Diffusion coefficients for S-Se interdiffusion in tiemannite (HgSe) single crystals have been determined in the temperature range 500 -700oC. The measured diffusivities may be fit by the equation..

Boctor, Nabil Z.

Brady, John B.

English

Smith College: Smith ScholarWorks

Smith ScholarWorks Geosciences: Faculty Publications Geosciences 1980 Interdiffusion of S and Se in Tiemannite Nabil Z. Boctor Carnegie Institute of Washington John B. Brady Carnegie Institute of Washington, jbrady@smith.edu Follow this and additional works at: https://scholarworks.smith.edu/geo_facpubs  Part of the Geology Commons Recommended Citation Boctor, Nabil Z. and Brady, John B., "Interdiffusion of S and Se in Tiemannite" (1980). Geosciences: Faculty Publications, Smith College, Northampton, MA. https://scholarworks.smith.edu/geo_facpubs/209 This Article has been accepted for inclusion in Geosciences: Faculty Publications by an authorized administrator of Smith ScholarWorks. For more information, please contact scholarworks@smith.edu American Mineralogist, Volume 65, pages 797-799, 1980Interdiffusion of S and Se in tiemanniteNesrL Z. BocroR AND JoHN B. BRADYGeophysical Laboratory, Carnegie I nstitution of Washingtonll/ashington, D. C. 20008AbstractDi-ffusion coefficients for S-Se interdi-ffusion in tiemannite (HgSe) single crystals have beendetermined in the temperature range 500"-700oC. The measured diffusivities may be fit bythe equationD:(s.7 x lo-r2) "*o*fr#cm2lsecAn activation energy for S-Se interdi-ffusion of 105 kJlmole is derived from the diffusiondata. The S-Se interdi-ffusion coefficients are larger than sulfur self-diffusion coefficients insulfides that have the same crvstal structure as tiemannite.IntroductionTo date most studies of sulfur diffusion have beenconcerned with the self-diffusion of this element insulfide minerals such as pyrrhotite, Fe,-,S (Condit elal., 1974), sphalerite, ZnS (Gobrecht et al., 1967)wurtzite, ZnS (Blount et al., 1967) and hawleyite,CdS (Kumar and Kroger, l97l; Sysoev et al., 1969).No data on sulfur diffusion in selenide-type mineralsare known. Tiemannite, HgSe, commonly containsminor amounts of sulfur substituting for Se in itsstructure. In some localities, however, the iso-morphous substitution of S for Se is very extensive.Almost the entire range of HgSe-HgS compositionshas been observed in nature, as at the Lucky BoyMine, Marysvale District, Utah (Bethke, 1957; Boc-tor, 1976). Tiemannite was selected for investigationof sulfur diffusion in selenide-type minerals because(l) equilibrium relations in the Hg-S-Se system arewell known (Boctor, 1976) and (2) high-purity singlecrystals of HgSe were available.Experimental methodsTiemannite is typically a nonstoichiometric com-pound. It may contain an excess of mercury over se-lenium of l.l-1.8 atom percent or an excess of sele-nium over mercury of 0.2-0.9 atom percent in thetemperature range 230"-700"C (Boctor and Kulle-rud, 1979). The tiemannite crystals used were all rec-0003-004x/80/0708-0797$02.00tangular slabs (-5 x 3 mm) cut from a large singlecrystal grown by the vapor-transport method in thepresence of excess mercury (Laboratory for CrystalGrowth, Purdue University). The crystals were com-positionally homogeneous and contained 1.3 atompercent excess Hg. The tiemannite crystals were pol-ished and completely surrounded by tightly packed,powdered synthetic cinnabar, HgS (<0.063 pm in di-ameter), in silica tubes with closely fitting silica rodsto reduce the vapor volume. The silica tubes wereevacuated. sealed under vacuum. and annealed at700o, 600", and 500oC, respectively, for periods of168, 288, and 408 hr. The vapor pressure over thecharges was that of the system, and no attempts weremade to control the sulfur or selenium fugacities. Ineach experfunent, the tiemannite crystal retained itsform and polished surfaces and was easily separatedfrom the HgS powder after the run. Compositionalprofiles were determined with the electron micro-probe from polished cross sections of each tiemannitecrystal. For Hg analyses, Ma ndiation was used; forS and Se analyses, Ka radiation was used. SyntheticHgSe was used as a standard for Se and Hg. TheHgS, provided by Materials Research Company, wasused as a standard for S. Atomic number, absorptionand fluorescence corrections of raw electron micro-probe data were performed with the MAGIC IV com-puter program of Colby (1971).797Downloaded from http://pubs.geoscienceworld.org/msa/ammin/article-pdf/65/7-8/797/4215670/am65_797.pdfby Smith College useron 25 March 2024BOCTOR AND BRADY: TIEMANNITEExperimental resultsMembers of the HgSe-HgS solid-solution seriesare cubic (sphalerite structure) above 345oC. Diffu-sion rates should therefore be independent of diffu-sion direction in tiemannite, a prediction confirmedby the results. Typical sulfur compositional profilesare shown in Figure I along with curves previouslyfitted to the data on probability paper (cl de Silvaand Mehl, 1951, p. 16l). Within the limits of accu-racy of the electron microprobe (t2 percent of themeasured concentration), the tiemannite crystalshave remained binary [(S + Se): Hg constant] duringthe diffusion experiments. Therefore, the boundaryconditions of the experiment are suitable for theBoltzmann-Matano solution (Matano, 1933). Thepreserved polished surface of each tiemannite crystalmarks a surface across which there has been an equaland opposite net flux of sulfur and selenium; thus thepolished surfaces are by definition Boltzmann-Ma-tano interfaces for these experiments. Although datawere not obtained for the selenium distribution in theHgS powder, knowledge of the location of the Boltz-mann-Matano interface permits the determination ofdiffusivities from the llsmxnnite 5ingle-crystal pro-files alone. A discontinuity in physical properties atthe interface between the tiemannite single crystaland the HgS powder does not preclude the use of theBoltzmann-Matano solution (Jost, 1950; Appel,1968).Fig. 1. Compositional profiles measured with the electronmicroprobe of the sulfur content of the tiemannite crystals withrespect to distance from the crystal surface. The curves are a bestfit ofthe data obtained using probability graph paper.Table L lnterdiffusion coefficients for S and Se in tiemannites / ( s  +  s e ) o,  cm2fsec7007006006005005000 . 50 . 20 . 50 . 20 . 50 . 23 . 52 . 70 . 91 . 17 . 21 . 1( 1 1 . 0 )  x  1 0 - 1 1( 1 1 . 0 )  x  1 0 - I 1( 1 0 , 8 )  x  1 0 - 1 1( t 1 . 0 )  x  1 0 - 1 1( 1 0 . 5 )  x  1 0 - 1 2( 1 0 . 5 )  x  1 0 - 1 2ESlopes and areas were obtained graphically fromthe compositional profiles and used to compute thediffusion coefficients listed in Table l. Uncertaintiesare based on the reproducibility of electron micro-probe and graphical determinations. No concentra-tion dependence of the interdifusion coefficients canbe verified within the limits of precision, although itappears that more sulfur-rich compositions yieldslightly higher diffusivities. Because the variation ofmolar volume with composition is not known, thediffusion coefficients could not be corrected for pos-sible volume effects. The measured diffusivities canbe expressed by the equationP : (5.7 x lO-''?) "*n fffi cm',/secAn activation energy for S-Se interdiffusion of 105kJlmole is derived from the data.DiscussionThe interdiffusion coefficients determined for tie-mannite are larger than sulfur self-diffusion coeffi-cients in sulfides with the same structure. such assphalerite (Gobrecht et al., 1961). This result is con-sistent with the suggestion of Stevenson (1973, p.435) that interdiffusion coefficients for the chalcoge-nides, because of thermodynamic nonideality, are ex-pected to be much larger than the self-diffusion coef-ficients. The activation energy for S-Se interdi-ffusiondetermined in this study is also within the range re-ported by Stevenson (1973, Table 7.1) for similarminerals.Mercury ores are believed to form in the temper-ature range 100"-250oC (Dickson, 1964). Membersof the tiemannite-metacinnabar series occasionallyshow compositional zoning (Bethke, 1957). The fastdiffusion rates at high temperatures we obtained sup-port a low-temperature origin for these ores. If themercury ores had experienced high temperatures,compositional zoning might not be preserved. Astudv of S-Se interdiffusion under hydrothennalDownloaded from http://pubs.geoscienceworld.org/msa/ammin/article-pdf/65/7-8/797/4215670/am65_797.pdfby Smith College useron 25 March 2024BOCTOR AND BRADY: TIEMANNITE 799conditions and an evaluation of the effect of varia-tions in l(S,) and /(Se) on the difusion coemcientsare needed, however, before the data can be appliedquantitatively to mercury ores.AcknowledgmentsThe authors are grateful to Drs. A. W. Hofmann, H. K. Mao,and H. S. Yoder, Jr., for critical comments on the manuscript.ReferencesAppel, M. (1968) Solution for Fick's 2nd law with variable diffusi-vity in a multi-phase system. ScrQrd Melallurgica, 2,217-222.Bethke, P. M. (1957) The Sulfoselenides of Meranry and Their Oc-currence at Marysvale, utah. Ph.D. Thesis, columbia Univer-sity, New York.Blount, H. G., G. A. Marlor and H. B. Richard (1967) Self diffu-sion of S in ZnS. "/. Appl. Phys., 38,3995.Boctor, N. Z. (19'16) The Mercary-Selenium-Sulfur System and ltsGeological Implications. Ph.D. Thesis, Purdue University, WestLafayette, Indiana.- and G. Kullerud (1979) Phase relations in the mercury-se-lenium system. In V. A. Zhaikov, V. I. Fonarev and V. A.Karikovshii, Eds., Problems of Physical-Chemical Petrology.Academy of Sciences, USSR, in press.Colby, J. W. (1971) MAGIC IV, a computer program for quan-titative electron microprobe analysis. Bell Telephone Laborato-ries, Allentown, Pennsylvania.Condit, R. H., R. R. Hobbins and C. E. Birchenall (1974) Self-dif-fusion of iron and sulfur in ferrous sulfide. Oxid. Met., 8, 409=455.de Silva. L. C C. and R. F. Mehl (1951) Interface and markermovements in difusion in solid solutions of metals. ?rans.AIME, t91,155-t73.Dickson, F. W. (1964) Stability of cinnabar in NarS solutions at50 to 250'C and l-1800 bars with geologic applications. Econ.Geol., 59,625-635.Gobrecht, H., H. Nelkowski, J. W. Baars and M. Weigt (1967) Selfdiffusion of sulfur in zinc sulfide. Solid Stote Comm., 5,777-778.Jost, W. (1950) Bemerkung zur mathematischem Behandlungkomplizierter Diffusionsprobleme. Z. Phys., I 27, 163-167 .Kumar, V. and F. A. Kroger (1971) Self ditrusion and the defectstructure of CdS. J. Solid State Chem., 3, 387-4ffi.Matano, C. (1933) On the relation betwcen the diffusion coefr-cients and concentrations of solid metals. Iap. J. Phys., 8, lO9-I  13 .Stevenson, D. A. (1973) Diffusion in the chalcogenides of Zn, Cd,and Pb. In D. Shaw, Ed., Atomic Dffinion in Semiconductors, p.431-542. Plenum Press, New York.Sysoev, L. A., A. Y. Gel'fam, A. D. Kovaleva and N. G. Krav-chenko (1969) Measurements of the coefficients of self diffusionof sulfur in CdS microcrystals. Izv. Akad. Nauk SSS.R Neorg.Mater., 5,2208-2209.Manuscript received, October 15, 1979;acceptedfor publication, April 14, 1980.Downloaded from http://pubs.geoscienceworld.org/msa/ammin/article-pdf/65/7-8/797/4215670/am65_797.pdfby Smith College useron 25 March 2024

Interdiffusion of S and Se in Tiemannite

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Interdiffusion of S and Se in Tiemannite

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