Oxidation of a segregated MoN layer grown on Fe(100)-3.5wt%Mo-N
| dc.contributor.advisor | Roos, W. D. | |
| dc.contributor.advisor | Swart, H. C. | |
| dc.contributor.author | Conradie, Rochelle | |
| dc.date.accessioned | 2017-06-19T06:28:57Z | |
| dc.date.available | 2017-06-19T06:28:57Z | |
| dc.date.issued | 2001-06 | |
| dc.description.abstract | English: The oxidation behaviour of the segregated MoN layer on the Fe(100)-3.5wt% Mo-N substrate was investigated in this study. Previous studies suggested the synergetic segregation of the Mo and N from the Fe(100)-3.5wt% Mo-N specimen. It has also been shown that the segregated Mo and N form a MoN surface compound. As an alloy element in stainless steels, the Mo aids in the inhibition of the oxidation and thus prevents corrosion Auger electron spectroscopy (AES) was used to obtain the experimental results. For this study the oxidation of a Fe(100) specimen and a Fe(100)-3.5wt% Mo-N specimen were investigated to establish a point of reference to describe the oxidation behaviour of the segregated MoN layer. Linear temperature ramping was used to segregate the Mo and N from the Fe(100)-3.5wt% Mo-N specimen. The specimens were exposed to an oxygen environment at various temperatures. The partial pressure of the oxygen was monitored with a mass spectrometer and was kept constant at 2 x 10-10 torr. The Auger peak-to-peak heights for the relevant elements in the specimens were measured as a function of the exposure time. Upon oxidation, the low energy Fe AES peak (47 eV) undergoes shape changes. The iron oxide has a dual peak with 42 eV and 52 eV kinetic energy respectively. The Fe(100) specimen surface reacted rapidly with the oxygen environment at room temperature to form an iron oxide, as depicted by the change in the low energy Fe AES peak. The exposures performed at 100°C and 200°C also resulted in oxide formation although the extent of the oxidation decreased with an increase in the temperature. Above 300°C indication of the Mo and N reacting with the oxygen environment. At 100°C and 200°C less oxide formation was detected and above 300°C there was only oxygen adsorption. The segregated MoN layer had a markedly different response to the oxygen exposure. The oxygen exposure performed at room temperature had a strikingly different course of the 0 Auger peak-to-peak height increase compared to that of the Fe(100) and Fe(100)- 3.5wt% Mo-N specimens exposure at the same temperature. The segregated MoN layer retards the surface reaction. A hypothesis formulated describes the MoN layer as a perforated layer that has some Fe exposed. The oxygen reacts rapidly with the exposed Fe. Longer exposures result in the dissociation of the MoN layer and the desorption of the Mo03 and NxOy compounds from the surface. Once the layer has dissociated completely the Fe will continue to react as for the other specimens. Oxidation occurs up to 300°C and at higher temperatures no oxide formation is detected. The changes in the low energy Fe AES peak are used to calculate the fraction oxide and metal contributing to the peak by using the Linear Least Squares method. The low energy Fe AES peak cannot be used for thickness calculations as it is subject to the backscattering term. The experimental data suggests that the backscattering term is a function of the exposure time. A first approximation is to assume a linear change with time. This approximation was applied successfully to the room temperature oxidation of the segregated MoN layer, but the same function could not be applied to the other two specimens, The thickness of the oxide was calculated using the change in the high energy Fe AES peak intensity. The O2 sticking coefficient for the exposure of the Fe(100) and the exposure of the segregated layer was also calculated and the differences in the values were attributed to the effect of the dissociation of the MoN layer on the adsorption of the O2 on the specimen surface. there was no oxide formation detected and therefore there is only oxygen adsorption at these temperatures. The Fe(100)-3.5wt% Mo-N specimen showed similar oxidation behaviour as was seen for the Fe(100) specimen. At room temperature the surface of the specimen reacted rapidly with the oxygen environment to form an iron oxide. There was no | en_ZA |
| dc.description.abstract | Afrikaans: Die oksidasie gedrag van die gesegregeerde MoN laag op die Fe(100)-3.5wt% Mo-N substraat is in hierdie studie bestudeer. Vorige studies het voorgestel dat daar kosegregasie van die Mo en N in die Fe(100)-3.5wt% Mo-N monster plaasvind. Dit is ook voorgestel dat die gesegregeerde Mo en N 'n MoN oppervlakverbinding vorm. As 'n allooi element in vlekvrye staal help die Mo die vertraging van die oksidasie van die staal en verhoed dus korrosie. Augerelektronspektroskopie (AES) is aangewend in hierdie studie om die eksperimentele data te verkry. Die oksidasie van 'n Fe(100) monster en 'n Fe(100)-3.5wt% Mo-N monster is bestudeer en aangewend as 'n verwyingspunt om die oksidasie gedrag van die gesegregeerde MoN laag te beskryf. Linêere temperatuur verhoging is gebruik om die Mo en N uit die Fe(100)-3.5wt% Mo-N monster te segregeer. Die monsters is blootgestel aan 'n suurstof atmosfeer by verskeie temperature. Die parsiële druk van die suurstof is met 'n massa spektrometer gemonitor en konstant gehou by 'n druk van 2 x 10-10 torr. Die Auger piek-tot-piek hoogtes van die relevante elemente in die monsters is gemeet as 'n funksie van die blootstellings tyd. Die vorm van die lae energie Fe AES piek (47 eV) verander wanneer die Fe chemies reageer met die suurstof. Die oksied het 'n duale piek by 42 eVen 52 eVonderskeidelik. Die Fe(100) monster oppervlak reageer vinnig met die suurstof atmosfeer by kamer temperatuur om 'n ysteroksied te vorm soos aangedui in die verandering in die lae energie Fe AES piekvorm. Alhoewel daar oksied vormasie by 100°C en 200°C is neem die graad van oksidasie af met 'n toename in die temperatuur. Bo 300°C is daar geen oksied vormasie waargeneem nie en by hierdie temperature is daar slegs suurstof adsorpsie. Die Fe(100)-3.5wt% Mo-N monster het soortgelyke oksidasie gedrag getoon as die Fe(100) monster. By kamer temperatuur reageer die oppervlak vinnig met die suurstof atmosfeer om 'n ysteroksied te vorm. Daar was geen teken dat die Mo an N met die suusrtof atmosfeer reageer nie. By 100°C en 200°C is daar minder oksied vormasie waargeneem en bo 300°C was daar slegs suurstof adsorpsie. Die gesegregeerde MoN laag het 'n wesenlike verskil in oksidasie gedrag getoon. By kamertemperatuur het die 0 Auger piek-tot-piek hoogte 'n merkwaardige verskil in verloop getoon i.v.m. die Fe(100) en Fe(100)-3.5wt% Mo-N monsters se 0 verloop by dieselfde temperatuur. Die gesegregeerde laag vertraag die oppervlak reaksie. 'n Hipotese is geformuleer om die gedrag te beskryf. Die hipotese lees dat die gesegregeerde MoN laag geperforeer is en dat daar steeds 'n bietjie Fe blootgestel is. Die suurstof reageer vinnig met die blootgestelde Fe. Verdere blootstelling lei tot die dissosiasie van die MoN laag en die desorpsie van NxOy en Mo03 verbindings vanaf die oppervlak. Wanneer die gesegregeerde laag heeltemal gedissosieer en gedesorbeer het reageer die Fe in die monster met die suurstof atmosfeer soos vir die ander monsters. Oksidasie is waargeneem tot by 300°C en geen oksied vormasie is waargeneem by hoër temperature nie. Die verandering in die lae energie Fe AES piek word aangewend om die fraksie oksied en metaal te bereken wat bydrae tot die gemete AES piek d.m.v. kleinste kwadraat passings. Die lae energie Fe AES piek kan nie suksesvol aangewend word vir die berekening van die oksiedlaag dikte me aangesien dit afhanklik is van die terugverstrooiingsfaktor. Die eksperimentele data dui aan dat die terugverstrooiingsfaktor 'n funksie is van die blootstellings tyd. As 'n eerste benadering word aangeneem dat die verandering in die terugverstrooiingsfaktor lineêr is met tyd. Die korreksie kan suksesvol aangewend word vir die kamertemperatuur oksidasie van die gesegregeerde MoN laag, maar dieselfde redenasie is nie geldig vir die oksiedasie van die ander monsters nie. Die dikte van die oksied is bereken deur die verandering in die piek intensiteit van die hoë energie Fe AES piek. Die O2 kleetkoeffiënt vir die suurstof blootstelling van die Fe(100) monster en die gesegregeerde laag is bereken en die verskille in die waardes is toegeskryf aan die invloed van die dissosiasie van die MoN laag op die adsorpsie van die O2 op die oppervlak van die monsters. | af |
| dc.identifier.uri | http://hdl.handle.net/11660/6372 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Oxidation | en_ZA |
| dc.subject | Molybdenum -- Oxidation | en_ZA |
| dc.subject | Dissertation (M.Sc. (Physics))--University of the Free State, 2001 | en_ZA |
| dc.title | Oxidation of a segregated MoN layer grown on Fe(100)-3.5wt%Mo-N | en_ZA |
| dc.type | Dissertation | en_ZA |