Non-PFOS, Permanent Mist Suppressants for Hard Chrome Plating, 

Decorative Chrome Plating and Chromic Etch Applications 

Neil Patton, Atotech Deutschland GmbH, Berlin, Germany 

Gene Barlowe, Atotech USA Inc., Rock Hill, SC 

Mist Suppressants are an important tool for reducing exposure of workers to Cr 

(VI) during plating and etching operations. A common raw material used for 

efficient mist suppressants was, and still is, PFOS. PFOS is subject to legislation 

across the world prohibiting its use for many applications. We will present 

developments and experiences with non-PFOS, permanent and non-permanent 

mist suppressants. 

For more information contact: 

Gene Barlowe 

Atotech USA Inc. 

1750 Overview Drive 

Rock Hill, South Carolina, 29730-2000, USA 

Phone – (803) 817 3500 

E-mail – gene.barlowe@atotech.com
The generation of a large amount of H2 and O2 gas bubbles due to electrolysis is a 

characteristic of even the most efficient chrome plating process. If no precautions 

are taken, these bubbles can cause a mist containing chromic acid to form above 

the chrome plating solution. 

 

Fig. 1 – Typical Hydrolysis during Chrome Plating 

Anode

Cathode

Chromic Acid Mist 

Gas bubbles due to hydrolysis 

The mist is due to the bubbles formed during electrolysis rising up through the 

solution and ‘bursting’ on the surface. This ‘bursting’ causes high speed droplets 

to be ejected from the surface of the solution. Collectively these form a mist. 

Fig. 2 – Formation of Mist Droplets (Jets) from Electrolysis Gas Bubbles 

The resulting speed of a droplet (jet) can be up to 10 m/s. 
As chromic acid is classified as toxic, there are regulations in all countries 

controlling the exposure of members of staff to chromic acid and especially from 

this mist above the plating bath. There are several proven preventive measures 

that can be implemented to reduce exposure. One of these measures is to use a 

suitable mist/fume suppressant. 

The picture below shows the mist generated from a high efficiency hard chrome 

plating solution, in a 1 liter beaker, plating at 50 A/dm2 (3.2 A/in2). 

Picture 1 –Mist Droplets from a Chrome Plating Solution without a Mist Suppressant 

Mist Droplets 

The size of the mist droplets and the height they have reached are easy to see in 

picture 1. 

The test was performed in a fumehood and the surroundings covered in paper to 

prevent contamination. It’s easy to see that the beaker, cathode rod and protecting 

paper are heavily contaminated with chromic acid due to the mist that has been 

generated. This is after just 5 minutes of plating. 
Reduction of the mist can be made in several ways, but a popular method is to 

employ a mist suppressant. 

Picture 2 –Hard Chrome Plating Solution without a Mist Suppressant 

Picture 3–With a Foaming Mist Suppressant Picture 4 –With a Low Foaming Mist Suppressant

When either a foaming or a low-foaming mist suppressant are used then 

contamination to the surroundings are significantly reduced. The beakers and 

surroundings tested with each version of mist suppressant showed no evidence of 

contamination even after several hours of plating. 

Most common mist suppressants are surfactant based and work by reducing the 

surface tension of the solution. This then has a two-fold effect on the generation 

of mist. A reduced surface tension reduces the size of the gas bubbles generated 

during electrolysis. These smaller bubbles travel slower through the solution and 

have less energy when they arrive at the solution’s surface. At the same time, the 

lower surface tension reduces the energy with which the resulting droplets are 

ejected into the air. Together, both of these effects can reduce the emission of 

droplets, and therefore mist generation, by over 98%. When a mist suppressant is 

properly applied, this has been found to be sufficient to reduce exposure to 

employees around plating installations. 
Due to the aggressive chemical and electrochemical environment of Chrome 

plating solutions, most mist suppressants are made from highly stable surfactants. 

PFOS (Perfluorooctanesulphonate) was, and still is, commonly used as the basic 

surfactant in popular mist suppressant products. 

Fig. 3 – PFOS Molecular Structure

PFOS is highly resistant to chemical attack and so is ideal for use in harsh 

environments like hot chromic acid plating baths. Unfortunately the extremely 

robust nature of PFOS means that it is not easily biodegraded or waste treated and 

so is released into the environment where it builds up. PFOS has been classified 

as a persistent, bioaccumulative and toxic (PBT) for some years now. 

The negative health effects of PFOS on animals and humans have been studied 

and were found to be unacceptablei,ii. As a result, there are several legislations 

worldwide restricting the marketing, production and sales of substances, including 

PFOS. In the US, the EPAiii included PFOS in a new table (3) of substances now 

subject to Significant New Use Rules (40 CFR 721.9852). This rule became 

effective on the November 11th 2007. There is an exemption for one form of 

PFOS, with CAS number 56 773-42-3, when it is used for metal finishing and 

electroplating applications including hard and decorative chromium plating, 

chromic acid anodizing or reverse etching, etching plastics prior to metallization, 

Nickel plating, etc. There is a more restrictive PFOS directive from the EUiv that 

came into effect on June 27th 2008. There is also a worldwide directive from the 

Stockholm Convention of Persistent Organic Pollutants, effective August 26th

2010, which will affect over 150 countries including Japan, implementing an 

effective ban of sales and production of all PFOS containing products starting 

from April 1st 2010. This may need work. Not sure I understood it. 

One of the main aims of these directives is to ultimately ensure the phase-out of 

the utilization of PFOS. There are currently exemptions in most of these 

directives for hard chrome platingv. However, there are several communities, 

organizations, and authorities that are campaigning for a complete ban on PFOS 

use. 
Due to the increased awareness of the HES risks, the use of PFOS has declined by 

over 95% in the last decade, leaving only a few specialized applications.

As the health and safety implications of the use of fume suppressants for Cr (VI) 

applications are serious, a suitable replacement for PFOS must be rigorously 

tested to ensure its suitability. Investigations into a large variety of alternative, 

non-PFOS candidate compounds have been going on for several years. 

Typical criteria for a good mist suppressant are: 

 Reduce surface tension to ≤ 30 Dynes/cm 

 At 30 Dynes/cm – have no discernible mist 

 No effect on plating quality or efficiency 

 No effect on bath stability 

 Be relatively stable - minimal dosing 

 Any break down products should not influence the bath quality or 

functionality 

 No PFOS should be generated or created 

Not all candidates are successful even if they seem to initially meet most of the 

criteria listed above. The unsuccessful candidate below gave insufficient mist 

suppression despite having a supposedly good surface tension of 29 Dynes/cm. 

Picture 5 –Unsuccessful non-PFOS Mist Suppressant
Permanent and non-permanent mist suppressant candidate compounds were tested 

and it was found that the non-permanent mist suppressant compounds were 

basically unsuitable for use in the field. 

Most non-permanent, non-PFOS mist suppressant candidates that were tested 

failed the functional test as on the previous page, but even those that passed most 

of the criteria, failed due to bath contamination. 

Typically, the non-permanent, non-PFOS compounds are inherently instable in 

standard hard chrome plating solutions and thus required constant dosing, even 

during idle times. When the bath was under plating conditions, even more dosing 

of the suppressant chemistry was generally needed. This can cause control issues 

and needs constant monitoring of the dosing equipment to ensure that the 

maximum surface tension limit is never exceeded. 

Apart from this, the biggest issue seen with this type of suppressant chemistry was 

the tendency for the excessive break down of the chemistry to form an ‘oil’ or 

‘scum’ on the plating bath surface that eventually interferes with the plating 

quality. 

The candidate tested below shows a more extreme example of this ‘oil’ or ‘scum’ 

formation. It is easy to imagine that parts plated in a solution containing this 

compound, with its surface ‘scum’ layer, would cause plating quality issues. 

Picture 6 –Unsuccessful non-permanent, non-PFOS Mist Suppressant
After extensive testing of suitable permanent, non-PFOS fume suppressant 

candidates, a family of products was finally developed, thoroughly field tested 

and brought to the market. 

There are two versions of permanent, non-PFOS mist suppressant that have been 

developed and are available on the market today. One is the foaming type and the 

other, a low-foaming type. Both are based on similar non-PFOS technology and 

have years of proven usage in the industry. These products can fully comply with 

PFOS legislation. 

Picture 7 – Foaming non-PFOS Mist Suppressant in a Decorative Chrome Plating Tank 

Picture 8 – Low-Foaming non-PFOS Mist Suppressant in a Hard Chrome Plating Tank

The low-foaming version of fume suppressants is, in general, more popular due to 

the lack of a thick foam blanket covering the entire surface of the plating solution. 

This helps to minimize the issue of H2 and O2 gas getting trapped in the foam 

blanket, which can lead to hydrogen explosions. It also means there should be 

less chance of foam being ‘sucked’ into the exhaust system on tanks with minimal 

free-board. 
Comparison tests between current, leading PFOS products have been made, and 

the newly developed non-PFOS products performed just as well. 

Picture 9 – A Hard Chrome Plating Solution with a 

PFOS, Permanent, Low-Foaming Mist Suppressant 

 

Picture 10 – A Hard Chrome Plating Solution with a 

Non-PFOS, Permanent, Low-Foaming Mist Suppressant
The preferred method for ensuring the best operation of a fume suppressant in a 

plating bath is to monitor and control the surface tension. 

The permanent, non-PFOS mist suppressants can easily be monitored and 

controlled by either stalagmometer or tensiometer surface tension measurement. 

0

10

20

30

40

50

60

70

80

0 0.5 1 1.5 2 2.5 3 3.5 4

Mist Suppressant Concentration [ml/l]

Surface Tension [mN/m]

Tensiometer

Stalagmometer

Fig. 4 – Surface Tension vs non-PFOS Mist Suppressant Concentration

The surface tension of a chrome plating bath can be reduced to 20 Dynes/cm 

using the non-PFOS products, but are commonly kept at an average of 30 

Dynes/cm. At this level, consumption of the mist suppressant is kept to a 

minimum and the Cr (VI) emissions are kept under control. 

When changing from a PFOS based product to a non-PFOS product there are 2 

options; a completely new make-up or a slide conversion. Both methods have 

been employed and studied. The most common method is to perform a slide 

conversion of an existing solution. This is generally an easy operation. The 

surface tension of the bath is analyzed and then the required amount of non-PFOS 

product is added to attain the desired surface tension. The non-PFOS product is 

subsequently dosed to maintain the surface tension within the desired range. 
When a slide conversion is made, under normal circumstances, the PFOS 

concentration in the solution should reduce over time. 

One example of a slide conversion shows the potential decline in PFOS over time. 

This was a decorative chrome bath that was converted to a foaming type nonPFOS mist suppressant. 

0

10

20

30

40

50

60

70

80

90

100

012345678

Months

Normalised PFOS Concentration

 

Fig. 5 – PFOS Concentration over Time after a Slide Conversion to a non-PFOS Product

It took 7 months to reduce the PFOS content to only 1% of the original level at 

this particular commercial plater. Different installations may yield different 

results due a number of factors. 

In conclusion, there are now suitable, successful and well proven permanent nonPFOS mist suppressants available in the market, both foaming and low-foaming, 

for hard chrome and decorative chrome plating as well as chromic acid etching. 

References 

i

 “Perfluoroctane Sulfonate (PFOS)”, Dossier prepared in support for a nomination of PFOS to the 

UN-ECE,LRTAP Protocol and the Stockholm Convention, dossier prepared by the Swedish 

Chemicals Inspectorate (KemI)and the Swedish EPA, Sweden, August 2004 ii “Environmental Risk Evaluation Report: Perfluorooctanesulphonate (PFOS)”, D. Brooke, A. 

Footitt, T.A. Nwaogu, Building Research Establishment Ltd., Risk and Policy Analysts Ltd. iii US EPA directive under section 5 (a) (2) of the Toxic Substances Control Act amending the 

Significant New Use Rule at 40 CFR 721.9582 adding table 3, exclusion (4) 

iv EU directive 2006/122/EC amending for the 30th time the council directive 76/769/EEC v

 Annex 3(c) of EU directive 2006/122/EC