Bi1/2Na1/2TiO3 Piezoelectric Ceramics
In recent years, research and hydrothermal method in the field of lead-free piezoelectric ceramics focused on lead-free piezoelectric ceramic powder synthesis, and thus the powder system for ceramic piezoelectric properties have been reported rarely, and therefore still the need for further research.
Preparation four: molten salt method
Molten salt method for preparing single-crystal particles is a simple and inexpensive technique, which synthesis is carried out in a low melting point melts, the molten salt does not promote the reaction only participate in chemical reactions. Weiwu Chen et al in Na2CO3, Bi2O3, TiO3, BaCO3, NaCI and KCI as raw material, mixed oxides and carbonates then mixed with the stoichiometric amount of salt, the salt is then heated to melt the reactants in a salt melt carrying out the reaction, the synthesized powder with hot deionized water several times to remove free chloride ions, the powder obtained BNBT perovskite structure. They are 850 degrees out of synthesized having a grain size less than 100nm powder BNBT6 pure perovskite structure, but a high degree of aggregation of the obtained powder, and is obtained at a temperature of 1100 degrees readily dispersible, non-agglomerated powder of size distribution around 1-3um.
BNT-based molten salt synthesis advantage of lead-free piezoelectric ceramic powder that: Process 1) simple operation, no other special equipment; 2) compared with conventional solid-state reaction method, the obtained powder particle size distribution of smaller and more uniformity; 3) Since a liquid phase reaction system, and therefore the synthesized product of the component ratio is accurate, uniform composition, no segregation; 4) in the course of the reaction and subsequent cleaning process, to facilitate removal of impurities, formation of high purity reaction product.
Preparation five: Sugar protect pyrolysis
Sugar protect pyrolysis is a new method for the synthesis of nanopowders recent BNT reported. LiSun and others to Bi (NO3) 3 * 5H2O, NaNO3, Ti (OBu4), glycerol, NH4NO3, and sucrose as a raw material, a three-step synthesis of BNT powder constituents of the perovskite structure, such as a specific process figure. BNT powder prepared by the ceramic piezoelectric constant d33 reach 80pC / N, and before the results reported solid phase reaction prepared by BNT ceramics (73pC / N) are close.
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Sugar protect pyrolysis preparation BNT-based lead-free piezoelectric ceramic powders advantage is that the process is simple and can be crystallized at a relatively low temperature to avoid over-grown grain. At the same time, but also helps to reduce the added sugar BNT powder grain size, which is directly due to increased sugar content in the system increases the carbon content, resulting in a reduction atmosphere, the reduction atmosphere is conducive to the formation of nano-powders BNT . Lisun others at lower temperature of 500 ° prepared particles uniform, good crystallinity, a diameter of about 50nm and BNT powder. Another use of the powder prepared by the method can solve the problem of nano-powder agglomeration, which is due to NH4NO3 as a foaming agent to help the system to form a porous structure, which effectively control the reunion.
But because the new method is still BNT powder solution was prepared using sugar thermal protection, yet to see the report on the use of this method for preparing other BNT-based ceramic powder, so the need to increase the experimental system to continue to study.
Synthetic preparation of highly active piezoelectric ceramic powder is a prerequisite for the preparation of high-performance piezoelectric ceramics. Low conventional solid state reaction method, although cost, high yield, the preparation process is relatively simple, but often coarse powder preparation, less active, less chemical uniformity, easy reunion. Sol - gel method, hydrothermal method, molten salt thermal protection laws and sugar solution and other wet chemical methods have their own advantages in the preparation of BNT-based ceramic powders, but the real industrial production needs further study, we believe that with the deepening of research and preparation methods of continuous improvement, performance BNT-based lead-free piezoelectric ceramics will continue to improve, replace ceramic leaded to unleaded final ceramic desire to achieve.
