Application of the surface potential data to elucidate interfacial equilibrium at ceria/aqueous electrolyte interface

Interfacial properties of ceria (CeO2) nanoparticles and highly organized ceria crystal planes {111} and {100} in the aqueous electrolyte solution were studied. It was confirmed by high resolution electron spectroscopy that a primary ceria nanoparticle consists mostly of two crystal planes {111} and {100} with different surface sites exposed to the aqueous electrolyte solution. Interfacial properties of ceria nanoparticles are directly related to the reactivity and surface densities of existing surface sites. However, surface characterization (potentiometric titrations and electrophoretic measurements) provides only some kind of average surface properties i.e. average surface charge densities and surface potentials. The point of zero charge (pHpzc) of ceria nanoparticles was measured to be between 6.4 and 8.7, depending on the electrolyte concentration, and the isoelectric point at pHiep = 6.5. With the purpose of understanding ceria nanoparticles surface charging the inner surface potentials of ceria macro crystal planes {111} and {100} were measured for the first time, by means of single crystal electrodes, as a function of pH and ionic strength. The inner surface potential directly affects the state of ionic species bound to a certain surface plane and is thus an essential parameter governing interfacial equilibrium. From the measured Ψ 0(pH) data and applying the Multi Site Complexation Model the thermodynamic equilibrium constants of doubly-coordinated ≡Ce2-OH (at the {100} ceria crystal plane) as well as singly-coordinated ≡Ce1-OH and triply-coordinated ≡Ce3-OH (at the {111} ceria crystal plane) were evaluated. The Ψ 0(pH) function differs for two examined ceria planes, however the inner surface potentials of both planes depend on ionic strength having a broad electroneutrality region between pH = 6 and pH = 9

Spektroskopski studij sintetskog forsterita dobivenog iz zeolitnih prekursora

Important ceramics materials are prepared from aluminosilicate based precursors using novel methods, offering at the same time a better control over many important properties. Forsterite, due to its good refractoriness with melting point at 2163 K, excellent electrical insulation properties even at high temperatures, low dielectric permittivity, thermal expansion and chemical stability, is a material of interest to engineers and designers especially as an active medium for tuneable laser and is also a material of interest to SOFC (Solid oxide fuel cells) manufacturers. The aim of this study is to investigate the synthesis of crystalline forsterite using different zeolite precursors previously activated by ball milling. Synthetic forsterite was synthesized from different zeolite precursors and MgO combining highenergy ball milling and thermal treatment of the mixture under determined conditions of time and temperature for each operation. In this research are studied the solid-state phase transformations taking place at temperatures below 1273 K. The obtained products were characterized using different spectroscopy techniques in comparison with surface analysis method and X-ray diffraction.Važni keramički materijali pripremljeni su iz alumosilikatnih prekursora, pri čemu su primijenjene novije metode, koje istodobno daju mogućnost intervencije u procese nastajanja i kontrolu nad mnogim svojstvima. Forsterit je silikatni materijal posebno interesantan inženjerima i konstruktorima procesne opreme, osobito u laserskoj tehnici i području gorivih čvrstih oksidnih ćelija (SOFC), zbog svoje kemijske stabilnosti, dobrih vatrostalnih karakteristika, tališta od 2163 K, izvrsnih električkih izolacijskih svojstava, male električne permitivnosti i slabog termičkog širenja. Cilj ovog rada je istraživanje na području sinteze kristalnog forsterita uz upotrebu različitih zeolitnih prekursora koji su prethodno aktivirani mljevenjem kugličnim mlinom. Sintetski forsterit dobiven je iz smjese MgO i različitih zeolitnih prekursora, kombinirajući visoko energijsko mljevenje i termičku obradu u kontroliranim vremenskim i temperaturnin uvjetima. U ovom istraživanju studirane su fazne transformacije čvrstog stanja koje se odvijaju na temperaturama ispod 1273 K. Dobiveni proizvod je opisan pomoću različitih spektroskopskih tehnika, analizom specifične površine i rendgenskom difrakcijom

Spektroskopski studij sintetskog forsterita dobivenog iz zeolitnih prekursora

Important ceramics materials are prepared from aluminosilicate based precursors using novel methods, offering at the same time a better control over many important properties. Forsterite, due to its good refractoriness with melting point at 2163 K, excellent electrical insulation properties even at high temperatures, low dielectric permittivity, thermal expansion and chemical stability, is a material of interest to engineers and designers especially as an active medium for tuneable laser and is also a material of interest to SOFC (Solid oxide fuel cells) manufacturers. The aim of this study is to investigate the synthesis of crystalline forsterite using different zeolite precursors previously activated by ball milling. Synthetic forsterite was synthesized from different zeolite precursors and MgO combining highenergy ball milling and thermal treatment of the mixture under determined conditions of time and temperature for each operation. In this research are studied the solid-state phase transformations taking place at temperatures below 1273 K. The obtained products were characterized using different spectroscopy techniques in comparison with surface analysis method and X-ray diffraction.Važni keramički materijali pripremljeni su iz alumosilikatnih prekursora, pri čemu su primijenjene novije metode, koje istodobno daju mogućnost intervencije u procese nastajanja i kontrolu nad mnogim svojstvima. Forsterit je silikatni materijal posebno interesantan inženjerima i konstruktorima procesne opreme, osobito u laserskoj tehnici i području gorivih čvrstih oksidnih ćelija (SOFC), zbog svoje kemijske stabilnosti, dobrih vatrostalnih karakteristika, tališta od 2163 K, izvrsnih električkih izolacijskih svojstava, male električne permitivnosti i slabog termičkog širenja. Cilj ovog rada je istraživanje na području sinteze kristalnog forsterita uz upotrebu različitih zeolitnih prekursora koji su prethodno aktivirani mljevenjem kugličnim mlinom. Sintetski forsterit dobiven je iz smjese MgO i različitih zeolitnih prekursora, kombinirajući visoko energijsko mljevenje i termičku obradu u kontroliranim vremenskim i temperaturnin uvjetima. U ovom istraživanju studirane su fazne transformacije čvrstog stanja koje se odvijaju na temperaturama ispod 1273 K. Dobiveni proizvod je opisan pomoću različitih spektroskopskih tehnika, analizom specifične površine i rendgenskom difrakcijom

Diffusion of cosmic-ray electrons in M 51 observed with LOFAR at 54 MHz

Context. The details of cosmic-ray transport have a strong impact on galaxy evolution. The peak of the cosmic-ray energy distribution is observable in the radio continuum using the electrons as proxy. Aims. We measure the length that the cosmic-ray electrons (CRE) are transported during their lifetime in the nearby galaxy M 51 across one order of magnitude in cosmic-ray energy (approximately 1-10 GeV). To this end we use new ultra-low frequency observations from the LOw Frequency ARay (LOFAR) at 54 MHz and ancillary data between 144 and 8350 MHz. Methods. As the the CRE originate from supernova remnants, the radio maps are smoothed in comparison to the distribution of the star formation. By convolving the map of the star-formation rate (SFR) surface density with a Gaussian kernel, we can linearise the radio-SFR relation. The best-fitting convolution kernel is then our estimate of the CRE transport length. Results. We find that the CRE transport length increases at low frequencies, as expected since the CRE have longer lifetimes. The CRE transport length is $l_{\rm CRE} = \sqrt{4Dt_{\rm syn}}$, where $D$ is the isotropic diffusion coefficient and $t_{\rm syn}$ is the CRE lifetime as given by synchrotron and inverse Compton losses. We find that the data can be well fitted by diffusion, where $D=(2.14\pm 0.13) \times 10^{28}~\rm cm^2\,s^{-1}$. With $D\propto E^{0.001\pm 0.185}$, the diffusion coefficient is independent of the CRE energy $E$ in the range considered. Conclusions. Our results suggest that the transport of GeV-cosmic ray electrons in the star-forming discs of galaxies is governed by energy-independent diffusion.Comment: Accepted to Astronomy and Astrophysics. 11 pages, 5 figures, 2 table

Nanostructure of thin silicon films by combining HRTEM, XRD and Raman spectroscopy measurements and the implication to the optical properties

A series of thin silicon films with different degrees of crystallinity were prepared by decomposition of silane gas highly diluted with hydrogen, in radiofrequency glow discharge. The crystallite size, shape, and the portion of crystalline phase were investigated by high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Raman spectroscopy (RS), and X-ray powder diffraction (XRD). The absorption coefficient (a) was calculated from the measurement of UV–vis-transmittance. By using RS, the volume fractions of the crystalline phase were estimated from the ratio of the integrated intensities of transversal optical (TO)-related crystalline and amorphous bands. These results were in excellent agreement with the mean crystallite sizes measured in HRTEM images and crystallite sizes refined from XRD measurements. The red shift of absorption, appearing as a result of the increase of the crystal fraction, depends on the size and distribution of nanocrystals

Mount-Etna-Lava-Supported Nanocarbons for Oxidative Dehydrogenation Reactions

The Mount Etna lava stones containing iron oxide particles can be used as catalyst and support to synthesize and immobilize carbon nanotubes and nanofibers. We report on the use of the obtained composite as catalyst for butadiene and styrene production. The catalyst is highly active in the mentioned oxidative dehydrogenation reactions and stable. The whole process is energy-saving, environmentally friendly, technically feasible, and with great potential for industrialization: from the syntheses of carbon nanotubes and nanofibers until their use in the catalytic reactions, no any wet-chemical pretreatment of lave stone or activation of catalyst is needed

Spectroscopic Investigation of MoO₃-Fe₂O₃-P₂O₅ and SrO-Fe₂O₃-P₂O₅ Glasses I

The relationship between the composition, structure and selected properties for four series of iron phosphate glasses containing MoO3 and SrO has been investigated. The three series of MoO3-Fe2O3-P2O5 glasses were prepared with increasing MoO3 content. In series A the molar Fe/P ratio was constant at 0.67, in series B the O/P ratio was 3.5, whereas, in series C the molar percentages of Fe2O3 was fixed at 40 mol%. In the fourth series, M, SrO was added to maintain the Fe/P ratio constant at 0.67. The structural changes in these glasses have been studied by Raman spectroscopy. The Raman spectra show that MoO3 is incorporated into the phosphate network. However, the structure/properties are strongly influenced by the overall O/P ratio. In glasses with O/P \u3e 3.5 the addition of MoO3 depolymerized some of the bridging oxygens in pyrophosphate units to form isolated (PO4)3− orthophosphate groups. The decrease in glass temperature, Tg, and glass density, D, increase in thermal expansion coefficient, α, and glass density, D, for these glasses are attributed to an increase in the number of weaker P-O-Mo bonds connected to both orthophosphate and pyrophosphate units. The replacement of the stronger P-O-P bonds for the weaker Mo-O-P bonds imparts greater covalency to the network and contributes to the lower bond strength as the bond covalence decreases from P-O to Mo-O. The addition of up to 20 mol% SrO does not produce any changes in the Raman spectra and any further disruption of pyrophosphate chains