Thermodynamic Estimation of the Parameters for the C–H–O–N–Me-Systems as Operating Fluid Simulants for New Processes of Powder Thermal Spraying and Spheroidizing

Abstract

Over the past few years, a group of new processes was developed for high-temperature, including plasma electric arc spraying (at ambient pressure) and spheroidizing of some ceramic and metal powder materials with the use of gaseous hydrocarbons in the heat carriers as well as with feeding of organic additions into a high-temperature jet, in particular, polymeric ones, to control porosity of sprayed metallic functional coatings. The paper considers the possibility to modify such technological processes by introducing solid fuel additions of a polymer type into the operating fluid of an apparatus for gasthermal (plasma or other) treatment, which provides melting of metal or oxide powders. For this, with the help of thermodynamic analysis, the processes have been evaluated at temperatures (300–3000) K for the set of such reacting five component systems as C–H–O–N–Me (at ambient pressure 0.101 MPa) with five variants of Ме – aluminum, titanium, chrome, copper, nickel. This makes it possible to consider these systems as simulants for potential technologies for the treatment of oxide powders (Al2O3, TiO2, Cr2O3) as well as metallic ones (Cu, Ni and their alloys). In order to obtain high exothermic contribution to the heating of powders, the combination “air + polymeric addition (polyethylene) of LDPE grade” was chosen as mixed heat carrier (operating fluid) for the basic version of simulated process. During the analysis of equilibria for the considered multicomponent systems (17 variants), a set of following parameters has been used to characterize the energy intensity of the target powder heating process: the equivalence ratio for reacting mixture and its adiabatic temperature; the energy efficiency of material heating with and without taking into account the effect of fuel addition; specific energy consumption for the powder melting; autothermicity degree of the process during the combined heating (electrothermal heating by the arc of plasma torch and heat flux from the “air + solid fuel additions” mixture) of refractory powders. As a result of the assessment, the preferred (from thermodynamic standpoint) regimes of the considered processes have been found and the possibility to realize an energy-efficient heating of these oxide and metal materials (without oxidation of the latter to CuOx, NiO) with a reduced part of the electric channel of energy transfer, resulted from the carrying out of appreciable effect of the fuel-initiated mechanism of heating in the analyzed C–H–O–N–Mesystems, has been shown in the paper.

Investigation of Upgraded Technology for Plasma Spraying of Bronze Powder Using the Combined Process with Hydrocarbon Additions

“…Figures 5-7 demonstrate the examples of the obtained results at the regimes with different level of the equivalence ratio (ER) [3][4]6].…”

“…According to the world leaders in a field of protective coatings (Oerlikon Metco AG (Switzerland), Praxair Surface Technologies (USA) and others), the most suitable materials for thermal spraying, including plasma methods, are powders (mainly metal and ceramic ones), which are used annually up to 100 kt [2][3][4][5][6]. Наука и техника.…”

“…powder materials. These technologies use both hydrocarbon gases as heat carriers (including plasma mixtures of methane with CO 2 ) to improve the velocity and thermal conductivity of plasma jets and intensification of particle melting in them, and with feeding of particulates or droplets of organic additives to the plasma jet to control the porosity and microstructure of sprayed metal and composite functional coatings, including for thermally resistant blades of gas turbines (in particular, according to the data [6,[9][10][11][12][13][14]). At the same time, in recent years, in particular, in Theoretical and Applied Mechanics Institute (Siberian Branch of the Russian Academy of Sciences), an adjacent promising air plasma spraying technology is being developed for use with new medium-power plasma torches to spray powders from a number of alloys, oxides (including doped alumina) and cermet compositions [8,[15][16].…”