ABSTRACT
A petroleum and coal industry’s byproduct i.e., pitch is a material of surprise and versatile character. Provided right treatment , these thermoplastic pitches can offer ultimate properties and desired mechanical and physical response . Pitch precursors mainly contain carbon and some fraction of volatiles. These are the complex mixtures of many polymers (Polycyclic aromatic hydrocarbon) and their crosslinking study is yet to be explored by researchers. With selective thermal and chemical treatment the physical response of pitch is improved since in its crude form , the pitch is not usable and offer high porosity and poor thermal behavior up on carbonization. An acid treatment increases the softening point which is then further used as a binder for thermally treated pitch primarily used as base matrix in order to develop carbon fiber reinforced carbon (C/C) composites. C/C composites in non-oxidizing environment offer the most robust response. These especial engineering grade composites have been developed from inexpensive coal tar and petroleum pitch and have been characterized thoroughly. Coal tar pitch based C/C composites have shown superior performance than the petroleum pitch based C/C composites which is obvious for the reason that the net carbon content in coal tar pitch is higher. Thermal and Themo-mechnical analysis have proved that these C/C composites offer insignificantly low weight loss ranging between 1-6% while the thermal expansion coefficient is also low and ranging in 1-5 PPM K-1. On the other hand, the compressive strength and flexural strength are as high as 100-350 MPa and 50-100MPa respectively. Porosity and density of developed C/C composites have been favorable and these values are quite low, porosity is estimated in the range of 5-12% while density is varying in the range 1.40-1.75 g/cc. Carbonized C/C composites also offer micro wear and the presence of high modulus carbon fiber improves the wear behavior upto a vast extent along with appreciable flame ablation resistance. Overall the composites developed form the PAN based chopped carbon fibers and coal tar and petroleum pitch based matrix have offered very high mechanical and thermal response and they are robust in nature.
INTRODUCTION
C/C composite is an ideal composite material for load bearing applications in aerospace engineering over range of temperature, thermal shielding of reentry vehicles, housing of nuclear reactors, compressive loading of discs in braking systems in automobiles etc. C/C composites are made from the carbonaceous matrix primarily responsible for transferring load to a reinforcement i.e. load bearing entity of a composite dispersed in the desired orientation depending on an end application. C/C composites exhibit excellent high-temperature mechanical properties, dimensional stability, substantially low friction and wear. The large-scale production of C/C composites is conquered by phenol-furfural resins, but recent findings have suggested new precursor materials. Among them pitch is one contender. The downside of pitch is its high volatile charge, which gives unacceptable porosity and low density upon carbonization. The hurdle is overcome by reimpregnation of the composite by the same pitch, making the process tedious and economically unsteady . The work taken in hand allows to obtain a C/C composite with conclusive density in the range of 1.5-1.72g/cm3.A selective and well formulated approach by changing the physical properties of pitch either chemically or thermally or both has benefited in avoiding reimpregnation processes. Crude pitch is thermoplastic in nature and tends to exodus upon heating from the preform, although there is an increase in viscosity which is usually seen after the temperature of 3000 C. In its crude form, pitch comprises of substantial amount of Polycyclic Aromatic Hydrocarbons and volatiles with molecular weight ranging in several thousands. Because of this, pitch has gained utmost interest in densification of C/C composites and in developing low density graphite electrodes. Also, from the literature survey, it is observed that no significant work has been carried out for C/C composites exclusively developed from pitch without reimpregnation processes and all the properties of C/C composites have been analyzed separately .Thorough assessments including controlled carbonization and well asserted chemical treatment have been exploited to overcome the process of re-impregnation and hence investigation on the same was undertaken. Removing the need of re-impregnation process have helped to fabricate C/C composite in mere 80 hours. The work presented discloses the properties and behaviors of such novel C/C composite with varying PAN based chopped carbon fiber reinforcement solely developed from pitch precursor.
EXPERIMENTAL
For fabrication of the green C/C composites, a hot compression technique was used followed by controlled carbonization in nitrogen atmosphere in a muffle furnace. The green composite samples were compressed at 240 kg/cm2 of pressure at 220°C. Chemical treatment of the pitch was carried out under constant stirring with variable concentration of acid. Thermal treatment of the pitch as carried out in SS container in a zero atmosphere at 400°C.
RESULT AND ANALYSIS
Flame ablation test setup
Microstructural studies
Thermogravimetric analysis
Coefficient of thermal expansion vs temperature plot
Coefficient of friction data
Compression test plot
Flexural test plot
Table 1: Characterization of chemically treated pitch
Table 2 Friction and hardness data
Table 3: Mechanical characterization of composites
Table 4: Physical characterization of composites
Conclusion
Robust c/c composites have been fabricated with varying reinforcement solely from petroleum pitch for the first time without cyclic reimpregnations. This class of materials have been known for their very high temperature stability and low erosion upon exposure with the high velocity flame It is evident form the mechanical analysis that the 25% of the reinforcement gives the last best results. It is also concluded that the hot compression moulding of thermally treated pitch matrix in presence of binder allows to fabricate the c/c composites with lower fiber content up to 25% by weight. Fiber bridging mechanism provides secondary stage rupture and improves toughness suggesting a favourable weak fiber matrix interaction. It is also established that the coefficient of friction increases from 0.124 to 0.152 for c/c composites containing 5% and 25% reinforcement respectively and takes a shooting value of 0.378 for a c/c composite specimen with 30% of fiber reinforcement.
Source: Rasmika H. Patel ,Shishobhan Sharma - Department of Materials Science, Sardar Patel University
The 10 largest coal producers and exporters in Indonesia:
- Bumi Resouces (BUMI)
- Adaro Energy (ADRO)
- Indo Tambangraya Megah (ITMG)
- Bukit Asam (PTBA)
- Baramulti Sukses Sarana (BSSR)
- Harum Energy (HRUM)
- Mitrabara Adiperdana (MBAP)
- Samindo Resources (MYOH)
- United Tractors (UNTR)
- Berau Coal
