Rass-O’-Nil® Flexo Rust Preventive Nano-technology
Rass-O’-Nil Flexo deposits a conductive polymerised metallic phosphate nano-coating. Rass-O’-Nil Flexo replaces oil and grease on CRCA and HR steel for white good and automobile industries by surface coating.
Rass-O’Nil Flexo Benefits:
• Degreasing process is eliminated at the customer end.
• Use of hazardous chemicals can be eliminated.
• Water rinse is eliminated.
• Use of manual wiping of oil at the customer end can be eliminated thereby labour cost can be saved.
Application method: Rass-O’-Nil Flexo can be applied with foam mopping on the CRCA and HR steel surface or by dipping the steel section and followed by squeezing and drying.
Corrosion Prevention Evaluation Methods:
1. Coating uniformity and micro structure observed through a Scanning Electron Microscope (SEM).
2. Coating weight by wet chemical methods.
3. Coating durability through Humidity Test/Indoor exposure test.
1. Coating uniformity and micro-structure
The coating matrix is based on organic polymer with phosphorous components, or a poly-phosphate deposit. This coating was distributed uniformly over the surface as shown in figure. This was unlike crystalline structure. The polymer matrix may act as a barrier in dealing the diffusion of moisture into the substrate as compared to conventional phosphate coating.
The coating weight was measured by dissolving the surface coating in alkali solution at 700C. The coating weight varies from 0.01 mg/m2 to 2.5 g/m2.
2. Coating durability:
The coating durability was checked as per Quaker’s specification. The poly-phosphate sheets were folded in a polyethylene sheets and kept inside the Humidity chamber at 500C temperature with 95% RH for 30 days. It was observed that few rust spots have been appeared on the surface. It was comparatively good as compared to oiled samples.
Humidity Test (After 30 days) Indoor Test (After 30 days)
Indoor Test: The test samples were also kept in the indoor atmosphere (inside room) for observing the surface appearance. It was found that the flexo coating sustaining for about 30 days without sign of rust as against 12 days of oiled samples.
APPLICATION OF RASS-O’-NILL-FLEXO ON TUBE
Rusted Tube Tube after Rass-O’-Nil Tube with scale and oil
Details of the evolution, testing the outcome of the deposition affect.
Corrosion occurs in the bare steel sheets and plates as a result of an electrochemical reaction between metal and the moisture present in the atmosphere .
In order to protect steel sheets against atmospheric corrosion, steel industries are using rust preventive oil (RPO) on the steel surface as a temporary measure during storage and transit .
There are many disadvantages pertinent to this practice at customer end such as appearance of red rust when sheet is stored for more than 2 to 3 months. Hence, for further protection, it is essential to use excess RPO on the surface. When oil quantity is in excess on the steel surface, problems related to slipping of the sheets on the conveyor during processing, difficulty in lifting of one sheets from one another due to sticking of sheets and higher consumption of alkali degreasing chemicals for removing excess oil form the sheets are encountered. Therefore, RPO coating of steel sheets are not very compatible with the surface pre-treatment lines in automobile and white good industries.
As a result, manual cleaning of the RPO coating is required prior to processing through different pre-treatment stages such as degreasing, phosphating and painting. If the oil is not completely removed, paint blistering can be experienced during the paint-curing cycle. Alternatively, if the paint is an air-dry paint, the presence of any oils beneath the paint and the steel surface can lead to premature separation of the paint during service .
The presence of the oil also causes a drop in the life of the welding electrode and degrades the quality of the welds . In order to avoid all the above problems, weld primer coating (a thin organic coating) and poly-phosphate ions coating may be the alternate solutions. Keeping all the above matters, the performance of a poly-phosphate ions coating in with nano sized particulate through uniform deposition has been focused on with the following attributes.
1. The coated steel surface will not lose its luster.
2. The coating will be corrosion resistant.
3. The coated steel is easy to handle without any slipping and sticking problem.
4. The Coating will eliminate if necessary zinc phosphate and chromate washing.
5. The coating will be further phosphatable and adheres to paint.
6. The coated steel will be weldable.
7. The coating will help eliminate degreasing and conventional phosphating and to avoid polyethylene sheet during press forming of component and customer end plastic rustling and minimizing environmental pollution.
8. The coated steel without painting will have better store life and appearance during transhipment and high sea exposure.
9. The coating also makes the electrical steel more conductive and effective for specialize electrical application.
2.3 Poly-phosphate ions coating characterization
2.3.1 Surface morphology and chemical bonding evaluation
The coating surface was observed with Scanning Electron Microscopy (SEM) model JXA 6400, JEOL, Japan. The elemental analysis of coating was carried out by energy dispersive spectroscopy (EDX), KEVEX Sigma, USA. The chemical bondings so formed due to this solution were evaluated by Raman spectroscopy and FTIR.
2.3.2 Forming behavior of poly-phosphate ions steel sheet
Erichsen cupping tests were carried out to evaluate the stretch ability of the Rass-O’-Nil Flexo poly-phosphate ions coated steel sheet. Bare steel specimens of the conventional RPO coating and Rass-O’-Nil Flexo poly-phosphate ions coated steel sheets were used for this test. The test included a blank diameter of 50mm (max), a blank holding force of 12.5kN and a drawing speed of 20mm/min. Evaluation of stretch ability was done based on the measured cup height known as limiting drawing height, till the cup fractured. The instrument used is Roll Amsler, BUP-200, Germany. The samples of dimension 250 X 110mm were subjected to this test. The test set up shown in Fig. 1.
2.3.3 Corrosion behaviour
220.127.116.11 Humidity test
The humidity cycle test was conducted as per DIN 51386 and the detail parameters for one cycle are presented in Fig. 2.
The coupons were folded with polyethylene sheets and exposed to humidity cabinet where the following cycle was maintained. Visual observations were made for red rust initiation. This test was carried out for 5 weeks.
Fig. 2. Humidity cycle for coating performance evaluation
2.3.32. Electrochemical Impedance Spectroscopic (EIS)
EIS measurements were done by using EIs-300, Gamry Instrument, USA, where applied potential was 10 mV over a nominal frequency range of 10 kHz in order to understand the coating – electrolyte interfacial behaviour in 3.5% NaCl solution which further helps in evaluating the corrosion resistance. The samples were masked with portaholes (3 cm2 area) and were exposed to the solution.
3.1.3. Raman spectroscopy of Rass-O’-Nil Flexo poly-phosphate ions coating.
Raman spectra were performed in a Renishow-1000 laser Raman spectroscopy instrument in the back scattering configuration at room temperature without vacuum pressure. The excitation source is 514.5 mm Ar-ions laser line. The laser line is in the range of 200 to 4000 cm–1. The laser beam uses a microscope objective of X 500. The spectral resolutions are 1.64cm– 1 and the optical power at the sample is maintained at 5 mw.
It was observed form Fig. 5 that there were two peaks at 1349 cm– 1 and cm– 1 revealing a polymeric Rass-O’-Nil Flexo poly-phosphate ions film on the surface . The peaks at 1349 cm -1 in the Raman spectrum may be confirmed that the films containing amorphous sp2-orbital carbon components, linked to phosphorus atom through oxygen and 1618cm – 1 may be due to Fe – P=O linkage. So may be explained that a high molecular weight carbon chain might be linked to iron substrate through O – P – Fe linkage.
Fig. 6. (a) SEM and (b) EDAX analysis on Rass-O’-Nil Flexo polyphosphate coating
Fig. 7. (a) Microstructure of steel sheet, (b) EDX plot
Fig. 8. Humidity test results of (a) Rass-O’-Nil Flexo poly-phosphate ions coating after 30 days, (b) phosphate coating after4h, (c) RPO coated steel sheet after 30 days.
3.3. Corrosion behavior of coating
3.3.1. Humidity test
The oiled and Rass-O’-Nil Flexo poly-phosphate ions steel samples were exposed humidity cycle test as mentioned in Fig. 2. The result of humidity test on Rass-O’-Nil Flexo poly-phosphate ions coated sheet is shown in Fig. 8. The humidity test result indicated that in case of Rass-O’-Nil Flexo poly-phosphate ions coating the increased resistance to moisture penetration was found superior compared to RPO sample. This manifested in decreased percentage of red rust appearance. This is shown in Table 3.
It was found that after 5 weeks of exposure, the red rust appeared more than 20% in case of RPO coating steel sheets and 10 – 15% appeared in case Rass-O’-Nil Flexo poly-phosphate ions coatings. The coating which shows less than 15% red rust after 4 weeks of exposure is found to be acceptable as per Quaker’s specification . The mechanism of red rust formation due to diffusion of water/moisture through the coating is explained in EIS study.
Red rust appearance in Rass-O’-Nil Flexo poly-phosphate ions coated steel sheet and RPO coated sheet
Time of exposure Rass-O’-Nil Flexo poly-phosphate ions steel sheet red rust, % Phosphated steel sheet red rust, % RPO red rust, %
2 h No Initiated No
4 h No 70 No
7 days No 100 No
14 days No 100 Initiated
21 days No 100 10 – 17
28 days Initiated 100 20 – 25
35 days 10 -15 100 25 -25
Rass-O’-Nil Flexo poly-phosphate ions coating was found to be superior in corrosion resistance compared to rust preventive oil (RPO) and conventional phosphate coating in 3.5% NaCl solution over the exposure time because Rass-O’-Nil Flexo poly-phosphate ions coating was chemically adhered to metal surface through Fe-P bonding as shown by FT-IR and Raman spectra. Therefore, this coating bond is strong and delays diffusion of water to the substrate significantly up to 15 days. In case of RPO and conventional phosphate coating, the diffusion of water is very prominent as there is no chemical bond that existed between substrate and coating interface.
The Rass-O’-Nil Flexo poly-phosphate ions coating capacitance was found constant with the elapse of time up to 15 days when compared to RPO coating and conventional phosphate coating, indicating that free electrolytes are not located at metal/coating interface which are the initiator of the corrosion.
Rass-O’-Nil Flexo Specifications:
• Appearance: Green/Dark Green/Bluish Green
• Specific Gravity: 1.02 to 1.61
• Boiling Point: 100 degrees C at 760 mm of Hg.
• Freezing Point: 16 degrees C
• Maximum Coverage area: One kilogram Rass-O’-Nil covers up to 750 square feet on fresh HR Coil sheet and up to 960 square feet on fresh CRCA sheet. Rass-O’-Nil’s cost per square feet is extremely economical. (By mop) For old and corroded structures the coverage will be lower and heavily rusted metal may require a double coat.
• Durability: Five years at least, from manufacture date, if stored in airtight and suitable containers.
• Drying time: One to ten minutes at ambient temperature.
• Acidity (pH): Mildly acidic (pH: 2.5 to 4.5 in leaching).
• Acidity of aqueous solution: (1% by volume) < 2 pH.
• Flammability: Not flammable.
• Miscibility in water: Miscible
• Loading/Unloading temperature: Ambient
• Storage temperature: Ambient
• Salt spray test: Satisfactory after 40 days exposure. Indian Standard: 13515 ’92 requires 30 days exposure. Satisfactory after 1540 hours exposure (ASTM B-117) with minimum surface treated hot-rolled steel test panels, cleaned of mill scale.
• Drying time: One to 10 minutes when applied on metal surface in normal conditions.
• phosphate deposit weight: After ‘flash’ dipping a clean mild steel plate in RASS-O’-NIL
• One second – 2.2 gm / square metre 15 minutes – 7.7 gm / square metre
• Five seconds – 4.5 gm / square metre 30 minutes -8.0 gm / square metre
• Ten seconds – 5.0 gm / square metre 45 minutes – 7.0 gm / square metre
Safety and physiological data: Rass-O’-Nil products do not harm the skin. A slight irritation may occur on skin contact. Gloves and safety goggles are recommended. Rass-O’-Nil products have no adverse effect on health of the person using them. See the Rass-O’-Nil Material Safety Data Sheet.
Roy Research and Technology, Kolkata, India;
The word-mark RASS-O’-NIL and RASS-O’-NIL graphic with steel-coils are registered trademarks of Roy Research and Technology.