Effect of CO{sub 2} concentration on YBa{sub 2}Cu{sub 3}O{sub 6+x} formation
- Univ. of Houston, TX (United States). Dept. of Chemical Engineering
Two reversible reactions are involved in YBa{sub 2}Cu{sub 3}O{sub 6+x} formation: a reaction between BaCO{sub 3} and CuO forming BaCuO{sub 2} and CO{sub 2}, and a reaction of BaCuO{sub 2} with Y{sub 2}O{sub 3} and CuO forming YBa{sub 2}Cu{sub 3}O{sub 6} which undergoes phase transformation to YBa{sub 2}Cu{sub 3}O{sub 6+x} upon cooling. In-situ isothermal time resolved HT-XRD of a thin film was used to quantify the effect of CO{sub 2} on the kinetics of the first reaction. Increased CO{sub 2} partial pressure shifts the reactions to higher temperatures. At high CO{sub 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{sub 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{sub 3} decomposition and a second-order nucleation rate for YBa{sub 2}Cu{sub 3}O{sub 6} formation. A comparison of the kinetics of a thin film (10 {mu}m) as determined by HT-XRD with those of a thick sample (2 mm) determined by TG revealed that the transport of CO{sub 2} within the sample pores and to the ambient gas significantly affect the decomposition of BaCO{sub 3}. For example, the formation of YBa{sub 2}Cu{sub 3}O{sub 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.
- Sponsoring Organization:
- Texas Center for Superconductivity, Houston, TX (United States)
- OSTI ID:
- 483848
- Journal Information:
- AIChE Journal, Journal Name: AIChE Journal Journal Issue: 4 Vol. 43; ISSN 0001-1541; ISSN AICEAC
- Country of Publication:
- United States
- Language:
- English
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