Effect of environmental media on ablation rate of stainless steel under femtosecond laser multiple raster scans

We investigate the influence of environmental media on ablation rate of AISI 443 stainless steel under femtosecond(fs) laser single raster scan and multiple raster scans in air, water, and methanol. Meanwhile, the development of ablation rate with the change of fs laser-induced surface morphology in the three environmental media is comparatively studied. The results show that environmental media as well as fs laser-induced morphology control the ablation rate with the increasing number of raster scans(N). Under single raster scanning(N = 1), the ablation rate is higher in liquid than in air due to the confinement of plasma, laser-induced shockwaves, and bubble-related mechanical forces. However, under multiple raster scans, the variation in ablation rate with the increase in N in these three environmental media is complicated and is largely determined by the surface morphology induced by previous fs laser ablation. When N > 20, the ablation rate is much higher in air than in liquids due to preferential ablation caused by the formation of nanostructures-textured mound-shaped microstructures in air. Besides, the redeposition of ejected ablated materials is also an important factor that affects the ablation depth.     

对初中化学第六章教学的几点意見

初中化学课本第六章氧化物、酸、碱和盐,这一章是在前几章的基础上,对物质系统研究的开始。课本对各类物质作了较系统的介紹,这为学生今后的继续学习打下了基础。在这一章的教学中主要关键是注意知识的系统性,除此以外,根据我校的教学经验,在这一章的教学中还应注意以下几点: 第一点是对盐的性质的教学,課本中对盐的性质只在物理性质方面作了簡单的介紹,说明所有的盐都是固体,通常是規则的晶体,許多种盐具有颜色,各种盐的溶解度各不相同。課本中根本沒提到盐的化学性质,根据需要我认为有补充盐的化学性质的必要。系統讲解盐的化学性质时,一方面对酸和碱的部分化学性质作了复习,同时也将盐的知识充实系统了,更重要     

微波低温制备Mg2Si0.4Sn0.6-yBiy热电材料的传输机理

德拜弛豫理论表明, 在频率为2.45 GHz的外加交变电磁场的作用下, 微波对极性分子的极化过程约为10^-10 s, 因此利用微波固相反应可以在短时低温条件下制备出纳米粉体材料. 本文以MgH₂代替Mg粉, 利用微波固相反应在低温下制备了Mg₂Si_0.4Sn_0.6-yBi_y (0 ≤y ≤q 0.03)固溶体, 并结合单带抛物线计算模型对其热电传输机理进行了分析. 研究结果表明: 利用该工艺可以有效抑制Mg的挥发和MgO 的生成, 在400 ℃保温15 min内即可完成MgH₂与Si粉和Sn粉的固相反应, 获得片层间距为100 nm的超细化学计量比产物; 杂质Bi的引入可以有效增加载流子浓度, 并引起晶格畸变, 在晶格畸变和样品特有的纳米片层结构的协同作用下, 声子得到有效散射, 样品具有最低的热导率1.36 W·m^-1·K^-1. 较低的有效掺杂率和复杂的能带结构具有降低能带态密度有效质量和减小载流子弛豫时间的双刃效应, 使得本征激发提前, 在600 K样品取得最大ZT值为0.66.