Carbon Phase Research Articles

Exploring the High-Pressure Phases of Carbon through X-ray Diffraction of Dynamic Compression Experiments on Sandia’s Z Pulsed Power Facility

The carbon phase diagram is rich with polymorphs which possess very different physical and optical properties ideal for different scientific and engineering applications. An understanding of the dynamically driven phase transitions in carbon is particularly important for applications in inertial confinement fusion, as well as planetary and meteorite impact histories. Experiments on the Z Pulsed Power Facility at Sandia National Laboratories generate dynamically compressed high-pressure states of matter with exceptional uniformity, duration, and size that are ideal for investigations of fundamental material properties. X-ray diffraction (XRD) is an important material physics measurement because it enables direct observation of the strain and compression of the crystal lattice, and it enables the detection and identification of phase transitions. Several unique challenges of dynamic compression experiments on Z prevent using XRD systems typically utilized at other dynamic compression facilities, so novel XRD diagnostics have been designed and implemented. We performed experiments on Z to shock compress carbon (pyrolytic graphite) samples to pressures of 150–320 GPa. The Z-Beamlet Laser generated Mn-Heα (6.2 keV) X-rays to probe the shock-compressed carbon sample, and the new XRD diagnostics measured changes in the diffraction pattern as the carbon transformed into its high-pressure phases. Quantitative analysis of the dynamic XRD patterns in combination with continuum velocimetry information constrained the stability fields and melting of high-pressure carbon polymorphs.

Effects of initial damage on self-healing of fly ash-based engineered geopolymer composites (FA-EGC)

The effect of initial damage levels on self-healing properties and the mechanism of fly ash-based engineered geopolymer composites (FA-EGC) was investigated. FA-EGC paste with an ultimate tensile strain exceeding 5.4% was prepared using fly ash, composite alkali activator, and PVA fibers. The FA-EGC specimens were pre-damaged by 1.5%, 2.0%, and 2.5% tensile strains, then self-healed for 7, 14, and 28 days. The self-healing properties of FA-EGC were studied by uniaxial tension, apparent crack characteristic, water absorption, and ultrasonic pulse velocity methods. The self-healing products were characterized by XRD, FTIR, BET, and SEM-EDS. The model of the relationship between initial damage levels and initial internal crack characteristics was built. The results showed that FA-EGC had significant multiple cracking characteristics, strain-hardening behavior, and ultra-high tensile ductility after 28 days of self-healing. After self-healing, the ultimate tensile strength of pre-damage FA-EGC recovered to 97.86% compared with the control specimen, and the ultimate tensile strain recovered to 94.50%. Moreover, the strain of ultra-high tensile ductility FA-EGC was up to 5%. Self-healing products were mainly amorphous aluminosilicate and calcium carbonate phases. The self-healing rate was determined by initial internal crack width according to the model, and FA-EGC had an initial damage threshold (about 2.0% tensile strain) with the lowest mean crack width and the highest self-healing rate.

Temperature-dependent oxidation kinetics and mechanical properties degradation of Cf/ZrB2-SiC composites

The oxidation kinetics and microstructures evolution of Cf/ZrB2-SiC composites are investigated by experimental characterizations. An empirical model containing multi-reaction systems is further established for predicting the specimen mass evolution during isothermal oxidantion. Based on the morphological observations and in-situ tensile responses, three oxidation mechanisms of carbon phase controlled by reaction and diffusion kinetic are categorized as uniform, non-uniform and superficial oxidation. The relationship between fracture modes and internal fibers microstructures indicates that the structural origin of the fracture mode transition is the toughening mechanism transition of fibers on the ceramics matrix induced by oxidative damage.

Ni- and Ni-Sn Anode Porous Layers for SOFCs Operating with Carbonaceous Fuels

Nickel metal layers with various morphologies have been investigated as electrical contact, electrocatalyst, and catalyst layer for high temperature hydrogen electro-oxidation reactions and heterogeneous reactions, such as steam methane reforming and water gas shift, in high temperature fuel cells supplied by carbonaceous fuels of various nature. From a heterogeneous catalysis perspective Ni metal alloy, with various dopant concentrations, have been studied to increase metal Nickel tolerance to carbon deposition, which is thermodynamically favoured in SOFC fed with a steam/methane molar ratio <2.0. Metallic nickel electric and thermal conductivity are typically of the order of 107 S/m and 102 W/m.K, respectively, while its coefficient of thermal expansion measures 12x106 m/m.C , making it a good and relatively cheap candidate for electric contact layers and current collectors. The optimization of its morphology is fundamental to improve the nickel layer mass transport properties in conjunction with its catalytic and electrocatalytic performance. Others have proposed and optimized Ni-based porous layers: Smorygo et al. investigated nickel metallic foam supports to promote steam methane reforming and found good corrosive resistance and stability1. Fu et al. studied the effects of modifying nickel foam with copper; they found that copper modification significantly reduced the amount of carbon deposition found in the foam after operation2. Enhanced stability of the foam was reported alongside the resistance to coking. Kan and Lee fabricated a tin-doped Nickel/YSZ anode catalyst which was proven to drastically improve cell stability at a comparable performance3. The cell performance and deposition rates were reported as highly dependent on the tin concentration.Our goal is to compare the electrochemical performance, the catalytic activity towards steam methane reforming reaction yield, and the resistance towards the Boudouard reaction for solid carbon formation of a Ni-based SOFC: i) without Ni porous layer; ii) with a 200 μm thick Ni porous mesh; iii) with a 200 μm thick NiSn porous mesh (porous nickel and nickel-tin mesh ‘Celmet’ are supplied by Sumitomo Electric Toyama Co., Ltd.). We investigate the electrocatalytic performance of the two Nickel-based porous layers on a Ni-YSZ/Ni-GDC|SSZ|LSC-YSZ button cell with 20mm diameter (active area 1.23 cm2). The porous meshes are characterized by a pore size of 230-250 μm (as depicted in Figure 1(v)). The cell assembly is depicted in Figure 1 (iv), where we show how the Ni porous mesh works both as a catalyst layer and a mass transport layer between the gas bulk phase and the triple phase boundary.The cells are operated between 700°C and 850°C with inlet feed compositions comprising CH4, H2, H2O, and N2 with varying S/C ratios from 2.5 to 0 (i.e., dry methane feed). The performance of the three configurations is expressed in terms of electrochemical impedance spectroscopy (EIS) and chronoamperometry measurements within the temperature and composition experimental matrix. X-ray diffraction (XRD) and fluorescence (XRF) are used to analyze the cells and meshes at beginning of life and post-mortem to identify any carbon phases forming on either surface. Scanning Electron Microscopy Energy Dispersion Spectroscopy (SEM-EDS) is used to identify carbon composition and map both the cell and mesh surfaces.The electrochemical performance between case i) and case ii) is reported in Figure 1(i), where polarization curves are summarized for a cell operating with a 1:1 mixture of H2/H2O at 750°C. The increased polarization of case ii) is associated to the additional series resistance of the Ni mesh on the anode layer. Preliminary operation with mixtures of CH4/H2O with S/C as low as 1.5 display performances in-line with expectations, while long-term degradation effects due to carbon deposition remain to be studied. XRD measurements report the formation of solid carbon on a Ni mesh operating with S/C=1.5 (see Figure 1(ii)) for a cell working at 750°C for less than 50 hours. From our preliminary results, we show that the addition of a porous nickel mesh results in methane reformation prior to reaching the cell anode. The deposition is characterized by XRD and SEM and reported along with the polarization curves and electrochemical impedance spectroscopy which define the performance of the cells. O. Smorygo et al., Int J Hydrogen Energy, 34 (2009).X. Z. Fu et al., Int J Hydrogen Energy, 35 (2010).H. Kan and H. Lee, Appl Catal B, 97 (2010). Figure 1

Joint application of fluid inclusion and clumped isotope (∆47) thermometry unravels the complexity of thermal and fluid‐flow history reconstruction in sedimentary basins—Upper Triassic Chaunoy Formation reservoirs (Paris Basin)

AbstractWe investigated calcites and dolomites precipitated during burial diagenesis of the Upper Triassic (Norian) continental siliciclastics from sub‐surface reservoirs of the northern Paris Basin (Chaunoy Formation) that experienced a thermal maximum &gt;100°C during Late Cretaceous times. Relative carbonate precipitation timing was established via petrographic analyses. The diagenetic carbonates were further investigated by fluid inclusion and clumped isotope (Δ47) thermometry. The two thermometric datasets were interpreted by evaluating the possible occurrence of inclusion thermal reequilibration and Δ47 solid‐state reordering, based on the known basin thermal history and the three existing Δ47 reordering models. By considering the fluid inclusion and Δ47 datasets obtained and the various Δ47 reordering models, different carbonate precipitation scenarios, in terms of timing and parent fluid composition (δ18Ofluid), were inferred. These results underline that in samples having experienced thermal maximum &gt;100°C, accuracy and interpretation of fluid inclusion and Δ47 thermometry data (especially on calcite) may be biased by thermal reequilibration and solid‐state reordering. The results converge towards the need of jointly applying fluid inclusion and Δ47 thermometry on the same carbonate phases to evaluate all the possible precipitation scenarios. The most likely carbonate precipitation scenarios, based on Δ47 thermometry data, point at the precipitation of two calcite phases during Early to Late Jurassic times and of one dolomite phase during the Late Cretaceous. The parent fluids possibly were original formation waters of the Chaunoy Fm. that mixed with brines migrating from the East, where time equivalent evaporitic deposits occur. The proposed precipitation model for calcites and dolomites, involving different pulses of brine migration, and the dominance of calcite phases were not recorded by previous studies on the Upper Triassic units. These latter results may be of interest to evaluate the reservoir potential of the Chaunoy Fm. in this underexplored portion of the Paris Basin.

Geometrical and chemical effects on the electrochemistry of single-wall carbon nanotube (SWCNT) network electrodes

Single-wall carbon nanotube (SWCNT) network is a promising electrode material for bio detection. Unfortunately, the associations between their physical as well as chemical properties and observed electrochemical performance are not known. This hinders any systematic optimization of the network properties towards specific analytes. Here we present a consistent physicochemical and electrochemical characterization of differently treated SWCNT networks. The results unambiguously show that (i) even if the electrochemical properties of different electrodes are practically identical when assessed by surface insensitive outer sphere redox (OSR) probes their behavior with inner sphere redox (ISR) probes can be drastically different. Further, (ii) the choice of the modification method (structural, chemical, electrochemical) heavily depends on nature of the target analyte, which are typically ISR probes. Although, (iii) chemical changes in the carbon phase appeared to be minor, effects of different treatments on oxidation states of Fe appeared to have a strong effect on the electrochemical performance of the networks in the case of ISR probes.

Synthesis and characterization of the porous activated carbon from end-of-life tire pyrolysis for CO2 sequestration

This research aims to synthesize and characterize the CO2 adsor+bent from waste tire (WT) as a precursor to produce porous carbon adsorbent material using a combination of thermal (pyrolysis, 600–700 °C) and chemical (H3PO4 and KOH) methods. The derived fine black powder was impregnated by 10–50 wt% polyethyleneimine (PEI) to produce porous carbon material (PEI-PCM) for evaluation of the performance of CO2 adsorption under TGA (micro-scale system). To observe the PEI loading and relevant CO2 capture selectivity characteristics, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, and Fourier transform infrared spectrometry (FT-IR) were carried out. The XRD pattern showed the main phase of amorphous carbon, graphite, and some impurities (ZnS). Type II adsorption isotherm is related with reducing of the specific surface area and pore volume from 78 m2·g−1 to 25.26 m2·g−1, 0.45 cm3·g−1 to 0.23 cm3·g−1, respectively. The FT-IR spectra indicated the bending of primary and secondary amine which belonged to PEI molecule. It can be concluded that PEI-PCM properties such as, pore-size distribution, pore volume and surface functional groups supported CO2 adsorption capability following surface structure modification. The 50 wt% PEI-PCM-P showed good adsorption capacity of 53.81 mg·g−1 at temperatures of 75 °C. As a result, the PEI-PCM was successfully developed for CO2 absorption application. This work can help mitigating the challenge of disposal of WT and realization of the bio-circular-green economy (BCG model).

Low‐temperature synthesis of HfC/HfO2 nanocomposites from a commercial single‐source precursor

AbstractA liquid‐phase polymer‐to‐ceramic approach is reported for the synthesis of hafnium carbide (HfC)/hafnium oxide (HfO2) composite particles from a commercial precursor. Typically, HfC ceramics have been obtained by sintering of fine powders, which usually results in large particle size and high porosity during densification. In this study a single‐source liquid precursor was first cured at low temperature and then pyrolyzed at varying conditions to achieve HfC ceramics. The chemical structure of the liquid and cured precursors, and the resulting HfC ceramics was studied using various analytical techniques. The nuclear magnetic resonance and Fourier transform infrared spectroscopy indicated the presence of partially hydrated hafnium oxychloride (Hf–O–Cl·nH2O) in the precursor. Scanning electron microscopy of the resulting HfC crystals showed a size distribution in the range of approx. 600–700 nm. The X‐ray diffraction of the pyrolyzed samples confirmed the formation of crystalline HfC along with monoclinic‐HfO2 and free carbon phase. The formation of HfO2 in the ceramics was significantly reduced by controlling the low‐temperature curing temperature. Pyrolysis at various temperatures showed that HfC formation occurred even at 1000°C. These results show that the reported precursor could be promising for the direct synthesis of ultrahigh temperature HfC ceramics and for precursor infiltration pyrolysis of reinforced ceramic matrix composites.

High pressure and high temperature phase transformations of covalent triazine-based frameworks

A monolithic two-dimensional (2D) biphenyl-linked triazine-based framework (CTF-2) showing merely slight crystallinity was prepared by Lewis acid-promoted polymerisation of 4,4′-biphenyldicarbonitrile in liquid TiCl4 at moderate temperature to avoid unwanted carbonization. The transformations of CTF-2 induced by high pressure (up to 60 GPa) and temperature (up to 2400 K) were studied by IR and in situ Raman spectroscopy as well as TEM microscopy. In contrast to graphitic C3N4 materials, CTF-2 exhibits high optical density and reduced fluorescence at high pressure, allowing laser-induced sample heating. Spectral data show the formation of sp3 hybridised carbon atoms and triazine ring distortion in CTF-2 material at pressures above 17 GPa. According to the pressure Raman effect, the bulk modulus of the high-pressure phase of CTF-2 (high-pressure phase CTF-2) was found to be 570 ± 10 GPa, which is a typical value for superhard carbon materials. Structural studies revealed nitrogen preservation in the specimen after high-pressure treatment and stability of the disordered sp3 states of the high-pressure phase CTF-2 in the quenched specimen. This behaviour is quite different from that of the quenched disordered sp3 states of high pressure pure carbon phases, which convert to the sp2 state at pressures below 3–7 GPa.

The influence of reactive MgO on the hydration and carbonation performance of slag-rich cement system

To enrich the choice of minor addition for cement production, the paper investigated the influence of reactive MgO on the long-term hydration and carbonation behavior of slag-rich cement paste. Three different mixtures (cement-slag-MgO, C3S-slag-MgO, and cement-slag) were adopted in the study, and specimens were sealed cured for 90 days, followed by a six-month accelerated carbonation test. It was found that the addition of MgO did not modify the phase assemblage evolution and microstructure development of slag-rich cement paste fundamentally during hydration and carbonation. Brucite occurred as the main hydration product of MgO. As for its carbonation product, Mg-containing carbonate phases and magnesium silicate hydrates were found to agglomerate with each other in the matrix. Compared with cement-slag mixture, cement-slag-MgO blend exhibited a slightly higher carbonation depth and a lower CO2 binding capacity. Brucite did bind some CO2; however, it cannot compensate the reduction of C–S(A)−H gel phase and portlandite due to the substitution of cement clinker with MgO. Therefore, the addition of MgO reduced the carbonation resistance of the corresponding system from a long-term perspective.

Flotation Decarbonization and Desulfurization of a High-Sulfur Bauxite in China

A high sulfur content is one of the challenges in the processing of refractory bauxites in China. The high carbon content of bauxite makes it more difficult to deal with. Desulfurization and decarbonization are the critical issues in the efficient exploitation of high-sulfur bauxite resources. An experimental study on the removal of sulfur and carbon in high-sulfur bauxite is proposed. The sulfur and carbon phases in high-sulfur bauxite were studied via X-ray diffraction and chemistry quantitative analyses. The results show that the sulfur phases in the high-sulfur bauxite mainly exist in the form of sulfide sulfur (pyrite), and the carbon phases in the sample mainly exist in the form of elementary substance carbon. The morphological features of pyrite in the high-sulfur bauxite were analyzed using a microscopic analysis and a scanning electron microscope (SEM). The pyrite exists in minerals in the forms of euhedral, semi-euhedral and other crystalline structures, with a particle size varying from several hundred microns to only a few microns. The raw ore, with a sulfur content of 4.78%, a sulfide sulfur content of 4.20%, a carbon content of 3.10% and an elementary substance carbon content of 2.46% goes through the “one roughing, one cleaning, two scavenging” process after a pre-decarburization, obtaining the total desulfurization recovery of 96.20% with a desulfurization tailing sulfur content of 0.38%, a carbon content of 0.27% and an alumina content of 71.85%, respectively. This work provides technical support for the efficient utilization of high-sulfur and high-carbon bauxite.

Mechanism of bonding, surface property, electrical behaviour, and environmental friendliness of carbon/ceramic composites produced via the pyrolysis of coal waste with polysiloxane polymer

A simple mixing-pressing followed by thermal curing and pyrolysis process was used to upcycle coal waste into high-value composites. Three coal wastes of different physicochemical properties were investigated. The hypothetical mechanisms of bonding between the coal particles and the preceramic polymer are presented. The textural properties of the coals indicated that the lowest volatile coal waste (PCD) had a dense structure. This limited the diffusion and reaction of the preceramic polymer with the coal waste during pyrolysis, thereby leading to low-quality composites. The water contact angles of the composites up to 104° imply hydrophobic surfaces, hence, no external coating might be required. Analysis of the carbon phase confirmed that the amorphous carbon structure is prevalent in the composites compared to the coal wastes. The dc volume resistivity of the composites in the range of 22 to 82 Ω-cm infers that the composites are unlikely to suffer electrostatic discharge, which makes them useful in creating self-heating building parts. The leached concentrations of heavy metal elements from the composites based on the end-of-life scenario were below the Toxicity Characteristic Leaching Procedure regulatory limits. Additionally, the release potential or mobility of the metals from the composites was not influenced by the pH of the eluants used. On the basis of the reported results, these carbon/ceramic composites show tremendous prospects as building materials due to these properties.Graphical

ELECTROLYTIC CATALYSTS BASED ON TUNGSTEN AND CARBON COMPOUNDS FOR THE HYDROGEN EVOLUTION REACTION

The hydrogen evolution reaction (HER) is one of the most promising methods of obtaining high-purity hydrogen. However, the high cost and limited resources of materials with low cathodic hydrogen evolution overvoltage values, such as platinum group metals, are the main obstacles to the use HER for obtaining hydrogen on an industrial scale. Therefore, it is necessary to develop new alternative materials and methods of their production. One of the promising materials are catalysts based on refractory metals, in particular tungsten carbides. Metal tungsten can also be used for these purposes. In our opinion, high-temperature electrochemical synthesis (HTES) in molten salts can be a promising method of obtaining materials with properties that meet the requirements for effective catalysts, namely: ultra-dispersity, high specific surface area, mesoporosity and defective structure, high chemical and electrochemical stability. Therefore, the purpose of this work is to evaluate the electrocatalytic activity of a group of materials for HER, which are obtained by HTES in melts. Four samples of electrolytic materials were chosen for the study: tungsten, carbon, tungsten mono- and semi-carbides (WC and W2С). All samples were characterized in detail using X-ray diffraction (phase composition), SEM (morphology), Raman spectroscopy (structure of carbon phases), DTG (free carbon content).&#x0D; Based on the analysis of the obtained data, it was established that all samples can be used as catalysts: crystallites have a nanometer size and a large number of structural defects; morpho­logy provides increased surface area; tungsten carbide particles are covered with a layer of free carbon, which prevents oxidation of carbide to WO3, which has a lower catalytic acti­vity; carbon particles are nanosized (20–30 nm) and contain a large number of structural defects; tungsten carbide-based samples contain free carbon, which increases the specific surface area, but does not cause clogging of pores.&#x0D; Polarization measurements were carried out at room temperature at a polarization rate of 5 mV/s in a standard three-electrode cell with an Ag|AgCl reference electrode. 1N H2SO4 was used as a base solution, which was bubbled with high-purity argon. Onset potentials for all samples are -0.05 – -0.25 V (in order WC/C – W2C/WC/C – C – W). The overvoltage and Tafel slope were calculated and WC/C composite was shown to have the lowest values of -0.2 V and -75 mV, respectively.&#x0D; Electrolytic composite of tungsten carbide/carbon have demonstrated the best characteristics, so we plan to continue the development of synthesis method of carbide compounds, which will allow us to reveal even greater potential of carbide catalysts and pave the way for their wide application in catalytic processes.

Mechanical-Thermal Stability of Micro Composite Based Porous Carbon from Coconut Shell (&lt;i&gt;Cocoa nucifera&lt;/i&gt;) Charcoal

Research on the mechanical thermal stability of micro-porous carbon-based micro composites with marine paint matrices has been carried out. Microporous carbon has the property of absorbing radar waves so it is very interesting to research and develop into a microwave shielding material synthesized from coconut shell (cocoa nucifera) by carbonization process at 600°C for 45 minutes. The molecular structure and phases of micro porous carbon were characterized using Fourier Transform Infrared (FTIR) and X-Ray Diffraction (XRD) with the results confirmed of micro carbon with reduced graphene oxide (rGO) phase. Furthermore, micro-composites made from porous micro carbon with marine paint as a binder were made using the wet mixing-casting method. Mechanical thermal testing was carried out by means of a shear test at a temperature range of 30 – 70°C using a Dynamics Mechanical Analysis (DMA) tool. The test results showed that the value of the storage modulus of porous micro carbon composites was 1.653 MPa, 10.196 MPa, 13.068 MPa, 118.567 MPa, respectively. The value of the composite storage modulus increases with increasing concentration of porous micro carbon with an optimum value of mechanical thermal stability at a composition of 70:30 %wt. The results of mechanical thermal testing showed that porous micro carbon with rGO phase from coconut shells has the potential to be used as an anti-radar shielding material. 068 MPa, 118.567 MPa. The value of the composite storage modulus increases with increasing concentration of porous micro carbon with an optimum value of mechanical thermal stability at a composition of 70:30 %wt. The results of mechanical thermal testing showed that porous micro carbon with rGO phase from coconut shells has the potential to be used as an anti-radar shielding material. 068 MPa, 118.567 MPa. The value of the composite storage modulus increases with increasing concentration of porous micro carbon with an optimum value of mechanical thermal stability at a composition of 70:30 %wt. The results of mechanical thermal testing showed that porous micro carbon with rGO phase from coconut shells has the potential to be used as an anti-radar shielding material.

Carbon nanofibers and polyvinyl-alcohol fiber hybrid-reinforced high-performance concrete: Mechanical property, chloride penetration resistance, and material characterization

The hybridization of nanomaterials and macroscopic fibers is currently a popular topic. The aim of this study was to explore the application potential of incorporating carbon nanofibers (CNFs) into concrete and to analyze the effect of CNFs dispersant on concrete slump and early strength. Polyvinyl alcohol (PVA) fibers and CNFs were used to prepare composite fiber-reinforced (CNFs-PVA) concrete to improve the continuity of concrete properties at the micron/nanometer scale. The engineering properties such as compressive strength, flexural strength and resistance to chloride ion erosion performance of the concrete were investigated, and the microstructure of concrete was characterized using X-ray diffraction (XRD), scanning-electron microscopy (SEM), and X-ray computed tomography (X-CT). The results showed that CNFs could improve the early strength. The combined use of CNFs and PVA increased the 28-day compressive and flexural strength by 23.38% and 28.73%, respectively, compared to the control group. Correspondingly, the electric flux and Migration rate of chloride ions (DRCM) were minimized. From the SEM and XRD test results, it is clear that CNFs and PVA fibers can: (i) bridge low-density C-S-H to form higher-density C-S-H gels, (ii) form longer chain-like fibers with enhanced load transfer and chloride binding capacity, (iii) act as internal curing agents to enhance hydration at the interface, (iv) promote the formation of the aluminum phase hydration products and calcium carbonate phase, and (v) CNFs and PVA refine the pore size by increasing the gel pores and reducing the percentage of microcracks. The combined results indicate that the improved performance of CNFs-PVA is due to the combined effect of bridging and nucleation of hydration products by CNFs, adsorption of hydration products by CNFs-PVA, and promotion of pore filling by the generated hydrides such as calcium carbonate and ettringite. These findings provide new insights for the design of high-performance concrete materials.

Low-volume-loss surface polishing with a krypton fluoride excimer laser for polycrystalline diamond films

Surface polishing of hard diamond coatings is a key technique for applying such coatings in industry. In this study, we demonstrated surface modification of polycrystalline diamond films with minimal volume loss of the films by vertical irradiation of KrF excimer laser beams. Optimized laser scanning selectively removed surface asperities and reduced the surface roughness from ∼0.1 to ∼0.05 μm. Raman spectroscopic measurements revealed that laser polishing involves the phase transformation of diamond to amorphous carbon phases and thermal oxidation or evaporation of the amorphous phases. The residual amorphous carbon was almost completely removed by subsequent laser irradiation at appropriate fluences. We consider that the surface texture inherent to polycrystalline diamond films plays an important role in the concentration of laser beams on the nearby film surface. From reciprocating slide-type friction tests, we found that laser polishing decreased the initial friction coefficient from 0.5 to 0.1–0.3 against alumina balls and reduced the abrasion of the mating materials.

Potential utilization of CO2 foams in developing lightweight building materials

Energy conservation and emission reduction are key focuses in the field of building engineering. In this study, carbon dioxide gas was utilized to develop carbon dioxide foam cement paste materials. The properties of the samples were evaluated by considering the optimal foaming agent, water-cement ratio, foam-grout ratio, and pump speed. To elucidate the carbonation mechanisms, the microstructure and phase composition were analyzed with X-ray diffraction and scanning electron microscopy, respectively. The results demonstrated that the 3-day compressive strength of the test sample was 272.72% higher than that of an air foam cement paste. Additionally, the carbon dioxide foam cement paste exhibited a lower density than ordinary cement-based paste, while its 3-day compressive strength was 14.08% higher than that of the ordinary cement-based paste. Moreover, the price per cubic meter of the carbon dioxide foam cement paste was 19.02% lower than that of the ordinary cement-based paste. The introduction of carbon dioxide foam led to the consumption of hydration products near the voids and accelerated the carbonation reactions of the cement particles around the void-cement interfaces. This promoted the solidification of the foam within the cement paste, ultimately enhancing the early strength of concretion.

Provenance of altered carbon phases and impact history of the Stac Fada Member, NW Scotland

AbstractThe Stac Fada Member (Stoer Group) is a ~1.2 Ga melt‐rich impact breccia preserved and intermittently exposed along the NW coast of Scotland. Using a combination of x‐ray diffraction and micro‐Raman spectroscopy, we identify potential coesite that is spatially associated with micron‐sized diamonds, as well as disordered carbon phases. Comparing the graphite G‐band of disordered carbon phases in the impact breccia to samples from underlying units indicates that most of the carbon in the Stoer Group was ultimately derived from the underlying Lewisian basement. Disordered carbon phases within the Stac Fada Member have been modified by mild heating within a hot ejecta blanket rather than shock pressure. We also report the first evidence for impact diamonds discovered within the Stac Fada Member. These diamonds have an average Raman shift of 1328.5 cm−1 and are present within both the impact breccia and the shocked gneiss clasts that are present in sandstones directly underlying the Stac Fada Member contact, and within sandstone rafts entrapped in the unit. These findings have implications for the timing of deposition of the Stac Fada Member, which must have occurred after ballistic ejection of Lewisian basement clasts during the impact event.

Mixed polymerization approach to GO-derived carbon foil-supported porous SiO2/C random nanocomposite films for Li-ion battery anodes with extraordinarily enhanced capacities by cycle-dependent size-reduction effect

As starting materials, tetraethyl orthosilicate, resorcinol and formaldehyde were used to prepare a distinctive composite film of SiO2/C two-phase interpenetrated porous nanostructures on the surface of carbon foil ((SiO2/C)@Cf) when the mixed polymerizations (condensations) on the surface of graphene oxide and subsequent heat treatment were carefully manipulated. The microstructures of as-prepared films were characterized by FESEM, TEM, EDS element mapping, BET, etc and their charging/discharging behaviors and electrochemical impedance spectra were quantitatively analyzed. It has been found that (SiO2/C)@Cf shows extraordinary capacity enhancement featured with excellent cycling capacity and rate performance as anode materials of Li-ion batteries, such as 1274 mAh g−1 after 2000 cycles at 1 A g−1 and 463.5 mAh g−1 at 5 A g−1, in comparison with the layered SiO2/C composite films. More interestingly, the CV curves of (SiO2/C)@Cf before and after 2000 cycles of charge/discharge evidently shows a remarkable initial pseudo-capacitive capacity and its unusual enhancement with increasing number of cycles, which should be attributed to the small size effect of SiO2 domains embedded in carbon phase and their gradual refinement, leading to an increase in the effective electrochemical reaction area and apparent diffusivity of Li-ions.

Mineralogy of the 1.45 Ga Wafangzi manganese deposit in North China: Implications for pulsed Mesoproterozoic oxygenation events

Abstract Ancient manganese (Mn) deposits are primarily characterized by the presence of Mn(II) carbonates that likely formed by the diagenetic reduction of precursor Mn(IV) oxides. As such, Precambrian sedimentary Mn deposits have been used as a line of evidence for the evolution of oxygen in Earth’s surface environments. However, recent studies have shown that these Mn(II)-carbonates have the ability to directly accumulate within anoxic water columns, where free oxygen does not play a role in their formation. This alternative pathway casts uncertainty on the robustness of using ancient Mn deposits to constrain the redox fabric of the past marine water columns. Here, we investigate the Wafangzi Mn and Fe ore deposit from the 1.45 billion-year-old Tieling Formation, North China. The deposit contains Mn(II, III) mineral phases (hausmannite, braunite) as inclusions, or unreacted residues, trapped within Mn(II) carbonate (Ca-rhodochrosite). Some nodules and oolites of Mn(II) and Fe(II)-carbonate phases are also present and display a banded structure with concentric rings. Mn(III) oxide (manganite) is present in a paragenetic assemblage along with hematite and replacement textures with braunite. The negative carbon isotope composition (δ13C, –7‰ to –4‰) from Mn(II) carbonate samples in the Wafangzi Mn deposit which are distinct from that of contemporaneous seawater (~0‰), along with petrographic and speciation analyses, collectively suggest that the Mn(II, III)- and Fe(II)-bearing mineral phases formed through the diagenetic reduction of primary Mn(IV)/Fe(III) minerals coupled to the oxidation of organic matter. Therefore, the Wafangzi Mn deposit suggests the presence of sufficiently oxygenated marine waters, overlying anoxic ferruginous deeper waters with a transitional manganous water layer that could have driven the redox cycling of Mn, Fe, and C. Given the contemporaneous economic Mn deposits in the 1.45 Ga Ullawarra Formation in Western Australia, our findings imply the existence of a transient, and perhaps widespread, pulsed oxygenation event in the mid-Proterozoic oceans.