Papers by Keyword: Thermal Treatment

Abstract: During procedure and heat treatment of magnesite in shaft and rotary furnaces, a great number of fine fractions are generated. In terms of MgO content, the fractions comprises the highest quality raw material. However, the desired degrees of calcination or sintering have not been achieved. For direct heat treatment of fine particles the microfluidic furnace has been proposed. The microfluidic furnace consists of the fluidization chambers in which the technology operations are being carried out. The furnace operates on the counter-current principle. The experiments of dust magnesite and flue gas calcination from rotary and shaft furnaces were carried out in the furnaces.

Abstract: Titanium dioxide (TiO₂) thin films were prepared by means of electrochemical anodisation or anodic spark deposition (ASD) from thin and flat metallic titanium (Ti) films pre-deposited on high quality quartz substrates by electron beam evaporation. AFM analysis indicates the formation of uniform mesoporous layers and a definite increase about 50% of the film thickness upon anodisation and about 90% upon annealing. Anodised mesoporous TiO₂ films have been characterized by Raman spectroscopy, which indicates the presence of well-defined peaks related to anatase structure. Phase transformation from anatase to rutile was observed after annealing at temperatures up to 900°C for 3h.

Abstract: Aluminum and zirconia oxides are ceramic materials widely used in the manufacturing of dental products, however, the thermal treatment stages demand high temperatures. Aiming at the reduction of the energy consumption and of the time necessary for the thermal treatments, this work intends to evaluate the influence of the microwave energy over the thermal processes of alumina substrate and of the alumina/zirconia system. The samples were made by slip-casting and then submitted to different thermal treatments. For the microwave oven, we used powers of 1.44 and 1.66 kW and heating times of 10, 15 and 20 minutes. The samples were submitted to the determination of physico-mechanical properties: flexural strength at three points, porosity and Vickers microhardness. Based on the analysis, we conclude that the microwaves energy is promising for the processing of dental ceramic, causing a significant reduction in the firing time.

Abstract: Phosphorus is a necessary nutrient element to all lives in the world. Distribution and phosphate rock reserves in the world disclose shortage crisis of phosphorus. Thus phosphorus recovery has been a research hot spot in the world. Mr.Ohtake’ group [1] recommended a new method to recover phosphorus from sewage sludge during heating process. It seems that nearly 90% of the poly-phosphate (poly-P) and 87% of total phosphate (T-P) can be released from cultivated sludge by heating at 70 °C for 1 hour. Meanwhile, released poly-P can precipitate with Ca in neutral condition without any pH adjustment. Sewage sludge was used in this research to identify its performance during thermal treatment. With the increase of temperature and heating time, release of poly-P and T-P increased obviously. However, poly-P would be hydrolyzed when temperature was higher than 80 °C. With addition of EDTA, release of poly-P increased nearly 100%. Migration of metal cations during thermal treatment can provide indirect evidence which kinds of metal cations would make impediment on poly-P release. A novel phenomenon was observed poly-P mixed with ortho-phosphate can precipitate with NH₄⁺ and Mg²⁺ as struvite at pH 8.5.

Abstract: In this study, CNTs samples were prepared by refluxing CNTs in nitric acid for 16 h at 110 °C and then followed by thermal treatment. The Co catalyst was synthesized by the strong electrostatic adsorption (SEA) method on the treated CNTs support. The Co/CNTs samples were then calcined at temperatures of 300, 350, 400, 450 °C. Samples were characterized by TEM and N₂ adsorption. The size of cobalt nanoparticles and the textural properties were influenced by the calcination temperature. The TEM results showed that cobalt nanoparticles were well dispersed on the treated CNTs support.

Abstract: RETRACTED PAPER: The fabrication of nanospinel zinc chromite (ZnCr₂O₄) crystals by the means of thermal treatment method from an aqueous solution containing metal nitrates, polyvinyl pyrrolidone (PVP), and deionized water was described in this study. The samples were calcined at various temperatures ranging from 773 to 973 K for the decomposition of the organic compounds and crystallization of the nanocrystals. PVP was used as capping agent to control the agglomeration of the particles. The characterization studies of the fabricated samples were carried out by X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), energy dispersed X-ray spectroscopy (EDX) and electron spin resonance spectroscopy (ESR). The corresponding peaks of Zn, Cr and O were observed in the EDX spectrum of the sample which confirms the formation of ZnCr₂O₄. The XRD patterns also confirmed the formation of the single faced nanocrystallines of spinel ZnCr₂O₄ with a face-centered cubic structure. The average particle size of the synthesized crystals was also determined from the XRD patterns using the Scherers formula which shows that the crystallite sizes increases with increase in calcination temperature and was in good agreement with the TEM images which shows cubical ZnCr₂O₄ nanocrystals with uniform morphology and particle size distributions. The ESR spectra confirmed the existence of unpaired electron in the fabricated samples and the increase in g-factor and decreases in resonant magnetic field (H_r) were observed as the calcination temperature increases.

Abstract: The paper presents the application of ultrasound measurements for the determination of structural alterations of concrete exposed to fire. Concrete is evaluated as an incombustible material, class A1, but the high exposure temperature, like in fire, may cause cracks and changes of internal structure. The ultrasound measurement is a nondestructive method. It is possible to measure ultrasound velocity before and after thermal loading. The ultrasound measurement could be used also at building side as to detect structural alterations after a fire or imperfection in concrete elements. Three different concrete mixtures were prepared and tested in this study. The basalt aggregate were used in the reference mixture and in a mixture with addition of polypropylene fibers (PP-fibers). The third concrete was made with light weight aggregates (LWA). The test slabs (dimension 10 × 30 × 1150 mm) were poured and cured in laboratory ambient (22°C and 40% RH) for 3 months. Then the slabs were exposed to fire, according to standard temperature-time curve ISO 834. The ultrasound velocity was determined on crossline screen of 10 points before and after heating of the concrete slabs. The results of ultrasound measurements indicate the changes of internal concrete structure. The cracks are formed by pressure of evaporating unbounded water and thermal extensibility of single components.

Abstract: In this work, we report polyurethane foam, sunflower husk and rice husk ash prepared via a thermal treatment process used as oil sorbents for oil spill cleanup. The oil sorbent was studied on the basis of microstructure and morphology using optical digital microscopy and scanning electron microscopy (SEM). The results of the SEM and optical microscopy studies strongly indicate that thermal treatment is a suitable method to improve structure of husk particles regarding porosity compared to virgin samples. The dependence of the sorption capacity of the sorbents on the amount of sorbent, sorption time and the thickness of the oil film, as well as the number of cycles of the sorbents were investigated.

Abstract: Bulk-heterojunction polymer solar cells (BHJ-PSCs) have attracted considerable attention because of their unique advantages of lightweight, low cost, mechanical flexibility and suitable for large-area fabrication ^[1–3]. In the last decades, much attention has been paid to the donor and acceptor system P3HT:PCBM, However, because of the relatively large bandgap of P3HT (∼1.9 eV) and the relatively small energy difference between the lowest unoccupied molecular orbital (LUMO) of PCBM and the highest occupied molecular orbital (HOMO) of P3HT, the photovoltaic performance of the PSCs based on P3HT:PCBM is still significantly lower than the inorganic solar cells. Recently more work has been done on the novel donor materials which have a reduced energy gap with an ability of harvesting more of the sun’s spectral emission and a high charge carriers mobility for charge transport. One of the most promising new donor polymer is poly [N-9"-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3' -benzothiadiazole)] (PCDTBT) with a HOMO level of 5.5eV which is 0.4 eV down-shifted than that of P3HT. When PCDTBT is blended with the fullerene acceptor PC₇₀BM, it showed excellent photovoltaic performance with a power conversion efficiency of ∼ 6%. ^[6]

Abstract: The Ni+W+Mo+Si composite coatings were prepared by electrodeposition under the galvanostatic conditions (j_dep = -100 mA cm^-2) from the nickel bath containing powders of tungsten, molybdenum and silicon. Thermal treatment of the obtained coatings was conducted in argon atmosphere. Chemical composition of the coatings was determined by energy dispersive spectrocopy (EDS). Phase composition investigations were conducted by X-ray diffraction (XRD) method. Studies of electrochemical corrosion resistance were carried out in 5 M KOH solution. On the basis of these investigations it was found that Ni+W+Mo+Si thermally treated coating is more corrosion resistant than Ni+W+Mo+Si as-deposited coating.