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

Ther-mal de-com-po-si-ti-on of a com-mer-ci-al pow-der of sil-ver oxi-de (Ag2O, Merck, p.a.), with the me-an par-tic-le di-a-me-ter of 740 nm has be-en in-ve-sti-ga-ted un-der non-isot-her-mal con-di-ti-ons in a re-du-cing at-mosp-he-re of 25% H2 in ar-gon. The pro-cess was conduc-ted and con-trol-led in a si-mul-ta-ne-o-us TG/DTA analyzer, at he-a-ting ra-tes of 2, 10 and 20 °C min-1. The re-si-du-al mass was al-ways aro-und 93,2 % of the ini-ti-al one, re-gar-dless of the he-a-ting ra-te, which, ac-cor-ding to the oxi-de sto-ic-hi-o-me-try, cor-re-sponds to me-tal-lic sil-ver as fi-nal pro-duct. The SEM mic-rop-ho-to-graphy in-di-ca-ted no sig-ni-fi-cant chan-ge in par-tic-le si-ze and morp-ho-logy du-ring re-duc-ti-on. The ther-mo-gra-vi-me-tric da-ta was used for ki-ne-tic analysis of re-duc-ti-on. Using Kis-sin-ger plot, the ini-ti-al va-lue of the ac-ti-va-ti-on energy was esti-ma-ted to amo-unt to 6.17 104 J mol-1. The ini-ti-al va-lu-es for ki-ne-tics pa-ra-me-ters we-re furt-her cal-cu-la-ted using dif-fe-rent met-hods of ki-ne-tic analysis. Both ac-ti-va-ti-on energy (E) as a fun-cti-on of con-ver-si-on de-gree (α), and pre-ex-po-nen-ti-al fac-tor (A) we-re cal-cu-la-ted by eit-her the Fri-ed-man (Ea = 5,38 104 J mol-1, A = 1,49 106 s-1) or mul-ti-he-a-ting ra-te Co-ast-Red-fern (Ea = 5,97 104 J mol-1, A = 3,90 105 s-1) iso-con-ver-si-o-nal met-hods. A rat-her com-plex de-pen-den-ce of ac-ti-va-ti-on energy on the con-ver-si-on de-gree was ob-ser-ved. A mo-re com-ple-te ap-pro-ach to de-ter-mi-ne the ki-ne-tic pa-ra-me-ters was do-ne by me-ans of non-li-ne-ar re-gres-si-on analysis (Ea = 6,00 104 J mol-1, A = 2,41 106s-1, n = 0,466 ).