André Pentenero

Study of gas-solid chemical interactions by noble gas molecular beams: IV. Adsorption states and oxidation of molybdenum and rhenium

Abstract The present work is the fourth part of a study using a molecular beam of noble gas atoms (He, Ne) to probe the state of a surface during oxidation at low oxygen pressure (10−5 10−9 torr) and temperatures from ambient up to 2300°K. This technique provides direct information concerning the number of important binding states, the heats of desorption and the surface coverage as a function of metal temperature and oxygen pressure. The experimental results indicate two and one oxygen binding states on Mo and Re, respectively, with binding energies of 139 and 93 kcal mol for Mo and 127 kcal mol for Re. The implication of these results in understanding the fundamental oxidation mechanisms of Mo and Re is discussed with the aid of models which have satisfactorily described tungsten oxidation under comparable conditions. It appears that the true mechanism for molybdenum is the same as that for tungsten whereas that for rhenium is striking different, contrary to previous interpretations.

Auger Spectrometry as a Tool for Surface Chemistry

Abstract In 1923 Auger [I] tried to get “some information on the trajectories of electrons extracted from gas atoms by an X-ray beam.”

Étude des interactions chimiques gaz-solide par la technique du faisceau moléculaire: V. réactions de l'oxygène et de l'oxyde de carbone avec des rubans polycristallins de tantale

Abstract We use the reflection of a noble gas (helium) molecular beam to study the superficial reactions of oxygen and carbon monoxide with polycrystalline tantalum. The fraction of the incident beam which is specularly reflected gives direct information on the formation of an oxygen chemisorbed layer and we observed only a single apparent binding state for oxygen chemisorbed on tantalum. The initial value of the sticking coefficient of oxygen on clean polycrystalline tantalum is 0.86, decreasing rapidly during the formation of a chemisorbed layer. The specularly reflected fraction of the incident beam is also modified by the chemisorption of carbon monoxide and this modification would confirm the dissociative character of the CO chemisorption on tantalum. The influence of the partial pressure of CO on the temperature at which the surface is completely covered by the products of the dissociative chemisorption of CO shows that the coverage becomes equal to unity at temperatures at which the solubility limit of CO is attained and tantalum carbide is formed.

Extraction d’un signal aléatoire gaussien modulant en amplitude un signal sinusoïdal

RésuméLes auteurs expriment la densité de probabilité R(x) d’un signal aléatoire obtenu en modulant un signal sinusoïdal par un signal aléatoire gaussien. Ils montrent qu’il est possible d’obtenir à partir d’un tel signal expérimental, la moyenne et l’écart type du signal gaussien. La méthode s’est révélée simple, précise et pouvant être automatisée à l’aide d’un analyseur multicanaux.