Solid Graphite Research Articles

Ultrasound assisted combustion synthesis of TiC in Al–Ti–C system

This research investigated the effects of high-intensity ultrasound on the combustion synthesis of TiC particles in Al–Ti–C system. The process involved that high-intensity ultrasound was applied on the surface of a compacted Al–Ti–C pellet directly through a Nb probe during the thermal explosion reaction. By comparing with the sample without ultrasonic treatment, it was found that the thermal explosion reaction for synthesizing TiC phase could take place thoroughly in the ultrasonically treated sample. During the process of synthesizing TiC phase, the dissolution of solid graphite particles into the Al–Ti melt, as well as the nucleation and growth of TiC particles could be promoted effectively due to the effects of ultrasound, leading to an enhancement of the formation of TiC particles. Ultrasound assisted combustion synthesis as a simple and effective approach was proposed for synthesizing materials in this research.

Temperature effect of friction and wear characteristics for solid lubricating graphite

Graphite is one of the effective lubricant additives due to its excellent high-temperature endurance and self-lubricating properties. In this study, wear behavior of graphite used as sealing materials to cut off hot gas is evaluated at room and elevated temperature. Wear occurs on graphite seal due to the friction of driving shaft and graphite. Thus, a reciprocating wear test to evaluate the wear generated for the graphite by means of the relative motion between a shaft material and a graphite seal was carried out. The friction coefficient and specific wear rate for the changes of applied load and sliding speed were compared under different temperature conditions considering the actual operating environment. Through SEM observation of the worn surface, the lubricating film was observed and compared with test conditions.

Degradation of the solid electrolyte interphase induced by the deposition of manganese ions

The deposition of manganese ions dissolved from the cathode onto the interface between the solid electrolyte interphase (SEI) and graphite causes severe capacity fading in manganese oxide-based cells. The evolution of the SEI layer containing these Mn compounds and the corresponding instability of the layer are thoroughly investigated by artificially introducing soluble Mn ions into a 1 mol L−1 LiPF6 electrolyte solution. Deposition of dissolved Mn ions induces an oxygen-rich SEI layer that results from increased electrolyte decomposition, accelerating SEI growth. The spatial distribution of Mn shows that dissolved Mn ions diffuse through the porous layer and are deposited mostly at the inorganic layer/graphite interface. The Mn compound deposited on the anode, identified as MnF2, originates from a metathesis reaction between LiF and dissolved Mn ion. It is confirmed that ion-exchange reaction occurs in the inorganic layer, converting SEI species to Mn compounds. Some of the Mn is observed inside the graphite; this may cause surface structural disordering in the graphite, limiting lithium-ion intercalation. The continuous reaction that occurs at the inorganic layer/graphite interfacial regions and the modification of the original SEI layer in the presence of Mn ions are critically related to capacity fade and impedance rise currently plaguing Li-ion cells.

Redox speciation analysis of dissolved iron in estuarine and coastal waters with on-line solid phase extraction and graphite furnace atomic absorption spectrometry detection

An automatic on-line solid phase extraction (SPE) system employing the flow injection (FI) technique directly coupled to a graphite furnace atomic absorption spectrometer (GFAAS) was established for speciation and determination of dissolved iron in estuarine and coastal waters. Fe(II) was mixed with ferrozine solution in a sample stream to form the Fe(II)–ferrozine complex which was extracted onto a C18 SPE cartridge, eluted with eluent and detected with GFAAS. In a parallel flow channel, Fe(III) was reduced to Fe(II) with ascorbic acid and then detected in the same way as Fe(II). The home-made interface between FI–SPE and GFAAS efficiently realized the sample introduction to the furnace in a semi-automated way. Parameters of the FI–SPE system and graphite furnace program were optimized based on a univariate experimental design and an orthogonal array design. The salinity effect on the method sensitivity was investigated. The proposed method provided a detection limit of 1.38nmolL−1 for Fe(II) and 1.87nmolL−1 for Fe(II+III). With variation of the sample loading volume, a broadened determination range of 2.5–200nmolL−1 iron could be obtained. The proposed method was successfully applied to analyze iron species in samples collected from the Jiulongjiang Estuary, Fujian, China. With the 2-cartridge FI–SPE system developed, on-line simultaneous determination of Fe species with GFAAS was achieved for the first time.

Direct determination of lead in plastic toys by solid sampling high resolution-continuum source graphite furnace atomic absorption spectrometry

Lead concentrations in various plastic toys were determined directly by solid sampling high resolution continuum source graphite furnace atomic absorption spectrometry.

Feasibility of Using AAS for the Characterization of a Tuna Fish Candidate Reference Material for Total Hg and Methyl-Hg Measurement

This work describes the evaluation of several parameters for preparing a tuna fish candidate reference material (RM) in order to measure its total Hg and methyl-Hg mass fractions by cold vapor atomic absorption spectrometry (CV-AAS) and solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS). Best results were acquired after extraction with toluene and L-cysteine for 15 min at 80 °C. The parameters investigated were stability of chemical composition during production, homogeneity and analyte segregation. No analyte segregation was observed and the material was shown to be stable even when stored at 50 °C for 10 months. Total Hg mass fraction was 3.03 ± 0.22 µg g-1 by CV AAS, 2.99 ± 0.43 µg g-1 by SS-GF AAS and 2.95 ± 0.15 µg g-1 by direct mercury analyser (DMA). Methyl-Hg mass fraction was 2.49 ± 0.13 µg g-1 by CV AAS and 2.44 ± 0.46 µg g-1 by SS-GF AAS.

四ホウ酸リチウムガラスビード粉末を直接導入した黒鉛炉原子吸光分析法による岩石中のジスプロシウムの定量

四ホウ酸リチウムガラスビード粉末を直接導入した黒鉛炉原子吸光分析法による岩石中のジスプロシウムの定量

Cadmium and lead in seafood samples determined by solid phase extraction and graphite furnace atomic absorption spectrometry

A sample preparation method has been developed to detect cadmium and lead in commercial frozen seafood samples. After being digested with concentrated HNO 3 in a closed polypropylene vessel, the clear sample solution was separated and preconcentrated by solid phase extraction using octadecyl silica membrane discs modified with 8-hydroxyquinoline prior to determination by graphite furnace atomic absorption spectrometry (GFAAS). The preconcentration conditions including pH, ligand quantity, eluent concentration, and volume were found to be effective with 10.0 mg of 8-hydroxyquinoline in 2.0 ml ethanol and pH 6.0. The retained cadmium and lead were efficiently eluted with 5.0 ml of 1.0 M HNO 3 and determined by GFAAS. The detection limits for cadmium and lead were 0.073 µg/l and 0.332 µg/l, respectively. The proposed method was tested with the certified reference material, DORM- 2 (Dogfish muscle), with good agreement. The recoveries were found to be 100-103% (n = 4) for Cd and 92-108% (n = 5) for Pb with relative standard deviation (n = 5) of 3% for Cd and 4% for Pb. The extraction was found to be unaffected by coexisting ions. The method was applied satisfactorily to the seafood samples and trace levels of cadmium and lead were found.

Determination of Cd, Ni and V in Spices by Solid Sampling High-Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry

This work describes a procedure for determination of Cd, Ni and V in spices by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) using direct solid sampling (SS). The use of Pd/Mg(NO3)2 as modifier for Cd, and an additional air-assisted pyrolysis step allowed the use of aqueous calibration for all analytes. Accuracy was checked by analysis of certified reference materials (CRMs) and the results were in agreement to certified values at 95% confidence level (t-test). Eight samples of spices were analyzed by the proposed procedure and by inductively coupled plasma mass spectrometry (ICP-MS). The found concentrations were 88-233 ng g-1 Cd , 113-2842 ng g-1 Ni and 154-1007 ng g-1 V, with precision generally better than 12%. Results obtained by the proposed procedure were in agreement with those obtained by microwave-assisted digestion and ICP-MS determination. The limits of detection were 0.2, 18 and 7 ng g-1 for Cd, Ni and V, respectively.

Влияние показателя поглощения тушащей жидкости на интенсивность кипения и испарения неоднородной капли в пламени

The numerical model and methodology of experimental researches of heat and mass transfer during the heating, boiling and evaporation of heterogeneous water droplet in a high-temperature area are presented in the work. The results of numerical and experimental researches of evaporation of water droplet with a solid graphite inclusion in a flaming combustion area are introduced. The conditions of an explosive vaporization mode realization in a contact zone of solid inclusion and liquid film (temperature of gaseous area is Tf > 1050 K and water film thickness is 5R > 0.210 -3 m) are determined. The main stages of studying process are fixed on video: the droplet heat-up, the beginning of bubble formation of vapor at the interface solid inclusion - liquid, the volume increase of vapor bubble, the droplet fission. The influence of optical water characteristic (absorption coefficient of radiant energy k x )onthe typical period t h from the beginning of heterogeneous liquid droplet heating to the realization of an explosive vaporization conditions is analyzed. It is shown that for droplets with liquid film size SR ~ 0.510 3 m the change of the absorption coefficient of radiant energy in a wide range =10 -3 ^10 2 m -1 doesn't influence on t h significantly. The application possibility of water unprepared (in the case of optical properties) in a special way (for example from open ponds at forest fire extinguishing) for extinguishing composition is substantiated, provided accounting of the absorption coefficient of the liquid in the process of selecting the characteristic sizes of the generated droplets.

Molten Carbonate Composition Effects on Carbon Electro-Oxidation at a Solid Anode Interface

The electrochemical oxidation of graphite is investigated to determine the relative influence of the composition of a molten carbonate electrolyte on a solid anode. The binary eutectics of sodium, lithium and potassium carbonates were investigated as well as ternary mixtures including the eutectic and combinations of systematically varied lithium content. It was seen that the combination of cations included in the carbonate melt can influence the electrochemical performance of graphite with binary combinations performing better than ternary in all cases. Very little change in the mechanistic behavior was observed through tafel analysis; instead it is proposed that the observed kinetic effects are a combination of the catalytic role of all metal cations present as well as the intercalation of lithium into the solid graphite electrode. The effect of lithium intercalation is suggested to lead to a change in the graphite surface polarity which affects product gas bubble formation and dislodgement at the solid anode. Increased lithium concentration, and it is assumed intercalation, encourages smaller bubbles to form which are dislodged at a faster rate than surfaces with less lithium intercalation in the ternary electrolyte. A threshold lithium concentration is reached above approximately 65 % where the electrochemical behavior is significantly changed and bubble formation behavior is no longer observed.

Study on nanosecond pulsed electron beam generation

The paper presents the findings of an investigation on volt-ampere characteristics of the diode with explosive emission cathodes of different constructions (blade metal-dielectric (MD-cathode) and solid graphite cathodes) under the change of the anode-cathode gap in wide ranges. The investigations were carried out using the TEA-500 pulsed electron accelerator. The total current of the electron beam was measured using the Faraday cup (FC). A 0.5-mm foiled glass fiber laminate was used as an emitting edge of the cathode in the experimental study with the explosive emission blade MD-cathode. Based on the obtained results, the conclusion was made that the graphite cathode has the most effective efficiency factor.

Studying of simultaneous extraction of As, Cd, Cr, Pb in saline water and determination by graphite furnace atomic absorption spectrometry

In this paper we studied a simultaneous extraction process of As, Cd, Cr and Pb in waters by solid phase extraction technique followedby graphite furnace atomic absorption spectrometry. Accordingly, As(V) was reduced to As(III) in 0.5 % sodium thiosulfate prior to form Me-PDC complex with ammonium pyrrolidinedithiocarbamate (APDC). The complexation reactions were optimized at pH 4.0 for As(III), Cd, Pb and at pH 4.7 for Cr(III), Cr(VI). The non-polar MePDC complexes were retained on SPEC18 cartridge. This method may help to eliminate matrix interferences as well as topreconcentrate the analytes at the factor of up to 20 times. Parameters influence upon the extraction procedure and analysis were also investigated. Detection limits of method was 0.328,0.011, 0.080 and 0.109 µg/L for As, Cd, Cr and Pb, respectively. The method has been successfully applied to the determination of these metal ions in brackish water and sea water collected at Tien Giang province.

Efficient Synthesis of Endohedral Metallofullerenes in 3-Phase Arc Discharge

Endohedral metallofullerenes and, in particular, trimetallic nitride endohedral metallofullerenes exhibit unique properties that differentiate them from other carbon nanomaterials. Future applications of these species are restricted due to high cost and low productivity of existing synthesis methods, which are primarily based on the use of a Krätschmer-Huffman two electrode in-line arc discharge reactor with packed electrodes. We have developed an alternative way for the synthesis of metallofullerenes that employs a 3-phase arc discharge system. The method has been validated and optimized for the synthesis of trimetallic nitride endohedral metallofullerenes, including Lu3N@C80. Experimental results have shown more than 400% increase in Lu3N@C80 yield and productivity, while eliminating the use of high cost process gases (i.e., helium). Moreover, a metal oxide powder feed and solid graphite electrodes are introduced to avoid the need for packed electrodes and to extend reactor run times.

Effect of Rod Material on the Impedance Behavior of Small Aspect Ratio Rod Pinches

A series of experiments on small aspect ratio rod pinches using solid tungsten, solid graphite, and thin-wall tantalum anode rods driven by a nominally 375-kV linear transformer driver, powered inductive voltage adder has characterized the impedance behavior over a range of aspect ratios and materials. For the tungsten and tantalum anodes, the impedance behavior is well described by the pinched current for self-magnetically insulated flow in a cylindrical geometry with ions present and gap closure velocities of 1-2 cm/μs. The graphite anodes always exhibited strong localized pinching of the electron beam onto the anode rod, with substantially higher operating impedance, as well as a delay in the formation of the plasma at the anode. The graphite anodes also had a longer radiation delay time, consistent with the longer anode plasma formation time.

Determination of Pb in glasses by direct solid sampling and high-resolution continuum source graphite furnace atomic absorption spectrometry: method development and analyses of glass samples

In this study, a new method was developed for the determination of Pb in glass samples by solid sampling graphite furnace atomic absorption spectrometry (SS GFAAS), and Pb concentrations of two glass samples were determined. For method development, the National Institute of Standards and Technology (NIST) SRM 612 glass standard was used. Different experimental and instrumental parameters were investigated, including sample mass introduced into the graphite furnace, use of a modifier, use of an aqueous standard solution for calibration curves, and different detection wavelengths. Pd(NO3)2+Mg(NO3)2 was used as a modifier for experiments. LOD values were 201.6pg Pb at 205.328nm with 3pixels (central pixel±1) and 11.2pg Pb at 283.060nm with 3pixels (central pixel±1). Then, Pb concentrations in two different glass samples were determined by SS GFAAS using aqueous Pb standard and solid standard (NIST SRM 612) for calibration. Thus, the study shows that SS GFAAS is a reliable method for the determination of Pb in glass samples with the advantageous using very small amount (30–100μg) of glass sample and no need to dissolve the glass by toxic and hazardous chemicals.

Tribological and micro/nano-structural characterization of some Fe-based sintered composites

Abstract New iron-based composites were investigated for applications within the friction materials domain. This study presents the elaboration and the structural and tribological characterization of iron-based friction composites containing iron, copper, graphite and/or nickel, introduced in a powder state. The technology employed for obtaining these materials is via a classical powder metallurgy route. The porosity of the studied materials, the tribological characterization, the roughness of researched composites and their structure are marked out. Results showed that the samples elaborated from the material with 10 wt.% Cu, 7 wt.% graphite, 12 wt.% Ni and the rest iron, compacted at 600 MPa, presented the best tribological behavior. The presence of pearlite, ferrite, nickel-based and copper-based solid solutions and free graphite in composite structures is highlighted.

A Novel CO2 Capture Process from Flue Gas with Recycling of Graphite Using Sodium—Conceptualization of the Process and Fundamental Process Description

Anthropogenic CO2 emission is identified as the major cause of climate change. The use of fossil fuels has to be accommodated, possibly with a CO2 capture process. Sequestration of captured CO2 at high pressure is proposed as a feasible option for future mitigation of climate change, though using fossil fuels. However, this needs significant energy input and carries the potential threat of a possible future catastrophe. Capture of CO2 with possible recycling is a long-term sustainable option. In this paper, a process involving a chain of reactions using solid sodium to capture both CO2 and SO2 from a flue gas is described. A significantly detailed description of both chemical reactions and physical processes is discussed. Recycling of captured CO2 and SO2 in the form of solid graphite and elemental sulphur (as the by-products) is the special feature of this process. However, critical selection of intermediate process liquids and equipment in this process needs further study for real-life implementation of this scheme.

Determination of sulfur in coal by solid sampling graphite furnace high-resolution molecular absorption spectrometry

An analytical procedure for quantitative analysis of sulfur in coal by direct solid sampling graphite furnace high-resolution continuum source molecular absorption spectrometry (HR-CS GF MAS) is described, which is based on the molecular absorption of tin sulfide. The heating program is optimized, and a series of chemical modifiers (Ir, Mg, Pd, Ru, W, Zr) are tested. All measurements are accomplished with an Ir coated platform and Pd as modifier, because the best results are achieved.Accurate results are obtained using the central SnS line of the band found at 271.578nm with precision values between 1 and 6%. A limit of detection of 10ngS absolute is achieved. Furthermore, the trueness of the procedure is verified by analysis of certified reference materials. Several coal samples with a concentration range from 0.8 to 21.7mgg−1S and three certified reference materials are analyzed. In all cases, simple calibration with aqueous standards is found to be possible and the sample throughput is 2–3 samples per hour (6 replicates per sample).

Analysis of Tribological Performance of Cu Hybrid Composites Reinforced with Graphite and TiC Using Factorial Techniques

In this study, a copper hybrid metal matrix composite reinforced with graphite (5, 10, and 15 vol%) and TiC (5, 10, and 15 vol%) was processed by a powder metallurgy route. Optical micrographs confirm the uniform distribution of reinforcements in the copper matrix. The hardness of the composites decreased with the addition of graphite. However, the addition of TiC into the copper matrix increased the hardness of the composites due to its high hardness. The influence of graphite percentages, load, sliding speed, and sliding distance on the wear of the as-sintered hybrid composites was studied based on the design of experiments. Analysis of variance (ANOVA) was used to study the effect of the parameters on the wear weight loss of the hybrid composites. The weight loss due to wear of the hybrid composites decreases from 0.1345 to 0.0830 g as the volume percentage of graphite increases from 5 to 15%. Results indicated that the normal load has greater static influence of 43.85%, sliding distance has an influence of 29.84%, percentage of graphite has an influence of 15.17%, and sliding speed has an influence of 1.83% on the weight loss of copper hybrid composites due to sliding wear. The worn-out surfaces were analyzed using electron microscopy, which reveals that the addition of both hard ceramic reinforcement TiC and soft solid lubricant graphite significantly improves the tribological performance of the copper composites.