Jan. 20, 1953 H, THURNAUER ETAL 2,626,220 INSULATING MATERIALS Filed May 20, 1947 1200III-III IIIT III III || | | | | | | | | | | | | | ||

OOO H H H

FIG. 1

NHE HSNEPH - O IO 20 30 40 5O 6O 7O 8O 90 PERCENTAGE Tio (by weight) BaTiO3-Tiog mixture

+4

+2 O FIG.2

O O 20 30 4-O 50 6O 70 8O 90 PERCENTAGE Tio (by weight) BaTiO3-Tio mixture Inventors: Hans Thurnauer James Deaderick

B (62%.e44their Attorney Patented Jan. 20, 1953 2,626,220

UNITED STATES PATENT OFFICE 2,626,220 NSULATING MATERAALS ians Thurmauer, Chattanooga, and J ames Deaderick, Signal Mountain, Tenn. Application May 20, 1947, Serial No. 749,339 5 Claims. (C. 106-39) 2 This invention relates to ceramic insulating barium titanate and 90 parts of titanium dioxide, materials having high dielectric constants and with a constant amount of additional fluxes, as desirable coefficients of capacity, and is a con is customary in this art, added to each mixture. tinuation-in-part of our application, Serial No. In the practice of our invention we can use pure 413,340, filed October 2, 1941, and issued as Patent barium titanate, BaTiO3, or we can use commer No. 2,429,588 of October 21, 1947. cial barium titanate which has a typical analysis Ceramic materials containing titanium dioxide as follows: TiO2 34.3%, BaO 63.9%, Fe2O3.03%, as one of their chief ingredients are known to other oxides 1.77%. have unusually high dielectric constants. Where We shall now describe ways by which our in as other ceramic materials, such as porcelain, 10 Vention can be practiced. steatite, lava, glasses, etc., have dielectric con Finely divided barium titanate, finely divided stants between 5 and 8, ceramic materials con titanium dioxide and finely divided fluxes ae taining a high percentage of titanium dioxide carefully mixed, either dry or wet, to form a have dielectric constants between 10 and 112. honogeneous mixture. We prefer the mixture to There are in commercial use ceramic materials be of such fineness as to pass a 325 mesh sieve, to be used as dielectrics in electric condensers but this is a matter of choice. If the mixture has which not only have high dielectric constants but been prepared wet, it is carefully dried, then or also have defined temperature coefficients of ganic binders, such as wheat flour, dextrine, etc., Capacity. Such condensers are used as balancing are added, as usual in this art, to facilitate sub or compensating units in oscillating circuits to 20 Sequent forming. The prepared ceramic “body' Compensate for capacitance and inductance is then shaped according to well-known ceramic changes due to temperature variations of climate methods, such as compression pressing, extrusion, or heating of the oscillating circuit during opera etc. In cases where a certain amount of plas tion. Such condensers have dielectric constants ticity is desired to form complicated shapes, mois between 6 and 110 and temperature coefficients ture may be added to the powder to improve its of capacity between plus 1.2X 104 mmf./mm.f./°C. plastic properties. to minus 7.5x10-4 mm.f./mmf./°C., mm.f. as here After forming, the shaped pieces are fired in used meaning micro-micro-farad. ceramic kilns in oxidizing or inert atmosphere The positive temperature coefficient of capacity to prevent the formation of any lower oxide forms usually is connected with the lower dielectric con of titanium, other than TiO2. The firing tem stant (e. g. 6) and the highest negative tempera perature has to be such that the pieces are fired ture coefficient of capacity with the highest di to full vitrification so that their moisture absorp electric constant (e. g. 110). A material With tion is less than 0.1%. The temperature of firing Zero temperature coefficient of capacity usually has been found to be ordinarily between 1200° C. has a dielectric constant between 17 and 19. and 1400° C. For the maintenance of an inert It is, of course, highly desirable to employ as atmosphere, we prefer the use of electrically fired dielectrics in condensers materials having the kilns, but do not exclude kilns fired with other highest possible dielectric constants in order to kinds of fuel. obtain condenser units of minimum physical di The vitrified ceramic materials manufactured mensions and dielectric capacities as high as pos by the above-mentioned method are mechanically sible. strong, have high dielectric strength, low dielec We have now been able to prepare ceramic elec tric loss factor at high frequency and are espe tric insulating materials, etc., which have excep cially suitable as dielectric media in condensers tionally high dielectric constants and tempera or capacitors. Any of the ceramic materials in ture coefficients of capacity within well defined the Series barium titanate-titanium dioxide may limits. be useful as a dielectric in a ceramic condenser, Our invention is based on the discovery of the depending on the temperature coefficient of ca unusual and unexpected electric insulating chair pacity or the dielectric constant of the assembled acteristics of barium titanate, and of barium unit desired, but of Special interest is the follow titanate when admixed with varying proportions ing coimposition: of titanium dioxide. Depending upon the final Per Cent properties, as to dielectric constant and tempera Barium titanate------98 ture coefficient of capacity desired, the propor Tribasic calcium phosphate (as a flux)------2 tion of barium titanate and titanium dioxide can This composition has been found to have the be varied between 100 parts of barium titanate 55 extremely high dielectric constant of 1200 (ap and 0 part of titanium dioxide and 10 parts of proximately twelve times higher than titanium 2,626,220 3 4 dioxide), a temperature coefficient of capacity be body formed from a mixture having a dielectric tween 40° C. and 80° C. of plus 12X10 composition of 68 to 100% barium titanate and mmf./mnnf./C., and a power factor of 1.0%. up to 32% titanium dioxide, said material having In the above example any of the common fluxes a dielectric constant between 100 and 1200. can be used in place of the calcium phosphate, 5 3. A ceramic insulator comprising a vitrified and we make no claim to the use of such fluxes body having a dielectric consisting of barium generally. In the preparation of ceramic in titanate and a dielectric constant of approximate sulating materials it is customary to mix the in ly 1200. sulating material with a suitable flux before the 4. A ceramic insulator comprising a vitrified material is fired. Likewise, the use of organic 10 body having a dielectric composed of barium ti binders before firing is conventional. tanate and up to 45% titanium dioxide, said body We have prepared a whole series of barium having a dielectric constant of between 32 and titanate-titanium dioxide dielectrics, varying in 1200. proportions from 100% BaTiO3 to 10% of BaTiO3 5. A ceramic insulator comprising a vitrified and 90% of TiO2. So that those skilled in the art 5 body having a dielectiro consisting of barium may be appraised of the electric characteristics titanate. of Such mixtures, we have shown, on the appended HANS THURNAUER. single sheet of drawings, two graphs covering JAMES DEADERCK. the system. BaTiO3-TiO2. Figure I shows the variation in dielectric constant, and Figure II 20 REFERENCES CTED shows the variation in capacity drift. The following references are of record in the We are aware that magnesium titanate has file of this patent: been used as a dielectric material, as in the patent to Alberts-Schonberg 2,165,819, and make UNITED STATES PATENTS no claim thereto. Magnesium titanate has a 2 5 Number Name Date dielectric constant of 15 to 18 whereas barium 2,165,819 Alberts-Schonberg --- July 11, 1939 titanate has a dielectric constant of about 1200. 2,218,655 Peterson ------Oct. 22, 1940 Other-important differences exist between the two 2,220,765 Hirose et al. ------Nov. 5, 1940 Substances, but the high dielectric constant of 2,277,733 Wainer et al. ------Mar. 31, 1942 barium titanate is outstanding. 30 2,277,734 Wainer et al. ------Mar. 31, 1942 Having described our invention, we claim: 2,429,588 Thurnauer et al. ---- Oct. 3, 1942 1. A Ceramic insulator comprising a vitrified FOREIGN PATENTS body formed from a mixture having a dielectric composition of 55 to 100% barium titanate and Number Country Date up to 45% titanium dioxide. 719,067 France ------1931. 2. A ceramic insulator comprising a vitrified