Hardide coatings are particularly effective at protecting against mineral acids, including HCl, Nitric acid and H2SO4 and resist Aqua Regia at room temperature.
Hardide coated 316 stainless steel samples
The Hardide coating was tested alongside a WC/Co detonation coating for resistance to nitric acid. The images below show two Hardide coated samples: one untested and one tested for 113 hours in 20% nitric acid.
| Untested |
|---|
| No immersion |
| Tested |
|---|
| 113 hours in 20% Nitric acid |
The Hardide coated sample is a yellowish colour due to slight surface oxidation, meanwhile its dimensions have not changed, the weight loss was not measurable – less than 0.001 g and its surface roughness remained the same as before testing – 0.10 micron Ra – which all indicates that the coating had not been attacked.
WC/Co coated sample
In the same test, the WC/Co detonation coated sample changed colour to dark grey, while the acid solution became rose coloured due to Cobalt leaching from the sample. The weight loss of the WC/Co sample after 46 hours 40 min was approx. 0.3 g. The roughness of the WC/Co sample before testing was 0.10 microns Ra increasing after testing in 20% acid to 0.41 microns Ra due to metal binder leaching. As a result of the increase in roughness the detonation coating can become extremely abrasive for seals and packing when exposed to aggressive media.
HYDROCHLORIC ACID RESISTANCE
| HCl Immersion |
|---|
| 28% Hydrochloric acid for 24 hours |
To determine resistance to HCl, a 4140 steel test ring with 50 microns of Hardide coating was immersed into uninhibited 28% Hydrochloric acid for 24 hours. As can be seen here, the appearance of the sample did not changed and no measurable weight loss or surface roughness change were detected.
