Silicate Samples Research Articles

Cambrian bimodal volcanism in the Lhasa Terrane, southern Tibet: Record of an early Paleozoic Andean-type magmatic arc in the Australian proto-Tethyan margin

This paper reports new zircon LA-ICP-MS U–Pb age and Hf-isotope, whole-rock major and trace element, and Sr–Nd isotope data from Cambrian metavolcanic rocks in the central Lhasa subterrane of southern Tibet. These rocks form a bimodal volcanic suite consisting mainly of silicic metavolcanic rocks with subordinate metabasalts. Five silicic metavolcanic samples dated at ca. 492Ma and one metabasalt sample yielding a near-concordant 206Pb/238U age of 492±4Ma indicate that mafic and silicic eruptions were contemporaneous. The metabasalts are mostly high-K calc-alkaline, enriched in Th, U, and light rare earth elements (LREEs), and depleted in Nb, Ta, Ti, Zr, and Hf, geochemically resembling the Andean arc basalts. The silicic metavolcanic rocks are high-K calc-alkaline and low in Nb and Zr. The metabasaltic rocks have negative whole-rock εNd(t) values (−4.7 to −3.5) and varying zircon εHf(t) values (−0.7 to +7.5), differing significantly from those of the silicic metavolcanic rocks, which yield negative whole-rock εNd(t) values of −8.4 to −7.2 and varying zircon εHf(t) values (−13.9 to −4.6). The metabasaltic rocks are interpreted as resulting from partial melting of an enriched lithospheric mantle source that was metasomatized by subduction-related components, whereas the silicic metavolcanic rocks were derived from basaltic melt-induced anatexis of the ancient Lhasa basement with inherited mantle melt signatures. The Western Qiangtang–Amdo–Tethyan Himalaya situated in the Indian proto-Tethyan margin and the Lhasa and other possible microcontinents or terranes (e.g., Gongshan, Baoshan, Tengchong, Burma, and Sibumasu) paleographically located in the Australian proto-Tethyan margin represent an early Paleozoic Andean-type magmatic arc facing the proto-Tethyan Ocean. The emplacement of the bimodal volcanic rocks and the development of the Cambro–Ordovician angular unconformity in the central Lhasa subterrane can be attributed to slab break-off of the proto-Tethyan Ocean lithosphere following the collisional accretion of microcontinents or terranes located outboard of the magmatic arc (possibly Eastern Qiangtang and South China).

Natural hydrous amorphous silica: Quantitation of network speciation and hydroxyl content by 29Si MAS NMR and vibrational spectroscopy

Natural and synthetic hydrous amorphous silicas were investigated with single-pulse 29Si magic angle spinning (MAS) NMR and with vibrational spectroscopic methods. Samples included a volcanically derived silica coating on young basalt from Kilauea, Hawaii, as well as hyalite (opal-AN), silica sinters, and synthetic silica gels and silicic acid. Pulse delays of up to an hour were employed for silica samples with slow spin lattice relaxation rates, and nearly fully relaxed spectra (90-100%) were demonstrably achieved for all samples. 29Si NMR spectra consisted of two broad, overlapping peaks at -111 and -102 ppm and a smaller peak at -92 ppm, corresponding to Q4, Q3, and Q2 sites, respectively. The Hawaiian silica coating and silicic acid samples displayed high Q3 and Q2 contents; in particular, the structural Si-OH content of the coating was unusually high for a natural silica (5.4 ± 0.4 wt% H2O). Saturation-recovery spectra of the Hawaiian silica with increasing delay times were consistent with “stretched exponential” relaxation behavior and three-dimensional distribution of paramagnetic centers. Attenuated total reflectance infrared (ATR-IR) and Raman spectra of the silica powders indicated fully amorphous structures, and displayed hydrous (SiO3OH) and anhydrous silicate vibrational bands in positions consistent with previous work. Raman spectra of some samples indicated modest grain to grain heterogeneity. Inferred Si-OH contents from ATR-IR band ratios were strongly correlated with hydroxyl contents calculated from NMR spectra. The high Si-OH content of the Hawaiian silica coating suggests it is diagenetically immature and has not been exposed to elevated temperatures.

New hierarchical zinc silicate nanostructures and their application in lead ion adsorption

A low cost and reliable hydrothermal method was developed for the tunable synthesis of flower-like and urchin-like zinc silicate nanostructures. High resolution TEM, XRD, solid state Si-29 NMR spectra and X-ray nanotomography revealed new morphologies and crystal structures. Solid state NMR indicated very different silicon bonding patterns between the two materials. For urchin-like zinc silicates, a synchrotron based three dimensional X-ray nanotomography technique provided unprecedented structural details and revealed structural defects during the assembly process. For flower-like zinc silicates, HRTEM images showed that their secondary nanopetals had a clay-like layered structure, resulting in a higher BET surface area of 236 m(2) g(-1) as well as higher adsorption capacity for lead ions at 210 mg g(-1) than reported zinc silicate samples. The adsorption isotherms and mechanism were investigated.

Origin of the suppressed matrix effect for improved analytical performance in determination of major and trace elements in anhydrous silicate samples using 200 nm femtosecond laser ablation sector-field inductively coupled plasma mass spectrometry

We have tested an ultraviolet (200 nm) femtosecond laser ablation (200FsLA) sector-field inductively coupled plasma mass spectrometry (SF-ICPMS) system for major and trace element analyses in anhydrous silicate glasses and minerals. Use of the 200FsLA minimized the matrix effect by 50% compared to that of a 193 nm nanosecond excimer LA. The origin of this improvement was identified as the suppression of ‘melting point (MP)-induced’ element fractionation at the LA site due to a decreased thermal effect of the 200FsLA. Sensitivity enhancement in elements with high first ionization energy remained for the basalt aerosols relative to silica-rich aerosols. This is interpreted as being due to the higher thermal conductivity of the basalt aerosols in the inductively coupled plasma enhanced ionization, which is essentially controlled by the first ionization energy of an element. This was confirmed by simulation using Saha's equation and by the analytical data after reduction of the MP-induced fractionation at the LA site. Accurate determination of trace elements (within 5% of accepted values) was achieved for MPI-DING glasses ranging from komatiite to rhyolite, using a single basalt glass BHVO-2G as the calibration standard. This method is also applicable to anhydrous silicate minerals such as plagioclase, pyroxenes, and garnet. However, SRM610 glass, which has a very different matrix compared to BHVO-2G, is preferred for zircon. Apart from this exception, the proposed method requires no external analytical techniques when the amounts of unmeasured elements in the materials, such as halogens or water, are negligibly low, which is the case for many geological materials.

Aluminium-derivatized silica monodisperse nanospheres by a one-step synthesis-functionalization method and application as acid catalysts in liquid phase

Aluminium-derivatized submicron-in-size silica spheres (Al-MSS), with controllable morphology, particle size, mesoporosity, and incorporation of an active phase at the internal surface, have been prepared by a one-step synthesis-functionalization method in view of potential applications in the liquid phase. Four Al-MSS samples were prepared with a molar Si/Al ratio in the initial gel of 44, 22, 11, and 7, and their properties were compared with those of a purely siliceous sample (MSS). Nitrogen adsorption, XRD, SEM and TEM studies revealed homodispersed particles with average diameters ranging between 350 and 520 nm and possessing radial porosity. BET specific surface areas were included between 900 and 1300 m2 g−1 and the average pore diameter varied from 3 to 3.4 nm. Surface reactivity and Al accessibility at the material surface were determined with measurements of two-cycle ammonia adsorption and EDX-based calculations. The best compromise between textural parameters, surface properties, and stoichiometric Al incorporation was achieved with Al-MSS-22. This sample was further characterized by 129Xe-NMR, 27Al-MAS-NMR, XPS, NH3-TPD and IR methods to confirm the high accessibility of its internal porous structure and the presence of weak Bronsted and strong Lewis acid sites on its surface. The catalytic behavior of Al-MSS-22 in the liquid phase was tested in esterification reactions of ethanoic acid with alcohols or polyols such as butanol, isoamyl alcohol, ethylene glycol, and glycerol. In the case of alcohols, the remarkable performance of this aluminosilicate was supported by conversion rates close to 100%, allowing the amount of the catalytic material to be significantly decreased compared with other systems already tested in the literature.

Low temperature conversion of linear C 4 olefins with acid ZSM-5 zeolites of homogeneous composition

Conversion of linear butenes over ZSM-5 zeolites leads to a large variety of products, from olefins to aromatics. At low temperature, these products are mainly olefins from C 3 = to C 13 =, with a predominance of dimeric products. The analysis of the product stream obtained by the reaction of n-butenes over several materials with MFI topology, but with different aluminum content provides evidence for an oligomerization–cracking–realkylation mechanism. The reactions occur predominantly in the catalyst bulk or at the external surface, depending on the amount of coke developed inside the catalyst. This behavior is determined by the concentration of framework Al and associated silanol groups, inducing coking. For Al-rich MFI samples, the amount of hard coke is sufficient to block the access of reactants to internal acid sites. As a result, extra-crystalline catalysis dominates, while the appearance of the individual products is consistent with that predicted by classical carbocation theory. For siliceous samples, hard coke formation is less pronounced, and evidence for shape selective product formation is present. Expected relations among structural, morphological and acidic properties of all MFI materials have been confirmed by XRD, SEM and BET and by 27Al MAS NMR, NH 3-TPD and FTIR.

Ore petrography of low-grade siliceous manganese ores from the Bonai-Keonjhar belt, Orissa, India: The influence of mineral-fabric on their beneficiation

Low grade siliceous manganese ores from the iron ore group of the Bonai-Keonjhar belt, Orissa, India are found mostly in shear zones. The ore characteristics of siliceous manganese ore samples from three different mines, viz. the Shankar (Barbil OMC lease hold area), the Sone-Patuli (Patmunda, OMM lease hold area), and the Musaghar (Roida, OMDC lease hold area), were studied. These siliceous manganese ores are of three types, respectively: (i) spongy-granular; (ii) massive-mosaic; and (iii) hard-mylonitized. The spongy-granular type contains granular, saccharoidal quartz and the major manganese mineral present is pyrolusite. The second type contains well crystallized quartz and cryptomelane, while the third has cherty, fine grained quartz (mylonite) along with romanechite. All three ores were subjected to physical beneficiation under similar conditions. Both gravity and magnetic separation techniques were employed. The mineral-fabric of the ores has been correlated to the extent of their beneficiation using these physical techniques. Of these three ores only the spongy-granular type responded well to upgrading. The feed with 22% Mn content could be upgraded to 44% with a 28% yield and a 49% recovery. The good response to beneficiation of the spongy-granular sample could be due to the large euhedral crystals of pyrolusite and the friable nature of the saccharoidal quartz. This study reveals the influence of mineral-fabric on beneficiation of low grade ore, siliceous Mn ore in particular.

High precision tungsten isotope measurement by thermal ionization mass spectrometry

We describe a new technique for measuring the isotopic abundance of 182W with improved precision in natural silicate samples. After chemical purification of W through a four-step ion exchange chromatographic separation, the W isotopic composition is measured as WO 3 − by negative thermal ionization mass spectrometry using a Thermo-Fisher Triton instrument. Amplifier biases are cancelled by using amplifier rotation, and Faraday cup biases are monitored by using a cup configuration that allows two-line data acquisition. Data are initially corrected for oxide interferences, assuming a predefined O isotope composition, and for mass fractionation, by normalization to 186W/ 184W or 186W/ 183W, using an exponential law. Despite these corrections, isotopic ratios exhibit small but strongly correlated variations. This second-order effect may reflect a mass dependent change of O isotope composition in the measured W (and Re) oxides, and is corrected by normalization to 183W/ 184W using a linear law. Repeated analysis of an Alfa Aesar W standard ( n = 39), and of three dissolutions of a La Palma (Canary Islands) basalt, applying the double normalization procedure, demonstrate external reproducibility of 182W/ 184W within ±4.5 ppm (2 σ SD). Repeated measurement of a gravimetrically prepared mixture of a natural W standard and a 182W enriched spike shows that differences in 182W/ 184W of ∼10 ppm can be well resolved using this method. The external reproducibility of ±4.5 ppm is ∼5 times more precise than conventional W isotope measurements by MC-ICP-MS. The new technique constitutes an ideal tool for investigating the W isotope composition of terrestrial rocks for potential contributions from the core, and late accreted extraterrestrial materials.

Rapid environmental analysis using molten salt fusion sample preparation

Abstract For the analysis of the isotopic composition of environmental samples, including transuranic materials there are many methods that exist. This paper describes the development of a high throughput method, which involves dissolving a soil into an aqueous matrix, producing a homogenous mixture, and separating radionuclides to enable the identification of specific isotopes. A standard method was modified via changes in oxidation, chemical exchange, decomposition, or rearrangements to form constituents that are more soluble in acidic aqueous solutions. To accomplish this, a molten-salt fusion, dissolution in dilutes nitric or hydrochloric acids, with subsequent separation using ion exchange, direct deposition, and counting by alpha-spectrometry was used. This method is ideal for silicate samples, but can be modified to accommodate more complex soil samples.

The influence of multivariate analysis methods and target grain size on the accuracy of remote quantitative chemical analysis of rocks using laser induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used to quantitatively analyze 195 rock slab samples with known bulk chemical compositions, 90 pressed-powder samples derived from a subset of those rocks, and 31 pressed-powder geostandards under conditions that simulate the ChemCam instrument on the Mars Science Laboratory Rover (MSL), Curiosity. The low-volatile (<2 wt.%) silicate samples (90 rock slabs, corresponding powders, and 22 geostandards) were split into training, validation, and test sets. The LIBS spectra and chemical compositions of the training set were used with three multivariate methods to predict the chemical compositions of the test set. The methods were partial least squares (PLS), multilayer perceptron artificial neural networks (MLP ANNs) and cascade correlation (CC) ANNs. Both the full LIBS spectrum and the intensity at five pre-selected spectral channels per major element (feature selection) were used as input data for the multivariate calculations. The training spectra were supplied to the algorithms without averaging ( i.e. five spectra per target) and with averaging ( i.e. all spectra from the same target averaged and treated as one spectrum). In most cases neural networks did not perform better than PLS for our samples. PLS2 without spectral averaging outperformed all other procedures on the basis of lowest quadrature root mean squared error (RMSE) for both the full test set and the igneous rocks test set. The RMSE for PLS2 using the igneous rock slab test set is: 3.07 wt.% SiO 2, 0.87 wt.% TiO 2, 2.36 wt.% Al 2O 3, 2.20 wt.% Fe 2O 3, 0.08 wt.% MnO, 1.74 wt.% MgO, 1.14 wt.% CaO, 0.85 wt.% Na 2O, 0.81 wt.% K 2O. PLS1 with feature selection and averaging had a higher quadrature RMSE than PLS2, but merits further investigation as a method of reducing data volume and computation time and potentially improving prediction accuracy, particularly for samples that differ significantly from the training set. Precision and accuracy were influenced by the ratio of laser beam diameter (∼490 μm) to grain size, with coarse-grained rocks often resulting in lower accuracy and precision than analyses of fine-grained rocks and powders. The number of analysis spots that were normally required to produce a chemical analysis within one standard deviation of the true bulk composition ranged from ∼10 for fine-grained rocks to >20 for some coarse-grained rocks.

Effect of water soluble PVA on the microstructure characteristics of C-S-H formed in Na2SiO3-Ca(NO3)2 solution system

The structure characteristics of hydrated calcium silicate synthesized by solution reaction method with the existing of water soluble polymer polyvinyl alcohol (PVA) are investigated. Using Na2SO3 and Ca(NO3)2 as the main raw materials, in the condition of 2%(in weight) addition of PVA and the water to solid ratio of 20, hydrated calcium silicate samples (Ca/Si=1.0 and 1.5) were prepared with 60 °C water bath. IR, BET, XRD and SEM methods were used to study the microstructure of the hydration products. The results showed that the addition of water soluble PVA did not alter obviously the amorphous structure characteristic of hydrated calcium silicate, but it had effects on the polymerization status of Si-O chain and the pore structure. The effects are somewhat obvious in the samples with the Ca/Si of 1.0.

Origin and age of the Eisenkappel gabbro to granite suite (Carinthia, SE Austrian Alps)

The northern part of the Karawanken plutonic belt is a gabbro–granite complex located just north of the Periadriatic lineament near the Slovenian–Austrian border. Petrographic and geochemical studies of the Eisenkappel intrusive complex indicate that this multiphase plutonic suite developed by a combination of crystal accumulation, fractional crystallization and assimilation processes, magma mixing and mingling. The mafic rocks are alkaline and have within-plate geochemical characteristics, indicating anorogenic magmatism in an extensional setting and derivation from an enriched mantle source. The mafic melts triggered partial melting of the crust and the formation of granite. The granitic rocks are alkalic, metaluminous and have the high Fe/Fe+Mg characteristics of within-plate plutons. Temperature and pressure conditions, derived from amphibole-plagioclase and different amphibole thermobarometers, suggest that the analysed Eisenkappel gabbros crystallized at around 1000±20°C and 380–470MPa, whereas the granitic rock crystallized at T≤800±20°C and≤350MPa. Mineral-whole rock Sm–Nd analyses of two cumulate gabbros yielded 249±8.4Ma and 250±26Ma (εNd: +3.6), garnet-whole rock Sm–Nd analyses of two silicic samples yielded well-constrained ages of 238.4±1.9Ma and 242.1±2.1Ma (εNd: −2.6).

Geochemical assessment of a siliceous limestone sample for cement making

A low grade siliceous limestone sample from the Jayantipuram mine of Andhra Pradesh, India, has been investigated for its suitability for cement making. Petrological as well as X-ray diffraction pattern studies indicated that the limestone sample was crystalline and dominantly composed of calcite and quartz. They are simple in mineralogy, and yet they have variable silica and lime contents. Geochemical analysis results of twenty five hand picked samples indicated that the limestone from the Jayantipuram mine shows a wide range of variations in LOI (29.94% to 40.64%), SiO2 (6.14% to 27.18%), CaO (37.93% to 50.78%), Al2O3 (0.49% to 2.27%) and Fe2O3 (0.28% to 2.4%). MgO, K2O, Na2O, TiO2 and MnO2 are present in traces. CaO with LOI shows a strong positive correlation where as CaO with SiO2 shows a strong negative correlation because of mineralogical factors. The chemical composition of the limestone reflects its mineralogical composition. The distribution of various elements in the acid-soluble fraction has been studied by the factor analysis method in order to interpret in terms of their mineralogy, sedimentary environment and diagenesis. Mineralogy, recrystallization and other diagenetic changes are the main factors affecting the distribution of the elements and their mutual relationships in the limestone. The aim of this paper is also to analyze how significantly the two parameters, silica modulus and lime saturation factor, influence this low grade siliceous limestone sample from the Jayantipuram mine of Andhra Pradesh, India, for the cement making process from the geochemical data.

Thermal conductivities study on silica aerogel and its composite insulation materials

This paper presents a theoretical and experimental study on thermal conductivities of silica aerogel, xonotlite-type calcium silicate and xonotlite–aerogel composite insulation material. The transmittance spectra of silica aerogel and xonotlite-type calcium silicate samples are obtained through FTIR measurements. The corresponding extinction coefficient spectra of the three materials are then obtained by applying Beer’s law. The thermal conductivities of aerogel, xonotlite-type calcium silicate, and xonotlite–aerogel composite insulation material are measured from 300 to 970 K and from 0.045 Pa to atmospheric pressure with the transient hot-strip (THS) method. The thermal conductivity models developed for coupled heat transfer of gas and solid based on the unit cell method are compared with the experimental measurement results. It is shown that the effective thermal conductivity models matches well with the experimental data. The specific spectral extinction coefficients of xonotlite-type calcium are larger than 10 m 2 kg −1, and the specific spectral extinction coefficients of aerogel are larger than 7 m 2 kg −1 over the whole measured spectra. The density of xonotlite-type calcium silicate is the key factor affecting the effective thermal conductivity of xonotlite–aerogel composite insulation material, and the density of aerogel has little influence. The effective thermal conductivity can be lowered greatly by composite of the two materials at an elevated temperature.

Melting Behavior of Siliceous Nickel Ore in a Rotary Kiln to Produce Ferronickel Alloys

Ferronickel alloys as a nickel source for high alloy steels such as stainless steels are produced from garnierite ores by means of a rotary kiln. That is basically modification of Krupp–Renn process by which clinkers, that are mixtures of ferronickel alloy particles and partially melted slag, can be extracted. It is necessary to have exact knowledge of how the ore is softening with increasing temperature because controlling this behavior is considered to be a key to stable operation.A study has been carried out to understand the melting behavior of pelletized siliceous nickel ore samples blended with limestone and anthracite heating up to 1300°C. Microscopic observation revealed that mineralogical phases in equilibrium were 2(Mg, Fe)O·SiO2 olivine and (Mg, Fe)O·SiO2 enstatite. It was further found that clear formation of liquid phase composed of CaO–SiO2–FeO–Al2O3–MgO system as a result of assimilation with CaO in the case of ore containing higher Al2O3 and CaO contents with lower MgO/SiO2 ratio. Besides, this type of ore had ability to be molten by itself to generate primary liquid inside the ore. The primary liquid formation could promote assimilation with CaO particles to spread liquid phase causing melting of the ore. Mineralogical phases at 1300°C calculated by thermodynamic software were in good agreement with the experimental results.In contrast, ore with lower Al2O3 and CaO contents with higher MgO/SiO2 ratio could not generate liquid phase even though limestone was blended. A number of remained CaO particles were observed without assimilating with the ore. It was therefore considered that higher assimilation ability of CaO with ore enhanced liquid formation and that this property was determined mainly by Al2O3 and CaO contents and MgO/SiO2 ratio of the ore.

Membrane Growth of Nanoporous Silicates via the Self-Assembly Monolayer

The self-assembly monolayer (SAM) method was used for membrane fabrication, in which Si wafers were treated separately with N-trimethoxysilylpropyl-n,n,n-tri-n-butylammonium bromide (TMSP-TBA) and N-trimethoxysilylpropyl-n,n,n-trimethylammonium chloride (TMSP-TMA) to form monolayers on the Si surfaces. To grow silicate membranes on the organosilyl-treated Si wafers, a series of silicate sols were prepared with composites of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) as silicate sources, and tetrapropylammonium bromide (TPABr) was used as an organic template. Their microstructures were investigated in detail by comparing them using SEM and XRD. The use of MTES hindered the formation of microporous channels in the calcined silicate samples. The calcined silicate samples became totally amorphous over 20% loading of MTES. In addition, their structural information was supported by spectroscopic (FT-IR and solid-state 29Si NMR) analyses.

Controllable Morphology and Photocatalytic Performance of Bismuth Silicate Nanobelts/Nanosheets

Bismuth silicate (BSO) nanobelts/nanosheets were successfully synthesized for the first time via a one-pot hydrothermal method. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), N2adsorption-desorption (BET), and UV-vis diffuse reflectance spectroscopy (DRS). The results showed that the concentration of cetyltrimethyl ammonium bromide (CTAB) had crucial effect on the formation of the phase and structure of BSO nanobelts/nanosheets, CTAB acted as a structure-directing reagent. A morphology-controlled process and formation mechanism are proposed. The bismuth silicate samples showed higher photocatalytic activity for the degradation of phenol and azo dye RhB than the commercial catalyst P25. The effects of surface area and morphology of the BSO samples on different photocatalytic activity were also discussed.

Synthesis and characterization of silica gel from siliceous sands of southern Tunisia

The present work aimed to achieve valorization of Albian sands for the preparation of sodium silicates that are commonly used as a precursor to prepare silica gel. A siliceous sand sample was mixed with sodium carbonate and heated at a high temperature (1060°C) to prepare sodium silicates. The sodium silicates were dissolved in distilled water to obtain high quality sodium silicate solution. Hydrochloric acid was then slowly added to the hydrated sodium silicates to obtain silica gel. The collected raw siliceous sands, as well as the prepared silica gels, were characterized by different techniques, such as X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis (DSC). XRF confirmed that the detrital sand deposits of southern Tunisia contain high amounts of silica, with content ranging from 88.8% to 97.5%. The internal porosity varied between 17% and 22%, and the specific surface area was less than 5m2/g. After the treatment described above, it was observed that the porosity of the obtained silica gel reached 57% and the specific surface area exceeded 340m2/g. Nitrogen adsorption isotherms showed that the prepared silica gels are microporous and mesoporous materials with high adsorption capacities. These results suggest that the obtained silica gels are promising materials for numerous environmental applications.

Na 2O solubility in CaO–MgO–SiO 2 melts

The sodium solubility in silicate melts in the CaO–MgO–SiO 2 (CMS) system at 1400 °C has been measured by using a closed thermochemical reactor designed to control alkali metal activity. In this reactor, Na (g) evaporation from a Na 2O– xSiO 2 melt imposes an alkali metal vapor pressure in equilibrium with the molten silicate samples. Because of equilibrium conditions in the reactor, the activity of sodium-metal oxide in the molten samples is the same as that of the source, i.e., aNa 2O (sample) = aNa 2O (source). This design also allows to determine the sodium oxide activity coefficient in the samples. Thirty-three different CMS compositions were studied. The results show that the amount of sodium entering from the gas phase (i.e., Na 2O solubility) is strongly sensitive to silica content of the melt and, to a lesser extent, the relative amounts of CaO and MgO. Despite the large range of tested melt compositions (0 < CaO and MgO < 40; 40 < SiO 2 < 100; in wt%), we found that Na 2O solubility is conveniently modeled as a linear function of the optical basicity ( Λ) calculated on a Na-free basis melt composition. In our experiments, γNa 2O (sample) ranges from 7 × 10 −7 to 5 × 10 −6, indicating a strongly non-ideal behavior of Na 2O solubility in the studied CMS melts (γNa 2O (sample) ≪ 1). In addition to showing the effect of sodium on phase relationships in the CMS system, this Na 2O solubility study brings valuable new constraints on how melt structure controls the solubility of Na in the CMS silicate melts. Our results suggest that Na 2O addition causes depolymerization of the melt by preferential breaking of Si–O–Si bonds of the most polymerized tetrahedral sites, mainly Q 4.

Simultaneous Determination of Cd, In, Tl and Bi by Isotope Dilution‐Internal Standardisation ICP‐QMS with Corrections Using Externally Measured MoO+/Mo+ Ratios

A method for the simultaneous determination of Cd with In, Tl and Bi by isotope dilution‐internal standardisation (ID‐IS) ICP‐QMS using the same aliquot for rare earth element and other trace element determinations was developed. Samples mixed with an enriched 149Sm spike were decomposed using a HF‐HClO4 mixture, which was evaporated and then diluted with HNO3. After determination of Sm by ID‐ICP‐QMS and Cd, In, Tl and Bi concentrations were determined using the 149Sm intensity as an internal standard. The interference of MoO+ on Cd+ was corrected using the MoO+/Mo+ ratio separately measured using a Mo standard solution, and the validity of the externally determined oxide‐forming ratio correction was evaluated. The MoO+/Mo+ ratios measured using the standard solution and samples were ∼ 0.0002 and &lt; 0.002, respectively. Detection limits for Cd, In, Tl and Bi in silicate samples were at levels of &lt; 1 ng g−1 with a total uncertainty of &lt; 7%. Cadmium in the carbonaceous chondrites, Orgueil (CI1), Murchison (CM2) and Allende (CV3) as well as Cd, In, Tl and Bi in the reference materials, JB‐2, JB‐3, JA‐1, JA‐2, JA‐3, JP‐1 (GSJ), BHVO‐1, AGV‐1, PCC‐1 and DTS‐1 (USGS) and NIST SRM 610, 612, 614 and 616 were determined to show the applicability of this method.