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A THERMOGRAVIMETRIC STUDY OF REDUCTION OF SILVER OXIDE UNDER NON-ISOTHERMAL CONDITIONS

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Author(s): D. Jelić1 | S. Mentus | J. Penavin-Škundrić | D. Bodroža | B. Antunović

Journal: Contemporary Materials
ISSN 1986-8669

Volume: 1;
Issue: 2;
Start page: 144;
Date: 2010;
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Keywords: sil­ver oxi­de | non-isot­her­mal ki­ne­tics | iso­con­ver­si­o­nal met­hods | re­duc­ti­on pro­cess | ther­mo­gra­vi­me­try

ABSTRACT
Ther­mal de­com­po­si­ti­on of a com­mer­ci­al pow­der of sil­ver oxi­de (Ag2O, Merck, p.a.), with the me­an par­tic­le di­a­me­ter of 740 nm has be­en in­ve­sti­ga­ted un­der non-isot­her­mal con­di­ti­ons in a re­du­cing at­mosp­he­re of 25% H2 in ar­gon. The pro­cess was conduc­ted and con­trol­led in a si­mul­ta­ne­o­us TG/DTA analyzer, at he­a­ting ra­tes of 2, 10 and 20 °C min-1. The re­si­du­al mass was al­ways aro­und 93,2 % of the ini­ti­al one, re­gar­dless of the he­a­ting ra­te, which, ac­cor­ding to the oxi­de sto­ic­hi­o­me­try, cor­re­sponds to me­tal­lic sil­ver as fi­nal pro­duct. The SEM mic­rop­ho­to­graphy in­di­ca­ted no sig­ni­fi­cant chan­ge in par­tic­le si­ze and morp­ho­logy du­ring re­duc­ti­on. The ther­mo­gra­vi­me­tric da­ta was used for ki­ne­tic analysis of re­duc­ti­on. Using Kis­sin­ger plot, the ini­ti­al va­lue of the ac­ti­va­ti­on energy was esti­ma­ted to amo­unt to 6.17 · 104 J mol-1. The ini­ti­al va­lu­es for ki­ne­tics pa­ra­me­ters we­re furt­her cal­cu­la­ted using dif­fe­rent met­hods of ki­ne­tic analysis. Both ac­ti­va­ti­on energy (E) as a fun­cti­on of con­ver­si­on de­gree (α), and pre-ex­po­nen­ti­al fac­tor (A) we­re cal­cu­la­ted by eit­her the Fri­ed­man (Ea = 5,38 · 104 J mol-1, A = 1,49 · 106 s-1) or mul­ti-he­a­ting ra­te Co­ast-Red­fern (Ea = 5,97 · 104 J mol-1, A = 3,90 · 105 s-1) iso­con­ver­si­o­nal met­hods. A rat­her com­plex de­pen­den­ce of ac­ti­va­ti­on energy on the con­ver­si­on de­gree was ob­ser­ved. A mo­re com­ple­te ap­pro­ach to de­ter­mi­ne the ki­ne­tic pa­ra­me­ters was do­ne by me­ans of non­li­ne­ar re­gres­si­on analysis (Ea = 6,00 · 104 J mol-1, A = 2,41 · 106s-1, n = 0,466 ).
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