The electric machinery industry is currently facing a significant challenge in the application of electrical contact materials with appropriate electrical and tribological performance. The use of conductive lubricants, including liquid, solid, and semi-solid varieties, represents a key approach to meeting technical and sustainable criteria. This strategy is closely linked to the development of multifunctional additives with excellent conduction properties in response to the growing concerns regarding the increased durability of electrical equipment. This paper provides a comprehensive review of prior research in this area, specifically studies investigating conductive lubricants incorporating conductive additives and demonstrating exceptional electro-tribological properties. Various conductive additives have been incorporated into these lubricants, each providing unique advantages, such as enhancing conductive connectivity, reducing friction and wear, and improving the dispersion of other functional additives. This review covers a range of conductive materials, including carbon-based materials (carbon nanotubes, graphene nanosheets, carbon black, etc.), ionic liquids (ILs), metals (soft metal-based composites, gallium-based liquid metals), MAX phases, semiconductors, and conductive polymers, and discusses their impact on the electrical conductivity and electro-tribological properties of conductive lubricants. Additionally, the electro-tribological properties of insulating lubricants are introduced. Promising conductive lubricants are identified based on comparisons of their electrical conductivity, coefficient of friction (COF), wear rate, and electrical contact resistance (ECR) under various current-carrying friction (CCF) conditions. In conclusion, it is found that conductive lubricants effectively reduce friction and wear under current-carrying conditions, thus contributing to the advancement of the electrical machinery industry. This paper also outlines potential research directions in this field, pointing to the promising future of conductive lubricants in enhancing the performance and sustainability of electrical equipment.

Dielectric behavior pertains to the polarization of cement-based materials, in which the positive and negative charge centers are separated. Recent work on the dielectric behavior of common Portland cement-based materials in a low frequency regime were carried out, including the dependence of dielectric behavior on microstructures, hydration process, loadings, etc. This review represented the results of dielectric behavior of common Portland cement-based materials over the past decade and introduced the dielectric measurement method and the dependence of polarization on aggregates, water cement ratio, stress/strain, and temperature. It is indicated that some movable ions in pore solution dominate the dielectric behavior, in which the electric dipoles are in series. Aggregates and admixtures affect dielectric behavior due to relevant changes in microstructures. Heating and compression strengthen the dielectric behavior, while cooling and tension weaken the dielectric behavior. In addition, some related future research aspects were also prospected.