PIONEER YEARS OF ELECTRON PROBE MICROANALYSIS IN SLOVENIA PIONIRSKO OBDOBJE ELEKTRONSKE MIKROANALIZE V SLOVENIJI FRANC VODOPIVEC Institute of Metals and Technology Lepi pot 11, 1000 Ljubljana, Slovenia Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 Two periods are found in the pioneer years of electrons probe microanalysis (EPMA) in Slovenia: • a longer period up to 1969 when an electron probe microanalyser was put in operation in the Institute of Metallurgy in Ljubljana, and • a shorter period after this date until the spreading of EPMA backed by sufficent research achievents demonstrating it wide field of use and the sufficient mastering of methodology. The use of EPMA up to 1969 was of marginal extent but not of marginal scientific merit and centred to topics of selective oxydation of alloys of iron vvith arsenic, copper, tin and antimony. The interest for EPMA and the conviction that it vvill greatly improve the quality of the actual research as vvell as open nevv topics helped significantly vvere great. Prof. D, Kolar and his collaborators vvere among the best prepared and also among the must successfull. With the cooperation of some younger scientists he accomplished several projects vvhich found significant interest in the international research community and vvere realised thanks to the fast governing of EPMA methodology. Let us quote only some achievements published up to some years after the putting in operation of EPMA in 1969: • binary phase equilibria diagrams vvere established for niobium, titanium and circonium carbides vvith iron, nickel, chromium and cobalt; • binary phase equilibria diagrams vvere established for uranium sulphide and sulphides of calcium, barium and strontium; • several projects vvere accomplished vvith the aim to understand better the microstructure of ferrite ceramics, its sintering process and the effect of microstructure and sintering on magnetic and electrical properties. In binary phase equilibria diagrams solid solubilities and eutectic compositions vvere determined. Also because of the contribution of prof. D. Kolar the pioneer period od EPMA in Slovenia vvas short and successful and helped to strengthen it as one of the base scientific facility for research of solid materials on microstructure level. Key vvords: electron probe microanalysis, selective oxydation, binary phase diagrams Fe - NbC, TiC, ZrC, activated sintering of Ba titanate, binary phase diagrams US and CaS, SrS and BaS Pionirsko obdobje elektronske mikroanalize (EMA) delimo na dva dela: • daljše obdobje do postavitve elektronskega mikroanalizatorja na tedanjem Metalurškem inštitutu v Ljubljani leta 1969 in • krajše obdobje po zagonu naprave in začetku njene široke uporabnosti kot dokaz zadostnega obvladovanja metodologije dela. Uporaba elektronske mikroanalize je bila do začetka leta 1969 v Sloveniji po obsegu marginalna, vendar ne marginalna po vsebini. Raziskave so od leta 1962 posegale na področje selektivne oksidacije predvsem zlitin železa z elementi z majhno afiniteto do kisika, na pr. arzen, antimon, kositer in baker. Zanimanje za EMA in pričakovanje, da bo omogočila kvaliteten skok v raziskovalnih projektih je bilo veliko, okolje pa pripravljeno na intenzivno uporabo nove metodike. Prof. D. Kolar je bil s sodelavci pri tem gotovo nadpovprečno uspešen. Bil je snovalec in izvajalec vrste raziskav, ki so prinesle temeljne novosti na nekaj področjih raziskovanja. Omenjene bodo le tri, ker so bili izsledki objavljeni najkasneje nekaj let po postavitvi naprave tudi zaradi zelo hitrega osvajanja metodologije dela, še posebej kvantitativne analize: • določeni so bili binarni ravnotežni fazni sistemi niobijevega, titanovega in cirkonijevega karbida s prehodnimi kovinami železo, krom, nikelj in kobalt; • določeni so bili binarni ravnotežni fazni diagrami uranovega sulfida s kalcijevim, stroncijevim in barijevim sulfidom; • izvršena je bila vrsta raziskav s ciljem, da se bolje razpozna mikrostruktura feritne keramike, proces njenega sintranja in vpliv sestavin in procesa sintranja na magnetne in električne lastnosti, V binarnih faznih sistemih je bila določena topnost v trdnih fazah ter temperature in sestava evtektikov. Tudi zaradi velikega prispevka prof. D. Kolarja in sodelavcev je bilo pionirsko obdobje EMA kratko in uspešno ter je metodo utrdilo kot eno od temeljnih pri raziskovanju vseh vrst trdne snovi na nivoju mikrostrukture. Ključne besede: elektronska mikroanaliza, selektivna oksidacija železa, binarni fazni diagrami železa NbC, TiC in ZrC, aktivirano sintranje Ba titanata, fazni diagrami US in CaS, SrS in BaS 1 INTRODUCTION This paper vvas prepared in the frame of the celebra-tion of the 65th jubilee of prof. dr. Drago Kolar, eminent scientists at the Institute J. Štefan and teacher of ceramic materials at the University of Ljubljana. I had the oppor-tunity to meet prof. Kolar in major extent after april 1969, vvhen the second electron probe microanalyser (EPMA) in the former Jugoslavia vvas put in operation in the former Institute of Metallurgy in Ljubljana. The EPMA vvas purchased by combining funding from the Institute of vacuum technique and electronics, Institute of automation, Institute for research of materials and structures, Institute of metallurgy, Metallurgy dpt of the University of Ljubljana, Slovenian Steelvvorks, and the Slovenian governement. The project vvas coordinated by the Institute of metallurgy and the EPMA installed in his premises. 2 EPMA IN THE WORK A SLOVENIAN RESEARCHERS UP TO 1969 From disponible data it seems that EPMA vvas first used in the vvork of a slovenian scientist in 1962 in the investigation of the selective surface oxydation of the al-loy Fe - 0.075% As1-2. Arsenic free energy of oxydation is smaller than that of iron. Consequently, by surface oxydation only iron reacts vvith oxygen, vvhile arsenic is segregated in the metal layer in contact vvith the oxyde. By EPMA the distribution of arsenic in the segregated layer obtained by electrolytic dissolution of |4m layers of metal and microradiochemical analysis vvas verified. The distribution vvas different after surface oxydation above and belovv AC3 because of the limited solubility of arsenic in y phase (figure 1). The results obtained by both methods did agree very good. In the same reference EPMA vvas used also to determine the composition of the eutectic FeO - 3Fe0P205 obtained at surface oxyda-tion of an Fe - 0.092% P alloy. In the follovving čase EPMA vvas used also in the investigation of the selective oxydation of iron. In iron al-loys vvith copper, arsenic, tin, and antimony by EPMA point, line and scanning analyses the sequence of forma-tion of solid and liquid phases in binary, ternary and qua-ternary equilibria vvas established as consequence of selective oxydation, f.i.: Y Yi + Yi + «i + 'Pi y Yi + lp2 Yt + «i + IP2 Yi + ai + 'Pi + !Pa vvith a, y as solid and lpi, lp2 as liquid phases. Figure 2: Optical, back scattered electrons and X rays scanning pictures of different elements in the segregated layer after air surface oxydation of an iron alloy at I200°C. Ref.3 and 4 Slika 2: Optični, elektronski in specifični X posnetki za različne elemente v segregirani plasti na železovi zlitini po oksidaciji na zraku pri 1200°C. Ref. 3 in 4 For EPMA methodology it is of special importance the fact that the distribution of segregated elements vvas demonstrated also by scanning elemental pictures (figure 2). No use of EPMA vvas found in printed vvorks of Slovenian scientists up to the start of the facility put in operation in 1969. Figure 1: Distribution of arsenic in the segregated layer of an Fe-0.075% As alloy after surface oxydation at 800 and 1000°C determined by electron probe microanalysis (EMA). Ref, 1 and 2 Slika 1: Porazdelitev arzena v segregirani plasti zlitine Fe-0.075% As po oksidaciji pri 800 in 1000°C določena z elektronsko mikroanalizo (EMA). Po virih 1 in 2 3 SOME DATA ON THE OPERATION OF EPMA FROM 1969 TO 1974 EPMA vvas ready for qualitative and semiquantitative vvork in april 1969. In table 1 statistics on the vvork up to m : ...... m Ss# w . ŠK % 3........... m • O j % \ j j^C, o S f • ' V ; ■'>■: 'V' f>< y' •VV/r: A': fX "M .... M ZSBTf« Ai avMcfMo O S S: Figure 3: Optical, back scattered electrons and X rays scanning pictures of different elements. Spherical nonmetallic inclusion in steel. Ref. 9 Slika 3: Optični, elektronski in specifični X posnetki za različne elemente. Kroglasti nekovinski vključek v jeklu. Po viru 9 1974 are shown. Allready in the first year the work per-formed for users outside of the Institute of metallurgy reached a level vvhich did not change significantly up to 1974. This level shovvs that EPMA was really needed and also satisfactorily exploited. Methods for qualitative and quantitative investigations for basic, applied, and de-velopment research as vvell as routine analysis for different institutions and industrial companies from geology, mineralogy, metallurgy, ceramic, building materials, electronics, and even forensic cases vvere developed fastly. The reader can have an idea on the level of quality and accuracy from the scanning picture in figure 3 as vvell as the composition of carbides and nonmetallic in-clusions in table 2. netics to less than half of the so far prescribed length10. It vvas established also that after homogenisation a virtually ideally homogeneus distribution vvas obtained in some cases, vvhile in čase of mutual interactivity also after long tirne homogenisation the average segregation vvas approaching a level significantly far from homogeneity. 4 EPMA IN THE RESEARCH OF D. KOLAR D. Kolar and his research collaborators vvere frequent clients of the EPMA laboratory during the first year vvith different topics from ceramic magnets, hard metals and phase equilibria diagrams. Several papers based signifi- Table 1: Clients for EPMA work Year Academic institutions Companies Payed working hours Articles1 1969 10 14 1276 1970 12 17 1330 6 1971 12 10 1335 8 1972 12 11 1330 5 1973 10 11 1301 2 1974 11 17 1241 10 In the year 1969 to 1974 54 different institutions and companies com-mitted once or several times EPMA vvork, 29 ind. companies commit-ted the investigation from 1 to 18 different specimens yearly. ' - Authors from the EPMA laboratory Table 2: Composition of nonmetallic inclusions and carbides F. Vodopivec und B. Ralic: Radex Rundschau (1975) 1, 289-294 Inclusion1 MnO FeO CaO Vsota ut.% 1 28.0 8.3 - 63 - 99.3 2 16.4 2.3 37.8 7.5 36.0 100 3 55.5 6.3 31.1 5.9 - 99.8 4 50.3 6.3 32.4 9.7 - 98.6 5 21.4 4.6 30.4 2.4 41 99.8 Carbide2 W V Fe Cr Mo C M6C2 56.0 3.1 28.6 4.75 2.25 1.93 (Wi.6Fe3.3Vo.36Cro.56Ci) MC 14.2 57.2 3.3 7.65 1.6 16.95 (Vp.91 Wo.()6Feo.()5Cr(). 11 Mop.o i C i) Correction calculation after Bence-Albee 1 6 8 ' Correction calculation after Philibert and Reed vA /V \ j \/ v' /v V" \ i ir, V M f \ H / N ^ 650 °C. !h Ilhš5 Ca J In combination vvith optical microscopy it vvas possible to find reliable ansvvers also for significant techno-logical problems, f.i. inhomogenity and kinetics of homogenisation of steels as vvell as copper and aluminium alloys, composition of nonmetallic phases in steels and alloys. The allready mentioned figure 3 shovvs a non me-tallic inclusion enriched at the surface by calcium and sulphur9. This vvas one of the first proofs for the reaction betvveen calcium bounds to aluminate or alumosilicate inclusions vvith sulphur in the liquid steel. The homoge-nising times for aluminium and copper alloys vvere di-minished on the base of investigations of segregation ki- 650 =C Figure 4: Distribution of alloying elements in an Cu 8% Sn 0,38% P alloy as čast and after homogenisation. Ref. 10 Slika 4: Porazdelitev legirnih elementov v zlitini Cu 8% Sn 0.38% P po litju in po homogenizaciji. Po viru 10 cantly on EPMA vvork were printed in international jour-nals. The authors is avare of the possibiIity that some of the phase diagrams were later modified on the base of results of improved EPMA. Also if it happened, it could not change the type of phase diagrams which have there-fore a permanent value. The ambition of the author of the present survey is not to present ali the vvork of D. Kolar in the quoted years, but to shovv that D. Kolar vvas prepared for EPMA and prepared to exploit optimally the nevv research facil-ity in Slovenia due to the putting in operation of EPMA and vvas able in this way to improve considerably the scientific value of his investigations. Figure 4 is taken from ref. 11, vvhere Drofenik and Kolar reported on the effect of BijOi addition on sintering process and properties of strontium ferrite. The atten-tion of the reader is called on the quality of electron and scanning pictures in figure 4. vvhere details near the size of |im are discernible. The morphology of bismuth oxyde containing phase shovvs that it fills as liquid spaces betvveen polyhedric grains of ferrite vvith higher melting point. EPMA shovved in this phase 50% BiiOj, 31% Fe203 and 19% of SrO. It vvas concluded that the addition of bismuth oxyde lovvered the sintering temperature and inereased the volume density and energy product (BH)m. In the same year Komac, Golič, Kolar, and Brčič12 es-tablished the crystal strueture, phase composition and transformation temperatures in binary phase equilibria systems US-CaS, US-SrS and US-BaS. EPMA vvas used for the determination of solid solubilities and eutectic compositions shovvn in table 3, vvhile figure 5 presents the phase diagrams US-CaS and US-BaS. Jurca, Kolar and Trontelj investigated the effect of nickel on activated sintering of tungsten and established that nickel is not found in solid solution in tungsten in a deteetable con-tent and that also at grain boundaries nickel is not found in appreriable quantity13-14. 1.2 to 2.8% vvas found for the solid solubility of tungsten in silver, vvhich is lovver than the value found in published phase diagrams. H00 - *N 1 v 1 \ \ \ ) 1"0' N----- 1 1 X 1 1 j 1710' j' \ t 1 1 tn 1 1 l | t—> [Mol V.) Figure S: Back scattered electron and X rays scanning pieture for different eiements. Sintered strontium titanate with addition of Bi2Oi. Ref. 11 Slika 5: Elektronski in specifični X posnetki za različne elemente. Sintran stroncijev titanat z dodatkom Bi203. Po viru 11 10 50 I Mol 7. Figure 6: Phase diagrams US-CaS and US-BaS. Ref. 12 Slika 6: Fazna sistema US-CaS in US-BaS. Po viru 12 2100 2200 2000 ' 1800 : 1600 ' 1100 1730' v __ Figure 7: Phase diagrams NbC-Fe and NbC-Cr. Ref. 15 Slika 7: Fazna diagrama NbC-Fe in NbC-Cr. Po viru 15 Table 3: Phase composition in binary phase equilibria systems US-CaS, US-BaS in US-SrS M. Komac, L. Golič, D. Kolar and B. S. Brčič: J. Less-Common Metals, 24 (1971) 121-128 System Phase US-CaS US-SrS US-BaS Solid solution US',% 3.5 3.5 3.0 Solid solution MS',% 4.0 n.d. n.d. Intermediate phase,% 50 50 50 CaUS2 SrUS2 BaUS2 Eutectic 1,% 33.0 33.0 38.0 Eutectic 2,% 50.5 53.0 n.d. ' - Maximal solubility by eutectic temperature Guha and Kolar15 investigated the phase equilibria diagrams niobium carbide with transition metals iron, chromium, nickel, and cobalt. Solid solubilities and eutectic compositions are shown in table 4 and the phase systems NbC-Fe and NbC-Cr in figure 6. Eutectic points are deplaced near the metal side and the solid solubilities are in the range 1 to 4.3% Guha and Kolar16 investigated also the phase diagrams TiC-Cr and ZrC-Cr in figure 7. EPMA results in table 5 indicate small solid solubility and eutectic point deplaced on metal side. Weight percent Cr Weiqh( oercent Cr Figure 8: Phase diagrams TiC-Cr and ZrC-Cr. Ref. 16 Slika 8: Fazna diagrama TiC-Cr in ZrC-Cr. Po viru 16 Table 4: Phase composition in binary phase equilibria systems NbC-Fe, NbC-Cr, NbC-Ni, and NbC-Co J. P. Guha and D. Kolar: J. Less-Common Metals, 29 (1972) 33-40 System Eutectic_Solid solution',wght.% _wght.% metal metal in NbC NbC in metal NbC-Fe 91.2 1.8 0.98 NbC-Cr 76.0 2.8 0.85 NbC-Ni 89.0 1.8 3.5 NbC-Co 88.0 L2__4.3 1 - Maximal solubility by eutectic temperature Table 5: Phase composition in binary phase equilibria systems TiC-Cr and ZrC-Cr J. P. Guha in D. Kolar: J. Less-Common Metals, 31 (1973) 331-343 System Eutectic Solid solution ',wght.% Metal, wght.% Metal in Carbide in carbide metal TiC-Cr 89.0±0.5 3.5 3.5 ZrC-Cr 88.0±0.5 4.5 0.2 1 - Maximal solid solubility at eutectic temperature Finally Guha and Kolar17 established also the phase diagram BaTi03-BaGeC>3 on figure 8 and 9, determined Mol 7. 8aCe0j Figure 9: Phase diagram BaTi03-BaGe03. Ref. 17 Slika 9: Fazni diagram BaTi03 - BaGeOj. Po viru 17 the liquidus and solidus temperature, the eutectic composition as vvell as the solid solubilities 1 of mol % BaTi03 in BaGeO., and 2.2 mol % of BaGe03 in BaTiOj at eutectic temperature. 5 CONCLUSION The slovenian research community obtained relativen late the possibility to use EPMA at acceptable time and expense as standard research method for in situ quali and quantitative investigations of solid materials. Statistical data show that the community was well pre-pared for the use of the new facility. For that reason, the use expanded relatively fast in research academic and in-dustrial laboratories in metallurgy, geology, mineralogy, ceramic, building materials and electronics. On average, in the first years more EPMA work was performed for industrial companies than academic institutions. D. Ko- lar was between the researchers which did profit the must from EPMA. Based on optical microscopy and EPMA he and his collaborators reported in international journals on significant findings on topics of magnet ce-ramics and binary phase equilibria systems of metals and carbides as well as sulfide compounds. It is therefore justifield to conclude that D. Kolar helped greatly to strengthen EPMA as rutine investigation method for ba-sic, applied and development research of metallic and non metallic materials. 6 REFERENCES 1 F. Vodopivec: Dr. thesis, University of Pariš, 1962 2F. Vodopivec, A. Kohn, J. Philibert et J. Manenc: Revue de Metallur-gie, 60 (1963) 801-818 3 L. Kosec: Mag. thesis, University of Ljubljana, 1967 4 L. Kosec, F. Vodopivec et R. Tixier: Metaux-Corrosion-Industries, (1969) No.525, 1-25 5F. Vodopivec und B. Ralic: Radex-Rundschau, (1975) 1, 289-294 6J. Philibert: Metaux-Corrosion-Industries, 40 (1964) no. 465, 157-176, no. 466, 216-240, no. 469, 325-342 7 A. E. Bence and A. L. Albee: J. ofGeology, 76 (1968) 382-403 8S. J. B. Reed: Brit J. Applied Physics, 16 (1965) 913-926 9F. Vodopivec in B. Ralic': Železarski zbornik, 6 (1972) 215-229 l0L. Kosec, A. Podgornik in B. Ralic: Rudarsko Metalurški Zbornik, 4 (1972) 417-428 " D. Kolar and M. Drofenik: Proceedings of the British Ceramic Soci- ety, N 18 1970 125-138 12 M. Komac, L. Golič, D. Kolar and B. S. Brčič: Journal of Less-Com- mon Metals, 24 (1971) 121-128 13S. Jurca, D. Kolar and M. Trontelj: Activated sintering of Tungsten: Proceedings ofthe Inf. Conf. on Powder MetaUurgy, Zakopane, 1971, 247-258 14D. Kolar, S. Jurca and M. Trontelj: Rudarsko Metalurški zbornik, (1970) 1,35-41 15J. P. Guha and D. Kolar: Journal of Less-Common Metals, 29 (1972) 33-40 l6J. P. Guha and D. Kolar: Journal of Less-Common Metals, 31 (1973) 331-343 17 J. P. Guha and D. Kolar: J. Materials Science, 7 (1972) 1192-1196