Liquidmetal alloy has high resistance to corrosion for a number of reasons. Firstly, crystal defects, such as grain boundaries and dislocations, can act like galvanic cells to initiate localized corrosion – Liquidmetal does not have any such defects. Secondly, the elements we use in Liquidmetal form mechanically stable oxides which act as a passivating layer. Thirdly, the passivating layers form uniformly on the Liquidmetal surface, and so passivating elements are more effective than similar elements in a crystalline alloy.
Over the years, Liquidmetal Technologies have done various corrosion studies on our materials, and we are taking the chance to summarize some of the results here.
Start with Liquidmetal (LM1b), the raw material was made by Materion, and the salt spray test was performed there too. The specimens were tested in the ‘as-cast’ state (they were de-gated with CNC mill, and then cleaned with acetone).
All corrosion testing was done in accordance with the ASTM B-117 standard for salt fog corrosion testing. A Singleton Corporation Model 32-9210 salt fog chamber was used for this testing. Each sample was exposed to a 5% sodium chloride salt spray solution for a period of 336 hours. The ASTM specification states that specimens will be exposed to a continuous spray of solution at a temperature of 35° C (95° F).
A visual inspection of these samples before and after the salt spray test showed that they were essentially unchanged. We then measured the surfaces with a Scanning Electron Microscope, increasing the magnification until 5,000x. Even at these magnifications, there were no visible changes in surface quality from the salt spray on the surface of the material.
More corrosion data comes from a 2005 report on the corrosion resistance of Liquidmetal alloy done under contract number F08637-03-C-6012, for airbase, aerostructures and aerospace environments for the Airbase Technologies Division of the Air Force.
Liquidmetal alloy (LM1) and 316 Stainless Steel were immersed in various solutions for 30 days. The test solutions were analytically diluted to 1L and inductively coupled plasma mass spectrometry was performed to determine elemental concentrations. The results are shown in the following graph.
There was a nearly negligible amount of dissolution in the NaOH (pH 13) and seawater solutions. But Liquidmetal clearly out-performed the stainless steel in the acidic solutions.
The Liquidmetal Alloy (LM1) was also immersed in vivo with Lactated Rangers solution at 37° C (98° F) for 30 days. Post-test specimens had no discernible weight loss or visual defects. Effluent analysis for LM1 was as follows:
The Liquidmetal team has also begun a saltwater immersion test with several Liquidmetal alloys, stainless steel and titanium. This test was begun on 14th June 2013, and we will report on the results as they emerge.