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TECHNICAL INSIGHTS ALERT

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HIGH-TECH MATERIALS ALERT

APRIL 14, 2000



Use of this information is determined by license agreement;

any unauthorized use is prohibited.

Copyright 2000, John Wiley & Sons, Inc.

ISSN 0741-0808



INTENSIVE PROCESSING OF STRUCTURED POLYMERIC MATERIALS

SUPERPLASTIC CERAMIC FIBER DEFORMS AT LOWER TEMPERATURES

TOUGHER GLASS COMPOSITES INSTEAD OF MONOLITHIC CERAMICS

CRYSTALS OF METAL SPHERES MAY ENABLE TUNABLE CPBGS

GET IN ON GROUND FLOOR OF BETTER NLO MATERIALS



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To get further details on the advances noted below,

just call/write/fax/e-mail the contact named

at the end of each briefing.

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INTENSIVE PROCESSING OF STRUCTURED POLYMERIC MATERIALS

     Intensive structuring, which is intensive processing of structured

materials, includes such processes as emulsification of high viscous polymeric

resins. In the March issue of "Chemical Engineering and Technology," Galip Akay

(University of Newcastle) reports the recent observation of flow-induced phase

inversion, or FIPI, which he uses as a new form of intensive structuring that is

especially suitable for highly viscous fluids such as polymeric resins (23[3]:

285-288).

     As Akay explained, when a material-A is mixed with material-B in the

absence of any significant deformation, the type of dispersion obtained (A-in-B

or B-in-A) is dictated by the thermodynamic state variables (TSVs), such as

concentration and surface activity. For instance, if prevailing TSVs favor the

formation of A-in-B type dispersion, B-in-A type dispersion can be obtained by

changing the TSVs. Or alternatively, the dispersion can be subjected to a

well-prescribed deformation, characterized by its rate and type (called

deformation state variables or DSVs) in order to invert the A-in-B type to

B-in-A type dispersion under constant thermodynamic conditions. Akay observed

that the phase inversion goes through an unstable co-continuous state (AB),

followed by a relatively stable multi-phase state of (A-in-B)-in-A, before

complete phase inversion to B-in-A. Because the unstable AB state results in the

change of the curvature of the phases and the activation energy required for

conversion to (A-in-B)-in-A, new

 processes and materials can be formed by interchanging TSVs with DSVs at that

point, which Akay calls flow-induced phase inversion.

     Because FIPI processes rely on the flow field/fluid microstructure

interactions, the control of the flow field is important, and is easily achieved

through laminar, and often, extensional flows in highly viscous fluids at low

temperatures using small volumes. However, generation and maintenance of

extensional flow fields are very difficult in systems with widely different

viscosities. So Akay developed an apparatus that not only provides deformation

and mixing of materials, but also generates uniform flow fields. Called a

multiple expansion contraction static mixer, the device allows measurement of

the pressure drop across each mixing stage and the collection of samples at the

inlet and outlet. For industrial applications a dynamic version of this mixer is

also available.

     So far, using FIPI processes, Akay and his colleagues have produced novel

multiphase materials such as thermoplastic latexes by high-temperature

emulsification of polymer melts in water, highly viscous polymeric resins,

microcellular porous polymers with well-controlled micro-architecture as support

in animal cell culture to develop in vitro organs (tissue engineering),

agglomerates/microcapsules, and multi-lamellar droplet dispersions in lyotropic

liquid crystals to obtain liquid detergents. In all cases, the final product has

an identifiable microstructure in the range of 0.01 micrometer to 100 micrometer

that develops during processing.

     According to Akay, one of the key benefits of FIPI processes is that they

are inherently intensive. They work at small processing volumes because the flow

field needs to be uniform and specific and they result in very high throughputs

because the critical deformation rate at which FIPI starts is often very high,

which can only be achieved in pressure-driven flows through capillaries. The

processes also promise to be environmentally friendly in that no solvents are

needed to achieve agglomeration, microencapsulation, or emulsification.

     The next step is to apply the principles of FIPI to other systems including

the low-temperature/high-pressure intensive processing of food emulsions such as

margarines, low-fat spreads and ice cream, intensification of crude oil/water

separation (demulsification), and applications in medical science.

     Patent applications have been filed in the UK (98 25161.4) and worldwide

(PCT WO 96/20270 and PCT/GB99/04076). This research was funded by the UK

Engineering and Physical Sciences Research Council (EPSRC) and industry,

including Astra-Zeneca, Gebruder Haake GmbH, Norsk-Hydro, ICI Paints, National

Starch and Chemical Co., Resonance Instruments Ltd., Rosand Precision Ltd., and

Unilever. It is available for licensing or joint ventures as well as R&D

collaboration.

     Details: Galip Akay, Professor, Dept. of Chemical and Process Engineering,

Merz Court, University of Newcastle, Newcastle-upon-Tyne, NE1 7RU, UK. Phone:

+44-191-222-7269. Fax. +44-191-222-5292. E-mail: galip.akay@ncl.ac.uk.

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Copyright 2000, John Wiley & Sons, Inc., New York, NY 10158



SUPERPLASTIC CERAMIC FIBER DEFORMS AT LOWER TEMPERATURES

     Superplasticity, found in molten glass or polymers, is the ability to

greatly deform without fracture, thanks to crystal grain rotation, grain

boundary slipping, or grain boundary liquid phases. Achieving superplasticity in

ceramics is a very hot topic. It has been reported that superplastic processing

is possible at around 1450 degrees C for an ionic crystal Y2O3-TZP (stabilized

tetragonal ZiO2 polycrystals) and at around 1600 degrees C for a covalent

crystal Si3N4/SiC composite, but these are relatively high temperatures.

     Recently in "Material Research Innovations," Yoshiharu Waku, a researcher

at the Japan Ultra-High Temperature Materials Institute, reports the development

of an entirely new amorphous ceramic fiber that deforms at significantly lower

temperatures, making it easier to process (3[4]: 185-189). The continuous fiber,

which is made with the melt extraction method, is comprised of the ceramic

Al31Gd9O60 and has a diameter of about 20 micrometers and fiber strength of 2

GPa. The fiber exhibits several improved physical properties compared to its

conventional counterparts, which include glass fiber and amorphous Al2O3 fiber.

For instance, since glass fibers contain a large amount of compounds such as

SiO2 and CaO, their strength starts to drop at a relatively low temperature.

Case in point, the S-glass fiber strength at 700 degrees C is about 36% of its

room temperature strength, whereas the amorphous continuous fiber shows no

strength deterioration at this temperature. In addition, glass fibers have a

Young's modul

us of about 70 GPa to 88 GPa, and amorphous fiber, about 150 GPa.

     More importantly, a conventional amorphous Al2O3 fiber cannot exist in a

supercooled liquid state, so it cannot undergo a jelly-like viscous flow

deformation. In contrast, the amorphous continuous fiber exists in a supercooled

state at roughly 920 degrees C, where it undergoes large viscous flow

deformation and can be freely shaped. This enables the researchers to fabricate

high-strength continuous fibers with uniform GdAlO3 nanocrystalline particles in

an amorphous matrix by a subsequent crystallization heat treatment step. In

terms of mechanisms, Waku and his coworkers suspect that the appearance of the

supercooled liquid state of the Al31Gd9O60 fiber is due to its stable amorphous

structure and the combination of Al, Gd, and O elements.

     Although this project is at a basic research stage, Waku and his coworkers

abundantly manufacture Al31Gd9O60 powder. He estimates that time to commercial

use in real applications is around three to four years.

     Three related patent applications have been filed in Japan, and the

technology is available for licensing, joint venture, or R&D collaboration.

     Details: Dr. Yoshiharu Waku, Project Manager, Japan Ultra-High Temperature

Materials Institute, Ube City, Yamaguchi 755-0001, Japan. Phone:

+81-836-51-7007. Fax: +81-836-51-7011. E-mail: waku@jutem.co.jp.

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Copyright 2000, John Wiley & Sons, Inc., New York, NY 10158



TOUGHER GLASS COMPOSITES INSTEAD OF MONOLITHIC CERAMICS

     The demand for structural ceramics has led to an increased interest in the

processing and characterization of continuous fiber-reinforced ceramic composite

systems. In particular, ceramic composites are being developed as alternatives

to monolithic ceramics because ceramic composites fail in a high-strain (0.5 %),

damage-tolerant manner, as compared with the brittle (less than 0.1% strain)

failure of monolithic ceramics and glasses.

     To achieve a tougher glass material, Dagmar Huelsenberg and Thomas

Leutbecher (Technical University of Ilmenau) have something else in mind: oxide

fiber-reinforced glass, or more specifically, glass fibers in glass matrix

composites. In the March issue of "Advanced Engineering Materials" they report

the results of the mechanical behavior of oxide fiber/glass matrix composites

without an interface layer and with carbon-coated reinforcing fibers (2[3]:

93-99). The researchers started with Nextel 440 and S-Glass fibers coated with

carbon using a continuous CVD technique at 900 degrees C in argon. The matrix

glasses used were a commercial borosilicate glass for the Nextel 440 fibers and

a sealing glass 756k for the S-Glass fibers. Then, using slurry infiltration and

hot-pressing of fiber tows, oxide fiber-reinforced glass composites were

synthesized.

     Testing of the sample composites with the carbon-coated Nextel 440 fibers

demonstrated the highest bending strength (around 350 MPa) and strain (roughly

0.7%), which is likely to be related to the low bonding between fiber and matrix

caused by the carbon coating on the fiber. Scanning microscopy investigations of

carbon-coated Nextel 440 fibers confirmed this by evidence of crack deflection.

The work-of-fracture for coated Nextel 440 composite was calculated to be 3250

N/m compared with 3 N/m for unreinforced glass. Work of fracture of the

CVD-coated S-Glass fiber/glass matrix composite was 950 N/m, which is also very

good.

     Details: Dagmar Huelsenberg, Professor, TU Ilmenau, FG Glas- und

Keramiktechnologie, PB 10 05 65, D-98684 Ilmenau, Germany. E-mail:

dagmar.huelsenberg@maschinenbau.tu-ilmenau.de.

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Copyright 2000, John Wiley & Sons, Inc., New York, NY 10158



CRYSTALS OF METAL SPHERES MAY ENABLE TUNABLE CPBGS

     Photonic crystals are important in active semiconductor device applications

because they allow polarization selectivity into the structure to exploit a

polarization-specific bandgap. They offer the potential to be used as mirrors

and elements for spontaneous emission control in semiconductor lasers or,

ultimately, optical computing. Some photonic crystals can yield sizable complete

photonic bandgaps (CPBGs), which is a frequency range within which the

propagation of light is forbidden in all directions and for both polarizations

of an electromagnetic wave. Tunable CPBGs promise the same control over the flow

of photons that ordinary crystals give over electrons, eventually enabling a

range of photonic information technology applications.

     However, the problems in the fabrication of three-dimensional CPBG

structures increase rapidly with decreasing wavelengths for which a CPBG is

required because of the simultaneous requirements on the modulation (the total

number and the length of periodicity steps) and dielectric contrast. In order to

achieve a CPBG below infrared wavelengths, the modulation is supposed to be on

the scale of optical wavelengths or even smaller and, as for any CPBG structure,

has to be achieved with roughly ten periodicity steps in each direction. This is

difficult to achieve using reactive ion and chemical etching techniques.

Achieving a practical CPBG in a face-centered-cubic (fcc) structure requires a

dielectric contrast roughly greater than 12, which makes fabrication of a

photonic crystal with an operational CPBG at optical wavelength seemingly

impossible.

     Alexander Moroz, a physicist at Utrecht University, is avoiding the

requirements on the dielectric contrast by using coated metallic spheres. In the

March 31 issue of "Condensed Matter," Moroz shows that simple fcc structures of

both metallic and coated metallic spheres are ideal candidates for achieving a

tunable CPBG for optical wavelengths.

     According to Moroz, modulation of the dielectric constant occurs naturally

in his materials because they are formed by monodisperse colloidal suspensions

of microspheres. The microspheres are known to self-assemble into

three-dimensional fcc crystals with excellent long-range order on the optical

scale, removing the need for complex and costly microfabrication. By using

different coatings and supporting liquids, the width and midgap frequency of a

CPBG could be tuned considerably. Depending on the scale and chosen material, a

CPBG could be opened anywhere in the range from radiowave down to ultraviolet

wavelengths, making the crystals an excellent template for multiplexing,

waveguiding, and optical chips.

     There are still some hurdles to commercialization, including the

fabrication of such photonic structures. The main problem is synthesizing large

enough spheres in order to reach a threshold value to open a CPBG. There are

methods to produce monodisperse gold colloids of several hundred nanometer

radius and larger, and recent results on the fabrication of such spheres from

silver, the most promising material in the visible spectra, are very promising.

However, one problem is controlling the size polydispersity of spheres to

trigger crystallization. According to Moroz, several groups, including his, are

now tantalizingly close to achieving this threshold.

     Moroz says that he and his colleagues are continuously seeking funding and

development partners.

     Details: Alexander Moroz, Faculty of Physics and Astronomy, Debye Research

Institute, Utrecht University, Postbus 80000, NL-3508 TA Utrecht, The

Netherlands. Phone: +31-30-253-2320. Fax: +31-30-253 2403. E-mail:

moroz@phys.uu.nl. URL:

www.amolf.nl/research/photonic_materials_theory/moroz/moroz.html.

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Copyright 2000, John Wiley & Sons, Inc., New York, NY 10158



GET IN ON GROUND FLOOR OF BETTER NLO MATERIALS

Recently HTMA told you that Oregon State University researchers Doug Keszler and

John Wager achieved chromatically red emission in ZnS:Mn phosphors, and

chromatically green emission in metal-doped SrS:Cu phosphors--the first time

full-range emission color control has been achieved in phosphor hosts

(3/3/2000).

     Keszler and his colleagues have a history of firsts, including the

discovery of cesium lithium borate (CsLiB6O10 or CLBO), which they patented, and

is already in use in the electronics industry for the manufacture of components

in cell phones, pagers, and PCs. Borate crystals of this type are nonlinear

optical (NLO) materials used to convert long-wavelength laser light to short

wavelengths for various uses, but it turns out that CLBO exhibits excellent

nonlinear optical properties and simplicity in growth compared to better-known

barium borate (beta-BaB2O4) and lithium barium borate (LiB3O5). In fact, CLBO

materials are more efficient than their predecessors, producing more than ten

times the UV power levels previously observed in all solid-state systems.

     However, Keszler and his colleagues want to raise the bar. Their current

challenge is to identify and grow crystals of a material that can be used to

directly generate wavelengths shorter than 200 nm, and there is currently no

crystal commercially available for this application. They are now moving beyond

the well-known borates to develop proprietary materials that will have both much

higher power capabilities and wider transparency ranges. While some of the work

is currently funded by the National Science Foundation, a joint venture or R&D

collaboration would aid in the development of such NLO materials, providing

another quantum jump in performance characteristics beyond those of CLBO and

related borates.

     The stakes are high, as deep-UV generation enables potentially lucrative

applications such as mask generation and diagnostics for deep UV

photolithography, SS laser systems for photorefractive keratectomy, and

industrial machining for electronics, MEMS, and emerging areas of

nanotechnolgies.

     Details: Douglas A. Keszler, Professor, Dept. of Chemistry and Center for

Advanced Materials Research, Division of Inorganic Chemistry, Oregon State

University, Gilbert Hall 153, Corvallis, OR 97331-4003. Phone: 541-737-6736.

Fax: 541-737-2062. E-mail: douglas.keszler@orst.edu. URL: www.chem.orst.edu.

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Copyright 2000, John Wiley & Sons, Inc., New York, NY 10158



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Copyright 2000, John Wiley & Sons Inc., New York, NY 10158