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Surface and intergranular segregation in Ni-Si alloys
A156 A.R. ZOMORRODIAN,
L. K O R N B L I T
* and A. IGNATIEV
Department of Physics, University of Houston, Houston, Texas 77004, USA Received 27 March 1984; accepted for publication 15 May 1984 Depth profiles of 3 and 4.5 keV N f ions implanted in Cu are studied in the - 200 to + 200°C temperature range. A strong nitrogen surface segregation is found at all temperatures. Above room temperature a pronounced bulk peak is observed in addition. The effects are interpreted as radiation induced segregation. Two types of defect induced segregation mechanisms are revealed. One is active at all temperatures and cause nitrogen to be displaced in the same direction as the defects. The other type of defect only migrates above room temperature and results in nitrogen segregation in the opposite direction of the defect flux. The data indicate that vacancy migration is responsible for the high temperature segregation.
940
Surface Science 152/153 (1985) 940-946 North-Holland, Amsterdam
THE SURFACE SEGREGATION OF TITANIA I N M A G N E S I U M
OXIDE
W.C. MACKRODT lC1 pie, New Science Group, P.O. Box 11, The Heath. Runcorn, Cheshire WA 7 4QE, UK P.W. TASKER Theoretical Physics Division, A E R E Harwell, O~,:on OXl l ORA, UK and E.A. COLBOURN ICI plc, New Science Group, P.O. Box 11, The Heath, Runcorn, Cheshire, WA 7 4QE, UK Received 2 April 1984; accepted for publication 1 l May 1984 A theoretical study of the segregation of titania (TiO2) at the (001) surface of magnesium oxide (MgO) based on atomistic simulation methods is reported. It is suggested that titanium ions in MgO exist almost exclusively as neutral impurity-vacancy pairs. The stability of those at the surface relative to the bulk is estimated, and from this the effective enthalpy of segregation is deduced. Finally the segregation behaviour of TiO 2 in MgO is compared with that of CaO.
Surface Science 152/153 (1985) 947-956 North-Holland, Amsterdam
947
SURFACE AND INTERGRANULAR SEGREGATION IN N i - S i ALLOYS G. LORANG,
L. M I N E L ,
S. B O U Q U E T
a n d J.P. L A N G E R O N
Centre d'Etudes de Chimie MktaUurgique, 15 Rue Georges Urbain, F-94400 Vit£v sur Seine, France Received 1 April 1984; accepted for publication 12 September 1984 Small quantities of silicon improve the intergranular corrosion resistance of nickel in sulphuric acid, except for diluted alloys (0 to 2 at% Si) where the increasing corrosion is attributed to silicon segregation [1,2]. We have used Auger electron spectroscopy (AES) in the E n ( E ) mode for segregation studies and described the utilization of the peak-to-background ratio (P/B) for quantitative analysis [3]. First we report the silicon behaviour at free surfaces of alloys and the influence of cosegregated impurities (mainly sulphur) on equilibrium coverage. After some annealing treatments, samples were broken in high vacuum and AES analyses of grain boundaries were performed and compared to free surface results.
L. K O R N B L I T
* and A. IGNATIEV
Department of Physics, University of Houston, Houston, Texas 77004, USA Received 27 March 1984; accepted for publication 15 May 1984 Depth profiles of 3 and 4.5 keV N f ions implanted in Cu are studied in the - 200 to + 200°C temperature range. A strong nitrogen surface segregation is found at all temperatures. Above room temperature a pronounced bulk peak is observed in addition. The effects are interpreted as radiation induced segregation. Two types of defect induced segregation mechanisms are revealed. One is active at all temperatures and cause nitrogen to be displaced in the same direction as the defects. The other type of defect only migrates above room temperature and results in nitrogen segregation in the opposite direction of the defect flux. The data indicate that vacancy migration is responsible for the high temperature segregation.
940
Surface Science 152/153 (1985) 940-946 North-Holland, Amsterdam
THE SURFACE SEGREGATION OF TITANIA I N M A G N E S I U M
OXIDE
W.C. MACKRODT lC1 pie, New Science Group, P.O. Box 11, The Heath. Runcorn, Cheshire WA 7 4QE, UK P.W. TASKER Theoretical Physics Division, A E R E Harwell, O~,:on OXl l ORA, UK and E.A. COLBOURN ICI plc, New Science Group, P.O. Box 11, The Heath, Runcorn, Cheshire, WA 7 4QE, UK Received 2 April 1984; accepted for publication 1 l May 1984 A theoretical study of the segregation of titania (TiO2) at the (001) surface of magnesium oxide (MgO) based on atomistic simulation methods is reported. It is suggested that titanium ions in MgO exist almost exclusively as neutral impurity-vacancy pairs. The stability of those at the surface relative to the bulk is estimated, and from this the effective enthalpy of segregation is deduced. Finally the segregation behaviour of TiO 2 in MgO is compared with that of CaO.
Surface Science 152/153 (1985) 947-956 North-Holland, Amsterdam
947
SURFACE AND INTERGRANULAR SEGREGATION IN N i - S i ALLOYS G. LORANG,
L. M I N E L ,
S. B O U Q U E T
a n d J.P. L A N G E R O N
Centre d'Etudes de Chimie MktaUurgique, 15 Rue Georges Urbain, F-94400 Vit£v sur Seine, France Received 1 April 1984; accepted for publication 12 September 1984 Small quantities of silicon improve the intergranular corrosion resistance of nickel in sulphuric acid, except for diluted alloys (0 to 2 at% Si) where the increasing corrosion is attributed to silicon segregation [1,2]. We have used Auger electron spectroscopy (AES) in the E n ( E ) mode for segregation studies and described the utilization of the peak-to-background ratio (P/B) for quantitative analysis [3]. First we report the silicon behaviour at free surfaces of alloys and the influence of cosegregated impurities (mainly sulphur) on equilibrium coverage. After some annealing treatments, samples were broken in high vacuum and AES analyses of grain boundaries were performed and compared to free surface results.