Method for measuring thermal contact resistance of graphite thin film materials

Thermal contact resistance (TCR) is an important parameter in thermal analysis of materials. Because of many influential factors, it is difficult to find a general model or computational formula to calculate the TCR of a solid interface. In many engineering applications, TCR values are usually obtained through experiments. Unlike extensive research focusing on ordinary columnar materials, this paper aims at measuring the TCR values of graphite thin film materials. The technical challenge is that it is not convenient to embed thermocouples into such materials. To overcome this challenge, a steady-state method using a copper heat flux meter is developed, which provides a useful tool for indirect TCR measurement. In our experiments, the TCR values of the graphite thin film materials are successfully measured under different temperature and pressure levels. The results provide a valuable guideline for the use of this type of material in high-temperature, high-pressure applications.     

Implication of Size-Controlled Graphite Nanosheets as Building Blocks for Thermal Conductive Three-Dimensional Framework Architecture of Nanocarbons

Preparation of three-dimensional (3D) networks has received significant attention as an effective approach for applications involving transport phenomena, such as thermal management materials, and several nanomaterials have been examined as potential building blocks of 3D networks for the improvement of heat conduction in polymer nanocomposites. For that purpose, nanocarbons such as graphene and graphite nanoplatelets have been spotlighted as suitable filler materials because of their excellent thermal conductivities (ca. 10²–10³ W·(m·K)^?1 along their lateral axes) and morphological merits. However, the implications of morphological features such as the lateral length and thickness of graphene or graphene-like materials have not yet been identified. In this study, a controlled dissociation of bulk graphite to graphite nanosheets (GNSs) using a low-cost, ecofriendly bead mill process was extensively examined and, when configured in a 3D framework architecture formation, the size-controlled GNSs demonstrated that the thermal conductivities of a 3D interconnected framework of GNSs and the corresponding polymer nanocomposite were intimately correlated with the size of the GNSs, thus demonstrating the successful preparation of an efficient thermal management material without highly sophisticated efforts. The capability of controlling the lateral size and thickness of the GNSs as well as the use of a 3D interconnected framework architecture should greatly assist the commercialization of high-quality graphene-based thermal management materials in a scalable production process.     

Subsurface cracks in AGR graphite bricks

Sub-surface cracks present difficulties for eddy current methods as the skin effect causes currents to flow preferentially near the surface. This work examines graphite as a case study for the qualitative assessment of sub-surface cracks and employs multi-frequency eddy current techniques. The research has particular relevance to Advanced Gas-Cooled Reactors (AGR׳s) as during their operation there is the potential for cracks to develop within moderator bricks. This work reports that subsurface slots of 18% brick thickness can be detected. This work confirms these results with a parametric 3D finite element study.     

Atomic scale mechanisms for the amorphisation of irradiated graphite

Molecular dynamics simulations using empirical potentials reveal HOPG graphite’s response to irradiations. Two different methodologies: displacement cascades and Frenkel pair accumulations, probe the primary damage and dose effect, respectively. This work reveals that in HOPG graphite primary knock-on atoms with initial energies less than 40 keV do not induce amorphisation by direct impact. Rather, defects stabilise and persist after a single irradiation event. However, amorphisation occurs via the accumulation of defects mimicking multiple events. Before amorphisation the graphite structure undergoes three stages of evolution characterised by (i) an increase in point defects; (ii) a wrinkling of graphene layers pinned by small amorphous pockets; and (iii) a full amorphisation of the structure via percolation of the small amorphous pockets. This structural evolution gives way to an irradiation induced volume change of the HOPG graphite. In the first stage, interstitials contribute, as expected, to c-axis swelling, while vacancies contribute to basal plane shrinkage. Subsequently, rippling of the graphene layers induces the overall volume to change. A power law relation illustrates the relation between the c-axis swelling and the basal-plane shrinkage as a function of the irradiation dose.     

Cu/Ag/石墨复合涂层电滑动摩擦磨损行为研究

运用等离子喷涂技术在C45E4基材上制备了Cu/Ag/石墨复合材料涂层。利用HST-100销-盘式摩擦磨损试验机,研究了不同电流强度对Cu/Ag/石墨复合材料涂层摩擦磨损行为的影响。利用场发射扫描电镜、能谱仪和X射线衍射技术对涂层结构、相组成、磨损形貌和磨屑进行了表征。涂层结构分析表明：Cu/Ag 合金形成了连续的导电通道而沉积的石墨颗粒具有明显的平行于基材的取向。随着电流从0增加到50A,复合材料涂层的磨损率随之增大,而且磨损率与施加的接触压力和滑动速度有紧密的联系。在本实验中,观察到在相同接触压力和滑动速度条件下,摩擦系数与电流强度几乎无关的现象。石墨转移膜和氧化物层是形成稳定滑动的主要因素。没有电流时,磨损机理主要是磨粒磨损,但随着电流的增强,电磨损变为滑动过程中复合材料的主要磨损机理。     

Influence of furfuryl moulding sand on flake graphite formation in surface layer of ductile iron castings

The influence of the use of moulding sand with furan resin, prepared both with fresh sand and reclaimed matrix, on the formation of a flake graphite formation at the surface layer of ductile iron castings has been investigated. A series of experimental heats of ductile iron cast in moulds made of moulding sand characterised by different levels of surface active elements (sulphur, oxygen) were performed. The effect of the wall thickness and the initial temperature of the metal in the mould cavity on the formation of flake graphite in the surface layer of the casting is shown in the paper. Investigations carried out by means of scanning electron microscopy (energy dispersive X-ray spectroscopy and wavelength dispersive X-ray spectroscopy) showed concentration of gradient profiles of surface active elements in the castings surface layer, which are responsible for their quality. Finally, it has been shown that there exists a significant effect of the quality of the sand on the formation of the flake graphite layer and the surface characteristics of ductile iron castings.     

Crystallography of graphite spheroids in cast iron

To further understand graphite growth mechanisms in cast irons, this study focuses on the crystal structure of a graphite spheroid in the vicinity of its nucleus. A sample of a graphite spheroid from a commercial cast iron was characterised using transmission electron microscopy. The chemical composition of the nucleating particle was studied at the local scale. Crystal orientation maps of the graphite spheroid revealed misorientations and twist boundaries. High-resolution lattice fringe images showed that the basal planes of graphite were wavy and distorted close to the nucleus and very straight further away from it. These techniques were complementary and provided new insights on spheroidal graphite nucleation and growth.     

Pentadecane functionalized graphite oxide sheets as a tool for the preparation of electrical conductive polyethylene/graphite oxide composites

Covalent functionalization of pentadecane-decorated thermally reduced graphite oxide (GO) sheets has been studied as a tool for the preparation of polyethylene/GO composites exhibiting rheological and electrical percolation thresholds. It was accomplished through pentadecane based radical addition onto unsaturated bonds located on the GO sheets' surface using dicumyl peroxide as hydrogen abstractor. This chemical functionalization influences the affinity of the formed pentadecane grafted GO sheets for various solvents. Then, the compounding of the composites pentadecane grafted GO/PE was performed at a processing temperature of 140 °C with 25, 20, 15, 10, 8 and 5 wt% loadings. Rheological and electrical percolation thresholds were found between 10 and 15 wt% for polyethylene/pentadecane functionalized graphene oxide composites while the composite graphite/PE at the same loading percentage did not reach any percolation threshold.     

基于产品平台的石墨产品分类研究

石墨作为重要的基础原材料和战略矿物资源,应用广泛,产品种类繁多。本文引用离散型工业中"产品平台"的概念与思想,对石墨产品进行纵向分类。将石墨产品中的"材料级石墨产品"替代离散型工业中"产品平台"的概念,并以提纯、细化、改性为技术主导方向对材料级石墨产品进行了系统分析与分类,为石墨产业链的延伸与优化提供依据。     

电炉炼钢与针状焦发展现状及市场分析

介绍了国内外电炉炼钢的发展和现状,阐述了我国石墨电极的发展现状和针状焦研发过程,并分析了针状焦国际和国内市场的基本情况及总体趋势,应加强对国产针状焦生产工艺和技术的研究,不断提高针状焦质量,加大油系针状焦投资。