Oxygen reduction on Cu–Zn alloys

The reduction of oxygen on brass type Cu77Zn21Al2 in contact with 0.1 mol L⁻¹ borax at pH 9.2 with and without chlorides was investigated and compared with the results on spectroscopic Cu. The surface film was characterized in situ by means of reflectance spectroscopy and by electrochemical impedance in the potential range negative to the open circuit potential. The main parameters associated to the kinetics of the oxygen reduction reaction were analyzed with a rotating disc electrode. The results show that within the potentials studied, a porous film was formed on brass while no significant spectral features were observed, except at −1.2 V where zinc oxo-hydroxides grow in chloride-free solutions and dissolve when chlorides are present in the system. The number of electrons exchanged for brass was close to 4 in both solutions, showing that oxygen is predominantly reduced to hydroxyl ions, with a reaction order equal to one. The residual presence of oxides on the surface results in Koutecky–Levich plots with slopes dependent on the applied potential and interfere with the calculation of the Tafel slope.     

Polyaniline Coating on Iron–Synthesis and Characterization

Protective coating has been used widely for metal corrosion control. Polyaniline (PANi) films can be electrosynthesized by oxidation of aniline on a metal surface from an aqueous acid medium. In this study, an iron surface was coated by polyaniline thin film. While iron easily oxidizes in acid solutions, the electropolymerization reactions were carried out in dilute acidic media. Rust, fats, etc. on the surface of iron were removed by alkali-ethanol solution, dichloroethylene, and, finally, hydrochloride (HCl) solution (10%), respectively. Coating was carried out in different potential (1.0, 1.5, and 2.5 V). To observe the effect of elemental contents of iron samples, spectral analysis also was taken before electropolymerization. Especially, effects of chromium and nickel elements were investigated. Physical resistance of the coating was examined by “band test.” Dissolving and defective coatings were also tested in acidic solutions and common organic solvents. In addition, to observe the morphology of coating, photos of samples were taken by scanning electron microscope (SEM) and metal microscope (MM).     

Ceramic varistors based on ZnO–SnO2

Model ceramic varistor formulations based on 98% ZnO–SnO₂ (plus 2% oxides of Bi, Co and Mn) were prepared by conventional powder processing routes; specimens were sintered at 1150–1275 °C. The product density increased with SnO₂ content, but decreased with increase in sintering temperature. The microstructures contained ZnO, Zn₂SnO₄ spinel and very small bismuth rich phases; with increasing Sn content the spinel became the dominant phase. From I–V measurements, the non-linear coefficients were found to be in the range 24–32. For all compositions, the α values decreased with increasing sintering temperature; the maximum α value was obtained with samples containing 20 mol% SnO₂ sintered at 1200 °C. Breakdown fields were in the range 3000–11000 V/cm and increased with increasing tin content. Leakage currents were in the range 1–11 μA. Tin substitution for Zn appears to cause a strong donor effect.     

Interpenetrating polymer networks based on uralkyd–butylmethacrylate

Two-component semi- and full-interpenetrating polymer networks (IPNs) of hydrogenated castor oil based uralkyd resin (UA) and poly(butylmethacrylate) (PBMA) were synthesized by the sequential technique. The elastomers obtained were characterized with respect to their mechanical properties such as tensile strength, elongation at break and hardness (Shore A). The apparent densities of these samples were determined and compared. Glass transition studies were carried out using differential scanning calorimetry. The thermal characterization of the elastomers was undertaken with the aid of thermogravimetric analysis. Phase morphology was studied by scanning electron microscopy. The effect of the variations of UA–PBMA on the above-mentioned properties was examined. The elongation percentage at break showed higher values in the case of all the semi-IPNs as compared to the full-IPNs.     

Metal–support interactions on rhodium model catalysts

Metal–support interactions on supported rhodium catalysts were studied by using specially prepared Rh/TiO₂/Mo model systems. For their characterization and the analysis of modifications due to various heat treatments several surface analytical methods were applied: low-energy ion scattering, X-ray photoemission spectroscopy and thermal desorption spectroscopy. Heating in ultrahigh vacuum to 670 K leads to Rh agglomeration followed (above 720 K) by encapsulation including the formation of reduced titanium oxide species. These morphological and chemisorption changes are reversible upon reoxidation and low-temperature reduction and thus exhibit the characteristic features of strong metal–support interactions. For the effective mechanism a reaction is suggested that involves oxygen chemisorption on the Rh clusters and partial reduction of the surrounding support oxide.     

Effect of heat treatment on electroless ternary nickel–cobalt–phosphorus alloy

Ternary Ni–Co–P and binary Ni–P alloy coatings were deposited on mild steel panels from an alkaline bath in the presence and absence of cobalt sulfate using an electroless process. The effects of heat treatment on surface topography and crystal orientation of Ni–Co(11.17%)–P(3.49%) alloy coatings were studied in contrast to that of Ni–P ones. It was found that the as plated Ni–Co–P alloy is a supersaturated solid solution of P and Co dissolved in a microcrystalline Ni matrix with 111 preferred direction. Heat treatment induces structural changes. The formation of Ni₃P phase precipitates and recrystallization of nickel occur when the sample is treated at > 400 °C for one hour. It is observed that the Ni diffraction lines of treated Ni–Co–P alloy at > 400 °C are shifted to lower angles as compared to those of treated Ni–P or as plated Ni–Co–P alloys. The surface topography of Ni–Co–P alloy also changes with heat treatment temperature. The surface topography and crystal orientation were characterized by means of scanning electron microscopy and X-ray diffraction, respectively. The hardness and corrosion resistance, in 5 wt % NaCl solution, of heat treated Ni–Co–P samples were studied.     

Effect of Storage Time on Wax–Wax–Hydrolyzate Canola Oil Oleogels

In this study, two natural waxes, beeswax (BW) and sunflower wax (SFW), are combined with their hydrolyzed variants to deliberately alter the waxes’ composition. The properties of the produced oleogels with different wax inclusion levels (4%, 8%, 12%, and 16% w/w) are investigated after defined intervals (2 days, 7 days, 3 weeks, and 3 months). To do so, the gels are monitored via penetrometry, microscopy, and calorimetry. Although the gels do not show any significant difference during storage in the micrographs, the calorimetric and firmness data reveal meaningful results. The heat of dissolution increases in every system investigated, indicating post-crystallization processes. Due to different solubilities of wax components, the critical gelling concentration is determined and the solid wax content is retrieved to further address the structure efficiency (S.E.). It is demonstrated that although the quantity of solids over time increases, the scaffolding effectiveness decreases in most cases. Only SFW, most likely due to sintering, shows an increase in S.E. over the storage time. Identified synergistic effects in BW and hydrolyzate mixtures decrease with increasing storage time. This work aims to contribute to a better understanding of the behavior of wax-based oleogels upon storage. Practical Applications: Although much is known about the gel properties of wax-based oleogels at short-term, the behavior over the storage period remains largely unresolved. However, this behavior is immensely important for a real application in fast and slow moving consumer goods. After all, products should always have the same consumer-relevant properties when stored at variable time frames. This applies to both food and pharmaceutical products. Knowledge of the behavior of wax-based oleogels in terms of a time-dependent change can help to choose a targeted product design and ensure product quality and consumer satisfaction.     

Processing–structure–adhesion relationship in CVD diamond films on titanium substrates

The hardness and adhesion properties of diamond films deposited on pure Ti and Ti–6Al–4V alloy are related to the structural characteristics of the films and of the intermediate layers formed at the film/substrate interface. Deposition experiments were performed by hot-filament CVD systematically varying the deposition temperature (650–850 °C) and time (60–360 min). The morphology and structure of the coatings and interfaces were investigated by optical and electron microscopy (SEM) and by the combined use of reflection diffraction (RHEED) and X-ray powder diffraction (XRPD), used also in the GID (Grazing Incidence Diffraction) mode. Hardness measurements (HV) of the deposits were made at a constant loading of 25 g on specifically prepared transversal sections of the specimen. Only small differences concerning the mechanical properties have been found for films grown on pure Ti and Ti–6Al–4V substrates. Adhesion of diamond on the substrate has been determined by the scratch test. The analysis of the micrographs of the indenter scratches and of the fracture-correlated acoustic emissions clearly indicates the occurrence of a multi-step detachment process, leading progressively to effective delamination of the diamond coatings.     

Euler multiphase-CFD simulation on a bubble-driven gas–liquid–solid fluidized bed

An integrated flow model was developed to simulate the fluidization hydrodynamics in a new bubble-driven gas–liquid–solid fluidized bed using the computational fluid dynamic (CFD) method. The results showed that axial solids holdup is affected by grid size, bubble diameter, and the interphase drag models used in the simulation. Good agreements with experimental data could be obtained by adopting the following parameters: 5 mm grid, 1.2 mm bubble diameter, the Tomiyama gas–liquid model, the Schiller–Naumann liquid–solid model, and the Gidaspow gas–solid model. At full fluidization state, an internal circulation of particles flowing upward near the wall and downward in the centre is observed, which is in the opposite direction compared with the traditional core-annular flow structure in a gas–solid fluidized bed. The simulated results are very sensitive to bubble diameters. Using smaller bubble diameters would lead to excessive liquid bed expansions and more solid accumulated at the bottom due to a bigger gas–liquid drag force, while bigger bubble diameters would result in a higher solid bed height caused by a smaller gas–solid drag force. Considering the actual bubble distribution, population balance model (PBM) is employed to characterize the coalescence and break up of bubbles. The calculated bubble diameters grow up from 2–4 mm at the bottom to 5–10 mm at the upper section of the bed, which are comparable to those observed in experiments. The simulation results could provide valuable information for the design and optimization of this new type of fluidized system.     

Studies on PA6–PP–wollastonite composite compatibilised by PP–graft–maleic anhydride prepared via pan milling

Abstract

A composite of PA6–PP–wollastonite compatibilised by PP-g-maleic anhydride has been prepared using pan type milling equipment, and its structure and properties investigated by IR, DSC, melt index measurements, SEM, and mechanical testing. The experimental results show that during pan milling, PP, PA6, and wollastonite are effectively pulverised, reaching better mixing owing to the very strong shear forces and pressure exerted by the pan type milling equipment. In particular, some PA6 polymer chains are grafted onto the wollastonite surface and the pan milling affects the crystallinity of PA6 and PP to some degree. The compatibiliser prepared via solid phase grafting of maleic anhydride onto PP via pan milling shows a reasonably good compatibilising effect on the composite, improving the morphology and therefore the mechanical properties of the composite. If combined with suitable coupling agent, the PA6–PP–wollastonite compatibilised by PP-g-maleic anhydride prepared via pan milling (wollastonite content 30 wt-%) possesses much better mechanical properties, its tensile strength increases from 54·6 to 58·6 MPa, and its notched Izod impact strength increases from 29·4 to 48·7 J m^-1, compared with the uncompatibilised system. Pan milling is a novel way to achieve desired structure and hence improved properties of polymer based materials via the polymer processing procedure.     

Effect of synthetic polymers on polymer–protein interaction

Synthetic polymers are often used for delivery of therapeutic drugs and proteins. We report the binding of milk β-lactoglobulin (β-LG) with poly(ethylene glycol) (PEG), methoxypoly(ethylene glycol) polyamidoamine (mPEG-PAMAM-G-3) and polyamidoamine (PAMAM-G4) nanoparticles in aqueous solution at pH 7.4, using Fourier Transform infrared (FTIR), circular dichroism (CD), fluorescence spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling. Structural analysis showed that polymers bind β-LG via both hydrophilic and hydrophobic contacts with overall binding constants K_{PEG-8000-β-LG} = 4.8 (±0.4) × 10⁴ M⁻¹ and K_{mPEG-PAMAM-G3-β-LG} = 5.8 (±0.6) × 10⁵ M⁻¹ and K_{PAMAM-G4-β-LG} = 6.7 (±0.9) × 10⁴ M⁻¹. The number of binding sites were occupied by polymers on protein (n) was 0.3 for PEG-8000, 0.4 for mPEG–PAMAM-G3 and 0.4 for PAMAM-G4. The order of binding is mPEG-PAMAM-G3 > PAMAM-G4 > PEG-8000. Transmission electron microscopy showed significant changes in protein morphology as polymer–protein complexation progressed with major increase in the diameter of the protein aggregate (180%). Furthermore, modeling showed several H-bonding systems between PEG and different amino acids stabilize polymer–β-LG complexes. mPEG-PAMAM-G3 is a stronger protein binder than PAMAM-G4 and PEG-8000.     

Recyclable biobased materials based on Diels–Alder cycloaddition

Poly(ethylene glycol) diglycidyl ether-furfurylamine (PGFA) containing pendant furan was synthesized, and a series of crosslinked materials with thermally reversible capacity were synthesized through a furan/maleimide Diels–Alder (DA) reaction between PGFA and bismaleimide (BMI). The kinetics of the PGFA/BMI DA reaction were studied by Fourier transform infrared spectroscopy (FTIR). The reaction conversion rate, the reaction rate constant, and the energy of the DA reaction at different temperatures were calculated. In addition, the retro Diels–Alder (rDA) reaction was studied via ¹H-NMR, differential scanning calorimetry, and in situ FTIR. The occurrence of the retro DA reaction has been characterized clearly. Finally, the mechanical properties of the materials were obtained by dynamic mechanical and tensile tests. The storage modulus decreased obviously when the temperature reached over 90 °C, which proved that the materials were thermally reversible at high temperature. By changing the proportion of the crosslinking agent BMI, the best-performing materials were obtained, and the properties of the materials were basically unchanged after recycling. Thus we have obtained an excellent reusable material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47352.     

Growth of 3C–SiC films on Si substrates by vapor–liquid–solid tri-phase epitaxy

Cubic SiC films (3C–SiC) were deposited on (111) Si substrates by a vapor–liquid–solid tri-phase growth method. In such a process a thin copper layer, which was evaporated on the Si substrate prior to the growth, was melted at high temperature as the flux and then methane (carbon source) was diffused into the liquid layer to react with Si, leading to the growth of SiC on the substrate. Copper showed some good properties as the flux, including high silicon and carbon solubility, low growth temperature and low volatility. Suitable growth parameters to go with the copper flux were identified, under which (111) textured 3C–SiC films were grown. Small numbers of (220) grains were observed to embed in the (111) films, which were difficult to avoid completely. Etching pits of the Cu melt on the substrate surface may act as the preferred sites for the growth of (220) grains.     

Kinetic study of CO hydrogenation on the MgO supported Fe–Co–Mn sol–gel catalyst

The kinetic of the Fischer–Tropsch synthesis over the MgO supported Fe–Co–Mn catalyst prepared using sol–gel procedure, was investigated in a fixed bed micro-reactor. Experimental conditions were varied as follow: reaction pressure 5–20 bar, reaction temperature 220–250 °C, H₂/CO feed molar ratio of 0.67–2 and space velocity range of 2400–3600 h^?1. 18 models according to the Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate equation were derived, and the reaction rate is fitted fairly well by one kinetic expressions based on LHWW mechanism. The kinetic parameters were estimated with non-linear regression method. The activation energy was obtained 110.9 kJ/mol for the best-fitted model.     

Comparative Study on Catalytic Performances for Low-temperature CO Oxidation of Cu–Ce–O and Cu–Co–Ce–O Catalysts

Two series of Cu–Ce–O and Cu–Co–Ce–O catalysts were prepared by co-precipitation method. The prepared catalysts were characterized by XRD, IR, TPR, XPS, BET and ICP-AES. The catalytic activities of the catalysts for low-temperature CO oxidation were evaluated through a microreactor-GC system. TPR results indicate that the addition of cobalt to the Cu–Ce–O can increase the dispersion of copper oxide, and the interaction between cobalt and copper can enhance the reducibility of each other. XPS analysis show that Ce⁴⁺, Cu²⁺, along with Co₃O₄, are present on the surface of Cu_0.4Co_0.6Ce₄ catalyst. The Co/Cu atomic ratio and the calcination temperature have significant effect on the activities of the catalysts. Compared with Cu₁Ce₄ catalyst, the Cu_0.4Co_0.6Ce₄ catalyst has better activity and thermal stability.     

Microwave dielectric materials based on the MgO–SiO2–TiO2 system

Ceramics in the system MgO–SiO₂–TiO₂ were prepared by standard mixed oxide route. By adding ZnO–B₂O₃ to the starting mixtures, the firing temperature of the ceramics could be reduced to 1160 °C. Small additions of MnCO₃ and CaTiO₃ improve microwave dielectric properties leading to an increase in insulation resistance and a decrease in temperature coefficient of capacitance. By adding Co₂O₃ grain growth can be inhibited and the dielectric Qf value greatly increased. The resultant ceramic material exhibited low dielectric constant and low dielectric loss: relative permittivity (ε_r): 20±2; temperature coefficient of capacitance (τ_c): 0±30 ppm/°C; Qf: 100,000 (at 10 GHz); insulation resistance: 10¹³ Ω cm:     

Academic Research on Drying in Brazil 1970–2003

ABSTRACT

Drying research in Brazil started to be significant from the early 1970s. At the end of the 1980s and the beginning of the 1990s, a few authors started to publish their works in indexed journals in English. Even so, many works were published in Portuguese. This compilation has the objective of showcasing the academic research done in Brazil from 1970 to 2003. This search was carried out using existing databases on Brazilian academic research. We located 705 works consisting of 82% M.Sc. and 18% Ph.D. theses. Tables listing the dried products and dryers studied are presented along with a discussion of the historical development of the Brazilian drying research and the new trends as well.     

Hybrid organic–inorganic coatings based on thiol-ene systems

Hybrid organic–inorganic coatings based on thiol-ene systems were obtained by a UV-thermal dual-curing process. An improvement in mechanical properties and surface hardness was achieved because of the presence of the inorganic filler generated in situ via the sol–gel process. TEM analysis clearly evidenced the reduction of the nanosize dimensions of the inorganic silica domains by increasing the coupling agent content in the photocurable formulation.     

Effect of oxidation treatment on KD–II SiC fiber–reinforced SiC composites

Continuous silicon carbide fiber–reinforced silicon carbide matrix (SiC_f/SiC) composites have developed into a promising candidate for structural materials for high–temperature applications in aerospace engine systems. This is due to their advantageous properties, such as low density, high hardness and strength, and excellent high temperature and oxidation resistance. In this study, SiC_f/SiC composites were fabricated via polymer infiltration and pyrolysis (PIP) with the lower–oxygen–content KD–II SiC fiber as the reinforcement; a mixture of 2,4,6,8–tetravinyl–2,4,6,8–tetramethylcyclotetrasiloxane (V4) and liquid polycarbosilane (LPCS), known as LPVCS, was used as the precursor; while pyrolytic carbon (PyC) was used as the interface. The effects of oxidation treatment at different temperatures on morphology, structure, composition, and mechanical properties of the KD–II SiC fibers, SiC matrix from LPVCS precursor conversion, and SiC_f/SiC composites were comprehensively investigated. The results revealed that the oxidation treatment greatly impacted the mechanical properties of the SiC fiber, thereby significantly influencing the mechanical properties of the SiC_f/SiC composite. After oxidation at 1300 °C for 1 h, the strength retention rates of the fiber and composite were 41% and 49%, respectively. In terms of the phase structure, oxidation treatment had little effect on the SiC fiber, while greatly influencing the SiC matrix. A weak peak corresponding to silica (SiO₂) appeared after high–temperature treatment of the fiber; however, oxidation treatment of the matrix led to the appearance of a very strong diffraction peak that corresponds to SiO₂. The analysis of the morphology and composition indicated cracking of the fiber surface after oxidation treatment, which was increasingly obvious with the increase in the oxidation treatment temperature. The elemental composition of the fiber surface changed significantly, with drastically decreased carbon element content and sharply increased oxygen element content.