The Measurement of Adhesion Force between Carbon Particles and the Substrate by AFM

Zhang Tianqi1, Peng Wei1, Shen Ke 1, Yu Suyuan2

(1. Institute of Nuclear and New Energy Technology of Tsinghua University, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of

Education, Tsinghua University2. Center for Combustion Energy, Key Laboratory for Thermal Science and

Power Engineering of Ministry of Educations, Department of Thermal Engineering, Tsinghua University)

OUTLINE

• Context• Motivation of Research on Adhesion Force• Experimental Preparations• Measurements• Results & Analysis

1. Context

Graphite materials in HTGRs is mainly used in: • fuel coating material;• reflector material;

Carbonaceous dust generated from: (Kissane (2009))• Graphite from abrasion in the core; • carbon from decomposition of hydrocarbons (oil contamination); • carbon from decarburization of steel alloys;

2. Motivation of Research on Adhesion Force

• Fad: an indicator of the solidity that a particle contacts with the wall;• a key factor in study of motion behavior of graphite dust.

mechanical decontamination ： about 60%

Photo and microscopy picture of a segment

• Johnson et al. (1971) proposed JKR model to calculate the intermolecular forces acting between two bodies. This model assumes a contact zone arising from elastic deformation due to interaction forces, and the contact area remained finite before critical pull-off force being imposed.

• graphite dust : 1. microns or sub-microns. Fad is quite small. 2. Irregular particles & rough surface.

• It is essential to employ fine measurement method to measure the force.

3. Experimental Preparations

• AFM• Measuring Principle & Force Curve• Substrate Samples & Particle Samples• Experiment Facilities

Atomic Force Microscope (AFM):

• a fundamental tool to get surface structures & surface forces

• extensively used in the polymer materials, microelectronics industry, biology, etc.

Measuring Principle & Force CurveAFM uses tiny cantilever, which could contact with the sample surface within the scope of atomic distance, to sensor the interaction force F.

The elastic cantilever flexes when sensing changes in stress. Position Sensitive Photo-detector outputs signal voltage U reflecting flexion of the cantilever when it is cast by a laser beam.

the spring coefficient of cantilever + “voltage- load” → the curve of F changing with sample displacement z is obtained

Schematic of AFM

approach – contact – loading – loading to preset voltage value – withdraw –abrupt separationThe retrieved force curve was initially overlapping the loading force curve due to the elasticity of particle samples.

However, a larger force was needed to separate the particle and the substrate. The extra exerted force was used for balancing out the binding force produced from the contact area. This part was regarded as the measured Fad.

A：approach

B：loaded

C：withdrawing

D：release

displament of sample stage z

intera

ction

force

F

D

BA

C

Substrate SampleStatement

1: Mica benchmark

2: Graphite IG110 Toyo TansoTM ,reflector material of HTR-10

3: Inconel 800H

good resistance to high temperature, irradiation, oxidation and acid or alkali, also has reliable performance in either machining or welding.Preferred material of heat transfer tube

Machined into different 2 roughness:IG110 IIG110 IIInconel 800 IInconel 800 II

Particle SampleStatement

Particle I mesophase

carbon microsphere

• carbon content: 98%wt • developed from asphalt and other liquid-phase

organic compounds• formed a microsphere under the action of

surface tension.

Particle II

fine debris of coating graphite on fuel elements

of HTR-10

• Collected from standard pebble-milling tests• 64% is natural flake graphite, 16% is the artificial

graphite and 20% is phenolic resin. • most of it took on shapes of flakes or layers

contributed by the natural graphite.

Particle III graphite powder NBG18

• produced by SGL Carbon Group (German)• reflector material of AVR• processed by mechanical crushing. • various shapes

Experimental Facilities

MFP- 3DTM (Asylum Research) produced by CypherTM

AFM System:

TL-CONT-10 type produced by NanosensorTM

Micro XAM – 3D white light interferometry profilometer

Surface Profile Analyzer:

Bare Cantilever:

Prepare the Modified Cantilevers

1 2pd d d

.

• SEM images verified that the particles were not submerged in the binder

• For irregular particles, equivelant particle diameter• dp of three samples : 7.71μm ， 7.99μm ， 4.69μm.

• Use expoxy as the binder;• put under the ultraviolet lamp for about 30 mins until the

binder cured;

Measurement

Adhesion Force Measurement

Randomly choose 8 test points in each substrate sample.

Repeatedly conduct measurements for 3 times in each point.

Sample I ： mesophase carbon microsphere

P1 P2 P3 P4 P5 P6 P7 P8

200

300

400

500

600

700

800

Adh

esio

n F

orce

/ nN

2#_800H_R1

P1 P2 P3 P4 P5 P6 P7 P8

200

300

400

500

600

700

Adh

esio

n F

orce

/ nN

2#_800H_R2

P1 P2 P3 P4 P5 P6 P7 P8

20

40

60

80

100

120

Adhesi

on F

orc

e /

nN

2#_IG110_R1

P1 P2 P3 P4 P5 P6 P7 P8-20

020406080

100120140160

Adhesi

on F

orc

e /

nN

2#_IG110_R2

Results & Analysis

Sample II ： fine debris of coating graphite on fuel elements of HTR-10

P1 P2 P3 P4 P5 P6 P7 P880

100120140160180200220240260280300

Adhesi

on F

orc

e /

nN

4#_800H_R1

P1 P2 P3 P4 P5 P6 P7 P8

150

200

250

300

350

400

450

Adhesi

on F

orc

e /

nN

4#_800H_R2

P1 P2 P3 P4 P5 P6 P7 P8-40-20

020406080

100120140

Adh

esio

n F

orce

/ nN

4#_IG110_R1

P1 P2 P3 P4 P5 P6 P7 P805

1015202530354045

Adh

esio

n For

ce /

nN

4#_IG110_R2

Sample III ： graphite powder NBG18

7#_800H_R1

7#_800H_R2

7#_IG110_R1

7#_IG110_R2P1 P2 P3 P4 P5 P6 P7 P8

200

300

400

500

600

700

800

Adh

ensi

on F

orce

/nN

P1 P2 P3 P4 P5 P6 P7 P8

200

300

400

500

600

700

800

Adh

ensi

on F

orce

/nN

P1 P2 P3 P4 P5 P6 P7 P8-10

01020304050607080

Adh

esio

n F

orce

/ nN

P1 P2 P3 P4 P5 P6 P7 P8-10

01020304050607080

Adh

esio

n For

ce /

nN

• The measured Fad densely distributed in repeated contacts of each test point, but sparsely scattered in different points.

• Data of Inconel 800H was more decentralized comparing with that of IG110.

• No perfect repeatability• The profile of substrate samples, the morphology of

particle samples and the contact mode are predicted to have impacts on the measured Fad .

Profile of Substrate Samples

A: mica

B: IG110 I D: Inconel 800H I

E: Inconel 800H IIC: IG110 II

Substrate

Average variation

Sa

（ nm）

RMS Roughness

Srms

（ nm ）

Profile Peak Density Sds

（ 1/nm2 ）

Average height Sz

（ nm ）

A: Mica 1.32 1.66 0.737 14.5B: G IG110 I 1139 1137 0.0141 9990C: G IG110 II 2586 3613 0.0181 47245D: Inconel 800H I 1438 1694 0.0128 12259E: Inconel 800H II 4628 5561 0.000282 30358

Table 1 Major Profile Parameters of Sample Substrates

dp of three particle samples is respectively: 7.71μm ， 7.99μm ， 4.69μm

Take average value: Adhesion Force Fad for 3 Carbon Samples

Fad for 3 Carbon Samples (nN)

mica G IG110 I G IG110 II Inconel 800H I Inconel 800H II

Particle I 733 57 55 475 498

Particle II 312 28 23 167 249

Particle III 8 32 23 474 499

ad

3

2F WRAccording to JKR model,

W or 3 Carbon Samples (mJ/m2)

mica G IG110 I G IG110 II Inconel 800H I Inconel 800H II

Sample I 40.4 3.1 3.0 26.1 27.4

Sample II 16.6 1.5 1.2 8.9 13.2

Sample III 0.7 2.9 2.1 42.9 45.2

Work of Adhesion W or 3 Carbon Samples

Qualitative Explanation

• Shape factor → Contact Area• Limited deformation

a ： Spheri cal Part i cl es

b ： Non-Spheri cal Part i cl es

W or 3 Carbon Samples (mJ/m2)

mica G IG110 I G IG110 II Inconel 800H I Inconel 800H II

Particle I 40.4 3.1 3.0 26.1 27.4

Particle II 16.6 1.5 1.2 8.9 13.2

Particle III 0.7 2.9 2.1 42.9 45.2

Work of Adhesion W or 3 Carbon Samples

Work of Adhesion W or 3 Carbon Samples (mJ/m2)

mica G IG110 I G IG110 II Inconel 800H I Inconel 800H II

Particle I 40.4 3.1 3.0 26.1 27.4

Particle II 16.6 1.5 1.2 8.9 13.2

Particle III 0.7 2.9 2.1 42.9 45.2

• asperities of sample substrate

• Roughness can reduce Fad in a certain scale; • However, when the size of asperities almost is equal to or

greater than dp, Fad increases with the increasing contact area.

• Thanks for your attention!

Force Curve AnalysisR2_40002Force

Particle Sample II vs. IG110 Sample Substrate

Standard Force Curve

R2_70001Force

• Sample I is mesophase carbon microsphere, prepared by Taiwan's chemical co., LTD. The carbon content reached 98%wt after carbonization in 1000 .℃

• This sample developed from asphalt and other liquid-phase organic compounds. The nematic-liquid-crystal mesophase carbon formed a microsphere under the action of surface tension. Mesophase carbon microspheres can be used for the preparation of isotropic graphite and lithium-ion battery anode materials (Ke Shen, 2009).

standard pebble-milling tests (referring to Germany)