RESUMEN
The mixed ionic and electronic oxide LaNi0.6Fe0.4O3-δ (LNF) is a promising ceramic cathode material for solid oxide fuel cells. Since the reaction rate of oxygen interaction with the cathode material is extremely important, the present work considers the oxygen exchange mechanism between O2 and LNF oxide. The kinetic dependence of the oxygen/oxide interaction has been determined by two isotopic methods using 18O-labelled oxygen. The application of the isotope exchange with the gas phase equilibrium (IE-GPE) and the pulsed isotope exchange (PIE) has provided information over a wide range of temperatures (350-800 °C) and oxygen pressures (10-200 mbar), as each method has different applicability limits. Applying mathematical models to treat the kinetic relationships, the oxygen exchange rate (rH, atom × cm-2 × s-1) and the diffusion coefficient (D, cm2/s) were calculated. The values of rH and D depend on both temperature and oxygen pressure. The activation energy of the surface exchange rate is 0.73 ± 0.05 eV for the PIE method at 200 mbar, and 0.48 ± 0.02 eV for the IE-GPE method at 10-20 mbar; for the diffusion coefficient, the activation energy equals 0.62 ± 0.01 eV at 10-20 mbar for the IE-GPE method. Differences in the mechanism of oxygen exchange and diffusion on dense and powder samples are observed due to the different microstructure and surface morphology of the samples. The influence of oxygen pressure on the ratio of contributions of different exchange types to the total oxygen exchange rate is demonstrated. For the first time, the rate-determining step in the oxygen exchange process for LNF material has been identified. This paper discusses the reasons for the difference in the mechanisms of oxygen exchange and diffusion.
Asunto(s)
Gases , Oxígeno , Cerámica , Difusión , ÓxidosRESUMEN
OBJECTIVE: To evaluate the effects of add-on treatment with trimetazidine, single dose and long-term, on clinical and objective parameters of ischemia in patients with stable angina pectoris receiving standard antianginal therapy. DESIGN: One-month single-blind, placebo-controlled study. PATIENTS: 40 patients with stable angina pectoris. INTERVENTIONS: Patients received 1-month treatment with either trimetazidine 20 mg (n = 20) or placebo (n = 20) 3 times daily in addition to standard antianginal therapy. MAIN OUTCOME MEASURES: All patients underwent bicycle stress tests at baseline and at 1 month to assess exercise tolerance. Patients receiving trimetazidine also underwent a stress test 2 hours after administration of a 60 mg single dose. Influence of trimetazidine on stress-induced left ventricular function was assessed in 11 patients, with dobutamine stress echocardiography performed at baseline and at 1 month. Clinical efficacy was evaluated in terms of mean weekly number of anginal episodes and weekly nitroglycerin (glyceryl trinitrate) tablet consumption during the study. RESULTS: Trimetazidine significantly improved most stress test parameters, after a single dose and after 1 month of treatment; the rate-pressure product remained unchanged. Dobutamine tests showed significant (p < 0.05) increases from baseline values in time to onset of anginal pain and threshold dobutamine dose (13.5 +/- 0.7 versus 10.2 +/- 0.8 min, and 43.6 +/- 2.8 versus 35.4 +/- 3.4 microg/kg/min, respectively). The severity of anginal pain and mean weekly number of anginal episodes was reduced significantly (p < 0.05) from baseline values after 1 months' treatment with trimetazidine (1.3 +/- 0.6 versus 2.3 +/- 0.3, and 6.6 +/- 1.4 versus 10.1 +/- 1.3, respectively). After 1 month, weekly consumption of nitroglycerin tablets was decreased by 3.1 from baseline values in the trimetazidine group but increased by 0.3 in the placebo-treated group. No patient withdrew due to treatment-related adverse effects. CONCLUSION: This study confirms the antianginal and anti-ischemic efficacy of single dose and long-term treatment with trimetazidine. Treatment with trimetazidine was well tolerated.