Papers by Keyword: Graphite

Abstract: This study contains results of carbonaceous SHS-refractory materials application for binding of the graphite products and melting of metals in the induction furnaces. The opportunity of producing strong graphite-graphite bond up to 5 MPa by means of the carbonaceous refractory material that demonstrated high chemical stability in the aggressive liquid metals and alloys environment has been shown. The results of the industrial tests of melting crucibles made of carbonaceous SHS-refractory materials have been presented in the case of aluminium melting. It has been shown that such crucibles stability is 5-6 times higher than that of standard graphite crucibles in aluminium melting conditions. The obtained research results testify that developed carbonaceous material is applied for lining of the induction furnace of melting unit is allow to increase the number of nonferrous metals (bronze) melting cycles from 5 to 6 times in comparison with the traditional graphite crucible melting. High chemical stability of the material to oxidizing environment as well as to metal melts is provided by formation of high-melting compounds in the carbonaceous exothermic systems during SHS-process.

Abstract: Taking α-quartz of different mass ratio mixed with graphite powder mixture as the initial materials, using the method of combining high-energy mechanical milling with high pressure and high temperature , this work inspected the influences of carbon content on the synthesis conditions of coesite. The experimental products were measured by XRD, TEM, and Raman. The results showed that the existence of carbon can obviously inhibit the formation of coesite, and the higher carbon content of initial materials the higher pressure on forming coesite is needed.

Abstract: The effect of Cu addition on structure and mechanical properties of the gray cast iron is studied. Copper is showed to affect the graphitization process. Copper content increase up to 6 ... 7 wt. % reduces the depth of the chill layer.With further increase of coppercontent the alloys tendency to chilling effectincreases.When the cast ironcontains from 0 to ~ 7% Cu, inclusions can’t be detected using only optical microscopy. In the cast iron with 14.7% Cu, distribution of inclusions has two peaks: 30 ... 40 ... 150 microns and 160 microns. Out-of-shape cupric inclusions of the size of ~ 1 micron are detected in the ledeburite cementite.Submicron inclusions are observed in the lamellar pearlite colonies. With increase of copper content up to ~ 7 wt. % cast iron hardness and microhardness of pearlite increases.

Abstract:

Glow Discharge Optical Emission Spectroscopy (GD-OES) is an analytical technique mainly used in the analysis of solid metallic samples. The technique requires a conductive sample as the analyte serves as the cathode when generating the glow discharge plasma. GD-OES is useful for both bulk quantification and depth profiling of thin layers of conducting materials. The objective of this study was to develop a new sample support matrix for the preparation of conductive pressed pellets suitable for the analysis of non-conducting materials with GD-OES. In previous work non-conducting powders, such as uranium oxide, have been mixed with fine metal powders such as copper, silver or tantalum. Another solution has been to use a quick setting, conductive thermoplastic, such as diallyl phthalate impregnated with copper, as support. Both of these methods are, however, expensive and fairly time consuming. Graphite, a cheap, readily available conductive powder, proved not to form a strong enough pellet to withstand the conditions required during the GD analysis. This limitation was overcome by the addition of a binding agent, bakelite, to produce a relatively cheap, conductive matrix for the analysis of non-conducting powders. Spectroscopically pure zirconium oxide was used as a reference material and mixed with various quantities of graphite and bakelite powder. Two distinct regions of linearity were obtained. Samples with less than six percent zirconium yielded a gradient of 0.0011 with an R² value of 0.9949. Samples with higher zirconium content yielded a gradient of 0.0042 with an R² value of 0.9991. These results indicate the suitability of this sample matrix for analysis of zirconium materials by GD-OES.

Abstract: Graphenes have aroused great interest among the scientists lately, due to their special physical properties which are supposed to be transferred to composite materials [1,2,3,6]. Some polymers show low mechanical properties which can be improved by adding various types of materials [9,13]. Using nanoparticles, an enhancement of mechanical, thermal and electrical properties can be obtained, even for small contents of additives [10,11,12,14,15,16]. The evaluation of mechanical properties of polymer composites with graphene can be achieved relying on the three-point bending tests [4]. This work presents a few conclusions resulting from the three points bending tests of the polyester composites with graphene and graphite [7,8].

Abstract: Frequency dependences of transmission and reflection coefficients, dielectric permeability of composite materials with the various content of carbon fillers (technical carbon, graphite) in polyurethane varnish in ranges of frequencies 26–40 GHz and 110–260 GHz are experimentally investigated. It was found that composite material 0.4 mm thick with 4–5 % graphite mass content has a transmission coefficient of less than minus 7 dB in the whole investigated range of frequencies and can be effectively used in devices of protection from electromagnetic radiation.

Abstract: Influence of modifying with silicocalcium (SiCa) on the structure and friction properties of the hypereutectoid steel alloyed with 8.85 wt. % of Cu was studied. SiCa modifying of the copper alloyed hypereutectoid steel, led to the formation of the vermicular graphite distributed in the indendritic space instead of cementite. Coefficient of friction reduction and increased wear resistance were marked in the copper alloyed hypereutectoid steel due to the presence of graphite and cupric inclusions in the steel structure. The wear resistance of the graphitized hypereutectoid steel alloyed with 8.85 wt. % of Cu was almost 5 times higher compared to the wear resistance of bronze BrA9J3L and 75% higher compared to the wear resistance of antifriction cast iron AChS-1.

Abstract: Expanded graphite is used as framework material in inorganic or organic heat storage materials commonly, of which the function is to improve thermal performance of the relevant materials. However, its negative effect is unclear. In this paper, the change of endothermic temperature of chemical heat storage material Ca_xZn_y(OH)_2(x+y) by graphite addition is reported. Differential scanning calorimetry (DSC) is employed to perform the measurement. The result shows that the initial temperature and width of the endothermic peak decrease due to the action of the added graphite slightly; Along with the increase of graphite content, the endothermic peak moves to lower temperature further, the width and height of the peak reduce simultaneously.

Abstract: Development of low-sulfur and Pb-free free cutting steel is significant because the use of S or Pb free-cutting steel can result in serious pollution. The hypoeutectoid graphitized free cutting steel was proposed. The graphitizaion is difficult due to slow graphitization process, so it is curcial to accelerate the graphitization process. The results show that, through appropriate composition design and technology, the C atom can quickly transform to grahite within 4 hours. The microstructure of the graphitized free cutting steel consists of ferrite, graphite and carbide. Moreover, the grain size of grapite is fine and the distribution is uniform, and the carbide mainly locate the ferrtie grain boundary or in the ferrite. In addition, the nuleation of graphite not only can take place on the second-pahse particles, but also spontaneous nuleation and growth.Key words: free cutting steel, hypoeutectoed steel, graphite, carbide, nucleation

Abstract: Graphite chip formation is important for the understanding of high speed milling of brittle graphite. This paper is aimed to reveal the influence of cutting conditions on the graphite chip formation in high speed milling. The relationship between the maximum undeformed chip thickness and cutting parameters was analyzed, and the influence of cutting parameters, tool geometry and milling patterns on the chip formation of brittle graphite was studied. It is concluded that the transitions of graphite chip formations were highly dependent on the undeformed chip thickness which is decided by the combination setting of feed per tooth and radial depth of cut. Big fractured block chip occurs more easily in up milling than down milling. Tool rake angle influences the chip formation according to the maximum undeformed chip thickness.