aspects on electrochemical healing

8/11/2019 Aspects on Electrochemical Healing

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Aspects on the electrochemical

healing of MAX phase ceramics

A.M. (Amor) Abdelkader*, S.J. Garcia, S. van der Zwaag

Faculty of Aerospace Engineering, Delft University of Technology,

Kluyverweg 1, 2629 HS Delft, The Netherlands*[email protected]

IOP Project Number SHM01027


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Background:

Healing a crack of 7 mm length and anaverage width of 5 m by well-adheringAl2O3 and loosely-bound TiO2 introduced

by thermal oxidation at 1100 C for 2 h.


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Electro-oxidative self healing of metalo-ceramic

Principle:M(Ti, Al)+ O-2= e-2+MO

Local increase of ions in the crack make it more anodic than thesubstrate


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2 ,

2 / 1

.

The electrolyte tested was aqueoussolution of H2O2, Na2SO4, NaOH andNa

2

CO3

Proof of concept using MAX ceramics


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The cracks on the surface of Ti2

AlC2

has been filled with awhite deposit from the Na2CO3 electrolyte


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Is it electrochemical deposit or just aphysically attached salt?

SEM of a surface crack after 1 hour of electrolysis at 2 V vs. Ag/AgCl reference inNa2CO3 solution


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Crack filling by oxides formed via controlledanodization process of the MAX samples in aqueoussolutions.

Cathodically deposit Al (and the other cation in the MAXif possible) in the crack using ionic liquids.

Localized electrophoretic deposition of oxides and/orcarbides of the MAX cations.

cathodically deposit charged complexes of the cations inthe MAX phase using aqueous or organic electrolytes

Electrochemical techniques for crackhealing in MAX phase ceramics


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Advantages:

Low energy consumption. In fact it could used toproduce energy with minor modifications.

Green and sustainable process.

Simple and scalable techniques.

Avoid consuming the substrate material in the hightemperature oxidation healing


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Studying the electrochemical behavior of

Ti2AlC in different solutions

, , /

.

1 3, , 2 2 10 1.


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In 3.5 Wt. % NaCl (OCP=- 0.139)


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In 1 M NaCO3 solution 10 mv/s (OCP=-

0.422)


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In 1 M H2SO4 10 mv/s (OCP=-0.194)


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AfterBefore


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Introducing 0.1 HCl to the anodizing solution at temperatures above 50 oC wasfound to break the MAX phase passivation. However, the required denies oxidelayer that is required for the self-healing was not obtained

Attempts to break the passive layer:


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0.05 MHCl

0.2 MHCl

0.3 MHCl

The breaking potential of the passive layer was found to shifted more negatively byincreasing the temperature or the HCl concentration


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It was found that once this layer break up the corrosion of the Ti2AlC proceedin a very fast rate and the corrosion product is not adherent to the basematerials and therefore can not be used for healing the crack.

SEM of the Ti2AlC sample after polarization In 0.3M HCl-2MH2SO4 for 2 Hours at constant potential of 3V and 70

oC


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, ,

/ .

0.122 ( H2O2, H3PO4,,HNO3) 10 1.


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The HCL was replaced by number of other gasses

in ordered to replace the aggressive Cl ions. ,

, / .

0.122 ( H2O2, H3PO4,, HNO3) 10 1.

More attempts to control the anodization of

MAX phase


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The obtained polarization curve was similar to that obtained for pure H2SO4solution


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Other aqueous systems: H2PO4-Base

solutions


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Is the passive layer caused by a cathodic

process.


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Is the electrochemical response of the crack

sample similar to that of the defect-freesurface?

0.000001

0.00001

0.0001

0.001

0.01

0.1

-0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5Applied Potential x 10 (V)

Current,(A/Cm2)

Crack

without crack


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Can we use this phenomenon to limit the

electrochemical process into the cracked area?Potentiostatic tests were carried out in 0.1 HCl-2 M H2PO4 at roomtemperature. The max sample polarized at 4 V versus Ag/Agclreference for time ranged between 5 to 30 minutes.


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After 30 minutes

The sample was corroded severely and about 1 mm-thick of thecorrosion product was covering the surface.


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After removing the corrosion product, the crack found to be filed with

amorphous material.


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After 5 minutes

The surface of the sample was partially covered by the corrosion

product. This product was limited only for the areas close to thecrack. Other areas was slightly corroded.


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After removing the corrosion

product


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More investigations on the filling materials

The sample after removing the corrosion product was heated in air

for 2 hours at 400 and 800 oC


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Heated at 400 oC


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Heated at 800 oC


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Attacking the materials surface by the electrolyte solutionto form filling materials from the bulk substrate needsvigorous conditions, and controlling the anodizationreaction is very difficult under such conditions.

This results showed clearly that the cracked surfaceperform differently than the defect-free surface towardthe applied current.

Controlling the electrochemical process for the area

around the crack was proved to be possible. A crack of 4mm length and width up to 100 micron wasfilled by amorphous carbon-base material


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Future work Phase I: Optimizing the anodization process by varying the

operating parameters. Electrolytes that have ions of the MAX matrixions should also be tested in the this phase.

Phase II: Testing the ability of healing the crack by depositing Alfrom ionic liquids.

Phase III: Investigating the electrophoretic deposition of aluminumand titanium carbides in the crack as a method of healing Al-Ti-baseMAXs.

Phase IV: investigate the deposition of Al and TI complexes ions in

the crack followed by controlled thermal dissociation to form oxidesor oxy-carbides.

Ti AlC d C AlC h diff


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Ti2AlC and Cr2AlC: how different

they are under corrosive conditions

Different cycles of potentiodynamic polarization were applied on the surface of

Ti2AlC and Cr2AlC in NaCl solution at room temperature between -1 to 2 Vversus Ag/AgCl reference. The potential sweep rate was fixed at 10 mV s 1 forall cycles. Between one cycle and the next, the sample was washed in water for

3 hours to remove any attached salt


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Ti2AlC

1st cycle 2nd cycle 3rd cycle


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Cr2AlC



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Proposed projectsProposed projects


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Conversion of CO2 polluted atmosphere into

functional material via an electrochemical method inionic liquid.

The major aim of the project is to develop novel ferromagnetic structures

based on SmCo5

nanowires encapsulated within CNTs by a practical processthat is both economically viable and environmentally friendly. The CNTs willbe synthesis in situ by electrolyse CO2 gas from polluted atmosphere.

(a). Magnetization vs. applied field curves, measured parallel and perpendicular to the applied field for the sample produced via electrodeoxidation ofCo

3O

4-Nd

2O

3precursors by applying 3.1 V in molten CaO-CaCl

2. (b) SEM images of flake-like particles consisting of NdCo5 coated with a thick graphite

layer produced via electrodeoxidation of Co-NdOxC

yprecursors (c) Hysteresis loops measured at 300 K for the flake-like particles.

New class of bulk nano-crystalline metallo-ceramics for


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New class of bulk nano crystalline metallo ceramics forultra high temperature application.

The purpose of this proposed project is to develop newclass of materials that can resist sever operatingconditions of high temperature gases, high energyplasma, and high level of radiation.

The first stage of the process will involve electrochemicalpreparation of fine powder of complex metallo-ceramic

examples include ( Ti-Al-V-N-C system, Nb-Hf-Ti-Csystem)

The second stage will involve compacting this nano-powder under special condition to form bulk materials in

different forms ( including complex shapes)


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Nano Nb9Hf1Ti05C powder prepared by electrochemical reduction of their oxides.

Electrophoretic deposition of complex carbides on

metallic substrates.

P i d h i i f f i l


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Preparation and characterisation of functional

oxides via electrochemical method in ionic liquids

The major aim of the project is to prepare

non-stoichiometric functional oxides byelectrochemical method using ionic liquidas electrolyte. The process will involve

partial reduction of the stable oxidesand/or deposit the functional radical fromthe electrolyte.


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A clearly visible white deposit

was observed on a gapbetween two sheets ofaluminum in Na2CO3 afterpolarized at constant potentialof 2V for 1 hour

Electrochemical healing of metals and alloys


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Thank You

aspects on electrochemical healing

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