Creusot-Loire

About: Creusot-Loire is a company organization based out in Suresnes, France. It is known for research contribution in the topics: Corrosion & Fluidized bed. The organization has 426 authors who have published 422 publications receiving 3842 citations.

A classification of hydrogen traps in steel

Abstract: In a s e r i e s of recen t papers , 1-3 the ways in which hydrogen t rapping by lat t ice defects can affect and cont ro l the na ture , extent and k ine t ics of hydrogen embr i t t l emen t , have been success fu l ly analyzed and modeled. Most impor tant ly , it was shown that a m i c r o s t r uc tu r e cons is t ing of a un i form d i s t r ibu t ion of fine, s t rong, hydrogen t raps should maximize an a l l oy ' s r e s i s tance to hydrogen. There fo re , if one is to des ign al loys exhibit ing such a m i c r o s t r u c t u r e , the need a r i s e s to know what kind of t r aps should be used. The a i m of this c lass i f i ca t ion is to answer that need. When a hydrogen atom jumps f rom a n o r m a l lat t ice s i te into a t rap , the probabi l i ty of an eventual r e t u r n to the f o r m e r si te is dec reased . The re a re two main r ea sons why, in a c rys t a l lat t ice, jump probab i l i t i e s should be modified: There exis t s a force that pushes the hydrogen a tom in a p r e f e r r e d d i rec t ion , F ig . 1 (a). In that case, the lat t ice is not m o d i f i e d i . e , the average jump height is u n c h a n g e d b u t it is ea s i e r , and thus more probable , for an a tom in si te B to jump in si te A than to jump in s i te C. Moreover , the backward jump will be more difficult than the forward jump. The a tom can then be sa id to be a t t rac ted to si te A. The lat t ice is d i s tor ted and may even be comple te ly modified, F ig . l(b). This t ime, the average jump height is changing f rom si te to s i te . These r ea sons a re suff icient to a r b i t r a r i l y d i s t in guish between two ex t reme types of t r aps . T r a p s where both c h a r a c t e r s a t t r a c t i v e and p h y s i c a l c o e x i s t wil l be designated as mixed t r aps . At t rac t ive T r a p s . Such a t r ap is i l l u s t r a t ed in Fig . l (c) . It is a region of the la t t ice , of d imens ion Di, where hydrogen atoms are subjected to an a t t rac t ive force . F o r c e s that could act on a diffusing a tom in a c ry s t a l la t t ice a re of four types, 4 and a re due e i ther to e l ec t r i c a l f ields, s t r e s s f ields, t e m p e r a t u r e g r a dients , or to the nonideal par t of a chemica l potent ia l g rad ien t . Because a hydrogen atom d i s so lves in t r a n s i t ion meta ls by giving up i ts excess e l ec t ron to the col lect ive e l ec t ron gas of the metal , 5 any defect that in t roduces an e lec t ron vacancy wil l a t t r ac t hydrogen to achieve local neu t ra l i ty . This wil l be the case for impur i t i e s on the left of the ma t r ix in the per iodic table.6 This is a typical example of an " e l e c t r i c a l f o r c e " . The second type of force is well documented in the l i t e r a tu r e , 5,7 and owes its o r ig in to t ens i l e " s t r e s s f i e ld s " induced by defects such as d i s loca t ions , coherent , and s emicohe ren t g ra in boundar ies and pa r t i c l e s , c r ack t ips , and so for th . Since the so lub i l i ty of hydrogen in s tee l i nc r ea se s with t e m p e r a t u r e , a t t rac t ive forces will be genera ted by " t h e r m a l g r a d i e n t s " whenever heterogeneous t e m p e r a t u r e d i s t r i b u -

An example of the effect of hydrogen trapping on hydrogen embrittlement

Abstract: The role of internal hydrogen in reducing the tensile reduction of area of iron-titanium alloys is examined. The population of hydrogen at potential crack nucleii is shown to be controlled by its dynamic interaction with mobile dislocations and its subsequent transport to fixed traps. Expressions are developed for both the number of hydrogen atoms at a given irreversible trap, as well as the time necessary to reach such a number. Reducing the number below the critical value to nucleate a crack, or increasing the time to reach this value will improve an alloy’s performance, and this improvement is related to controllable external and metallurgical variables. These predictions of the model are shown to be consistent with companion experimental data, and with the trap theory of hydrogen embrittlement.

Process and device for controlling the temperature of a reaction carried out in a fluidized bed

Abstract: Method and a device for controlling the temperature of a reaction carried out within a vessel in a fluidized bed containing solid particles which can be entrained with the smoke and then recovered in a separating device and recycled into the fluidized bed after passage through a heat exchanger where they yield up their heat. The flow of particles separated from the smoke is divided into two parts, a hot part recycled directly into the fluidized bed and a cool part constituted by particles taken up at the outlet of the separating device and passed into the heat exchanger to constitute a reserve of cold material which can be mixed with the hot part before reinjection into the fluidized bed, the relative flow rates of the hot particles and of the cold particles being regulated so as to control the flow-rate and the average temperature of the flow of particles recycled into the fluidized bed for maintaining at the desired level the reaction temperature in the midst of the latter.