Search results for "Solid"
showing 10 items of 3575 documents
Doped ZnS:Mn nanoparticles obtained by sonochemical synthesis.
2010
A study of sonochemically synthesized ZnS:Mn nanoparticles is presented. The particles prepared at low rf power (about 20 W) and room temperature coalesce to form morphologically amorphous large species (30-100 nm in diameter). As the power is increased in the range from 20 to 70 W, and the solution temperature is raised to 60 to 80 degrees C, finer particles are produced with the size ranging from 2 to 20 nm and improved crystallinity. The results indicate the dispersion of the Mn(2+) ions at near-surface sites in the particles. It is shown that the sonochemically fabricated particles approach the quality of the ones obtained by a standard chemical route and show a reasonable luminescence …
Absorption edge in silica glass
2005
Measurements of optical absorption in the v-UV range in a variety of silica glass are used to determine the width of the absorption edge (Urbach energy). Measured values range from 60 meV up to 180 meV. So high a variability over silica types is tentatively ascribed to the different disorder degree, which characterizes different materials.
Heat Capacity and Dielectric Properties of the PNN-PT Ferroelectric Ceramics
2012
A study of dielectric permittivity and heat capacity of the (1-х)PbNi1/3Nb2/3O3 – хPbTiO3 solid solution system (x = 0.3, 0.4, 0.5) within the 290–700 K range is reported. Temperatures of phase transitions Tm determined from maximums of dielectric permittivity ϵ depends on the content of PbTiO3. A broad phase transition is shown to proceed in the 0.7PbNi1/3Nb2/3O3–0.3PbTiO3 composition around 312 K. Specific to phase transitions anomalous heat capacity is observed at Т ≈ 520 K in all compositions studied.
Thermal properties of ferroelectric 0.7PbNi1/3Nb2/3O3–0.3PbTiO3ceramics
2013
A study of heat capacity as function of temperature of the 0.7PbNi1/3Nb2/3O3–0.3PbTiO3 solid solution within the 120–800 K range is reported. Broad anomalies on the curve of heat capacity are revealed in the 250–450 K and 450–650 K intervals peaking at 520 K and a λ-anomaly at T ≈ 225 K. Results are discussed with account for dielectric and structural data.
Creation of paramagnetic defects by gamma irradiation in amorphous silica
2000
An electron spin resonance (ESR) study of the defects induced by γ-rays in various types of natural and synthetic silica is reported. Three main structures were identified: the E′ center and two doublets with field splitting of 7.4 and 11.8 mT, respectively, both centered around the E′ center signal. Another structure partially overlapping the E′ center line was also detected, consisting in three peaks with a maximum field splitting of 1.36 mT. We have investigated the growth kinetics of these centers on increasing the y-ray accumulated dose. In all investigated materials the growth of E′ centers can be interpreted as caused by γ-activated conversion of one or more precursors. The 1.36 mT s…
SPICE model for resistive gas and odour sensors
1999
A generalised PSPICE model of resistive gas/odour sensors is presented. The model simulates the response of both polymeric and metal oxide devices, as well as an integrated resistive heater that is used to set the operating temperature. In both cases there was good agreement between the observed responses and the PSPICE simulated responses to rectangular pulses of gases. The PSPICE model is not only simpler and faster to use than analytical solutions, but also should permit the rapid prototyping of associated drive circuitry.
Dry synthesis of B-MFI, MTN- and MTW-type materials
1997
Abstract B-MFI and MTN-type materials were synthesized via the fluoride route from dry powders in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO 2 · Al 2 O 3 gels at 700°C were transformed into MTN-type material in the presence of dried NH 4 F and TMACl. Amorphous precursors obtained by drying SiO 2 gels at 700°C were transformed into B-MFI in the presence of dried NH 4 F, B 2 O 3 and TPABr. Water is formed as a reaction product. However, the water vapor pressure is appreciably below the water vapor saturation pressure under the given reaction conditions. In addition, syntheses using seed crystals were carried out successfully.
Fundamentals of photocatalysis: The role of the photocatalysts in heterogeneous photo-assisted reactions
2021
Abstract This chapter provides some general definitions of heterogeneous photocatalysis and evaluates its performance, which is influenced by the parameters most closely related to the properties of the solid material that acts as a photocatalyst. It also discusses aspects of heterogeneous photocatalytic reactions and explains the properties that influence photoactivity. Finally, the chapter examines thermodynamic and kinetic features, including mechanistic details and parameters to define the reaction rate and correlates them to the effects of the interaction of light with the photocatalyst surface and adsorption-desorption of species involved in heterogeneous photo-assisted reactions.
A life cycle scenario analysis of different pavement technologies for urban roads.
2019
In the past, lowest price was the award criterion, given that structural capacity and safety were assured. In the last years, environmental, energy, and long-term impacts have been introduced (climate change, resource depletion, energy consumption, generated solid waste, discharged water, and emissions). Unfortunately, the introduction of new pavement technologies and materials (i.e., waste plastics) affects maintenance and rehabilitation processes and call for accurate and timeliness studies and criteria. Consequently, this paper presents an energy and environmental assessment of an Italian urban road and considers different material-related scenarios that fully comply with emerging techno…
I beni relazionali nei gruppi di formazione universitaria: un contributo di ricerca
2009
The aim of the study is to identify relational goods in the transcriptions produced by sound recording of a median group experience at University of Palermo. In particular, the present work proposes to analyze the most representative qualities of this phenomenon and summarized them in the following indicators: 1) emergent fact; 2) recognition; 3) solidarity. Our theoretical hypothesis is based on the fundamental group analytic epistemological assumption that defines relation as the beginning of the development of human psyche and considers the Group a primary matrix in which originate subjectivity and human relationship (Lo Verso, 1994; Mitchell, 2000). Therefore, the group becomes the elec…