Onset of smoldering in cotton: Effects of density

The ignition temperature for smoldering in cotton has been determined for several densities. Experiments and consistent theoretical calculations show that an increase in density leads to decrease in ignition temperature. Experimentally it is found that repeated heating of a cotton sample results in a higher ignition temperature than for samples heated once, as a result of partial decomposition during heating. For the lowest density investigated, smoldering occurs but is not self-sustained. The smoldering front moves through the cotton with a velocity independent of the density. The mass loss rate due to smoldering increases with density. It can be concluded that density affects both the ignition temperatures and the mass loss rates in a systematic way.     

Microbeam Irradiation as a Simultaneously Integrated Boost in a Conventional Whole-Brain Radiotherapy Protocol

Microbeam radiotherapy (MRT), an experimental high-dose rate concept with spatial fractionation at the micrometre range, has shown a high therapeutic potential as well as good preservation of normal tissue function in pre-clinical studies. We investigated the suitability of MRT as a simultaneously integrated boost (SIB) in conventional whole-brain irradiation (WBRT). A 174 Gy MRT SIB was administered with an array of quasi-parallel, 50 µm wide microbeams spaced at a centre-to-centre distance of 400 µm either on the first or last day of a 5 × 4 Gy radiotherapy schedule in healthy adult C57 BL/6J mice and in F98 glioma cell cultures. The animals were observed for signs of intracranial pressure and focal neurologic signs. Colony counts were conducted in F98 glioma cell cultures. No signs of acute adverse effects were observed in any of the irradiated animals within 3 days after the last irradiation fraction. The tumoricidal effect on F98 cell in vitro was higher when the MRT boost was delivered on the first day of the irradiation course, as opposed to the last day. Therefore, the MRT SIB should be integrated into a clinical radiotherapy schedule as early as possible.     

Analysis of defect mechanisms in nonstoichiometric ceria–zirconia by the microwave cavity perturbation method

In this microwave study, the defect chemistry of ceria–zirconia solid solutions (CZO, Ce_1−yZr_yO_2−δ) was investigated at high temperatures by a resonant microwave method. Specifically, the effects of temperature and Zr content on the dielectric properties and defect chemistry mechanisms in CZO were analyzed. Experiments were performed on a series of different CZO powders (y = 0.2, 0.33, 0.50, 0.67). Measurements at 600°C and different oxygen partial pressures (p_O2 = 10⁻²⁶–0.2 bar) confirm a dominant n-type conduction of small-polarons in CZO due to the preferred formation of oxygen vacancies, which is also supported by a multimodal analysis. Polarization losses were found to be negligible in the GHz range. Furthermore, an increased relative permittivity was observed in CZO, which correlates with the concentration of oxygen vacancies in CZO. Our microwave study is the first to provide a comprehensive data set for the dielectric properties of CZO powder sample in a wide range of different conditions. In addition, the connection of dielectric properties to CZO defect chemistry mechanisms is presented. The results are in good agreement with findings in the literature and may contribute to a better understanding of microwave-based state diagnosis of CZO-based materials, as it discussed for three-way catalysts.     

A radiant heat flux apparatus for measuring the thermal response of polymeric materials to high temperatures

An efficient and economical experimental apparatus has been designed and built which delivers a known radiant heat flux and simultaneously measures the in-depth temperature profiles in polymeric materials. Test samples are maintained in a controlled environment and are heated radiantly by a silicon carbide heating element capable of producing heat fluxes up to 7.0 cal/cm²-sec. The experimental data produced by this device are extremely accurate and therefore are suitable for use in verification of numerical models. The utility of the apparatus was demonstrated by measuring temperature profiles to approximately 1000°C in a glass-filled phenol-formaldehyde resin.     

Mechanisms responsible for the onset of selective laser flash sintering of 8-YSZ

Selective laser flash sintering (SLFS) is a variation of flash sintering where the only external heat source is a scanning laser. The scanning laser locally heats a region of the sample between two electrodes, initiating measured current flow at a threshold electric field and laser energy density. This study focuses on understanding how charge transport occurs during stage I SLFS in 8 mol% yttria stabilized zirconia. Two potential charge transport mechanisms are considered: (1) a continuous current moving along a hot line between electrodes and (2) charge transported in a discrete bundle within a hot spot, localized to the area under the laser beam. Two laser scan patterns are employed to experimentally determine how charge is transported during stage I SLFS. Numerical modeling is used to estimate the temperatures at which SLFS initiates, which allows the calculation of charge carrier densities and mobilities relevant for the onset of SLFS. Results demonstrate that both a discrete bundle of charges and continuous flow of charge carriers contribute to the current at the onset of SLFS.     

High energetic materials: Reaction of Azides with Dioxygenyl Salts

The reactivity of sodium azide, activated sodium azide and hydrazinium azide towards various dioxygenyl salts was studied. Under no circumstances the formation of dioxygenyl azide, O₂N₃, could be observed. This is in agreement with high level quantumchemical ab initio computations at correlated level (MP2, PMP2, CISD), predicting the decomposition of hypothetical O₂⁺(g)/N₃⁻(g) to be thermodynamically highly favorable (MP2: −326; PMP2: −328; CISD; −369 [kcal/mol]). The combustion of O₂BF₄ with either N₂H₅N₃ (spontaneous reaction on contact in a coaxial solid-propellant system) or NaN₃ (safe to handle, highly exothermic reaction after ignition) is discussed in terms of high-energy-density materials (HEDM).      

Non-oxide CMC fabricated by Fused Filament Fabrication (FFF)

The present study introduces an approach to additively manufacture non-oxidic Ceramic Matrix Composites (CMCs) by the Material Extrusion (MEX)-based Fused Filament Fabrication. Therefore, highly SiC particle filled thermoplastic filaments were developed containing short fibers and/or long fibers to maintain shape during the thermal treatment and exhibiting flaw tolerant behavior. Polymer Infiltration and Pyrolysis (PIP) was applied to densify the microstructure. It is shown that a low content of long fibers of about 5 % can already exhibit damage tolerance comparable to steel reinforced concrete. Thus, the mechanical behavior is different to conventional fiber composites with significant higher fiber volume content. Nevertheless, these results enable new opportunities for producing advanced complex CMC components by means of Additive Manufacturing (AM).