bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Binding Mode in the Dynamic Coordination Chemistry of Porphyrins
Authors: Boitrel Bernard , Le Gac Stéphane , Ndoyom Victoria
Published: February 2020

In our on-going research program dedicated to the coordination of various cations of medical interests, we have been studying different types of porphyrinic architectures.1 Among these cations, bismuth appears as a plausible candidate for alpha-radiotherapy.2 Considering the decay scheme of its 213 isotope, it is obvious that the coordination chemistry of bismuth3 and lead4 and to some extent, thallium are somehow related and exhibit some similarities.

For instance, we have shown that an unprecedented transmetalation mechanism involving a daughter radionuclide is expected to increase the rate of 213Bi incorporation leading to 1Bi.5

Moreover, we will detail and demonstrate that this peculiar behaviour is rationalized by a translocation-coupled transmetalation mechanism, leading to the formation of a dinuclear complex in which coexist the long-known out-of-plane (OOP) coordination mode and the newly reported hanging-atop (HAT) coordination mode.6

 This HAT binding mode is found in both homo- and heterobimetallic complexes with lead and bismuth (see both X-ray structures above) and represents the prerequisite for metal migration processes according to which these dinuclear complexes behave as allosteric Newton’s Cradle-like devices (NCD).7 This NCD behaviour can be extended to other metal complexes and controlled and/or initiated in different ways.8

 

 1. Lemon, CM; Brothers PJ.; Boitrel B. Dalton Trans.
2011,
40, 6591-6609.

2. Yao Z; Zhang M; Garmestani K; Axworthy DB; Mallett RW; et al. Clin. Cancer Res.
2004, 10, 3137-3146.

3. a) Michaudet L; Richard P; Boitrel B. Chem. Commun.
2000, 1589-1590. b) Boitrel B; Breede M.; Brothers PJ; Hodgson M; Michaudet L; Rickard CEF; Al Salim N Dalton Trans.
2003, 1803-1807.c) Halime Z; Michaudet L; Razavet M; Ruzié C; Boitrel B. Dalton Trans.
2003, 4250-4254. (d) Boitrel B; Halime Z; Michaudet L; Lachkar M; Toupet L. Chem. Commun.
2003, 2670-2671. (e) Halime Z; Lachkar M; Roisnel T; Furet E ; Halet J-F; Boitrel B, Angew. Chem. Int. Ed., 2007, 46, 5120-5124.

4. Halime Z; Michaudet L; Lachkar M; Brossier P; Boitrel B. Bioconjugate Chem., 2004, 15, 1193-1200.

5. Le Gac, S.; Najjari, B.; Motreff, N.; Remaud-Le Saec, P.; Faivre-Chauvet, A.; Dimanche-Boitrel, M.-T.; Morgenstern, A.; Bruchertseifer, F.; Lachkar, M.; Boitrel, B. Chem. Commun.
2011,
47, 8554 - 8556.

6. Le Gac S.; Najjari B.; Fusaro L.; Roisnel T.; Dorcet V.; Luhmer M.; Furet E.; Halet J.-F.; Boitrel B. Chem. Commun., 2012, 48, 3724-3726.

7. Najjari B.; Le Gac S.; Roisnel T.; Dorcet V.; Boitrel B. J. Am. Chem. Soc.,
2012, 134, 16017-16032
.

8.
a) Le Gac, S.; Dorcet, V.; Fusaro, L.; Boitrel, B., Chem. Eur. J.
2013,
19, 13376-13386.  b) Le Gac, S.; Najjari, B.; Dorcet, V.; Roisnel, T.; Fusaro, L.; Luhmer, M.; Furet, E.; Halet, J.-F.; Boitrel, B., Chem. Eur. J.
2013,
19, 11021-11038. c) Le Gac, S.; Fusaro, L.; Roisnel, T.; Boitrel, B., J. Am. Chem. Soc.
2014,
136, 6698-6715.

Figure 1
From Breathing Pores to Three-Dimensional Ionic Self-Assembly Under Electrochemical Control
Authors: Mertens Stijn F. L. , Cui Kang , Ivasenko Oleksandr , Mali Kunal , Walter Michael , Feng Xinliang , Müllen Klaus , De Feyter Steven
Published: February 2020

Molecular self-assembly at the solid–liquid interface is highly developed, yet still faces several challenges, in particular related to reaching into the third dimension. Here, we demonstrate the spontaneous and reversible transition between two- and three-dimensional self-assembly of a charged polyaromatic molecule at the solid–liquid interface under electrochemical conditions, using in situ scanning tunnelling microscopy. By tuning the interfacial potential, we can selectively organise our target molecules in an open porous pattern, stretch these pores to accommodate another molecule and form an auto-host–guest structure, or stack the building blocks in a stratified bilayer. Using a simple electrostatic model, we rationalise which charge density is required to enable bilayer formation, and conversely, which molecular size/charge ratio is necessary in the design of new building blocks. Our findings could form the basis of electrochemically controlled dynamic host–guest systems and 3D structures such as artificial receptors.

References

[1] K. Cui, K.S. Mali, O. Ivasenko, D. Wu, X. Feng, M. Walter, K. Müllen, S. De Feyter, S.F.L. Mertens, Angew. Chem., Int. Ed. 53, 12951 (2014).

[2] K. Cui, O. Ivasenko, K. S. Mali, D. Wu, X. Feng, K. Müllen, S. De Feyter, S. F. L. Mertens, Chem. Commun. 50, 10376 (2014).

Figure 1
Silicon Nanocrystals Coated By Porphyrins As Light-Harvesting Antennae
Authors: Ceroni Paola , Locritani Mirko , Fermi Andrea , Bergamini Giacomo , Yu Yixuan , Korgel Brian A.
Published: February 2020

Silicon (Si) is a widely used semiconductor, in part because it is abundant, widely available and essentially non-toxic. From the photophysical point of view, it exhibits weak light absorption and emission because it has an indirect bandgap. Conversely, Si nanocrystals (SiNCs) in the quantum size range (2-12 nm) can be made as viable light emitters with emission wavelength that can be tuned from the near-infrared (NIR) into the visible by decreasing their size [1-3].  Covalent Si-to-carbon bonding also offers the possibility of integrating inorganic and organic components into robust structures. Most optical studies of SiNCs have focused on alkyl-passivated nanocrystals, while little is known about the interaction between such nanocrystals and chromophoric units attached to the core. Therefore we have studied the interaction of an inorganic silicon nanoparticle core with appended organic chromophores for the development of novel luminescent materials.

The synthesis of luminescent colloidal nanocrystals of silicon is still a difficult task in terms of reliability and reproducibility. We report the thermal decomposition of hydrogen silsequioxane, followed by etching and hydrosilylation [4]. This method isolated SiNCs with good yields, high surface coverage and exceptional control over the dimensions and optical properties of the materials.

In the present work, the H-terminated  nanocrystals were used as a platform for co-passivation with dodecene and different organic chromophores [5] by thermal hydrosilylation. For example, we functionalised two families of SiNC of average diameter of 2.5 and 5 nm with porphyrin chromophores: porphyrin excitation results in an efficient energy transfer to the nanocrystal core. To the best of our knowledge this is the first time in which highly efficient light harvesting from photoactive units to the silicon core have been demonstrated. This approach enabled us to circumvent the drawback of the low molar absorption coefficient of SiNCs. The investigated hybrid material exhibits high quantum yield also in the NIR spectral region with lifetime in the µs range.

[1] Brus, L. E.; Szajowski, P. F.; Wilson, W. L. Harris, T. D.; Schuppler, S.; Citrin, P. H. J. Am. Chem. Soc.
1995, 117, 2915-2922.

[2] Mastronardi, M. L.; Henderson, E. J.; Puzzo,D. P.; Ozin, G. A. Adv. Mater.
2012, 24, 5890-5898.

[3] Kelly, J. A.; Hendersonw, E. J.; Veinot, J. G. C. Chem. Commun. 2010, 46, 8704–8718

[4] Hessel, C. M.; Reid,D.; Panthani, M. G.; Rasch, M. R.;Goodfellow, B. W.; Wei, J.; Fujii, H.; Akhavan,V.; Korgel, B. A. Chem.
Mater.
2012, 24, 393−401.

[5] Locritani, M.; Yu, Y.; Bergamini, G.; Molloy, J. K.; Baroncini, M.; Korgel, B. A.; Ceroni, P. J. Phys. Chem. Lett.
2014, 5, 3325-3329.

Figure 1
Role of the Heme Axial Ligand on the Reactivity of High-Valent Oxo-Iron Porphyrin Intermediate
Authors: Fujii Hiroshi
Published: February 2020

High-valent iron oxo species have been known as the key reaction intermediates in the catalytic cycles of oxygen activating iron enzymes.  In heme enzymes, oxoiron(IV) porphyrin π-cation radical species named compound I were characterized in the catalytic cycles of peroxidases, catalases, and cytochrome P450.  These heme enzymes have the same heme (iron protoporphyrin IX), but different heme proximal (axial) ligands; histidine in peroxidase, tyrosine in catalase, and cysteine in cytochrome P450, which are highly conserved in these heme enzymes.  Therefore, the axial ligand has been believed to tune the reactivity of compound I.  To reveal functional role of the axial ligand, the axial ligand effect on the reactivity of high-valent iron oxo species has been studied systematically with synthetic enzyme model complexes.  In this presentation, we present how the heme axial ligand modulate the reactivity of compound I.  Compound I model complexes, (TMP+
·)FeIVO(L), changed its reactivity by identity of the axial ligand, but the reactivity did not correlate with any spectroscopic data of (TMP+
·)FeIVO(L), such as the redox potential and Fe=O bond strength.  Surprisingly, a clear correlation was found between the reactivity of (TMP+
·)FeIVO(L) and FeII/FeIII redox potential of (TMP)FeIIIL, the final reaction product.  Axail ligand-exchange experiments and theoretical calculations showed linear free-energy relationship, in which the axial ligand modulates the reaction free energy by changing the stability of (TMP)FeIII(L) more significantly than (TMP+
·)FeIVO(L).  All results indicate that the reactivity of compound I is controlled by thermodynamic stability of the ground state of the final reaction product, not but compound I itself.  Therefore, the heme axial ligand activates compound I by stabilizing the resting state, not by activating compound I.  The proposed mechanism can be explained by the trans-ligand effect of the oxo-ligand, which migrates from compound I to substrate in the reaction.
The Heme in Bacterioferritin Is Crucial to Bacterial Iron Homeostasis
Authors: Rivera Mario , Yao Huili , Wang Yan , Lovell Sott
Published: February 2020

Ferritin-like molecules are unique to cellular iron homeostasis because they can store iron at concentrations much higher than those dictated by the solubility of Fe3+. However, very little is known about the protein interactions that deliver iron for storage or promote the mobilization of stored iron from ferritin-like molecules. Bacterioferritins, which are iron storage proteins uique to bacteria, are spherical and hollow proteins that assemble from 24 identical subunits and 12 hemes. This talk will summarize our unique results demonstrating that (1) the function of bacterioferritin (BfrB) is required for P. aeruginosa growth under iron restricted conditions, (2) the function of BfrB in bacterial iron homeostasis requires binding and electron delivery by a cognate ferredoxin, Bfd, (3) the crucial BfrB/Bfd interface, defined by our X-ray crystallographic work, is highly complementary and likely conserved in a number of pathogens, and (4) blocking the BfrB/Bfd interaction leads to altered iron homeostasis, lowers P. aeruginosa fitness and exposes a bacterial vulnerability that may have significance in future development of novel antibiotics.
Developments of Porphyrin Derivatives As Photosensitizers for Photodynamic Therapy
Authors: Horiuchi Hiroaki
Published: February 2020

Photodynamic therapy (PDT) is accepted as one of the promising treatments for cancers. In PDT, three individually nontoxic components (photosensitizer, light, and molecular oxygen) are combined only in tumor tissue to produce reactive oxygen species (ROS), particularly singlet oxygen. Thus the patient can improve the quality of life by PDT different from conventional therapies, such as radiotherapy, surgery or chemotherapy. To develop PDT, improvements of the photosensitizing drug are required. Mainly, there are two methods to improve photosensitizers. The first is improvement of photodynamic activity. The second method is to reduce side effects. Tetraphenylporphyrin (TPP) is one of the most fundamental photosensitizers for PDT and thus we have tried to improve its activity and also tried to suppress its side effects.

First, we have tried to improve the activity. Factors controlling the activity involve accumulation efficiency to tumors, cellular uptake efficiency, light absorption efficiency in the red to near-IR region, and quantum yield of singlet oxygen sensitization. We substituted silyl groups to water-soluble TPP derivatives, because silicon is considered to have potential for improving pharmacological and/or photochemical efficiencies. Quantum yield of singlet oxygen sensitization has evaluated by monitoring near-IR phosphorescence from singlet oxygen sensitized, and found that silylation improve the quantum yield. Cell-culture studies have been carried out to evaluate pharmacological properties. We found that silylation also improve cellular uptake efficiency. We carried out in vivo study by using tumor-bearing mice. Silylation also improve selective accumulation efficiency. As a results of these improvements, in vivo PDT activity was found to be enhanced by silylation significantly [1].

Second, we have tried to suppress the side effects. Although the photosensitizer used for PDT possesses tumor selectivity, its concentration is not negligibly small in normal tissue such as skin. Photosensitizers themselves show no side effects in the dark, but under the sun or room light, the side effect will be induced. Thus patients have to remain in a dark room until almost all the photosensitizers injected are eliminated. These long periods are one of the reasons for hesitation in selecting PDT as a cancer treatment. To suppress the side effects, we introduced ON/OFF switching mechanism to photosensitizers. We selected very simple modification i.e. just introduction of amino group(s) to phenyl moiety of TPP derivative to switch photosensitization efficiency by acidity. In the neutral condition, the photosensitization efficiency was low (OFF state) because of photo-induced electron transfer quenching from the aromatic amine moiety to porphyrin moiety. In the acidic condition, the photosensitization efficiency recovered (ON state) by the protonation of amino group. This system is expected to be as a pH-activatable photosensitizer.

[1] H. Horiuchi et al., Chem. Eur. J., (2014), 20, 6054.
Engineering Self-Assembled Materials through Serendipity
Authors: Bonifazi Davide
Published: February 2020

Organic architectures are considered amongst the most promising candidates for engineering molecular-based devices. It is however necessary to develop systems that can form at interfaces organized molecular assemblies featuring addressable and controllable arrangements. In this respect, the hierarchical self-assembly of organic molecules featuring complementary non-covalent recognition sites allowing the simultaneous assembly of several units and long-range order is one of the most promising approaches.

In this talk, I will describe our approaches to engineer multidimensional structures through the exploitation of weak interactions established by programmed molecules. Quoting a letter (dated 28 January 1754) from Horace Walpole to Horace Mann, he said he formed it from the Persian fairy tale “The Three Princes of Serendip”, whose heroes "were always making discoveries, by accidents and sagacity, of things they were not in quest of". Therefore, specific serendipitous examples will be discussed with the attempt to answer to the question of whether and how the supramolecular approach can bridge organic chemistry with molecular organization and to which extend we can achieve macroscopic functions solely through molecular engineering.
Electroreduction of Oxygen with Brominated Metallo-Corroles
Authors: Elbaz Lior , Levi Naomi , Gross Zeev , Mahammed Atif
Published: February 2020

Fuel cell technology raised new interest over the past two decades due to the increasing oil prices, non-sustainability of fossil fuel and the consequences of combustion on air pollution and climate changes. Two aspects limit the practicality and energy conversion efficiency in polymer electrolyte membrane fuel cells: the rate-limiting oxygen reduction reaction at the cathode and the low abundance and high cost of platinum, which still remains the most efficient catalyst.

Significant effort has been made to develop alternative non-precious metal catalysts (NPMCs) for oxygen reduction. Many of those catalysts have been inspired by biological processes in that their active centers consist of transition metal complexes such as metallo-porphyrins. So far, studies conducted with such catalysts show that their activity and stability is lower than that of the state-of-the-art platinum based catalysts. In most recent years a new class of NPMCs has shown great promise; the metallo-corroles.

A series of first row transition metal β-pyrrole-brominated 5,10,15-tris(penta-fluorophenyl)- Corroles [M(tpfc)Br8, M=Mn, Fe, Co, Ni and Cu] were synthe-sized and tested as catalysts for oxygen reduction in acidic aqueous solutions. Both the reduced form and the oxidized forms of these corroles were chara-cterizes by means of NMR, EPR and UV-vis measurements. Rotating Ring-Disk electrode (RRDE) was used to test the kinetic performance of these corroles in the catalytic reaction of oxygen reduction (ORR). The corroles were adsorbed on a high surface area carbon powder (BP2000) prior to electro-chemical measurements, to create a unique composite material. The comparison between the corroles with different metal centers showed a favorable catalytic performance of the ORR in the case of the Co-Corrole, which showed an onset potential of only 0.8V vs. RHE (Figure 1).

Figure 1
N-H Hydrogen Bonding in Porphyrins - from Conformational Design to Supramolecular Chemistry
Authors: Senge Mathias O.
Published: February 2020

Typically porphyrin N-H units are not involved in intermolecular hydrogen bonds as they are ‘shielded’ by the macrocycle system. However, two possibilities exist to utilize the pyrrole nitrogen atoms in such bonds. A) Porpho(di)methenes and phlorins (calixphyrin-type systems) contain sp3-hybridized meso positions and the interruption of the aromatic system gives rise to specific cavities and often roof- or bowl-shaped conformations making the core nitrogen and N–H units more accessible for coordination. B) Likewise, saddle-distorted nonplanar porphyrins are very basic and can bind anions and neutral molecules via N-H hydrogen bonds. Similarly, specific conformations and binding motifs can be accessed in porphyrin dications (N22,N24-dihydroporphyrins) depending on the type, number, regiochemistry and steric bulk of substituents in the respective free base porphyrin. The different approaches will be compared and analyzed with regard to the design of ion-pair receptors for small molecules and anions and the formation of functional supramolecular complexes.
Electrochemical and Spectrochemical Studies of Diphosphorylated Metalloporphyrins: Unusual Formation of Phlorin Anion
Authors: Fang Yuanyuan , Chen Ping , Jiang Xiaoqin , Manowong Machima , Gorbunova Yulia G. , Sinelshchikova Anna , Enakieva Yulia Yu. , Tsivadze Aslan , Stern Christine , Bessmertnykh-Lemeune Alla , Guilard Roger , Kadish Karl M.
Published: February 2020

Two series of diphosphoryl-substituted porphyrins were synthesized and characterized by electrochemistry and spectroelectrochemistry in benzontrile, dichloromethane and pyridine containing 0.1 M tetra-n-butylammonium perchlorate. The investigated compounds are represented as 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrins and 5,15-bis-(diethoxyphosphoryl)-10,20-di(p-carbomethoxyphenyl) porphyrins (Chart). The porphyrins with non-redox active metal centers undergo two ring centered oxidations and two ring centered reductions, the latter of which is followed by a chemical reaction to give a phlorin anion. The phlorin anion is electroactive and can be reoxidized to give back the starting porphyrin or reversibly reduced to give a phlorin dianion. Each redox reaction was monitored by thin-layer UV-visible spectroelectrochemistry and an overall reduction mechanism is proposed.

Figure 1
Reactivity and Spectroscopic Studies of Oxygen Reduction Reaction of Bio-Inspired Molecular Catalysts
Authors: Ohta Takehiro , Nagaraju Perumandla , Naruta Yoshinori
Published: February 2020

Studies of oxygen reduction reaction (ORR) catalyzed by bio-inspired porphyrin catalysts is important for developing non-precious metal catalysts of fuel cell and for fundamental understanding of the reaction mechanism.  Molecular catalysts have advantage in study of ORR with more facile access to the reaction mechanism experimentally compared to biological and inhomogeneous systems.  We have previously shown that an axial ligand tethered iron porphyrin complex shows a crucial role in dioxygen activation [1].  As a next generation model a hanging hydrogen bond donor was incorporated at the distal site of heme that could stabilize heme bound intermediates and may induce proton-coupled electron transfer mechanism.  In ORR desorption of an OH ligand and formation of OOH intermediate are most energy demanding steps [2].  Our new model showed that the hydrogen bonding interaction can alter the thermodynamic properties of ORR facilitating efficient electron transfer to heme bound O2.  Resonance Raman studies of reaction intermediates provide direct evidence of reaction mechanisms as well as probe of metal-ligand and ligand internal covalency: As expected the incorporated hydrogen bond donor was found to interact with heme bound oxygen ligand.  The thermochemical properties of ORR were examined with density functional theory calculations, demonstrating H-bonding and axial ligation of heme are crucial structural mechanism in activation of O2.  The Sabatier principle states metal-ligand interaction is a descriptor of catalysts [2].  However in inhomogeneous system the reaction mechanism is not understood well due to difficulty of vibrational spectroscopic studies of the in situ reaction.  Thus our approach to study ORR provides deep insights into the molecular mechanism of electrocatalysts.  The structure/reactivity correlation gained by our reactivity and spectroscopic studies of bio-inspired molecular catalysts will be discussed.

[1] (a) J.-G. Liu, T. Ohta, S. Yamaguchi, T. Ogura, S. Sakamoto, Y. Maeda, Y. Naruta, Angew. Chem. Int. Ed., 48, 9262-9267 (2009).  (b) T. Ohta, J.-G. Liu, Y. Naruta, Coord. Chem. Rev., 257, 407-413 (2013).

[2] J. K. Nørskov et al., J. Phys. Chem. B, 108, 17886-17892 (2004)
Localized Corrosion of Carbon Steel in Simulated Concrete Pore Solution: Influence of Chloride Ion and Temperature
Authors: Sharifi-Asl Samin , Kursten Bruno , Macdonald Digby D
Published: February 2020

Passivity breakdown on carbon steel, which is  the reference candidate material for fabricating high-level nuclear waste containers in Belgium, has been studied and the data are interpreted in terms of the point defect model (PDM).  The near normal distribution in breakdown potential, measured in deaerated simulated concrete pore water solution (pH  12.5) at different chloride concentrations and temperatures are in satisfactory agreement with prediction of the PDM.  An increase in temperature from 25°C to 85°C results in a decrease in localized corrosion resistance according to a linear relationship between the critical breakdown voltage, Eb
, and log(chloride activity) for all chloride concentrations.  The linear dependence of the passivity breakdown potential on the square root of potential scan rate (ν1/2), as predicted by the PDM, yields an estimate of the critical areal concentration of condensed cation vacancies at the metal/film interface (ξ<=5.45×1014cm-2 at 85oC and <=1.07×1014cm-2 at 55oC ) that leads to the passivity breakdown.  The experimental distributions in the breakdown potential for carbon steel at 55oC and 85oC are in satisfactory agreement with the relevant calculated distributions.

Acknowledgment: The authors gratefully acknowledge the support of this work by ONDRAF-NIRAS of Belgium.
Electrochemical Measurement and Modeling of Corrosion Inhibition of Ternary Mixtures of Homologous Surfactants
Authors: Zhu Yakun , Free Michael L
Published: February 2020

In the present study, the corrosion inhibition efficiency (IE) of different mixtures of three homologous cationic surfactants, benzalkonium chlorides (ADBAC), were investigated using electrochemical measurements. There is excellent agreement between IE measured from EIS and LPR of the discussed mixture of ADBAC surfactants: C12Cl/C14Cl/C16Cl=0.70/0.25/0.05. The calculated adsorption free energy indicates that the adsorption mechanism of mixtures 0.70/0.25/0.05 is a mixed form of physisorption and chemisorption. A new critical micelle concentration (CMC) prediction model for ternary mixtures of homologous surfactants, on the basis of previous work, is developed over a wide concentration range of salt from 0.2% to 5.0% NaCl. The developed corrosion IE prediction model based on CMC prediction is an effective method that can be used for corrosion IE prediction of various mixed surfactant systems at various salt concentrations.
Microscopic Surface Studies of Modified Nickel-Based Superalloy 718 after Corrosion Fatigue in Simulated Sour Environment
Authors: Ziomek-Moroz Margaret , Hawk Jeffrey A. , Collins Keith , Rozman Kyle , Thodla Ramgopal , Gui Feng
Published: February 2020

The Unites States predicted 60% growth in energy demand by 2030 makes oil and natural gas primary target fuels for energy generation. The fact that the peak of oil production from shallow wells (< 5000 m) is about to be reached, thereby pushing the oil and natural gas industry into deeper wells. However, drilling to depths greater than 5000 m requires materials with high strength-to weight ratio, excellent corrosion resistance in H2S-contating sour environments, and high toughness.

Ni-based superalloy, also called Alloy 718, has been considered for use as a bottom-hole component during offshore drilling due to its good general corrosion resistance and lack of magnetism. However, its susceptibility to environmentally assisted cracking (EAC)  has not been studied for microstructures with increased high strength. To fill this technology gap, the National Energy Technology Laboratory in collaboration with DNV is currently studying mechanisms of fatigue crack growth rate (FCGR) for Alloy718, oil grade version, in simulated sour well environments.

The FCGR behavior of oil grade Alloy 718, was investigated by monitoring crack growth rate in deaerated 0.2% and 20 % NaCl solutions, respectively, in contact with H2S and CO2 as a function of frequency. The partial pressures for H2S (pH2S) was 692 kPa and for CO2 (pCO2) was 3458 kPa in each solution. Each fatigue experiment was performed at 177°C at ΔK=1392 Nmm-3/2 and R=0.2 in the frequency sequence 1Hz/ 0.3Hz/ 0.1Hz/ 0.03Hz/ 0.01Hz/ 0.003Hz followed by ΔK=522 Nmm-3/2 and R=0.7 in the sequence 1Hz/ 0.3Hz/  0.1Hz/ 0.03Hz/ 0.01Hz in an autoclave. Surface investigations were augmented by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). In this study, research focused on surface analyses supported by the fatigue crack growth rate measurements.

SEM backscatter electron (BSE) micrograph of the fracture surface after the fatigue experiment carried in 0.2% NaCl containing CO2 and H2S revealed no accumulation of the corrosion products The EDS chemical analysis near the crack tip found mostly nickel. In general, only transgranular crack growth was observed over the investigated ΔK and frequency scans.

SEM investigations of the fracture surface of the sample after the fatigue test in the 20% NaCl containing CO2 and H2S. sour environment at 177°C revealed the presence of secondary cracks, bright inclusions, and beach marks. The EDS chemical analysis of the bright inclusion, showed a (Nb, C)-rich phase. Also, corrosion products were not detected near the crack tip.

It appears that the passive layer is disturbed by the cyclic stress in each solution. The presence of secondary cracks at the crack tip of Alloy 718 in 20% NaCl/pH2S = 692 kPa/ pCO2=3458kPa indicates that this environment is more aggressive than 0.2% NaCl/ pH2S = 692 kPa/ pCO2=3458kPa.
Effect of Zinc Diffusion Distribution on Corrosion Behavior of Brazed Tube/Fin Assemblies of Aluminum Automotive Condensers
Authors: Guia-Tello Juan C. , Pech-Canul Maximo A. , Pech-Canul Martin I. , Gorocica-Diaz Jorge A. , Arana-Guillén René , Puch-Bleis José
Published: February 2020

The aim of this research is the evaluation of corrosion behavior in Sea Water Acidified Accelerated Test (SWAAT) solution of tube/fin assemblies from two aluminum condenser prototypes with micro-channel tubes having similar compositions but different amount of sprayed zinc per unit area (5.5 and 4.2 g/m2, respectively).  Such assemblies (Fig. 1) were brazed in a laboratory furnace under a pure nitrogen atmosphere. In order to simulate conditions for different diffusion rate and penetration depth, two sets of brazing parameters were selected: set A (610°C, 4min) and set B (600°C, 2min). The results of potentiodynamic polarization and electrochemical impedance measurements showed for both prototypes that the sample brazed under set B parameters exhibited lower corrosion rate compared to that brazed under set A parameters. The sample with lowest corrosion rate was the one with microchannel tubes containing 5.5 g/m2 of zinc before brazing. The observed corrosion behavior was correlated to zinc diffusion profiles obtained from SEM-EDS analysis. Galvanic current measurements showed that for short immersion times (1h) the tube is anodic to the fins, but the current is not stable and there is an evolution to lower values, suggesting that for long immersion periods there might be a inversion in the galvanic coupling.

Figure 1
Aluminum Corrosion Mitigation in Alkaline Electrolytes By Hybrid Inorganic/Organic Inhibitor System for Power Sources Applications
Authors: Gelman Danny , Lasman Itay , Elfimchev Sergey , Starosvetsky David , Ein-Eli Yair
Published: February 2020

The changing and expanding needs in the energy market, ranging from power grid energy storage system to portable power sources have necessitated the development of efficient, inexpensive, and high performance battery systems to better deal with the challenges posed by the nascent green economy and non-oil based transport system. One of the promising avenues for achieving these goals is the development of aluminum battery systems based on aluminum and aluminum alloys as anodes. The main advantages presented by this system are rather low equivalent weight of the aluminum, its high natural abundance in the Earth’s crust, its low price, and its safety characteristics; also, it is substantial that aluminum and its byproducts are non-toxic and environmentally friendly. Using aluminum for these applications requires overcoming various obstacles when using different electrolyte solutions. When using aluminum in alkaline based systems the corrosion rate is very high therefore, blemishes its use in alkaline based batteries. High parasitic corrosion rate impairs the functionality of the battery due to capacity lost, dangerous hydrogen generation and significantly shorten its shelf life. Although aluminum alloys can reduce parasitic corrosion, they are frequently complex and rather expensive materials. A promising solution to the undesired corrosion is to use inhibitors which mitigate self-corrosion. Different types of inhibitors are available for use at this time, but none of them mitigate the corrosion of aluminum in alkaline solution to the extent of commercialization of a battery system. In this work, an investigation was performed on the effect of a hybrid organic\inorganic inhibitor, poly(ethylene glycol) di-acid (PEG di-acid) and zinc oxide (ZnO), in a 5M KOH solution. The inhibitors behavior on a pure aluminum was studied electrochemically, microscopically, crystallographically, and element analysis tests were performed. Moreover, the performance of aluminum air cells with alkaline solutions utilizing the hybrid inhibition approach was evaluated by galvanostatic measurements (discharge). The results of our study clearly showed that there is a distinct and strong relation between the mitigation of the corrosion to the presence and concentration of both PEG di-acid and ZnO in the solution.  It was found that with the use of hybrid inhibition approach more than one order of magnitude redaction in corrosion currents and double the capacity of aluminum-air battery were achieved.

Figure 1
A Citrate-Based Coating System for AZ31 Magnesium Alloys
Authors: Chu Yu-Ren , Lin Chao-Sung
Published: February 2020

In light of highly active chemical properties of magnesium, surface modification is always essential to control its corrosion behavior in application.  Among the various modification processes, conversion coating is widely used due to its simplicity.  For the past decades, many conversion coating systems, including chromate, permanganate, phosphate, stannate, and cerium-based system, have been developed.  However, with ever-increasing concerns about environmental issues, a green process without the use of potentially hazardous species is required.  This study thus aims at developing a citrate-based coating system for AZ31 magnesium alloys.

  Prior to coating process, the AZ31 plates were abraded using emery paper up to 1200 grit, rinsed with deionized water, and dried by a stream of air. The conversion solution was applied to the AZ31 using a roll coater, and subsequently heated by hot air of approximately 75 °C for drying.

  The citrate-based coating system employs trisodium citrate as solute that is dissolved in aqueous or glycerin solution.  The coating formed in both solutions exhibits an identical surface morphology.  However, with sulfate ions coexisting with citrate, the coating formed in aqueous solution shows a completely different morphology.  Together with the change in the microstructure, the effect of sulfate ions is also observed in electrochemical analyses, including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).

  To further enhance the corrosion resistance, a post treatment using a citrate-based polyamide, poly(hexamethylene succinimide-co-citramide) (PSICA), is also proposed in this study.  It was found that the total impedance of the AZ31 in EIS increases from around 5,000 to 10,000 Ωcm2 after citrate-based conversion coating, and can be further elevated to near 15,000 Ωcm2 with the PSICA post treatment.
(Invited) Cr Volatility, Protective Coatings and SOFC Interconnect Testing
Authors: Froitzheim Jan , Alnegren Patrik , Falk-Windisch Hannes , Grolig Jan Gustav , Sachitanand Rakshith , Sattari Mohammad , Svensson Jan-Erik
Published: February 2020

High chromium ferritic steels are today the most commonly considered material for SOFC interconnects due to a combination of desirable properties, such as matching thermal expansion coefficient with other cell components but most importantly better machinability and price compared to ceramic alternatives. Yet, the high operating temperature (600-900°C) causes some materials degradation issues that need to be addressed in order achieve the desired long term stability over operating periods of several 10.000h.

The main function of the interconnect is to separate the fuel compartment from one cell from the air compartment of the neighboring cell and to conduct electricity between adjacent cells. Consequently the electrical conductivity needs to remain high throughout the fuel cell stack operating life time and thus the formed oxide layers need to be electrically conductive and thin. Secondly, volatilization of chromium from the oxide scale of metallic interconnects has shown to cause detrimental effects on the cathode in SOFCs.

In the current study oxidation behavior, chromium evaporation and oxide scale resistance of ferritic steel substrates are investigated in controlled atmospheres that simulate the environment of an operating SOFC stack. Additionally samples coated with nanometer scale dual coatings of Co and Ce were tested. The dual coating substantially increased the performance of the ferritic substrates by i) significantly reducing oxidation rate, ii) increasing scale adherence,  iii) diminishing chromium evaporation by 90 % via the formation of a Co-Mn-spinel cap layer and iv) substantially reducing the area specific resistance.
(Invited) Oxidation Mechanisms of Alloys for Advanced Ultra-Super Critical Steam Applications
Authors: Holcomb Gordon R
Published: February 2020

This research supports efforts to design and build safe and cost-effective advanced ultra-supercritical (A-USC) steam boilers and turbines, with increases in energy production efficiency and reductions in emissions, including CO2. A 1 liter flowing steam autoclave, rated to 346 bar/704°C and 228 bar/760°C, was constructed and steam oxidation tests conducted.   Comparison tests were run at 1 bar.  Parabolic rate constants were estimated from mass change data and compared with literature values from longer duration tests—but none at this high of combined temperature and pressure.  Test materials included Ni-base alloys H230, H263, H282, IN617, IN625 and IN740.  At high pressures the oxide scales were thicker and parabolic rate constants one–to-two orders of magnitude higher than at 1 bar.  The 1 bar data matched literature values for chromia, while the 267 bar data had a higher oxidation rate.  Possible causes for increased oxidation rates with increased pressure were examined.  Increased solid state diffusion within the oxide scale is quantifiable and accounts for a modest increases in expected corrosion rate and scale thickness.  Increased amounts of hydrogen in the alloy, injected into the metal during steam oxidation at high pressures, may increase oxygen permeability and thus lower the ability of the alloy to establish a chromia scale—an increase in the critical Cr content for chromia scales.
Effect of Sulphur on Fe-20Cr-(Mn, Si) Alloy Corrosion in CO2-H2O Gases at 650°C
Authors: Yu Chun , Nguyen Thuan Dinh , Zhang Jianqiang , Young David John
Published: February 2020

The oxyfuel process is a new technology in which coal combustion occurs in oxygen rather than air, producing a flue gas made up mainly of CO2 and H2O.  This makes CO2 collection and sequestration feasible. The traditional low Cr martensitic steels used successfully in conventional power generation are vulnerable to corrosion in oxyfuel atmospheres. As a result, a higher Cr concentration is required to form a protective chromia scale. Because of flue gas recirculation and the lack of nitrogen dilution in the oxyfuel process, a relatively high content of sulphur is present in the gas. Although the effect of sulphur on Fe-Cr corrosion in CO2-H2O atmospheres is not clear, it is believed to be adsorbed on oxide surfaces and grain boundaries, affecting mass transport of carbon.

The present research investigates the effect of sulphur on the corrosion of Fe-20Cr, Fe-20Cr-2Mn and Fe-20Cr-0.5Si (all in wt%) alloys in Ar-20%CO2-20%H2O with and without additions of SO2 at concentrations of  0.1%, 0.5%, and 1.0%, at 650°C. Corrosion kinetics were measured via weight gains in isothermal time lapse experiments. Corrosion products were characterized using X-ray diffraction, cross-section metallography, scanning electron microscopy and transmission electron microscopy together with energy dispersive spectroscopy.

In the sulphur-free gas, Fe-20Cr and Fe-20Cr-2Mn alloys experienced breakaway oxidation, forming a thick, iron-rich oxide scale, together with extensively precipitated intergranular and intragranular carbides within the alloys. Adding SO2 to the gas significantly improved the corrosion resistance of Fe-20Cr and Fe-20Cr-2Mn alloys by forming thin protective Cr2O3/ MnCr2O4
scales.  The formation of carbides was also significantly retarded due to preferential adsorption of sulphur blocking the diffusion of carbon. The Fe-20Cr-0.5Si alloy developed a protective, thin oxide scale in both sulphur-free and sulphur-containing gases.  This is attributed to the formation of a thin silica layer at the chromia scale-alloy interface.  This layer slowed oxide scaling by impeding outward metal diffusion, and prevented internal carburization by blocking carbon entry.
Characterization and Simulation of Residual Stress Generation during the Oxidation of Silicon Carbide
Authors: Krishnamurthy Ramanathan , Mogilevsky Pavel , Przybyla Craig , Parthasarathy Triplicane , Hay Randall
Published: February 2020

Oxidation of SiC-containing turbine and other structural components during high temperature operation generates residual stresses that can potentially lead to life-limiting environmentally assisted crack growth and failure. Currently, residual stress generation and/or relaxation during thermal oxidation of SiC is poorly understood. Here a combined experimental-modeling framework is introduced that provides new insight into the mechanisms of oxide formation, and, the magnitudes of the residual stresses induced when SiC is subjected to an oxidizing environment. SiC plates are oxidized at several temperatures over varying time periods, where after laser interferometry is employed to characterize the deformation induced in the plate due to the buildup of residual stress from the formation of the oxide. In this manner, values of the mismatch strain generated upon oxidation are extracted. In parallel, an integrated modeling approach for SiC oxidation is introduced that incorporates the essential physics associated with the diffusion of oxidant and effluent species, reaction at/near the interface, stress generation and viscoelastic/plastic relaxation mechanisms that accompany oxidation, respectively, and their interplay. Results are discussed regarding the generation and evolution of stress as the passive oxide layer grows at different temperatures in the range 500-1000ºC range. Insights obtained on the role of viscoelastic/plastic accommodation in oxidation and residual stress relaxation, and, the mechanisms underlying stress generation, are discussed. The impact of oxidation on environmentally assisted failure of SiC structures is also addressed.
Reaction Mechanism of CaO-MgO-Al2O3-SiO2 (CMAS) Corrosion in Pyrochlore Thermal Barrier Coatings
Authors: Wang Honglong , Sheng Zhizhi , Agubra Victor , Zhang Xingxing , Tarwater Emily , Fergus Jeff W.
Published: February 2020

Higher working temperatures improves the energy conversion efficiency in gas turbine engines so thermal barrier coatings are applied to protect the blades to increase the operating temperature.  However, CaO-MgO-Al2O3-SiO2 (CMAS) from volcanic ash and other debris can lead to corrosion of the coating. Rare earth zirconates with the pyrochlore structure are promising thermal barrier materials due to their low thermal conductivity and better corrosion resistance compared to the common thermal barrier material, yttria stabilized zirconia (YSZ). CMAS reacts with the pyrochlore materials to form cubic fluorite and silicate phases which can inhibit the corrosion process. In this presentation, Gd2Zr2O7 and Sm2Zr2O7 were used to study the corrosion mechanism of CMAS on pyrochlore materials.
(Invited) A Wet Process of Copper Wiring on Surface Modified Polyimide Film By Aminosilanes
Authors: Osaka Tetsuya , Yokoshima Tokihiko , Kagawa Hiroki , Hachisu Takuma , Sugiyama Atsushi
Published: February 2020

Polyimide (PI) film is widely used in several applications especially in the electronics industry, e.g., as a base material for ﬂexible printed wiring assembly, because of its excellent mechanical and thermal stability and a low dielectric constant. Our group proposed an all-wet process to fabricate the diffusion barrier layer and Cu wiring by using an organosilane layer as an adhesive/catalyst layer as shown in fig. 1 [1, 2]. Additionally, wet processes offer relatively simple procedures and tools, and usually are cost effective.

In previous study, an immobilized aminosilane film on polyimide works as an adhesion layer and a catalyst supporting layer for electroless deposition (ELD) of NiB. Adhesion of NiB-ELD film on ultra-smooth polyimide is a particular need for realizing a high-density printed circuit board [3]. We have reported that an induction time of NiB-ELD was changed by the number of amino groups in aminosilane, and a shorter induction time was found in the aminosilane having two or three amino groups as compared with that having single.

Our recent critical problem is in the step of Cu deposition onto NiB-ELD: a low reduction rate of cupric ion in sulfuric acid, or if the reduction proceeded, the film peeling was observed. We therefore used the alkaline electrolytes developed by Japanese company or it’s improved to fabricate Cu wiring, and examined thermal annealing effect on the electronic conductivity, crystallinity.

References

[1] T. Osaka, M. Yoshino, “New Formation Process of Plating Thin Films on Several Substrates by Means of SAM (Self-Assembled Monolayer) Process”, Electrochim. Acta, 53, 271 (2007).

[2] M. Yoshino, T. Masuda, T. Yokoshima, J. Sasano, Y. Shacham-Dimand, I.Matsuda, T. Osaka, A. Hashimoto, Y. Hagiwara, I. Sato, “Electroless Diffusion Barrier Process Using SAM on Low-k Dielectrics”, J. Electrochem. Soc, 154, D122 (2007)

[2] T. Osaka, S. Wakatsuki, T. Masuda, M. Yoshino, N. Yamachika, J. Sasano, I. Matsuda, Y. Okinaka, “A Wet Process for Forming an Adhesive Copper Layer on Polyimide Film”, Electrochemistry, 76, 191 (2008).

Figure 1
Direct Copper Electroplating on Polyimide Film By Using Ni As Barrier and Conductive Interlayer
Authors: Chan Po-Fan , Huang Shang-En , Dow Wei-Ping
Published: February 2020

Ni interlayer is formed on the polyimide(PI) film by sequential steps: PI ring-opening by KOH(aq), ions exchange between K+ and Ni2+, and the reduction of Ni2+. Dimethylamine borane (DMAB) with a specific additive is used as the reducing agent. The specific additive plays an important role that it not only shortens the Ni2+ reduction incubation time, but also makes the Ni film uniform and conductive. We also compared reducing agent DMAB with reducing agent NaBH4. The reducibility of NaBH4 is higher than that of DMAB, but NaBH4 produced a dark and non-conductive Ni film because it contained a small amount of boron. FTIR and AFM were used to measure the functional group and surface roughness after PI ring-opening, and surface morphology after each steps were observed by SEM. Pinholes were formed on the Cu/Ni/PI when KOH strongly reacted with PI, and these caused adhesion problem between the deposited metal and the PI film. In this process, adhesion issues are summarized in the following two points: one is PI shrink and cracks formation in the ions exchange step because the pH difference between the first two steps is too big , the other is the moisture content in the ring-opened PI would affect the subsequent steps. As a result, with the specific additive in the reducing agent, copper can directly electrodeposition on the Ni/PI, and the adhesion between the deposited metal and PI film is depended on the condition of the ring-opening and the ions exchange steps.
Fabrication of Mechanically-Robust Cu Films on Flexible Substrates Using Electron Beam Irradiation
Authors: Choi In-Suk , Joo Young-Chang , Lee So-Yeon , Lee Ji-Hoon
Published: February 2020

A primary challenge for a designing of flexible and stretchable devices is to prevent the mechanical failure of the metallic electrodes and interconnects integrated on polymeric substrates under mechanical deformation, e.g., tension, compression, and bending. Herein, we firstly demonstrated that the irradiation of e-beam could significantly improve the mechanical stability of Cu film deposited on polyimide (PI) substrate. The 100nm thick Cu film was deposited on the PI substrate by thermal evaporation and then directly irradiated by low power of e-beam using the scanning electron microscope (SEM). When we applied a tensile strain of 30 %, the e-beam irradiated Cu film on the PI substrate did not exhibit any significant damage, whereas the pristine Cu films did form channeling cracks or delamination. Furthermore, the resistance of the irradiated Cu film increases much less than that of pristine Cu film at a strain of 30%. The mechanical stability was possibly improved due to the enhancement of adhesion between Cu and PI by e-beam irradiation. We believe that our new finding will open up a new facile method to enhance the reliability of metal interconnects and electrodes in the flexible and stretchable devices.