【作者】 张鹏；

【导师】 张煜；

【作者基本信息】 贵州大学 ， 化学工程与技术， 2020， 硕士

【摘要】 硫酸钡作为一种重要的化工原料,被应用于众多行业,随着硫酸钡应用研究的不断深入,对硫酸钡品质提出了新的要求,尤其是纯度和形貌可控的超微硫酸钡新品种的研究,受到广泛关注。目前国内硫酸钡的制备方式多采用的是直接沉淀法,因其反应速率较快,无法控制晶体的生长速度,难以控制硫酸钡晶体的形貌。离子交换法作为一种新颖的合成方式,其原理是利用反应物与生成物之间溶度积的差异,在固-液体系中实现离子交换、沉淀转化,其本质是复分解反应,可更方便对反应速率进行控制。基于此,本论文提出了以碳酸钡和硫酸盐为原料,采用离子交换法制备形貌多样化的沉淀硫酸钡,考察反应体系中硫酸钡晶体结构、形貌等随反应条件的变化规律,并采用Materials studio软件对硫酸钡晶体生长机理进行分析,为后续合成可控硫酸钡晶体的研究提供一定的理论支撑。论文首先以碳酸钡和硫酸钾为原料,考察了反应条件对硫酸钡得率的影响,结果表明:在最优反应条件下,硫酸钡得率最高可达98.25%,硫酸钡结晶度较好,形貌为六棱柱形。该反应过程属于液-固相非催化反应,为放热反应,晶核生成阶段属于外扩散,动力学方程为:y=509.7X-5.82682,活化能为-4.238k J/mol;晶体生长阶段属于内扩散,动力学方程为:y=597.3X-6.44104,活化能为-4.966k J/mol。论文分析了NH₄⁺、Na⁺和K⁺离子在硫酸钡结晶过程中的作用机理,实验结果表明:在相同条件下,K⁺能促进硫酸钡的生成,其次是Na⁺,最后是NH₄⁺。NH₄⁺、Na⁺和K⁺进入硫酸钡的晶格中取代Ba²⁺,形成杂质缺陷,由于离子半径间的差异,改变了晶胞体积。硫酸钡晶体的形貌随着硫酸盐中阳离子的种类及浓度的变化而改变,在含有NH₄⁺的溶液中得到的硫酸钡晶体形貌为不规则的片状;当溶液中存在Na⁺时,硫酸钡晶体形貌随着其浓度的升高,由长方体形转变为片状;当溶液中含有K⁺时,硫酸钡晶体形貌随着其浓度的升高而变化,分别为长方体形和六棱柱形。论文探讨了阳离子表面活性剂CTAB与DTAB对反应体系,晶体结构和形貌的影响,结果表明:阳离子表面活性剂不会促进或抑制反应的进行,但硫酸钡晶体形貌随着表面活性剂种类、浓度以及体系的反应温度的变化而变化。当反应体系中存在CTAB时,硫酸钡晶体的形貌随着CTAB浓度的增加,由六棱柱形向长方体形转变,随着反应温度的增加,硫酸钡晶体形貌由片状变为长方体形;当反应体系中存在DTAB时,硫酸钡晶体的形貌随着DTAB浓度的增加,由不规则的形貌向长方体形转变,随着反应温度的增加,硫酸钡晶体形貌由片状变为六棱柱形。最后,本文通过Materials Studio软件Morphology模块中的BDFH模型和AE模型从理论上对硫酸钡晶体的平衡生长形态进行模拟计算;采用Forcite模块对表面活性剂与硫酸钡分子间的相互作用进行动力学过程模拟计算,结果表明:两种模型计算的硫酸钡晶体形貌都为六面双锥柱状,晶面（110）、（1^—10）、（^—1^—10）、（^—110）、（0^—20）和（020）构成了硫酸钡晶体的六个柱面,晶面族{111}、{101}、{021}构成了硫酸钡晶体的锥面。表面活性剂DTAB与硫酸钡晶面的更容易相互作用,易吸附于晶体上,而CTAB的吸附能力较弱。随着温度的升高,CTAB和DTAB与晶面的相互作用减弱,表面活性剂不容易吸附在晶面,升高反应温度会导致晶体形貌发生变化。更多还原

【Abstract】 As an important chemical raw material,barium sulfate is used in many industries.With the development of the application field of barium sulfate,the new requirements for the quality of barium sulfate have been proposed,especially research on the new varieties of ultra-fine barium sulfate with high purity and controllable morphology has attracted wide attention.At present,precipitated barium sulfate is synthesized by direct precipitation in China,but the crystal growth rate cannot be controlled duo to the faster reaction rate and is difficult to control the morphology of barium sulfate crystals.As a novel synthesis method,the principle of the ion-exchange method is to use the difference in the solubility product between the reactants and the product to achieve ion-exchange and precipitation transformation in the solid-liquid system.The essence of that is the displacement reaction,which makes it easier to control the reaction rate.Based on that,the ion-exchange method for generation barium sulfate with various shapes by using barium carbonate and potassium sulfate as raw materials was proposed.In addition,the changes of crystal structure and morphology of barium sulfate with reation conditions were investigated,the synthesis mechanism of barium sulfate crystal was analyzed by using materials studio software,which provide theoretical support for the following study of synthetic barium sulfate crystal controllability.In this paper,the effects of reaction conditions on the yield of barium sulfate was investigated by using barium carbonate and potassium sulfate as raw materials.The results show that the best yield of barium sulfate is about 98.25%and the shape is hexagonal prism with good crystallinity under the optimal process conditions.Moreover,the reaction process belongs to the liquid-solid phase non-catalytic exothermic reaction,and the nucleation stage belongs to external diffusion,the kinetic parameters have been calculated:kinetic equation（y=509.7X-5.82682）and activation energy（-4.238k J/mol）of this reations;The grain growth stage belongs to internal diffusion,and the kinetic parameters have been calculated:kinetic equation（y=597.3X-6.44104）and activation energy（-4.966k J/mol）of this reations.Secondly,mechanisms of NH₄⁺,Na⁺and K⁺ions in the crystallization process of barium sulfate were investigated.It turns out that compared with Na⁺and NH₄⁺,K⁺can promote the formation of barium sulfate under the same conditions.NH₄⁺,Na⁺and K⁺ions can replace Ba²⁺of the lattice,and form impurity-defect.The cell volume was changed due to the difference in ion radius.The morphology of barium sulfate changes with the type and concentration of sulfate,The morphology of barium sulfate is irregular shape in ammonium ions solution;The morphology of barium sulfate changes form cuboid to sheet shape with increase of Sodium ions concentration;The morphology of barium sulfate changes form cuboid to hexagonal prism with increase of Potassium ions concentration.The effect of CTAB and DTAB on reaction system crystal structure and morphology were disscussed.The results show that cationic surface active agent cannot promote or inhibit the reaction.However,the morphology of barium sulfate changed with surfactant type,surfactant concentration and reaction temperature.The morphology of barium sulfate changes form hexagonal prism to cuboid with increase of CTAB concentration,the morphology of barium sulfate changes form sheet shape to cuboid with increase of temperature in CTAB.The morphology of barium sulfate changes forms irregular shape to cuboid with increase of DTAB concentration,the morphology of barium sulfate changes form sheet shape to hexagonal prism with increase of temperature in DTAB.At last,the equilibrium growth morphology of barium sulfate have been simulated by using BDFH model and AE model of Materials Studio software.Interaction between surfactant and barium sulfate have been simulated through Forcite module of Materials Studio software.The results show that the morphology of the barium sulfate was hexagonal bipyramid by simulation of two models.The crystal faces（110）、（1^—10）、（^—1^—10）、（^—110）、（0^—20）and（020）constitute the six cylinders of barium sulfate,the family of crystal planes{111},{101}and{021}constitute the cones of barium sulfate.Compared with CTAB,Interaction between DTAB and barium sulfate was strong,DTAB is easy to stick to the crystal.With the increase of temperature,interaction between surfactant and barium sulfate was weak,surfactant is not easy to stick to the crystal,this can result in changing the morphology of barium sulfate.更多还原