Electrolytic copper powder is usually referred to as the dendritic copper powder and it is obtained after various processes, all of which make it a highly useful product. The production methods are briefly discussed below along with all the excellent properties and characteristics that this powder holds.

All these excellent characteristics when combined together make this product a highly useful product and then make it eligible to be used in various industries as to give maximum benefit to the industries as well as humans too because this definitely makes human life easier through its vast range of applications.

Introduction

Electronic copper powder (ECP) (also known as Dendritic Copper Powders) is made by a process known as electrolysis process and then ECP is processed in some of our modern facilities that are based on a particular purpose. If raw materials are chosen carefully and processing parameters are controlled, one can engineer the characteristics which can enable us to provide our customers with tailored solutions.

Heavy, medium and light variants are included in the dendritic copper powders range and they have high, medium, and low apparent densities and their morphologies are very dissimilar and range from extremely acicular to irregular/pseudo-spheroidal. The most suitable grade should be selected for the application as it is of major importance and the range facilitates remarkable electrical conductivity, high compressibility, good Green Strength, and it also influences porosity.

Electrolytic Copper Powder Properties

The particle's distribution and grain size, flowability, apparent density, and specific surface area are some of the most significant characteristics of a metal powder. The behavior of the metal powder is characterized by these characteristics as they are also called the decisive characteristics. There were reports on the morphologies of copper powder particles correlated with the flowability and apparent density.

According to the investigations, if the structure of the powder particles is more dendritic then the copper powder’s apparent density will be lower. A method was proposed by Popov et al. to determine the critical apparent density as it allows electrodeposited copper powder’s free flow. Experiments can be done to determine the volumetric mass or apparent density. The volumetric mass or apparent density is known as the mass per unit volume. The same volume is occupied by the powder particles from the same fraction of different powders, but it depends on the metallic copper’s structure, displaying dissimilar apparent densities.

Temperature

The morphology of the copper powder along with copper ion concentration and current density is majorly influenced by temperature. At 60 and 45 C, we obtained powder’s velvety structure, which is different in comparison with the structure that’s obtained at 30°C. Surface area is increased as a result of this structure along with a decrease in the apparent density.

Density values

When their morphologies change, the values of copper powder's apparent density also change. Copper powder's apparent density will be lower if the cauliflower-like structure of the powder is smaller and if the structure is bigger then the apparent density will be higher too. Thus, you can change the electrolysis parameters to control the copper powders' apparent densities. CD, Cu ion temperature, and concentration are the electrolysis parameters, and depending on them, 3.43 g cm-3 and 0.38 g cm-3 are the apparent densities of copper powders.

Making of copper powder

In an electrolyte that consists of sulphuric acid and copper sulfate solution together with additive, stainless steel is used as the cathode, and pure copper metal is used as an anode to make copper powder. No mechanical scraper is needed in this process for removing the powder from the cathode, instead, a cheaper reducing is used to anneal the powder. It allows the copper scrap to be used in producing the copper powder. The process is easy, simple, economically good, and can produce powder in small or large quantities of P /M grade.

Morphology of powder

Electrodeposited metals have many properties, the most significant one is their morphology and that depends on the deposition process’s kinetic parameters and the current density or deposition overpotential. Their many characteristics are interesting and required for the application of metal powders. The sintered product’s quality, apparent density, specific surface area, corrosion resistance, flow rate, bulk weight, and the shape and size of the particles. Generally, its morphology is determined by the size and shape, however suitable electrolysis regimes might influence them.

Powder metallurgy

Metal powders are being made in large amounts due to the fast increase in the importance of powder metallurgy, and a big part of them is made by electrolysis right now. One can obtain all of the materials in the powder form but there are some particular material characteristics that determine the selected method for the formation of powder. Liquid metal atomization, electrolytic deposition, chemical reaction, and mechanical commuting are the four major categories of fabrication methods. Electrolytic metal powder displays a dispersed electrodeposit detached from the electrode through tapping or in a way consisting of numerous sizes and forms of the particles.

Production Method of Electrolytic Powder

High-quality products are usually yielded by the electrolytic powder production method. Those products can be sintered and well pressed. Recently, it is seen that the production of such products is possible by these different electrolysis regimes, not only for obtaining powders with various characteristics but also for predicting the powder’s decisive properties, which are extremely significant for suitable applications and quality of the powder.

Characteristics

The shape (morphology) and size (granulometry) of the particle are the major properties of the powders. These characteristics determine the potential areas of the powders’ applications and their technological characteristics like apparent density, surface area, flowability, bulk density, etc. From a technological aspect, copper deposits attained at overpotentials and high current densities are extremely significant. Porous and open structures of copper deposits are ideal to be utilized as the electrodes in electrochemical devices like chemical sensors, batteries, and fuel cells, however, the very high surface area is important to evaluate some of the electrochemical reactions.

Example

For instance, high activity is shown by copper for nitrate ion reduction along with the reaction in which the nitrate is lessened to ammonia in sulfate media and aqueous acidic perchlorate in high yield. Keeping in mind the copper deposits of high technology importance, it is important to understand this process’s effect on copper’s electrodeposition under these conditions. Due to that, one of the purposes to read this paper is to examine this process's effect on the electrodeposition of copper at over-potentials. Copper powders of different characteristics can be obtained through electrodeposition under various operating conditions from diverse electrolyte solutions.

Overpotential wave shape

If overpotential wave shapes change, then the same effects can be attained during pulsating overpotential deposition. Particles of different morphologies are produced on metal powder’s electrodeposition through pulsating overpotential as compared to the particles attained in a classic potentio-static deposition. Moreover, usage of a pulsating overpotential deposition is easier in the laboratory-scale cell but there are some problems on a practical scale due to the requirements of a higher power and a high-speed potentiostat.

Output current

Reversing current is the output current for input pulsating overpotential, and the same effects can be expected on the grain size and morphology of the powder particles in the deposition by reversing current and by pulsating overpotential. Although obtaining reversing currents on a practical scale is easier and copper powder’s deposition by reversing current holds a major practical significance as compared to pulsating overpotential deposition. Different methods like laser analysis, image analysis, sieve analysis, etc. are used to determine the granulometry of powders, but the main question is that how adequately does the powder granulometry be explained by them.

Results

Powder granulometry can’t be adequately described by the results of the sieve analysis. Powder particle morphology is characterized by description (accrual, dish-shaped, angular, spherical) or quasi-quantitatively, for instance, by geometrical parameters mean. The shape of the particle becomes significant with time for real particles’ characterization in addition to the size of the particles. Valuable service can be provided through image analysis.

Method for measuring

Direct and indirect are the two groups in which the methods that are utilized for measuring the size of the powder particles, enabling the analysis of the particle size distribution, could be divided. Transmission microscopy, electron, and optical scanning are used as direct methods for mapping the geometry of the individual particles. The indirect methods are based on laser analysis, sieve analysis, and other physical effects.

Stereological methods

The powder can be described precisely by the usage of stereological methods based on their planar images. Parameters like perimeter, area, and roundness are beneficial for powder characterization for individual objects. Roundness is a shape factor giving minimum unity’s value for a circle.

Powder samples

At lower current density, both types of dendrite were observed in the powder samples. Ramify 3D dendrite and massive dendrites are the two types. Massive dendrites despaired with an increase in the current density. Further analysis of the copper powder particles’ surface morphologies showed that the morphology of the surface changes considerably with an increase in the current density. Extremely rough polycrystalline faces were observed at current density with extreme unevenness in order to have ideal conditions there for the growth of crystal (mixed activation-diffusion control) and to create new nuclei.

Faces of dendrites

Octahedral and flat cubic faces define some of the dendritic branches of massive dendrites. The diffusion control share is also increased with an increase in the current density and in that increase, particles become more dendritic, with a fern-like and a corn-like structure. The tertiary branches ramify along the edges of the cube most probably in the respective direction. At 4 different current densities, we obtained particle-size distributions of copper powders.

Decrease in particle size

According to the observation, there comes a decrease in the mean size of the particle with an increase in the current density. On further analysis, it was shown by the results that more than 50% of the values were less than 50 µm and 52.90-73.63 µm range is the obtained mean values particle sizes. There is a decrease in the mean particle size when there comes an increase in the current density.

Deviation

Just like with examined samples containing dendrites of small granulation, the insignificant deviation can be explained with unreliability with single samples. Roundness, perimeter, and area are the selected relevant parameters to describe copper powder particles through the usage of quantitative microscope analysis. It was seen during this analysis at the lower current density especially, there were distinctly voluminous particles. Also, there was an assumption that particles of this kind arose in deposition conditions at the end of the growth of the particle.

Distribution of particle size

The typical particle-size distributions that are attained of the copper powder particles by the reversing current are well-known. According to the reports of various times, electrodeposited powder particles are less branched and more compact if reversing current or pulsating overpotential is used to obtain powder as compared to obtaining powder in constant current electrolysis. It can be explained during the anodic period by metal's selective dissolution in electrode surface's various points, meaning that as compared to a protrusion or the flat surface, protrusion's dissolution is faster with tip radii.

Moreover, if there is an increase in the current density, it can result in a decrease in the size of the mean powder particle in constant current electrolysis. According to images, in the case of production of power with reversing current, the particle’s size increases with an increase in the average current density. The following way can be used to explain this.

Nucleation

Nucleation is a process that’s extended in time and doesn’t occur over the whole surface of the cathode simultaneously. In regards to size, crystals that are earlier generated are significantly larger as compared to the crystals that are generated later. The smaller nuclei made during the cathodic pulse will be partially or totally dissolved during the anodic pulse during the anodic time because of the lower grains' faster dissolution, and during the next cathodic pulse, the current density on the smaller grains will be favored due to their more negative reversible potentials and there will be favorable towards the growth of larger grains. The range of the mean particle sizes that are attained from cumulative distribution curves is from 93.38-107.79 µm.

Definition of powder

The dimensions of powder are smaller than 1 mm and powder is known as a finely divided solid. Its relatively high surface area to volume ratio is the powder's significant characteristic. Initial powders should meet some requirements which depend on the product's shape.

Requirements to fulfill

Technological characteristics (pressing ability, flow rate, bulk weight, etc.), chemical (dissolved or adsorbed gas contaminants, chemically bonded, admixture and basic metal content), and physical (surface’s state, size, and particle size distribution) are the requirements that need to be fulfilled. High purity products are allowed by the electrolytic powder production method especially those that are well-pressed and sintered. Recently, it is seen that it is possible through various electrolysis regimes for obtaining powders with a broad amount of characteristics but for predicting the powder's decisive properties that hold a lot of significance for the suitable purpose and the quality of the powder.

Electrolytic Micron Powder Applications

Some of their characteristics gained a lot of interest in the metal powder applications, for instance, sintered product’s quality, apparent density, specific surface area, corrosion resistance, flow rate, bulk weight, and the shape and size of the particles. All of these characteristics are dependent on the particles' size and shape which the electrolysis regimes can influence. A particle can't be divided as it is powder's smallest unit. Also, in general, powder metallurgy only deals with smaller particles than sand (0.1-1 mm) and larger particles than smoke (0.01-1 m). Most of the metal powders are the same as the hair of a human in terms of the hair's diameter and size (25-200 m).

In order to form electrolytic powder in a specific range of physical characteristics, the following variables should be necessarily controlled. Those variables are:

a. Powder removal time

b. Electrode spacing

c. Cathode and anode's type and size.

d. Current density

e. Circulation rate of Electrolyte

f. Temperature of Electrolyte

g. Composition of Electrolyte (the content of copper and acid)

Strong variable effects

The apparent density is strongly affected by the above variables. One can obtain particles (granules) of different shapes but it depends on the metal’s nature and the manufacturing process. According to the size of the particles, an electron scanning microscope, optical scanning microscope, magnifying glass, naked-eye, and direct observation is used to identify the shape.

Scanning electron microscope

When it comes to observing metal powder's discrete characteristics, one of the best available tools is scanning electron microscope (SEM). Although, the apparent density of one of the most important properties of the powder. Apparent density is represented by the ratio between the volume and the mass. A drop of the powder is freely thrown through a tunnel for filling a cylindrical container of 25 cm3 for being measured.

A series of factors determine the metal powder’s apparent density. Following are the most important factors; porosity and rugosity of granules, the shape of the powder (the powder will be denser if the shape is regular), oxidation level, metal true density, and granulometry (the density will be higher if the granule distribution is looser, the density will be lower if the granule distribution is more concentrated. In the case of rather regularly shaped or spherical powders, when the size gets smaller, the density gets higher, however, in foliated or dendritic powder's case, the density will be lower if they are finer).

Volume

Almost similar volume is occupied by the powder particles from different powders' same fractions, but with significantly different metallic copper structures. The structure of electrodeposits determines the difference in copper powders' apparent densities attained under various conditions. If the structure of the powder particles is more dendritic then the copper powder’s apparent density will be smaller,

Production enhancement

When the solution's circulation rate is increased, the temperature is decreased, the solution's viscosity is increased, supporting electrolyte's concentration is increased, and the concentration of deposition ion is increased, then there will be an improvement in the formation of more dendritic powder particles and vice versa. According to a report, when the above parameters are changed, it can significantly change the apparent density of electrodeposited powders. However, it was also seen that there can be a broad variation in the structure and shape of the powder particles by utilizing various regimes in the electrodeposition at an occasionally changing rate.

Effects on morphologies

We examined the effects of the temperature of electrolyte and the concentrations of copper ion on the apparent densities and morphologies of copper powders. The current efficiency of hydrogen evolution evaluates these parameters. Moreover, the morphology of the copper powders is analyzed by utilizing scanning electron microscopy (SEM). According to findings, the concentration of the copper ion and temperature of the electrolyte determines the morphology under the same current density conditions. Disperse and porous copper powders were attained at Cu ions’ low concentrations at a potential of 1000±20 mV and 150 mA cm-2.

Changes observed

At increasing concentrations of Cu ion at the same CD, the morphology of the powder changed to stalk-shock-like, shrub-like, and coral-like from the cauliflower-like, disperse, and porous. Also, the apparent density and morphology of the powder changed with an increase in the temperature. For various metallurgy applications of powder, there were suitable copper powder’s apparent density values.

Usage & Application

In various technologies, markets, and applications, dendritic Copper Powder is being utilized because of its broad range of physical characteristics. One of its typical usages is adding it into iron powder for enhancing the characteristics of the sintered parts particularly for thin-walled parts where higher Green Strength is needed for minimizing the segregation. Its other usages are winning of precious metals, electrical contacts, electronics, anti-fouling paints, carbon brush, diamond tooling, brazing and welding, conductive greases and oils, decorative applications, friction components, etc.

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Conclusion

The dendritic copper powder which is a term used for electron copper micron powder is one of the best products that has been introduced in the industries and ever since it has been introduced, the industries are only getting benefits out of it as it holds characteristics that are excellent in nature and therefore are enabled to be incorporated in various applications. 

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References:

http://www.doiserbia.nb.rs/img/doi/0352-5139/2012/0352-51391100196O.pdf

http://aspace.agrif.bg.ac.rs/bitstream/handle/123456789/280/277.pdf?sequence=1&isAllowed=y

https://cer.ihtm.bg.ac.rs/bitstream/handle/123456789/694/10.1.1.657.2729.pdf?sequence=1

https://ronaldbritton.co.uk/metals/products/electrolytic-copper/

http://www.makin-metals.com/copper-powders/dendritic-copper-powders/

http://www.techno-preneur.net/technology/new-technologies/metallurgytechnique/electrolytic.html