5 Tips Hidup Tanpa Ropol – Perkongsian Terbaik Tuan Norizan

5 Tips Hidup Tanpa Ropol – Perkongsian Terbaik Tuan Norizan

 

Nickel-based Coatings May Slow Corrosion in Solar Power Plants

NREL engineer Judith Gomez-Vital examines several nickel-based coating options to reduce corrosion rates in concentrating solar power plants. Photo by Dennis Schroeder, NREL.

 New research1 from the U.S. Department of Energy’s (DOE) (Washington, DC) National Renewable Energy Laboratory (NREL) (Golden, Colorado) has found a potential nickel-based coating solution to slow corrosion rates at concentrating solar power (CSP) plants. With low-cost thermal storage, these solar power plants enable better electrical distribution and support overall grid reliability, the NREL says.

“We are very excited about the potential implications to provide corrosion-resistant coatings for CSP applications that could improve the economic viability,” says Johney Green, the NREL’s associate laboratory director for mechanical and thermal engineering sciences.

Problems with Molten Salts

To function, CSP plants require high-temperature fluids such as molten salts in the range of 550 to 750 °C to store heat and generate electricity. Molten salts mixtures containing sodium chloride (NaCl), potassium chloride (KCl), and magnesium chloride (MgCl2) are commonly used for both heat transfer fluid and thermal energy storage because they can withstand high temperatures and retain the collected solar heat for many hours.

At those high temperatures, however, the salts can eat away at common iron-nickel (FeNi) alloys such as Incoloy 800H (UNS N08810) and AISI 310 (UNS S31000) stainless steel (SS) used in the heat exchangers, piping, and storage vessels of CSP systems, the NREL explains.

To commercially use the molten salt mixtures, the corrosion rate must be slow—less than 20 μm/y, the NREL says—so that a CSP plant can achieve the projected 30-year service life for its containment materials.

By comparison, bare SS alloys tested in a molten chloride corroded as fast as 4,500 μm/y, the NREL says.

Nickel-based Solutions

To address this problem, NREL engineer and researcher Judith Gomez-Vidal began applying different types of nickel-based coatings, commonly used to reduce oxidation and corrosion, to the SS alloys. For her experiments, the 800H and 310 alloys were polished using abrasive paper until the surface was flat, and then machined to 8 mm in diameter and 12 mm in height. The nickel-based coating deposition was set up to have thicknesses of ~1 mm for electrochemical corrosion tests.

One such nickel coating, NiCoCrAlYTa, comprised of 23.0 wt% Co, 20.0 wt% Cr, 8.5 wt% Al, 0.6 wt% Y, and 4.5 wt% Ta, with the balance Ni, showed very strong performance. It limited the corrosion rate to 190 μm/y—not yet at the goal, but an enormous improvement compared to uncoated SS in the form of a 96% reduction in the corrosion rate.

That particular coating was preoxidized in air at 900 °C for 24 h with a heating/cooling rate of 0.5 °C/min. From there, metallographic characterization of the corroded surfaces using electron microscopy and imaging showed a uniform and dense layer of aluminum oxide (Al2O3) was formed before exposure to the molten chloride system. This, in turn, considerably reduced the alloy’s corrosion.

“The use of surface protection is very promising to mitigate corrosion in molten salts, in particular to those surfaces exposed to chlorine-containing vapor,” Gomez-Vidal says.

The corrosion evaluations were performed at 700 °C in a nitrogen atmosphere using a potentiostat. A Type-K thermocouple in an alumina well was used near electrodes to record temperatures, and the electrochemical cells were sealed and purged with nitrogen for about 24 h before corrosion testing.

Potentials were continuously recorded after the alloy’s immersion in the molten chloride, and polarization studies were conducted immediately after by applying cathodic and anodic external potentials. More than three coupons per test were performed under the same conditions to evaluate the consistency of the results.

“The chromium and aluminum in the coating were preferentially oxidized during preoxidation,” Gomez-Vidal says. “This oxide layer could help increase the corrosion resistance of the coatings. Alumina is a protective oxide with few defects in its structure, which minimizes or avoids the diffusion of elements. Thus, corrosion is controlled or mitigated.”

Further Rate Reductions Needed

Even with the 96% improvement in efficiency, the corrosion rate of 190 μm/y is still significantly more than the target of 20 μm/y or less needed for CSP plants to achieve a 30-year service life. As a result, more research is planned.

“The rates of corrosion are still considerably high for CSP,” Gomez-Vidal says. “This effort highlights the relevance of testing materials durability in solar power applications. More R&D [research and development] is needed to achieve the target corrosion level needed, which could include the synergy of combining surface protection with chemical control of the molten salt and the surrounding atmosphere.”

Further tests will require evaluation of the coatings under thermal cycling and the introduction of oxygen-containing atmospheres to increase the oxidation potential of the systems. The NREL notes that the addition of oxygen ensures the formation of protective scales that could reform in the presence of oxygen if cracks appear during operation.

Similarly, Gomez-Vidal says she has found other projects in which Al2O3 layers are able to form and remain adhered to the surface in the presence of air during thermal cycling of samples.

The research is funded by the DOE’s SunShot Initiative, which is a national effort to drive down the cost of solar electricity and support solar adoption. The program is aimed to make solar energy a low-cost electricity source through R&D efforts with both public and private partners.

The NREL is the DOE’s primary national laboratory for research and development on renewable energy and energy efficiency. The NREL is operated for the DOE by the Alliance for Sustainable Energy, LLC (Lakewood, Colorado) nonprofit group.

Source: NREL, www.nrel.gov. Contact Judith Gomez-Vidal, NREL—email:judith.vidal@nrel.gov.

References

1 “NREL Investigates Coatings Needed for Concentrating Solar Power,” NREL News Releases, Sept. 18, 2017, https://www.nrel.gov/news/press/2017/nrel-investigates-coatings-needed-for-concentrating-solar-power.html (Oct. 11, 2017).

Singapore water pipe bursts caused by corrosion

Bukit Batok water pipe bursts caused by corrosion: PUB

SINGAPORE: The two water pipe bursts in Bukit Batok last week were caused by corrosion in the pipes, the director of PUB’s water supply (network) department Michael Toh said on Wednesday (Oct 4).

Mr Toh was speaking during a site visit to Block 222, Bukit Batok East Avenue 3, where residents saw water shooting up several metres high at a carpark near the block after a water pipe burst last Sunday.

The incident came just days after a water pipe burst at Bukit Batok West, causing a three-storey-high geyser at a traffic junction.

The two leaks resulted in an estimated 7,580 cubic metres of water loss – roughly equivalent to three Olympic-sized swimming pools. About 7,500 cubic metres of water was lost from the first leak, and 80 cubic metres from the second.

As a result of the leaks, PUB will be conducting checks on all 100km of water pipes in Bukit Batok estate. Checks are expected to be completed by next week.

The agency will also replace the pipes in the vicinity of Bukit Batok Street 21, which are about 170m long, by December.

 The pipe that burst at Bukit Batok West measured 700mm in diameter and was one of the major water pipes supplying water to the Bukit Batok estate. It had no prior leaks.

The second pipe at Bukit Batok East – which is smaller at 150mm in diameter -had two leaks on Oct 1 and one leak in 2012.

ACOUSTIC TECHNOLOGY TO TEST FOR LEAKS

Mr Toh explained that each kilometre of Singapore’s 5,500km of water pipes is checked at least once a year. The last time water pipes in the Bukit Batok estate were checked was in January, and no leaks were detected then.

“All our pipes are laid underground; so the challenge for us is how do we have a look underground,” said Mr Toh.

To test for leaks, PUB uses acoustic technology. Data loggers are temporarily attached to pipe valves, where they “listen” for increased noise – which may be an indication that a leak has occurred.

More sensors will also be installed in pipes to detect leaks.

Mr Toh added that PUB takes each incident seriously.

“Every leak is disruptive, and in Singapore’s context water is so precious to us,” he said.

Read more at http://www.channelnewsasia.com/news/singapore/bukit-batok-water-pipe-bursts-caused-by-corrosion-pub-9278262

8 Tips Terokai Pekerjaan Di Luar Bidang Pengajian

Menarik juga article yg zhsarer jumpa ni. Boleh baca keseluruhan article disini;

8 Tips Terokai Pekerjaan Di Luar Bidang Pengajian

Positive Living

Image result for positive living

5 Habits for Positive Living

  1. Believe in yourself
  2. Help someone in need
  3. Live your passion
  4. Get daily inspiration
  5. Be honest

Tazkirah-1

Please Watch Out!

images (1)

Watch your thoughts, they become your Words

Watch your words, they become your Behaviour

Watch your behaviour, they become your Habits

Watch your habits, they become your Values

Watch your values, they become your Character

Watch your character, it becomes your Destiny

 

Really and Excuse

Image result for excuses

If you really want to do something, you will find a way.

If you don’t, you will find an excuse.

Why Metals Corrode

The driving force that causes metals to corrode is a natural consequence of their temporary existence in metallic form. To reach this metallic state from their occurrence in nature in the form of various compounds (ores), it is necessary for them to absorb and store up the energy required to release the metals from their original compounds for later return by corrosion. The amount of energy required and stored varies from metal to metal.

Full article click Why Metal Corrode

Using Scanning Kelvin Probe for Coating and Corrosion Study

 Scanning Kelvin Probe (SKP)

images (1)

Principle

Scanning Kelvin probe (SKP) is a technique allowing a non-contact measurement of the  surface of a metal giving values of corrosion potentials that can be calibrated to a standard scale [1].  The SKP uses a scanning vibrating gold tip as a quasi-reference electrode that enables it to map electrochemical potentials, even beneath a coating, thus allowing potential measurements of corrosion processes occurring in blisters and delaminated areas as well as at defects. SKP allows an image to be constructed that shows the potential distribution on the sample and identifies anodic and cathodic regions at defects and beneath the organic coating. This technique is very useful in corrosion studies around defects as a function of time as it produces results that can be related to the mechanistic description of the process [2].

The scanning Kelvin probe is a vibrating capacitor device used to measure the work function difference between a conducting specimen and a vibrating tip. If an external electrical contact is made between the specimen and the probe, their Fermi levels equalise and the resulting flow of charge produces a potential gradient between the plates, which is equal to the difference in the electronic work function. A variable ‘backing potential’ applied to the circuit is recorded at the unique point where the (average) electric field between the plates vanishes, resulting in a null output signal. For corrosion studies, the scanning Kelvin probe gives the potential of the specimen at that point that can then be calibrated to a standard scale.

Experimental Details

 The KP Technology SKP system is shown in Figure 1. The SKP was operated using a circular silver tip with a 0.5mm flat end. Typically, the probe was set to vibrate at frequency of 60Hz with amplitude of 32μm and a gradient of 300, which gave a tip-sample separation of 64μm at closest approach. Measurements were taken using a sample backing voltage, Vb, in the range of + 5000mV. This instrument uses a non-null technique that calculates the null point from the AC current at two bias values. This also allows automatic height control. For an area scan, the tip starts back left and then moves in a meander pattern, whereas for a line scan the tip start back left and moves in a line until the scan is complete. The SKP data was plotted using Origin 7.0. The area maps are based on 625 measurements and are presented in terms of relative potentials (arbitrary scale).

1

Figure 1 – Schematic of SKP set up (after SKP Technology Ltd)

 Electrochemical Calibration

Calibration of the SKP was carried out by using several cylindrical metal samples (zinc, iron and copper) containing a reservoir of solution. The saturated solutions (ZnSO4 for zinc, NaCl for iron and copper) were poured in the reservoir and connected to a saturated calomel electrode, SCE. The SCE was connected to a voltmeter so the potential reading of the respective metal sample can be recorded. The SKP was then used to take potential measurements at the surface of the solution. Both potentials measured using a voltmeter and SKP were then plotted together to determine the calibration factor. The calibration graph (Figure 2) has a gradient of 1.0434, thus confirming a 1:1 relationship between the electrochemical potential of the corroding metal and work function measured by SKP. The measured offset of 12.932mV can be used to convert the SKP raw data into electrochemical potential vs. SCE.

2

Figure 2 – SKP calibration graph for Zn, Fe and Cu metal standard vs. Ag probe tip

Determination of Coating Performance by SKP

One of the main significant advances of using SKP in coating studies is to better understand corrosion mechanisms under paint as well as the capability to produce maps illustrating potential and current distribution at a defect area. The mechanisms of the delamination process of organic coatings on steel have been investigated using local electrochemical and physical techniques. Stratmann et al. employed a scanning Kelvin probe to measure potential distributions at a buried coating/substrate interface. Their studies were done under accelerated corrosive conditions and minimal surface treatments, therefore the prediction of delamination rate measured was far bigger than the value from commercial technical samples [3]. Reddy, Doherty and Sykes have studied the mechanism of corrosion on a steel panel with a circular scribe defect painted with pigmented coating. They used SKP to examine the corrosion propagation at the defect and its periphery and discovered a reversal of anodes and cathodes at the scribe, beneath the coating. They have suggested that the reversal is due to the accumulation of the corrosion product at the defect. Potential mapping of electrochemical behaviour underneath the coating can lead to better understanding of the mechanism involved in coating breakdown. Later work by the same authors introduced an interpretation of the potential maps in terms of corrosion cells beneath the coating through generation of current maps, as they experienced difficulty from the former in identifying the correct region of electrochemical activity . They concluded that current mapping could reveal patterns of anodic and cathodic activity at a defect and the area surrounding it. As indicated in Figure 3 by the shaded scale next to each map, the lightest areas on the map represents anodic sites, whereas the darker areas represent cathodic sites.

 

34

(a) potential map                                                  (b) current map

Figure 3 –  SKP map for an 60 μm epoxy/talc coating on steel substrate exposed to 3% NaCl solution after 12 hours immersion [4]

References

  1. M. Rohwerder, M. Stratmann,  P. Leblanc, G.S. Frankel, Application of scanning Kelvin probe in corrosion science in Analytical Methods in Corrosion Science and Engineering, P. Marcus and F. Mansfeld (editor) , Taylor & Francis, 2006.
  2. I.D. Baikie, P.J.Estrup, Low cost PC based scanning Kelvin probe. Review of scientific instruments, 1998. 69(11): p. 3902-3907.
  3. K. Ogle, S. Morel, N. Meddahi, An electrochemical study of the delamination of polymer coatings on galvanized steel. Corrosion Science, 2005. 47(8): p. 2034-2052.
  4. B. Reddy, J.M. Sykes, Degradation of organic coatings in a corrosive environment: A study by scanning Kelvin probe and scanning acoustic microscope. Progress in Organic Coatings, 2005. 52(4): p. 280-287.

For my work on using SKP click Investigation of blister formed on coated mild steel using scanning kelvin probe

6look at these beautiful colours came from data by SKP

Skip to toolbar