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1. Which is a NOT line-of-sight process? (Repeat2010) not repeat! but which is a line of sight process(a) Physical vapor deposition(b) Flame spray(c) Chemical vapor deposition(d) Hardfacing(e) High velocity oxy fuel spray

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2. There are “Basic Rules for Thermal Spray”. Pick out the one example from those below that is incorrect.

(a) Adjust the “Tv+p” conditions for different processes and materials.(b) Spray with correct and adequate surface preparation.(c) Do not use TS coatings as structural members.(d) Always consider the feed rate and spray distance.(e) Edges should not be chamfered and corners radiused.

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3. Wire-arc spray requires feedstocks that are/ have: (Repeat2010)(a) Electrically conductive.(b) Ductile.(c) High melting point.(d) Non reactive with oxygen(e) Combustible

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4. Refer to Figure 9 which shows a diagram of a HVOF torch. Identify the part that is labelled “A”.(a) Oxygen line(b) Fuel line(c) Powder injector(d) Combustor(e) Water cooling

Figure 5

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5. What is the best medium to use for starting a non transferred arc plasma spray torch.(a) A gaseous mixture of hydrogen and nitrogen(b) High purity argon(c) High purity helium(d) A gasous mixture of helium and hydrogen(e) High purity oxygen

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6. Refer to Figure 9 which shows a diagram of a plasma spray torch. What is the flame temperature at 20mm downstream from the torch and labelled “Y”?(a) 1000˚C (b) 3000˚C (c) 5000˚C (d) 10000˚C (e) 20000˚C

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7. Which of the following particle morphologies is considered ideal as a feedstock powder from only the viewpoint of feeding?(a) An angular shaped feedstock powder(b) A spherical shaped feedstock powder that has a very large range of particle size distributions(c) A blended powder of angular metal particles and spherical ceramic particles(d) A perfectly spherical-shaped particle with a very narrow particle size distribution(e) Agglomerated feedstock powder

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8. The powder characteristics of a certain type of partially stabilised zirconia have been summarised in Figure 7. Which of the following would be the most preferred thermal spray feedstock?

Figure 8

(a) Fused and crushed(b) Sintered and crushed(c) Spray dried(d) Plasma fused(e) Sol gel

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9. The prime characteristic of a gas atomized powder is:

(a) Angular and irregularly shaped particles. (b) Generally spherical shape, in a variety of sizes.(c) Extremely fine sizes (<1 micron).(d) Exceptionally high degree of porosity.(e) Very economical powder production method

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10. This question relates to the powder manufacturing and the resulting morphology. Which of the following statements best describes the manufactured morphology of the powders?(a) Gas atomised powders result in a dense and spherical morphology.(b) Gas atomised powders have a porous and angular morphology.(c) Water atomised powders result in a porous and spherical morphology.(d) Agglomerate and sintered powders have dense and spherical morphology.(e) Sintered and crushed powders are spherical and porous.

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11. The prime characteristics of a crushed and milled powder are:(a) Smooth edges and close control of particle sizes.(b) Angular features and a tendency to manufacture sub-micron particles (fines).(c) Angular features and very wide particle-size distribution.(d) A spherical morphology and ability to produce a homogeneous chemical composition.(e) A agglomerated feedstock powder that has a very large range of particle size distributions

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A B

C D

Figure 9

12. Figure 7 above summaries the various thermal spray feeding systems. Identify which of the following statements is correct.(a) All of the thermal spray feed systems shown can be used for the wire-arc spray process.(b) Label ‘A’ is a gravity and vibration based system(c) Label ‘B’ describes a system that can be used for wet powders.(d) Label ‘C’ is a fluidized bed based system(e) Label ‘D’ describes rotating wheel system.

Answer is

7

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HES6127 Surface Engineering 10

13. Which of the following is not an advantage of the sol-gel manufacturing technique?(a) Ability to produce spherical powders which are free-flowing.(b) Closely controlled powder composition, as sol-gel is based on solution chemistry.(c) It is a high-temperature process; very dense materials can be produced.(d) The degree of powder porosity can be controlled.(e) Very small primary particle sizes can be achieved (2-20nm)

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14. There are four major types of feedstock morphology for carbide, the characteristics of each individual morphology can be seen in Figure 8. Please identify powder feedstock morphology describe and labeled “C”?

(a) Sintered(b) Coated(c) Agglomerated(d) Spheroidized(e) Cladded

Figure 10

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15. With respect to safe thermal spray operations, which of the following lists best describe the essential personal protective equipment (PPE) for all thermal spray operators.(a) Ear plugs, plastic glasses, plastic gloves, cloth mask(b) Cork acoustic barrier, plastic glasses, plastic mask, leather glove(c) Ear plugs, plastic gloves, lab coat, steel cap boots(d) Ear plugs, leather gloves, face shield with welding glasses, fine particulate respirator mask(e) Plastic glasses, fine particulate respirator mask, lab coat, leat

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HES6127 Surface Engineering 10

16. What is the best way to improve the impact resistance and reduce coating brittleness in thermally sprayed components?(a) Post heat treat(b) Spray hot(c) Use no preheat(d) Machine the coating(e) Quench the coating in oil after spraying

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17. Heat-treated steel substrates should not be preheated above 150°C (300°F) and kept at high temperature for long times because:

(a) Only thin coatings can be applied.(b) Coatings will be very hard.(c) Preheating may change prior heat-treated properties of the substrate.(d) Coatings will not oxidize.(e) The coating may react strongly with the substrate

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18. What is the first step in substrate surface preparation?(a) Masking(b) Grit blasting for roughness(c) Preheating(d) Cleaning to remove grease and oils(e) Macro roughening by machining

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19. Part and gun relative motion are critical for many reasons. Which of the following is most likely to occur if motion is not properly managed?(a) Coatings are uneven.(b) Coatings will turn black.(c) The gun will not operate.(d) The substrate will oxidize.

Answer is

HES6127 Surface Engineering 10

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20. What is the best way to remove dust, debris and loose particles while spraying?(a) Use a long stand-off (spray distance).(b) Use a high preheat temperature.(c) Use directed clean, dry compressed air streams to blow away particles.(d) Spray slowly and at low spray rate.(e) Increase the powder feedrate.

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21. When sectioning thermal sprayed tungsten carbide coatings it is important to minimize surface damage in the form of high plastic deformation. What type of cutting tool is used for fine and delicate specimen sectioning

(a) Band saw(b) High-speed aluminum oxide grinding wheel(c) Water jet cutter(d) A low-speed diamond wheel cutter(e) Wire electrical discharge machining

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22. Which of the following figures best describes the correct orientation when sectioning thermal sprayed coated samples?

(a) Figure 1(b) Figure 2(c) Figure 3(d) Figure 4(e) None of the above

Figure 1 Figure 2

Figure 3 Figure 4

Figure 12

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23. What is the main objective of grinding and polishing?

(a) Material removal(b) Induce scratches on the material(c) Achieve mirror like finish on the surface(d) Remove material defects(e) Prepare the sample for SEM(f) Remove soft phases of a coating

12

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13

24. Sectioned thermal sprayed samples can be embedded in resin to facilitate their handling and to improve the preparation result. Specimens that need perfect edge retention or protection of layers require mounting. Choose the correct 2 types of mounting below

(a) Cold mounting & Liquid mounting(b) Warm mounting & Gas mounting(c) Liquid mounting & Hot mounting(d) Hot mounting & Cold mounting(e) Gas mounting & Cold mounting

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25. The two types of residual stresses that can be generated in producing a thermally sprayed coating. (Repeat2010)(a) Shear stress and tensile stress(b) Tensile stress and uniaxial stress(c) Shear stress and uniaxial stress(d) Compressive stress and shear stress(e) Tensile stress and compressive stress

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26. How many layers are there if the individual splat thickness is 5 µm and the total coating thickness is 0.5 mm?

(a) 1,000 layers(b) 100 layers(c) 10,000 layers(d) 250 layers(e) 2500 layers

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27. The tensile strength of plasma and thermally sprayed coatings is:(a) Higher than conventional wrought, cast, or forged materials.(b) Approximately equal to conventional wrought, cast, or forged materials.(c) Much less than conventional wrought, cast, or forged materials.(d) Impossible to determine.(e) None of the above.

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28. The strength of plasma and thermally sprayed materials is due to the phenomenon of: (Repeat2010) (a) Van der Waals forces between particles.(b) Metallurgical bonding.(c) Phase transformations.(d) Mechanical interlocking of particles with a roughened surface.(e) None of the above.

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29. Refer to Figure 11. If failure occurs between the bond coat and substrate, identify the correct failure locus description.

(a) Adhesive ceramic-bond coat failure.(b) Adhesive failure.(c) Adhesive substrate- bond coat failure.(d) Cohesive bond coat failure.(e) Cohesive substrate- bond coat failure.

Figure 13Answer is

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30. Ceramic , thermal barrier coatings are best sprayed by which method? (Repeat2010)(a) Plasma spray (b) HVOF(c) Flame(d) Wire-arc(e) Cold spray

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31. Refer to the below (Figure 13) and select the most appropriate response from those supplied (Repeat2010)

(a) The part of the figure referred to as “A” indicates the “target”.(b) The part of the figure referred to as “A” indicates the “ion flux”. (c) The part of the figure referred to as “A” indicates the “plasma”.(d) The part of the figure referred to as “A” indicates the “substrate”.(e) The part of the figure referred to as “A” indicates the “anode”.

Figure 14

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32. Which of the following statement is incorrect when using the XPS technique?(a) Identification of all elements (except hydrogen and helium) present in the outer 100 Å of a

sample(b) Non-monochromated x-ray sources can possibly damage sample during analysis(c) Quantitative 2D chemical maps using imaging-XPS.(d) Know the surface concentrations of elements present(e) Detection of positive and negative ions up to masses of 10,000 Da

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33. For imaging SIMs, the primary ion beam, with a lower number of ions per pulse, is rastered across the surface and spectra collected, calculate the time required for acquisition of a image SIM using the information provided below.

(a) 20 minutes(b) 2000 minutes(c) 30 minutes(d) 300 minutes(e) 3000 minutes

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34. The best material that has been identified for preventing protein adsorption in polymer “brush” coatings is:

(a) poly(ethylene glycol) (PEG)(b) n-heptylamine (HAPP)(c) allylamine (AAPP)(d) polyacylamide(e) poly(ethylene terephthalate) (PET)

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1. A chemical reactor fabricated in Inconel 625 requires a localized coating of Inconel 625. The type of corrosion which is being prevented is:(a)Heat-affected zone.(b)Crevice.(c) High-temperature oxidation.(d)Pitting.

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2. A plasma sprayed coating of alumina was applied to protect equipment against hot exhaust gases at temperatures up to 1250°C (2280ºF). Proper bond coats and substrate materials with close matched CTEs were used, yet the coating failed after only 3 hours in service. What was the most likely cause?(a)Used combustion wire to apply the bond coat.(b)Contaminated alumina ceramic.(c) Rapid corrosion of the substrate by sulfides.(d)Gamma-to-alpha conversion of the alumina.

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3. The source of variance not attributable to the tensile test method is:(a) Alignment of pull bars.(b) Thickness of adhesive layer.(c) Loading rate.(d) Splat-to-splat cohesion.

Answer is

19

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4. The figure 44 associated with this question shows how hardness is related to the relative abrasive wear resistance. Select the most appropriate alternative from the options below.(a) The wear resistance of iron will always be better than that of copper under all circumstances

and conditions.(b) The data for molybdenum indicates that, under the conditions of this test arrangement, it

exhibits good relative abrasion resistance compared to the other materials.(c) There is a scientific relationship between hardness and relative abrasive wear resistance that

is based on well-defined physical principles.(d) There is always a linear relationship between hardness and relative abrasive wear resistance.(e) Hardness is identical the modulus of a material because the engineering dimensions are the

same.Answer is

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5. Which flattened droplet (shown in the figure 35) best describes impact onto a well heated polished substrate?

Fig. 35Answer is

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6. Which secondary gas would be the most effective in ensuring that powder is melted in a shorter distance?(a)Nitrogen(b)Helium(c) Hydrogen(d)Oxygen

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20

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7. Based on your knowledge of particle velocities in the plasma, what is the typical traverse time of a particle in a plasma?(a) 10 milliseconds(b) 1 millisecond(c) 100 milliseconds(d) 100 nanoseconds

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8. The particle size distribution is an important measure in thermal spray technology. A wide particle size distribution leads to(a) Higher powder flowability(b) Improved deposition efficiency(c) A broad particle trajectory(d) Less ultrafines

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9. What mechanism can be used to form chemical bonding between a thermal-sprayed metal and a ceramic substrate?(a) The oxygen-metal eutectic.(b) Scrubbing the substrate with hot gasses prior to deposition.(c) Using metal oxide bond coats.(d) SiC gritblast the substrate before deposition.

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10. The figure 45 below represents the following.(a)Thermal spray deposition onto the bottom of a Jominy bar.(b)Oil quenching of a shaft component.(c) A test that will allow hardness profiles to be determined.(d)Surface preparation of the end of a steel bar.(e)Extrusion of a steel bar that needs to be cooled.

Fig 45 Answer is

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11. Given a stable and consistent thermal jet source, what is the next most important thermal spray

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process parameter to control?(a)Spray distance and motion(b)Powder characteristics and feed(c) Surface preparation and treatment(d)The spray environment

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12. A cast iron printing cylinder was required to have a finish coating of austenitic stainless steel on its surface. The casting surface was first cleaned, then machined for macro roughening, thermally sprayed with molybdenum and then finish thermally sprayed with stainless steel. The molybdenum thermal spray coating is termed:(a)A bond coating.(b)Masking(c) Preheating(d)Feathering.

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13. During start-up of a plasma spray process it is observed that powder flow from the powder feed tube is very irregular and it has been ascertained that the problem lies in the powder delivery system. Which of the following statements is correct?(a) The powder morphology is angular and thus the hall flow value is not acceptable for a thermal

spray powder.(b)The powder must be wet and is thus agglomerating within the powder feeder.(c) It is certain that a fluidized-bed feeder is being used and thus the use of a rotating wheel

system will alleviate this problem.(d) The so-determined powder feeding problem is a complex technical difficulty that involves

many interrelated aspects of thermal spray technology.Answer is

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14. Refer to the figure 26 below that derives from a patent titled “A Method of Producing Bodies and Coatings of Glass and Other Substances”. Indicate the best choice from the statements provided below.(a) The figure represents a primitive plasma spray technology.(b) The figure shows how liquids can be atomized in a vacuum.(c) The figure is related to modern high velocity oxygen fuel and D-gun technology.(d) The figure depicts a method of atomizing a solid rod; the particles of which are then blown

against a substrate to establish a coating.(e) The figure is a primitive method for the creation of thin, CVD coatings.

24

Fig.26

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15. Which gas combination is most commonly used in powder flame spraying?(a)Acetylene/ oxygen(b)Hydrogen/ oxygen(c) Propane/oxygen(d) Butane/ oxygen

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16. Combustion flame-spray coatings, once the industry mainstay, are not as commercially dominant a process now because:(a) Ceramic coatings could not be sprayed.(b) Coating porosity is too high.(c) The process is not as tolerant of a wide range of materials as other thermal spray processes.(d) The process is not economically competitive.

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17. Which coating process cannot apply oxide-ceramics?(a) Chemical vapor deposition(b) Physical vapor deposition(c) Thermal spray(d) Electroplating

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18. Which is the high-temperature phase for low-carbon steel?(a)Cementite(b)Austenite(c) Martensite(d)Ferrite

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19. Refer to the figure 6 below to answer the following question. The figure represents the iron- carbon phase diagram. Choose the most appropriate alternative from the list below.(a)Field A and Field B are separated by the solidus line.(b)Field C represents the cementite phase.(c) Point b is the eutectic composition.(d)Point b is the peritectic composition.(e)Field D represents the precipitation of only the gamma phase.(f) None of the above is correct.

Fig.6

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20. Use the unlabeled schematic phase diagram (fig.9). Select the most appropriate statement from those provided below.(a)The “A” region represents the ‘normalization’ heat treatment process.(b)The “A” region represents the ‘full anneal’ heat treatment process.(c) The “B” region represents the ‘normalization’ heat treatment process.(d)The “C” region represents the ‘full anneal heat treatment process.(e)Alternatives B and C are correct.

Fig.9

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1

21. The following statements refer to welding processes. Which one of these statements is considered as an advantage of welding?(a) Impossible to dissemble joints without destroying detail parts.(b)Joints of exceptional structural integrity and efficiency will not accidently loosen or dissemble.(c) Unbalanced heat input leads to distortion or residual stresses.(d)Heat of welding degrades base properties.(e)Requires considerable operator skill.

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22. Indicate the most accurate statement of those presented below as it relates to hardfacing.(a) Hardfacing must be carried out under vacuum conditions.(b) The surface finish of a welding process that is carried out to hardface an engineering

component is always very smooth.(c) All materials, including ceramics, polymers and composite materials can be manufactured by

means of a hardfacing process.(d) The hardfacing process is defined as an omni-directional process.(e) The adhesion of welding and hardfacing processes is via a diffusional mechanism.(f) A heat affected zone (HAZ) is not an artifact of a hardfacing process.

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23. A process is required to improve the wear resistance and fatigue resistance of steel gears. What surface hardening treatment would be most appropriate for this gear?(a) Carburizing(b) Carbo-nitriding(c) Flame hardening(d) Induction hardening(e) Nitriding(f) All of the above

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2

24. The figure 1 relates to physical, intrinsic properties of various materials. Parts (A) and (B) relate to two different properties. The horizontal scales are only indicated for reference purposes. Choose the most appropriate alternative from the list below.(a) Part (A) refers to the tensile strength of the materials.(b) Part (A) is the ratio of the tensile strength to density of the materials.(c) Part (B) refers to the tensile strength of the materials.(d) Part (B) is the ratio of the tensile strength to density of the materials.(e) Part (B) relates to the absolute electrical conductivity of the materials.(f) None of the above is correct.

Fig:1

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3

25. The figure 2 below relates a normalized property to behaviour at various temperatures. Choose the most appropriate alternative from the list below.(a)The vertical axis is expressed in terms of ‘yield point to weight’.(b)There are no such materials as ‘Cb and Mo based alloys’.(c) The vertical axis is the absolute tensile strength.(d)The vertical axis is the tensile strength that has been normalized with respect to density.(e)The ‘Ti alloys’ are misrepresented as are functional at much higher temperatures.(f) The vertical axis represents a thermal property such as expansion coefficient.

Fig. 2

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26. Refer to the figure 3 below and look at the ‘???’ identification that is indicated for ‘Type of Material 3’. Choose the most appropriate alternative from the list below.(a) This material is most probably a composite or hybrid material because the Young’s modulus

is very large.(b) Metals have the greatest Young’s modulus; thus, this material is most probably a high alloy

tool steel.(c) This material is either tungsten carbide or diamond since these are known to great Young’s

Modulus values.(d)This material is a carbon fibre reinforced material that is similar to Kevlar.(e)This material is either aluminium oxide or another form of glass.(f) It can only be determined that this materials is an alloy since only such materials can exhibit

the best extrinsic properties.

Fig. 3Answer is

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