Influence Of Carbon Impurities Research Articles

Molecular dynamics study of melting and crystallization of nickel nanoparticles with carbon impurity

ABSTRACT Molecular dynamics simulations were used to investigate the melting and crystallization processes of nickel nanoparticles and the influence of carbon impurities on these processes. It is shown that melting and crystallization temperatures are inversely proportional to particle diameter: as particle size decreases and the proportion of free surface area increases, melting temperatures during heating and crystallization temperatures during cooling decrease. The presence of carbon impurity atoms reduces both melting and crystallization temperatures. Carbon atoms often formed clusters within the metal consisting of several carbon atoms, which distorted the nickel crystalline lattice around them, leading to earlier melting of the metal. During crystallization as a result of cooling from the melt, impurity carbon atoms, especially clusters of them, tended to anchor primarily at grain boundaries and triple junctions.

Effect of Carbon on the Emission Performance of Tungsten Electrode Electron in Gas Discharge Lamps

Tungsten electrodes are widely used as electric light sources because of their excellent performance. Impurity elements, such as carbon, can be easily introduced during the preparation of lamp tubes; therefore, it is necessary to analyze the influence of carbon impurities on the performance of gas discharge lamps and propose reasonable solutions. In this study, we investigated the manner in which carbon enters a gas discharge lamp and compared the electron emission properties of carbon and noncarbon electrodes through extensive experiments. The results showed that the current density was reduced by more than 50% at 1450°C, and the most obvious change was 75.00%. Furthermore, we propose a detailed solution for the introduction of carbon, which provides technical support for the quality control of gas discharge lamps.

The influence of carbon impurities on the formation of loops in tungsten irradiated with self-ions

The microstructure changes taking place in W under irradiation are governed by many factors, amongst which C impurities and their interactions with self-interstitial atoms (SIA). In this work, we specifically study this effect by conducting a dedicated 2-MeV self-ions irradiation experiment, at room temperature. Samples were irradiated up to 0.02, 0.15 and 1.2 dpa. Transmission electron microscopy (TEM) expectedly revealed a large density of SIA loops at all these doses. Surprisingly, however, the loop number density increased in a non-monotonous manner with the received dose. Performing chemical analysis with secondary ion spectroscopy measurements (SIMS), we find that our samples were likely contaminated by C injection during the irradiation. Employing an object kinetic Monte Carlo (OKMC) model for microstructure evolution, we demonstrate that the C injection is the likely factor explaining the evolution of loops number density. Our findings highlight the importance of the well-known issue of C injection during ion irradiation experiments, and demonstrate how OKMC models can help to rationalize this effect.

A spectroscopic study of trivalent cation (Cm3+ and Eu3+) sorption on monoclinic zirconia (ZrO2)

This study investigates the retention of trivalent actinides (Cm3+) and their lanthanide analogues (Eu3+) on monoclinic zirconia (ZrO2), a solid phase known to form on the zircaloy cladding material surrounding spent nuclear fuel (SNF) rods. Two zirconia solids with varying carbon content were utilized. The influence of carbon impurities on the ZrO2 surface charge was investigated via zeta-potential measurements. Batch data was collected for various Eu3+ concentrations, while the Cm3+ surface speciation was studied on the molecular level with laser spectroscopy (TRLFS). The spectroscopic sorption data was modelled using the Diffuse Double Layer (DDL) model. The ZrO2 surface charge measurements yielded a pHIEP of 6 which was influenced by the presence of inorganic and organic carbon species. The pH-dependent uptake of Eu3+ showed a maximum sorption above pH 5.5, with no impact of the carbon concentration. The speciation of the trivalent metal, however, was different in the presence of intrinsic organic carbon in the sample, resulting in the formation of an organic Cm3+-complex on the surface. This ternary complex was absent on the ZrO2 material with low carbon content. Here, the surface speciation was dominated by Cm3+ and Cm3+-hydrolysis complexes which could be well described by our DDL model.

Influence of carbon impurities and oxygen vacancies in Al2O3 film on Al2O3/GaN MOS capacitor characteristics

Effects of carbon impurities and oxygen vacancies in Al2O3 film on the characteristics of Al2O3/GaN MOS capacitors were studied using the different atomic layer deposition (ALD) precursor and high-pressure water vapor annealing (HPWVA). Trimethyl aluminum (TMA: Al(CH3)3) and dimethyl aluminum hydride (DMAH: Al(CH3)2H) were used as ALD precursors to control the carbon impurities. On the other hand, oxygen vacancies in Al2O3 film were suppressed using the HPWVA. The DMAH precursor reduced the concentration of carbon impurities in the ALD Al2O3 film. It was found that the interface trap density (Dit) was mainly affected by the carbon impurities rather than the oxygen vacancies at the Al2O3/GaN interface. On the other hand, voltage stress induced flat band voltage (VFB) shift was attributed to both the carbon impurities and the oxygen vacancies.

Effects of carbon contaminations on Y2O3-stabilized ZrO2 thin film electrolyte prepared by atomic layer deposition for thin film solid oxide fuel cells

In this study, influence of carbon impurities on characteristics of ALD-YSZ films is systematically investigated. Carbon concentration in ALD-YSZ films was controlled by changing Y2O3 ratio in YSZ super cycle. To examine electrochemical characteristics of ALD-YSZ films, nano-porous templates based thin film solid oxide fuel cells (TF-SOFCs) were fabricated with ALD-YSZ thin film electrolyte and examined at 500°C. Open circuit voltages (OCVs) of TF-SOFCs with ALD-YSZ were clearly dependent on carbon contaminations. High carbon concentration caused leakage current through internal short circuit, and then, OCVs of TF-SOFCs were decreased. Post-processing of ALD-YSZ thin film electrolyte improved OCVs of TF-SOFCs.

Lithium ion intercalation mechanism for LiCoPO4 electrode

Abstract Recently, there exists a discrepancy on the lithium ion de-intercalation mechanism for LiCoPO4 electrode. In the present work, the study was focused upon exploring the origin of this discrepancy by studying the dependence of the impedance spectrum on the state of charge and the carbon content. For the pure LiCoPO4 electrode, the two plateaus in the charge curve are at 4.82 and 4.92 V. We have also studied the variation of electrochemical impedance spectroscopies (EISs) with the state of charge. The EIS measurement has shown that the total interfacial resistance increases as the state of charge increases for the pure LiCoPO4 electrode. If higher content of sucrose was added in the precursor (this implies higher carbon content in the synthesized sample), only one potential plateau can be found in the charge curve. For this electrode, the total interfacial resistance decreases with the state of charge. Especially, the total interfacial resistance has a dramatic decrease when the state of charge increases from 20% to 40%. It is believed that the influence of carbon impurity on the variation tendency of the EIS pattern may reflect the change of the fine structure. For the pure LiCoPO4 electrode, the intermediate phase is Li0.20~0.45CoPO4.

Effect of Carbon Impurities on Hot-Pressed ZrB2-SiC Ceramics

The influence of carbon impurities on phase composition, microstructure, and mechanical properties of hot-pressed ZrB2–SiC ceramics was studied. Carbon was either present in the starting ZrB2 powders or introduced due to the carbon-rich sintering environment. Carbon present in the starting ZrB2 powders removed the inherent oxygen impurities to enable ceramics that appeared phase pure by X-ray diffraction, had smaller average grain sizes, and had higher Vickers’ hardness, but lower fracture toughness. Carbon introduced from the sintering environment led to the formation of secondary ZrC, allowed the microstructure to coarsen, and decreased the fracture toughness. This study showed that ZrB2–SiC ceramics with refined microstructure could be obtained by introducing carbon impurities in the starting ZrB2 powders, whereas the densification should be carried out at lower temperature to avoid the carbon uptake from sintering environment.

Hydrogen-Induced Stress Relaxation in Thin Pd Films: Influence of Carbon Implementation

The influence of carbon impurities on mechanical properties of thin Pd film in the process of hydride formation and its disintegration has been investigated "in situ" by means of atomic force microscopy (AFM). Pd interaction with hydrogen leads to the formation of hydride PdHx, if critical conditions of pressure and temperature are reached (equilibrium hydrogen pressure over PdHx at 298 K is approximately 1 kPa). The lattice constant of PdHx is larger than that of the original metal, and the hydride formation generates high stress within the film. As a consequence, the reversible formation of well organized mesoscopic protrusions on the film surface is observed. In this paper, we focus our investigation on the mechanical response which occurs when, prior to hydride generation, carbon atoms are incorporated into the bulk of the film. The systems characterized by carbon incorporation from the two opposite sides of thin palladium film (HOPG substrate and hydrocarbon fragments deposit from a gas-phase reached by preadsorption of ethylene) are compared. For both cases the mechanism of mechanical response is the same, but very different from that registered for pure thin palladium film. Carbon impurities induce, during PdHx decomposition, creation of an organized network of cracks which divides the continuous film into separated domains. The mechanisms of carbon introduction occurring in both cases have been proposed.

Influence of Carbon Impurity on Net Erosion of Reduced-Activation Ferritic/Martensitic Steel and Tungsten Materials Exposed to Hydrogen and Carbon Mixed Ion Beam Relevant to Fusion Plasma Boundary

Using a simulation code for dynamic interactions between energetic ions and solid materials, the influence of C impurity concentration on net erosion of reduced-activation ferritic/martensitic steel, RAF (Fe in the simulation), and W materials exposed to a 0.33 keV H+ and 1 keV C+ impurity mixed ion beam relevant to a fusion plasma boundary has been studied. A comparison of the simulation results between the Fe and W materials at C impurity concentrations less than C: 1.00% is described and discussed. In particular, emphasis is paid to a quantitative comparison between depth profiles of C impurity deposited on the materials and the experimental data, which were obtained by the H and C mixed ion beam exposure experiments of RAF (F82H in the experiment) and W materials. For the W material, chemical erosion (CH4 emission) of the deposited C impurity by the H+ impact is taken into account in the simulation. The C impurity concentration causes a significant difference in net erosion between the two materials. For the Fe material, net erosion is suppressed with increasing C impurity concentration. In contrast, for the W material, net erosion is enhanced. In the depth profile, there is also a significant difference between the two materials. At C: 0.11%, the impinging C impurity is hardly deposited on the Fe material. For the W material, the depth profile at C: 0.11% shows a local peak around a certain depth, which is in good agreement with the experimental data at 653 K. This agreement indicates no contribution of the chemical erosion in the H–C–W system, which is quite different from that in the H–C system where the chemical erosion occurs. The difference seems to indicate that the chemical erosion in the H–C–W system is dependent upon amounts of the deposited C impurity or the binary alloy phase change between W and C. When the C impurity concentration increases to C: 0.84%, the impinging C impurity is deposited on the Fe material. The depth profile shows a maximum at the top surface, which reproduces the experimental data at 453 K. For the W material, the depth profile at C: 0.84% shows almost the same tendency as that at C: 0.11%, but shows a larger amount of the deposited C impurity. The simulation result at C: 0.84% is in disagreement with the experimental result at 653 K, which shows a maximum at the top surface. This disagreement is not fully explained by only the chemical erosion.

Carbon in iron phases under high pressure

The influence of carbon impurities on the properties of iron phases (bcc, hcp, dhcp, fcc) has been studied using the first‐principles projector augmented‐wave (PAW) method for a wide pressure range. It is shown that the presence of ∼6 at. % of interstitial carbon has a little effect on the calculated structural sequence of the iron phases under high pressure. The bcc → hcp transition both for pure iron and iron containing carbon takes place around 9 GPa. According to the enthalpies comparison, the solubility of carbon into the iron solid is decreased by high pressure. The coexistence of iron carbide (Fe3C) + pure hcp Fe is most stable phase at high pressure compared with other phases. Based on the analysis of the pressure‐density dependences for Fe3C and hcp Fe, we suggest that there might be some fraction of iron carbide present in the core.

Influence of carbon impurity on microstructures and electrode properties for V-based battery alloys

Abstract The influence of the carbon impurity on the microstructure, hydrogen storage, and electrochemical performance of alloy V4TiNi0.65Co0.05Nb0.047Ta0.047 were investigated by varying the weight percent of added carbon in the range of 0–1%. The hydrogen storage ability and discharge capacity were significantly decreased in the presence of a smaller content carbon. This is ascribed to the solution of carbon into the V–Ti-based main phase. A new TiC phase was clearly observed when the added carbon content was over 0.6 wt%.

Influence of carbon impurity on the microstructure of beryllia ceramics

Carbon exerts a significant influence on the microstructure of beryllium ceramics. With the introduction of activated carbon into the composition of the ceramic its microstructure undergoes changes. Even small amounts of carbon (about 0.1%) lead to the development of pores. With increase in carbon concentration there is an increase in the amount of large pores. The distribution of pores over the specimen's cross section is irregular.

Desorption from powdered ZnO during electron bombardment and interaction with atomic hydrogen

Electron bombardment of ZnO powder leads to desorption of CO2. The presence of CO2 molecules at ZnO surfaces after chemisorption of oxygen was recently established from photodesorption experiments, leading to the conclusion that carbon impurities were active during oxygen chemisorption. Atomic hydrogen has earlier been found to chemisorb on ZnO single crystals, the adsorbed atoms acting as electron donors. We have tried to evaluate the possible influence of carbon impurities on this reaction with ZnO powder. It was found that adsorption of hydrogen atoms causes an increase of conductance, accompanied by desorption of CO and O. No significant desorption of CO2 was found.