The Synthesis Of Nano-CaCO₃ And CaCO₃ Host Red Luminescent Materials By Solid State Reaction

CaCO3 have been widely used in plastics, rubber, paint, ink, paper, pharmaceutical, food and household chemicals and many other fields. In addition, it can be applied as excellent host materials for luminescence materials due to their good absorption for UV light and low cost. CaCO3 have three crystal structures:calcite, aragonite and vaterite, different application of CaCO3 has different requirements on its crystal morphology and particle size, so the control preparation of CaCO3 with different crystals, morphologies and size is important. At present, the main producing technique for CaCO3 in industry scale are carbonization or precipitation, both methods are to be carried out in aqueous solution and the reaction conditions must be strictly controlled, also have certain requirements for equipment. Solid state reaction has the following several advantages:the produce process is simple, easy to operate, energy saving, environmental friendly, and can avoid the hard agglomeration phenomena which easy happened in liquid phase reaction. In this article, the raw materials such as CaCl2·2H2O, Ca(Ac)2, Ca(NO3)2·4H2O, Ca(OH)2, (NH4)2CO3, NH4HCO3, Na2CO3and NaHCO3 were used as reactants, to prepare nano-calcium carbonate and red luminescence material(CaCO3:Eu3+) through the solid phase reaction at room temperature.The influence of some factors, such as different calcium salts, carbonates, modifiers, milling time, molar ratios of reactants, on the particle size, crystal structure, and morphology of CaCO3 was studied. The luminescence properties of CaCO3:Eu3+were also studied. As a comparison, the properties of CaCO3 and CaCO3:Eu3+ synthesized by liquid phase precipitation method was also investigated. The main contents and results are shown as follows:1. The synthesis of calcite CaCO3. When CaCl2·2H2O was applied as calcium source, and reacted with (NH4)2CO3, NH4HCO3, NaHCO3, Na2CO3 in solid phase, or Ca(OH)2 was applied as calcium source, and reacted with (NH4)2CO3, calcite CaCO3 can be synthesized successfully.2. The preparation of vaterite CaCO3. When Ca(Ac)2 was applied as calcium source, and reacted with (NH4)2CO3, NH4HCO3, NaHCO3in solid phase, or Ca(NO3)2·4H2O was applied as calcium source, and reacted with (NH4)2CO3, vaterite CaCO3 can be synthesized successfully.3. Different source of calcium have a great influence for the crystal forms of calcium carbonate, this effect is related to the following two aspects:(1) the acid -base intensity of calcium source. The order of acid -base intensity of four kinds of calcium source and the corresponding crystal forms are as follows: Ca(OH)2 (calcite)> Ca(Ac)2 (vaterite+a small amount of calcite)> Ca(NO3)2 (vaterite)> CaCl2 (vaterite+calcite), both two calcium sources, i.e.Ca(OH)2 with stronger alkaline or CaCl2 with slight acid, are easy to generate calcite calcium carbonate, the other both two calcium sources, i.e.Ca(Ac)2 with weak alkaline and neutral calcium salt Ca(NO3)2 are helpful to generate vaterite calcium carbonate.(2) ion size. The ions with small radius, such as H+, OH-,Cl-, are beneficial to the synthesis of calcite calcium carbonate, the other ions with large radius, such as Ac-, NO3-, are helpful to the synthesis of vaterite calcium carbonate.4. The effect of Ethanolamine on particle size, morphology and dispersity of calcium carbonate. When CaCl2·2H2O react with NH4HCO3, small amount of ethanolamine has no obvious effect on calcium carbonate particle size, but the dispersion is improved significantly. With the increase of the amount of ethanol amine, the particle size of calcium carbonate increases, and is beneficial to the formation of calcite calcium carbonate. While CaCl2·2H2O react with (NH4)2CO3, ethanol amine is helpful to the formation of vaterite calcium carbonate.5. Crystal structure and morphology of calcium carbonate synthesis by precipitation method. When CaCl2, Ca(NO3)2 and Ca(Ac)2 reacted respectively with NaHCO3、NH4HCO3 in aqueous phase, the prepared calcium carbonate are consisted of vaterite and very small amounts of calcite with petal morphology. When reacted with Na2CO3 or (NH4)2CO3 by liquid phase reaction, the vaterite calcium carbonate with spherical structure obtained. Among them, the calcium carbonate particles synthesized by using Ca(Ac)2 as reactant have a relatively small size.6. The intensity of emission spectrum of prepared luminescent material CaCO3:Eu3+ has a great relationship with its particle size. The smaller the particle, the greater the emission peak intensity. The size of particles synthesized by Solid phase reaction is smaller than that synthesized by liquid coprecipitation method, so has a stronger intensity of emitted light. Vaterite-based CaCO3:Eu3+ is given priority to red light emission, but calcite-based CaCO3:Eu3+ is given priority to orange-red light emission, and the luminous intensity of the former is higher than the latter.