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62 CER~.qIC It',TSUl AT=GN . ~ _ %~ ~ By J. ~0 Dead`.rick American Lava Corpor&t~..cn Cha Toga 9 Tents The year :~947 reflected a confirming trend of, the cerar.iic ;.ndus-tr~y toward the development of electrical insulating materials with comer losses at higher frequencies. Low loss ceramic-to-~.~+~al hermetic serifs play a vital rode fin the efficient operation of vacuum tubes at m~crow£ve~fr~qu~ncies, consequently a great deal of at,tent~on was directed to the ~nves'~'gaticin Of sui~ab e sealir~g materials and techniques. Scark F~ Using Sakelite as a binder, a]..umi.na spark Slugs are automatically -mod. by the A. CO Soa.r~ng Plug Company T;td.) The insu7.`to;~s Are stead in a 'fish temperature furnace to vitr .ficat~ onO Assembly of the insulator and. .rneta7 parts is accom~list.,ed with Pyrex glass pellets and a copr!;r sealing compound fused +,o- gether under pres sure at 900°C O Gainer patentec9.2 a spark plug insulator comprising a fired mixture con- taining a major proportion of zirconium oxide rails mag~neslum oxide, +,h~ modal proportion of zirconium oxide to magnesium oxide being began 2 to ~ and 1 to 20 Schaefer patented3 a vitreous alumina base cellar c ns Mating material containing at least 121: clay and a small amount of a~kaline-earth p~nos-:nate, the aluminum oxide content being at least 73%. Vitrification temperatures es Jot as 14000c were obtained. Glass ._ A patent4 tics obtained on ? glass having a pointer factor less tran o.C6!~;9 a dielectric constant of at least 7, and a softening t~mr,ercture below 600°Co It contains net more than 50% Sigh, less than about 6G; Pro, and the balance of .r.~!ore than 5% of the alkali met=1 oxides K 0, kayos and Li2O, in the ratio 4 to 1~5 F2Oi1 Na2O and IS to 4(K2O and Na2O)51 TiO2. Monack5 describes the manufacture of glass-konded mica And discusses the effect of forming methods on properties of the finished ii~sul&tor. Raw materials, mixing, preforming, dr>-ing' ~.olding and heating are discussed fit length. A resort from Ger~nanv6 relates the theol~etic~1 and practical aspects of bonding glasses and ceramic materials of wnequ=] thermal expansions, inch uding guiding rifles for the manufacture of bonding g]-asses Loving various thermal ex- pansion coefficient=.
63 c,t,eat ~ te an] Other L2~:i~h Frecue~.c.y Miat,er~ als ~ v-itril~ied ceramic 'cod~,T7 composed primarily of the magnesium orl,h.osili- cate 2~Dlig0.Si.O¢, is oha~`acter~zed bar very 70~'? dielectric Joss and high electrical resistance at~6le~r&ted tem?eratu.resO The cLys:.ca].. properties of this material are l~.~.sted for compar~so:~ with st~atite and zircon porce3~.ainO It is useful for coaxial ].i~.:e spacers, vacu~m-tight me~a]-ceramic seals and other applicati.ons Were CON{ Oslo fa.ctc~r i s of prime - ~nportance. [~.Cicre~scopic and X-rar e;<am-naui.o;-ls of a series of steatite bodies in- d~cate that low 'oss ceramic materials consist of very small, perfect crystals ho}~logenec~us~y distributed in a clean strain-free and ankali-eree glass. Recent developments in alkaline earth pore ~orste~ite bodies and zircon porcelains indicate that the crystal fine phase Is not km ted to magnesium metasilicate in Qua TOSS ~.odies. Thiess9 patented an electrical lusty ator composition firing at about 1250 to 3303OC consisting of about 75 to 90% talc, about 3 to 20$ of a glass con- sisting essential!:, of calcium magnesium koros~licate, and about 3 to 15% aluminum silicate. The insulators were characterized by a power factor of less than 0.1% c radio frequencies and a fle.;u.r~. strength of about 2O,0('O lbs. per Sgei~o Ceramic t.4ateri&ls of filth Permit,tivit~r The Jational. Tweak of Standardsl° investigated the properties of harium- strcntium titanate dielectrics. Test results on shrinkage, porosity, heat treat- nient, power factors dielectric cc::st~nt and the r.na' expansion are given. A Ales measurements of K and Q were made at a ~req'.~.ency of 3C0O megacycles per second. K values ranging from 34 for n,aC 4TiO~ to several thousand for specimens composed of Patio and. orTiO mere measured. ~'he d.ielectr~c constant was not affected by ar~.at~o~s in freq.l.ency within the range 50 to 20,000 kc. per sec. Most con~posi- tiQriS exhibited large negative temperature coefficients of,K, but some were suitable for use it? filter or storage condensers a ' Rathl' obtained a Latent on sistered ceramic 'insulating trikes made.:from mixtures of t,ita.ni'n With crude commercial yttrium oxide (75q~ yttrium oxide) or With . . .. Haste materials obtained inthe treatment' of ~.olla.zite sand which contain about 65% lanthanum oxide. These bodies combine a high dielectric constant with I.o~'di- electric loss. An example of a.membe~ of this group is titanic 83.4% and lanthanum oxide I 16.6% by weight fired to.9eger cone,l3 to 14. It has a dielectric constant 0[ 829 loss angle tan - 9 x 10 49 aid a temperature coefficient of car~aclty of inl~lS Bl5 x ]~0 ~ T`7ainerl2 patented a ceramic dielectric composition,having a controllable -tenpere.ture coefficient of capacity comprising substar.tlally entirely predetermined quantities of at least into of the titivates of cal,ci,~,, barium =!~d,stront~inn and Braving ~ dielectric constant greater than l '/. '
64 Navias and Greenl3 patented ceram.c comr,os~tions charactc-rized by 'or power facts and Cow hygrosco,?~cityO These con!positic~ns consist by Height of at leas+ 70% of ~ refractory titanium compound, the reminder being a mixture of clay and a fluoride from the alkaline-~-arth fluorides and lead fluoride. Thurnauer and Deaderic; 4 patented 2 ceramic dielectric com~ositicn having a dielectric constant of 37 and a. temperature coefficient of di`~.ectr~`c constant of substantially zero and compris;.ng about 43$ ratios, 55% Tics and 2! CaPC O The electri.c&3 Properties of La.~iC - Tick mixtures are seven. , ~ 4 Metal Ceramic Combinc.tions }hetal-to -c cramic sea].s15 are prepared b;- the ~pclicati on of tithe nits hydride to the ceramic and bonding to metals or other similarly prepared cera~.i~s by brazing or silver soldering at about 1000°C. The bond thus formed is gas tight a~d suitable for vacuum applications. During the solar the Germans developed a similar type of metal-~-ce-ram~c seal employing molybdenum-iron silicates es ~ base- for brazing materials such is silver, silver alloys and copper. The German seals have been improved for high frequency use in this country by the use of ceramics with loner electrical losses. Complete details of the process are described) . Mcnackl7 classifies glass-to-meta'' seals according to function, geometry, or type of glass. Properties of sealing glasses mrort~.nt to successful joints include thermos scous, pLysi¢aI, Electra Cal and ~ho+~o-elas-tic ch£:racteristi:cs. Metals should hate (] ~ uniform tli~rmQl expansion, (2) stability: during seal making, (ON good adhesion to g]3S53 (~ i0W cJectr-ical resistance of the oxide films (5) minimum gas evolution, and (6) lor cost. In a later publication the same au+hor:8 states that the successful p,reparation of glass-to-metal seals depends not onl~,T upon agreement of glass ?.n~ metal thermal expansion coefficients but also upon Agreement throughout the entire elongation curare. Seals are class) fled on Chic basis of facts on9 geometry and type of glass. I:ata on metals alloys, and corn?os~te Wires is given. ST`o~tcornings of theoretical considerations are discussed. The presence of-a metal oxide film is felt to be necessary in metal-to- g]~ss combinations. If perfectly matching thermal expansion properties arc not possible, successful seals me.y be formed ~4 tl,o metal is thin and ductile enough to be deformed by differential expansions . Met~l-to-ceramic seals developed by Telefunken20 replaced glass ..s the bonding agent by a sPeci&1 ceramic pc^.st~ composed of the followings 10~20 steatite, 1.44 zettlitz kaolin, 0.48 zirconium and 0~24 kg of potassium feldspar. Fold spar in the mixture insures tightness, and a rigid ~roo,edure is outlined.
65 I.li scel 3 a.neous A review of the chief c~aracteris'~ics of dielectric materials9 lee. res~.stivi';.y `?^nd dielectric const;ant9 is presented by Hausner2~. The same authored discusses in another paper the principles of electrical conductivity and their a~?plica-bJon to ceramic .se~n--conductors. Studies Were made on com::'osit.ons consisting mainly of Viol, Fe203, F'e;}O4, ZrO2 and others. The el:-i'ec+s of ~ompos::ti.ox~s on te.m~erat;ure coeffic~,ienJ~ o' resistance were investigated. The recl.~ct,ion. of oxides With its effect on conducting properties Was also determined. Brunetti and Curt~s23 present a. comprehensive treatment of the "field of pr-.rited circuits. The various methods of app~yi.rlg conducting and resisting .fi]ms to i.nsu:Lat~ materials are fu1.ly c~.escrited.. Precautions and limitations are disc. ussed. A monolithic structure com;~risi.n& alternate layers of vitreous low logy en~.~e:l: and conductive silver film its described by Bradford' Weller and McNeil [O't' use as capacitor having electrical characteristics sim-~.~-a~~ to mica. The process i.5 based on the laying dorsal by spra.y:~g, of layers o. enamel. a].ternati~lg with layers c.f conc3Luct~ing s~...lver paste 6.~eposil;ed by silk Screen or squeegee r~r..nting. Upon c:.,rv ng, tile plates are cut to the desired pat~er:Lls and fired for abc:ut 12 hours. S=~..~7er is exposed at certain Foibles for a.~ta.clling leads. Single Un:LtS may have ca'~ac..ties of' frown 15 to 50()0 Gruff. and. ccmbinat,ior~s of ca~aci+Jors9 resistc~re, acid inductances may be contained. ~n a single unit if desired. The c=~aci.tors show a small :.ncre~ase in cacac:~i,y and dissipation facLo:r vat ;h a rice in temperatures arid t'~er-: are usable up to 1 25°O Hi Ah no change ire temperature co~f'fi cier~tO - Borate' Breckenri~ge and Brc~rnJo`~?25 describe a machine for forming thin ceramic die' ectric sheets for capacitors . ~ ceramic slip is Elutoma+.ical.1.~y deposited con a sta::r~less Steel belt moving through a Writing tunnel. The dried sheets are stri,~ped frost the belt and cut to size either before or a.f'cer firings Sheets may be p~ocuccd Troll, .006 to .030 luck in t'-iic!~less 'loving un' form density after firing and Story good dielectric st.rength.
66 BIBLIOGRAPHY 1. Anon., Times Rev. Ind., 1 (2) 26 (1947) . . . 2. Gainer, Eugene, DO S. Pat. 2~427~034 (1947) . . 3. Schaefer, C. F.' U. S. Pat. 2~419~290 (1947) ,. . . . . 4. is. Armistead, A. H. Jr., U. S. Pate 2,431,98O (1947) . . Monack, A. Jig Rapid Insulator Production with Glass-3onded Mica. Ceram. Ind. 48 (2) 59-649 Ibid (3) 76-SO' Ibid (4) 98-10O, Ibid (5) 76-77' 49 (1) 74-76 (1947) 6. Klump and Gohike, Bonding of Glasses and Ceramic Material with Different Coefficients of Thermal Expansion. Report PB 24~960 (1946) ~ 7. - Thurnauer, Hans, Forsterite' a Low Loss Ceramic Dielectric Immaterial. Tele-Tech, 6 (2) 86-87, 130 (i947) 8. Rigterink, M. D., Microscopic and X-Ray Investigation of Some Steatite Bodies. Jour. Am. Ceram. Soc. 30 (7) 214-218 (1947) 9. Thiess, [. E., DO S. Pat. 2,419,472 (1947) 10. Bunting, E. N., Shelton, G. R., Creamer, A. S., Properties of Bari~m- Strontium Titanate Dielectrics. Jour. Am. Ceram. Soc. 30 (4) 105-125 (1947) 11. Rath, A., U. S. Pat. 2~4329250 (1947) . ., 12. Gainers E.' U. S. Pat. 2,420,692 (1947) 13. Navias, Louisa Green, R. L., U. S. Pat. 2,424,111 (1947) U. Thurnauer, Hans' Deaderick, James, U. S. Pat. 2,429,5SS (1947) 15. Bondley, R. J., Metal-Ceramic Brazed Seals. Electronics 20 (7) 97-99 (1947) 16. Williams, Neal T., [,etal-Ceramic Vacuum Seals. The Review of Scientific Instruments 18 (6) 394-397 (1947) 17. Monack, A. it, Theory and Practice of Glass-tetal Seals. Glass Ind. 27 (at 389-94, 408- U. 42O9 (9) 446-49, 464-70, 4769 (10) 502-04, 522-28; (11) 556-599 576-78, 582 (1946) 18. Monack, A. J ~ Glass-to-Metal Seals in Electronic Components and Applications. Elec. dig., (39) 96-101, 162-l8O (1947) 19. Partridge, J. H., Glass-to-Metal Joints. Sheet Metal Ind. 24 (237) 119-128 (1947)
67 20. Kuh~er9 a., ~eta]-Cera~ic Seals- Stiles 2~7) i94-204 `1947) 210 22 i . ~; . . 8.allsn~r ~ ~ o ~. Die] emetic (calculations. CeramO Age g 49 ~ 4) 165-166 (1947J Iausner, 7~. ]~99 Semicond.'cting Ceramic 3ff~.teriaDs. Bow. As. Ceram. Scc. 30 <9! 29~-296 `~9,~7) - 23r~me~ti9 CledO' `,ur~i.s, Roger A., Ne B . S. ~,i~ cular 468 43 pp., :1947 Printed Circuit Techniques. Bradford, 5. I., Weller, T3. I. and McNe~gh+9 a. A., Printed Vitreous }enamel Components. Electronics 20 (12) low] 08 (1947) Ho-a G. N.g Brecl~enridge, A, -IT. -and Bro~P~lovi, J. .~.:i.' Fabrication of Thin (,e-ramic Sheets for Capacitors. yours An. reran. Soc. 30 (g) 237-242 (1947) . . .
