Kinetics and substitution mechanism in the reaction of the seven-coordinate complexes bis-μ-diphenylphosphido- and bis-μ-dimethylphosphido-octacarbonyldimolybdenum (MoMo) with tri-n-butyl-phosphine

Activation procedures and hydrogen exchange reactions with six Group VIII transition metal catalysts (Pt, Pd, Ru, Rh, Ir, Ni) are reported for three characteristic reaction systems: (i) deuterium oxide/benzene, (ii) deuterium oxide/naphthalene, and (iii) deuterium oxide/n-octane. Results of these exchange reactions indicate that both π-complex adsorption and the dissociative π-complex substitution mechanism previously established for platinum are applicable to other Group VIII transition metal catalysts. For general catalytic labelling with isotopic hydrogen, platinum was found to be the most efficient of the catalysts investigated.

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Coupled substitutions in PGE-enriched cobaltite: new evidence from the Rio Jacaré layered complex, Bahia state, Brazil

Mineralogical Magazine ◽

10.1180/minmag.2015.079.5.12 ◽

2015 ◽

Vol 79 (5) ◽

pp. 1185-1193 ◽

Cited By ~ 1

Author(s):

Andrei Y. Barkov ◽

Yana Fedortchouk ◽

Robert A. Campbell ◽

Tapio A.A. Halkoaho

Keyword(s):

Layered Intrusion ◽

Fluid Phase ◽

Primary Phase ◽

Sulfur Fugacity ◽

Type Molecule ◽

Substitution Mechanism ◽

Compositional Variability ◽

New Evidence ◽

Layered Complex ◽

Grain Core

AbstractMicrocrystals of platinum-group element (PGE)-bearing cobaltite occur in the Gulcari A deposit of vanadiferous titanomagnetite in the lower zone of the Rio Jacaré mafic-ultramafic layered intrusion, Brazil. Aggregates of cobaltite and sperrylite are cluster-like and developed generally along the boundary of Fe-Ti oxide grains with deuteric silicates. Our observations of cryptic zoning, compositional variability and interelement correlations are based on 37 analytical points (wavelength-dispersion spectrometry mode) of cobaltite, and indicate that Ir and Rh behave uniformly with Ni and antipathetically with Co which, in turn, correlates directly with S content. Iridium, Rh and Ni apparently substitute for Co in the As-enriched grain core, and the substitution mechanism invokes solid solution with a cattierite-type molecule: (Ni + Ir + Rh) + (AsS) = Co + (S2). The PGE-bearing cobaltite probably crystallized as a primary phase at 500 to 300°C, from microvolumes of a late fluid phase. The observed enrichment in S and decrease in the As:S ratio at the cobaltite grain margins is a reflection of the increase in sulfur fugacity (fS2) with decrease in temperature of crystallization.

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The substitution mechanism of Au in In-, Fe- and In-Fe-bearing synthetic crystals of sphalerite, based on the data from EPMA and LA-ICP-MS study

LITOSFERA ◽

10.24930/1681-9004-2019-19-1-148-161 ◽

2019 ◽

pp. 148-161 ◽

Cited By ~ 2

Author(s):

D. E. Tonkacheev ◽

D. A. Chareev ◽

V. D. Abramova ◽

E. V. Kovalchuk ◽

I. V. Vikentyev ◽

...

Keyword(s):

Depositional Environments ◽

Salt Flux ◽

Research Subject ◽

Trace Impurities ◽

Valuable Component ◽

Experimental Conditions ◽

Icp Ms ◽

Substitution Mechanism ◽

Synthetic Crystals ◽

Good Agreement

Research subject.Sphalerite (ZnS) is a widespread mineral that can be found in various depositional environments. During formation, this mineral can accumulate minor and trace impurities, with gold being one of the most valuable component. The issue of the chemical state of Au in sphalerite has been much discussed recently.Methods.Samples of In-, Fe- and In-Febearing sphalerite with a composition ranging from 0 to 2.5 mol.% In2S3 and 0 – 40 mol.% FeS were synthesized in an Ausaturated system using gas transport and salt flux techniques. The resulting products were subsequently investigated using EPMA and LA-ICP-MS.Results.All the elements under investigation are found to be homogeneously distributed within the sphalerite matrix. After quenching, sphalerite is shown to retain Au. Our data indicates that the observed increase in Au concentration is caused by the presence of In (up to 1.02 wt % Au) and, to a lesser extent, by that of Fe (up to ≈600 ppm Au). These elements substitute Zn in the crystal structure of sphalerite following the scheme Au+ + In3+(Fe3+) ↔ 2Zn2+, which is in good agreement with previous data obtained using the XAS method.Conclusions.A higher sulphur fugacity in the system leads to a more significant accumulation of Au in sphalerite. The concentration of Au in pure sphalerite does not exceed 10 ppm under our experimental conditions and does not depend on the activity of sulphur in the system.

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Ti-substitution mechanism in plutonic oxy-kaersutite from the Larvik alkaline complex, Oslo rift, Norway

Mineralogical Magazine ◽

10.1180/0026461046840215 ◽

2004 ◽

Vol 68 (4) ◽

pp. 687-697 ◽

Cited By ~ 2

Author(s):

H. Satoh ◽

Y. Yamaguchi ◽

K. Makino

Keyword(s):

Negative Correlation ◽

Closed System ◽

Mineral Chemistry ◽

Formula Unit ◽

Alkaline Complex ◽

Crustal Thinning ◽

Substitution Mechanism ◽

Plutonic Complex ◽

O Isotope ◽

Ti Substitution

AbstractAmphibole in the Larvik alkaline plutonic complex in the Oslo rift, Norway, has Ti-rich compositions from edenite through pargasite to kaersutite, and has a large H+ deficiency (0.7–1.1 atoms per formula unit: a.p.f.u.) with a large oxy component in the amphibole OH– site (O2– = 2 – (OH + F + Cl) = 0.2–0.9 a.p.f.u.), similar to the mantle-derived kaersutites. Their compositions reveal a characteristically low Fe3+/(Fe3++Fe2+) ratio (<0.23) and a high F concentration (0.3–0.9 a.p.f.u.). Correlation with the Fe3+ ratio caused by Fe2+ + OH– = Fe3+ + O2– + 1/2H2 substitution is negligible, which is supported by H and O isotope compositions. A possible substitution, [6]Al3+ + OH– = [6]Ti4+ + O2– may be operative for Larvik kaersutites when the O2–/Ti is 1.0. A relatively larger O2–/Ti ratio (1.2—2.0) suggests an another kaersutite substitution mechanism, [6]R2+ + 2OH– = [6]Ti4+ + 2O2–, where [6]R2+ = Fe2+ + Mg + Mn. These effects might result in the limited O2–/Ti ratio value from 1.0 to 2.0.A negative correlation between Ti and F, suggesting F incorporation into kaersutite may diminish the O2–/Ti ratio, not only due to the occupation of this non-oxy species in the O3 site, but also due to F—Ti avoidance. Composition-dependent H and O isotope variations (δD = –106 to –71% and δ18O = 4.6–5.2%) suggest equilibrium in the closed-system magma with differentiation. The mineral chemistry of Larvik oxy-kaersutitic amphibole could reflect the crystallization in a closed-system magma during rifting with passive crustal thinning at the Oslo palaeorift.

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Micro- and nano-size hydrogarnet clusters in calcium silicate garnet: Part II. Mineralogical, petrological, and geochemical aspects

American Mineralogist ◽

10.2138/am-2020-7257 ◽

2020 ◽

Vol 105 (4) ◽

pp. 468-478 ◽

Cited By ~ 2

Author(s):

Charles A. Geiger ◽

George R. Rossman

Keyword(s):

Calcium Silicate ◽

Hydrogen Diffusion ◽

Ir Absorption ◽

Diffusion Behavior ◽

Substitution Mechanism ◽

And Behavior ◽

First Time ◽

Nano Size ◽

Silicate Garnet ◽

Thermal Stability Of

Abstract The nominally anhydrous, calcium-silicate garnets, grossular (Ca3Al2Si3O12), andradite (Ca3Fe23+Si3O12), schorlomite (Ca3Ti24+[Si,Fe23+]O12), and their solid solutions can incorporate structural OH-, often termed “water.” The IR single-crystal spectra of several calcium silicate garnets were recorded between 3000 and 4000 cm–1. Spectroscopic results are also taken from the literature. All spectra show various OH- stretching modes between 3500 and 3700 cm–1 and they are analyzed. Following the conclusions of Part I of this study, the garnets appear to contain local microscopic- and nano-size Ca3Al2H12O12- and Ca3Fe23+H12O12-like domains and/or clusters dispersed throughout an anhydrous “matrix.” The substitution mechanism is the hydrogarnet one, where (H4O4)4– ↔ (SiO4)4–, and various local configurations containing different numbers of (H4O4)4– groups define the cluster type. A single (H4O4) group is roughly 3 Å across and most (H4O4)-clusters are between this and 15 Å in size. This model can explain the IR spectra and also other experimental results. Various hypothetical “defect” and cation substitutional mechanisms are not needed to account for OH- incorporation and behavior in garnet. New understanding at the atomic level into published dehydration and H-species diffusion results, as well as H2O-concentration and IR absorption-coefficient determinations, is now possible for the first time. End-member synthetic and natural grossular crystals can show similar OH- “band patterns,” as can different natural garnets, indicating that chemical equilibrium could have operated during their crystallization. Under this assumption, the hydrogarnet-cluster types and their concentrations can potentially be used to decipher petrologic (i.e., P-T-X) conditions under which a garnet crystal, and the rock in which it occurs, formed. Schorlomites from phonolites contain no or very minor amounts of H2O (0.0 to 0.02 wt%), whereas Ti-bearing andradites from chlorite schists can contain more H2O (∼0.3 wt%). Different hydrogarnet clusters and concentrations can occur in metamorphic grossulars from Asbestos, Quebec, Canada. IR absorption coefficients for H2O held in hydrogrossularand hydroandradite-like clusters should be different in magnitude and this work lays out how they can be best determined. Hydrogen diffusion behavior in garnet crystals at high temperatures is primarily governed by the thermal stability of the different local hydrogarnet clusters at 1 atm.

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Distribution and Substitution Mechanism of Ge in a Ge-(Fe)-Bearing Sphalerite

Minerals ◽

10.3390/min5020117 ◽

2015 ◽

Vol 5 (2) ◽

pp. 117-132 ◽

Cited By ~ 35

Author(s):

Nigel Cook ◽

Barbara Etschmann ◽

Cristiana Ciobanu ◽

Kalotina Geraki ◽

Daryl Howard ◽

...

Keyword(s):

Substitution Mechanism

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Substitution mechanism and structural study of MnO-doped Bi2VO5.5-δ

Solid State Ionics ◽

10.1016/j.ssi.2012.05.001 ◽

2012 ◽

Vol 219 ◽

pp. 20-28 ◽

Cited By ~ 4

Author(s):

Gang-Qin Shao ◽

Xiao-Hua Yu ◽

Wei Cai ◽

Hong-Xing Gu ◽

Jian Li ◽

...

Keyword(s):

Structural Study ◽

Substitution Mechanism

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Synthesis of Novel High Silicate-Substituted Hydroxyapatite by Co-Substitution Mechanisms

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.330-332.87 ◽

2007 ◽

Vol 330-332 ◽

pp. 87-90 ◽

Cited By ~ 10

Author(s):

J.A. Stephen ◽

J.M.S. Skakle ◽

Iain R. Gibson

Keyword(s):

Chemical Structure ◽

Bone Repair ◽

Unit Cell ◽

Secondary Phases ◽

Co Substitution ◽

Phosphate Ions ◽

Substitution Mechanism ◽

Coupled Substitution ◽

High Silicate

Silicate substituted hydroxyapatite bioceramics have been shown to enhance bone repair in vivo compared to hydroxyapatite (HA), although the amount of silicate ions that can be substituted alone into the hydroxyapatite structure is limited to approximately 5.2 wt%, or 1.6 wt% Si. This study describes the substitution of greater levels of silicate ions via co-substitution of silicate ions with trivalent yttrium ions, without resulting in the formation of any secondary phases. This substitution mechanism involves a coupled substitution of yttrium and silicate ions for calcium and phosphate ions, respectively, and enables a level of silicate substitution up to approximately 9 wt%. Two different substitution mechanisms result in subtle differences in the crystal structure. When the mechanism xY3+ + xSiO4 4- was used, a small decrease in the a-axis, but no change in the c-axis, of the unit cell compared to HA was observed. In contrast, when the mechanism x/2Y3+ + xSiO4 4- was used, a significant increase in the c-axis of the unit cell was observed, compared to HA. XRF analysis and FTIR spectroscopy supported the proposed substitution mechanisms. These novel substitution mechanisms not only enable greater levels of silicate-substitution in HA to be prepared, but also allow the production of compositions with the same level of silicate substitution, and with subtle differences in chemical structure.

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