Carlos R. Michel

Grain-size effects on gas response in nanostructured Gd0.9Ba0.1CoO3

The perovskite Gd(0.9)Ba(0.1)CoO3 was prepared via solution and solution-polymerization methods in aqueous media. The thermal decomposition of precursor powders produced well crystallized nanostructured materials possessing an extensive nanoporosity. The average particle size obtained by the solution route was 150 nm, whereas by the solution-polymerization method was 61 nm. The characterization of gas response, performed on thick-films, revealed that the electrical resistance variation increases with reducing grain size. In oxygen, the films prepared with powder of solution-polymerization registered an increment of 1000%, compared to the powder made by the solution route, whereas in carbon dioxide was 1100%.

Effect of the Preparation Method on the Gas Sensing Properties of Nanostructured CoAl2O4

To study the effect of the preparation method on the gas-sensing behavior of nanostructured CoAl 2 O 4 , this oxide was prepared by three different synthesis routes. Two of them based on nonaqueous solution media employing triethanolamine and hexadecyltrimethylammonium bromide in ethanol, and the third, in an aqueous solution-polymerization method using polyvinyl alcohol and sucrose. In order to obtain solid precursor materials from the solutions, evaporation was made by applying microwave radiation. Further thermal decomposition of precursors at 600°C in air produced single-phase nanostructured CoAl 2 O 4 with the spinel cubic structure. Structural characterization was made by X-ray powder diffraction. The particle size was determined by transmission electron microscopy; the smaller nanoparticles were observed in the sample prepared with triethanolamine, with an average size of 8 nm. The gas-sensing characterization was made in thick films prepared by the screen-printing method. In CO 2 , a strong relationship between particle size and gas response was measured in the dynamic response of resistance and polarization tests. The optimal CO 2 response of the films was observed between 400 and 450°C. Even though a reliable CO 2 detection was recorded in the three films, they were insensitive to O 2 under the experimental parameters used.

Characterization of Extruded Blends of Corn and Beans (Phaseolus Vulgaris) Cultivars: Peruano and Black-Querétaro under Different Extrusion Conditions

The effect of extrusion conditions in blends of corn and beans (Phaseolus vulgaris) of cultivars Peruano and black-Querétaro were investigated in this study, as an alternative to obtain snack foods. The type of cultivar and beans percentage, and also the extrusion conditions (moisture and temperature) influenced the physicochemical (color and breaking strength) and the functional (water absorption index, water solubility index, and oil absorption capacity) properties of the extrudates. The microstructures showed the presence of cavities and starch granules gelatinized (melted) and plasticized; while, the x-ray powder diffraction patterns revealed the presence of monohydrate glucose due to starch dextrinization. The results demonstrate that extrudates with good properties can be obtained from blends of corn and beans, under selected extrusion conditions, depending on the bean cultivar.

Improvement of the Gas Sensing Properties in Nanostructured Gd0.9Sr0.1CoO3

Global warming has become one of the most important issues worldwide (Kerr, 2007). The emission of large amounts of CO2 has been identified as its main cause (Karl et al., 2003; Parry et al., 2008). In order to determine the concentration of this and other polluting gases, researchers around the world have developed solid state chemical sensors. Even though SnO2, ZnO, TiO2 and WO3 have been some of the most studied gas sensor materials, other oxides, with unique physical and chemical properties are also appropriate for this application (Yamazoe, 2005). Ternary and quaternary oxides, whose crystal structures are the perovskite or spinel, have notable electrical and catalytical properties, useful for gas sensing purposes (Brosha et al., 2000; Dutta et al., 2004; Kong et al., 1996; Kosacki et al., 1998; Post et al., 1999; Suo et al., 1997).

CHAPTER 3 – CO2 Response of Nanostructured CoSb2O6 Synthesized by a Nonaqueous Coprecipitation Method

Publisher Summary This chapter discusses the CO2 response of nanostructured CoSb2O6 synthesized by a nonaqueous coprecipitation method. CO2 plays an important role in preserving the average atmospheric temperature; the emission of this gas in large amounts during recent decades is producing a phenomenon of great concern to mankind, global warming. With the goal of developing reliable solid-state gas sensors, notable scientific research has been made worldwide. As a result, several compounds such as SnO2, ZnO, WO3, TiO2, and other inorganic oxides have been intensively tested for the detection of toxic gases like CO and NO2. In addition to the oxides already mentioned, several oxides possessing different crystal structures have been studied for gas-sensing purposes. A nonaqueous coprecipitation method based on PVP in ethyl alcohol was used for the preparation of CoSb2O6. Using this simple method, CoSb2O6 was obtained at a low calcination temperature, with good control on the stoichiometry. The synthesis of nanostructured CoSb2O6 by a nonaqueous coprecipitation method using polyvinyl pyrrolidol (PVP), cobalt nitrate, and antimony trichloride in ethyl alcohol is also discussed in this chapter. The relationship between the PVP concentration in solution and the surface morphology is investigated in the study. The potential application of nanostructured CoSb2O6, as an environmental gas-sensor material, is studied by measuring the dynamic variation of resistance in air, CO2, and O2. The CO2-sensing response is also studied by recording intensity vs. voltage graphs at different CO2 concentrations.

Gas Sensing Response in Nanostructured CoAl2O4 Spinel Prepared by Soft-Chemistry Methods.

Semiconductor transition metal oxides are suitable materials for environmental gas sensing applications due to their gas sensitivity, crystal structure stability and reproducibility in gas detection [1]. On the other hand, the chemical activity and electrical conductivity in these materials may be enhanced when their average particle size is reduced into the nanometer scale [2]. Nanoporosity and good connectivity between nanoparticles also play an important role in this application by increasing the specific surface area, and facilitating the electrical conduction respectively [3, 4].