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Published By Publishing House Technologija

2029-7289, 1392-1320

2022 ◽  
Author(s):  
Li FAN ◽  
Xue-ying LI ◽  
Haiyan CHEN ◽  
Hailiang DU ◽  
Lei SHI

In the present work, four groups of spherical chromium carbide reinforced NiCrBSi hardmetal coatings were prepared on AISI 4145 steel by plasma transferred arc (PTA) technique. The corrosion behavior of the four as-received hardmetal coatings in 0.5 mol/L H2SO4 solution was investigated by polarization curve and electrochemical impedance spectroscopy (EIS). The results revealed that more Cr-rich carbides (Cr3C2, Cr7C3 and M23(C, B)6) are formed in the chromium carbide reinforced coatings, while for the NiCrBSi hardmetal coating only Cr7C3 carbide was detected by XRD. The polarization results show that the chromium carbide reinforced NiCrBSi hardmetal coatings have positive corrosion potential and lower corrosion current, providing a better protective effect to the substrate metal. The combined effects of Cr-rich carbide ceramic phases and a more stable passive film of Cr2O3 greatly improved the corrosion resistances of the chromium carbide reinforced NiCrBSi hardmetal coatings. The coating with the highest spherical chromium carbide addition has more pores because of the thermal stress due to the difference of thermal expansion coefficient between the NiCrBSi bonding phase and chromium carbide reinforced phase. The negative effects of the pores weaken the corrosion resistance, and the coating with the 30% chromium carbide content shows the best corrosion resistance. For NiCrBSi hardmetal coatings with higher reinforced chromium carbide content, the repeatability of the corrosion current obtained by polarization fitting is not as good as that of coatings with lower chromium carbide content. The repeatability of polarization results becomes worse when the specimens keep in a more stable passive state.


2021 ◽  
Author(s):  
Tonis PAARA ◽  
Sven LANGE ◽  
Kristjan SAAL ◽  
Rünno LÕHMUS ◽  
Andres KRUMME ◽  
...  

The effect of nanoclay additive on polyamide film oxygen permeability is investigated from the perspective of possible use as a laminate component for low-cost food packaging material. Montmorillonite nanoclay was melt-mixed in an industrial grade polyamide by twin-screw extrusion and the mixture was hot-pressed to a ~50 µm thick film. The film with 10 wt.% of nanoclay loading showed a 17 % decrease in the oxygen transmission rate (OTR), as compared to the pristine polyamide film (72 and 87 cm3/m2∙24 h, respectively). Despite the relatively high loading of the filler the obtained OTR exceeds that of the food packaging preferred upper limit of 10 cm3/m2∙24 h. XRD measurements confirmed the near-complete exfoliation of the nanoclay platelets. The platelets were found to be at an average angle of 9.5 degrees relative to the film’s surface plane. To comply with the requirements for food packaging, this angle needs to be decreased down to 0.4 degrees. To achieve this, different film-making methods enabling better control over the filler particles’ orientation need to be explored. Nanoclay addition increased the films’ yield strength (23 % for 10 wt.% film) and stiffness, while not affecting the films’ optical appearance.


2021 ◽  
Author(s):  
Myoung Youp SONG

One of the candidates for metallic interconnects of solid oxide fuel cells is ferritic stainless steel, Crofer 22 APU. Ferritic stainless steel Crofer 22 APU specimens with different surface roughness were prepared by grinding with SiC powder papers of various grits and then thermally cycled in air. Variation in the microstructure of the samples having different roughness with thermal cycling was investigated. Polished Crofer 22 APU specimens after three and five thermal cycles had relatively flat oxide layers with thicknesses of about 13.8 and 17.9 μm, respectively. Micrographs of a trench made by milling with FIB (focused ion beam) for a Crofer 22 APU specimen ground with grit 80 SiC powder paper after 8 thermal cycles (total oxygen exposure time of 200 h at 1073 K), captured by ESB (energy selective back-scattering) and SE2 (type II secondary electrons), showed that the surface of the sample was very coarse and its oxide layer was undulated. In the oxide layer, the phase of the sublayer was Cr2O3, and that of the top layer was (Cr, Mn)3O4 spinel. The surface of the sample ground with grit 80 SiC powder paper was very rough after 60 thermal cycles (total oxygen exposure time of 1500 h at 1073 K). The polished Crofer 22 APU is a better applicant to an interconnect of SOFC than those with rougher surfaces.


2021 ◽  
Author(s):  
Mikail ASLAN

Carbon nanodots, one of the last members of the nanocarbon family, show superior properties, such as low-cost production, good conductivity, and optical properties, nontoxic behavior, high biocompatibility, and eco-friendly nature. Understanding the effect of metal doping on the modification of the electronic structure of carbon nanodots is critical for enlarging its potential applications. In the present study, in terms of structural, energetic, and electronic analyses, X-doped carbon nanodot structures (X = B, N, Si, Al, Co, Au, Pd, and Pt) and their SO2 adsorption abilities were examined comprehensively by employing DFT. Results depict that embedding the heavy impurity metals (Pd, Pt) to the nanodot structures does not improve the SO2 sensing ability of carbon nanodot materials relatively. However, the doping of the low concentrated metals to the carbon nanodots may be one of the best ways for enhancing the SO2 trapping ability of the carbon nanodot materials since the calculated results having high adsorption energy values indicate SO2 gas molecule is easily adsorbed on the surface of doped carbon nanodots. This means higher adsorption capability compared to pure ones. Thus, it is suggested that the doped carbon nanodots consisting of B, Si, and N impurity atoms may be good candidates for effective SO2 sensing (adsorptions).


2021 ◽  
Author(s):  
Inga GRIGORAVICIUTE-PURONIENE ◽  
Iryna YEVCHUK ◽  
Oksana DEMCHYNA ◽  
Mariia ZHYHAILO ◽  
Khrystyna RYMSHA ◽  
...  

Cross-linked organiс-inorganic sulfo-containing membranes of various compositions based on acrylic monomers (acrylonitrile, acrylic acid, 3-sulfopropylacrylate potassium salt, ethylene glycol diacrylate) and sol-gel systems of tetraethoxysilane have been developed. Synthesis of the polymer matrix was carried out by UV-initiated polymerization of the monomer mixture and the inorganic component was formed in situ while conducting the sol-gel process of the precursor. FTIR, SEM, EDS, DMA, impedance spectroscopy were used to characterize the synthesized materials. The influence of inorganic component content on the properties of the membranes was investigated. DMA results show that an increase in silica content leads to a decrease in packing density and an increase in structural heterogeneity in sulfo-containing polyacrylate/silica membranes. The highest values of proton conductivity 1.12 ꞏ 10−2 Sm/cm at 60 °C were found in membranes containing 3 wt.%. of the added sol-gel system. Further increase of silica content does not increase the proton conductivity of the membranes. The proton transfer activation energies in the membranes were calculated from the temperature dependence of proton conductivity. The obtained cross-linked sulfo-containing organic-inorganic materials can be used for the development of proton-conducting membranes for fuel cells.


2021 ◽  
Author(s):  
Ruifeng CAO ◽  
Taotao WANG ◽  
Yuxuan ZHANG ◽  
Hui WANG

Improved heat transfer in composites consisting of guar gel matrix and randomly distributed glass microspheres is extensively studied to predict the effective thermal conductivity of composites using the finite element method. In the study, the proper and probabilistic three-dimensional random distribution of microspheres in the continuous matrix is automatically generated by a simple and efficient random sequential adsorption algorithm which is developed by considering the correlation of three factors including particle size, number of particles, and particle volume fraction controlling the geometric configuration of random packing. Then the dependences of the effective thermal conductivity of composite materials on some important factors are investigated numerically, including the particle volume fraction, the particle spatial distribution, the number of particles, the nonuniformity of particle size, the particle dispersion morphology and the thermal conductivity contrast between particle and matrix. The related numerical results are compared with theoretical predictions and available experimental results to assess the validity of the numerical model. These results can provide good guidance for the design of advanced microsphere reinforced composite materials.


2021 ◽  
Author(s):  
Olga BULDERBERGA ◽  
Andrey ANISKEVICH

The effect of ultraviolet (UV) exposure on the service-life of thermochromic microcapsules integrated into the epoxy matrix was investigated. The microcapsules of the formaldehyde shell contain the core of thermochromic leuco dye. Seven sets of epoxy resin samples filled with concentrations from 0 to 10 wt.% of microcapsules were investigated. The composite samples were exposed to UV for approximately 1000 h. For the quantitative evaluation of colour change under UV, a fast and simple original procedure based on samples’ image treatment was developed. With the exposure time intervals of 50 h, samples were taken out from the UV light chamber to evaluate the exposure effect on their reversible thermochromic ability and mechanical properties. Periodical evaluation of the UV light effect on mechanical properties during the exposure was performed by microhardness tests. Tensile tests of the samples till the fracture were performed every 200 h. The critical time under the exposure of the UV lamp that destroys the reversible thermochromic reaction of the microcapsules was defined as 200 h. At the same time, it has been found that the mechanical properties of the epoxy resin under the same UV source were not strongly affected after 1000 h of irradiance and changed in the frame of ~ 10 %.


2021 ◽  
Author(s):  
Shahid Hussain ABRO ◽  
Alidad CHANDIO ◽  
Asif Ahmed SHAIKH ◽  
Norbaizura NORDIN ◽  
Hamza SUHARWARDI

An attempt has been made in the present research work to investigate the role and influence of chemical effect of aluminum addition in the experimental steel towards the formation of k-carbides. Two steel grades were made with and without aluminum addition by induction melting furnace and were cast to ingots. Steel A has no aluminum addition and steel B has some aluminum content. These ingots were then solution heat treated on a temperature of 1200°C for 2-hours’ time and were cooled in the air. After that, they were hot rolled to drawn in plate and sheet. The small samples were cut from bulk and were then heat-treated at 800°C for 1 hour and quenched. Microstructure by OM and SEM was captured. In steel A there was no k-carbide present in the matrix and surprisingly in steel B, small fine k-carbides were present this was then confirmed by XRD later. OM, SEM, and TEM analysis revealed that the presence of k-carbides in steel B makes less dense. It was concluded that aluminum in conjunction with nitrogen forms the small nitride particles having a high melting point does not dissolve during the melting and casting such particles are known as AlN or aluminum nitride particles was observed by TEM along with EDS was the main reason to support the formation of k-carbides, these fine nano level k-carbides are orderly distributed in the steel matrix as was shown by XRD peaks.


2021 ◽  
Vol 27 (4) ◽  
pp. 470-476
Author(s):  
Gizem MANASOGLU ◽  
Rumeysa CELEN ◽  
Mine AKGUN ◽  
Mehmet KANIK

In this article, the surface roughness and friction coefficient values of graphene coated fabrics were examined. Fabrics were coated with three different graphene concentrations (5 %, 10 % and 20 %) with the knife-over-roll principle. The surface roughness of samples was measured by Accretech Surfcom 130A. Various surface roughness parameters of the coated fabrics were evaluated. Static and kinetic friction coefficients of coated fabrics were measured by Labthink Param MXD-02 friction tester using the standard wool abrasive cloth. It was observed that the coating concentration affected the frictional and roughness properties of fabrics. Experimental results showed that fabric surface roughness and friction coefficient values decreased significantly, especially at 20 % concentration. It was concluded that the coated fabrics produced could be used in applications such as anti-wear clothing.


2021 ◽  
Author(s):  
Kemal ŞAHBUDAK

In this work, the properties of alkali silicate geopolymer type materials and diatomite as additive to fly coal ash was investigated using thermic coal plant’s fly ash in alkaline solution. The reacted products of alumino-silicate geopolymers using fly ash plus diatomite were pseudo-amorphous aluminosilicate gel and calcite and their mechanical and thermal properties were evaluated by the addition of diatomite. The compressive strength of this geopolymer is similar to that of the Portland cement mortar of PC20 (± 20 %) when cured for 28 days while the density and thermal properties are much lower that indicates the insulator properties. Alkaline solution was produced by NaOH in different concentrations to determine the least alkaline solution molarity in the range of 1 M, 3 M and 5 M. The characterization of geopolymers were done by using XRD for phase analysis, SEM for surface and morphological evaluation, compression tests for mechanical properties and transient plane source thermal analysis for thermal insulation properties. The results showed that, 1 M of NaOH alkaline solution and 10wt% diatomite addition can provide enough strength of 18 MPa which is a good candidate for constructional materials. The thermal conductivity coefficient of 10 wt.% diatomite added geopolymer was evaluated as 0.0018 W/m×K which can also be a good candidate for insulator materials to be used in green lateral wall production.


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