MAGNESIUM SURFACE SEGREGATION AND ITS EFFECT ON THE OXIDATION RATE OF THE (111)SURFACE OF AL-1.45AT-PERCENT-MG

被引:32
作者
BLOCH, J
BOTTOMLEY, DJ
MIHAYCHUK, JG
VANDRIEL, HM
TIMSIT, RS
机构
[1] UNIV TORONTO,DEPT PHYS,TORONTO,ON M5S 1A7,CANADA
[2] UNIV TORONTO,ONTARIO LASER & LIGHTWAVE RES CTR,TORONTO,ON M5S 1A7,CANADA
[3] CANADA LTD,AMP,MARKHAM,ON L3R 1E1,CANADA
[4] NUCL RES CTR NEGEV,DEPT PHYS,IL-84190 BEER SHEVA,ISRAEL
基金
加拿大自然科学与工程研究理事会;
关键词
ALKALI METALS; ALLOYS; ALUMINUM; MODELS OF SURFACE KINETICS; 2ND-HARMONIC GENERATION; SURFACE SEGREGATION;
D O I
10.1016/0039-6028(95)90027-6
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The temperature dependence of the surface segregation of magnesium onto the (111) surface of Al-1.45at%Mg and its subsequent effect on the oxygen adsorption rate have been studied using optical second harmonic (SH) generation. The SH intensity increases with Mg surface segregation up to 495 K but decreases at higher temperatures due to Mg evaporation. A. bulk diffusion model for Mg segregation was found to be inconsistent with the data. Rather, the segregation rate was found to obey a simple one-dimensional nucleation and growth kinetic law with an activation energy of 7.2 +/- 0.6 kcal/mol and a free energy for segregation of 4.9 +/- 0.3 kcal/mol. The surface modified by the Mg segregation exhibits a sharp increase in the initial oxygen adsorption rate. This is consistent with a multi-site adsorption mechanism. At high annealing temperatures where the Mg surface concentration decreases due to evaporation, the oxygen adsorption rate also decreases. The initial sticking coefficient of the Mg-rich sites increases with Mg surface concentration; its maximum value is found to be of the order of unity, more than 10 times than that of the clean Al(111) surface.
引用
收藏
页码:168 / 176
页数:9
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