Physicochemical Evolution Research Articles

Mantle-Derived Cargo vs Liquid Line of Descent: Reconstructing the P–T–fO2–X Path of the Udachnaya–East Kimberlite Melts during Ascent in the Siberian Sub-Cratonic Lithosphere

Abstract Disentangling the physico-chemical evolution of the melts that give rise to kimberlites during their genesis, ascent through the sub-cratonic lithosphere and emplacement in the crust is challenging. This is because the extensive entrainment and assimilation of, and reaction with, mantle-derived material makes kimberlites mixtures of xenocrystic, magmatic components and alteration minerals, rarely preserving evidence of their original melt composition. Here, a detailed textural and compositional study of coherent and volcaniclastic kimberlite units from the Udachnaya–East pipe (Siberian craton) was performed to reconstruct the pressure–temperature–oxygen fugacity-compositional (P–T–fO2–X) path of kimberlite melts during their ascent through the sub-cratonic lithosphere. Routine and high-precision electron microprobe analyses of olivine, phlogopite and Fe–Ti oxides enabled to discriminate the mantle-derived cargo from the magmatic components, and thus make inferences on the liquid line of descent (LLD) of proto-kimberlite to kimberlite melts. Most of the olivine cores in Udachnaya–East kimberlite are xenocrystic and record conditions of last equilibration in the Siberian sub-cratonic lithospheric mantle at T–P ranging from 812–1227°C at 3.1–5.4 GPa, to 871–1170°C at 4.6–7.0 GPa, depending on the chosen model geotherm (35 mW/m2 vs 40 mW/m2). Based on their Ni, Cr, Mn, Al and P vs Mg/Fe systematics, olivine core populations were associated to the sheared, granular garnet-bearing or spinel-bearing cratonic peridotites. The occurrence of olivine Internal Zones (I) having the same composition as Fe-rich cores, as well as rare mantle-derived xenocrystic cores of phlogopite, bear witness of mantle metasomatism preceding kimberlite ascent. The assimilation of mantle material by initially H2O- and P-rich proto-kimberlitic melts is recorded by the cotectic formation of magmatic olivine Internal Zones (II) and phlogopite Internal Zones around resorbed xenocrystic cores. The LLD then evolved by inducing cotectic precipitation of olivine, phlogopite rims and Cr-spinel at P of 1.5–3.0 GPa, T of 1120–1250°C and fO2 from −2.8 to −1.6 ΔFMQ. Ilmenite–magnetite pairs in the groundmass record the later conditions of crystallization that occurred at P of ~1.0 GPa, T from 1133°C down to 1000°C and fO2 of +0.3 to +0.9 ΔFMQ. These results confirm the progressive oxidation of the melt that finally led to the formation of calcite, apatite and Mg-rich olivine and phlogopite rinds. The F-enrichment of phlogopite rinds reflects a late decrease of the H2O/CO2 activity of the melt that evolved toward alkali-carbonated composition. Our results showed that the crystal cargo of kimberlites can be used to track all processes acting in between the melt-rock reactions in the mantle and the emplacement in the crust.

Magma Evolution and Constraints on the Graphite Mineralization Hosted by the Huangyangshan Alkaline Granite Suite in the East Junggar of Xinjiang Province: Evidence from In Situ Analyses of Silicate Minerals

The Huangyangshan super-large graphite deposit, located in the East Junggar area of the Xinjiang Province, is hosted in and has closely temporal, spatial, and genetic relationships with the Huangyangshan alkaline granites. There are such silicate minerals as amphibole, biotite, pyroxene, and plagioclase occurring in the graphite-bearing granites. The integration of the electron microprobe analysis (EMPA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) enabled us to reveal the physicochemical conditions and evolution process, as well as the relationship of alkaline magmatism with graphite mineralization. The results show that the amphiboles generally have low Al and high Ti, K, Si, and Fe contents, as well as similar rare-earth elements (REEs) patterns and trace element distribution patterns to granites with significantly negative Eu anomalies. In the analyzed samples, primary biotite belongs to Fe-biotite and has characteristics of high Si and Fe and low Al and Mg contents. In the graphite orbicules, the pyroxene phenocrysts develop multiple zonal structures and are characterized by high Si and low Ca and Fe contents. The dominant plagioclase phenocrysts in the graphite orbicules are oligoclase and andesine, with normal and occasionally oscillatory zoning. The calculated crystallization temperature of the pyroxene, amphibole, and primary biotite in graphite orbicules are 840–1012 °C, 681–761 °C, and 658–720 °C, respectively, corresponding with their crystallization order. The pressure and depth calculation results of the amphibole, representing those of the magmatism, are 157–220 Mpa and 5.95–8.32 km, respectively. Both amphibole and biotite crystallized in a reducing environment with extremely low oxygen fugacity. The elemental compositions of these silicates indicate that the Huangyangshan pluton experienced significant mixing of mafic mantle-derived magma and felsic crust-derived magma. The cores of graphite orbicules were formed in a relatively earlier magmatic stage, while the granites and their dioritic enclaves were formed in a later magmatic stage. During magmatism, the mixing of mantle-derived basic magma had an important influence on the evolution and differentiation of the melts. According to the coexisting sulfides with graphite and compositional difference of amphibole and biotite in the granites and graphite ores, the graphite mineralization might be triggered by a magma mixing process.

Garnet geochemistry of the giant Beiya gold–polymetallic deposit in SW China: Insights into fluid evolution during skarn formation

The Beiya deposit in the central Jinshajiang–Ailaoshan metallogenic belt of SW China is the country’s largest gold skarn and third largest gold deposit. In this study of the Beiya deposit, we use garnet mineralogy and geochemistry to delineate three skarn alteration zones (i.e., contact, proximal and distal skarn). We investigate the possible controls on the rare earth element (REE) incorporation into skarn-type garnet, the ore-fluid evolution, and metasomatic dynamics. Garnet in the Beiya deposit belongs to the grossular–andradite solid solution series, and comprises three types: (1) Grt1 andradite (Adr67–88Grs9–32) in the contact skarn, exhibiting light REE (LREE) enrichments, heavy REE (HREE) depletions, and positive Eu anomalies; (2) Oscillatory-zoned Grt2 andradite (Adr55–98Grs1–44) in proximal skarn, which has moderate to low LREE/HREE enrichments and varying Eu anomalies; (3) Grt3 andradite (Adr29–76Grs22–69) in distal skarn with low LREE/HREE enrichments and minor negative Eu anomalies. Grt1, Grt2 and Grt3 yielded lower intercept U–Pb ages of 36.4 ± 1.8 Ma (MSWD = 0.87, n = 67), 34.8 ± 0.7 Ma (MSWD = 1.8, n = 31) and 33.4 ± 1.0 Ma (MSWD = 1.2, n = 25). Garnet shows compositional changes from Grt1 to Grt3 due to the fluid-wallrock reactions. With decreasing andradite and increasing grossular contents, the (La/Yb)N ratio decreases. Ore-forming fluids changed from diffusive metasomatism to infiltration metasomatism, and then again to diffusive metasomatism. Meanwhile, the ore-fluid physicochemical conditions changed from acidic to near-neutral (both oxidised), whilst the water/rock ratio first increased and then decreased. The proximal skarn recorded high water/rock ratio with intermittent boiling events, leading to fluctuating oxygen fugacity, which is conducive to ore deposition. Therefore, the skarn-type garnet composition from the various alteration zones can reveal the fluid activity and physicochemical fluid evolution path, preserving rich information about the mineralisation process.

Solar pyrolysis of biomass - part II: The physicochemical structure evolution of char

Dynamic solar pyrolysis experiments of willow pellets with different thicknesses (3 mm, 1 mm and 0.5 mm) were conducted at heat flux densities of 0.5 and 1.1 MW/m2 to study the physicochemical structure evolution of char. Characterizations of the physical structure showed that the reflectivity of char surface firstly reached the minimum value of 7.3 % and then rebounded to 15.3 %. The specific surface area decreased with reaction time from 13.2 to 2.0 m2/g, indicating its poor microscale pore structure (pore size ≤500 nm). The 3D scanning conducted by computed tomography (micro-CT system) showed that the residue pellet has unique hierarchical layers with different density and porosity. The lamellar structure can be also found inside the char layer which may be due to the increasing temperature gradient and the internal pressure caused by the volatile release. Concerning the chemical structure evolution, the secondary coking of the heavy compounds in volatiles introduced more oxygen-containing groups and alkyl side chains into the char layer. The aromatic rings system in the inner part of char was developed through removal of side-chains and functional groups. Further structure ordering of char surface was contributed by dehydrogenation and condensation. These differences between two parts of char can be attributed to the poor heat and mass transfer properties of lamellar structure. This work reveals the unique structural characteristics of solar pyrolysis char, which complements the solar pyrolysis mechanism and provides a new insight into the structural evolutions.

Identifying xenocrystic tourmaline in Himalayan leucogranites

Abstract Tourmaline is a common autocrystic mineral in granitic and pegmatitic rocks that records valuable information on the physicochemical evolution of magmas. However, xenocrystic tourmaline that does not crystallize from host magmas is also common but seldom reported and notoriously difficult to identify. Here, autocrystic (Tur G) and xenocrystic (Tur P) tourmalines are identified in two-mica granites and granitic pegmatites from the Cuonadong leucogranites, eastern Himalaya. Electron backscatter diffraction (EBSD), coupled with electron-probe micro-analysis (EPMA) and laser ablation ICP-MS analyses (LA-ICP-MS), is used to discriminate xenocrystic from autocrystic tourmaline. Although both tourmalines have slightly different chemical compositions, the differences are insufficient to permit unambiguous discrimination. However, EBSD systematically shows complex intra-crystalline orientations and deformation xenocrystic grains, and undeformed crystal lattices are predominant in autocrystic grains. EBSD could be a useful tool to identify the origin of tourmaline in granitic rocks, particularly when geochemical analyses and/or geochronological measurements are inconclusive.

Reburning pulverized coal with natural gas/syngas upgrading: NO reducing ability and physicochemical structure evolution of coal char

The lifting gas activates the coal particles, which increases their ability to reduce NO. This technique overcomes the oxygen consumption of large pulverized coal in the early stages of re-firing during air/flue gas transport of pulverized coal. This study conducted experiments on a planar flame burner bench to analyze the physicochemical structure evolution of coal coke after natural gas and syngas activation using FTIR, XPS, and BET. The NO reduction capacity was tested on a micro fluidized bed reaction test bench. The results show that natural gas's upgrading effect is better than syngas. Hydrogen and hydrocarbon radicals generated by the reaction of natural gas with oxygen play a significant role in activation. After upgrading by natural gas, the specific surface area of carbon increased by about 54.2 %, the total pore volume increased by about 51.2 %, the whole oxygen-containing groups decreased by nearly 4.4 %, the total amount of alkyl complexes increased by about 3.6 %, and the nitric oxide reducing ability increased by almost 75 %. The technology minimizes expensive reactive gases while ensuring less reburned coal is used to reduce NOx emissions.

Physicochemical Heterogeneity in Silicon Anodes from Cycled Lithium-Ion Cells.

The severe capacity fade of lithium-ion cells with silicon-dominant anodes has hindered their widescale commercialization. In this work, we link cell capacity fade to the heterogeneous physicochemical evolution of silicon anodes during battery cycling. Through a multilength scale characterization approach, we demonstrate that silicon particles near the anode surface react differently from those near the copper current collector. In particular, near the anode surface we find an amorphized wispy silicon encased in a highly fluorinated matrix of electrolyte-reduction products. In contrast, closer to the current collector, the silicon retains more of its initial morphology and structure, suggesting the presence of isolated particles. The results show that the accessibility of active silicon to lithium ions varies across the anode matrix. Material and cell designs, which minimize electrode expansion resulting from the in-filling of pores with the solid electrolyte interphase (SEI), are needed to enhance anode homogeneity during the electrochemical cycling.

Lithospheric mantle provinces and crust-mantle decoupling beneath northeastern China: Insights from peridotite xenoliths

AbstractThe origin and evolution of the subcontinental lithospheric mantle (SCLM) underlying orogenic belts bordering cratons, as either newly added domains or strongly reworked older cratonic lithosphere, remains controversial. This limits our understanding of deep lithospheric behavior and processes during plate convergence. Here, we use detailed petrology, whole-rock and mineral compositions, and in-situ Sr isotopic compositions for spinel-facies peridotite xenoliths from Jiaohe (northeastern China) in the southeastern Central Asian Orogenic Belt (CAOB), which is pinched between two NE-striking Mesozoic to Cenozoic giant trans-lithospheric fault systems. These data are combined with whole-rock Re-Os isotope and platinum-group element compositions and literature data, to explore the physicochemical evolution of the regional SCLM and examine crust-SCLM relationships for this vast swath of continental lithosphere.Lherzolites predominate at Jiaohe, and have higher whole-rock Al2O3 contents than harzburgites (2.27–3.46 wt% versus 0.84–1.02 wt%), but exhibit FeO enrichment similar to harzburgite (bulk FeO up to 9.54 wt%). The lherzolitic clinopyroxenes (Cpx) have higher heavy rare earth element (HREE) levels (2.79–5.11 ppm) and Ti/Eu (3882–6864), coupled with wider variation of 87Sr/86Sr (0.7021–0.7038) and lower average fO2 (oxygen fugacity relative to the fayalitemagnetite-quartz buffer; FMQ-1.92 ± 0.55) compared to the harzburgites (HREE: 0.94–2.11 ppm; Ti/Eu: 163–2044; 87Sr/86Sr: 0.7032–0.7036; fO2 = FMQ-1.25 ± 0.20). All these observations suggest that the lherzolites were produced by adding Cpx ± spinel to the protoliths from reducing silicate melts, whereas the harzburgites may have originated from a remnant, highly depleted mantle domain that variably interacted with silica-undersaturated oxidizing melts.Bulk-rock and mineral compositional relationships as well as fO2 for peridotite samples from the southeastern CAOB (including Jiaohe) are similar to those of the northeastern NCC (including Huinan). Their characteristics contrast with those from the northwestern CAOB, suggesting that they belong to distinct lithospheric provinces with respect to both composition and oxidation state. Jiaohe harzburgites yield Paleoproterozoic Re depletion Os model ages (TRD up to 1.76 Ga), similar to Huinan peridotites (up to 1.92 Ga), just 170 km away, and may also represent strongly reworked cratonic mantle. By analogy with evidence from recent continental collision zones, the Jiaohe SCLM may have originated as cratonic SCLM that migrated northeastward during plate convergence along giant translithospheric fault systems.

Prussian Blue Analogues for Potassium-Ion Batteries: Application of Complementary Operando X-Ray Techniques

In the last 5 years, potassium-ion batteries (PIBs) have been considered as a promising post-lithium-ion battery technology, much due to cost effectiveness and a variety of electrode materials available [1]. Prussian Blue Analogues (PBAs), with advantages such as simple synthesis, high capacity, and eco-friendliness, have gained a huge interest [2–4] and here we present a detailed study on the electrochemical mechanism of K x Mn2/3Fe1/3[Fe(CN)6] y .zH2O. We do this by combining complementary operando techniques: X-ray diffraction and X-ray absorption spectroscopy, supported by ex situ 57Fe Mössbauer spectroscopy. Chemometric analysis of the operando data allows us to follow the physico-chemical and structural evolution during electrochemical cycling, providing deeper understanding. From this, a reversible phase transition between monoclinic and cubic crystal structure was observed during the oxidation/reduction of Mn species. The local geometry information on Fe and especially Mn, as obtained from the EXAFS data analysis, serves to explain the volume expansion of the Fe–CN–M (M = Mn, Fe) framework during the extraction of potassium. This paves the way for optimizing the PBA composition for PIB application.

Torrefaction of low-value agro-industrial wastes using macro-TGA with GC-TCD/FID analysis: Physicochemical characterization, kinetic investigation, and evolution of non-condensable gases

Two low-value agro-industrial residues, passion fruit peel waste (PF) and pineapple peel waste (PA), were considered in this study as feedstocks to produce solid biofuels by torrefaction. The experiments were conducted in a macro-TGA with GC-TCD/FID analysis to investigate their torrefaction characteristics. The GC-TCD/FID analysis allowed quantifying the non-condensable gases, including CO, CO2, CH4 and H2. The impacts of pretreatment with torrefaction on the physicochemical properties were investigated by using proximate analysis, ultimate analysis, and calorific values. The torrefaction of PF and PA was investigated at three different temperatures (200, 250, and 300 °C) and two residence times (15 and 60 min). The torrefaction pre-treatment led to higher levels of elemental carbon, fixed carbon, HHV and energy density than in the raw biomass. Experimental results showed that the most favorable torrefaction condition for producing a solid biofuel with a high energy density is a moderate temperature of 250 °C and 15 min of residence time. Two models were applied to the torrefaction kinetics of the two agro-industrial wastes: one with the one-step method and the other with the two-step method. The two-step reaction method was the most appropriate for describing the torrefaction behavior of the two agro-industrial wastes in all conditions studied. As determined by the two-step reaction method, the torrefaction activation energies ranged from 17.9 to 199.9 kJ mol−1 for PF and 5.3–84.0 kJ mol−1 for PA. Findings from this study are potentially valuable for the design of large-scale equipment for the torrefaction of PF and PA residues.

Influence of wetting fluids on the compressive strength, physicochemical, and pore-structure evolution in lime-treated silty soil subjected to wetting and drying cycles

The long-term benefit brought in lime-treated soil can be altered by the nature of the surrounding wetting fluid, thus, affecting its durability. However, studies regarding such impact are limited. In this study, the influence of different wetting fluids on the microstructural, physicochemical modifications, and Unconfined Compressive Strength (UCS) evolution of lime-treated soil is investigated. Lime-treated soils are subjected to wetting and drying cycles using 0.10 M and 0.60 M NaCl solutions, demineralized water, and Methyl Methacrylate. The results show that despite the soil being exposed to several wetting and drying cycles, the UCS evolved positively compared to the reference specimen. However, this evolution varies with the types of wetting fluids the specimens are exposed to. The NaCls-and Methyl Methacrylate-subjected soils showed an increase in UCS up to about 3 times, while the UCS increase is about 2 times in the corresponding demineralized water subjected soil. Similarly, the extent of the variation of the final pH and the cumulative calcium concentrations measured in the effluent is marked by the wetting fluids available in the surrounding medium. At the pore structure level, the presence of NaCl solutions and Methyl Methacrylate solvent as a wetting fluid was observed to enhance the evolution of pores smaller than 3000 Å. However, such a phenomenon is less significant in the demineralized water-subjected soil. Thus, the study confirms that the type of wetting fluid plays an important role in the evolution of lime-treated soil during the wetting and drying cycles.

Tourmaline growth in pelitic schist and quartzite: A textural, chemical and B-isotopic study from the Gangpur Schist Belt, eastern India

Tourmaline is the principal repository of boron in crustal rocks and therefore useful for tracing B-cycling during prograde dehydration and retrogression of supracrustal rocks. Here, we use the major-trace element, and B isotope composition of tourmaline from schists, quartzites, and tourmaline-quartz veins of the Gangpur Schist Belt in eastern India to constrain the source of boron and the physicochemical evolution of B-rich fluids during prograde dehydration metamorphism. Tourmaline growth and re-equilibration in rocks of the Gangpur Schist Belt was a multi-stage process involving several fluid sources. The δ11B varies between −6‰ and −18‰, indicating a dominantly continental source for boron. Tourmaline in schists, quartzites, and tourmaline-quartz veins grew over a wide range of P-T conditions and record multiple episodes of metamorphic dehydration between ca. 1.6 Ga and ca. 0.95Ga. The tourmaline in tourmaline-quartz veins and quartzites has lighter B-isotope composition, typical of continental detritus, while those in the schists and quartzites record pelite-dehydration signature with values decreasing gradually from ca. −12‰ in the cores to ca. −17‰ in the rims. Heavier isotopic compositions (δ11B of ca. −6‰) measured in some grains in the pelites and quartzites indicate boron contribution from meta‑carbonate sources. The mixing of a heavier B-rich metacarbonate-derived fluid with pelite-derived metamorphic fluids could explain the lower B-isotope values in such tourmaline. The study also attempts to constrain the controls on the intake of trace elements in tourmaline. The results suggest that the partitioning of Mn, Y, V, Co and Ti in tourmaline is affected by the growth of porphyroblast phases such as garnet, staurolite, and biotite, while Li, Sr, Zn and Sn reflect the signature of the metamorphic fluid.

Alternative flotation collectors for the environmental desulfurization of gersdorffite (NiAsS) bearing mine tailings: Surface chemistry

Environmental desulfurization by froth flotation is a promising technique for the control of acid mine drainage (AMD) and has already been applied in a wide variety of mining operations to prevent environmental risks. This paper aims to address the flotation challenges of gersdorffite for environmental purposes. Gersdorffite, a Ni-As-sulfosalt (NiAsS) frequently encountered in many gold mine wastes, is a major source of contamination. Gersdorffite surface characterization was conducted using diffuse reflectance infrared fourier transform (DRIFT) spectroscopy and optical microscopy, to gain a better understanding of the physicochemical evolution of the mineral surface. The main parameters evaluated were the impact of air-oxidation (aging) and the effect of pH at different values using different reagents (soda ash (NaOH) and lime (CaO)) on the mineral surface chemistry. Collector adsorption behavior was also studied using four collector types as alternatives to xanthate, mainly based on dithiophosphates (DTP) and mercaptobenzothiazole (MBT). Dry grinding of the gersdorffite generated a thin and heterogeneous particle coating mainly composed of arsenic oxides (arsenite and arsenate) and nickel sulfates (NiSO4), with minor elemental sulfur. Hydroxylated Ni species (Ni-OH) were also observed. MBT molecules were found to be the most active compound responsible for the adsorption of the collectors as demonstrated by the adsorption isotherms and the DRIFT spectra. The results of this study have led to a better understanding of gersdorffite surface chemistry before and after the collector adsorption, which should impact its flotation behavior.

Release characteristics of AAEMs and physicochemical structural evolution of char during rapid coal pyrolysis

Rapid pyrolysis experiment of Zhundong coal was conducted in a high-frequency furnace to investigate release characteristics of alkali and alkaline earth metals (AAEMs) and its correlation with changes of physical and chemical properties of char. Residence time and atmosphere during pyrolysis were important process parameters that affected the migration characteristics of AAEMs and physicochemical structural evolution of char. Experimental results show that the release of AAEMs in coal char increases over time. The maximum release rate of Na, Mg and Ca is 61.05%, 64.47%, and 44.01%, respectively. Promoting effect of CO2 on release of Na mainly occurs in the initial stage of rapid pyrolysis, nevertheless the promoting effect on release of Mg and Ca mainly is in the middle and late stage. CO2 accelerates release of AAEMs by promoting release of volatiles, facilitating decomposition of oxygen-containing functional groups and aliphatic functional groups, and promoting formation of cracks on surface of coal char.

Shrinkage, hydration, and strength development of limestone calcined clay cement (LC3) with different sulfation levels

This study investigated autogenous shrinkage of limestone calcined clay cement (LC3)-based mixes with various sulfation levels of hemihydrate. Physicochemical evolution and strength development were also monitored. Superior mechanical performance of the mixes was achieved at an optimal sulfation level, although the shrinkage was reduced with the sulfate content. Calorimetry data showed the hemihydrate delayed and broadened the second aluminate peak. Both gypsum and ettringite formed early during hydration, and carboaluminates were observed after 3 days of curing. Ettringite in the LC3 mixes was of smaller sizes in comparison to that in the ordinary Portland cement (OPC) mixes, attributable to the pore refinement in the LC3 matrices. The content of portlandite (Ca(OH)2) was reduced with the curing time due to pozzolanic reactions. The findings demonstrated a coupling effect of both the chemical and microstructural change on the observed autogenous shrinkage and the consequent performance of LC3-based concrete composites.

Effects of Water-to-Binder Ratios (W/B) and Superplasticizer on Physicochemical, Microstructural, and Mechanical Evolution of Limestone Calcined Clay Cement (Lc3)

Effects of Water-to-Binder Ratios (W/B) and Superplasticizer on Physicochemical, Microstructural, and Mechanical Evolution of Limestone Calcined Clay Cement (Lc3)

Experimental study of the influence of the relative humidity of leaves and their link to adhesion losses in the wheel-rail contact

Every autumn, low levels of wheel–rail contact adhesion caused by leaves on the railhead surface are reported by train drivers. These incidents cause problems for the safety and regularity of rail traffic and occur predominantly at the beginning and end of the day when high humidity levels are achieved. At those moments the air temperature reaches the dew point temperature creating moisture on the railhead and oxides which react chemically with dead leaves found on the railhead surface. This article presents the results of a test campaign performed on a ring-on-disc tribometer with the aim of reproducing and studying the development of a loss of adhesion at an imposed slip rate. This type of tribometer enables a realistic approximation of the tribological circuit of a rail–wheel contact. Several samples of pollution responsible for adhesion losses were collected on the French railway network during fall and reproduced in a laboratory on a tribometer under imposed relative humidity and slip conditions. The results indicate the presence of reproducible phenomena modulated by variations in hygrometry and imposed slip rates. The decrease in hygrometry of the external third bodies introduced into the contact is at the origin of the generation of debris from the first bodies in contact. This presence of wear debris is reflected by an increase of the power dissipated by friction. Conversely, increasing the hygrometry decreases the ability of the third body to raise adhesion levels on contact and reduces the generation of debris from the first bodies. The results obtained from the analysis of the force and power quantities related to the contact reproduced in the laboratory allow the authors to confirm that the presence of water has a significant effect on the mechanical and physico-chemical evolution of the adhesion of a rail–wheel contact polluted by a third external (leaf-like) body.

The Formation of Magmatic-Hydrothermal Features in Sn-Mineralized and Barren Tasmanian Intrusions, Southeast Australia: Insights from Quartz Textures, Trace Elements, and Microthermometry

Abstract Tasmania is the most important tin province in Australia, having been endowed with >0.65 Mt Sn. Some granitic intrusions in western Tasmania have distinctive tourmaline- and quartz-rich magmatic-hydrothermal features, whether they are mineralized (e.g., Heemskirk Granite) or barren (Pieman Heads Granite). The Devonian Heemskirk and Pieman Heads plutons crop out on the western coast of Tasmania and are characterized by similar mineralogical and geochemical compositions and ages. The magmatic-hydrothermal textural features include tourmaline patches, tourmaline orbicules, and tourmaline-muscovite veins, as well as miarolitic cavities and quartz-fluorite-sulfide veins in the Heemskirk Granite. Cathodoluminescence (CL) imaging, laser ablation-inductively coupled plasma-mass spectrometry, and microthermometric analyses of quartz have revealed the physicochemical evolution of the magmatic-hydrothermal fluids from which these tourmaline- and quartz-bearing assemblages precipitated. High Ti quartz (20–28 ppm) in tourmaline patches, orbicules, and cavities typically have homogeneous CL-bright intensity, whereas CL-dark fractures have cut and/or offset the CL-bright and -gray domains that characterize low Ti quartz (3.4–8.5 ppm) from the tourmaline veins. The earliest fluid inclusion assemblages in the quartz-tourmaline orbicules and cavities have a salinity range from 3 to 14 wt % NaCl equiv with intermediate density and were probably trapped at lithostatic pressures of 1.57 ± 0.2 kbar and temperatures of 550° to 570°C, suggesting a depth of 5.9 ± 0.8 km. Prolonged depressurization and cooling may have led to the evolution of a brine (~39 wt % NaCl equiv salinity) from the primary magmatic liquid, which formed halite-bearing hypersaline inclusions in the tourmaline orbicules. Continuous pressure decrease explains the intense brittle failure and fluid migration outward from the apical portions of the pluton, where magmatic fluids partially mixed with and were cooled by external meteoric water. These mechanisms triggered the formation of tourmaline-muscovite-quartz veins and local cassiterite-bearing greisens from a moderate-salinity fluid (~12 wt % NaCl equiv) at temperatures of ~300°C and hydrostatic pressures of 120 bars. Retrograde dissolution textures evident from CL-bright quartz cores surrounded by oscillatory growth zones with gray CL response characterize the low Ti (<1 ppm) and high Al (500–1,000 ppm) quartz from the fluorite-sulfide veins that precipitated from a low-salinity (5.7 wt % NaCl equiv) acidic fluid at temperatures of 200° ± 25°C and hydrostatic pressures of <50 bars. High Sb concentrations (up to 80 ppm) in quartz may be an indicator of low-temperature base metal mineralization related to granitic intrusions. Abundant fluid percolation, protracted fractional crystallization, and high tin concentrations in exsolved hydrothermal fluids may explain why the Heemskirk Granite is well endowed in Sn and base metal deposits, whereas the Pieman Heads Granite is barren.

Out-of-equilibrium processes in crystallization of organic-inorganic perovskites during spin coating

Complex phenomena are prevalent during the formation of materials, which affect their processing-structure-function relationships. Thin films of methylammonium lead iodide (CH3NH3PbI3, MAPI) are processed by spin coating, antisolvent drop, and annealing of colloidal precursors. The structure and properties of transient and stable phases formed during the process are reported, and the mechanistic insights of the underlying transitions are revealed by combining in situ data from grazing-incidence wide-angle X-ray scattering and photoluminescence spectroscopy. Here, we report the detailed insights on the embryonic stages of organic-inorganic perovskite formation. The physicochemical evolution during the conversion proceeds in four steps: i) An instant nucleation of polydisperse MAPI nanocrystals on antisolvent drop, ii) the instantaneous partial conversion of metastable nanocrystals into orthorhombic solvent-complex by cluster coalescence, iii) the thermal decomposition (dissolution) of the stable solvent-complex into plumboiodide fragments upon evaporation of solvent from the complex and iv) the formation (recrystallization) of cubic MAPI crystals in thin film.

Thermal Properties of the H2O–CO2–Na2CO3/CH3OH/NH3 Systems at Low Temperatures and Pressures up to 50 MPa

Experimental data on the thermal properties of aqueous solutions at low temperatures and high pressures are necessary to perform an accurate geochemical modeling of ocean worlds, that is, those planetary bodies that can sustain significant reservoirs of the interior liquid for long time periods. We used differential scanning calorimetry (DSC) to determine the values of specific heat capacity and enthalpy of dissociation of CO2-clathrates in the presence of sodium carbonate, ammonia, and methanol at temperatures ≥233 K and pressures ≤50 MPa. We monitored the physicochemical evolution of the systems along the pressure–temperature paths through Raman spectroscopy. The protocol used to form the CO2-clathrates influenced the thermal behavior of the system. Partial recrystallization events from ice to CO2-clathrate during slow heating resulted in out-of-equilibrium heat capacities (Cp) of < 1 J g–1 K–1. After complete melting of the solids, the final aqueous solutions had Cp 2–3 J g–1 K–1. Final fluids richer in dissolved CO2 had a lower Cp. The addition of carbonates and methanol led to a decrease in the melting temperature of both ice and clathrates. Ammonia reacted with CO2 to rapidly form ammonium bicarbonate; however, ice and CO2-clathrates could also stabilize in parallel. In all the studied systems, the formation of clathrates from aqueous solutions without the application of clathrate stabilizers, mechanical agitation, or synthesis from crushed ice led to a low guest occupancy, forming less-stable clathrates with low enthalpies of dissociation (130–275 J g–1). These results have important planetary implications related to the thermal behavior of bodies rich in the compounds of the systems studied, as can be the case of Enceladus. In this research, we show that the level of cage occupancy in clathrates plays a key role in their thermal behavior. Highly occupied clathrates will be robust and will contribute to the retention of heat inside the planetary bodies due to their characteristic low thermal conductivity. However, poorly occupied clathrates will dissociate more easily than water ice, allowing greater heat fluxes through the icy crust and favoring the dissipation of heat to the exterior.