Search

In recent years, nanoparticles have emerged as an important player in a broad range of applications, especially thanks to recent advances in their synthesis. The silver and copper nanoparticles are often used due to their antibacterial and fungicidal activities, and this article presents the results of the nanoparticle synthesis using electrical glow discharge generated directly in a volume of their salt solutions. Therefore, there is no influence of air (i.e. reactive nitrogen species) as it is usual in other commonly used approaches. Nanoparticles were prepared under various experimental conditions, and they were characterized by ultraviolet/visible spectrometry, dynamic light scattering, X-ray photoelectron spectroscopy, and high-resolution scanning electron microscopy. Particles were produced without any surfactant or stabilizing agent, and some of them showed higher resistance against agglomeration during their short-term (days) storage. The nanoparticle formation mechanism was confirmed by the fast camera imaging. Thus, the developed approach can be applied for simple environmentally friendly nanoparticle production for various applications.

The formation of a rigid, tough interface based on a nacre-like structure in carbon fiber (CF) composites is a promising way to eliminate low delamination resistance. An effective method of coating CFs is electrophoretic deposition (EPD), which, in the case of dissimilar components like graphene oxide (GO) and polymeric glue, usually requires chemical bonding/strong interactions. In this work, we focus on chitin nanocrystals (ChNCs), leading to an excellent mechanical performance of artificial nacre, where favorable interactions and bonding with GO are controlled by degrees of deacetylation (5, 15, and 30%). We prepared coatings based on GO/ChNC adducts with 95/5, 90/10, 50/50, and 25/75 ratios using optimized EPD conditions (pH, concentration, voltage, and time). The prepared materials were characterized using FTIR, TEM, XPS, SEM, DLS, and XRD. SEM evaluation indicates the formation of a homogeneous interlayer, which has a fair potential for chemical bonding with the epoxy matrix. Short-beam testing of epoxy matrix composites indicates that the coating does not decrease stiffness and has a relatively low dependence on composition. Therefore, all coatings are promising for a detailed study of delamination resistance using laminate samples. Moreover, facile EPD from the water solution/suspension has a fair potential for industrial applications. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The concrete has been and at the same time will be the most used construction material worldwide. It is exposed to various physical and chemical degradation processes that deteriorate its properties and shorten its service life in most applications. As most of the detrimental effects on concrete come from the ambient environment, the quality of concrete surface plays a key role in the overall concrete performance. It should be resistant to abrasion, free of microcracks and open pores to prevent ingress of water, aggressive solutions, and gases. To enhance the properties of the concrete surface, various approaches can be used. The treatment via silicate-based sealers is becoming increasingly popular in concrete technology, especially in preventing deterioration when exposed to highly aggressive environments. This contribution focuses on applying unconventional test methods (e.g. combined scratch/acoustic emission method) to detect the fundamental properties of the treated cementitious surfaces will also provide a new perspective approach of material testing, which may be in the future advantageously used in technical practice. The present combined scratch/acoustic emission test evaluation will provide an excellent insight into lithium silicate sealers’ physical behaviour on fine-grained cement-based materials during this test.

Protection of concrete against aggressive influences from the surrounding environment becomes an important step to increase its durability. Today, alkali silicate solutions are advantageously used as pore-blocking treatments that increase the hardness and impermeability of the concrete's surface layer. Among these chemical substances, known as concrete densifiers, lithium silicate solutions are growing in popularity. In the present study, the chemical composition of the lithium silicate densifiers is put into context with the properties of the newly created insoluble inorganic gel responsible for the micro-filling effect. Fourier-transform infrared spectroscopy was used as a key method to describe the structure of the formed gel. In this context, the gelation process was studied through the evolution of viscoelastic properties over time using oscillatory measurements. It was found that the gelation process is fundamentally controlled by the molar ratio of SiO2 and Li2O in the densifier. The low SiO2 to Li2O ratio promotes the gelling process, resulting in a rapidly formed gel structure that affects macro characteristics, such as water permeability, directly related to the durability of treated concretes. [ABSTRACT FROM AUTHOR]

This study investigates the relationships between the hydration kinetics of waterglass-activated slag and the development of its physical-mechanical properties, as well as its color change. To modify the calorimetric response of alkali-activated slag, hexylene glycol was selected from various alcohols for in-depth experiments. In presence of hexylene glycol, the formation of initial reaction products was restricted to the slag surface, which drastically slowed down the further consumption of dissolved species and slag dissolution and consequently delayed the bulk hydration of the waterglass-activated slag by several days. This allowed to show that the corresponding calorimetric peak is directly related to the rapid evolution of the microstructure and physical-mechanical parameters and to the onset of a blue/green color change recorded as a time-lapse video. Workability loss was correlated with the first half of the second calorimetric peak, while the most rapid increase in strengths and autogenous shrinkage was related to the third calorimetric peak. Ultrasonic pulse velocity increased considerably during both the second and third calorimetric peak. Despite the modified morphology of the initial reaction products, the prolonged induction period, and the slightly reduced degree of hydration induced by hexylene glycol, the overall mechanism of alkaline activation remained unchanged in the long-term perspective. It was hypothesized that the main issue of the use of organic admixtures in alkali-activated systems is the destabilizing effect of these admixtures on soluble silicates introduced into the system with an activator. [ABSTRACT FROM AUTHOR]

Superhydrophobic surfaces were prepared using a two-step method that involved the etching of AZ31 and AZ91 magnesium alloys and then modifying the etched alloys with stearic acid. Magnesium alloys etched with ZnCl2 and SnCl2 exhibited surfaces roughened with micro- and nanoscale hierarchical structures consisting of two chemically distinct regions (Zn/Zn(OH)2 or Sn/SnO2 and Mg(OH)2). An optimum etching time of ten minutes was chosen for both etchants. Superhydrophobic surfaces with the highest contact angle were prepared when stearic acid reacted with the etched alloys at 50 °C for 4 h. Stearic acid was bound as zinc stearate and magnesium stearate on Mg alloys etched with ZnCl2 and SnCl2 solutions, respectively. The superhydrophobic process on AZ31 alloys etched with ZnCl2 and SnCl2 improved the corrosion resistance in phosphate buffered saline (PBS) solution compared to bare AZ31 alloy, with the use of ZnCl2 etchant leading to better results. An improvement in the corrosion resistance of AZ91 alloy was observed when the stearic-acid-modified AZ91 alloy was etched with SnCl2. In contrast, the use of ZnCl2 etchant to pretreat AZ91 alloy resulted in a significant deterioration in corrosion properties compared to bare AZ91 alloy. The microstructure of the Mg alloy had an impact on the etching and modification process. On the basis of the findings, a characterization of the chemistry of etching magnesium alloys and the formation of superhydrophobic surfaces was proposed. Magnesium alloys were prepared with superhydrophobic surfaces, incorporating antibacterial metals, features which may increase their potential for use in medical applications. [ABSTRACT FROM AUTHOR]

The application of concrete surface treatment has been widely investigated in recent decades. Treatment with silicate-based sealers is becoming increasingly popular in concrete technology, especially in preventing deterioration when exposed to extremely aggressive environments. Nowadays, lithium silicate sealers have been growing in market share in comparison to sodium or potassium silicates. Therefore, this study is focused on the development of a new generation of lithium silicate sealers improved by selected organic admixture. Hexylene glycol was used as an effective improvement for the lithium silicate sealer in terms of controlling the gelation process, which is the crucial mechanism to block existing capillary pores on the concrete surface resulting in increase the impermeability of the concrete's surface layer and thus the durability of the entire system. The gelation process was studied by means of a rheological approach, whereas scanning electron microscopy equipped with EDS was chosen as a key method to observe and analyze the surface treatment. Subsequently, the treatment functionality was determined based on water permeability measurement. The gained knowledge helped to predict the service life of surface treated concrete and opened an opportunity to produce more sustainable building materials. [ABSTRACT FROM AUTHOR]

Belite-rich cement is a low carbon footprint binder. However, its use is accompanied by a low initial rate of hydration. This can be partially eliminated by grinding to a high specific surface or through the addition of admixtures (mineralizators or activators). The influence of alkaline activators CaSO4, Na2SO4 and Na2CO3 (in the amount of 5 wt.% related to the clinker weight) on the hydration course, as well as the quantity of hydration products in belite-rich cements, were investigated in this paper. Belite-rich clinker was laboratory-synthetized and ground together with activators to prepare various belite-rich cements. Next, the hydration kinetics and the hydrated phase assemblage were investigated using isothermal calorimetry, X-ray powder diffraction and thermogravimetric and differential thermal analyses. The use of selected admixtures allowed us to obtain belite-rich cements with higher hydraulic activity in the initial period. [ABSTRACT FROM AUTHOR]

One of the most important technological problems associated with alkali-activated materials (AAM) is large shrinkage. A possible solution to decrease the extensive drying shrinkage of these materials is the use of shrinkage-reducing admixtures (SRAs). The promising group of SRAs, from the perspective of using in AAMs, are amino alcohols. However, the efficiency of reducing the drying shrinkage strongly depends on their chemical structure. Hence, the study is focused on the molecular architecture of amino alcohol surfactants and its relation to the affected properties of alkali-activated blast-furnace slag systems. Selected amino alcohols were tested in terms of the ability to reduce the surface tension of pore solution as well as to influence the drying shrinkage, hydration mechanism and mechanical properties of AAMs. The study confirms that the length and branching of the alkyl chain linked to the amino group play the key role in SRA efficiency. Amino alcohol surfactants with a high-carbon alkyl chain decreased dramatically both the surface tension and the drying shrinkage, but simultaneously negatively affected the process of alkali activation, resulting in a deterioration of the mechanical properties. Conversely, the addition of 0.5 w/ % of the surfactants with a low molecular weight, such as 2-(Methylamino)ethanol, showed a slight improvement of the compressive strength after 7 d and 28 d, and at the same time reduced the drying shrinkage by 30% compared to the reference sample. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The study deals with the methodology for determining the chemical composition of alkaline silicate solutions. Nowadays, the most widely used method in the industry is the acid-base titration. This technique is very accurate for the determination of alkali content (e.g. Na2O, K2O, Li2O). However, the problem arises in the titration of SiO2, since the color change of the methyl red indicator is very slow and therefore the equivalence point is unclear. The main aim of this work is to present the benefits of conductometric titration, where the equivalence point is indicated by a sudden change of conductivity. The applicability of the method has been verified with other analytical techniques, such as ICP-OES and gravimetric analysis. The results mutually confirmed similar values of the obtained silicate module (molar ratio of SiO2 and alkaline oxide) both in the case of sodium, potassium and lithium water glasses. Contrary, the previous acid-base titration recorded deviations of a few percent. Based on the obtained results, one can say that the conductometry is a very promising method providing an accurate, fast, and instrumentally undemanding chemical characterization of alkaline silicate solutions. [ABSTRACT FROM AUTHOR]

In recent years, the use of various nontraditional cements and composites has increased. Alkali-activated materials, especially those based on alkali activation of blast-furnace slag, have considerable potential in construction industry. However, alkali-activated slag binders exhibit significant shrinkage, in some circumstances several times greater than portland cement-based materials, which hinders wider use of these materials in numerous applications. Therefore, the use of specific admixtures suitable for alkaliactivated systems is necessary. This paper is consequently focused on testing the efficiency of shrinkage-reducing additives based on polypropylene glycols, as well as their influence on the hydration mechanism and mechanical properties of prepared alkali-activated materials. [ABSTRACT FROM AUTHOR]

Alkali-activated matrices are suitable materials for the immobilization of hazardous materials such as heavy metals. This paper is focused on the comparison of immobilization characteristics of various inorganic composite materials based on blast furnace slag and on the influence of various dosages of the heavy metal Pb on the mechanical properties and fixation ability of prepared matrices. Blast furnace slag (BFS), fly ash, and standard sand were used as raw materials, and sodium water glass was used as an alkaline activator. Pb(NO3)2 served as a source of heavy metal and was added in various dosages in solid state or as aqueous solution. The immobilization characteristics were determined by leaching tests, and the content of Pb in the eluate was measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). The microstructure of matrices and distribution of Pb within the matrix were determined by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). Increasing the dosage of the heavy metal had negative impacts on the mechanical properties of prepared matrices. The leaching tests confirmed the ability of alkali-activated materials to immobilize heavy metals. With increasing addition of Pb, its content in eluates increased. [ABSTRACT FROM AUTHOR]

The fixation of heavy metals (Ba, Cu, Pb) in an alkali-activated matrix was investigated. The matrix consisted of fly ash and blast furnace slag (BFS). The mixture of NaOH and Na-silicate was used as alkaline activator. Three analytical techniques were used to describe the fixation of heavy metals—X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD). All heavy metals formed insoluble salts after alkaline activation. Ba was fixed as BaSO4, and only this product was crystalline. EDS mapping showed that Ba was cumulated in some regions and formed clusters. Pb was present in the form of Pb(OH)2 and was dispersed throughout the matrix on the edges of BFS grains. Cu was fixed as Cu(OH)2 and also was cumulated in some regions and formed clusters. Cu was present in two different chemical states; apart from Cu(OH)2, a Cu–O bond was also identified. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Lignite can be applied directly in natural form on agricultural fields as a soil conditioner. However, there is little information on leaching of risky compounds by its interaction with water. South Moravian lignite was therefore extracted with water at 25 °C and 2.3 % of water-soluble fractions were obtained from lignite corresponding to 0.3 % of total organic carbon. All ten fractions form aromatic and aliphatic structures with oxygen-containing functional groups such as carboxyl groups, alcohols, ethers, esters, can be characterized as fulvic-like and humic-like substances. According to the XPS spectra, the fractions contain two nitrogen forms, one of which is ascribed to pyrroles and the second is related to protonated amines or quaternary nitrogen. Analysis at molecular level showed that the fractions contain compounds such as benzene carboxylic acids and their derivatives, small aliphatic diacids, fatty acids and polyols. Most of the identified molecules reflect clearly the presence of microbial remains in the lignite structure since microbial activity during coalification is well known. The differences between the individual fractions are negligible, especially after 21 days of extraction. From environmental point of view, it seems that the identified compounds do not represent a toxic risk. [ABSTRACT FROM AUTHOR]

The aim of this paper is the introduction of a sophisticated testing method, X-ray photoelectron spectroscopy (XPS), used to study the interface between the hydrated cement phase and polymer after mechanochemical activation, which is fundamental for the creation of macro-defect-free (MDF) composites. The XPS results clearly explain the hypothesis of a chemical reaction mechanism in the interphase regions affecting the final properties of the MDF materials. [ABSTRACT FROM AUTHOR]

This work deals with the use of laser-induced breakdown spectroscopy (LIBS) for determining the surface density of titanium in ultrathin layers, particularly in ultrathin layers on a steel sheet. The results obtained by LIBS spectroscopy were compared with those obtained by wavelength dispersive X-ray fluorescence spectroscopy (WDXRF), X-ray photoelectron spectroscopy (XPS) and laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOF-MS). A simple, cheap and efficient method for the determination of the surface density of titanium in thin layers has been developed. [ABSTRACT FROM AUTHOR]

Composition analysis of the so-called red corrosion on gold coins, plus discussion on its origin and possibilities of removal of the red stains are presented. Suggestion of a new alternative non-chemical method in cleaning of gold coins is published. [ABSTRACT FROM AUTHOR]

Portland cement-based products are the most commonly used building materials. Worldwide production accounted for about 2.5 billion metric tons. However, it is well known that the production of Ordinary Portland Cement (OPC) is associated with generating of by-product materials. Cement kiln dust is one of secondary material of cement manufacturing process. Purpose of this work is to use this undesirable material for development of new cementitous material similar to Portland cement-based concrete, which is convenient in terms of energy and is environmental-friendly at once. This article presents preparation and composition of new alkali activated material, called geopolymer, synthesized from blast furnace slag and fly ash activated by sodium hydroxide and cement kiln dust as well as the potential to immobilize heavy metals in its structure. Study was mainly based on SEM-EDX, XRD and ICP-MS analyses. [ABSTRACT FROM AUTHOR]

Alkali-activated systems (AAS) represent an ecologically and economically sustainable inorganic binder as an alternative to ordinary Portland cement (OPC). One of the main benefits of AAS is their durability in aggressive environments, which can be equal or even better than that of OPC. In this paper, the influence of the type of alkaline activator in alkali-activated blast furnace slag (AAS) in terms of resistance to sulfur dioxide corrosion was investigated. The durability testing process was based on the CSN EN ISO 3231 standard and simultaneously compared with mortar samples prepared by using Blastfurnace cement CEM III/A 32.5R. The degradation progress was evaluated by employing several different methods such as observing the compressive strength development, weight change evaluation, non-destructive testing methods like ultrasound or impact echo technique, or visual phenolphthalein technique. Subsequently, fundamental characterization of samples by the XRD method was performed during the degradation test. The obtained results indicate that none of the testing methods used could be prioritized over others to determine the resistance of AAS against the action of sulfur dioxide. For this reason, the durability testing of AAS remains an issue, and the development of specific standards considering the behavior of AAS seems necessary. [ABSTRACT FROM AUTHOR]

The very early stages of alkaline activation of slag control its rheology and setting, but also affect its hydration, which occurs later. Simultaneously, these parameters are dictated by the nature and dose of the alkaline activator. Therefore, we investigated and compared the changes in slag particles (SEM, BET, laser diffraction), as well as in the pore solution composition (ICP–OES), pH, and conductivity, of alkali-activated slag (AAS) pastes containing the three most common sodium activators (waterglass, hydroxide, and carbonate) and water during the first 24 h of its activation. To ensure the best possible comparability of the pastes, a fairly nontraditional mixture design was adopted, based on the same concentration of Na+ (4 mol/dm3) and the same volume fraction of slag in the paste (0.50). The results were correlated with the pastes' hydration kinetics (isothermal calorimetry), structural build-up (oscillatory rheology), and setting times (Vicat). Great differences were observed in most of these properties, in the formation of hydration products, and in the composition of the pore solution for each activator. The results emphasize the role of the anionic groups in the activators and of the pH, which help predict the sample's behavior based on its calorimetric curve, and offer data for further comparisons and for the modelling of AAS hydration for specific activators. [ABSTRACT FROM AUTHOR]

Hybrid systems represent a new sustainable type of cement combining the properties of ordinary Portland cement and alkali-activated materials. In this study, a hybrid system based on blast furnace slag and Portland clinker was investigated. The economic aspects and appropriate waste management resulted in the usage of technological waste from water glass production (WG-waste) as an alkaline activator. Although the Portland clinker content was very low, the incorporation of this by-product significantly improved the mechanical properties. Nevertheless, the high amount of alkalis in combination with possible reactive aggregates raises concerns about the risk of alkali–silica reaction (ASR). The results obtained from expansion measurement, the uranyl acetate fluorescence method, and microstructure characterization revealed that the undesirable effects of alkali–silica reaction in mortars based on the hydration of hybrid cement are minimal. [ABSTRACT FROM AUTHOR]

Herein, we presented electromagnetic interference shielding characteristics of NiFe2O4 nanoparticles—in-situ thermally-reduced graphene oxide (RGO)—polypropylene nanocomposites with the variation of reduced graphene oxide content. The structural, morphological, magnetic, and electromagnetic parameters and mechanical characteristics of fabricated nanocomposites were investigated and studied in detail. The controllable composition of NiFe2O4-RGO-Polypropylene nanocomposites exhibited electromagnetic interference (EMI) shielding effectiveness (SE) with a value of 29.4 dB at a thickness of 2 mm. The enhanced EMI shielding properties of nanocomposites with the increase of RGO content could be assigned to enhanced attenuation ability, high conductivity, dipole and interfacial polarization, eddy current loss, and natural resonance. The fabricated lightweight NiFe2O4-RGO-Polypropylene nanocomposites have potential as a high performance electromagnetic interference shielding nanocomposite. [ABSTRACT FROM AUTHOR]

Cement kiln by-pass dust (CKD) is a fine-grained by-product of Portland clinker manufacturing. Its chemical composition is not suitable for returning back into feedstock and, therefore, it has to be discharged. Such an increasing waste production contributes to the high environmental impact of the cement industry. A possible solution for the ecological processing of CKD is its incorporation into alkali-activated blast furnace slag binders. Thanks to high alkaline content, CKD serves as an effective accelerator for latent hydraulic substances which positively affect their mechanical properties. It was found out that CKD in combination with sodium carbonate creates sodium hydroxide in situ which together with sodium water glass content increases the dissolution of blast furnace slag particles and subsequently binder phase formation resulting in better flexural and compressive strength development compared to the sample without it. At the same time, the addition of CKD compensates the autogenous shrinkage of alkali-activated materials reducing the risk of material cracking. On the other hand, this type of inorganic admixture accelerates the hydration process causing rapid loss of workability. [ABSTRACT FROM AUTHOR]

The performance of immunosensing devices crucially depends on the methodology of antibody or antigen immobilization on the sensor surface. Hence, the stable intermediate layers capable of specific and reproducible binding of antibodies are required. Herein, we introduce the amine rich (NH x concentration of 6 at.%) layers prepared by pulsed plasma polymerization of cyclopropylamine (CPA) for functionalization of the quartz crystal microbalance (QCM) surface by the antibody specific to human serum albumin. In these layers the amine groups serve as anchor for the antibody binding. The sensitivity of QCM sensors prepared in this way surpasses the one for the previously reported sensors functionalized by the thiol-based self-assembled monolayers by the factor of 2. Our results thus show that CPA plasma polymers have a significant potential for further development of the active layers for biosensing applications. [ABSTRACT FROM AUTHOR]