【作者】 李丽匣；

【导师】 韩跃新；

【作者基本信息】 东北大学 ， 矿物加工工程， 2008， 博士

【摘要】 碳酸钙晶须是一种环境友好型晶须材料,具有原料来源广泛、性能优良、无毒、价格低廉等优点,可用于塑料、涂料、橡胶、摩擦材料、造纸、医学等领域,因此碳酸钙晶须的制备及应用技术引起了人们越来越多的关注。然而在我国此种产品却仍然处于研究与开发阶段,与日本、美国相比有较大差距。本文系统研究了碳酸钙晶须的制备、表面改性技术,并将改性后的晶须应用于聚丙烯(PP)树脂中,研究晶须对复合材料的增韧、增强效果。以生石灰为原料,在普通重力场中,采用工业上制备轻质碳酸钙的碳化法,以可溶性磷酸盐为晶型控制剂,首次采用一步法合成晶型完整、长径比大、尺寸均匀的碳酸钙晶须。测定晶型控制剂添加量、初始石灰乳浓度、反应温度、二氧化碳通气速度、搅拌转速等合成条件对产品性能的影响,得到合成碳酸钙晶须的适宜条件。结果表明,将消化后的熟石灰配制成3.0wt.%的乳液,控制n(P/Ca)(可溶性磷酸盐与Ca(OH)2物质的量比值)为0.25,反应温度75℃,CO2通入速度16.2L/(h·kgCa(OH)2),搅拌转速2000rpm,可制备出结晶良好、文石相含量88.3%、晶须长度及长径比分别为231μm、15.3的碳酸钙晶须产品,所得产品结晶程度高,稳定性好。借助于X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅立叶红外光谱(FTIR)、热重—差示扫描量热分析(TG-DSC)等检测手段,结合晶体化学、物理化学等经典理论,分析碳酸钙晶须结晶过程中可溶性磷酸盐的控制作用机理,研究文石碳酸钙晶须的晶体生长规律。研究结果表明,在最开始的料浆中加入可溶性磷酸盐以后,磷酸盐与Ca(OH)2反应生成了热力学上最稳定的磷酸钙化合物—羟基磷灰石Ca10(P04)6(OH)2(HA),HA呈短柱状,长度约80nm,宽度约20nm。通入CO2初期,[CO32-·(OH)]与[PO43-]发生部分替代,形成B型碳酸羟基磷灰石(B-HA),以此作为结晶中心诱导文石相碳酸钙的异相成核,另有一部分HA选择吸附在碳酸钙的侧面,控制其的生长状态,Ca2+与CO32-不断叠加生长成为文石相碳酸钙晶须。采用单因素条件试验方法,选用硬脂酸、硬脂酸钠、十八酸锌、钛酸酯等表面改性剂对碳酸钙晶须进行湿法表面改性。采用活化指数、接触角作为改性效果评价指标。分别考查了改性剂种类、用量、初始料浆浓度、改性温度、改性时间、搅拌转速、烘干温度等因素对表面改性效果的影响,得到了碳酸钙晶须适宜的改性条件。优选出硬脂酸钠进行改性,当改性剂用量3%,初始料浆浓度为8%,改性温度为80℃,改性时间为20min,搅拌转速为1500rpm,烘干温度为100℃,烘干时间为3h时,改性产品的活化指数、接触角、吸油量分别达到100%、146.66°、64ml/100g,晶须的分散性和流动性也明显提高。结合SEM、XRD、TG-DSC、FTIR等检测手段,分析了硬脂酸钠对碳酸钙晶须的改性机理。结果表明,硬脂酸钠没有改变文石碳酸钙晶须的物相,当在碳酸钙晶须料浆中加入硬脂酸钠的无水乙醇溶液后,CH3(CH2)16COO-离子和Ca2+、Ca(OH)+、CaHCO3+离子结合生成难溶的(CH3(CH2)16COO)2Ca膜包覆在碳酸钙晶须的表面。在碳酸钙晶须与硬脂酸根的吸附中,存在化学吸附与物理吸附层,化学吸附层非常牢固,物理吸附层比较容易解吸。将改性后的碳酸钙晶须按照不同比例添加到PP树脂基体中,考查碳酸钙晶须对复合材料力学性能的影响。选择悬臂梁缺口冲击强度衡量复合材料韧性的改变、拉伸强度和拉伸弹性模量两个参数衡量复合材料刚性的改变、断裂伸长率衡量复合材料塑性的改变。随着晶须添加量的增加,冲击强度先增加后减小,拉伸强度略微减小,拉伸弹性模量增加,断裂伸长率呈下降趋势,当晶须添加量在一定范围内时,可以提高复合材料的韧性和刚性,使综合力学性能有所提高。本文的研究成果对于我国丰富石灰石资源的开发、碳酸钙晶须的规模化生产及应用具有一定的指导意义。更多还原

【Abstract】 Calcium carbonate (CaCO3) whiskers, an environment-friendly whisker material,is characterized by wide raw material sources, good performance, nontoxic and low price, and widely used in various fields such as plastics, coating, rubber, friction, paper-making and pharmaceutics. The synthesis, surface modification and application of CaCO3 whiskers have attracted more and more researches’ attention due to low costs, high whiteness, and contamination-free. However, such product still stays in reaserch stage in China, and there is a big gap compared with that in JP and US.Synthesis, and surface modification of CaCO3 whiskers were engaged in this subject, and modified whiskers were added into polypropylene to investigate the toughening and reinforcing effects.CaCO3 whiskers were direct synthesized at first time from CaO by carbonization method with soluble phosphate as controlling agents, and additives dosage, initial Ca(OH)2 solid concentration, reaction temperature, CO2 flow rate and agitation speed were investigated to achieve the optimum conditions. The results revealed that initial Ca(OH)2 solid concentration of 3.0wt.%,phosphate dosage of n(p/Ca) of 0.25,reaction temperature of 75℃, low CO2 flow rate of 16.2L/(h·kgCa(OH)2) and agitation speed of 2000rpm are beneficitial to formation of aragonite whiskers. Well crystallized CaCO3 whiskers with aragonite content of 88.3%,length of 23μm and aspect ratio of 15.3 were synthesized.The effect mechanism and whiskers growth law were suggested in terms of XRD, SEM, TEM, FTIR and TG-DSC characterization results and related theorys of crystal chemistry and phsical chemistry. It has been indicated that the most stable calcium phosphate in thermodynamics, hydroxyapatite (HA) with length of 80nm and width of 20nm more or less, is formed through the reaction of soluble phosphates and Ca(OH)2 before the introduction of CO2, and then [CO32-(OH)] enters the crystal lattices of HA to replace partially [PO43-] yielding B-carbonate HA in the early stage of CO2 introduction, which induces aragonite to heterogeneously nucleate as nucleation center thereafter, and grows into CaCO3 whiskers by the continuous stack of Ca2+ and CO32-, and other HA selectly adsorbed onto the flanks of CaCO3 to control crystal morphology.Wet surface modification was carried out with surfactants such as stearic acid, sodium stearate, zinc stearate and titanate, etc, and modification effects were characterized with activication index and contact angle. Surfactant types, dosage, initial slurry concentration, modification temperature, modification time, agitation speed, and drying temperature were studied to achieve the optimum conditions as following:better surfactant is sodium stearate, srufacant dosage of 3%,initial slurry concentration of 8wt.%,modification temperature of 80℃,modification time of 20min, agitation speed of 1500rpm, drying temperature of 100℃, and drying time of 3h. The activication index, contact angle and oil absorption value of CaCO3 modified under the optimum conditions are 100%,146.66°and 64ml/100g, and the dispersibility and fluidity of CaCO3 whiskers are improved largely.The modification mechanism of sodium stearate was suggested in terms of SEM, XRD, TG-DSC,and FTIR characterization results. It has been revealed that sodium stearate had not change the CaCO3 whiskers phase, and the insoluble (CH3(CH2)16COO)2Ca was generated by reactions of CH3(CH2)16COO- and Ca2+,Ca(OH)+,or CaHCO3+ onto the surface of CaCO3 whiskers when ethyl alcohol solution of sodium stearate was added into. Chemical adsorption layer as well as physical adsorption layer existed between CaCO3 and sodium stearate, the former is very strong and steady, while the latter is faint and easy to desorb.Modified CaCO3 whiskers of different additions were put into polypropylene to perform effects on mechanical property of composite materials. Cantilever notched impact strength is chosen to evaluate toughening, tensile strength and tensile modulus of elasticity are adopted to estimate rigidity, breaking elongation is introduced to appraise plasticity. Impact strength increased and then decreased, tensile strength slightly reduced, tensile modulus of elasticity increased and breaking elongation decreased with addition of whiskers. The properties of toughening and rigidity of composity materials were improved when certain CaCO3 whiskers were added.Research results above have guiding meaning to exploitation of the aboundant lime resources in China and industrialized production of CaCCO3 whiskers.更多还原