WO1991015437A1 - Fibres ceramiques ultrafines - Google Patents

Fibres ceramiques ultrafines Download PDF

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Publication number
WO1991015437A1
WO1991015437A1 PCT/US1991/002029 US9102029W WO9115437A1 WO 1991015437 A1 WO1991015437 A1 WO 1991015437A1 US 9102029 W US9102029 W US 9102029W WO 9115437 A1 WO9115437 A1 WO 9115437A1
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WO
WIPO (PCT)
Prior art keywords
fibers
solution
precursor
metal oxide
zirconia
Prior art date
Application number
PCT/US1991/002029
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English (en)
Inventor
Gary L. Messing
Derek W. Sproson
Shi Chang Zhang
Original Assignee
Research Corporation Technologies, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Research Corporation Technologies, Inc. filed Critical Research Corporation Technologies, Inc.
Publication of WO1991015437A1 publication Critical patent/WO1991015437A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B20/00—Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
    • C04B20/0048—Fibrous materials
    • C04B20/0056—Hollow or porous fibres
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/62227—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products obtaining fibres
    • C04B35/62231—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products obtaining fibres based on oxide ceramics
    • C04B35/6225—Fibres based on zirconium oxide, e.g. zirconates such as PZT

Definitions

  • This invention relates to the production of ceramic fibers. More particularly, this invention relates to the production of discontinuous ultrafine ceramic fibers.
  • Ceramic fibers include a wide range of amorphous Q and polycrystalline fibers which are used at high temper ⁇ atures. Chemically, ceramic fibers are generally classified as oxide or nonoxide fibers. The ceramic fibers described herein have also been referred to in the prior art as refractory fibers. Sometimes the terms have been used c interchangeably. However, those skilled in this art today appear to prefer the term ceramic fibers and that term will be employed herein. It is understood that by this desig ⁇ nation, those materials which can be formed into ultrafine fibers by the process described herein and which may have
  • the ceramic fibers which are the subject of this application are of the oxide type. Examples of oxide ceramic
  • 5 fibers include alumina-silica fibers, high silica fibers, zirconia fibers, beryllia fibers, magnesia fibers, and alumina fibers as well as fibers prepared from compositions from which a sol can be prepared. These fibers generally xz have diameters of 0.5 to 10 urn and are manufactured in lengths ranging from 1 cm to continuous filaments. Any of the manufacturing techniques employed to produce ceramic fibers produce a product which may contain a significant quantity of the ceramic material in particulate rather than o in fiber form. These unfiberized particles are commonly referred to in the art as shot. The presence of shot is normally undesirable, since it reduces the thermal efficiency of the fibers.
  • a chromia modified alumina-silica fiber produced a upper temperature limit above 1400°C.
  • a boria modified 30 alumina-silica fiber also produced a fiber which could be used continuously at temperatures above 1400°C.
  • a precursor process developed by Union Carbide Corporation involved the use of an organic polymer fiber as
  • 35 1 a precursor which absorbed the dissolved metal oxides.
  • the treated fiber Subjecting the treated fiber to heat, burned out the organic fiber, leaving the metal oxide as a polycrystalline ceramic in the shape of the precursor polymer fiber.
  • Employing 5 zirconium oxides permitted the development of zirconia fiber useful at temperatures in excess of 1600°C.
  • Babcock & ilcox developed a process of spinning, blowing or drawing a viscous aqueous solution of metal salts to produce fibers which could be converted to the oxide form of the salts in a subsequent Q heat treatment.
  • Mixtures of metallic salts permitted the preparation of fibers of combinations of metal oxides.
  • Imperial Chemical Industries developed a process which eliminated the requirement for the use of an organic precursor fiber.
  • This process resulted in a significant reduction in the manufacturing cost of such oxide fibers as zirconia and alumina.
  • a metal salt such as aluminum oxychloride or acetate for an alumina fiber, or zirconium oxychloride or acetate for a zirconia fiber
  • a polymer such as pol (vinyl alcohol)
  • the solution is further thickened by evaporation and then extruded through a spinneret to produce fibers which are collected on a drum where they are fired to a temperature of 800 ⁇ C to provide the desired oxide fiber.
  • the firing removes the organic polymer thickener and produces a fiber with a diameter of 3 to 5 urn and a low degree of porosity.
  • the fibers may be heated to 1400 to 1500°C to eliminate the porosity.
  • An alumina-silica fiber may be prepared in basically the same process from a solution of aluminum acetate mixed with a dispersion of colloidal silica and dimethylformamide.
  • Zirconia fibers often require the addition of a material known as a phase stabilizer, since zirconia undergoes a volume change associated with a monoclinic- tetragonal crystal phase transformation at 1000 to 1200°C. This volume change limits the utility of zirconia in certain end use applications.
  • U.S. 3,704,147 of Hardy discloses the preparation of zirconia or alumina fibers by spray drying a highly viscous solution of the metal oxide where the solution has a viscosity in excess of 500 cp at 25°C.
  • the spray dryer is operated using an atomizer disk spun at speeds in excess of 35,000 rpm onto which the viscous solution is introduced. Air inlet temperatures of 200 to 250°C and air outlet temperatures of 100 to 120°C are employed. Subsequent to the separation of the fibers, they are calcined at temperatures of 700 to 1000°C. Fibers having a diameter of 1 to 10 urn and lengths of up to and exceeding 1 mm are prepared by this method.
  • discontinuous, discrete ceramic fibers are prepared by employing an aqueous solution of a chemical precursor of the desired oxide composition, adjusting the solution viscosity to about 50 to about 140 cp and the surface tension of the
  • a fiber is formed as a result of its high viscosity which continuously breaks off to form discrete, discontinuous fibers, for example, fibers of about 0.1 to 20 cm in length and diameters of about 1 to 5 urn, although fibers of longer or shorter length or greater or smaller diameter can be prepared by the subject method.
  • the fibers produced are rapidly dried before they contract to thicker diameter fibers or a droplet morphology. The rapid drying process results in the production of fibers, since it preserves the ligaments formed during the atomization of the solution. After being rapidly dried in the first high temperature zone, a higher degree of heat is
  • a solution viscosity of about 50 to about 140 cp at ambient temperature have been found useful for many solutions, but it is the combination of solution viscosity, 5 solution surface tension and atomization parameters which must be coordinated to provide fibers of the desired properties.
  • solution viscosity about 50 to about 140 cp at ambient temperature
  • 5 solution surface tension about 5 solution surface tension
  • atomization parameters which must be coordinated to provide fibers of the desired properties.
  • one of ordinary skill in the art can, without undue experimentation, adjust the viscosity and surface tension of the solution, the o atomizing conditions and the high temperature conditions to provide fibers having the desired properties.
  • this invention relates to a process of preparing discontinuous discrete ceramic fibers which comprises: (a) atomizing an aqueous solution of a precursor of a metal oxide into a first high temperature zone under conditions of solution viscosity, solution surface tension, atomization and temperature in the first high temperature zone effective to form ligaments of said solution 0 and remove the aqueous phase from said ligaments so as to provide discrete, discontinuous fibers, and
  • Figures 1A and IB are phtomicrographs of. zirconia fibers prepared from different zirconia precursors.
  • Figures 2A, 2B, 2C and 2D are photomicrographs of zirconia fibers showing the effect of the concentration of 10 the precursor in the initial solution.
  • Figures 3A and 3B are photomicrographs showing the effect of employing a polymeric binder in the zirconia precursor solution.
  • Figures 4A and 4B are photomicrographs of 15 commercial zirconia fiber and Figures 4C and 4D are photomicrographs of zirconia fiber prepared by the process of the subject invention.
  • the present invention relates to the process for the preparation of ceramic fibers by a process described
  • P ⁇ as spray pyrolysis.
  • the subject process prepares discrete, discontinuous fibers by employing an aqueous solution of a chemical precursor of the desired oxide composition. The viscosity and surface tension of the solution are adjusted and then the solution is sprayed or atomized into a heated
  • discontinuous ceramic fibers of such diverse materials as zirconia, zinc oxide, ferrite, alumina, silica, alumina-
  • 35 2 like may be prepared by employing an appropriate precursor.
  • Aqueous solutions of the precursor in concentration of 20 to 30, preferably 22 to 25 wt.% (as the metal oxide) have been found to be useful in the instant process.
  • aqueous solutions of such precursors as zirconium acetate, zirconium hydroxyacetate and the like may be employed.
  • aluminum oxychloride, aluminum chlorate, aluminum lactate, and aluminum acetate and the like may be employed when alumina fibers are to be 0 prepared.
  • ZnO precursors such as zinc acetate, zinc chlorate, zinc nitrate, zinc chloride, zirconyl nitrate, zirconyl chloride and the like and ferrite precursors such as nitrates, acetates, chlorides and the like salts of iron and such other metals as manganese, zinc, nickel and the like may 5 be employed when oxide fibers of these materials are to be prepared by the process of this invention. Where desirable, mixtures of the precursor salts may be employed.
  • aqueous solution containing at least 1 wt.% o of the metal compound, as the oxide will be compatible with any viscosity increasing polymer added to the aqueous solution and will be converted to the appropriate oxide by calcination of the discontinuous fiber prepared therefrom.
  • the viscosity of the solution must be adjusted to about 50 to about 140 cp, preferably about 100 to about 125 cp at 25°C and the surface tension of the solution
  • aqueous solutions of a medium molecular weight polymer such as poly(vinyl alcohol) may be employed to increase the viscosity of the solution.
  • a medium molecular weight polymer such as poly(vinyl alcohol)
  • poly(vinyl alcohol) has been found to be useful.
  • Other polymeric materials such as methyl cellulose, polyethylene oxide, hydroxyethyl cellulose and the like, may likewise be employed to adjust the viscosity of the solution, but poly(vinyl alcohol) is preferred.
  • high purity water soluble polymers such as poly(2-ethyl-2 oxazoline) or poly(propylene carbonate), both of which are commercially available, can be substituted for the preferred poly(vinyl alcohol).
  • the surface tension may be adjusted by means of a surfactant, such as an alcohol ethoxylate.
  • Particularly useful are those surfactants sold under the Brij tradename by ICI Americas Inc.
  • One particularly useful surfactant is Brij-58 where the alcohol ethoxylate is of the formula, C 16 H 33 tOCH 2 CH 2 ⁇ 20 OH..
  • the heated zones which are employed to prepare the discontinuous fibers may be located in a single vessel, such as a two zone heated furnace, or a separate vessel or furnace m ay be utilized for each zone. It has been found that the initial zone into which the solution is sprayed should be operated at a temperature of approximately 300 to 400°C with the fibers being retained therein for a period sufficient to rapidly dry the fibers as they are formed. Heating periods of about 1 to about 6 seconds, preferably about 2 to about 3 seconds have been found useful for this purpose. Once the fibers have been dried, they may be collected and passed to the second zone which is operated at a higher temperature to permit calcination of the fibers.
  • the fibers may be continuously passed from the first zone into the second higher temperature zone for calcination.
  • the heating zones are located in a vertical furnace such that the fibers are initially formed in the lower temperature zone, and once they are dried they are carried by air flow into the calcination zone.
  • the calcination zone should be operated at a temperature of 1000 to 1400°C for effective calcination of the fibers.
  • Spray nozzles of various types have been effectively employed, although atomization with a two-fluid nozzle employing air as a second fluid have been found effective for this purpose.
  • a flow rate of about 12 ml/min. and a pressure of about 15 psi have been found to be useful.
  • Effective pressurized atomizers are those which provide liquid droplets of about 50 um or less. For a uniform product, it is important that the flow rate be stable and the gas pressure be maintained substantially constant.
  • the calcined fibers produced by this technique are both discrete and discontinuous, being about
  • the fibers are also ultrafine, having diameters of about 1 to about 5 um.
  • the discrete fibers produced by this process are crystalline in nature and may be produced in a wide range of crystallinity by regulating the time and temperatures, particularly in the calcination zone.
  • the fibers are X-ray amorphous before being calcined. However, the crystallinity can be varied from 0 to 100% through control of calcination time and temperature.
  • the fiber diameter and length are primarily controlled by atomizer pressure, solution viscosity, solution surface tension, concentration and solution flow rate. Where the fibers removed from the calcination zone contain an incompletely decomposed precursor or are of too low crystallinity, the fibers may be heated subsequently to produce the desired phase compositions.
  • the process of this invention can provide ceramic fibers in either a solid or hollow configuration.
  • hollow fibers are prepared if higher concentration and high viscosity solutions are supplied to the atomizer at a higher flow rate thus attaining a higher heating rate.
  • low solution concentration and viscosity at l° w flow rate solid fibers are obtained.
  • the formation of solid or hollow fibers by the method of the subject invention depends on the concentration of precursors in the solution. Using low relative solution concentration allows for more shrinkage of the solution precursor ligament before the precursor precipitates. Although the presence of the polymer affects the precipitation of the precursor, one having ordinary skill in the art can determine without undue experimentation the exact conditions required to provide the desired fiber. For example, it is known that solid fibers form when the initial precursor concentration is about 22 to 24 wt.% Zr0 2 in the zirconium acetate solutions. Solid fiber formation is also enhanced by using heating rates lower than those associated with spray pyrolysis ( ⁇ 300°C/sec) . Further, the slower the heating rate, the larger will be the fiber diameter.
  • the liquid precursor ligament has sufficient time to contract and spheriodize instead of forming a fiber.
  • Hollow fibers can be obtained by starting with highly concentrated solutions up to the saturation limit of the precursor salt and employing faster heating rates than are employed for producing solid fibers.
  • the fiber length * (x ) formed from a liquid is controlled by
  • V is the fiber elongation velocity
  • R is the initial fiber radium
  • ' is the liquid viscosity
  • ⁇ is the liquid surface tension.
  • fiber length is increased by increasing flow rate to the atomizer and atomizer pressure.
  • fiber diameter is decreased for the same conditions leading to increased fiber length.
  • low flow rates yield fibers of ⁇ 2um diameter and > 2 ⁇ m diameter fibers for rapid flow rates.
  • the fiber diameter is also controlled by adjustments in the viscosity to surface tension ratio.
  • phase stabilizers may be employed.
  • yttria and other phase stabilizers may be added to a zirconia precursor solution to provide the meta stable zirconia crystal.
  • the following examples illustrate the practice of the process of the subject invention. In all of these examples, the preparation of discrete, discontinuous zirconia fiber is illustrated. The preparation of zirconia fiber is made for illustrative purposes only and is not to be taken as limiting the subject invention, since those skilled in the art can readily appreciate that the process illustrated in these examples may be readily adapted to prepare metal oxide, discrete discontinuous fibers of other metals.
  • This example illustrates the preparation of zirconia fibers from different precursors.
  • aqueous solution of zirconium acetate and zirconyl nitrate was prepared by dissolving a quantity of the salts in water.
  • an aqueous solution of zirconium hydroxyacetate and zirconyl nitrate was prepared.
  • Yttrium nitrate was added to each solution to provide a Y-0-, concentration of about 5 wt.% of total oxide yield. Upon calcination this provided a yttria phase stabilizer in the zirconia fiber.
  • the aqueous solutions were stirred until all the salts were dissolved and the solution became clear.
  • Each viscous solution was atomized by means of a two-fluid nozzle employing air at a pressure of 15 psi and an aqueous solution flow rate of 12 ml/min.
  • the solution was atomized into a vertical furnace operating at a temperature of about 400°C.
  • the discrete fibers were formed and dried, they were collected in a cotton bag.
  • the fibers were deep gray or brown in color and were quite flexible.
  • the collected fibers were then heated in a calcination zone at a temperature from 900 to 1600°C.
  • the calcined fibers were white and cotton-like.
  • Figure 1A shows a micrograph (250X) of the fibers prepared from the acetate precursor
  • Figure IB shows a micrograph (1250X) of those prepared from the hydroxyacetate precursor.
  • Figure 1A shows a higher fiber yield
  • Figure IB shows a large fraction of particulate matter or shot.
  • the zirconia was tetragonal phase with a grain size of 0.1 and 0.2 um at 1200 and 1400°C, respectively.
  • FIG. 1 This example illustrates the effect of precursor concentration in the solution.
  • solutions of the acetate precursor were prepared in four weight percent concentrations, 23.5%, 24.8%, 26.6% and 27.4%, as zirconium oxide.
  • the calcined fibers prepared from the solutions were evaluated by X-ray diffraction and SEM.
  • Figures 2A, 2B, 2C and 2D are micrographs at a magnification of about 10OX and correspond to the solution concentrations of 23.5 to 27.4%, respectively. These micrographs suggest that the particulate fraction in the fibers increases with increasing oxide content.
  • the zirconia was in tetragonal form with grain sizes of 0.2 and 0.4 um for calcination at 1400 and 1600°C, respectively.
  • This example illustrates the effect of the surface tension of the aqueous solution on the subject fibers of the invention.
  • Two zirconium acetate precursor solutions (25 wt.% Zr0 2 ) were prepared at a viscosity of about 120 cp, in a fashion similar to that of Example 1, except that a nonionic surfactant was added to one solution to reduce its surface tension from 47 dynes/cm 2 to 39 dynes/cm2.
  • the surfactant employed was an alcohol ethoxylate of the formula
  • This example illustrates the difference between commercially available zirconia fibers and those prepared according to the subject invention.
  • Example 1 fibers prepared from the acetate precursor were compared with commercial zirconia fibers known by the tradename of Zircar. Micrographs of the Zircar fibers are shown in Figures 4A and 4B, while those prepared by the subject invention are shown in Figures 4C and 4D.
  • the Zircar fibers have a diameter greater than 10 um, while the fibers prepared by the invention have a diameter of 1 to 3 um.
  • the Zircar fibers also exhibit a crack-like morphology, while the fibers prepared by the subject invention are solid and do not exhibit those defects. Microstructurally the fibers prepared according to the invention are much finer and have a more uniform grain size relative to the Zircar fibers in the prior art. Further, fibers of the subject invention can be produced in either solid form or with hollow cross sections by adjusting the solution concentration and viscosity as described hereinbefore.
  • This example illustrates the use of the zirconia fibers of the subject invention.
  • Example 1 were passed through compression rolls and needled into flexible blanket form and subjected to temperatures of 1200 to 1600°C.
  • the blankets remained flexible and exhibited insulating properties comparable to those of commercially available needled blankets prepared from Zircar zirconia fibers.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Inorganic Chemistry (AREA)
  • Inorganic Fibers (AREA)

Abstract

On prépare des fibres céramiques discrètes et discontinues en vaporisant un sol ou une solution visqueuse d'un précurseur d'un oxyde métallique dans une zone réchauffée où les fibres discrètes et discontinues sont produites. La calcination subséquente des fibres produit des fibres de céramique d'oxyde métallique discrètes et discontinues.
PCT/US1991/002029 1990-03-30 1991-03-26 Fibres ceramiques ultrafines WO1991015437A1 (fr)

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US502,154 1990-03-30

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19758431B4 (de) * 1996-01-21 2004-01-15 Rennebeck, Klaus, Dr. Verfahren zur Herstellung von Mikrohohlfasern und deren Weiterverarbeitung zu Formkörpern
EP2045552A3 (fr) * 2007-07-17 2011-08-17 Heraeus Electro-Nite International N.V. Dispositif d'utilisation à des températures supérieures à 1 000 °C ou dans de l'acier en fusion et son utilisation

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3082051A (en) * 1959-07-24 1963-03-19 Horizons Inc Fiber forming process
US3094385A (en) * 1960-10-13 1963-06-18 Gen Electric Method for the preparation of alumina fibers
US3125416A (en) * 1964-03-17 Method for producing high purity monocrystalline
US3503765A (en) * 1966-02-14 1970-03-31 Babcock & Wilcox Co High temperature alumina-silica fibers and method of manufacture
US3607025A (en) * 1968-04-25 1971-09-21 Du Pont Silica-deficient mullite fiber and a process for its production
US3704147A (en) * 1969-05-06 1972-11-28 Atomic Energy Authority Uk Fibrous inorganic materials
US3950478A (en) * 1972-03-15 1976-04-13 Imperial Chemical Industries Limited Process for producing alumina fiber
US3982955A (en) * 1971-12-22 1976-09-28 Bayer Aktiengesellschaft Aluminum oxide fibers and their production
US4097392A (en) * 1975-03-25 1978-06-27 Spang Industries, Inc. Coprecipitation methods and manufacture of soft ferrite materials and cores
JPS61289130A (ja) * 1985-06-13 1986-12-19 Toray Ind Inc 高強度・高靭性を有するジルコニア繊維の製造方法

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3125416A (en) * 1964-03-17 Method for producing high purity monocrystalline
US3082051A (en) * 1959-07-24 1963-03-19 Horizons Inc Fiber forming process
US3094385A (en) * 1960-10-13 1963-06-18 Gen Electric Method for the preparation of alumina fibers
US3503765A (en) * 1966-02-14 1970-03-31 Babcock & Wilcox Co High temperature alumina-silica fibers and method of manufacture
US3607025A (en) * 1968-04-25 1971-09-21 Du Pont Silica-deficient mullite fiber and a process for its production
US3704147A (en) * 1969-05-06 1972-11-28 Atomic Energy Authority Uk Fibrous inorganic materials
US3982955A (en) * 1971-12-22 1976-09-28 Bayer Aktiengesellschaft Aluminum oxide fibers and their production
US3950478A (en) * 1972-03-15 1976-04-13 Imperial Chemical Industries Limited Process for producing alumina fiber
US4097392A (en) * 1975-03-25 1978-06-27 Spang Industries, Inc. Coprecipitation methods and manufacture of soft ferrite materials and cores
JPS61289130A (ja) * 1985-06-13 1986-12-19 Toray Ind Inc 高強度・高靭性を有するジルコニア繊維の製造方法

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19758431B4 (de) * 1996-01-21 2004-01-15 Rennebeck, Klaus, Dr. Verfahren zur Herstellung von Mikrohohlfasern und deren Weiterverarbeitung zu Formkörpern
EP2045552A3 (fr) * 2007-07-17 2011-08-17 Heraeus Electro-Nite International N.V. Dispositif d'utilisation à des températures supérieures à 1 000 °C ou dans de l'acier en fusion et son utilisation

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