.I ,-_.._ ------- --.-. . -_ _-.------- . @ B N F - . 9 7 O M V ~ - --.-- . .-.---.-_I- - -1 !. UNI)ERST,\NI)IN,GAAND CONTROLLING ~ ~ E L T C R Y ~ T A L L I Z ~ \ ~ . ~ ~ $ ~ . intensities, indicating tliat some, but not all of tlie material rcmaincd

amorphous. This mcans that the mixing and kiicading action insidc tlic torque rheometer changed tlie morpliology of tlic glass from wholly amorphous to scmi-crystalline like Sales and co-workers [9-IO] fouiid for biliary lcau

i pliosphate glasses.

Tlie GPP was subjectcd to continuous sinusoidal shear flows for I C 'Iiours at 402 "C. Tlie flow was provided by a dynamic mecliariica. .spectrometer. The viscosity Iq*(l rad/s)l of tlic GPP iiicreascd monotonicall\ ; with time f (Figure 2) At long times. tlic growth of Iq*l was exponential wit1 , time. The exponcntial dependence represents strong sensitivity o f tlie Iq*l o

- . * * I I@ uh!L/jjjED tlie GPP melt to oscillatory shear flows at 402 "C. This beliavior is ascribed ic

r3 E ~ E 1 v&J&SSY PI-KOSPIXATE POLYMERS

taigbea, B.C. Salesb and G.H. BeallC b-1

Science and Engineering, Iowa State University,

Laboratory, Oak Ridge, TN 3753 1 . CScience and Technology Group, Corning, Inc., Corning, NY 1483 1

p~Rra'vo'' fl >P.n-:-Q--y 1NTRODUCTIO

inibient conditions are polymers. It is now generally recognized that inorganic ;

"'&

Many materials such a 8 b norganic phosphates that form stable glasses at

,Iiospliatc glasses are polymeric i n nature in &e sense that they are composed of :liainlikc or network structures like organic polymers (1-31, While great xicccss lias bccn achieved in tlie understanding o f atomistic structure and i properties o f siinplc glassy phosphate polymers, the dynamics of melt ! :corganization o f the molecular cliains required for crystallization of tlie glassy i 2olynicr near tlie melt temperature are unknown. Tlie effects of both :omposition and melt processing conditions on the structure/property rclationsliips for tllc glassy phosphate polymer (GPP) are unknown. I n addition, I

I i o systematic studies have been made on how the medium range order [(P04)n I diains] changes melt processing and the effects of these clianges on i xystallization kinetics and on chemical durability of the final GPP. Furthermore, tlic nielt rheology (elasticity and viscous flow) of this special class J f phosphate glasses (and even simple binary phosphate glass system) is poorly ~nderstood arid little documented [4-5].

This work describes one attempt to systematically study the :rystnllization bcliavior and kinetics of one glassy phosphate polymer at its melt processing temperature (cu. 400 "C) under both quiescent and dynamic shear mid flow conditions. Tlie results arc lielpiiig us to understand effects of both zoniposition and melt processing conditions on tlie structure/property :elationships for the GPP. In turn, tliis understanding represents a first step :oward cstablisliing rational design principles to guide preparation and ivocessing of GPP to produce new niaterials and new devices.

i

EXPERIMENTAL I

A standard GPP manufactured by Corning, Inc. was used. The general somposition o f llic GPP was xM20 +yZnO +zP2O5 (where M is an alkali such 3s Li, Nn or K; x 0.5). Tlie exact composition and I dctails o f tlie preparation method lias been reported [4, 6-81. A standard Haake ' torque rheometer was used to prepare the GPP samples with varying processing 1 liistories ns rcportcd prcviously [GI. Standard HPLC [9-IO] and Differential Scanning Calorimetry (DSC) were used as part of a routine characterization of tlic GPP following established procedures. A novel insitu DSClXRD instrument i was used to study the irielt crystallizntion as functions of temperature and shear : distortion following the methods reported previously. A mechanical spectrometer in tlie parallel configuration was used to measure the viscosity of tlie GPP under oscillatory shear flows at temperatures above its glass transition (cmperature o f about 270 "C The density of tlie GPP was found to be 2.43 g ciii-

0.25, y 0.5, 0.29 < z

3 nt.rooni temperature.

IZESULTS AND DISCUSSION Tlie unprocessed GPP showed 110 lit

tcmperature. Two very broad peaks observed at approximately 6.0 and 3.5 A io the XRD pattern indicated tlic presence 6f amorphous materials. Tlie I-IPLC experiments revealed that the GPP contained a broad distribution of 12 corner- linked tetrahedra and a mean theoretical chain length of 12 (Figure 1). In Figure I , tlie position in time and the area under each peak indicate rcspcctivcly the identity and quantity of a particular phospliate anion designated P I , Pa, P3 ......... PI1. The P3,, y d P4, indicate presence of rings of Irimctnpliosphatc and tetrametaphospliate, respectively. The broad enveloppe after 40 niin is ascribed to unresolvable mixture of longer phosphate chains (> P12) niid Iargcr pliosplintc ring structures.

Tlic formation of a white discontinuous pliase was observed in tlic GPP during mixing and kneading at temperatures around 400 "C in the Haake@ lorquc rlicomcter. Glass crystallization was confirmed by the appearance of ' sliarp pcaks in tlic XRD pattern for the GPP after it was removed from the rticomctcr. Tlic cliaracteristic broad peaks at 3.5 A and 6.0 A exhibited by the . enproccsscd glass wcrc present in the XRD pattern but at greatly rcduccd

istrain-induced crystallization of tlie GPP. l i e time dependcncc of Iq*l i: 'strongly controlled by tlie strain ./ and angular frequency o [5]. Tlic slicar- induced crystallization was found to depend on the composition (and liencr

' crosslink density of tlie cliains). The crosslinking o f chains restricts motion: needed for ordering molecules into crystals.

I Non-linear regression analysis was used to obtain tlic time fonsct for i 20% rise in tlie magnitude 1q*1 and tlie Iq*J growth ratc constant ~ - 1 observed a

: long times [5]. Tlie latter parameter was identified from a non-linear fit to tlic I . data assuming tlie functional form: Iq*l = qo + q I exp{f IT). The paramete: ifonset may be used as a first estimate of the processing tiinc prior to ai exponential rise in the melt viscosity, making it possible for the first time I( control extent of melt crystalli7~1tion of the GPP during proccssing. Figurc': i shows that the GPP may be processed at 400 "C for about 54 minutes berore tli- ,melt viscosity increased by about 20%. Additional details on tlic mc: !crystallization induced by oscillatory sliear flows and flie strain dependcncc o ![onset for tlie GPP are reported elsewliere [5]. I-liglier strains shortened fOI1sc: 1 and consequently accelerated the nielt crystallization. Tlic slicar-iiiduccc ;crystallization was Confirmed by X-ray cxpcrimcnts pcrrornied 011 GPP iiiclt. 'with different processing history. i

Quiescent crystal growth o f the GPP was monitorcd in tlie DSCIXRI: !experiments over a 16-liour period. Diffraction patterns for tlic glass as tli: !temperature was elevated from 30 to 400 "C at 10 "Clmin, and then during tlig !first 59 minutes after reaching 400 "C are shown in Figure 3. Tlie patterns sliov !the transformation o f tile glass from an amorplious material (only a portion o , the broad amorphous scattering signal is evident) to a inatcrial with some sliort- .: range crystalline order after tlie temperature surpassed tlie Tg (272 "C) o f tli< *unprocessed glass. Tlie largest scattering peaks for tlie micro-crystallinl material arc located at 28 values o f 26.3, 27.3, and 31.1" (3.39, 3.26, and 2.8'

i A, respectively). The quiescent crystallization proceeded slower tliai crystallization under the shear and flow conditions iii tlie lorquc rlicomcter. Tlit i appearance of long-range crystalline order in tlie rheometer saniplcs occurred ii

i less than I hour compared to 4 hours for the quiescent experiment. !

Tlie DSC data sliowed a. thermal transition was observcd with . I !maximuin heat loss occurring at 325 "C [GI. This thermal transition pcak i i believed to be due to a Combination oE (1) tlie transition from a glassy to me1 state; and (2) formation of the microcrystalline material. A second very weal

! exotherm that is associated with appearance of tlie long-range crystalline orde i was observed at longer times (260-320 minutes) [5].

I Tlie strong tendency of tlie GPP to forin niicrocrystallites (Figures 2 ant - 3) under shear deformation and elevated tcinpcratures st~pports the liypotlicsi: : that tlie glass structure consists of polypliosphate chains distributed randoinl: i and crosslinked by the cation modifiers in thc disordered glass pliasc [4] simila ! to others reported for binary phosphate glasses [9. 11-13]. Applicatioii of tlii sliear distortion during flow of the glass melt in a torque rlicomcter causcd t h t

i randomly oriented polypliosphate chains to become preferably alligned tliu i i giving rise to the observed highly ordered microcrystallites in tlic XRD pattcrii' j of tlie glasses. This explanation of tlie phosphate glass structure evolutioi ;during shear flow is consistent with that rcportcd by others on simple binar: lead-iron-phosphate glasses based on EXAFS and X-ray absorption ncar-cdgc

!structure experiments [9]. Furtlicr work is nccdcd to undcrstand tlic rolc of tlir . various metal cations on tlie process-induced crystallization of tlie present GPP Some explanations of the effcct of substituting various alkalis for zinc on t h c structure and properties of GPPs is reported elsewlicrc [4].

The phases in the XRD patterns of the glasses wcrc not idciitifiabli . indicating that tlie obscmed niicrocrystalline statcs niay bc transition statc: during the transformation of the glassy to tlie macrocrystallilie statcs at loligc tinie scales. Tlie cxistcnce of tliis Iiiglily-ordered fnnsition sfatc is consislcn

. with tlie traditional proccss of glass dcvitrificntion in two scpante rcgiincs: i.c.

. .- ,. . - . . .. , . . - - -. ... - _._ . . . -. ._ _._. ._._ _.. . . . .-.- .. . . . . . . _-_- ---.- -.-_____- . . __. .. --. - -. . . - - .-. iuclcation of microcrystallites followed by the growtli of inncrocrystallites ! . Additional results reported previously suggest that crystallization rates of 3PP dcpend strongly on tlic structure and composition of tlie GPPs wliicli iii .

determines their resistance to aqueous solutions and other chemical : ronnients as well as tlicir rcactivity towards organic polymers i n glass-! ; incr composites [4]. The observed liquid crystallinity of tlie GPP is akin to cxliibitcd by thermotropic liquid crystalline organic polyiiicrs near their, '

opliasic-isotropic liquid phase transition [ 14-16]. Highly crystalline : aiiis iiiay form wit!iin a fluid amorphous matrix. The breadth of X-ray. xtioii peaks observed for the niicrocrystalline phase is characteristic of 3

:rials having very small domains (400 .A) of crystalline order. These :rvatioiis are consistent with iiielt rheology data of tlie GPPs reported,

I

rvlicre [5]. . . . . i .

0 1 0 2 0 3 0 4 0 5 0 6 0 Time (mins)

NCLUSIONS 1 I

OF shear deformation (or mixing). The evolution of structure during shear i f of the GPP melt can be explained by re-ordering of polyphosphate i ecular chains or liquid crystalline structures in the melt state. Semi- i ititative melt processing parameters such as onset time for crystallization, j ir strain. and rate can be used to control the GPP crystallization. The: ytical techniques used in this study are considered to be novel and efficient liaracterizing effects of crystallization during flow of phosphate glass melts rlicometcr or in other melt processing equipment such as an extruder.

The crystallization rates of tlie GPP was increased by [he amount and

!

We are particularly grateful to the CORTEMO technical team, Drs. i dace Quinn and Ron Johnson without whose support and eiicouragcmeiit I work would liave been impossible. Portions OF this work were published in i riotis papers.

FERENCES I Warren. J. Aiiier. Ceraiir. SOC. 21 (1938) 259. Van Wazer, in Inorganic Polymrs, F.G.A. Stone and W A G . Graham, Eds., Academic Press, New York, 1962. Zacliariasen, J. Aiizer. Clierrz. Soc., 54 (1932)3841. Quinn, P.D. Frayer, and G.M. Beall, in Encycl. Polym. Sci. Tech., (1995) (ill press); G.H. Beall in Proc. XVII Intl. Congress on Glass, Beijing, China. October 9-14 (1995); C.J. Quinn, J.E. Dickinson, and G.H. Beall, Intl:; Congress on Glass: Bull. Spanish Society of Ceramics and Glass, 31-C, 4 I (1992) 79.; G.H. Beall and C. J. Quinn, US Patent 4 940 677 (1990) (assigned to Corning Inc.).; G. H. Beall, J. E. Dickinson, and C. J. Quinn. I

Sammlcr, J.U. Otaigbe, M.L. Lapham, N.L. Bradley, B. Moiialian, and C.J. Quiiin, J. Rlreol. 40 (2) (1996) 285.; J.U. Otaigbe and B. C. Monaliaii, / Crowder, C. E., J. U. Otaigbc, M. A. Barger, R. L. Sammler, B. C. Monahnn

I Ray, N. H., J. N. C. Laycock, and W. D. Robinson. 1973. Glass Tecltltology I 14:2. see also Ray, N.H. 1973.5. Polym. Sci. 1 I , 2169.

I Greaves, S.J. Gurman, L.F. Gladden. C.A. Spence. P. Cox, B.C. Sales, L.A. i Boalncr and R.N. Jenkins, PliiiosoplzicaI Magazine B 58 (3) (1988) 271. i

! Sales. 1.0. Rainey and LA. Boatner. Plys. Rev. Lett. 59 (1987) 1718. Sales, R.S. Ramsey, J.B. Bates and LA. Boatner, J. Non-Crysl. Solids 87 i Van Wazer. Pliosphorozis and its conrpounds: Clreiiiistiy, Vol. 1 (.Wiley,

Mcadowcroft and P.D. Richardson, Traits. Faruduy SOC. G 1 ( I 9G5) 54. Pawlikowvski, G. T., D. Dutta, and R. A. Weiss. A~lrr. Rev. Ply.% Chcrri. 42 i

N. Yoon. L. F. Charbonncau, and G. W. Calundann, A h . Mater. 4(3) ( I 992) 206. F. Wissbrun, Brit. Polynr. J.. Dec.. (1980) 163.

:rrorvlcrlg1rrcnfs .i

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I

1 US Pat. 4 996 172 (1991) (assigned to Corning Inc.). i

unpublished work. f i and C. J. Quinn. 1996. J. Norr-Cryst. Solids. In press.

Oiiyiriuka. E. C. 1993. J. Norr-Cryst. SoIids 163:268-273. I

(1986) 137. I

Ncw York, 1958) Ch. 12. i

i (1991) 159. - -

Fig. 1. Liquid chromatogram of thc GPP showing a rich spcctrum of polypliosphatc chains up to 11 PO,.

I

! i I

I 1 1 , I I

8. i t.

1. t. n 4' i .

I !

t

1 I i

I

0 2W 4M) 600 800 Io00 t , minutes

i I !Figure 2. Time dcpcndcncies of the zcro-shcar viscosity qo = Iq*(l rad/s)l for itlie GPP under oscillatory shear flow in the parallcl plate.configuration ( I jrad/s, 402 "C; strain = 30%) I

i

I

89 mln @ 400 C 74 niln 0 41H1 C 59 mln @ 41H) C 44 mln 0 400 C 29 mln Q 400 C 14 niln Q 41H) C 330 - 4110 C 1x0 - 3110 C 31) - 15U C 30 c

8

2-THETA (deg) ! *Figure 3. Insitu XRD patterns of tlie GPP heatcd to 400 "C showing cvidcncc jof microcrystalline material at 400 "C. The lower four scans wcrc obtained x !the samplc tcmpcnture was incrcascd to 400 "C. I

I

i

. I

. . . . . -- .. . .~ . - r -

DISCLAIMER

This report was prepared as a n account of work sponsored by a n agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liabili- ty or responsibility for the accuracy, completeness, or usefulness of any information, appa- ratus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily conshitUte or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors exprrssed herein do not necessar- ily state or reflect those of the United States Government or any agency thereof.

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