The thermal behavior of the oxide ion-conducting solid
electrolyte
Bi4YbO7.5 was investigated using a combination
of variable temperature X-ray and neutron powder diffraction, thermal
analysis (DTA and TGA), and ac impedance spectroscopy. The title compound
shows a fluorite-type structure throughout the measured temperature
range (20–850 °C), with a phase separation at ca. 600
°C into a cubic δ-type phase and an orthorhombic phase
of assumed stoichiometry Bi17Yb7O36. This type of transition is a relatively common feature in bismuth
oxide-based systems and can limit their practical application. Here,
the transition was carefully studied using isothermal measurements,
which showed that it is accompanied by changes in oxide-ion stoichiometry,
as well as significant disorder in the oxide ion sublattice in the
δ-type phase. These results correlate with the observed electrical
behavior. Analysis of the total neutron scattering through reverse
Monte Carlo (RMC) modeling reveals details of the coordination environments
for both cations. The oxide-ion vacancy distribution seems to be consistent
with a favoring of ⟨100⟩ vacancy pairs, although ⟨110⟩
vacancy pairs exhibit the highest frequency as they have the maximum
likelihood. A vacancy ordering model based on three vacancies per
cell is presented.
Using one-step method, rigid polyurethane foams were made, modified with developed fire retardant systems containing halogen-free flame retardants and nanofillers in the form of multi-walled carbon nanotubes or nanoscale titanium dioxide. The materials were subjected to a test using a cone calorimeter and smoke-generating chamber, and selected samples were further analyzed via thermogravimetry and oxygen index. Moreover, the products of thermal degradation of selected samples were identified using gas chromatography with mass spectrometer. Conducted flammability tests confirmed the presence of a synergistic effect between the used nanofillers and halogen-free flame retardants. It has been observed that the carbonized layer, the formation of which favored the presence of nanoadditives, inhibits the combustion process. Furthermore, nanofillers influenced favorably reduction in the amount and the number of occurring products of thermal degradation.
Rigid polyurethane foams were obtained using two types of renewable raw materials: bio-polyols and a cellulose filler (ARBOCEL® P 4000 X, JRS Rettenmaier, Rosenberg, Germany). A polyurethane system containing 40 wt.% of rapeseed oil-based polyols was modified with the cellulose filler in amounts of 1, 2, and 3 php (per hundred polyols). The cellulose was incorporated into the polyol premix as filler dispersion in a petrochemical polyol made using calenders. The cellulose filler was examined in terms of the degree of crystallinity using the powder X-ray diffraction PXRD -and the presence of bonds by means of the fourier transform infrared spectroscopy FT-IR. It was found that the addition of the cellulose filler increased the number of cells in the foams in both cross-sections—parallel and perpendicular to the direction of the foam growth—while reducing the sizes of those cells. Additionally, the foams had closed cell contents of more than 90% and initial thermal conductivity coefficients of 24.8 mW/m∙K. The insulation materials were dimensionally stable, especially at temperatures close to 0 °C, which qualifies them for use as insulation at low temperatures.
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