The Purification of Boric Acid and Preparation and Characterization of Aluminum Borate Whiskers and Phosphors

The Purification of Boric Acid and Preparation and Characterization of Aluminum Borate Whiskers and Phosphors
　　Boron compounds are an important series of products in the inorganic salts industry. The relative of products development and theory researches have become a hot topic, especially in the high tech domains, such as the Aerospace etc for many years. Boric acid is widely used in the boron compounds, not only its functional value, but also it is an essential raw materials for the synthesization of boron functional products. However, the impurities of boric acid has been limited its range of use, but also greatly limited the purification technology of boric acid in the domestic. Currently, some special purposes boric acid, such as optical materials and so on, basically depends on imports in rare earth magnets the domestic markets. Considering our country owns massive boron resources (storage level stands third in the world), this dissertation, that is based on the national and liaoning province’s boron resources developmental strategy, develops the removal of iron impurties of boric acid and the synthesis of aluminoborate functional materials.
　　The main frame construction of dissertation is that:To take industrial boric acid as raw material develops the removal of iron impurties of boric acid which takes electro-optical level special-purpose boric acid as target. Based on this, it combines high pure aluminum alkoxide to research on the synthesis of aluminum borate whiskers and its fluorescence materials which solved key technologies and the technology based question, to promote boric acid and containing boron functional materials performance, as well as expands its application domains to provide the technical supports and the theory basis. The results are listed below:1. Use the complexation-crystallization method to conduct the directional purification of boric acid. Based on chemical solubility product and complexing balanced theory, the purified technology of complexation-crystallization, which applies the different solubility of boric acid at different temperature and crystal characteristic, has been proposed. The experiment has studied the types of complexant, amounts and solvent systems etc to affect the removal of iron impurities of boric acid, also studied technical conditions such as crystal temperatures, crystal ways, crystal time to control surface absorption or smuggles of impurities. ICP-AES, UV-Vis-IR adsorption were used to characterize the products. Having formed technical system of the complexation-crystallization method to remove iron impurities of boric acid through the experimental datum induction and theoretical analysis, the iron content of boric acid reduces from 100ug/g to lug/g; the purity of boric acid increases from 98.7% to 99.9%. Simultaneously, calcium, chromium, cobalt, nickel, titanium, copper imprities have been removed. This technology has been used to produce the special optical glass in chengdu some enterprise.2. To base on high pure boric acid and high pure aluminum alkoxide as reactants study the synthesis of aluminum borate whiskers. The traditional aluminum borate whiskers have been used inorganic aluminum sources, boric acid and boron oxide etc as raw materials. The dissertation, that studys formative reaction rule and crystal characteristic of aluminum borate, besides the consideration of the characteristic of raw material purity, replaces the inorganic aluminum sources with aluminum isopropoxide and combine solated superfine characteristic of aluminum isopropoxide, simultaneously, considering traditional aluminum source to form the comparison. Experimental study focused on the aluminum borate whiskers to control the crystal structure and morphology to grope the optimized synthetic method of aluminum borate whiskers.
　　The technical conditions such as, molar ration Al/B, calcination temperature, calcination times, different aluminum sources, etc, which have affected the crystal structures and morphology formation, have been systematically investigated. TG-DTG, XRD, FT-IR, SEM, TEM were used to characterize the products. The results showed that high-purity raw materials can improve the cleanliness of the products surface and maintain the consistency of dimensions, replacing the traditional inorganic aluminum sources with the aluminum alkoxide can reduce the diameters of aluminum borate whiskers, increasing the aspect ration. In the optimal synthesis conditions, the whiskers are very neat and straight with an diameter ranging from 200 to 300nm and lengths ranging from 3 to 5μm, aspect ratio is greater than 10. This research provides the foundation for the following the synthesis of rare earth doping in aluminoborate.In addition, in view of the high temperature synthesis of aluminum borate whiskers by solid state reaction, combustion synthesis of Al18B4O33 Whiskers has been demonstrated through a rational chemical reaction, which realized the low temperature synthesis of Al18B4O33 Whiskers by urea as combustion agent. Comparing to the high temperature solid state reaction, combustion http://www.chinamagnets.biz/ method reduces the reaction temperature 200℃to provide a new idea for the synthesis of aluminum borate whiskers research.3. Synthesis and characterization of rare earth doped aluminum borate phosphor. Al18B4O33 Whiskers ion-coating and gel nano-coating methods are synthesized Al18B4O33:Eu3+,Tb3+ phosphors, respectively. Comparing with Al18B4O33 Whiskers ion-coating method, gel nano-coating method abtainning products have a more uniform appearance and more luminous intensity. Therefore, this dissertation mainly focuses on the gel nano-coating method to synthesize Al18B4O33:Eu3+,Tb3+ phosphors. Considering traditional aluminum source to form the comparison and the technical conditions such as, molar ration Al/B, purity of raw materials, calcination temperature, calcination times, etc, which have affected Al18B4O33:Eu3+,Tb3+ phosphor luminescence intensity.
　　The results showed that high purity of raw materials can increase the luminous intensity of the product and traditional inorganic aluminum salts are replaced with aluminum alkoxide to solve agglomeration disadvantages of high temperature solid state method. The fluorophor coexists the crystal phase Al18B4O33 and the aluminoborate glass phase and Eu3+, Tb3+ ions are incorporated into aluminobarate glass phase. When the molar ratio Al/B is equal to 1:1, it found that the emission spectra of Eu3+,Tb3+ co-doped Al18B4O33 samples significantly enhance the red light, indicating the phosphor existence of Tb3+ to Eu3+ energy transfer by comparing the Eu3+,Tb3+ co-doped Al18B4O33 with Eu3+ single-doped Al18B4O33.In addition, It uses gel nano-coating method to synthesize Eu3+, Tb3+ excitation GdAl3(BO3)4 high-purity ultra-fine red and green phosphors, basing on structural diversity from the realization of rare-earth ions Eu3+, Tb3+ doping aluminum borate crystal substrate to improve luminous efficiency and color purity. Experimental study focused on the Gd3+ concentration to affect the binary system Al2O3-B2O3 crystal structure and luminescence properties to determine the optimal performance of the phosphors. The results showed that Al2O3-B2O3 binary system http://www.chinamagnets.biz/ turned into the hexagonal GdAl3(BO3)4 from the orthorhombic Al18B4O33, while GdAl3(BO3)4 crystal phase content increased with the increasing of Gd3+ content. Moreover, Gd3+ has the sensitization to Eu3+ and Tb3+ luminescence, Gd3+ also has a certain degree of quenching concentration.