si . MATEMALS FO* 3DO-500°C MACNF.TIC COMPONENTS*

K. H. Weichold and R. K. Pandey Oepartaent of ^Electrical Kagiticering ^ Texas AIM University NOflfil v College Station, TX 77M3 WW I8WI Of THIS WBPBWT AM tltMIBU. B D. W. ralmer Sandia Labor a tori':* RHimnrf^lraiOTWtlu but ivili

exposure to a high-temperature environment. The investigation of materials presented in this work Core materials and winding wire For audio and rf proceeded as follows: A material was first investi­ transfomen have been investigated to 500°C. Audio gated for stability over tha temperature range by cores o( 2 V Pormendur bad par amor, er stability from observing magnetic parameters inferred from its hys­ 25 to 500°C and during aging nt «0°C. Hi^i fre­ teresis curve; secondly) the material was subjected quency ferrite material. Mix 63, displayed usefulness to thermal annealing at 450°C in air. tf it showed up to 300°C. Both anodized (lunimn and cernmie- little change in hysteresis after 100-200 hours, coated copper wire function to 500°C in low voltage annealing was continued to 1,000 hours. Table I lists or large gauge applications. Components based on the measured Curie points, advantages, and high- these materials operate reliably to 500°C. temperature aging data for the materials investigated.

Introduction The following magnetic properties were measuredt

It is often taken for granted that transformers saturation induction, Sa; residual induction, Brj

have inherent environmental ruggedneaa, especially coercive field, ttc; permeability, |i; and the hys­

with regard to operating temperature range. Despite teresis loss Wn. These parameters are shown in the this perception, in practice commercial magnetic com­ hysteresis loop of Figure 1; the hysteresis loss is ponents are flL beat capable of sustained 700°C the area enclosed by the curve. In general, for operation. nevertheless, there exist a number of high-tcaperaturc transformers, it is desirable to have potential uses vhich demand higher operational tem­ & high-Curie temperature and a high-permeability peratures: geothermal downhole Logging instrumenta­ material that exhibits a low-hysteresis loss. With tion. (200-*)00°C),1 jet engine transducer imped­ this in mind, the materials of Table I were selected. ance matching (300-45O°C), petroleum veil instru­ Experimental data waa extracted from serial hysteresis mentation (maximum of 225°C), magnetic bearings (up to curves such 'aa those shown in Figure 2 for Deltamax, 525°C),2 and nuclear plant monitors (300-500°C). Hot ice that at 480aC all ferromagnetic response lias disappeared—the Curie point has been reached. This Previous hi rfi-temperature magnetic material suthod gave a Curie ten p.; rat ace of 330°C Cor amor­ investigations »*»^ have been concerned with rotat­ phous METCTAS 2605S, a marginal value for geothermal ing machinery and apace power applications. This use. investigation searched for signal transformer core and winding materials which retained useful magnetic Although all the parameters of Figure 1 were and electrical properties at higli temperatures. The investigated, the temperature dependence of hysteresis materials studied include audio frequency core alloys loss and permeability were crucial in selecting mate­ (Delt.imax—NisoFeso, nmorphotia METGLAS 2605S— rials for use as high-temperature transformers. Fig­ Fe B ure 3 ahnws the temperature dependence of the hys­ 82 12SJ-6i Silectron—Feo,7Si3? Supermendur and 2 V rermeudur Go^gFc/,*)!^), high-fraquency ferrite mate­ teresis Loss of the four remaining materials; samples rials (Mix 63), and wire (anodized aluminum and had already undergone 450°C annealing. The 2 V ceramic-coated wire). PernuMidur, Silectron, and Deltaranx all show s desir­ able decrease in hysteresis loss, Deltaaax showed the The immediate need for both J-.igi:-temperature, largest decrease because it has the lowest Curie point high voltage transformers ati-i magnetic multipliers in of the four—about 4S0°C. Supcrmondur demonstrated geothcrraai downhole instrumentation instigated this an undesirable increase, indicative of a similar deg­ research. The high-voltage transformer is intended radation in other properties auch .is the saturation to charge a storage capacitor to 2 kV from the avail­ induction and coercive field which occurred on a time able 100 V cable signal for cither a downholc detona­ scale nf hour3 at 't50°C. tor circuit or a nuclear particle detector power supply. Lie multiplier is intended for lonjt~tert> Figure 4 S'IOWS the temperature dependence of the downhole nDJsiircments (yeare nt 300°C). In this permeabilities of 450°C annealed samples. Again application, a transducer-multiplier combination would Doltamax showed the largest decrease, while Supermen- be left hardwired downliole to be only occasionally dur demonstrated an increase. While it is desirable interrogated from the surface. to Iinv« a large permeability, the other parameters of Supounendtir change so drastically that the usefulness Ribbon Core Materia Is' of this material for a high-temperature transformer is Iimited. Materials used for the above applications muse exhibit stable magnetic properties over the temrcrn- A further factor affecting material choice ia turc range oE interest. Additionally, these material* •atariat nnnealing. In general, the oriencen" (grain must exhibit the same stability during prolonged and mngncticnlly) and amorphous materials showed the most rapid aging. Figure 5 shows the cnimgca in hys­ teresis loss as a function of annealing Circe. The *This work wad supported hy the 0. S, Department of 2 V, Pcrracndur, Deltnnnx, and Supermeedur all stabi­ Kncrgy. lized after an initial small ch.tnge in hys teres la

DISTRIBUTION OF THIS DOCUMENT fS UNLIMITHI lea*. In contrast, Silectron did not ntabilize during Ceramic-coated copper and nickel wire were also eftinc and aWa't be eliminated from consideration. tested in an effort to obtain high-voltage, high- temperature, fine-gauge windings. Insulation break­ 11M decisive factor ii\ waking * choice between down tests indicated a 200 V failure at room tempera­ 2 V Permendur, Deltaeax and Supermendur is the perme- ture versus ISO V at 300°C. This breakdown value ftbUity change, illustrated in Figure i. The graph was hijdity preaaure sensitive, particularly at high shows that the permeability of bath Supermendur and temperature. Unfortunately, the finer-gauge ceramic Silectron decrease Markedly with increasing annealing wire also demonstrated a larger variance in breakdown time. On th* basis of high-temperature aging, Delta- voltages and more sensitivity to handling. max was shown satisfactory in extended us* up to ebout 350°C, whereas 2 V Fermendur performed well at ' least These two commercial wire systems plus prototype to 500°C. The 2 V Permendur transformer* will glass-coated wires made at Sattclle and General- apparently operate stably above 500°C, but no suit­ Electric'"1 arc undergo i ng further tests in order to ably insulated witilling wire is currently available. arrive at a high-voltage, 500°C, fine-gauge winding. Ferritc Core Materials Components There aralloy 4750 cores (Do1 teaax family) were material had a measured Curie temperature of 460"C used for operation up to 300-350°C, whereas unori- and a permeability of 140 at 25°C. Parameter cnted 2 V Peraendur cores were used for higher tea-: changes with temperature indicate functionality to at peraturea. Typical units were designed for 400-3000 least 300°C; for example., the change in permeability Hz operation to be compatible with the effective low- fron 25 to 300°C was 17 percent. The major drawback pass filter provided by the long instrument-to-truck of this material was a targe increase in hysteresis cable. It was necessary to use ceramic rather than losa with 470°C aging. The degradation seen resem­ standard glass fcedthroughs on the hermetic metal bles oxygon induced ferrite aging;" encapsulation package to maintain the necessary isolation above techniques are being pursued. 3D0°C. Efforts to fabricate 500°C, high-voltage transformers (greater than 100 V) with fine aluminum, High-temperature evaluation of ferrites has just or ceramic wire (£34 or finer) have not been begun. Promising simple (one metal) ferrites wist successful. first be examined} particularly lithium, nicV-il, and iron. However, mixed systema will probably be needed Test results on two fieldable units, a step-up to achieve optimum high-temperature performance* The transformer and a multiplier, suggest the high' first goal is a I to 5 MHz ferrite with a permeability temperature potential of these materials. Lifetimes of 2000 and parameter stability to at least 300°C. exceeded 1,000 hours at 350°C for Deltaraax and 450°C for 2 V Peraendur cores. The transformers Wire for Windings based on 4750 functioned well up to 460°C where within 1°C their operation stopped. Hot only did Two high-temperature,, magnetic winding wires are the voltage output go to zero, but the input and out" commercially available—anodized aluminum and put impedances changed' radically indicating the Curie ceramic-coated copper or nickel. Both type? are leaa temperature. Although the components functioned to forgiving to the natural mechanical and chemical 460°C, the aging vaa fast above 350°C with 4750 stress common in component winding than standard cores. In comparison, the 2 V Permendur showed no enamel-contod copper. To test the integrity of the3e change in output voltage up to 500°C—the limit of wires, voltage breakdown tests were performed .it 25 the winding wire. Aging at 450°C for 1,000 hours and 300°C. Tests were run directly off the spool produced little change. The lead-to-case isolation on both straight segments and on windings on a 1/4" for these units is greater than 10. HM at 450°C. The madrel. When either wire type was tested with local­ Multiplier is capable of multiplying a dc variable ized stress created either by wrapping the wire over voltage by an ac reference with a linearity of £ 3 a sharp edge or crossing two wire segments, the percent ov.;r a dynamic range of -50 tt 50 V (or -5 breakdown voltagti at the point of stress was highly to +5 mA). pressure sensitive. Test results quoted below are for a loosely wound configuration with no high-stresi Conclusions points. Neither wire system had practical high vol­ tage, high-tempsrature integrity in n gunge finer A number of deolgn lessons have been gleaned from Chan #34. this research nnd prototype development. First, crystallograpliically and magnetically nonoriented core The principal wire used in this investigation materials must be used. Second, Z V Permendur has the was nnodized, annealed aluminum wire.' Insulation maximum operating temper attire and life of the audio is provided by aluminum oxide formed by an anodization frequency materials tested. Third, Mix 63 Ferrite proccas. This oxide was found to have a breakdown has adequate properties for use with rf signals up to voltage which varied from 170 Vdc to ever 250 Vdc at at loaat 300°C. Fourth, targe diameter wire must rooa temperature. The lorg* variation in breakdown be uaed in high-voltagef high-tempotatore trans­ indicates an initial oxide of nonunj form quality. formers, l-istly, more development is neidcd on fine Furthermore, this insulation was sensitive to chemical gauge wires ond ferrite material*. These findings and mechanical dnmng<: by simple handling. Dielectric have been confirmed with commercial fabrication of breakdown was particularly troublesome for gauges Magnetic components functional to 500°C. firer than 032. Attempts to use any finer wive windings, particularly above 350°C and 100 V, were generally not successful.™ »* C. K. An»«te*d <«. M. favlovie, 0. H. UM, J. J. Unc»;o Pre**, 1973. Clack* and M. Spewoek, "Pro^trtigw of Hagaatic H. KsVraan and C. L. Ltard, "Practical Hagnttlc Hateriala for Jin in Kigh-Tcwperatttra H>aca Bearings," fEEB Spectrum, pf 26-30 (SeptetAtr Power System,* HASA Special Publication, ittiA 1979). SP-3043, 1967. 4. Sarrsgncr, "Investigation of Magnetically 6. C. Heck, Kagnecic Hsterialt and Their ApsUca- Soft, Uifch-TewpirntHrq Uobiilt-lron \lloy," HASA tiff-^, Crane, Ruaaak and Company, 1173. Technical Hote, KA3A TND-3W3, October 1966. 7. Purchased from Pcrsaluster, Borbtnk, CA. J. P. Barrongcr, "Electrical and Bcchanicffl S. H. Tekosfcy of Cenaral Magnetics, Blonnficld, HI. Properties . of n Superior Hi ph'Temperature 9. Tly-Tewp Transducers, Philadelphia, PA.

Cobalt-If on Magnetic Hate*-ial(" "SASA Technical" 10. Ongoing Investigation at Bsttelle and Central Hote, NASA TN0-4551, Hay 1968, tileetrie sponsored by C. JU LeedecVe at 9andia.

Table I

Curie Core Material Toip(°C5 Advantage* Aging COMMat* Amorphous HETGIAS 260SS* 330 lov toss latEG changes uLth aging; low-Curl* probably due to crystallisation temperature

Deltaaax** 480 coomon core i00°C aging occurs during unoriented F«50Hi50 Material firat 400 hours Stipe nsenduc** 940 high degradation at 500°C( large stagnatleally r"e49Co$oV2 permeability Chang** in saruration after ordered 100 hours

2 V Penaendur** 940 excellent aininal aging after 1,000 hours unoriented Fe49Co^9V2 stability

Sitectron" 730 standard targe change in permeability grain FenjSij transformer after 100 hours oriented material

Mix 63 Ferrite*** 460 high sensitive to oxygen at high frequency tctapernturea •Provided by Allied Chemical **Provided by Arnold Engineering ***?tovided by Ami dor* Associates

HUK Density, B Flux Density, fl

^LH<^$J:i^^.

Flr:»rc 2 Tpmiicr.miru depeml.mce of the (ivyterc*!* loop Ftgyr« 1 Hysteresis loop for ;t limnetic wateri.il'. for nett^a-ax CirMttnry unit,-*). 2V PERHENDUK

700 900 Hours

Figure 3 Percentage of room temperature hystere«l* lost a« a function of temperature for samples annealed at 450*C.

Figure S Percentage of hysteresis losa as a function of annealing time. Sanple annealing temperature 450'C; data taken at 450-C.

Figure 6 Percentage of room temperature permeability as a function of temperature for samples annealed at ASO'C.

Figure 6 Percentage of perineabllity as a function of annealing time. Sample annealing temperature 450BC; data cnlten at 450'C.