CA1121391A

CA1121391A - Basalt glass-ceramic fibers and method of production

Info

Publication number: CA1121391A
Application number: CA000330245A
Authority: CA
Inventors: Hermann L. Rittler
Original assignee: Corning Glass Works
Current assignee: Corning Glass Works
Priority date: 1978-09-25
Filing date: 1979-06-21
Publication date: 1982-04-06
Also published as: FR2436757B1; JPS6320781B2; GB2031870A; FR2436757A1; JPS5547241A; DE2938421A1; GB2031870B; US4199336A

Abstract

ABSTRACT OF THE DISCLOSURE

Fine-grained, polycrystalline, basalt-type glass-ceramic fibers. having a crystal content of at least 35% and particular application as fiber reinforcement in concrete structures, are disclosed. A method of production comprises treating a vitreous fiber in the temperature range of 900 to 1250°C. for a time not exceeding ten minutes, and preferably less than one minute.

Description

Rittler 29 ~ 3.~3~

BA5ALT GLASS- OE RAMIG FIBERS AND ~ETHOD OF P~ODUCTION

Back~round of the I'nv'ention This invention relat~s to ~ine-grained, polycrystalline, glass-ceramic fibers produced from ~itreous f.ibers of a basalt-type ma~erial, and particularly useful for reinforcing purpo.ses.
It has.become customar~ to. employ asbestos fibers as a reinforcing agent in concr~te structures such as pipes, tiles, pan~Is, and t~e l.ike.',How.~ver, an e~tensi~e search has been underway for a suitabIe'suhstitute b.ec.ause of the heal.t~ hazards in~olved in handling asbestos ma~erial.
Glass fi.hers ha~e.'b.een among the'various al.ternati~es under. cons.ideration. Since 1.935,, the glass fiber industry has become fin~ly establis~ed, and glass fibers are used in many widely di~ersified applications. One such application is the reinforc~ment of plastic materials. used in molding structures ran.ging, from musical instruments to automobile bodies .
Unfortunately9 commercially a~ailab.le glass fibers have failed to pro~ide all of' the c~aracteristics required for concret~ reinforcement. In particular, the a~ailable fibers lack'resistance'to the.'alkaline, environment that prevails whe~ the~ c~mmon caments, suc~ as Portland c~ment, are mixed wit~ water. G~asses, hav~ ~een develope~ having a high'resistance to an al~alLne.'en~i~onment, but-the diffi-cul~y in producing fibers from such glas,ses, and/or the intrinsic eost of such fiber production, ha~e militatPd against their consideration for th~s purpose.
Basalt-type materials are widely availab,Ie, and rela-tively inexpensi~e~ natural materials. They are generally ~ 3 ~ ~

classified in m~neralogy as.bas.ic. ~olcanic rocks wherein thees.sential. constituents are t~è.min~rals feldspar, pyroxene, and magnetite, with'or without oL.i~ine, and a blac~ basalt glass. It has.been recognized .that .they are resistant to alkaline'attack, a charac.ter.istic that makes them of particular inter.est in connection wit~'alkaline. en~ironments such as .
ar~'encou~tered in concr~te'wo.rk.. Basalt materials are also easily meIt d and drawn as- f.ibers., a further fact that' makes them of interest as po.tent~al concrete reinforcement ~ibers.
A detailed description'of these ~aterials, their-physical and chemical characte~.istics~, and their commercial.history, is .set for.th'in U.S. Patent ~o. 3:,557,575, granted.January 26, 197~ to G.: H. Beall and H.` L.' Rittler.
. That patent disclo.ses the'production of glass-ceramic articles from ba~alt~type'~aterials. ~n accordance wIth its method', a basa1t type batc~,' containing at least.5~/O Fe203, is meLt~d;. ~he meIt is cooled be~ow 'its. trans~ormation range .
and a glass article shaped t~refro~; the glass is.'heat treated.in the'range'of 640-6J5C.: to orm magnetite. nu~.Iei;
and the nuc.~'eated glass is fur.ther ~eat treated to.cause crystallization on the nuc.~ei. T~us, the patent teaches that a ~agnetite'crystal phas~'can be obtained by.heat treatment in the.range of'6J5-80QC.', while heat treatment .
at a higher .tempera~ure in the.'ra~ge'o'850-10~0.C. f~rms a clinopyro~ene-magnetite mixe~ p~ase in wh~'ch the former predominates. Heat treat~ent t~mes of 0.5 to 4 hours are su~ges.ted.
.
It is ob.served that the'g~ass-ceramic bodies. ha~e' su~s~antially better resis~a~ce to attack by eit~er 'acid or alkaline~solutons than do corresponding glass bodles. This resistance'is ascribed to a residual glass phase rich in -alumina and silica. The patent warns that large plagioclase sp~erulites tPnd to form if heat .treating temperatures above 1000.C. are. emplo.yed.
Recentl.y, it was proposed, in U.S. Patent No. 4,008,~94, granted February 15, 1977 to the. inv~ntors Beall and Rittler, that the'resist:ance o:basalt-t~pe'glass fi~ers to alkaline attack be'impro~ed by in~luding 1 to 15% zirconia (Zr~2~ in t~e compositi.on of the ~asalt meIt from which the fibers w~re drawn. The patent fu~ther suggests that the glass .
10 fibers. may ~e paxtially-crystal~ized by internal crystal-liæation to. de~elop magnetic proper~es. Heat treatments . . .
ranging in time from 1 to:4 hours, and in temperature from 650 to 900C.., are'proposed to dev~l.op a crystal phase compo.sed of ~agnetite.'(Fe304),. ulvospinel (Fe2TiO2), or solid solution~ of these crystal fo'rms. Necessarily, -suc~' crystal phases represent only a minor degree of crystallization since'~he'total content of'Fe203 plus TiO2 in the glass is no moxe'than about 10 to 15% by w~ight. The patent also notes that .t:emperatures much i~ excess of 900C . ought to be .
avoided since coarse grained crystals of pyroxenes can d~velop.
~t has b.ePn recognized that glas-s ceramic materials tend to ha~e greater in~er.ent ~e~kanical strength t~an their glass precursors sincc a d'ominant-cr.ystal str~c.ture is develop.e~ that is homogeneous and relatively fine-grain~d.
In contrast,: large,' coar.se'crystals in a body normally tend to weaken the material and render it brittle, and hence are avoide:d.

Prior ~Art ~ .

In addition to the literature re~eren~es thus far cited, the following patents are also considered o interest --3~

~ ~ 2~ 3 ~ ~
ln connection with ~asalt mate~ials and fiber formation therefrom:
U.S. Patent ~o. 1,108,00.7, granted ~ugust 18, 1914 ta F. Ribbe, which'discloses. casting ~us.ed basalt,' cooling the castings belo~,'500C., and~ reheating to 800C.' to de~itrify .
the castings.
U.S'.' Patent No. 1,8.93.,'3~2,. granted January.3, 1933 to H. L. Wat~on, w~ich'disc~'oses'. controlling the devitrification of t~è. Ribbe product:by coordinating either an oxidation or a reducing atm~sphere,'duri~g melting wit~ a subse~uent devitrificat~on s.tep specific to the`'me~ting.a~mosphere.' U~S. Patent' ~o. 1,438.,428, granted December 12,. 1922 to Paul'D~,' w~irh disclo:ses drawing fibers from a molten basalt bath'and de~it~lfying t~ese'i~ers at a temperature of'800C..
:~U..S'. Patent No..3,'92~:,497, granted'December 30, 1975 ta Colin ~la~k-Monks> which'desc~.ibes basalt--type'c'omposit~ons that ca~ be'fiberized and ~ecr.yst~llized ~y heating a~o~e the softening point, preferably in the range of 650 to 800.C'.
U.S'.' Patent No~ 3:,881,945, granted May 6, 1975 to F. J.
Trojer e~ al., which'disclo.ses a method of producing a "ceram,ic-'glassl' ib ~, of: impr.ove~ modulus of' elasticity ln whIc~'a glass i~er is drawn,. separated into t~o. vitreous ~hases, and one of'~he~e phases is tken crystallized in part at,leas~.
:U.S.' Pa~ent ~o. 4,042.,:362~. granted Augus~ 163 1977 to J. F. MacDoweLL et al., ~hich'dis~lo.ses'a` method of.rapidly nucLeating and crystallizing glasses by heat-treatment of a fe~ minut~s to an hour, and r.e~iews' prior disclo:sures of rapid crystallization techni.q.ues, The patent does no~
mention basalt-type materials.
Thus, ~i~reous fibers may be formed from melts oE
natura~ basalt minerals, from such'natural materials modified by additives, or from syn~hes.ized batches in t~e.nature o~
glass.batches. Furt~er, thes'e~ fiber.s may be devitrified by conventional. heat treatment; .os may ~a~e a magnetic crystal phase of minor ~agni'Lud~'.de~el.op.ed ~y internal nuc.leation.
Ho~Qver,.it wa~ld be desirabLe'to pr.oduce a ~ore. hi~hly crystalliz.ed, fine-grained fiber of' a glass-ceramic nature from a. basalt-type mat rial. Fur.t.~er, it would be even more desirab.le to. pr.ovide'a metho~:of production compatib.le with oxdinary iber. drawing practice.

'S'ummar~ of .the I'nven~ion It.is :then a bas.ic purpose'of'the present invention to pr.ovide'glass-:ceramic f.ibers havi~g a basal~-type composition and a crystal phase of: substantial' magnitude, pre.~erab~
.
o~e$.50%. A: fur.t~er purpo.se ls to produce sueh fibers having a sufficientl~ fine-grai~ed crystalline phase to be resi~ient, while also.being. highIy resistan~ ~o. chemical .
at~ack, particu~arly from a~ alkalin environment. ~not~er purp.ase'is:~o pr.ov.ide a con~e~ent, inexpens.i~e met~od of producing :such fibers. A st~ urt~er puxpose is to pr.ovide a method o converting a ba~alt-type .iber from a ~itr ous stat~'to a glass-ceramic state'as the fi~er is being drawn from a melt.
In furt~Terance o~ th~se and other purposes, I ha~e now discovered tha~ vitreous ~asalt fibers, having a diame:ter not .
greater than about 250 mlcrons, can be internally cr~stallized to fo~m corresponding glass-ceramic ibers having a ~f~:~3~3~
magnetite-clinopyroxene mixed crystal phase constituting at least 35% of the fiber and preferably over 50%. I have further found that such fibers can be produced by a heat treatment not exceeding ten minutes in duration and preferably less than one minute. This discovery makes it feasible to continuously draw fibers from a basalt melt, and to subject these fibers to the necessary heat treatment for internal crystallization while they are being drawn and before being gathered, chopped, or otherwise processed for addition to concrete mixtures as reinforcement.
In accordance with my method, a vitreous basalt fiber is subjected to a heat treatment in the range of 900 to 1250C. for up to ten min~tes, preferably for a time less than one minute. Since the actual temperature of a fiber is virtually impossible to measure during a short exposure time, the characteristic temperature range represents temperatures to which the fiber is exposed, and which it is assumed that it reaches during such exposure.
Thus the invention provides a method of pxoducing reinforcing glass-ceramic fibers having a fine-grained, poly-crystalline phase which comprises, melting a raw material batch composed predominantly of a basalt-type material; forming vitreous fibers from such melt; forming magnetite nuclei in the glass fibers; and developing a mixed magnetite-clinopyroxene crystal phase on such nuclei, the crystal phase being at least 35% of the fiber, wherein the crystal phase is developed by heating the fiber at a temperature in the range of 900-1250C. for a time not exceeding ten minutes.

~f~P3~

The Drawings The invention is hereafter described with reference, in part, to the attached drawings wherei.n, FIG. 1 is a reproduction of an electron photomicro-graph of a fiber in accordance with the present invention, FIG. 2 is a magnified photograph of a basalt glass fiber after treatment in a test solution, FIG. 3 is a magnified photograph of a basalt glass-ceramic fiber after treatment in the same test solution, and FIG. 4 is a schematic illustration, with the apparatus partially in section, of a conventional fiber drawing process - 6(a~ -incorporating the ~harac.teristic. heat treating StQp of. the present i~vention.

General D'es ripti'on The:gLass~-ceramic f.iber of' the.present in~ention is prQduced by l~ternally nuc~'eating and cr~stalllzing a corres-ponding glass fiber ha~ing a ~asalt-~type composit~on. The cs~stal phas~'in .the'glass-:~r'Em~c,'$ibèr ls a mixture of magnetite'and cli~opyrox2ne'~augit~' crystals that sonstitutes at.least.35Vk of' the'iber: and p.r,~ferably o~er:5Q~.
- . Thè'.term.'l'iber" i5 u~e~, ,as a matter of' con~enience, .
to. include'bo.t~ ibers and, ~il'am~ts:. Thus, the'glass-cer:am,ic fiber. of'.the in~e~tLOn may be a ~ormal, fiber on the o.rder.,o' s.everal' microns di'am~ter, .or it may range in size up ta. a fil'ament having a di'~meter ~of about ten ~ils or 250 mi-crons. Larger sizes t:end to beha~e as con~entional bodies ra~her.,than, f.ibers.
Permissi~.l'e'crystal si~e'wi~ ~ary with ~iber. di'am~ter, the ratia of'f.iber. di~m~ter to c~ystal size'~eing at least ~'0:1, and usu~Ily subst~ntiall.y grea~e~. For most applica-tions reIa~ively small di'~ete~, or. fine, fibers on theor~ex- of:.ten to twenty mierons axe'contemplate~. In :s.uch .
f1bers.,- aN a~erage crystal ~lzé l.es.s ~han a half ~ic~on is pr,efe~r,e~.
F~GURE l,of t~e accompanying. d~awing is an el.ect~on phQt~micrograph'showing t~e'crystal distri~ution and sizP in a typical ~.iber ,of' the i~ention. . T.he'fiber depic.te~:is. 13 microns in di-ameter and was: c~.'ystalli.zed ~ceramme~ from a basalt glas~, ~.iber by heat trea'~ment, for 30 seconds at 1000C.. The'whi~'marker at.th~ tt~ of the picture is one'micron in length.' It will.be obser~ed ~at thé'c~:ystal content in the micrograph~approx~mates. half o~'the.fiber cross section, th~s indicating approximat~ly 50% crystal phase by volume.
Also, there'are.'no crystals:over a micron in size and average'size i9 substantially less than a half' micron. A
parti-cular ~eature'of'the pre.sent glass-ceramic fibers is their fin~-grained cr.ystal struc~e whereby a r.esil.ient fiber adap.ted to ~einf~rcing. use'is obtained. At the'same .time t~.e'f.iber' has the outstanding chemical resistance, partlcularly to. alkaline'solution , that was noted for basalt.bodies in U.:S'. Patent: No. 3','557,575.
Bas.ically, productio~: o~' t~e p~.esent fibers conte~plates thr.ee's.teps. First, crushed ~asalt rock, optionall~ con-taining. var~ous additives as ~odiiers, is mel.ted in a cruc.ib.le,' pot,.or: continuo~s glass meIting ~mit, d~pending on the'quantity of product want~d and t~è manner of; ~ibe~
formation to be'utilizad. S.eco'nd, when a sultab.ly ~omo-~
g~neous: melt Ls attained, 'amorp~bus f.i~ers æ e'produce~ from t~è'meIt in any con~ent~onaI manner. such'as. dra~ing, spinning, or bIowing~ Since'fiber orie~tat~on is important in reinforce-ment appLicativns,- fibers for this purpose wili: norm~lly be drawn, wound on a drum, and sub.sequentl~ cut into bundles.
Finall~, t~e f.ibers are'.s~j'ec.ted to a hea~ treatment to con~ert:th~m rom the.'vitreous state'to the glass-cer'a~ic state'by.internal d-evelopm~nt.of' a palycr:ystalline phase.
This. heat-trea~ment consists of: ex~osing the'fibers.to a .
temperature'in t~e'range'of' 900 to 1250~'. or a time not exceeding ten ~inut~s~ and prefer.ably less ~han one minu~e.
It is. e~plained in cons~derabIe'de~ail in Uni.ted States Patent' ~o. 3,'557:,'575 ~kat :t~ere arP'~arious types o basalt-representing cons.iderable'~ariation in composition, 3~
the ma~or constituents being SiO2, A1~03, MgO, CaO and iron oxides, and the alkalies, Na2O and K2O, being present in lesser amounts. The patent identifies and gives examples of three major types of basalt, but indicates that tholeiitic basalts have several advantages for glass and glass-ceramic production.
Inasmuch as a specific basalt composition is not a critical element in the present invention, the teachings of the patent, relative to composition and melting procedures, are generally applicable to the present invention.
Reference is also made to United States Patent No.
4,008,094 where the composition of a particular tholeiitic basalt from West~ield, Mass. is set forth, and the modifications of this basalt with additions of zirconia to its melt are disclosed. These modified compositions represent preferred materials for the present invention.
The heat treatment of the present invention is particularly adapted to integration with a conventional fiber drawing process. However, the invention is not limited to any specific method of fiber formation. Thus, it is possible to ~orm fibers, cool them to ambien~ temperature, and then reheat them in accordance with the invention. In ~act, as an experimental expedient, the work herea~ter d~scribed was performed in this manner.
Likewise, any conventional heat treating means, readily adapted to fiber treatment, may be employed. For example, fibers may be drawn through a tubular heater, or between opposed radiant heaters.

~ 3 ~ ~

In c~mme~cial practice, a g~a~s iber drawing o~eration ~ill normally be employed, and th~ ~eat treating s.tep of the'present i~vention coordinated ~i'th'such'dra~ing operation into. onei continuous sequence.'. This i5 illustrated schematic-ally in FIG."4 wherein a conti~uo.us glass fiber. or ~ilament 1 ls shown.being drawn E~'om orl~.ice.2 of' a heate~ bushing 3 contai~in~ a mol.ten ~ath'of. ~asalt 4 ha~ing a composition such:as .sho~ above.' As ~ er l..ls. drawn- from orif.ice 2, t~e.'fiber rap.i~ly cool's-,. but~s .~ick~ drawn inta a r-e~eating zone:5 whi:ch is maintained at a te~perature of`700 to 1250¢., pref.P~.abIy in the.'range o~.'1000 to 1100C.,.b~
~adiant. heat s:ources'6. Fiber~ 1 pas.ses rap.idly thx.ough reheat-zQne'5.i~ a period: o~'.time normall~ substan~ially - less:tha~ one'minute.' .T~e's.tep.s or stages in..t~e'nu~leation and ~r.ystal-lization of: a ~asalt glass bod~ ar~'depic.ted and descr.ib.e~
in som~ detail i~ Patent ~o..3:,'557',:5.75. Ree~ence.is made' .
thereto inasmuc~'as ~t is.belie~.e~ hat cr;ystallization pro~eeds in the'same ~anne~ in the'pr.e~ent-fibers,: but' ~uch .
more rapidly. Th~s, it ap.pears t~at, as a basalt-type'glass-i~e~ is. d~aw~ from orifice;~,..it cool:s and b.ec'om'es n~cleated.
Then,- as:the~'nu~leat~d ~ er pas.ses throug~ r.eheat zone'5, a polyc~.yst~ 'phase'g$ows: on's:uc~ ~uclei...In.'accordance wit~ .thé.'patent t~achIn~,' mag~-etIte'nucIèi orm and,. at low .
temperatux.es, a ~agnetit~'cr:~stal phase would gro~'on the .
n~cl'ei. At t~e higher .t'~mperatux.eb of' the present in~ention, a silicat2'pyro~ene-type'cr~s~al phase als-o de~elops a~d predominate~s .
It. is my .belie~ .that:th~s desirable mixed cr.ystal or-mation, which'o'ccurs ln:acc'orda~ce'~Ith ~he pr~sent in~ention and contrary ta prioX pre~ictl-ons, is associated wi~h tEle ~ 3 ~ ~

essentially instantan~ous xesponse o fibPrs to heat~ng and cooling conditIo~s. Thus, extended times are not requirea to att~in cr.ystallization. Hence,' crystallization temperatures may.be'reached, and also released, almost instantan~ously.
This situation differs markedly from that in a large bo'dy, a ~act not fully apprecia~ed ~ereto~oxe. The. extremeLy rapid cr.y~tallization which'o.ccurs at.t~ high te~peratur.es charac-te~.istic of'.the present ~n~cntion produces a relativeIy .
fine-grained crystal phase'in t~e fib~r. Consequently, a fi~er produced ~y t~e pr~sent mPthod is less brittle than one'pro.duced b~. known lower tempexature, longer time treatments which te~d to pro.duce l æ.gex. size'crystals.
As the crystallized or glass-ceramic fi~er leaves t~e reheat zone, it c~ols and' may be wound on a drum or tuxned to a horiz~ntal dir.ection by a guide.Cas s~own) for.other h~ndling, eit~er being sta~ard f.iber handling prac~ices.
For reinforcement purposes, ~.ibers are nornall.y plac.ed in a cement s.llrrry in paral.leI, oriented relation. To t~is end, a roll of iber on a drum,. for. example,` may be chopped in knoT~n m~nner into.bundles o~' desir~a lengt~ for pIacing in a con~r.e.t~ matrix.
The present in~ention may also be carr.ied. out in conjunctio~ wi~h a p~lsing heat treat~ent technique as describe~ in de~ail and cIaimed in ~y companion appLication U.S. Patent 4~201,559, entitled "Method of Producing a Glass-Ceramic" and filed September 25, 1978. In particular, applica-tion of heat tv a basalt fiber in short pulses tends to product an appreciably finer grain crystal phase with the resulting fiber having appreciably greater resilience than attained with a slngle heat treatment of similar duration. For a39~
example, a 20 s:econd ~eat t~eàtment may be applied as 10 two second pulses rather t~an a con~inuous 20 s:econd treat~ent.

- S'n'eci~ic`D'escription TabLe I se:ts fort~,' in terms o'parts by wei~ht on an o~ide.basis,: t~'composit~ons 0~'3:e~eral exemplar~ meIts which'wer~'used in studyi~g t~e.'ps.esent.i~ention. T~e' additives> indicated in oxide ~o'rm, were'either added in t~is for~ or as nitr.ates or carbonates in accordance'~it~' known glass making prac~ice.

- TABLE I

' 1 23 . 4 :5 6 . Basalt ; 100. 100 lQO 100 100 100 Zr2 ~ 2:.. 5 :7:.:5 2.5 3.'0 7.5 TiO ~ :-5~. a : Si~2~ ~ _ . 10 7 - . lQ
Na20 - - . lQ 7 - . lO
CaO ~ 10 As i~dicated earlier, tha bas~c composition o the basalt used is not critical to the pr~sent in~ention and it is coIIte~lated that any o~: ~he known basalts ma~ b~ employed.
How~ver, a low alkaIi (R2O2 content, prefe~abIy less than 5~/0, generally pr.ov~des bett~r che~ic~l durabilit~ in the end product. For th~s rea~on, t~e ea~Iier referred to th~leiitic basalt fro~ ~estfieId, ~ass. was employed in the co~P.pos~tions o ~able I. This basalt ~as the follo~in$ approx~ate analysis in weight perce~ on an o~ide basis:
SiO2 52.0 CaO ~.3

2 1 0' Na2~ 3.2 A1203 14.1 K20 1.2 MgO 6.4 Fe203 12.8 The basalt component was cxus~ed to pass through a No.
50 Uni.ted States Sta~dard S.ie.~e C29.7' microns~ a~d t~en blended with additives in ~ineI~ di~.ided form to achie~e a homogene.ous mixture for mel.ting. The'batch ~i~ for each' compositi.o~ was then deposite.d i~ a platinum crucib.le ~hich was placed in a gas ired furnace'operating at ab:out 1500C.
After ho.l~ing at that temperature for a~out 6. hours, a homo:geneous- melt resulted and glas~ fibers of var~ing size were'drawn fr'om t~e''melt; fo~ use i~ present s:tudies. Flat mo.l.ded plates. of glass w~re'also poured for use in measuring phys.ical prop'er~ies.
It is generally:accep.ted that t~e nuc.lei formation preceding crystallization is of'a magnetite nature,' the ece`ssary iron oxide being present ln the basalt composi-tion. Accordingly, a mildly oxidize~ melt is :desired w~erein the Fe~3/Fe~2 rati.o.is on. the ord~r o~' 1 o~ ab.ove.' For .t~is purpo.se, a ew pa~.ts. by. we'ight of ammonium nltr.ate (~H'4NO3) were:included in each'~atch prior to' melting. It will:bé apprec.iated that the.oxides of: either t~tanium or zirconium, if present, may also contr.i~ute to the nucl'e~
formation.
It has b.een ob.ser~ed that :the.'degree of crys~allinity is affected by f.ibér. di'a~t~ as well as time'and ~'empera-ture'of'heat treatme~t. ~n general, longer times and higher .temperatur.es enhance'the.'degx:ee of'cryst~llinity attained. For any gi~e~ tempera~ure and timP,' c~ystalli-zation takes place more~rapidly ln a smaller fiber.
These'effects are il:lustrated by. certain studies reported be~ow,' as well as.b~ r.eference to U.S.' 4',008jO94.
In that pa~ent, heat treating .te~peratures did not e~ceed gooQc. and the crystal phase formed was magnetite and/or ulvospin~-I. As no.ted earlier, this ~epresents only a minor part of the glass-~
The.various effects on deg~ee of crystallinity and rateo~ cr.ystallization are'seen fr`om the.ollowing tab.le which records. cer'ammlng schedules.'emplo.yed on various size ~ibers and th~ cr.ystal phases ob.sexve~.

- ' Heat Trea't~e~t Fiber. size ~mlcrQns) Time'(sec.) Temp. (QC) C'r.ystal Phase 13' 8~ gao Magneti.te + Augite 13' 20 1000 " "
900 " "
12~ '80 ~00 Magnetite 125 80 1000 Magnetite'~ Augite 250 30 1000 l -250 60 1000 " "
250 8 1150 Magnetite T.hus, ~the.'present ob.s:er~ation~tend to con:~i'rm prior ex~er.ience'in larger.bodies. that .the n~clei whic~.form initially æ e'magnetite,' and that such'nuc.'lei grow'on them~eLves or. enlarg~ under either short-t~e'or low .tem-perature, conditions. T~s is part~ula~ly ~rue'in lar.ger ; size, ~ilame~tary bo~ie~ ~her~'cr.~stallization is slow~.r .
.The.'pr~s~nt in~en~ion is ~ased on th~ disco~er~ ~hat a combination o~:magnetite'and ~au~ite'crystals for~ under the uniqu~ high .te~pera~ure,' sh~rt t:ime cr~stallizing conditions of' the present me~hod. Furt~er, this mixed cr~stal phase gro~s in the'su~stantially uniform,. ~ine-grained manner.that is. ckaracteri~.tic of glass-:cer'a~ic materials.-~ 3~ ~

It may be observed,. however, that min~um crystal-li2ation conditions can not.b~`used with relatively large fiLaments~ T:hus higher ~emperature'crystallization tem-peratur.es, :i.e., on t~e or.des' of 100~-1100C., and at least ten seconds time, are'rec'ommended ~or ilaments greater than 2~' microns ln di'ameter.
In or.der to.'compare'thé'c~emical dura~i1ity of:basalt glass and has.alt glass-ceramic`~ibers, and particularLy to determine're~ative utilit~ for. c'ement reinforcing purposes, a supply o'13'micron basalt.glass ibbr ~as drawn rom a meIt of composition 2. A portion of this ~iber was cer'ammed, that is, con~er.ted to the glass.-ceramic state.b~ heat treatment .
for 120'.s:e:co.nds at 1000C., and a s.econd portion was retained in the'glass state.' S'a~p.les of each'were exposed for nine (9) weeks at:51C.: to a standard cement effluent, known as Lawxence's~lutionJ and being a sod.'iu~ salt buf;fered, saturated solution o~: calc:ium hydrox.i~e.' ~ollowing this e~po:sure,: the glass and.glass-ceramic fibers w~re'removed, rinsed ~nd photograp.~ed at ~arious magnificatIons.
FI:GUgES. 2 and.3 are'photo.graphic reproductions of' the glass-and glas-s-:ceramic fibers., ~.es~ectively, at 20ao times magniicaci.o~. It will.be'o.bs.e~ed that the glass ~ibers are`co~ere~ ~Lth t~e reactio~' product of glass and ~est solutIon. I~ contrast, :t~'cerammed fibers~sho~ much'less evidence of reaction, ex~ept along a cord line'in the ibe~.
This. clearly evidences the.'superior qualities o~' t~e present cerammed ~ibers for cemen~ rein~oxcing purposes.
It wil~ be appxeciated t~a~-a glass cord is~ usually an inho~ogenei~y of: distinct~ di~ferent composition fro~, and hcnce qui~e'unrepresen~a~i~e'of', t~e glass. It can usually b~ eliminat~d by controlled melting and/or stirring of ~he melt .

Claims

I CLAIM:

1. A fine-grained glass-ceramic fiber having a diameter not greater than about 250 microns, being crystallized from a basalt-type glass, having a mixed crystal phase composed of magnetite and a clinopyroxene, and the crystal content being at least 35% by volume of the fiber.

2. The fiber of claim 1 wherein the crystal size does not exceed one tenth the diameter of the fiber.

3. The fiber of claim 2 wherein the fiber diameter is less than 25 microns and the average crystal size is less than a half micron.

4. The fiber of claim 1 wherein the crystal phase con-stitutes at least 50% of the fiber.

5. A method of producing reinforcing glass-ceramic fibers having a fine-grained, polycrystalline phase which comprises, melting a raw material batch composed predominantly of a basalt-type material, forming vitreous fibers from such melt, forming magnetite nuclei in the glass fibers, and developing a mixed magnetite-clinopyroxene crystal phase on such nuclei, the crystal phase being at least 35%
of the fiber, wherein the crystal phase is developed by heating the fiber at a temperature in the range of 900°-1250°C.
for a time not exceeding ten minutes.

6. A method in accordance with claim 5 wherein the heat treatment time is less than one minute.

7. A method in accordance with claim 5 wherein the tem-perature range is 1000-1100°C.

8. The method of claim 5 wherein the basalt-type material is a tholeiitic basalt having an R20 content below 5%.

9. The method of claim 5 wherein the batch is maintained mildly oxidizing o provide a Fe+3/F+2 ratio of at least one .

10. The method of claim 5 wherein at least one fiber is drawn from the melt, cooled, and rapidly reheated by passing through a reheating zone as part of a continuous operation.

11. The method of claim 5 wherein heat treating temperature is within the range of 1000° to 1100°C.

12. In a method of producing reinforcing glass-ceramic fibers having a fine-grained polycrystalline phase, and wherein fibers composed predominantly of basalt are inter-nally crystallized by heat treatment to form the polycrystal-line phase, the improvement whereby the heat treatment to produce the polycrystalline phase comprises subjecting the fibers to a temperature in the range of 900° to 1250°C. for a time not exceeding ten minutes.

13. The method of claim 12 wherein the temperature is in the range of 1000° to 1100°C.

14. The method of claim 12 wherein the time of heat treat-ment is not over one minute.