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Crystallization is a well-recognized practical means of improving the brittleness of glass.
Many glass-ceramics have been investigated, and some have been incorporated into
practical materials. Glass-ceramics in the MgO–Al2O3–SiO2 (MAS) system have attracted
much interest on account of their superior mechanical and thermal properties, i.e., high
strength and stability at high temperatures.
To investigate the effect of nucleating agents, this study investigates the crystallization
behavior of an MgO–Al2O3–SiO2-MoO3 glass with high % wt molybdenum oxide and low
% wt nickel oxide addition. Under a not reducing condition, crystals formed in the bulk of
the super cooled liquids, whereas melting in air yielded only surface crystallization. The
purpose of using of Nickel oxide as nucleating to modify the mechanical properties, is
based on the manipulation of the grain size during the solidification process. The first
crystalline phase precipitated inside the glass was α-cordierite and β-cordierite in glasses
doped with nickel oxides. Nickel oxide yielded a finer microstructure of the glass-ceramic.
Measurements of ac-susceptibility and dc-magnetization
were carried out on samples of Ni1−xZnxFe2O4 nanoparticles
(x = 0, 0.25, 0.5, 0.75) with average diameters D ≈
7 nm. Values of the superparamagnetic blocking temperature
TB were obtained from the characteristic temperature behavior
of the imaginary susceptibility χimag. An Arrhenius-type
law, which accurately describes the relationship between the
observation time τobs and the blocking temperature, was used
to determine the effective energy barrier to magnetization reversal
Ueff. A Zn-content dependence of the energy barrier is
observed, where Ueff changes little for 0 ≤ x ≤ 0.25, it peaks
at x = 0.5, and decreases back upon further Zn-doping. The
large increase of Ueff at x = 0.5 is attributed to an enhanced
magnetic anisotropy induced by the crossover between two spatial
arrangements of spins in the A and B sub-lattices of the
ferrimagnetic inverse spinel.
Carbon black supported materials based on polythiophene and cobalt or nickel were studied as oxygen reduction catalysts. Polythiophene was chemically polymerized onto carbon black, and modified with cobalt or nickel salts to obtain carbon supported polythiophene-cobalt and polythiophene-nickel. For reasons of comparison, the precursor, unmodified carbon-supported polythiophene was studied, as well as unsupported polythiophene particles. In order to study the physical, chemical and electrochemical properties, TGA, SEM, EDAX and electrochemical methods were used. SEM images show porous materials with a particle size of around 110 nm for the carbon supported materials. EDAX tests confirmed the presence of approximately 7 wt% of either cobalt or nickel in the modifiedmaterials. Cyclic voltammetry confirmed the presence of ORR peaks in the cathodic area in all materials, except for polythiophene only. Based on kinetic parameters obtained using RDE tests and on electrochemical stability as determined from potentiostatic test, it was concluded that the material with best ORR catalytic activity is carbon supported polythiophene-cobalt.
Juan Manuel Quintana Melgoza (2001)
Presentamos un estudio fisicoquímico del tungstato de níquel (NiWO4). En este trabajo se realiza la metodología de síntesis, la identificación estructural, la medición de área superficial, la medición de tamaño promedio de cristal y la actividad catalítica en la reacción modelo de conversión simultanea de óxido nítrico (NO) y monóxido de carbono (CO), ambos contaminantes mayoritarios de la atmósfera. La síntesis de NiWO4, se lleva a cabo mediante la reacción química de una mezcla estequiométrica de metatungstato de amonio octadeca hidratado [H26N6,O41,W12,.18H2,O] y nitrato de níquel hexahidratado [Ni(NO3)2,6H2,O] en un flujo de oxigeno de 20 mL/min dentro de un intervalo de 400 °C a 800 °C durante una hora de reacción. La composición elemental, la estructura morfológica y la identificación estructural de las partículas de NiWO4, NiO, y WO3, se obtienen por espectroscopia de dispersión de energía, microscopia electrónica de barrido y difracción de rayos-X. La identificación estructural de NiWO4, se efectúa por microscopia electrónica de transmisión de alta resolución. La reducción catalítica de NO con CO se realiza en el intervalo de (250 a 700) °C en un flujo de 60 mL/min. En otro experimento, la reacción catalítica se lleva a cabo dentro del intervalo de (25 a 400) °C con un flujo total de reactivos de 200 mL/min. En ambos casos, se utiliza la relación NO/CO= 1/5 sobre NiWO4, NiO, y WO3, respectivamente, para obtener dióxido de carbono (CO2,) y nitrógeno (N2,). Primer caso, la conversión de NO en 100 % se alcanza a 500 °C por NiWO4, a 575 °C por NiO, y para WO3, ocurre desactivación a 625 °C, Segundo caso, la conversión de NO en 100 % se alcanza a 400 °C por los tres catalizadores. Además, la reacci6n-se realiza en exceso de CO sobre los catalizadores a 450 °C variando la relación de reactivos NO/CO de 0.2 a 1.0 en un flujo de 60 mL/min, mostrando que el exceso de reductor favorece la conversión de NO por NiWO4, y WO3, pero no por NiO. En este estudio, también se muestran los resultados de los parámetros que determinan la actividad de los catalizadores, tales como: velocidad especifica de reacción, energía de activación, selectividad, área superficial y tamaño promedio de cristal.
In this work, we present a study of nickel tungstate (NiWO4,). The study is based on the synthesis, structural characterization, surface area, average crystal size and catalytic activity measurements. The catalytic activity was tested on a model reaction of simultaneous conversion of nitric oxide (NO) and carbon monoxide (CO), both great atmospherical pollutants. NiWO4, was synthesized from a stoichiometric mixture of ammonium metatungstate (H26,N6,O41W12,18H2,O)and nickel nitrate (Ni(NO3)2,6H2,O) followed by varying temperatura treatment from 400 °C to 800 °C using an oxygenflow of 20 mL/minfor 1 hour. Elemental composition, morphological structure and structural characterization of NiWO4, NiO, and WO3,particles were obtained by energy dispersive spectroscopy, scanning electron microscopy and X-ray diffraction. Structural characterization of NiWO4, has been performed by high resolution transmission electron microscopy. Thecatalytic reduction of NO by CO took place in the temperature range (250 to 700)°C in a gas flow of 60 mL/min. The catalytic reaction was carried out at temperature (25 to 400) °C range at a gas flow of 200 mL/min. In both cases, we used the ratio NO/CO= 1/5 over NiWO4, NiO, and WO3, respectively to obtain carbon dioxide (CO2,) and nitrogen (N2,) products. For the first case, NO conversion was 100 % at 500 °C for NiWO4, at 575 °C for NiO, and for WO3,it was inhibited at 625 °C. For the second case, the NO conversion was 100 % at 400 °C “for all catalysts. Additionally, catalysts are tested at 450 °C varying the volume ratio of reactants NO/CO from 0.2 to 1.0 at a gas flow of 60 mL/min. These measurements indicated that the CO excess increase the NO conversion by NiWO4, and WO3, but not for NiO. In this study, we also present the results of parameters that determine the activity of catalysts, such as: specific rate of reaction, activation energy, selectivity, surface area and average crystal size.
Sintesis, Tungstato de niquel, Óxido de niquel, Tridxido de tungsteno, Caracterización estructural, Area superficial, Tamafio promedio de cristal, Reduccién catalitica, Óxido nitrico, Monóxido de carbono, Synthesis, Nickel tungstate, Nickel oxide, Tungsten trioxide, Structural characterization, Surface area, Average crystal size, Catalytic reduction, Nitric oxide, Carbon monoxide CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA OTRAS ESPECIALIDADES FÍSICAS
"Nonvolatile rewritable organic memory devices based on poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and nitrogen doped multi-walled carbon nanotube (NCNT) nanocomposites were fabricated on glass and PET substrates. Organic memory devices with bistable resistive switching were obtained using very low NCTN concentration (similar to 0.002 wt%) in the polymeric matrix. The memory devices exhibited a good ON/OFF ratio of approximately three orders of magnitude, a good retention time of 10(4) s under operating voltages <= vertical bar 4V vertical bar and a few hundredths of write-read-erase-read cycles. The bistable resistive switching is mainly attributed to the creation of oxygen vacancies. These defects are introduced into the thin native Al oxide (AlOx) layer on the bottom electrode during the first voltage sweep. The well-dispersed NCNTs immersed in PEDOT:PSS play a key role as conductive channels for the electronic transport, hindering the electron trapping at the AlOx-polymer interface and inducing a soft dielectric breakdown of the AlOx layer. These PEDOT:PSS NCNTs memory devices are to easy to apply in flexible low-cost technology and provide the possibility of large-scale integration."
Oxide based nanostructures were grown by aerosol assisted chemical vapour deposition onto borosilicate glass substrates covered by a TiO2 thin film as a buffer. Details of the experimental setup and general synthesis conditions were reported elsewhere1,2. Nanostructures were a multilayered coating composed by: oxides of Ti, Ti-Fe, Ti-Ni, and TiOx-FeOx. All the nanostructures were covered by a continuous layer of Pt nanoparticles. Microstructure of the samples were analysed by electron microscopy and x-ray diffraction. Optical properties were also determined in the UV-visible-near IR interval. Finally photocatalytic generation of H2 was evaluated in a batch reactor under visible light irradiation, using a filtered low vapour pressure Hg lamp of 250 W. H2 evolution was tested every hour by gas chromatography. Table 1 resumes the principal characteristics of the different coatings and generated H2 in μmol.h-1.g-1, taking into account their mass.
We report the synthesis of nickel microspheres and their structural and electrochemical characterization. The materials were prepared by the microemulsion technique from NiSO4∙6H2O and NaOH, and using NaH2PO2∙H2O as a reducing agent. Sodium dodecyl sulfate (SDS) was used as a surfactant. The following ternary formulations were used for their synthesis: N1 (90%H2O-7.5%SDS-2.5%Pentanol), N2 (92.5%H2O-5%SDS-2.5%Pentanol), N3 (95%H2O-3.75%SDS-1.25%Pentanol) and N4 (99%H2O-0.75%SDS-0.25%Pentanol). The catalysts were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The catalytic activity for ethanol oxidation in an alkaline medium was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The average diameters of the nickel microspheres ranged from 0.375 to 1.476 m. On subjecting the materials to heat treatment in a nitrogen atmosphere at 300 °C for 4 h, mixtures of polycrystalline Ni and nickel phosphide (Ni3P) were obtained. The best performance for the ethanol oxidation reaction (EOR) in an alkaline medium was recorded with non-heat-treated nickel microspheres, presenting a maximum peak potential at approximately 0.7 V vs. Hg/HgO with normalized currents between 10.774 and 18.198 mA(mgcat)-1. These results indicate that nickel microspheres are potential candidates for use as anodes in alkaline direct alcohol fuel cells (A-DAFCs).
"Nickel hydroxide β–Ni(OH)2 hexagonal nanosheets were synthetized via a hydrothermal exfoliation process. The practical microwave-assisted hydrothermal method facilitated obtaining layered nickel 3D nanoplates with cerium functionalization in 5 h. The as-produced nanostructures were characterized by XRD, XPS, FESEM, FTIR, PL, UV–vis, and BET techniques. The hydroxilated structures are nano-thick hexagonal plates with sides 28 nm in length and an average thickness of 5 nm. UV and PL irradiation was used to study the photoactive properties in the degradation of a pharmaceutical emerging pollutant, naproxen. UV–vis spectroscopy and high-performance liquid chromatography monitoring indicated that the Ni(OH)2-Ce nanostructures are an effective photocatalyst for naproxen degradation, including 40% mineralization of this highly recalcitrant drug. The photocatalyst showed stability for two consecutive cycles, preserving its photoactive and structural characteristics. Ce3+-doped nanoplates and surface functionalized Ce4+ act as charge separators and scavenging agents for the enhanced photodegradation of naproxen."
"The coarsening kinetics of gamma' precipitates in Ni-rich Ni-Ti alloys are studied using a Ni-11-5 wt% Ti and pure Ni diffusion couple. The formed concentration gradient allowed to study the aging process at 1023 K (750 degrees C) in Ni-rich Ni Ti alloys with Ti content from 8-62 to 11-15 wt% Ti. In general, during the coarsening of gamma' precipitates, the experimental coarsening kinetics do not fit well to the LSW or TIDC theoretical models and anomalous behaviour of coarsening rate constant (k(r)) associated with gamma' volume-fraction is confirmed at high values."
Graphene is a ground-breaking two-dimensional (2D) material that possesses outstanding
electrical, optical, thermal, and mechanical properties and that promises a new
generation of devices. Despite all these, some applications require graphene-based
materials with different characteristics, such as good solubility in organic solvents and
a specific band gap to be dispersible in polymer nanocomposite matrix and applied as
active layer, electron transport layer (ETL) or hole transport layer (HTL) in organic
photovoltaics. Chemically modified graphene derivatives are studied, searching for
better dispersions and even more properties for different applications. Most of the
attention has been drawn to dispersions of graphene oxides or highly reduced graphene
oxides. Therefore, this allows an opportunity to study the characteristics of materials
with intermediate oxidation degrees and its applications.