Effect of CO₂ concentration on YBa₂Cu₃O_6+<i>x</i> formation

• T. Kohav

• K. M. Forster

• J. T. Richardson

• D. Luss

抄録

Two reversible reactions are involved in YBa 2 Cu 3 O 6+ x formation: a reaction between BaCO 3 and CuO forming BaCuO 2 and CO 2 , and a reaction of BaCuO 2 with Y 2 O 3 and CuO forming YBa 2 Cu 3 O 6 which undergoes phase transformation to YBa 2 Cu 3 O 6+ x upon cooling. In‐situ isothermal time resolved HT‐XRD of a thin film was used to quantify the effect of CO 2 on the kinetics of the first reaction. Increased CO 2 partial pressure shifts the reactions to higher temperatures. At high CO 2 partial pressure (>2 vol. %), the rate of the first reaction becomes essentially a step process with a very high activation energy. Noninstantaneous nucleation of the reaction products occurs at low CO 2 partial pressure (0.5–1%) and temperatures (700°C). The data fit a 2‐D diffusion‐controlled mechanism with a zero nucleation rate for BaCO 3 decomposition and a second‐order nucleation rate for YBa 2 Cu 3 O 6 formation. A comparison of the kinetics of a thin film (10 mm) as determined by HT‐XRD with those of a thick sample (2 mm) determined by TG revealed that the transport of CO 2 within the sample pores and to the ambient gas significantly affect the decomposition of BaCO 3 . For example, the formation of YBa 2 Cu 3 O 6 in a thick precursor layer occurs in the 840 to 940°C range, exceeding by about 200°C that in which it is formed in thin films.

収録刊行物

• AIChE Journal

  AIChE Journal 43 (4), 1091-1099, 1997-04

  Wiley

キーワード

• General Chemical Engineering
• Environmental Engineering
• Biotechnology

詳細情報

• CRID: 1360862722823123328
• NII論文ID: 30010298993
• DOI: 10.1002/aic.690430422
• ISSN: 15475905
• ISSN: 00011541
• Web Site: https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Faic.690430422
• Web Site: https://onlinelibrary.wiley.com/doi/full/10.1002/aic.690430422
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