KR20200036492A - Superhydrophobic - superoleophilic nickel foams and method for making same - Google Patents

Abstract

The present invention relates to a superhydrophobic-superoleophilic nickel foam coated with a coating mixture comprising polytetrafluoroethylene (PTFE) and hydrophobic fumed silica, as well as a method for preparing the same. The method for preparing a superhydrophobic-superoleophilic nickel foam comprises steps of: preparing slurry; providing a nickel foam to be coated with the slurry; and dip coating the nickel foam with the slurry. According to the present invention, the nickel foam may be coated with a coating mixture comprising polytetrafluoroethylene (PTFE) and hydrophobic fumed silica to prepare a superhydrophobic-superoleophilic nickel foam, thus having an effect of facilitating a separation between water and oil.

Description

Superhydrophobic-superoleophilic nickel foam and its manufacturing method {SUPERHYDROPHOBIC-SUPEROLEOPHILIC NICKEL FOAMS AND METHOD FOR MAKING SAME}

The present invention relates to a method for producing a nickel foam having a superhydrophobic-superoleophilic function, and more particularly, to a method for producing a nickel foam having a superhydrophobic-superoleophilic function using a simple dip coating method.

Technology for separating water and oil due to environmental pollution due to oil spill is being studied more and more, and the effect of oil spill on the environment has been studied and reported. These water and oil mixtures are emanating from a variety of industrial sectors such as the petroleum, manufacturing, mining, metal processing and processing industries, textiles, leather processing and processing industries, food processing and restaurants, where the oils contained are dispersed fine oil particles. Due to this, it is very difficult to separate energy intensively. In particular, the massive oil spills from accidents such as the Deepwater Horizon spill in the Gulf of Mexico required a robust and economical way to separate the mass-produced oil and water mixtures. One method for separating water and oil mixtures was the use of superoleophilic and superhydrophobic surfaces, which have recently attracted attention. After studying the surface chemistry of the lotus leaf by Barthlott and Neinhuis, a super hydrophobic material was prepared. This is mostly possible by lowering the surface free energy or increasing the surface roughness of the solid, and the superhydrophobic surface manufacturing method used so far is dip coating, electrospinning, electrochemical deposition, electroless deposition, self-assembly by layer, chemical angle, It was possible to separate water and oil using a superhydrophobic / superoleophilic mesh manufactured using chemical vapor deposition. It also joined rough separation, such as industrial wastewater. The efficiency of separation depended on a combination of factors including, but not limited to, fluid viscosity, pore size, surface tension and fluid flow rate. However, the superhydrophobic / superoleophilic mesh made of the existing polyurethane (PU) sponge has excellent separation efficiency during continuous flow, but due to its high flexibility, it has a disadvantage that it cannot support the weight when the process is increased. Therefore, there is a need for an invention for a superhydrophobic / superoleophilic binder that can overcome the weight of adsorbed oil and maintain its existing function.

G. Kwon, E. Post, A. Tuteja, Membranes with selective wettability for the separation of oil / water mixtures, MRS Communications, 5 (2015) 475-494. A. S. K. Kumar, S. S. Kakan, and N. Rajesh, A novel amine impregnated graphene oxide adsorbent for the removal of hexavalent chromium, Chem. Eng. J., 230 (2013) 328-337.

The object of the present invention is to overcome the weight of the absorbed oil while overcoming the weight of the absorbed oil by dip-coating the binder mixture for oil / water separation in a foam foam having stronger rigidity than a superhydrophobic / superoleophilic binder made of a conventional polyurethane (PU). It is to provide a foam that can serve as a binder for oil / water separation of.

In order to achieve the above object, the present invention is to prepare a superhydrophobic-superoleophilic nickel foam and slurry coated with a coating mixture comprising polytetrafluoroethylene (PTFE) and hydrophobic fumed silica. , Preparing a nickel foam to be coated with the slurry, and dip coating the nickel foam to the slurry provides a superhydrophobic-superoleophilic nickel foam production method.

According to the present invention as described above, by coating a nickel foam foam with a coating mixture comprising polytetrafluoroethylene (polytetrafluoroethylene, PTFE) and hydrophobic fumed silica (hydrophobic fumed silica), superhydrophobic-superoleophilic nickel foam can be produced There is an effect to facilitate the separation of water and oil through this.

1 shows a schematic view of the preparation step and coating process of the nickel foam.
FIG. 2 shows an image of each of the uncoated nickel foam and the coated nickel foam and each FE-SEM image, and also shows the TGA analysis values of the coated nickel foam.
Figure 3 shows the wettability test results for water and hexane of the nickel foam and the non-coated nickel foam and the contact angle image of different aqueous solutions.
4 shows a process in which oil and water mixtures are separated from each other through coated nickel foam.
5 illustrates separation efficiency of the coated nickel foam, separation efficiency according to cycle time, water contact angle (WCA), and flow rates for different oils.
6 shows a schematic diagram of a liquid wetting model in a coated nickel foam.

Hereinafter, the present invention will be described in detail.

According to an embodiment of the present invention, a superhydrophobic-superoleophilic nickel foam (Ni foam) coated with a coating mixture containing polytetrafluoroethylene (polytetrafluoroethylene, PTFE) and hydrophobic fumed silica (hydrophobic fumed silica) is provided.

The coating mixture may further include polyvinylidenefluoride (PVDF).

The polytetrafluoroethylene may be 60 wt% compared to 100 wt% of the coating mixture.

The hydrophobic fumed silica may be silica treated with a silanol group on the surface, and may be 20 wt% compared to 100 wt% of the coating mixture.

The polyvinylidene fluoride may be dissolved in 8% by weight of DMSO.

The nickel foam (Ni foam) is porous,

The porosity may have a three-dimensional structure interconnected.

The nickel foam (Ni foam) may have an intrusion pressure of 7.5 to 8.0 kPa.

The present invention provides a method for producing superhydrophobic-superoleophilic nickel foam according to another aspect.

The superhydrophobic-superoleophilic nickel foam production method may include preparing a slurry, preparing a nickel foam to be coated with the slurry, and dipping the nickel foam into the slurry.

The slurry may include polytetrafluoroethylene (PTFE), hydrophobic fumed silica, and polyvinylidenefluoride (PVDF).

The polytetrafluoroethylene (polytetrafluoroethylene, PTFE) and hydrophobic fumed silica (hydrophobic fumed silica) and polyvinylidene fluoride (polyvinylidenefluoride, PVDF) mixing ratio may be 60: 20: 20 wt% weight ratio.

The polyvinylidene fluoride (PVDF) may be dissolved in 8 wt% of DMSO.

The manufacturing of the slurry may further include ball grinding.

The nickel foam has a pore size of 250 to 450 μm, a non-uniform porous structure, and the porous structure may be an interconnected three-dimensional structure.

The step of preparing the nickel foam may further include ultrasonic washing the nickel foam with acetone, ultrasonic etching the ultrasonic foam with the HCl solution, and drying.

In the dip coating step, the step of immersing the nickel foam in the slurry and the step of drying the immersed nickel foam in the oven may be repeated three times.

Nickel foam (Ni foam) has recently been used as a substrate for oil moisture separation material because it is a porous material having a low density, high mechanical performance and high thermal stability. In addition, since nickel foam has a multi-linked structure, nickel foam impregnated with superhydrophobic and superoleophilic was able to effectively perform multi-layer separation of water and oil mixtures. In addition, the advantage of using a metal foam instead of a non-metallic sponge is that it supports the weight of more oil than a polyurethane (PU) sponge. PU sponges have good separation efficiency during continuous flow of water and oil mixtures, but due to their high flexibility, the process becomes larger and longer and thus unable to support its weight. Therefore, in order to overcome these drawbacks, a metal foam was selected as a nickel foam, and in fact, the nickel foam provided stiffness to overcome the weight of the adsorbed oil.

PTFE was used because of its low surface energy and hydrophobic fumed silica (R805) to increase the surface roughness. PVDF is a hydrophobic fluorinated polymer with low free energy, thermal stability, wear resistance, chemical inertness and mechanical properties. Since the adhesion to the PVDF metal surface is strong, it is used as a binder in the preparation of the lithium ion battery electrode, and thus, in the present invention, it serves to lower the binder and the surface energy.

The dip coating method is simple and fast and does not require the use of expensive reagents such as fluoroalkyl silanes, yet the coated nickel foam produced through Examples 1 to 3 can create a surface that is coactively covered with flororine, making it rough and A solid connection structure was created to improve super hydrophobicity.

Experimental substrates used to carry out the examples are poly vinylidene uoride in powder form (PVDF, MW = 534,000), polytetrafluoroethylene in powder form (PTFE, FW = 100.0), AEROSIL fumigated modified silica (R805) and nickel foam (volume density: 0.32 g / cm ³ , thickness 1.35 mm, average pore diameter: 130 μm, pore number: 110 PPI) was purchased from Sigma Aldrich. Calcium chloride (99.0%), potassium hydroxide (at least 85.0%), hydrochloric acid (35.0 to 37.0%), hexane (at least 95.0%) and dimethyl sulfoxide (DMSO) were purchased from Deoksan reagent, Olitania Extra Virgin Olive Oil And soybean oil were purchased from local markets. All chemicals were used as is without further purification, and deionized water was prepared using AquaMax-Ultra deionized water.

Hydrophobic R805 forms agglomerates by forming hydrogen bonds between fumed silica particles through surface silanol groups group treatment, and these agglomerates form -CF2- groups and hydrophobic chains of R805 (-C ₈ H ₁₇ ) in PTFE and PVDF. It has strong adhesion to PTFE and PVDF due to the attraction of van der Waals forces due to its presence. These small agglomerates dispersed in the coating mixture resulted in a roughened surface, improving super hydrophobicity.

Hereinafter, the present invention will be described in more detail through examples. These examples are only for illustrating the present invention, it will be apparent to those skilled in the art that the scope of the present invention is not to be construed as limited by these examples.

Example 1. (Preparation of dip-coating mixture)

60 wt% of PTFE, 20 wt% of R805, and 20 wt% of PVDF were mixed, and the PVDF was dissolved in 8 wt% of DMSO. And when mixing the above materials, a slurry was prepared by performing ball grinding at 1000 rpm for 30 minutes using a 2 mm zirconium ball in an MSG-D500 ball mill.

Example 2. (Preparation of nickel foam to be coated with PTFE)

A piece of 4 cm x 4 cm nickel foam was ultrasonically cleaned for 10 minutes in acetone to remove grease, and then etched again in 1mole HCl for 10 minutes to remove the oxide layer. Then, the nickel foam was dried for 30 seconds using compressed air, and then dried in an oven at 100 ° C. for 15 minutes.

Example 3. (Nickel foam dip coating)

The slurry prepared in Example 1 was poured into about 20 ml Petri dish (85 mm diameter, 10 mm height), and the 4 cm x 4 cm nickel foam prepared in Example 2 was immersed in the slurry contained in the Petri dish for 1 minute. And immediately dried in an oven at 115 ° C. for 120 minutes. The immersion process and the drying process were repeated three times to obtain relatively uniform coding.

The images summarizing the processes of Examples 1 to 3 are shown in FIG. 1, and schematic diagrams of a preparation step and a coating process of the nickel foam are shown.

Measurement Example 1. (Water separation experiment)

㎡). 상부 유리관에 기름/물 혼합물을 넣고 분리하되, 분리 공정은 기름이 물보다 비중이 낮아 물 위에 위치함으로, 기름과 발포 폼을 접촉시키기 위해 유리관을 기울였다. First, oil and water were prepared by mixing 20 ml each in a 1: 1 volume ratio. At this time, the oil used was hexane, soybean oil, and olive oil as different oils to prepare an oil / water mixture. And the nickel foam prepared in Example 3 was fixed between two glass tubes having a diameter of 20 mm (effective area of the nickel foam),

㎡). The oil / water mixture was added to the upper glass tube and separated, but the separation process was performed because the oil had a lower specific gravity than water, so the glass tube was inclined to contact the oil and foam.

The separation efficiency was calculated as the ratio of the residual volume to the initial volume of the mixture when the oil no longer drips from the filter and was calculated using Equation 1 below.

[Calculation formula 1]

(1)

(One)

Where V ₁ is the volume of oil after separation and V ₀ is the initial volume before separation. Flux (F) measurements under fixed gravity pressure were performed on the aforementioned oil and calculated using Equation 2 below.

[Calculation formula 2]

는 코팅 된 니켈 발포 폼의 유효 면적 (㎡)이다.Where ΔV is the volume change (Liter) and Δt is the time change (hour)

Is the effective area (m²) of the coated nickel foam.

)은 아래의 계산식 3을 이용하여 계산되었다. Intrusion pressure indicating the maximum weight of water that the coated nickel foam can withstand (

) Was calculated using Equation 3 below.

[Calculation formula 3]

는 물의 밀도, g는 중력의 가속도이며, h는 코팅 된 니켈 발포 폼이 지탱할 수 있는 물의 최대 높이이다. here

Is the density of water, g is the acceleration of gravity, and h is the maximum height of water that can be supported by the coated nickel foam.

The measurement results are shown in FIG. 4, and the calculation results are shown in FIG.

Referring to Figure 4 (a) is a coated Ni foam is fixed between two glass tubes. (b) is a scene where water does not pass through the coated foam. (c) is a scene where hexane passes through the foam. (d) is a mixture of hexane and water. (e) is a mixture of soybean oil and water. (f) is a mixture of olive oil and water. (g) is a scene in which the mixture of hexane and water in FIG. 4 (d) is separated. (h) is a scene in which (e) soybean oil and water mixture in FIG. 4 are separated. (i) is a scene of (f) olive oil and water mixture of Figure 4 is separated.

5, (a) shows the separation efficiency of the coated nickel foam when separating oil and water. (b) shows the separation efficiency and WCA of the coated nickel foam according to the number of oil and water separations. (c) shows the flow rate of the coated nickel foam for different oils.

Measurement example 2. (Measurement of contact angle, contact force, wet energy and diffusion coefficient)

The contact angle, contact force, wet energy and diffusion coefficient of the coated nickel foam were measured and confirmed using a SEO Phoenix 300 touch contact angle analyzer. And the coated nickel foam was observed using a field emission scanning transcription microscope (Thermal type FE-SEM Hitachi S-5000), and digital images were taken using a Lumia DMC 1x10 camera.

The measurement results are shown in Tables 1 and 2 and 3 below, and Table 1 shows the wetting properties of the PTFE-coated nickel foam.

Property Water HCl KOH NaCl Hexane olive oil Wetting Energy [mNm ^-1 ] -48.32 -44.38 -41.39 -41.57 76.79 72.04 Spreading Coefficient [mNm ^-1 ] -121.12 -117.18 -114.19 -114.37 -0.69 -0.76 Work of Adhesion [mNm ^-1 ] 24.48 28.42 31.41 31.23 148.15 144.84

Referring to Table 1 above, wetting energy, spreading coefficient, and adhesion to oil were 72, -0.76, and 144 mNm ^-1 or higher, respectively. In addition, it was found that water having a wet energy, spreading coefficient, and adhesion to an aqueous solution had the lowest values of -48, -121 and 24mNm ^-1 . Therefore, the superhydrophobicity was confirmed by confirming that the coated Ni foam has an ultra-low water affinity. Referring to FIG. 2, (a) is a nickel foam without coating, and (b) and (c) are (a) is an image taken with FE-SEM. (d) is a coated nickel foam, and (e) and (f) are images of (d) taken with FE-SEM. (g) shows the results of TGA analysis on the coated nickel foam.

And the nickel foam without coating, and the nickel foam foam coated according to Examples 1 to 3, as shown in Figures 2 (a) and (d), can be confirmed that the color of the nickel foam changed dramatically after coating. Could.

가 405 ℃이고

가 523 ℃ 이며, 250 ℃ 이하의 온도에서 열 안정성을 나타내었다. R805와 PTFE의 탄화수소 사슬은 연소되어 고온에서의 무게 손실을 보였다. TGA 분석이 대기 중에서 수행되었기 때문에

이후, 니켈 발포 폼 표면의 니켈 산화물의 형성으로 인해 백분율 중량이 다시 상승하기 시작하였다.Referring to Figure 2, (g) shows the TGA results. Coated nickel foam

Is 405 ℃

Is 523 ° C, and showed thermal stability at a temperature of 250 ° C or less. The hydrocarbon chains of R805 and PTFE burned and showed weight loss at high temperatures. Because the TGA analysis was done in the air

Thereafter, the percentage weight began to rise again due to the formation of nickel oxide on the surface of the nickel foam.

Referring to Figure 3 (a) is a contact angle image of deionized water. (b) is a contact angle image of 1M HCl. (c) is a contact angle image of 1M KOH. (d) is a contact angle image of 1M NaCl (21.58 μL of water droplets each). (e) is a test result of wettability for water and hexane of the coated nickel foam. (f) is the test result of wettability of water and hexane of nickel foam without coating treatment. As shown in (f), it had both lipophilicity and hydrophilicity. The coated nickel foam had both OCA (oil contact angle) of hexane and olive oil at 0 °. 3 (a) to 3 (d), the WCAs for different aqueous solutions were 155 °, 153 °, 152 ° and 152 ° for pure water, 1M HCl, 1M KOH and 1M NaCl, respectively.

The superoleophilic properties of the coated nickel foam with reference to the experimental results in FIG. 3 can be described by the Wenzel equation as follows.

[Calculation formula 4]

Here, θ _c is the apparent WCA of the rough substrate, θ ₀ is the WCA of the intrinsic plane, and r is the surface roughness factor. In the experiment, θ ₀ was confirmed to be 113 °. The Wenzel equation shows that the lipophilicity of the foam can be improved by increasing the surface roughness and low surface energy of the coated nickel foam.

Cassie models can be used to illustrate the super hydrophobicity of nickel foam. Due to the roughness and the low surface energy of the surface, water droplets penetrate the rough surface, trapping the air between water and bubbles, forming an air layer, making it superhydrophobic. The Cassie equation can be written as:

[Calculation formula 5]

는 WCA (155 °),

는 평평한 표면의 WCA (113 °),

는 표면의 면적 분율이다. 따라서, 더 큰 거칠기 표면에 대해

가 감소하면 WCA가 증가한다. 코팅 된 니켈 발포 폼은 표면이 거칠고 WCA가 크기 때문에 상대적으로 작은 면적 분율을 나타냅니다. 이러한 관찰은 코팅이 니켈을 초 흡수성 및 초 소수성으로 만든다는 것을 보여준다.here

WCA (155 °),

WCA (113 °) on a flat surface,

Is the surface area fraction. Thus, for larger roughness surfaces

Decreases, WCA increases. Coated nickel foam has a relatively small area fraction due to its rough surface and large WCA. These observations show that the coating makes nickel super absorbent and super hydrophobic.

In addition, FIG. 6 shows a schematic diagram of a liquid wetting process in a coated nickel foam, showing the principle of superhydrophobicity and superoleophilicity of the nickel foam produced by the methods of Examples 1 to 3.

Referring to FIG. 6, (a) shows that the foamed foam exhibits superhydrophobicity because water having an intrusion pressure of ΔP> 0 in the atmosphere cannot penetrate through the foam. In (b), since the intrusion pressure in the atmosphere is ΔP <0, the oil cannot withstand the pressure of the atmosphere, and thus exhibits superoleophilicity in which the oil can pass through the foam. As shown in (b), it was confirmed that the separation efficiency was slightly decreased after 10 cycles of repeated separation were performed. The WCA of the coated nickel foam decreased from super hydrophobic to hydrophobic as the cycle increased. The flow rate decreased as oil viscosity increased as expected, and hexane had a very high flow rate of 12525 Lm ^-2 h ^-1 , 63 times higher than that of commercial filtration membranes (20-200 Lm ^-2 h ^-1 ), and soybean oil 2191 Lm. ^-2 it has a flow rate of h ^-1, olive oil and finally with the lowest flow rate had the lowest flow rate of 1860 Lm ^-2 h ^-1.

(c) After the oil penetration, some oils can be trapped between the gaps between PTFE, R805 and PVDF molecules, and the foam foam is superhydrophobic and water resistant because the intrusion pressure is ΔP> 0. Where O is the center of the meniscus sphere and O ₁ and O ₂ are the centers of the cross-section of the foam.

The high flow rate is attributed not only to the high porosity of the foam, but also to the superhydrophilicity and superoleophilicity of the coated foam.

However, in general, if the penetration pressure (ΔP) is exceeded, the pore bottom may get wet. This can be explained as follows.

[Calculation formula 6]

Where γ is the surface tension, R is the radius of menstruation, l is the perimeter of the pore, θ_A is the forward contact angle of the bubble, and A is the pore area. From Equation 6, if θ _A > 90 °, there will be no intrusion to some extent because Δ P> 0. WCA was> 150 ° for different pH aqueous solutions in the coated nickel foam as shown in Figure 3, thus the coated? Ll foam was superhydrophobic, and the water was coated as shown in Figure 4 (b). Could not pass through the foam. The oil contact angle (OCA) was almost 0 °, which means that ΔP <0 can allow the oil to quickly pass through the nickel foam (Figure 4 (c)). As the oil penetrates through the pores, the water properties of the coated foam improve the superhydrophobicity and high WCA in the coated nickel foam, which confines the oil (but it is small enough that the pores of the nickel foam are not blocked). ΔP was calculated using Equation 3, which was about 7.8 kPa, suggesting that water could not penetrate the foam foam coated below this intrusion pressure.

As described above, specific parts of the present invention have been described in detail. For those skilled in the art, this specific technique is only a preferred embodiment, and it is obvious that the scope of the present invention is not limited thereby. something to do. Therefore, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (16)

A superhydrophobic-superoleophilic nickel foam foam coated with a coating mixture comprising polytetrafluoroethylene (PTFE) and hydrophobic fumed silica.
According to claim 1,
The coating mixture is polyvinylidene fluoride (polyvinylidenefluoride, PVDF) superhydrophobic-superoleophilic nickel foam.
According to claim 1,
The polytetrafluoroethylene is a superhydrophobic-superoleophilic nickel foam, characterized in that the coating mixture is 60wt% compared to 100wt%.
According to claim 1,
The hydrophobic fumed silica is a superhydrophobic-superoleophilic nickel foam, characterized in that the surface is a silanol group-treated silica. According to claim 1,
Superhydrophobic-superoleophilic nickel foam, characterized in that the coating mixture is 20wt% compared to 100wt%.
According to claim 2,
The polyvinylidene fluoride is a superhydrophobic-superoleophilic nickel foam, characterized in that 8wt% dissolved in DMSO.
According to claim 1,
The nickel foam is porous,
The porosity is a superhydrophobic-superoleophilic nickel foam, characterized by an interconnected three-dimensional structure.
According to claim 1,
The nickel foam is a superhydrophobic-superoleophilic nickel foam, characterized in that the intrusion pressure is 7.5 to 8.0 kPa.
In the superhydrophobic-superoleophilic foam,
Preparing a slurry;
Preparing a nickel foam to be coated with the slurry and
A method of manufacturing a superhydrophobic-superoleophilic nickel foam that includes dipping the nickel foam into the slurry.
The method of claim 9,
The slurry is polytetrafluoroethylene (polytetrafluoroethylene, PTFE) and hydrophobic fumed silica (hydrophobic fumed silica) and polyvinylidene fluoride (polyvinylidenefluoride, PVDF) superhydrophobic-super lipophilic nickel foam production method.
The method of claim 10,
The polytetrafluoroethylene (polytetrafluoroethylene, PTFE) and hydrophobic fumed silica (hydrophobic fumed silica) and polyvinylidene fluoride (polyvinylidenefluoride, PVDF) mixing ratio of 60: 20: 20 wt% superhydrophobic-chochin characterized in that the weight ratio Method for manufacturing oily nickel foam.
The method of claim 10,
The polyvinylidene fluoride (polyvinylidenefluoride, PVDF) is a superhydrophobic-superoleophilic nickel foam manufacturing method characterized in that 8wt% dissolved in DMSO.
The method of claim 9,
The manufacturing method of the slurry further comprises a super-hydrophobic-superoleophilic nickel foam foam manufacturing method further comprising ball grinding.
The method of claim 9,
The nickel foam has a non-uniform porous structure with a pore size of 250 to 450 μm,
The porous structure is a superhydrophobic-superoleophilic nickel foam production method characterized in that the interconnected three-dimensional structure.
The method of claim 9,
The step of preparing the nickel foam,
Ultrasonic cleaning the nickel foam in acetone;
Ultrasonically etching the ultrasonically cleaned nickel foam in an HCl solution, and
A method of producing a superhydrophobic-superoleophilic nickel foam, further comprising drying.
The method of claim 9,
The dip coating step,
Immersing the nickel foam in the slurry, and
A method of manufacturing a superhydrophobic-superoleophilic nickel foam, characterized in that the step of drying the immersed nickel foam in an oven is repeated three times.

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