X射线衍射研究球磨Si_3N_4粉末的特征

CHARACTERIZATION OF MILLED Si_3N_4 POWDER USING X-RAY DIFFRACTION

Si_3N_4,粉末在行星球磨机中以酒精为研磨液进行湿磨,直至195小时。采用X射线粉末衍射研究了Si_3N,粉末晶块尺寸值和晶格畸变量与研磨时间的关系,晶块尺寸值与晶格畸变量的分离基于两项宽化效应对布拉格角的依赖不同:结果表明:在最初50小时研磨中,晶块细化很快,超过170小时后,晶块不再减小;经195小时球磨.粉末晶块尺寸值从未磨样的0.23μm减少到0.074μm:经计算得未磨样最小位错密度为O_D=5.7×10~8cm^(-2);球磨195小时样品最小位错密度为μD=5.4×10~10cm^2。这么高的位错密度通常会引起粉末严重畸变。 而所测晶格畸变量在最初7O小时的研磨中出乎意料地减小很快,从未磨样品晶格畸变量的0.032%减少到0.013%。这种高位错密度与低残留弹性应变说明位错是以降低应变的方式排列,如此一种排列方式可能是位错的多边排列,亦不能排除由于部分非晶化对对降低应变的的作用。

Si3N4 powder has been milled using a planetary ball mill for up to 195 h. Alcohol is used as the milling fluid-The crystalline size and lattice distortions'were studied as a function of milling time using X - ray powder diffraction technique. The basis for the separation of the contributions of crystalline size and lattice distortion is the dependence of the different angles of the two broadening effects. The results show that the crystalline size decreased rapidly during the first 50 h of milling. Above 170 h no further decrease of the crystalline size occurre-d.The crystalline size decreased from 0. 23 um in the unmilled sample,to 0. 074um in the 195 h milled sample. Lattice distortion decreased from 0. 032 to 0. 013% during the first 70 h of milling. The calculations give a dislocation density ,5. 7x 109cm-2 for the unmilled powder and 5- 4X 1010cm-2 for the powder milled for 195 h. These values indicate a high degree of deformation. However ,the distortions decrease unexpectedly during the first 70 h of milling. The high dislocation density .together with the low value of stored elastic strain,suggests that the dislocation are arranged in configurations that reduce their strain energy. Such a configuration could be a polygo-nized arrangment of the dislocations and a contributing factor to the low strain due to partial amorphization of the powder cannot be excluded.