Decrease in the Crystallite Diameter of Solid Crystalline Magnetite around the Curie Temperature by Microwave Magnetic Fields Irradiation

A decrease in the crystallite diameter of ferrites irradiated with microwaves has been considered as a non-thermal effect of so-called de-crystallization; however, its mechanism has not been elucidated. We hypothesized that a decrease in the crystallite diameter is caused by interaction between the ordered spins of ferrite and the magnetic field of microwaves. To verify this, we focused on magnetite with a Curie temperature of 585 °C. Temperature dependence around this temperature and time dependence of the crystallite diameter of the magnetite irradiated with microwaves at different temperatures and durations were investigated. From the X-ray diffraction data, the crystallite diameter of magnetite exhibited a minimum value at 500 °C, just below the Curie temperature of magnetite, where the energy loss of the interaction between magnetite’s spins and the microwaves takes the maximum value. The crystallite diameter exhibited a minimum value at 5 min irradiation time, during which the microwaves were excessively absorbed. Transmission electron microscopy observations showed that the microstructure of irradiated magnetite in this study was different from that reported previously, indicating that a decrease in the crystallite diameter is not caused by de-crystallization but its similar phenomenon. A decrease in coercivity and lowering temperature of Verwey transition were observed, evidencing decreased crystallite diameter. This study can thus contribute to the development of the theory of a non-thermal effect.

Photoabsorption effect in the thin films of the CdPbS solid solutions

In this work, we have attempted to detect the photoadsorption effect using various photoactivation sources of semiconductor layers of CdxPb1–xS solid solutions that are sensitive to the presence of nitrogen dioxide in air. For this purpose, CdxPb1–xS films (up to 600 nm thick) were synthesized from the citrate – ammonia reaction system by the chemical bath deposition (CBD) on glass and sitall substrates. Using XRD analysis, we determined the structure and composition of CdxPb1–xS solid solutions. It was found that all films crystallize in the cubic structure B1 of lead sulfide. Taking into account the content of the substituting component in the samples and comparing it with the equilibrium phase diagrams of the PbS-CdS system, we concluded that the obtained solid solutions are strongly supersaturated in nature. The cadmium content in the PbS lattice increases in films deposited on sitall and glass from 3.9 to 5.9 and from 4.3 to 5.4 at.% with an increase in the deposition time from 60 to 120 minutes, respectively. It must be noted that their crystallinity degree increases with increasing deposition time. The size of the particles forming the layers was determined by SEM microscopy. The predominant crystallite diameter is 250-300 nm. The sensory properties of films of CdxPb1–xS solid solutions with respect to the presence of nitrogen dioxide with a concentration of 100 mg/m3 in air were studied using preliminary photoactivation by various sources with a radiation wavelength from 420 to 1000 nm. For the first time, a positive photoadsorption effect was revealed for CBD produced films of CdxPb1–xS solid solutions. The preliminary photoactivation of the films with a blue lamp (760–1000 nm) for 9-13 minutes allows the film to increase the response to NO2 more than doubled. A high relaxation rate of CdxPb1–xS -based sensor elements after contact with nitrogen dioxide was shown to be 4–10 minutes, which allows to reuse it.

Effect of pH Value on Synthesis and Properties of Zinc Cobalt Ferrite Nano Powders Prepared via Co-Precipitation Method

The effect of pH value on the synthesis of zinc cobalt ferrite nano powder via co-precipitation method was investigated. Zinc cobalt ferrite (Co0.6Zn0.4Fe2O4) precipitated using a solution of nitrate raw materials under different pHs (pH=8, 10, 11, 12 and 14) and calcined at 750 °C for 2 hours. The obtained nano-powders were characterized by X-ray diffraction (XRD), Williamson-Hall relations and Extrapolate functions, field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) measurements. The amount of pH had a significant effect on the structural and magnetic properties of the synthesized powders. At pHs 8 and 10, a tensile strain and above that a compressive strain was created in the system. By changing the tensile strain to compression the crystallite diameter increased, so that the crystallite diameter increased from 19.3 nm at pH 8 to 47.8 nm for pH =11. The HC of the all samples was in the range of 140-150 Oe. The saturation magnetization, anisotropy and Bohr magneton constants were 100.38 emu/gr, 15357.70 erg/Oe and 4.27, respectively for the synthesized sample at pH=11, which were higher than the other samples. These changes are due to the effect that pH has on the parameters of the crystallite diameter, particle size and also on the cation distribution of the ions in tetrahedral/octahedral spaces.

Elucidation of the Degradation of Poly Aromatic Hydrocarbon (PAH) in Coals During Pyrolysis

In this paper, we explore the use of high resolution transmission electron microscopy (HRTEM) in the degradation of the poly aromatic hydrocarbon (PAH) in coals of different ranks subjected to chemical plus heat treatment. The crystallite diameter on peak (10) approximations, La (10), of 37.6 Å for the high rank coal char at 700 oC fell within the HRTEM’s range of minimum-maximum length boundary of 11 x 11 aromatic aromatic fringes (28 – 44 Å). The La (10), 30.5 Å for the low rank lignite chars fell nearly on the minimum-maximum length range of 7 x 7 aromatic fringes (17 – 28 Å).The HRTEM results showed that the high rank anthracite chars at 700 oC comprised a higher distribution of larger distribution of larger aromatic fringes (11 x 11 parallelogram catenations). The mechanism for the similarity between coal chars of different ranks was the greater transition occurring in the low rank coals (lignite and sub-bituminous) to match the more resistant medium and high rank coals (bituminous – anthracite). This emphasized that the transitions in the properties of the low rank coals were more thermally accelerated than those of the high rank coals. The total PAHs detected in the coals of different ranks during pyrolysis are dominated by two- and three- ring PAHs. The amount of PAHs increase and then decrease with increase in pyrolysis temperature.

Biotemplate Synthesis of Porous Ceria Fiber and Study on its Catalytic Performance

Hierarchical porous ceria with nanocrystalline was successfully synthesized using filter paper as biotemplate. Unique biomorphic microstructures were characterized by Field Emission Scanning Electron Microscope (FESEM), transmission electron microscopy (TEM) and nitrogen absorption-desorption technique. The obtained ceria material showed the repetitious biomimetic structure consisting of fibre with diameter of ca. 1-3 μm and nanopores which had 2-4 nm apertures. The small crystallite diameter (6-8 nm) and the high specific surface area (71.3 m2·g-1) of porous CeO2 were measured by wide-angle X-ray Diffraction (XRD), high resolution TEM (HRTEM) and the BET method. While the concentration of acid fuchsine was 20 mg/L, the porous sample had a higher decoloring rate in a shorter time than others. The decoloring rate can reach 100% after 200 min.

Hierarchical Porous TiO2 Fibre Synthesized by Cotton Template and its Photocatalytic Performance

Hierarchical porous TiO2 fibre was successfully synthesized using cotton as template. Microstructures of product were characterized by Field Emission Scanning Electron Microscope (FESEM), nitrogen absorption-desorption technique and transmission electron microscopy (TEM). Titanium oxide material was characterized by repetitious networks consisting of the fibres with diameter of ca. 3-8 μm. The results showed that the products were composed 2-5 nm piled pores stacked by polycrystalline TiO2 nanoparticles. The small crystallite diameter (6-10 nm) and the high specific surface area (83.7 m2·g-1) of sample was believed to be resulted from wide-angle X-ray Diffraction (XRD), high resolution TEM (HRTEM) and the BET method. While the concentration of methylthionine chloride solution was 20 mg/L, catalyst amount 0.1 g/L, the reaction had a higher decoloring rate following irradiation with a UV light source, the decoloring rate can reach over 100% after 250 min.

Selective Catalytic Reduction of Nitric Oxide with Fe-Mn-Ce Metal Oxide-Based Catalysts

Nanosized cerium-manganese ferrite particles were prepared by co-precipitation approach. The structural evolutions and morphological characteristics of the nanopowder were investigated using X-ray diffractometry, transmission electron microscopy and thermo-gravimetry. XRD results showed that particles with crystallite size in nanometer scale were formed. TEM studies showed the morphology of the prepared cerium-manganese ferrite with a crystallite diameter of 20 nm at the calcination temperature of 500°C for 4 h. The catalyst showed high activities for SCR of nitric oxide with ammonia.

Diffusion Length Measurements of Minority Carriers in Si-SiO2 Using the Photo-Grating Technique

We have studied the microstructure, the transport and the phototransport properties of the Si crystallites network in Si-SiO2 composites. We have found that in our co-sputtered samples the average crystallite diameter, d, decreases from 40 to 5 nm as the content of the silicon, x, decreases from 80 to 40 volume%, and that the percolation of the network sets is at x ≈ 40 vol%. A simultaneous study of the photoluminescence (PL) shows the, quantum confinement, expected red shift of its peak with increasing d. On the other hand the very strong observed decrease of the PL intensity with x is interpreted here as due to a deconfinement effect that is dominated by the increase in the cluster size of connected Si crystallites. The results suggest that a closed random packing of the Si crystallites will be the preferred network for high intensity electroluminescence.