Solubility Of Pt Research Articles

Highly siderophile element fractionation during chondrite melting inferred from olivine-rich primitive achondrites

Metal-silicate segregation is one of the most fundamental mechanisms in planetary differentiation, with primitive achondrites offering important constraints on this process. Brachinites and brachinite-like achondrites (BLA) are olivine-dominated primitive achondrites that experienced up to ∼20% partial melt removal under relatively oxidized (ΔIW ∼ −1) conditions within an initially chondritic parent body and represent residues after inefficient metal-loss. We present bulk rock and in situ lithophile and highly siderophile element (HSE) abundance systematics as well as 187Re-187Os data for five olivine-rich primitive achondrites. These new data confirm classification of Reid 013 as a brachinite, three of the samples as BLA (Northwest Africa [NWA] 6874, NWA 7499, and Miller Range 090805), and the final sample as an ungrouped primitive olivine-rich achondrite (NWA 7680). An aliquot of MIL 090805 shows amongst the highest total HSE contents (>35 ppm) and the highest Pt content (∼23 ppm) of any primitive achondrite. Compiled HSE data for brachinites and BLA show correlations between total HSE abundance, Pt enrichment, and average olivine Fo. This correlation can be explained by variable melting (∼10–20%) of an H ordinary chondrite-like protolith, with retention of both Fe-metal and a Pt-rich alloy phase distinct from the observed Fe-metal phases in more depleted residues. Such a Pt-alloy phase is likely stabilized by elevated abundances of the HSE during chondrite melting and the low solubility of HSE in melts. Rhenium-Os isotope data in the studied samples has been modified by recent mobilization of Re during terrestrial weathering, with the limited range of measured 187Os/188Os in brachinites and BLA supporting minor fractionation of Re/Os during melting and an ancient (∼4.5 Ga) partial melting event to explain their compositions. These results indicate that models of planetary differentiation should consider the low solubility of Pt in chondrite melts and the potential for alloy formation to modify HSE abundances of silicate mantles.

Solubility of Platinum in Pyrite and Pyrrhotite

A temperature range of processes leading to the concentration of Pt in the crust widely varies from high-temperature orthomagmatic to low-temperature hydrothermal and biogenic. Pyrite FeS2 and pyrrhotite Fe1–xS are important components of sulfide ores, which contain platinum-group elements. Fe sulfides typically host from a few hundreds to a few tens ppm of dispersed (invisible) Pt. In this work, we summarized the available data on the solubility of Pt in pyrite and pyrrhotite, supplement them with the results of synthesis of these minerals in the presence of Pt phases, and present a model that can describe the solubility of Pt in a broad range of temperature and S2 fugacity. The resulting equations allow the calculation of the solubility of Pt (ppm) in a temperature range of 300 < t < 1100°C and S2 fugacity up to the equilibrium with Sl. Tables with the solubility of Pt in pyrite and pyrrhotite depending on temperature and S2 fugacity are presented. Isopleths of the solubility of Pt in Fe sulfides are plotted on a log f(S2)–1000/T diagram. The analysis of the position of the main field of ore formation on this diagram showed that pyrite and pyrrhotite dissolve up to a few and a few hundreds of ppm Pt, respectively, upon conditions typical of ore formation: t < 700°C and log f(S2) < –4. These estimations coincide with maximum Pt contents determined in minerals of natural sulfide ores.

Increased brain uptake of pterostilbene loaded folate modified micellar delivery system

Effective chemotherapy for clinical treatment of brain diseases is still lacking due to the poor penetration of the blood-brain barrier (BBB). The aim of this study was to construct a folate modified pterostilbene (Pt) loaded polymeric micellar delivery system (F-Pt/M) with mPEG-PCL as carrier material to aim at penetrating the BBB for brain tissue targeting via receptor-mediated endocytosis. In this study, F-Pt/M was prepared using thin-film hydration method and then optimized by response surface methodology (RSM) with the entrapment efficiency (EE), drug loading (DL) and hydrodynamic diameter (HD) as indexes. The average hydrodynamic diameter and zeta potential of optimal F-Pt/M were 133.2 nm and 24.6 mV, respectively. DL (18.3%) and EE (98.6%) made the solubility of Pt in water about 25 times higher than that of crude Pt. Results of DSC evaluation revealed that drugs were successfully encapsulated inside the polymeric micelles. TEM images showed that homogeneous spherical micellar structures with a narrow size distribution were developed. The release result in vitro showed that F-Pt/M presented sustained release behavior compared to control free Pt solution. Compared to non-targeted Pt/M, F-Pt/M had a significantly higher cytotoxicity against FR-overexpressing A172 cells. In vitro cellular uptake tests illustrated that the micellar delivery system could significantly improve the accumulation of drugs in target cells via receptor-mediated endocytosis. BBB penetration value (P) of F-Pt/M was about 4 folds higher than that of free Pt group. In addition, drug targeting index (DTI) was calculated to determine targeting of F-Pt/M to the brain which was found to be 4.89, implying improved brain targeting was achieved. Hence, the developed F-Pt/M exhibited great potential for delivering more drug molecules across the BBB for the treatment of brain diseases.

Pt accelerated coarsening of A15 precipitates in Cr-Si alloys

The effect of alloying Cr-rich Cr-Si alloys with Pt was investigated by a combination of complementary experimental methods and atomic scale modelling. The investigated Cr-Si and Cr-Si-Pt (Cr ⩾86 at.%) alloys developed a two-phase microstructure consisting of Cr solid solution (Crss) matrix and strengthened by A15 precipitates during annealing at 1200°C. It was found that additions of 2 at.% Pt increase the coarsening rate by almost five times considering annealing times up to 522 h. Pt was found to change the precipitate matrix orientation relationship, despite its low influence on the Crss matrix/A15 precipitate misfit. Through this experimental and modelling approach new insight has been gained into mechanisms of enhanced coarsening by Pt addition. The increased coarsening is principally attributed to a change in interface composition and structure resulting in different thermodynamic stabilities: Pt-containing A15 phase was found to have a broader compositional range if both elements, Pt and Si, are present compared to only Si. Additionally, the Crss phase was found to have a higher solubility of Pt and Si over just Si. Both factors additionally facilitated Ostwald ripening.

The solubility of platinum in magmatic brines: Insights into the mobility of PGE in ore-forming environments

Several field-based studies have proposed that late-stage magmatic aqueous brines may be responsible for the transportation and redistribution of platinum-group elements (PGE) in mafic–ultramafic igneous systems. We experimentally studied the solubility of Pt in high-temperature aqueous brines as a function of oxygen fugacity (ƒO2), temperature (T), pH and total chloride concentration (Cltotal) in a S-free system. Experiments were conducted at 800–1000 °C and 200 MPa in an externally-heated rapid-quench Molybdenum-Hafnium Carbide (MHC) pressure vessel assembly. We employed the synthetic fluid inclusion (SFI) technique to trap and sample pre-equilibrated, high-salinity brines in quartz cylinders subjected to in situ fracturing during experimental run conditions. Platinum solubility was observed to have a positive correlation with ƒO2, temperature, fluid acidity and Cltotal (salinity). A log Pt versus log ƒO2 diagram derives a weighted-error linear regression slope (m) = 0.48 ± 0.04 which demonstrates that Pt is present in the 2+ oxidation state over the studied ƒO2 range. At relatively oxidizing conditions, 1.44 log units above the Ni-NiO oxygen buffer (NNO+1.44), aqueous brines (containing 63 NaCl eq. wt.%) with a mildly acidic fluid composition (pH = 6.03) can dissolve up to ∼100 µg/g Pt at 900 °C and 200 MPa. Aqueous brines with identical fluid compositions yield a solubility of 4–13 µg/g Pt under more reducing conditions (NNO–0.41 to NNO–1.42). Thermodynamic model calculations suggest that both PtCl2 and PtCl3− are the dominant Pt(II)-chloride complexes which facilitate the transport of Pt in high-temperature aqueous vapors and brines. In fluid compositions with Cltotal >32 m (mol/kg H2O), PtCl3− complex is expected to be the dominant Pt species. In natural mafic–ultramafic systems, high-salinity, orthomagmatic aqueous brines may be important transporting agents if such magmatic fluids can participate in the dissolution of Pt-enriched base-metal sulfides or react with discrete insoluble Pt phases imposing a relatively high activity of Pt (i.e., Pt3Fe). Furthermore, precipitation of Pt from aqueous brines is promoted by a decrease in ƒO2, temperature, acidity and Cltotal.

Experimental Study of Pt Solubility in the CO-CO2 Fluid at Low fO2 and Subsolidus Conditions of the Ultramafic-Mafic Intrusions

The solubility of Pt in CO-CO2 fluid was studied experimentally at P = 50–200 MPa and T = 950 °C. A mixture of MgC2O4 and MgCO3 was used as a source of the fluid. Upon the reaction of the Pt capsule walls and the fluid, a carbonyl of platinum is formed. The use of the high-temperature quartz ceramics as a fluid trap avoids the effect of mechanical contamination with Pt from the eroded capsule walls. The total content of platinum in the porous fluid traps was measured by the Electrothermal Atomic Absorption (ET-AAS) method. In some experiments, the local analysis of traps was carried out by the Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) method. The composition of fluid in bubbles captured in an albite glass trap was studied by micro-Raman spectroscopy. On the capsule walls and MgO, Pt “whiskers” of submicron diameter were observed, which were formed as a product of carbonyl decomposition during quenching. About 5–15% of carbonyl withstands quenching resulting in 1.5 to 2 ppm Pt soluble in acetone (runs at P = 200 MPa) in a quartz glass trap. The amount of Pt soluble in acetone from the capsule walls corresponds to a concentration of up to 8 ppm in the fluid. A high content of soluble Pt of 2000–3000 ppm was determined in a carbon coated MgO matrix. Our study demonstrated that the solubility of Pt in the CO-CO2 fluid is 15–150 ppm, presumably in the form of Pt3(CO)62− under conditions corresponding to the conditions of the subsolidus stage of layered ultramafic-mafic and ultramafic-alkaline intrusions formation. Our preliminary data showed that this solubility will increase with the addition of water at low fO2.

The Nature and Composition of the J-M Reef, Stillwater Complex, Montana, USA

Abstract In this contribution, we analyze 30 years of mine development data and quantitatively identify the processes that control the grade and tenor of the mineralized rock. An assay database of more than 60,000 samples was used to examine variations in ore grade and tenor of the sulfide mineralization in the J-M reef horizon of the Stillwater Complex along the strike and down the dip of the deposit in the area of the Stillwater mine. We compare these results with data from the East Boulder mine and whole-rock lithogeochemistry of samples collected along the entire strike length of the complex. We find significant variation in the composition of the reef sulfides in different spatial domains of the Stillwater mine area and between the Stillwater and East Boulder mines. Most of the variation in the grade and tenor can be explained by a variation in the mass of silicate magma with which the sulfide liquid equilibrated (i.e., R factor); however, geochemical and textural evidence suggests that parts of the reef may have experienced significant S loss following initial sulfide melt segregation. Some variability in the reef tenor and grade can be attributed to variable amounts of sulfur loss due to low-temperature hydrothermal fluids and the overestimation or underestimation of metal concentrations in reef assays due to the nugget effect. Furthermore, we address the Pd/Pt ratio of the reef samples and suggest that the lower solubility of Pt in the parental silicate melt may have caused the crystallization and removal of Pt alloys at some point before the melt reached sulfide saturation and Pt could partition into the sulfide liquid. This disparity between the prior evolution of Pt and Pd in the silicate melt resulted in the observed Pd/Pt ratio of ~3.65 across all areas of the reef—a value significantly larger than anticipated for primitive mantle-derived magmas.

Bulk Liquid for the Skaergaard Intrusion and Its PGE-Au Mineralization: Composition, Correlation, Liquid Line of Descent, and Timing of Sulphide Saturation and Silicate–Silicate Immiscibility

AbstractPreferred and modelled bulk composition of the Skaergaard intrusion are compared to coeval basaltic compositions in East Greenland and found to relate to the second evolved cycle of Geikie Plateau Formation lavas and coeval Skaergaard-like dikes in major and trace element (Mg# ∼45, Ce/Nb ∼2·5, (Dy/Yb)N ∼1·35), and precious metal composition (Pd/Pt ∼3, Au/Pt ∼2) as well as in age (∼56 Ma). Successful comparisons of precious metal compositions only occur with Skaergaard models based on mass balance. The bulk liquid of the intrusion evolved along the liquid line of descent to immiscibility between Si- and Fe-rich silicate liquids after ∼90% of crystallization (F = ∼0·10) in agreement with experimental constraints. Immiscibility led to accumulation and fractionation of the Fe-rich silicate melt in the mushy floor of the intrusion and continued accumulation of granophyre component in the remaining bulk liquid. The composition of plagioclase in the precious metal mineralized gabbro and modelling of Pd/Pt and Au/Pt in first formed droplets of sulphide melt suggest that sulphide saturation was reached in interstitial melts in crystal mushes in the floor and roof and in bulk liquid with a composition equivalent to that of the bulk liquid at lower UZa times and after crystallization of 82–85% of the bulk liquid (F = 0·19–0·16). Prior to sulphide saturation in UZa type melt, the precious metals ratios of the bulk liquid were controlled by the loss of Pt relative to Pd and Au in agreement with the low empirical and experimental solubility of Pt of ∼9ppb compared to a much higher value for Pd and Au. The relative timing between sulphide saturation (F = ∼0·18) and immiscibility between silicate melts (F = ∼0·10) and modelled precious metal ratios underpin the proposed multi-stage model for the mineralization, advocating initial accumulation in the mushy floor of the magma chamber controlled by sulphide saturation in mush melts rather than bulk melt, followed by redistribution of precious metals in a macro-rhythmic succession of gabbroic layers of the upward migrating crystallization zone.

Platinum transport in chloride-bearing fluids and melts: Insights from in situ X-ray absorption spectroscopy and thermodynamic modeling

Abstract Hydrothermal chloride-rich fluids are identified at the late stages of the formation of platinum group element (PGE) deposits in giant layered intrusions, and are considered as the PGEs transport media in Cu(-Mo,Au) porphyry systems. In order to quantify the hydrothermal mobility of Pt we performed an investigation of the speciation of Pt in hydrothermal chloride-bearing fluids and dry melt by means of X-ray absorption spectroscopy (XAS). The experiments consisted in recording the Pt L3-edge X-ray absorption near edge structure/extended X-ray absorption fine structure (XANES/EXAFS) spectra of Pt-bearing fluids obtained by dissolution of Pt metal in KCl/HCl and CsCl/HCl fluids in the temperature range from 450 to 575 °C at pressures from 0.5 to 5 kbar. A spectrum of Pt dissolved in dry CsCl/NaCl/KCl + K2S2O8 melt was recorded at 650 °C. The capillary method, when the experimental solution together with Pt(cr) is sealed inside a silica glass capillary, was used. As was determined from the XANES spectra, in all the experimental systems Pt existed in the +2 oxidation state. Analysis of EXAFS spectra showed that Pt is coordinated by four Cl atoms with RPt-Cl = 2.31 ± 0.01 A independently of the T-P-compositional parameters. No evidence of the formation of complex with alkali metal cations in the second coordination sphere of Pt was found by the analysis of the EXAFS spectra of concentrated CsCl brines and melt. Our results imply that PtCl42− is the main Pt-Cl complex which predominates in hydrothermal fluids at t > 400 °C and fluid density d > 0.3 g·cm−3. Experimental data obtained for dry melt of alkali metal chlorides suggest that Pt-Cl complexes can dominate Pt speciation in chloride-bearing aluminosilicate melts where Cl exhibits a salt-like atomic arrangement and ionic bonding. The literature data on the Pt solubility constant, P t ( c r ) + 2 H C l ( a q ) o + 2 C l - = P t C l 4 2 - + H 2 ( a q ) , are compiled and fitted to the simple density model equation log K s o ( P t C l 4 2 - ) = 0.973 - 8202 · T ( K ) - 1 - 5.505 · log d w + 2223 · log d ( w ) · T ( K ) - 1 , where d(w) is the pure water density in g·cm−3. The equation, combined with the extended Debye-Huckel equation for activity coefficients, can be used to calculate the solubility of Pt up to 1000 °C/5 kbar. It accurately predicts the solubility of Pt in concentrated chloride brine (up to 50 wt% NaCl) at parameters of magmatic-hydrothermal transition (800 °C/1.4 kbar). At fluid/vapor density below 0.3 g·cm−3 a neutral complex PtCl2°(aq) is suggested as the dominant Pt species. Our data demonstrate that Pt is highly mobile in high-temperature oxidized chloride-rich hydrothermal fluids. For example, at 800 °C/2 kbar the concentration of Pt can reach a few wt% in the 1 wt% HCl/50 wt% NaCl fluid which is in equilibrium with magnetite-hematite buffer. Once a Cl-reach fluid exsolves from alumuinosilicate melt, Pt follows Cl and enriches the fluid phase where it exists mostly in the form of PtCl42−. Decrease of temperature, acidity, and fluid chlorinity results in precipitation of Pt from the fluid phase.

(Invited) Effects of Ionomers and Fabrication Methods on Both Performance and Durability of Low-Pt-Loading PEFC Cathode Catalyst Layer with Carbon or Conductive Ceramic Supported Pt Catalyst

For the large-scale commercialization of polymer electrolyte fuel cells (PEFCs), it is very important to reduce the amount of Pt by developing highly efficient cathode catalyst layers (CLs) due to the high cost and limited availability of Pt resources. In previous work, we demonstrated the importance of two factors for the design of high performance cathode CLs. The first is higher effective Pt surface area (S(e)Pt), which practically contributes to the oxygen reduction reaction [1]; for example, the n-Pt/AB250 catalyst, for which all of the Pt particles exist only on the AB250 exterior surface, was shown to be highly attractive in order to generate the large current densities required by actual fuel cell operation [2]. The second is the optimized distribution of ionomer on the surfaces both of Pt particles and carbon particles; for example, short-side-chain (SSC) perfluorosulfonic acid ionomers with high ion-exchange capacity (IEC) have shown better continuity and uniformity on Pt and graphitized carbon black particles than conventional ionomers, and this has led to the improvement of both the mass transport and the proton-conducting network in CLs [3].In the first approach for this study, [4] we investigated the effects of high oxygen permeability ionomers and IEC on the cathode performance and durability of PEFCs. The high oxygen permeability ionomers are expected to increase the flux of oxygen near the Pt surface of the three-phase boundary, which is critical in the case of extremely low Pt loadings. The low Pt loading cathode CLs are prepared from an AB250-supported Pt catalyst. From the current-voltage (I-E) curve measurements, the high oxygen permeability ionomers improved the cathode performance without any adverse effects (Fig. 1). During durability testing, the high IEC ionomers lead to increased solubility of Pt and caused severe Pt agglomeration and a large amount of redeposition of Pt particles in the membrane. Based on these results, we propose a strategy of ionomer property selection to improve both cell performance and durability. In the second approach, [5] we focused on the catalyst material and CL fabrication method and prepared low Pt loading CLs with Pt/Ta-SnO2 by the electrospray (ES) method. Two CLs were prepared by the ES method with different volume ratios of ionomer binder to support material (I/S), I/S = 0.7 and 0.2, and were compared to that prepared by the pulse-swirl-spray (PSS) method. Both ES CLs had higher porosity than that for the PSS CL, and had improved ionomer coverage and increased electrochemically active surface area (ECA) and mass activity at 0.85 V. In particular, that for the ES with I/S = 0.2 had high porosity and remarkably increased cell performance (Fig. 2). The improvement obtained by use of the ES method can be explained on the basis that the coverage and uniformity of ionomer are increased due to the small droplet size. The performance of the ES cells is high, particularly under high back-pressure conditions, because of the improved transport of both O2 and protons. ES is an attractive method for the reduction of the Pt loading while improving cell performance. AcknowledgmentThis work was supported by funds for the “Superlative, Stable, and Scalable Performance Fuel Cell” (SPer-FC) project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. The authors are grateful to Asahi Glass Co., Ltd. for kindly providing the experimental ionomers and oxygen permeability results. Also, the authors are grateful to Asahi Kasei Corporation and Denki Kagaku Kogyo Co., Ltd. for kindly providing the experimental ionomer and the experimental AB support, respectively. The authors are also grateful to Tanaka Kikinzoku Kogyo K. K. for kindly preparing the supported Pt catalyst.

Formation of PtSn4 and PtSn in the initial reaction between Pt and molten Sn

The initial reaction between Pt and molten Sn has been studied by dipping tests of 1 and 2 s. It was found that both PtSn and PtSn4 formed in the first second of contact. PtSn formed 7 nm (1 s) and 20 nm (2 s) thick layers on top of the Pt substrate but PtSn4 formed scattered particles in the liquid Sn. No orientation relationship was found between Pt and PtSn. PtSn nucleates heterogeneously on Pt by its larger energy of formation than PtSn4 and PtSn4 nucleates in liquid Sn by the very low solubility of Pt in molten Sn.

Phase equilibria in Ti–Ni–Pt ternary system

Abstract Phase equilibria in Ti–Ni–Pt ternary system have been experimentally determined through diffusion triple technique combined with alloy samples approach. Assisted with electron probe microanalysis (EPMA) and X-ray diffraction (XRD) techniques, isothermal sections at 1073 and 1173 K of this system were constructed and existence of ternary phase Ti2(Ni,Pt)3 was confirmed. In addition, binary compounds Ti3Pt5 and TiPt3– were found to be stable at 1073 and 1173 K, and remarkable ternary solubility in some binary compounds was detected, e.g., solubility of Pt in TiNi can be up to about 36% (molar fraction) at 1073 K and 40% (molar fraction) at 1173 K. Furthermore, a ternary invariant transition reaction TiNi3+Ti3Pt5→Ti2(Ni,Pt)3+TiPt3+ at a temperature between 1073 and 1173 K was deduced.

Measurement of phase equilibria in Ti-Co-Pt ternary system

Phase equilibria in the Ti-Co-Pt ternary system were measured through diffusion triple and alloy sampling. Based on the results from Electron Probe Microanalysis (EPMA) and X-ray diffraction (XRD) techniques, the isothermal sections of the Ti-Co-Pt system were constructed, which consist of 16 and 13 three-phased regions at 973 and 1173K, respectively. A new ternary phase τ was detected, which contains 23.6–29.9at% Pt at 973K and 27.4–40.1at% Pt at 1173K. Furthermore, an invariant reaction between 973 and 1173K was deduced, i.e. τ + Ti4Pt3 ↔ Ti3Pt + TiPt. By the way, the solubilities of Pt mainly substituting for Co in TiCo and TiCo3 respectively increase from 22.4at% and 26.1at% at 973K to 23.8at% and 33.1at% at 1173K.

Effects of Both Oxygen Permeability and Ion Exchange Capacity for Cathode Ionomers on the Performance and Durability of Polymer Electrolyte Fuel Cells

For the large-scale commercialization of polymer electrolyte fuel cells (PEFCs), it is very important to reduce the amount of Pt by developing highly efficient cathode catalyst layers (CLs) due to the high cost and limited availability of Pt resources. We investigate the effects of high oxygen permeability ionomers and ion exchange capacity (IEC) on the cathode performance and durability of PEFCs. The high oxygen permeability ionomers are expected to increase the flux of oxygen near the Pt surface of the three-phase boundary, which is critical in the case of extremely low Pt loadings. The low Pt loading cathode CLs are prepared from the AB250-supported Pt catalyst. From the current-voltage (I-E) curve measurements, the high oxygen permeability ionomers improve the cathode performance without any adverse effects. During durability testing, the high IEC ionomers lead to increased solubility of Pt and cause severe Pt agglomeration and a large amount of redeposition of Pt particles in the membrane. Based on these results, we propose a strategy of ionomer property selection to improve both cell performance and durability.

Solubility of platinum-arsenide melt and sperrylite in synthetic basalt at 0.1 MPa and 1200 °C with implications for arsenic speciation and platinum sequestration in mafic igneous systems

To better understand the Pt-As association in natural magmas, experiments were done at 1200°C and 0.1MPa to measure the solubility of Pt and Pt-arsenide phases (melt and sperrylite, PtAs2), as well as to determine the oxidation state, and identify evidence for Pt-As complexing, in molten silicate. Samples consisting of synthetic basalt contained in chromite crucibles were subject to three experimental procedures. In the first, platinum solubility in the synthetic basalt was determined without added arsenic by equilibrating the sample with a platinum source (embedded wire or bead) in a gas-mixing furnace. In the second, the sample plus a Pt-arsenide source was equilibrated in a vacuum-sealed fused quartz tube containing a solid-oxide oxygen buffer. The third approach involved two steps: first equilibrating the sample in a gas-mixing furnace, then with added arsenide melt in a sealed quartz tube. Oxygen fugacity was estimated in the latter step using chromite/melt partitioning of vanadium.Method two experiments done at high initial arsenic activity (PtAs melt+PtAs2), showed significant loss of arsenic from the sample, the result of vapour transfer to newly-formed arsenide phases in the buffer. Method three experiments showed no loss of arsenic, yielding a uniform final distribution in the sample. Analyses of run-product glasses from experiments which did not show arsenic loss reveal significant increase in arsenic concentrations with fO2, varying from ∼10ppm (FMQ-3.25) to >10,000ppm (FMQ+5.5). Despite very high arsenic loadings (>1000ppm), the solubility of Pt is similar in arsenic-bearing and arsenic-free glasses. The variation in arsenic solubility with fO2 shows a linear relationship, that when corrected for the change in the activity of dissolved arsenic with the melt ferric/ferrous ratio, yields a solubility-fO2 relationship consistent with As3+ as the dissolved species. This result is confirmed by X-ray absorption near edge structure (XANES) determination on run-product glasses.Levels of arsenic required for Pt-arsenide saturation are 50–500ppm over the fO2 range of most terrestrial basalts (FMQ to FMQ-2), >100× higher than the arsenic concentrations typical of such magmas, indicating significant enrichment of arsenic is required if Pt-arsenide saturation is to occur. In contrast, the level of dissolved Pt required to saturate in sperrylite is >8× lower than for pure Pt, suggesting that arsenic enrichment could lead to Pt removal at concentrations much less than required for pure metal saturation.

Effect of counterpart metals in carbon-supported Pt-based catalysts prepared using radiation chemical method

The process of nanoparticle formation by radiation chemical synthesis in a heterogeneous system has been investigated. Carbon-supported Pt-based bimetallic nanoparticles were synthesized using a high-energy electron beam. Rh, Cu, Ru, and Sn were used as counterpart metals. The nanoparticles were characterized by inductively coupled plasma atomic emission spectrometry, transmission electron microscopy, X-ray diffraction, and X-ray absorption spectroscopy. PtRh formed a uniform random alloy nanoparticle, while Cu partially formed an alloy with Pt and the remaining Cu existed as CuO. PtRu formed an alloy structure with a composition distribution of a Pt-rich core and Ru-rich shell. No alloying was observed in PtSn, which had a Pt-SnO2 structure. The alloy and oxide formation mechanisms are discussed considering the redox potentials, the standard enthalpy of oxide formation, and the solid solubilities of Pt and the counterpart metals.

Phase Equilibria in the Fe–Ho–Pt Ternary System at 1173 K

The solid-state phase equilibria in the Fe–Ho–Pt ternary system at 1173 K (Ho ≤75%) were investigated by x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy techniques. The 1173 K isothermal section consists of 18 single-phase regions, 33 two-phase regions, and 16 three-phase regions. At 1173 K, we observed that the maximum solid solubility of Pt in Fe17Ho2, Fe23Ho6, Fe3Ho, and Fe2Ho is below 1 at.%. The binary phase Fe5Ho was not observed. The maximum solubility of Ho in α-Fe is about 1 at.%, and it is below 1.5 at.% in γ-(Fe, Pt), FePt, FePt3, and (Pt, Fe) (the solid solution of Fe in Pt). The existence of HoPt5, HoPt3, HoPt2, Ho3Pt4, HoPt, Ho5Pt4, Ho5Pt3, Ho2Pt, and Ho3Pt is confirmed, and the maximum solid solubility of Fe in them is below 1 at.%.

Thermodynamic properties of platinum chloride complexes in aqueous solutions: Derivation of consistent parameters from literature data and experiments on Pt(cr) solubility at 400–475°C and 1 kbar

The solubility of Pt(cr) in acidic chloride solutions was measured at 400–475°C and P = 0.8–1.0 kbar using an autoclave technique and the analysis of the dissolved component after quenching. The PtCl 3 − complex was identified as the main Pt species at experimental parameters, m(NaCl) = 0.1–3.0 mol/kg H2O and m(HCl) ∼0.01. The thermodynamic parameters of the Helgeson-Kirkham-Flowers (HKF) model were determined for Pt2+ and Pt-Cl complexes (PtCl n 2−n n = 1–4) by analysis of literature data and their adjustment with obtained results. The solubility of Pt under supercritical P-T parameters calculated using these parameters is similar to Pd solubility. The thermodynamic properties and HKF model parameters for aqueous species determined in this study were incorporated into the on-line version of the FreeGC database (http://www-b.ga.gov.au/minerals/research/methodology/geofluids/freegs_about.jsp), which allows calculation of the Gibbs free energy of system components and equilibrium constants of reactions with these species.

The Design and Characterization of a Novel beta-casein Nano-vehicle Loaded with Platinum Anticancer Drug for Drug Delivery

We developed a drug-delivery system comprising a novel platinum drug (Pt(II) complex) entrapped within β-Casein (β-CN) nanoparticles referred to as nano-vehicles. Fluorescence spectroscopy, UV-Vis spectrometry, dynamic light scattering (DLS), and scanning electron microscopy (SEM) were used to characterize the β-CN-Pt(II) complex . What was apparent in this study was that the solubility of Pt (II) complex increased in the presence of β-CN. Furthermore, fluorescence spectroscopy results revealed the binding of the β -CN micelle to the platinum complex at pH 7.0. The tryptophan fluorescence intensity further revealed that the optimal loading molar ratio of β-CN: Pt (II) complex was 1:3 (with β-CN at 1 mg/mL). Under these conditions, the optimal nano-vehicle was formed based on the DLS results. Results from the DLS and SEM analyses are proof for the formation of the β-CN-Pt(II) complex nanoparticles with a very good colloidal stability and an average particle size of 250 nm. Finally, the cytotoxicity of free- and encapsulated-Pt (II) complex was evaluated using colorectal carcinoma HCT116 cells, as a cancer model cell line, because platinum drugs have been used mostly for treatment of Gastrointestinal cancers. Results indicated that the cytotoxicity and cellular uptake of the drug was enhanced when entrapped in β -CN nanoparticles. Polymeric micelles are internalized into the cells via fluid-state endocytosis. These findings suggest that β-CN is an excellent nano-vehicle for targeted delivery of platinum drugs, which are generally recognized as safe (GRAS) and potentially useful in pharmaceutical industries.

The solubility of platinum in silicate melt under reducing conditions: Results from experiments without metal inclusions

The solubility of Pt in silicate melt was investigated at conditions of 2073–2573K, 2GPa and ∼IW −1.5 to +3.5. These are the first measurements of Pt solubility under conditions more reducing than the iron-wüstite buffer (IW) which are demonstrably free from contamination by metal-inclusions. Pt solubility increases with increasing temperature and decreasing oxygen fugacity. The ability of carbon to enhance Pt solubility under reducing conditions (<IW +2) was tested by performing a set of isobaric, isothermal experiments which utilised graphite and PtIr alloy capsules. Analyses of the run-product glasses from these experiments show no correlation between dissolved C and Pt contents. In light of this result, the dissolution of Pt as a neutral species is suggested as being responsible for the observed relationship between solubility and fO2. A compilation of data from this study, Ertel et al. (2006) and Mann et al. (2012), suggests that pressure has no significant effect on solubility between 2 and 18GPa. Metal–silicate partition coefficients calculated from our Pt solubility data show that, for core–mantle equilibrium at IW −2, Pt concentrations in the primitive upper mantle (PUM) can be satisfied if the temperature of equilibration is >3500K. Under these conditions however, the estimated Pt/Os ratio is ∼40,000 times higher than that estimated for the PUM (Brandon et al., 2006). Instead, the PUM composition is generated most readily by metal–silicate equilibrium at more modest temperatures (∼3100K), followed by a late accretion of chondritic material subsequent to core formation.