改进观察实验几例

在自然教学实践中,我们发现有些实验效果还不够理想,学生理解起来仍然感到不容易懂。针对这些问题,发动自然教师进行研究,改进观察实验设计。以下是我们研究改进的几个例子。 1.第八册《毛细现象》一课,实验二:找一些粗细不同的吸管,将它们的一端浸入水中,看一看有什么现象发生?由于吸管缝隙过大实验效果不明显,做此实验需用毛细管,但许多学校又没有。我们将此实验改为用三根粗细、长短相同的玻璃管,在玻璃管底端放入一小团棉花以防止装入管内的砂子漏出。将砂子分成粗、中、细三种,分别装入三个玻璃管内。把三个玻璃管同时放入水中观察,由于细砂颗粒小,它们之间的缝隙小,水上升得较快。

Effects of surface roughness of substrate on properties of Ti/TiN/Zr/ZrN multilayer coatings

Ti/TiN/Zr/ZrN multilayer coatings were deposited on Cr_17Ni_2 steel substrates with different surface roughnesses by vacuum cathodic arc deposition method. Microstructure, micro-hardness, adhesion strength and cross-sectional morphology of the obtained multilayer coatings were investigated. The results show that the Vickers hardness of Ti/TiN/Zr/ZrN multilayer coating, with a film thickness of 11.37 μm, is 29.36 GPa. The erosion and salt spray resistance performance of Cr_17Ni_2 steel substrates can be evidently improved by Ti/TiN/Zr/ZrN multilayer coating. The surface roughness of Cr_17Ni_2 steel substrates plays an important role in determining the mechanical and erosion performances of Ti/TiN/Zr/ZrN multilayer coatings. Overall, a low value of the surface roughness of substrates corresponds to an improved performance of erosion and salt spray resistance of multilayer coatings. The optimized performance of Ti/TiN/Zr/ZrN multilayer coatings can be achieved provided that the surface roughness of Cr_17Ni_2 steel substrates is lower than 0.4μm.