基于废弃硅钼棒全物质利用的钼合金表面耐高温涂层的构筑与抗氧化机制研究

In response to the national call for "promoting the recycling of resources and improving the treatment of solid waste", especial for the rare metal of molybdenum, moreover for waste MoSi2 heating elements, we create the novel idea for the recovering and reusing the waste MoSi2 heating elements without any separation and remove, which is not a selective recycling, and it is a 100% reusing. The waste MoSi2 heating elements will be the raw materials for the high-temperature anti-oxidation coating on the Mo-based alloys by atmospheric plasma spraying (APS), and the coating construction principle and high temperature anti-degradation mechanism will be pursued..The waste MoSi2 heating elements will be determine by advanced material methods, such as XRF, XRD, SEM, EPMA, etc. The phase composition, the mapping and contents of chemical elements and the microstructure will be investigated. The waste MoSi2 heating elements will be ground to the particles with the size about 100 μm, and as a candidate, the particles will be ground to the powders with the size of 5-10 μm, and then the agglomerated powders is prepared using a centrifugal spray drying and high-temperature treatment. The as-prepared powders were deposited on Mo substrates via APS, and the parameters of APS will be studied, and the phase and microstructure evolution of APS powders will be discussed, and the physical model will be founded. The waste MoSi2 coating will be characterized by SEM, TEM, 3D-XRM, XPS, etc, furthermore, the coating surface composition, valence state will be studied, and the cross-section microstructure will be analyzed, and the interface between the coating and substrates will be investigated..The static and cyclic oxidation test will be conducted in air from 1200 to 1500 ℃, the oxidation kinetic curve will be built, and the microstructure and chemical compositions development of the coating will be analyzed using SEM and EPMA, in addition, the interface of surface/coating/substrates will be investigated, the mapping and diffusion path of the chemical elements of Mo, Si and O will be revealed. The formation and growth mechanism of surface scale for the coating will be discussed. The oxidation-resistant and thermal shock performance and degradation mechanism for waste MoSi2 coatings at high-temperature are concluded..The present work will develop the novel recycling of waste MoSi2 heating elements, in particular, without any separation and removing, which is strong beneficial to the strategy of "no-waste society".

面向国家“推进资源循环利用和加强固体废弃物处理”的重大战略，针对大量废弃硅钼棒未能有效利用的问题，在前期选择性回收的基础上，提出废弃硅钼棒“全物质利用”的新思想，即以废弃硅钼棒为原料，采用等离子喷涂技术在钼合金表面制备耐高温涂层，使废弃硅钼棒得到整体再利用，实现零废物排放。为此，本项目将确定废弃硅钼棒的相组成、元素存在形式和分布状态，探明不同相的含量；建立并优化废弃硅钼棒粉末的等离子喷涂工艺，确立相关参数，明确喷涂过程原料颗粒的演化机制，揭示涂层的构建原理；阐明涂层的组织结构，明晰界面结合特征和性能；重点澄清涂层的高温静态氧化、循环氧化特性，理解Mo、Si、O等化学元素的迁移路径及其相结构的进展和转化规律，探明表面膜的成膜机理和表面膜/涂层/基体三界面发展规律，揭示涂层的抗高温氧化机制。为废弃硅钼棒的全物质再利用，建立“无废硅钼棒”理念，甚至构建“无废社会”提供必要的理论依据和技术支持。

随着矿产资源的开发，工业固体废弃物逐渐堆积造成了资源的严重浪费。而通过综合利用废物资源来实现“零废弃”，已成为全球可持续发展的关键。具体针对硅钼棒，目前工厂和实验室有大量退役组件未获得有效利用。而硅钼棒优异的高温抗氧化特性能够让其重新应用于高温涂层领域，这对开发新型耐高温抗氧化涂层具有重要的意义。本项目以废弃硅钼棒为主要原料，在难熔金属钼表面制备MoSi2基复合涂层，分析了复合涂层的微观结构、高温抗氧化性能及其退化机制，建立了涂层在高温烧结后的残余热应力有限元模型，探究了涂层表面复相氧化膜在高温环境下的生长行为，阐明了相关的高温抗氧化防护机理。结果显示：单一的MoSi2涂层内出现贯穿裂纹，而通过还原硅钼棒制作工艺后制备的复合涂层获得了更为完整和致密的结构，并观察到无缺陷的Mo5Si3扩散层。在1500°C氧化300分钟后，含膨润土的复合涂层在高温氧化过程中获得了相对更低的质量增加和较薄的表面氧化膜，这表明复合涂层仅在经历少量的表面氧化后就形成了完整的SiO2氧化膜。通过浆料技术制备的MoSi2涂层在高温烧结后呈现较低的孔隙率和无裂纹的形貌，并在高温氧化后表现出优异的抗氧化性能。此外，通过两步法制备的MoSi2-ZrB2/MoSi2梯度涂层呈现出无裂纹的形貌，并在涂层/基体界面处生成有利于结合的Mo5Si3和MoB扩散层。1500℃氧化100小时后，MoSi2-ZrB2/MoSi2复合梯度涂层整体呈现极低的氧化速率常数和质量变化，表现出优异的高温抗氧化性能。本项目在Corrosion Science、Journal of the European Ceramic Society等高水平期刊发表论文16篇，研究成果实现了对废弃硅钼棒的全物质再利用，同时揭示了高温氧化元素的迁移特征和对应的涂层抗氧化机制，对于促进钼工业的可持续发展以及建设“无废社会”将产生积极的推动作用。