Pressure-induced novel structure with graphene-like boron-layer in titanium monoboride

The recent discovery of the novel boron-framework in boron-rich metal borides with complex structures and intriguing features under high pressure has stimulated the search into the unique boron-network in the metal monoborides or boron-deficient metal borides at high pressure. Herein, based on the particle swarm optimization algorithm combined with first-principles calculations, we thoroughly explored the structural evolution and properties of TiB up to 200 GPa. This material undergoes a pressure-induced phase transition of $Pnma$ $\to $ $Cmcm$ $\to $ $Pmmm$. Besides of two known phases $Pnma$ and $Cmcm$, an unexpected orthorhombic $Pmmm$ structure was predicted to be energetically favored in the pressure range of 110.88-200 GPa. Intriguingly, the B covalent network eventually evolved from a one-dimensional zigzag chain in $Pnma$-TiB and $Cmcm$-TiB to a graphene-like B-sheet in $Pmmm$-TiB. On the basis of the microscopic hardness model, the calculated hardness ($H_{\rm v}$) values of $Pnma$ at 1 atm, $Cmcm$ at 100 GPa, and $Pmmm$ at 140 GPa are 36.81 GPa, 25.17 GPa, and 15.36 GPa, respectively. Remarkably, analyses of the density of states, electron localization function and the crystal orbital Hamilton population (COHP) exhibit that the bonding nature in the three TiB structures can be considered as a combination of the B-B and Ti-B covalent interactions. Moreover, the high hardness and excellent mechanical properties of the three TiB polymorphs can be ascribed to the strong B-B and Ti-B covalent bonds.     

瞬态发射光谱法研究正十二烷燃烧反应特性

采用加热激波管和增强型CCD瞬态光谱测量系统,在波长范围200~900nm,点火压力4.0atm,点火温度(1 200~1 300)K,当量比0.5、1.0和2.0的条件下,实时测得了正十二烷/空气和正十二烷/氧气/氩气燃烧过程的瞬态发射光谱.结果表明:燃烧过程在此波段内的主要发射光谱带归属于反应中间产物OH、CH和C2自由基;在不同当量比条件下,燃烧过程中OH(306.4nm)/CH(431.4nm)/C2(516.4nm)的光谱强度显著不同,贫油情形有利于OH自由基生成,富油情形有利于C2自由基生成;浴气的不同会导致燃料燃烧温度的不同,从而引起燃料燃烧发射光谱的不同.所测燃烧反应自由基的时间分辩光谱直观反映出正十二烷燃烧过程中重要中间产物OH、CH和C2的变化情况.研究结果有助于认识正十二烷燃烧反应特性和验证其燃烧反应机理.     

漆黄素与酸、碱、盐反应的动态紫外吸收光谱

采用ICCD动态光谱探测系统,对6.25×10-5 mol/L浓度漆黄素分别与不同浓度盐酸溶液、氢氧化钠溶液和硝酸钠溶液的反应过程进行了实时吸收光谱测量。结果显示,漆黄素与不同浓度的NaOH溶液都能发生反应,特别与浓度0.04mol/L的NaOH溶液反应最为明显,反应过程中有中间产物的331nm和393nm光谱吸收峰出现;漆黄素只与部分浓度NaNO3溶液发生反应,但与0.5mol/L的NaNO3溶液反应非常明显。这些反应的最终产物都非常稳定。本实验首次发现6.25×10-5 mol/L漆黄素还能与一个特定浓度6mol/L的HCl溶液发生反应,并观察到了其最终产物在237nm和314nm的两个吸收光谱峰。本文研究结果为了解漆黄素与酸、碱、盐等物质反应的特性提供了实验依据。