Papers by Keyword: Graphite

Abstract: Bipolar plates are a key part of fuel cells. The optimal hot press temperature, pressure, and time were determined in this study. The press condition can directly affect the relative density, thereby improving the conductivity and mechanical property. Several carbon black doped samples were also successfully prepared on the basis of the optimized preparation method. Results show that carbon black optimized the conductivity due to the “conduction bridge”. The maximum conductivity and bending strength reached 345 S/cm and 32.5 MPa, respectively. Key words: fuel cells; bipolar plate; graphite; composite materials.

Abstract: Alkaline activated materials and geopolymers are recently widely involved in studies concerning their potential for advanced composites with enhanced electrical properties. This paper reports self-sensing behaviour of fly ash mortar doped with carbon black or graphite conductive admixture subjected to loading in three-point flexural test. Development of self-sensing properties and deformations of all mortars was initially investigated under flexural loading cycles with constant amplitude, final stage of the experimental part consisted in loading till fracture. Both reference and modified geopolymers failed to achieve satisfactory self-sensing performance during the cyclic loading but certain differences in fractural properties were observed.

Abstract: Electrical conductive composite materials are nowadays widely used in many industrial applications include building materials. One of the possible applications is as a resistance probe. Those probes were designed to monitor internal structural changes of building materials built into construction and to predict their durability, over-load, or defects. Mostly used composite materials are silicate or biopolymer-based with carbon-based filler. This article is dedicated to the study of the microstructure of silicate-based electrically conductive composites with graphite-based fillers. The microstructural shape of fillers was chosen concerning preserving as high conductivity as possible. Furthermore, the effect of moisture on the electrically conductive properties of the silicate composite was monitored.

Abstract: Graphite is a versatile material which is also used in various load bearing applications such as thrust bearings and dies for mechanical pressing such as hot pressing. Natural graphite has anisotropic layered structure which reduces its (compressive) strength in axes which are not parallel to c-axis. To increase strength, isotropy is introduced in graphite structure by breaking down its layers and minimizing grain size. We performed an in-depth characterization of relative aniostropy in graphite using pole figure density mapping. Locally available graphite samples were characterized by XRD and pole figures/3-D orientation distribution function (ODF). SEM and hardness testing were also performed to substantiate the pole density method. Results show that it is possible to characterize (qualitative/quantitative) isotropy or lack thereof in graphite by correlating it with the distribution of crystallinity/pole density mapping of (002) poles and 3D ODF figures.

Abstract: Carbon and low-alloys steel components are used in various stages of steam power plants which are operating at elevated temperatures (up to 530°C). Long-term exposure of low-alloy steel components at elevated temperatures inevitably result in some kind of structural degradation; for example, creep cavitation, carbide coarsening and/or spheroidization, and, less commonly, also graphitization. Graphitization can be detected mainly in carbon steels, but also in 16Mo3 steel where the ferritic matrix is strengthened by Mo in the solid solution. The absence of strong carbide forming elements (typically Cr, V, Nb) is the principal reason why these steels are susceptible to cementite decomposition and graphitization much more than the other creep resistant steels. The paper describes microstructure and material properties of superheater 16Mo3 tube, in which graphite was found after 70,000 hours of exposure at 445 °C. The actual material properties were compared to another tube of the same material delivered in the as-received state. The comparison was based on evaluation and testing of mechanical strength, fracture properties and microstructure. Creep resistance of the steel was studied using small punch creep tests (SPCT).

Abstract: This study is to determine the effect of graphite as reinforcement material on natural resources carbon foam on the mechanical and physical properties. Sucrose is used as carbon precursor and graphite with various concentration from 0 wt% to 0.3 wt% was added into the carbon foam. Carbon foam was prepared by using template method followed by pre curing and carbonization process. Pre curing process was take place at 250°C and carbonization process was carried out at 900°C under inert atmosphere. The morphology, porosity, density and compressive strength were characterised in this experiment. Through Scanning Electron Microscope (SEM), graphite can be seen clearly embedded into the ‘window’ and fill the void space. Porosity of carbon foam decrease when the concentration of graphite increase and the density of carbon foam increase when the concentration of graphite increase. Carbon foam with 0.3 wt% graphite added shows the highest compressive strength (1.84 N/mm²) compared with carbon foam without graphite added (0.95 N/mm²). The properties of carbon foam are significantly influenced by the addition of graphite loading.

Abstract: Graphene oxide (GO) is an oxidized nanosheets of graphite with a 2D planar structure. GO could be readily complexed with bio-entities as it possesses many oxygen-containing functionalities on its surface. The preparation process is fast, easy, and cost-effective. It was prepared using modified Hummers’ method in acidic solution as a primary solvent and potassium permanganate as an oxidizing agent. Afterwards, it was successfully characterized by FTIR, UV-visible spectroscopy, as well as XRD and Raman spectroscopy, and finally, SEM analysis. It was observed that the formed GO is mainly composed of carbon and oxygen elements rich in oxygen functional groups. Furthermore, the existence of (001) plane in XRD interprets the complete oxidation of graphite with d-spacing 9 Å. Moreover, Raman spectroscopy displayed the sp³ carbon hybridization, besides, the I_D/I_G ratio is found to be 0.84, which confirms the disorder between graphene oxide layers. The SEM images also pointed out that graphene oxide sheets were regularly stacked together as flake-like structures. Accordingly, the richness of oxygen-containing functionalities was confirmed. Hence, it is appropriate to be used as a base transducer for biosensing applications.

Abstract: In the article first tests of production of YSZ ceramic coatings using PS-PVD method on graphite were presented. The influence of hydrogen addition on structure and morphology of columns was analyzed. It was shown that width of the columns increased with the increase of hydrogen content in the plasma. The presence of re-solidified oxide vapors between ceramic columns was observed. The obtained results showed the possibility of using of YSZ ceramic layer as a protective layer for metallurgical applications.

Abstract: Graphite is a strategically scarce resource, and the preparation of high-purity graphite is the prerequisite and basis for the application of graphite. In order to determine the optimal purification technology parameters of an ultra-large flake graphite mine pneumatic separation ore with a fixed carbon content of 77.69%, a particle size of mainly 10 to 40 mesh, and main impurities of calcium carbonate, iron oxide and silica , two additional experiments of acid method and alkali method were added on the basis of alkali-acid method, to investigate the purification effect of different technological processes and acid leaching times on graphite raw materials, as well as to analyze the retention extent of different methods and alkali fusion temperature on graphite ultra-large flake structure. The results show that all three methods can increase the fixed carbon content of graphite to above 99%. However, compared with the acid method and the alkali method, the alkali-acid method can obtain high-purity graphite while also better protecting the graphite's ultra-large flake structure. The optimal fusion temperature is 400 °C, the optimal acid leaching time is 30% sulfuric acid thrice and 5% hydrofluoric acid once. After purification, the fixed carbon content of the product exceeds 99.97%.

Abstract: Properties of cast iron on the bimetallic part depend on the initial structural state of the cladded cast iron and technological parameters of its induction cladding process. Methodology of predicting the properties of the cast iron in the bimetallic valve tappets ICE largest hardness billets was used for cladding, the silicon content in the alloy cladding and the technological parameters of the process, as well. A hereditary relationship between the initial state of the cast iron of the semi-finished product, used for induction cladding, and the structural state of the layer of weld on the steel base of the part, has been established.