László Trif

Controlled synthesis and characterization of biodegradable, stereomer co-polycondensates of l-malic acid

A one-pot synthesis of stereomer cross-linked copolymers of l-malic acid with tuned properties is reported. The β-cyclodextrin, as co-monomer with several OH groups, was applied to promote the polyester formation with higher, pre-defined molecular weight. The importance of the experimental conditions for preparation of polymers with tailor-made, optically active compositions is described, and their structures are characterized by different techniques such as thermogravimetry–differential scanning calorimetry−mass spectrometric evolved gas analysis, infrared spectroscopy and specific rotation. To our knowledge, first time was used the specific optical rotation for characterization of retention of the optical activity in the course of the synthesis.

Microbiologically influenced corrosion (MIC)

Abstract Microbiologically influenced corrosion (MIC) refers to the influence of microorganisms on the kinetics of corrosion processes of metals and nonmetallic materials, caused by adhering to the interfaces (usually referred to as “biofilms”). The corrosion-relevant microbes like to attach to solids via exopolymeric substances (EPS), which give the main component of the slime and form biofilms at the solid–liquid interface. Not only single stains but also diverse bacterial communities (e.g., iron and manganese and sulfur oxidizers and reducers, slime formers, acid producers, etc.) are able to produce biofilm. There are gradients of microorganisms, oxygen concentrations, and pH values inside the biofilm, which consists mostly of water, microbial metabolites, exopolymeric substances, organic, and inorganic molecules of the aqueous environment. Beneath this biofilm, corrosion initiates and progresses resulting in localized corrosion that can lead, if remained uncontrolled, to pinholes and leaks. This chapter discusses the different microbes responsible for MIC in oil and gas industry, classification of microorganisms, MIC mechanisms, and biofilm development and factors necessary for its formation. Finally the chapter briefly discusses current knowledge gaps in understanding and managing MIC and future research and engineering trends to close these gaps.

New comonomers in malic acid polyesters

Here, we report the synthesis of polyesters of l-malic acid, β-cyclodextrin, and two other comonomers, resorcinol and salicylic acid that, involved in the polyester chain by direct polycondensation, could improve the antibacterial activity. The copolymers were characterized by thermal analysis, infrared spectroscopy as well as by specific optical rotation values. The thermogravimetric and differential scanning calorimetry (TG–DSC) measurement results showed the influence of the comonomers on the thermal stability of the copolymers, which was higher when ZnO was present in the reaction mixture. The FTIR spectra confirmed the presence of the comonomers in the polyesters and the influence of the ZnO on the products. The specific optical rotation values showed similar tendency, and the results were in accordance with those got by TG–DSC and FTIR techniques. In short, the zinc oxide helped not only in ester formation but improved the polyester stability. Results allowed elaboration of reproducible polyester synthesis with tailor-made characteristic.

The corrosion study of ZrO2 coatings on metals

The ZrO2 coatings were deposited by sol-gel techniques on copper and steel. The film morphology has been investigated by AFM technique. The performance of ZrO2 films as protective layers was investigated by electrochemical techniques and optical microscopy. Firstly, the electrochemical behaviour of the uncoated copper and steel substrates was investigated by cyclic voltammetry in HCl (1 M) and NaOH (0.4 M) solutions having various pH values. Secondly, the anticorrosion protective effect of sol-gel ZrO2 coatings was evaluated by potentiodynamic measurements in degrading media in which substrates were immersed for 1-90 days. The comparisons of electrochemical parameters allow an explanation of the role of the ZrO2 coatings in the increased resistance of steel and copper against corrosion in moderately aggressive environments..

Electrochemical and surface analytical techniques applied to microbiologically influenced corrosion investigation

Abstract Suitable application of techniques for detection and monitoring of microbiologically influenced corrosion (MIC) is crucial for understanding the mechanisms of the interactions and for selecting inhibition and control approaches. This paper presents a review of the application of electrochemical and surface analytical techniques in studying the MIC process of metals and their alloys. Conventional electrochemical techniques, such as corrosion potential (Ecorr), redox potential, dual-cell technique, polarization curves, electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) analysis, and microelectrode techniques, are discussed, with examples of their use in various MIC studies. Electrochemical quartz crystal microbalance, which is newly used in MIC study, is also discussed. Microscopic techniques [scanning electron microscopy (SEM), environmental SEM (ESEM), atomic force microscopy (AFM), confocal laser microscopy (CLM), confocal laser scanning microscopy (CLSM), confocal Raman microscopy] and spectroscopic analytical methods [Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS)] are also highlighted. This review highlights the heterogeneous characteristics of microbial consortia and use of special techniques to study their probable effects on the metal substrata. The aim of this review is to motivate using a combination of new procedures for research and practical measurement and calculation of the impact of MIC and biofilms on metals and their alloys.

Preparation and Characterization of Nanostructured Ferrite Materials by a Nitrate-Citrate Self-Combustion Sol–Gel Synthesis

New chemical synthesis procedure for the preparation of nickel zinc doped W-type hexagonal barium ferrite and aluminium doped yttrium-iron garnet nanoparticles has been developed, using the nitrate-citrate sol-gel auto-combustion method (NCSAM). The crystalline phase attributes, microstructure, morphology, specific surface area, Curie temperature (TC), permeability, thermal behavior of the as-burnt phase and the heat treated powders were characterized using XRD, SEM, FT-IR, BET, TG-DTA and AC magnetic permeability with frequency shift. In the case of the hexaferrite, the pure W-type ferrite phase is formed during 4 hour annealing at a temperature of 1200 °C, the garnet phase is formed at a lower temperature i.e. 1000 °C. Furthermore it has been confirmed, that the AC magnetic permeabilities of the garnet materials are strongly depending on the chemical composition.

Adhesion of Steel and PMMA by Means of Laser Radiation

As the utilization of plastics is growing in our devices, their joining with other structural materials, like metals is more and more necessary. A novel method for joining polymeric materials and metals is the laser assisted metal plastic joining. The method is in focus of several researches. However, the mechanism of joint formation is not described sufficiently yet. In this study, the adhesion between structural steel and PMMA plastic and the phenomena of bubble formation is investigated. Scanning electron microscopy (SEM), thermogravimetry and mass spectrometry (TG-MS) were used to analyze joining interfaces and changes in the plastic material. Results show good adhesion between the mentioned materials and the important role of bubbles in the evolution of joining force.

Preparation of spherical agglomerates from potash alum

Salt hydrates are low-cost, readily available PCMs (phase change materials). As a core material for encapsulation the salt agglomerates can be prepared by spherical agglomeration, a well-known method to produce drug loaded microspheres in the pharmaceutical industry, but not used for PCM formulation. The two basic mechanisms in spherical crystallization are spherical agglomeration (SA) and the quasi emulsion solvent diffusion (QESD) processes. The spherical agglomerates of aluminium potassium sulfate dodecahydrate (potash alum dodecahydrate), a highly water soluble material, were produced by spherical crystallization technique in four different solvent systems. In water (good solvent)–ethanol–dichloromethane (poor solvent) ternary solvent system the agglomeration takes place by the SA mechanism. In water–ethanol–n-hexane, water–ethanol and water–isopropyl alcohol solvent systems spherical particles were produced by the QESD method. Both procedures were proved to be feasible for the preparation of spherical salt hydrate particles as core material for microencapsulation. This method gives important basis to produce phase change materials from suitable salt hydrates. The potash alum content in the spherical agglomerates was analysed by conductivity and thermogravimetric measurements and their composition by XRD. Volume weighted mean diameters (D(4,3)) of the microparticles were 66 μm, 79 μm, 89 μm, and 684 μm formed in water–ethanol–n-hexane, water–ethanol, water–isopropyl alcohol, and water–ethanol–dichloromethane solvent system, respectively. Potash alum dodecahydrate is a double salt. Due to its different solubility in the four different solvent systems it crystallized out not only as potash alum, but also in other salt forms. The enthalpy changes of spherical agglomerates produced from different solvent systems were increased proportionally with potash alum contents.

Thermal Energy Storage By Microcomposite Of A Phase Change Material And Ethyl Cellulose

Abstract Phase change materials (PCMs) are capable of storing and releasing large amounts of latent heat thermal energy when undergoes phase change. They are developed for various building applications such as thermal energy storage, thermal protection, cooling, air-conditioning, waste heat recovery and for solar heating systems. Paraffin PCMs have low cost and a moderate thermal energy density, though a low thermal conductivity. PCM microencapsulation is one of the best tools to enhance the heat transfer rate by enlarging the surface area. In this work ethyl cellulose as an environmental friendly encapsulating material was used to entrap n-hexadecane PCM by an emulsion-solvent evaporation method using poly(vinyl alcohol) (PVA), Tween 80 or poly(methacrylic acid sodium salt) (PMAA) emulsifier. The structure of the forming microparticles was predicted by determining the interfacial tensions between the phases. Both theoretically and in the experiments, composites prepared with PMAA showed the most desirable properties regarding the size (average: 80 m) and the latent heat storage capacity (of melting and freezing were 111.4 J/g and 117.9 J/g, respectively), furthermore, there was no significant temperature and enthalpy change observed after 1000 heating-cooling thermal cycles, thus, this microcomposite can be considered as suitable encapsulated PCM for thermal energy storage applications.