intelligence in novel materials

32 Oilfield Review

Intelligence in Novel Materials

Rashmi BhavsarNitin Y. VaidyaRosharon, Texas, USA

Partha GangulyAlan HumphreysAgathe RobissonHuilin TuNathan WicksCambridge, Massachusetts, USA

Gareth H. McKinleyMassachusetts Institute of TechnologyCambridge, Massachusetts

Frederic PauchetClamart, France

For help in preparation of this article, thanks to Hiroshi Hori,Sagamihara, Kanagawa, Japan.CQG (Crystal Quartz Gauge), FUTUR, Isolation Scanner, Q-Marine, Q-Seabed, Sonic Scanner and sonicVISION are marks of Schlumberger.CryoFit is a mark of Aerofit Products Inc.Motion Master is a mark of LORD Corporation.Simon Nitinol Filter is a mark of C.R. Bard, Inc. or an affiliate.Smart Magnetix is a mark of Biedermann Motech GmbH.

Defined as materials whose properties can be varied controllably in response to

changes in their environment, smart materials can convert one type of energy to

another. This opens the way to use them for performing the complex functions of

sensors and actuators—sometimes several functions simultaneously—in a device

essentially consisting of a single piece of a single substance.

Throughout history, people have shaped tools fromthe materials at hand. With better under standingof material properties came the ability to fabri -cate materials with designed character istics.Currently, a materials category that is experi -encing extensive research and some application is“smart materials.”

Some smart materials are widely known.Piezoelectric lighters and igniters in gas stoves,grills and other gas appliances produce a spark,or electric discharge, without using an electriccircuit—just by striking a piezoelectric crystalwith a spring-loaded hammer. This property ofpiezoelectric materials to “feel” pressure andrespond by generating electric potential is usedin a wide range of smart applications. Othersmart materials respond to different externalstimuli, such as temperature, electromagneticfields and moisture.

What all smart materials have in common isthe ability to convert one type of energy toanother. Piezoelectric materials can convertmechanical energy to electric energy, and viceversa. Other smart materials convert betweenother types of energy. A key to practical appli -cations is the fact that this conversion can occurin a controlled manner. Materials that manifestthis property of responding in a controllablefashion to changes in the environment arecommonly termed smart materials.1

The two main types of energy-conversiondevices are sensors and actuators, and these arethe principal applications of smart materials. Asensor converts an action to a signal, whereas anactuator converts a signal to an action.Conventional sensors and actuators are typicallyconstructed of multiple materials and havemovable parts. Some smart materials can per formthe functions of several materials and partssimultaneously, thus simplifying the device designand having fewer parts to break or wear down.

From the standpoint of practical appli cations,of greatest interest are materials that convertmechanical energy to thermal, electric, magneticor chemical energy, and vice versa. In addition topiezoelectric materials converting mechanicalenergy into electricity, other smart materials thatare utilized in commercial applications includeshape-memory alloys that respond mechanicallyto applied heat; magneto rheological andmagneto strictive materials, whose properties arecontrolled by the application of magnetic fields;and materials that swell when chemicallyactivated. This article will look at some of thesematerials, their current applications and theirpotential for use in future oilfield applications.

1. Schwartz MM (ed): Encyclopedia of Smart Materials.New York City: John Wiley & Sons, 2002.

2. Otsuka K and Wayman CM (eds): Shape MemoryMaterials. Cambridge, England: Cambridge UniversityPress, 1998.

3. Kauffman GB and Mayo I: “The Metal with a Memory,”Invention & Technology Magazine 9, no. 2 (Fall 1993): 18–23, http://www.americanheritage.com/articles/magazine/it/1993/2/1993_2_18.shtml (accessedDecember 4, 2007).

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Thermally Activated Materials: Total RecallSome materials can be deformed but then regaintheir original shape when heat is applied. Theseare called shape-memory materials. Alloys withproperties later found to be directly related tothe shape-memory phenomenon have beenknown since the 1930s.2 However, technologicalapplication of this phenomenon did not occuruntil almost three decades later.3 In early 1958, William J. Buehler, a metallurgist at theNaval Ordnance Laboratory (NOL), White Oak,Maryland, USA, began to test various alloys to beused for the nose cone of a submarine rocket. Hedetermined that a nickel-titanium alloy had thehighest impact resistance and other beneficialproperties, such as elasticity, malleability andfatigue resistance. Buehler named this alloy

Nitinol, combining the chemical symbols ofnickel, Ni, and titanium, Ti, with the laboratory’sacronym, NOL.

The first hint of the unusual properties ofNitinol was seen in 1959 when Buehlerdiscovered the alloy’s exceptional temperature-dependent acoustic-damping characteristics,which suggested temperature-dependent changesin the alloy’s atomic structure. But the final steptoward the discovery of shape memory was madein 1960 at a meeting of NOL management. Theywere presented with a Nitinol specimen thatwould demonstrate the alloy’s favorable fatigue-resistance properties. The specimen was a longNitinol strip folded repeatedly to form a zigzagprofile. The directors bent and unbent the

specimen and were satisfied with its mechanicalcharacteristics. One of the managers decided tocheck the alloy’s thermal properties using acigarette lighter. Amazingly, when the com pressedstrip got hot, it stretched out longitudinally.

It took a few more years to understand themechanism of shape memory. One importantdiscovery was that Nitinol can exist as twodifferent temperature-dependent phases; shapememory is possible because of phase transitionsbetween these phases. To fix the original shape,or to “train” a specimen to “remember” thisshape, the Nitinol specimen must be annealed atapproximately 500°C [932°F] for an hour while itis held in a fixed position. Heating gives rise to ahigh-temperature, hard, inelastic phase calledaustenite. Subsequent cooling, or quenching, of


the specimen produces a low-temperature, elastic,more deformable phase called martensite. If thetrained specimen is deformed and heated again,the thermal motion causes the atoms to form theaustenite lattice, thus restoring the originalshape of the specimen (above). The annealingand quenching temperatures, as well as otherproperties, depend strongly on the alloy compo -sition and additives used.

The above procedure describes the so-calledone-way shape-memory effect, in which thematerial remembers a single shape. By appro -priate training, some shape-memory materials canremember two different shapes, one at lowertemperature and the other at higher tempera ture,thus exhibiting a two-way shape-memory effect.

To date, shape memory has been observed indozens of two- and three-component metalalloys, of which, along with Nitinol, copper-zinc-aluminum [CuZnAl] and copper-aluminum-nickel[CuAlNi] alloys are most widely used. Anotherpromising group of materials is shape-memorypolymers, which became commercially availablein the 1990s.4

The first commercial application of shape-memory materials was CryoFit shrink-to-fit pipecouplings developed in 1969 to join hydrauliclines in F-14 fighter aircraft.5 The tubularcouplings are easily installed by positioning themachined and liquid-nitrogen-cooled coupling on

the pipe ends to be joined and allowing it towarm to ambient temperature. As the couplingwarms, it shrinks and crimps down on the pipesto form a tight joint (right).6 Following this, theuse of shape-memory couplings was extended tooil and gas pipelines, water pipes and other typesof pipes and tubes. A wide range of various shape-memory fasteners, such as rings and clamps, wasalso developed.7

Another important area of application ofshape-memory materials is medicine. The mostreadily observable medical shape-memory deviceis dental braces. Nitinol-based braces were firstused in patients in 1975 and patented in 1977.8

Traditional dental braces include a stainless-steel wire, which is insufficiently springy andrequires frequent readjustments. In contrast, aNitinol wire not only is springier, but alsoprovides a constant load on the teeth, thusrequiring fewer or no readjustments. A Nitinolwire is initially molded to obtain a correct shape;then an orthodontist attaches it to the patient’steeth, bending it as necessary. Body heatactivates the Nitinol wire, restoring it to theoriginally molded shape.

A similar procedure is used in shape-memoryorthopedic staples and plates, which acceleratethe healing of bone fractures. However, perhapsthe most important, truly vital medicalapplications of shape memory are in cardio -

vascular surgery.9 An example is the SimonNitinol Filter device, a Nitinol wire sieve that isinserted into a blood vessel to trap clots travelingin the bloodstream.10 The trapped clots graduallydissolve and an embolism, or obstruction of theblood vessel, is thus prevented. The Simon

34 Oilfield Review

> Mechanism of shape-memory effect. On cooling, the high-temperatureaustenite phase with a face-centered cubic lattice transforms into thelow-temperature martensite phase. Because of stresses experiencedduring cooling, the martensite produced from austenite undergoes crystaltwinning: the formation of adjacent layers related by mirror symmetry.Deformation removes twinning. Untwinned martensite has a tetragonalcrystal lattice. Heating the deformed untwinned martensite converts itback to the austenite phase.

Cooling

DeformationHeating

Austenite

Untwinned Martensite

Twinned Martensite

> Photograph of CryoFit shrink-to-fit coupling(top) and the principle of its use (bottom). Thecoupling is machined at ambient temperatureuntil its inner diameter is somewhat smaller thanthe outer diameter of the pipes to be joined (A).Then the coupling is cooled in liquid nitrogen andmechanically expanded so that its inner diameteris slightly larger than the outer diameter of thepipes (B). The expanded coupling easily slipsover the pipe ends (C). The coupling is properlypositioned and allowed to warm to ambienttemperature. During warming, it shrinks back toits original smaller size to form a tight joint (D).(Photograph courtesy of Intrinsic Devices, Inc.,reference 5. Drawings courtesy of ATI WahChang, reference 6.)

A

C

D

B

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Spring 2008 35

Nitinol Filter sieve is inserted using a catheterwhile being in a cooled, deformed martensiticstate, and then it expands to full size whenwarmed by body heat (right).

Electrically Activated Materials: Smart as PaintA large range of applications has been createdusing piezoelectric smart materials. The piezo -electric effect, also called the direct piezoelectriceffect, is the ability of certain materials—minerals, ceramics and some polymers—toproduce an electric charge in response to anapplied mechanical stress. The converse effectcan also be seen, in which piezoelectric materialsare deformed in an applied electric field.

The direct piezoelectric effect was discoveredby the brothers Pierre and Jacques Curie in 1880.They noticed that compressing a quartz crystalplate cut at a certain orientation gave rise toelectric charges on plate faces opposite to thecompression direction: a positive charge on oneface and a negative charge on the other.Expanding the crystal plate also generatedelectric charges, but if the charge on a face whilecompressing was negative, then the charge onthis face while expanding was positive, and viceversa. The direct piezoelectric effect occurs if anelastic deformation of a solid is accompanied byan asymmetric distortion of the distribution ofpositive and negative charges, dipoles or groupsof parallel dipoles (Weiss domains) in thestructure of the solid so that a total dipolemoment is induced; that is, the solid is polarized.The converse piezoelectric effect takes place ifan applied electric field causes such a distortionof the distribution of charges, dipoles or Weissdomains that this leads to geometric distortions,manifested as mechanical strains (right).

> Simon Nitinol Filter. The schematic (top) shows the deployment of thedevice on a catheter. Also included are the front and side views in thedeployed state (bottom). (Copyright Brazilian Journal of Medical andBiological Research; used with permission, reference 9.)

Simon Nitinol Filter Being Deployed

Side ViewFront View

4. Lendlein A and Kelch S: “Shape-Memory Polymers,”Angewandte Chemie International Edition 41, issue 2(June 12, 2002): 2034–2057.

5. “Use of Shape Memory Alloys in High ReliabilityFastening Applications,” http://www.intrinsicdevices.com/history.html (accessed December 24, 2007).

6. Tuominen S and Wojcik C: “Unique Alloys for Aerospaceand Beyond,” Outlook 16, no. 2 (2nd Quarter 1995),http://www.wahchang.com/pages/outlook/html/bkissues/16_02.htm (accessed December 24, 2007).

7. Stöckel D: “The Shape Memory Effect: Phenomenon,Alloys, Applications,” Report (2000), NDC, Nitinol Devices& Components, Inc., Fremont, California, USA,www.nitinol-europe.com/pdfs/smemory.pdf (accessedDecember 24, 2007).

8. Andreasen GF: “Method and System for OrthodonticMoving of Teeth,” US Patent No. 4,037,324 (July 26, 1977).

9. Machado LG and Savi MA: “Medical Applications ofShape Memory Alloys,” Brazilian Journal of Medicaland Biological Research 36, no. 6 (June 2003): 683–691,www.scielo.br/pdf/bjmbr/v36n6/4720.pdf (accessedDecember 19, 2007).

10. Duerig TW, Pelton AR and Stöckel D: “SuperelasticNitinol for Medical Devices,” Medical Plastics andBiomaterials 4, no. 2 (March 1997): 30–43.

> Direct and converse piezoelectric effects. In the direct piezoelectriceffect, compressing and expanding a piezoelectric material samplegenerate opposite electric charges on respective faces of the sample (top).In the converse piezoelectric effect, application of voltage to apiezoelectric material sample causes deformation Δh (bottom right). Thiscontrasts with the direct piezoelectric effect, in which deformation Δhproduces voltage (bottom left).

No strain Compression Expansion

Piezoelectricity Converse Piezoelectricity

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To date, piezoelectricity has been detected inmany types of materials. The Curie brothersdiscovered piezoelectricity in naturally occurringminerals, such as quartz, tourmaline, topaz andRochelle salt (sodium potassium tartratetetrahydrate, or KNaC4H4O6·4H2O). Of these, onlyquartz is now used commercially. All otherpractically important piezoelectric singlecrystals—such as ammonium dihydrophosphate[NH4H2PO4], gallium orthophosphate [GaPO4],and lanthanum gallium complex oxides—aregrown artificially.

Although single-crystal piezoelectric materialscontinue to be developed, the most extensivelyused class of piezoelectric materials is nowpolycrystalline piezoelectric ceramics, whichhave much wider ranges of useful characteristicsand work under broader operating conditions.Currently, the largest group of piezoelectricceramics is materials consisting of crystalliteswith the perovskite structure.11 These arecomplex metal oxides with the general formulaABO3, where A and B are cations of differentsizes. The cation A includes elements such as Na,K, Rb, Ca, Sr, Ba and Pb, and B includes Ti, Sn, Zr,Nb, Ta and W. Sometimes A and B each mayrepresent two or more of these cations, providedthat the total stoichiometry is satisfied (forexample as in lead zirconate titanate,PbZrxTi1−xO3). The main examples of perovskite-like piezoelectric ceramics are barium titanate[BaTiO3] (the first piezo electric ceramicdiscovered), lead titanate [PbTiO3], leadzirconate titanate (the most widely usedpiezoelectric ceramic to date), lead lanthanumzirconate titanate [Pb1−xLax(ZryTi1−y)1−x/4O3]and lead magnesium niobate [PbMg1/3Nb2/3O3].12

After the sintering stage in manufacturing,dipoles in such ceramics are parallel only withineach domain, whereas the domains are polarizedrandomly.13 An elastic deformation of a set ofrandomly polarized dipoles cannot lead to anasymmetric distortion of the charge distributionand, therefore, cannot result in piezoelectricity.Therefore, the last stage of manufacturing ofpiezoelectric ceramics is always the applicationof a strong electric field at elevated temperature,after which the domains are polarized approxi -mately identically and the substance becomespiezoelectric (above).

Some polymers can be piezo electric or can bemade so. Piezoelectricity was discovered ordeveloped in a number of natural polymers,including keratin, collagen, some polypeptides andoriented films of DNA, and synthetic polymers,such as some nylons and polyurea. However,currently the only commer cially availablepiezoelectric polymers are polyvinylidenedifluoride (PVDF) and its copolymers withtrifluoroethylene and tetra fluoro ethylene.14 PVDFis a semicrystalline synthetic polymer with thechemical formula (CH2–CF2)n. PVDF is producedin thin films, which are stretched along the filmplane and polarized perpendicular to this plane toproduce piezoelectric properties (right).

Because piezoelectric materials can convertmechanical energy to electric energy and viceversa, their applications are dominated byvarious electromechanical sensors and actuators.The piezoelectric effect is used in sensors forvarious physical quantities (such as force,pressure, acceleration, side impact and yaw rate),and in microphones, hydrophones, ultrasonicsensors, seismic sensors, acoustic pickups andmany other devices.

An interesting example of a continuouslydistributed piezoelectric sensor is piezoelectric,or smart, paints.15 Such paint can be preparedusing lead zirconate titanate ceramic powder asa pigment with epoxy resin as a binder. Themixture is coated on a surface and cured andpolarized at room temperature. The resultingpaint film acts as a vibration and acoustic-emission sensor for the entire surface. Thesesmart paints can be used to cover large surfaceareas of individual structural elements and evenentire constructions, such as bridges, to monitortheir integrity. Recent controlled weatheringtrials on river-crossing bridges in the UK andFinland have shown that the piezoelectric-paintsensors can survive harsh outdoor conditions andremain functional for at least six years.16

36 Oilfield Review

> Polarization effects. Dipoles in sintered ceramics are parallel only withineach domain, whereas the domains are polarized randomly (left). Afterpolarization in strong electric field Ep at elevated temperature, the domainsare approximately aligned and the substance becomes piezoelectric (right).

Before Polarization

E p

After Polarization

> Polyvinylidene difluoride (PVDF) treatment toimpart piezoelectric properties. In a melt-castpolymer film, crystallites (tens to hundreds ofnanometers in size) are randomly distributedamong amorphous regions (top). Stretching thepolymer film (middle) significantly aligns polymerchains in the amorphous regions in the sheetplane and facilitates uniform rotation of thecrystallites by an electric field. Polarizationthrough the film thickness (such as by usingdeposited metal electrodes) makes the filmpiezoelectric (bottom). (Figure courtesy of NASA;used with permission, reference 14.)

Melt-Cast

Crystallineregion

Amorphousregion

Electrically Polarized

Elec

tric

field

dire

ctio

n

Mechanically Oriented

Stretchdirection


Spring 2008 37

Other important examples of piezoelectricactuators are loudspeakers, piezoelectric motorsand high-precision microactuators. High-precision microactuators use the fact that smallchanges in voltage applied to piezoelectricmaterials cause small changes in their shape.This allows fine control of positions and displace -ments of parts and elements, which is critical inthe operation of a variety of devices from inkjetprintheads to guidance systems.

The most significant class of piezoelectricdevices is piezoelectric ultrasonic generators,which, unlike magnetostrictive or other types ofultrasonic generators, provide the most efficientgeneration of ultrasound with controlled powerand frequency. Ultrasound in such generators isproduced using the converse piezoelectric effect.Here, a cyclic application of voltage to apiezoelectric material causes it to expand andcontract, thus emitting a pressure wave.

The creation of piezoelectric ultrasonicgenerators has opened the way for an extremelywide array of applications. The first practicalapplication of piezoelectricity was a piezo -electric quartz ultrasonic generator in an activesonar designed to detect submarines duringWorld War I in 1915.17 Since then, this appli -cation has grown to an extensive collection ofmethods for detecting inhomogeneities invarious media. Flaw detection using ultrasonictechnology tests a broad range of materials andconstructions, including various pipes and pipe -lines. For the general public, the most commonapplication is medical ultrasonography, atechnique for visualizing internal tissues andorgans of the body, especially obstetric ultra -sonography for visualizing an embryo or fetus inutero, which has become a standard procedure ofprenatal care in many countries.

Piezoelectric devices are also found innumerous oilfield applications. A quartzpiezoelectric element is an important part of theSchlumberger CQG Crystal Quartz Gauge, whichis used as a pressure sensor in a wide variety oftools. Piezoelectric ceramic devices also play akey role in Schlumberger seismic, sonic andultrasonic logging instrumentation: as pingers

and hydrophones in the Q-Marine single-sensormarine seismic system and Q-Seabed multi -component seabed seismic system, and asreceivers and monopole transmitters in the SonicScanner acoustic scanning platform, IsolationScanner cement evaluation service andsonicVISION sonic-while-drilling tool. Althoughcurrent applications are limited to sensors,future oilfield applications might utilize thepiezoelectric effect for energy harvesting andmicroactuators.

Magnetically Activated Materials: FastStrength of Minute ParticlesAnother category of smart materials ismagnetorheological (MR) fluids. These fluidshave rheological properties that may be varied byapplying a magnetic field. The change is propor -tional to the magnetic field intensity, can becontrolled very accurately by varying thisintensity, and is immediately reversible afterremoving the field.

A typical MR fluid is a suspension of micron-sized (usually 3 to 8 microns) magneticallysusceptible particles (generally 20 to 40% byvolume of pure iron particles) in a carrier fluid,such as mineral oil, synthetic oil, water orglycol.18 Various surfactants, including oleic andcitric acids, tetramethylammonium hydroxideand soy lecithin, are also added to MR fluids toprevent particles from settling. MR materialssystems may be manufactured as gels, foams,powders, greases, and even solid elastomers.

Without a magnetic field, particles in an MRfluid are randomly distributed. Once a magneticfield is applied, the particles align with themagnetic field to form chains, which resist flow or shear deformation in the directionperpendicular to the magnetic field directionand dramatically increase the viscosity (or moreaccurately, yield strength) in this direction(above). As soon as the magnetic field isremoved, the chains of particles disintegrate(through random Brownian forces) and theinitial viscosity is restored.

11. Perovskite (named after Lev A. Perovski, a Russianmineralogist) is a natural calcium titanate [CaTiO3] with a pseudocubic lattice. This class of solids includes many technologically important ceramics, such assemiconductors and magnetic, ferroelectric andpiezoelectric materials.

12. Kholkin A, Jadidian B and Safari A: “Ceramics,Piezoelectric and Electrostrictive,” in Schwartz MM(ed): Encyclopedia of Smart Materials. New York City:John Wiley & Sons (2002): 139–148.

13. Sintering is a method for forming objects from agranular material by heating the material close to itsmelting point until its particles adhere to one other.

14. Harrison JS and Ounaies Z: “Piezoelectric Polymers,”ICASE Report No. 2001-43, NASA/CR-2001-211422,http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020044745_2002075689.pdf (accessed December 24,2007). (Color added to original figure.)

15. Egusa S and Iwasawa N: “Piezoelectric Paints as OneApproach to Smart Structural Materials with Health-Monitoring Capabilities,” Smart Materials andStructures 7, no. 4 (August 1998): 438–445.Egusa S and Iwasawa N: “Piezoelectric Paints:Preparation and Application as Built-In VibrationSensors of Structural Materials,” Journal of MaterialsScience 28, no. 6 (March 1993): 1667–1672.

16. Hale JM and Lahtinen R: “Piezoelectric Paint: Effect ofHarsh Weathering on Aging,” Plastics, Rubber andComposites 36, no. 9 (November 2007): 419–422.

17. Sonar, an acronym for sound navigation and ranging, is a technique that uses underwater sound waves todetect and locate submerged objects. Active sonarsproduce a pulse of sound and then listen for reflectionsof the pulse. Passive sonar equipment only listens forunderwater sounds without transmitting.

18. Henrie AJM and Carlson JD: “Magnetorheological Fluids,”in Schwartz MM (ed): Encyclopedia of Smart Materials.New York City: John Wiley & Sons (2002): 597–600.

> Applying a magnetic field to magnetorheological (MR) fluids. Without amagnetic field, ferrous particles are randomly distributed in a nonmagneticoil to form an MR fluid (top). Once a magnetic field is applied, the particlesalign with the magnetic field to form chains, dramatically increasing theviscosity in the direction perpendicular to the field direction (bottom).

Magnetorheological Liquid

Carrier fluid

Ferrous particles

Mag

netic

fiel

d di

rect

ion

Chains of particlesaligned with the field


MR fluids were discovered in the 1940s andearly 1950s at the National Bureau of Standards,Gaithersburg, Maryland.19 A number of deviceswere developed based on dry magnetic powders,such as a magnetic-powder brake. However,these early MR fluids and devices had limited lifeand stability, and it was not until the early 1990sthat progress in materials science and controlelectronics renewed interest in these materials.

MR fluids attract interest because of theirunique ability to undergo a rapid, abruptincrease in viscosity, corresponding to an almostinstantaneous transition to a semisolid state, inresponse to application of a magnetic field. Therestoration to the initial viscosity after removingthe magnetic field is equally rapid with responsetimes as short as 6.5 ms.20 Therefore, MR fluidshave mostly been used in various dampingsystems. MR fluids were first commercialized in1995 in fluid rotary brakes for aerobic exerciseequipment. Other commercially availableproducts using MR fluids are dampers for real-

time vibration-control systems in heavy-dutytrucks, adjustable shock absorbers for oval- and dirt-track automobile racing, and lineardampers for real-time gait control in advancedprosthetic devices.21

An example of this last application is theMotion Master MR fluid damper in the SmartMagnetix prosthetic leg (above).22 The MR fluiddamper in the prosthetic responds 20 timesfaster than prior state-of-the-art mechanical orhydraulic designs. The total response time,40 ms, is similar to the response time for signalsin the human knee.23 This improvement helps thenew prosthetic more closely mimic natural loco -mo tion and makes it more convenient for the user.

Another class of magnetically activatedmaterials is magnetostrictive substances.Magnetostriction is the property of ferromag -netic materials to change their shape in response to application of a magnetic field.24

Magnetostriction was discovered in 1842 byJames P. Joule, who noticed that the length of asample of iron changed after a magnetic field

was applied. Along with this effect, which is alsoreferred to as the Joule effect, there is areciprocal effect, called the Villari effect, inwhich applying a stress to a material causes achange in its magnetization.

This behavior resembles both the direct andconverse piezoelectric effects. In fact, themacroscopic mechanisms of piezoelectricity andmagnetostriction resemble each other, with thedifference that piezoelectric effects aredetermined by the action of an electric field oncharges, electric dipoles or domains of electricdipoles, whereas the magnetostrictive effects arecontrolled by the action of a magnetic field onmagnetic domains—regions of uniform magneti -zation. A magnetic field applied to aferro magnetic specimen shifts magneticdomains, causing macroscopically detectablechanges in the shape and size of the specimen.And conversely, an applied stress causes amechanical shift of magnetic domains, therebyaltering the magnetization of the specimen.

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> A schematic of the Motion Master MR fluid damper (LORD Corporation) in the artificial knee of theSmart Magnetix prosthetic leg (Biedermann Motech) (left) and a schematic of the MR fluid damper(right). (Used with permission from LORD Corporation, reference 22.)

MR damping system

Control devices

Prosthetic Leg

Wires toelectromagnet

Bearingand seal

MR fluid

Coil Annular flowchannel

Diaphragm

Magnetorheological Damping System

Accumulator

Piston


Spring 2008 39

The direct magnetostrictive (Joule) effect isused in magnetostrictive actuators, while theVillari effect is used in magnetostrictive sensors.Applications of magnetostriction include tele -phone receivers, hydrophones, magneto strictiveultrasonic generators for sonars, linear androtational motors, and various sensors fordeformation, motion, position and force.

Chemically Activated Materials: How Swell They AreChemical activation of materials is an almostendless topic. Here, we address only thechemical activation of polymers under exposureto liquids. This phenomenon is general enough tooccur in everyday life and also specific enough tounderlie smart applications, including some inthe oil field. Most people have observed bothintentional and unintentional swelling ofpolymers in ordinary life. For example, spillingcoffee or tea onto a book lets the natural polymercellulose contained in the book paper swell, andpreparing gelatin desserts makes use of theproperty of the polymer gelatin to swell in water.However, such swelling behavior can also bedeleterious: industrial companies may incurgreat losses if even a small gasket made of apolymer unsuitable for the existing operatingconditions swells and degrades, causing leakageor other dangerous consequences.

On the other hand, people have long foundways to use polymer swelling in a controllableway, as in food processing, medicine (absorbentmaterials), chemical spill kits and construction(various fillers). An example of the modernapplication of controllable polymer swelling inmedicine is targeted drug-delivery systems.25 Thesimplest form of such a system is a capsule witha drug-containing core and a swellable coating.The properties of the coating are designed sothat the coating gradually swells and the drug isreleased at given rates at given places as thecapsule is transported through the gastro -intestinal tract. More intricate designs includemultilayer and multidrug capsules, sometimesprovided with special drug-delivery ports.

Swellable polymers are starting to beemployed in oilfield applications. They are usedin swellable packers for zonal isolation andefficient borehole water control (above right).For zonal isolation, a series of unswollen oil-sensitive packers is run into the well. When theyare exposed to oil, they swell and seal off theformation face, creating intervals isolated from

each other. For water control, an unswollenwater-sensitive polymer (elastomer or composite)packer is installed in the well. If waterencroaches into the wellbore, the packer swellsand seals the wellbore at that location, isolatingthe interval so that water influx decreases and oilproduction increases.26

Swellable packers are advantageous com -pared with conventional ones as they aregenerally less expensive, contain no movingparts, and require no mechanical or hydraulicactuation mechanism. All the functions of theseelements are performed by a single piece ofpolymeric smart material.

19. Rabinow J: “Magnetic Fluid Torque and ForceTransmitting Device,” US Patent No. 2,575,360(November 20, 1951).Rabinow J: “The Magnetic Fluid Clutch,” Transactionsof the American Institute of Electrical Engineers 67(1948): 1308–1315.

20. Weiss KD, Duclos TG, Carlson JD, Chrzan MJ andMargida AJ: “High Strength Magneto- and Electro-Rheological Fluids,” Society of Automotive EngineersTechnical Paper Series, no. 932451, Warendale,Pennsylvania, USA (1993): 1–6.

21. Carlson JD and Sproston JL: “Controllable Fluids in2000—Status of ER and MR Fluid Technology,” paperpresented at the Actuator 2000—7th InternationalConference on New Actuators, Bremen, Germany,June 19–21, 2000.

22. http://www.lord.com/Home/MagnetoRheologicalMRFluid/Applications/OtherMRApplicationSolutions/Medical/tabid/3791/Default.aspx (accessed January 5, 2008).

23. Bullough WA: “Fluid Machines,” in Schwartz MM (ed):Encyclopedia of Smart Materials. New York City: JohnWiley & Sons (2002): 448–456.

24. Not only can a ferromagnetic material be magnetized inan external magnetic field, but it remains magnetized afterremoving the field. Examples of ferromagnetic materialsare iron, nickel, cobalt, some rare-earth elements andsome alloys and compounds of these elements.

25. Wise DL (ed): Handbook of Pharmaceutical ControlledRelease Technology. New York City: Marcel Dekker, 2002.

26. http://www.tamintl.com/pdf/FreeCapAd1JPT.pdf(accessed January 11, 2008).

> Photograph (top), schematic (middle) and illustration of swelling (bottom) of a swellable packer.

Swelling

Antiextrusion caps

Swellable packer


An early success story of swellable polymersoccurred during World War II, when swellablerubber materials were used in self-sealing fueltanks in aircraft.27 A self-sealing tank was madeof two layers of rubber; the outer layer wascomposed of cured rubber and the inner one wasof oil-swellable uncured rubber. The inner layerwas lined with a fuel-impervious material toprevent the uncured rubber from contacting thefuel while the tank was intact. If a bullet or otherprojectile punctured the tank, the fuel spilledand contacted the uncured rubber, which

swelled and thus sealed the puncture. Such self-sealing fuel tanks are still being used.

These self-sealing rubber materials may beconsidered predecessors of the modern conceptof self-healing materials. In the latter, a healingagent does not form an adjacent layer but isenclosed in microcontainers, such as micro -capsules or hollow microfibers, and uniformlydistributed throughout the material to beprotected.28 In self-healing polymer materials,the healing agent is typically the correspondinguncured polymer. If a self-healing polymer

material is damaged, these microcontainersrupture and release the healing agent, whichinfiltrates into the damage site, polymerizes—ifnecessary, a polymerization catalyst is also addedto the bulk of the material—and thus heals thedamaged area (left).29 This procedure mimics theself-healing functions of biological tissues, whoseresponse to damage is often secretion of healingfluids. To follow nature further, some proposalssuggest piercing a material with a vascularnetwork that can carry a circulating healingagent throughout the material.30

Self-healing materials are also beginning tomake their mark in oilfield applications. Forexample, Schlumberger recently announced theavailability of its FUTUR active set-cementtechnology that automatically seals microleaksin a cement sheath (see “Ensuring ZonalIsolation Beyond the Life of the Well,” page 18).The FUTUR cement system, pumped and placedin the same way as any ordinary cement, containscomponents that remain dormant until exposedto hydrocarbons, such as those seeping thoughmicrocracks in the cement sheath. The contactwith hydrocarbons activates the FUTUR cementsheath, which self-repairs within hours withoutintervention. This prevents many undesirableevents after the cement has set, such as annularmigration of fluids behind the casing betweenzones, sustained casing pressure at surface,surface casing leaks and crossflows.31

Toward Novel Smart MaterialsThese examples of materials and processes areonly a small sampling of the world of smartmaterials and their applications. Smartmaterials abound and can be encountered in avariety of devices from simple piezoelectriclighters and igniters to complex ultrasonicinstrumentation.

Even ordinary materials can be made smartor responsive. Self-healing cement is an exampleof an abundant, everyday material that has beenengineered to take on smart properties foroilfield application. Promising candidates forsmart-material adaptation may be all around us,waiting to be discovered.

Investigation into smart materials is one ofthe new research directions at Schlumberger-DollResearch Center in Cambridge, Massachusetts.This includes defining and executing a road-map for actuation technology in various oilfield applications.

40 Oilfield Review

27. Gustin E: “Fighter Armour,” http://www.geocities.com/CapeCanaveral/Hangar/8217/fgun/fgun-ar.html(accessed February 28, 2008).

28. Shah AD and Baghdachi J: “Development andCharacterization of Self-Healing Coating Systems,”http://www.emich.edu/public/coatings_research/AmitPresentation.pdf (accessed January 14, 2008).

29. White SR, Sottos NR, Geubelle PH, Moore JS,Kessler MR, Sriram SR, Brown EN and Viswanathan S:“Autonomic Healing of Polymer Composites,” Nature 409(February 15, 2001): 794–797.

30. “Self-Healing Composite Materials,” http://www.aer.bris.ac.uk/research/fibres/sr.html (accessed January 14, 2008).

31. Moroni N, Panciera N, Zanchi A, Johnson CR, LeRoy-Delage S, Bulte-Loyer H, Cantini S, Belleggia Eand Illuminati R: “Overcoming the Weak Link in CementedHydraulic Isolation,” paper SPE 110523, presented at theSPE Annual Technical Conference and Exhibition,Anaheim, California, November 11–14, 2007.

> Self-healing material, in which 200-micron microcapsules containing apolymerizable healing agent and polymerization catalyst particles areembedded. Damage causes crack propagation (top); the crack rupturesmicrocapsules, releasing a healing agent (middle); the healing agentcontacts the catalyst, polymerizes and heals the damaged area (bottom).(Adapted with permission from Macmillan Publishers Ltd., reference 29.)

Catalyst

Microcapsule

Crack

Healing agent

Polymerized healing agent

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Spring 2008 41

A significant part of implementing theroadmap involves defining and developingcommon technological building blocks that canbe integrated in various ways to provideactuation applications. This will be accomplishedby studying actuation systems—actuators,sensors, system dynamics and control, and novelmechanisms—and applying smart materials toinvent new actuating systems (right).

While materials-science researchers areexcited about the enormous potential of smartmaterials, these new materials are unlikely tosupplant the standard materials we use every day.The vast majority of materials are structural—selected not only for their proper ties, but becausethey are cheap and abundant. Smart materials,like other functional materials, including

tungsten filaments in light bulbs, platinum-rhodium wire in thermocouples and diamond tipsin drill bits, typically have small-volumeapplications. These require unique proper ties forwhich there are few or no substitutes, and thuscost is less of an issue. For sophisticated oilfieldtools, smart materials may allow implementationof new technologies, miniaturization of parts andenhanced reliability in the increasingly harshdownhole environment. —VG

> A researcher (above) studying the thermo -mechanical properties of a specimen of amaterial at Schlumberger-Doll Research (SDR)Center, Cambridge, Massachusetts (below left).


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