Posts About Cleaner

Is surface profile of the substrate pertinent for an effective adhesion of the electrodeposit? Does it only improve the aesthetics or also influence the functional properties? What are the options? Do treatment methods vary with substrates?

This short paper answers these questions and offers a synopsis of those processes. The processes are blasting, mechanical polishing, vibratory bowl movement, bright dip, chemical polishing, and electropolishing. 

Blasting

Industry uses abrasive or sand and glass bead blasting methods to clean and change the surface profile of the substrates before plating. Silica, aluminum oxide, and glass beads are the often-used media at various grit sizes. Machines and manual booths (closed) are used to execute these methods. This is an age-old technique. It is a simple process, but leaves impregnated particles on the surface and, if not properly removed, might affect the next processes (cleaning and plating).

Polishing

On mechanical polishing and similar category falls polishing, buffing, lapping, and grinding. Unlike buffing, polishing removes the metal surface. Lapping and grinding change the surface significantly. Industry uses muslin, canvas, leather, etc. as polishing wheel materials. Muslin is most extensively used as a buffing wheel. These mechanical processes are used to improve the aesthetic appeal of the substrates. As further pre-cleaning is involved before polishing, the polished and buffed substrates reduce the load on plating line’s pretreatment processes.

Vibratory Bowl Movement

Deburring and improving Ra value of metals are the primary applications of the vibratory bowl movement method. We can use this method on several metals and substrates (before plating) like copper and beryllium alloys, stainless steel alloys, low and high carbon steel alloys, nickel and titanium alloys, and several others. Size and shape of the substrates, media, chemicals used during the bowl movement, speed of the movement and time control the resultant finish. Unlike mechanical polishing and blasting, the process doesn’t leave residues on the substrates.  

Bright Dip

As the name implies, this process improves the brightness of the substrate. It improves the surface profile and helps aid oxide layer removal. This is an immersion process mostly using an acidic solution for 5 seconds to 5 minutes. Commonly used substrates are ferrous, copper, beryllium, aluminum, stainless steel, nickel, and Monel alloys. Zirconium, titanium and silver metals can also be bright dipped. These processes cost less, and the solution life is short.

Chemical Polishing

Chemical polishing process is like bright dip, but removes more substrate material. Many copper alloys and a few ferrous alloys can be chemically polished. Some chemicals are toxic and need good air ventilation for a friendly environment, health and safety practices.

Electropolishing

Electropolishing is an anodic process. Electrolysis selectively removes micro – peaks of the substrate metal. This process offers superior passivation and corrosion resistance properties on 300 and 400 series stainless steel alloys. The passivation properties got from electropolishing are better than nitric acid and citric acid passivation processes. Common metals electropolished are 300 and 400 series stainless alloys. Other alloys are Al, Cu, Monel, nickel, silver, zinc, tin, Co, Ti, and low and high carbon alloys.

Summary

These methods can alter the surface profile of the substrate metal before electroplating. Cost, chemical hazard, and awareness distinguish the choice and application of these methods. Each method has advantages and disadvantages.

Blasting is the easiest. Vibratory bowl movement and electropolishing methods offer the best aesthetics and functional properties after the deposition process.

We can enhance the deposit brightness, leveling characteristic, adhesion and surface profile Ra values using any of these processes.

Surface profile of the substrate, specifically surface activity and its receptivity to accept electroplating deposit, spontaneously determines the morphology.

A deposit with good morphology will possess an adherent deposit. There is a myth and inadequate science work related to surface profile and adhesion. A few sectors do well with improving surface activity, and a sector is vulnerable. This short paper intends to shine light, dissipate a myth, and suggest improvements with supporting information.

Cleaning & Activation

It is a normal practice to blast a metal surface to improve cleanliness. This approach predates the 60s, when cleaner science had made minimal progress. Over the years proprietary plating supply houses like Atotech, MacDermid Enthone and Coventya had conducted extensive research and offer an array of cleaning products. We released a short paper explaining the importance of cleaning on April 1, 2019.

In the absence of an effective cleaning process, blasting the surface is pertinent. It is an important treatment method on applications where we require higher Ra values or unique aesthetic appeal. Rather, if one blasts a surface merely to improve adhesion, then it is time to debunk the myth! Now, I’ll back up the purpose with facts and information.

To get an adherent deposit the metal surface must be clean, active and receive nucleation (form a unimolecular layer) within the first 10 or 20 seconds regardless of the current distribution pattern. A spontaneous and uniform deposit formation is important. The critical nucleation time varies between substrates and the deposit element’s electrode potential.

A truly active surface allows effective nucleation.

A poor nucleation layer will disrupt crystal growth and cause re-nucleation of the crystals. This disruption leads to deposit non-coherence and inconsistency in physical characteristics, resulting in premature product failure. Impregnated blasted media is very difficult to obliterate the surface and in most cases leaves a residue, hinders nucleation or continuity and uniformity of the deposit. An electropolished surface address this concern and enables epitaxial or pseudomorphic growth when and where applicable. This surface possesses very low Ra values, are active and free from foreign materials. If it drives you to get the most adherent deposit, electropolished surface is one of the best means to achieve this endeavor.

Surface Profile & Adhesion

A truly active metal surface can form a thick intermetallic layer and develop a single domain deposit morphology (columnar structure) through the process. A single domain columnar structure deposit will possess a distinct grain boundary.

This mechanism is not independent of process control. The author of this paper had conducted extensive research over a decade on this matter, and so did a few other scientists from our society during the 80s and till now. A deposit with an intermetallic layer forms the most adherent deposit. In order for a non-electropolished surface to form an intermetallic layer, it must possess an active surface. We know that an electropolished surface possesses lower Ra value, but we require more controlled studies to validate the relationship between the surface profile and adhesion. On this subject, good surface profile implies a clean, smooth and active surface.

Morphology & Physical Characteristics

Most adherent deposits possess good morphology. A deposit with an intermetallic layer and undisrupted columnar structure will have greater than 20% improvement in physical characteristics such as hardness, tribology, and corrosion resistance properties. 

Summary

Blasting is a valuable pretreatment method, but an ambitious applicant must recognize that residue left on the surface affects the deposit characteristics, and it is not a certain choice in pursuit of an adherent deposit. Electropolishing is not practical on many applications. Exceptional cleaning and activation are viable and important.

Accomplishing an intermetallic layer on all applications is an unreasonable expectation, but a clairvoyance can set that as an aim. This aim is akin to lean’s one-piece flow and six-sigma.

In short, be mindful of the relationship between activation, morphology and physical characteristics.

Notes:

Material scientists and electrochemists now and then use different terminologies when referring to the same concept. Some terms used in this paper are no exception.

I used material scientist as a substitute for metallurgist. The global technical community replaced the term metallurgy with physical characteristics in 2010.

You are welcome to post a comment or email with questions to [email protected] if a concept is abstruse.

Formulating cleaners such as alkaline soak cleaner and electro cleaner are imperative, though not as significant and lucrative as formulating plating baths containing primary and secondary brightener systems.

Unlike quite a few decades ago, current cleaner formulations contain methodically investigated inorganic and organic ingredients which are effective and comply with the environmental regulations. 

Different sectors and industries use solvent, alkaline soak and electro cleaners uniquely. Does the industrial practice catch up with scientific advancement? Good formulations are available! Did the market seize the opportunity? 

This blog highlights the value of a good cleaner, identifies a simple step in choosing a cleaner, and list a few potential ingredients and their properties. 

A carefully chosen cleaner can remove organic residues from the substrate thoroughly. Decrease the cleaning time and (or) improve cleanliness. Cut cost by increasing the cleaner life and minimize environmental impact.

Go over a material safety data sheet (MSDS) to select a cleaner, however, a proprietary chemical supplier could throw a curve ball. Section 2 of an MSDS must contain hazardous ingredient listed with Chemical Abstracts Service (CAS) registry number and the concentration. The reader can find specific CAS related information on this link. 

Before considering the inorganic and organic ingredients, process owner must know their processes and supply chain well. Knowing and considering the substrate(s) and their corrosion properties in most cases are explicit. Sometimes information is hidden and implicit on aspects such as oils, lubricants, and kinds of paraffin used. Application time, heat treatment (if applicable) and their intricate factors on some instances might not be clear. Source and purity of water, properties such as temporary and permanent hardness are vital for the makeup of cleaner solution and rinsing.

Alkalinity, buffer, water softening, chelation, and surface tension are a few important solution properties to observe. The process owner should assess the presence and concentrations of sodium hydroxide, carbonate, phosphate, silicate, amines, and surfactants and relate to the application (s). A surfactant can be anionic, non-ionic and (or) amphoteric. It changes the surface tension and wettability of the solution.

Briefly put, irrespective of reasons and justifications, focussing on cleaners and improving the cleaning performance is worth the effort and not a hard nut to crack using the listed suggestions.