Abstract:Abstract. Cobalt-ferrite (CoFe 2 O 4 ) nanoparticles (CFNPs) are obtained using direct plasmachemical synthesis in the plasma of a low-pressure arc discharge. The formation of the CFNPs with an average size of 9 nm and a narrow granulometric composition is established employing the methods of X-ray structure analysis and transmission microscopy. The CFNP behavior upon high-temperature annealing is analyzed. The CFNP functional groups are determined using the infrared Fourier spectrum. The results of the X-ray … Show more
“…The enthalpy of TiO 2 formation is -944.74 kJ/mol; therefore, the synthesis with the aid of the low-pressure plasmachemical process is very efficient. The experimental setup and the dependence of the powder properties on the conditions of sputtering were considered in detail in [16,17]. The cathode made of VT1-00 titanium alloy with a diameter of 80 mm and a length of 100 mm was placed on a watercooled copper current distributor.…”
Abstract. The synthesis of titanium dioxide (TiO 2 ) nanoparticles with different percentage of anatase and rutile phases is investigated. The synthesis is performed by controlling the oxygen percentage in the gas mixture in the plasmachemical evaporation-condensation process employing a low-pressure arc discharge. In all our experiments, the pressure in the plasmachemical reactor and the average size of particles remain constant and are 60 Pa and 6 nm, respectively. The crystal structure of synthesized TiO 2 is studied using X-ray diffraction; the morphology of the particles is analyzed employing transmission electron microscopy. Using Xray phase analysis, it is established that the concentration of the TiO 2 anatase phase decreases upon a decrease in the oxygen concentration in the gas mixture. It is shown that the TiO 2 anatase phase is more efficient for photocatalytic decomposition of methylene blue than the rutile phase.
IntroductionTitanium dioxide (TiO 2 ) is one of the most studied materials; it has many applications in industry and research, especially in photocatalysis [1,2]. A comprehensive review of the surface properties of TiO 2 , in which the interrelation between the structure and properties is emphasized, is given in [3]. The photoactivity of TiO 2 is pointed out in [4] as one of the most interesting and attractive properties. Experimental and theoretical investigations of the structural and electronic properties of TiO2 are described in [5]. TiO 2 can exist in a few stable crystalline forms the most widespread of which are anatase, rutile, and brookite [6]. The energy properties of TiO 2 polymorphs (relative to the rutile phase) was studied in [7], where it was found that they are lower by 0.71 kJ/mol for the brookite and are higher by 2.61 kJ/mol for the anatase. The brookite phase is stable only at very low temperatures and, therefore, is almost of no practical importance. The rutile and anatase phases usually coexist as mixed phases; that is why some efforts are necessary for obtaining the required pure phase. In recent years, the anatase phase of TiO 2 has aroused great interest owing to the technological applications in paints, pigments, and photocatalysis. It was reported that anatase has a higher photocatalytic activity than rutile [8]. Thus, the synthesis of TiO 2 with a preset crystalline phase on a large scale is of great practical importance. Although the chemical methods make it possible to obtain TiO 2 in large amounts [9], their structure, however, is mainly amorphous. It is shown in [10] that the presence of amorphous structure in TiO 2 reduces its photacatalytic activity and, consequently, the synthesis of nanocrystalline TiO 2 is an urgent problem. The results of chemical synthesis show that the time and the temperature of calcination greatly affect the TiO 2 nanopowder [11]. Although the phase transformations of TiO 2 during annealing of chemically synthesized TiO 2 have been studied by many researchers [12], the data on the temperatures in the reactions are controversial. Th...
“…The enthalpy of TiO 2 formation is -944.74 kJ/mol; therefore, the synthesis with the aid of the low-pressure plasmachemical process is very efficient. The experimental setup and the dependence of the powder properties on the conditions of sputtering were considered in detail in [16,17]. The cathode made of VT1-00 titanium alloy with a diameter of 80 mm and a length of 100 mm was placed on a watercooled copper current distributor.…”
Abstract. The synthesis of titanium dioxide (TiO 2 ) nanoparticles with different percentage of anatase and rutile phases is investigated. The synthesis is performed by controlling the oxygen percentage in the gas mixture in the plasmachemical evaporation-condensation process employing a low-pressure arc discharge. In all our experiments, the pressure in the plasmachemical reactor and the average size of particles remain constant and are 60 Pa and 6 nm, respectively. The crystal structure of synthesized TiO 2 is studied using X-ray diffraction; the morphology of the particles is analyzed employing transmission electron microscopy. Using Xray phase analysis, it is established that the concentration of the TiO 2 anatase phase decreases upon a decrease in the oxygen concentration in the gas mixture. It is shown that the TiO 2 anatase phase is more efficient for photocatalytic decomposition of methylene blue than the rutile phase.
IntroductionTitanium dioxide (TiO 2 ) is one of the most studied materials; it has many applications in industry and research, especially in photocatalysis [1,2]. A comprehensive review of the surface properties of TiO 2 , in which the interrelation between the structure and properties is emphasized, is given in [3]. The photoactivity of TiO 2 is pointed out in [4] as one of the most interesting and attractive properties. Experimental and theoretical investigations of the structural and electronic properties of TiO2 are described in [5]. TiO 2 can exist in a few stable crystalline forms the most widespread of which are anatase, rutile, and brookite [6]. The energy properties of TiO 2 polymorphs (relative to the rutile phase) was studied in [7], where it was found that they are lower by 0.71 kJ/mol for the brookite and are higher by 2.61 kJ/mol for the anatase. The brookite phase is stable only at very low temperatures and, therefore, is almost of no practical importance. The rutile and anatase phases usually coexist as mixed phases; that is why some efforts are necessary for obtaining the required pure phase. In recent years, the anatase phase of TiO 2 has aroused great interest owing to the technological applications in paints, pigments, and photocatalysis. It was reported that anatase has a higher photocatalytic activity than rutile [8]. Thus, the synthesis of TiO 2 with a preset crystalline phase on a large scale is of great practical importance. Although the chemical methods make it possible to obtain TiO 2 in large amounts [9], their structure, however, is mainly amorphous. It is shown in [10] that the presence of amorphous structure in TiO 2 reduces its photacatalytic activity and, consequently, the synthesis of nanocrystalline TiO 2 is an urgent problem. The results of chemical synthesis show that the time and the temperature of calcination greatly affect the TiO 2 nanopowder [11]. Although the phase transformations of TiO 2 during annealing of chemically synthesized TiO 2 have been studied by many researchers [12], the data on the temperatures in the reactions are controversial. Th...
“…So far, a number of thermal plasma based processes have been developed. Among them, the vacuum arc plasma evaporation (VAPE) method is commonly used for deposition of thin films [12] and nanoparticles fabrication [13][14][15][16].…”
Properties of nanodispersed powder copper oxide, synthesized during arc sputtering of copper in a gas mixture of low pressure oxygen, were studied. It was shown that the particles possess nanometer size and narrow size distribution. The issue of reduction, recrystallization and sintering of nanodispersed powder were discussed.
“…The current interest in magnetic nanosystems [1,2] is caused not only by peculiarities of changes in the fundamental properties of nanoparticles corresponding to the decrease in size, but also by their potential applications in modern/advanced high-technology functional devices [3].…”
Peculiarities of low-temperature behavior of the magnetic properties of disordered spinel ferrites, prepared by means of dilution with P 2 O 5 amorphizing agent and by rapid quenching, were investigated. A sharp increase in the saturation magnetization σ S , of ferrite compositions (1-x)MeFe 2 O 4 •xP 2 O 5 (where Me is Ni, Fe, Mn, etc.), was observed at temperatures T < 80 K. It was established that the temperature dependences of σ S and χ-1 (where χ is the magnetic susceptibility) of the nickel ferrite composition (x = 0.6) have an extremum at T = 11 K. In this case, the effect of "memory" is observed for σ S (T), which represents the dependence of σ S (T = 4.2 K) on the magnitude of the magnetic field in which cooling was carried out. The asymptotic Curie temperature was determined by extrapolation of the linear part of the χ-1 (T) dependence, and found to be equal to-150 K. We present an analysis of the observed dependences from the point of view of a complex magnetic state, combining the features of the near antiferromagnetic and ferrimagnetic boundary-surface spin ordering.
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