## Abstract

Grain growth kinetics in CaTiO_{3}-perovskite + FeO-wustite aggregates were studied at the conditions of T = 1223-1623 K, P = 0.1 MPa and P = 200 MPa. Starting samples were fabricated by hot-pressing mechanically mixed powders of CaTiO_{3} + FeO with FeO = 0%, 1%, 3%, 6%, 10%, 20% and 100% by weight in a gas-medium apparatus at 1323 K and 300 MPa for 5 h. The increase of grain size (G) of CaTiO_{3} with time (t) follows a growth law: G(n) - G_{0}(n) = κ · t(κ = κ_{0} exp(-(Q/RT)). Two grain growth regimes are observed at T < 1523 K and T ≥ 1523 K. For T < 1523 K, the best fits of the data to the growth law yield growth exponents of n = 2.2 ± 0.2, 3.0 ± 0.3 and 3.5 ± 0.3 for samples with FeO = 0%, 3% and 10% respectively. Under these conditions the rate constants, κ, obey an Arrhenius relation with Q = 206 ± 35 kJ/mol and 385 ± 65 kJ/mol for samples with FeO = 3% and 10%. Grain growth of CaTiO_{3} becomes sluggish when FeO content exceeds 6%. For T ≥ 1523 K, the best fits of the data to the growth law yield n = 2.5 ± 0.2 for both samples with FeO = 3% and 10%. The activation energies (Q) were determined as 71 ± 30 kJ/mol and 229 ± 45 kJ/mol for samples with FeO = 3% and 10%, respectively. The TEM observations show a remarkable difference in the distribution and geometry of FeO below and above 1523 K: nanometer-sized particles of FeO were observed along CaTiO_{3} grain boundaries in samples annealed at T < 1523 K. No FeO particles were detected along CaTiO_{3} grain boundaries in samples annealed at T ≥ 1523 K, but large clusters of FeO particles are observed locally indicating a fast separation of FeO from CaTiO_{3}. Thus we conclude that the slow growth rate of CaTiO_{3} at T < 1523 K is due to the pinning by FeO particles at grain boundary, and that the change of grain growth kinetics in CaTiO_{3} at T ≥ 1523 K may relate to the separation of FeO from CaTiO_{3}, which we interpret as due to the phase transformation of CaTiO_{3} at around 1523 K.

Original language | English (US) |
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Pages (from-to) | 11-19 |

Number of pages | 9 |

Journal | Physics and Chemistry of Minerals |

Volume | 27 |

Issue number | 1 |

DOIs | |

State | Published - Nov 1999 |

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