ASTM D1384 Glassware Corrosion Test Strategies for Fuel Cell Coolants

For instance, conventional ICE vehicles function most efficiently at higher temperatures; existing systems seek to cool the engine to around 95 °C during normal operations.  

Meanwhile, batteries and electric motors in battery electric vehicles generate substantial amounts of heat, but they function most efficiently in a cool environment. Thus, adequate cooling, especially of the battery pack, is essential. Tribologists suggest thermal management in hybrid vehicles is further complicated by the high operating temperatures for ICE vehicles and lower temperatures desired for batteries, electric motors and inverters.  

Fuel cell vehicle and battery electric vehicle makers have devoted their research efforts to battery, electric motors, fuel cell design and vehicle comfort accessories. However, they have largely neglected the need for a new generation of coolants for fuel cell and battery electric vehicles. One of the reasons for this may be that EV coolant specifications were not available, so automakers resorted to “off-the-shelf” conventional coolants for BEVs.  

However, as we now know, EVs require specific coolants made for EVs, particularly with respect to electrical conductivity requirements, corrosion protection and compatibility of new metals and plastic materials. Therefore, historical coolant testing methods for those conventional coolants cannot be transferred over to testing of EV coolants and require some changes and modifications.  

This article will discuss how the author’s lab used different ASTM D1384 testing strategies to address the new challenges posed by conditions within EVs—specifically with respect to FCEVs—even as ASTM has not yet finalized testing standards for these new vehicles. 

ICE Coolant History 

First, to understand the development of coolant technology over the years, let’s conduct a brief review of automotive coolant innovation.  

The first vehicle coolant was water, owing to its excellent heat transfer capacity. However, because of the relatively high freezing point and relatively low boiling point of water, it became clear formulators needed to add something to expand the temperature range of vehicle coolants. Formulators began adding ethylene glycol to water in an equal mix, thus accomplishing the goal of significantly expanding the coolant’s temperature range.   

However, another major problem emerged: corrosion.  

To combat the issue of corrosion of engine parts, coolant formulators developed and used corrosion inhibitors. Later in the 20th Century, organic acid technology offered extended coolant life. Finally, hybrid organic acid technology utilized both organic and inorganic additives.  

All of that brings us to the present day and the ongoing development of EVs and EV coolants.  

EV Coolant Requirements 

That brings us to the important question of specifications. What do EV coolants need to be able to do that conventional coolants cannot?

Temperature is a critical factor that affects performance and durability of the fuel cell system. The appropriate operating temperature range of proton exchange membrane fuel cells is around 80 °C.  

The fuel cell coolant pathway also differs from that of the ICE coolant. Fuel cell coolant passes through high- and low-temperature loops. The former includes the fuel cell stack, while the latter covers cooling for various electronics in the vehicle.  

Furthermore, EVs require much lower electrical conductivity. Electrical conductivity is a new requirement for EVs; ICE vehicles were not tested for this property.  

However, now we have tested electrical conductivity of conventional ICE coolants for comparison with EV coolants and found electrical conductivity of the ICE coolants fell in the range of 3,000-5,000 microsiemens per centimeter. Meanwhile, OEMs are requiring electrical conductivity of below 100 µ/cm for battery electric vehicles. Fuel cell industry specifications for electrical conductivity are even stricter, coming in at below 2 µ/cm.  

Fuel cell vehicles feature new material mixes—these materials include aluminum, plastic, stainless steel, silicone and resin— compared to their ICE predecessors. For example, cast iron and solder are common materials in the ASTM D1384 glassware corrosion test for conventional automotive coolants; however, these materials are not present in the fuel cell.  

As mentioned, EV makers have also developed a variety of designs for BEV and FCEV motors. Although several designs have emerged over the years for BEVs, the “blade” battery design has proved the most popular. Similarly, the proton exchange membrane—also known as a polymer electrolyte membrane—fuel cell has emerged as the preference in automotive applications.  

As a result, test methods must also address the conditions and materials of these new vehicles.  

Corrosion Testing Challenges and Important Variables 

In addition to variations in materials, formulation and testing challenges exist. Selecting the right chemistries for corrosion inhibitors has therefore never been more important, particularly when it comes to electrical properties and the high and still-emerging performance requirements for EVs.  

ASTM standards exist for ICE vehicle coolants, as defined by ASTM D3306 for light-duty vehicles and ASTM D6210 for heavy-duty vehicles. There are four different ASTM standard tests for corrosion:  

• ASTM D1384: corrosion test for engine coolants in glassware  
• ASTM D2570: simulated service corrosion testing of engine coolants  
• ASTM D4340: corrosion of cast aluminum alloys in engine coolants under heat-rejecting conditions 
• ASTM D2809: cavitation corrosion and erosion-corrosion characteristics of aluminum pumps with engine coolants. 

The traditional ASTM D1384 glassware corrosion test includes exposing the six metals to corrosive water under the following conditions:  

• 88 °C for 336 hours 
• Air flow of 100 mL per minute 
• Volume of 750 mL per test 
• Salts in the water of sodium sulfate, sodium chloride, sodium bicarbonate (corrosive water). 

Following completion of the test, the metal coupons are weighed for weight loss or weight gain (a positive number indicates weight loss, while a negative indicates weight gain). 

Figure 1. ASTM D1384 glassware corrosion test results 

The author’s research lab selected four samples: DFC, EFC, NFC and KFC of MEG and DI water OAT (organic acid technology) chemistry. The lab planned ASTM D1384 glassware corrosion test strategies to compare corrosion protection. For example, during the traditional ASTM D1384 glassware corrosion test, DFC coolant passed for four out of the six metals (ASTM-prescribed limits are in the far-right column of Figure 1), while EFC passed four out of six and NFC failed for all six metals. Testings were planned at varying temperatures and in various types of water, both for determining corrosion inhibition and impact on pH and electrical conductivity.  

The DFC and EFC coolants were also tested without corrosive water at 88 °C and 100 °C. (See Figure 2). 

Figure 2: ASTM D1384 glassware corrosion test results without corrosive water at 88 °C and 100 °C

The lab also used the test to assess the impact of temperature on pH and electrical conductivity after the completion of the ASTM D1384 glassware corrosion test (see Figure 3), although this is not the requirement of ASTM D1384 report.

The author’s research lab conducted a modified ASTM D1384 test for the fuel cell metals of 304L and 316L steel as well as 5052 and 6061 aluminum.  

Figure 3: ASTM D1384 glassware corrosion test results showing changes in pH and electrical conductivity at 88 °C and 100 °C

Under these test conditions, the glassware corrosion test ran for 336 hours at 88 °C.  

The corrosion test results show that NFC generally performed worse than DFC and EFC. Meanwhile, DFC and EFC posted similar results, except for 5052 aluminum. However, both came in outside of the ASTM limit.  

Testing for changes in pH and electrical conductivity shows DFC exhibiting superior stability of pH and electrical conductivity levels relative to EFC and NFC.   

In addition to the above data, those running the tests also compared visual appearances of coupons after completion of the testing. They used coupon pictures after the test as an additional observation for comparison. 

Modified ASTM D1384 Testing for Chinese Aluminum Coupons 

Meanwhile, coolants used in Asia call for testing different aluminum metal coupons along with fuel cell metals like 304L and 316L steel. Hence, different aluminum alloys were tested for a test duration of 672 hours at 80 °C. Figure 4 displays these results. 

Figure 4: ASTM D1384 glassware corrosion test data for Chinese aluminum coupons

In the assessment of pH and electrical conductivity changes over time, the pH of the coolants fell by comparable percentages. In terms of electrical conductivity, however, DFC exhibited the lowest percentage change.  

As for visual appearance of the coupons, DFC performed better with respect to aluminum corrosion than EFC and NFC.  

Korea Testing per KS M2144:2019 

Finally, Korean corrosion testing (see Figure 5) was carried out at 80 °C for 504 hours.

Figure 5: Korean aluminum coupon ASTM D1384 glassware corrosion test results

This testing utilizes Korean metals of AC4C aluminum, ALDC12 aluminum, 7075 aluminum, 304L steel and 316L steel. Visual inspection of the coupons shows DFC performing slightly better than KFC but significantly better than EFC. The aluminum coupons in the KFC test bundle show slight darkening relative to the DFC coupon.  

Field Trial Results 

The author’s research team conducted testing in the controlled environment of the lab. But what about results in the field?  

The author’s research lab selected the DFC sample and sent for a field trial in the fuel cell, hydrogen-powered 2021 Hyundai NEXO SUV. This was an effort to tie test method results with field performance.  

Through 40,000 miles, the data show that the DFC coolant has remained stable in terms of both pH and electrical conductivity.  

Conclusions 

The EV space, particularly fuel cell technology, continues to evolve. For now, however, we can take the following from the aforementioned analysis and test results: 

• Low electrical conductivity coolant needs robust corrosion inhibitors to protect multiple metals used in fuel cell vehicles (and battery electric vehicles).  
• The ASTM D1384 multi-metal corrosion test holds good for evaluating corrosion protection of EV metals.
• ASTM Committee D15 is working on formulating a specification draft and test protocol for EVs.   

In summary, automotive cooling has come a long way in the past century. Furthermore, changes in testing are likely to continue as ASTM finalizes standardization in this space.  

For now, however, coolant formulators are working with the automotive industry to develop specifications and parameters for coolant testing that are relevant to the operation and material makeup of EVs.  

There remains a long road ahead, but beginning with these strategies and changes at the laboratory level, the EV horizon continues to inch closer and closer, one mile—or kilometer, depending on your part of the world—at a time.  

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Govind Khemchandani is senior director, R&D: cooling systems and lubricants for Dober Chemical Corp. He can be reached at gkhemchandani@dober.com