Narrow Results

The carbon is an important element which belongs to group 14 of the periodic table and shows multiple applications in our daily life as well as at the industrial scale. It is a promising element which represents the liquid–liquid phase transition (LLPT) phenomena. Additionally, it shows interesting anomalous behavior with some usual thermodynamic properties such as heat capacity ($C_p$) near about the liquid–liquid phase coexistence temperature ($T_c$). Hence, it is quite challenging and difficult to simulate carbon at or near the liquid–liquid phase coexistence temperature. This anomalous behavior also creates complications in computing the precise and equilibrated thermodynamic properties close to $T_c$. Therefore, we have studied the thermodynamic behavior of liquid and solid (diamond) states of carbon at liquid–liquid phase coexistence temperature ($T_c$) while transforming from liquid to solid state and achieving the equilibrated liquid and solid states individually. Additionally, we have also performed a similar analysis on melting temperature ($T_m$) to compare the system trends and its thermodynamics behavior in liquid and solid states, respectively. Furthermore, all the predicted thermodynamic results are quite consistent and able to show the equilibrium changes at the liquid–liquid phase coexistence temperature ($T_c$) and melting temperature ($T_m$), respectively.

The structural and mechanical properties of 9R diamond and 12R diamond have been investigated by using the first-principles calculations. The elastic constants, bulk modulus and Young’s modulus at various pressures have been investigated. The elastic anisotropy under pressure from 0 to 100 GPa has been studied. From our calculations, we found that 9R diamond and 12R diamond have similar high elastic constants and elastic modulus as lonsdaleite and diamond. The detailed ideal strength calculations show that 9R diamond and 12R diamond are intrinsic superhard materials.

The structural, mechanical and electronic properties of recently reported superhard material C${}_{28}$ are studied by first-principles calculations. The unit cell of C${}_{28}$ is composed of 28 carbon atoms and all sp³ hybridized bonds. From 0 GPa to 100 GPa, C${}_{28}$ satisfies the mechanical stability criteria and the phonon spectrum of C${}_{28}$ has no imaginary frequency, which means that C${}_{28}$ is mechanically and dynamically stable. The results of hardness calculated show that C${}_{28}$ is a potential superhard material with the Vickers hardness of 84.0 GPa. By analyzing the elastic anisotropy, we found that elastic anisotropy of C${}_{28}$ increases with pressure. The calculations of band structure demonstrates that C${}_{28}$ is an indirect bandgap semiconductor with the gap of 4.406 eV. These analyses demonstrate C${}_{28}$ is a superhard semiconductor material.

To explore the practicability of C₆₀ synthesis under extreme conditions (high pressure and high temperature), trinitrotoluene (TNT), trinitramine (RDX) and graphite mixtures of different proportions were detonated in a vacuum container, and the detonation products were collected for detecting. The results of mass spectroscopy, high performance liquid chromatography showed significant signals of C₆₀, which proved that C₆₀ could be synthesized by detonating the mixture of TNT and graphite (in 6:4 and 7:3 mass ratio, respectively), the detonation pressure and temperature were calculated around 13 GPa and 2000 K, respectively. Both experiment results and theoretical analysis showed the importance of detonation pressure and cooling temperature in detonation synthesis of C₆₀.

In this paper, we report strong variations in the Raman spectra of different carbon allotropes samples, for temperatures ranging from 83 K to 1123 K. The temperature dependence of D and G peak frequencies in the Raman spectrum of diamond, graphite, graphene, and carbon nanoparticles (CNPs) with 20 nm dot-size were investigated. These effects caused by temperature can be estimated from the changes in position and in linewidth of peak full width at half maximum (FWHM) G in the Raman spectrum of each sample. The broadening for each allotrope under the same conditions of temperature were: diamond ~ 4 cm^-1, graphite ~ 50 cm^-1, graphene ~ 5 cm^-1 and nanoparticles ~ 7 cm^-1. We also used scanning electron microscopy (SEM) to study the morphology and determine the size of the samples. According to the experimental data, the residual structural disorder and stress present in the samples are enhanced with temperature and responds for the observed changes in the Raman spectra. We present a systematic study of the temperature-dependent Raman spectra of four carbon allotropes.

A systematic investigation of structural, mechanical, elastic anisotropy and electronic properties of a recently reported novel superhard material orthorhombic $C_{20}$ ($o$-$C_{20}$) under pressure is performed utilizing the density functional theory in this work. The crystal structure parameters are obtained at zero as well as at high pressure. Pressure induced elastic constants $C_{ij}$, polycrystalline aggregate elastic modulus $(B,G,E)$, $B/G$ ratio, and Debye temperature changes for $o$-$C_{20}$ have been determined. The crystal elastic anisotropies of the ultra-incompressible $o$-$C_{20}$ are investigated in the pressure range of 0–100 GPa. The Lyakhov–Oganov model is applied to predict the hardness as functions of pressure. The calculated results reveal that $o$-$C_{20}$ possesses high elastic anisotropy under zero pressure and high pressure, and the hardness of $o$-$C_{20}$ decreases with pressure, while the Debye temperature behaves with the opposite trend. The results of electronic structure indicate that $o$-$C_{20}$ exhibits insulator characteristics, and the band gap increases with pressure. This work is expected to provide a useful guide for the future synthesis and application of $o$-$C_{20}$.

This paper reports on the successful deposition of phosphorus (P)-doped n-type (p-C:P) carbon (C) films, and fabrication of n-C:P/p-Si cells by pulsed laser deposition (PLD) using graphite target at room temperature. The cells performances have been given in the dark I–V rectifying curve and I–V working curve under illumination when exposed to AM 1.5 illumination condition (100mW/cm², 25°C). The n-C:P/p-Si cell fabricated using a target with the amount of P by 7 weight percentages (Pwt%) shows the highest energy conversion efficiency η = 1.14% and fill factor FF = 41%. The quantum efficiency (QE) of the n-C:P/p-Si cells are observed to improve with Pwt%. The dependence of P content on the electrical and optical properties of the deposited films and the photovoltaic characteristics of the n-C:P/p-Si heterojunction solar cell are discussed.

The successful deposition of boron (B)-doped p-type (p-C:B) and phosphorous (P)-doped n-type (n-C:P) carbon (C) films, and fabrication of p-C:B on silicon (Si) substrate (p-C:B/n-Si) and n-C:P/p-Si cells by the technique of pulsed laser deposition (PLD) using graphite target is reported. The cells' performances are represented in the dark I–V rectifying curve and I–V working curve under illumination when exposed to AM 1.5 illumination condition (100 mW/cm², 25°C). The open circuit voltage (V_oc) and short circuit current density (J_sc) for p-C:B/n-Si are observed to vary from 230–250 mV and 1.5–2.2 mA/cm², respectively, and to vary from 215–265 mV and 7.5–10.5 mA/cm², respectively, for n-C:P/p-Si cells. The p-C:B/n-Si cell fabricated using the target with the amount of B by 3 Bwt% shows highest energy conversion efficiency, η = 0.20%, and fill factor, FF = 45%, while, the n-C:P/p-Si cell with the amount of P by 7 Pwt% shows highest energy conversion efficiency, η = 1.14%, and fill factor, FF = 41%. The quantum efficiencies (QE) of the p-C:B/n-Si and n-C:P/p-Si cells are observed to improve with Bwt% and Pwt%, respectively. The contributions of QE are suggested to be due to photon absorption by carbon layer in the lower wavelength region (below 750 nm) and Si substrates in the higher wavelength region. The dependence of B and P content on the electrical and optical properties of the deposited films, and the photovoltaic characteristics of the respective p-C:B/n-Si and n-C:P/p-Si heterojunction photovoltaic cells, are discussed.

This paper reports on the successful deposition of boron (B)-doped p-type (p-C:B) and phosphorus (P)-doped n-type (p-C:P) carbon (C) films, and the fabrication of p-C:B on silicon (Si) substrate (p-C:B/n-Si) and n-C:P/p-Si cells by a pulsed laser deposition (PLD) technique using a graphite target at room temperature. The boron and phosphorus atoms incorporated in the films were determined by X-ray photoelectron spectroscopy (XPS) to be in the range of 0.2–1.75 and 0.22–1.77 atomic percentages, respectively. The cells performances have been given in the dark I–V rectifying curve and I–V working curve under illumination when exposed to AM 1.5 illumination conditions (100 mW/cm², 25°C). The open circuit voltage (V_oc) and short circuit current density (J_sc) for p-C:B/n-Si are observed to vary from 230 to 250 mV and from 1.5 to 2.2 mA/cm², respectively; they vary from 215 to 265 mV and from 7.5 to 10.5 mA/cm², respectively, for n-C:P/p-Si cells. The p-C:B/n-Si cell fabricated using the target with the amount of boron by 3 weight percentages (Bwt%) showed the highest energy conversion efficiency, η = 0.20% and fill factor, FF = 45%. The n-C:P/p-Si cell fabricated using the target with the amount of 7 Pwt% showed the highest η = 1.14% and FF = 41%. The quantum efficiency (QE) of the p-C:B/n-Si and n-C:P/p-Si cells were observed to improve with Bwt% and Pwt%, respectively. The contribution of QE in the lower wavelength region (below 750 nm) may be due to photon absorption by the carbon layer, in the higher wavelength region it was due to the Si substrates. In this paper, the dependence of the boron and phosphorus content on the electrical and optical properties of the deposited films and the photovoltaic characteristics of the respective p-C:B/n-Si and n-C:P/p-Si heterojunction solar cells are discussed.

Crystalline cubic silicon carbide (3C-SiC) surface layers have been prepared by carbon-ion implantation into silicon (100) using a MEVVA ion source and subsequent annealing at 1250°C for 2 h. The obtained films have been characterized by SEM, XRD, and micro-Raman analysis. The effect of carbon-ion dose on the surface morphology of the ion-implanted samples has been investigated. Rectangular patterns are observed on the surfaces of carbon-ion-implanted silicon substrates. It is found that the amount of rectangular patterns increases with ion dose, suggesting the dependence of surface morphology on ion dose. The formation of rectangular patterns has been elucidated in this paper.

The Fe–C–H interaction near defects in iron structures was studied using qualitative structure calculations in the framework of the atom superposition and electron delocalization molecular orbital. Calculations were performed using three Fe clusters to simulate an edge dislocation, a divacancy; both in bcc iron and a stacking fault in an fcc iron structure. In all cases, the most stable location for C atom inside the clusters was determined. Therefore, H atom was approximated to a minimum energy region where the C atom resides. The total energy of the cluster decreases when the C atom is located near the defects zone. In addition, the presence of C in the defects zone makes no favorable H accumulation. The C acts as an expeller of H in a way that reduces the hydrogen Fe–Fe bonds weakening.

Recent research has shown that fly ash may catalyze the oxidation of elemental mercury and facilitate its removal. However, the nature of mercury-fly ash interaction is still unknown, and the mechanism of mercury retention in fly ash needs to be investigated more thoroughly. In this work, a fly ash from a coal-fired power plant is used to characterize the inorganic and organic constituents and then evaluate its mercury retention capacities. The as-received fly ash sample is mechanically sieved to obtain five size fractions. Their characteristics are examined by loss on ignition (LOI), scanning electron microscope (SEM), energy dispersive X-ray detector (EDX), X-ray diffraction (XRD), and Raman spectra. The results show that the unburned carbon (UBC) content and UBC structural ordering decrease with a decreasing particle size for the five ashes. The morphologies of different size fractions of as-received fly ash change from the glass microspheres to irregular shapes as the particle size increases, but there is no correlation between particle size and mineralogical compositions in each size fraction. The adsorption experimental studies show that the mercury-retention capacity of fly ash depends on the particle size, UBC, and the type of inorganic constituents. Mercury retention of the types of sp² carbon is similar to that of sp³ carbon.

The solution plasma process (SPP) has attracted considerable attention for the synthesis of carbon nanomaterials; the SPP uses electrical discharges generated directly by a bipolar pulsed power supply for various combinations of the solvents and solutes in the solution. However, the SPP requires high-temperature heat treatment for enhancing conductivity and exhibiting catalyst activity. Furthermore, the metal used as the electrode in the SPP is generally sputtered during discharge. This study presents the feasibility of reducing the heat-treatment step and solving the problem of sputtering of the metal electrodes by simply increasing the repetition frequency of the bipolar pulsed power. During synthesis, the pulse frequency acts as the graphitization catalyst. The enhancement of crystallinity was further confirmed by X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The findings of this study are expected to contribute toward research on improving the properties of carbon for various applications of the SPP synthesis methods.

This study examines the machinability of hybrid fiber metal laminates (HFML), which are made by nickel–chromium alloy (IN-625) metal-cored carbon (Ca)/aramid (Ar) fiber laminate using ultrasonic vibration-coupled microwire electrical discharge machining (UV-$\mu$WEDM). Since UV-$\mu$WEDM parameters significantly impact the erosion rate ($E_R$) and surface undulation ($S_U$), the main objective was to identify the optimal machining parameters. The input variables include the pulse on ($P_{\text{on}}$), pulse off ($P_{\text{off}}$), current ($I_C$), cutting inclination ($C_I$), and servo voltage ($S_V$) coupled with ultrasonic vibration (UV). The empirical findings show that the servo voltage ($S_V$) significantly impacts $E_R$ (73.93%) and $S_U$ (70.02%). The performance categorization order of significant influencing variable is $S_V>P_{\text{off}}>C_I>P_{\text{on}}>I_C$. The desirability interpretation generated the optimum setting for minimizing $S_U$ and maximizing $E_R$ is $P_{\text{on}}=8\mu$s, $P_{\text{off}}=14\mu$s, $S_V=50$V, $I_C=3$A, and $C_I=30^{\circ }$. Scanning electron microscopic (SEM) images were used to perform the micro-interlayer analysis on the machined surface. Moreover, creating an appropriate HFML is necessary to cut various shapes and sizes to satisfy the demands of diverse applications. 60% of components in the aerospace sector are reportedly rejected in real time due to dimension departure, poor surface finish, and damage found in the final assembly. Investigating the viability of cutting-edge machining techniques like UV-$\mu$WEDM is crucial to minimize damage and improve the quality of HFMLs.

This paper highlights the reinforcement of two different fibers in the manufacturing of hybrid laminate composites. The feasibility of glass and carbon fiber-based hybrid composites is proposed for various high performances due to their versatile mechanical properties. However, anisotropic and non-homogeneity nature creates several machining challenges for manufacturers. It can be regulated through the selection of proper cutting conditions during the machining test. The effect of process constraints like spindle speed (rpm), feed rate (mm/min), and stacking sequences ($C)$ was evaluated for the optimum value of thrust force and Torque during the drilling test. The cost-effective method of hand layup has been used to fabricate the composites. Four different hybrid composites were developed using different layers of carbon fiber and glass fiber layers. The outcomes of variables on machining performances were analyzed by variation of feed rate and speed to acquire the precise holes in the different configurations. The application potential of the proposed composites is evaluated through the machining (drilling) efficiency. The optimal condition for the drilling procedure was investigated using the multiobjective optimization-Grey relation analysis (MOO-GRA) approach. The findings of the confirmatory test show the feasibility of the MOO-GRA module in a machining environment for online and offline quality control.

This paper reports the synthesis and characterization of ternary nanocomposites consisting of polyaniline (PANI), multiwalled carbon nanotubes (MWCNTs) and manganese dioxide (MnO₂) at different MWCNT–MnO₂ loadings. The composite electrical percolation threshold is investigated as well. The in situ nanocomposites were characterized by UV-visible, Fourier transform and Raman spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, and electrical conductivity measurements. The conductivity of the nanocomposite reached up to 78.79 Scm^-1 with 50 wt.% addition of MWCNT–MnO₂ with good conduction stability and reversibility. The percolation threshold of this nanocomposite was achieved at 0.5 wt.%. Using the scaling law of the percolation theory, it was found that the theoretical conductivity of the nanocomposite exhibited an exponential factor, (t) of 1.38 instead of the universal t value of 2.

In this study, silver orthophosphate@carbon layer (Ag₃PO₄@C) core/shell heterostructure photocatalyst was prepared for the first time. The results showed that a uniform carbon layer was formed around the Ag₃PO₄. By adjusting the hydrothermal fabrication parameters, the thickness of carbon layer could be easily controlled. Furthermore, the Ag₃PO₄@C had remarkable light absorption in the visible region. Photocatalytic tests displayed that the Ag₃PO₄@C heterostructures possessed a much higher degradation rate of phenol than pure Ag₃PO₄ under visible light. The enhanced photocatalytic activity could be attributed to high separation efficiency of photogenerated electrons and holes based on the synergistic effect between carbon as a sensitizer and Ag₃PO₄. Recycle tests showed that the Ag₃PO₄@C core/shell heterostructures maintained high stability over several cycles. The good stability could be attributed to the protection of insoluble carbon layer on the surfaces of Ag₃PO₄ crystals in aqueous solution.

The increasing energy crisis promotes the study on novel electrode materials with high performance for supercapacitive storage and energy conversion. Transition metal phosphates have been reported as a potential candidate due to the unique coordination and corresponding electronic structure. Herein, we adopted a facile method for preparing NaCoPO₄@C derived from a metal organic framework (MOF) as a bifunctional electrode. ZIF-67 was synthesized before a refluxing process with Na₂HPO₄ to form a precursor, which is transformed into the final product via calcination in different atmospheres. Specifically, the resultant NaCoPO₄@C exhibits a high specific capacitance of 1178.7Fg${}^{-1}$ at a current density of 1Ag${}^{-1}$ for a supercapacitor. An asymmetric supercapacitor (ASC) assembled with active carbon displays a high capacitance of 163.7Fg${}^{-1}$ at 1Ag${}^{-1}$. In addition, as an oxygen evolution reaction (OER) catalyst, the NaCoPO₄@C electrode requires only 299mV to drive a current density of 10mAcm${}^{-2}$. These results suggest that the rational design of MOF-derived NaCoPO₄@C provides a variety of practical applications in electrochemical energy conversion and storage.

Multi-element doped porous carbon materials are considered as one of the most promising electrode materials for supercapacitors due to their large specific surface area, abundant mesoporous structure, heteroatom doping and good conductivity. Herein, we propose a very simple and effective strategy to prepare nitrogen, sulfur co-doped hierarchical porous carbons (N-S-HPC) by one-step pyrolysis strategy. The effect of sole dopants as a precursor was a major factor in the transformation process. The optimized N-S-HPC-2 possesses a typical hierarchically porous framework (micropores, mesopores and macropores) with a large specific surface area (1284.87m² g${}^{-1})$ and N (4.63 atomic %), S (0.53 atomic %) doping. As a result, the N-S-HPC-2 exhibits excellent charge storage capacity with a high gravimetric capacitance of 360F g${}^{-1}$ (1 A g${}^{-1})$ in three-electrode systems and 178F g${}^{-1}$ in two-electrode system and long-term cycling life with 87% retention after 10,000 cycles in KOH electrolyte.

Nanofluids are promising in solar harvesting and solar thermal utilization. Ethylene glycol (EG) nanofluids have the advantages of high boiling point and low volatility, and therefore are highly desired in some circumstances. In this study, the solar harvesting and solar thermal conversion properties of EG were significantly enhanced by carbon chain nanostructures (CCNSs). The prepared CCNSs/EG nanofluids showed greater optical absorption compared to EG in the wavelength range from 250nm to 1400nm. The solar weighted absorption factor (Am) of the CCNSs/EG nanofluids was 95.9% at the mass fraction of 0.05 wt.%. The enhancement was 649.2% compared to that of EG. The photothermal conversion efficiency was determined to be 97.7% and the enhancement of 83.0% was achieved. An enhancement of 1.2% in thermal conductivity was also been observed. These enhancements can be ascribed to the special architectures of the CCNSs that provide fast transfer path for the generated heat.