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Some observations on the thermochemistry of telluric acid

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Abstract

The thermal degradation of H6TeO6 in air has been evaluated critically. Evidence is presented for a decomposition mechanism involving step-wise dehydration of H6TeO6 via non-stoichiometric amorphous solids to polymetatelluric acid and up to a composition corresponding to pyrotelluric acid. No morphological changes were observed during these structural variations and no evidence was found for the formation of allotelluric acid. Further dehydration is accompanied by reduction, which, depending upon the experimental conditions accounts for the considerable variety of results reported previously. Crystalline Te(VI)-Te(IV) oxides are obtained at about 550‡ from which TeO2 is formed by additional calcination at about 620‡.

Résumé

On a réexaminé la dégradation thermique de l'acide orthotellurique. L'absence de variations morphologiques dans l'intervalle de 120‡–200‡ exclut la formation de l'acide allotellurique. Ensuite, l'analyse thermique différentielle conduit par décomposition progressive à l'acide polymétatellurique et à l'acide pyrotellurique. La déshydratation à l'air donne lieu à des substances amorphes et est accompagnée simultanément de perte d'oxygène. On obtient des anhydrides cristallins contenant Te(IV) et Te(VI) à 550‡ et TeO2 à 620‡.

Zusammenfassung

Es wird über hydratisierte Zwischenstufen wÄhrend der thermischen Abbau von OrthotellursÄure berichtet. Die Abwesenheit morphologischer Änderungen und die beobachtete plastische Deformationen im 120‡–200‡ Bereich schliessen die Bildung metastabiles AllotellursÄure aus. Dagegen führen partielle EntwÄsserungsversuche an der Luft zu der Annahme von PyrotellursÄure. AbhÄngend von den Versuchsbedingungen werden DTA und TG Kurven produziert deren Verlauf nicht charakteristisch ist für separate Wasser oder Sauerstoffabgabe. Kristallinische Tellurium(VI, IV) Oxyden entstehen bei 550‡ und die übergang zum Telluriumdioxyd ist vollendet bei 620‡.

РЕжУМЕ

БылА пРОВЕДЕНА кРИтИ ЧЕскАь ОцЕНкА тЕРМИЧЕскОгО РАжлОж ЕНИь Н6тЕО6 В АтМОсФЕР Е ВОжДУхА. пРЕДстАВлЕН ы ДОкАжАтЕльстВА МЕх АНИжМА РАжлОМЕНИь, жАклУЧАУ ЩИИсь В стУпЕНЧАтОИ ДЕгИДРА тАцИИ Н6тЕО6 ДО пОлИМЕтАтЕллУРОВОИ кИслОты с ОБРАжОВАНИ ЕМ пРОМЕжУтОЧНых НЕстЕхИОМЕтРИЧЕскИ АМОРФНых тЕл И с ДАльНЕИшИМ пРЕВРАЩЕ НИЕМ ДО пИРОтЕллУРОВ ОИ кИслОты. В пРОцЕссЕ ст РУктУРНых пРЕВРАЩЕНИИ НЕ НАБлУ ДАлОсь кАкИх-лИБО МОРФОлОгИЧЕскИх ИжМ ЕНЕНИИ И НЕ БылО ОБНАР УжЕНО ДОкАжАтЕльстВ ОБРАж ОВАНИь АллОтЕллУРОВ ОИ кИслОты. ДАльНЕИшАь ДЕгИДРАт АцИь сОпРОВОжДАЕтсь ВОсс тАНОВлЕНИЕМ, кОтОРОЕ жАВИсИт От ЁкспЕРИМЕ НтАльНых УслОВИИ. ЁтИ М И ОБЩьсНьЕтсь жНАЧИтЕ льНОЕ РАжНООБРАжИЕ пРИВЕДЕННых РАНЕЕ РЕ жУльтАтОВ. пРИ тЕМпЕР АтУРЕ ОкОлО 550‡ БылИ пОлУЧЕНы кРИст АллИЧЕскИЕ Te(VI)—Te(IV) ОкИслы, Иж кОтОРых жАтЕМ пРИ ДОпОлНИтЕльНОМ пРОк АлИВАНИИ ОкОлО 620‡ ОБРАжУЕтсь тЕ О2.

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Authors and Affiliations

  1. Montedison Research Laboratories “G. Donegani”, Montedison, Research Centre, 20021 Bollate Milano, Nooara

    J. C. J. Bart, A. Bossi, P. Perissinoto, A. Castellan & N. Giordano

  2. Montedison Research Laboratories, Priolo, Siracusa, Italy

    J. C. J. Bart, A. Bossi, P. Perissinoto, A. Castellan & N. Giordano

Authors
  1. J. C. J. Bart
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  2. A. Bossi
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  3. P. Perissinoto
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  4. A. Castellan
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  5. N. Giordano
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Additional information

The authors are indebted to Dr. A. Marzi for the optical observations and for preparation of the microphotographs.

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Bart, J.C.J., Bossi, A., Perissinoto, P. et al. Some observations on the thermochemistry of telluric acid. Journal of Thermal Analysis 8, 313–327 (1975). https://doi.org/10.1007/BF01904009

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  • DOI: https://doi.org/10.1007/BF01904009

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