Mixture Of Graphite Powder Research Articles

Carbon Nanotubes Based Glucose Needle-type Biosensor.

A novel needle-type biosensor based on carbon nanotubes is reported. Thebiosensor was prepared by packing a mixture of multi-wall carbon nanotubes (MWCNTs),graphite powder and glucose oxidase (Gox) freeze-dried powder into a glass capillary of 0.5mm inner diameter. The resulting amperometric biosensor was characterizedelectrochemically using amperometry in the presence of hydrogen peroxide and in thepresence of glucose. The glucose biosensor sensitivity was influenced by the glucoseoxidase concentration within the MWCNTs mixture. The optimized glucose needle-typebiosensor displayed better sensitivity and stability, and a detected range of up to 20 mM.Based on its favorable stability, the needle biosensor was first time used in real-timemonitoring system as a kind of online glucose detector. The decay of current response isless than 10% after 24-hour continuous observation.

Development of Ultra-Carbon Steel Prepared by Mechanical Alloying and Subsequent Hot Pressing

It is known that the most effective way to improve mechanical properties of steels is by microstructural refinement. Iron and graphite powders mixture with hypoeutectoid composition were mechanically alloyed (MAed) and subsequently hot pressed (HPed) to provide steels with fine structure. Mechanical Alloying (MA) was carried out using a planetary ball mill for 100, 200 and 300 h, while HP at 41 MPa at various temperatures: 610oC (below), 730oC (near) and 800oC (above the eutectoid transformation point A1). The mechanically alloyed (MAed) powders were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM). While, the HPed compacts were characterized by SEM, Vickers hardness and tensile test. During MA, refinement of crystallite, formations of super-saturated iron solid solution and Fe/C amorphous phase occured first. With further MA time, these phases might begin to transform to more stable phases such as carbides. In the case of HP at 610oC (below A1), very fine cementites were precipitated in fine ferrite grain with sub-micron meter in the size. However, the mechanical properties cannot be attained because of low sinterability. At 730oC (near A1), the strength reaches the maximum value. With further temperature increase (at 800oC), the sintering progressed well and the coarsening occured, resulting the decrease in strength. However, the fracture strain increased significantly. The steels obtained in the present study had mechanical properties comparable to those of standard (JIS) steels through the welle stablished heat treatment such as normalizing and thermal refining.

Investigation of TiC–C Eutectic and WC–C Peritectic High-Temperature Fixed Points

TiC–C eutectic (2,761°C) and WC–C peritectic (2,749°C) fixed points were investigated to compare their potential as high-temperature thermometric reference points. Two TiC–C and three WC–C fixed-point cells were constructed, and the melting and freezing plateaux were evaluated by means of radiation thermometry. The repeatability of the TiC–C eutectic within a day was 60 mK with a melting range roughly 200 mK. The repeatability of the melting temperature of the WC–C peritectic within 1 day was 17 mK with a melting range of ∼70 mK. The repeatability of the freezing temperature of the WC–C peritectic was 21 mK with a freezing range less than 20 mK. One of the TiC–C cells was constructed from a TiC and graphite powder mixture. The filling showed the reaction with the graphite crucible was suppressed and the ingot contained less voids, although the lack of high-purity TiC powder poses a problem. The WC–C cells were easily constructed, like metal–carbon eutectic cells, without any evident reaction with the crucible. From these results, it is concluded that the WC–C peritectic has more potential than the TiC–C eutectic as a high-temperature reference point. The investigation of the purification of the TiC–C cell during filling and the plateau observation are also reported.

Laboratory production of zirconium carbide compacts for use in inert matrix fuels

Zirconium carbide is being actively considered for use as an inert matrix material in composite nuclear fuel for gas-cooled fast reactors. ZrC can be produced either by the endothermic carbothermal reduction of zirconium dioxide or by the direct exothermic reaction of pure zirconium and graphite powder mixtures. The exothermic reaction is classified as combustion synthesis or self heating synthesis. Experiments were conducted to demonstrate the combustion synthesis reaction of zirconium and graphite powders and measure the ignition and adiabatic temperatures. The heat released during this short reaction time was sufficient only to partially sinter the compacts to less than 40% theoretical density. Subsequently, compacts of ZrC were similarly produced by combustion synthesis followed by a short, high temperature hold at 2440 °C to relieve residual stresses in the compacts following the rapid reaction sintering. External pressures of up to 5.2 MPa were used as an additional driving force for sintering. The effects of reactant particle size and degree of uniaxial pressing on the product density and porosity were also studied. Higher densities in the fabricated compacts were noted for higher uniaxial pressures irrespective of powder size. Also, smaller powder sizes produced compacts up to 92% TD, while larger particle sizes produced compacts up to 84% TD for the same pressure. The compacts were characterized based on composition, microstructure, and density/porosity. Results of the different experiments are presented.

A homojunction of single-crystallineβ-Ga2O3 nanowires and nanocrystals

A homojunction of single-crystallineβ-Ga2O3 nanowires and nanocrystals was realized.Ga2O3 nanowires weresynthesized at about 850–950 °C using a mixture of Ga2O3 and graphite powder with vapor phase epitaxy. It was found that theβ-Ga2O3 nanocrystals form a single unit with the nanowires and arepart of the same single crystal with a perfect lattice. Growth ofβ-Ga2O3 nanocrystals follows the growth direction of the mainβ-Ga2O3 nanowires. The distance between neighboring atoms inβ-Ga2O3 nanowires was 0.522 nm, which is similar to the theoretical value for bulkβ-Ga2O3.

Fabrication and Characterization of In-Doped Zinc Oxide Nanodisks

In-doped ZnO nanodisks were successfully fabricated by thermal evaporation Zn, In2O3 and graphite powder mixture without catalyst. Morphology, structures and components of ZnO nanodisks were investigated by SEM, HRTEM, EDS and X-Ray diffraction. ZnO nanodisks have perfect hexagonal shape, with 1~3μm size and 40~100 nm in thickness. The nanodisks are single-crystalline ZnO with wurtzite structure and In content of nanodisks reaches 2.2%. The growth along [0001] is suppressed leading to the formation of ZnO nanodisks. Room temperature photoluminescence spectra of the nanodisks shows that the UV emission peak blueshifts and becomes broader after doping.

Growth and Auger electron spectroscopy characterization of donut-shaped ZnO nanostructures

Zinc oxide (ZnO) nanodonuts have been obtained by vapor phase transport process utilizing a mixture of ZnO, graphite and erbium oxide powder as the evaporation source. ZnO nanodonuts prepared under various thermal processes indicate that ZnO nanodonuts start forming during the initial thermal ramp up stage. A subsequent holding of the growth temperature at 1000 °C causes the nanodonut to evolve into perfectly donut-shaped nanostructure. Additional deposition of ZnO on top of the nanodonut during the holding of the furnace temperature at 1000 °C result in partially filled nanodonuts or hemispherical nanostructures, or donuts that are completely buried beneath ZnO film. Auger electron spectroscopy depth profile analysis indicates that the deposited ZnO film is stoichiometric, whereas the nanodonuts and the completely filled hemispherical nanostructures are porous and are oxygen deficient. The volume density of the nanodonut is estimated to be 20% that of the background ZnO film.

Carbon paste electrode incorporating multi-walled carbon nanotube/cobalt salophen for sensitive voltammetric determination of tryptophan

A modified carbon paste electrode is prepared by incorporating multi-walled carbon nanotube (MWCNT) and cobalt salophen (CoSal). A mixture of fine graphite powder with 10 wt% of MWCNT is applied for the preparation of carbon paste (by dispersing in Nujol) and finally modified with CoSal. The electrocatalytic oxidation of tryptophan (Trp) is investigated on the surface of the MWCNT/CoSal-modified electrode using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Using the modified electrode, the kinetics of the electro-oxidation of Trp is considerably enhanced, by lowering the anodic overpotential through a catalytic fashion. The mechanism of electrochemical behavior of Trp at the surface of modified electrode is analyzed by investigating the effect of sweep rate and pH on the responses of CV method. The prepared modified electrode showed voltammetric responses with high sensitivity and selectivity for Trp, which makes it very suitable for sub-micromolar detection of Trp. The electrode is able to completely resolve the voltammetric response of Trp from potentially interfering species, e.g. ascorbic acid (AA) and cysteine, which can be oxidized effectively on the surface of the modified electrodes with transition metal complexes. The voltammetric studies using the modified electrode showed three well-resolved anodic peaks for AA, cysteine and Trp, revealing the applicability of the electrode for simultaneous electrochemical detections of these compounds in mixtures. A linear dynamic range of 5 × 10 −5 to 5.0 × 10 −7 M for Trp is obtained in buffered solutions with pH 4.0. The linear range of the calibration curve remains constant in binary mixture solutions of Trp and cysteine or AA. By use of modified electrode, the voltammetric detection limit for Trp in DPV measurements was 1.0 × 10 −7 M. The reproducibility of the electrode response, based on 6 measurements during 1 month, was 2.2% for the slope of the calibration curve. High sensitivity and selectivity together with sub-micromolar detection limit of the electrode response make it very suitable for the determination of trace amounts of Trp in pharmaceutical and clinical preparations.

L-Glutamate biosensor for estimation of the taste of tomato specimens

An amperometric biosensor has been developed for measurement of Umami, or the taste based on the amount of L-glutamate, in tomato foods. The biosensor is based on an enzyme-mediator system in which L-glutamate oxidase is used for biochemical oxidation of L-glutamate and a tetrafulvalene-tetracyanoquinodimethane (TTF-TCNQ) paste, prepared from the mixture of TTF-TCNQ salt, graphite powder, and silicone oil, serves as the mediator. The limit of detection, calculated by use of a four-parameter logistic model, was 0.05 mmol L(-1), and the limit of quantification was 0.15 mmol L(-1). The correlation coefficient (R2) was 0.990 and the relative standard deviation was no more than 1% (n=5). The response time (tau (95)) was 20-50 s, depending on concentration. The repeatability of the sensor was better than 5% (n=10). The sensor developed was stable for more than ten days.

Preparation of Dispersion-Strengthened Coppers with Niobium Carbide and Niobium Boride by Mechanical Alloying

The present study examines nanocomposites prepared by mechanical alloying of copper with other transition elements, which will produce a dispersion of stable boride and carbides reinforcement particles within a nanostructured copper matrix, at room temperature. Copper, niobium, boron and graphite powder mixtures were mechanically alloyed for several hours in a planetary ball-mill, in argon atmosphere and using a stainless steel container. The powder mixtures were produced with nominal composition of 10-30 vol.% NbC and 7-10 vol.% NbB2, using powders of pure elemental Cu, Nb, synthetic graphite and crystalline boron. The microstructural changes during milling of these powder mixtures were studied using X-ray diffraction, optical microscopy, scanning electron microscopy and microhardness measurements.

Large-scale fabrication of metallic Zn nanowires by thermal evaporation

Metallic Zinc (Zn) nanowires in large quantity are synthesized by thermal evaporation and vapor transport methods at low substrate temperature (100–200 °C) in the furnace tube placed in a conventional furnace in flowing Ar gas. A mixture of ZnO and graphite powder (ratio 2:1 by weight) is heated at nearly 1000 °C in the tube. Zn nanowires and other Zn nanostructures are formed at the end of the furnace tube at low temperatures. Upon annealing the as-made Zn nanowires at 500 °C for 1 h, oxidation occurred to form ZnO nanowires. Transmission electron microscopy images confirm that the annealed material is good-quality crystalline ZnO nanowires. Cathodoluminescence and photoluminescence spectra also show the band edge ultra violet peak emission at 381 nm and a broad band centered at 495 nm, which are the characteristics of ZnO material.

Structural characterization of GaN single crystal layers grown by vapor transport from a gallium oxide (Ga2O3) powder source

The sublimation growth technique is highly attractive as a commercially viable GaN substrate technology on account of its simplicity and relatively high growth rates. Sublimation growth of GaN using GaN powder source, however, is hampered by formation of liquid Ga in the source. To overcome this limitation, an oxide transport process using a mixture of gallium oxide (Ga2O3) powder and graphite powder as precursors with nitrogen gas as carrier and ammonia as the source of nitrogen has been developed. GaN layers grown by this process were studied by optical microscopy, synchrotron white beam x-ray topography (SWBXT) and high resolution x-ray diffraction (HRXRD) to characterize their structural properties. Studies reveal that the GaN layers grown are single crystal but characterized by dislocation densities and impurities higher than those obtained using GaN powder source. Observed defect distribution is correlated with growth conditions to deduce optimal growth procedure.

Synthesis and luminescence properties of novel ZnO nanostructures: micro and nanospheres, polyhedral cages, tetra-pods, needles, tipped nanorods, nanowires and other “microphone–shaped” structures

ABSTRACTNovel ZnO nanostructures such as hollow nanospheres, nano-cages, nanoneedles, tetra-pods, nanowires, aligned nanorods and nanotubes are synthesized via thermal evaporation of ZnO and graphite powder mixtures in reduced oxygen atmosphere in the presence of argon and nitrogen flows. The ZnO nanostructures, especially nanospheres, have a unique shape and are hollow inside with walls densely decorated with aligned nanowires. Photoluminescence of synthesized ZnO structures measured at 300 K exhibits a strong near band edge peak at ∼380 nm and deep level green band centered at ∼550 nm. Fabricated ZnO structures can be studied for various applications in optoelectronics and sensors.

Catalytic and non-catalytic growth of amorphous silica nanowires and their photoluminescence properties

A simple method based on the thermal oxidation of Si wafers in presence of a mixture of MgO and graphite powder was developed for large-scale synthesis of very long amorphous silica nanowires. The synthesis was done with and without gold as the catalyst. Almost aligned uniform nanowires with diameters within 60–90 nm and length up to few hundred micrometers were obtained using gold as the catalyst while bicycle chain like nanowires were obtained in absence of the catalyst. The growth sequence of the nanowires was observed through scanning electron microscope. Both forms of the nanowires emitted blue lights at 414 nm (3 eV) under excitation at 250 nm.

Mechanochemical activation of aluminum: 1. Joint grinding of aluminum and graphite

Changes in the crystal structure and composition of aluminum and graphite powder mixtures in the course of their joint mechanical treatment in a vibration mill were monitored by the adsorption and X-ray diffraction techniques. It was shown that, at absorbed energy doses of 8–10 kJ/g, the grinding and mixing of aluminum with graphite is completed by the formation of an intermediate structure of Al/C composite, where aluminum showed an anomalously high reactivity. The interaction of aluminum with water was used to study its reactivity in the composite. The formation of the composite preceded the stage of chemical interaction between carbon and aluminum atoms.

Direct laser sintering of iron–graphite powder mixture

Abstract In the present work, the role of graphite addition on the laser sintering of iron powder was studied. Powder mixtures containing iron and 0.4, 0.8, 1.2, and 1.6 wt.% graphite were prepared by blending elemental powders. These powders were sintered layer-by-layer under nitrogen atmosphere using a continuous wave CO 2 laser beam. A laser power of 70–225 W, scan rate of 50–600 mm s −1 , scan line spacing of 0.1–0.3 mm, and layer thickness of 0.1 mm was used. It was found that the processing parameters play a key role on the densification of the iron–graphite powder mixtures. The addition of graphite enhances the densification of the iron powder and improves the surface quality of the laser sintered parts when optimized manufacturing conditions are applied. The graphite content has a significant influence on the internal pore structure of the sintered parts. They are gradually changed from interconnected networks to closed and spherical shaped pores with increasing graphite content. The metal matrix structure consists of different phases such as ferrite, austenite, and tempered martensite, which highlights the heterogeneous distribution of dissolved carbon in the iron matrix. This article presents the experimental details of the microstructural evolution in laser sintered iron–graphite powder mixtures. The role and key importance of graphite addition to iron powder in the laser sintering process is addressed.

Enhancement of the analytical properties and catalytic activity of a nickel hexacyanoferrate modified carbon ceramic electrode prepared by two-step sol–gel technique: application to amperometric detection of hydrazine and hydroxyl amine

The electroless sol–gel technique was used for the construction of nickel hexacyanoferrat (NiHCF) modified carbon composite electrodes (CCEs).This involves two steps: formation of a carbon ceramic electrode fabricated by nickel powder and then immersing the electrode into a sodium- hexacyanoferate solution for the immobilization of NiHCF films. The cyclic voltammety of the resulting modified CCEs prepared under optimum conditions, shows a well defined surface redox couple due to the [NiIIFeIII/II(CN)6]−2/−1 system. The effect of different alkali metal cations in supporting electrolyte on the behavior of the modified electrode were studied. The charge transfer coefficient (α) and charge transfer rate constant (ks) for modified films were calculated. Hydrazine and hydroxylamine have been chosen as a model to elucidate the electocatalytic ability and analytical parameters of NiHCF modified CCE prepared by one and two-step sol–gel techniques and these compounds determined amperometically at the surface of modified electrodes. The latter shows a good electocatalytic activity towards the oxidation of hydrazine and hydroxylamine in the pH range 3–8 in comparison with CCEs modified by homogeneous mixture of graphite powder, Ni(NO3)2 and Na2[Fe(CN)6], (one-step sol–gel technique). Furthermore, the catalytic rate constant, linear dynamic range, limit of detection, and sensitivity for hydrazine and hydroxylamine detections were evaluated and compared with CCEs prepared with one-step sol–gel method. The modified CCEs containing NiHCF shows good repeatability, short response time, t 90%<3s, long term stability (3 months) and excellent catalytic activity. Furthermore, the method of preparation is rapid and simple and the modified electrodes are renewed by simple mechanical polishing and immersing in [Na3Fe(CN]6] solution.

Preparation and electrocatalytic oxidation properties of a nickel pentacyanonitrosylferrate modified carbon composite electrode by two-step sol–gel technique: improvement of the catalytic activity

The sol–gel technique was used to construct nickel pentacyanonitrosylferrate (NiPCNF) modified composite ceramic carbon electrodes (CCEs). This involves two steps: forming a CCE containing Ni powder and then immersing the electrode into a sodium pentacyanonitrosyl-ferrate solution (electroless deposition). The cyclic voltammograms of the resulting surface modified CCE under optimum conditions show a well-defined redox couple due to the [Ni IIFe III/II(CN) 5NO] 0/−1 system. The electrochemical properties and stability of the modified electrode were investigated by cyclic voltammetry. The apparent electron transfer rate constant ( k s) and transfer coefficient ( α) were determined by cyclic voltammetry being about 1.1 s −1 and 0.55, respectively. Sulfite has been chosen as a model to elucidate the electrocatalytic ability of NiPCNF-modified CCE prepared by one- or two-step sol–gel technique. The modified electrode showed excellent electrocatalytic activity toward the SO 3 2− electro oxidation in pH range 3–9 in comparison with CCE modified by homogeneous mixture of graphite powder, Ni(NO 3) 2 and Na 2[Fe(CN) 5NO] (one-step sol–gel technique). Sulfite was determined amperometrically at the surface of this modified electrode in pH 7. Under the optimized conditions the calibration curve is linear in the concentration range 2 μM to 2.0 mM. The detection limit (signal-to-noise is 3) and sensitivity are 0.5 μM and 13.5 nA/μM. The modified carbon ceramic electrode containing nickel pentacyanonitrosylferrate shows good repeatability, short response time, t (90%) <2 s, long-term stability (3 months), and it is renewed by simple mechanical polishing and its immersing in Na 2[Fe(CN) 5NO] solution. The advantages of the SO 3 2− amperometrically detector based on the nickel pentacyanonitrosylferrate-doped CCE is high sensitivity, inherent stability at wide pH range, excellent catalytic activity and less expense and simplicity of preparation. This sensor can be used as amperometric detector in chromatographic instruments.

Effects of lubrication procedure on the consolidation, sintering and microstructural features of powder compacts

The role of lubrication procedure on the consolidation behavior of metallic powders and subsequent microstructural development during sintering was investigated. Iron powder and iron–0.8 w/o graphite powder mixture were used as model materials. The effects of die wall lubrication procedure were compared to the traditional admixed powder lubrication method. The influences of manufacturing parameters such as the compacting pressure in the range of 150–800 MPa and the sintering temperature from 400 to 1300 °C were studied. It was found that the lubrication procedure has a great influence on the consolidation and microstructural features of the materials investigated. Admixed lubricant aids the densification in the low-pressure region but limits the maximum density at high pressure. On the other hand, die wall lubrication offers the possibility of achieving the required density in single pressing for parts made by conventional double pressing and double sintering route or by warm compaction technique. The method also results in the formation of more metal/metal contacts during compacting, which leads to better green strength. Moreover, during sintering at moderate temperatures the area of metallic contacts is more and stronger compared to the powder lubricated specimens. Consequently, better mechanical properties are obtained. However, after sintering at a high temperature (>1000 °C) only less total porosity of the unlubricated compacts attributes to higher performance.

Large-quantity free-standing ZnO nanowires

Large-quantity (grams) one-dimensional ZnO nanowires of different sizes have been synthesized by a simple thermal evaporation of ZnO powder in a tube furnace at a temperature controlled to 1000–1200 °C and pressure to 1–2 Torr air. A mixture of ZnO and graphite powder was used as the source. Fine graphite flakes were used to promote the growth. The graphite flakes are the key for large-quantity yield and were easily removed by oxidation in flowing O2 at about 700 °C for 1–3 h. The scanning- and transmission-electron-microscopic studies show that the diameter and length of the nanowires vary from 20 to 100 nm and 0.5 to 10 μm, respectively. Room temperature photoluminescence studies found that the luminescent intensity depends on the processing conditions. A reduced band edge ultraviolet (380 nm) and deep-band green (520 nm) emission have been observed for these nanowires. Most importantly, the method can be extended to any other oxide nanowires that will be the building block of future nanoscale devices.