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The metal finishing industry plates hard and decorative hexavalent chromium processes from 1920s. It is an acknowledged industry standard and preferred choice because of its exceptional physical characteristics. US Environmental Protection Agency (EPA) and Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) had listed chromium trioxide as a hazardous chemical because of its carcinogenic property.

 

Applications

Many aerospace components use hard chromium, the automotive sector primarily uses decorative and other sectors use both decorative and hard chromium plating deposits. A deposit thicker than 1.2 micron are functional (hard) and any lesser are decorative. The industry favors chromium because of its oxidation resistance properties. Among groups 4, 5, and 6 elements of periodic table we plate only chromium using an aqueous solution. Ionic liquids can deposit most of the transition elements. Aqueous hexavalent Cr deposit has exceptional tribological and corrosion resistance (not all formulations) properties. We plate the deposit on high strength steels and nickel alloys (with Wood’s nickel strike). This deposit exists in alpha phase, is crystalline and forms limited compounds or components with occlusion of hydrogen and carbon developing internal deposit stress (refer ASM Handbook for more information). The electrolytes’ low cathode current efficiency allows greater tribological properties. This is because the deposit has hydride and carbide compounds. These hydrides and carbides develop deposit intrinsic stress and effect deformation property of the deposit (Hooke’s law describes elastic properties of materials or deposit).

 

Extensive applications and good properties make environmental directions a challenge to meet. Before we get deeper, let us get a historical perspective.

 

History

Around 1910, a researcher accidentally developed the original hexavalent chromium plating formula comprising chromium trioxide and sulfuric acid. He assumed chromium trioxide was a trivalent salt until another scientist corrected the misinterpretation within two years.  

 

Research

From that time substitute methods such as trivalent chromium plating, cobalt alloy deposits, electroless Ni deposits with P or B alloys were developed and are a focus of continuing research. High temperature and room temperature ionic liquids for deposits such as trivalent chromium, niobium, aluminum, molybdenum is in study.

 

Alternate Choices

Chromium Plating

Trivalent Chromium Plating

Decorative trivalent and hexavalent deposits have similar properties because of the thickness limit and electrolysis mechanisms of the respective electrolytes. Electrolysis mechanisms change as electrolysis progresses and the deposit characteristics vary with thickness. There are scientific papers on this phenomenon. On hard Cr applications major variation is on macro-cracks, which develops after baking. When analyzing macro-cracks, a seldom adhered to practice is to compare the microstructure on transverse sections. Refer to ASTM E3 – Microstructure and Properties for more information. A few applications use nickel undercoat to negate the effect of macro-cracks.

 

Other Electrolytic Methods

A few specialists recommend electroless Ni-P, electroless Co – P and electroless Co as substitutes to hexavalent hard chromium plating deposit. But the author of this paper doesn’t consider these as dependable alternatives. Only electroless Ni-B (mid boron) deposit possesses tribological properties, but it doesn’t offer comparable wear and corrosion resistance properties of hard hexavalent Cr plating deposit.

 

Ionic Liquid Methods

Room temperature ionic liquid electrolysis is an effective alternate. Aluminum deposit offers many unique advantages. However, it is still an emerging technology.

 

Vapour Deposition Methods

There are two types of vapour deposition methods – physical vapour deposition (PVD) and chemical vapour deposition (CVD). We can apply CVD on several transition metals. Of particular interest to this topic are CVD deposits of Ta and Nb.

 

Thermal Spray Coating

On economy, versatility and diversity of options, the thermal spray coating processes is the best alternate to hexavalent Cr plating method. There are five different methods available in the market – oxyfuel wire (OFW) spray, electric arc wire (EAW) spray, oxyfuel powder (OFP) spray, plasma arc (PA) powder spray, and high velocity oxyfuel (HVOF) powder spray. Refer to ASM Handbook Volume 18 for more information on this subject. However, on many applications the line-of-sight characteristic will limit the thermal spray method. There is continuous research in this field, and recently a few companies have taken the processes to a new level.

 

Summary

Bottom line, trivalent chromium plating, vapour deposition, and thermal spray methodologies are operative substitutes to hexavalent hard chromium plating process. Application demand, cost and the required physical characteristics determine the value of a specific method.

 

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The true plating capability refers to a process which performs as almost as expected. It executes with lesser labour, zero downtime, greater process control and with exceptional physical characteristics. Though it might appear simple, most job and captive plating shops seldom meet an effective realization of the said ability.

 

Challenge

Most processes have unique challenges. Cyanide and electroless electrolytes, precious metal plating like gold and silver, aluminum anodizing and stainless steel electropolishing need exclusive tactics. Cost metrics and process complexity varies within these processes.

 


An important holdup most stumble is accepting the status quo. Process failures, downtime, delays, etc. are perceived as a norm. As it occurred yesterday and transpires with others too!



Also, people with emotion become agnostic to methods, tools, concepts, and approaches. While, data science and artificial intelligence sans use of emotion.


This short paper aims to show a path toward a true electroplating capability.

 

Here is a simple infographic of vital elements to attain this goal:

True Electroplating

 

As shown in this graphic, our intent is at the core of our actions! Begin with intent to achieve infinite results.

 

We need knowledge and creativity with intent. The staff must have a comprehensive training on electroplating, lean, statistical process control, and total quality management. A good understanding of periodic table and electromotive force (emf) potential is mandatory. A process control is contingent on sampling and analytical techniques, and database integration with spontaneous communication and reaction.

 

Consider using 6 process development and control (PDC) tools as recommended by Advint’s earlier blog as an alternative to 7 quality control (QC) tools.

 

Plant Design and Automation

On no occasion reckon to aid a true electroplating feat with an inextricable and poor electroplating equipment design.

 

A nimble design with a correct choice of electrolyte chemistry, materials selection, engineering capabilities, rectifier controls and calculations such as ampere hour control, serial communication are indispensable.

 

Choose IGBT rectifiers for nickel, copper, silver, zinc and chromium plating applications. IGBT will be suitable for most anodizing applications, but sometimes a SCR rectifier or a half wave SCR rectifier will be essential.

 

Plating equipment and the manufacturer play a significant role in the plan of a new line. The project managers of most manufacturers do not have industrial plating experience. Under these situations, planning on processing, development tools, creativity and method become imperative.

 

True Electroplating Rewards


When a process performs, employee and customer satisfactions are at its zenith. You get to eat your competitor’s dinner.


How Can We Help

  • Advint’s prudent offering of advisory services empowers clients to achieve true plating capability.
    • Advint’s proprietary Time Change Management (TCM) tool aid metal finishers master productivity management, total quality management, and optimization of physical characteristics of the deposit.
    • We apply an algorithm software to deconstruct big data and conduct predictive analysis.
    • Advisory service includes backing platers in the project phase of electroplating plants.
    • The work supports research and REACH alternates.
  • Our online training course accommodates corporates and individual professionals.

 

 

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Acknowledgement of the influential in electroplating develops our learning of the fundamentals, and it improves our research.


There are thousands of contributors who served the electroplating industry and academia for over a century.

Who tops your list?

What did they do?

Why is it important?

What did we learn?


This short paper lists 8 innovators, two focused on electrochemistry and the rest on industrial plating (electrolytic, autocatalytic, ionic & aqueous). Their contributions enabled our understanding, improved our applications, and helped us to advance the technology.

 

Let us see who they are, when and what did they offer to the field and its benefits.

 

Michael Faraday

During 1832 Faraday published a paper relating the quantity of electricity with the amount of metal liberated at the electrodes resulting in two laws. When we think of electroplating, Faraday’s laws are probably the first to come to our mind. Mastering a process or shining at customer satisfaction does not end without due consideration of an electrolyte’s current efficiency and the feasibility of a deposit.

 

Walther Nernst

Nernst equation is the fundamental equation of electrochemistry and for the electrode processes. An ardent electroplating researcher shall begin and ensure a thorough understanding of Nernst equation and its concept. We can plate several transition metals, post transition metals, and metalloids. Some using aqueous electrolytes and room temperature ionic liquids, and most using high temperature ionic liquids. A modest approach to choose the electrolyte and the element for the deposition process is to comprehend Nernst equation and its concept. An interstitial or interatomic alloy electrodeposit choice is no exception to this subject.

 

Abner Brenner

Brenner conducted many studies on electroplating deposits. We conspicuously recognize for his preliminary contributions on electroless nickel plating invention around 1946. Though he got black non-adherent dendrites in the initial testing, his research allowed significant growth in electroless Ni-P and Ni-B deposition processes, and plating on plastics.

 

Richard Hull

Hull cell device is common in most electroplating laboratories. Most platers gain Hull cell testing skills or aspire to become good at it! Hull around 1930s invented a testing cell and derived a formula to calculate the effective current density of an electrolyte. Hull cell unit and its formula is quite easy to use! Is the design of the unit and its formula an ordinary achievement?

 

Oliver Watts

Professor Watts reported on 1931 his work on nickel plating bath comprising nickel sulfate, nickel chloride and boric acid at a higher temperature. Many used nickel-plating electrolyte using the same inorganic constituents at room temperature or at 120ºF. Watts was the first to report the benefits of thick and uniform deposit at 145ºF and 160ºF. Since then we began calling this electrolyte a Watts nickel plating solution.

 

Donald Wood

Wood was an expert in cyanide silver plating, and that is what he did for most of his career. We know him for his invention of chloride-based nickel strike bath during early 1940s. The Wood’s nickel strike formulation enabled the global industry to plate on all ferrous, nickel, titanium and aluminum alloys.

 

Donald Cook

Even if you are well read in the industry, you might not have heard about Dr. Donald Cook! Cook coined the term ‘metaliding’. Metal finishing industry did not see the effects of his research. But if I didn’t mention his name with others, it would be amiss as he is alike Nernst and Brenner. No one would have worked on more transition elements and diffused into others than him! His knowledge in electrochemistry and chemistry of halides was impeccable, and he distinguished the ins and outs of transition metals of group 3 to 11 of the periodic table. But his only focus was in high temperature ionic liquids.

 

Seymour Senderoff

We know Dr. Senderoff for his invention of spiral contractometer used in hard hexavalent chromium and nickel sulfamate plating applications to detect internal stress in the deposit. He worked for Dr. Brenner for several years and later focused on high temperature ionic liquid tantalum plating. It was my source of pride to continue on his research and improvise his formulation.

 

electroplating leaders

 

So, what is the learning?

Recognizing these pioneers and their work must transcend awareness and dwell on a deeper understanding of their explanations and research outputs.

Faraday and Nernst focussed on the fundamental of electrochemistry. Cook and Senderoff concentrated mostly on high temperature ionic liquid electrolysis (plating and diffusion). Brenner, Hull, Watts and Wood dedicated their research on commercial electrolysis. Nevertheless, all played a revolutionary role in electroplating applications.

 

Here are the examples of teachings from a few of these pioneers’ work:

Nernst’s invention allowed us to relate electrode potential, valency of the metal ion and current. Hull’s work brought to light Tafel’s, Butler’s and Volmer’s work. Wood’s invention signified electromotive force (emf) series and distinguished strike, flash plating, and plating. Cook’s and Senderoff’s developments emphasized the importance of eutectic temperature, phase diagram, liquidus temperature of salts, fluxing effect and ionic conductivity of electrolytes.

 

Hope you find this paper valuable and you dig deeper on these matters!

Post your comments and write about who tops your list.

 

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A recently published paper by a senior staff on a leading American magazine was unclear about the electroplating terms, like covering and throwing powers. Many times, we see vague interpretation and wrong distinction on these terms.

 

Advint’s online electroplating training and E-book offers right definition, explanation of identical terms and concepts. So, I’ll abstain from offering an elucidation here and write on the effects and recommendations.

 

The supplementary purpose of this paper is to emphasize the importance of correct interpretation of underlying electrolysis mechanism, terms, concepts of electrochemistry and electroplating fundamentals.

 

The confusion on these terms occurs when one draws a literary meaning on these words, reads leading technical magazines and science journals, and listens to veterans in this field.

 


Dr. Samuel Glasstone’s An Introduction to Electrochemistry delivers the clearest definition of throwing power of an electrodeposition process.


To correctly understand the terms, deeply observe acid chloride zinc or Watts nickel plating and cyanide copper or cyanide silver plating processes. Careful analysis of these electrolytes using a Hull cell will make clearness of these terms.

 


Handbooks and electroplating books frequently cannot document and analyze all developments, and now and then it misconstrues the depth of progress in the metal finishing field.


 

Confidentiality and hidden knowledge within the industry is the reason for such limitations. This limits awareness of all electrolyte properties and their formulations options with benefits. Many large organization’s operating procedures and practices also deter the best ability of a process.

We recommend you to question, test and re-consider critical attributes and formulations, including the references of Advint’s e-book guide to get a model electroplating routine.

 

Why is it imperative to comprehend properly?

Choosing a suitable electrolyte and maintaining the concentration of anions and organics will enable us to:

  1. improve product quality
  2. improve deposition thickness with due consideration for product geometry
  3. meet functional and customer criterions
  4. improve process control
  5. reduce cost associated with rework and under or over thicknesses
  6. minimize or eliminate problem solving time
  7. correctly comprehend fundamental electrolysis mechanisms

How can you learn the correct terms?

Advint’s virtual course E-book syllabus covers relevant electroplating terms and concepts.

We recommend referring authentic resources, test yourself by analyzing electrolysis and deposition mechanisms on various electrolyte formulations and metal deposits.

 

To the Point

In this short paper, we discussed why right construal of a plating term is important. We reviewed how to access the pertinent information and the reasons for confusions. A diligent comprehension of the terms will help advance the metal finishing capability to what it’s worth.

 

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The purpose of filtration goes beyond the removal of total suspended solids (TSS) from electrolytes like chromium conversion coating, electrolytic plating, electroless plating, anodizing, electro-polishing, and immersion electroplating processes.


Though filtering an electrolyte is the prime aim, the flow of electrolyte, its velocity, uniform distribution and consistency effects the deposit physical characteristic and morphology.


 

In this short paper, we will review the apparent and not so obvious functions of filter systems and recirculation of electrolyte. We will also look at the filtration merits for processes such as Watts’ nickel, electroless Ni-P, electroless Ni-B, precious metals plating such as gold and silver, hexavalent and trivalent chromium conversion coatings, immersion plating and plating on plastic. We will assess design criterions for filtration, properties of electrolytes and potential benefits of optimized filtration systems regarding deposit morphology.

 

Electrolyte Properties

Not all electrolytes have similar filtration or flow requirements. A Watts nickel electroplating electrolyte and simple cyanide gold plating electrolyte differ in the formation of suspended solids and the intensity of flow. The volume of the solution and turnover of the components require horizontal disc filter system for nickel plating, whereas most precious metal plating solutions would require cartridge filters. Horizontal disc filter systems design is over 150 years old and had stood the test of time and quality. In cartridge filters, size and pore size are important. Here the distinction is the property requirement of electrolyte, where concentration of metal ions at the vicinity of the cathode is influenced by flow (not the only variable) and is related to the current efficiency of the electrolyte. With Watts’ nickel, we require a vigorous agitation and flow when compared with cyanide gold electrolyte, which requires less agitation and a gentle flow.

 

System Design

To ensure the filtration is effective and flow is uniform, we must consider plumbing the inlet pipe near the bottom of the tank and the outlet at the diagonally opposite end of the top. It is important to ensure never the electrolyte flow directly impinges on the part, as this will negate plating in that area. A simple reference to the supplier’s technical data sheet will help determine the motor capacity of the filtration system (flow rate per hour).

 

Deposit Characteristics

The filtration system’s primary purpose is to filter the solution and remove TSS. Sometimes filtration might not be necessary, and recirculation might suffice. On most applications, consistent flow, required velocity, optimal distribution will help deposit morphology and crystal growth. Resistance created by the cartridge alters flow. Change in velocity of the flow and the distribution pattern effects crystal habit, domain growth, and continuity of the deposit. Tribological and corrosion properties of any deposit is improved and are consistent when the growth continues without interruption and the growth rate or rate of discharge of ions are steady.

 

Electroplating Filtration System

Summary

In this paper, we saw the importance of filtration, options available in the market, the vital reasons for proper design and specifications of the system, and the benefits of having consistent flow and distribution on various electrolytes.  We discussed distinct properties of acid and cyanide-based electrolytes, metals with high and low electrode potentials (nickel and gold), and their respective filtration requirements and benefits of specific choices.

We recommend process engineers to assess the simple but important filtration system on aspects such as systems design, required flow functionality from electrolyte properties perspective. And interpret deposit properties like tribology and corrosion or others when determining flow velocity, distribution and consistency.

 

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Surface and metal finishing field is going through continuous research and developments driven by REACH and process improvement demand. Some developments and contributions are on trivalent chromium, satin nickel, anodizing, aluminium conversion coatings, plating on aluminium, plating on plastic (PoP), and phosphating. A few proactive applicators focus on automation, process control, use of statistics, and bath purification.

Registration, Evaluation, Authorisation, and Restriction of Chemicals (REACH) had listed substances of lead, cadmium, chromium, cobalt, mercury, arsenic and solvents such as methanol and trichlorobenzene, and more.

 

Environmental concerns and market’s competitive spirit have motivated research and creativity. Let us overview the recent progresses with a few examples.

 

Trivalent Chromium

REACH, RoHS, and other environmental agencies across the globe had listed chromium trioxide (chromic acid) as a hazardous substance. Demand for decorative chromium in automotive sector (plating on plastic) and hard chromium in aerospace sector have forced the drive on trivalent chromium research for over several decades. Various formulations use chloride and sulfate salts of chromium to get the desired deposit properties. Industry had made much progress on advancing decorative chromium and modest improvements on hard chromium.

 

Anodizing

Boric acid and tartaric acids are replacing chromic acid in aluminum anodizing applications. Type 1 and type 2 anodizing using chromic acid and sulfuric acid contributed gigantically to the industry. Research and applications in boric and tartaric acids are making steady progress in the industry to replace hazardous chromic acid and extremely corrosive sulfuric acid.

 

Aluminum Conversion Coatings

Lanthanoids and actinoids had offered an interesting array of properties to replace hexavalent and trivalent chromium substances used in the conversion coatings. Other mineral and polymer-based formulations are in development and offered in the industry to meet vast conversion coatings demand of major sectors. Conventionally conversion coatings are an immersion process. Spray conversion coatings are finding unique value with some challenges.

 

Phosphating

Recent hard work is on to eliminate chromium and nickel from zinc phosphating and other phosphating applications. These newly developed formulations work at lower temperatures than the conventional processes.

 

REACH List Electroplating Changes

 

Automation


We need to move away from the traditional process improvement methods and be proactive in quality and cost reductions to achieve with ease the true electroplating capability.


Automation is the way to go!

 

Use automation to control the process parameters such as pH, metal content concentration, uniform current distribution (computational fluid dynamics (CFD)) and focus on creativity with human potential maximization aim.  The resultant distribution of the deposit depends on the choice of DC electroplating rectifiers above and beyond other parameters.

 

An Idea in Brief


We listed a few prominent thematic changes in our field. There are others like elimination of bioaccumulate perfluoro octane sulfonate (PFOS) and identification of boric acid alternatives on Watts nickel plating and acid chloride zinc plating applications.


 

While the listed developments are interesting and credible, we advise the process owner not be credulous when choosing a new formulation or a process. On some cases, the developments are significant and on some there are gaps in the meeting of required deposit physical characteristics. We recommend a process owner to acquaint with the salesman’s enthusiasm and a researcher’s curiosity, consequential in being carried by advantages and not projecting a balance of pros and cons!

 

Advint’s advisory services help clients on the best choice of processes, DC rectifiers and automation.

 

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Achieve a profound change in electroplating process control by asking inquisitive questions. Use emotional intelligence with curiosity, be intuitive, lay emphasis on quality over cost, and maximize human and automation potentials.  


 

Who does not want to advance their process performance? If we can improve the process without adding cost it is a windfall, correct? Maximizing automation of power supplies on electroplating, anodizing and electropolishing metal finishing applications is one such method. Automation helps process control. Above automation comes intuitive mind. Intuition is a derived from knowledge and experience. You ought to combine intuition with equipment capability. In this short paper we will review functions, capabilities and advantages of insulated gate bipolar transistor (IGBT) switch mode rectifier and silicon-controlled rectifier (SCR).

 

Intuition

Einstein nurtured his intuition from his experience working as a patent clerk while developing his theory of Special Relativity. His presence of mind and theoretical knowledge was instrumental in his brilliant work. Intuition and experience also played a significant role. Likewise, you can use your keen and meticulous observation skills, creativity, innovative mind, knowledge and experience to automate your plating and other metal finishing processes. Managing desires and possessing a non conforming mindset are nuts and bolts to achieve this trait.

Combine this attribute with knowledge in automation and on capabilities such as ampere hour reading and application of current during electrolysis for the finest results. Required capabilities for processes such as anodizing of aluminum, hexavalent or trivalent hard chrome plating, nickel and cadmium plating vary because of electrolytic conditions and electrode potentials.

 

Automation


Start with questions!

What are the automation opportunities?

Which option makes available the most benefit with less cost and complication?


 

Automating DC power supply is one of the best choices on an electrolytic process. An excellent choice on a rectifier allows the cathode to receive optimal current. Note, there is a difference between applied and received current. One can read previous articles in this page on current distribution, throwing and covering powers.

 

A rectifier with RS 485 and 4-20mA analog signal capability and ampere hour (AHR) meter can enable metering of process chemicals during electrolysis. Who doesn’t want consistent output quality? We must reduce variations within input variables to get the desired output quality. Among input variables there are parameters which vary by electrolysis and others vary primarily because of drag in and drag out of chemicals. It is pertinent to account for both types of variables. Rectifier, PLC and metering system can be programmed ingeniously to realize this aim.

 

With power supplies, begin by choosing between IGBT switch mode or SCR thyristor DC rectifiers. Ripple factor, unit weight, voltage and amperage accuracy are better with the IGBT rectifier. Ripple is a measure of purity of DC output of a rectifier. Many electrolytic processes, especially precious metals plating like gold and silver plating are sensitive to a higher ripple percentage. When a SCR rectifier is used at a lower amperage than the rated capacity of a rectifier, ripple is high. Whereas with IGBT rectifiers ripple factor is consistent and independent of DC output voltage. Green Power’s DSP digital control allows increased longevity with less maintenance of rectifier and comes with a very high accuracy. The DSP technology is proprietary to Green Power Co. Ltd. When compared with SCR thyristor rectifiers, IGBT power supplies possess higher efficiency and power saving capability.

 

In a nutshell, by choosing IGBT rectifier you choose better technology, save space and power, improve accuracy resolution and accuracy, and negate the effect of ripple factor. Use of RS485 MODBUS protocol can integrate with programmable logic controller (PLC) and control current, dosing systems and enable trickle current mode at the start of the process.

 

An Idea in Brief

 

 


Achieve a profound change in electroplating process control by asking inquisitive questions. Use emotional intelligence with curiosity, be intuitive, lay emphasis on quality over cost, and maximize human and automation potentials. 


We can automate hoist, process sequences, filtration and dosing systems, and rectifiers technologies with this outlook. A splendid choice of DC power supply is important. Both IGBT and SCR rectifiers offer unique advantages depending on the electrolytic process. Aluminum and hydrogen electrolysis, electrowinning and electroforming requirements differ from that of electroplating, anodizing and electropolishing. We recommend considering your process requirements with the capabilities of IGBT and SCR rectifiers.

On precious metals plating applications distinguish between applied and actual current. Due cognizance can affect the consistency of deposit thickness and the deposit characteristics. When sourcing a rectifier consider buying from reputed a manufacturer who conducts active research and continuously improve on their design and functionality.

 

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Managing time with a data-driven approach offers incredible value in process management and customer service on electroplating and anodizing applications. Analytical data, awareness of chemicals and deposit properties with a historical context add value to engineers and aspiring scientists in the metal finishing field.

 

Spot and quick tests offer incredible insights for the metal finishing processes. What is a spot test? Are these tests reliable?

 

High temperature oxidation resistance is a valuable elemental and deposit property. What does it mean? Which elements possess this property? We will review the value of this physical property.

 

Surface and metal finishing offer a variety of options such as plating, anodizing, coloring of metals and electropolishing. Plating on several substrates such as plastic, steel, stainless steel, Invar, Kovar, nickel, aluminum, and titanium alloys are common. Elements like gold, silver, nickel, chromium, zinc and cadmium are plated. We choose the deposit based on consideration for cost, corrosion resistance and tribology properties.

 

Other than plating, we can electropolish and anodize metals such as stainless alloys. Applicators anodize on aluminum, magnesium, titanium, niobium, tantalum, etc.

 

Anodising is an electrolytic process in which we make an Al alloy anodic with a metal cathode on an acidic electrolyte. There are three classes of coating. We anodize with and without sealing.

 

This short paper explains which element to choose as deposit or substrate. It lists spot and quick tests available in the market. Review brightener chemistry and history. Discuss inhibitors, chemicals used for coloring metals and chromium conversion coatings.

 

Spot Tests

Several wet and instrumental analyses methods are used to conduct qualitative and quantitative analysis of elements. The advantage of these methods are accuracy and data reliability. But these test methods are time consuming and some are expensive. When you need a quick feedback, consider conducting spot tests on deposits and effluents. The sensitivity of spot test reaction can be at ppm levels. Elements such as aluminum, stannous tin, gold, silver, iron, nickel, palladium, lead, zinc, cadmium, chromium and copper can be tested. Many of these tests can take less than 5 minutes.

We can detect heavy metals, hexavalent ions and cyanide content in the effluent. You can distinguish between cadmium or zinc plating deposits using spot tests.

 

Here is a list of some organic chemicals used for spot tests:


Diphenyl carbazone

Dimethyl glyoxime

Tri-ammonium aurine-tricarboxylate

Nitro-bruciquinone hydrate

p-Dimethylamino benzylidene rhodamine

diphenyl thiocarbozone

sym-Diphenyl-carbazide

(1-2-Hydroxy-5-sulpho-phenyl)-3 phenyl-5-(2-carboxy-phenyl)-formzan) sodium salt

1-(2-Pydridyl-azo)-2-naphthol


Refer to Chem Spider for further information on any chemicals.

 

For further information on spot tests, read the book - Analysis of Metal Finishing Effluents and Effluent Treatment Solutions. This is a book written by Duncan MacArthur, Fred Stevens, and G. W. Fischer.

 

Chemicals

Did you know tobacco and licorice were one of the earlier brighteners used? Several decades ago, or even a century back, the use of brighteners or additives were very limited. Even the awareness of organic brightener science did not exit. Like many inventions, use of organic chemicals as a brightener was an accident. Tobacco was one of earlier recorded chemical used as additive. More than a century ago a plating operator who had the habit of chewing tobacco drooled the juice onto a plating solution during electroplating. Later noticed that a plated lot had a brighter appearance. Further investigation revealed the brightness influence of tobacco on plating deposit.

People used licorice during earlier days. It had a presence in the industry for some time and even now to an extent. Licorice extract is a carbohydrate and its chemical name is glycyrrhizin. They used it as an additive.

 

The additive was prepared by weighing a known quantity of licorice root and steep in a boiling water until colour saturation occurred. For 100 L plating solution, 100 grams of root was steeped in 0.5 L of boiling water.

Pickling and acid activation are a very common process at a steel mill, metal foundry, and a metal finishing processing plant. Conditional on activation and deposition bonding requirements, a substrate such as copper alloys or steel alloys would require activation under strongly acidic conditions. Use of strong acids such as hydrochloric acid, sulfuric acid and hydrofluoric acid can etch the substrates.

 

We commonly use sodium fluoride as an inhibitor. On picking applications, industry used antimony trioxide as an inhibitor.

 

Copper alloys such as brass tarnish in the presence of oxygen from atmosphere. Brass plated deposit do the same. An organic coating can prevent tarnish. Benzotriazole coating forms a thin layer in an immersion process, and the layer protects copper alloys from tarnish.

 

Brass plating is an alloy deposition process. The electromotive force potential of copper and zinc makes cyanide brass plating one of the most complex electrolytic processes. Attainment of a consistent and durable colour is tricky. Proper use of current density with an excellent choice of rectifier (IGBT or SCR) with an organic coating ensures great cosmetic appeal with durability.

We can also colour brass. One such colour is blue. An immersion process at high temperature in the presence of sodium sulphite and lead acetate colours brass substrates. Other than brass, we can colour stainless steel alloys using dichromate salts.

 

Yellow chromate on zinc deposit is one of the popular choices. We recognize the yellow chromate for brilliance of colour and corrosion protection. There is a subtle colour difference different between hexavalent and trivalent chromates. Chromates sometimes leaves iridescent finish. A protective coating similar to benzotriazole layer reduces iridescent streaks.  One can get a reddish tone on the yellow chromate formulation. Use of a sulfate ions and nitric acid offers a reddish yellow chromate finish.

 

Occasionally people refer to chromate or chromium plating as chroming. Chroming is a colloquial speech term and we prefer you avoid using informal terms to avoid confusion and for use of clear language communication. Hexavalent Cr and (cyanide) cadmium is listed by Registration Evaluation Authorization and Restriction of Chemicals (REACH). We now replace cadmium plating with zinc / nickel alloy. Sacrificial protection of cadmium under saline conditions are inimitable.

 

Deposit Properties

Observing electromotive force series of elements and their potentials (negative or positive / active or noble) suggests evidences on fascinating deposit, material or electrolyte properties. We are referring to properties such as high temperature oxidation resistance and conductivity.


Pilling and Bedworth conducted a seminal work on high temperature oxidation.


Chromium, tantalum, zirconium and gold possess exceptional high temperature oxidation resistance properties. What is high temperature oxidation resistance?


The volume of oxide is greater or lesser than the parent metal, it produces or cannot produce an effective protective property.


What does a reference to protective property mean? It refers to the formation of an oxide layer, such as tantalum oxide, chromium oxide and zirconium oxide on the metal or the deposit. The refractory metals offer oxidation resistance up to ~ 600ºF. Oxidation and healing property are the principal reason hexavalent hard chromium plated components had gained wide popularity. Many applications of aerospace and automotive industries require components to posses tribological properties at a higher temperature. Wear, lubrication, and friction are such examples. The oxides can re-form and withstand high temperatures during these mechanical transformations. Tantalum, zirconium, niobium, and chromium metals are a few among the best to possess such a property. Other than oxidation properties, these elements are susceptible to corrosion resistance from acids, alkalis, organic media and other reagents. We measure high temperature oxidation in ratio and Pilling - Bedworth (PB) ratio of corrosion resistant metals range between 0 and 4. Higher the number better the corrosion resistance. PB ratio is the ratio of the metal oxide volume divided by the metal volume. Chromium PB ratio is 2. All chromium electroplating deposits do not have the same corrosion resistance properties. Corrosion resistance of decorative Cr plating is because of nickel undercoat. Most hard chromium deposit do not have any corrosion resistance. However, a few formulations containing fluoride ions in the electrolyte possess high corrosion resistance. Some hard-hexavalent Cr deposits pass 500 hours of neutral salt spray test (NSST). We mainly attribute the variations to formulation, processing, and process control.

 

Other than refractory metals, precious metals such as gold plating deposit possess high temperature oxidation resistance. Industry uses gold plated components on space applications because of high temperature oxidation resistance, conductivity, high surface stability, high resistance to tarnish, and chemical corrosion. Both trivalent and monovalent salts are used to deposit gold from electrolytes. Precious metals like gold, silver and palladium can be plated on several substrates such as stainless steel, Kovar, Inconel, magnesium, aluminum and titanium alloys efficaciously.

 

Besides lightweight, the stubborn oxide layer makes aluminum and titanium alloys indispensable in our daily lives.

 

Previous paragraph mentioned about the conductivity of deposit. What about electrolyte conductivity? Change of ion activities with concentration affects electrolyte conductivity. Understanding interionic attraction theory of electrolytes are essential to improve conductivity.

 

Value

Whether you are an engineer or a research scientist, understanding element and deposit properties, electrolyte capabilities and limitations, and vitality of unique chemicals are important. A process design engineer with a good understanding on these characteristics can design products with superior corrosion and tribological properties. The matters covered in this paper such as high temperature oxidation resistance can help a designer identify suitable metal as substrate and a deposit.

 

We identify some chemicals listed in this paper as hazardous or carcinogen per Registration Evaluation Authorization and Restriction of Chemicals (REACH). REACH is a European Union regulation. You can also find additional information on carcinogens by visiting the website of National Institute of Environmental Health Sciences (NIEHS) under the National Toxicology Program (NTP). Observing regulatory compliance and identifying risk mitigation plan will drive an organization’s governance.

 

REACH, quality demand, and customer requirement will call for a transformed focus on a few facets such as colouring of metals, plating solution additives, chromium conversion coating and anodizing. An ardent electroplating specialist must consider all the services, test methods and fundamental concepts.  

A leader must prepare electroplating companies to manage complex processes. An agile metal finishing organization aiming to survive even under adverse conditions shall be data driven, ensure speed of business is appreciable, work faster, and inculcate easy-to-use test methods. We know many that plating companies who are not data driven do not grow or adapt to developing changes.

 

Spot testing of effluent, electrolyte or deposit is an under used method, and will help gather data with speed and ease. Other quick tests like pH measurement, specific gravity, litmus, refractometer, and profilometer are all easy and inexpensive. This do not mean volumetric and instrumental analysis offer less value. Both methods are vital for many electroplating operations. The choice depends on their technical ability, product testing requirements and financial capability. The examples of these instruments are atomic absorption spectroscopy, scanning electron microscopy, induced couple plasma (ICP), x-ray diffraction, x-ray fluorescence and electron microprobe analysis. We use these units for elemental analysis at lower concentration with a top-level accuracy. XRD and EPMA can detect light elements such as lithium, oxygen and carbon with an outstanding repeatability and reproducibility.  

We deliberated chemicals, methods, properties, and data driven approach. Cognizance of these matters without a long-term analysis and reaction plan is not noteworthy!  Consider use of run chart, control chart and Process Development and Control (PDC) tools with a visual dashboard.

Readers can find a value on other short papers written on this page previously. Please read articles on electrode potential, IGBT and SCR power supplies, current distribution, throwing power, periodic table, Time Change Management (TCM), Process Development & Control (PDC) tools, and communication. A complex electrolysis process requires a multidimensional approach on disciplines such as science, mathematics, technology and management. There are many vital aspects involved in this field such as automation, process control, business development methodologies, and so on. Fundamentals, laws, equations, and concepts govern electrolysis. Though not needed on a day-to-day basis, these are important to be aware and apply. Discipline, observation, data, patterns, and behaviors are critical for one to succeed at a higher level. Though there will be a scientific explanation for all outputs, one needs to treat the work as art! This is imperative because of our limitations – time and knowledge. Hence, at Advint we offer on guidance on subjects related to laboratory practices, equipment engineering, automation, productivity, lean, statistical process control (SPC) tools, and management. Advint’s virtual Electroplating Training explains all these subjects comprehensively. 

 

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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.

 

electropolishing electroplating surface profile

 

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 adviser@theadvint.com if a concept is abstruse.

 

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This paper is about the Hawthorne effect, the obvious but not so obvious effects, and the necessity.

 

Electroplating, anodizing, electro-polishing and complex processes such as plating on plastics require leadership drive to advance operations and engineering performance, and sustain on the growth.

 


An exemplary leader sets the expectation, creates necessity, delegates responsibility and confirms accountability without micromanaging the trivial effects.


We can set a clear expectation on variables such as electrochemical variables, process yield, product flow, inventory management, employee and executive management engagement.

 

Hawthorne Effect

The Hawthorne effect is the improvement detected because of a noticeable observation of the process. In reality, it does not confine the effect to a process, rather it encompasses to an employee performance. In both cases, it is a top-down approach, but ends with a continuous observation from all levels. When a leader sets the expectation, consistently follows up, align the goals with his or her actions, and supports their team to succeed, the team would achieve operational excellence in the long term. Observation and commitment to improvement must include all critical key performance indicators (KPI’s).

 

Obvious but not so Obvious

In retrospection, every challenge we overcame and the opportunities for improvement would become obvious to us. But this is late, as by this time we would have non-conformances, cost infliction and customer dissatisfactions. It is prudent to detect the obvious challenges and opportunities in real time. Earlier the opportunities were present, but hidden. We miss as it is not obvious!

 

If I did not communicate, think about the current COVID-19 pandemic. The issue originated in December 2019 and peaked in China during mid-February 2020. If the issue was apparent to global leaders and commoners around January, would the consequences be the same?


Revealing the hidden challenges in actual time is the heart of your effort in improving effectiveness.


 

How to expose these challenges? What prevents us from reading between the lines? The answer is not simple. This would be contingent on the leader’s emotional intelligence, knowledge of the subject and availability of visual data and information on real time.

 

Electroplating anodizing process line

 

Yield Shadows Necessity

We can achieve metal finishing processes and business effectiveness by focusing first on necessity. One must focus on the necessity to perform, collaborate, and on satisfaction (employee and customer). Yield will shadow the necessity–big or small; it is for you to choose! Clear responsibility and unambiguous accountability are the means to achieve necessity.

 

An Idea in Brief

Electroplating and other metal finishing processes are complex, as we all know. Market and customers are demanding. Contingencies like the COVID-19 pandemic will subject job shops and captive platers to hardship.


At these and regular times, being conscientious of the process variables, exposing the hidden opportunities on real time, and starting with a focus on necessity are three important steps to achieve effectiveness in the manufacturing operation.


 

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Venkat Raja
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March 1, 2021
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