EFFECTS OF POROSITY ON RE-IGNITION CHARACTERISTICS OF A SURROGATE MATERIAL

This study is part of a larger project which aims at studying the re-ignition behaviour of charring solid fuels under fire conditions. The main objective of this part of the work was to investigate the role of material porosity on the re-ignition characteristics of the fuel. For this purpose, experiments were carried out on a set of surrogate ceramic samples to de-couple the pyrolysis and combustion processes from those associated with heat transfer. The surrogate samples were made out of magnesia silica ceramic with porosity levels of 72.9%, 53.5%, and 35%. Experiments were conducted in a modified cone calorimeter over a range of heat fluxes between 40 to 60 kW/m2. The re-ignition delay was found to be significantly affected by the material porosity. The higher the porosity, the longer the re-ignition delay time. For samples having the same porosity level, the re-ignition delay time was primarily a function of sample thickness and the external heat flux. Thicker samples generally showed shorter reignition delays. The results of this study will be used in future work to quantify the impact of porosity on the re-ignition behaviour of real samples

Effect of Porosity on Re-ignition Characteristics of a Surrogate

ABSTRACT This study is part of a larger project which aims at studying the re-ignition behaviour of charring solid fuels under fire conditions. The main objective of this part of the work was to investigate the role of material porosity on the re-ignition characteristics of the fuel. For this purpose, experiments were carried out on a set of surrogate ceramic samples to de-couple the pyrolysis and combustion processes from those associated with heat transfer. The surrogate samples were made out of magnesia silica ceramic with porosity levels of 72.9%, 53.5%, and 35%. Experiments were conducted in a modified cone calorimeter over a range of heat fluxes between 40 to 60 kW/m 2 . The re-ignition delay was found to be significantly affected by the material porosity. The higher the porosity, the longer the re-ignition delay time. For samples having the same porosity level, the re-ignition delay time was primarily a function of sample thickness and the external heat flux. Thicker samples generally showed shorter reignition delays. The results of this study will be used in future work to quantify the impact of porosity on the re-ignition behaviour of real samples

Structure, Stability, and (Non)Reactivity of the Low-Index Surfaces of Crystalline B2O3−I

Diboron trioxide (B2O 3) assumes critical importance as an effective oxidation inhibitor in prominent chemical applications. For instance, it has been extensively used in electrolysis and ceramic/glass technology. Results are presented of accurate quantum mechanical calculations using the PW1PW hybrid HF/DFT functional of four low- index surfaces of the low-pressure phase of B2O : (101), (100), (011), and (001). Bond lengths, bond angles, and net Mulliken charges of the surface atoms are analyzed in detail. Total and projected density of states as well as surface energies are discussed. The occurrence of tetrahedral BO 4 units on the lowest energy structures of two of these surfaces has been demonstrated for the first time. The corresponding surface orientations incur larger energies in reference to the two orientations featuring only BO3 units. All of the four investigated lowest energy structures have no dangling bonds, which reasonably relates to the experimentally observed low reactivity of this compound. Findings in this paper pave the way for potential interest in the perspective of future studies on the surfaces of amorphous B2O3, as well as on the hydroxylation of both crystalline and amorphous B2O3

Structural thermal stability of graphene oxide-doped copper-cobalt oxide coatings as a solar selective surface

3d transition metal oxides based thin film coatings such as copper-cobalt oxides exhibit high absorption in the visible region and low emittance in the infra-red to far-infra-red region of the solar spectrum which is favourable for use as potential selective surface materials in photothermal devices. These materials have the potential to minimize heating while increasing absorption in the operative spectrum range and therefore achieve higher solar selectivity. A series of mixed copper-cobalt metal spinel oxides (CuxCoyOz) doped with graphene oxide thin films were deposited on commercial grade aluminium substrates using a sol–gel dip-coating technique at an annealing temperature of 500 °C in air for 1 h. Characterizations of the synthesized films were carried out by high temperature synchrotron radiation X-ray Diffraction (SR-XRD), UV-Vis, Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron microscopy (XPS) techniques. High thermal stability of coatings with multiple phases, binary and ternary metal oxides, was defined through SR-XRD study. FTIR analysis shows moderate (<80%) to high (up to 99%) reflectance in the infra-red region while the UV-Vis investigations demonstrate that, in the visible region, solar absorption increases gradually (up to 95%) with the addition of graphene oxide to the CuxCoyOz coatings. With the incorporation of 1.5 wt% of graphene oxide to the copper-cobalt oxide coatings, a high solar selectivity of 29.01 (the ratio of the average solar absorptance in visible and the average thermal emittance in infra-red to far infra-red region; α/ε) was achieved

Multipurpose overhead compressed-air foam system and its fire suppression performance

Peer reviewed: YesNRC publication: Ye

An effective fixed foam system using compressed air

Peer reviewed: YesNRC publication: Ye

Sequestration of atmospheric CO₂ in a weathering-derived, serpentinite-hosted magnesite deposit: ¹⁴ C tracing of carbon sources and age constraints for a refined genetic model

The Attunga magnesite deposit is texturally and geochemically distinct from other spatially associated, serpentinite-hosted magnesite deposits in the Great Serpentinite Belt, New South Wales, Australia, such as the hydrothermal Piedmont magnesite deposit or widespread silica–carbonate alteration zones. Cryptocrystalline magnesite at Attunga predominantly occurs in nodular masses and irregular, desiccated veins that occupy pre-existing cracks and pore spaces resulting from fracturing and weathering of the host rock. Incipient weathering of the serpentinite host rock is accompanied by a decrease in volume and the mobilisation of MgO and CaO from the serpentinite. Pore spaces and permeability created during weathering and fracturing of the host rock provide access for CO₂-, MgO- and CaO-bearing meteoric waters which led to an increase of volume during carbonation. SiO₂ is only mobilised during more advanced stages of weathering and late stage infiltration of SiO₂-bearing waters and precipitation of opal-A lead to local silicification of the serpentinite. Stable carbon and oxygen isotope signatures show that nodular magnesite at Attunga has formed under near-surface conditions incorporating carbon from C3-photosynthetic plants and oxygen from meteoric waters. Radiocarbon concentrations in the magnesite preclude subducted carbonaceous sediments as the source of carbon and, together with distinct stable carbon and oxygen isotope signatures, indicate that magnesite at Attunga precipitated from low temperature, supergene fluids. Even though there is no direct geochemical and isotopic evidence, some textural observations and field relationships for weathering-derived magnesite deposits suggest the prior existence of a possibly Early Triassic, hydrothermal magnesite deposit at Attunga. The presence of a pre-existing magnesite deposit may entail the localised formation of the weathering-derived magnesite at Attunga, but the predominance of weathering-related textures and geochemical signatures indicate that weathering is the integral magnesite mineralisation process at Attunga. Conventional radiocarbon ages of about 50 ka represent a maximum age constraint for the formation of the magnesite deposit during Quaternary weathering. A significant amount of atmospheric CO₂ has been sequestered via the biosphere and carbonation of serpentinite at Attunga

Kinetic modeling of low-temperature oxidation of coal

A kinetic model has been developed for determining the rate of oxygen consumption and production of carbon oxides during the oxidation of coal at low temperatures (i.e. <100°C), based on current understanding of the mechanism of coal oxidation. The chemical reactions considered in the model include two parallel sequences consuming oxygen and two thermal decomposition pathways producing carbon oxides. The resulting rate expressions reflect the contributions of various reactions consuming oxygen and producing carbon oxides and predict the effects of temperature, oxidation time and [O₂] in the gas phase. The general form of the rate expressions confirms that chemisorption is relatively fast, only playing an important role at the early stage of coal oxidation. With the formation of stable and unreactive oxygenated complexes in a coal’s structure, the oxidation of coal is dominated by thermal decomposition of oxygenated complexes