Protective properties of epoxy-based organic coatings on mild steel

The protective properties of epoxy-based organic coatings on mild steel substrates have been studied using the electrochemical impedance spectroscopy (EIS) technique. The effects of coating composition, film thickness and curing temperature on the lifetime of the epoxy coating were investigated. The results obtained indicate that the film composition dramatically affects the rate of corrosion of the metallic substrate. Coatings with low and high content of curing agent exhibit early failure when exposed to an air-saturated 0.5 M aqueous solution of NaCl. Extended lifetimes were observed for samples with a content of the curing agent equal to 8.5% by weight. An increase in lifetime was also observed on increasing the film thickness and the curing temperature. The failure mechanism seems to occur in two steps: the first step is related to water uptake in the film while the second step is related to Cl⁻ ion diffusion through the coating. The results have been interpreted in terms of a model in which the dielectric properties (capacitance and resistance) of the coating depend strongly on the coating composition and are affected by both the water and salt uptake into the film.     

Efficiency,recovery and productivity of continuous reverse osmosis systems: new closed expressions

Numerical and approximate analytical solutions for salt concentration polarization in hyperfiltration with laminar flow in a flat sheet configuration are presented. The analysis accounts for the variation of the water flux in the longitudinal direction. Approximate solutions were obtained with an integral method which was found to provide good agreement with the numerical solution. The integral method allows one to obtain closed expressions for the productivity Q, the recovery R and the efficiency E of a reverse osmosis system which can be applied relatively quickly in design calculations.In this analysis the physical properties of the solution are taken to be constant.     

Protein ultrafiltration: an experimental study

An experimental study was carried out on the ultrafiltration (UF) of protein-containing solutions under different conditions, as compared with a solution of a linear synthetic polymer. Three different fluidynamic regimes were investigated, namely, unstirred batch system, stirred batch system, and recirculating system. The results obtained substantially agree with the predictions of the gel polarization model. A significant effect of the electrolytes on the UF flux has been observed, which can be attributed to solute–solute interaction. The influence of different UF membranes has also been investigated.     

Mechanical strength of PET fibers treated in cold plasma and thermal exposed

As a followup to previous work, experiments with argon and oxygen Radio Frequency plasma treated polyethylene terepthalate (PET) exposed to 100 °C after cold plasma treatment were performed. Tensile tests results in monofilaments treated in oxygen and argon plasma for 5 s, 20 s, 30 s, and 100 s showed a decrease in the average tensile strength compared with the untreated fibers. It was also observed that the reduction in mechanical strength is more significant for argon plasma and very sensitive to the treatment time for oxygen plasma. Experimental data obtained from tensile tests in samples thermal exposed to 100 °C after plasma treatments indicate the same influence of treatment times on mechanical strength, as observed for cold plasma treated fibers. Furthermore, an increase in tensile strength when compared with the samples unexposed to 100 °C was observed. Scanning electron microscopy, used to analyze effects of cold plasma treatment on fibers surfaces, indicates differences in roughness profiles depending on the type of treatment. The distance of roughness interval, D_ri, was a parameter introduced to relate the fibers surface condition and average tensile strength. Statistical analysis of experimental data was performed to explain influences of treatment time, and environmental and temperature effects on mechanical properties.     

The use of nested desirability functions and quality indices for multi-response robust parameter design problems

A multi-response robust parameter design (RPD) problem-solving technique based on desirability functions is presented in which the means and variances of all responses are placed on a level playing field. The proposal allows a decision maker to integrate their preferences for the individual means and variances. It is shown that the ensuing operating point is a system setting that produces a mutually robust set of responses. In addition, this article offers an approach to assess several RPD strategies via quality indices. The measures presented here allow for a more knowledgeable and comprehensive evaluation of the competing RPD strategies.     

A new hydroxyapatite-based biocomposite for bone replacement

Since the 1970s, various types of ceramic, glass and glass–ceramic materials have been proposed and used to replace damaged bone in many clinical applications. Among them, hydroxyapatite (HA) has been successfully employed thanks to its excellent biocompatibility. On the other hand, the bioactivity of HA and its reactivity with bone can be improved through the addition of proper amounts of bioactive glasses, thus obtaining HA-based composites. Unfortunately, high temperature treatments (1200 °C ÷ 1300 °C) are usually required in order to sinter these systems, causing the bioactive glass to crystallize into a glass–ceramic and hence inhibiting the bioactivity of the resulting composite. In the present study novel HA-based composites are realized and discussed. The samples can be sintered at a relatively low temperature (800 °C), thanks to the employment of a new glass (BG_Ca) with a reduced tendency to crystallize compared to the widely used 45S5 Bioglass®. The rich glassy phase, which can be preserved during the thermal treatment, has excellent effects in terms of in vitro bioactivity; moreover, compared to composites based on 45S5 Bioglass® having the same HA/glass proportions, the samples based on BG_Ca displayed an earlier response in terms of cell proliferation.     

High Temperature Oxidation and Microstructural Evolution of Modified MCrAlY Coatings

Thermal sprayed MCrAlY coatings are widely used as a bond coat in thermal barrier systems to protect the substrate from corrosion and high temperature oxidation and to improve the compatibility between the ceramic top coat and metallic substrate. In this paper, the high temperature oxidation resistance of MCrAlY coatings with modified compositions was evaluated; in particular, the effect of the addition of reactive and refractory elements (Ta, Re, Si, and Hf) was investigated. MCrAlY coatings were obtained by high velocity oxygen fuel spray and vacuum plasma spray techniques; samples were exposed to air at 1423 K (1150 °C) and the oxidation kinetics were evaluated by measuring the thickness of the thermally grown oxide (TGO) scale at several exposure times. Experimental data confirmed that the oxidation resistance of MCrAlY coatings is strictly related to the amount of the reactive and refractory elements in the starting powders and that a thorough understanding of the microstructural modifications taking place during oxidation is essential for controlling TGO growth and thermal barriers’ durability.     

A new potassium-based bioactive glass: Sintering behaviour and possible applications for bioceramic scaffolds

Providing structural support while maintaining bioactivity is one of the most important goals for bioceramic scaffolds, i.e. artificial templates which guide cells to grow in a 3D pattern, facilitating the formation of functional tissues. In the last few years, 45S5 Bioglass^® has been widely investigated as scaffolding material, mainly for its ability to bond to both hard and soft tissues. However, thermal treatments to improve the relatively poor mechanical properties of 45S5 Bioglass^® turn it into a glass-ceramic, decreasing its bioactivity. Therefore, the investigation of new materials as candidates for scaffold applications is necessary. Here a novel glass composition, recently obtained by substituting the sodium oxide with potassium oxide in the 45S5 Bioglass^® formulation, is employed in a feasibility study as scaffolding material. The new glass, named BioK, has the peculiarity to sinter at a relatively low temperature and shows a reduced tendency to crystallize. In this work, BioK has been employed to realize two types of scaffolds. The obtained samples have been fully characterized from a microstructural point of view and compared to each other. Additionally, their excellent bioactivity has been established by means of in vitro tests.     

PDGF/PDGFR: A Possible Molecular Target in Scleroderma Fibrosis

Systemic sclerosis (SSc) is a clinically heterogeneous disorder of the connective tissue characterized by vascular alterations, immune/inflammatory manifestations, and organ fibrosis. SSc pathogenesis is complex and still poorly understood. Therefore, effective therapies are lacking and remain nonspecific and limited to disease symptoms. In the last few years, many molecular and cellular mediators of SSc fibrosis have been described, providing new potential options for targeted therapies. In this review: (i) we focused on the PDGF/PDGFR pathway as key signaling molecules in the development of tissue fibrosis; (ii) we highlighted the possible role of stimulatory anti-PDGFRα autoantibodies in the pathogenesis of SSc; (iii) we reported the most promising PDGF/PDGFR targeting therapies.     

Thermo-optic design for microwave and millimeter-wave electromagnetic power microsensors

Rendina et al. recently proposed the original configuration of an electromagnetic power sensor for microwaves and millimeter waves that is based on an optically interrogated all-silicon chip [Electron. Lett. 35, 1748 (1999)]. Here we theoretically analyze and discuss in detail the performances of such a new class of nonperturbing and wideband probe in terms of sensitivity, resolution, intrinsic detectivity, linearity, and response time. Good agreement between theory and experiments is demonstrated. In particular, minimum resolutions of approximately 1 mW/cm2 are obtained at frequencies beyond 10 GHz. The dependence of response on the geometrical and electromagnetic parameters of the sensing element is analyzed, and on this basis the possibility of achieving optimized configurations is discussed.