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Heat Treatment of Cast Iron
Published in Bankim Chandra Ray, Rajesh Kumar Prusty, Deepak Nayak, Phase Transformations and Heat Treatments of Steels, 2020
Bankim Chandra Ray, Rajesh Kumar Prusty, Deepak Nayak
Initially, these alloys solidify to form primary austenite. The first appearance of combined carbon in the form of cementite occurs from the eutectic reaction at 1143°C. However, the graphitization process is aided by various factors like high carbon content, high temperature, and the proper amount of graphitizing elements, such as silicon. It has been experimentally proved that with proper control of the above factors, the alloy follows the stable iron–graphite equilibrium diagram, forming austenite and graphite at the eutectic temperature of 1143°C. The graphite appears as several irregulars, elongated and rounded plates that provide gray cast iron its natural grayish or blackish fracture. It may be noted that the flakes are three-dimensional particles. During the continued cooling process, additional carbon precipitates because of the decline in carbon solubility in austenite. The carbon precipitates as graphite or as proeutectoid cementite, which quickly graphitizes. The matrix that embeds the graphite decides the strength of the gray cast. The condition of the eutectoid cementite largely determines the nature of this matrix. For example, if the composition and rate of cooling are so adjusted that the graphitization of eutectoid cementite happens, then a fully ferritic matrix is produced.
Chapter 1: Functional mesoporous carbons from template methods for energy storage and conversion
Published in Jian Liu, San Ping Jiang, Mesoporous Materials for Advanced Energy Storage and Conversion Technologies, 2017
Hao Tian, Shaomin Liu, San Ping Jiang, Jian Liu
Secondly, the catalytic graphitization is an effective method to synthesize graphitic carbon with high crystallinity in mild conditions. With the help of catalysts (Fe, Ni and Co), relatively low pyrolysis temperature will be needed to prepare porous carbon materials with high graphitic structure by using mesoporous silica incorporated with metal salts as templates [26,136,144–151]. For example, a solid-state method by using metal pthalocyannines and SBA 15 was employed to prepare highly graphitic ordered mesoporous carbon materials. The degree of graphitization was enhanced by metal catalysts and the pore and graphitic structure remained complete during heat treatment, leading to high oxidative stability and capacitance [151]. In addition, the carbon materials synthesized from soft template method showed high graphitization degree in the presence of metal salts under 900°C heat treatment, resulting in superior capacitive performance (155 F/g) over a wide range of scan rates, even up to 200 mV/s. But the main disadvantage for this method is that synthesis of template is usually a time-consuming and high-cost process.
Materials
Published in Sumit Sharma, Composite Materials, 2021
The melt spinning of pitch fibers from the raw material can occur after the carbon content reaches the range 91%–96.5% and the mean molecular weight is at least 400. After pitch fibers are spun, they are subjected to an oxidizing gas at a temperature below the spinning temperature, or they are subjected to another chemical treatment that renders them infusible. In one method, for example, pitch fibers are treated for 7 hours at a temperature of l00°C with air containing ozone; thereafter, the temperature is raised at l°C minute−1 up to 300°C. This stage of processing is critically important to guarantee that pitch fibers will retain their shape under heat treatment during carbonization and graphitization. However, if they are exposed to oxidization for too long, the fibers become brittle. The carbonization of pitch fibers occurs at somewhat higher temperatures. The heating rate between 100°C and 500°C is critical to prevent fiber rupture from the released volatiles. A typical heating schedule would call for heating from 100° to 500°C at 5°C hour−1 and from 500° to 1100°C at l0°C hour−1. The cool down from 1100°C is usually controlled to be less than 30°C hour−1. If desired, the carbonized pitch fibers can be further heated in an inert atmosphere to produce a graphitic microstructure. Graphitization temperatures are typically between 2500°C and 3300°C. Total graphitization times are generally very short, on the order of a few minutes. The properties of the three types of PAN fibers and the rayon fiber are given in Table 2.6 for comparison.
Simple carbon fiber graphitization device for in-situ measurement of small angle X-ray scattering (SAXS)
Published in Instrumentation Science & Technology, 2021
Peng Xiao, Dongfeng Li, Yanjun Gong, Shujiao Zhang, Guang Mo, Zhihong Li
The measurements began after the introduction of the sample, the integration of the graphitization device, collimation of the beam, introduction of nitrogen into the glass tube at a rate of 0.5 L/min, and supplying the power. The graphitization temperature ranged from 1450 °C to 2100 °C. The exposures were made approximately every 50 °C for 30 seconds below 1700 °C and 10 seconds above 1700 °C. When the temperature reached a specified value, the voltage and temperature were held constant.
Recent progress in the conversion of biomass wastes into functional materials for value-added applications
Published in Science and Technology of Advanced Materials, 2020
Graphitic carbon is commonly obtained from soft carbons (e.g. petroleum coke) via heating above 2100°C [118]. The in-plane structure of graphene layers in the graphitic carbon is almost similar to that in graphite. It is produced by various synthetic methods to increase the degree of graphitization, including direct heating of porous carbons at 2500–3000°C, and catalytic graphitization where in-situ graphitic nanostructure was obtained by metal catalysts [119].