Self-assembled nano-phase particles for enhanced oxygen barrier coatings on polymeric materials

Aqueous-based inorganic–organic hybrid coating materials comprising self-assembled nanophase particles (SNAP) were investigated for their potential to confer high gas barrier performance to flexible polymeric substrates, particularly to improve suitability of the substrates as encapsulation materials for organic photovoltaic (OPV) devices. Potential benefits of this approach include versatility in barrier coating formulation to achieve specific barrier properties, and application of coatings in a reel-to-reel process under ambient conditions. The present study focused on enhancement of the oxygen barrier performance of polypropylene (PP) substrates by applying SNAP-based coatings with and without the addition of an oxygen scavenging additive. SNAP particles were characterised using ²⁹Si NMR and dynamic light scattering, and coatings were analysed using atomic force microscopy and X-ray photoelectron spectroscopy. SNAP particle preparation and coating formulation was optimised with respect to oxygen transmission rate (OTR) of the coating on PP, and mechanical properties of the coating solution. In the absence of oxygen scavenger, the lowest OTR attained for the SNAP-based coatings was 0.87 cm³ mil m⁻² day⁻¹ atm⁻¹. The OTR was further reduced to 0.22 cm³ mil m⁻² day⁻¹ atm⁻¹ on addition of 9,10-anthraquinone-2,6-dissulfonic acid (AQDS) into the coating as an oxygen scavenger. These results represent a decrease in OTR by 4 orders of magnitude compared with uncoated PP, and the oxygen barrier obtained by addition of AQDS surpasses the performance of many plastic materials considered to be high oxygen barriers in the food and pharmaceutical industries.     

A-type zeolite containing Ag/Zn as inorganic antifungal for waterborne coating formulations

The biocide cations Ag⁺ and Zn²⁺ were hosted in the cavities of an ordered aluminosiliceous framework. Starting from sodium A-type zeolite (NaA), LTA containing Ag⁺ (AgA), Zn²⁺ (ZnA) and Ag⁺/Zn (AgZnA) at different cation exchanged levels was obtained and its antifungal properties were evaluated. To determine the minimum inhibitory concentration (MIC) of the exchanged zeolites against Aspergillus niger, [Ag⁺] and [Zn²⁺] values ranging from 50 < [Ag⁺] < 1000 mg L⁻¹ to 650 < [Zn²⁺] < 2000 mg L⁻¹, respectively, were used for NaA, and for AgZnA: 30 < Ag⁺ < 250 mg L⁻¹. The zeolite sample having [Ag⁺] = 100 mg L⁻¹, [Zn²⁺] = 90 mg L⁻¹ produces a growth inhibition comparable to that achieved with 230 mg L⁻¹ of Ag⁺¹ (MIC value obtained for the single cation). The antifungal activity of these products after incorporation in waterborne coating formulations was also determined. Results indicate that Ag⁺ and Zn²⁺ supported on A-type zeolite could be a beneficial tool for the development of waterborne coatings with a longer protection against microbiological attack when compared to traditional organic biocides.     

Electrochemical studies on the alternating current corrosion of mild steel under cathodic protection condition in marine environments

Alternating current (AC) corrosion of mild steel in marine environments under cathodic protection (CP) condition was studied. Electrochemical studies at the two protection potentials namely −780 and −1100 mV versus SCE were examined by different techniques. DC polarization study was carried out for mild steel in natural seawater and 18.5 g/L NaCl solution to evolve corrosion current density. The corrosion rate determination, pH of the end experimental solution and surface morphology of the mild steel specimens under the influence of different AC current densities were studied. The amount of leaching of iron into the solution was estimated using inductively coupled plasma spectrometry. All these techniques revealed that AC influences the corrosion of mild steel in the presence of marine environments even though CP was given. Surface micrographs revealed that spreading of red rust products noticed on the mild steel surface. At −780 mV CP, red rusts are visually seen when the AC source was above 10 A/m² in both the media but red rusts are appeared after 20 A/m² in the case of −1100 mV CP. Weight loss measurements coupled with surface examination and solution analysis is a effective tool to characterize and quantify the AC corrosion of mild steel in marine environments.     

Marine microbial fuel cell: Use of stainless steel electrodes as anode and cathode materials

Numerous biocorrosion studies have stated that biofilms formed in aerobic seawater induce an efficient catalysis of the oxygen reduction on stainless steels. This property was implemented here for the first time in a marine microbial fuel cell (MFC). A prototype was designed with a stainless steel anode embedded in marine sediments coupled to a stainless steel cathode in the overlying seawater. Recording current/potential curves during the progress of the experiment confirmed that the cathode progressively acquired effective catalytic properties. The maximal power density produced of 4 mW m⁻² was lower than those reported previously with marine MFC using graphite electrodes. Decoupling anode and cathode showed that the cathode suffered practical problems related to implementation in the sea, which may found easy technical solutions. A laboratory fuel cell based on the same principle demonstrated that the biofilm-covered stainless steel cathode was able to supply current density up to 140 mA m⁻² at +0.05 V versus Ag/AgCl. The power density of 23 mW m⁻² was in this case limited by the anode. These first tests presented the biofilm-covered stainless steel cathodes as very promising candidates to be implemented in marine MFC. The suitability of stainless steel as anode has to be further investigated.     

Asymmetric TiO2 hybrid photocatalytic ceramic membrane with porosity gradient: Effect of structure directing agent on the resulting membranes architecture and performances

Asymmetric TiO₂ hybrid photocatalytic ceramic membranes with porosity gradient have been fabricated via acid-catalyzed sol–gel method. Different structure directing agents (SDAs) i.e. Pluronic P-123, Triton X-100, Tween 20 and Tween 80 were incorporated in the preparation of TiO₂ sol to obtain a porous multilayered TiO₂ coated on the alumina ceramic support. Six different SDA-modified membrane specimens were fabricated. Four of which were coated with the TiO₂ sols prepared using only one type of SDA. The remaining two specimens were fabricated via multilayer coating of different TiO₂ sols prepared using different types of SDAs. Physico-chemical and morphological properties of different TiO₂ layers were thoroughly investigated. The membrane M1 which had the most porous TiO₂ sub-layers showed a high pure water permeability of 155 L m⁻² h⁻¹ bar⁻¹. The membrane showed a relatively high Rhodamine B (RhB) removal of 2997 mg m⁻² over 8 h treatment duration in the batch photoreactor, second only to the Pluronic-based TiO₂ membrane (specific RhB removal of 3050 mg m⁻²). All membrane specimens exhibited good performances while operated in the flow-through photocatalytic membrane reactor. Over 91% of RhB removal capability was retained after 4 treatment cycles. All membranes also showed self-cleaning property by retaining >90% of initial flux after 4 treatment cycles. The flexibility of optimizing membrane performances by fine-tuning the porosity gradient configuration of the photocatalytic layer has also been demonstrated.     

Flat-plate submerged membrane bioreactor for the treatment of higher-load graywater

Graywater treatment has been the focus when topics of decentralized treatment systems are discussed. In this paper, the treatment of higher-load graywater, a mixture of washing machine and kitchen sink wastewater, was investigated. A 10 L lab-scale submerged membrane bioreactor (subMBR) was operated with a flat-plate membrane for 87 days. Permeate was intermittently withdrawn at constant transmembrane pressure (TMP) induced by water level difference and without pump requirement. The pollutants' removal and membrane behavior were monitored. The COD removal was around 96% and a permeate COD of about 26 mg L^− 1 was obtained. The total linear alkylbenzene sulfonate (LAS) removal achieved was > 99%, indicative of its non-inhibited degradation even at influent concentration of 30.8 mg L^− 1. The subMBR was operated at almost stable and constant flux of 0.22 m³ m^− 2 d^− 1 at a mean HRT of 13.6 h.     

Thermal conductivity in mullite/ZrO2 composite coatings

Mullite-based multilayered structures have been suggested as promising environmental barrier coatings for Si₃N₄ and SiC ceramics. Mullite has been used as bottom layer because its thermal expansion coefficient closely matches those of the Si-based substrates, whereas Y–ZrO₂ has been tried as top layer due to its stability in combustion environments. In addition, mullite/ZrO₂ compositions may work as middle layers to reduce the thermal expansion coefficient mismatch between the ZrO₂ and mullite layers. Present work studies the thermal behaviour of a flame sprayed mullite/ZrO₂ (75/25, v/v) composite coating. The changes in crystallinity, microstructure and thermal conductivity of free-standing coatings heat treated at two different temperatures (1000 and 1300 °C) are comparatively discussed. The as-sprayed and 1000 °C treated coatings showed an almost constant thermal conductivity (K) of 1.5 W m⁻¹ K⁻¹. The K of the 1300 °C treated specimen increased up to twice due to the extensive mullite crystallization without any cracking.     

Electrodeposition of platinum on polytyramine-modified electrodes for electrocatalytic applications

Cyclic voltammetry was used in order to deposit conducting polytyramine (PTy) on graphite substrates. In acidic media, ca. 40 deposition cycles resulted in the formation of stable polymer films with reasonably good resistivity. Electrochemical deposition of platinum on the PTy-covered graphite substrate allowed us to obtain a composite material that exhibits, for a platinum loading of 0.34 mg cm⁻², a specific electrochemically active surface area of the Pt particles of ca. 57 m² g⁻¹. Good electrocatalytic activity of this electrode material for phenol oxidation in acidic media was found, and the results suggested that, when deposited as small particles in a PTy matrix, platinum is less sensitive to deactivation by phenol oxidation polymeric products.     

Preliminary study on suspension plasma sprayed ZrO2 + 8 wt.% Y2O3 coatings

ZrO₂ + 8 wt.% Y₂O₃ powder of a mean diameter d_VS = 38 μm was milled to obtain fine particles having mean size of d_VS = 1 μm. The fine powder was used to formulate a suspension with water, ethanol and their mixtures. The zeta potential of obtained suspensions was measured and found out to be in the range from −22 to −2 mV depending on suspension formulation. The suspension was injected through a nozzle into plasma jet and sprayed onto stainless steel substrates. The plasma spray experimental parameters included two variables: (i) spray distance varying from 40 to 60 mm and (ii) torch linear speed varying from 300 to 500 mm/s. The microstructure of obtained coatings was characterized with scanning electron microscope (SEM) and X-ray diffraction (XRD). The coatings had porosity in the range from 10% to 17% and the main crystal phase was tetragonal zirconium oxide. The scratch test enabled to find the critical load in the range of 9-11 N. Finally, thermal diffusivity of the samples at room temperature, determined by thermographic method, was in the range from 2.95 × 10⁻⁷ to 3.79 × 10⁻⁷ m²/s what corresponds to thermal conductivities of 0.69 W/(mK) and 0.97 W/(mK) respectively.     

High-temperature removal of cadmium from a gasification flue gas using solid sorbents

In this work, the retention capacity of solid sorbents for cadmium species present in coal gasification flue gases at high temperature was investigated. The influence of HCl(g) on the gas atmosphere was also evaluated. The study was carried out in a laboratory scale reactor, using synthetic gas mixtures with the sorbent as fixed bed. The sorbents tested were kaolin, limestone, alumina and fly ashes. The results obtained were compared with data from the works of other authors, who used similar solid sorbents in typical coal combustion flue gases. Whereas in the combustion atmospheres described in the literature, kaolin, limestone and alumina showed high retention capacities for cadmium compounds (0.5-40 mg g⁻¹), in the coal gasification atmospheres studied in the present work, the amount of cadmium captured by these solid sorbents was negligible. Fly ashes were found to be the most efficient for retaining cadmium in gasification atmospheres, their maximum retention capacity in the conditions studied being approx 0.75 mg g⁻¹.     

Electrode properties of a double layer capacitor of nano-structured graphite produced by ball milling under a hydrogen atmosphere

Nano-structural graphite prepared by ball milling under H₂ or Ar atmosphere was studied as an electrode for electric double layer capacitors (EDLCs) by means of a conventional 2-electrode galvanostatic method. Especially, the product prepared under H₂ atmosphere using zirconia balls revealed 500 m² g⁻¹ surface area and showed 12 F g⁻¹ specific capacitance, which was comparable to that of an activated carbon with large specific surface area of 3000 m² g⁻¹ examined as a reference. A proper condition of the milling time is rather a shorter time than ∼8 h, where the graphitic feature is remained in the ball milled product. On the other hand, for the sample prepared by using steel balls, the specific capacitance per surface area was several hundreds times smaller than the others, indicating that the small amount of Fe contamination during milling played a negative role for the EDLC properties.     

Exploring the use of near infrared reflectance spectroscopy to predict minerals in straw

The use of near infrared reflectance spectroscopy (NIRS) to predict minerals concentration (K, Na, Ca, Mg, Fe) in straw samples was investigated in this study. A total of 222 straw samples were collected in rural area of most provinces in China. Two types of straw samples were prepared, directly cut specimens and oven-dried, milled specimens. The spectra of two kinds of samples were employed to correlate with minerals concentration. Different spectral pre-treatments and regression methods were trialled to optimize the calibration. Coefficient of determination in prediction and standard error of prediction (SEP) were 0.69, 0.54, 0.73, 0.79, 0.41 and 3.77 mg g⁻¹, 0.69 mg g⁻¹, 0.58 mg g⁻¹, 0.31 mg g⁻¹, 0.11 mg g⁻¹ for directly cut straw; 0.85, 0.70, 0.82, 0.85, 0.63 and 2.35 mg g⁻¹, 1.46 mg g⁻¹, 0.47 mg g⁻¹, 0.27 mg g⁻¹, 0.13 mg g⁻¹ for dried milled samples, respectively.     

Characterisation of thermal barrier coatings and ultra high temperature composites deposited in a low pressure plasma reactor

A low pressure plasma process working at 600-800 Pa was used to deposit from aqueous solution ZrO₂-4 mol% Y₂O₃ (Yttria partially stabilized Zirconia-YpSZ) layers and stacks of Ta₂O₅/YpSZ layers for use as thermal barrier coatings (TBC). The observation of the cross section revealed a high porosity. The thermal diffusivity of the layers (1 × 10⁻⁷ m² s⁻¹) was measured by a laser flash technique and compared with values obtained on air plasma sprayed material (3 × 10⁻⁷ m² s⁻¹). The plasma reactor were also used to deposit ZrB₂-ZrO₂-SiC layers used as Ultra High Temperature Composite (UHTC) from aqueous solutions of zirconyl and Boron nitrates containing suspensions of SiC. Layers up to 100 μm thick were obtained on SiC substrates. XRD was used to study the crystallinity of the layer. The presence of ZrB₂ and SiC phases was confirmed after the deposition. XRD analysis showed that heat treatment at 1073 K under oxidizing conditions led to the loss of ZrB₂ and the appearance of ZrO₂ phases. To understand the behaviour of the layers to interaction with atomic oxygen (combustion for TBC and spacecraft re-entry phase for UHTC), we have measured the atomic oxygen recombination coefficient to determine the number of adsorption sites on the surface of the coatings. This was accomplished by using a low pressure plasma reactor coupled with optical spectroscopic measurements as a diagnostic technique.     

Modification of macroporous stainless steel supports with silica nanoparticles for size selective carbon membranes with improved flux

Silica nanoparticles were slip cast into porous stainless steel supports, which were then coated with polyfurfuryl alcohol and pyrolyzed to make nanoporous carbon membranes. The single gas permeances of the membranes formed on modified stainless steel supports were found to be between two and three orders of magnitude larger than the permeances of nanoporous carbon membranes (<10⁻¹¹ mol m⁻² s⁻¹ Pa⁻¹) synthesized on unmodified supports. Importantly, these high permeances (10⁻⁸-10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹) were achieved within the same range of O₂/N₂ selectivities (3-5) that we have observed for single gases permeating at much lower fluxes through the nanoporous carbon membranes on unmodified supports. The nanoporous carbon membranes also were formed by combining the silica nanoparticles with polyfurfuryl alcohol resin and applying the mixture directly onto an unmodified support. This simpler process was as effective in producing selective-high permeance membranes. In both cases the significant increase in permeance without loss of selectivity is attributed to the silica nanoparticles filling the macropores of the stainless steel supports, thereby leading to the formation of very thin but selective carbon layers.     

Corrosion performance of waterborne coatings for structural steel

Among recently developed waterborne coatings, epoxy and acrylic based coatings have a special place. To study this kind of anticorrosive coatings, use is normally made of natural exposure and laboratory tests. The literature has recently reported that the salt spray test is not suitable for selecting/studying anticorrosive waterborne coatings. In this paper, the authors present the main results obtained in an experimental study involving laboratory tests and natural exposure in two atmospheric test sites of different corrosivity categories. The natural exposure and accelerated tests are complemented by other measurements in the laboratory, involving water uptake, adhesion and electrochemical measurements, to understand the anticorrosive performance of the paint systems under study. As accelerated tests, salt spray and prohesion were used. Indirect measurements of adhesion were made using cross-cut and pull-off tests. Electrochemical impedance spectroscopy (EIS) and noise (EN) were used for electrochemical characterization. The study concludes that the best anticorrosive behaviour was shown by epoxy-polyamide paint systems, including zinc-rich primers. The correlation between the results of salt spray and natural exposure in marine test sites was significantly better than that obtained using the prohesion test. The electrochemical results showed that it is very important to pay special attention when interpreting this kind of results.     

Solventborne paint systems on carbon steel and hot-dip galvanized steel for a wide range of atmospheric exposures

The paper analyzes the performance of solventborne paint systems applied on carbon steel and hot-dip galvanized steel in a wide range of atmospheric exposures. The study has involved paint systems exposure for 3.5 years in eight natural atmospheres. The atmospheric conditions cover from temperate rural climates to tropical severe marine and Antarctic coastal regions. The paint systems included several alkyds formulated with a variety of pigments (anticorrosive and barrier), epoxies, chlorinated rubber, and zinc-rich (ethyl silicate and epoxy). It has been concluded that in rural and urban atmospheres alkyd systems afford equivalent anticorrosive protection of steel to the epoxy/polyurethane system. The toxic red lead pigment may be replaced in long linseed-oil alkyd primer paints by non-toxic pigments, such as a mixture of micaceous iron oxides (MIO) and black iron oxides or zinc phosphate, without affecting the anticorrosive properties of the paint system. In aggressive atmospheres (industrial, marine), paint systems including zinc-rich primers or applied on galvanized steel must be used, especially in surface regions with coating faults (scribes).     

Thermal stability in oxidative and protective environments of a-C:H cap layer on a functional gradient coating

Three types of hydrogenated amorphous carbon (a-C:H) coatings were synthesized on stainless steel substrates by a Plasma Assisted CVD process, containing hydrogen contents in the range from 25 to 29 at.%. The effect of annealing up to 600 °C in two different environments on both the structure and the mechanical properties of the coatings were investigated by means of Differential Scanning Calorimetry/Thermogravimetry (DCS/TG), Raman Spectroscopy and Depth Sensing Indentation. The results indicate that the structural modifications occurred in the coatings in both protective and oxidative atmospheres up to 400 °C were due to a complex atomic rearrangement involving the dehydrogenation reaction. A small weight loss, detected by isothermal TG analysis confirmed the H₂ effusion. This dense effect proceeds without a change of hardness which was maintained in the diamond-like regime. The annealing in non-oxidative ambiance at temperatures above 500 °C causes both gaseous products effusion and sp³ to sp² transformation. Raman parameters and hardness values were, under these conditions, similar to those known for a typical graphite-like regime. While the onset temperature of the graphitization process was found to be almost independent of the H content range investigated, the situation was completely different in relation to the oxidation reaction. The highest oxidation resistance was found for coatings with the lowest H content.     

CO tolerance effects of tungsten-based PEMFC anodes

The performance of proton exchange membrane fuel cells (PEMFC) fed with CO-contaminated hydrogen was investigated for anodes with PtWO_x/C and phosphotungstic acid (PTA) impregnated Pt/C electrocatalysts. A quite high performance was achieved for the PEMFC fed with H₂ + 100 ppm CO with anodes containing 0.4 mg PtWO_x cm⁻² and also for those with 0.4 mg Pt cm⁻² impregnated with ca. 1 mg PTA cm⁻². A decay of the single cell performance with time is observed, and this was attributed to an increase of the membrane resistance due to the polymer degradation promoted by the crossover of the tungsten species throughout the membrane.     

Carboxymethylchitosan + Cu mixture as an inhibitor used for mild steel in 1 M HCl

The inhibition effect of Carboxymethylchitosan (CMCT), Cu²⁺, and CMCT + Cu²⁺ mixture on the corrosion of mild steel in 1 M HCl has been investigated using gravimetric and electrochemical techniques. CMCT + Cu²⁺ mixture acts much more effectively than the inhibiting action of each additive separately. In addition, higher efficiency is achieved for the mixture of 20 mg L⁻¹ CMCT + 10⁻⁴ M Cu²⁺. The efficiency of the optimal mixture increases with the temperature in the range 298-353 K. Activation energy of corrosion reaction in the presence of the optimal mixture of the inhibitors is much lower than that exhibited in 1 M HCl solution. The inhibition mechanism proposed in this paper is based on the results of conductometric investigations.     

Improvement of the electrochemical behavior of steel surfaces using a TiN[BCN/BN]n/c-BN multilayer system

The aim of this work is to improve the electrochemical behavior of AISI 4140 steel substrates by using a TiN[BCN/BN]_n/c-BN multilayer system as a protective coating. We grew TiN[BCN/BN]_n/c-BN multilayers via reactive r.f. magnetron sputtering technique, systematically varying the length period (Λ) and the bilayer number (n), maintaining constant the total thickness of the coating and all other growth parameters. The coatings were characterized by FTIR spectroscopy that showed bands associated to h-BN bonds, and c-BN stretching vibrations centered at 1385 cm^− 1 and 1005 cm^− 1, respectively. Film composition was studied via X-ray photoelectron spectroscopy where typical signals for C1s, N1s and B1s are shown. The electrochemical properties were studied by electrochemical impedance spectroscopy and Tafel curves. In this work, the maximum corrosion resistance for the coating with (Λ) equal to 80 nm was obtained, corresponding to n = 25 bilayers. The polarization resistance and corrosion rate were around 10.1 kOhm cm² and 0.22 mm/year; these values were 83 and 15 times higher, respectively, than uncoated AISI 4140 steel substrate (0.66 kOhm cm² and 18.51 mm/year). Optical microscopy was used for surface analysis after corrosive attack. The improvement of the electrochemical behavior of the AISI 4140 coated with this TiN[BCN/BN]_n/c-BN multilayer system can be attributed to the presence of several interfaces that offer resistance to diffusion of Cl⁻ of the electrolyte toward the steel surface.