US2836501A - Electrostrictive ceramic materials - Google Patents

Description

United States atent ELECTROSTRICTIV E CERAMHC MATERIALS Joseph W. Crownover, Sherman Oaks, Calif assignor to Electric Machinery Mfg. Company, Minneapolis, Minn, a corporation of Minnesota Application November 4, 1955 Serial No. 545,130

6 Claims. Cl. 106-449) No Drawing.

The earlier application discloses an invention which seeks to utilize the electrostrictive properties of high dielectric ceramic materials and to provide ceramic materials having enhanced electrostrictivc properties. The invention of this application provides improved electrostrictive ceramic materials and compositions in which the desired characteristics are otherwise improved and stabilized and in which the reproducibility of the materials is improved.

In the improved compositions of this invention, the electrostrictive property of the material has been enhanced and stabilized and the piezoelectric property has been rendered insignificant or negligible. The electrostrictive composition of this invention is adapted for use in various types of transducers, such as switches, relays, motors, loud speakers, etc., and makes possible the practical design and application of many new types or" transducers wherein electrical impulses are transduced into mechanical motion which was otherwise not possible. The ceramic materials of this invention are materials which retain only a negli iole or insignificant polariza tion charge, and the significance of this is that if polarization of the ceramic may be retained and increased, it may also be decreased with the result that the ceramic as an actuator or transducer is unstable and is not prac tical for use in many types of transducers, such as relays. In the compositions of this invention in which the electrostrictive property is utilized, the lack. of stability resulting from reliance on polarization charge oi the ma- I terial is eliminated.

Electrostriction in the broadest sense of dielectrics pertains to an interrelationship between the electric field and the deformation of the dielectric in that field. Although this includes the piezoelectric phenomenon, most authorities, in order to avoid confusion, reserve the term electrostrictive for the efiect wherein the deformation of the dielectric material subjected to an electrostatic field is proportional to the square of the impressed electric field, thereby being independent of the applied fields polarity. The distinction is explained in the volume by Cady Piezoelectricity (McGrav/ dill Book Co., 1946). Where the polarization charge is not being depended on for the deforming and actuating effect, the device operates effectively in one mechanical direction for either polarity of applied potential.

The compositions of this invention, which are essentially barium titanate ceramics, provide a very large dimensional change when subjected to electrostatic fields,

Patented May 27, 1958 and this dimensional change results from the electrostrictive properties of the materials.

In accordance with the foregoing, it is an object of the invention to provide improved compositions having pronounced electrostrictive properties and which do not retain any significant polarization charge, comprising barium titanate composition including other compositions as additives.

Another object of the invention is to provide improved electrostrictive ceramics comprising barium titanate as a predominating constituent and including as an additive calcium stannate.

Another object of the invention is to provide improved electrostrictive ceramics comprising barium titanate as a predominating constituent and including as additives, aluminum oxide, calcium oxide, copper oxide, iron oxide, magnesium oxide, lead oxide, silicon dioxide, strontium oxide, zirconium dioxide, titanium dioxide, and calcium stannate.

Another object of the invention is to provide improved electrostrictive ceramics comprising barium titanate as a predominating constituent and having as a constituent in a minor percentage calcium stannate and titanium dioxide and having trace additives in a range of percentages of aluminum oxide, calcium oxide, copper oxide, iron oxide, magnesium oxide, lead oxide, silicon dioxide, strontium oxide and zirconium dioxide.

In general, the novel compositions of the present invention comprise fired mixtures of barium titanate and calcium stannate, and in minor percentages additives of the compositions indicated in the table which follows. The general classes of compositions covered by the invention are indicated in the table. As appears in the table, the calcium stannate content of the material will be in the range of from 2% to 8%. For most of the samples the titanium dioxide additive is .9%. As to the other additives, that is, the aluminum oxide, calcium oxide, copper oxide, iron oxide, magnesium oxide, lead oxide, silicon dioxide, strontium oxide and zirconium dioxide, these additives will be in the percentage ranges as indicated in the table, these ranges and the ranges for barium titanate being percentages of the composition without the added titanium dioxide and calcium stannate.

In the preparation of the compositions of the invention, the ingredients as indicated in the table are in the form of comminuted ceramics. The ceramic bodies may be prepared in a manner conventional with barium titanate electrical ceramics or ceramic films, the desired amounts of titanium dioxide and calcium stannate in comminuted form being mixed in a resin binder and the body then formed into a film and fired using conventional techniques. Such conventional techniques are illustrated in such patents as Lies No. 2,539,446, Howatt No. 2,486,410 and Kulcsar No. 2,735,024. Or, the preparation of the compositions may be essentially in accordance with the method of my earlier filed application, Serial No. 425,664, filed April 26, 1954. in accordance with that method, the materials in the proportions as given in the table are mixed with a liquid thermoplasticresin and a suitable plasticizer in proportions to form a thick liquid adapted to flow on to a moving fiat surface in a uniform.

layer. In other words, the basic materials are formed in very thin sheets of uniform thickness by a slip casting process with the ceramic particles dispersed uniformly through a body of polymerized thermoplastic resin. As.

an example of the composition of the liquid mix, it may comprise the comminuted ceramic materials, a low molecular weight liquid polyvinyl chloride resin and a,

suitable plasticizer. The relative Weights of the various components, as an example, are within the proportions. 10 to 12 pounds of comminuted ceramic, 1 to 3 pounds. of liquid polyvinyl chloride and 1 to 3 pounds of the.

' is-uniform within very small tolerance limits. I V .the slip is deposited on the surface, a thin layer; of part- 'in conjunction with a longer time' duration of heat treatthe Ware without deforming or injuring it. The ware atures for sinteringare' critical and should lie within plasticizer, with exactpropqrtions depending upon the thickness of the slip desired.

These ingredients are mixed to form a liquidhaving a viscosity similar tothat'ofa heavy paint. :Theliquid is then deposited upon -a pro-heated. moving. surface in. such away that thethickness of the thin layer, or slip,

' Before ing agent, such as mineraloil, is sprayed thereon in order to prevent coagulation of portions of the thin layer, or

slip, after deposition thereof upon the moving snrfac'e; and also to aid in the removal of the product therefrom after subsequent heat treatment.

The moving surface, which may comprise a thin metallic member, is preheated to a temperature somewhat in above the polymerization temperature of the resin used and when the thin layer of slip is deposited on the] surface, those portionsof the layer adjacent to'the heated surface will be momentarily heated to the polymerization temperature of the resin, resulting in the formation 2 of an-adherent film of liquid on the surface. The fact that polymerization is induced in that portion of the resin in intimate contact with the surface 'is sufiici-ent to aid materially in the production of a uniformly thin layer, or film, of slip material.

The thin slip layer is next subjected to an elevated temperature for a length of time suificient to complete the 'curing of the resin to produce a tough, flexible sheet or ware withinv which the ceramic. particles are surrounded ment of the slip.

cated in the table by the figure appearing under the heading identified as strain factor. This-factor" is= rep-' resentative of the electrostrictive response ofthe materialto appliedvoltage. In' these compositions, the amount of the trace additivesin each composition wasin'ithe percentage range indicated in the table. The compositions in the table are arranged in the. order first of increasing percentage of calcium'stannate and then increasing percantage of titanium dioxide. in the strain factor, it is shown by the table that the strain factor is substantial for all of the compositions shown within the range of 2% to 8% of calcium stannate.

trio and respond to theapplicationxof voltage in thc;

same sense irrespective of its polarity," that is, they are not charged either before or during their use in various types of transducers. 1

With further reference to the hereinafter set forth table,

it will be noted thatwith barium titanate of'95.61%

purity, i. e. containing 4.39% by weight of trace additives: 30

and with the minimum percentages of titanium dioxide (0.9) and calcium stannate (2.0),,thepure barium titanate and trace additives will constitute 97.1% by weight 7 of the electrostrictive material.

of purity of the barium titanate, the traceadditives will constitute 4.26% by weight of the material. r

13 110 A1 CaO, OuO F6203, MgO, PbO, SiO SrO, ZlOz, T102, 0581103, Strain percent percent percent 7 percent percent percent percent percent perpercent perpercent Factor Samplef I p r cent cent 1 0, j r

98. 91-95. 61 0. 45-0. 75 0. 020-030 002-. 006 005-0. 1 0l. 50 01-. 24 30-1. 50 .3-. 90 005-. 20 9 2.0 4. 6 A T 98. 91-95. 61' 0. 45-075 0. 020-0. 30 .002-. 006 .005-0.l .01. 50 0l. 24 .30-1. 50 '.3-. 00 .005. 20 9. 6.0 I 6. 9 B 7 98. 91-951 01 0. 45-0. 75 0. 020-0. 30 002 006 005-0. 1 01-. 50 01-. 24 30-1150 3-. 90 005-. 20 9 6. 5. 5 C 98. 91-95. 61 0.45-0.75 0. 020-0. 30 .002-. 006 .005-01 .O1.50 0l. 24 .30-1. 50: .3-. 90 .005-. .9 7.0 4.8 .D" 98. 91-95. 61 0.45-0.75 0. 020-0. (102-. 000 .005-0. 1- 01. 50 01. 24 30-1. 50 .3. 00 005-. 20 .9 7. 5 '6. 2 J. E 7 98. 91-05. 61 0. -0. 75 0. 020-0. 30 002-. 000 005-0. 1- 01-. 01. 24 30-1. 50' 3-. 90 005-. 20 S) 8. 0 4. 8 F. 98. 91-95. 61 '0. 45-0. 75 0020-0. 30 002-. 006 005-0. 1 V 101-. 50 01-. 24 .30-1. 50 13 90 005-. 20 1. 25 7. 5 7; 4 "G 98. 91-95. 61 0. 45-0. 75 0. 020-0. 30 002-. 006 005-0. 1 0l. 50 01. 24 30-1. 50' 3- 90 005-. 20 l. 5 7. 5 1 '5. 8 TH;

Removal of the ware from the metallic surface is I claim:

effected by means of a-knife or blade setat a slight angleto the surface and in contact therewith to separate is then cut to size and baked at the sintering temper ature of the ceramic to bring about burning out'of the polymerized resin and .to induce combination and unit-. ing together of the ceramic particles. QT he oven temperthe range 2430? to 2460i For example, slntering of a'sample of Ware at 2440 for one hour gives very favorable results. 1 Y r The ceramic-materials having compositions as in the foregoing wereformed into thin sheets and for p urpose v of examining their electrostrictive properties, the sheets.

'were' cut into strips of suitable .widthand length.

Electrodes were applied to oppositefacesof the strips and a preferred way of .doing this is by painting the opposite faces with silver painter other electrically conductive of arr-actuator, for example, it maybe mounted'asa' cantilever member or it maybe mounted at bothends'.

'Theyapplic'ation of voltage between theelc'ctrodes. will 7 'result irran expansionofthe material in the direction-'70 between theelectrodes and-aconstriction or contraction.

- in the other dimensions. JLThe effect is quadratic',,,asshasi i been explained inthefparent application referredto above That is, thejdeformationofthefmaterial is; in. the same.

' and 09% to 1.5% by weight of titanium dioxide.

material; Such a stripmay be'mounted in the-manner 1. A fired ceramic electrostrictive'material-composed of barium titanate having not more than 4.39% -by Weight of trace additives and containing-2% to 8% 7 weight of calcium. stannate and 0.9% to 1.5% by weight 'of titanium dioxide. i 1 1 v 2. A fired ceramic electrostrictive material composed .of barium titanate having not more than 4.39%"hy weight of trace additives including traces of metal oxides and containing 2% to 8% by weight of calcium stannate 3. Aflfired ceramic electrostrictive material composed titanium dioxidep e h V 4. A barium titanate electrostrictive material composed of a composition expressed as BaO, TiO S110 and'CaO such that the C210 and SnO are combined to' give a calcium stannateconteht of 2% to 8% by iweightl f and there is sufiicient TiO .to combine with all, of' the i weight. 7,

5. A barium BaO to leave an excess of T10 0f 0.9% to 1.5 by

The mag-, nitude of the response, that :is-, the deformation, is indi- While there is variation 7 Thus, with this degree 7 7 p H titanate electrostrictive material comsense irrespective of'the polarity of theiappli'ed'voltage. posed of a composition expressed, as B210, TiO Silos 5 and C210 and including traces of metal oxides of not more than 4.26% by weight, the CaO and SnO being combined to give a calcium stannate content of 2% 'to 8% and there being suflicient TiO to combine with all of the BaO to leave an excess of TiO of 0.9% to 1.5% by weight.

61 A barium titanate electrostrictive material composed of a composition expressed as BaO, Ti0 SnO and CaO and including traces of A1 0 CuO, Fe O MgO, PbO, SiO S10 and Zr0 totalling not more than 4.26% by Weight, the CaO and SnO being combined to give a calcium stannate content of 2% to 8%; and there 6 being sufficient Ti0 to combine with all of the BaO to leave an excess of TiO;, of 0.9% to 1.5% by weight.

References Cited in the file of this patent UNITED STATES PATENTS 2,402,515 Wainer June 18, 1946 2,452,532 Wainer Oct. 26, 1948 2,705,204 Shen et a1. Mar. 29, 1955 FOREIGN PATENTS 698,946 Great Britain Oct. 28, 1953

Claims (1)

1. 6. A BARIUM TITANATE ELECTROSTRICTIVE MATERIAL COMPOSED OF A COMPOSITION EXPRESSED AS BAO, TIO2, SNO2 AND CAO AND INCLUDING TRACES OF AL2O3, CUO, FE2O3, MGO, PBO, SIO2, SRO AND ZRO2 TOTALLING NOT MORE THAN 4.26% BY WEIGHT, THE CAO AND SNO2 BEING COMBINED TO GIVE A CALCIUM STANNATE CONTENT OF 2% TO 8%, AND THERE BEING SUFFICIENT TIO2 TO COMBINE WITH ALL OF THE BAO TO LEAVE AN EXCESS OF TIO2 OF 0.9% TO 1.5% BY WEIGHT.