【作者】 陈松；

【导师】 张多默；

【作者基本信息】 中南大学 ， 有色金属冶金， 2003， 博士

【摘要】 Co₃O₄粉末在催化剂、磁性材料及电化学等领域有着十分广泛的应用。随着这些行业的发展，传统的湿法制备Co₃O₄粉末的生产工艺已不能满足市场对粉末的粒度和形貌的要求。探索合适的控制粒度和形貌的方法与理论，对于优化Co₃O₄粉末的生产工艺及开发新产品具有十分重要的意义。 本课题研究了在低浓度沉淀体系和高浓度沉淀体系中制备单分散Co₃O₄粉末时粒度与形貌的变化规律，并提出了新的控制方法与理论。 低浓度钴盐溶液体系中，采用均匀沉淀法能够较好地控制粒子的成核与长大，实现LaMer曲线所描述的将成核与生长分开。利用电导率仪在线测定反应和陈化过程中溶液电导率的变化，发现反应开始时的溶液的电导率有一明显的下降，随后趋于平缓。可以认为，电导率的突降是由于“爆发”成核使溶液中离子浓度迅速降低引起的。突降后的趋势反映了粒子的生长过程。电导率的变化可以成为确定溶液中粒子成核过程和生长过程的判据。根据电导率突降的时刻改变反应条件或终止反应，可以获得一定粒度的单分散粉体。 均匀沉淀体系中，反应物浓度的不同使粒子呈现出形貌的多样性。其原因在于初始晶粒中阴离子的种类和化学计量数的差别使其化学组成产生差异。沉淀粒子的化学式确定为：Co^Ⅱ,Ⅲ（OH）_0.83（CO₃）_0.49A_y0.14H₂O(在密闭反应器中制备的粒子，式中：A为NO₃^-、SO₄^2-或Cl^-；y[A]分子量≤12.9)和Co^Ⅱ,Ⅲ（OH）_0.83（NCO）_xA_y·0.14H₂O(在敞开的反应器中制备的粒子，式中：A为NO₃^-、SO₄^2-或Cl^-；42x+y[A]分子量≤44.82)。阴离子(SO₄^2-、Cl^-、NO₃^-)主要通过部分取代初始晶粒中的CO₃^2-而影响其极性点位置和极性大小及生长过程的动力学，改变粒子的形貌。阴离子影响程度的强弱与离子半径有关。离子半径越大，对形貌的影响越强，顺序为SO₄^2-＞NO₃^-＞Cl^-。 在高浓度钴盐溶液体系中，分别用碳酸铵和草酸铵作沉淀剂。高反应物浓度体系中，聚集生长过程是粒子长大的主要方式，形貌和粒度的控制主要是通过控制聚集生长而实现的。根据Gibbs吸附定律，新生成的沉淀物粒子具有吸附周围介质中的分子或离子以降低其表面能的能力。可以设计一个低界面张力的体系，使粒子在其中处于热力学稳定状态，成为具有特定形貌和粒度的单分散体系。同时，吸附作用又会使粒子表面带电，产生团聚电垒。ζ电位能够反映粒子表面带电情况，因此粒子ζ电位的变化可以作为定义这一体系的依据。在博士学位论文摘要一定条件下，根据不同的体系所得粒子的乙电位随pH值变化的趋势，通过调整反应和陈化过程的pH值和离子强度，能够控制体系的界面张力，制备出单分散钻化合物沉淀。化学式可以表示为c。”，m（NH4）。.12（OH）。38（CO3）。.8:Ay·o.36HZO（其中:A为NO3一、5042一或el一;y[A]杆、蒸6.89）;形貌有片状、柱状、纺睡形等，粒度范围分别是0.05林m一0 .09林m，0.08拼m一0.15林m，0.15林m一0.25林m，0.3林m一0.4林m，0.4林m一0 .55件m和0.9林m一1 .2林m等。 用草酸按沉淀制取草酸钻的过程中，反应条件对草酸钻的松装密度产生很大的影响。钻盐浓度越高，草酸钻的针状形貌变得粗短，松装密度变大。反应温度越高，草酸钻的松装密度也变大。草酸馁的加入速度增大时，草酸钻的松装密度变小。溶液中NH4+的加入，在高pH值条件下，存在钻氨的络合反应和钻的沉淀反应，草酸钻仍保持针状形貌:在低pH值条件下，随着NH4十加入量的增多，草酸钻形貌变得粗短，长径比、粒度减小;最后呈方形，松装比重增加。 在高浓度沉淀体系中，提出了通过调节颗粒界面张力来控制粒子的聚集。低界面张力体系中，特定形貌和粒度范围的粒子将稳定存在，不随陈化时间的延续而改变。二次成核和Ostwald陈化现象都被抑制。虽然动力学因素在这种形貌、粒度的控制方法中起到一定的作用，但这种低界面张力的控制方法可以认为是基于热力学稳定作用的控制。 此外，还研究了沉淀物在热分解过程中颗粒粒度与形貌的变化规律及相关机理。制备出尖晶石型C伪04粉体，粒度分布为:0.08林m一0 .16拼m，0.18林m一0.23林m，0.22林m一0.3林m，0.3林m一0.4林m，0.3林m一0.6林m，0.75林m一l林m等。钻的碳酸盐沉淀受热分解，存在部分eoZ+氧化成c了十，生成中间产物Hcoo:的步骤。而草酸钻的热分解首先生成金属钻，随后由于所处氧化性气氛的作用，形成C0304。由于“局部规整”作用，锻烧产物与前驱物呈现出形貌上的继承性，然而，这种继承性因前驱物化学组成而异。分解温度较高时，产物呈现多孔特征，过高的分解温度和过长的锻烧时间都会使粉末出现烧结、二次成核和生长等现象，使粒子粒度增大。锻烧前驱物组成中的阴离子在热分解过程中起到空间阻隔、自身氧化和提供氧源的作用，对尖晶石型Co3O4的形成温度、粒度、孔隙度等有较大的影响。更多还原

【Abstract】 Co3O4 powder has extensive applications in the fields of catalysis, magnetic material and electro-chemistry. More and more strict specifications are needed for Co3O4 powder in market. According to Co3O4 powder production process of hydro-chemistry method, it is of great signification to develop the right method and theory to control the particle morphology, size and size distribution for preparing high quality Co3O4 powder.In this paper, the basic change laws of the morphology, size and size distribution of the dispersed Co3O4 powder were studied by precipitation in diluent and concentrated solutions of cobalt salt system. The new control method and theory were developed.In diluent cobalt solution, the stages of nucleation and growth were easily divided by homogeneous precipitation process just as what described as La Mer model. In this study, an electrical conductivity detect was applied on line to record the change of the solution electrical conductivity during the reaction and aging. It was found that at the early period of the precipitation the solution electrical conduction rose slowly to a certain extent and then a sudden drop happened following with the gradual restore to a lower but smoother value. It could be determined that the sudden drop was due to the ion concentration decrease quickly because of the burst nucleation. The growth stages could be defined to be the following course of the smooth electrical conductivity. The change of the solution conductivity could be taken as a sign to discriminate the nucleation and growth stages. According to the change of the solution conductivity, it could be determined whether it was needed to finish. reaction or change corresponding conditions, and the mono-disperse powders with definite size were obtained during the experiment.In the homogeneous precipitation system, under the condition of the different reagents concentration, the precipitation particles with diverse morphologies were obtained. The main reason was that the primary particles had different chemical compositions for the effects of the different kinds of anions and stoichio-chemical compositions of the primary particles. The chemical formula of particles was confirmed. TheyABSTRACTare CoIun(OH)o.83(CO3)o.49 Ay 0.14H2O(in tightly-capped reactor: A stands for NO3\ SO42" or Cl"; y[A] moiecuiar weight 12.9) and Co"jnmoiecuiar weight (OH)0.83(NCO)xAy 0. 14H2O. (in open reactor A stands for: NO3\ SO42" or Cl’; 42x+ yCA]?weigh44.82). By replacing CO32" partly in the primary particles by the anions (SO42\ NO3\ Cl") and influencing the chemical polar positions and degrees, the growth kinetics were changed, which led to the formation of particles with different morphologies. The effect degree of the anions depended on the co-existing anion radius in the reaction solution, and their effects on the particles could be showed as S042>C1>N03-.In concentrated solution of cobalt salt precipitation system, the effects of reagents of ammonia carbonate and ammonium oxalate was studied respectively. In concentrated solution, the main mechanism of the particle growth was aggregation. The control of morphology and size was realized by means of controlling the aggregation process. According to the Gibbs Law, the early-formed fine particles had the ability of absorbing molecules or ions in the solution to decrease the interface energy of the precipitation system, which gave an idea of by designing a lower interface tension system to make the particles exist in the thermo-dynamic stable state and produce the mono-disperse system with special morphology and size. The surface of particles was charged by adsorption effect and so the electric barriers against the aggregation between particles were established. The adjusting of surface charging of the particles could be performed by the reference of the zeta potential of the particles in the suspension. The experimental results showed that the zeta potential could be taken as a sign to guide the designing of this kind of stable system. According更多还原