Platinum Capsules Research Articles

Experimental Modeling of Decarbonation Reactions, Resulting in the Formation of CO2 Fluid and Garnets of Model Carbonated Eclogites under Lithospheric Mantle P,T-Parameters

First experimental modeling of decarbonation reactions resulting in the formation of CO2-fluid and Mg, Fe, Ca, and Mn garnets, with composition corresponding to the garnets of carbonated eclogites of types I and II (ECI and ECII), was carried out at a wide range of lithospheric mantle pressures and temperatures. Experimental studies were performed on a multi-anvil high-pressure apparatus of a “split sphere” type (BARS), in (Mg, Fe, Ca, Mn)CO3-Al2O3-SiO2 systems (with compositional variations according to those in ECI and ECII), in the pressure interval of 3.0–7.5 GPa and temperatures of 1050–1450 °C (t = 10–60 h). A specially designed high-pressure cell with a hematite buffering container—preventing the diffusion of hydrogen into the platinum capsule—was used, in order to control the fluid composition. Using the mass spectrometry method, it was proven that in all experiments, the fluid composition was pure CO2. The resulting ECI garnet compositions were Prp48Alm35Grs15Sps02–Prp44Alm40Grs14Sps02, and compositions of the ECII garnet were Prp57Alm34Grs08Sps01–Prp68Alm23Grs08Sps01. We established that the composition of the synthesized garnets corresponds strongly to natural garnets of carbonated eclogites of types I and II, as well as to garnets from xenoliths of diamondiferous eclogites from the Robert Victor kimberlite pipe; according to the Raman characteristics, the best match was found with garnets from inclusions in diamonds of eclogitic paragenesis. In this study, we demonstrated that the lower temperature boundary of the stability of natural garnets from carbonated eclogites in the presence of a CO2 fluid is 1000 (±20) °C at depths of ~90 km, 1150–1250 (±20) °C at 190 km, and 1400 (±20) °C at depths of about 225 km. The results make a significant contribution to the reconstruction of the fluid regime and processes of CO2/carbonate-related mantle metasomatism in the lithospheric mantle.

Concerning the incorporation of potassium in the crystal structure of combeite (Na2Ca2Si3O9)

Potassium incorporation in the structure of combeite has been studied in detail. Since natural combeites are known to contain only small amounts of potassium focus was laid on the Na-rich part of a hypothetical solid-solution series with composition Na2-xKxCa2Si3O9. Samples were prepared from mixtures of silica and the corresponding carbonates for nominal compositions with x = 0.2, 0.3 and 0.5, heated from ambient temperature to 1350 °C and slowly cooled to 1000 °C. After disintegration of the carbonates, the platinum capsules used as sample containers were welded shut in order to avoid losses of the volatile K2O and Na2O components. From all three batches potassium containing combeite crystals could be retrieved. Single-crystal diffraction experiments revealed the following compositions: Na2.10(1)K0.11(1)Ca1.90(1)Si3O9, Na2.09(1)K0.18(1)Ca1.91(1)Si3O9 and Na2.13(1)K0.18(1)Ca1.87(1)Si3O9. Consistently, the trigonal crystals (space group P 31 2 1) contained (i) (K + Na):Ca ratios larger than 1:1 and (ii) potassium concentrations lower than those in the starting mixtures. Since the K-contents of the samples obtained from the runs with x = 0.3 and 0.5 were almost identical, the solid-solution seems to be rather limited with an upper boundary of about one potassium atom per unit cell. The structure of the K-containing combeites is very close to the K-free structures reported in the literature. It can be described as a mixed tetrahedral-octahedral network in which additional K, Na and Ca cations are incorporated for charge compensation. A detailed analysis of the topological features of the net is presented. From the six observed extra-framework sites only the M22 position showing a coordination environment with ten next oxygen neighbours is involved in the K-substitution. Potassium uptake is also reflected in increasing values for the lattice parameters a and c as well as the unit-cell volumes. Actually, the c-axis is more affected from the incorporation of the comparatively large K+-cations.

Element loss to platinum capsules in high temperature pressure experiments

Element partition coefficients play key roles in understanding various geological processes and are typically measured by performing high-temperature–pressure (HTP) experiments. In HTP experiments, samples are usually enclosed in capsules made of noble metals. Previous studies have shown that Fe, Ni, and Cu readily alloy with noble metals, resulting in significant loss of these elements from the experimental samples. The loss of elements could severely undermine phase equilibrium and compromise the validity and accuracy of the obtained partition coefficients. However, it remains unclear if other elements (in addition to Fe, Ni, and Cu) will also be lost from samples during HTP experiments, and how to minimize such losses. We performed a series of experiments at 1 GPa and 1400 °C to investigate which elements will be lost from samples and explore the influence of capsule materials and oxygen fugacity ( f O2 ) on the loss behavior of elements. The starting material is a synthesized basaltic glass consisting of 8 major elements and 37 trace elements. The sample capsules included platinum (Pt), graphite-lined Pt, and rhenium-lined Pt, and the experimental oxygen fugacity ( f O2 ) was buffered from <FMQ-2 to ~FMQ+5. Results show that: (1) 15 elements (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Cd, In, Sn, W, and Mo) were lost from the sample due to direct contacting and alloying with Pt under graphite-bufered conditions; (2) graphite and Re lining can physically isolate the starting material from Pt and prevent the loss of V, Cr, Mn, Fe, Zn, Ga, Ge, Cd, In, Sn, W, and Mo, but only slightly reduce the loss of Ni and Cu; and (3) element loss can be significantly reduced under oxidizing conditions, and all elements except Cu were retained in the samples under Ru–RuO 2 buffered conditions. These findings provide several viable capsule assemblies that are capable of preventing or reducing element loss, which may prove useful in determining accurate partition coefficients in HTP experiments.

Experimental study of amphibole crystallization from the highly magnesian melt of Shiveluch volcano

The paper reports results of an experimental study of amphibole crystallization from the highly magnesian andesite melt of Shiveluch volcano, Kamchatka. The experiments were carried out in IHPV at 300 MPa and 940–980°С in iron-saturated platinum capsules, using rapid quenching and temperature oscillations (in some experiments). The redox state of iron in the system was measured before and after the experiments using Mössbauer spectroscopy. The maximum size of the experimental amphibole crystals (up to 200 μm) was close to those of natural amphibole phenocrysts in the volcanic rocks of Shiveluch volcano. The experimental data show that the content of octahedrally coordinated Al (Al6) in the amphibole considerably varies with small variations in the intensive parameters (P, T, and fO2) and composition of the melt, and the maximum Al6 concentration can be evaluated only by using a reasonably large dataset of amphibole analyses. A modified 13eCNK method is suggested to calculate the values of Al6 and Fe3+/Fe2+ with regard for the Ti concentration and the probable partial transfer of Mg into site B in high-Mg amphibole. Calculations with this modified technique yield lower Fe3+/Fe2+ and higher Al6 values. Our experimental data show that the temperature of amphibole liquidus crystallization decreases from about 990 to 960°C when the oxygen fugacity drops from NNO + 1.5 to NNO + 0.4. In view of this, the transition from amphibole-bearing to anhydrous mineral assemblage in the magmas of Shiveluch volcano might have been caused by variations of the oxygen fugacity but not water. The application of our geobarometer to amphiboles from Shiveluch volcano (extrusions Krasnaya and Karan) yields the highest pressure estimate of above 1 GPa, corresponding to the P-T conditions of the melting of garnet-bearing amphibolite in the lower crust.

Carbon solubility in silicate melts in equilibrium with a CO-CO2 gas phase and graphite

The solubility of carbon in silicate melts (Fe-free MORB basalt, Fe-free andesite and Fe-free rhyolite) coexisting with graphite and a CO-CO2 fluid phase was measured to 3 GPa and 1500 °C. Experiments in the 0.2–0.5 GPa range were carried out in an internally heated pressure vessel equipped with a rapid-quench device. In these experiments, glass powder and pure CO gas were directly loaded into platinum capsules; during the runs, graphite precipitated, indicating that the equilibrium 2 CO = C + CO2 in the gas phase was reached. Experiments at higher pressures were carried out in a piston cylinder apparatus, starting with glass powder, graphite, and Ag2C2O4 as a source of CO2. Carbon contents in quenched glasses were measured by secondary ion mass spectrometry (SIMS). Bulk carbon solubility is directly proportional to pressure and follows Henry’s law with good approximation. The effect of temperature on solubility is small. Henry coefficients of bulk carbon solubility obtained by fitting all data were 2.15 ppm C/MPa for MORB, 1.57 ppm C/MPa for andesite and 2.14 ppm C/MPa for rhyolite. In almost all samples, bulk carbon contents were higher than the content of oxidized carbon (CO2 and carbonate). The difference is interpreted to be due to dissolved CO, consistent with bands in the 2100–2200 cm−1 range of the infrared and Raman spectra. For MORB, the solubility cCO of CO (expressed as wt.% carbon) may be described by the relationship log cCOMORB = −5.20 + 0.80 log fCO (R2 = 0.83), where fCO is CO fugacity, while the rhyolite data are best described by log cCORhyolite = −4.08 + 0.52 log fCO (R2 = 0.72). Our data imply that the solubility of carbon in silicate melts depends very strongly on whether or not graphite saturation in the gas phase is reached, as the equilibrium with graphite affects the fugacity of CO and CO2. If the equilibrium 2 CO = C + CO2 is attained through graphite precipitation, bulk carbon solubility will be close to the solubility of CO2 over a wide pressure and temperature range, since the gas phase consists mostly of CO2. Only at low pressures of a few 100 MPa or below, the fraction of CO in the gas phase becomes so large that bulk carbon solubility is significantly reduced compared to CO2. Low carbon solubilities may also be observed in situations where graphite precipitation is kinetically inhibited. This could have been the case in the source region of lunar fire fountain eruptions, where dissolved CO may have caused vapor saturation up to 4 km below the lunar surface. We argue that in a Hadean magma ocean on Earth, extensive graphite precipitation and a low atmospheric pressure on the surface could have stabilized a CO-rich atmosphere that may have limited carbon sequestration in the core. We suggest that dissolved CO in glasses may be easily overlooked, because the infrared extinction coefficient for CO (966 ± 229 l mol−1 cm−2 in rhyolite glass) is more than one order of magnitude lower than that of CO2 or carbonate.

Experimental Study of Unequilibrated Silica Transfer from Liquid Water to the Vapor Phase

Experiments were carried out in hermetically sealed platinum capsules, with water saturated with silica with respect to quartz at 300°C in the lower parts of the electric furnaces, where the temperature slightly increases upward at 0.15°C/cm. Our earlier studies (Alekseyev and Medvedeva, 2017) have shown that these exactly experimental parameters are favorable for silica transfer from the liquid to vapor phase. The statistically processed experimental results show that the molal silica concentration in the liquid phase (m) exponentially decreases with time. This dependence and the fact that the newly produced opal occurs on the capsule walls above the meniscus are consistent with the distillation model. The scatter of the experimental m values turned out to be caused not by differences in the temperature gradient in different wells of the electric furnaces but by the natural roughness of the inner walls of the capsules, which differed from one capsule to another and could even change with time in any given capsule. In the capsules with roughness artificially made on their walls, m decreased much more rapidly, and not only in the bottom but also in the upper parts of the electric furnaces, where temperature decreased upward (–0.08°C/cm). This may suggest that the discovered phenomenon is spread in nature more widely than surmised previously, because this phenomenon does not strongly depend on the direction of the temperature gradient, and voids in natural rocks usually have rough walls.

Gold diffusion into and out of quartz-hosted fluid inclusions during re-equilibration experiments at 600–800 °C and 2 kbar

Fluid inclusions were synthesized in quartz and subsequently re-equilibrated in fluids of different compositions to investigate whether the Au content of fluid inclusions can be modified via Au diffusion through the host quartz. In one experiment fluid inclusions containing 5wt% KCl were synthesized in platinum capsules at 2kbar, 800°C and then re-equilibrated at the same conditions for 4days in a fluid containing 20.1wt% NaCl, 3.5wt% HCl and ~100ppm Cs enclosed in a gold capsule. LA-ICP-MS analyses of 5–10 fluid inclusions before and after the re-equilibration experiment demonstrate that the inclusions gained up to 570ppm Au and up to 0.23wt% Na during the re-equilibration process. Their unchanged high K-content and the absence of Cs within the inclusions proves that they remained physically closed during the re-equilibration, and thus that Na and Au were gained by diffusion through the quartz lattice. In a similar experiment conducted at 600°C the fluid inclusions gained up to 140ppm Au within 14days. Reverse experiments were conducted by synthesizing Au-bearing fluid inclusions in gold capsules and then re-equilibrating them in platinum capsules, which caused the inclusions to lose up to several hundred ppm Au. In both type of experiments Au diffusion appears to have been driven by chemical potential gradients of Au between the fluid inclusions and the external fluid. Additional experiments were performed to test whether Au is able to diffuse into fluid inclusions in response to loss of H+, or indirectly as a consequence of diffusional Cu-gain and corresponding formation of Cu-rich sulfide daughter crystals. However no evidence for Au uptake via such mechanisms was found.If Au concentrations in natural, quartz-hosted fluid inclusions from magmatic-hydrothermal ore deposits are affected, then they likely lost Au rather than gained it. At temperatures below 400°C diffusional loss or gain of Au is considered unlikely in magmatic-hydrothermal systems, but potentially was significant in samples from orogenic Au gold deposits.

Coupled Experimental Study and Thermodynamic Optimization of the K2O-MgO and K2O-MgO-SiO2 Systems

Key phase diagram experiments were conducted to reveal the phase diagram of the K2O-MgO system using thermal analysis and equilibration techniques with sealed platinum capsules. The peritectic reaction of liquid + MgO → K6MgO4 was determined at 1131 K ± 14 K (858 °C ± 14 °C) for the first time. Based on the critical evaluation of all the literature data and the present experimental results, the thermodynamic optimizations of the K2O-MgO and K2O-MgO-SiO2 systems were performed to obtain a set of model parameters describing the Gibbs energies of all phases in the ternary systems. All reliable phase diagrams and thermodynamic properties of the K2O-MgO and K2O-MgO-SiO2 systems were well reproduced from the optimization. The optimized set of the Gibbs energies of all phases can be used to calculate any unexplored phase diagrams and thermodynamic properties in the system.

Synthesis, synchrotron diffraction study and twinning in Na2Ca4Mg2Si4O15 – a heteropolyhedral framework compound

Abstract The formation of polycrystalline Na2Ca4Mg2Si4O15 from solid state reactions has been studied between 800 and 1050°C. Single crystals of the compound have been grown in a closed platinum capsule by slow cooling in the temperature range between 1300 and 1000°C. Basic crystallographic data are as follows: monoclinic symmetry, space group P12/c1, a=7.1717(3) Å, b=5.3512(2) Å, c=16.4789(7) Å, β=90.911(4)°, V=632.33(4) Å3, Z=2. A conspicuous feature of the crystals is an intensive lamellar non-merohedral twinning clearly observable already under a petrographic microscope. The diffraction pattern can be explained as a superposition of two reciprocal lattices with a two-fold axis parallel to [001] being the twin element. Using synchrotron radiation it was possible to solve the crystal structure of Na2Ca4Mg2Si4O15 from a twinned data set. Least-squares refinements resulted in a residual of R(|F|)=0.031 for 2899 observed reflections with I>2σ(I) and 127 parameters. The crystal structure contains both [Si2O7]-dimers and insular [SiO4]-moieties. Tetrahedra and [MgO6]-octahedra form a three-dimensional framework whose topological characteristics have been studied. The remaining calcium and sodium cations are distributed among four crystallographically independent positions located in voids of the network. On a microscopic scale the twinning observed in the diffraction experiments could be explained by the existence of a 21-screw axis parallel to [001] in (¼, 0, z) mapping both domains onto each other. A comparison with related compounds having an A+ 2B2+ 6Si4O15 stoichiometry is presented. More than 25 years after its first observation in refractories our investigation clarifies the crystal structure of a silicate that is of relevance for both Materials science and high pressure research.

Development of Chinese Standard Type of Rhodium-Iron Resistance Thermometer

New rhodium alloy wires with 0.52 % atomic of iron have been drawn, and several batches of RhFe thermometer with strain-free construction and helium-filled platinum capsule have been made using these new alloy wires and old alloy wires which were made in the 1980s in China. In one of the constructions, the coil of wire is inserted into twisted glass tubes, and in the other, it is laid in grooves on a fused-silica crossed frame. The resistance versus temperature relationship and interpolating characteristic of Chinese RhFe thermometer are similar to those of Tinsley 5187U thermometer from 1.5 K to 27 K. The resistance changes of most thermometers are less than that of equivalent to 0.2 mK at 4.5 K after they are exposed to fifty thermal cycles from room temperature to liquid helium temperature. This standard type of rhodium-iron resistance thermometer is now commercially available. Instead of the regular annealing temperature, which is $$750\,^{\circ }$$ C, two batches of RhFe thermometers are made with the annealing temperature of $$850\,^{\circ }$$ C and $$950\,^{\circ }$$ C. The interpolating characteristics of RhFe thermometers will be studied to find new calibration method.

Titanium-hydroxyl defect-controlled rheology of the Earth's upper mantle

Experiments were conducted with hydrous olivine to investigate the defect responsible for the influence of water (hydrogen structurally incorporated as hydroxyl) on the olivine rheology. Solution–gelation derived Fo90 olivine doped with nominally 0.04–0.1 wt.% TiO2 was first hot-pressed and then deformed in platinum capsules at 300 MPa confining pressure and temperatures from 1200–1350°C. The water content was not buffered so that deformation occurred at water-undersaturated conditions. Due to the enhanced grain growth under hydrous conditions, the samples were at least a factor of three more coarse-grained than their dry counterparts and deformed in powerlaw creep at differential stresses as low as a few tens of MPa. Since all experiments were conducted at the same confining pressure, the essentially linear relationship between strain rate and water content was for the first time determined independently of an activation volume. Infrared spectra are dominated by absorption bands at 3572 and 3525 cm−1. These bands also predominate in infrared spectra of natural olivine, and can only be reproduced experimentally in the presence of titanium. In contrast to the previous interpretation of the hydrous rheology in terms of intrinsic point defects, the experiments show that extrinsic defects (impurities) in natural olivine play the dominant role for water weakening at the water contents expected for most of the upper mantle.

Rb2Ca2Si3O9: the first rubidium calcium silicate

Abstract The crystal structure of Rb2Ca2Si3O9 has been characterized by X-ray diffraction techniques and Raman spectroscopy. Crystal growth was performed by the flux method in closed platinum capsules using a polycrystalline ceramic precursor as well as RbCl as a mineralizer. The crystal structure was solved from a single-crystal diffraction data set acquired at 23 °C and refined to a final residual of R(|F|)=0.022 for 1871 independent reflections. Basic crystallographic data are as follows: monoclinic symmetry, space group type P1n1, a=6.5902(3) Å, b=7.3911(3) Å, c=10.5904(4) Å, β=93.782(3)°, V=514.72(3) Å3, Z=2. With respect to the silicate anions the compound can be classified as a sechser single-chain silicate. The undulated chains run parallel to [-101] and are connected by Rb and Ca cations, which are distributed among four crystallographically independent sites. In a first approximation the coordination polyhedra of the two different calcium ions in the asymmetric unit can be described by distorted trigonal prisms and tetragonal pyramids, respectively. The two rubidium sites exhibit more irregular coordination spheres with eight to nine next neighbors. Structural investigations on the new phase are completed by solid state micro-Raman spectroscopy. DFT-calculations were employed for the interpretation of the spectroscopic data including the allocation of the bands to certain vibrational species.

Soret coefficients of alkali oxides in alkali borate glass melts

We measured the Soret coefficients of alkali oxides in binary alkali borate glass melts. The alkali borate glasses, 15(mol %)Li2O–85B2O3, 15Na2O–85B2O3, and 15K2O–85B2O3, were encapsulated in platinum capsules and heat-treated at 1000°C with a temperature gradient in a tube furnace. After the heat treatment, the compositional distribution of the glass sample was measured by Raman spectroscopy. The Soret coefficients of the alkali oxides Li2O, Na2O, and K2O increased with the atomic numbers of the alkali metal ions. This indicates that alkali oxides more easily have high concentration in cold regions as the atomic numbers of the alkali metal ions in the alkali oxides increase. This result provides new information about the diffusion properties in glass melts.

Water, the other network modifier in borate glasses

In the present study we have investigated whether the effect of water on properties of borate glasses resembles that of alkali oxide. Soda–lime–borate glasses with nominal compositions of x Na2O, 10 CaO, (90-x) B2O3 (x=5, 15 and 25mol%) were doped with up to 8wt.% H2O by processing glass powder+distilled water in platinum capsules in an internally heated gas pressure vessel at 1523K and 500MPa. The water content of hydrous glasses was determined by Karl-Fischer titration and near-infrared spectroscopy. The glass transition temperature Tg. was derived from DTA and micropenetration experiments for which the effect of water loss at the surface of the hydrous glasses was studied. Heating glass samples at 10Kmin−1 in the DTA resulted in Tg values which are close to T12 isokom temperatures confirming the equivalence of enthalpy relaxation and viscous relaxation for borate glasses. For all three glass series it is shown that Tg strongly decreases whereas the liquid fragility strongly increases upon the addition of water. These findings reveal that H2O primarily causes breaking of B–O–B bonds rather than supporting 4-fold coordinated boron as it is well-known for alkali oxides in this concentration range.

Experimental synthesis of isochemical kelyphite — a preliminary report

We observed the breakdown of natural garnet in a high–pressure experiment (0.85 GPa and 1100 °C for 2 days) using a piston–cylinder apparatus. Two different types of kelyphites were formed: (1) isochemical and (2) metasomatic. The isochemical kelyphite was composed of orthopyroxene + spinel + plagioclase, whereas the metasomatic one, having a composition altered significantly from the original garnet, was composed of olivine + spinel + plagioclase. These synthetic kelyphites were studied and characterized using EPMA, SEM, EBSD, and TEM and were shown to have many microstructural features as well as their mineral assemblages in common with observed natural kelyphites. The kelyphitization was very heterogeneous and local and was apparently controlled by grain surfaces and intra–grain cracks in garnet. The metasomatic kelyphite apparently formed by a reaction between garnet and aqueous fluids that may have been introduced from outside the platinum capsule through holes accidentally made in the capsule.

Use of platinum capsules in the study of the carbon and hydrogen solubility in silicate melts in equilibrium with liquid iron alloys at high pressures and temperatures

Use of platinum capsules in the study of the carbon and hydrogen solubility in silicate melts in equilibrium with liquid iron alloys at high pressures and temperatures

Short communication: High-pressure synthesis and crystal structure of a novel Mg3CuHx ternary hydride

A novel ternary hydride in the Mg–Cu–H system has been identified by a new synthesis method based on the direct reaction of simple hydrides under high-pressure and moderate-temperature conditions. A well-crystallized sample was obtained in a piston-cylinder hydrostatic press at moderate pressures of 3.5 GPa and temperatures around 850 °C starting from mixtures of MgH2 and Cu enclosed in platinum capsules. X-ray and neutron powder diffraction analysis were used to identify the purity of the samples and provide an accurate description of the crystal structure features. The crystal structure of Mg3CuHx was determined by ab-initio procedures from neutron powder diffraction (NPD) data in the cubic space group F-43m (No. 216), with lattice parameter a = 6.285 Å. The hydrogen positions were determined by Fourier synthesis revealing the introduction of hydrogen atoms in the system. A final Rietveld refinement of the structure gives up a Mg3CuH0.6 composition, which is consistent with the Fourier synthesis. Thermogravimetric analysis (TGA) has been carried out to determine the hydrogen desorption temperature, and to confirm the hydrogen contents. A destabilization with respect to MgH2 hydride, with a reduction of the desorption temperature of approximately 240 °C, suggests that Cu-doping of MgH2 may find applications in the hydrogen storage field.

Modeling a Hypothetical170Tm Source for Brachytherapy Applications

Purpose: To perform absorbed dose calculations based on Monte Carlo simulations for a hypothetical170Tm source and to investigate the influence of encapsulating material on the energy spectrum of the emitted electrons and photons. Methods: GEANT4 Monte Carlo code version 9.2 patch 2 was used to simulate the decay process of170Tm and to calculate the absorbed dose distribution using the GEANT4 Penelope physics models. A hypothetical 170Tm source based on the Flexisource brachytherapy design with the active core set as a pure thulium cylinder (length 3.5 mm and diameter 0.6 mm) and different cylindrical source encapsulations (length 5 mm and thickness 0.125 mm) constructed of titanium, stainless-steel, gold, or platinum were simulated. The radial dose function for the line source approximation was calculated following the TG-43U1 formalism for the stainless-steel encapsulation. Results: For the titanium and stainless-steel encapsulation, 94% of the total bremsstrahlung is produced inside the core, 4.8 and 5.5% in titanium and stainless-steel capsules, respectively, and less than 1% in water. For the gold capsule, 85% is produced inside the core, 14.2% inside the gold capsule, and a negligible amount (<1%) in water. Platinum encapsulation resulted in bremsstrahlung effects similar to those with the gold encapsulation. The range of the beta particles decreases by 1.1 mm with the stainless-steel encapsulation compared to the bare source but the tissue will still receive dose from the beta particles several millimeters from the source capsule. The gold and platinum capsules not only absorb most of the electrons but also attenuate low energy photons. The mean energy of the photons escaping the core and the stainless-steel capsule is 113 keV while for the gold and platinum the mean energy is 160 keV and 165 keV, respectively. Conclusions: A170Tm source is primarily a bremsstrahlung source, with the majority of bremsstrahlung photons being generated in the source core and experiencing little attenuation in the source encapsulation. Electrons are efficiently absorbed by the gold and platinum encapsulations. However, for the stainless-steel capsule (or other lower Z encapsulations) electrons will escape. The dose from these electrons is dominant over the photon dose in the first few millimeter but is not taken into account by current standard treatment planning systems. The total energy spectrum of photons emerging from the source depends on the encapsulation composition and results in mean photon energies well above 100 keV. This is higher than the main gamma-ray energy peak at 84 keV. Based on our results, the use of 170Tm as a brachytherapy source presents notable challenges.

Trace element partitioning between ilmenite, armalcolite and anhydrous silicate melt: Implications for the formation of lunar high-Ti mare basalts

We performed a series of experiments at high pressures and temperatures to determine the partitioning of a wide range of trace elements between ilmenite (Ilm), armalcolite (Arm) and anhydrous lunar silicate melt, to constrain geochemical models of the formation of titanium-rich melts in the Moon. Experiments were performed in graphite-lined platinum capsules at pressures and temperatures ranging from 1.1 to 2.3 GPa and 1300–1400 °C using a synthetic Ti-enriched Apollo ‘black glass’ composition in the CaO–FeO–MgO–Al 2O 3–TiO 2–SiO 2 system. Ilmenite–melt and armalcolite–melt partition coefficients ( D) show highly incompatible values for the rare earth elements (REE) with the light REE more incompatible compared to the heavy REE ( D La Ilm – melt 0.0020 ± 0.0010 to D Lu Ilm – melt 0.069 ± 0.010 for ilmenite; D La Arm – melt 0.0048 ± 0.0023 to D Lu Arm – melt 0.041 ± 0.008 for armalcolite). D values for the high field strength elements vary from highly incompatible for Th, U and to a lesser extent W (for ilmenite: D Th Ilm – melt 0.0013 ± 0.0008, D U Ilm – melt 0.0035 ± 0.0015 and D W Ilm – melt 0.039 ± 0.005, and for armalcolite D Th Arm – melt 0.008 ± 0.003, D U Arm – melt 0.0048 ± 0.0022 and D W Arm – melt 0.062 ± 0.03), to mildly incompatible for Nb, Ta, Zr, and Hf (e.g. D Hf Ilm – melt 0.28 ± 0.05 and : D Hf Arm – melt 0.76 ± 0.07). Both minerals fractionate the high field strength elements with D Ta/ D Nb and D Hf/ D Zr between 1.3 and 1.6 for ilmenite and 1.3 and 1.4 for armalcolite. Armalcolite is slightly more efficient at fractionating Hf from W during lunar magma ocean crystallisation, with D Hf /D W = 12–13 compared to 6.7–7.5 for ilmenite. The transition metals vary from mildly incompatible to compatible, with the highest compatibilities for Cr in ilmenite ( D ∼ 7.5) and V in armalcolite ( D ∼ 8.1). D values show no clear variation with pressure in the small range covered. Crystal lattice strain modelling of D values for di-, tri- and tetravalent trace elements shows that in ilmenite, divalent elements prefer to substitute for Fe while armalcolite data suggest REE replacing Mg. Tetravalent cations appear to preferentially substitute for Ti in both minerals, with the exception of Th and U that likely substitute for the larger Fe or Mg cations. Crystal lattice strain modelling is also used to identify and correct for very small (∼0.3 wt.%) melt contamination of trace element concentration determinations in crystals. Our results are used to model the Lu–Hf–Ti concentrations of lunar high-Ti mare basalts. The combination of their subchondritic Lu/Hf ratios and high TiO 2 contents requires preferential dissolution of ilmenite or armalcolite from late-stage, lunar magma ocean cumulates into low-Ti partial melts of deeper pyroxene-rich cumulates.

Diffusion of the 35S isotope in soda–lime–silica and sodium trisilicate glass melts

The diffusivity of sulphur in nominal 10 Na2O–16 CaO–74 SiO2 (NCS) and 26 Na2O–74 SiO2 (NS3) melts was investigated in the temperature range 1273–1473K using the 35S radioactive isotope in a sandwich setup. Samples were sealed in platinum capsules and run with vertical alignment at 100MPa confining pressure in an internally heated gas pressure vessel. Using the lowest diffusion coefficient D (m2s−1) for each temperature the Arrhenian relations logD=−(4.6±0.3)−(216±7)kJ mol−1/RT for NCS and logD=−(6.3±0.6)−(167±17)kJ mol−1/RT for NS3 were determined. Viscosity of the melts was used to test the applicability of the Stokes–Einstein (SE) and the Eyring (EY) equations to sulphur diffusion. The SE equation yields unrealistically low radii of the diffusing particles, a consequent of the non-molecular structure of the silicate melts. On the other hand, the Eyring relation yields reasonable jump distances of 550pm (NCS) and 750pm (NS3) by fitting the diffusion data to the EY equation. These large values imply that sulphate ions (ionic diameter=290pm) migrate as large entities through the silicate network.