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The E1' center in natural quartz: its formation and applications to dating and provenance researches

Toyoda S.

Geochronometria

2011

Vol. 38, no. 3

242-248

Quartz is one of the minerals useful for electron spin resonance (ESR) dating. The E1' center is one of well-known paramagnetic defects in crystalline quartz. This center has a unique feature; its intensity increases on heating. An electronic process to explain this increase was found to be con-trolled not only by the number of oxygen vacancies, which are the precursors, but also by the number of Al hole centers, which depend on the previous radiation dose and on the Al concentration. The maximum intensity on heating is called the heat treated E1' center, which has been posited to correspond to the number of oxygen vacancies in quartz and was found to be correlated with the ages of the host granites (Toyoda and Hattori, 2000). The experimental results on spin-spin relaxation times of the E1' center indicate that external beta and gamma rays create oxygen vacancies in natural quartz rather than alpha or alpha recoil particles (Toyoda et al., 2005). The correlation between the numbers of the oxygen vacancies in quartz and the ages of the host granite made it possible to distinguish the quartz of a sedimentary reservoir from another with different age of crystallization (Toyoda and Naruse, 2002). Quartz fractions extracted from leoss and atmospheric deposition in Japan and from sediments in Japan sea were analyzed by ESR. The temporal change of the contributions from two dust sources in China were discussed in the context of climate change.

Effect of atmosphere change paths on the induced chemical expansion

Valentin O., Blond E., Julian A., Richet N.

Materiały Ceramiczne

2010

T. 62, nr 3

283-287

This study presents the relevant aspects of the approach developed at Institut PRISME to model strain in the mixed ionic and electronic conductors (MIEC) membrane for reforming of methane into synthesis gas (H2/CO). This macroscopic approach is based on the assumption of strain partition and on the choice of oxygen activity as a state variable. It leads to a thermo-chemo-mechanical model taking into account oxygen diffusion as well as elastic, thermal and chemical expansion phenomena. A chemical expansion model is proposed. The kinetics of a macroscopic bulk diffusion model has been fitted by simulation to chemical dilatometry tests. The transient and the steady-state stress distribution in a membrane reactor for partial oxidation of methane (POM) have been simulated in various conditions.

Niniejsze praca przedstawia stosowne aspekty podejścia do modelowania odkształcenia w membranie z mieszanych przewodników jonowych i elektronowych (MIEC) dla reformingu metanu w procesie syntezy gazu (H2/CO), rozwiniętego w Instytucie PRISME. To makroskopowe podejście opiera się na założeniu o podziale odkształcenia i na wyborze aktywności tlenu jako parametru stanu. Prowadzi to do termo-chemo-mechanicznego modelu biorącego pod uwagę dyfuzję tlenu, a także zjawiska ekspansji sprężystej, cieplnej i chemicznej. Zaproponowano model rozszerzalności chemicznej. Kinetyka w makroskopowym modelu dyfuzji objętościowej została dopasowana za pomocą symulacji do testów chemicznej dylatometrii. Rozkład naprężeń w stanie nieustalonym i ustalonym w reaktorze membranowym do częściowego utleniania metanu (POM) został zasymulowany w różnych warunkach.