Performances of Concrete under Elevated Curing Temperature

The behaviors of concrete at elevated curing temperature were studied. The test results show that when concrete is cured at elevated temperature , a harmful consequence occurs. The later strength decreases significantly compared to that under normal curing condition. Incorporating silica fume, fly ash and slag or lowering wl c ratio can effectively alleviate this harmful consequence. Comparatively, incorporation of silica fume is the most efficient means to decrease the later strength reduction. The harmful consequence is not caused by the difference in degree of hydration since the degree of hydration is similar between elevated curing temperature and normal curing conthion . The SEM analysis shows that it is the uneven distribution of hydration products caused by elevated curing temperature that leads to the later strength reduction of concrete.     

Migration of hindered amine light stabilizers in automotive clearcoats

The diffusion behavior of two hindered amine light stabilizers (HALS) [bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidinyl)-sebacate and bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-sebacate] in an automotive clearcoat has been quantified via time-of-flight secondary ion mass spectrometry. Diffusion couples made from clearcoats with and without HALS allow for the estimation of the diffusion coefficient of one of the HALS. The high diffusion coefficient of one of the HALS contradicts the presence of HALS gradients in weathered coating systems. This discrepancy is ascribed to a decreasing diffusion coefficient of the HALS in the coating matrix due to a weathering-induced increase in the T _g of the clearcoat.     

The thermal stability of the polymorphs of hexanitrohexaazaisowurtzitane,Part I

Phase transitions in the α-, β-, γ-, and ϵ-polymorphs of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW) have been studied as a function of temperature. Described are the results of high temperature equilibrium solvation studies coupled with Fourier transform infrared spectroscopy (FTIR) for the identification of polymorphic conversion. These results are augmented by data in Part II from differential scanning calorimetry (DSC), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and optical hot stage microscopy⁽⁶⁾. The thermodynamic stability order of ϵ > γ > α-hydrate > β is shown, with the epsilon polymorph the most thermodynamically stable phase of HNTW at room temperature. The existence of multiple α-hydrate phases is shown to complicate the determination of the equilibrium P-T phase diagram of HNIW.