Corrosion is an electrochemical reaction familiar to us all. In the general case, a metal is oxidized and thus moves from a solid to a liquid (ionic) state resulting in the solid sample losing mass. About 3% of the Gross Domestic Product (GDP) of the U.S. is spent every year combating the effects of this seemingly simple process of corrosion. Corrosion affects the oil company that is pumping hot crude through miles of pipelines, the military that spends billions on ships and aircraft that spend their entire active life at sea, the civil engineer designing rebar support for the concrete in bridges, the automobile industry looking at the effects of road salts or galvanic couples, to the bio-material scientist developing medical stints and joint replacements that are implanted into people in hospitals every day. Corrosion is a real world problem, the effects of which should be considered any time a metal is put into service in a salty, humid environment.
Princeton Applied Research offers a range of electrochemical instruments and accessories to assist the corrosion scientists in their research. Whether a potentiostat/galvanostat for corrosion rate measurements, a corrosion cell for experimenting with coupons, or a scanning system for both quantative and qualitative measurements, all of our products are backed by Princeton Applied Research’s excellent reputation for both design and support.
When selecting a system, it’s critical to select the system that’s best for your needs, both now and in the future. Different specifications are important to different applications:
The PARSTAT 2273 potentiostat/galvanostat offers a 100 Volts of compliance voltage. A potentiostat’s compliance voltage determines how much power it can output to control the cell. Resistive electrolytes, like those sometimes found in corrosion….oil, concrete, soil…may require a potentiostat with a high compliance to overcome that resistive environment, so it is important that your potentiostat has enough for all your future applications.
The VersaSTAT 3F potentiostat/galvanostat is a floating-ground adaptation of the popular VersaSTAT 3. Only one earth-ground point can exist in each cell. Multiple earth-ground points can generate ground loops, which can cause oscillations and result in untrustworthy, unpredictable data. The VersaSTAT3F is isolated from earth-ground, so it can be used to test cells with grounded electrodes (such as autoclaves or rebar).
The VersaSTAT4 potentiostat/galvanostat has additional low current ranges and bandwidth filters compared to the VersaSTAT 3. Corrosion currents can be very low. This is a desired trait as small currents equates to a low corrosion rate, but also a more difficult value to measure. Small electrodes even with moderate current-densities may also generate small current. Also, it is not unusual for corrosion samples to have high capacitance due to their size or oxidize coatings. The additional filtering and ranges in the VersaSTAT 4 give more hardware options for selecting the best possible configuration to test your sample.
The M370 scanning electrochemical workstation is a modular system. The scanning base can be outfitted with different components to perform Scanning Vibrating Probe (SVP/SVET), Scanning Kelvin Probe (SKP), Scanning Droplet System (SDS), Local Electrochemical Impedance (LEIS), Scanning Electrochemical Microscopy (SECM), and Non-contact Surface Profiling (OSP) experiments. The scanning techniques available with the M370 platform provide local information about the electrochemical events at your sample’s surface. The corrosion mechanism is often a non-uniform aggressive process, such as pitting. You can watch pits initiate and passivate with SVP. You can measure values from SKP in the absence of electrolyte or in a humid environment, which can be correlated to Ecorr. You can move a constantly flowing droplet across the sample’s surface, confining your working area to that of the droplet with SDS. You can study scratch tests on organic coatings with LEIS. You can study the fundamentals of a controlled electrochemical process with the increased spatial resolution available with SECM. You can measure topography with OSP.
The K0047 Corrosion Cell is being used worldwide in numerous laboratories doing corrosion testing. This cell was designed to be in compliance of several of the most popular ASTM standards for electrochemical corrosion testing. The K0235 Flat Cell is designed to accept flat samples of varying sizes, exposing only a specific area with each experiment.
Both the VersaSTAT and PARSTAT family of potentiostats have on-board frequency responses analyzers (FRA) options for performing Electrochemical Impedance Spectroscopy (EIS) measurements. An external Lock-in Amplifier or Frequency Response Analyzer is not required to add EIS functionality to these instruments. EIS is incredibly useful, for example, when separating the sample’s response into the portion representing the organic coating (e.g, paint) from that of the underlying bare metal.
We use the term potentiostat as a common reference to these instruments, but they are actually much more. Each of our potentiostats can also function as a galvanostat or as a zero resistance ammeter (ZRA). A galvanostat applies the signal as a current and measures the response of voltage. In corrosion, galvanostatic control is required for tests such as Galvanostatic LPR. This experiment is very useful in continual monitoring tests where the Reference Electrode is susceptible to bubbles, such as in oil. In G-LPR, a bubble on the Reference Electrode still creates a bad data point, but the system does not lose control of the cell, as would happen under potentiostatic control.
A zero resistance ammeter (ZRA) does not apply a signal, but passively measures both the current and voltage as a response. ZRA mode is particularly useful in studying galvanic corrosion or electrochemical noise. Galvanic corrosion occurs any time two metals are in contact in an electrolyte – such as seen in a weld or even when the screw in a medical implant is a different metal than the implant. Electrochemical noise is an experiment that studies the random attack of two identical materials. From the system’s point-of-view, two metal electrodes are connected through the system in a virtually identical fashion. In the Galvanic Corrosion experiment the metals are dissimilar; whereas, in Electrochemial Noise the metals are the same.
For DC corrosion techniques with PARSTATs and GPIB-controlled systems, PowerCORR offers 12 standard techniques, including Tafel, Linear Polarization Resistance, Cyclic Polarization, and Potentiostatic. For EIS techniques, PowerSINE offers the same flexibility as PowerCORR, including the ability to place up to four different plots on the screen simultaneously (a powerful tool for ease of EIS data interpretation). For equivalent circuit modeling of EIS data, the software ZSimpWin is available to statistically compare acquired data with that of selected models. The VersaSTAT potentiostats operate in the popular VersaStudio software. VersaStudio is an interface that combines intuitive sequence programming with highly flexible data graphing options.
All of these points emphasize how important it is to select a company with the proven reputation for well-designed products. As a corrosion scientist, you want to make sure that your structure is around 10, 25, or 50 years from now. Shouldn’t you select a company that has been around that long as well? No one has done it longer; and we think that no one does it better.