Technical Post: Production of Silver-Copper Micro/Nano Powders by Wet Chemical Method [SMM Silver Conference]

On May 16th, at the 2025 SMM (6th) Silver Industry Chain Innovation Conference, hosted by SMM Information & Technology Co., Ltd. (SMM), co-organized by Ningbo Haoshun Precious Metals Co., Ltd. and Quanda New Materials (Ningbo) Co., Ltd., and strongly supported by sponsors including Fujian Zijin Precious Metals Materials Co., Ltd., Huizhou Yian Precious Metals Co., Ltd., Jiangsu Jiangshan Pharmaceutical Co., Ltd., Zhengzhou Jinquan Mining and Metallurgy Equipment Co., Ltd., Hunan Shengyin New Materials Co., Ltd., Zhejiang Weida Precious Metals Powder Materials Co., Ltd., Guangxi Zhongma Zhonglianjin Cross-border E-commerce Co., Ltd., Suzhou Xinghan New Materials Technology Co., Ltd., Yongxing Zhongsheng Environmental Protection Technology Co., Ltd., IKOI S.p.A, Hunan Zhengming Environmental Protection Co., Ltd., Kunshan Hongfutai Environmental Protection Technology Co., Ltd., and Shandong Humon Smelting Co., Ltd., Zhang Meng, Director of the Powder R&D Department at Suzhou Xinghan New Materials Technology Co., Ltd., shared insights on the production of silver-copper micro-nano powders using the wet chemical method.

Wet Chemical Production of Silver-Copper Micro-Nano Powders

► Objectives

To provide silver, copper, nickel, silver-coated copper, and silver-coated nickel micro-nano powders in tonnage quantities while ensuring batch-to-batch stability.

► Monitoring Indicators

Morphology, size, particle size distribution, crystallinity, specific surface area, tapped density, bulk density, impurity content, resistivity, oxidation resistance resistivity, density, pH, compatibility, etc.

► Challenges

1. Controllable preparation of metal powders

Permutations and combinations of parameters: reactants, temperature, pressure, concentration, time, stirring, additives, pH, etc.

Chemical thermodynamics/kinetics, electrochemistry, crystal growth, Ostwald ripening, etc.

2. Scale-up of the system

From mL/g level to L/kg level to m³/t level; three transfers (momentum, heat, mass) and one reaction, with scale-up effects.

3. Batch-to-batch stability

Preparation stage: Determine the process window based on the allowable data fluctuation range. Post-processing stage: Sieving, powder blending, modification, etc. Cost issues, quality inspection, and quality control.

Wet Chemical Silver Powder

Silver powder production: High-purity silver powder is prepared using a liquid-phase chemical method with silver nitrate as the raw material. Particle morphology and size can be controlled by adjusting process parameters such as temperature, reaction time, and reducing agent dosage during the reaction process.

Application areas: Suitable for use in silver paste for crystalline silicon solar cells, 5G filters, and low-temperature electronic silver paste.

Product characteristics:

1. It has good dispersibility and can be well integrated with solvents and organic phases; it is not prone to agglomeration and can be easily formulated into a paste. 2. High crystallinity. 3. Low shrinkage and good filling properties. 4. Low burning loss. 5. Adjustable sintering temperature and good electrical conductivity. 6. Adjustable particle size distribution from tens of nanometers to several micrometers, mainly including spherical powder, flake powder, rod powder, wire powder, etc.

• Low-temperature sintering high-activity silver powder

It can be pressureless sintered below 150°C to form an integrated conductive and thermal conductive network, exhibiting excellent conductive and thermal conductive properties. The stable integrated conductive and thermal conductive network enables low-temperature sintering and high-temperature service. It is used in fields such as conductive adhesives, thermal conductive adhesives, electronic pastes, and functional device packaging.

• One-dimensional silver powder

Conductive ink, transparent electrodes: high electrical conductivity, strong anti-interference ability, high stability, strong flexibility, and resistance to bending.

Applications of silver powder: PV pastes

Low contact resistance, low line resistance, high filling rate, good printability, and linearity.

Applications of silver powder: conductive/thermal conductive adhesives

The conductive/thermal conductive adhesives formulated by our partner using Xinghan silver powder have a volume resistivity as low as the 10⁻⁶ Ω·cm magnitude and a thermal conductivity coefficient of approximately 10 W/m·K.

Wet-chemical silver-coated copper powder

The silver-coated copper powder with a dense and uniform coating is prepared using the displacement-reduction method. The developed production process can achieve efficient coating from submicron to micron scale, and from spherical, flake, and rod shapes.

Application Scope (Application)

It is used for preparing medium-to-low temperature pastes such as conductive pastes, conductive printing inks, conductive adhesives, and membrane switches, and can replace silver powder in the electronics industry.

Product Features (Features)

1. Uniform and dense silver layer with strong oxidation resistance; 2. High crystallinity; 3. Concentrated particle size and good dispersibility; 4. Good electrical conductivity; 5. Adjustable silver content.

Development of silver-coated copper powder with low silver content, high density, and high oxidation resistance (spherical and flake shapes)

When silver-coated copper powder with 14% silver content is placed in an air environment at 140°C, the resistivity increases after 8 days and eventually stabilizes at around 2.3×10⁻⁵ Ω·cm.

The suspected causes of silver-coated copper failure are: 1) copper diffusion into the silver layer, 2) silver ion migration, and 3) copper oxidation. Through theoretical calculations and experimental verification, 1) and 2) can be neglected under the service conditions of silver-coated copper. Therefore, we have focused our R&D efforts on how to inhibit copper oxidation. The first row in the figure below shows the state before failure, and the second row shows the state after failure.

Quantitative detection of the coating density of silver-coated copper powder

HP targets copper to react and produce copper ions.

HP flows into the copper surface through the gaps in the silver layer and reacts with the copper. Due to the varying degrees of silver coating density, the contact area between HP and copper differs, leading to varying degrees of corrosion on the copper. The amount of corroded copper is thus reflected by the final measured copper ion content, which is then converted into an indication of oxidation resistance.

This system reacts rapidly and allows for precise detection.

As the same sample is left for a longer period, its color deepens, indicating more copper precipitation. At the same time, for different samples, the lighter the color, the less copper precipitates, and the better the density. The amount of precipitated copper can be accurately titrated using EDTA.

Nickel powder coated with wet-chemical silver

Compared to silver-coated copper, it has stronger oxidation resistance and can be used at higher temperatures.

The purity of the nickel core is >99.95%, and the thickness of the silver shell is adjustable from 50-300 nm. The composite structure of the nickel core and silver shell combines the high strength of nickel with the high electrical conductivity of silver.

• Copper powder production: High-purity copper powder is prepared using a liquid-phase chemical method with copper salts as the raw material. Controlled preparation can be achieved at the nanoscale, submicron, and micron levels in terms of particle size, and directional adjustment can be achieved in terms of morphology, including spherical, flake, and dendritic shapes.

Application: Used in the manufacturing of terminals and internal electrodes for multilayer ceramic capacitors, electronic pastes for electronic components, etc.

Features: 1. Uniform particle size with good dispersibility, 2. High crystallinity, 3. Oxidation resistance.

Development of monocrystalline copper powder with high electrical conductivity and oxidation resistance

Key to excellent performance: Monocrystalline structure, preferred crystal plane: The resistance of monocrystalline copper is close to that of silver; the (111) plane is the preferred crystal plane, significantly enhancing the oxidation resistance of Cu.

Submicron and nanoscale copper powder: Its room-temperature resistance is of the same order of magnitude as that of silver powder; its sintered resistance can be comparable to that of silver powder; after oxidation resistance treatment, its oxidation resistance resistance is significantly improved.

In addition, a brief introduction to Suzhou Xinghan New Material Technology Co., Ltd. is provided.

》Click to view the special report on the 2025 SMM (6th) Silver Industry Chain Innovation Conference