Ecologically friendly conversion coatings with special wetting behaviors for wax prevention

RSC Advances ◽  
2016 ◽  
Vol 6 (31) ◽  
pp. 26045-26054 ◽  
Author(s):  
Weitao Liang ◽  
Liqun Zhu ◽  
Chang Xu ◽  
Weiping Li ◽  
Huicong Liu
Keyword(s):  
Conversion Coating ◽  
Schematic Diagram ◽  
Conversion Coatings ◽  
Wax Deposition ◽  
Sem Image ◽  
Wetting Behaviors ◽  
Deposition Test

(A) SEM image of the Zn coating; (B) SEM image of the conversion coating; (C) schematic diagram of the Zn coating in the wax deposition test; and (D) schematic diagram of the conversion coating in the wax deposition test.

scholarly journals Effect of Temperature on Corrosion Resistance of Layered Double Hydroxides Conversion Coatings on Magnesium Alloys Based on a Closed-Cycle System

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1658
Author(s):  
Xiaochen Zhang ◽  
Zhijuan Yin ◽  
Bateer Buhe ◽  
Jiajie Wang ◽  
Lin Mao ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Chemical Composition ◽  
Photoelectron Spectroscopy ◽  
Conversion Coating ◽  
Effect Of Temperature ◽  
Conversion Coatings ◽  
Closed Cycle ◽  
Cycle System ◽  
Double Hydroxide ◽  
Double Hydroxides

The effect of temperature on the corrosion resistance of layered double hydroxide (LDH) conversion coatings on AZ91D magnesium alloy, based on a closed-cycle system, was investigated. Scanning electron microscopy (SEM), photoelectron spectroscopy (XPS), and X-ray diffractometry (GAXRD) were used to study the surface morphology, chemical composition, and phase composition of the conversion coating. The corrosion resistance of the LDH conversion coating was determined through electropotentiometric polarisation curve and hydrogen evolution and immersion tests. The results showed that the conversion coating has the highest density and a more uniform, complete, and effective corrosion resistance at 50 °C. The chemical composition of the LDH conversion coating mainly comprises C, O, Mg, and Al, and the main phase is Mg6Al2(OH)16CO3·4H2O.

RF Test Article Experiment on the Impact of Non-Hexavalent Chromium-Based Conversion Coatings on Electrical Assemblies

2018 ◽  
Vol 2018 (1) ◽  
pp. 000712-000717
Author(s):  
Joshua S. Petko ◽  
Philip A. Lovell ◽  
Jeremy D. Clifton ◽  
Alexander J. Bersani ◽  
Karl F. Schoch
Keyword(s):  
Hexavalent Chromium ◽  
Conversion Coating ◽  
Type I ◽  
Type Ii ◽  
Conversion Coatings ◽  
Environmental Testing ◽  
Rf Test ◽  
Test Article ◽  
And Performance ◽  
The Impact

Abstract Conversion coatings are treatments applied to aluminum structures to inhibit corrosion while maintaining electrical conductivity. In aerospace applications, the most common type of conversion coatings (MIL-DTL-5541 Type I) contain hexavalent chromium compounds as the corrosion-inhibiting agent. These Type I conversion coatings have a long pedigree and are highly effective in preventing corrosion; however, the hexavalent chromium compounds in these coatings are carcinogenic and water-soluble. Therefore, the use of these compounds is highly regulated in order to protect both workers and the public, leading to high cost in both use and disposal. Regulations are also beginning to restrict outright use, where new designs for the DOD are prohibited from using Type I coatings by DFARS 48 CFR Parts 223 and 252 and all use has been prohibited by Europe by REACH regulations since September 2017. In response, more environmentally friendly non-hexavalent chromium-based processes, referred to as MIL-DTL-5541 Type II conversion coatings, have become available. However, the long term reliability and performance impacts resulting from the use of these coatings are not fully understood and there is an ongoing effort in the aerospace industry organized by NASA to fully define these impacts while hardware is still in the design stage. While significant work has been performed to define the corrosion performance of various type-II conversion coatings, there has been minimal work performed to quantify the impact a type-II conversion coating would have on RF electrical assemblies. The standard methodologies defined by MIL-DTL-81706B have significant limitations and cannot fully capture the impact at microwave frequencies. For this reason, an investigation is underway at Northrop Grumman to quantify the impact these coatings may have on the quality, reliability, and performance of our electronic systems. At IMAPS 2017, Northrop Grumman introduced a RF test article designed to assess the longitudinal impact a Type II conversion coating would have on RF electrical assemblies where plated printed wiring boards (PWBs) and aluminum structures come in intimate contact. The test article features a specialized suspended stripline/microstrip stepped impedance filter designed to de-tune in the presence of galvanic corrosion. This talk follows the work presented in IMAPS 2017 by discussing an experiment where three different populations of test articles, each coated with a different type of conversion coating, are subjected to environmental testing. This talk also discusses how an initial measurement of these test articles before environmental exposure showed little difference between these populations. Finally, this talk reviews the initial results of this experiment, discussing environmental testing and the RF measurements captured during these tests.

Experimental Assessment of Microwave Loss Caused by Non-Hexavalent Chromium-Based Conversion Coatings

2017 ◽  
Vol 2017 (1) ◽  
pp. 000146-000150
Author(s):  
Joshua S. Petko ◽  
Philip A. Lovell ◽  
Jeremy D. Clifton ◽  
Paul H. Cohen ◽  
Karl F. Schoch
Keyword(s):  
Hexavalent Chromium ◽  
Environmental Exposure ◽  
Conversion Coating ◽  
Type I ◽  
Type Ii ◽  
Conversion Coatings ◽  
Test Methodology ◽  
Microwave Loss ◽  
Chromium Compounds ◽  
The Impact

Abstract Conversion coatings are used to inhibit corrosion on aluminum structures while maintaining electrical conductivity. The most common type of conversion coatings in aerospace applications (MIL-DTL-5541 Type I), contain hexavalent chromium compounds as the corrosion-inhibiting additive. These Type I conversion coatings have a long pedigree and are highly effective in preventing corrosion; however, the hexavalent chromium compounds in these coatings are carcinogenic and water-soluble. Therefore, the use of these compounds is highly regulated in order to protect both workers and the public leading to high cost in both use and disposal. In addition to these regulations, use of these materials on new designs for DOD is prohibited by DFARS 48 CFR Parts 223 and 252, and is scheduled to be prohibited in Europe in September 2017 by REACH regulations. In response, new more environmentally friendly non-hexavalent chromium-based processes are becoming available. Coatings resulting from these types of processes are referred to as MIL-DTL-5541 Type II conversion coatings. The long term reliability and performance impacts resulting from the use of these coatings are not fully understood and there currently is an effort in the aerospace industry organized by NASA to fully define these impacts while hardware is still in the design stage. While significant work has been performed to define the corrosion performance of various type-II conversion coatings, there has been minimal work performed to quantify the impact a type-II conversion coating would have on RF electrical assemblies. Of particular interest is the impact a conversion coating can have on microwave loss at higher frequencies. Many RF electrical assemblies use aluminum radiator and waveguide structures to transfer energy between components and radiate into freespace. If microwave losses increase due to a change in conversion coating, there could be negative impacts to key performance parameters such as system sensitivity, dynamic range, noise figure, and radiated power. Understanding this impact is critical in determining whether the design change impact is isolated only to the conversion coating or whether it propagates to other subcomponents to compensate for the loss in performance. The standard way to quantify the electrical resistance of conversion coatings is defined by MIL-DTL-81706B. The test involves collecting a DC resistance measurement on a processed panel using a two-probe measurement with 200 psi of pressure applied to the probes. The resulting value is averaged from 10 samples of data collected across the panel. While this test in MIL-DTL-81706B is well defined, it has significant limitations that caused this research to seek another way to quantify this value. First, the repeatability of the two-point probe is not consistent across the panel. Some of the conversion coatings can be brittle and can easily be disturbed by the force applied by the probes. The poor repeatability is exacerbated when the test articles are environmentally exposed, leaving a non-uniform surface. Finally, this test methodology is performed at DC, which does not directly quantify the impact of the coating at microwave frequencies due to phenomena such as skin effect and potential plasmonic response. This talk discusses an experiment performed to assess the impact of the use of type-II conversion coatings on microwave loss. In order to assess this impact, a set of precision machined waveguide structures were used as test articles in the experiment. The advantage of using this waveguide-based approach is that it provides a distributed surface to assess the average impact of conversion coatings on surface resistivity. This average resistivity more closely maps to the RF losses seen by microwave systems. In addition, testing the waveguide test article provides a very repeatable test methodology; waveguide technology is very mature from a manufacturing perspective. Also, the waveguide flanges provide a repeatable way to connect to the test article so long as they are masked or cleaned after any potential environmental exposure. Finally, the rectangular shape of the waveguide can be canonically described by a closed form expression, improving understanding of the specific mechanisms leading to the loss. This talk discusses an experiment where multiple 3-foot pieces of WR-28 were used as test articles. The WR-28 test articles were chosen to assess the impact to performance at Ka-band. The 3-foot sections are convenient articles because they can easily be measured on a workbench while at the same time being electrically long at Ka-band (on the order of 100 wavelengths). This talk discusses three different populations of test articles, each coated with a different type of conversion coating. This talk also discusses how an initial measurement of these test articles before environmental exposure showed little difference between these populations. Finally, this talk will discuss plans for environmental testing and in-process RF measurements to be captured during these tests.

RF Test Article to Assess the Impact of Non-Hexavalent Chromium-Based Conversion Coatings on Electrical Assemblies

2017 ◽  
Vol 2017 (1) ◽  
pp. 000046-000051 ◽  
Author(s):  
Joshua S. Petko ◽  
Philip A. Lovell ◽  
Jeremy D. Clifton ◽  
Paul H. Cohen ◽  
Karl F. Schoch
Keyword(s):  
Hexavalent Chromium ◽  
Galvanic Corrosion ◽  
Ground Plane ◽  
Conversion Coating ◽  
Type I ◽  
Type Ii ◽  
Conversion Coatings ◽  
Rf Test ◽  
Test Article ◽  
The Impact

Abstract Conversion coatings are used to inhibit corrosion on aluminum structures while maintaining electrical conductivity. The most common type of conversion coatings in aerospace applications (MIL-DTL-5541 Type I), contain hexavalent chromium compounds as the corrosion-inhibiting additive. These Type I conversion coatings have a long pedigree and are highly effective in preventing corrosion; however, the hexavalent chromium compounds in these coatings are carcinogenic and water-soluble. Therefore, the use of these compounds is highly regulated in order to protect both workers and the public leading to high cost in both use and disposal. In addition to these regulations, use of these materials on new designs for DOD is prohibited by DFARS 48 CFR Parts 223 and 252, and is scheduled to be prohibited in Europe in September 2017 by REACH regulations. In response, new more environmentally friendly non-hexavalent chromium-based processes are becoming available. Coatings resulting from these types of processes are referred to as MIL-DTL-5541 Type II conversion coatings. The long term reliability and performance impacts resulting from the use of these coatings are not fully understood and there currently is an effort in the U. S. aerospace industry organized by NASA to fully define these impacts while hardware is still in the design stage. While significant work has been performed to define the corrosion performance of various Type II conversion coatings, there has been minimal work performed to quantify the impact a Type II conversion coating would have on RF electrical assemblies where plated printed wiring boards (PWBs) and aluminum structures come in intimate contact. The primary concern for these assemblies is that these junctions are inherently susceptible to galvanic corrosion; PWBs are clad with copper, which is highly cathodic while aluminum is highly anodic. In order to reduce the potential for galvanic corrosion, PWBs in DOD applications are typically plated with SnPb coating which is less cathodic than the copper. In addition, an immersion bath is used to coat the aluminum with a conversion coating that is less anodic. Changes to the conversion coating could increase the galvanic corrosion occurring at this junction. In addition, RF signals may also be negatively impacted by changes to the electrical resistivity and parasitic capacitances caused by changes to this junction. For this reason, it is highly desirable to create a RF test article that is highly sensitive to the impacts of galvanic corrosion at the junctions of passivated aluminum and plated printed wiring boards. This talk discusses a RF test article that is designed to assess the longitudinal impact of galvanic corrosion on electrical assemblies. The test article features a specialized suspended stripline/microstrip stepped impedance filter that is designed to de-tune in the presence of galvanic corrosion. The design of this filter uses a pair of machined aluminum housings to sandwich a thin two sided printed wiring board. The high-impedance sections of the filter employ cavities above and below the thin PWB to create an effective airstripline transmission line. The low-impedance sections of the filter employ a PWB ground plane to create a microstrip mode. Small aluminum feet are machined in the bottom aluminum housing to create an electrical contact between the aluminum housing and PWB ground plane. These feet are designed to function as sacrificial elements that corrode away in the presence of galvanic corrosion, creating series capacitance in the ground signal path. This talk reviews recent test results that show how the response of this specially designed filter changes in the presence of galvanic corrosion and compares these results with electrical simulations. This talk also discusses how information gained from the filter response can be used to assess the electrical impact of Type II conversion coatings. Finally, this talk will discuss the experimental design needed to quantify the impact of Type II conversion coatings with respect to the current baseline processes.

Evaluation of Environmentally Friendly Zr Based Nano Structured Conversion Coating for HRS (Hot Rolled Steel) in Powder Coating

2009 ◽  
Vol 283-286 ◽  
pp. 316-322 ◽  
Author(s):  
Bulent Tepe ◽  
Banihan Gunay
Keyword(s):  
Heavy Metal ◽  
Ambient Temperature ◽  
Contact Time ◽  
Environmentally Friendly ◽  
Powder Coating ◽  
Conversion Coating ◽  
Rolled Steel ◽  
Conversion Coatings ◽  
Hot Rolled ◽  
Hot Rolled Steel

Metals, despite their deterioration in a corrosive atmosphere, continue to dominate the automotive, agricultural, furniture, process and appliance industries and HRS (Hot Rolled Steel) plays a significant role in those areas. Powder coating on HRS is widely employed for protective and aesthetic purposes. Prior to powder coating, phosphating conversion coating is often used to increase effectiveness of protection. However, due to tightening environmental legislations, phosphating process is now problems for industry. Therefore, newly developed environmentally friendly conversion coats are introduced to industry. In this study a new environmentally friendly zirconium fluoro-based (H2ZrF6) generation of conversion coating has been introduced to replace the conventional phosphating conversion coatings process. It is deposited on the surface with a thin nanometre range, therefore shortening the process, which also has advantages such as being free of heavy metal and operating in low or ambient temperature. The present work closely examines Zr based nano structured conversion coatings for HRS. Extensive corrosion and adhesion studies are carried out on differently prepared HRS test panels, pre-treated with Zr based conversion coating in various conditions, such as different composition ratio, temperature and contact time.

Properties of Conversion Coating of Magnesium Alloys by a Phosphate-Permanganate Solution

2005 ◽  
Vol 488-489 ◽  
pp. 665-668 ◽  
Author(s):  
Shu Sen Wu ◽  
Ming Zhao ◽  
Ji Rong Luo ◽  
You Wu Mao
Keyword(s):  
Corrosion Resistance ◽  
Magnesium Alloys ◽  
Adhesion Force ◽  
Conversion Coating ◽  
Resistance Test ◽  
Az91d Alloy ◽  
Conversion Coatings ◽  
Good Adhesion ◽  
Better Than

A chromium-free conversion coating for AZ91D magnesium alloys has been obtained by using a phosphate-permanganate solution. Examinations have been carried out on the conversion coating for morphology, composition, adhesion force and corrosion resistance. Results show that the conversion coatings are relatively uniform and continuous, with thickness from 7µm to 10µm. They exhibit good adhesion to matrix and have some non-penetrate tiny holes on the surface. The main elements of the conversion coating of AZ91D alloy are Mg、O、P、K、Al、Mn. Results of corrosion resistance test indicate that the corrosion resistance of the conversion coating by phosphate-permanganate solution is in match to that of the conversion coating formed in a chromate solution, but for the corrosion resistance after painting, the former is better than the later.

A New Rust Conversion Coating and its Working Mechanism in Rust Remove and Painting

2014 ◽  
Vol 484-485 ◽  
pp. 12-16 ◽  
Author(s):  
Hai Yan Hu ◽  
Xi Qiu Fan ◽  
Qing Shan Ji
Keyword(s):  
Conversion Coating ◽  
Conversion Coatings ◽  
Working Mechanism ◽  
Series Of Experiments ◽  
Corrosion Science

In this study we prepared a new rust conversion coating and examined its corresponding characteristics through a series of experiments. And at the end of the paper, we summarized the working mechanism of it. All the results may help to promote the development of rust conversion coatings and anti-corrosion science.

Characterization and Corrosion Studies of Amorphous/Nanocrystalline Conversion Coatings Formed by Applying Static Magnetic Field on AZ91 D Magnesium Alloy

2011 ◽  
Vol 189-193 ◽  
pp. 805-809 ◽  
Author(s):  
Ming Zhao ◽  
Liang Zhu ◽  
Guang Ping He
Keyword(s):  
Magnetic Field ◽  
Magnesium Alloy ◽  
Static Magnetic Field ◽  
Nanocrystalline Structure ◽  
Amorphous Structure ◽  
Conversion Coating ◽  
Conversion Coatings ◽  
Artificial Defect ◽  
Az91d Magnesium Alloy ◽  
Electrode Technique

The present work explores an environmental friendly method for forming conversion coatings on AZ91D magnesium alloy by applying a static magnetic field. An amorphous / nanocrystalline conversion coating was developed on magnesium alloys in a phosphate-permanganate aqueous solution under a 0.5 Tesla magnetic field. The examinations of the microstructure and phase compositions reveal that the conversion coating is composed of an amorphous structure and nanocrystalline structure with mean size less than 10 nm. In a corrosive chloride solution, the amorphous/nanocrystalline conversion coating with an artificial defect were investigated by scanning vibrating electrode technique (SVET)/ scanning ion-selective electrode technique (SIET) system. The micro-electrochemical results reveal that the amorphous / nanocrystalline conversion coating as a good barrier layer can provide effective corrosion protection for AZ91D magnesium alloy.

Evaluation of the Growth Mechanism of Ti-Containing Conversion Coatings Using XPS

2015 ◽  
Vol 227 ◽  
pp. 159-162 ◽  
Author(s):  
Wlodzimierz Tylus ◽  
Juliusz Winiarski ◽  
Bogdan Szczygieł
Keyword(s):  
Chemical Composition ◽  
Deposition Time ◽  
Fold Increase ◽  
Weak Acid ◽  
Conversion Coating ◽  
Mechanical Resistance ◽  
Time Interval ◽  
Conversion Coatings ◽  
Electrogalvanized Steel ◽  
Mechanical Properties And Corrosion

Ti-containing coatings as chromate replacement were prepared on electrogalvanized steel. Zinc coatings were deposited from a weak acid chloride bath. Cr-free conversion coatings were deposited from bath composed of: TiCl3, H2SiF6, H2O2 and oxalic acid. XPS was used to evaluate chemical composition of the coatings as a function of deposition time. Deposited coating were of conversion type. Regardless of the achieved conversion coating thickness, Zn from the substrate was always present. In the coatings were identified: Zn2SiO4 / Zn4Si2O7(OH)2, ZnTiO3, ZnO, Zn (OH)2, Zn0, SiOx and Ti-O-Si in varying proportions. The chemical composition of the outer surface of the coating depended on deposition time, e.g. in a time interval 0-300 s 30 fold increase of the Si:Ti ratio and 20 fold of the Si:Zn ratio were observed. Estimated thickness of conversion coating was 3, 14, 35, and 100 nm for the time deposition of 1, 40, 80 and 300 s respectively. It is the proposed model for distinguishing Zn (0) phase from Zn (2+) quantitatively, based on the Zn L3M45M45 spectrum. The composition of the ZnTiSi conversion coating determined its mechanical properties and corrosion resistance. Standard tests carried out showed that the coatings obtained at the time of 20-40 s had the best corrosion performance and mechanical resistance

EIS Study of Molybdate Conversion Coatings Formed on AZ91D Magnesium Alloy

2011 ◽  
Vol 189-193 ◽  
pp. 279-285
Author(s):  
Li Ping Wu ◽  
Zhong Dong Yang
Keyword(s):  
Corrosion Resistance ◽  
Charge Transfer ◽  
Magnesium Alloy ◽  
Charge Transfer Resistance ◽  
Conversion Coating ◽  
Conversion Coatings ◽  
Bath Composition ◽  
Optimum Conditions ◽  
Transfer Resistance ◽  
Az91d Magnesium Alloy

An environmentally friendly molybdate conversion coating based surface treatment was developed for AZ91D magnesium alloy. The EIS technique was employed to study the effects of the conversion bath composition and temperature on the corrosion protection performance of molybdate conversion coatings on AZ91D magnesium alloys. The optimum conditions under which obtained conversion coatings showed the best corrosion resistance were determined. The Nyquist results showed that the value of charge transfer resistance increased by 22.5 times for the sample treated in the optimized molybdate conversion bath.

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