Studying corrosion phenomena

Described as the biggest advance in microscopy since the electron microscope, the second-generation scanning Kelvin probe has been unveiled by Australian scientists. The now patented CSIRO EvolutionProbe follows hard on the heels of the development of the prototype scanning Kelvin probe launched a year ago by CSIRO.

The new-generation version has been named the CSIRO EvolutionProbe (CEP) because of its exciting new features for real-time study of corrosion and other surface chemistry phenomena. Already the CEP has provided insights into the chemical and electronic nature of metal surfaces including:

• Bulk and surface paint coatings properties;
• Defect sites in paint coatings;
• Oxide coatings;
• Localised corrosion;
• Under paint corrosion.

The CEP can be used for a range of applications, from accelerated testing to quality control and quality assurance, and product/process refinement and development. Accelerated testing gives a researcher the advantage of completing research programs in a much shorter time period, reducing the costs associated with infrastructure and human resources.

Using the CEP system for quality control and assurance can give industries options where these procedures entail laborious exercises which can be highly influenced by human error. Finally, for getting a product to market faster, or establishing the viability and efficiency of a new process, the CEP offers many advantages if included in a suite of mainstream analytical tools.

In particular, the CEP offers easy quantification of the previously complex measurement of tribocharging effects. The generation of static electricity by friction - or tribocharging - and the magnitude of the charge and how fast the static charge decays, can all be measured quickly by the CEP.

The developer of the CEP, Aaron Neufeld of CSIRO Sustainable Materials Engineering (SME) says, "This means we can tailor surface chemistry to minimise the effect of static charging. In effect, the CEP is a key to commercialising new technologies such as composite materials, where tribocharging may create product, production or packaging difficulties. This has enabled us to begin to unravel the riddle of unwanted tribocharging effects on polymer films."

Neufeld says, "Just as importantly it can help to identify a replacement solution for the many current environmentally unfriendly antistatic compounds containing fluorines." Like its predecessor, the CEP is an instrument that reveals previously unobserved electrical interactions taking place on the surface of materials.

"The CEP is the only analytical instrument that can provide information about electrochemical reactions and surface changes on coated metal products affected by the thin films of moisture typically deposited as dew or rain," Neufeld says.

The CEP falls into the generic instrument category of scanning probe microscopes, the two most common commercially available instruments being atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). The EvolutionProbe is a technique complementary to these existing techniques.

CSIRO's current research has shown that with metal surfaces contaminated with salt, corrosion takes place not only after the initial deposition of the salt, but for up to 3-4 cycles of high and low humidity after that initial deposition.

The CEP can capture a picture of these electrochemical reactions within minutes compared to other instruments, which take hours and then only offer data from a small section of material.

Atmospheric corrosion of metals is induced by thin layers of water or micro-droplets on the surface of the metal. The CEP can detect the chemical reactions that are going on in those thin layers of water or within a micro-droplet. Hence, corrosion can be purposely initiated at a specific spot on a metal surface and monitored with reference to the surrounding material.

Data acquired from the CEP is displayed real-time, and acquisition control parameters can be changed on-the-fly. This feature of the software controlling the instrument allows the operator to determine the spatial relationships between corrosion reactions without having to wait until the end of the experiment. It also allows the operator to choose specific areas of interest for analysis in greater detail.

"As we have preciously reported," Neufeld says, "CSIRO's secret is the way we have managed to reduce the effect of noise interference on the operation of the probe." The CSIRO SME group has developed a holistic model to predict the effect of the environment on infrastructure components.

This model, supported by the CEP and its predecessor the scanning Kelvin probe, have helped bring CSIRO a new understanding of how fast corrosion initiation proceeds and the chemical changes occurring on the surface of metal.

Neufeld says, "Our studies have shown that a specific type of mechanism occurs involving the reaction of the zinc metal with oxygen from the air." Understanding this mechanism fully has allowed the group, led by Dr Ivan Cole, to develop new metallic coatings to counteract the damaging reactions in corrosion.

CSIRO is now actively seeking partners for the commercial development of the EvolutionProbe.