Short Multi-walled Carbon Nanotubes Research Articles

Electrical breakdown of short multiwalled carbon nanotubes

Electrical breakdown of short (∼50nm) multiwalled carbon nanotubes (MWNTs) is studied utilizing mechanically controllable break junction technique with gold electrodes. Measurements of the conductance-bias characteristics near the breakdown point revealed two different types of breakdown behavior for the short MWNTs. In one type designated as type I, the conductance increases nearly linearly with the bias and, over the breakdown point, decreases stepwise. On the other hand, in the type-II breakdown, the conductance shows a transient and irreversible increase right before the breakdown and subsequently jumps to zero. We consider that the type-II breakdown in vacuum is contact related, whereas the type-I breakdown occurs through the usual MWNT heating.

The investigation of adsorptive performance on modified multi-walled carbon nanotubes by mechanical ball milling

Different lengths of short multi-walled carbon nanotubes (MWNTs) were prepared by mechanical ball milling over 12 h. TEM observation indicated that the extent of shortening and opening of MWNTs increased on prolonging the milling time. The short nanotubes with length of 100–200 nm were obtained after ball milling for 30 h. The adsorptive performance for aniline in aqueous solution indicated that the adsorptive capacity of short open-ended MWNTs increased obviously from 15 to 36% compared to the unmilled MWNTs. The measurements of pore size distribution proved that the inner pore diameter of 3 nm remains constant and the aggregated pore diameter decreased obviously after ball milling. The increasing and expanding of hystersis loop in N 2 adsorption–desorption isotherms confirmed that the capillarity plays an important role in adsorption on the milled short MWNTs.

Carbon nanotubes as elements to focus electron beams by Fresnel diffraction

Fresnel diffraction of electrons at curved edges can be used to focus electrons onto a spot when the concave side of the edge is transparent. It is shown that short multi-wall carbon nanotubes with diameters of the inner hollow core of a few nanometers act as electron focusers when they are aligned parallel to the beam in an electron microscope. The electron beam is focused onto the projected center of the tube, where an amplification of the electron intensity by several times can be attained.

Preparation of short carbon nanotubes by mechanical ball milling and their hydrogen adsorption behavior

Short multi-wall carbon nanotubes (MWNTs) with open tips were obtained by mechanical ball milling. The microstructure characteristics of MWNTs before and after ball milling were checked by transmission electron microscopy (TEM). The effect of ball milling on the hydrogen adsorption behavior of the MWNTs was studied. The hydrogen adsorption experiments were carried out at room temperature under a pressure of 8–9 MPa. The hydrogen adsorption capacity of carbon nanotubes milled for 10 h was 0.66 wt%, which was about six times that of MWNTs without milling. For the carbon nanotubes milled with MgO for 1 h, a hydrogen adsorption capacity of 0.69 wt% was obtained. The enhancement of hydrogen adsorption might result from the increase of defects and surface area of the MWNTs caused by ball milling.

Production of short carbon nanotubes with open tips by ball milling

Short multi-wall carbon nanotubes can be obtained by ball milling. The average length of the ball milled carbon nanotubes, synthesised by decomposition of acetylene on different types of supported metal catalysts, is ca. 0.8 μm. The cleavage was caused by the collision between one agate ball and the nanotube powder contained in an agate mortar.

Production of short multi-walled carbon nanotubes

Multi-walled carbon nanotubes made by catalytic-pyrolysis of ethylene have curved bodies and exhibit entangled masses. Their average length is on the scale of microns, which is not suitable for carbon nanotubes to be used as a nanometer-scale material. Boiling carbon nanotubes in concentrated nitric acid or grinding in a ball mill can break the nanotubes. The average length of the nanotubes will be reduced and they will be relatively straight. In addition, on boiled carbon nanotubes, we find –OH, >CO and –COOH functional groups. In this state, the nanotubes can be dispersed evenly in a matrix when used to make a composite, which can result in an enhancement of the composite's properties, especially the mechanical properties.