română ANGELA SPOIALĂ, CORNELIA-IOANA ILIE, GEORGIANA DOLETE, ROXANA-DOINA TRUȘCĂ, LUDMILA MOTELICĂ, OVIDIU-CRISTIAN OPREA, DENISA FICAI, ANTON FICAI, ECATERINA ANDRONESCU, LIA-MARA DIȚU
Abstract
The purpose of this article was to synthesize antimicrobial composite membranes using chitosan (CS) and zinc oxide (ZnO) nanoparticles as adsorbents for the removal of heavy metals. Chitosan/ ZnO composite membranes were prepared through the electrospinning method. The ZnO nanoparticles concentration from the CS/ZnO composite membranes was 1% and respectively, 5%. The synthesized membranes were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis (DTA), hydration capacity, antimicrobial assessments and, heavy metal retention through the inductively coupled plasma mass spectrometry (ICP-MS) analysis technique. The thickness of the as-prepared CS/ZnO composite membranes was 20µm (CS/ZnO 1%) and 30µm (CS/ZnO 5%). The appearance of the synthesized membranes indicated a smooth and uniform morphology, which suggested the integration of zinc oxide nanoparticles into the obtained membrane. Fourier transform infrared spectroscopic measurements showed the existence of relevant functional groups of both chitosan and ZnO in the composite membranes. ICP-MS measurements provided information regarding the capacity of retention of these membranes, indicating that CS/ZnO 5% had the highest retention rate. The as-obtained CS/ZnO composite membranes are expected to be used as adsorbent materials for water purification applications.
Keywords
ZnO; chitosan; nanocomposite membranes; antimicrobial; water purification
ALI SABERI VARZANEH, MAHMOOD NADERI
Abstract
Curing and compaction are two major factors in the interface bond strength of concrete and repair mortars. Ignoring these two factors would create fine holes in the concrete-mortar interface and reduce the adhesion. Hence, the present study has aimed to evaluate the effects of initial pressure and fiber on adhesion between mortars and concrete substrates using the twist-off and pull-off tests. The effects of fibers on the shrinkage of mortars are also discussed. The influences of pre-pressure and fibers on the adhesion of the two layers were demonstrated using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. The results indicated that initial pressure had positive impacts on the interface shear and tensile bond strength in the twist-off and pull-off tests, and the effect of pre-pressure was greater on mortars with more aggregates. Moreover, fibers reduced the mortar shrinkage and increased the adhesion. Considering the high correlation between the twist-off and pull-off results, affordable and available twist-off apparatus can be employed instead of expensive pull-off apparatus to measure the concrete-mortar adhesion.
Keywords
Twist-off, Pull-off, Pre-pressure, Bond, Fiber
ALINA MELINESCU, ENIKÖ VOLCEANOV, MIHAI EFTIMIE, DAN BATALU, ADRIAN VOLCEANOV, LAVINIA GABRIELA POPESCU
Abstract
Our work was focused on enhancing the deposition rate, homogeneity, and hardenability on low carbon steel surfaces of Ni-P-TiO2 nanocomposite comparatively with Ni-P coating. Two bath compositions were developed for the electroless deposition, namely Bath (A), composed of nickel sulphate and sodium hypophosphite aqueous solutions and various admixtures to stabilize and accelerate the deposition rate during plating, and Bath (T): Bath (A) to which nanosized TiO2 particles were added in amount of 10 g/l. The deposition rates, co-deposition of particles, and roughness was influenced by the nano powder concentration, temperature, agitation rate, pH, and deposition duration in the bath. The adhesion and uniformity of the composite layers analyzed metallographically and by SEM are appropriate, so the interface of the composite layer with the support steel is perfectly continuous, without discontinuities and the layer is uniform. After deposition the coating was amorphous. Due to the heat treatment, the hardness of the electroless Ni-P- nanocomposite coating is significantly increased. The performance of the Ni–P-TiO2 nanocomposite coatings is analyzed for their surface morphology, phase composition, wear and hardness to assess wear characteristics, and compared with Ni–P alloy coatings. The change in hardness with heat treatment exhibits a similar trend for these coatings, which suggests that the hardening mechanism upon annealing is the same for both electroless Ni–P and Ni–P-TiO2 nanocomposite coatings.
Keywords
Electroless plating, Coatings, Ni-P-TiO2 nano-composite layer, steel substrate
LÜTFIYE DAHIL, KHALED NIMER MOHAMMED AL-NIMER
Abstract
In the present study, crash simulations for thin-walled circular and square cross-section samples made of intra-layer glass-carbon/epoxy hybrid composite, and aluminum have been conducted; and energy absorption capacity and deformation modes are obtained. Results related to some post-collision parameters such as variation of displacement and force are presented for each combination of cross-sectional geometry and material, as well. Numerical method is validated by a previous experimental drop-weight study. Numerical calculations have shown that the hybrid composite sample of square cross-section exhibits the highest load resistance and maximum crash energy absorption, while aluminum samples have a low load resistance and energy absorption capacity the circular Al samples have smaller displacement than that of the square samples.
Keywords
Intra-layer hybrid composites, numerical modeling, drop weight impact test, folding
I. REGINA MARY , T.BHAGAVATHI PUSHPA
Abstract
This paper shows the study of a statistical approach for finding the optimum values of the dependent and independent factors in Geopolymer concrete (GPC) composites using 75:25 of fly ash and Ground Granulated Blast Furnace Slag (GGBS). The input parameters considered in this study were alkali/binder, binder content and water/solids ratio. These factors affect the fresh and hardened properties of Geopolymer concrete such as slump value, compressive strength and split tensile strength for 28 days ambient curing. Response Surface Methodology (RSM) technique was used to optimize the trial mixes using Box-Behnken Design (BBD) by considering three factors. Results show that the optimum compressive strength of 57.05 MPa, optimum tensile strength of 4.52 MPa and optimum slump value of 135.034 mm was achieved by using optimum alkali/binder ratio, binder content and water/solids ratio of 0.386,420 kg/m3 and 0.17 respectively. The desirability achieved for the optimum value is 0.9212 and the mean error was less than 5%. ANOVA results of the regression studies showed that each factor contribute significantly to the strength development of GPC.
Keywords
Response Surface Methodology, ANOVA, regression, Box-Behnken, Geopolymer concrete, optimum value
LÜTFIYE DAHIL, KENAN KAYA, ÖMER FARUK ERKENDIRCI, CIHAN SEZER
Abstract
The present study experimentally investigates tensile strength and impact toughness of plain composites made of carbon, glass, Kevlar, and steel wire mesh fabric; and hybrid composites of carbon-Kevlar reinforcement with polyethylene matrix. Composites are prepared by employing a hot press technique, where reinforcement fabrics, as well as polyethylene film are stacked in varying number of layers. Samples were cut from the composite plates for uniaxial tensile loading and low-velocity Charpy impact tests, as well as for resin burn-off process. It is shown that number of layers affects tensile and impact characteristics, as in general, tensile strength of composites increases with number of layers. Also, impact energy absorbed by the specimens is also proportional to number of layers.
Keywords
CUVINTE CHEIE (ENGLEZĂ)
MD INSIAT ISLAM RABBY , SITI UJILA MASURI, N.M.S. HASSAN, SK MAHAFUJUR RAHMAN, TAZEEN AFRIN MUMU, MAHFUZ ALAM
Abstract
A triangular corrugated pipe was studied numerically along with Al2O3-water, CuO-water, and SiC-water nanofluids, to identify the thermal capacity for laminar flow. Ansys fluent software and steady-state control volume method were applied for simulation purposes. Hence, different volume fractions (1% - 5%) of CuO, Al2O3, and SiC nanoparticles were considered to mix with water to suspend nanofluids. 400 to 1200 Reynolds number with a constant wall heat flux of 1000 W/m2 were considered to calculate the heat transfer rate. In addition, the required pumping power for such enhancements was determined as well. The simulation results highlighted that corrugated pipe provided highest improvement in heat transfer with increase in Reynolds number compared to straight pipe. Consequently, the mixing of nanoparticles in the working fluid showed more enhancement. For the corrugated pipe, at Re =1200, CuO-water, Al2O3-water, and SiC-water nanofluids showed a maximum 11.94%, 8.96%, and 9.15% enhancement respectively of Nusselt number compared to water. Furthermore, CuO-water, Al2O3-water, and SiC-water nanofluids showed enhancement in pumping power compared to water. Additionally, a correlation to predict the Nusselt number for nanofluid and triangular corrugated pipe was also developed by using Buckingham π Theorem, which showed good agreement with numerical results. However, it can be concluded that corrugated pipe, along with nanofluids, provide enhancement in heat transfer for the laminar developed region of a pipe.
Keywords
Nusselt number; nanofluids, volume concentration, Buckingham π Theorem, pumping power