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Study On Characteristic Of Barium Titanate Powder Synthesized By Hydrothermal Method And Properties Of Its Ceramics

Posted on:2012-04-27Degree:MasterType:Thesis
Country:ChinaCandidate:J Q LiFull Text:PDF
GTID:2131330335979683Subject:Materials Physics and Chemistry
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The crystal structure, particle size, morphology and dispersion properties are important characteristics for evaluating the quality of barium titanate (BT) powder, which have great influence on the burnality and physical properties of BaTiO3 ceramics. In order to obtain BT powder of high purity, small particle size, and good dispersion property, the paper is based on the Ti(C4H9O)4-Ba(OH)2·8H2O-NH4OH system, and studies about the influences on particle characteristic of BT powder from the hydrothermal synthesis process and the dispersing agent. The properties of BT powders obtained from different titanium sources are compared. The phase transition mechanisms are studied. Using the doping technology, the paper also studies influences and working mechanisms from the pretreatment and small addition amount of Strontium, Yttrium, or Manganese on the burnality and dielectric properties of BT ceramics. The results are as following:The BT powders are obtained from Ti(C4H9O)4-Ba(OH)2·8H2O-NH4OH hydrothermal system in pure water medium. The BT crystals obtained by using precursor process have better crystalline and less impurities. Higher temperature can promote the crystal growth. The BT powders show larger particle size and higher tetragonal phase percentage. Increasing the ratio of Ba/Ti or the reactant concentration of the medium leads to supersaturation of the starting reaction system, which can quicken the nucleation rate, and give BT powder of smaller particle size. Prolonged reaction time is good for crystal growth, and the particle size increases. When the burning temperature is settled, increasing the hydrothermal process temperature, reaction time, or the Ba/Ti ratio is good for phase transition to tetragonal phase. However, increasing the concentration of the medium will prevent the transition to tetragonal. Higher burning temperature is also good for the phase transition to tetragonal phase. Several kinds of BT powders obtained from different titanium sources are studied. The BT powder obtained from Ti(C4H9O)4 with using precursor process is of the smallest particle size. At certain burning temperature, it can achieve the highest tetragonal percentage. The BT powder obtained from TiCl4 is less effective, and the BT powder obtained from TiO2 show the largest particle size and the least tetragonal percentage.The BT powder made from hydrothermal synthesis always shows aggregation. In order to improve the powder dispersion, inhibit the large particle size from the crystal growth caused by the aggregation and the wider range of particle size distribution, influence on the particle size and dispersion from three dispersion agents are studied. The experiment results show that ethylene glycol can inhibit the growth of the BT crystal, and can improve the dispersion. As the amount of ethylene glycol increases, the particle size decrease gradually. When the concentration of ethylene glycol is of 1 vol% to 3 vol%, the particle size calculated by Scherrer Equation, specific surface area equivalent method, laser particle size analysis, and observed directly through transmission electron microscope are consistent to be only about 45 nm. The powder tends to be single dispersion. Polyacrylic acid can also improve dispersion of BT powder. The influence from sodium carboxy methylcellulose is not obvious.The BT powder obtained from hydrothermal synthesis give ceramics of low density when burned at 1250℃. Increased sintering temperature leads to large crystal size or abnormal crystal growth, and decreased density and dielectric property. Doping and pretreatment of the powder can improve the burnality and microstructure of the BT ceramic, and thus increase the dielectric property of the ceramics. Doping of Strontium, Yttrium, or Manganese, using ethanol as the grinding medium, and preheating at 900℃can promote the BT crystal phase transition to tetragonal. The doping and pretreatments are also good for increased ceramic density and fine particle size. Doping of Strontium, Yttrium, or Manganese all can improve the dielectric constant of BT ceramics at room temperature. Doping of Strontium of only 1.0 mol% can increase the dielectric constant to over 2400. Doping of Yttrium of only 0.3 mol% can increase the room temperature dielectric constant to over 21000. Doping of manganese of only 1.0 mol% can increase the dielectric constant to over 2700. Doping of Strontium can decrease the Curie temperature of the BT ceramic, while doping of Yttrium and Manganese will increase the Curie temperature of the ceramics. Manganese shows the most influence, as the ceramics'Curie temperature increases by 8℃compared with the ceramics without doping. The room temperature dielectric constant of the BT ceramic decreases with the increased frequency, and arrives at the steady constant at around 10 KHz.
Keywords/Search Tags:barium titanate, hydrothermal synthesis, phase transition, dispersing agent, dielectric property of ceramic
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