US3486867A

US3486867A - Methods for fiberizing encapsulated materials in glass

Info

Publication number: US3486867A
Application number: US577080A
Authority: US
Inventors: Roger E Wilson
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1966-09-02
Filing date: 1966-09-02
Publication date: 1969-12-30
Anticipated expiration: 1986-12-30

Description

ment of any royalties'thereon or therefor.

" referred to as' an encapsulating material, an I toform a high density "compact; I 1 1 Thereaften'a sintering or hot pressing operation is per- 3,486,867 METHODS FOR FIBERIZING EN CAPSULATED MATERIALS IN GLASS i Roger E. Wilson, Silver Spring, Md., assignor to the United Statesof America as represented by the Secretary of the Navy s No Drawing. Filed Sept. 2, 1966, Ser. No. 577,080 I Int. Cl.C03b 37/02 4Claims Ans'rR'A'c'ron THE nrsct'osru U A process for producing high strength reinforcing fibers which includes blending the powders of a fiberizable glass material and adesired material to be fiberized, hot pressing the blendand attenuating to fiberize 'the constituent materials.

The inventiondesc'ribed herein may be manufactured of America for governmental purposes without the pay- This invention relates to improvements in techniques for processingfusible'materials into a'fiberous form. More and used by or for the Government of'the United States particularly, the invention relates to a method for forming fine, high-strength, reinforcing fibers froni'fusible mate- Prior attempts to overcome the inability of'present day methods to fiberize melts of the strongestand most desirable reinforcing fusible'materials' have been unsuccessful.

'due, to a large extent, to certain inherent characteristic shortcomings of the' particular type of'material utilized, such as an insufficiently high viscosity characteristic and an insufiiciently pronounced inverse temperature-viscosity relationship.

a method of fiberizing any" fusible material and of producirig'a'n article-of manufacture therefrom.

Another object of the present invention is to providea method for producing high strength reinforcing fibers.

*Accdrdingly, it is an object of this invention to provide -The' foregoing and other objects areattained by blehding a powder ofa' material desiredto be fiberized'with the powder of a suitable fiberizable materiah' hereinafter 'omp'ressing the powders'to a degreeisufiicient formed, further densifying the matrix. This is renewed by a reheating and drawing of the dense composite material into fibers. Theencapsulated'flmoltenparticles are thus drawn into fine reinforcing fibers within the encapsulating material.

Other objects, advantages novel features o f the invention will become apparent from the following detailed description of the inventionuw In the practice of this invention, .fiberiz ation of any I fusible material is accomplished by encapsulating small particles of the material'desired to be fiberized in a fiberizable material and attenuating or drawing down the cross sectional area of both contemporaneously.

The size of the powder particles of the parent material and of the material to be fiberized may vary over a wide range. Particle size of the parent material controls how close encapsulated particles may approach each other in the hot pressed composite and ultimately the spatial positioning of the fibers after attenuation. The particle size of the nonfiberizable material determines the diameter of the fine reinforcing fiber formed, for a given amount of attenuation of the matrix material. After attenuation, the fibers of the nonfiberizable material may either be removed from 3,486,867. Patented Dec. 30, 1969 the fiberizable encapsulating material by a solvent solution or in the alternative, may be left within it as a reinforcement therefor. Fibers of most materials show greatly enhanced physical properties as compared to the massive forms of these materials, and regardless of whether the fibers are removed from the encapsulating material or left therein as a reinforcing medium therefor, they retain their strength. Ifthe fibers are removed, they may be utilized to reinforce any suitable material as desired. However, if

the reinforcing fibers are left in the matrix, several advantages results, i.e., improved physical characteristics, such as, an increased modulus of elasticity and. increased strength of the parent material. The parent or encapsulating material generally has a lower Youngs modulus than the nonfiberizable encapsulated material, such that the parent material will be stiffened by the'reinforcing fibers, thus inc easing the rigidity and'strength of the specimen.

Reinforcing materials having a higher coefficient of thermal expansion than the parent material, when encapsulated in a parent material, contracts more than the parent material during cooling after attenuation, such that the surface of the parent material is placed in compression and thereby greatly strengthened.

Encapsulation of particles of a nonfiberizable material in a suitable fi'berizable material followed by attenuation at a temperature at which the nonfiberizable material is molten, is a significant step in the practice of this invention. The fiberizing ability of one material is used to fiberize another which may not by itself be fiberizable and the shortcomings displayed by the melts of the strongest and most desirable fusible materials such as metallic elements, oxides, carbides, silicides and nitrides are overcome to the extent of providing a high viscosity and a sufficiently pronounced inverse temperature-viscosity relationship for effecting fiberization. The softening point of the parent material and the melting point of the nonfiberizable material are characteristics which should be recognized as prime factors in the selection of materials for the process of fiberization.

, Densification of the matrix materials during hot pressing is normally accomplished by standard hot pressing methods or some variation thereof, such for example, as isostatic hot pressing. However, if sintering rather than hot pressing methods are employed, while maintaining the temperature near. the softening point of the parent material, the nonfiberizable particles being molten, would di ss lve in the parent material or if insoluble would tend to' undesirably coalesce therein. To circumvent these problems and achieve a dense compact specimen encapsulating powdered particles of nonfiberizable material, blended powders of these materials are hot pressed at a temperature well below the softening point of the parent material at pressures on the order of several thousands of pounds per square, inch. For instance, fused silica compacts may be hot pressed at temperatures below 1400 C. at pressures in the vicinity of 5000 p.s.i., thereby permitting the use of nonfiberizable particles having a melting point above 1400 C. and below the fiberizing temperature of silica (2000-2300 0.). In the case of a matrix utilizing workable segments or specimen of a size conducive to convenient handling during heating and attenuating, with the size of each segment being governed by the apparatus utilized for drawing out the specimen. Any appropriate technique for reducing the cross sectional area of the specimen is suitable for drawing the specimen and may, for example, take the form of a blast of steam, gas or liquid against the molten specimen. Alternatively a mechanical pulling device or the action of a centrifugal force type device may be utilized.

During attenuation i.e., reduction of the cross sectional area of the specimen, heat is applied to a small area of the material which is immediately fiberized and cooled. In heating a specimen of the parent and nonfiberizable materials to a molten state, the fiber drawing temperature vs. time relationship must be maintained within limits, such as to be insufficient to allow oxides to dissolve or for insoluble particles to coalesce within the specimen. Failure to observe the aforementioned relationship will result in either a large decrease in viscosity or the formation of globules which will not remain disseminated evenly throughout the composite.

Although examples of specific elements are hereinafter set forth, the general principles employed in the practice of the process of the instant inventive concept can be applied to all nonfiberizable materials which form a melt, provided an encapsulating material is used with a fiberizing temperature above the melting point of the nonfiberizable material.

Glasses of the very soft low melting types up to fused silica may be used to encapsulate and attenuate various materials, such as metallic alloys, oxides, nitrides, carbides, borides, silicides, and fiorides.

Properties of materials reinforced by high strength fibers can be altered by selection and control of various factors or relationships of the component materials, such as the encapsulating reinforcement fibers, diametric sizes of reinforcing fibers, heat treatment during and after attenuation, oxidation or other surface treatment of added particles before hot pressing and shape of fibers.

Some examples of elements which may be encapsulated in silica glass and attenuated in the practice of this inventive concept are given below with their melting points. The examples are merely illustrative and should not be construed as limiting the invention.

Oxides which may be used with silicaglass are:

' C. Alumina 2050 Titania 1840 Mullite 1850 Spinel 2135 Chromium oxide 1990 Zircon 1775 Powders of the constituent materials utilized in the instant fiberizingprocess are intimately mixed by blending or grinding. During grinding, the freshly exposed surface tends to oxidize, which may be desirable in' the formation of a strong glass-.to-fiber bond, but may be undesirable for other applications. This oxidation process may becontrolled by performing the grinding function within specially controlled surroundings, such as a helium atmosphere or within a water or alcohol solution.

What is claimed is: p

1. A method of producing high strength reinforcing fibers comprising the steps of intimately blending the powder of a material to be encapsulated which is not by itself fiberizable, which forms a melt and which is selected from the group consisting of silicon, chromium, cobalt, zirconium, titanium, iron, nickel, stainless steel, alumina, titanic, mullite, spinel, chromium oxide and zircon with the powder of an encapsulating fiberizable glass material which exhibits a fiberizing characteristic at a temperature slightly above the melting point of the material to be encapsulated, compressing the composite of said materials at a temperature slightl below the softening point of the encapsulating material at pressures in the order of several thousand pounds per square inch, to form a dense compact matrix, severing the matrix into workable segments, locally heating a small area of the segment to fiberizing temperature and immediately attenuating to fiberize the constituent materials therein.

2. A method of producing high strength reinforcing fibers as set forth in claim 1, and including the step of blending a gettering agent within the composition of materials to absorb the residual gasses entrapped in the compressed matrix during hot pressing.

3. A method of producing high strength reinforcing fibers as set forth in claim 2, wherein the step of attenuating each molten segment includes the drawing down in cross-sectional area of each segment while cooling the composite of materials until fiberization of the constituent materials is accomplished.

4. A method of producing high strength reinforcing fibers as set forth in claim 3, further including the step of removing the reinforcing fibers from the attenuated segments of material by dissolution of the encapsulating material.

References Cited UNITED STATES PATENTS 2,908,545 10/1959 Teja.

3,177,057 4/1965 Potter et al. 18 X 3,362,803 I 1/1968 Danniihl et a1 652 X