Atomic force microscopy investigation of electrochemically produced carbon nanotubes

Carbon nanostructures have been synthesized in NaCl-MgCl₂ and in NaCl-CaCl₂ salt melts and the extracted material was investigated by tapping-mode atomic force microscopy (TM-AFM) and scanning electron microscopy. Some interesting new nanostructures were found and investigated as torus-shaped carbon structures with a ring diameter of 300-400 nm and 10-15 nm height. These tori are closely related to the wrapped SWNT rings described recently. They are probably formed during the electrolysis. A chain-like structure was also revealed.     

Amorphous alloys and differential scanning calorimetry (DSC)

Journal of Thermal Analysis and Calorimetry - A remarkable number of scientific papers are available in the literature about the bulk amorphous alloys and metallic glasses. Today, DSC is an...     

Nanotubes: number of Kekulé structures and aromaticity

Carbon nanotubes (CNTs) are composed of cylindrical graphite sheets consisting of sp(2) carbons. Due to their structure CNTs are considered to be aromatic systems. In this work the number of Kekulé structures (K) in "armchair" CNTs was estimated by using the transfer matrix technique. All Kekulé structures of the cyclic variants of naphthalene and benzo[c]phenanthrene have been generated and the basic patterns have been obtained. From this information the elements of the transfer matrix were derived. The results obtained indicate that K (and the resonance energy) is greater if tubulenes are extended in the vertical than in the horizontal direction. Tubulenes are therefore more stabile than cyclic strips. An illustration, obtained by using scanning probe microscope, has been attached to affirm the existence of thin CNTs.     

Interfacial criteria for stabilization of liquid foams by solid particles

The stability criteria of liquid foams, stabilized by solid particles have been derived, based on the interfacial separating pressure, acting between two neighboring bubbles (foam cells). Different structures of solid particles in the cell walls have been considered, all being able to stabilize liquid foams with an increasing probability, according to the following row: structure LP1 (loosely packed single layer of particles) → structure CP1 (closely packed single layer of particles) → structure LP2C (loosely packed double layer of clustered particles) → structure LP2+C (loosely packed ‘double+’ layer of clustered particles) → structure CP2 (closely packed double layer of particles) → structure CP2+ (closely packed ‘double+’ layer of particles). It has been shown that the contact angle should be higher than a certain value Θ_o, in order to ensure stability of bubble–particles agglomerates. On the other hand, different structures of particles can stabilize the foam, if the contact angle is below the certain value (90° for the CP1 and LP1 structures, 129° for the CP2, LP2C and LP2+C structures and 180° for the CP2+ structure). The optimum value of the contact angle, being able to stabilize the foam is a difficult function of different parameters, but has been found in the interval between 50 and 90°. It has been shown that the possibility to stabilize liquid foams is connected with the value of the dimensionless quantity PR_s/σ (P: the pressure, destabilizing the foam; R_s: the radius of the stabilizing particles; σ: the surface tension of the liquid). When PR_s/σ>40, foam stabilization is absolutely impossible. When PR_s/σ<40, foam stabilization becomes possible, but it has high probability only at PR_s/σ<4. From this condition the maximum size of the particles, being able to stabilize liquid foams can be found. Trial calculations showed that particles smaller than 3 and 30 μm in diameter are requested for stabilizing water based, and liquid aluminum based foams, respectively.     

Intercalation of Sodium and Lithium into Graphite as a First Stage in an Electrochemical Method for Producing Carbon Nanotubes

A cyclic voltammetry method is used to show that the process of reduction of sodium (and, possibly, lithium) out of melts of corresponding chlorides on the molybdenum, glassy-carbon, and graphite electrodes is complicated by the process of dissolution of the corresponding alkali metal in the melt. A notion called “reversibility of material balance” is introduced. The notion reflects the ratio of the amount of substance that undergoes oxidation in the anodic half-cycle of a voltammetric curve to the amount of substance that is deposited in the cathodic half-cycle of the curve. The adsorption of sodium and lithium on glassy carbon and graphite plays an important role in the process of reduction, leading to an increase in the reversibility of the process. This is pronounced especially strongly at potential scan rates below 1 V s^?1. The sodium intercalation into graphite leads to a decrease in the reversibility of the process of reduction, the more so at potential scan rates below 0.03 V s^?1. However, the intercalation of lithium (probably because of its small atomic radius) does not exert practically any influence on the reversibility of process at the above potential scan rates.     

Physical,Chemical, and Electrochemical Behavior of Boron Oxide in Cryolite-Alumina Melts

Preparation of aluminum alloys in an aluminum electrolyzer considerably reduces the cost price of the resulting ligatures. Introduction of new oxides into molten cryolite frequently disturbs the electrolyzer operation. The behavior of boron oxide in molten cryolite and the possibility of stabilizing the electrolyzer operation were studied.     

Interfacial Forces in Dispersion Science and Technology

Interfacial forces determine many phenomena in dispersion science and technology. Eight types of interfacial forces are classified in this article. A general equation for all of them is derived here, with particular equation for each of them (being valid for simplified geometries, such as spheres, cylinders, etc.). As a new element, an interfacial anti-stretching force is introduced in this article, being equivalent to the definition of the interfacial energy in terms of tension as understood by Young. The differences and similarities between the interfacial gradient force and the interfacial spreading force (the Marangoni force) are shown. The well-known case of the liquid bridge induced interfacial force is supplemented by its less known version of a gaseous bridge induced interfacial force.