Silica reinforcing character

Boron oxide particles were incorporated to silicone rubber-based mixes containing fumed silica (reinforcing filler) and reference mineral fillers - aluminum hydroxide, wollastonite, calcined kaolin, mica (phlogipite) and surface modified montmorillonite with dimethyl-dihydrogenatedtal-low quaternary ammonium salt. Acidic character of boron oxide, which can disturb the peroxide curing process, was compensated by addition of magnesium oxide. The influence of boron oxide particles on properties of composites was determined and mechanism of their ceramization process studied. 

As can be seen, the model fits reasonably well the experimental G data but cannot meet the asymmetric shape of G" vs. strain data. The exponent m is depending on the reinforcing character of the filler, as well as the critical strain y. A similar assessment of the Kraus equations with a silica (40 phr) filled polydimethylsiloxane composite yielded the same conclusions regarding the low strain deficiencies of Equation 5.39. For such a silica filled material, fit parameter values were as expected different, i.e., 0.02 and m 0.45 for G (Yo) Yc 0.01 and m 0.35 for G"(Yo)-... 

IPNs are also attractive for development of materials with enhanced mechanical properties. As PDMS acts as an elastomer, it is of interest to have a thermoplastic second network such as PMMA or polystyrene. Crosslinked PDMS have poor mechanical properties and need to be reinforced with silica. In the IPNs field, they can advantageously be replaced by a second thermoplastic network. On the other hand, if the thermoplastic network is the major component, the PDMS network can confer a partially elastomeric character to the resulting material. Huang et al. [92] studied some sequential IPNs of PDMS and polymethacrylate and varied the ester functionalities the polysiloxane network was swollen with MMA (methyl methacrylate), EMA (ethyl methacrylate) or BuMA (butyl methacrylate). Using DMA the authors determined that the more sterically hindered the substituent, the broader the damping zone of the IPN (Table 2). This damping zone broadness was also found to be dependant on the PDMS content, and atomic force microscopy (AFM) was used to observe the co-continuity of the IPN. 

In the field of high temperature thermal insulation advantage is taken of the special powder properties and the amorphous character of fumed silicas. In principle, mixtures of fumed silicas, an opacifier to reflect the heat radiation and a small quantity of mineral fibers for reinforcing are used for temperatures up to 1000°C. It is necessary to density the mixture to approximately 200 g/1 to obtain the minimum of the superposition of gas and the solid state thermal conduction. Important is also the absence of mineralizing ions, like sodium or potassium, to prevent sintering effects. Commercial thermal insulation systems based on this principle have thermal conductivities of approximately 25 mW/mK at a mean temperature of 200°C and of approximately 30 mW/mK at a mean temperature of 4(X)°C. Therefore, they are... 

In sharp contrast with carbon black, there is no standard classification for commercially available silica but elementary particle size and the morphology of the reinforcing object (that we call the "cluster" in the case of silica, keeping the term "aggregate" for carbon black) are recognized as two important parameters for reinforcement performance. However, surface character-isdcs play a larger role in the case of silica than for carbon black, thanks to the rich surface chemistry of silica particles. 

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