Studies in gas-solid reactions: Part II. An experimental study of nickel oxide reduction with hydrogen
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I N the p r e c e d i n g p a p e r a m a t h e m a t i c a l m o d e l was p r e s e n t e d for the r e a c t i o n of p o r o u s m e t a l oxides with a r e d u c i n g gas. The m o d e l i n c o r p o r a t e d s t r u c t u r a l p a r a m e t e r s , such as grain s i z e , p o r o s i t y and t r u e p o r e diffusivity, which could be m e a s u r e d or p r e d i c t e d independently of the r e d u c t i o n p r o c e s s . It was s u g g e s t e d , t h e r e f o r e , that if the t r u e h e t e r o g e n e o u s r a t e constant w e r e known, then the o v e r a l l r e a c t i o n r a t e could be p r e d i c t e d on the b a s i s of the m o d e l and independent physical measurements. The p u r p o s e of the p r e s e n t p a p e r is to d e s c r i b e an e x p e r i m e n t a l study, involving the s y s t e m : nickel o x i d e hydrogen, a i m e d at e x a m i n i n g the a p p r o p r i a t e n e s s of the s t r u c t u r a l m o d e l p r e s e n t e d p r e v i o u s l y . In the following, e x p e r i m e n t a l m e a s u r e m e n t s will be p r e s e n t e d on the k i n e t i c s of the r e a c t i o n of p o r o u s nickel oxide p e l l e t s with hydrogen under c o n t r o l l e d conditions. Also d e s c r i b e d will be independent m e a s u r e m e n t s c a r r i e d out f o r the c h a r a c t e r i z a t i o n of the p o r o u s solid; t h e s e l a t t e r data a r e u s e d in computing the t h e o r e t i c a l r e s u l t s which a r e then c o m p a r e d with experimental measurements. R e g a r d i n g the o r g a n i z a t i o n of the p a p e r , Section 1 is c o a c e r n e d with the e x p e r i m e n t a l technique u s e d in the reduction studies, and the measurements characterizLug the porous solids are reported in Section 2. The measured and the predicted reaction rates are compared in Section 3 for a variety of conditions, and a general discussion is presented in Section 4.
in addition, the heat of reaction is small so that thermal effects were of secondary importance. Fig. i shows a schematic diagram of this apparatus, the principal components of which are described in the following. The nickel oxide pellet was suspended inside the r e action tube, which consisted of an inconel pipe, 3 ft long and about 2 in. in diam. The lower 22 in. of the pipe were filled with woven copper pads, to provide adequate surface area for preheating the reactant gas. The reaction tube was placed inside a Marshall model 1034 non-inductively wound tubular furnace, of 2~i in. ID with a heated length of 14-} in. The temperature in the hot zone was measured by four sheathed "Conmx" chromel-alumel thermocouples located both above and below the sample. Power was supplied to the furnace by a R.I. Controls " P h a s e r " solid state power controller model number PR-230-50. The dc control signal to this unit was provided by a Robertshaw precision electronic controller model number 381. Through this arrangement the temperature of the hot zone could be maintained to within • 5:C.
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