română RADU MIREA
Abstract
Current paper is aiming to show the obtained results in obtaining and characterization of graphite-based and metal composite materials suitable to be used in high voltage application of automotive field. Thus, 4 types of materials have been processed and tested in order to assess their suitability to be used as current collector material for trolleybus. The novelty of this work is the new innovative technological process for obtaining the carbon/metal composite material used in the manufacture of sliding contacts for electrical current collector heads, as well as the characteristics obtained for this material. All 4 obtained materials have been characterized from structural (by optical microscopy), mechanical (density, electrical resistivity, hardness) and functional point of view (wear after 1000 working hours, electric discharge and electric load) and it was determined that the material which uses chemically copper covered graphite is the most suitable of them and has been chosen to be further developed by the end beneficiary.
Keywords
graphite, carbon composite, high voltage, carbon/metal
I. DIAZ-PEÑA, J.R. GONZÁLEZ-LÓPEZ, M.Z. FIGUEROA-TORRES, F.R. RUVALABA-AYALA, J.M. VILLARREAL-ORTEGA AND A.A. ZALDÍVAR-CADENA
Abstract
In the production of Mg-Ni alloys in an inert atmosphere, LiH additions have been used to improve hydrogenation-dehydrogenation kinetics and their effect on hydrogen storage efficiency. However, it is important to understand the effects of producing these types of alloys in uncontrolled atmospheres exposed to air. The effect of LiH additions were studied in Mg–5Ni-alloy systems prepared by mechanical alloying exposed to air. The dispersion analysis of 5 wt.% of Ni in the magnesium matrix was performed using Image J software before the evaluation of LiH additions. Alloys systems were hydrogenated in a Parr reactor at 200 ºC, 250 ºC and 300 ºC and a constant hydrogen pressure of 2 MPa. SEM, XRD, XPS and TGA characterization techniques were used to study microstructure, identification of phases in the steps of hydrogenation-dehydrogenation and formation of oxidation species. The efficiency of hydrogen storage was measured to quantify mass loss related to hydrogen lost. Results showed than mass lost related to hydrogen in this system is between 3.17 and 3.66 wt. %. The analysis of characterization showed not all hydrogen was released in a Mg-5Ni-4.8LiH alloy dehydrogenated at 300 °C very probably due to the formation of oxidation species of magnesium and lithium and its effect as a barrier for hydrogen diffusion and formation of MgH2. Magnesium and lithium oxidation species could be formed by factors as handling of samples without an inert atmosphere, additions of LiH and hydrogenation and dehydrogenation temperatures.
Keywords
Hydrogen storage, Magnesium, Lithium hydride, Oxidation, Characterization
LAKSHMI R, KATHIRVEL P, PRASANNAN D, SAKTHIVEL E
Abstract
This study presents the effect of Nano Silica and Metakaolin as additive materials in developing High Performance Concrete substituted with Super Absorbent Polymer (SAP) as an internal curing agent. Mechanical properties were evaluated by conducting compressive, tensile, and flexural strength tests and a Modulus of Elasticity test. Microstructural (Sorptivity and Scanning Electron Microscopy) tests were carried out to investigate the influence of additive materials on HPC mixes to investigate the hydration products. The results revealed that Nano Silica and Metakaolin have a high pozzolanic character, which increases the packing density of concrete and facilitates impermeability. It is inferred that using 10% of Metakaolin and 3% of Nano silica in weight replacement of cement could accelerate the strength improvement at an early stage of hydration and increase the concrete s resistance to meet the demands of corrosion resistance and water permeability.
Keywords
Nano-silica, High performance concrete, Super Absorbent Polymer, Internal curing, Strength Characteristics, Durability.
MARIANA-GRAȚIELA VLADU, MIHAELA CARMEN EREMIA, ILEANA PARASCHIV, AMALIA ȘTEFANIU, ANCA DANIELA RAICIU
Abstract
Some microorganisms have the natural ability to produce polyhydroxyalkanoates (PHAs) and to store them intracellularly in the form of granules, under certain conditions, as a result of fermentative bioprocesses. Among the best-known PHA producers are bacteria of the genus Pseudomonas. In the present research were used three Pseudomonas sp. strains isolated from nature, from various types of organic materials. PHAs biosynthesis was performed for 48 hours, at 30 ±1.5oC and 220 rpm in a liquid medium containing sodium octanoate as a carbon source. During fermentations, process’ parameters were monitored and optimized. The best results in terms of PHAs production were recorded by the strain P. putida ICCF 391. The best carbon source conversion was accomplished by the strain P. putida B1.
Keywords
Polyhydroxyalkanoates, Pseudomonas sp., PHO biosynthesis, sodium octanoate, natural polyesters.
REFFAS SID AHMED
Abstract
Polymer tubes are widely used in various industries due to their excellent mechanical and thermal properties, including stiffness, wear resistance, and dimensional stability. To ensure their reliability in critical applications, particularly under repeated mechanical stress or in demanding environments, it is essential to understand their mechanical behavior and long-term durability. An experimental study based on thermal and mechanical tests highlights the importance of durability in characterizing the microstructure of polyacetal.
Keywords
Polymer, Load, Three-point bending, Damage,Thermal analysis, Durability
HÜLYA TEMİZER, ÖZLEM ÇAVDAR
Abstract
In this study, fly ash (FA) from Sivas/Kangal thermal power plant and blast furnace slag (BFS) from Bolu cement industry were used as the main binder materials. Based on both the literature and preliminary tests, samples were prepared with 85% blast furnace slag and 15% fly ash (85BFS15FA) as the main binder. In addition, the effect of geopolymer main binders and different additives such as mine waste, marble powder, and titanium dioxide were evaluated under various working conditions. The aim was to observe the effect of three different levels and 6 different parameters on the geopolymer samples using the Taguchi optimization method. Accordingly, the L27 orthogonal matrix was created. Three different molar ratios (8M, 10M, 12M) of sodium hydroxide (NaOH) solution and sodium silicate (Na2SiO3) solution were used as alkaline activators. Physical and some mechanical tests such as flexural strength, compressive strength, water absorption, and void ratio were performed on the 7, 28, 56, and 90-day samples, and Taguchi and ANOVA statistical analyses were performed on the 90-day samples. The highest compressive strength observed among 108 samples reached 65.75 MPa in the S20 samples (90-day). Taguchi and ANOVA statistical analyses identified curing temperature as the most significant parameter influencing the geopolymer samples. Additionally, the Signal to Noise ratio data indicated that the optimal curing temperature, determined to be the most effective based on the Larger is better criterion, was found to be 75 ̊C.
Keywords
Blast furnace slag, Fly ash, Geopolymer, Waste binders
ANANTHI A
Abstract
The longevity of the buildings is determined by the durability of the concrete, which is its most important attribute. Weld slag was used as a fine aggregate in high performance fibre reinforced concrete (HPFRC) combinations, and their durability was evaluated. In order to generate sixteen series of HPFRC mixes (70 MPa), weld slag (WS) and various fibre fractions were utilized. There are various amounts of fibre (0%, 0.1%, 0.3%, and 0.6%) added to the weight of cement. Different amounts of weld slag (0%, 10%, 20%, and 30%) were used in place of the fine aggregate. The tests for corrosion, sorptivity, permeability, salt and sulphate attack, and water absorption are used to evaluate the HPFRC test specimens durability. The findings of the durability test show that the combination of employing up to 10% weld slag in place of fine aggregate and adding 0.3% fibre volume proportion is more durable.
Keywords
High Performance Concrete, Durability, Permeability, Sulphate attack, Corrosion
ÖZLEM ÖZKAN ÖNÜR, ÖZGÜR YERLİ
Abstract
The construction technology, design, and materials of historical structures and their surroundings are among the most important documents of history. The use of original materials in maintenance and repair work is crucial for preserving these structures with their original qualities. In this study, the aim was to produce cement-free lime mortars for the sustainability of natural stones used in the floor covering of Topkapı Palace, one of the most important structures of cultural heritage. In mortar production, 30% air lime was used as a binder, along with varying ratios of brick fragments and dust, yellow sand, clay lime and quartz aggregate, fly ash, tooth snag water, glass fiber, and water. Physical and mechanical analyses of the produced mortars were conducted, as well as FESEM-EDS and XRD analyses for the internal structure of the materials. According to the analysis results, it was determined that the tooth snag water used instead of water had no mechanical effect on the mortars, while fly ash and glass fiber had positive effects on their physical and mechanical properties. These mortars, which have a calcite mineral structure, contain high amounts of Ca, C, O, Si, Mg, Al, and small amounts of Fe and S elements. It can be recommended to use glass fiber and fly ash added mortars, which have high porosity, low unit volume weight, and sufficient compressive strength, in the hard ground pedestrian paths of the structure.
Keywords
Composite Material, Flooring Mortar, Historical Building Surroundings, Lime, Pozzolan.