Thermal Stability and Flammability of Styrene-Butadiene Rubber-Based (SBR) Ceramifiable Composites
Ceramifiable styrene-butadiene (SBR)-based composites containing low-softening-point-temperature glassy frit promoting ceramification, precipitated silica, one of four thermally stable refractory fillers (halloysite, calcined kaolin, mica or wollastonite) and a sulfur-based curing system were prepared. Kinetics of vulcanization and basic mechanical properties were analyzed and added as Supplementary Materials. Combustibility of the composites was measured by means of cone calorimetry. Their thermal properties were analyzed by means of thermogravimetry and specific heat capacity determination. Activation energy of thermal decomposition was calculated using the Flynn-Wall-Ozawa method. Finally, compression strength of the composites after ceramification was measured and their micromorphology was studied by scanning electron microscopy. The addition of a ceramification-facilitating system resulted in the lowering of combustibility and significant improvement of the thermal stability of the composites. Moreover, the compression strength of the mineral structure formed after ceramification is considerably high. The most promising refractory fillers for SBR-based ceramifiable composites are mica and halloysite.
Calcium and aluminum-based fillers as flame-retardant additives in silicone matrices. III. Investigations on fire reaction
The flame retardancy of silicone composites containing calcium- and aluminum-based fillers has been investigated using several methods including cone calorimeter, Pyrolysis Combustion Flow Calorimeter (PCFC), thermogravimetric analysis and pyrolysis-gas chromatography-mass spectrometry analysis (Py-GC/MS). The fire reaction of precipitated calcium carbonate, calcite, calcium hydroxide, aluminum trihydrate, boehmite and alumina-based composites was correlated mainly with their thermal stability, while for mica and wollastonite-based composites, a barrier effect was also evidenced. The endothermic effect was not established as an efficient flame retardancy mechanism for the silicone composites containing hydrated fillers. Mica composite exhibited the best flame retardancy, in terms of depressed HRR, among all investigated formulations. Finally, a unique behavior was observed during the cone calorimeter test of calcium hydroxide-based composite, which co-crystallization with silica occurs exclusively at high heat flux.
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.