Jelena Škamat

Preparing Al-Mg Substrate for Thermal Spraying: Evaluation of Surface State After Different Pretreatments

The article deals with the pretreatment technique for preparing the surface of aluminum alloy EN AW 5754 before thermal spray. The surface after different pretreatments, including degreasing with acetone, chemical etching with acidic and alkali solutions, grit-blasting, cathodic cleaning, and some combinations of these techniques, has been studied. The investigation of pre-treated surfaces covered the topographical study (using scanning electron microscopy, atomic force microscopy, and 3D profilometry), the chemical analysis by x-ray photoelectron spectroscopy, the evaluation of surface wettability (sessile drop method), and the assessment of surface free energy. Compared with all the techniques used in present work, the cathodic cleaning and its combination with grit-blasting provide the most preferable chemistry of the surface. Due to the absence of hydroxides at the surface and, possible, due to the diffusion of magnesium to the surface of substrate, the surface wettability and the surface free energy have been significantly improved. No direct correlation between the surface topography and the surface wettability has been established.

Reuse of ultrafine mineral wool production waste in the manufacture of refractory concrete

The paper deals with the mineral wool production waste (cupola dust - CD), presents CD characterization and aims to reuse CD in production of refractory concrete with calcium aluminate cement. The study of CD covers its chemical, phase and thermal analyses along with the morphological study and determination of particles size distribution. Zeta-potential, electrical conductivity and pH values of CD suspension are presented in the paper as well. Commercial microsilica additive in refractory concrete has been replaced with cupola dust. Compositions of refractory concrete have been prepared by incorporating 1%, 2% and 3% of CD. The bulk density, ultrasonic wave velocity, cold crushing strength and thermal shock resistance of the created refractory concrete have been determined. Based on experimental results, it has been found that cupola dust may be used for the production of refractory concrete. The environmental impact related to the CD reuse in refractory concrete production has been evaluated as well.

Action of the Products of Biofuel Combustion on the Phase Composition and Structure of Refractory Material

The changes occurring in the phase composition and microstructure of aluminum-silicate refractory material which disintegrated during operation in a solid-biofuel combustion unit were investigated. The main reasons for the disintegration of the material were determined on the basis of investigations performed by using modern methods and analyzing the results in comparison with published data on the chemical composition of volatile products of biofuel combustion and their physical-chemical properties.

Thermite welding of Cu–Nb microcomposite wires

Abstract Thermite welding of Cu–Nb microcomposite wires was investigated. Suitable compositions of thermite material and slag were determined from the equation of the exothermic combustion synthesis reaction. The phase compositions of the thermite mixture and slag determined by X-ray diffraction analysis correspond to those assessed from the equation. According to non-destructive radiographic testing, the joint structure does not have welding defects. Microstructural examination of the joint cross-section with scanning electron microscopy showed that the Cu–Nb wire retained its shape and microstructure and only a thin surface layer of wire was melted during welding. The difference in electrical resistances of the conductor and welded joint was below 20 %. The thermite joint can withstand a maximum load equal to 62.5 % of the load-bearing capacity of microcomposite conductor.

Welds of Dissimilar Steel 1.0038/1.4301: Increasing Corrosion Resistance by the Optimization of Welding Parameters and Post-Weld Processing

The corrosion of exploited motor vehicles and important or potentially dangerous structures is not a new problem of engineering [1]. However, nowadays, it still remains one of the most burning questions of manufacturing welding structures. There are a number of established methods and technological solutions allowing improvements to the premature corrosion resistance of exploited welded joints and structural elements. In the majority of cases, different protective coatings are used. However, protective coatings are not applicable for some structures in food and medical industry as well as for some other big dissimilar-material structures of a complicated shape. In such cases, the corrosion resistance of welded structures may be provided by other technological means. The present research is aimed at investigating the efficiency of such methods. Several different welding technological solutions and post-weld surface treatments have been applied. The corrosion resistance of the obtained welded joints has been evaluated conducting tests on corrosion under laboratory conditions. The obtained results and conclusions of the present research may be useful for manufacturers solving the problems of the corrosion resistance of welded dissimilar-steel structures.

The Investigation of Properties of Insulating Refractory Concrete with Portland Cement Binder

The present work contains the results of experimental study on properties of insulating refractory concrete created on the basis of Portland cement (PC) binder and modified with microsilica (MS). The experimental compositions were made using Portland cement, lightweight aggregates (expanded clay and vermiculite) and microsilica additives. It was established that MS additives enable significant improvement of mechanical properties and thermal shock resistance of PC-based insulating concrete with values comparable to insulating refractory concrete based on calcium aluminate cement.

About the Possibility of Using Ultrasound in Thermal Spray Technologies

The present article introduces a survey on ultrasonic technologies applied to material processing and describes the possibilities of improving the quality of coating made by thermal spraying introducing ultrasound into the covering process. The article contains the results of some other research works and discusses a number of conclusions about the possibilities of applying ultrasound in thermal spray technologies.

Advanced Materials Research and Technologies Development: Lithuanian Experience

Lithuania, as a small country, cannot afford creating new knowledge in all the fields of science. It is reasonable to firstly focus on those fields in which Lithuania already has scientific and industrial potential and that clearly declare the biggest demand for innovations as well as capability to invest into innovations. Research institutions here usually focus on fundamental research but both the revenues and the human resources of research institutions are rather poor. Dispersion of the Lithuanian potential of science and studies and the absence of critical mass represent the main reasons why R&D lacks effectiveness. The paper presents the main research fields and high-tech research institutions in Lithuania.