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– The current study aims to prepare an Nb,Ta-containing ordered mesoporous catalyst MCM-41, using hydrated mixed oxide of niobium and tantalum, extracted from the columbite ore processing, as an alternative source of these metals. Direct hydrothermal synthesis was employed to incorporate the metals into the molecular sieve structure using the TEOS + sodium silicate mixture as silica source and varying Nb and Ta content in terms of Si/Me (Me = Nb and Ta) molar ratios of 60, 30 and 15 to evaluate the influence of the charge of these metals on both structural formation and properties of the material. The material was characterized by XRD, SEM, TEM, N2 adsorption, UV–Vis-DRS, and FTIR investigations to the incorporation of the metal into the MCM-41 framework. The techniques employed proved the successful replacement of Si atoms by metallic cations of Nb and Ta. The catalyst showed good structural order preservation and surface area (>600 m2 g-1) with mesoporous behavior with capillary condensation even at a higher metal load. This research signifies a successful procedure of a novel bimetallic mesoporous material with promising properties for several applications using an abundant ore as a metal source.

WC-Ni nanoparticles were synthesized using the gas-solid reaction method in a fixed-bed reactor. The studied parameters were the influence of the synthesis temperatures (800 °C, 850 °C and 900 °C), the reaction time (90 min, 120 min, and 150 min) and the nickel concentration (5 wt%Ni, 10 wt%Ni and 15 wt%Ni) on the average crystallite size by means of a 2³ factorial experimental design based on the results obtained by XRD. These powders had their chemical and morphological characteristics evaluated using XRD, BET, SEM and EDS analyzes. The XRD analysis results show that the method was effective in obtaining WC-Ni nanostructured composite powders with good particle dispersion, desired purity, mean crystallite size ranging from 24.2 nm to 38 nm, and surface area ranging from 24.6 m2/g to 46.7 m2/g. The statistical analysis showed that the synthesis temperature variable had the greatest influence on the increase in crystallite size. Furthermore, the combination of temperature and isotherm also has a relevant effect on the response variable (crystallite size).

2030 This paper presents new results for the recycling of electronic waste, specifically those from printed circuit boards (PCBs) of obsolete computers of the Federal University of Rio Grande do Norte. The main objective of this study is the comprehension of the extraction process of tin and cop per from PCBs by a hydrometallurgical route followed by electrodeposition using copper electrodes. PCBs powder were leached using 1N HNO3 and 3N HCl (aqua regia) aqueous solutions. The process permitted the extraction of all tin present on the PCBs. The electrodeposition processes were performed with currents from 0.5 to 1.5 A, at a constant time of 60 min, with and without mechanical stirring, and with different concentrations of leachate. The results showed that diluting the leachate favors the extraction of tin from the solution. At certain conditions we were able to extract approximately 100% of the tin, copper and lead present in the leachate

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International audience

International audience; The catalytic efficiency as well as the electrical conduction mechanism of Ce2(WO4)3 powders synthetized for the oxidation of methane were investigated. Total and partial oxidation reactions were observed in the temperature range between 600 and 750 °C under CH4/dry air flux, for low CH4 concentrations. The electrical conduction mechanism is based on electron tunneling at low temperature (< 650 °C) and hopping over an ion barrier at high temperature, which favors the catalytic oxidation of CH4 in air; these mechanisms occur during the partial and total oxidation under weak gas flow. The occurrence of these types of conduction mechanism was related both to the distorted monoclinic structure of Ce2(WO4)3 and to the larger structural cavities, as evidenced respectively by X-ray diffraction analyses (Rietveld analyses) and high-resolution transmission electron microscopy. The oxidation state of cerium is 3 + in the compound, as revealed by XPS investigations.

BaCeO3 has attracted great interest in research worldwide, whether doped with other elements on the site A and / or B of perovskite ABO3 or not, thus enabling its use in different applications. However, the properties exhibited by perovskite depend on partial or total replacement at the site, as well as the applied synthesis method. In this work we studied crystal structure, crystallographic parameters, morphology and textural properties of BaPrO3 perovskite synthesized by EDTA-Citrate complexation process. The adopted methodology makes it possible to obtain powders with orthorhombic crystal structure ( a=6.07 Å; b=6.3 Å e c=8.7 Å) and crystallite size of approximately 100 nm. That perovskite has dense and irregular agglomerates with surface area and pore volume of about 2.37 m2 g-1 and 0.7x10-8m3g-1, respectively. Finally, the methodology has demonstrated effectiveness in achieving crystalline phase with similar characteristics and properties obtained by different methods.

BaCeO3-based ceramics are ionic and electronic conductors that can be applied to oxygen sensors, solid oxide fuel cells and oxygen permeable membranes. However, the low chemical stability at high temperatures of these materials motivates studies involving doping of A and/or B sites of the perovskite structure. In this context, the present work aimed to synthesize a new BaCe0.8Pr0.05Cu0.15O3-δ material using the chemical route of complexation which combines EDTA-Citrate with pH variation. The powders obtained at pH 3 or 11 and calcined up to 900 ºC are thermally unstable. The cubic perovskite BaCe0.8Pr0.05Cu0.15O3-δ with crystallite size between 99.4 nm and 131.6 nm was obtained along with barium carbonate traces. In the powders calcined at 1000 ºC the pH increase decreases the amount of barium carbonate (17.3% to pH 3, 3.4% to pH 7 and 1.8% to pH 11), but increases the size of grains with irregular shapes.

Cerium molybdate semiconductive nanoparticles were synthesized by the EDTA-citrate combined complexation method. Gel thermal degradation behavior, phase formation, morphology, composition and band gap of cerium molybdate powders were characterized by TG/DSC, XRD, SEM/EDS and DRS analysis, respectively. The nanoparticles were synthesized by fixing the pH of the reaction medium to 9, producing an organometallic gel which was heated to 230 ºC obtaining a precursor powder. The precursors were calcined in a temperature range of 450 - 800 ºC for 3 h. The cerium molybdate powders were characterized and the phase evolution, morphology and band gap changes with the increase of calcining temperature were investigated. It was observed that the calcining temperature directly influences the formation of the crystalline structure, appearance of other phases in the materials and the particle size.

The carbides of refractory metals like tungsten carbide (WC), tantalum carbide (TaC) and niobium carbide (NbC), has been extensively studied due to their applications in several areas of industry, because of their specific properties; such as high melting point, high hardness, wear resistance, oxidation resistance and good electrical conductivity. The tungsten carbide, particularly, is generally used at hardmetal industries due to its high hardness and wear resistance. New synthesis techniques have been developed to reduce the synthesis temperature of refractory metal carbides using more reactive precursors and gas-solid reactions for carbon reduction. The result is producing pure carbides suitable properties for production of high quality cemented carbides and more selective catalysts. In this work, pure and nanostructured WC was obtained from the ammonium paratungstate hydrate (APT), at low temperature and short reaction time. Hydrogen (H2) and methane (CH4) were used as a reducing gas and carbon source, respectively. The precursor and obtained product were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results obtained by diffraction of X-rays showed that complete reduction and carburization of APT have been took place resulted in pure WC formation. The average crystallite size was in nanometer order reaching values of approximately 20.8 nm and a surface area (BET) of 26.9 m2/g.

Nanoparticles of cobalt ferrite (CoFe 2 O 4 ) were synthesized by the EDTA/Citrate complexing method and hydrothermal method without addition of surfactant. The influence of the pH of the reaction medium (8, 9 or 10), the temperature of the thermal treatment (600 °C, 800 °C or 1000 °C for the EDTA/Citrate method, and 120 °C, 140 °C or 160 °C for the hydrothermal method), and the duration of the thermal treatment (2, 4 or 6 h for the EDTA/Citrate complexing method, and 6, 15 or 24 h for the hydrothermal method) on the average crystallite size was studied by means of an experimental design based on the results obtained by XRD. Statistical analysis led to quantification of the influence of the synthesis parameters on the crystallite size of the powders. Results showed that the pH of the reaction medium is the parameter that shows the greatest influence on the growth of the crystallites of the powders obtained by the hydrothermal method, while calcination temperature is the most significant one for the powders produced by the EDTA/Citrate complexing method.

In this paper, the study of an acid and thermal treatment in a mixture of niobium and tantalum oxides obtained from columbite mineral was performed. Initially, the mineral was physically prepared by milling and sifting, followed by characterization by X-ray diffraction (XRD), X-ray fluorescence (XRF) and Scanning Electron Microscope (SEM). Subsequently, the mineral performed an acid leaching in order to remove iron and manganese present in its composition. A second acid leaching was necessary to eliminate the persistent cassiterite impurity by precipitation of Nb and Ta hydrated oxides. These oxides were characterized by XRF, XRD and SEM. Then the oxides were calcined at 800 °C, 900 °C and 1000 °C at different heating rates and calcination times to study their crystallization. The mixed oxides were characterized by XRF, XRD, SEM and nitrogen adsorption (BET method). The influence of heating rate was verified at 800 °C. An increase in crystal size was observed when the rate was reduced from 10 °C.min−1 to 5 °C.min−1. Greater crystallinity and formation of peaks related to the change of phase from hexagonal to orthorhombic were observed when the temperature was raised from 800 °C to 900 °C. At the temperature of 1000 °C, intermediate and low peaks related to formation of monoclinic phase of niobium pentoxide were observed. The change in calcination time from 5 h to 10 h at 1000 °C caused reduction in Nb2O5 to NbO2 and a decrease in crystal size and hence an increase in the surface area. The oxides heated at 900 °C showed the largest surface area.

The present paper's objective was to synthesize and characterize both the oxalic niobium precursor (NH4)3NbO(C2O4)3.H2O, and the product of its doping with Cu and calcining, CuNb2O6. In order to obtain the niobium precursor, commercially available niobium oxide (Nb2O5) was subject to fusion with potassium bisulfate (KHSO4). Once leached with water, the powder was complexed with oxalic acid and ammonium oxalate. The as produced material was manually mixed with copper nitrate Cu(NO3)2.2H2O (25% Cu molar) and calcined at 1000°C in a muffle furnace. CuNb2O6 was then obtained. The precursor was characterized by XRD, SEM, FT-IR, XRF, TG/DTG. The calcination product was characterized by XRD, XRF and SEM. Results show that single phase CuNb2O6 could be obtained by this method without Nb2O5 contamination.

This work reports the production of WC-10 wt%Ni nanostructured powders synthesized via carboreduction of a mixture of APT and low-temperature nickel nitrate with a short reaction time in a single synthesis process. The powders were characterized by XRD, TG/DSC, SEM, EDS, TEM and particle size analysis. The WC-10 wt%Ni powders were consolidated by the Spark Plasma Sintering process at different temperatures (1350 °C and 1450 °C). The effect of the sintering temperature on the mechanical properties and microstructure of the sintered composites was investigated through Vickers hardness and density measurements, as well as by SEM and EDS analyzes. The produced powders presented an average crystallite size of 24 nm for the WC and 41 nm for Ni. The samples sintered at 1350 °C showed the best results in terms of morphology and mechanical properties of Vickers hardness (2120 HV) and density (97.67%) when compared to samples sintered at 1450 °C which showed Vickers hardness of 945 HV and a density of 94.60%. The preparation of nanocomposite powders by carboreduction is a highly promising strategy for manufacturing hard metals by SPS, ensuring homogeneity of the phases and refined grain sizes, as well as providing good densification and excellent WC-Ni hardness.

2030 This paper proposes the synthesis characterization and factorial design for the development and composition of carbon quantum dots (CQDs). These are promising nanomaterials obtained from two renewable precursors which are biomass-derived materials namely chitin (CH), chitosan (CS), and graphite (G) as a third material used. These raw materials are low cost, non-toxic, and eco-friendly. The combination of these nanoparticles at quantum composition dots has shown promising properties of high thermal conductivity and high solar absorption. The determination of composition of (CQDs)n using 32 full factorial design with two factors at (CH/CS) ratio and mass (G) was first realized. The response surface methodology (RSM) was used to investigate the effect of band gap energy (Eband gap) engineering for semiconductor CQDs obtained via hydrothermal carbonization synthesis at 200 °C for 6 h and characterization of the composition (CQDs)9 to present Eband gap value of 3.16 eV and present the data with quantum yield of 17.1% thus promising for solar energy conversion application

With the increase in the national and world energy demand, we have sought the development of new processes of energy production that have a positive cost-benefit ratio with low environment risk, and that is ease for transportating and using. In recent years transitional metal carbides have received special attention in the area of heterogeneous catalysis, due to their physical and chemical properties. The molybdenum carbide (Mo2C) is an excellent low cost catalytic material. Doping it with nickel is thought to yield satisfactory catalytic activity. Thus, this work aims to develop the study of the synthesis, characterization and sintering of semiconductor materials with carbide type structure, using the gas-solid reaction method in a fixed bed reactor. The composition of the materials studied was Ni-doped Mo2C in the percentage of 5 and 10% of this dopant. This material had its chemical and morphological characteristics evaluated using the XRD, TGA, BET, dilatometry, SEM and EDS analyzes. When analyzing the results of the characterization by XRD, it was possible to identify the characteristic phases of carbides and nickel metal, in the surface area analysis for the different percentages of dopant, we can say that as the dopant content increased, an increase occurred in its surface areas. When plotting the isotherms of adsorption x dessortion and comparing with the models suggested by IUPAC, it was possible to identify that they are isotherms similar to the type II model, which characterize non-porous materials.

The catalytic efficiency of ternary strontium cerium tungstate Sr0.5Ce0.35WO4, for the production of syngas through methane oxidation, was investigated and compared to those of binary strontium tungstate SrWO4. Total and partial oxidation reactions were observed for both samples in the temperature range 600–750 °C under CH4/dry air flux. At high CH4 concentration and low temperature with the ternary tungstate as catalyst, the partial oxidation, leading to CO/H2, prevails. This indicates the potentiality of the new strontium cerium tungstate scheelite compound for the catalysis of CH4. Sr0.5Ce0.35WO4 and SrWO4 exhibit different conduction mechanisms. Conduction in the binary compound is related to the overlapping large polaron tunneling model, whereas conduction in the ternary one is due to a correlated barrier hopping phenomenon. The activation energies, in the low temperature range where the partial oxidation occurs, are significantly lower for the ternary compound than for the binary one. These electrical tendencies favor both partial and total oxidation of methane. The correlated barrier hopping conduction in the ternary compound leads to a better partial oxidation rate than conduction through large polaron tunneling.

The use of niobium containing materials' has gained much attention of the scientific community in the late years due its various applications in diverse fields. NbC is a highly versatile material. Copper addition may alter several of its properties, such as morphology, crystal structure etc. as well as enhance its catalytic behavior. Nanostructured NbC with copper addition synthesis' presented here had the precursor [(NH4)3[NbO(C2O4)3]xH2O] as starting material, which was doped with Cu(NO3)2 at 5% and 10% (molar) ratios. Doped NbC was obtained via gas solid reaction in fixed bed reactor at lower temperature (980°C) and with shorter reaction time (2h) than traditional methods. Reaction products' were characterized by XRD, crystal sizes were estimated according to HWL method, and SEM, XRF, BET and laser particle size analysis were performed. XRD indicated the formation of NbC and Cu phases with cubic crystal structure of ~20nm. SEM showed slight morphological change upon increasing copper content, indicating a less porous structure, which is consistent with BET data (43.7m2/g for 5%Cu-NbC and 37m 2/g for the 10% Cu-NbC). Crystal size calculations showed that increasing dopant content particle sizes were also increased, probably due to the presence of the dopant, in some extent, in the crystal structure.

O carbeto de Tântalo (TaC) e um material extremamente duro, apresentando elevada dureza, elevado ponto de fusao, elevada estabilidade quimica, boa resistencia ao ataque quimico e choque termico e excelente resistencia a oxidacao e corrosao. Desta forma, este trabalho teve como objetivo a obtencao de TaC nanoestruturado a partir do precursor tris(oxalato)oxitantalato de amonio hidratado, atraves de reacao gas-solido a baixa temperatura (1000°C) e curto tempo de reacao. Os materiais obtidos foram caracterizados atraves de difracao de Raios-X (DRX), Refinamento Rietveld, Microscopia Eletronica de Varredura (MEV), Espectroscopia de Infravermelho (espectroscopia IV), Termogravimetrica (TG). Atraves das analises de DRX e do refinamento Reitiveld para o TaC com S = 1,1584 observou-se a formacao do carbeto de tântalo puro com estrutura cubica e tamanho medio de cristalitos na ordem de 12,5 nanometros

The objective of this work is obtaining W-30 wt% Cu composite powder from ammonium paratungstate hydrated (APT) and hydrated copper nitrate and investigating the influence of some production process parameters of W- 30 wt% Cu in particles form which results in high sinterability and densification of W-30 wt% Cu composite. To achieve this objective, the powder was obtained by manually mixing the APT and copper nitrate and reducing under a hydrogen atmosphere at 800 °C and then compacting at 500 MPa and sintering in a tubular furnace at 1200 °C for 60 minutes. The obtained materials were characterized by XRD, SEM, EDS, particle size analysis, density and microhardness measurements. The composite powder showed a good homogenization of Cu in W with very fine and agglomerated particles and a mean crystallite size of 25.64 nm. SEM coupled with EDS with mapping analysis revealed a homogeneous distribution of Cu and W in the sintered sample. The composite had a relative density of 96.77% and a microhardness of 523.66 HV. Therefore the method of obtaining the composite powder is feasible to sinter W-30 wt% Cu powder due to a greater dispersion and homogenization of phases and the average particle size.

57Fe Mossbauer spectroscopy and X-ray diffractometry were used to study EUROFER or VVER ferritic reactor steels mechanically alloyed with TaC or NbC. Significant changes were found in the Mossbauer spectra and in the corresponding hyperfine field distributions between the ball milled pure steel and that alloyed with TaC or NbC. Spectral differences were also found in the case of use of same carbides with different origin, too. The observed spectral changes as an effect of ball milling of the reactor material steels with carbides can be associated with change in short range order of the constituents of steel.

Mechanical properties of ferritic-marensitic steels can be improved through dispersion of fine particles with large industrial applications like nuclear, military and aeronautic areas. Steels used at nuclear reactors suffer some damage when exposure to various kinds of radiation such as gamma, plasma, neutrons among others. Special steels have been studied to resist these processes in which cause a significant degradation of these materials. Reduced activation ferritic/martensitic steels (RAFM) are used for fusion structural materials with the substitution of some alloying elements such as Mo, Nb and Ni present in the commercial martensitic steels by other elements which exhibit faster decay of induced radioactivity, such as Ta, W and V. This present work study the development of EUROFER97 steel reinforced with 3wt% of tantalum carbide (TaC).

Several kinds of alloys Ni-based, Fe-based and Al-based oxide dispersion strengthened (ODS) and carbide dispersion strengthened (CDS) have been produced through mechanical alloying. Precipitation-strengthened or dispersion-strengthened steels are a kind of high strengthened steel using fine precipitation or dispersion of carbides. This work present a study of EUROFER97 steel powder reinforced with 3%wt of niobium carbide. The starting materials were wet-milled in a high-energy planetary ball mill for several times up to 5 hours. The ratio of ball to powder weight was 15:1. The milled powders were characterized by SEM, XRD, EDX and laser scattering. The results are presented on base of a microstructure analysis of composite particles of steel-carbide as a function of milling time.

The nanocrystallites in a metal matrix composite (MMC) have wide importance in the sintering area. The nanocrystallites have been related with properties such as hardness and density of 316L steel matrixes. The Y2O3 and TaC dispersion in steel crystalline structures affects these properties and the sintering process. This study analyze: the 316L steel, Y2O3 and TaC crystallite size; TaC and Y2O3 dispersion in milled powder composite; MMC nanocrystallite size and micro-strain during milling process of 316L-(CFC) steel and the effects of dispersion in sintered MMC. The alloy was submitted to high energy milling. MMC was characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The diffraction was analyzed by Rietveld’s refinement method, DBWS 9807 program, and crystallite size and micro-strain were performed using Scherrer’s equation and Williamson-Hall’s method.

Sintered stainless steel has a wide range of applications mainly in the automotive industry. Properties such as wear resistance, density and hardness can be improved by addition of nanosized particles of refractory carbides. The present study compares the behavior of the sintering and hardness of stainless steel samples reinforced with NbC or TaC (particles size less than 20 nm) synthesized at UFRN. The main aim of this work was to identify the effect of the particle size and dispersion of different refractory carbides in the hardness and sintered microstructure. The samples were sintered in a vacuum furnace. The heating rate, sintering temperature and times were 20°C/min, 1290°C and 30, 60 min respectively. We have been able to produce compacts with a relative density among 95.0%. The hardness values obtained were 140 HV for the reinforced sample and 76 HV for the sample without reinforcement.

Steel is an alloy EUROFER promising for use in nuclear reactors, or in applications where the material is subjected to temperatures up to 550°C due to their lower creep resistance under. One way to increase this property, so that the steel work at higher temperatures it is necessary to prevent sliding of its grain boundaries. Factors that influence this slip contours are the morphology of the grains, the angle and speed of the grain boundaries. This speed can be decreased in the presence of a dispersed phase in the material, provided it is fine and homogeneously distributed. In this context, this paper presents the development of a new material metal matrix composite (MMC) which has as starting materials as stainless steel EUROFER 97, and two different kinds of tantalum carbide-TaC, one with average crystallite sizes 13.78 nm synthesized in UFRN and another with 40.66 nm supplied by Aldrich. In order to improve the mechanical properties of metal matrix was added by powder metallurgy, nano-sized particles of the two types of TaC. This paper discusses the effect of dispersion of carbides in the microstructure of sintered parts. Pure steel powders with the addition of 3% TaC UFRN and 3% TaC commercial respectively were ground for 5 hours in the planetary mill. Each of the resultant particulate samples were cold compacted under a uniaxial pressure of 600MPa in a cylindrical die 5 mm in diameter. Subsequently, the compressed were sintered in a vacuum oven at a temperature of 1250°C with an increment of 20°C and 10°C per minute and maintained at these isotherms for 60 minutes. The distribution, size and dispersion of steel and composite particles were determined by X-ray diffraction, laser particle size and scanning electron microscopy(SEM). The structures of the sintered bodies were observed by optical microscopy(OM) and scanning electron microscopy(SEM).

The main purpose of this paper is to present a spray dryer device developed to synthesize ammonium niobium-oxalate precursor powder with controlled grain size. The dryer device is manufactured using stainless steel 304 and measures 0,48m in outside diameter and 1,9m in height. The spray dryer has a cylindrical shape assembled on a conical base. The central chamber is heated by three 4 KW resistances and is equipped with serpentine coil heaters placed around its main body. This configuration guarantees that the air is at the same temperature of the chamber walls and the adherence of the powder particles on the wall is prevented. The precursor solution is atomized on the air stream downwards from the top to the bottom, at low rates. Powder particles are collected on a 0,4m diameter horizontal plate placed at the bottom portion of the dryer and the wet air is released from the chamber by the opening located under the collecting plate. The synthesis of the niobium oxalate precursor and the results of the decomposition process are described.

International audience; Nano-octahedral grains of cobalt ferrite (CoFe2O4) with size around 20 nm were synthesized by a hydrothermal route. X-rays and electron diffraction, along with scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and thermogravimetric analysis were used to characterize the powders. Images and simulations of high-resolution electron microscopy allowed the identification of the shape of the grains. Process parameters such as temperature and time of reaction, reagents concentration, and pH of the reacting medium were optimized. The surfactant cetyltrimethylammonium bromide (CTAB) hindered the formation of goethite, which favored the production of a pure CoFe2O4 powder. The oxidation state of cobalt atoms on the ferrite structure was also influenced by CTAB. The control of the shape of the grains was associated mainly to the nature of the precipitating agent.

A complex rare-earth tungstate structure, present in a two-phased powder, was solved by electron diffraction, precession and high-resolution electron microscopy. The orthorhombic space groupPbnmand the atomic positions deduced from X-ray diffraction experiments were confirmed for Ce10W22O81. AC2/cmonoclinic superstructure, with cell parametersa= 7.8,b= 36.1,c= 22.2 Å and β = 100.2°, was shown and attributed to a partial oxidation of Ce3+leading to interstitial oxygen ions.

The transport properties and reactivity in gases of a BaCeO 3 perovskite phase have been investigated to develop new materials for methane conversion in microsystems. The polycrystalline material has been synthesized at moderate temperature using a specific modified EDTA-citrate complexing methodology. The BaCeO 3 phase has been characterized by X-ray diffraction (XRD), thermogravimetry and differential thermal analyses (TG/DTA), scanning and transmission electronic microscopy techniques (SEM, TEM), energy dispersive X-ray (EDX) and surface area analyses. A Rietveld analysis of diffraction profiles has allowed determining the structural parameters of the as prepared material. Next, the catalytic efficiency of the BaCeO 3 phase with air-methane gas flows has been characterized by Fourier transformed infrared (FTIR) spectroscopy: the conversion rate of CH 4 into CO 2 has been determined from the intensities of CO 2 absorption bands, as a function of temperature (from 450 to 750 °C) and reaction time. Finally, the electrical conduction of compacted BaCeO 3 pellets has been determined from electrical impedance spectroscopy analyses between 300 °C and 950 °C. A series of electrical transitions correlated with well known structural changes has been observed between 300 °C and 950 °C. The starting catalytic activity of BaCeO 3 might be correlated to the enhanced ionic conduction observed above 450 °C.

A rotating cylinder reactor was designed for the synthesis of niobium carbide powders at 1173 K. Niobium carbide, NbC, was prepared by carbothermal reduction starting from commercial niobium pentoxide powders. The reactor was heated using a custom-made, two-part, hinged, electric furnace with programmable temperature control. The design and operational details of the reactor are presented. The longitudinal temperature gradient inside the reactor was determined. Total reaction time was monitored by a gas chromatograph equipped with an FID detector for determination of methane concentrations. The results show that time of reaction depended on rotation speed. NbC was also prepared in a static-bed alumina reactor using the same conditions as in the previous case. The niobium carbide powders were characterized by X-ray diffraction and compared with commercially available products. Morphological, particle size distribution and surface area analyses were obtained using SEM, LDPS and BET, respectively. Therefore, the present study offers a significant technological contribution to the synthesis of NbC powders in a rotating cylinder reactor.