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Lunar and Planetary Science XXX 1749.pdf

INTERSTELLAR : I. CONDENSATION AND NUCLEATION. Andrew W. Phelps, University of Dayton Research Institute, Materials Engineering Division (300 College Park, Dayton OH, 45469-0130, [email protected]).

Introduction: The formation mechanism(s) of (3C) is formed by the ABCABC.... stacking of meteoritic and interstellar diamond dust grains has planes in the (111) direction and 2H diamond been a subject of debate for many years but few is formed by the ABAB.... stacking of carbon planes explanations have provided the predictive tools with along the c-axis of its hexagonal lattice. The next which to further explore and understand diamond nearest neighbor bonding is identical in all of the grain formation by direct astronomical observation. polytypes but the symmetry of the structure is The discovery that some of these carry pre- different. 2H diamond has a "boat" structure as solar isotopic xenon ratios means that they have contrasted with the chair structure of cubic [1] survived intact since before the formation of the solar diamond . The existence of was system. predicted in the early 1960s based on anomalous x- ray diffraction lines found in some natural diamond The first step in exploring diamond formation in crystals and based on diamond's similarity to silicon space is to set all that is 'known' about how diamond carbide[3] and was discovered in some and forms, how forms, their stability during meteor craters and was synthesized in the laboratory equilibrium, and anything else that places a genetic between 1965 and 1967[4,5]. The structures of the interpretation on what should be, at first, strictly an polytypes of diamond have recently been observational exercise. A natural temptation is to reviewed[1,6-8]. assign a genetic interpretation to a set of facts. However, it can be very difficult to retrace one's steps Diamond polytype identification is possible with and start fresh if an incorrect genetic interpretation is infrared and Raman spectroscopy and electron and X- [6-9] [10,11] [12] prematurely applied. ray diffraction . The 4H, 8H , 6H , 15R[13], and 21R[14,15] diamond polytypes have been Diamond grains are found in all manner of identified using this information. interstellar material. Meteorites that exhibit large amounts of alteration, deformation and shear such as Table 1. X-ray d-spacing for diamond polytypes. Å 3C 2H 4H 6H 8H 10H-2 10H-1 15R 21R and , meteorites that appear D I I I I I I I I I relatively unaltered such as , metal-rich 2.18 100 28 10 5 8 11 3 meteorites, and chondritic porous (CP) aggregate 2.17 9 4 29 9 2.16 37 have all been identified as carriers of 2.15 43 24 diamond, graphite, and other . The 2.14 26 60 29 mineralogical record of diamond in meteorites is 2.11 100 100 2.08 100 100 80 fairly well documented but requires a thorough re- 2.06 100 50 57 100 80 65 84 100 100 analysis with modern analytical techniques. The 2.03 96 24 2.01 56 19 published diffraction and vibrational spectroscopic 1.96 31 data contains large gaps and sometimes suffers from 1.95 11 having been ‘pre-analyzed’. This and the following 1.93 50 18 14 2 46 6 1.90 12 paper in this series will attempt to bring some of the 1.84 43 3 1 existing data on meteoritic, synthetic, and terrestrial 1.75 5 0 1 diamond together with current understanding about 1.67 2 1 2 1.58 0 2 diamond formation processes to develop a predictive 1.50 17 2 1 1 model of interstellar diamond formation and 1.42 0 4 3 1.37 5 occurrence. 1.36 2 Diamond polytypes: Diamond exists in several 1.35 15 15 5 8 3 1.28 23 23 10 crystalline forms called polytypes that can have 1.26 25 29 33 35 44 37 48 37 32 cubic, hexagonal, or rhombohedral symmetry[1]. 1.24 22 Most terrestrial diamond is cubic while that found in 1.22 5 15 4 1.18 10 4 meteorites may have any of the three forms above. 1.16 27 23 10 8 23 1 3 There is only one form of cubic diamond but there 1.14 8 are several hexagonal, and rhombohedral diamond 1.10 8 7 2 2 1.09 4 1 2 1 3 polytypes. The best known polytype other than 1.08 16 16 18 19 29 20 32 21 15 diamond is lonsdaleite (2H diamond) which is the 1.07 6 3 1 2 carbon equivalent of wurtzite[2]. The diamond 1.06 3 3 1 1 3 3 polytypes are characterized by the stacking Table 1 is useful for identifying diamond arrangement of their carbon layers. Cubic diamond polytypes based on their d-spacing. The intensities of Lunar and Planetary Science XXX 1749.pdf

INTERSTELLAR DIAMOND. I. CONDENSATION AND NUCLEATION: A. W. Phelps

the various bands were calculated for X-ray exposed to more hydrogen and oxygen than it will diffraction but may be applied equally well to ever be to fellow un-reacted carbon atoms. The vast electron diffraction. Electron diffraction is preferred bulk of all carbon found near its source star should be to X-ray diffraction for identifying the different in the form of light hydrocarbons and CO. diamond phases due to the low X-ray scattering cross Diamond can form from nearly any carbon source section of diamond. Data has been collected from under the right circumstances and condensed [6,9] several sources . Using this table it is possible to graphitic carbons and PAH’s could and probably do review some diffraction data for meteoritic diamond form some amount of interstellar diamond. However, and see that much more structural information is Occam’s razor requires that diamond be formed via available than previously thought. the simplest method from the most prevalent source The diffraction patterns for Novy Urey, Dyalpur, materials[24]. The gasses around a carbon star would and Goalpara diamonds reported by provide a suitable feedstock source and diamond Vdovykin[16] indicate not only cubic and 2H phases growth would not have to rely on random collisions but other hexagonal and rhombohedral phases as with other bits of condensed carbonaceous well. Novy Urey seems to be limited to cubic, 2H, materials[25]. and 8H diamond, while Dyalpur, shows evidence of Many types of diamond are found in many types 6H, 8H, and 10H polytypes and Goalpara shows of meteoritic material. The variation in polytype evidence of the 8H, 10H, and 21R polytypes in abundance appears to reflect the nature of the host. addition to the cubic and 2H phases. The Haverö How the diamonds got there and what they mean will [17] ureilite appears to have 8H and 10H-1 polytypes be examined with their nucleation and growth in the [18] in addition to cubic and 2H diamond . The North second paper in this series. Haig ureilite appears to have a mixture of 2H, 6H, Acknowledgment: This work is supported in and 8H polytypes[19]. Data presented by Clarke et al.[20] suggests that Allan Hills A77283, an iron part by the NASA Office of Space Sciences under similar to Canyon Diablo, has some 15R Grant no. #NAG5-4575. in addition to 2H and that a sample of Canyon Diablo References: [1]Spear K. E. et al., J. Mater. Res. may have some 21R. Data presented for several CP 5, 2277-85 (1990). [2]Verma A. R. and Krishna P., aggregates and carbonaceous chondrites by Polymorphism and Polytypism in Crystals (Wiley, Rietmeijer and Mackinnon[21] suggest that two CP NY 1966). [3]Ergun S. and Alexander L. E., Sci. aggregates (W7029*A and W7010*A2) have a 21R 156, 1770-1 (1967). [4]Frondel C. and Marvin U. B., polytype component in addition to the 2H already Nat. 214, 587-689 (1967). [5]Bundy F. P. and observed. A third CP grain (W7029*A) seems to Kasper J. S., J. Chem. Phys. 46, 3437-46 (1967). have mostly 2H, 6H, and 8H polytype components. [6]Phelps A. W. et al., Mater. Res. Soc. Symp. Proc. Data for the three carbonaceous chondrites appears to 162, 213-7 (1990). [7]Phelps A. W. et al., J. Mater. be significant in that only the 8H polytype appears to Res. 11 (1993). [8]Phelps A. W., Ph. D. Thesis, Penn be present with 2H diamond in Allende CV3 and State, 1990. [9]Holcombe C. E., USAEC Report Y- Cold Bokkeveld C1 and that 8H and/or 10H-1 1887 (1973). [10]Howard W. N. et al., 2nd New polytypes appear to be present in Orgueil C1. Re- Diamond Sci. Tech. Conf., Pittsburgh, 1991. indexing old diffraction patterns is not limited to [11]Howard W. N. et al., J. Appl. Phys. 68, 1247-51 meteoritic diamond. The diffraction pattern for (1990). [12]Frenklach M. et al., J. Appl. Phys. 66, ‘’ from a shocked graphitic gneiss in the Ries 395-9 (1989). [13]Kapil R. et al., Thin Sol. Films Crater[22,23] indexes to a mixture of lonsdaleite and 312, 106-10 (1998). [14]Kapil R. et al., Appl. Phys. 15R diamond. This is not too surprising in light of Lett. 68 (18), 2520-2 (1996). [15]Klein C. A. et al., the fact that the material is found intercalated with Electrochem. Soc. Proc. 91-8, 435-42 (1991). graphite and that hexagonal and rhombohedral [16]Vdovykin G. P., Carbonaceous Matter in polytypes share a basal plane very similar to that of Meteorites, NASA, 1970). [17]Vdovykin G. P., graphite[1,6,7]. Meteor. 7 (4), 547-52 (1972). [18]Marvin U. B. and Carbon Source: Identifying the source of carbon Wood J. A., Meteor. 7 (4), 601-10 (1972). in interstellar diamond grains may not be as simple as [19]Vdovykin G. P., Dokl. AN SSSR 186, 1171-3 locating a nearby carbon star. Carbon particles are (1969). [20]Clarke R. S., Jr. et al., Nat. 291, 396-8 usually described as condensing from energetic (1981). [21]Rietmeijer F. J. M. and Mackinnon I. D. carbon atoms and much work has gone into modeling R., Nat. 326, 162-5 (1987). [22]El Goresy A., Naturwiss. 56, 493-4 (1969). [23]El Goresy A. and Cx clusters as the starting points for carbon grain nucleation. However, the physical chemistry of Donnay G., Sci. 161, 363-4 (1968). [24]Anders E. carbon makes this scenario unlikely. Energetic and Zinner E., Meteor. 28, 490-514 (1993). carbon atoms and radicals are extremely reactive and [25]Blake D. F. et al., Nat. 332, 611-3 (1988). their source stars are principally sources of hydrogen, helium, and oxygen. A hot carbon atom will be