Development of heating elements based on conductive polymer composites for electrofusion welding of plastics

Conductive polymer composites have been developed based on high-density polyethylene filled with carbon black (HDPE-CB), capable of generating heat when an electric voltage is applied. For each voltage value, the composite reached a constant value of equilibrium temperature, which obeyed a quadratic dependence on voltage and a linear dependence on electric power. The possibility of using such composites as heating elements (HE) for electrofusion welding of polyethylene adherents was evaluated in two modes, ''hard'', when high voltage was applied for a short welding time, and ''soft'', in which a stepwise regime of the applied voltage and a longer welding time were used. The latter provided a stronger welded joint. Using HE based on the HDPE-CB composites for welding of butt and lap joints of the polymer materials enabled to obtain welded joints with high strength.     

Morphological characteristics of mechanically processed ZnO and MnO2 powder mixtures

The evolution of structural-morphological characteristics of ZnO + 1 wt.% MnO₂ and ZnO + 10 wt.% MnO₂ samples during prolonged mechanical treatment (MT) was investigated by X-ray, AFM, LPS, SEM and IR methods. Changes in crystallite size due to mechanical activation were determined from X-ray measurements. These results were correlated with changes in particle size followed by SEM and AFM. Particle and aggregate size distributions were determined from LPS measurements. Interpretation of the evolution of IR-absorption peaks during mechanical activation using the theory of average dielectric constants enabled analysis of changes of particle and agglomerate shapes. All these results enabled establishment of a relationship between crystallites, particles, aggregates of particles, and superficial processes that occur during mechanical activation.     

Surface functional groups of carbons and the effects of their chemical character, density and accessibility to ions on electrochemical performance

Wood origin activated carbon was oxidized and then treated with melamine and urea followed by carbonization at 950 °C in an inert atmosphere. The samples were characterized using elemental analysis, adsorption of nitrogen, Boehm titration, FTIR and XPS. Testing the carbons as the electrode materials in supercapacitors indicated that the electrochemical behavior of modified samples is governed mainly by the specific types of functional groups. Both surface chemistry and texture of carbons are affected by the nitrogen source and the type of oxygen functionalities preexisting on the surface. The modified carbons revealed significantly enhanced capacitances in 1 M H₂SO₄ reaching 300 F/g and the capacitance retention ratio is 86% at the current load of 1 A/g. Perfect correlations were found between the number of basic groups and the gravimetric capacitance and between the normalized capacitance in micropores and the distribution of quaternary and pyridinic-N-oxide nitrogen species on the surface of the micropores. The pseudocapacitance on N and O atoms is particularly dominant at higher current loads and the charge on quaternary nitrogen and pyridinic-N-oxide enhances the electron transport through the electrode improving the rate performance of treated samples. The micropores were found to be most effective in a double-layer formation.     

Modeling of laser cladding with diode laser robotized system

The choice of proper working conditions is a problem for any processing. But for laser processing this procedure is much more serious. The final results of the processing are usually influenced by over 100 factors. So the best way to choose more cheaply and fast the working conditions is to use the processing simulation. Different tactics of this procedure is discussed and the statistical modeling is accepted. The actual model for laser cladding is developed based on the experimental results of steel cladding with diode laser robotized system. This model can be used to find the optimal working conditions for laser processing in practical use.     

Intelligent index selection for case-based reasoning

In this paper, we present an indexing technique for case-based reasoning called D-HS^E, that is shown to be more competent than and twice as efficient as the commonly used R-tree. D-HS^E was designed to addresses periodical competency shortcomings of the related D-HS^M index but unfortunately in doing so some efficiency was seen to be sacrificed. In order to address this problem of competency verses efficiency, we propose an intelligent selection algorithm that automatically analyses the case-base and decides which index (D-HS^M or D-HS^E) should be used to optimize performance. The algorithm is designed to favour competency at the expense of efficiency where a competency gain is deemed highly likely to be achieved by using the less efficient approach. In effect we are proposing a flexible indexing scheme that is aware of changes within its environment and which reacts to these changes to optimize performance.     

Changes in graphite oxide texture and chemistry upon oxidation and reduction and their effect on adsorption of ammonia

Two graphite oxides were prepared by a subsequent two-step oxidation of commercial graphite. The samples were then reduced with hydrazine hydrate. Surface characterization before and after exposure to ammonia was carried out using X-ray diffraction, Fourier-transform infrared spectroscopy, potentiometric titration, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, thermal analysis and nitrogen adsorption. The results indicated significant differences in the texture and chemistry of the materials, which had effects on their ammonia adsorption capacity. Strong oxidation led to relatively amorphous samples with a developed porosity owing to the treatment. Acidity is governed by the presence of sulfonic and carboxylic groups. Even though these groups react with ammonia, the significant adsorption capacity is linked to the presence of surface epoxides, which can react with ammonia leading to the formation of amines. While treatment with hydrazine expanded the surface area of the mildly oxidized sample, in the case of strongly oxidized graphite only surface chemistry was affected and a significant amount of nitrogen was introduced to it. Creation of porosity after reduction did not enhance ammonia adsorption due to the absence of reactive oxygen (epoxides) sites.     

Evaluation of hydrogen stresses in metal and redistribution of hydrogen around crack-like defects

The problem of the mutual influence between diffusion processes and the stress field in metal–hydrogen systems is generally formulated. Thermodynamic analysis of the stress–strain state of an elastic body under conditions of changes in concentration of available hydrogen, is performed. This formed a basis for estimation of the relative expansion of hydrogenated metal. Forces in the metal, caused by hydrogen effect, have been found to have the gradient character. The key equations for evaluation of the interaction of stresses and hydrogen concentration are constructed accounting hydrogen-induced stresses. In the quasi-stationary case for low-variable stresses the system of such equations is reduced to one concentration equation. Its solution is can be constructed in a closed form. As a result, the variation of stresses, depending on the depth of hydrogen penetration from the surface, is calculated. The dependence of hydrogen concentration and distribution in a strip vs. time laps has been determined.     

Combined Effect of Nitrogen‐ and Oxygen‐Containing Functional Groups of Microporous Activated Carbon on its Electrochemical Performance in Supercapacitors

Microporous activated carbon originating from coconut shell, as received or oxidized with nitric acid, is treated with melamine and urea and heated to 950 °C in an inert atmosphere to modify the carbon surface with nitrogen‐ and oxygen‐containing groups for a systematic investigation of their combined effect on electrochemical performance in 1 M H₂SO₄ supercapacitors. The chemistry of the samples is characterized using elemental analysis, Boehm titration, potentiometric titration, and X‐ray photoelectron spectroscopy. Sorption of nitrogen and carbon dioxide is used to determine the textural properties. The results show that the surface chemistry is affected by the type of nitrogen precursor and the specific groups present on the surface before the treatment leading to the incorporation of nitrogen. Analysis of the electrochemical behavior of urea‐ and melamine‐treated samples reveal pseudocapacitance from both the oxygen and the nitrogen containing functional groups located in the pores larger than 10 Å. On the other hand, pores between 5 Å and 6 Å are most effective in a double‐layer formation, which correlates well with the size of hydrated ions. Although the quaternary and pyridinic‐N‐oxides nitrogen groups have enhancing effects on capacitance due to the positive charge, and thus an improved electron transfer at high current loads, the most important functional groups affecting energy storage performance are pyrrolic and pyridinic nitrogen along with quinone oxygen.     

The question of differences between iodine numbers of coconut oil and of the corresponding soapstock fatty acids

Summary Experiments have been made on coconut oil from pure endosperm, pure testa, and normal mixtures of the two. These experiments have shown that the spread in iodine value between refined coconut oil and the fatty acids found on the corresponding soapstock are greater than can be accounted for by the proportion of testa oil present in extracted whole crude oils. Furthermore the iodine value of the free fatty acid fraction of pure endosperm oils was found to be higher than that of the combined fatty acids in the same oils by an amount which varied inversely as the degree of hydrolysis which had occurred in the oil. From this it appears that preferential hydrolysis plays an important part in the production of coconut oil soapstock having higher iodine values than those of the corresponding refined oils. Attention is also called to some European publications which deal with this question and to the possibility that molds may be involved through their ability to decompose short chain acids to ketones.