At about 20 minutes after the beginning of the heating, zirconium i 2 -i; oxychloride and aqueous hydrogen peroxide vigorously reacted to generate a large amount of bubbles. Thereafter, the generation of bubbles was reduced. After "30 minutes, the reaction was completed.

Two hundred parts of the resulting reaction proOtict was boiled to evaporate off some of its water content to concentrate the product to 100 parts by weight. Although the resulting concentrate had an extremely low viscosity (50 cp), an aqueous solution of this reaction product was converted to zirconia in a yield of 35% by heating it at a temperature of about 1,OOOOC.

To one hundred parts of this aqueous solution were added 14 parts of an aqueous solution of yttrium chloride (yield of Y203: 18%) and 5 parts of polyethylene oxide as a spinnability-imparting sizing agent. These were mixed, and thereafter spun by a centrifugal spinning method to prepare a fiber precursor. The fiber precursor was then fired at a temperature of lj3000C. The characteristics of the resulting zirconia fibers are shown in Table 1.

Comparative Example 1 Zirconia fibers were produced as in Example 1 except that 8 parts of an aqueous solution of yttrium chloride (yield of Y203: 18%) was added directly to the aqueous zirconium oxychloride solution (yield of zirconia: 19%) of a concentration of 50% used in Examplip 1.

The characteristics of the resulting zirconia fibers are shown in Table 1.

Example 2

The concentrate of the reaction product obtained in Example 1 was further concentrated to 50 parts. The resulting concentrate was a solution having a viscosity of 100,000 poi.ses and exhibiting -transparency and spinnability. The yield of zirconia from this solution was extremely high. (70%) The resultina o concentrate was spun under an extrusion pressure of 5 kg/CM2 by means of an extrusion spinning machine having a 0.1 millimeter spinneret. The resulting fiber precursor was fired at a temperature of 1,3000C to produce zirconia single fibers. The characteristics of the resulting fibers Table 1.

are shown in 4 Table 1

Example 1 Comparative Example 2 Example 1

Average f iber diameter, 5 5 20 micrometer Average riber length, 20 20-30 continuous fiber millimeter Chemical component ZrO 2 93 93 100 Y 2 0 3 7 7 - Tensile strength, kglmm' 120 no more than 5 100 Crystal system tetragonal tetragonal monoclinic 1

Claims

1. A zirconium-containing aqueous solution comprising the reaction product of an aqueous solution of zirconium oxychloride with hydrogen peroxide.

2. The zirconium-containing aqueous solution according to claim 1, wherein the reaction product is a concentrate.

3. A process for producing a zirconium-containing aque.ous solution which comprises the steps of add.ing aqueous hydrogen peroxide to an aqueous solution of zirconium oxychloride and reacting the zirconium oxychl-oride with the hydrogen peroxide under heating and under such conditions that substantially no crystalline zirconia is formed.

4. The process according to claim 3, wherein the reaction of the zirconium oxychloride with the hydrogen peroxide is carried out at a temperature of from 300C to 75C.

5. The process according to claim 3, wherein the reaction product of zirconium oxychloride with hydrogen peroxide is a concent-rate obtained by, evaporating the water content thereof.

6. A process for producing zirconia fibers which comprises the steps of cold spinning the product of reaction of an aqueous solution of zirconium pxychloride with aqueous hydrogen peroxide to form a fiber precursor and then firing said precursor.

7. The process according to claim 6, wherein said reaction product is one obtained by the reaction at a temperature of from 300C to 750C.

8. The process according to claim 6, wherein said reaction product is a concentrate obtained by evaporating the water content thereof.

i Published 1988 at The Patent Office, State House, 66.71 High Holborn. London WCIR 4TP. Purther copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87.