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A few Aspects of the Current Understanding of DPF Materials Thermal and Mechanical Properties
(2016)
Bi-continuous porous ceramics for filtration applications possess a particularly complicated microstructure, whereby porosity and solid matter are intermingled. Moreover, they very often display a microcrack network, resulting from the strong anisotropy of the microscopic coefficient of thermal expansion (CTE). Mechanical, thermal, and filtration properties, they all strongly depend on the morphology of both solid matter and porosity, and on the degree of microcracking (also, the microcrack density), which is in its turn tightened to the grain size.
Recent industrial and academic research has enormously progressed in understanding the microstructure-property-performance relationships existing in these complicated materials:
- Using 3D computed tomography (CT) at different resolutions, and several X-ray refraction-based techniques, porosity and pore orientation could be quantitatively evaluated (in the example of cordierite).
- Neutron and X-ray Diffraction has been instrumental to disclose a) the non-linear character of the stress-strain response, and b) the negative CTE of these materials, and its consequences on the materials properties;
- Analytical and numerical models have been elaborated to rationalize these behaviours in terms of microcracking and microstructural features.
Here these results will be reviewed, and a outlook at (some of the) outstanding problems will be given.
About 80 % of all fire fatalities in Germany occur in fires in homes1. UK statistics show that living and bed room fires are more often responsible for fatalities than kitchen fires although kitchen fires occur much more often2. It has been known for some time that modern materials tend to burn differently from older materials and it has been acknowledged that the amount of combustible plastics in homes has increased significantly over the last decades3-7. To investigate the influence of modern furniture and ventilation conditions of fires in homes a series of four large scale tests in two living rooms with adjacent rooms was performed by BAM and the Frankfurt fire service8. Two living rooms, one with older furniture and one with modern furniture were tested twice each. Each test started with the ignition of a paper cushion on an upholstered chair. The influence of modern materials on the fire development was investigated as well as the influence of the ventilation on the fire development. Two tests with closed windows and two tests with open windows were performed. Temperatures were measured in the living rooms and the adjacent rooms, gas compositions were measured in the adjacent rooms and videos were taken in all rooms. The ventilation as well as the different materials influenced the fire development regarding temperatures in the rooms and smoke production and composition significantly. The fire in the living room with modern furniture developed faster than the same setting with older furniture. More ventilation (open window) led to higher temperatures in the rooms and faster fire development as well. Smoke gas composition was measured in the adjacent rooms to assess the positive effect for a person being in the adjacent room and not in the room of fire origin. In all settings an upholstered chair was the first burning item. The modern upholstered chair was investigated in three pre-experiments under different conditions to enhance the understanding of the living room fires. The measured mass losses and derived mass loss rates have been used for numerical modelling of the pre-experiments.