The influence of dielectric media on nano-structured tungsten carbide (WC) powder synthesized by electro-discharge process

Highlights

• More powder was produced in the negative pole mode.

• WC_1−x and W₂C are the main phases produced in kerosene and deionized water, respectively.

• WC and W–WC are the main phases produced in kerosene and deionized water after carburization process, respectively.

Abstract

In this investigation, nano-structured tungsten carbide (WC) powder has been synthesized using electro discharge process with tungsten and graphite electrodes submerged in two different dielectrics (kerosene and deionized water). The effect of input parameters (current and pulse duration) in the electro discharge process on the amount of powder production, structure, phases, morphological properties, and size distribution of particles were studied. The obtained results illustrated that, in the majority of setup settings, the amount of nano-structured powder in the kerosene was noticed to be approximately four times greater than the amount of powder produced in deionized water dielectric. Furthermore, it was observed that the particle size in kerosene dielectric (10–30 nm) was smaller than the particle size in deionized water (30–80 nm). According to XRD patterns, WC_1−x phase in kerosene and W₂C phase in deionized water were the main phases of synthesized powder. After producing WC_1−x and W₂C, both powders were put into the carburization operation under the Nitrogen gas to produce WC phase.

Introduction

In recent years, the wide range of nano-structured materials application in different fields, including, but not limited to metallurgy, biology, photonic, optic, and catalysis has led to great efforts in synthesizing nano-structured powders [1]. Due to exceptional mechanical and metallurgical properties, such as high melting temperature (2600–2850 °C), high hardness (16–22 GPa 500 g load Vickers) along with a high fracture toughness (28 MPa m^1/2), high compressive strength (5 GPa at 20 °C), and high resistance against oxidization and corrosion [2], [3], tungsten carbide nano-powder is being used nowadays as the main substance in manufacturing cutting tools, shaping tools, and mining instruments which can be employed in high pressure, temperature, and corrosion circumstances [4]. In addition to the above-mentioned characteristics, tungsten carbide powder is used in coating space traveling equipment, automotive industries, and home appliances due to its high resistance against abrasion [5]. Recently, it has been confirmed that tungsten carbide exhibits similar behaviors to Pt in several catalyst reactions and could be a good replacement for Nobel metals (Pt, Pd, Ir) [6], [7].

There are a significant number of procedures to synthesize WC. However, the characteristics of the powder produced by each procedure could be different.

Nanosized tungsten carbide powders have been produced by various methods such as the mechanical alloying (MA) [8], [9], [10], thermo-chemical spray drying process [11], [12], [13] and chemical vapor condensation (CVC) [14], [15], [16]. The electro discharge procedure between two submerged electrodes in liquids has been considered as a low-cost and simple methodology to synthesize nano-particles of different materials in recent years [17], [18], [19], [20], [21], [22], [23], [24], [25]. Ishigami et al. reported synthesis of carbon nanotubes, using electrical discharge between two graphite electrodes submerged in liquid nitrogen [17]. Sano et al. employed water instead of liquid nitrogen as a dielectric to synthesize carbon nanotubes [18]. In another research conducted by Parkansky et al. the electrical discharge process between nickel, tungsten, steel, and graphite electrodes submerged in ethanol was introduced to synthesize the desirable powders [19]. Bera et al. synthesized carbon nanotubes composed of palladium nano-particles through an electro discharge process between two graphite electrodes submerged in palladium solution [20]. Guo et al. recently observed that encapsulated nano-particles made of Ni, Co, and Fe in carbon shells could be produced by electro discharge process between one electrode of these materials and another electrode of carbon in the solutions of NiSO₄, CoSo₄ and FeSO₄ [21]. Burakav et al. [22] utilized the electro discharge process between pairs of electrodes made of Cu, WC, and Zn in an aqueous solution of CuCl₂ in order to synthesize the encapsulated nano-particles of copper in a carbon shell. Ethylene alcohol and water were used for synthesizing tungsten and oxidized zinc nanoparticles, respectively. Hong [23] successfully produced tungsten carbide nano-particles using the electro discharge between two tungsten and graphite electrodes submerged in a dielectric of kerosene-base. Muthakarn et al. produced carbon nano-particles using the electro discharge process between two graphite electrodes submerged in alcohol and Alcan’s [24]. Kuo Hsiung Tseng et al. produced nano-particles of gold by incorporation of an electro discharge procedure between two electrodes of gold and ethanol dielectric [25].

In this research, the synthesis of nano-structured tungsten carbide (WC) powder using electrical discharge process between two graphite and tungsten electrodes in two different dielectrics (deionized water and kerosene) was investigated. Furthermore, the stages and the methods used to form nano-particles of tungsten carbide (WC) and the effect of various parameters on the structure, phases, sizes, and the amount of production were examined.