Mechanical strength oxygen effect

Moisture and oxygen must be rigorously excluded from the system if the synthesis is to be successful. Inadvertant introduction of trace protic impurities of metal oxides during the synthesis leads to the formation of polydimethylsilioxane homopolymer. This material, present in even small amounts, is detrimental to the mechanical properties of the final block copolymer. This effect can be illustrated by deliberately including known amounts of polydimethylsiloxane in a block copolymer of demonstrated mechanical strength. These effects are summarized in Table I. 

Figure 2 shows isothermal oxidation curves of TiAl and TiAl-0.2Zr in oxygen under atmospheric pressure [31], Here, Am-A1 means the mass gain due to oxidation per surface area of the original specimen. It can be understood that the addition of 0.2Zr is very effective to decrease the oxidation rate at 1200 and 1300 K. However, this effect disappears at 1350 and 1400 K. Thus, it can be said that the effect of Zr addition is limited to temperature up to around 1300 K. This temperature is, however, much higher than the maximum application temperature considered which is limited by the mechanical strength of TiAl-base materials at present. 

Wu, Z Thursfield, A., Metcalfe, I. and Li, K. (2012) Effects of separation layer thickness on oxygen permeation and mechanical strength of DL-HFMR-ScSZ. Journal of Membrane Science, 415-416,229-236. 

The thermal stability of polyethylene (PE) decreases sharply in the presence of oxygen. This effect is clearly observed at elevated temperatures, which promote rapid development of the oxidative processes that essentially decrease the mechanical properties of PE. Thus, low-pressure PE (0.93 g/cm ) completely loses its mechanical strength after exposure at 100 "C for 48 hours in air the impact viscosity of such a material is only 7% of its initial value [1]. 

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