Nano-antimony-doped Tin Oxide (ato) Powder Preparation And Slurry Stability

Nanomaterial is a new knowledge which was developed in the late of last century. It studies objects size in 1～100 nm. When materials are in nanometer size, there are many excellent properties compared to that of the ordinary materials. Hence, nanomaterials are a hot research field in this century. Nanomaterials are a very important research field to be supported in many countries including China. Nanometer antimony doped tin dioxide (ATO) powders were prepared by co-precipitation method in this thesis. The properties of these powders prepared at various conditions were discussed here. At the same time, the stability of these powders dispersed in water was discussed.Both glass and plastics are very excellent transparent materials, however, they are liable to generate static electricity on their surface because they are insulators. Various displays made by glass or plastics often become difficult to be visible because dust or the like is attracted by static electricity. It is a good method to paint some transparent conductive materials on these insulators. Tin oxide is a wide optical band gap semi-conductive material. It is a good transparent material in visible and near infrared zone. When SnO2 in it's strict stoichiometric state, its resistance is very high and it is nearly an insulator. Non-stoichiometric SnO2 has some conductivity because of oxygen vacancies. However, the conductivity of this SnO2 is unstable because oxygen vacancies can react with oxygen in the ambient. This greatly limits the application of SnO2. Additions of some Group V elements such as Sb can form a donor centre very close to conduction band of SnO2. The donor in SnO2 will increase both carrier concentration and carrier mobility. Thereby the conductivity is increased. The sel-gel method, hydrothermal, co-precipitation and spray pyrolysis are commonly used for antimony doped tin oxide powders preparation at present. There is not an effective process for commercial production of ATO in domestic market. All of these ATO powders or paste used in displays is imported.In this research, two cheap inorganic materials, SnCl4.5H2O and SbCl3, were used as raw materials of Sn and Sb, and ammonia solution was used as precipitation reagent. Sn(OH)4 and Sb(OH)3 precipitations are the results of these precipitation reactions.Then antimony doped tin oxide powders were formed. The transmission electron microscopy (TEM) was used to estimate particle size, investigate particle morphology and particle conglomeration state. The x-ray diffraction (XRD) was used to characterize the crystalline size and phases of ATO powders. At the same time, the state of Sb in SnO2 lattice was studied. The purity of these powders was examined by Electron Probe technique. Thermal analysis was applied to analyze the thermal properties of the dried gel which would study the change in calcination. Optical transmission of films prepared by these ATO powders was carried out by UV-vis spectrophotometer using a double beam. Doped element and calcination effect on the optical transmission of films was studied. Four-point probe method was used to study the electrical properties of films prepared by these ATO powders.The effects of different preparation parameters on the powders properties were studied. Both SnCl4.5H2O and SbCl3 were dissolved in ethanol or hydrochloric acid, the effect of solvent type on ATO powder size is very small through TEM. The solution dropwise methods were discussed, too.The reaction pH is always an important parameter in hydrolysis reaction. The solution pH value decides whether the hydrolytic precipitation reaction of SnCl4 or SbCl3 could take place. If the solution pH value is very low, neither SnCl4 nor SbCl3 could be hydrolyzed. Once the pH value is above some value, both SnCl4 and SbCl3 are hydrolyzed. In this thesis, the precipitation reaction was taken place in pH range from 2 to 10. XRD and TEM results showed that the grain size was the biggest when reaction pH was 6.The concentration of Sb is one of the most important parameters which affect properties of ATO powders. In this research, concentration of Sb range from 1-20%(WT) was studied. Addition of Sb could decrease the SnO2 grain size. The conductivity of SnO2 increased quickly with small addition of antimony then reached a maximum value at proper addition of antimony. Further addition of antimony, the conductivity became stable. However, the optical transmission of SnO2 films decreased with antimony addition.Both the co-precipitation reaction temperature and the dry gel calcination temperature are important preparation parameters in preparing nanoparticles by co-precipitation method. The reaction speed of precipitation is very slow when the reaction takes place at low temperature. However, if the reaction temperature is too high, NH3 volatilizes.333K is a proper value for ATO powder preparation. When metal oxides are prepared by hydrolysis reaction, the hydrolysis product should be calcined to remove bound water and made the product crystallized. In this thesis, the dry gels were calcined at different temperatures as follows:373K,473K,673K, 873K, et al. The results showed that both the crystalline size and particle size increased with increasing calcination temperature. Therefore, we could control calcination temperature to get the grain size and particle size which we needed. Resistance of powders calcined at different temperatures showed that there was a crucial relationship between calcination temperature and powder conductivity. The thermogravimetric analysis and differential scanning calorimetry analysis result and the comparison standard free energy of Sb2O3 and Sb2O5 formation, valence state of Sb in the powders was mainly+5. When Sb was in pent-value state, a donor centre was formed in SnO2. Therefore, both carrier concentration and carrier mobility were increased. If the calcination temperature was enhanced than some value, the conductivity could not increase. On the contrary, the conductivity decreased slightly. Two reason might account for this, one was Sb volatilization, the other was that there were some Sb+5 changed into Sb+3. The color of ATO powder changed from light brownish-yellow into blue with increasing calcination temperature.Particle dispersity was greatly affected by additions of dispersant in the process of powder preparation. Non-ionic surfactants such as polyethylene glycol and polyvinyl pyrrolidon improved these powders in a monodisperse state. At the same time, ionic surfactants made the powder congregated. The monodisperse state of these powders was also affected by the precipitation washing methods. The impurity ions removed different from different washing methods, and some impurity ions such as Cl- might make the powder congregated.The preparation parameters were optimized. We got monodisperse, spherical or spheroidal ATO powders with particle size range from 15nm to 30nm in laboratory. ATO powders bought from Japanese and South Korea companies and our laboratory sample were analyzed by XRD. The XRD patterns showed that these three ATO samples had similar XRD patterns. The crystalline size of our sample was between that of these foreign samples. Impurity analysis showed that powders prepared by co-precipitation had high purity.Nanoparticles often aggregate because of their ultra fine particle size and very large surface areas, hence, some excellent nanoproperties are lost. All of these ATO used in domestic market are in paste state. In this thesis, the dispersion stability of our ATO paste sample was discussed.These ATO particles in liquid were sheared at high speed and milled at low speed. Some dispersants were added to the paste to improve dispersion stability. This stability was estimated by the sediment volume at the tube bottom after staying static for equal time. The most stable dispersion sample had the least sediment volume. If ATO particles were dispersed in distilled water, the system had better be kept in neutral. At the same time, low system temperature was beneficial to the dispersion stability. Some proper dispersants improved the stability greatly. The results showed that the proper dispersant weight was 2～4% of the ATO particles.Using ATO powders prepared by co-precipitation, optimizing the preparation parameters, we got ATO water paste which had remained in stable dispersion state over 10 months.