超临界CO2流体中电沉积类石墨碳薄膜的研究

Graphite-like carbon films have attracted attention of many researchers due to their low internal stress, good adhesive strength, high hardness, low friction coefficient and low wear rate. Although those films can be obtained by electrodeposition, high temperatures and high voltages are required. Moreover, the growth of the film is still quite difficult. It is important to develop a method to prepare graphite-like carbon films with a high deposition rate at a low voltage around room temperature. In this project, carbonates will be used as carbon sources and the graphite-like carbon films will be prepared using electrodeposition with low voltages around room temperature. The friction coefficients of the deposited films will be measured to study the effects of deposition parameters on the friction properties of those films. The deposition will be performed in supercritical CO2 which will promote diffusion of carbon sources towards the electrode. Cosolvents, e.g. methanol, will be used to increase the solubilities of carbonates in supercritical CO2. Additives, such as choline chloride, will be applied to improve the conductivity and adjust the morphology and the structure of the deposited films. In some cases, the additive can also be a carbon source. This project is not limited to electrodeposition of graphite-like carbon thin films. Through the study of the mechanisms, it will also provide some guidance for future studies on metal-doped carbon-like graphite.

由于类石墨碳薄膜具有内应力小、结合强度好、硬度高、摩擦因数小和磨损率低等优点，近年引起了人们的广泛关注。但是，目前现有方法大多需要在高电压或高温下进行，且膜难于生长，所以在常温、低电压条件下快速制备类石墨碳薄膜就显得尤为重要。本研究拟以碳酸盐为碳源，在常温和低电压条件下，通过电化学沉积法制备类石墨碳薄膜，同时考察不同方式下制备的类石墨碳薄膜对摩擦性能的影响。通过超临界CO2流体的使用，提升碳源分子在电极界面的快速扩散；通过夹带剂如甲醇等的使用提升碳源在CO2流体中的溶解度；通过添加可增加电沉积溶液电导、可调控电沉积薄膜结构、生长取向且可作为碳源的添加剂如氯化胆碱，实现常温、低电压条件下的类石墨碳薄膜的快速电沉积。本研究不仅仅局限于电沉积类石墨碳薄膜，通过机理的研究，对实现类石墨碳薄膜中掺杂金属元素的研究均起到指导作用。

由于类石墨碳薄膜具有内应力小、结合强度好、硬度高、摩擦因数小和磨损率低等优点，近年引起了人们的广泛关注。目前，碳膜的制备主要采用气相沉积技术，但沉积条件苛刻，设备昂贵。液相电沉积是一种很有前途的制备碳膜的替代技术，而传统的液相电沉积碳膜需要有机溶剂作为碳源，需要在高电压或高温下进行，且膜难于生长，所以在常温、低电压条件下快速制备类石墨碳薄膜就显得尤为重要。.本研究以超临界二氧化碳（scCO2）流体为电解液溶剂和碳源。scCO2不但可以提供高碳源浓度，它还具有低黏度、高扩散速率和极佳的整平能力等优点，有利于电化学沉积。通过甲醇共溶剂向scCO2中引入四丁基六氟磷酸铵作为导电盐，成功地在室温附近低电压（<10 V）沉积获得了类石墨碳膜。通过改变scCO2的临界参数、沉积电压、电解质浓度，探究不同工艺条件对电沉积碳膜的形貌、结构、相关性能的影响。随着沉积电压的增大，电流效率不断减小，而碳膜的沉积速率先增大后减小，在5.0 V沉积薄膜速率较快且薄膜形貌性能较好。压力的增加会降低沉积速率，温度升高会使体系黏度减小，离子迁移速率增大，反应速率加快。碳膜的沉积有效提高了304不锈钢的疏水性能、摩擦学性能和耐腐蚀性能。发现ID/IG的比值与sp3碳相对含量呈反比例关系，sp3碳相对含量增加会提高疏水性能和摩擦学性能，样品的耐腐蚀性能主要与沉积碳膜的厚度呈正相关。沉积获得的碳膜存在较大的内应力，随着厚度的增加有裂纹产生。通过在电解液中加入乙酰丙酮镍，向碳膜中掺杂金属镍。掺杂镍元素有效降低了内应力，相对于纯碳膜，镍掺杂碳膜的ID/IG比值普遍有所提高，说明薄膜中sp2碳相对含量增多，石墨化程度增加，电导率提高。沉积镍掺杂碳膜不锈钢的疏水性能更佳，表面硬度增大，摩擦学性能显著提高。