Natural Molybdenite Research Articles

THE SYSTEM Os-Mo-S

Phase relations in the system Os–Mo–S were studied in a 1000°C isothermal section by the technique of evacuated silica glass tubes. Molybdenite forms stable assemblages with erlichmanite (OsS2) and osmium, whereas Mo2S3 coexists with Os, Mo and Mo–Os alloys. Experiments aimed at the determination of the solvus between MoS2 and OsS2 were conducted at temperatures in the range 600–1200°C. Molybdenite dissolves 0.24 and <0.2 at.% Os at 1200°C and 1000°C, respectively; below 1000°C, the Os content is below 0.1 at.%. Concentrations of Os in natural molybdenite are extremely low, on the order of ppb, and therefore are extremely unlikely to reach the experimentally established limit of solubility. Erlichmanite is stable in the stability field of pyrrhotite, which corresponds to a geologically common activity of sulfur. Therefore, Os is expected to be bonded to sulfide under the same conditions under which molybdenite occurs in nature.

Electronic “Edge” State on Molybdenite Basal Plane Observed by Ultrahigh-Vacuum Scanning Tunneling Microscopy and Spectroscopy

An electronic state heretofore unreported has been found on a cleaved basal plane of a natural molybdenite (MoS2) single crystal by ultrahigh-vacuum scanning tunneling microscopy (UHV-STM), and examined in detail both by STM and scanning tunneling spectroscopy (STS). The new electronic state resides on the edge of the upper terrace of MoS2(0001), manifesting itself in the form of bright ridges with a width of ca. 4 nm along the step edges in negatively sample-biased STM images. This ridge structure is nonexistent in STM images taken with positive sample biases. STS showed that the local density of states (LDOS) on such ridge structures is much higher than that on the terraces in the range of 0.2–1.2 eV below the Fermi edge. The nature and origin of this high LDOS at the step edges are discussed.

Cobalt Chemical Vapor Deposition Process on Molybdenite Basal Plane Observed by Ultrahigh-Vacuum Scanning Tunneling Microscopy

The processes of high-temperature (473 K) resulfidation and cobalt carbonyl adsorption by chemical vapor deposition (CVD) on a cleaved basal plane of a natural molybdenite (MoS2) single crystal were examined by ultrahigh-vacuum scanning tunneling microscopy (UHV-STM) on the nanometer scale. The resulfided cleaved molybdenite basal plane showed a displacement of upper terraces, and a sinusoidal structure at step edges, both of which may be caused by the electronic effect at the surface. Cobalt carbonyl appeared to be adsorbed at both the S- and Mo-terminated edges, resulting in an agglomeration at the step edges on lower terraces with a width of a few tens of nanometers. When this surface with adsorbed carbonyl was sulfided at 513 K for 1 h, most of the adsorbed carbonyl clusters appeared to be desorbed while a small part were dispersed on the terraces in small clusters of 10–20 nm in size. The obtained results are discussed in terms of the preparation of Co-Mo hydrodesulfurization (HDS) catalysts.

Structural change of mechanically activated molybdenite and the effect of mechanical activation on molybdenite

denite is also used as an important raw material of oxidization roasting for the preparation of ammonium molybdate in molybdenum industry [7,8] and as one of the main naturally metallic minerals associated with gold. [9] Furthermore, the extraction of nonferrous metals from sulfide ores belongs to the technically difficult and economically important tasks. The more chemically stable the sulfide, the more difficult the extraction is. Thus, either drastic reaction conditions have to be applied or the chemical stability of sulfides has to be modified by a suitable chosen preleaching treatment. The mechanical activation of the ore by intensive grinding is a typical representation of the second way. [10] In our previous investigation, [11‐16] mechanical activation of galena, pyrite, and sphalerite can effectively reinforce the corresponding hydrometallurgical processes, but galena, pyrite, and sphalerite have different mechanisms of mechanical activation, which owes to different structural changes during mechanical activation of sulfide ores. Therefore, it is meaningful to investigate the effect of mechanical activation on molybdenite by studying the oxidation behavior and the structural changes of nonactivated and mechanically activated molybdenite. In this article, natural molybdenite ore was purchased from a domestic concentration plant, and its chemical compositions are presented in Table I. It was found by X-ray diffraction (XRD) analysis that the natural molybdenite contained hexagonal molybdenite as a predominant component. The natural molybdenite was floated with � 50 ppm xanthate as a floatation reagent. Forty grams of floated molybdenite and 200 mL CCl4 were added into a 250 mL flask, refluxed for 72 hours, and then filtrated to leave xanthate in the filtrate and obtain a filter residue; the filtrate residue was dried at 80 °C in vacuum to get nonactivated molybdenite. Mechanically activated molybdenites are obtained by grinding nonactivated molybdenite as in Reference 16 for 40, 120, 260, and 480 minutes, respectively.

Macroscale NTIMS and microscale LA-MC-ICP-MS Re-Os isotopic analysis of molybdenite: Testing spatial restrictions for reliable Re-Os age determinations, and implications for the decoupling of Re and Os within molybdenite

We present a detailed study of Re-Os age determinations for eight natural molybdenite samples of like polytype (2H), spanning a range of age, natural grain size and deposit type. The focus of the study is to critically evaluate the effects of sampling, sample preparation and aliquant size on the accuracy and reproducibility of Re-Os ages for these molybdenite samples. We find that for some molybdenite samples, analysis of small sample aliquants (<20 mg) may not yield accurate or reproducible Re-Os ages, whereas analysis of larger aliquants from the same mineral separate do yield reproducible Re-Os dates. Such an observation is best explained if Re and 187Os are internally decoupled within molybdenite grains. This finding is supported from spot analyses by laser ablation MC-ICP-MS analyses presented here and is consistent with previously published observations.The degree of decoupling between Re and 187Os appears to increase both as a function of increasing grain size, and increasing age of molybdenite. From detailed dating of individual molybdenite mineral separates, we provide approximate minimum aliquant amounts required for reproducible Re-Os age dating, as a function of molybdenite age and grain size. Geologically younger, naturally fine-grained molybdenite samples appear to show little Re and 187Os decoupling, and reproducible ages can be determined from some samples with as little as 1 mg of aliquant. Geologically old, and coarse-grained molybdenite samples may require as much as 40 mg of aliquant from a much larger mineral separate to overcome Re and 187Os decoupling. The mechanism(s) of Re and 187Os decoupling within molybdenite is not constrained by this results of this study, but the observation that the degree of decoupling increases with grain size (distance) and age (time/geologic history) may suggest primary diffusive control. Assuming that Re and 187Os decoupling in molybdenite results primarily from diffusion of 187Os, apparent diffusion coefficients are calculated (D = x 2/t). Estimates of D for Os made in this way range from 2.8 × 10 −26 to 2.1 × 10 −21 m 2/s, which are broadly similar to experimentally derived diffusion coefficients for Os in Fe-sulfide minerals and for Re in molybdenite at temperatures <500°C.

Crater structures on a molybdenite basal plane observed by ultra-high vacuum scanning tunneling microscopy and its implication to hydrotreating

Atomic structure of a natural molybdenite (MoS2) single crystal basal plane was examined by ultra-high vacuum scanning tunneling microscopy (UHV-STM). Numbers of crater structures with diameters ranging from 5 to 9 nm were observed on pristine as well as on high-temperature (473 K) resulfided surfaces. Atomic structures within these craters were continuous from the surrounding terrace, with no step structures at the rims of the craters. Atoms in the bottom of the craters showed higher corrugations compared to the terrace atoms, indicating higher electronic density of states in the craters. Its implication on hydrotreating activity over curved MoS2 nanoparticles is discussed.

Experimental alteration of molybdenite: evaluation of the Re–Os system, infrared spectroscopic profile and polytype

Experiments have been carried out to clarify the effect of alteration on Re–Os system, near infrared (NIR)–infrared (IR) spectroscopic characteristics and polytype of a natural molybdenite mineral (MoS 2). The molybdenite sample was placed in H 2O and various media of 0.1 mol/L NaCl, NaHCO 3, CaCl 2, and AlCl 3 solutions, and heated in a sealed quartz tube at a temperature of 180°C for 20 d. The unaltered and altered samples were subsequently used for analysis of Re and Os, NIR microscopic observation, and NIR–IR spectroscopy, and microfocus X-ray diffraction (XRD). Molybdenites subjected to NaCl and NaHCO 3 solutions give younger Re–Os ages than that of the original unaltered molybdenite. No significant changes in d spacing and width of micro-XRD patterns can be found in these altered molybdenite, indicating the possibility of Re–Os fractionation without significant structural conversion of molybdenite mineral. These results strongly suggest that the Re–Os system in molybdenite would be frequently disturbed if it has experienced alteration, because alteration by the low salinity (<1%), low temperature (∼180°C) hydrothermal solution containing NaCl and/or CO 2 is commonly found in the natural environment. We maintain, therefore, that one set of analyses of Re and Os in a sample is not enough to determine whether the obtained Re–Os age has been affected by postdepositional alteration, but systematic replicate analyses are indispensable. Additionally, pulverizing all the collected molybdenite in a sample might give misleading results because portions, which have been altered and experienced Re–Os fractionation, may possibly mix into the undisturbed sample and be homogenized. The molybdenite used for the experiment was originally opaque under NIR light. Infrared microscopic and spectroscopic profiles show that some parts of the molybdenite subjected to CaCl 2 and AlCl 3 solutions become transparent to NIR. Increased NIR transmittance is possibly attributed to the removal of the impurity band in molybdenite. It was also found in this study, however, that change in IR profile does not correlate with the Re–Os fractionation and, therefore, IR measurement solely is not useful to detect disturbance of Re–Os systematics of molybdenite in alteration.

Polarized X-ray absorption spectra and electronic structure of molybdenite (2H-MoS2)

Polarized S K- and L-edge, Mo L3- and L2-edge x-ray absorption near-edge structure (XANES) of natural molybdenite (2H-MoS2) have been measured with synchrotron radiation. These results are qualitatively interpreted using the energy band model of molybdenite and provide important information on the unoccupied states of molybdenite. The valence band (VB) maximum of molybdenite is characterized by fully occupied Mo 4dz 2, and the conduction band (CB) minimum of molybdenite is characterized by unoccupied Mo 4d states. The unoccupied Mo 4d band is split into two sub-bands, designated as t 2g − /t 2g + and e g − /e g + sets. Although the relative energy of these two sets are difficult to be evaluated, probably the former has the lower energy than the latter, both two sets have the combination wave functions of the other unoccupied Mo 4d components, rather than the simple 4dx 2 — y2 and 4dxy states. The unoccupied Mo 4d sub-bands contain significant DOS of both S 3 p- and 3 s-like states, indicating strong hybridization with S 3s and 3 p states. In the lower energy sub-band, the DOS of the S pz- and px,y-like states are very similar. However, in the higher energy sub-band, the DOS of the S 3 px,y-like state is lower than that of the S 3pz state. Polarized S K-edge XANES also reveal the features of antibonding S pz- and px,y-like states in molybdenite. The feature assigned to the S 3 pz-like states is stronger and sharper, and shifts to lower energy by about 2 eV relative to that for the S 3 px,y-like states.

A vibration spectroscopic study of the interaction between some sulphide minerals and O, O-diethyl dithiophosphate ions in aqueous solution

The reactions between sodium O, O-diethyl dithiophosphate and the natural sulphide minerals acanthite, arsenopyrite, chalcocite, chalcopyrite, covellite, galena, marcasite, millerite, molybdenite, orpiment, pentlandite, pyrrhotite, pyrite, realgar, sphalerite and troilite have been studied in aqueous solution. Qualitative analysis of the species present on the surfaces before and after treatment with O, O-diethyl dithiophosphate ions has been performed by means of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Nuclear magnetic resonance (NMR) has been used to identify some of the O, O-diethyl dithiophosphate species formed on the mineral surfaces. O, O-Diethyl dithiophosphate ions are sorbed to the surfaces of the studied minerals according to one of the following two reaction mechanisms: (1) formation of a solid metal O, O-diethyl dithiophosphate with low solubility in water, and (2) formation of bis( O, O-diethyl dithiophosphoryl) disulphide, the oxidation product of the O, O-diethyl dithiophosphate ion in a redox reaction with highly oxidising species such as the S 2O 2− 8 and/or S 2O 2− 7 ions. The results of this study have made it possible to predict the mechanism of how oxidised sulphide mineral surfaces interact with O, O-dialkyl dithiophosphate ions from the knowledge of the shortest SS distance in the sulphide mineral. When the SS distance is very short as in the disulphide ion, about 2.2 Å, fairly large amounts of highly oxidising species are formed in the mineral surface during grinding in presence of air and these cause formation of large amounts of bis( O, O-diethyl dithiophosphoryl) disulphide during treatment with O, O-dialkyl dithiophosphate ions in aqueous solution. When the shortest SS distance is in the range 3.1–3.4 Å, which is significantly shorter than the SS distances in close-packed structures containing only sulphide ions (greater than 3.6 Å), small amounts of bis( O, O-diethyl dithiophosphoryl) disulphide are formed on the surfaces. When the shortest SS distance is longer than 3.6 Å, no bis( O, O-diethyl dithiophosphoryl) disulphide is formed on the mineral surfaces and only precipitation of a solid metal O, O-dialkyl dithiophosphate on the surface can take place. No evidence for chemisorption of O, O-dialkyl dithiophosphate ions to sulphide minerals as surface complexes has been found.

High‐resolution transmission electron microscopy of hexagonal and rhombohedral molybdenum disulfide crystals

Natural (molybdenite) and synthesized molybdenum disulfide crystals have been studied by high-resolution transmission electron microscopy. The image simulation demonstrates that the [0001] and [0110] HRTEM images of hexagonal and rhombohedral MoS2 crystals hardly disclose their stacking sequences, and that the [2110] images can distinguish the Mo and S columns along the incident electron beam and enable one to determine not only the crystal structure but also the fault structure. Observed [0001] images of cleaved molybdenite and synthesized MoS2 crystals, however, reveal the strain field around partial dislocations limiting an extended dislocation. A cross-sectional image of a single molecular (S-Mo-S) layer cleaved from molybdenite has been observed. Synthesized MoS2 flakes which were prepared by grinding have been found to be rhombohedral crystals containing many stacking faults caused by glides between S/S layers.

Cross-Sectional Observations of Layer Structures and Stacking Faults in Natural and Synthesized Molybdenum Disulfide Crystals by High-Resolution Transmission Electron Microscopy

Cross sections of the (0001) layers in natural (molybdenite) and synthesized molybdenum disulfide crystals have been observed by high-resolution transmission electron microscopy. The image simulation for hexagonal and rhombohedral MoS 2 crystals which are perfect and contain various types of stacking faults shows that the Mo and S columns along the incident electron beam can be distinguished in the [2110] images and hence the stacking sequence of Mo and S layers can be determined. The layer structures and the formation mechanisms of the stacking faults which have been found in natural and synthesized molybdenum disulfide flakes are presented

Determination of osmium abundance in molybdenite mineral by isotope dilution mass spectrometry with microwave digestion using potassium dichromate as oxidizing agent

An efficient and reliable method was developed for the accurate determination of osmium abundance in molybdenite (MoS2) by isotope dilution mass spectrometry. The sample solution of molybdenite was prepared by acid decomposition using the microwave digestion technique with addition of potassium dichromate (K2Cr2O7) as oxidizing agent and osmium in the sample solution was purified by distillation. There was no change in the ratios of 187Os derived from molybdenite relative to 192Os of an osmium standard with progress of distillation, indicating that isotopes of osmium derived from the two sources were completely homogenized. The precision of the osmium abundance obtained in the developed method was 1%(1σ). The technique was applied to a natural molybdenite sample for Re—Os age determination and the result was in good agreement with that obtained by the U—Pb method for zircon.

Crystallinity of rf-sputtered MoS2 films

The crystallinity and morphology of thin, radio-frequency (rf) -sputtered MoS2 films deposited on 440C stainless steel substrates at both ambient (∼70°C) and high temperatures (245°C) were studied by scanning electron microscopy (SEM) and by x-ray diffraction (Read thin-film photography and 0−20 scans). Under SEM the films exhibited a “ridgelike” (or platelike) formation region for thicknesses between 0.18 and 1.0 μm MoS2. X-ray diffraction was shown to give more detailed and accurate information than electron defraction, previously used for elucidating the structure of sputtered lubricant films. Read thin-film x-ray diffraction photographs revealed patterns consistent with the presence of polycrystalline films and strong orientation of the MoS2 crystallites. Correlation of those patterns with 0−20 scans of the films indicated that the basal planes of the MoS2 crystallites [i.e., the (001) planes] were perpendicular to the substrate surface plane, and that various edge planes [i.e., the (h k 0) planes] in the individual crystallites were parallel to the surface plane, in agreement with previous observations of thinner films. Sliding wear caused the crystallites to orient with their basal planes parallel to the surface plane. The crystallite lattices in all films in this study were shown to exhibit compressive stress (∼ 3%–5% with respect to natural molybdenite) in the direction perpendicular to the (h k 0) planes, and the worn films were expanded (i.e., exhibited tensile stress) perpendicular to the (001) plane. In addition, the shapes of the x-ray diffraction peaks were strongly influenced by the presence of oxygen impurities and/or sulfur vacancies in the MoS2 lattice, indicating that x-ray diffraction may provide a simple quality-control test for the production of a film with optimum lubricating properties.

High-reflectance and single layer MoS 2: two new forms

MoS 2 has been prepared in two new physical forms by treatment of sulfided Ni-Mo/Al 2O 3 catalysts with hydrofluoric acid. The first consists of O.2 × 3 mm pellets which do not have the cleavage present in natural molybdenite but upon crushing produce irregular shiny particles. These highly reflecting particles are crystalline and contain five to ten MoS 2 layers per crystallite. In the second form essentially all the MoS 2 is present as single layers either supported on or mixed with carbon.

Electrical conductivity, thermoelectric power and hall effect in p-type molybdenite (MoS 2) crystal

Principal electrical conductivities and seebeck coefficients, as well as Hall effect, in p-type single crystals of natural molybdenite (MoS 2) have been investigated within the temperature range 100°K to 850°K. The results have been discussed and the values of different parameters of the charge carriers obtained.

Low-temperature heat capacity of anisotropic crystals lamellar molybdenum disulfide

Heat capacities of natural molybdenite crystals were made to test the T 2 limiting law for the heat capacity of a lamellar lattice near T → 0. The findings are at variance with those of Smith et al. and accord with theoretical studies of Newell in that the T 3 limiting law is upheld. The results also permit a more accurate evaluation of the thermodynamic functions: at 298.15 K C p ( T), S o( T), and −{G o (T) − H o (0)} T are (15.19 ± 0.03), (14.96 ± 0.02), and (6.475 ± 0.03) cal th K −1 mol −1.

Integral-breadth analysis of x-ray line broadening in cold-worked natural molybdenite (MoS 2) crystal : R Pratap and R K Gupta, Phys Stat Sol (a), 9 (2), Feb 1972, 415–421

Integral-breadth analysis of x-ray line broadening in cold-worked natural molybdenite (MoS 2) crystal : R Pratap and R K Gupta, Phys Stat Sol (a), 9 (2), Feb 1972, 415–421

Alkali metal intercalates of molybdenum disulfide

Natural molybdenite and single crystals of MoS2 grown by chemical vapor transport were intercalated with the alkali group of metals (Li, Na, K, Rb, and Cs) by means of the liquid ammonia technique. Stoichiometries and x-ray data of all intercalates were determined and a complete indexing of the x-ray patterns of K0.4MoS2 and Rb0.3MoS2 was achieved. The x-ray results show insignificant changes in the ao axis and considerable expansion of co axis after intercalation (Δco : 6.745, 2.704, 4.286, 4.899, and 7.312 Å for Li0.4MoS2, Na0.3Mos2, K0.4MoS2, Rb0.3MoS2, and Cs0.3MoS2, respectively). All intercalated crystals were superconducting (Tonset: 3.7, 4.1, 6.1, 6.25, and 6.30 for Li0.4MoS2, Na0.3MoS2, K0.4MoS2, Rb0.3Mos2, and Cs0.3MoS2, respectively). The superconductivity is believed to be due to an electron transfer from the alkali metal to an empty band of MoS2, resulting in an increase in electron density as well as in the density of states at the Fermi surface.

The Surface Deformation Caused on Natural Molybdenite by Abrasion

It has been investigated the surface deformation caused by uni-directional abrasion on a cleaved surface of natural molybdenite by various electron techniques, that is, low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED), scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The main results obtained are as follows;(1) LEED patterns from the abraded surfaces on which many friction tracks are observed by SEM exhibit still MoS2 (1 × 1) structure. RHEED examination shows that the surface deformation depends on the angle between the incident beam and the direction of grinding. With the beam parallel to the direction of grinding, the streaks extending vertically to the cleaved surface appear. In the direction perpendicular to it abrasion tends to cause an orientation of the crystallites, their cleavage planes being parallel to the surface.(2) For the cleaved surface and the abraded one, the ratio of sulfur to molybdenum Auger peak height is found almost the same. But the ratio of carbon to molybdenum Auger peak height for the abraded surface is larger than for the cleaved one.

Etch Pits in Natural Molybdenite

Etch pits 50 and more molecular layers deep have been observed on the surface of natural molybdenite crystals exposed to oxygen at temperatures in the region of 650°C. The geometry and manner of growth of the etch pits suggest that etching takes place through the intermediary of a two-dimensional gas of adsorbed oxygen molecules on the surface of the crystal. For the five samples studied this explanation of the etch pits leads to the conclusion that the fraction of adsorption sites occupied by adsorbate molecules lies in the range θ=2.3×10−3−3.6×10−2. The average activation energy of a molecular etch reaction is 33.7 kcal/mole or 1.43 eV.