Properties of Nanocomposite Ag-Cu Colloids Prepared by Electrical Spark Discharge Method

Abstract

Electrical spark discharge was used to prepare nano Ag–Cu colloids with an electrical discharge machine, deionized water (DW) as the dielectric fluid (DF), and at room temperature and normal pressure. The upper and lower electrodes of the electrical discharge machine were pure Ag and Cu wires or composite metal wires with an Ag–Cu ratio of 92.5:7.5 or 72:28. The optimal T_on–T_off, process time, and current for colloid production were identified as 30–30 µs, 5 min, and approximately 11 A, respectively. The absorbance, characteristic wavelength, particle size distribution, and suspension stability were, respectively, 0.586, 406 nm, 101 nm, and 28.1 mV for the colloids prepared using pure Ag and Cu wires; 0.509, 419 nm, 197.5 nm, and −6.67 mV for the 92.5:7.5 composite wires; and 1.479, 407 nm, 85.27 nm, and14.8 mV for the 72:28 composite wires. The diffraction peaks of the Ag and Cu particles shifted for the composite-produced colloids; this was likely caused by internal structural defects in the composite metal wires. Transmission electron microscopy was used to analyze the nanomaterials. The average Ag and Cu lattice widths, respectively, were 0.234 nm and 0.207 nm for the pure-metal wires, 0.243 nm and 0.210 nm for the 92.5:7.5 composite wires, and 0.243 nm and 0.210 nm for the 72:28 composite wires. X-ray diffraction (XRD) analyses were conducted to determine the crystal orientations of the nano Ag–Cu particles and revealed that nano Ag–Cu colloids prepared using pure Ag and Cu wires had an Ag–Cu particle ratio of approximately 97:3.

1. Introduction

Materials, such as metals, ceramics, and polymers, are typically studied as bulk materials [1]. Conversely, nanotechnology research focuses on the chemical and physical properties of substances at the nanoscale. Nanotechnology is the rapid and effective control of atoms, molecules, or supermolecules [2] to create new material structures by reassembling the materials. The aim of nanotechnology is to explore new material characteristics and phenomena, using knowledge and nanotechnology to create new functionalities [3]. Traditional materials can be converted into nanomaterials through methods such as vapor deposition and milling. Nanomaterials are typically defined as materials with at least one dimension ranging between 1 and 100 nm. These materials can be categorized as zero-dimensional materials [4,5] such as nanopoints or nanoparticles (e.g., nanocrystals [6]); one-dimensional materials such as nanowires [7,8]; two-dimensional materials such as superlattices [9,10]; and three-dimensional materials [11]. Nanotechnology was first suggested by Richard Feynman, a Nobel winner, who imagined storing the entire Encyclopedia Britannica on the head of a pin by shrinking it by a factor of 40 million. At the nanoscale level, materials exhibit different thermal [12], electrical, and magnetic [13] properties than their bulk counterparts. The chemical stability of materials also changes. These differences in material behavior [14] as nanostructures are central to the development of nanotechnology.

Ag is a precious ductile metal with a metallic-white luster and is known for its excellent thermal and electrical conductivity among the transition metals [15]. It is more abundantly distributed than many other metals in nature, but it is rare in the Earth’s crust. Ag can exist in its pure form or within ores containing Pb, S, Cu, and Zn; it is extracted from ore through refining processes [16]. Cu, a group-11 element and one of the earliest metals used by humans, is known for its high ductility and thermal and electrical conductivity. Cu is commonly found in naturally occurring Cu ore that can be extracted to obtain high-Cu-content concentrates [17]. Cu is distributed throughout the Earth’s crust (accounting for approximately 0.01% of its content) and oceans. Nano-Ag is considered the optimal catalyst for oxidation reactions, and the factors influencing its catalytic performance include the manufacturing methods, reaction conditions, and particle size [18]. According to density functional theory, when Cu is bound with other metal oxides, it becomes a highly active catalyst [19]. Nanoscale metal oxide particles are regarded as crucial nanomaterials that possess unique and useful physical and chemical properties. They are widely used as catalysts and are often combined with other metal nanoparticles.

Several studies have reported the preparation of Ag–Cu or Cu–Ag nanoparticles and nanoalloys using ESDM or closely related discharge-based techniques in liquid or aqueous media [20,21,22]. Previous works have investigated alloy formation mechanisms, oxidation behavior of Cu, particle size reduction, and functional properties such as antibacterial or catalytic performance [23]. In many cases, these studies employed single-metal electrodes, chemical additives, or post-treatment processes to control composition and stability. Despite these advances, a systematic comparison between pure-metal electrodes and pre-alloyed Ag–Cu composite electrodes operated under identical electrical spark discharge conditions remains limited [24]. In particular, the role of internal structural heterogeneity and defect distribution in composite metal wires, and their influence on phase evolution, lattice distortion, diffraction peak shifts, and colloidal aggregation behavior of the resulting nanoparticles, has not been sufficiently clarified.

Accordingly, this study focuses on the controlled preparation of Ag–Cu nanocolloids in deionized water without the use of chemical reducing or stabilizing agents via the electrical spark discharge method. By comparing pure Ag and Cu electrodes with Ag–Cu composite electrodes of different compositions under identical discharge parameters, this work aims to investigate how electrode material characteristics influence the optical response, hydrodynamic aggregation behavior, phase composition, and structural features of the resulting nanocolloids.

In this study, an electrical discharge machine was used in conjunction with a dielectric fluid to perform the Electrical Spark Discharge Method (ESDM) for preparing nano Ag–Cu colloids. Different nanocolloids were prepared using different materials as the upper and lower electrodes, resulting in three different types of nanocolloids. For the first type, pure Ag (99.99%) and pure Cu (99.99%) wires were the upper and lower electrodes, respectively. The second type was produced by using composite metal wires with an Ag–Cu ratio of 92.5:7.5 as the electrodes. The electrodes for the third type were composite metal wires with an Ag–Cu ratio of 72:28. These three types of nano Ag–Cu colloids were subsequently analyzed to assess their characteristics.

2. Materials and Methods

2.1. Principles of ESDM

EDSM is performed by immersing two electrodes in a dielectric fluid and applying a direct-current (DC) voltage to create a strong electric field. This disrupts the insulation capacity of the dielectric fluid, initiating an electrical spark discharge between the electrodes, increasing their temperature. The electrodes rapidly melt to form tiny particles, which then quickly cool to form nanoparticles. During the discharge process, electrons migrate from the negative to the positive electrode, producing high thermal energy upon high-speed collisions, melting or vaporizing the materials on the electrode surfaces into nanoparticles. When the discharge ceases, the dielectric fluid returns to its insulating state. The entire discharge process is depicted in Figure 1. The stages are as follows:

• Predischarge: The upper electrode moves slowly towards the lower electrode, gradually increasing the gap voltage V_gap and the electric field strength between the electrodes without exceeding the dielectric strength of the fluid, thus maintaining its insulating state, as shown in Figure 1a.
• Discharge initiation: When the distance between the two electrodes reaches 30 µm, this distance is maintained and the electric field strength across the electrode gap exceeds the insulation strength of the dielectric fluid. Electrons detach from the surface of the lower electrode and migrate to the upper electrode, and the atoms or molecules in the dielectric fluid produce free electrons. A discharge channel gradually forms between the electrodes, as shown in Figure 1b.
• Ionization: Electrons move from the lower electrode to the upper electrode, forming a discharge channel. This process involves collisions with neutral atoms between the electrodes, exciting the outer valence electrons of the neutral atoms and forming positive ions and free electrons, as shown in Figure 1c.
• Fusion action: The kinetic energy of the free electrons and positive ions converts to thermal energy, creating an electrical spark that melts or vaporizes the electrode surfaces. This causes metal particles to splash into the dielectric fluid and form nanoparticles, as shown in Figure 1d.
• Discharge termination: The T_off phase begins, and both V_gap and I_gap gradually decrease. The discharge channel swiftly disappears, and the nanoparticles remain suspended in the dielectric fluid as its insulating state is restored, as shown in Figure 1e.
• Insulation restoration: At the end of the T_off phase, both V_gap and I_gap drop to zero, and the dielectric between the upper and lower electrodes returns to an insulating state. The nanoparticles remain suspended in the dielectric fluid until the next discharge pulse cycle, as shown in Figure 1f.

2.2. Preparation of Nano Ag–Cu Colloids Using ESDM

Traditional electrical discharge machines comprise a direct current pulse power supply, servo control system, control panel, upper electrode, and lower electrode (workpiece). In this study, ESDM and an electrical discharge machine were employed to prepare nanocolloids. A schematic diagram of the electrical discharge machine is shown in Figure 2. The upper and lower electrodes were wires made of pure Ag and Cu, with an Ag–Cu ratio of 92.5:7.5 or 72:28. The electrically conductive material placed at the upper electrode was secured using a fastener on the electrical discharge machine. The electrically conductive material at the lower electrode could not remain stable in the dielectric fluid; thus, the electrically conductive material was embedded in an auxiliary fixture to secure the lower electrode. A DC pulse power supply was connected between the two electrodes.

Nano Ag–Cu colloids were prepared with pure Ag (99.9%) and Cu (99.9%) wires, composite metal wires with an Ag–Cu ratio of 92.5:7.5, and composite metal wires with an Ag–Cu ratio of 72:28. The process parameters were also varied. The resulting colloids were analyzed using UV–vis spectroscopy and a nanoscale particle size and potential analyzer. The best nanocolloids fabricated using each of the three materials were selected and analyzed using XRD and TEM for comparison.

All electrode wires had a diameter of 1 mm, and the DF was DW (150 mL) at room temperature and normal pressure. The variable process parameters were T_on–T_off and the peak current (IP). The fourth IP setting created nano Ag–Cu colloids with two different absorbance levels (

Table 1. Parameter settings.

Content	Explanation
Wire material	Ag wire, Cu wire, and composite Ag–Cu wire
Dielectric fluid	Deionized water
Dielectric fluid volume	150 mL
Voltage setting	140 V
Capacitance setting	OFF
Ton–Toff	10–10, 30–30, 50–50, 70–70, 90–90, 110–110 µs
Current setting (IP)	4
Sensitivity knob	1/2
Servo knob	1/2
Ambient temperature/pressure	Room temperature/normal pressure
Total manufacturing process time	5 min

). Lower IP settings resulted in a smaller particle sizes and lower nanocolloid concentration, and higher IP settings resulted in particles sedimentation and higher nanocolloid concentrations. The discharge characteristics of the electrical discharge machine were closely related to the environmental manufacturing process parameters set on the control panel, showing that environmental manufacturing process parameter settings significantly affected nanocolloid characteristics.

2.3. Analyses of Nano Ag–Cu Colloids

A UV-Vis spectrometer (Thermo-Helios Omega, Thermo Scientific, Waltham, MA, USA) was used to measure the absorbance of the nanocolloids. The differences in the molecular structures of the nanocolloids were indicated by a redshift or blueshit of the characteristic wavelength, and the nanocolloid concentration was linearly correlated with absorbance.

Additionally, a nanoparticle size and potential analyzer (Zetasizer Nano ZS90, Malvern, UK) was used for the characterization. This instrument employs 90° dynamic light scattering [25] and laser Doppler electrophoretic light scattering technology [26] to sequentially measure the particle size distribution and zeta potential of nanocolloids. A particle size analyzer measures particle size as the particle size distribution in intervals. The precision of the results varies between analyzers applying different techniques.

A transmission electron microscope (JEM-2100F, JEOL, Tokyo, Japan) was used to observe the sizes and distributions of nanoparticles.

An X-ray diffractometer (EMPYREAN, PANalytical, Worcestershire, UK) was used for nondestructive detection of the crystal structures of the nanocolloids. The nanocolloid crystal structures were studied, and the crystal symmetry and crystal orientations were analyzed.

3. Results and Discussion

3.1. Optical Property Analyses of Nano Ag–Cu Colloids Prepared Using Pure Metals and Composite Metal Wires

ESDM was used to prepare nanocolloids from pure metal wires or composite metal wires. The variable process parameters were T_on–T_off, the IP setting, and the total process time. The total process time was 5 min, the IP setting was 4 (11.88 A), and T_on–T_off was 10–10, 30–30, 50–50, 70–70, 90–90, or 110–110 µs. Figure 3a presents the surface plasmon resonance (SPR) results for nano Ag–Cu colloids prepared using pure metal wires for each T_on–T_off. The results were blueshifted as T_on–T_off increased (415 nm, 406 nm, 410 nm, 410 nm, 417 nm, and 417 nm, respectively), suggesting that the nanocolloid particles were growing in size. For the Ag–Cu ratio of 92.5:7.5 [Figure 3b], T_on–T_off was 10–10, 30–30, 50–50, 70–70, 90–90, or 110–110 µs, and the measured SPRs were 424 nm, 419 nm, 428 nm, 425 nm, 420 nm, and 420 nm, respectively, again indicating a blueshift as T_on–T_off increases and suggesting gradually growing nanocolloid particle sizes. The results for the Ag–Cu ratio of 72:28 in Figure 3c (400 nm, 407 nm, 412 nm, 417 nm, 422 nm, and 416 nm) are similar.

The characteristic peak wavelengths and absorbance rates of the nano Ag–Cu colloids were obtained for each material and T_on–T_off; these are listed in

Table 2. Optical properties of the colloids.

	Material	Pure Metal Wire		Composite Metal Wire (92.5:7.5)		Composite Metal Wire (72:28)
Parameter (µs)		SPR (nm)	Absorbance	SPR (nm)	Absorbance	SPR (nm)	Absorbance
10–10		415	0.527	424	0.702	400	0.982
30–30		406	0.586	419	0.509	407	1.479
50–50		410	1.086	428	0.371	412	0.661
70–70		410	0.877	425	0.419	417	0.439
90–90		417	0.878	420	0.477	422	0.459
110–110		417	0.898	420	0.767	416	0.590

.

3.2. Particle Size Distribution and Zeta Potential

The Ag–Cu composite nanocolloids prepared with a T_on–T_off of 30–30 µs were analyzed using the Zetasizer. Figure 4a presents the size distribution; the main peak is at 538.1 nm (75.7% of the total) with a standard deviation (St Dev) of 117.6 nm. The secondary peak at 116.3 nm accounts for approximately 24.3% of the total, with a St Dev of 19.76 nm. Larger particles absorbed more scattered light than smaller particles. Figure 4b presents the nanocolloid volume distribution results. The primary peak is at 562 nm, accounting for approximately 63.1% of the total, with a St Dev of 132.3 nm; and the secondary peak is at 108.9 nm, accounting for approximately 36.9% of the total, with a St Dev of 21.65 nm. The volume distribution was obtained by calculating and converting light intensity distribution data; both peaks exceeded 100 nm mainly because of the characteristics of nano Cu particles. Figure 4c shows the nanocolloid number distribution results. The primary peak is at 101 nm, accounting for approximately 98.6% of the total, with a St Dev of 18.89 nm; and the secondary peak accounts for only approximately 1.4% of the total, with a St Dev of 117.2 nm. The spectrum had no other significant peaks. The number distribution was obtained by calculations from the volume distribution. The peak exceeded 100 nm mainly because of the characteristics of nano Cu particles. Figure 4d shows the nanocolloid zeta potential analysis results. The zeta potential value was 28.1 mV, and the St Dev was 4.16 mV. The zeta potential was less than 30 mV, indicates that the ionic repulsion on the surfaces of the nano Ag–Cu particles is less than the viscosity within the nanocolloids. The suspension stability was better than that of nanocolloids prepared using other parameters. The particle size information presented in this section is derived from dynamic light scattering (DLS) measurements and therefore represents the hydrodynamic behavior of particle agglomerates in suspension. As a result, the DLS data are interpreted in terms of relative aggregation behavior and colloidal stability under different discharge conditions, rather than as absolute primary particle size distributions.

Table 3. Particle size distribution and zeta potential of nano Ag–Cu colloids prepared using pure metal wires.

Ton–Toff (µs)	Light Intensity Distribution (nm)	Volume Distribution (nm)	Number Distribution (nm)	Zeta Potential (mV)
10–10	774.0	799.00	710.6	5.8
30–30	538.1	562.00	101	28.1
50–50	356.0	48.83	4599	19.5
70–70	208.5	65.79	5399	18.9
90–90	4056.0	58.48	4504	26.0
110–110	4455.0	57.68	4829	22.6

,

Table 4. Particle size distribution and zeta potential of nano Ag–Cu colloids prepared using composite metal wires with an Ag–Cu ratio of 92.5:7.5.

Ton–Toff (µs)	Light Intensity Distribution (nm)	Volume Distribution (nm)	Number Distribution (nm)	Zeta Potential (mV)
10–10	748.7	763.5	708.90	−0.512
30–30	856.2	920.1	197.50	−6.670
50–50	4944.0	5139.0	437.20	2.830
70–70	498.6	5569.0	473.80	−0.691
90–90	531.5	550.5	94.13	−0.898
110–110	813.4	830.0	172.60	−0.609

and

Table 5. Particle size distribution and zeta potential of nano Ag–Cu colloids prepared using composite metal wires with an Ag–Cu ratio of 72:28.

Ton–Toff (µs)	Light Intensity Distribution (nm)	Volume Distribution (nm)	Number Distribution (nm)	Zeta Potential (mV)
10–10	251.6	4441.00	56.41	4.21
30–30	231.8	48.97	44.43	4.92
50–50	341.8	346.60	335.00	3.52
70–70	91.28	91.77	91.77	3.68
90–90	461.7	5590.00	81.44	0.76
110–110	4377.0	4745.00	391.80	7.25

present the analysis results for each prepared nano Ag–Cu colloid. Nanocolloids prepared using a T_on–T_off of 30–30 µs had the highest zeta potential and the smallest particle size distribution; thus, they were the best among the six types of nanocolloids prepared. Accordingly, this study selected a T_on–T_off of 30–30 µs as the optimal manufacturing process parameter for the electrical discharge machine.

Table 3, Table 4 and Table 5 show that the nano Ag–Cu colloids had wide particle size distributions and small zeta potentials, indicating that the repulsion between nano Ag–Cu particles was less than their attraction; thus, smaller particles tended to aggregate into larger particles.

3.3. TEM Analyses

In this study, transmission electron microscopy (TEM) was employed as a qualitative characterization technique to confirm nanoparticle formation, examine particle morphology, and resolve lattice fringes for crystallographic analysis. Owing to the pronounced aggregation observed in the as-prepared nanocolloids, TEM images were not used for quantitative particle counting or for constructing a statistical particle size distribution. All nanocolloids were characterized in their as-prepared state without additional dispersion treatments, such as ultrasonic sonication. This approach was adopted to preserve the intrinsic aggregation behavior and interparticle interactions arising from the electrical spark discharge process in deionized water, and to reflect the native colloidal characteristics under chemical-free conditions. Nano Ag–Cu colloids were prepared at a T_on–T_off of 30–30 µs using pure Ag and Cu wires, composite metal wires with an Ag–Cu ratio of 92.5:7.5, and composite metal wires with an Ag–Cu ratio of 72:28. The nanocolloids were then magnified and examined using TEM. The results are presented in Figure 5. All images were taken at a magnification of 20,000× and a scale of 500 nm. In all colloids, large particles were attracted to each other, resulting in substantial aggregation and particle overlapping. This result is consistent with the measurements obtained from the nanoparticle size distribution and potential analyzer.

The magnification and scale were set to 800,000 and 10 nm, respectively (Figure 6), for TEM because the high energy of the TEM electron beam burned the surfaces of the Ag–Cu particles at higher magnification. preventing imaging of the crystal lattice lines of the Ag–Cu particles. Even when the image scale was reduced from 10 nm to 500 nm, the Ag–Cu particles were still damaged by the electron beam energy.

Figure 7a–c presents TEM images of nano Ag–Cu colloids prepared at a magnification and scale of 800,000× and at 10 nm, respectively. For the pure Ag and Cu wires, 92.5:7.5 wires, and 72:28 wires, the nanocolloid particle sizes were 12.41, 27.27, and 16.44 nm, respectively.

Figure 8a–c display TEM lattice lines of the nano Ag–Cu colloids at 5 nm. The alternating gray and white layers represent the surface lattice structure widths of the Ag–Cu particles, and approximately ten lattice widths were measured for both the Ag and Cu lattices, and their average was taken for each colloid. The average Ag and Cu lattice widths were, respectively, approximately 0.234 and 0.207 nm for the pure Ag and Cu wires, 0.243 and 0.210 nm for the composite 92.5:7.5 wires, and approximately 0.241 and 0.211 nm for the composite 72:28 wires.

3.4. XRD Analyses

In addition to X-ray diffraction (XRD) analysis, localized TEM–EDS measurements were performed on representative regions of the Ag–Cu nanocolloids to qualitatively confirm the coexistence of Ag- and Cu-containing phases. The EDS spectra show distinct Ag and Cu signals together with a pronounced oxygen contribution, which is consistent with partial oxidation of Cu and supports the phase identification results obtained from XRD.

Due to the highly localized nature of TEM–EDS measurements and the influence of oxidation and background signals, these data are interpreted only as qualitative evidence and are not used to determine the average particle composition or elemental ratios. Accordingly, compositional discussion in this study is primarily based on XRD phase identification in combination with lattice-level observations from TEM, which are sufficient to support the discussion of phase evolution and structural characteristics addressed herein. Figure 9 representative TEM image and corresponding localized EDS spectrum of Ag–Cu nanocolloids prepared by ESDM in deionized water. The TEM image illustrates the aggregated morphology of the as-prepared nanocolloids, while the EDS spectrum confirms the presence of Ag and Cu signals together with a pronounced oxygen contribution. The oxygen signal is attributed to partial oxidation of Cu and is consistent with the phase identification results obtained from XRD analysis. The localized TEM–EDS measurement is provided for qualitative confirmation of Ag–Cu phase coexistence and is not intended to represent the average particle composition or elemental ratios.

The XRD analysis results of the nano Ag–Cu colloids prepared using pure Ag and Cu wires are shown in Figure 10a. The scanning parameters were a scanning angle 2θ of 10° to 90°, total scanning time of 15 min, and Ag and Cu elemental analyses. The analysis results for each sample were matched with a database.

For the pure metal wires, the reference code with highest similarity was 96-150-9855, indicating an Ag–Cu ratio of 97:3 and confirming that nano composite Ag–Cu particles were produced through electrical spark discharge. The Ag–Cu diffraction peaks (blue points) were at 38°, 44°, 64°, 77°, and 81°, correlating with the Ag–Cu analysis phases of (111), (020), (022), (131), and (222), respectively. The strongest diffraction peak indicated a particle lattice spacing of 0.23 nm. For the colloids prepared with the 92.5:7.5 composite wires [Figure 10b], the matching reference codes were 03-065-2871 (green points) and 01-078-1588 (blue points), corresponding to Ag and Cu oxide, respectively. The Ag angles at 38°, 44°, and 64° corresponded to the phases (111), (200), and (220), respectively, and the Cu oxide angles of 38° and 44° corresponded to phases (202) and (220), respectively. The reference spectrum did not perfectly match the results, suggesting that another element had been introduced to the composite metal wires. A higher content of undesirable elements was associated with greater internal structural defects in the composite metal wires; these defects were exacerbated when the wires were converted to the colloid nanostructure. These crystal defects affected the diffraction peak positions and intensity. For the colloids prepared with the 72:28 composite wires, [Figure 10c], the matching reference code was 01-087-0717. The blue points in the figure indicate Ag diffraction peaks at angles of 38°, 44°, 64°, 77°, and 81° and corresponding to the (111), (200), (220), (311), and (222) phases, respectively. All of the Ag element diffraction peaks can be observed in the figure, suggesting that as the ratio of the second element in the Ag–Cu composite metal wires increased (72:28), the internal structural defects of the wires worsened. These defects were exacerbated after nanosizing, causing phase shifts in the diffraction peaks of the spectrum.

4. Conclusions

An electrical discharge machine was used to perform ESDM in deionized water with electrodes of pure metal (i.e., Ag and Cu), composite metal with an Ag–Cu ratio of 92.5:7.5, and composite metal with an Ag–Cu ratio of 72:28. No other chemical substance or agent was added during the preparation process. The rapid mass production of nano Ag–Cu colloids was achieved. Nano Ag–Cu colloids prepared with the three electrode types and six T_on–T_off values were compared:

(1)

UV–vis spectroscopy results indicated that a Ton–Toff of 30–30 µs blueshifted the characteristic peak wavelengths, indicating that the nano Ag–Cu particles were smaller. The characteristic peak wavelengths of nano Ag–Cu colloids prepared using pure Ag and Cu wires were at 390–410 and 210–230 nm, corresponding to Ag ions, nano Cu oxide, and nano Ag particles, respectively. The characteristic peak wavelengths of the nano Ag–Cu colloids prepared using the composite metals were identical to those of the colloids prepared with the pure metals.

(2)

The particle size distribution and zeta potential of the nano Ag–Cu colloids were 101 nm and 28.1 mV, respectively, for when prepared using pure Ag and Cu wires but 197.5 nm and −6.67 mV for the composite metal wires. The colloids prepared using composite metal wires had worse suspension stability.

(3)

Images were magnified to a scale of 5 nm to perform lattice width measurements. The Ag and Cu lattice width, respectively, were approximately 0.234 and 0.207 nm for the nanocolloids prepared using pure Ag and Cu wires, 0.243 and 0.210 nm for the composite 92.5:7.5 wires, and 0.241 and 0.211 nm for the composite 72:28 wires. Thus, the Ag–Cu particle sizes were consistent regardless of the electrode material.

(4)

XRD was performed to examine the crystal structure of the nano Ag–Cu particles. For the particles produced from pure metal wires, the Ag–Cu ratio was approximately 97:3; no diffraction peaks for nano Cu oxide were observed. By contrast, the particles prepared produced from composite metal wires had peaks for Ag particles and Cu oxide particles. The characteristic diffraction peaks were shifted backward, suggesting the presence of internal structural defects in the composite metal wires. The addition of a secondary element during the production of composite metal wires disrupted the internal structure of the primary metal base, altering the metal wires and leading to spectral shifts due to nanoscale structural damage.