Solid State Phenomena Vols. 121-123

Abstract: An angular velocity of flow sensor for liquids based on single-walled carbon nanotube thin films is presented. The carbon nanotubes in this study were fabricated on Si substrate by hot filament chemical vapor deposition (CVD). The experimental results showed that the flow-induced current on the surface of carbon nanotube thin films was closely depended upon the angular velocity, concentration, properties and temperature of the liquids. The current increased with increasing angular velocity, concentration and temperature of the liquids. In this study, the liquids such as water, NaCl solution and other electrolyte were flowing over the sensor. The results obtained were also discussed. The theoretical and experimental studies have shown that there was electronic friction and electron drag effect of carbon nanotubes in flowing liquids. This effect in carbon nanotubes can be used for a new flow sensor.

Abstract: A layer of Manganese dioxides (γ-MnO2) was absorbed upon carbon nanotubes (CNTs) surface by using a chemical deposit process. The morphologies of the MnO2/CNTs composite were characterized using transmission electron microscopy (TEM), energydispersive X-ray spectrometry (EDS), X-ray diffraction (XRD) and laser Raman spectroscopy (RS). It is found that absorbed layer belongs to the γ-MnO2 nanoparticles in size about 10 nm, and coated homogeneously around the CNTs. It is expected that this MnO2/CNTs composite will be widely applied to make supercapacitors.

Abstract: To avoid microcrack formation caused by the addition of heterogeneous sintering aids, nano hydroxyapatite powder was prepared by precipitation method and doped into commercial hydroxyapatite powders as homogeneous sintering aid. Gelcasting method was used to prepare these hydroxyapatite green bodies. Densification of the blended powder was performed by pressureless sintering in air atmosphere at the range 1100°C to 1400°C for 2h, with a step size of 50°C. The results showed that the nano particle can greatly improve the densification process of the green bodies, and at 1300°C, which is the highest sintering temperature for hydroxyapatite without decomposition in the air atmosphere, the relative sintering densities of the doped green bodies and the ones without doping were 93.99% and 83.13% respectively.

Abstract: In order to meet the requirements of various applications, considerable efforts have been focused on the new approaches for synthesizing carbon nanotubes. Recently, simple thermal chemical vapor deposition growth technique by pyrolyzing ethyl alcohol has been developed. However, this method needs metallic catalyst. Here, we demonstrate that it is possible to synthesize multi-walled carbon nanotubes without the aid of any catalyst. The as-synthesized products were analyzed by high-resolution transmission electron microscopy (HRTEM). The HRTEM images show that the products are straight multi-walled carbon nanotubes. The synthesis technique of carbon nanotubes is cost-effective because of the catalyst-free process.

Abstract: Herein mesoporous CeO2 with high thermal stability was synthesized via a new hydroxycarbonates based hydrothermal threatment approach in present of hexadecyltrimethylammonium bromide (CTAB). IR and XRD prove the coexistence of hydroxycarbonate cerium and CTAB in precursors. TEM micrographs show that non-ordered pore structure is formed in the product, and average particle size of 20 nm is obtained even after calcined at 1173 K. BET results exhibit that the pore structure is stable when the calcination temperature is below 923 K. However, While calcinated at 1173 K, the average particle size is 20 nm, the BET surface area and pore volume can remain as high as 31.07 m2/g and 0.21 cm3 g-1.

Abstract: A simple thermal chemical vapor deposition (STCVD) growth technique of multi-walled carbon nanotubes (MWCNTs) is present. Carbon nanotube film was synthesized on the Pt plate substrates by pyrolysis of ethyl alcohol as carbon source at lower reaction temperature at atmospheric pressure by using simple apparatus. The as-synthesized MWCNTs were characterized by both scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The electrical property of an individual MWCNT was evaluated by I-V measurement. The electrical resistance of single MWCNT is about 450 k/ in linear region under bias voltage between 2 to 4 V. It can undergo a large current of 6 2A at 4 V

Abstract: Colloidal silica particles, Bimodal size distribution, Nucleation Abstract. Colloidal silica particles with bimodal size distribution have been prepared by the hydrolysis of tetraethylorthosilicate in alcoholic solutions of water and ammonia as catalyst. Experimental conditions such as concentration of NaCl, amount of water and reaction temperature were investigated to reveal the formation mechanism of the colloidal silica particles. The nucleation process of colloidal silica particles with bimodal size distribution depends on the hydrolysis rate of TEOS and the ionic strength of reaction media. The hydrolysis reaction is the rate-limiting step during the nucleation process. Nucleation involving background ions generated by TEOS hydrolysis reaction and addition of electrolyte(NaCl) is another potentially important factor for nucleation process of electrically charged clusters. A critical value of ionic strength exists in the reaction to form bimodal size distribution particles.

Abstract: The CdS/PVP fibers have been successfully prepared by electrospinning. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis absorption spectra were used to characterize the structure. Results showed that the concentration of polymer solutions and the CdS amount in the solvent influenced the morphology and the diameter of the electrospun fibers. The electrospinning from CdS/PVP in ethanol produced a structure having a combination of fibers, ribbons, beads and an unexpected half hollow sphere (HHS) structure. When the weight ratio of CdS:PVP was kept at 1:1000, the morphologies of electrospun products changed from HHS, to beaded fibers and ribbons, to beaded fibers, and to bead-free fibers with the increasing of the PVP concentration.

Abstract: The effects of an organic solvent on the electrospinning of water-soluble polyacrylamide with ultrahigh molecular weight were investigated. An organic solvent, DMF, was introduced to the polyacrylamide aqueous solution and subsequently, transparent spinning solutions were obtained. The spinning solution was electrospun at the voltage of 10 kV and the electrospun products were examined by scanning electron microscopy (SEM). Results indicated that all the electrospinning products including colloidal particles, beaded fibers and smooth fibers were fabricated in the DMF/H2O bi-component solvent and the morphology of electrospun products changed from smooth fiber to beaded fiber with the increasing amount of DMF used.