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The Cyclone Global Navigation Satellite System spacecraft were designed to track hurricanes but they can also monitor microplastics in the oceans. (Image credit: NASA)

A satellite system designed to track hurricanes can reveal where damaging microplastics accumulate in the ocean. A new study now reveals why.

In 2021, researchers from the University of Michigan and Southwest Research Institute found that spacecraft from the Cyclone Global Navigation Satellite System can distinguish areas in the ocean with higher concentrations of microplastics.

From their orbit some 333 miles (536 kilometers) above Earth, these satellites are able to see odd patches in the ocean with smaller and fewer waves, which were found to be areas with high concentrations of microplastics on the surface. In the new study, the researchers have now revealed what exactly is happening in the microplastic-laden water, and they hope the results will make this new satellite monitoring method more reliable.

Microplastics are a huge environmental problem. Less than 5 millimeters across, these minuscule fragments of plastic waste are polluting the entire planet, including the bodies of humans and animals on all continents and in the oceans. Microplastics have been found in drinking water as well as in the food we eat. In the world’s oceans, microplastics are particularly harmful. According to the University of Plymouth(opens in new tab) in the U.K., there are trillions of microplastic particles polluting the marine environments and they are being swallowed up by all kinds of marine creatures from the tiniest plankton to giant whales. These tiny pieces of rubbish are particularly hard to clean up due to their small size, and up until recently were also hard to track, as scientists had to rely on patchy eye-witness accounts.

The new satellite tracking method could improve microplastic monitoring, which in turn could make clean-up efforts easier.

In the new study, researchers from the University of Michigan wanted to test why exactly it is that water thickly polluted with microplastics forms smaller waves. They experimented in a laboratory, creating artificial waves in a small pool. They found that the reason for this reduced wave size in the polluted water is not due to the microplastics alone, and instead is also caused by the presence of surfactants, oily chemicals that these plastics are frequently infused with to alter their properties.

Researchers tested how microplastics affect the ability of water to form waves. (Image credit: Robert Coelius, Michigan Engineering)

“We can see the relationship between surface roughness and the presence of microplastics and surfactants,” Yulin Pan, a naval architecture and marine engineering assistant professor at the University of Michigan and corresponding author on the paper, said in a statement(opens in new tab). “The goal now is to understand the precise relationship between the three variables.”

The researchers want to develop a model that would allow them to not only monitor microplastics from space but also to predict the motion of plastic-polluted water in the ocean.

The study(opens in new tab) was published on Feb. 8 in the journal Scientific Reports.

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Introduction to 4142 alloy steel:
4142 steel is an ultra-high-strength steel with high strength and toughness, good hardenability, no obvious temper brittleness, high fatigue limit, multiple impact resistance after quenching and tempering, and good low-temperature impact toughness. This steel is suitable for manufacturing large and medium-sized plastic molds that require a certain strength and toughness. Usually, surface quenching after quenching and tempering is used as a heat treatment solution.

4142 alloy steel chemical composition:
Carbon C: 0.40～0.45%
Silicon Si: 0.15～0.35%
Manganese Mn: 0.75～1.00%
Sulfur S: ≤0.040%
Phosphorus P: ≤0.035%
Chromium Cr: 0.80～1.10%
Molybdenum Mo: 0.15～0.25%

17-7PH or Type 631 (UNS S17700) is a chromium-nickel aluminum precipitation hardening stainless steel used for spring applications in numerous industries.

7-7 Precipitation hardening alloys can be formed in the soft austenitic state and hardened to high strength levels by low-temperature heat treatment. The low temperature allows for minimal deformation compared to conventional quench and temper hardening processes. In the soft austenitic annealed condition, 17-7 is highly formable and is ideal for operations such as drawing, bending, and end forming. 17-7 is readily weldable in both the annealed and heat-treated conditions.

Element:
Carbon: 0.09 max

Manganese: 1.00 max

Phosphorus: 0.040 max

Sulfur: 0.030 max

Silicon: 1.00 max

Chrome: 16.00 – 18.00

Nickel: 6.50 – 7.75

Aluminum: 0.75 – 1.50

Iron: Balanced

Physical properties:
Melting point: 2550 – 2640°F (1400 – 1450°C)

Density: 0.282 lb/in3 / 7.8 g/cm3

Tensile Modulus of Elasticity (RH 950 and TH 1050): 29.6 X 10 6 psi / 204 GPA

Mechanical behavior:
Condition: annealed
Tensile Strength Minimum (psi): 130,000

Yield Strength Min. 0.2% Offset (psi): 40,000

2″ Elongation Typical: 35%

Hardness: Rockwell B85

Condition: hardened + aged (TH1050)
Typical Tensile Strength (psi): 200,000

Yield Strength Typical 2% Shift (psi): 185,000

% elongation at 2″: 9%

Hardness: Rockwell C40

Condition: hardened, low temperature quenching + aging (RH950)

Typical Tensile Strength (psi): 235,000

Yield Strength Typical 2% excursion (psi): 220,000

% elongation at 2″: 6%

Hardness: Rockwell C48

Condition: Cold Rolled/Worked + Aged (CH900)
Typical Tensile Strength (psi): 265,000

Yield Strength Typical 2% excursion (psi): 260,000

% elongation at 2″: 2%

Hardness: Rockwell C49

heat treatment:
17-7 requires three basic steps in heat treatment:

Austenitic conditioning.

Cooling transforms austenite to martensite

Precipitation hardening to TH 1050 or RH 950 conditions

Alternatively, to obtain the highest mechanical properties from the alloy, the condition A material is transformed to martensite by cold reduction to condition C in the rolling mill. Hardening to condition CH 900 is accomplished by a single low-temperature aging heat treatment.

1. What are martensitic stainless steel and duplex stainless steel?

The microstructure is martensitic at room temperature, and its mechanical properties can be adjusted by heat treatment. In layman’s terms, it is a type of hardenable stainless steel. The steel grades belonging to martensitic stainless steel include 1Cr13, 2Cr13, 3Cr13, 4Cr13, 3Cr13Mo, 1Cr17Ni2, 2Cr13Ni2, 9Cr18, 9Cr18MoV, etc.

2. Commonly used welding methods

Welding Martensitic stainless steel can be welded by various arc welding methods. At present, electrode arc welding is still the main method, but the use of carbon dioxide gas-shielded welding or argon and carbon dioxide mixed gas-shielded welding can greatly reduce the hydrogen content in the weld, thereby reducing the sensitivity of the weld to cold cracking.

3. Common welding materials

(1) Cr13 martensitic stainless steel electrodes and wires

Usually, when the weld has high strength requirements, the use of a Cr13 martensitic stainless steel electrode and wire can make the chemical composition of the weld metal similar to that of the base metal, but the weld has a greater tendency to cold crack.

Precautions:

a. Preheating before welding is required, and the preheating temperature should not exceed 450°C to prevent embrittlement at 475°C. After welding, heat treatment is carried out. The post-weld heat treatment is to cool to 150-200 ° C, keep it warm for 2 hours so that all parts of the austenite are transformed into martensite, and then immediately perform high-temperature tempering, heating to 730-790 ° C, and then holding time is every 1mm plate thickness is 10min, but not less than 2h, and finally air-cooled.

b. In order to prevent cracks, the content of S and P in electrodes and wires should be less than 0.015%, and the content of Si should not be greater than 0.3%. The increase in Si content promotes the formation of coarse primary ferrite, resulting in a decrease in the plasticity of the joint. The carbon content should generally be lower than that of the base metal, which can reduce the hardenability.

(2) Cr-Ni austenitic stainless steel electrodes and wires

The Cr-Ni austenitic steel-type weld metal has good plasticity, which can relieve the stress generated during martensitic transformation in the heat-affected zone. In addition, the Cr-Ni austenitic stainless steel weld has a high solubility for hydrogen, which can reduce the diffusion of hydrogen from the weld metal to the heat-affected zone and effectively prevent cold cracks, so preheating is not required. However, the strength of the weld is low and cannot be improved by post-weld heat treatment.

4. Common welding problems

(1) welding cold crack

Due to the high chromium content of martensitic stainless steel, its hardenability is greatly improved. Regardless of the original state before welding, welding will always produce a martensite structure in the area near the seam. As the hardening tendency increases, the joint is also more sensitive to cold cracking, especially in the presence of hydrogen, and martensitic stainless steel will also produce more dangerous hydrogen-induced delayed cracking.

measure:

1) The cooling rate can be slowed down by using a welding current with a large line energy and a large welding current;

2) For different steel types, the temperature between layers is different, generally not lower than the preheating temperature;

3) Slowly cool to 150-200°C after welding, and perform post-weld heat treatment to eliminate welding residual stress, remove diffused hydrogen in the joint, and improve the structure and performance of the joint.

(2) Embrittlement of the heat-affected zone

Martensitic stainless steel, especially martensitic stainless steel with higher ferrite-forming elements, has a greater tendency for grain growth. When the cooling rate is small, coarse ferrite and carbides are easily produced in the welding heat-affected zone; when the cooling rate is high, the heat-affected zone will harden and form coarse martensite. These coarse structures reduce the plasticity and toughness of the welded heat-affected zone of martensitic stainless steel and cause embrittlement.

measure:

1) Control a reasonable cooling rate;

2) Choose the preheating temperature reasonably, and the preheating temperature should not exceed 450°C, otherwise, the joints may be embrittled at 475°C if they are exposed to high temperatures for a long time;

3) Reasonable selection of welding materials to adjust the composition of the weld to avoid the generation of coarse ferrite in the weld as much as possible.

5. Welding process

1) Preheating before welding

Preheating before welding is the main technological measure to prevent cold cracks. When the mass fraction of C is 0.1%~0.2%, the preheating temperature is 200~260°C, and it can be preheated to 400~450°C for high rigidity weldments.

2) Cooling after welding

After welding, the weldment should not be tempered directly from the welding temperature, because the austenite may not be completely transformed during the welding process. If the temperature is raised and tempered immediately after welding, carbides will precipitate along the austenite grain boundary and austenite Transformation to pearlite produces a coarse-grained structure that seriously reduces toughness. Therefore, the weldment should be cooled before tempering, so that the austenite in the weld and heat-affected zone is basically decomposed. For weldments with low rigidity, it can be cooled to room temperature and then tempered; for weldments with large thickness, a more complicated process is required; after welding, cool to 100-150°C, keep warm for 0.5-1h, and then heat to tempering temperature.

3) Post-weld heat treatment

The purpose is to reduce the hardness of the weld and heat-affected zone, improve plasticity and toughness, and reduce welding residual stress at the same time. Post-weld heat treatment is divided into tempering and complete annealing. The tempering temperature is 650-750°C, hold for 1 hour, and air-cool; if the weldment needs to be machined after welding, in order to obtain the lowest hardness, complete annealing can be used. The annealing temperature is 830-880°C, and the heat preservation is 2 hours. Then air cool.

4) Selection of welding rod

Electrodes for welding martensitic stainless steel are divided into two categories: chromium stainless steel electrodes and chrome-nickel austenitic stainless steel electrodes. Commonly used chromium stainless steel electrodes are E1-13-16 (G202), and E1-13-15 (G207); commonly used chromium-nickel austenitic stainless steel electrodes are E0-19-10-16 (A102), E0-19-10-15 (A107), E0-18-12Mo2-16 (A202), E0-18-12Mo2-15 (A207), etc.

Welding of duplex stainless steel

1. Weldability of duplex stainless steel

The weldability of duplex stainless steel combines the advantages of austenitic steel and ferritic steel and reduces their respective shortcomings.

(1) The sensitivity to hot cracks is much smaller than that of austenitic steel;

(2) The sensitivity to cold cracks is much smaller than that of general low-alloy high-strength steel;

(3) After the heat-affected zone is cooled, more ferrite is always retained, thereby increasing the corrosion tendency and the susceptibility to hydrogen-induced cracking (brittleness);

(4) Duplex stainless steel welded joints may precipitate δ phase embrittlement. δ phase is an intermetallic compound of Cr and Fe. Its formation temperature ranges from 600 to 1000 ° C. Different steel types have different temperatures for forming the δ phase;

(5) Duplex stainless steel contains 50% ferrite, which also has brittleness at 475°C, but is not as sensitive as ferritic stainless steel;

2. Selection of welding method

TIG welding is the first choice for duplex steel welding, followed by electrode arc welding. When submerged arc welding is used, heat input and interlayer temperature should be strictly controlled, and large dilution rates should be avoided.

Notice:

When using TIG welding, it is advisable to add 1-2% nitrogen to the shielding gas (if N exceeds 2%, it will increase the tendency of pores and the arc is unstable), so that the weld metal absorbs nitrogen (to prevent the surface area of the weld from diffusing loss of nitrogen), which is conducive to stabilizing the austenite phase in the welded joint.

3. Selection of welding consumables

Welding consumables with higher austenite-forming elements (Ni, N, etc.) are selected to promote the transformation of ferrite to austenite in the weld.

2205 steel mostly uses 22.8.3L welding rod or wire, and 2507 steel mostly uses 25.10.4L welding wire or 25.10.4R welding rod.

4. Welding points

(1) Control of welding heat process Welding heat energy, interlayer temperature, preheating, and material thickness will all affect the cooling rate during welding, thereby affecting the structure and performance of the weld and heat-affected zone. In order to obtain the best weld metal properties, it is recommended that the maximum interpass temperature be controlled at 100°C. When heat treatment is required after welding, the interpass temperature may not be limited.

(2) Post-weld heat treatment It is best not to heat-treat duplex stainless steel after welding. When heat treatment is required after welding, the heat treatment method used is water quenching. During heat treatment, the heating should be as fast as possible, and the holding time at the heat treatment temperature is 5 to 30 minutes, which should be sufficient to restore the phase balance. Metal oxidation is very serious during heat treatment, and inert gas protection should be considered.

Only two more new solar arrays are to be installed after a successful spacewalk.

The International Space Station (ISS) has a fourth new solar array thanks to the work of two NASA astronauts on a seven-hour spacewalk.

Frank Rubio and Josh Cassada, both flight engineers on the space station’s Expedition 68 crew, again ventured outside of the orbiting complex on Thursday (Dec. 22) to install a new ISS Roll-Out Solar Array (iROSA) to augment the station’s power supply. The spacewalk was a near repeat of the extravehicular activity (EVA) that Rubio and Cassada performed almost three weeks ago, but this time focused solely on a power channel located on the station’s port-side truss.

The two astronauts also reversed roles, with Rubio serving as the lead spacewalker (EV-1) for Thursday’s outing. Rubio and Cassada began the spacewalk at 8:19 a.m. EST (1319 GMT), exiting the U.S. Quest airlock and quickly getting to work on their first assigned tasks. As Cassada set up a foot restraint at the end of the station’s Canadarm2 robotic arm, Rubio configured the cables that they would later connect to tie the new array into the station’s 4A power channel.

NASA astronaut Frank Rubio (in the foreground) transitions along the space station as fellow NASA astronaut and Expedition 68 crewmate Josh Cassada moves an International Space Station (ISS) Roll-Out Solar Array (iROSA) on the end of the Canadarm2 robotic arm during a spacewalk on Thursday, Dec. 22, 2022. (Image credit: NASA TV)

The two astronauts then worked together to free the iROSA from the platform on which it was launched and temporarily stowed on the station. Like the array that was installed on Dec. 3, the 4A iROSA was delivered to orbit by a SpaceX CRS-26 Dragon cargo spacecraft, which arrived at the ISS on Nov. 27.

After Rubio freed the last bolt holding the array in place, Cassada, now positioned at the end of the robotic arm, took hold of the assembly to carry it to its installation site. At the controls of the Canadarm2 was NASA astronaut Nicole Mann, with Koichi Wakata of the Japan Aerospace Exploration Agency (JAXA) coordinating her actions with Cassada outside.

“Just a head’s, Koichi,” radioed Cassada during a break between moves, “that last one stopped a little quickly on me. If you see it ramping up on the next one, can you give me a heads-up? That would be awesome.” Although weightless in the microgravity environment of space, the mass of the 750-pound (340-kg) still had significant inertia when being moved.

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Rubio transitioned along the truss to meet Cassada at the P4 site. The two spacewalkers then unfolded the iROSA from its launch configuration and then secured the array atop a mounting bracket installed on an earlier EVA. Using a power tool specifically designed for astronauts to use on spacewalks, Rubio tightened the four bolts on the right and left sides of the iROSA to hold the assembly open.

After waiting for the space station to be in “eclipse,” or when it was in the shadow of Earth, such that the existing solar array wings were not producing electricity, Rubio and Cassada then integrated the iROSA into the 4A power channel by attaching cables connecting the new array to the station.

A new International Space Station (ISS) Roll-Out Solar Array (iROSA) unfurls in front of the legacy 4A solar array wing, augmenting the power for the orbiting complex. (Image credit: NASA TV)

At that point, all that was left to do was let the iROSA unfurl. With the release of two bolts, the potential energy stored by the rolled-up carbon composite booms caused the array to unroll on its own to its full 63-foot (19-meter) length with no motor needed.

“We can finally run that microwave we’ve wanted to run,” said Cassada, joking about the extra power from the new array.

The whole process took about 10 minutes. Cassada tightened two bolts to stiffen the array and its installation was complete.

The ISS Roll-Out Solar Arrays are being installed in front of, and partially overlaying, slightly-degraded, existing solar panel wings. When used in tandem and once all six iROSAs are in place, the upgraded power system will increase the space station’s electricity supply by 20 to 30 percent.

Cassada and Rubio completed the spacewalk by cleaning up and taking inventory of their tools before reentering the airlock at 3:27 p.m. EST (2027 GMT), seven hours and eight minutes after they began the EVA.

Thursday’s excursion had been scheduled for Wednesday but was delayed a day because the space station needed to be maneuvered away from an approaching piece of Russian rocket debris. It was the third spacewalk for both Rubio and Cassada. They now have logged 21 hours and 24 minutes working the vacuum of space.

The EVA was the 12th for the year, the fourth for Expedition 68, and the 257th since 1998 in support of the assembly and maintenance of the ISS.