化学镀液中微细颗粒的分散行为

发布时间：2018-06-25 16:45

本文选题：颗粒 + 包覆改性　；参考：《南京航空航天大学》2015年博士论文

【摘要】：添加润滑颗粒(如Mo S2)或硬质颗粒(如金刚石)的化学复合镀层具有优异的摩擦磨损性能,工业应用前景广阔。目前制备复合镀层过程中普遍使用表面活性剂改善微细颗粒在化学镀液中润湿性及分散特性,然而使用表面活性剂也存在负面作用,影响复合镀层性能进一步提升。针对这一问题,本课题提出用颗粒表面包覆改性的方法解决颗粒润湿性及分散问题,主要研究工作及成果:1、采用非均匀形核法对金刚石和Mo S2颗粒进行表面包覆改性;利用扫描电镜(SEM)、热重/差热同步热分析仪(TG/DSC)、x射线衍射仪(XRD)等手段对改性颗粒进行表征;测试了颗粒改性前后在化学镀液中zeta电位及悬浮稳定性。结果表明:金刚石和Mo S2颗粒表面均成功包覆了Al(OH)3层,包覆颗粒表面形貌明显变化;包覆层及350℃煅烧产物均为非晶态结构,产物为亚稳态氧化铝;改性金刚石和改性Mo S2颗粒等电位点均远离了化学镀液p H值(酸性镀液p H约5.0),在该p H值范围内改性颗粒zeta电位大于未改性颗粒的,提高了改性颗粒在化学镀液中的悬浮液稳定性。2、基于Washburn方程采用薄板毛细渗透法测量了金刚石和Mo S2颗粒改性前后对各种探针液体的接触角,并利用YGGF方程计算颗粒改性前后的表面自由能及其分量;提出了一个判断颗粒改性前后亲水/疏水性变化的判据。结果表明:改性Mo S2颗粒对水的接触角由70.8?减小为55.2?,润湿性提高;改性金刚石接触角由44?增大到48.5?,润湿性略下降;未改性Mo S2表面能及其分量与有类似表面及结构的Talc表面能接近;而改性Mo S2和改性金刚石表面能则与氧化铝表面能一致;酸性分量与碱性分量之比(?+/?-)作为一个新的判据均适用于两种颗粒改性前后亲水性变化的表征。3、利用DLVO理论(和XDLVO理论)建立了化学镀液中颗粒间相互作用模型;预测了金刚石和Mo S2两种颗粒改性前后在化学镀液中的分散稳定性;计算了颗粒改性前后相互作用力变化;以颗粒沉降实验及粒度分布演变验证了模型。结果表明:化学镀液中颗粒间相互作用位能曲线特征可以很好地预测化学镀液分散体系的稳定性。化学镀液及低稀释比例镀液中,颗粒作用位能曲线不存在势垒,颗粒在任何间距均为引力作用,因此易团聚而快速沉降;随化学镀液稀释比例增大,位能曲线出现较大正势垒,此时颗粒能保持单分散状态,沉降速率慢而稳定分散效果明显,其中未改性金刚石稳定悬浮至少稀释100倍,未改性Mo S2至少200倍。改性颗粒在化学镀液及稀释镀液中都没有大的正势垒,不能稳定悬浮;但在化学镀液中,改性颗粒间总作用引力明显小于未改性颗粒的,更易于实现颗粒的动态稳定分散。4、利用湍流理论和团聚体强度理论建立了化学镀槽中流体与颗粒间作用模型;分别采用团聚体静态结合强度和动态结合强度与不同湍流尺度区域流体应力进行比较,判断团聚体被流体破碎分散的可能性;并通过测量流场中颗粒粒度分布进行模型验证。结果表明:团聚体动态结合强度模型可以很好地预测流场中颗粒团聚体的分散状态,与实际粒度分布特征相一致;化学镀槽中流场中团聚体稳定性与原始颗粒粒径,团聚体直径及搅拌强度都有关;相同条件下,改性颗粒团聚体比未改性颗粒团聚体更易于破碎分散。5、未使用表面活性剂制备了含改性颗粒Ni-P-Mo S2/Al2O3化学复合镀层,对镀层组织形貌特征及摩擦磨损性能进行了评价,并与Ni-P-Mo S2化学复合镀层进行了对比。结果表明:含改性Mo S2颗粒的复合镀层的显微硬度、摩擦系数及磨损量均与其表面形貌特征相关,而表面形貌特征取决于制备时的搅拌强度和颗粒包覆率,其中搅拌速率为700rpm,颗粒包覆率为7%时制备的镀层表面组织致密,400℃热处理后硬度最高可达958Hv,且摩擦系数和磨损量都较小;颗粒改性前后在镀层中沉积部位不同,改性颗粒主要分布在镀层表面胞状体内部和表面,而未改性颗粒主要在胞状体根部,也影响复合镀层形貌及性能;含改性Mo S2复合镀层比含未改性颗粒镀层具有相对低的摩擦系数和磨损量,进一步提升了性能。
[Abstract]:The chemical composite coatings (such as Mo S2) or hard particles (such as diamond) have excellent friction and wear properties and have a bright future in industrial applications. At present, surface active agents are widely used in the process of preparation of composite coatings to improve the wettability and dispersion of fine particles in the electroless plating solution. However, the use of surfactants also has negative effects. Surface action affects the performance of composite coating further. Aiming at this problem, this topic proposes to solve the problem of particle wetting and dispersing with the modified method of particle surface coating. The main research work and results are as follows: 1, the surface coating of diamond and Mo S2 particles is modified by non-uniform nucleation method; the thermal weight / differential heat is used by scanning electron microscope (SEM). The modified particles were characterized by synchronous heat analyzer (TG/DSC) and X ray diffractometer (XRD). The zeta potential and suspension stability in the electroless plating solution were tested before and after the modification. The results showed that the surface of the diamond and Mo S2 particles were successfully coated with 3 layers of Al (OH), the surface morphology of cladding particles was obviously changed, and the calcined products of the coating and 350 C were calcined. The amorphous structure is amorphous, the product is metastable alumina, and the potential points of modified diamond and modified Mo S2 particles are all far away from the P H value of the electroless plating solution (acidic solution P H about 5). The zeta potential of the modified particles in the P H value is larger than that of the unmodified particles, and the stability of the suspended particles in the electroless plating solution is enhanced by.2, based on Washburn square. The contact angle between the diamond and Mo S2 particles was measured before and after the modification of the diamond and Mo particles, and the surface free energy and its components before and after the modification of the particles were calculated by using the YGGF equation, and a criterion to judge the hydrophilic / hydrophobicity of the particles before and after the modification was proposed. The results showed that the modified Mo S2 particles were in contact with water. The angle is reduced from 70.8 to 55.2, the wettability is increased, the contact angle of modified diamond is increased from 44 to 48.5, and the wettability is slightly decreased; the surface energy and its component of the unmodified Mo S2 are close to the Talc surface with similar surface and structure, while the surface of the modified Mo S2 and the modified diamond surface can be consistent with the alumina surface; the ratio of acid and alkaline components (? +) As a new criterion, it is applicable to the characterization of the hydrophilic change of two kinds of particles before and after the modification of.3. Using the DLVO theory (and XDLVO theory), the interparticle interaction model in the electroless plating solution is established, and the dispersion stability of the two particles in the electroless plating solution before and after the modification of the diamond and Mo S2 particles is predicted, and the interaction between the particles before and after the modification of the particles is calculated. The results show that the characteristics of the interparticle interaction potential curve in the electroless plating solution can predict the stability of the electroless plating solution well. The potential energy curve of the particles in the electroless plating solution and the low dilution ratio plating bath has no potential barrier and particles at any distance. All of them are gravitational, so it is easy to gather and settle quickly. With the increase of the dilution ratio of the electroless plating solution, the potential energy curve has a larger positive barrier. At this time, the particle can maintain a single dispersion state, the settling rate is slow and the stable dispersion effect is obvious, in which the unmodified diamond is stabilized at least 100 times, and the unmodified Mo S2 is at least 200 times. There is no large positive barrier in both the plating bath and the diluted solution, and the suspension is not stable. However, in the electroless plating solution, the total effect of the modified particles is less than that of the unmodified particles, and it is easier to realize the dynamic and stable dispersion of.4. The possibility of breaking and dispersing the fluid in the aggregate is judged by the comparison of the static bond strength and dynamic bond strength with the fluid stress in different turbulent scale regions, and the particle size distribution in the flow field is measured by the model. The results show that the dynamic combined strength model of the aggregate can be used to predict the flow in the flow field well. The dispersion state of the particle aggregates is in accordance with the actual particle size distribution characteristics. The stability of the aggregate in the flow field in the electroless plating bath is related to the original particle size, aggregate diameter and agitation strength. Under the same condition, the modified particle aggregate is more easily broken and dispersed.5 than the unmodified particle aggregate, and the modifier is prepared without using surface active agent. The microstructure and friction and wear properties of the coated Ni-P-Mo S2/Al2O3 composite coating were evaluated and compared with the Ni-P-Mo S2 chemical composite coating. The results showed that the microhardness, friction coefficient and wear amount of the composite coating containing modified Mo S2 particles were related to the surface morphology and surface morphology characteristics. It is determined by the stirring strength and the coating rate of the particles, in which the stirring rate is 700rpm, the coating surface is dense when the coating rate is 7%, the hardness of the coating is up to 958Hv after heat treatment at 400 C, and the friction coefficient and the wear amount are smaller, and the deposited parts in the coating are different before and after the particle modification, and the modified particles are mainly distributed in the coating. The inner and surface of the surface of the surface, while the unmodified particles are mainly in the root of the cell, also influence the morphology and properties of the composite coating, and the modified Mo S2 composite coating has a lower friction coefficient and wear amount than the unmodified particle coating, and further improves the performance.
【学位授予单位】：南京航空航天大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB306

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