Papers by Keyword: Cluster

Abstract: The oscillations presence of the substance condensed state parameters and the n-alkanes combustion process was analyzed. It is shown that the smallest substance structural unit that describes such features is a dimer, a hexamer for methane, and a trimer for ethane. The cluster "equivalent length" based on the framework number atoms in the continuous chain and without taking into account cluster side parts was used as a modulating parameter. Attention was drawn to the dependences similarity for water solubility and the autoignition temperature of n-alkanes. It is proposed to take into account clustering involving water molecules for the water solubility, and oxygen molecules in the peroxide groups form that form similar clusters for combustion processes. It is accepted that the solubility limit is determined by the condition of all water molecules aggregation by the substance, and in combustible mixtures the substance aggregates all available oxygen in the air. Corresponding peroxide proportions allow the burning limits, detonation limits, stoichiometric concentration and cold flame limit to be described. An approximation formula has been developed that describes the general dependence of the n-alkanes and 2-methylalkanes autoignition temperature based on values of the cluster length and the monomer molecular weight.

Abstract: The processes model in a flame during the n-alkanes air mixture combustion initiation is proposed, taking into account the supramolecular structures formation possibility in the peroxide clusters form. This approach is justified by the n-alkanes melting temperatures correlation with their autoignition temperatures and anti-knock indexes. The condensation possibility is provided for such high molecular structures. Boiling temperatures values at flame front pressures characteristic were evaluated. To predict the peroxide clusters melting temperatures, a formula developed earlier for the hydrocarbons condensed state was used, which takes into account the length and molecular weight of modeled clusters. Expected peroxide clusters melting temperatures were predicted for conditions of dimeric and tetrameric structures. A linear dependence was used to recalculation the obtained values in boiling temperatures. It is shown that the calculated clusters phase transitions characteristic temperatures can be realized in the flame front preparatory zone. Based on the condensation theory, the flame front thickness and the minimum non-extinguishing sphere radius during ignition were estimated: the obtained data closely coincide with these parameters known values.

Abstract: The relationship between substance characteristic temperatures: autoignition, melting, flash, boiling is demonstrated and analyzed. Based on the oscillatory and step changes presence, a conclusion was made about the supramolecular structures presence and periodicity in the n-alkanes homologous series. A method for modeling equivalent lengths of peroxide supramolecular structures for predicting the explosion and fire hazard parameters of n-alkanes is proposed. An approximation dependence was developed for predicting autoignition temperatures t_ai of n-alkanes. It is shown that stoichiometric concentrations of the various supramolecular peroxide structures formation accord to different flammability and explosion limits. A correlation between t_ai and Anti-Knock Index (AKI) was established. An approximation dependence was developed for predicting n-alkanes AKI. The detonation propensity index К_D was introduced based on cluster supramolecular structures modeling and melting temperatures. It is shown that К_D indicator correlates with the n-alkanes AKI and with the explosives detonation velocity. The possibility of taking into account during calculations the supramolecular structures presence at the combustion stage confirms their existence.

Abstract: The article considers the possibility of controlling the macromolecular structure of ternary alloys in the form of compact coatings, which are obtained by electrochemical means. This method of obtaining metal clusters is more economical than from plasma one. The influence of the cluster structure of the synthesized coatings in the form of a triple alloy of polyligand complex electrolytes on their functional properties is shown. There are presented the results of testing coatings from this ternary alloy of different elemental and cluster composition for microhardness according to Vickers. The highest microhardness was obtained by the coating with the lowest molecular weight of the cluster, which provided a denser packing of atoms.

Abstract: The presence of melting temperatures oscillatory and stepwise changes for hydrocarbons four homologous series is demonstrated and analyzed. The oscillating dependence is manifesteds on the principle of «even-odd» molecules with different deviations from linearity. According to the working hypothesis, this is due to the presence of the matter smallest structural unit in the cluster form of with a certain coordination number. The oscillation of melting temperatures in hydrocarbons series is explained by the fact that clustering can occur both at the site of the final carbon in the molecule and at other carbons in the molecule chain, and this fact depends on the «even-odd» effect. Based on the known values of melting temperatures in homologous series, the clusters probable structure is assumed. It is shown that graphs for the calculated values of equivalent lengths of these clusters correlate with corresponding graphs for hydrocarbons melting temperatures. An approximation formula has been developed to predict melting temperatures of hydrocarbons based on the values of the equivalent length and the cluster molecular weight, which operates with an approximation coefficient of 0.997 and a mean deviation of 4.2 K.

Abstract: Anisotropy of a powder ferromagnetic product can be created by focusing separate particles in the direction of a certain crystallographic axis in a magnetic field. By fitting modes of electromagnetic field it is possible to regulate the intensity of clusters movement and powder particles, as well as to destroy clusters up to the separate particles. At the increase of constant magnetic field induction up to a certain value, typical for every material, the intensification of processes of secondary aggregation and formation of anisotropic layer structure takes place. A design model of magneto-vibrational state of finely divided powder suggested in the article enables to calculate the parameters of electromagnetic field, which provide optimal characteristics of a powder product. It has been shown that, at a certain ratio of parameters of electromagnetic field in a dispersive ferromagnetic medium, a chain system is formed. The chains are focused along magnetic-field lines and execute a vibration in a variable inhomogeneous magnetic field, according to the law of a string with fixed ends.

Abstract: In this paper we report on investigation of the viscoelastic and rheological properties of early synthesized and characterized nanosuspensions by acoustical method, allowing to obtain the characteristic curves of shear elastic moduli and to assess the degree of "hardening" and structuring of the suspension. The paper is rising the question of fundamental problem - the structuring the nanosuspension, that might shed a light on the possibility of "engineering" the structure of a liquid by controlling and regulating the degree and nature of intermolecular interaction.

Abstract: Within the framework of the cluster model of the structure of disordered condensed media, using the pair potential of Mie interaction with the effective depth of the potential well, the relation was obtained for calculating the heat of sublimation of small cluster systems containing up to 500 particles. It is shown that the heat of sublimation of small clusters, referred to the energy of pair interaction between particles, is a universal function of the number of particles in the cluster system, which can be mathematically represented as the square of the hyperbolic tangent. The proposed model makes it possible to estimate the potential energy of the global minimum of the cluster system.

Abstract: A self-assembled ZnO tail-like cluster (TC) had been successfully synthesized by a simple chemical vapor deposition method. Scanning electron microscopy observations show that ZnO TC is composed of bushy ZnO microwires with flower-shaped cross sections. Long and narrow furrows can be clearly observed on the surface of the ZnO TC. A possible growth model is proposed to discuss the formation mechanism. The analytical result indicates that the flower-shaped ZnO microwires are formed by the lateral coalescence of ZnO wires at high temperature. The room temperature PL spectrum shows a prominent UV emission band around 380 nm, and no green emission is found, implying that the unique flower-shaped ZnO microwires have high optical quality. This controlled growth of ZnO TC may have implication for potential applications in novel optoelectronic micro/nanodevices in the near future.

Abstract: Using molecular dynamics method to study the cascade collision for the case of PKA(Primary Knock-on Atom) atoms at different distance from the grain boundary(GB) of iron chromium alloy. It is found that the PKA atoms at the GB will produce a large size cluster (size from 11 to 409 ) consisting of interstitial and vacancies, and many small clusters (number from 5 to 50). The size and number of the cluster depend heavily on PKA energy, while depend weakly on temperature. The PKA atom at distance of 1nm from the GB, sometimes produces large size defect clusters both inside and outside the GB region. When the PKA atom is at 1nm, 2nm and even 3nm, 4nm from the GB, the GB will effectively absorb the interstitial atoms. It is found that the atomic ratio of Cr-interstitial to total interstitial produced at the GB region is much less than one at outside of GB region.