Thermal analysis of polyurethane elastomers matrix with different chain extender contents for thermal conductive application

Polyurethane elastomers (PUR) based on polypropylene glycol and 4,4′-diphenylmethane diisocyanate were prepared with various monoethylene glycol (mEG) contents. The aim of this study is to find a reliable polymer matrix for composites of improved thermal conductivity and testing fully in order to collect knowledge about its structure. Thermal conductivity was improved from 0.255 to 0.329 W m^?1 K^?1 when increasing chain extender content. This attributed to a high appearance crystalline ordering level when adding high mEG content. Differential scanning calorimetry revealed a low transition temperature of soft segment at the same temperature around ??64 °C, due to constant polyol content. The enthalpy of melting increases with increasing mEG content. This is due to the increasing crystalline phase and hard segment phase separation within the PUR structure. Dynamic mechanical analysis results show the glass transition temperature of soft segment in the same temperature range between ??57 and ??52 °C and intensity peak of tanδ tends to decrease when mEG content was increased. On the other hand, the glass transition temperature of hard segment tends to increase from 10 to 93 °C and has high intensity peak of tanδ with increasing mEG content. Increasing the chain extender content can be enhancing the hard segment length in PUR structure and affecting both soft segment motion and hard segment motion. Increasing hard segment length might be obstructing soft segment motion and influence hard segment motion which is hard to move at low temperatures. Phase separation of soft and hard segment clearly observed using the DMA technique.

     

Revelation of Causes of Colour Change in Beryllium-Treated Sapphires

Blue sapphires are treated with Be in oxidizing atmosphere to change the blue colour into yellow. Untreated and Be-treated samples are examined using laser ablation inductively coupled-plasma-mass spectrometry （LA-ICP- MS）, electron spin resonance （ESR） and ultraviolet-visible （UV-vis） spectroscopy. The results show that the yellow colouration in Be-heated blue sapphires is not due to Be diffusion from the surface of sapphire. Be behaves as a sole catalyst in this process. We find that the charge transfer between the ferrous （Fe^2＋） and ferric （Fe^3＋） is the reason of the colour change. The above conclusions are confirmed by ESR measurements to determine the connections between the Fe3＋ ions before and after Be-treated heat treatments.