Mitigation of Silicon Contamination in Fuel Cell Gasket Materials through Silica Surface Treatment

Gaskets and seals are essential components in the operation of proton exchange membrane (PEM) fuel cells and are required for keeping hydrogen and air/oxygen within their individual compartments. The durability of these gaskets and seals is necessary, as it influences not only the lifespan but also the electrochemical efficiency of the PEM fuel cell. In this study, the cause of silicon leaching from silicone gaskets under simulated fuel cell conditions was investigated. Additionally, to reduce silicon leaching, the silica surface was treated with methyltrimethoxysilane, vinyltriethoxysilane, and (3,3,3-trifluoropropyl)trimethoxysilane. Changes in the silica surface chemistry were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, elemental analysis, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Inductively coupled plasma-optical emission spectroscopy analysis revealed that surface-treated silica was highly effective in reducing silicon leaching.

The Synergistic Inhibitions of Tungstate and Molybdate Anions on Pitting Corrosion Initiation for Q235 Carbon Steel in Chloride Solution

In this work, the synergistic inhibitions of tungstate (WO₄^2-) and molybdate (MoO₄^2-) anions, including role and mechanism, on the initiation of pitting corrosion (PC) for Q235 carbon steel in chloride (Cl^-) solution were investigated with electrochemical and surface techniques. The pitting potential (E_p) of the Q235 carbon steel in WO₄^2- + MoO₄^2- + Cl^- solution was more positive than that in WO₄^2- + Cl^- or MoO₄^2- + Cl^- solution; at each E_p, both peak potential and affected region of active pitting sites in WO₄^2- + MoO₄^2- + Cl^- solution were smaller than those in WO₄^2- + Cl^- or MoO₄^2- + Cl^- solution. WO₄^2- and MoO₄^2- showed a synergistic role to inhibit the PC initiation of the Q235 carbon steel in Cl^- solution, whose mechanism was mainly attributed to the influences of two anions on passive film. Besides iron oxides and iron hydroxides, the passive film of the Q235 carbon steel formed in WO₄^2- + Cl^-, MoO₄^2- + Cl^-, or WO₄^2- + MoO₄^2- + Cl^- solution was also composed of FeWO₄ plus Fe₂(WO₄)₃, Fe₂(MoO₄)₃, or Fe₂(WO₄)₃ plus Fe₂(MoO₄)₃, respectively. The film resistance and the defect quantity for Fe₂(WO₄)₃ plus Fe₂(MoO₄)₃ film were larger and smaller than those for FeWO₄ plus Fe₂(WO₄)₃ film and Fe₂(MoO₄)₃ film, respectively; for the inhibition of PC initiation, Fe₂(WO₄)₃ plus Fe₂(MoO₄)₃ film provided better corrosion resistance to Q235 carbon steel than FeWO₄ plus Fe₂(WO₄)₃ film and Fe₂(MoO₄)₃ film did.

Melt Blending Modification of Commercial Polystyrene with Its Half Critical Molecular Weight, High Ion Content Ionomer, Poly(styrene-ran-cinnamic Acid) Zn Salt, toward Heat Resistance Improvement

A half-critical weight-average molecular weight (M¯w) (approximately 21,000 g mol⁻¹), high-ion-content Zn-salt poly(styrene–ran–cinnamic-acid) (SCA–Zn) ionomer was successfully synthesized by styrene–cinnamic-acid (10.8 mol %) copolymerization followed by excess-ZnO melt neutralization. At 220 °C, the SCA–Zn’s viscosity was only approximately 1.5 magnitude orders higher than that of commercial polystyrene (PS) at 10² s⁻¹, and the PS/SCA–Zn (5–40 wt %) melt blends showed apparently fine, two-phased morphologies with blurred interfaces, of which the 95/5 and 90/10 demonstrated Han plots suggesting their near miscibility. These indicate that any PS–(SCA–Zn) processability mismatch was minimized by the SCA–Zn’s half-critical M¯w despite its dense ionic cross-links. Meanwhile, the SCA–Zn’s Vicat softening temperature (VST) was maximized by its cross-linking toward 153.1 °C, from that (97.7 °C) of PS, based on its half-critical M¯w at which the ultimate glass-transition temperature was approximated. Below approximately 110 °C, the PS/SCA–Zn (0–20 wt %) were seemingly miscible when their VST increased linearly yet slightly with the SCA–Zn fraction due to the dissolution of the SCA–Zn’s cross-links. Nevertheless, the 60/40 blend’s VST significantly diverged positively from the linearity until 111.1 °C, revealing its phase-separated morphology that effectively enhanced the heat resistance by the highly cross-linked SCA–Zn. This work proposes a methodology of improving PS heat resistance by melt blending with its half-critical M¯w, high-ion-content ionomer.

An electrochemical study of pH influences on corrosion and passivation for a Q235 carbon steel in HNO3-NaNO2, HAc-NaNO2 and HCl-NaNO2 solutions

In this study, the influences of different pH values on the corrosion and passivation behaviors of a Q235 carbon steel in HNO₃-NaNO₂, HAc-NaNO₂ and HCl-NaNO₂ solutions were studied by electrochemical methods. The manifestations of the electrochemical characteristics were revealed and the variations in the electrochemical parameters were clarified. Moreover, for the Q235 steel in the three solutions with different pH values, the decrease in the corrosion current density (i _corr) and the increase in the charge transfer resistance (R _ct) in each solution, indicated a decrease in the corrosion rate. The decrease in the critical passivation current density (i _crit) and increase in the passive film resistance (R _f) suggested the reinforcement of passivation capability. On the other hand, in the three solutions at the same pH value, the corrosion rate increased and the passivation capability weakened in HNO₃-NaNO₂, HAc-NaNO₂ and HCl-NaNO₂ solutions. Simultaneously, the related electrochemical mechanisms of corrosion and passivation for Q235 carbon steel in acidic solutions containing nitrite anions (NO₂ ^-) were also discussed.

The relationship between activation-passivation transition and grain boundary dissolution on four steel samples in acidic solutions containing NO2. RSC Adv 2019;9:23589-23597. [PMID: 35530634 PMCID: PMC9069641 DOI: 10.1039/c9ra03983j]

Herein, for four steels (L80, N80, X65 and Q235) in acidic solutions (HNO₃, HCl, HAc and CO₂) containing NO₂⁻, the relationship between the activation–passivation (A–P) transition and the grain boundary dissolution (GBD) was studied by potentiodynamic polarization curve (PPC) measurements and scanning electron microscopy (SEM) observations. In the specific pH range of acidic solutions, where the four steels showed an electrochemical characteristic of the A–P transition, GBD was observed on the steel surface; however, at low or high pH values of the acidic solutions, the four steels respectively showed the electrochemical behavior of activation (A) or self-passivation (sP), and GBD was not observed on the steel surface. The effects of the acid type, pH value and steel type on the electrochemical characteristic of the A–P transition and the occurrence of GBD were also discussed in detail. Via this study, it was confirmed that under the electrochemical characteristic of the A–P transition, the occurrence of GBD was a general corrosion behavior of carbon steels and alloy steels in acidic solutions containing NO₂⁻.

The relationship between activation–passivation transition and grain boundary dissolution for L80, N80, X65 and Q235 steels in HNO₃, HCl, HAc and CO₂ solutions containing NO₂⁻ was studied by electrochemical tests and microstructural observations.

The Preparation, Characterization and Formation Mechanism of a Calcium Phosphate Conversion Coating on Magnesium Alloy AZ91D

The poor corrosion resistance of magnesium alloys is one of the main obstacles preventing their widespread usage. Due to the advantages of lower cost and simplicity in operation, chemical conversion coating has drawn considerable attention for its improvement of the corrosion resistance of magnesium alloys. In this study, a calcium phosphate coating was prepared on magnesium alloy AZ91D by chemical conversion. For the calcium phosphate coating, the effect of processing parameters on the microstructure and corrosion resistance was studied by scanning electron microscope (SEM) and electrochemical methods, and the coating composition was characterized by X-ray diffraction (XRD). The calcium phosphate coating was mainly composed of CaHPO₄·2H₂O (DCPD), with fewer cracks and pores. The coating with the leaf-like microstructure provided great corrosion resistance to the AZ91D substrate, and was obtained under the following conditions: 20 min, ambient temperature, and no stirring. At the same time, the role of NH₄H₂PO₄ as the coating-forming agent and the acidifying agent in the conversion process was realized, and the formation mechanism of DCPD was discussed in detail in this work.