Native Nickel Research Articles

Effect of substituted cobalt–chromium–iron oxides’ dissolution kinetics in oxidizing formulation on decontamination process

Removing radioactive corrosion products from Cr-containing iron oxides require a multi-step and multi-cycle decontamination process. The present article brings out the effect of divalent metal ion substitution on the release rate of chromium in the oxidative pre-treatment step. The non-stoichiometric cobalt chromium ferrites were synthesized, characterized and effect of Zn2+/Ni2+ substitution on the dissolution behavior was probed. The dissolution rates decreased with increasing the degree of inclusion and showed minima at ~ 0.4–0.6 atom% which is explained on the basis of lattice structure. It is concluded that the dissolution kinetics of native nickel–chromium ferrites in reactors increases with metal ion inclusion.

Platinum-bearing Fe-Mn oceanic crust on basalts: mineralogy and model of formation

Fe-Mn oceanic crust on basalts of the guyot in the Mid-Pacific Seamount (Pacific Ocean, depth 2486 m, chemical composition (wt %): Mn 24.2, Fe 12.6, Ni 0.59, Co 0.72, Cu 0.13; (ppm) Pt 0.35, Pd 0.0052), was studied using 3D-technology of mineralogical research. In addition to dominaiting vernadite and goethite, the following minerals are identified in the hydroseparation (HS) concentrates of the crust: 1) rock forming and accessory minerals of basalts (clinopyroxene, plagioclase, potassium feldspar, biotite, ilmenite, titanomagnetite, Ti-chrome spinel, zircon, apatite); 2) sulfides that are identical to those from the basalt substrate (pyrite, chalcopyrite, bornite, chalcocite, tennantite, nickel pentlandite Ni4S3, sphalerite, galena, argentite/acantite, molybdenite); 3) native metals (iron, nickel, copper, titanium, tungsten); 4) iron silicides (gupeiite Fe3Si, xifengite Fe5Si3, and hapkeite Fe5Si3); 5) platinum group minerals - unnamed (Cu,Pt)4Si and rustenburgite (Pt,Pd)3(Sn,Sb). The complexes of ore minerals in basalts are identical to those of the Fe-Mn crusts. Basalt accessories are assumed to be primary phases and a source of metals for the formation of native minerals. “Microdroplets” of native iron Fe, (Fe,Ni), nickel Ni, (Ni,Cr), (Ni,Fe) and copper Cu (sizes 20–100 microns, degree of sphericity up to 100%) represent the products of their crystallization from metal melts in basalts, transported by deep fluid into Fe-Mn crusts on these rocks. The zoned microglobules of 20–70 microns sizes with iron or native nickel (core) + successive rims of wüstite-magnetite and Fe-Mn hydroxides were identified. They were apparently formed during the movement of these solid microparticles (from bottom to the top) along intergranular spaces and other permeability channels in basalts under conditions of increasing oxygen fugacity and falling temperature at various levels of deep fluid infiltration. The crystallization of native metals in the Fe-Mn crust that are characterized by low-temperature (10 °C) and oxidizing (fO2 MHG magnetite-hematite-goethite) conditions of mineral formation is impossible. The goethite replacement to different extent of many grains of relict Fe-minerals (sulfides and native metals) that are “foreign” to the Fe-Mn crust have been established. Fe-Mn crusts were formed as a result of the precipitation of colloidal particles Mn2+(Ba2+и Sr2+), to a lesser extent of the iron hydroxide Fe(ОН)3, as well as the concentration and transformation of micrograins of minerals of other metals, extracted by fluid from basaltic substrates. The comparison of the physico-chemical parameters of crystallization of basalts and native metals suggests another source of formation of native minerals in basalts, different from the postmagmatic basaltic fluid, i.e. deep-seated sharply reducing "hot" gas flows associated with superplumes. The mineralogical data determines a volcanogenic-fluid-oceanic model for the formation of Fe-Mn crusts on underwater oceanic elevations.

Native Nickel–Iron Metals from Lonar Crater Impactites (India) and Regolith of the Moon

Native Nickel–Iron Metals from Lonar Crater Impactites (India) and Regolith of the Moon

Native Nickel–Iron Metals from Lonar Crater Impactites (India) and Regolith of the Moon

The Lonar crater (India) is the best preserved and most studied on Earth, formed in basalts, which makes it possible to conduct a comparative study with impact transformations of mineral matter on the Moon and other planets of the Solar System. Comparative studies have shown that impactor material, both on the Earth and on the Moon, is present in impactites not only in a geochemically dispersed form, as previously thought, but also in the form of individual submicron particles distributed in the molten target material. These are particles of native nickel, taenite, and high-nickel kamacite, which, apparently, are the transformed material of the impactor. High-nickel submicron metal inclusions are widespread in the impactites of the Lonar crater, as they were found in all studied preparations made from materials collected from different points along the rim of the crater. The high-nickel particles found in this study are an additional argument in favor of the previously stated assumption about the chondrite type of impactor.

СЕРЕБРЯНАЯ МИНЕРАЛИЗАЦИЯ В ГЛУБИННЫХ МАГМАТОГЕННЫХ СИСТЕМАХ ДРЕВНИХ ОСТРОВНЫХ ДУГ: ИЛЬДЕУССКИЙ УЛЬТРАОСНОВНОЙ МАССИВ, СТАНОВОЙ МОБИЛЬНЫЙ ПОЯС (ДАЛЬНИЙ ВОСТОК РОССИИ)

The Triassic (232–233 Ma) Ildeus mafic-ultrabasic massif is a fragment of a large mineralized magmatogenic system formed within the Stanovoy mobile belt at the Mesozoic stage of its evolution. Ultrabasic rocks are represented by cumulative plagioclase- and amphibole-bearing dunites, peridotites, websterites, and pyroxenites; basic rocks are gabbro-anorthosites, norites, and two-pyroxene gabbro. Most intrusive rocks of the Ildeus magmatogenic system experienced ultramafic (serpentine, chlorite, talc, carbonates) and acidic (quartz, biotite, potassium feldspar, secondary micas) metasomatism. Geochemical characteristics (calc-alkaline differentiation trend, negative anomalies of highly charged incoherent elements) indicate the subduction nature of the primary magma in the Ildeus system. The ultrabasic rocks are intruded by intermediate-acid intrusions with geochemical characteristics of adakite. Magmatic-stage silver mineralization is represented by microinclusions of cuprous silver, alloys of silver, copper, gold and zinc, acanthite and silver halides in association with pentlandite, chalcopyrite, bornite, and pyrrhotite. These rocks are characterized by microinclusions of native platinum, gold, tungsten, bismuth, lead, PGE alloys, W-Co-Ti, Sb-Pb, Cu-Zn-Sn, minerals of Ag-Cu-Sb-Se-S and Zn-Ni systems -Co-Fe-S, barite, chlorapatite and Bi-Sn-Pb chlorides. At the metasomatic stage, native silver, Au-Ag alloys, silver and copper chlorides, acanthite, silver and lead tellurides coexist with digenite, heathlewoodite, pyrite, sphalerite, galena, native nickel and gold, Cu-Zn alloys, sulfides of the Pb-As- Cu-Fe-S and bismuth chloride. At the magmatic stage, silver minerals crystallized under reducing conditions in the presence of high-temperature aqueous fluids enriched in sulfide sulfur, halogens, and volatile siderophile (W, Pt) and chalcophile (Ag, Bi, Sn, Sb, Pb) metals that entered the primary melt from serpentinites, metamorphosed gabbroids, and metal-bearing pelagic sediments of the subducting oceanic plate. Metasomatic parageneses of silver minerals were formed under oxidized near-surface conditions with the participation of low-temperature water-salt solutions with elevated concentrations of sulfate sulfur, arsenic, and tellurium. A two-stage model is proposed for the formation of silver mineralization in island arc magmatic systems, in which the high-temperature magmatic stage of formation in deep crustal parts is replaced by low-temperature hydrothermal ore formation processes in near-surface conditions.

Mineralogy of chromitites of mount Poklonnaya of the Karabash massif, South Urals

Mineral composition of chromitites and host serpentinites from a quarry at Mt. Poklonnaya of the Karabash serpentinite massif is studied using optical and electron microscopy. In addition to previously known native osmium and laurite, eight minerals of platinum group elements (PGE) are found: isoferroplatinum, irarsite, iridium, naldrettite, cuproiridisite, sperrilite, tolovkite and erlichmannite. It is found that magnesioalumochromite is the early magmatic Cr-spinel and magnesiochromite and ferrichromite are late magmatic. The earliest native iridium and native osmium are replaced by PGE sulfdes, arsenides and stibnides. Magnesiochromite is associated with native gold, Ni chalcohenides (gersdorffte, millerite, pentlandite, heaslewoodite) and chalcopyrite. The formation of Cr-magnetite, magnetite, native iron, native nickel, galena and barite is related to serpentinization. Carbonates (calcite and dolomite), brucite, andradite, sepiolite and an unidentifed Ca-silicate formed at the latest stage of serpentinization. Secondary Ni minerals (gaspeite, nepuite, «garnierite») are most likely the products of the latest mineral-forming process.

Awaruite, a new large nickel resource. Part 1: Physicochemical properties and their implication for mineral processing

Nickel is an important component of stainless steel and a wide range of applications which are critical for the transition to clean energies including electric vehicle batteries. Awaruite is a native nickel–iron alloy that has gained interest as a possible new economic source of nickel. In the last decades, there have been discoveries of awaruite, mostly with more significant amounts of nickel sulphides, that have demonstrated the potential for awaruite to contribute to the economics of a deposit. This study is focused on the very large Baptiste deposit in central British Columbia, Canada where awaruite is the primary nickel mineral. Most of published data on awaruite are focused on geology, and important fundamental physiochemical properties have still not been determined. These properties are fundamental for the set-up of a flowsheet that will enable its large-scale processing. The limited information available of this nickel–iron alloy can be complemented with the available information of a synthetic alloy with the same elemental composition. The synthetic awaruite alloy has demonstrated remarkable magnetic properties, and based on those properties, it was named permalloy. In this study, physicochemical properties of native and synthetic awaruite were measured including chemical composition, crystallographic structure, and magnetic properties. The native awaruite composition from the Baptiste deposit averages 77.3 % nickel, 21.0 % iron, 1.1 % cobalt and 0.6 % copper. Natural and synthetic awaruite have the same crystallographic characteristics and similar ferromagnetic behaviour. The measured initial volumetric magnetic susceptibility for native awaruite was 14.4 and the saturation magnetization was 750kA/m. Awaruite has the potential to be concentrated in a unique and valuable nickel concentrate of distinctive characteristics including its very high nickel content, which lowers both the downstream costs and the carbon intensity. Furthermore, the negligible content of sulphur and penalty trace elements, such as mercury, antimony, and arsenic in a potential awaruite concentrate, minimizes the costs of refining it. The physicochemical data in this study provides information to reliably set up a mineral processing flowsheet, which is discussed in this work.

Awaruite (Ni3Fe), a new large nickel resource: Electrochemical characterization and surface composition under flotation-related conditions

Awaruite is a native nickel–iron alloy (Ni3Fe), found in serpentinized ultramafic rocks, that has gained interest as a possible source of nickel. FPX Nickel is advancing a very large awaruite deposit in central British Columbia, Canada, on which this work is based. To date there is limited information available regarding the flotation conditions to selectively concentrate awaruite from gangue minerals in serpentinite ores. The aim of this work was to investigate the floatability of awaruite in different solution conditions with a xanthate collector. Awaruite readily floated in acidic solution with a xanthate collector but not in neutral and alkaline solutions. Voltammograms on awaruite indicated that the alloy shows an active passive transition behaviour in acidic solution and passive behaviour in neutral and alkaline solutions. The passivation layer formed in neutral and alkaline solutions showed to inhibit the interaction between xanthate and awaruite surface. Infrared spectra on awaruite showed the presence of xanthate compounds attached to the surface in acidic condition at potentials higher than the reversible potential of xanthate/dixanthogen. Based on experimental results, it was postulated that xanthate chemisorbs on awaruite and then it oxidizes to form dixanthogen. Also, it was demonstrated that when passivated, awaruite quickly activates in acidic solution, good flotation performance was achieved with 10 min of conditioning, and similar performance was obtained after 30 min of conditioning. This work serves as a confirmation that is possible to float awaruite using xanthate, a well-known collector that offers selectivity over oxides and silicate minerals, which are the main gangue minerals in serpentinite ores.

EVIDENCES OF WEATHERING OF IRON-NICKEL AND TROILITE IN THE GRUZ'KE Н4-TYPE CHONDRITE

Terrestrial weathering of the Gruz'ke chondrite was investigated by considering its initial chemical, structural, and mineralogical characteristics. The spread of corrosion and degree of alteration were related to the high content of Fe-Ni metal, the phase inhomogeneity and the different concentration of Ni in the metal, as well as, the shock metamorphism features, and the residence time of the meteorite sample in a soil environment. The formation of secondary oxide veins and oxide rims, consisting of iron hydroxide pseudomorphs was caused by the selective corrosion of kamacite α-(Fe,Ni), compared to taenite γ-(Fe,Ni) and troilite FeS. A spatial relationship between shock metamorphism features, namely areas of plastic deformation, shock heating and weathering of the meteorite matter, has been confirmed. A secondary Ni-enriched phase, which contains 71.34 to 72.94 wt.% Ni, probably corresponds to awaruite (Ni2Fe to Ni3Fe) or native nickel. This phase is described for the first time as corrosion product of Fe-Ni grains in the Gruz'ke chondrite. We assume that this phase was formed during the alteration of Fe-Ni metal. Fe was removed from the meteorite metal during the corrosion process, while sulfur was introduced. The formation of iron hydroxide pseudomorphs caused changes in primary chemical and structural properties of some crystals of nickel-iron metal and troilite. Thus, the use of weathered mineral grains to interpret the pre-terrestrial conditions of the chondrite matter formation and evolution is limited. In spite of the changes in chemical and mineral composition, the corrosion products of nickel iron and troilite have consistent low chlorine content.Therefore we assume that the akaganeite β-FeO(OH,Cl) secondary phase is unlikely to form. It will prevent further alteration of the Fe-Ni metal and ensure long-term storage and preservation of the meteorite sample for further laboratory research and storage in the museum collection.

Mechanisms of long-range edge retraction of metal bilayer films

The agglomeration of thin films on substrates is driven by minimization of the free surface and film/substrate interface energies and has been studied extensively for single component metal films. Only a few studies have investigated the agglomeration of kinetically constrained metal bilayer films, for which unusual long-range edge retraction was recently reported. This study has explored the agglomeration of kinetically constrained thin films of Au and Ni that were subsequently deposited on SiO2/Si substrates and annealed under high vacuum conditions at 545, 675, and 730 °C. Long-range edge retraction of the metal bilayer films revealed seven regions across the receding edge that are microstructurally distinct. The absolute and relative widths of the regions depend on the deposition sequence of the two metal films and annealing temperature. Arrhenius analysis of growth rates for different regions was used to identify energy barriers for mass transport mechanisms. The presence of native nickel oxide was found to have a significant effect on the kinetics of long-range edge retraction. The experimental results suggest that the formation of multiple regions across the receding edge is part of the kinetic evolution of long-range edge retraction of metal bilayer films.

Real-time imaging of nanoscale electrochemical Ni etching under thermal conditions.

The ability to vary the temperature of an electrochemical cell provides opportunities to control reaction rates and pathways and to drive processes that are inaccessible at ambient temperature. Here, we explore the effect of temperature on electrochemical etching of Ni–Pt bimetallic nanoparticles. To observe the process at nanoscale resolution we use liquid cell transmission electron microscopy with a modified liquid cell that enables simultaneous heating and biasing. By controlling the cell temperature, we demonstrate that the reaction rate and dissolution potential of the electrochemical Ni etching process can be changed. The in situ measurements suggest that the destabilization of the native nickel oxide layer is the slow step prior to subsequent fast Ni removal in the electrochemical Ni dissolution process. These experiments highlight the importance of in situ structural characterization under electrochemical and thermal conditions as a strategy to provide deeper insights into nanomaterial transformations as a function of temperature and potential.

Efficacy of ozone for removal of pesticides, metals and indicator virus from reverse osmosis concentrates generated during potable reuse of municipal wastewaters

This study evaluated ozone treatment to address concerns regarding the discharge to marine waters of chemical contaminants and pathogens in reverse osmosis (RO) concentrates generated during the potable reuse of municipal wastewaters. Previous studies indicated that contaminants can be sorted into five groups based on their reaction rate constants with ozone and hydroxyl radical to predict degradation of chemical contaminants during ozonation of municipal effluents. Spiking representatives of each group into five RO concentrate samples, this study demonstrated that the same contaminant grouping scheme could be used to predict contaminant degradation during ozonation of RO concentrates, despite the higher concentrations of ozone and hydroxyl radical scavengers. The predictive capability of the contaminant grouping scheme was further validated for four contaminants of concern in RO concentrates, including the pesticides fipronil and imidacloprid, and the metal chelates Ni-EDTA and Cu-EDTA. After measuring their ozone and hydroxyl radical reaction rate constants, these compounds were assigned to contaminant groups, and their degradation during ozonation matched predictions. Addition of 300 mg/L CaO at pH 11 achieved partial removal of the native nickel and copper by precipitation. Ozone pretreatment further enhanced precipitation of nickel, but not copper. Ozonation achieved 5-log inactivation of MS2 in all five concentrate samples at 1.18 mg O3/mg DOC. Ozonation at 0.9 mg O3/mg DOC formed 139–451 μg/L bromate. Pretreatment of RO concentrates with chlorine and ammonia reduced bromate formation by a maximum of 48% but increased total halogenated DBP concentrations from 20 μg/L to 36 μg/L. Regardless, neither bromate nor trihalomethane concentrations exceeded threshold concentrations of concern for discharge to marine waters.

АКЦЕССОРНЫЕ САМОРОДНЫЕ МЕТАЛЛЫ И ИХ ОКСИДЫ ИЗ МАССИВНЫХ ХРОМИТИТОВ КЕМПИРСАЙСКОГО УЛЬТРАМАФИТОВОГО МАССИВА (ЮЖНЫЙ УРАЛ, КАЗАХСТАН)

Актуальность исследования обусловлена недостаточной всесторонней изученностью минералогических аспектов ультрамафитовых реститовых массивов, что не дает возможности их обобщения на минералогическом уровне и восстановления полной истории их формирования и преобразования, а также решения целого ряда спорных вопросов петрологии данных объектов. Минералогия самородных металлов и их оксидов из реститовых ультрамафитов является крайне слабо изученным направлением. Цель: изучение минерализации самородных металлов и их оксидов в густовкрапленных и сливных хромититах Кемпирсайского ультрамафитового массива, реконструкция механизма ее формирования. Методы: изучение рудной минерализации в аншлифах с использованием поляризационного микроскопа AxioScope Carl Zeiss; диагностика химического состава рудной минерализации методом рентгеноспектрального микроанализа с применением электронного сканирующего микроскопа Tescan Vega II LMU, оборудованного энергодисперсионным спектрометром (с полупроводниковым Si(Li) детектором INCA x-sight) INCA Energy 450 и волнодисперсионным спектрометром INCA Wave 700. Результаты. Впервые в хромититах Кемпирсайского массива выполнена детальная диагностика акцессорной минерализации самородных металлов и их оксидов, по результатам которой выявлены и охарактеризованы: самородный никель, самородное серебро, самородная медь, самородное железо, аваруит, касситерит, монтепонит, цинкит. Концентрирование рассмотренной минерализации, очевидно, было связано с ее мобилизацией в процессе серпентинизации и преобразования первичных силикатов, а также хромшпинелидов и сульфидов при восстановительных условиях. Образование металлов автор связывает с тенденцией Ni и подчиненного Fe высвобождаться из кремнекислородных связей первичного оливина, а Cu и Zn – из связей сульфидов и хромшпинелидов и переходить в форму свободных элементов. Очевидно, привнос части элементов (Cd, Sn) осуществлялся и самими серпентинизирующими растворами. Дальнейшая судьба данных металлов определялась их концентрированием и последующим отложением из высоконасыщенных надкритических флюидов.

Mineralogy and geochemistry of the Sikait U-Au-bearing lamprophyre dyke, South Eastern Desert, Egypt

A 150-m-long mineralized lamprophyre dyke intrudes mylonite-melange at the eastern side of Wadi Sikait and granite at its western side. Its petrographic, mineral, and geochemical characteristics were investigated in order to determine its genetic history as well as the petrogensis of the hosted mineralizations. Rocks of the Sikait lamprophyre dyke have a porphyritic and, less commonly, aphanitic texture. They consist of REEs-U-Th- and Nb, Ta-bearing minerals in addition to Au and native nickel, zircon, and fluorite. The ratios of LREEs to each of the HREEs, MREEs, and HFSE are relatively high. The U and Th contents in the part of the dyke existing in granite are slightly high than those in that hosted by the mylonite-melange. The Sikait lamprophyre dyke has a calc-alkaline affinity and metaluminous to peraluminous. Its parent melts were derived from a mantle metasomatised by carbonatitic fluids. The protolith was subjected to slight to moderate partial melting in shallow to intermediate depths. During the emplacement of the dyke, U was released from its mineral precursors, transported, and redeposited under favorable condition. Its concentration in the part of the dyke hosted by granite was increased by the action of young surficial processes. On the other hand, Au was derived from the ophiolitic metagabbros and serpentinites that over thursted on the mylonites. It was precipitated from mesothermal and epithermal solutions. The Sikait dyke was affected by several alteration processes; the most common of which is hematitization and metasomatic carbonatization.

Rhizosphere chemistry and above-ground elemental fractionation of nickel hyperaccumulator species from Weda Bay (Indonesia)

The identification and use of hyperaccumulator plants in mining projects has been recognized as an important component of mine planning at several sites around the world. The objective of this research was to provide information on relevant plant tissue chemistry and an indicative assessment of the potential for phytomining at Weda Bay Nickel (WBN), Halmahera. The first stage was the identification of native nickel hyperaccumulator plants. In total, 280 plant tissue samples from 10 nickel accumulator species and 46 matching rhizosphere soil samples were collected. Chemical analyses of plant tissue samples were performed and physico-chemical parameters of the rhizosphere soils were also measured. A total of three species were considered as metal crops: Rinorea aff. bengalensis (up to 22,200 mg kg−1 dry weight at 2 m above ground level), Ficus trachypison (1060 mg kg−1) and Trichospermum morotaiense (5180 mg kg−1), but only R. aff. bengalensis has sufficiently high Ni concentrations in biomass to warrant field trials. Utilising a successional planting strategy, F. trachypison and T. morotaiense could be used to facilitate site conditions, followed by the metal crop R. aff. bengalensis. Using this design, a nickel yield of 330 kg per hectare would be possible every 4 years. In addition to allowing the recovery of nickel, this approach could be an integrated mine site rehabilitation strategy to mitigate environmental impacts, improve soil quality and facilitate transition to other land-uses such as native forest.

First finding of native Nickel in cumulates of the Canindé Domain, Brazil

First finding of native Nickel in cumulates of the Canindé Domain, Brazil

Properties of Reduced Carbon Dioxide Fluid: Evidence from Experimental and Thermodynamic Modeling

It is shown experimentally that fluid mostly consisting of CO2 and CO is a good solvent for many petrogenic and ore components under high P–T parameters. Siderite decomposed to oxides and a mixture of CO2 and CO was the source of the fluid in the experiment. It is demonstrated that an ultrapotassic alkaline melt was formed on the oxide matrix as a result of fluid transport of the components of the basaltic melt at 2–5 kbar and 900–1000°C. This melt is characterized by high concentrations of Rb, LREE, Sr, and Ba. The mechanism of solubility of metals in the carbon dioxide–reduced fluid includes the formation of volatile carbonyls. As is evident from thermodynamic modeling, the stability of Ni(CO)4 at high pressure reaches magmatic temperatures. The finding of native nickel in aerosols during eruption of the Tolbachik Volcano in 2012–2013 is explained by decomposition of carbonyl from fluid of a deep origin during magma ascent.

Vacancy-Induced Semiconductor–Insulator–Metal Transitions in Nonstoichiometric Transition Metal Oxides

Metal–insulator transitions in strongly correlated transition metal oxides (TMOs) induced by electrochemical charging have been attributed to formation of vacancy defects. However, the role of native defects in affecting these transitions is not well understood. This presentation will discuss a new type of phase transition in p-type, nonstoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition along with the complete reversal of conductivity from p- to n-type at room temperature induced by the interaction of native vacancy defects with redox species such as Li+ during electrochemical charging. Direct observation of vacancy-ion interactions using in-situ near-infrared photoluminescence spectroscopy show that this transition is a result of passivation of native nickel (cationic) vacancy defects and subsequent formation of oxygen (anionic) vacancy defects driven by Li+ insertion into the lattice. Changes in the oxidation states of nickel due to defect interactions probed by X-ray photoemission spectroscopy support the above conclusions. In contrast, n-type, nonstoichiometric tungsten oxide shows only insulator-to-metal transition, which is a result of oxygen vacancy formation. The defect-property correlations shown here in these model systems can be extended to other oxides to enable rational engineering of a new robust class of nanoscale, low temperature TMO catalysts and sensors having tailored functionality and selectivity.

Noble metals in graphite-bearing rocks of the Liumao deposit (China)

Native gold, platinum, nickel, and other ore minerals have been discovered in graphite-bearing rocks of the Liumao deposit (Heilongjiang province, China). The results obtained are similar to the previously published materials on the mineralogy of carbon-rich formations of the Tamga and Turgenevo deposits (Primorye, Russian Far East) located in the same region of graphitization in the Khankai terrane as the Chinese object. The defined similarities are most likely explained by participation of deep reduced fluids in the process of ore genesis.

Vacancy-Induced Semiconductor-Insulator-Metal Transitions in Nonstoichiometric Nickel and Tungsten Oxides.

Metal-insulator transitions in strongly correlated oxides induced by electrochemical charging have been attributed to formation of vacancy defects. However, the role of native defects in affecting these transitions is not clear. Here, we report a new type of phase transition in p-type, nonstoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition along with the complete reversal of conductivity from p- to n-type at room temperature induced by electrochemical charging in a Li+-containing electrolyte. Direct observation of vacancy-ion interactions using in situ near-infrared photoluminescence spectroscopy show that the transition is a result of passivation of native nickel (cationic) vacancy defects and subsequent formation of oxygen (anionic) vacancy defects driven by Li+ insertion into the lattice. Changes in the oxidation states of nickel due to defect interactions probed by X-ray photoemission spectroscopy support the above conclusions. In contrast, n-type, nonstoichiometric tungsten oxide shows only insulator-to-metal transition, which is a result of oxygen vacancy formation. The defect-property correlations shown here in these model systems can be extended to other oxides.