First-Principles Study on the Effect of Pure and Oxidized Transition-Metal Buffers on Adhesion at the Alumina/Zinc Interface

Phys. Chem. Chem. Phys.

et al. 2018

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The weak interaction between zinc and silica is responsible for a poor performance of anti-corrosive galvanic zinc coatings on modern advanced high strength steels. With the goal of identifying its microscopic origin, we report an extensive ab initio study on the structural, electronic, and adhesion characteristics of a variety of model zinc/β-cristobalite interfaces, representative for different oxidation conditions. We show that the weakness of the zinc-silica interaction at non polar interfaces is driven by the presence of surface siloxane rings. These latter are drastically detrimental to interface adhesion when intact and their breaking is impeded by a large energy barrier. Conversely, the characteristics of polar interfaces are principally driven by the capacity of zinc to screen the surface compensating charges and to form O-Zn bonds. This screening is especially efficient in an oxygen-rich environment where the substrate-induced partial oxidation of the zinc deposit produces a considerable enhancement of interface adhesion. The identified microscopic mechanisms of interface interactions furnish precious guidelines towards practical attempts to improve adhesion. In particular, processes which enable breaking the surface siloxane rings are expected to noticeably reinforce the interaction at non-polar interfaces.

Section: Discussionmentioning

confidence: 99%

Structural, electronic and adhesion characteristics of zinc/silica interfaces: ab initio study on zinc/β-cristobalite

Phys. Chem. Chem. Phys.

et al. 2018

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“…The above settings assure a satisfactory agreement between calculated and experimental characteristics of the bulk materials as demonstrated in Figure 1, which displays the oxygen conditions under which the metals under consideration and their oxides are stable. Figure 2 shows the models of oxidejoxide, metaljmetal, and oxidejmetal interfaces used pigure IX gritil vlues of oxygen hemil potentil ove whih oxidtion of metls is thermodynmilly fvoredF 23 hpEvd results re ompred to vlues dedued from the experimentl stndrd enthlpies @per oxygen tomA of oxide formtion ¡ f H 0 @PWVFISuAF 32,33 pigure PX hemti representtion of A oxidejoxideD A metljmetlD nd A oxidejmetl interfesF yxygen toms re represented y smll red llsD tions nd metl toms y lrge lue nd golden llsD respetivelyF 34 in the lultionsF ell lultions on individul interfes were performed in superlttie geometry involving two identil interfes per periodi unit ell nd hving the inEplne lttie prmeters xed to the theoretil ulk lumin ones @ a a R:VI # eAF hriven y the el 2 y 3 @HHHIA sustrteD orundum struture ws lso ssumed for hromium nd iron oxE ides nd three EwGQyGwE @HHHIA triElyers with @I ¢IA inEplne periodiity were used in superlttie lultionsF gonverselyD the metl omponents were represented y seven dense tomi lyers gr@IIHAD pe@IIHAD xi@IIIA nd n@HHHIAD for whih the est inEplne ommenE surility with the oxides ws provided y @distortedA @ he onsequenes of the lttie distortion imposed in the lultions n e estimted y ompring surfe nd dhesion energies otined with the interfe struture mthing tht of lumin or orresponding to struturl verge of the two mterilsF por exmpleD in the se of el 2 y 3 jgr 2 y 3 interfe @Q7 lttie mismthAD surfe nd dhesion energies hnge y less thn HFIEHFP t=m 2 F his dierene is somewht lrger @HFPEHFR t=m 2 A in the se of el 2 y 3 Gpe @IQ7 lttie mismthAF he impt of the unertinties due to the hoie of exhngeEorreltion funtionl nd of interfe models will e disussed in the following setionsF Monte Carlo Metropolis simulations. he wg wetropolis lgorithm 38 ws used to generte the thermodynmilly most fvorle sequenes of omponents in the lumin j 1 j 2 j 3 j:::j N jzin superstrutureF et eh wg stepD two rndomly hosen omponents i nd j were tentE tively exhnged nd the new ongurtion ws epted with proility p a minI; exp@ ¡i=k B AD where k B is the foltzmnn onstnt nd is the tempertureF ¡i represents the hnge of the totl formtion energy i a i aluminajX 1 int C i X 1 jX 2 int C ::: C i X N jzinc int indued y the exhngeF sn the present simultionsD we hve used a ISHH u @k B = $ HFI t=m 2 A nd PH ¢ IH 6 wg steps nd the results were verged fter system equilirtion of IH 6 stepsF As to represent a realistic composition prole of the buer and to enable mixing and/or separation of each of its components, the latter were represented by several replicas each and the position of each replica was independently optimized.…”

Section: Computational Methods and Settingsmentioning

confidence: 99%

Improving Adhesion at the Alumina/Zinc Interface by Stainless Steel Buffers

et al. 2017

J. Phys. Chem. C

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The weak interaction between zinc and alumina is responsible for a poor performance of anti-corrosive galvanic zinc coatings on modern advanced high strength steels. In this context, we report a theoretical study on the eect of realistic multi-component metal buers on the adhesion strength of a model-alumina(0001)jzinc interface. Relying on results of ab initio calculations on relevant individual oxidejoxide, oxidejmetal, and metaljmetal interfaces (separation and interface energies), we determine by Monte Carlo simulations the thermodynamically preferred sequence of components in a multicomponent buer, as a function of buer composition and oxygen conditions. We nd that stainless steel buers considerably enhance the overall strength of the aluminajzinc interface. Most importantly, we show that a partial oxidation of multi-component buers, which is unavoidable under realistic conditions, does not degrade their performance. This advantageous property relies on the separation of metal and oxide components in the buer and on the resulting suppression of weakly interacting oxidejzinc, and moderately strong aluminajmetal interfaces. More generally, owing to the possibility of selective oxidation and component segregation, multi-component buers appear as promising solutions for adhesion improvement at weakly interacting metaljoxide interfaces.

“…In this context surface pre-hydroxylation appears as a promising route towards breaking surface siloxanes and improving the interface adhesion. 11 Aside application of inox buffer layers, as proposed for the similar zinc/alumina interfaces, 12,13 an alternative solution may rely on the formation of a mixed interfacial oxide phase, such as zinc silicate Zn 2 SiO 4 . [14][15][16] Such interfacial phase would impact the interactions occurring at the interface and, depending on the thermodynamic conditions, could enhance the adhesion through various pathways.…”

Section: Introductionmentioning

confidence: 99%

Surface thermodynamics of silicate compounds: the case of Zn₂SiO₄(001) surfaces and thin films

Baima

Phys. Chem. Chem. Phys.

et al. 2019

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Silicate compounds are ubiquitous in nature and display a vast variety of structures and properties. Thin silicate films may also form under specific conditions at interfaces between metals and silica. In the present study, we focus on zinc silicate and present a thorough density functional theory-based study of polar and non-polar (001) surfaces of various stoichiometry of its tetragonal polymorph t-Zn 2 SiO 4 . At the non-polar surfaces, the main features are the existence of the chain reconstruction at the ZnO termination, and the presence of unsaturated surface silanols at the SiO 2 termination. Stabilization of polar surfaces is provided by the formation of O 2− 2 peroxo groups, reduction of the surface or subsurface Si atoms or formation of Zn 2+ 2 groups, depending upon the surface stoichiometry. While the non-polar stoichiometric and ZnO rich terminations are the most stable in a large part of the accessible phase diagram, the SiO 2 termination is less stable due to the absence of siloxane group formation. We show that, while bulk Zn 2 SiO 4 is stable with respect to decomposition into the ZnO and SiO 2 oxides, the same is not true for ultra-thin films due to the fundamental difference of silicate and silica surface energies. Preliminary results show that a similar conclusion could be drawn Fe 2 SiO 4 . This study opens towards a deeper understanding and possible improvement of zinc adhesion at silica surfaces, of crucial industrial importance.