Papers by Keyword: Phase

Abstract: The early stage development of the cement microstructure is a crucial aspect affecting the overall performance of cementitious materials. The formation of hydration products depends on the presence of water and carbon dioxide, as well as on the distribution and re-crystallization of the cement particles. In this paper we evaluate the micromechanical properties evolution of cement phases over first 28 days after casting by the electron microscopy and static areal indentation.

Abstract: A dense TiO₂ film was fabricated on the titanium surface using the anodization technique. Surface morphology and phase structure of anodic TiO₂ film were investigated before and after the hydrothermal exposure at 160 °C for 24 h. The hydrothermal solution was 3.5 wt% NaCl solution and the films were either immersed in NaCl solution or exposed to water vapor during the exposure. It was found that the as-prepared anodic TiO₂ film consisted primarily of amorphous oxides and exhibited a relatively smooth surface. After the hydrothermal exposure, lots of rod-like crystals were formed on the solution-immersed film, while aggregated fine nanoparticles emerged on the vapor-exposed one. Thin film X-ray diffraction analysis indicated that the hydrothermal exposure transformed amorphous oxides into crystalline anatase. The corrosion behavior investigation showed that the structural transition of anodic TiO₂ film during the exposure reduced the corrosion resistance of anodized titanium greatly.

Abstract: The hydrophobicity enhancement of structural materials is a contemporary topic of discussion. This paper deals with the effect of crystalline admixture (CA) on the microstructure of the cementitious composite in first four weeks after the production. Previous investigation was performed on the referential specimens consisting only from pure cement. The samples of pure CA and cement modified by 1% of CA with same w/c ratio were examined and compared in this paper. By investigation of these materials on the micro-scale in the time, it is possible to identify the development of the microstructure of each and determine the impact of the modification. For this purpose, backscattered electrons microscopy (BSE) with energy-dispersive X-ray spectroscopy (EDX) was used for phase analysis as well as instrumental nano-indentation to obtain the micro-mechanical properties. The presented results show the evolution of mechanical properties and microstructure in time and the impact of the crystalline admixture on modified cement.

Abstract: In this paper we present preliminary results of ballistic testing and thermal measurement of a functional structure consisting of phase change material (PCM) and soft armour layers made of Kevlar. The purpose of this study is to explore the feasibility of combining thermal management with ballistic protection in a single system such that the thermal stress of dismounted combat personnel may be mitigated to an extent while wearing their body armour in hot and humid environments. Under such conditions the breathability of smart textiles will offer little to no benefit. In our study each Kevlar sheet is coated with PCM from Microtek Laboratories Inc. and bonded with normal PVA wood glue. Twenty coated layers were prepared for ballistic testing and compared with twenty pure Kevlar layers as reference. The cooling power of the soft armour insert (SAI) with PCM was measured on a heated sweating manikin. The proof of concept results show that the SAI with PCM only produced a mild cooling effect, which may lower skin temperature and provide a mild cooling sensation for a body region that would otherwise allow limited heat loss, due to the impermeability of the SAI.

Abstract: The transformation of the structure, phase and chemical composition of the diffusion coatings of the system Al-Ni and Al-Cr-Ni at 1100 °C is studied. It is shown that the diffusion redistribution of Al by the coating thickness during the heat treatment is slower in the system Al-Cr-Ni than in the binary system Al-Ni.

Abstract: Phase composition, defect substructure, and mechanical and tribological properties of the steel Hardox 450 surfaced with С-V-Cr-Nb-W wire are analyzed relying on procedures of transmission diffraction microscopy, mechanical and tribological methods. As a result of surfacing, wear resistance of the material is 138 – 153 times higher than that of the steel Hardox 450, and the friction factor diminishes 2 – 2.5 times. The changing dislocation substructure and phase composition of the deposited metal are analyzed in the paper. The authors have come to the conclusion that the change in analyzed properties is caused by initiation of a multiphase nanostructure. It has been revealed that its strengthening is possible due to the developing of the α-matrix martensitic pattern and a high inclusion of the volume fraction of iron-, chromium-, tungsten,- and niobium-based carbide phase. It has been ascertained in the paper that the iterative surfacing results in attenuation of the oxide phase and in the significant growth of the volume fraction inclusion of the carbide phase.

Abstract: In this paper, the isothermal model of the initial stage of ion implantation process taking into account internal boundary is presented. It is assumed that implantable impurity generates mechanical perturbations. These waves can propagate with different velocities before and after the border. The examples of the waveform evolution at transition across the boundary for different combinations of the model parameters are presented.

Abstract: The formation of swirl to improve mixing in the fuel-air mixture through induced turbulence, by making changes in the combustion chamber geometry has been the key interest mentioned in the published research, academic and commercial works. The occurrence of shock waves has long been the effect of engine detonation. Both these things involve variation in the fluid’s dynamic characteristics, thermodynamic and physical states that are controllable by the use of mechanically produced waves. This paper aims at exploring the ways by which optimal combustion can be achieved through wave assisted combustion.

Abstract: Fe-Si alloys with various concentration of Al (0, 1, 3 and 5 % by mass) were synthesized by a spark plasma sintering technique. The specimens were prepared in an evacuated chamber of less than 4 Pa and under compressive stress of 40 MPa. During spark discharge, the heating rate was fixed at 10°C/min. After the SPS process was completed, the specimen surfaces were ground with silicon carbide papers. The metallographic characterization was performed by mean of X-ray diffraction (XRD) and scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDX) spectroscopy. According to sintering curves, all samples seem to have a similar sintering behavior. The densification of specimens was completed in the temperature range of about 1020-1050°C. Microstructure and phase characterization revealed that the alloys were mainly composed of FeSi₂ and FeSi phases containing oxide inclusions. The SEM images indicated that the fraction of FeSi phase and oxide inclusions appears to decrease with increase in Al concentration in the Fe-Si alloy.

Abstract: The purpose of this work is to search reduced graphene oxide (RGO) phase by identifying the molecular bonding, energy band gap and phase of old coconut shell. The characterization was performed by using FTIR, Uv-Vis and XRD spectroscopy. The heating temperature used in this work was 400°C and 600°C. Furthermore, the type of heating atmosphere used in this research covers nitrogen, ambient air with and without rinsing step. The XRD analysis shows that the RGO phase is formed by turbostatic structure which is a pile of random arrangement of parallel layers that make up the graphite structure with cliftonite phase at temperature 400°C and 600°C. In the inert nitrogen gas treatment, there are two impurity phases such as potassium chlorate (KClO₄) and sulfur (S₁₁). The molecular bondings of C=C, C-C, C-O, C=O, C-H and O-H appeared on the FTIR spectra of the samples were indentified. Analysis by using linear regression and absorbance edge methods was conducted to result in energy gap in the range from 0.14 to 0.67 eV, indicating that the produced samples are semiconducting materials.