Zhang Yangyang,Sun Yanjie,Shen Peiliang,Lu Jianxin,Cai Yamei,Poon Chi Sun
The direct use of both seawater and sea sand in concrete production has been becoming attractive for some marine and coastal engineering where the availabilities of freshwater and river sand are limited. To further expand the use of seawater (e.g., using seawater as both mixing and curing water), this work provided fundamental research regarding the effects of using seawater as the mixing and curing water on the physicochemical properties of Portland cement pastes. The sub-samples at different depths of the seawater mixing and curing samples were extracted and separately analyzed. The chemical changes were quantitatively investigated, and the relation between the physical behaviors and the chemical changes was studied. The results showed that in the outer region of the samples, the ettringite content was significantly increased, but the content of Friedel’s salt was slightly reduced. Moreover, a large amount of calcium hydroxide was dissolved, but correspondingly, magnesium hydroxide (MH) crystals with various particle sizes were formed. Also, the sodium ions in the seawater were incorporated into the structure of calcium silicate hydrate gel, resulting in the formation of silica dimers with a shorter silica chain and the increase of nanopore volume (increasing by 22% in the inner region and 36% in the outer region). In addition, seawater increased the ion transport rate, but the blocking effect of the MH crystals on the samples largely decreased the rate. The changes in the crystalline and amorphous hydration products potentially influenced the strength development.
Wang Meng-Fei,Lai Hua-Jun,Liang Ji-Sheng,Chen Jun-Liang,Ding Wang-Yang,Zhou Qi,Peng Ying,Liu Cheng-Yan,Miao Lei
SiGe-based thermoelectric (TE) materials have gained increasing interests due to their low maintenance costs, environmental friendliness and long lifespan. However, the intrinsically high thermal conductivity of Si-based materials also results in poor TE properties. In this investigation, a zirconia (ZrO 2 ) composite strategy was applied to an n-type SiGe alloy, tremendously elevating its TE performance. After mechanical alloying and spark plasma sintering (SPS) processes, the ZrO 2 induced the formation of nanopores in the SiGe matrix via phosphorus adsorption. Moreover, such increase in porosity enhanced the phonon scattering and dramatically suppressed lattice thermal conductivity, from 2.83 to 1.59 W·m −1 ·K −1 at 873 K. Additionally, reduced phosphorus doping led to an increase in Seebeck coefficients and a relatively minor decrease in electrical conductivity. The power factor didn’t deteriorate significantly, either, as its maximum of ~ 3.43 mW·m −1 ·K −2 was achieved at 873 K with (Si 0.8 Ge 0.2 ) 0.097 P 0.03 (ZrO 2 ) 0.003 . In short, a peak figure of merit ( ZT ) of ~ 1.27 at 873 K and an average ZT ~ 0.7 from 323 to 873 K were obtained. This study demonstrates that the electrical and thermal transportation of SiGe material can be synergistically tuned by compositing ZrO 2 , illustrating a novel strategy to optimize the TE properties of bulk materials. Graphical abstract
危险品化学品经营许可证（带存储）