Conversion of diamond polishing powder to high-density isotropic nano-crystalline graphite through spark plasma sinterin
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Conversion of diamond polishing powder to high‑density isotropic nano‑crystalline graphite through spark plasma sintering Rajath Alexander1 · K. V. Ravikanth1 · M. R. Gonal1 · A. P. Srivastava1 · Kinshuk Dasgupta1 Received: 5 December 2019 / Accepted: 31 March 2020 © Springer Nature Switzerland AG 2020
Abstract Conversion of diamond polishing powders into graphite nano-crystals and simultaneous densification to high-density graphite were achieved through spark plasma sintering at 2000 °C with 45 MPa pressure. The sintered graphite had a density of 1.84 g/cm3 and hardness of 12.1 ± 0.4 HV. The phase evolution was characterized by X-ray diffraction and Raman spectroscopy. Scanning electron microscopy and transmission electron microscopy revealed that the converted highdensity graphite consisted of randomly oriented nano-crystalline grains. The formed graphite was also isotropic in nature. Keywords Diamond · Graphite · Raman spectroscopy · Electron microscopy · Spark plasma sintering
1 Introduction Graphite is a material with unique properties that enable it to be utilized in applications ranging from household to aerospace. Many critical applications, like nuclear, aerospace, and military, demand retention of strength at high temperatures, which high-density graphite (> 1.8 g/ cm3) can provide [1, 2]. High-density graphite possesses enhanced mechanical properties like compressive, flexural and tensile strength in comparison with low-density graphite ( 2500 °C). This may be due generation of very high localized temperature due to plasma formation between the powder particles [19] during SPS. Geuntak et al. [20] has also shown that the interior of SPS die is significantly hotter than the surface where temperature measurement is taken. In our case, the pyrometer readings were measured on the die surface which was 5 mm away from the surface of the sample. Hence even though the pyrometer showed the
Fig. 6 Densification curve of the sample obtained through ram movement of SPS
Vol.:(0123456789)
Short Communication
SN Applied Sciences
(2020) 2:835
temperature of 2000 °C, the actual temperature inside the sample could be significantly higher causing effective graphitization.
4 Conclusions We could convert the low cost diamond polishing powders into high-density sintered graphite using SPS in a single step. The temperature (2000 °C) and time (30 min) utilized in SPS were significantly lower than that of the commercial production of highly dense graphite that requires temperature above 2500 °C and several days for completion. XRD patterns and Raman spectra confirmed 100% conversion of diamond into graphite. The grains were nano-crystalline in nature with random orientation. A density of 1.84 g/cm3 with a hardness of around 12.1 ± 0.4 HV could be achieved. XRD and dilatometer data depicted isotropy in the samples. The process may be useful for producing small-sized high-density graphite pellets for different applications.
Compliance with ethical standards Conflict of interest The authors claim that there is no
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