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CERAMIC INSULATION R. Thurnauer and J. . W. Deaderick American Lava Corporation Chattanooga, Tennessee During 1946 so~ very interesting resurge on ceramic insulation proteins There released Which, for security reasons, were held beck during the war years O Furthermore, investigators Rho ~rintted Europe immediate! y after cessation of hostilities reported new aeve1~nmenta which are currently published by the (From I. Department of Commerce. Pore elain The ~ro3erttes of Zircon ~orcelai n are described in a Baler by Ralston Russell, Jr. and W. C. Mohrl. Zircon porcelain, Accruing to the definition given in this parer, consists of at Tenet 505O by weight of zircon,, and is completely ~ritrified. The chi ef advantage of thin materta~ ~ ~ tts good thermal shock resistance, high mechanical a~cren=th,, and low dielectric loss at high frequencies and elevated temperatures. Failure of electrical equipment, due to flashover at high a' titudes S presents ~ ~rob, em for the designer of electrical equipment. Of a er)ecial interest, therefore, is a Cater by C* V. Fields and G. L. Cad'`rel1 g describing laboratory fIashover tests on capacitor Rain bushings under conditions airnu~a ting antitrades up to 5O,000 ft.~ M. D. Rlgterlnk and R. O. ~=risdale3, searching for a bese for deposited carbon resistors, devel oped alkaline earth porcelains from mixtures of clay, flint, and synthetic fluxes, composed of clay,, calcined Both et least three alkaline earth C)XideSe These ceramic bodies are characterized by excellent dielectric properties, low coefficient of thermal expansion, l.!hite color, and smooth surface. The ~ atter is of special im- ~orte.nce, since carbon resistors of this type are produced by Cu~Gting spirals into the carbon coated body. Any imperfect) on of the cerami c causes bridging over and spoilage of the retie_ tore. Precision resistors of this type replaced Afire wound reelectors during the sear. Tlenry lI Re.usner4 di scusses design features of high vo~ tege insulators ,, to Are vent n~rerheating and f, ashover at n ormal working vo:Ltages . 51~+ite e-end Other H' ~-Frequen~ I_ ~ A Anger Sneer Dielectric and Insulating Materials in ~ 72 -

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Radio Engineering discusses high frequency insulating materials developed during the roast few yee.rs, esoecla~ly steatite, titanla bodies, and methods of attaching metal parts by soldering to metallized Finns on the ceramic darts. while this parer does not present any novel materials or idea, it is noteworthy for JAGS eb~ e summe.ri Ration of the subject. In a similar Gray, a career by J. Gingold6 reviews vitri- fied electrical inuring materials developed and used during the last scorn decades. E. F. Richter7 measured the resistances of hard porcelain. Steat;ite, and Ger=.en tyke dielectric materis ls of high dielectric constant. These meterie.~s are known under the trade-names of "Calite", "Condensa't ~ "Temna", and "Ardost~n" . Measurements were taken-~t 50 circles' 100; volts between 20 to 500C. Furthermore, variations of die] ectric power factor arid dielectric constant with temperature ere discussed. A. J. Mone.ck8 cites a brief history of the development and Latent literature of glees. bonded mica. Re gives method of Production, electrical, and mechanical nronertiea of thi ~ type of insulating material. E. Albers-Schoenberg9 patented the manufacture of in_ suletors made from ai1limanite or ~nullite and crystal fine fused MgO Al CON for heavy duty resistors. The Al;'O3 totals over 50 darts by sleight, the MgO 3 to 8 pants, and most of the remainder i ~ lion . ~ Ceramic Material ~ of An: Eugene Waineri patented a ceramic composition c om~ri- sing strontium ~Gitanate and alkaline earth etannate. The result is ~ ~na.terial of very high dielectric constant. The Same inventor obtained four snore patents in the same fieldl--],~2,)3,34 covering combinations of titar~ates and stanna4ces of the alka~ine-earth metals and barium titanate in combination with alka~ine-earth zirconate. The Production of thin ceramic plates was of importance during the war because of a threatening mica shortage. A French Patently confrere the manufacture of thin ceramic ~ tes . A ceramic waste is spread either on a refractory elate or between taco refractory plates coated with graphite, dried, and fired to form thin dielectric elates for condensere. After firing in a redlucing atmosphere, the orates are ellbeequentl y fired in an oxidizing atmosphere to remove the graphite coating. - Aver de Bretteville, Jr.~.6 describes cathode-ray oscillo<~i~^ men made on a fired disc of haying titanate, its' analyze he entire charging and d1 Charging cycle. The

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nP~te~ia1 showered s2.turation of the dielectric flux density with inc~ee.sing voltage end is therefore a nest- type of ferro electric materiel. Dielectric constant Beaks were observed near -70, 10, and - 120C ~ A. Ron Hi;~e~ ~ ~d ~sociatesl7 describe the results of an inves~Gig~o~tion into the di electric properties at various te=- ~ere ture s end f Sequent i es o' ti Cant um di oxide, some e.Ika~ i ne earth titanates, and some mixtures and solid solutions of barium and ~ tr ont! um ~ o~ ounds Is . Loule 13e.vlas and R. L. Grsenl8 measured the dielectric losses and dielectric constants of 104 glasses ~ using the reso_ Snag charity muddy at 3000 and 10,0~)0 megacycles and proposed cuel=tative exn1~nat:.~s of the mecharlism producing energy s.b_ sorption and die3Lect,ri ~ losses at very high frequencies, based on -he t~s and numbers of the interstitial dons e Joh., Gallupl~ found the t electrolysis occurs in the stems of soft gIess tube envelopes due to bombardmer~t by reverse emission from the rectifier elates. R. P. Hood20 patented a "less having low loss factor. Tt iS made of crystal ~ i red boric aci ~ introduced into ~ boro- 8i~ic.~te glass to ~ ower the Coverer factor. F ~ J. Williams and J. A. Orsino21 lncor7oore.ted a lead_ niches glare i n ~ storage battery., to decrease the end_of~charge vo~ ta~e by G ontinua1 ly supplying nickel ions to the electrolyte. The cold ce.~city of the bakery eras also increas ed. Rinving Leung22 measured the specific electric rests_ trance of ir~dus+~ria? glasses between 400 and 1000C. The loga- rithm of the resist, vity was found to be a ll near function of the inverse of the absolu. e temperature bet'~reen 500 Gina 800C. Polarization of the electrodes above 800C. became significant. Electric condensers using glass as dielectric were Patented in Switzerland 3. Glass plates, ha~rlng the desired capacity, with metal foil s es inter~nediate layers, are stacked and the s tac k he et e d under ~ li ght Once ~ ~ ure unti 1 the ~1~s ~ softens and the metal folds Isabel in the glass. The block is Allen cooled slowly. 8. 0. Dorst24 patented an electric condenser which has a vltreoue condenser d'electrlc material, consist, ng substan_ t:ially of a Potassium lead silicate which can be identified as compound in the fired ceramic material. _ 74 -

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Metal Ceramic Combinati ons A two stage audio amplifier can be compel etely assembled on a small steatite plate and has been used in large quantities during the war for the UeS. Army' ~ Droximit;y fuze25. The com- r'1 ete circuit is stencil ~ ed on a fired steatite al ate using Figurer paint for conductors,~and mixtures of inert ~neterials smith carbon for resistorse A German_Dutch natent26 suggest for vacuum tight joints l?et'veen Nepal s and ceramic bodies a silver paste containing 0.05 to l~ silicon. Firing in a reducing atmosphere or vacuum is suggested for steatite and oxidizing at~nosphere for porcelains. A. L. Long27 describes techniques of making glass to metals seals. Such scale are made with tungsten, molybdenum, Kovar, Fern'co, platinum, nlat;in~n alloys., and copper clad nickel_ iron alloys. viscel~ aneous The importance of X-rays for ceramic testing and research has been discussed at length by G. L. Clark28. In addition to the marry tasks already Serf orbed in the laboratory by X-rays, such as X-ray spectrographic analysis, quantitative analysis, cryatal~o~a~hy' and molecular analysis, the rapid progress in radiography offers ~reluable aid to ceramic research. H. Froehlich29 developed a quantitative theory for the dielectric Properties of crystalline solids, consisting of di- ~olar long-chain molecules. `rernn~ent Reports At the end of the war in Europe, several agencies of the American and British Government sent technical experts into occupied countries to obtain technical information on plant o~ere..tion methods, new methods and research carried out during the star. The U.S. Government also sponsored ~ variety of research pro jects in the United States during the war and conies of all reports are noes available in microfilm and ~hotoatatic form. A ?'Biblio~-a.r~hy of Scientific and Indu.~rial Reports" is pubs ished by the United States Deportment of Commerce, containing abstracts of these record. Or special interest to Ceramic Insulation re- s epoch are the f ongoing reports . C. L. Snyder30 reports inspection trills through ceramic ant;s in Germany. Sub`lec=~s covered are: gIe..ss to metal seals, ra.cuum tight crank medium, high dielectric constant and ma,~r~etic ceramic materials, shark plug core Production methods, resistors and. titanium dioxide manufacture, and production of The-rmistn.rs. Methods of Maxine alumina spark plug cores are described by Leroy _ 75 -

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D. Kile,;31. A brief survey of avail. able in~o-~n~tion on the synthesis o~ mica resee~'rch in Germany is Liven by P. M. Tyler32. Nervier with Dr A. Dietzel, credited with the basic invention, and Dr. A. Eltei, are given. Synthet.lc block mica 400 sq. cm. in area and ~erfec~Gly fed at has been produced. C. B. Pittin~er33 investigated the chernice ~ composition o~ ceramic meJGer'al from the terminal well of a Ger~nan stark ~lug. R. H. 1'cCarthy34 rem orts on ceramic development in (errand on materials faith high dielect~ ic constant ~d ferro_ m.~gnetic ceramics, developed by Dr. F. Rother. Palston Russell ,, Jr.35 describes the e~ect-~ice.] and technical ceramic ind.us~ry in Germany. The manufacture of sin- tered alumina is covered in detail. He a] go deal ~ Erich Steatit ceroTnics, materials of high dielectric constant, and moldable me ca products . Hans ]'hurnauer36 covers the activities of some German. producers of technical ceramics for high frequency insulation, including information of high and lo'' tension insulating materials e.nd on ceramics used for eJectroheating Burrower. R. L. Stone37 investigated shrinkage control in steatite porcelains for radio arid racer equipment. Be also investigated the effect of various organic binders on pressing properties of such material s. ~ G. Phtilin-~3~3 reported on the ceramic industry in he rmany . Int errs e-,~s ski th a number of Berman c erami c s c i enti ~ t s are given retiring to ceramic raw materials and their benefi- c n.ti on. _ 76 -

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BIBLIOGRAPHY 1. Etueeell, Ralston, Jr. and Mohr, W. C., Characteristics of Zircon Porcelain. Jour. Am. Ceram. Soc. 30 (~) 32~55 (1947) Fields, C. V. anct Cadwell, a. a., Investigation of Porcelain Insulators at High Altitudes. Trans. Amer. Tnst. Elec. Engre. 65 ( 10 ) 656_60 ( 1946 ) Rigterink, M. D. and Grisdale, R. 0., Alkaline Earth Porce- lains Possessing Low Dielectric Loss. Jour. Am. Ceram. Soc. 30 ~ ~ ~ 78-~l ~ 1947 ~ Hausner, H. R. , Design Criteria for Hi gh Voltage Ceramic Insulators. Ceram. Age, 47 (4) 135-139 1946) Anon. New Dielectric and Insulating Materials in Radio I:ngine ertr~g, Engineer 181 (4717 ) 519_20 ( 1946 ) 6. Glngold, J., Survey of Ceramic Insulating Materi ale. Ceram Ind. 46 ( 3 1 72_ 74 ( 1946 ) 7. Richter, Ee F. ~ Dielectric Loss Factor and Lose Index of Ceramic Materials at Alternating Voltage of Technical Frequeney- and Temperature between 100 and 500C. Physik. Z., 41, 229-33 (1940), Chem. zentr. 1941 I, 415. Chem. Abe. 37, 507 (1943) 8. vonack, A. J., Glass Bonded Mica-- Development and Use. Elec. Mfg. ~ 3~ (5) 106_109, 208-220 (-1946) . Al bere_Schoenberg ~ E . , Germ. Pat . 10. Wainer, E. , U.~. Pat. 2,399,082 (1946) 1 1 .- gainer , E ., U. ~ . Pat . 2, 402 , 515 ~ 1946 -) 12. 13. 1~ .. . 15 . . . 719,229 (1942 ) Wainer, En ,, U. S e Pat e Wainer, Ee ~ UeE3e Piate retrainer, E. ~ U.S e Pat. Lo-e~'e Redio A. O., French Pat. 887 , 632 ( 1943 ) 16. de Brettevll~e, Jr. A., Oscillogralsh Study of Dielectric Properties of Barium Titanate. Jour. Amer. Cera~ne Soc. 29 (11) 30~_307 (1946) 17. von H-iT)~el A., Breckenrldge, P. G., Cheeley, F. G., Tl~za High Dielectric Constant Ceramics. Ind. Eng. Chem. 38 (115 109 7_1109 ~ 1946 ) 2,402,516 2,402,517 2,402,518 1946 ) ( 1946 ) ( 1946 ) L . ,

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18. Navias, L. and Green, R. L. , Dielectric Properties of Glasses at IT1tra High Frequencies end their Relation to Composition. Jour. Amer. Ceram. Soc. 29 tlO) 267-76 (1946) Ig. Gallur,, J., Electrolysis Phenomena in Soft Glass Stems of Rectifier Tubes. Jour. Amer. Cereal. Soc. 29 (10) 277-81 (1946) 20. Rood, ~ A., Ups. Pat. 2,410,286 (1946) 21. cart lliams, F. 3. and Oreino, J. A., Lead_Nickel Glass Con- trolled Chemical Durability for Storage Battery Use. Jour. Amer. Ceram Soc. 29 (11) 313-16 (1946) 22. Lenny, K., Measurement of the Electric Resistlvity of Glasses. Comet . Rend. 223 ( 5 ) 236-37 ( 1946 ) ?5. Renter 3'aswerk Schotta. Gen. Swiss Pat. 227,689 (1943) 24. Dorst3 S. Get UeSe Pelt. 2~290,947 (1942) Brunetti, O. and Khouri, A. S., Printed Electronic Circuits. Electronics (19 (4) lG4-108 tl946) 26. Scientia Patent; Verger. O.M.B.H., Dutch Pat. 54,195 (1943! 27. Long, A. G. ~ Technique of Glass to Meta1 Sealing with Special Reference to vacuum Tight Seals. Jour. Soc. Glass Tech. 50 ( 1X7 ) 67-89 ~ ~ 1946 ) 28 Clark, O. L. ~ Roentgen Ceramics - Past, Present and Future. J our her. CeramO Sac. 29 (7) 177_186 (i946) 2g. Froehlich, H., Quantitative Theory of Crystalline Solids. Proc. Roy. Soc. London) 186 A, 390-414 (1946) 30. Snyder, Chris-.vPher L., Specialized Ceramic Products. Their us e in Ger man ~ on~.^unic ati on e quince n t . Rep ort PB 1291 ( 1945 ) 31. Kinney, Leroy D., mechnlca1 Inspection of Robert Bosch Plant re Ceramics. Report PB 2012 (1945), also PB 18,147 (1945) 32. Tyler, P. M., Synthetic filch. Retort PB 3,864 (1945) 33. Pittinger, C. B. Jr. a Ceramic material from German Spark P11~. Report PB 4 ~ 750 ( lg41 ) r'~_~+ `~- "room] lo. ae~relo~ment by Dr. F. ~ 34. McCarthy, R. H. ~ no )~ -a vie _..__ Rother. Report PB 6~496 35. Russell, Ralston Jr., The electrical and technical ceramic industry of GeT~nany. Report PB 18,776 (1945) 36. Thurnauer, lIans, High of Germany. Report PB frequency technical ceramic materials 6, 494 ; 1945 ) _ 78 ~

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37. Stone, R. L., Shrinkage control in steatite porcelains for radio and radar equipment. PB 32 171 (1944), PB 32 i72 (1944) PB 32, ~ 73 (1944), PB 3P,175 (1944,, PB 32,174 (19445 38. Phil ripe, J. . , Re nor t on the ceramic industry in Germany. Retort PB 2R,892 and PB 28, 892S (1945~_~1946) - 79