No abstract

Negative thermal expansion (NTE) is an abnormal physical behavior that has promising applications for high precision thermal control. Since Prussian blue analogues have the two central linking atoms of -C≡N-, they have large structure exibility and are suitable to explore new NTE materials. However, understanding the nature of structure exibility from the point of view of chemical bonding is important and urgent. Here, we adopt for the rst time rst-principles calculations to predict that the cubic TiCo(CN) 6 and ScCo(CN) 6 have NTE behavior. The calculated results for M in MCo(CN) 6 (M = Fe, Ti and Co) indicated that the Sc-N bond is the strongest, but with the weakest direction dependence among the M-N bonds in the three systems. The lattice dynamics calculations results revealed that the low-frequency phonon vibration modes for NTE in MCo(CN) 6 have much stronger relationship with the M-N bond feature. The present work reveals the important role of the related bond in the NTE open-framework materials.

No abstract

No abstract

Abstract:Corrosion of steel bars in concrete structures is initiated as a result of concrete carbonation and/or 9 chloride intrusion, and influenced by their interaction. This paper presents an experimental investigation into the 10 effect of chloride ions on carbonation of cement paste by means of X-ray CT techniques and mercury intrusion 11 porosimetry(MIP), which is benchmarked by the conventional phenolphthalein method. A group of the cement 12 paste cylinders with different amounts of chlorides ions were manufactured and cured before they were subjected 13 to an accelerated carbonation process in a conditional cabinet regime for different ages. The carbonation front of 14 the cement paste was first evaluated using phenolphthalein method. This was followed by an investigation of 15 microstructure evolution of the cement paste using XCT and MIP techniques. The experimental results show that 16 the carbonation of a cement paste increases with its water to cement ratio and with carbonation ages, but decrease 17 with its amount of chloride ions. In particular, it has been found that increases of chloride ion of a cement paste 18 refine its porous structures, decrease its porosity and eventually mitigate its carbonation rate. The relevant results 19 can be referred to for durability design and prediction of reinforced concrete structures. 20