Behavior of blended cement mortars exposed to sulfate solutions cycling in relative humidity

In recent years, several cases of damage to concrete structures due to sulfate exposure have occurred essentially in the above ground parts of structures. Such distress, often characterized by white efflorescence and surface scaling, is driven by salt crystallization in pores and/or repeated reconversions of certain sulfates between their anhydrous and hydrated forms under cycling temperature and relative humidity (RH). However, the effect of the water/cementitious materials ratio (w/cm), pozzolanic additions, and other parameters on the durability of cement-based materials under such exposure conditions is still misunderstood. In this study, 12 cement mortars having different w/cm (0.30, 0.45, and 0.60) and made with ordinary portland cement (OPC) or OPC incorporating 8% silica fume, 25% class F fly ash, or 25% blast furnace slag were made. Standard bars from each of these mortars were submerged in both 10% magnesium sulfate (MgSO₄) and 10% sodium sulfate (Na₂SO₄) solutions; their expansion and surface degradation was monitored for up to 9 months. In addition, cylinders made from these 12 mortars were partially submerged in 50-mm-deep 10% MgSO₄ and 10% Na₂SO₄ solutions. Half of the cylinders were maintained under constant temperature and RH, whereas the others were subjected to cycling RH. The effect of the w/cm and mineral additions on the classic chemical sulfate attack and development of efflorescence was investigated, and the results are discussed in this article.     

Approximate migration coefficient of percolated interfacial transition zone by using the accelerated chloride migration test

In this study, the electrochemical technique is applied to accelerate chloride ion migration in cement-based material to estimate its migration coefficient. In order to investigate the chloride migration coefficient of percolated interfacial transition zone (ITZ) on the chloride migration coefficient of specimen, specimens with cylindrical aggregates of the same height as the specimen were cast and tested. In this study, the volume fraction of aggregate is constant and the varied lateral surface area of the aggregate cylinder was obtained by using different diameters and number of aggregate. The chloride migration coefficient of cement-based material was determined experimentally as a function of the lateral surface area of aggregate. A model obtained for the migration coefficient of cement-based material and the regression analysis are used to determine the approximate chloride migration coefficient of the percolated ITZ. Based on the experimental and regression analytical results, the approximate percolated ITZ migration coefficient is 40.6, 35.5, and 37.8 times of the altered migration coefficient of matrix mortar for the water/cement (w/c) ratio of 0.35, 0.45, and 0.55, respectively.     

Cracking behavior and delamination mechanism of lamellar structured TBC with localized mixed oxides

Mixed oxide (MO) with localized growth feature and high growth rate remarkably affects the lifetime of thermal barrier coatings (TBCs), which indicates that clarifying the ceramic cracking mechanism induced by MO is critical for developing new coatings with high durability. Two kinds of TBC models involving spherical and layered mixed oxides are created to explore the influence of MO growth on the local stress state and crack evolution during thermal cycle. The growth of α-Al₂O₃ is also included in the model. The undulating interface between ceramic coat and bond coat is approximated using a cosine curve. Dynamic ceramic cracking is realized by a surface-based cohesive interaction. The ceramic delamination by simulation agrees with the experimental observation. The effects of MO coverage ratio and growth rate on the TBC failure are also discussed. The results show that the MO growth causes the local ceramic coat to bear the normal tensile stress. The failure mode of coating is turned from α-Al₂O₃ thickness control to MO growth control. Once the mixed oxide appears, local ceramic cracking is easy to occur. When multiple cracks connect, ceramic delamination happens. Suppressing MO formation or decreasing MO growth can evidently improve the coating durability. These results in this work can provide important theoretical guidance for the development of anti-cracking TBCs.     

The Durability of Adhesively-bonded Ti-6Al-4V

The durability of chromic acid-anodized Ti-6Al-4V alloy, adhesively-bonded with FM-5 supported polyimide adhesive has been studied. The performance tests compared titanium samples that had been thermally treated and bonded, and samples that were bonded and thermally treated. Following the thermal treatment, the durability was examined (1) by immersing wedge-type specimens in boiling water and measuring the crack growth and (2) by measuring the lap shear strength for single lap specimens. In the wedge tests, failure occurs within the adhesive for specimens treated at temperatures below 371°C for less than one hour. For treatments at higher temperatures and for longer periods of time, failure occurs within the anodic oxide. From the lap shear tests, the principal finding is that the lap strength decreases with increasing treatment time at constant temperature and with increasing temperature at a fixed time. For the lap specimens, failure occurs to a greater extent within the oxide as the treatment time and temperature increase. Surface analysis results indicate the formation of an aluminum fluoride species. It is reasoned that the formation of fluorine-containing materials weakens the oxide and promotes failure within the anodic oxide.     

H2O-tolerant monolithic catalysts for preferential oxidation of carbon monoxide in the presence of hydrogen

Pt–Fe/mordenite (4 wt% Pt–0.5 wt% Fe) powder catalysts were wash-coated onto ceramic straight-channel monoliths by using silica- and/or alumina-sol as a binder, and were evaluated for the preferential oxidation of carbon monoxide (PROX) in a hydrogen-rich gas. In a synthetic reformate gas (1% CO, 1% O₂, 5% H₂O, 20% CO₂, and balance H₂), the CO concentration was reduced to less than 20 ppm at temperatures ranging from 100 to 130 °C. After a certain period of the PROX reaction, condensation of H₂O in the pores of the mordenite-support occurred over the monolithic catalyst, which was wash-coated with alumina-sol, in the lower temperature range (100–120 °C), resulting in a rapid increase in CO concentration. The monolithic catalyst wash-coated with silica-sol, however, showed an excellent tolerance against H₂O condensation and offered a stable catalytic performance, maintaining a CO concentration of ca. 20 ppm for 200 h. The H₂O-tolerant characteristic was attributed to the relatively small adsorption amount of H₂O over the silica-modified monolithic catalyst.     

The durability of different elements doped manganese dioxide-coated anodes for oxygen evolution in seawater electrolysis

Manganese-molybdenum (Mn-Mo), manganese-molybdenum-vanadium (Mn-Mo-V), manganese-molybdenum-iron (Mn-Mo-Fe) and manganese-iron-vanadium (Mn-Fe-V) anodes were prepared by anodic electrodeposition on iridium oxide-coated titanium substrates for oxygen evolution in seawater electrolysis. XRD, FESEM, EDX and oxygen evolution efficient analysis revealed that the prepared anodes had a γ-MnO₂ structure and show a unique mesh-like nanostructure. Oxygen evolution efficiencies were all measured to be more than 99%. The durability tests were performed at 1000 A·m^− 2 in 3.5 wt% NaCl solution at pH 12 and 90 °C. The Mn-Fe-V anode was the most stable electrode during the sea water electrolysis, and maintained an oxygen evolution efficiency of 87.96% even after 500 h. It has been found that the main reason for the eventual decrease in oxygen evolution efficiency was partly because of the peeling and electrochemical dissolution of the oxide layer after electrolysis. Also, it was found that the addition of iron and vanadium would maintain a high level of oxygen evolution efficiency during electrolysis.     

Al2O3-nanodiamond composite coatings with high durability and hydrophobicity prepared by aerosol deposition

We attempted the room-temperature fabrication of Al₂O₃-based nanodiamond (ND) composite coating films on glass substrates by an aerosol deposition (AD) process to improve the anti-scratch and anti-smudge properties of the films. Submicron Al₂O₃ powder capable of fabricating transparent hard coating films was used as a base material for the starting powders, and ND treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) was added to the Al₂O₃ to increase the hydrophobicity and anti-wear properties. The ND powder treated by PFOTES was mixed with the Al₂O₃ powder by ball milling to ratios of 0.01 wt.%, 0.03 wt.%, and 0.05 wt.% ND. The water contact angle (CA) of the Al₂O₃-ND composite coating films was increased as the ND ratio increased, and the maximum water CA among all the films was 110°. In contrast to the water CA, the Al₂O₃-ND composite coating films showed low transmittance values of below 50% at a wavelength of 550 nm due to the strong agglomeration of ND. To prevent the agglomeration of ND, the starting powders were mixed by attrition milling. As a result, Al₂O₃-ND composite coating films were produced that showed high transmittance values of close to 80%, even though the starting powder included 1.0 wt.% ND. In addition, the Al₂O₃-ND composite coating films had a high water CA of 109° and superior anti-wear properties compared to those of glass substrates.     

Compared imbibitions of ordinary and high performance concrete with null or positive water pressure head

A method to simultaneously measure the moisture diffusion coefficient, D_θ, of unsaturated concrete, and the saturated concrete hydraulic conductivity, K_l, was developed for cylindrical specimens placed on a container filled with water that could be maintained at a given hydraulic pressure. Ordinary Portland cement Concrete (OPC) with a moderate and High Performance Concrete (HPC) with a low water to cement ratio were tested. The time dependent distribution of water content in the specimens was measured using a non-intrusive method based on gamma-ray attenuation. The measurements were conducted with varying hydraulic head (positive or null). Boltzmann's transformation was used to analyze the experimental results obtained at different hydraulic pressures and the difference between the null (or atmospheric) and positive pressure results is used to accurately determine K_l and also D_θ . This paper will present the results obtained using this original method, possible interpretations and future research.     

Review: Durability and Degradation Issues of PEM Fuel Cell Components

Besides cost reduction, durability is the most important issue to be solved before commercialisation of PEM Fuel Cells can be successful. For a fuel cell operating under constant load conditions, at a relative humidity close to 100% and at a temperature of maximum 75 °C, using optimal stack and flow design, the voltage degradation can be as low as 1–2 μV·h. However, the degradation rates can increase by orders of magnitude when conditions include some of the following, i.e. load cycling, start–stop cycles, low humidification or humidification cycling, temperatures of 90 °C or higher and fuel starvation. This review paper aims at assessing the degradation mechanisms of membranes, electrodes, bipolar plates and seals. By collecting long‐term experiments as well, the relative importance of these degradation mechanisms and the operating conditions become apparent.     

植物油砂复用性

测定了植物油砂旧砂性能,分析了植物油旧砂对油砂性能影响规律;结果表明,植物油旧砂的使用将在一定程度上恶化油砂性能。植物油砂复用的有效途径是将少量旧砂与新砂一起配制成单一砂或将植物油砂旧砂配制的油砂作为型（芯）背砂使用;分析了植物油矿复用的经济效益和环境效益。