UDC 666.2.01

DEVELOPMENT OF A MOLD EQUIPMENT

FOR ELECTROPHORETIC SHAPING OF CERAMIC PRODUCTS

E. I. Suzdal’tsev1 and D. V. Kharitonov1

Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp. 12 – 19, October, 2003.

A brief review of the previous studies aimed at the development of techniques for fabrication of large-sized,thick-walled, complex-profiled ceramic components from aqueous slips of inorganic materials is given.

This work is concerned with the development of a moldequipment for the electrophoretic shaping of large-sized,thick-walled ceramic products of complex profile preparedfrom aqueous lithium aluminosilicate glass-based slips.

We have gained some experience in this field [1 – 4].Thus, in [1], methods for accelerated molding of ceramiccomponents from inorganic materials (quartz and lithiumaluminosilicate glasses) were discussed and potentialities ofthe electrophoretic deposition method for production of ce-ramics (in particular, from quartz glass slips) were demon-strated. It was shown in [2, 3] that this method can be usedfor preparing ceramics from lithium aluminosilicate glass.A literature survey [4] has provided evidence for electropho-resis as a promising route towards shaping ceramics from in-organic slips. Still, at present, no reliable electrophoretictechnique is available for preparation of large-sizedthick-walled engineering components with complex profile.The present study is concerned with some aspects of thischallenging problem.

It was shown in the aforementioned work [2] that glassceramic preforms of lithium aluminosilicate compositionprepared by electrophoretic deposition in some of theirphysicomechanical properties did not differ much from, oreven were superior to, ceramic products obtained by the tra-ditional technologies. However, the electrophoretic deposi-tion method, for all its strengths, had serious limitations —the attempts to shape a large-sized thick-walled complex-profiled engineering component met with little success.A conclusion was drawn from the literature survey in [4]:For an electrophoretic deposition technology to be effective,two practical problems are to be solved — the proper selec-

tion of a material for the electrodes of an electrophoretic setup[5, 6], and the properly selected design of this setup [7, 8].

SELECTION OF MATERIAL AND DESIGN

OF SHAPING ELECTRODE (ANODE)

The principle of electrophoretic shaping of ceramic pro-ducts is as follows. The particles that are suspended in a slipstart moving under the action of an electric field (generatedby applying voltage to the electrodes of a mold equipment)towards the electrode that bears an opposite charge to be-come deposited on it; thereby, a body for the preform is built(see Fig. 1). Positive or negative charge can be applied to theshaping electrode (depending on the surface charge of theparticle); usually, the shaping electrode serves as an anodeconsidering that the particles typically carry a negativecharge. The cathodic processes are of minor importance forelectrophoretic deposition, whereas the processes that occuron the anode merit more attention.

Electric current passing through the aqueous slip causeswater electrolysis, which is manifested in the release of oxy-gen at the anode, and of hydrogen at the cathode. The re-

Refractories and Industrial Ceramics Vol. 45, No. 1, 2004

581083-4877/04/4501-0058 © 2004 Plenum Publishing Corporation

1 Tekhnologiya Research and Production Enterprise, Obninsk,Kaluga Region, Russia.

Power source

Fig. 1. Schematic diagram of the electrophoretic shaping of ceram-ics from an aqueous slip.

leased oxygen may behave in two ways. First, it is capable ofreacting with the material of anode during the entire processof the preform buildup and thus becomes bound to it. Se-cond, the oxygen can form a protective oxide film which willprevent further oxidation of the anode material. The releasedoxygen, unable to further react with the anode material, willaccumulate at the anode surface. Situations may arise whereoxygen is unable to escape through the contact clearance be-tween the anode surface and preform surface, which will fi-nally lead to the break of accumulated oxygen through thedeposited material and to impairment of its structural integ-rity (formation of pits, blisters, or blow-holes). Therefore,the choice of a proper material for the shaping electrode (an-ode) has become an issue of major concern.

Results obtained in [3] on slips of lithium aluminosili-cate composition showed that the best materials for the an-ode were brass and copper.

Still, the design of a large-sized shaping electrode of com-plex profile remained an issue of pivotal importance. Manu-facture of such an electrode from all-metal sheets or billets ispossible only under industrial conditions using special tech-nological facilities, which will require much labor input anduse of expensive materials (copper, brass).

Early attempts to prepare the shaping electrode in theform of a core (as in the conventional slip-casting techno-logy) over which a sheath was spread (made up from a brassmesh) as a replica of the inner surface of the preform [2] metwith little success; the sheath became unfit for use after thesecond molding. Furthermore, extraction of the core from thebody of the shaped preform proved to be a delicate operation.

Therefore a large-sized shaping electrode of complexprofile for electrophoretic molding of ceramic preforms was

proposed (Fig. 2). Its main components are: A layer of plas-ter 1 (or any suitable material) shaped in conformance withthe required profile (corresponding to the inner profile of thepreform) is applied to a framework 2; next, the plaster iscoated with an adhesive 3 (for example, epoxy resin) and ametallic wire (copper) 4 is closely wound around. The driedand hardened surface of the electrode is finished by grindingto the required size and shape.

The advantages of this engineering solution are:– large-sized cores of any size and profile can be pre-

pared;– smooth surface of the core that allows easy extraction

of the core from the body of the shaped preform;– the core can be easily prepared under laboratory con-

ditions;– small consumption of the material.Using this electrode, large-sized ceramic products of

complex shape with a smooth inner surface can be preparedby electrophoretic deposition.

DESIGN OF THE COUNTERELECTRODE

Design and fabrication of the counterelectrode for a moldequipment intended for electrophoretic shaping of large-sized complex-profiled preforms likewise has been a chal-lenging problem.

All-Metal Counterelectrode

In our early work [2], a plaster mold with a mesh spreadover its working surface was considered; the deposited mate-rial was built up in two ways — on a plaster and on a brassplate. With the material built up on the plaster, the electro-lyzed water moved to the brass plate and then upwelled tothe surface (towards the feeding hole). This behavior sug-gested an idea that the plaster might in principle be replacedby another brass plate.

Further experiments carried out with such a mold [3]gave good results: The physicomechanical properties ofspecimens shaped by the new method were not inferior tothose by the conventional technology.

In all fairness, the preforms prepared by this method dis-played a somewhat rough surface viewed on the cathode sidefor the reason that part of the electrolyzed water did notupwell in time (Fig. 3); however, this shortcoming couldreadily be removed by machining.

Development of a Mold Equipment for Electrophoretic Shaping of Ceramic Products 59

2

3 4,

1

2

Fig. 2. A large-sized ogival shap-ing electrode for electrophoreticmolding of ceramic preforms:1 ) plaster layer; 2 ) framework;3 ) epoxy resin; 4 ) metallic wire.

Fig. 3. The surface of a specimen viewed on the cathode side.

This technique was used to fabricate a pilot lot of Disk-type products (Fig. 4) in which the preforms had dimensions:� 180 mm and � = 10 – 12 mm. The molding time was20 – 30 min against 8 – 9 h by the traditional technology.

Thus, one comes to the conclusion that conventionalplaster molds can be removed from the technology of ce-ramic shaping from aqueous slips. The use of all-metal cop-per plates for both anode and cathode gives a higher qualityof the product and saves production time appreciably (byseveral tens).

Counterelectrode: a Mesh Spread

over the Plaster’s Working Surface

The above scheme with two metallic plates was quitegood for flat preforms (such as disks); however, molding

large-sized complex-profiled preforms would re-quire the use of all-metal electrodes of profiledconfiguration. Therefore attempts were made todevelop a counterelectrode of simpler design. Amold equipment (shaping electrode + counter elec-trode, a brass mesh spread over a plaster mold) wasconstructed for electrophoretic shaping of large-sized complex-profiled preforms (preform dimen-sions: base diameter = 250 mm, h = 650 mm,� = 17 mm); a total of ten tests was carried out us-ing this equipment (for more detail, see [2]).

Regrettably, no preform of good quality couldbe prepared by this technique, mainly because ofthe poorly conditioned working surface of the plas-

ter mold (pits and high spots), which prevented the easy ex-traction of preforms. Still, it is felt that this method of elec-trophoretic deposition, properly modified, can be used tofabricate large-sized, thick-walled (about 17 mm) preformsof uniform density in a time-saving regime.

Counterelectrode: a Mesh Inside the Plaster Mold

The difficulties emerging from the poor quality of thesurface of a counterelectrode made of a brass mesh spreadover the plaster mold led to the suggestion of using a con-ducting plaster surface as the electrode.

To start with, a plaster mold 25 mm thick with a meshspread over the back side (opposite to the shaping surface)was used; for better contact with the surface of the mold, themesh was coated with plaster. Voltage of about 100 V was

applied to the mold ready for operation; however,no electrophoresis effect could be observed.

To improve the design, the mesh was fastenedto the plaster using nails (20 mm in length, 1.2 mmin diameter, with a nail spacing density �nail =1 nail�cm2 ). The voltage applied was 100 V. Anelectrophoretic deposition effect was observed.The deposited layer had a rough surface, with highspots located exactly opposite the driven-in nails(which indicated an uneven current distributionover the surface of the mold); however, the densityof deposition was uniform (2.120 � 0.006 g�cm3 ).As can be seen in Fig. 5, it took 30 min for the de-position process to start after the voltage had beenapplied. Possibly, this lapse of time is needed for aplaster layer 5 mm thick (measured as the distancebetween the nail tip and the shaping surface of theplaster mold) to be impregnated with water. Thissuggested a variant: With the mesh coated withplaster to a depth of about 5 mm from the surface,an electrode with a uniform current distribution(and, consequently, leading to a good quality of thesurface) can be obtained.

Based on accumulated experience, a plastermold with a brass mesh embedded to a depth of3 – 5 mm was fabricated and a series of experi-

60 E. I. Suzdal’tsev and D. V. Kharitonov

Fig. 4. Disk-type shaped components.

TABLE 1. Properties of Specimens Obtained Using a Mold with a Plastered Mesh

Voltage,V

Chargeon plaster

tdepos ,min

Green preform Sintered material�,

MPa�, g�cm3 P, % �, g�cm3 P, % W, %

Finely dispersed slip T63 = 1.0%

Conven-tionallymolded

– 35 –40 h

2.103 13.46 2.536 0.11 0.04 114

10 + – 2.083 14.28 2.506 0.09 0.03 113

20 + – 2.074 14.65 2.502 0.19 0.08 –

40 + 88 2.079 14.32 2.499 0.16 0.07 104

60 + – 2.078 14.47 2.501 0.19 0.07 110

80 + 80 2.078 14.47 2.500 0.12 0.05 –

300 + 70 2.069 14.85 2.482 0.19 0.08 98

Medium-dispersed slip T63 = 1.0%

Conven-tionallymolded

– 35 –40 h

2.102 13.50 2.500 0.15 0.06 119

5 + 180 2.116 12.92 2.506 0.35 0.14 117

10 + 150 2.108 12.25 2.498 0.24 0.10 –

15 + 100 2.104 13.42 – – – 114

5 – 150 2.090 13.99 2.486 0.37 0.15 –

10 – 100 2.075 14.61 2.469 0.00 0.00 109

15 – 80 2.070 14.81 2.477 0.30 0.12 –

mental runs was carried out; relevant results are given in Ta-ble 1. Preforms shaped in such molds displayed a good qua-lity of surface and satisfactory physicomechanical properties.

A comparison of the data in Table 1 shows that the prop-erties of specimens prepared by the newly designed tech-nique do not differ much from those prepared by the conven-tional method. The deposition rate and the density wereshown to be different for different substrate (Fig. 6). Thus,the material buildup on plaster took 30% more time than onthe plate, which is presumably associated with the higher re-sistivity of the plaster surface.

The material deposition rates measured at different volta-ges are shown in Fig. 7. As can be seen, it took a lapse ofsome 30 min for the onset of deposition, in agreement withthe previous observation.

However, it must be conceded that the electrode thus de-signed was little suited for shaping large-sized preformssince the plaster coating with its thickness of about 5 mmwas not strong enough to sustain loading and was prone tobuckling and fracture. With the mesh embedded to a largerdepth (about 10 mm), the electrophoretic deposition was vir-tually impossible; therefore one had to search for ways of in-creasing the plaster conductivity.

Counterelectrode: a Mesh Embedded

in the Plaster + Graphite Mold

The problem of increasing the plaster conductivity wassuccessfully resolved using a mold material with graphiteadded.

Five plaster molds (for shaping preforms with dimen-sions of 20 � 70 � 140 mm) containing different amounts ofgraphite added: 10, 20, 30, 40, and 50% against the plastermass. The mesh in these molds was embedded to a depth ofabout 10 mm (with a depth of 20 mm, no electric conducti-vity in the plaster material could be recorded).

The molds were used to shape specimens under an elec-tric field strength 10 V�cm; relevant data are given in Ta-ble 2. The electrophoretic deposition process was observedto start as soon as voltage was applied. The deposition ratecurves are shown in Fig. 8.

Data in Table 2 and Fig. 8 show that with increase ingraphite content the deposition rate tended to increase (from

55 min for 10% graphite to 40 min for 50%); simultaneously,a deterioration of properties was observed (bending strengthdecreased by about 10% and porosity tended to increase).Optimum concentration for the graphite filler was thus cho-sen to be within 10 – 20 wt.%.

Adding graphite in higher concentration caused a soften-ing of the plaster matrix and, as a consequence, deteriorationof its strength properties (see Table 3) and shorter service lifeof the mold. By way of example, a mold with 40 – 50%graphite became unfit for use in as little as two shaping cycles.

Development of a Mold Equipment for Electrophoretic Shaping of Ceramic Products 61

140

120

100

80

60

40

20

02 4 6 8 10 12 14 16 18 20

Dep

osi

tio

nti

me,

min

Layer thickness, mm

Fig. 5. The deposited layer thickness plotted against the depositiontime using a nailed-mesh electrode.

200

180

160

140

120

100

80

60

Dep

osi

tio

nti

me,

min

5 10 15

Voltage, V

Deposited on plasterDeposited on plate

Fig. 6. Time of deposition for a preform 20 mm thick plotted as afunction of the voltage applied.

180

150

120

90

60

30

02 4 6 8 10 12 14 16 18 20

Dep

osi

tio

nti

me,

min

Layer thickness, mm

3

2

1

Fig. 7. Deposition rate curves measured in a mold with embeddedmesh (material deposited on plaster bearing a charge “+”):1 ) U = 15 V (about 7.5 V�cm); 2 ) U = 10 V (about 5.0 V�cm);3 ) U = 5 V (about 2.5 V�cm).

TABLE 2. Properties of Specimens Shaped in Moldswith Different Content of Graphite Filler at Electric FieldStrength 10 V�cm

Graphitefiller

content,%

Depositiontime for pre-form 20 mmthick, min

�,g�cm3 P, %

Bendingstrength,

MPa

0 � 48 h 2.510 0.1 113

10 55 2.485 0.1 111

20 52 2.478 0.2 110

30 48 2.478 0.4 108

40 43 2.471 0.3 97

50 40 2.468 0.6 99

Based on the above results, a mold equipment for elec-trophoretic shaping of a small-sized complex-profiles prod-uct of Vstavka (Insert) type (with dimensions base diameter= 34 mm, h = 45 mm, � = 10 mm; see Fig. 9) was built.

A schematic diagram of the mold equipment ready foroperation is shown in Fig. 10.

The principle of operation is simple: slip is pouredthrough feeding hole 1 in the space between metal core 2 andmold 3 (made up from a mixture of 80 – 90% plaster +20 – 10% graphite), and voltage is applied to core 2 and elec-trode 4 (embedded in the plaster graphite mold). Suspendedmaterial is deposited on the core (anode), and water is driventowards the mold (cathode) to be absorbed by the mold’s ma-terial; preforms thus shaped exhibit a high-quality surface.

The graphite binder, owing to its lubricating ability, al-lows easy extraction of the shaped preform from the moldimmediately after the deposition process has come to an end;in traditional technology, this could be done only after thepreform had shrunk (typically, after the lapse of one hour, oc-casionally not without damage to the surface of the preform).Furthermore, in the mold equipment thus designed, the elec-trode, being embedded in the mold, does not come in directcontact with the preform shaped and thus allows a less stricttolerance on size, profile, and metal used.

However, all attempts to prepare preforms similar to thatin Fig. 10, only of larger size, met with little success: the pre-forms, with smooth inner and outer surfaces, even readily ex-tracted, sustained damage (fractured when handled).

The fact that small-sized preforms could be readily ob-tained and those of larger size failed may possibly be ex-plained by an adverse effect due to the scaling factor.

Counterelectrode: a Mesh Embedded

in a Mold with a Reinforced Fore-Electrode Layer

Based on the previously gained experience — both en-couraging and not very — we returned to the variant with anelectrode embedded to a depth of 3 – 5 mm. In this configu-ration, a good electrophoretic was observed; however, thefore-electrode plaster layer was prone to easy damage.Therefore an idea was suggested to have this layer rein-forced.

Figure 11 shows a mold equipment intended for shapinglarge-sized preforms (in this particular case, with dimensionsbase diameter = 250 mm, h = 650 mm, � = 17 mm). Themain components of this device are: shaping electrode (core)1, brass electrode 2 embedded in the mold body 3, andfore-electrode plaster layer 4 reinforced with a cloth.

The principle of operation was as follows. Slip waspoured in the space between the plaster mold and the core;voltage was applied to shaping electrode 1 and electrode 3

embedded to a depth of 1 – 5 mm from the profile-formingsurface. Material was deposited on the core (anode); water

62 E. I. Suzdal’tsev and D. V. Kharitonov

3

4

2

1

Fig. 10. A mold equipment for electrophoretic shaping of Vstavka(Insert)-type preforms: 1 ) feeding hole; 2 ) core; 3 ) plaster-graphitemold; 4 ) electrode.

Fig. 9. Vstavka (Insert)-type products.

TABLE 3. Properties of Graphite-filled Plaster Molds

Graphiteconcentration, %

Porosity, %Axial compressive

strength, MPa

0 62.70 1.00

10 69.29 0.77

20 70.04 0.72

30 70.20 0.60

40 71.19 0.40

50 72.00 0.26

60

50

40

30

20

10

02 4 6 8 10 12 14 16 18 20

Dep

osi

tio

nti

me,

min

Layer thickness, mm

10%

20%

30%50%

40%

Fig. 8. Deposition rate curves for molds with different concentra-tions of graphite filler.

was driven towards the mold to moisten the fore-electrodelayer 4 (reinforced with a cloth, for example, a gauze ban-dage), which improved conductivity and electrophoreticshaping parameters. Under these conditions, water was di-verted completely, and preforms with a smooth surface couldbe obtained.

The use of a reinforced fore-electrode layer made it pos-sible to extend the service life of the mold to ten shaping cy-cles, whereas in all previous techniques the service life didnot exceed two shaping cycles. Furthermore, in the moldequipment thus designed, the electrode, being embedded inthe mold, does not come in direct contact with the preformshaped and thus allows a less strict tolerance on size, profile,and metal used.

Thus, based on the studies, it has been shown that theelectrophoretic deposition method can be used for fabrica-tion of large-sized, thick-walled, complex-profiled ceramicproducts from aqueous slips based on lithium aluminosilicateglass; preforms prepared by this technology have a more uni-form density than those prepared by conventional technolo-gies. Furthermore, preforms can be shaped using finely dis-persed slips.

Materials have been chosen and electrodes designed forthe fabrication technology of large-sized complex-shapedproducts.

Mold equipments have been developed for electropho-retic shaping of complex-profiled preforms from aqueousslips. However, optimization of this technology will requirefurther study in the field.

REFERENCES

1. E. I. Suzdal’tsev and D. V. Kharitonov, “The molding of pre-forms from aqueous slips of inorganic material: the state-of-the-art,” Ogneup. Tekh. Keram., No. 12, 4 – 7 (2002).

2. E. I. Suzdal’tsev and D. V. Kharitonov, “Potentiality of the elec-trophoretic deposition method for molding components fromlithium aluminosilicate glass,” Ogneup. Tekh. Keram., No. 2,20 – 25 (2003).

3. E. I. Suzdal’tsev and D. V. Kharitonov, “An electrophoretic depo-sition method for molding components from slips of inorganicmaterials,” Ogneup. Tekh. Keram., No. 3, 13 – 18 (2003).

4. E. I. Suzdal’tsev and D. V. Kharitonov, “Methods for the electro-phoretic shaping of ceramic products from aqueous slips of inor-ganic materials (an overview),” Ogneup. Tekh. Keram., No. 9,16 – 25 (2003).

5. Aveline, “Façonnage par Électrophorése,” L’industrie cerami-

que, No. 581, 28 – 31 (1966).6. F. S. Éntelis and M. E. Sheinina, “Electrophoretic shaping of por-

celain components,” Steklo Keram., No. 11, 19 – 21 (1979).7. F. S. Éntelis and M. E. Sheinina, “Cathodes for electrophoretic

shaping of porcelain cups,” Steklo Keram., No. 12, 11 – 12(1977).

8. N. V. Solomin and V. F. Tsarev, USSR Inventor’s Certificate

No. 439486, IPC C 04 B 33�00. A Method for Molding Ceramic

Components [in Russian] (1972).

Development of a Mold Equipment for Electrophoretic Shaping of Ceramic Products 63

34

2 1

Preform

Fig. 11. A mold equipment for electrophoretic shaping of large-sized, thick-walled, complex-profiled preforms (preform dimen-sions: base diameter = 250 mm, h = 650 mm, � = 17 mm): 1 ) shap-ing electrode; 2 ) electrode; 3 ) plaster mold; 4 ) fore-electrode layer.