Jakub Tkacz

Comparison of Electrochemical Methods for the Evaluation of Cast AZ91 Magnesium Alloy

Linear polarization is a potentiodynamic method used for electrochemical characterization of materials. Obtained values of corrosion potential and corrosion current density offer information about material behavior in corrosion environments from the thermodynamic and kinetic points of view, respectively. The present study offers a comparison of applications of the linear polarization method (from −100 mV to +200 mV vs. EOCP), the cathodic polarization of the specimen (−100 mV vs. EOCP), and the anodic polarization of the specimen (+100 mV vs. EOCP), and a discussion of the differences in the obtained values of the electrochemical characteristics of cast AZ91 magnesium alloy. The corrosion current density obtained by cathodic polarization was similar to the corrosion current density obtained by linear polarization, while a lower value was obtained by anodic polarization. Signs of corrosion attack were observed only in the case of linear polarization including cathodic and anodic polarization of the specimen.

Some Issues of Shrinkage-Reducing Admixtures Application in Alkali-Activated Slag Systems

Significant drying shrinkage is one of the main limitations for the wider utilization of alkali-activated slag (AAS). Few previous works revealed that it is possible to reduce AAS drying shrinkage by the use of shrinkage-reducing admixtures (SRAs). However, these studies were mainly focused on SRA based on polypropylene glycol, while as it is shown in this paper, the behavior of SRA based on 2-methyl-2,4-pentanediol can be significantly different. While 0.25% and 0.50% had only a minor effect on the AAS properties, 1.0% of this SRA reduced the drying shrinkage of waterglass-activated slag mortar by more than 80%, but it greatly reduced early strengths simultaneously. This feature was further studied by isothermal calorimetry, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Calorimetric experiments showed that 1% of SRA modified the second peak of the pre-induction period and delayed the maximum of the main hydration peak by several days, which corresponds well with observed strength development as well as with the MIP and SEM results. These observations proved the certain incompatibility of SRA with the studied AAS system, because the drying shrinkage reduction was induced by the strong retardation of hydration, resulting in a coarsening of the pore structure rather than the proper function of the SRA.

UV-cured TiO2 electron transport layers for printable solar cells

This article is focused on the development of new formulations of inks for printed electron transport layers based on titanium oxide. The electron transport layers were prepared from a suspension consisting of titania nanoparticles and a novel organo-silica binder. The layers are post-processed by low temperature UV curing instead of thermal annealing. The UV-cured TiO2 layers were applied in inverted-structure organic bulk heterojunction solar cells with the active layer from a PCDTBT:PC60BM blend. These devices achieved a power conversion efficiency comparable to devices with TiO2 layers prepared by the common sol–gel process relying on high-temperature calcination. Thus the novel UV curable TiO2 formulation is promising as printable electron transport layers for flexible devices, which are not compatible with thermal processing.

Silver Nanoparticles Stabilised by Cationic Gemini Surfactants with Variable Spacer Length

The present study is focused on the synthesis and investigation of the physicochemical and biological properties of silver nanoparticles stabilized with a series of cationic gemini surfactants having a polymethylene spacer of variable length. UV-VIS spectroscopy, dynamic light scattering, scanning electron microscopy and zeta potential measurements were applied to provide physicochemical characterization of the silver nanoparticles. The mean size values of the nanoparticles were found to be in the 50 to 115 nm range. From the nanoparticle size distributions and scanning electron microscopy images it results that a population of small nanoparticles with the size of several nanometers was confirmed if the nanoparticles were stabilized with gemini molecules with either a short methylene spacer (two or four −CH2− groups) or a long spacer (12 −CH2− groups). The average zeta potential value for silver nanoparticles stabilized with gemini molecules is roughly independent of gemini surfactant spacer length and is approx. +58 mV. An interaction model between silver nanoparticles and gemini molecules which reflects the gained experimental data, is suggested. Microbicidal activity determinations revealed that the silver nanoparticles stabilized with gemini surfactants are more efficient against Gram-negative bacteria and yeasts, which has a direct relation to the interaction mechanism of nanoparticles with the bacterial cell membrane and its structural composition.

Unconventional fluoride conversion coating preparation and characterization

Purpose The purpose of this paper is to compare electrochemical corrosion characteristics of conventional and unconventional fluoride conversion coating prepared on magnesium alloy. Design/methodology/approach The chemical reaction of AZ61 with 38 wt.% hydrofluoric acid (HF) for 24 h was used as a conventional way of fluoride conversion coating preparation. The unconventionally prepared coating was created in Na[BF4] salt melt at 450°C for 2 h. Morphology and chemical composition of prepared fluoride conversion coatings were studied with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Electrochemical corrosion characteristics of the coatings were analyzed in Hank’s solution using potentiodynamic tests. Findings Both the coating preparation ways resulted in the creation of uniform conversion coatings with the same thickness (1.3 ± 0.1 μm). Some defects were observed on the coatings surface; however, the defects did not reach the AZ61 surface. Electrochemical tests performed in Hank’s solution at 37°C showed an improvement of corrosion resistance of AZ61 treated with fluoride conversion coatings when compared to the untreated material. Unconventionally prepared coating reached better electrochemical corrosion characteristics when compared to the conventionally prepared coating. Originality/value Electrochemical corrosion characteristics of AZ61 magnesium alloy can be improved with fluoride conversion coatings. Two methods are used in the literature for the coatings preparation. The conventional method is based on dipping of the coated material to the HF, and the unconventional method lies in dipping of the sample to the Na[BF4] salt melt. The main purpose of the present study is to analyze the conventionally and unconventionally prepared coatings in terms of chemical analysis, morphology and material corrosion protection (electrochemical corrosion characteristics), while the data are not provided in the literature, according to the authors’ knowledge. Very similar coatings were prepared using both the methods from the morphological and chemical composition point of view. However, unconventionally prepared coating created in Na[BF4] salt melt reached better electrochemical corrosion characteristics compared to the coating prepared in HF.

Corrosion behavior of wrought magnesium alloys AZ31 and AZ61 in Hank’s solution

Abstract Corrosion behavior of wrought magnesium alloys AZ31 and AZ61 was studied in Hank’s solution. Potentiodynamic curves measured after short-term of exposure showed higher corrosion resistance of AZ31 magnesium alloy in comparison with AZ61 magnesium alloy. On the contrary, long-term tests measured by electrochemical impedance spectroscopy showed higher corrosion resistance of AZ61 magnesium alloy in comparison with AZ31 magnesium alloy.

Influence of Ammonia Content in SNCR Fly Ash on Phase Composition and Morphology of Autoclaved Aerated Concrete (AAC)

In production of AAC the fly ash was used as a source of SiO2 for many years. Now, after introducing a selective non-catalytic reduction (SNCR) technology to coal combustion process, the fly ash contain ammonia in a form of soluble salts, such as NH4HSO4 and (NH4)2SO4, which causes problems during manufacturing the AAC. Among all the influence of ammonia ions to the phase composition of the final product was not fully described. The main aim of this contribution is to describe the influence of ammonia to phase composition and morphology of autoclaved aerated concrete (AAC). For preparing AAC in laboratory conditions, the fly ash with various content of ammonia was used. The amount of ammonia before and after the hydrothermal reaction was measured by VIS spectrofotometry. The phase composition of prepared samples was determined by means of X-ray diffractometry and confirmed by TG-DTA analysis. The influence of the ammonia to the morphology of final products was studied by scanning electron microscopy.

Buccal adhesive films with moisturizer- the next level for dry mouth syndrome?

Graphical abstract Figure. No Caption available. Abstract This study was undertaken to prepare films by solvent evaporation method comprising well‐known polymers in order to investigate their potential for buccal suitability. Mucoadhesive films were manufactured using different polymers such as ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose as well as carboxymethyl cellulose. Buccal films were evaluated in regards of mucoadhesiveness, swelling and physico‐chemical properties. Furthermore rheological measurement and adhesion study were carried out on the buccal porcine mucosa. Moreover, allantoin as humectant was incorporated and trans‐mucosal water loss was determined. The results showed that physico‐chemical, buccal adhesive and swelling properties varied depending on the composition of the polymers. The findings indicated films containing allantoin to be suitable for buccal application. In completion, adhesive films are appropriate and promising formulations in the treatment of various disease in the intraoral cavity.

The influence of starting materials´ solubility on tobermorite structure formation under the hydrothermal conditions

Overall, the tobermorite mineral crystallises under the hydrothermal conditions from the CaO-SiO2-H2O system. The system of calcium hydrosilicates species is extremely complex and many factors play an important role. The solubility of starting materials belongs to one of the most important factors. Dissolution rates of SiO2 source are significantly affected by their particle size distribution. Also the starting cation ́s concentration in the aqueous solution affects the yield of the hydrothermal reaction. The main aim of this contribution is to study the influence of water-to-solid ratio on tobermorite crystallization. The effect of particle size of various sources of SiO2 was also studied. The cost effective Ca and Si sources was primarily favoured. The C/S ratio of the experiments was set to 0.83. All syntheses were performed at 180 °C in laboratory steel autoclaves. The prepared powdered samples were characterized in order to determine the phase composition by using of X-Ray diffractometry. The thermal behaviour of prepared samples was studied by TG-DTA analyser. Morphology and particle size of synthetized powdered products was studied by scanning electron microscopy.

TiO2 Surface Coating of Mn-Zn Dopped Ferrites Study

This study deals with TiO2 coating of powder Mn-Zn ferrite in order to recieve photocatalytic layer on the top of these particles, forming core-shell catalyst. Powder catalysts are of great advance over the world due to the high surface area, considering the kinetics proceeds through heterogenous phase boundary catalysis. However their withdrawal from cleaning systems often requires energetically and economically demanding processes such as filtration and ultrafiltration. Since the ferrite is magnetic, the advantage of such formed core-shell photocatalyst is easibility of removing from photocatalytic decomposition system using external magnetic field. In this study the surface coating is performed, using Ti alkoxides mixtures with nanosized TiO2 particles and C and Au coating to form film layer of TiO2 on the surface of ferrite. XRD, SEM – EDS analyses are employed to study surface coating.