Reprinted from

Powder Tcchnology 88 (1996) 305-307

P. Somasundaran, Xiang Yu 2

Langmuir Center for Colloids and Interfaces. Columbia University. New York. NY 10027. USA

Received 28 November 1994; revised 27 March 1995; accepted 19 February 1996

ELSEVIER

POWDER TECHNOLOGYAn International Journal on the Science and Technology of Wet and Dry Particulate Systems

L.J. Ford (Widnes, UK)J.A. Grace (Vancouver. BC, Canada)E. Heidenreich (Braunschweig- Thune. Gennany)M. Horio (Tokyo, Japan)K. linoya (Kyoto, Japan)A. W . Jenike (Westford, MA, USA)M.A. Judd (Durban. South Africa)B.H. Kaye (Sudbury. Ont., Canada)P .C. Knight (Neston, UK)T.P. Meloy (Morgantown. WV, USA)J.M. Newton (London. UK)J. Novosad (Prague. Czech Republic)P. Salatino (Naples. Italy)B. Scarlett (Delft. Netherlands)K.V. Thambimuthu (Ottawa. Ont.. Canada)D.T. Wasan (Chicago,lL. USA)

Editor-in-ChiefJP.K. Seville (Birmingham, UK)

Regional EditorsJ.R. Coury (Sao Carlos, Brazil)L.-S. Fan (Columbus, OH, USA)G. Jimbo (Nagoya, Japan)A. Ueberman (Fremont. CA, USA)J.A. Raper (Kensington, NSW, Australia)

Editorial BoardH. Arastoopour (Chicago, IL, USA)P .C. Arnold (Woliongong, NSW, Australia)J. Bridgwater (Cambridge, UK)B. Briscoe (London, UK)T.G. Calk:ott (Mayfield, NSW, Australia)R. Clift (Gui/dford. UK)R. Davies (Wilmington, DE. USA)J.A. Dodds (Nancy. France)H. Fissan (Duisburg, Gennany)

Founding EditorJ.G. Williams (Bradford, UK)

Issues are sent by SAL (Surface Air Ufted) mail wherever thisservice is available. Ainnail rates are available upon request.Please address all requests regarding orders and subscriptionqueries to:

ELSEVIER SCIENCE S.A.PO Box 564, 1001 Lausanne, SwitzerlandTelephone: +41 (21)3207381Fax: +41 (21) 3235444E-mail: essa-o@elsevier.ch

Customers in the United States and Canada may obtain infomla-tion from:ELSEVIER SCIENCE INC.Attn.: Joumallnformation Center, 655 Avenue of the AmericasNew York, NY 10010, USATelephone: + 1 (212) 633-3750Fax: + 1 (212) 633-3764Telex: 420-643 AEP UI

USA mailing Info: Powder Technology (ISSN 0032-5910) ispublished monthly by Elsevier Science S.A. (PO Box 564, 1001Lausanne). Annual subscription price in the USA is US$1475.00(valid in North, Central and South America only), including airspeed delivery. Application to mail at second class postage rate ispending at Jamaica, NY 11431.USA POSTMASTER: Send address changes to Powder Tech-nology, Publications Expediting Inc., 200 Meacham Avenue,Elmont, NY 11003. AIRFREIGHT AND MAILING in the USA byPublications Expediting Inc., 200 Meacham Avenue, Elmont, NY

11003.

Aims and ScopePapers will be accepted on all aspects of the fonnation of particlesand their characterisation and on the study of systems containingparticulate solids. No limitation is imposed on the size of the par-ticles, which may range from submicron, as in pigments or aero-sols, to that of mined or quarried materials.The following list of topics is not intended to be comprehensive,but rather to indicate typical subjects which fall within the scope ofthe joumal's interests:. Formation of particles by comminution, attrition, precipitation,crystallisation and agglomeration.. Characterisation of the size, shape, surface area, pore structureand strength of particles and agglomerates.. Packing. failure, flow and penneability of assemblies of parti-cles. Interactions between particles and their environment includ-ing surface chemistry and physics and covering wetting anddispersal of particles and the properties of aerosols, colloids and

suspensions.. Particle-particle interactions, including van der Waals, capil-lary, electrostatic and other forces.. Handling and processing operations including storage, meter-ing, conveying, mixing, chemical reaction, heating, drying, fluidi-sation, compaction, aggregation. classification, and removal ofparticles from fluids.. Applications of particle technology in processing and in produc-tion of components using particulate matter.. Papers discussing technological experience and criticalreviews of existing knowledge in specialised areas will also bewelcomed.

Abstracting ServicesThis joumal is cited by the following Abstracting Services: Alumin-ium Industry Abstracts, Analytical Abstracts, Cambridge ScientificAbstracts, Chemical Abstracts, Chemical Engineering Abstracts,Compendex Plus, Current Contents, FIZ Kar1sruhe, RuidAbstracts, INSPEC, Metals Abstracts, Metal Powder Report,PASCAUCNRS, Physikalische Berichte, Wor1d Surface CoatingsAbstracts.

Advertising InformationAdvertising orders and enquiries may be sent to: International:Elsevier Science, Advertising Department, The Boulevard,Langford Lane, Kidlington, Oxford OX5 1GB, UK. Tel.: +44(1865) 843 565. Fax: +44 (1865) 843 952. USA and Canada:Weston Media Associates, Dan Lipner, PO Box 1110, GreensFarms, CT 06436-1110, USA. Tel.: +1 (203)2612500. Fax:+ 1 (203) 2610101. Japan: Elsevier Science Japan, 9-15Higashi-Azabu1-chome, Minato-ku, Tokyo 106; Tel: +81-3-5561-5033; Fax: +81-3-5561-5047.

Subscription Information 1996Volumes 86-89, each volume containing 3 issues, are scheduledfor publication Prices are available from the publishers upoo

request. Subscriptions are accepted on a prepaid basis only.

POWDERTECHNOLOGY

ELSEVIER Powder Technology 88 (1996) 305-307

P. Somasundaran, Xiang Yu 2

Langmuir Center for Colloids and Interfaces. Columbia University. New York. NY 10027. USA

Received 28 November 1994; revised 27 March 1995; accepted 19 February 1996

Abstract

The papers presented in this session on dispersion, rheology and mixing cover a broad spectrum of topics ranging from instrumentation forbetter characterization, to process development for improved stabilization, selective flocculation and dense packing, to modeling of colloidaldispersions. There are also some, but limited, efforts to understand the mechanisms involved in these processes. Importantly, there is a cleartrend to adapt, modify and develop techniques and instrumentations for even the difficult to characterize, highly concentrated dispersions.While the reported works deal with different systems, they aU address a common problem: control of interfacial properties via chemical orphysical means to achieve the desired stability or flocculation of suspensions and in some cases selectively.

Keywords: Dispersion; Rheology; InstJ1l~DtatiOD; Process develop~Dt

1. Introduction

In this review, new aspects covered by the papers presentedin this session are summarized and research opportunities arediscussed from the point of view of process and productdevelopment needs. Essentially, there are four topics thathave been dealt with: instrumentation, process development,product development, and mechanisms and modeling.

Most of the advances presented are in the area of instru-mentation and are as follows:

(i) A new technique is presented by Nikolov and Wasanto characterize suspensions by measuring capillary forcerequired to break structures. On the basis of the thresholdpressures for breaking coarse particle structure and fine par-ticle structure, a model is developed and used for predictingsedimentation of suspensions. One basic assumption is thatfines are trapped within a network of coarse particles, how-ever, there is no direct evidence presented for this. We havefound also the opposite case of coarse particles trapped withina network of particles as the characteristic structure of phos-phatic clay colloidal suspension. We think that the type ofstructure will depend upon the particle size distribution andrelative proportion of coarse and fines. and is in turn respon-sible for sedimentation or lack of it. In fact, an importantopportunity exists here to determine the structure and corre-

late it with sedimentation so that reliable mechanisms respon-sible for stability and sedimentation can be developed.

(ii) Direct measurement of floc breakage by in-situ lasermicroscopy reported by Peng and Williams is an interestingand useful development. Floc formation and breakage weremeasured using this technique and effects of agitation inten-sity. flocculant dosage and solid concentration were studied.Artifacts due to flocs breakage in the syringe etc. can be aproblem during such measurements.

(iii) A combination of rotating and vibrating viscometershave been used by Kawatra and Bakshi to determine changesin rheological properties. For non-Newtonian fluids. therotat-ing viscometer gave higher viscosity than the vibrating one.

(iv) Two flotation machines have been developed for coalby Leschonski. Benker and Schmidthals. Mineralization isbrought about in this case in a film under the action of cen-trifugal force. In the weir machine. separation is then carriedout in a shallow area. Reportedly with weir cell. the samerecovery is obtained as in conventional machine. but through-put is twenty-four times higher. No information has beensupplied on power consumption or application to coals ofdifferent grades.

There are also a number of papers that describe new pro-cesses:

(i) stabilization using modified polymers;(ii) mechanical agitation proposed to disperse floc;( iii) mixing related solid state reactions;(iv) magnetic flocculation making use of paramagnetic

forces;

I Presented at the Particle Technology Forum, Denver, CO. USA. August

17-19,1994.2 Present IMIdress: Corporate Resean:h Center. International Paper. Long

Meadow Road. Tuxedo. NY 10987, USA

0032-5910/96/S15.00 C 1996 Elsevier Science S.A All rights reserved

PIISO032-5910(96)03135-X

306 P. Somasundaran, X. Yu / Powder Technology 88 (1996) 305-307

(v) in-situ sol precipitation of tin oxide for dense ceramic

production;(vi) controlled aggregation of titania for ceramic

membranes.It is clear that some of these investigations will lead to

better products. However, a major deficiency of these is alack of understanding of mechanisms responsible for themodification, but there are some papers that deal with somemechanistic aspects. For example, evolution of floc structuresduring shear induced flocculation has been studied by a com-bination of Coulter counter and image analysis. Fractal anal-ysis showed that the fractal dimension is decreased duringfloc formation due to an increase in porosity, and finallyleveled off. The role of magnetic forces in magnetic floccu-lation has been analyzed. For flocculation and stabilizationof slurries, polymers and surfactants are often used to obtainthe desired results, but the actual state of aggregation obtainedis dependent, in addition to the amount of the reagentadsorbed, on the nature of conformation and orientation ofthe adsorbates. This aspect also has been touched upon in onepaper - clearly there are no guidelines as to what type of

conformation is best for flocculation or dispersion.

One of the most challenging problems in this area is Iing the desired stability of dispersions by the addichemicals. Even though flocculation processes hav,used for thousands of years, the mechanisms remairand there exists no universal guidelines on the ch<chemicals for a given system. The lack of selecti"adsorption of reagents on desired particles is also an unproblem [7]. As mentioned in the paper by Mathur, Pand Moudgil, the development of highly selective rethat will possess specific interactions between the ad!and adsorbent is a very challenging task.

As mentioned earlier, dispersions are also findingbiological applications. However, this important asp.unfortunately been omitted in this session. Biological s:are extremely complex with often net work of differeDof interfaces involved. The similarity of behavior cwith that of other colloidal particles in nature and the beof DNA with that of polyelectrolytes in terms of ads<and aggregation opens up a lot of opportunities for Iscientists. Surface modification of implant materials t(them more compatible with living tissues, the prevenpromotion of cell adhesion on special substrates, antrolled drug release on designated targets are onlyexamples that are of particular interest [8].

2. Research opportunities

4. Adsorption at interfacesBoth the increase in quantity and quality of publications inthe colloidal field during past few years clearly shows thatinterfacial property control is receiving the attention it hasalways deserved. Most importantly, significant progress hasalso been made in developing equipment and techniques fordirect observation of surface properties and species usingnanoscopes and chemical probes. Monitoring interactionforces between particles and a plate with or without adsorbedspecies has been made possible by the development of themicroforce balance and the atomic force microscope [1,2].The orientation, conformation and other microstructuralproperties of adsorbed layers of polymers and surfactants canbe measured by small-angle light and neutron scattering, flu-brescence and electron spin resonance (ESR) techniques [3-6] . These techniques are yielding a large amount of data thatshould prove helpful in the development of theoretical modelswith predictive capabilities.

Interfacial properties of particulate substances are )modified or controlled by the adsorption of surfapolymers and inorganic materials. The factors aftadsorption include the nature of both adsorbent andbate, and solvent properties. While there is consicinformation on adsorption of surfactants and polymerdictive capability is sorely lacking, with the result that I

ical tests have to be carried out for every new system.case of polymers, it is necessary to determine, in addithe adsorption density, the fraction of segments bolsurface, the distribution of segments near the surface vand orientation in general in order to develop a fullstanding of the role of polymers in controlling dispersi,flocculation.

It is also important to note the non-equilibrium nalpolymer adsorption in most applications [9]. Furthe1additional complications arise from the polydispersitypolymer. Also, it has been found that adsorption denwell as the kinetics depends not only on the molecular'of the polymer but also on the mode of polymer addilis critical to generate more information on the kineticsadsorption and various intermediate stages involved.

Spectroscopic techniques are now widely used tomine the fraction of segments bound to the surface IFourier-transform (FfIR) infrared spectroscopy can bsince the absorption peaks can shift on transfer of pc

from the solution to the particle surface. Using spinESR can also be used to monitor mobility changes cau

3. Applications of dispersions

Colloidal dispersions are now used in almost every indus-try during one processing stage or another. More recently,nanosize particles and their dispersions are finding use in theprocessing of high performance electronic and ceramic mate-rials. Colloidal dispersions have also significant bioapplica-tions, which includes microencapsulation, slow drug releaseand the prevention or promotion of cell adhesion. In all thesecases, at lcast onc intcrfacc is involved and its properties needto be controlled to obtain the desired performance.

P. Somasundaran. X. f" I PowMr Technology 88 (/~) 105-307 307

6. Theory and model verificationadsorption, panicularly of segments of trains. Nuclear mag-netic resonance (NMR) is less sensitive, however it has theadvantage that it does not have the problems caused by theuse of probes which possibly affect properties of polymers.Clearly, it is important to be fully aware of the drawbacks ofall the techniques and wherever possible, to obtain informa-tion with more than one technique.

Another important parameter of polymer adsorption is thenature of the distribution of segments in the interfacial regionand the resultant adsorption layer thickness. Changes in thehydrodynamic diameter of particles due to adsorption havelong been used to estimate the adsorbed layer thickness. Thehydrodynamic diameter of particles can be detennined usingthe traditional settling and viscosity experiments as well asby use of photon correlation spectroscopy. Recently thesmall-angle neutron scattering technique has also been usedto measure the distribution of segments in the vicinity ofsurface.

There have been a number of attempts at theoretical mod-eling and visualization of colloidal dispersions. Computersimulation of polymer conformation in solution and at inter-faces has been developed and verified by experimental results[ II J. However, due to the electrostatic fon;es involved, themost often used water soluble polymers, polyelectrolytes,have proved to be the most difficult to model. To date, it isstill not possible to precisely predict the adsorption or dis-persion behavior of a given polymer/solid/solution system.There is a need to develop relationships between the chemicalstructure of a polymer or surfactant and its performance inspecific colloidal-solvent systems. Also, it is important tonote that even though conformation has been shown to havea significant influence on the performance of the polymer ondispersion, its role is not precisely known.

Earlier theories are being continuously modified. Forinstance, additional terms have been a(kjed into the DL VOtheory. Although considerable progress has been made inunderstanding particle interactions, most research effortsaddress only one specific problem. The lack of an integratedapproach causes severe difficulties when applying existingtheories to new systems. Similarly, advance is needed insimulating and modeling colloidal particulate processes witha larger number of particles and a shorter simulation time.The development of animated displays of the movement ofcolloidal particles in processes can in the future be expectedto yield new insights into the underlying mechanisms andthus lead to the design of more efficient processing schemes.

Clearly colloidal processes in real-life systems are verycomplex. and theories taking into account all the possibleinte~tions between various components in the systems,while desirable. may have to await much more collaborativeeffort between the various disciplines involved.

5. Characterization of particles and dispersions

References

Traditicnal methods used to characterize the properties ofparticle surfaces and dispersions such as zeta potential, sus-pension stability as measured by settling rate and viscosity ofsuspensions are still widely used and yield large amounts ofuseful data especially for industrial applications. As paperspresented in this session show, these techniques have beengreatly improved in terms of both accuracy and reliability. Itis clear that the rheological investigation of concentrated dis-persions does offer a powerful means for studying concen-trated dispersions where the interactions between particlesare not the same as dilute dispersions. Modified and imJX'Ovedinstrumentations, such as electrokinetic sonic amplitude sys-tem (ESA) and the stream potential meter, have made itpossible to measure the surface charge of particles in conccn-trated dispersions without any need for dilution and the resul-tant destruction of any network structure. In addition tothe laser microscopy discussed in this session, we havefound cross-area transmittance (CAT) scan useful forobtaining direct information on size as well as structure offtocs [10].

During the last twenty years there has also been consider-able experimental work devoted to determining the forcesbetween colloidal particles. Nikolov and Wasan have dis-cussed an elegant new equipment, the capillary force balance,to characterize dispersions. There is a also large amount ofwork on interactions between molecularly smooth mica plateswith and without adsorbed species, using the surface forceapparatus. More recently, the atomic force microscope isbeing used to obtain direct information on such interactionsbetween surfaces. However, the direct measurement of inter-actions between two individual colloidal particles has not yetbeen fully achieved.

[1] E.J.W. Verwey and J.Th.G. Ovetbeek. T7Ieory of the Stability ofLyophobic Colloidf. El~Yier, New VOlt. 1948.

[2] DJ. Shaw. Introduction to Colloid and Suiface Chemistry.8utterwonh-Heinemann. Oxford. 1991.4 edD.

[3] M. WiDDik, MA. Winnik and S. Tazuke. J. Pitys. Chelll., 91 (1987)2039.

[4] P. Chalklar. P. Somasundaran. K.C. Watemlall and NJ. Turro.LangIIIMir, 3 (1987) 297.

[5] K. 0Iar. A.P. Gast and C.W. Frank.lAIIgmuir, 4 (1988) 989.[6] I.D. Robb and R. Smith. Polymer. 18 (1977) 500.[7] 8.M. MO4Idgil. S. Bdli in K.A. Matis (ed.), FIo~ Sc~-'

Engineering, Marcel Dekker, New York.. 1995. pp. 415-440.[8] H.M. Rernz. Cosmet. Toiletries, 103 (1988) 70.[9] X. Yu aDd P. Somasundaran. J. Colloid /1tU1/tIce Sci.. 177 (1996)

283.[10] P. Somasundaran. Y. Huang and C. Gyte. Powder Techllol.. 53 (1917)

73.[II] J. Scheuljens and G. Fleer in Th. Tadros (ed.). Effect of Polymers on

Dispersi(Jfl Properties. AcIMSemic Press. LOIMIoD. 1982 n 42-

Guide for AuthorsTypes of contributions should be saved in the native format of the word processing program used.- normal length research papers Most popular word processor file fOfmats are accept~e.though we cannot- reviews of specialised topics within ~ scope of the journal guarantee the usability of all formats. The cisk format. word-prooessor- letters format, file name(s) and the title and authors of the article should be indi-- correspondence cated on the cisk. The content of the disk must correspond exactly to the- book reviews hard copy version of the paper.Suggestions for review artides will be welcomed. and prospective authorsshould obtain preliminary approval from Professor J.P.K. Seville beforepreparing such an article. Manuscript Preparation

Language. Papers will be published in English. Authors in Japan pleasenote that information about how to have the English of your paper dlecked.corrected and improved (before submission) is available from: EcitorialService. Elsevier Science Japan. 9-15 Higashi-Azabu 1-chome. Minato-ku. Tokyo 106. Japan; Tel: +81-3-5561-5032; Fax: +81-3-5561-5045.Some ftexibiUty of presentation will be allowed. but au1hors are \Jrged toarrange tie subject matter clearly under such headings as Introduction.Experimental. Results. Discussion, etc. All contributions should indudeconcise. informative Abstract. and a maximum of six Keywords. Refer-ences should be numbered consecutively throughout Ihe text and shouldbe collected together in a reference list (headed References) at Ihe end oftie paper. An equations. tables and legends should be n~bered consec-utively and separately throughout Ihe paper.Wustrations. Une drawings should be in a form suitable for reproduction.IUustralions can be printed in coIourwhen lhey are judged by Ihe Editor tobe es~tial to tie presentation. The publisher and Ihe au1hor will ead1bear part of the extra costs involved. Further infOfmation conceming colourillustrations and Ihe costs to the author can be obtained from the publisher.

ProofsAuthors witl receive proofs whidl they are requested to correct and retumas soon as possible. No new material may be inserted in the text at thetime of proof-reading. A Note added in proofmust be dated and the authormust have requested and received the E<itor's approval.

Submission of papersAuthors should submit a disk together with three copies of their artides(complete in all respects) direct to one of the Editors at the a<*iress givenbelow:Professor J.R. Coury, Universidade Federal de Sao Carlos, Centro diCiencias Exatas e de T ecnologia, Departamento de Engenharia Quimica,Via Washington Luiz, Km 235, C.P. 676, 13565-905 SAo Car1os, SP, Brazil,Fax: +55 (162) 74 8266Professor J.P .K. Seville, School of Chemical Engineering, The Universityof Birmingham, Edgbaston, Bimlingham B15 2TT, UK, Fax: +44 (121)4145377, E-mail: Powder1echObham.ac.ukProfessor L.-S. Fan, Oepar1ment of Chemk:aJ Engineering, Ohio StateUniversity, 140 West 19th Avenue, Columbus, OH 43210-1180, USA,Fax: +1 (614)2921929, E-m~:fan.10osu.eduProfessor G. Jlmbo, Chubu Powtech Plaza laboratory, Room 507,Chukei Builcing, Mei-eki, 4-4-12, Nakamura-ku, Nagoya 450, Japan,Fax: +81 (52) 586 5676Mr A. lieberman, Particle Measuring Systems Inc., 46500 FremontBlvd., Fremont, CA 94538, USA, Fax: + 1 (510) 490 8213, E-mail:fremont 0 pas.comDr J.A. R8per. School of Chemical Engineering, University of New SouthWales, PO Box 1, Kensington, NSW 2033, Australia, Fax: +61 (2) 3855966, E-mail:j.raperOunsw.eoo.au

Contributions are accepted on the understanding that authors haveobtained the necessary authority for publication. Submission of an articlemust be accompanied by a statement that the article is ori~ and unpub-lished and is not being considered for publication elsewhere. Upon accep-tance of an article by the journal, the author{s) will be asked to transfer thecopyright of the article to the pubtisher. This transfer will ensure the widestpossible dissemination of information.

OffprintsTwenty-five offprints of each paper will be S\4JpIied free of charge to theauthor(s). Additional offprints may be ordered at prices shown on the off-print order form which accompanies the proofs.

There are no page charges.

Further InformationAll questions arising alter acceptance of a paper. especially ttIose C«I-ceming proofs. should be directed to the Editorial Office. Elsevier Sdence.at the address given on the inside front cover. A more detailed guide forthe preparation of manuscripts is available from the Editorial o~.

Disk PreparationThe final text may be submitted on a 3.5" cIsk (in addition to the hard copiesand original figures). Double density (DO) or high density (HO) disks for-matted for IBM compatibles or Apple Macintosh are preferred. The files

Copyright C 1996 Elsevier Science SA AU rights reserved. 0032-591 ()'96/$15.00

This journal and the kldividual con!ri)utions contained in it are protected by the copyright of Elsevier Science S.A., and the folbwW1g terms and con<itXJn5 apply totheir use:

Photocopying

for aU other photOCopyWlg, including multiple or systematic COPyklg, copying for advertising or promotional purposes, resale, and aU forms of document delivery.Special rates are available for educational ilstitutions that wish to make photocopies for non-Pf1>fit educational classroom use.In the USA, users may clear permissions and make payment through the Copyright Clearance Center, Inc., 222 RosewoOO Drive, Danvers, MA 01923, USA. In theUK, users may clear pemVssions and make payment thf1>.qI the CopYf9lt Licensing Agency Rapid Clearance SefVIce (CLARCS), 90 TottenhamCour1 Road,London WI P OLP, UK. In other countries where a local copyright clearance centre exists, please contact it for inforrnatkJn on required permissions and payments.

Derivative WOl'k8Subscribers may reproduce tables 01 contents or prepare lists 01 articles including abstracts for kltemal ci~ulation within their institutions. Pennission of the publisheris required lor resale or distribution outside the institution.Permission of the publisher is required for aU other derivative works. inclu<ing compilations and translations

ElectronIc Storage

the address indicated.

photocopying, recording or otherwise. without prbr written pelmisshJn of the publishet:

Dlsclai-.No responsibility is assumed by the pubIisIIer tor any iniuIY and'or damage to persons or property as a matter of products liability. n8f1igence or otherwise, or ~any use or operation of any methods, products. inSlroctiorls or kJeas contained in the materiaf herein.

Although 8N advertising materiaf is expected to confonn to ethlcaf (me<kaf) standatds, inclusion in this publication does not constitute 8 guarantee or ~tof the quality or value of such prorJIK;1 or of the claims made of it by its manufacturer.

@ The paper used in this publication meets the requirements 01 ANSI/NISO Z39.48-1992 (Permanence of Paper).

Printed in The Netherlands