română AYLIN AKYILDIZ
Abstract
There has been a rapid increase in interest in nanotechnology and nanoparticles. Nanotechnology has been increasingly brought into the study of cement-based materials in the recent years. Adding nanosized particles in small amounts as materials can affect their properties significantly. In this study, the effect of nano magnetite Fe3O4/humic acid mixture (used as addition of 0.1, 0.5, 1, 1.5, 2, 3, 4 and 5% in mass of the cement) on the microstructural development and mechanical properties of cement composites has been investigated. Hence, samples size of 40•40•160 mm were produced using obtained cement based composites. After 28th days, flexural and compressive strength and water absorption experiments were implemented for cement based mortar samples. The microstructural analysis of mixtures nanoparticles were performed by scanning electron microscopy. Results were compared with the reference composite. As a result, 1% substitution nanoparticles with cement supplied best performance in terms of strength, water absorption.
Keywords
Compressive strength; Fe3O4/humic acid nanoparticles; Mortar; Nanoparticles
COSMIN MIHAI MIRIŢOIU, DUMITRU BOLCU, MARIUS MARINEL STĂNESCU, ALIN DINIŢĂ, ALEXANDRU RĂDOI
Abstract
In this paper the mechanical characteristics of a new gree resin, with and without natural reinforcement are presented. In the fist part of the investigation, from the tensile test, some mechanical characteristics are determined, such as: breaking strength, elongation at break, Poisson ratio, static Young modulus and tensile stiffness. A representative image with the samples breaking section using the scanning electron microscopy analysis has been presented. Then, from the free vibrations recording by clamping the bar at one end and leaving it free at the other, the damping factor per unit mass, per unit length, the dynamic flexural stiffness, dynamic Young modulus and the loss factor are determined. Using the thermogravimetric analysis (TGA), the thermal stability of the studied resin is investigated. In the las part of the study, some green composites by using the poposed resin reinforced with wheat straw fibers are manufactured. It has been found out that the proposed eco-resin reinforced with wheat straw has incresed mechanical properties compared to other eco-resins from the engineering literature such as: soy based resins (reinforced with cotton, jute, flax, kenaf, hennequen or hemp), polylactic acid resin reinforced with wheat straw and so on.
Keywords
green composite, green resin, static behaviour, dynamic behaviour, wheat straw
YASSINE BELAICHE, ABDELHAMID KHELEF, SALAH EDDINE LAOUINI, ABDERRHMANE BOUAFIA, MOHAMMED LAID TEDJANI, AHMED BARHOUM
Abstract
Artemisia herba-alba is a medicinal plant, and its essential oil is used as an antiseptic and antispasmodic. In this study, green synthesis of silver/silver oxide (Ag/Ag2O) nanoparticles was successfully synthesized from Artemisia Herba-Alba aqueous leaves extract. The effect of temperature, reaction time, the concentration of AgNO3, the quantity of plant extract, and pH on the synthesis process of Ag/Ag2O was optimized. More interesting, the results showed that only 5 min were required for reducing 1 mM AgNO3 into Ag/Ag2O NPs at room temperature. The crystalline nature of Ag/Ag2O NPs with an average crystallize size of 10.7-36.8 nm. The green synthesizing Ag/Ag2O NPs having in general a spherical morphology with particle/aggregate size less than 100 nm. The maximum UV-Vis absorption peak of Ag/Ag2O NPs was observed at the range of 418- 435 nm giving optical band gaps of 2.05-2.30 eV. The TGA/DTA analysis shows significant organic contents (18 wt%) were physically and chemically adsorbed on the dry weight Ag/Ag2O NPs. Artemisia herba-alba is a source of phytochemicals for effective and prompt fabrication of Ag/Ag2O NPs with relevant insecticidal and anti-bactericidal activity against species of high public health importance.
Keywords
silver /silver oxide nanoparticles; Artemisia Herba-Alba; Silver nitrate AgNO3; Green Synthesis, XRD
ALINA MELINESCU, ENIKŐ VOLCEANOV , MIHAI EFTIMIE, ADRIAN VOLCEANOV, LAVINIA POPESCU, ROXANA TRUȘCĂ
Abstract
Electroless nickel is applied to many types of substrates to take advantage of the coating`s properties. The final electroless nickel-based deposit quality is only as good as the quality of the base substrate metal since the coating`s ability to level or hide imperfections in the base material is poor. In fact, any defect in the substrate will be more visible after the part is plated with electroless nickel. A variety of contaminants include machining oils, drawing lubricants, buffing compounds, sulfurized oils, chlorinated oils, waxes, etc. Experimental work was carried out in order to establish the effectiveness of the method for degreasing thin low carbon steel strips before chemical coating. One alkaline (Solution A) and two acidic based on deoxidants (Solution B and Solution C) were tested at a temperature of 750C.
Before the chemical deposition of Ni-P și Ni-P-Al2O3 coatings, water break test was performed on steel substrate to evaluate the presence of hydrophobic contaminants, which can be detrimental to adhesion of coatings. Nickel sulphate hexahydrate was used as the source of nickel and sodium hypophosphite was used as the reducing agent, which also serves as the source of phosphorus in the coating. Sodium acetate, ammonium sulphate, sodium citrate, sodium dodecyl sulphate and lead acetate were used as additives in the plating bath, to accelerate the rate of deposition of the coating or as stabilizers to prevent the decomposition of the plating bath. During plating (45 minutes), the temperature of the bath was maintained at 80 oC using a constant temperature bath and the pH of the bath was maintained at 5.2.
The waterbreak test has been used to evaluate how clean a surface may be. The test is based on the ability of a properly cleaned surface to retain an unbroken film or sheet of water. Normally, dirty surfaces show a water break.
The samples of thin steel strip before and after deposition electroless Ni-P and Ni-P-nano - Al2O3 layers were characterized regarding the chemical composition, layer thickness, macroscopic appearance, uniformity and adhesion.
The chemical composition of steel substrate and of the layers was determined by X-ray Fluorescence. In order to investigate the morphology and microcomposition of metallic substrate and of deposition layers and thickness coating for the samples were studied by using Scanning Electron Microscope coupled with Energy-Dispersive X-ray Spectroscopy
Keywords
electroless plating, steel surface pretreatment, Ni-P and Ni-P-Al2O3 composite coating
ENIKŐ VOLCEANOV, MIHAI EFTIMIE , ALINA MELINESCU, ADRIAN VOLCEANOV, ADRIAN SURDU
Abstract
This work emphasizes on the development of electroless nickel composite coatings with the incorporation of oxide nanosized hard particles embedded in Ni-P matrix to improve their performance. The preparation of electroless nickel composite coating bath, methods to introduce hard particles in the bath, factors that affect the particle incorporation in the coating and its effect on coating structure is discussed in detail. The nickel-phosphorus coatings alloy layer was deposited by an autocatalytic process, without external power input is from this point of view an major advantage over electrolytic nickel plating technology. However, the autocatalytic Ni-P coatings deposition has a drawback, namely the low speed of layer deposition. Our investigations were focused on enhancing the deposition speed and homogeneity of the Ni – P –XO coatings, where XO is a mixture of Al2O3 + ZrO2, nanoparticles (ratio of 95: 5 by weight) deposited on low carbon content steel strip substrates
The chemical cell (bath) was formulated for 10/L oxides admixture and then connected by immersing the pre-treated steel substrate in the electroless bath solution for 15, 30, 45 and 60 minutes, respectively. The pH of the solution was kept between 4.58 and 6.23. The temperature was controlled in the bath in 60 oC -98oC range. Different stirring intensities in 50 - 400 rpm range were tested. There was almost no difference between Ni-P coating adherence versus Ni-P-(Al2O3+ZrO2) coating obtained by electroless plating. Moreover, electroless plating have nearly constant coating thickness across all surfaces, including edges and complex interior geometry. Nodularity of the Ni-P globules is reduced due to incorporation of second phase oxide nanoparticles.
Keywords
Electroless Composite Coatings, Nickel, Nano-sized oxide powders, Process Parameters