Mahmoud Morsi M
Mechanical Engineering Department, College of Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.
Interdisciplinary Research Center for Advanced Materials, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia.
Materials (Basel). 2022 Oct 17;15(20):7236. doi: 10.3390/ma15207236.
The native oxide layer that forms on copper (Cu) metal spherical particle surfaces under ambient handling conditions has been shown to have a significant effect on sintering behavior during microwave heating in a previous study, where an abnormal expansion was observed and characterized during sintering of Cu compacts using reducing gases. Because microwave (MW) heating is selective and depends greatly on the dielectric properties of the materials, this thin oxide layer will absorb MW energy easily and can consequently be heated drastically starting from room temperature until the reduction process occurs. In the current study, this oxide ceramic layer was qualitatively and quantitatively characterized using the carrier gas hot extraction (CGHE) method, Auger electron spectroscopy (AES), and a dual-beam focused ion beam (FIB)/scanning electron microscope (SEM) system that combines both FIB and SEM in one single instrument. Two different commercial gas-atomized spherical Cu metal powders with different particle sizes were investigated, where the average oxygen content of the powders was found to be around 0.575 wt% using the CGHE technique. Furthermore, AES spectra along with depth profile measurements were used to qualitatively characterize this oxide layer, with only a rough quantitative thickness approximation due to method limitations and the electron beam reduction effect. For the dual-beam FIB-SEM system, a platinum (Pt) coating was first deposited on the Cu particle surfaces prior to any characterization in order to protect and to preserve the oxide layer from any possible beam-induced reduction. Subsequently, the Pt-coated Cu particles were then cross-sectioned in the middle in situ using an FIB beam, where SEM micrographs of the resulted fresh sections were characterized at a 36° angle stage tilt with four different detector modes. Quantitative thickness characterization of this native oxide layer was successfully achieved using the adapted dual-beam FIB-SEM setup with more accuracy. Overall, the native Cu oxide layer was found to be inhomogeneous over the particles, and its thickness was strongly dependent on particle size. The thickness ranged from around 22-67 nm for Cu powder with a 10 µm average particle size (APS) and around 850-1050 nm for one with less than 149 µm.
在先前的一项研究中已表明，在环境处理条件下铜（Cu）金属球形颗粒表面形成的原生氧化层对微波加热过程中的烧结行为有显著影响，该研究中在使用还原气体烧结铜压块的过程中观察到并表征了异常膨胀。由于微波（MW）加热具有选择性且很大程度上取决于材料的介电性能，所以这一薄氧化层会很容易吸收微波能量，进而从室温开始就会被剧烈加热，直到发生还原过程。在本研究中，使用载气热萃取（CGHE）法、俄歇电子能谱（AES）以及一种将聚焦离子束（FIB）和扫描电子显微镜（SEM）结合在一台仪器中的双束聚焦离子束（FIB）/扫描电子显微镜（SEM）系统，对该氧化陶瓷层进行了定性和定量表征。研究了两种不同粒径的商用气体雾化球形铜金属粉末，使用CGHE技术测得粉末的平均氧含量约为0.575 wt%。此外，利用AES光谱以及深度剖面测量对该氧化层进行了定性表征，但由于方法限制和电子束还原效应，只能得到大致的定量厚度近似值。对于双束FIB - SEM系统，在进行任何表征之前，首先在铜颗粒表面沉积一层铂（Pt）涂层，以保护并保存氧化层，防止任何可能的束致还原。随后，使用FIB束对涂有Pt的铜颗粒在原位进行中间横截面切割，在36°角的样品台倾斜角度下，使用四种不同的探测器模式对所得新鲜截面的SEM显微照片进行表征。使用经过改进的双束FIB - SEM装置成功实现了对该原生氧化层更精确的厚度定量表征。总体而言，发现原生氧化铜层在颗粒上是不均匀的，其厚度强烈依赖于粒径。对于平均粒径（APS）为10 µm的铜粉，厚度范围约为22 - 67 nm；对于粒径小于149 µm的铜粉，厚度范围约为850 - 1050 nm。
