UCTEA Chamber of Metallurgical & Materials Engineers’s Training Center Proceedings Book

696 IMMC 2018 | 19th International Metallurgy & Materials Congress

Collection of Metal Powders From Recycled Hard Particle Embedded Composite Cutting Tools

Tansu Altunbaşak¹, Mehmet Kul², İshak Karakaya¹

¹Middle East Technical University, Faculty of Engineering, Department of Metallurgical and Materials Engineering,Ankara, Turkey²Cumhuriyet University, Faculty of Engineering, Department of Metallurgical and Materials Engineering, Sivas,Turkey

Abstract

Diamond particles embedded cutting sockets which are placed on the circumference of the metal disc in industry to cut hard materials are discarded after completing their economic life. However, large quantities of metals and diamond particles remain in the discarded sockets. An electrochemical recycling procedure to form metal powders and gain diamond particles comprehensively and efficiently have been studied. The effects of temperature, acid concentration, copper ion concentration of the electrolyte and current density were studied. Collected metallic powders were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and single point Brunauer, Emmett and Teller (BET) analysis. Results show how to optimize the process parameters to obtain compact and dense metallic powders.

1.Introduction

Cutting, forming and processing operations of hard materials like concrete, stone, marble etc. are done with diamond particle embedded composite cutting tools mainly due to their relatively advanced properties like high hardness, wear resistance, low friction coefficient and low coefficient of thermal expansion [1], [2]. Among the many methods, powder metallurgy is the most commonly used technique to produce cutting inserts employing embedded diamond particles into metal matrix. As metal matrix constituents; cobalt, copper and tin are used usually while, diamond and hard particles are used as reinforcement of composite cutting tools to improve strength and hardness [3]. Approximately 400 m of stones can be processed until the end of life of cutting tools [4].

Natural sources run out day by day and recycling of discarded valuable particles and metals gain importance at present. Currently used recycling method for waste cutting tools is acid dissolution technique [5]. In this technique by utilizing characteristics of diamond or tungsten carbide which are insoluble in acid, however metals are soluble. Furthermore, after recovery of diamond, filtered solution that carries

metal ions is discarded [6]. This study puts forward a new method for recycling of materials used in diamond particle embedded composite cutting tools comprehensively and efficiently by means of an electrochemical process. In other words, objective of the study is not only recovering of diamond and other valuable particles, but also recycling of metals by co-deposition of metal powders.

The waste diamond cutting tools which contain at least 10% of residual diamond and combined with the metallic matrix [4] used as anodes were dissolved by application of power in relatively weak acid electrolytes. Diamond particles which sink to the bottom of the electrolyte were collected after filtration so that they could be used again. Dissolved metal ions from anode and electrolyte were collected as a powder from at the cathode. Obtention of metal powders in various surface morphologies, shapes and sizes is possible by electrodeposition by changing electrodeposition conditions like the type of the electrolyte, metal being deposited, temperature, pH, current density etc. Therefore, besides collection of diamond particles, effects of temperature, current density, acid and CuSO4 concentrations of electrolyte on the powder properties were examined.

Full factorial methods were conducted to see parameters that affect the results of experiment with changing the parameters and parameter’s interaction with each other. Such statistical tools have been enlarged to decrease to save time and costs of each trial. In this study full factorial design were conducted before experiments to find important parameters of metal powder electrodeposition and its critical influence on the specific surface area of electrodeposited metal powders. The main goal of design of experiment (DOE) is associate the dependent variables (metal powder properties) with the independent variables (experiment conditions) coming along with the interaction factors.

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2. Experimental Procedure

Waste diamond tools contained diamond particles embedded to an 85 % Cu and 15 % Sn containing metal matrix having rectangular surface was employed as anode and AISI304 stainless steel sheet as cathode in this study. COMSOL Multiphysics Modeling software program [7], as illustrated in Figure 1, was used to determine cell design for homogenous dissolution and deposition simulation of the process. The shapes of anode and cathode assemblies were determined from the results of this program. As it can be seen, comparison of profile changes of electrodes was shown for assemblies employing anodes with and without masks after 1 hour of electrolysis. According to simulation outputs, avoiding excessive dissolution of the edges of the prismatic anodes and enhancing uniform deposition on cathodes was achieved by masking anodes with a dielectric material.

Figure 1 Electrode thickness change after 1 hour of electrolysis in which anode material was (a) without and (b) with mask.

Electrodes were kept parallel to each other by using 3 cm inter electrode distance. All experiments were performed for 3 hours using 500 rpm stirring. After 3 hours of electrolysis with different parameters as given in Table 1, while galvanostatically deposited copper powders were scraped from the stainless steel cathode easily, diamond and tin particles which sank to the bottom of the electrolyte were filtered from the

electrolyte. Collected copper powders were washed with ethanol and then with 0.1 molar benzoic acid solution for remaining acid and preventing oxidation of copper powders.

Table 1 Electrolysis parameters Parameters

Current Density (A/dm2) 8,37-10,46-12,5Cu Ion Concentration (g/L) 10-15

Temperature ( C) 20-30-40Acid Concentration (M) 0.25-0.5-1

3. Results and Discussion

3.1. Effects of Electrolysis Parameters on Powder Morphology

At the end of experiments diamond particles and tin powders which were settled to the bottom of the electrolyte, were easily recovered after filtration and washing with ethanol and benzoic acid. Collected tin powders and diamond particles are exhibited in Figure 22.

Figure 2 Collected (a) diamond particles (b) tin powders from electrolyte.

According to full factorial design outputs, some of the SEM images of galvanostatically deposited copper powders under different conditions are shown in Figure 3 to make comparison of the effects of parameters on the morphology of the copper powders. As it can be seen in Figure 3a and Figure 3b effect of acid concentration on the morphology of the deposited copper powders is exhibited. Increasing acid concentration promoted the formation of cauliflower like morphology with a slightly more branched structure as shown in Figure 3b. The powders produced from the electrolyte that contained less acid concentration had compact corncob like morphology as shown in Figure 3a.As a general knowledge by increasing sulfuric acid concentration in the electrolyte, H+ ion concentration of the electrolyte rose, which means that hydrogen evolution reaction was dominant at high concentrations of sulfuric acid. Hydrogen evolution changed the morphology of the electrodeposited copper powder by changing hydrodynamic conditions near the cathode layer [8].

UCTEA Chamber of Metallurgical & Materials Engineers’s Training Center Proceedings Book

698 IMMC 2018 | 19th International Metallurgy & Materials Congress

Comparing Figure 3a and Figure 3c showed that temperature had important impact on the morphology of the copper powders. The movement of ions in the electrolyte was easier throughout the electrolyte when fluidity of the electrolyte was increased by increased temperature. Concentration layer was disturbed at cathode surface when dragged ions reached cathode surface, as a result concentration polarization and accordingly cell voltage decreased [9]. Therefore, increasing temperature caused changing morphology of copper powders from compact and globular powders to more dendritic structure.

Compact and more dense copper powders were attributed to increasing copper ion concentration of electrolyte from 10 g/L to 15 g/L as compared in Figure 3d and Figure 3a. When sufficiently and constantly feeding of copper ions to the cathode surface was accomplished, H2 overvoltage decreased and accordingly concentration polarization. Decreasing cathodic polarization and overvoltage near cathode surface due to high concentration of copper ions made easier coalescence of copper atoms [10]. Increasing Cu2+ ions induced decreasing relative concentration of H+ ions, but it must be considered to yield sufficient hydrogen evolution to stir the solution [11]. Therefore, concentration of electrolyte was carefully adjusted so that evolved hydrogen was high enough to change hydrodynamic conditions near cathode by hydrogen evolution.

Current density had also noticeable effect on the microstructure of the electrodeposited copper powders. Increasing current density from 8.4 to 12.5 A/dm2 was shown in Figure 3a and Figure 3e respectively. By high current density, high magnetic field was created which led ions to hit the cathode surface and because of overpotential direct reduction of ions took place and production of powders with dendritic in shape was noticed [12]. From another point of view, increasing current density not only promoted powder deposition rate, it also accelerated hydrogen evolution reaction. Hydrogen evolution changed the morphology of the electrodeposited powder as stated previously by stirring the electrolyte.

Result of morphological examination summarized as decreasing current density, acid concentration and increasing temperature and copper ion concentration caused formation of compact, dense copper powders.

Figure 3 Copper deposits obtained at (a) 8.4 A/dm2 current density, in 15 g/L Cu2+ and 0.25 M H2SO4 electrolyte at 40oC, (b) 8.4 A/dm2 current density in 15g/L Cu2+ in 1 M H2SO4 at 40oC, (c) 8.4 A/dm2 current density in 15 g/L Cu2+

in 0.25 M H2SO4 at 30oC, (d) 8.4 A/dm2 current density, in 10 g/L Cu2+ and 0.25 M H2SO4 electrolyte at 40oC and (e) 12.5 A/dm2 current density in 15 g/L Cu2+ in 0.25 M H2SO4at 40oC.

3.2. Effects of Electrolysis Parameters on Crystallographic Orientation of Powders

The diffraction patterns of the electrodeposited copper powders with different electrodeposition conditions are displayed in Figure 4. The diffraction patterns showed intensities of diffraction from randomly distributed planes. The highest diffraction peak is produced by the most densely packed plane of copper powders which is (111) plane. XRD patterns of electrodeposited copper powders exhibited in Figure 3 are shown in Figure 4. To make comparison the effect of current density on diffraction patterns of powders; diffraction patterns of copper powders produced at 8.4 A/dm2 and 12.5 A/dm2

are shown. The diffraction pattern of the electrodeposited copper powders at high current density had high intensity of (111) plane which means that increasing current density brought about deposited copper powders mostly oriented at one direction and dendritic powders were attained. The diffraction patterns from all powders produced at different electrolysis parameters were in accord with the SEM images of powders as shown in Figure 3.

The summary of all diffractions is; increasing current density and acid concentration, decreasing copper ion

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concentration and temperature prompted dendritic copper powders which had higher intensities of (111) diffraction peaks.

Figure 4 XRD patterns of electrodeposited copper powders produced at different parameters.

3.3. Surface Area of Powder

For handling and sintering purposes powders with smaller surface area to mass ratio are preferred. Therefore, BET analysis was performed on powders collected during electrolysis experiments. Effects of parameters studied during electrolytic powder formation on specific surface area of powders are shown in Figure 5. BET analysis results were also in accord with X-Ray and SEM results.

Figure 5 Main effects plot for specific surface area.

Figure 5 showed that current density had the highest impact on the surface area and then temperature, copper ion concentration came but, acid concentration of electrolyte had much less effect on surface area. The regression analysis gave a regression formula that shows how parameters affected the surface area is given as;

𝑚 𝑔(1)

Where; A: current density (A/dm2), B: temperature (°C), C: Cu2+ ion concentration (g/L) and D: acid concentration (M) of the electrolyte.

4. Conclusion

• Complete recovery of the diamond cutting tools was achieved by electrolysis at low acid concentrations. Diamond particles and tin powders were directly collected.

• Effects of current density, temperature, acid and CuSO4 concentrations were important on the morphology and surface area of electrodeposited copper powders.

• Decreasing current density and sulfuric acid concentration, increasing temperature and Cu2+ ion of electrolyte promoted the formation of compact, dense copper powders having small surface area to mass ratio.

• Among four parameters that were examined in this study, current density was the most influential parameter according to SEM, XRD and BET analysis result.

Acknowledgements

Authors acknowledge the Scientific and Technological Research Council of Turkey (TÜB TAK) for financial support provided through the project 116M406.

References

[1] M. Jennings and D. Wright, Ind. Diam. Rev., 49 70–75. [2] L. Wang, G. Zhang, and F. Ma, Rare Met., 31 (2012) 88-91.[3] C. Browning, US Patent Number 4,739,745, 1988. [4] A. L. D. Skury, G. S. Bobrovnitchii, S. N. Monteiro, and C. C. Gomes, Sep. Purif. Technol., 35 (2004) 185–190,. [5] H. Xian, Gu. Xue, L. Ping, H. Kai, and X. Kai, Hydrometall., no. 03 (2005). [6] X. Q. Zheng, D. Z. Meng, and X. M. Zhou, Jiangxi Chem. Ind., 4(2008) 197. [7]COMSOL Multiphysics, Version 5.2, <www.comsol.com> Dated: 10.04.2017 [8] N.D. Nikoli , K.I. Popov, Lj.J. Pavlovi , M.G. Pavlovi ,Sensors 7 (2007) 1 15[9] A. Amadi, D.R. Gabe, M. Goodenough, 21 (1991) 1114 [10] N.D. Nikoli , L. J. P., M.G. Pavlovi , K.I. Popov, Powder Technology, 185(2008) 195–201. [11] N.D. Nikolic', K. I. Popov, Electrodeposition of Copper Powders and Their Properties, Ed. by S.S. Djokic', Electrochemical Production of Metal Powders, Springer Science, 2012 New York[12] E. Akbarzadeh, Z. Kheiroddin, Particle Shape and Size Modification and Related Property Improvements for Industrial Copper Powder, World Engineering Congress, 2–5 August 2010, Kuching, Sarawak, Malaysia