Synthesis And Thermoelectric Properties Of Ca₂Co₂O₅

Abstract:With the development of human society and economy, energy shortage and environmental pollution are gradually becoming the highlights. Thermoelectricity is one kind of green and environmental energy technology, which is widely used in refrigeration and power generation. Oxide thermoelectric materials are newly emerging potential thermoelectric materials, which are more durable to oxidation, more clean and having a more extensive applied temperature range, a longer working life, a superior thermoelectric performance than other materials. The common methods to synthesize oxide thermoelectric materials are solid-state method, sol-gel method and ball-milling method. However, solid-state method requires higher reaction temperature and longer reaction time, sol-gel method is apt to cause surplus of oxide and organics and produce loose powders, ball-milling method is inclined to pollute the raw materials, introduce crystal lattice stress and cause a higher energy consumption. Therefore, in this paper, homogeneous precipitation was applied to prepared Ca2Co2O5powders using Calcium Nitrate, Cobalt Nitrate and Urea as raw materials. The mole ratio of Calcium Nitrate and Cobalt Nitrate, the mole ratio of Urea and Nitrate, the heating time, the heating temperature and the stirring conditions to synthesize precursors were investigated. The calcination temperature, the calcination time and the calcination atmosphere to prepared the Ca2Co2O5powders were studied. Moreover, the formation mechanism of homogeneous precipitation to fabricated Ca2Co2O5powders were also discussed. Finally, Ca2Co2O5ceramics were fabricated by cold pressing and sintering process. The impacts on synthesizing Ca2Co2O5ceramics of the dosage of binder, the molding pressure and molding time were investigated and the compressive property and thermoelectric performance of Ca2Co2O5ceramics were tested and analysed. Some conclusions were drew as follows:Uniform plate-like Ca2Co2O5powders with a particle size of1μm can be successfully synthesized by using homogeneous precipitation. Ca2Co205ceramics with a smooth surface and compact interior, which possess a compressive strength of90MPa, can be conveniently prepared by cold pressing then sintering technique. It is revealed from the mechanism study of homogeneous precipitation that cations in solution are precipitated in the form of alkali carbonate. It is demonstrated from the tested result of thermoelectric performance that Ca2Co2O5ceramics fabricated by homogeneous precipitation and cold pressing then sintering technique can obtain a good thermoelectric performance. Totally, there are32pieces of figures,12sheets of tables and101pieces of references.