Preparation Of Calcium Carbonate Whiskers Using Calcite Carbonate And Study Of Reaction Mechanism

Calcium carbonate whisker is a green new inorganic whisker material,with a wide range of sources,low prices,excellent performance,non-toxic and so on.It was widely used in plastics,coatings,rubber,friction materials,paper,medicine and other fields.And it can be used in many low-end materials to enhance its body performance.Therefore,the development of calcium carbonate whisker technology has become new hotspot of the current research for the development of inorganic whiskers.In this experiment,calcite calcium carbonate was selected as raw material.After calcination at high temperature,calcium carbonate whiskers were prepared by one-step carbonization and gas-liquid intermittent carbonation respectively.One-step carbonization method was to digest calcined calcite fully,add magnesium chloride as a form control agent,introduce into the carbon dioxide and ultimately prepare calcium carbonate whiskers.Then,the effects of stirring rate,reaction temperature,Ca?OH?₂ concentration,Mg/Ca ratio and reaction time on the preparation of calcium carbonate whiskers were investigated.Moreover,the reaction mechanism of one-step carbonation to prepare calcium carbonate whiskers was discussed.And the carbonization reaction thermodynamics and MgCl₂ mechanism were analyzed.In addition,the thermodynamic model of Ca?OH?₂-H₂O-MgCl₂-CO₂ reaction system was established.The morphology,structure and composition of the product were characterized by SEM and XRD.Finally,the optimum conditions for the preparation of calcium carbonate whiskers using the one-step carbonization method were summarized as follows:the ratio of magnesium to calcium was 2,the reaction temperature was 110?,the amount of carbon dioxide was 100 mL/min,the concentration of calcium hydroxide was 0.5mol/L,the stirring speed was 150 r/min and the reaction time was 1 h.The prepared calcium carbonate whiskers were 1⁴?m in diameter and 15³0?m in length.Gas-liquid intermittent carbonation method was to make ammonia reaction by calcining calcite and a certain percentage of ammonium salt solution,and then pass into the ammonia and carbon dioxide to prepare calcium carbonate whiskers.Then,the effects of the temperature of the steaming,the ratio of reactants and the time of steaming on the result of steaming were studied.Moreover,the effects of reaction temperature,stirring speed,carbon dioxide inflow rate,ammonia concentration and aging time on the morphologies of calcium carbonate whisker were investigated.And the morphology,structure and composition of the product were characterized by SEM,XRD and thermogravimetry.In addition,its growth mechanism was discussed.Finally,the optimum conditions for the preparation of calcium carbonate whiskers using optimum gas-liquid method were summarized as follows:the steam temperature was 100?,the ratio of ammonia chloride and calcium oxide in ammonium chloride was 1:2.2,steaming time was 2 h,reaction temperature was 90?,stirring speed was 400 r/min,carbon dioxide flow rate was 100 mL/min,ammonia concentration was 0.5mol/L and aging time was 1 h.The prepared calcium carbonate whiskers was 98.77%in whisker content,about 10 in aspect ratio,and 98.6 in whiteness.