Transport properties of carbon nanotube–metal nanocomposites

The performed investigations permit to reveal the effect of giant magnetic resistance in the specimens of the compacted nanocarbon materials containing multi-walled carbon nanotubes modified with the transition metals (Fe and Co).     

Flow injection determination of metoclopramide based on KMnO4—HCHO chemiluminescence in a micellar medium

A novel flow injection chemiluminescence (CL) analysis method for the determination of metoclopramide in the presence of sodium dodecyl sulfonate (SDS) surfactant micelles is described. This method is based on the luminescent properties of the KMnO₄-HCHO-metoclopramide in acid medium sensitized by SDS. The optimized experimental conditions were evaluated and the possible mechanism was discussed. The CL increase is linearly related to the concentration of metoclopramide in the range 0-80.0 μg/ml with a detection limit of 31.3 ng/mL (S/N=3).The relative standard deviation for 20.0 μg/ml samples was 2.6% (n=11). The proposed method has been successfully applied to the determination of metoclopramide in tablets.     

夹管电磁阀定量-流动注射分光光度法测定海水中总溶解氮

采用三个夹管电磁阀联用代替传统六通阀的样品定量方法,自制一套多通道流动注射分光光度分析仪,并优化仪器的最佳测试条件,实现了海水中总溶解氮含量的测定。本分析系统结构简单,操作方便,测定频率为27个.h-1。测试结果表明,总溶解氮的线性范围分别为50.0～1 000.0μgN.L-3(r≥0.999),检出限为7.6μgN.L-3。加标回收率为87.3～107.2%,RSD为1.35～6.32%(n=6)。经t检验分析,本方法与国标方法测定数据不存在显著性差异,可适用于海水中总溶解氮快速测定分析。     

A new configuration of the Moxon–Rae detector based on Si detector

A new Moxon–Rae detector configuration based on Si semiconductor detector was proposed in this paper. Three γ-ray sources, ¹³⁷Cs, ⁶⁰Co, and ²⁴Na, were employed to make actual measurements using the new Moxon–Rae detector. The measured pulse height spectra and detection efficiencies were compared with the EGS4 simulated values. The results revealed that the proposed new configuration is indeed a successful method and specially a useful technique for higher energy γ-ray measurement.     

Temperature and carbon source effects on methane–air flame synthesis of CNTs

We have conducted experimental and numerical studies on flame synthesis of carbon nanotubes (CNTs) to investigate the effects of three key parameters – selective catalyst, temperature and available carbon sources – on CNT growth. Two different substrates were used to synthesize CNTs: Ni-alloy wire substrates to obtain curved and entangled CNTs and Si-substrates with porous anodic aluminum oxide (AAO) nanotemplates to grow well-aligned, self-assembled and size-controllable CNTs, each using two different types of laminar flames, co-flow and counter-flow methane–air diffusion flames. An appropriate temperature range in the synthesis region is essential for CNTs to grow on the substrates. Possible carbon sources for CNT growth were found to be the major species CO and those intermediate species C₂H₂, C₂H₄, C₂H₆, and methyl radical CH₃. The major species H₂, CO₂ and H₂O in the synthesis region are expected to activate the catalyst and help to promote catalyst reaction.     

Effects of Ni catalyst–substrate interaction on carbon nanotubes growth by CVD

An investigation of the effects of substrate type and various treatments on carbon nanotubes (CNT) growth, using an evaporated Ni thin film as a catalyst, is presented. Barrier layers of SiO₂, Si₃N₄, and TiN on Si were used as substrates. The catalyst-insulating substrate systems have been processed in several gaseous atmospheres (Ar, NH₃ and H₂) and in the temperature range 700–900 °C, in order to obtain the most appropriate morphology, size and density of catalyst particles as seeds for the subsequent CNT growth. On this kind of substrates, the smallest nanoparticles were obtained on SiO₂ layers, in H₂ or NH₃ atmosphere even at 700 °C. However, the best vertically aligned and well-graphitized CNT resulted from the NH₃ annealing process, followed by the CNT deposition at 900 °C in C₂H₂ and H₂.On TiN conducting substrates, the best vertically aligned CNT were deposited using a shorter annealing step and a deposition process at reduced pressure. The samples were characterized by means of scanning electron microscopy (SEM) and Raman spectroscopy analysis.     

Synthesis of carbon nanotubes on Ni-alloy and Si-substrates using counterflow methane–air diffusion flames

We have conducted an experimental study to investigate the synthesis of multi-walled carbon nanotubes (CNTs) in counterflow methane–air diffusion flames, with emphasis on effects of catalyst, temperature, and the air-side strain rate of the flow on CNTs growth. The counterflow flame was formed by fuel (CH₄ or CH₄ + N₂) and air streams impinging on each other. Two types of substrates were used to deposit CNTs. Ni-alloy (60% Ni + 26% Cr + 14% Fe) wire substrates synthesized curved and entangled CNTs, which have both straight and bamboo-like structures; Si-substrates with porous anodic aluminum oxide (AAO) nanotemplates synthesized well-aligned, self-assembled CNTs. These CNTs grown inside nanopores had a uniform geometry with controllable length and diameter. The axial temperature profiles of the flow were measured by a 125 μm diameter Pt/10% Rh–Pt thermocouple with a 0.3 mm bead junction. It was found that temperature could affect not only the success of CNTs synthesis, but also the morphology of synthesized CNTs. It was also found, against previous general belief, that there was a common temperature region (1023–1073 K) in chemical vapor deposition (CVD) and counterflow diffusion flames where CNTs could be produced. CNTs synthesized in counterflow flames were significantly affected by air-side strain rate not through the residence time, but through carbon sources available for CNTs growth. Off-symmetric counterflow flames could synthesize high-quality CNTs because with this configuration carbon sources at the fuel side could easily diffuse across the stagnation surface to support CNTs growth. These results show the feasibility of using counterflow flames to synthesize CNTs for particular applications such as fabricating nanoscale electronic devices.     

Effect of carbon black on properties of 0–3 piezoelectric ceramic/cement composites

0–3 cement-based piezoelectric composites were fabricated using sulphoaluminate cement and piezoelectric ceramic [0.08Pb(Li_1/4Nb_3/4)O₃ · 0.47PbTiO₃ · 0.45PbZrO₃] [P(LN)ZT] as raw materials by compressing technique. The influences of carbon black content on the piezoelectric and dielectric properties, electric conductivity and impedance were investigated. The results indicate that the piezoelectric strain constant d₃₃ and piezoelectric voltage constant g₃₃ of the composites increase gradually with a suitable carbon black addition. When the carbon black content is 0.3 wt%, both of the piezoelectric strain constant d₃₃ and piezoelectric voltage constant g₃₃ of the composite exist the maximum value, which are 17.45 pC N⁻¹ and 36.3 mV m N⁻¹, respectively. As the carbon black content increases, the dielectric constant ε_r, dielectric loss tanδ and electric conductivity σ of the composites all increase, while the impedance decreases. In the frequency range tested, the more the carbon black content, the higher the ε_r value. The planar electromechanical coupling coefficient K_p, the thickness electromechanical coupling coefficient K_t and the mechanical quality factor Q_m are almost unaffected by the carbon black content.