română MÜNIR TASDEMIR, UMUT YERLESEN
Abstract
In the present work, high density polyethylene based composites filled with glass spheres (hollow) and HDPE/glass spheres (filled with alumina silicate) particles were prepared. Fillers contents in the HDPE were 5, 10, 15, and 20 wt%. The mechanical, morphological and tribological properties of the polymer composites were investigated. Substantial improvements in the some mechanical properties were obtained by the addition of filler. For example, the results showed that the elasticity modulus of composites improved with increasing the glass spheres content. The addition of fillers to the HDPE changed significantly the friction coefficient and wear rate of the composites. HDPE filled with a high level content of fillers showed higher wear rate than pure HDPE under dry sliding. The structure and properties of the composites are characterized using a scanning electron microscopy (SEM).
Keywords
Tribological behavior, Wear, Mechanical properties, Friction, Polystyrene, High density polyethylene, Glass sphere
FLORENTINA GRIGORE, MAGDALENA LUNGU, DORINEL TĂLPEANU, ALINA MELINESCU, GEORGETA VELCIU
Abstract
In this paper it is shown the obtaining of dense hydroxyapatite (HA) through the technology of sintering with spark plasma discharge (Spark Plasma Sintering-SPS). From hydroxyapatite powder obtained by the method of precipitation from solutions of salts have been sintered disc through the SPS to 1100°C, and 950°C for 5 minutes. In a conventional method of powder uniaxially pressing disks were obtained that were sintered at 950°C and 1100°C with landing 2 hours at final temperature. The samples obtained have been characterized by analysis of X-ray diffraction for the study of the composition and analysis of phases electronic microscopy (SEM) for revealing the microstructure. Samples of HA obtained by sintering the plasma discharge (SPS) ahead of those obtained by conventional process showed a dense structure with low porosity and physical-mechanical properties, improved hardness of at least 2.49 GPa and Young’s modulus of at least 65 GPa.
Keywords
biomaterials, dense hydroxyapatite, SPS, hardness
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Year
2015
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Issue
45 (2)
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Pages
155-159
ALINA MELINESCU, MIHAI EFTIMIE
Abstract
In the present paper it was studied the synthesis of tialite-based ceramic materials with partially stabilized zirconium dioxide.
For the synthesis were used: kaolin, TiO2, ZrO2 and Al2O3 as raw materials. On the thermal treated samples were determined the real mineralogical composition by using x-ray diffraction (Shimadzu 6000), the firing contraction, the water absorption and the apparent density. The microstructure of ceramics was determined by scanning electron microscopy (SEM / Hitachi 2600N). The dilatometric analysis (Netzsch DIL 402 PC) was carried on the optimal samples, the coefficient of thermal expansion values being in agreement with the literature data.
Keywords
tialite, low thermal expansion, SEM
DANIELA MELIŢĂ, ANCA COJOCARU, ROXANA TRUŞCĂ, ŞTEFANIA STOLERIU
Abstract
Present paper proposes a new obtaining method for partially oxidized zirconium used to hard tissue implants. This proposed method allows partial oxidation by anodization at different voltages. To characterize the obtained surfaces was used electrochemical impedance spectroscopy (EIS) in phosphate buffer (PBS). By SEM analysis were highlighted the differences between the original alloy microstructure and oxidized surfaces. It was pointed out the presence of a continuous and consistent oxide layer formed by anodising at a voltage of 10 V.
In terms of hardness, the oxidized surfaces presents a decrease of average value for hardness. By FT-IR spectrometry coupled with optical microscopy (OM) analysis has been proved the presence and homogenous distribution of the specific absorption band of monoclinic zirconium oxide, which confirm the presence of a large amount of oxide on the alloy surface oxidized at a voltage anodising 10 V.
The biocompatibility of obtained surfaces was done by specific tests: SBF immersion and cell viability. Demonstration of cells viability and morphology of MG-63 cell line was carried out by lactate dehydrogenase method (LDH).
Keywords
partially oxidized zirconium, anodization, biocompatibility
ALIONA ILJINA , KESTUTIS BALTAKYS, ANATOLIJUS EISINAS
Abstract
The influence of hydrothermal synthesis duration at 200°C temperature on the crystallinity and stability of gyrolite was determined. Gyrolite was synthesized for 120, 168, 336, and 504 h at 200°C from a stoichiometric composition (molar ratio of CaO/SiO2 = 0.66) of the initial CaO and SiO2nH2O mixture. It was determined that after 120 – 168 h of hydrothermal synthesis, gyrolite formed as the final product, because the increment of the intensities (from 112.55 to 130.57 a. u.) and crystallite size (from 46.2 nm to 55.3 nm) of the main diffraction peak (d ~ 2.273 nm) were observed. Meanwhile, after 336 – 504 h of treatment, gyrolite became metastable because traces of a new compound of calcium silicate hydrate – truscottite were formed. The calculated thermodynamic parameters of hypothetical recrystallization reactions of gyrolite confirmed the obtained experimental results: the formation of truscottite is more possible because the obtained Gibbs free energy value of this compound is the lowest one (ΔG = -39.8 kJ). Also, it was determined that the duration of hydrothermal synthesis has influence on the gyrolite specific surface area, dominant pore size and their differential distribution by the radius. It should be noted that synthetic gyrolite can be used as adsorbent for Zn2+ ions removal, because its adsorption capacity (27.91 mg Zn2+/g) is higher than natural clinoptilolite (25.00 mg Zn2+/g).
Keywords
gyrolite, truscottite, calcium-silicate-hydrate, hydrothermal synthesis, specific surface area
ALIN GIONEA, ECATERINA ANDRONESCU, VASILE-ADRIAN SURDU, ROXANA TRUŞCĂ, ANDREIA ILIE, ŞTEFANIA STOLERIU
Abstract
The aim of this study is to obtain yttria-stabilized zirconia ceramics with possible applications in dentistry. Firstly, it was obtained zirconia powders doped with different amounts of yttrium oxide (2 mol%, 2.5 mol% and 3 mol%), using the sol-gel method. After synthesis, the powders were dried at 100°C and then heat treated to 500°C for 3 hours. In order to obtain dense ceramics, powders were uniaxial pressed and then the compact green bodies were isostatically hotpressed for 1h and 2h, at temperatures between 1200°C-1300°C, under 150MPa, in argon atmosphere. After the sintering process, the phase composition and microstructure were determined through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Were also studied ceramic properties like apparent density and compressive strength.
Keywords
zirconia, hot isostatic pressing, ceramic, compressive strength
DANIELA L. BURUIANA, GEANINA L. TIRON, ŞTEFAN PINTILIE, CRISTIAN SILVIU SIMIONESCU, ŞTEFAN BALTĂ
Abstract
The influence of the TiO2 and ZnO nanoparticles on the permeation properties of PSf membranes was studied at 32 wt.% PSf and 0.125 wt.% nanoparticles. The membranes were prepared by phase inversion method using 1-methyl-2-pyrrolidone (NMP) and deionized water as coagulant. The influence of TiO2 and ZnO nanoparticles on the permeation properties was determined using dead-end filtration equipment at a constant pressure of 10 bars. Membranes hydrophilicity was investigated using contact angle method and the morphology were studied by SEM analysis. The addition of nanoparticles increase the permeability and the hydrophilicity of the PSf membranes, the optimum results for permeation properties were obtained using ZnO nanoparticles.
Keywords
TiO2, ZnO, nanoparticles, PSf, membranes
V. KARAYANNIS , X. SPILIOTIS, A. DOMOPOULOU, K. NTAMPEGLIOTIS, G. PAPAPOLYMEROU
Abstract
The utilization of huge amounts of coal/lignite fly ash as efficient secondary resources for substituting standard clays in the manufacturing of value-added construction ceramic products is of increasing importance. Fly ash, composed of silica, alumina and other useful oxides, represents an attractive starting material for ceramics, and also the hollow spheres it contains can promote pore-forming for improving thermal insulation and facilitating thorough firing to attain energy savings. Use of ash will contribute to production cost alleviations and environmental protection with natural resources conservation, turning waste from one industry into useful feedstock for another one, which is strongly endorsed by current environmental policies. In the present work, the valorization of lignite high-Ca fly ash in the optimized synthesis of building bricks is investigated. Brick specimens were formed from various clay/ash mixtures by extrusion and firing (850, 950, 1050 and 1150oC). The ceramic microstructures obtained were examined by XRD and SEM-EDAX, and also shrinkage, density, water absorption capacity, open porosity, thermal conductivity and strength before and after frost resistance testing were determined. According to the results, rich-in-Ca fly ash can efficiently be used as admixture into construction ceramics, as the mechanical performance does not significantly deteriorates by the embodiment of low ash percentages in the bulk of ceramics, whereas the thermal conductivity decreases indicating a potential significant gain in thermal insulation capability. Besides, the thermal conductivity also decreases with decreasing the sintering temperature from 1050oC down to 850oC, while the other properties remain practically unaffected, and therefore the optimum firing conditions could be lowered in a full scale operation of potential commercial interest to achieve energy savings.
Keywords
High-Ca fly ash, admixture, construction ceramics, microstructure, thermal conductivity, physico-mechanical properties
MIHAI EFTIMIE, ALINA MELINESCU
Abstract
The recovery of glass waste resulted from CRT (cathode ray tubes) in glass ceramic materials can have possible uses in composite materials. The recipes were calculated using as much waste as possible, using 2% and 5% TiO2 as nucleating agent. The ratio of CRT glass used for the neck:funnel:panel components were 5:30:65%, identical to the ones in CRT. We determined the following physical and mechanical properties: density, thermal expansion, hydrolytic stability. In order to characterize in terms of composition and microstructure, the analyses were carried out using X-ray diffraction and scanning electron microscopy measurements, showing the influence of the nucleating agent and thermal treatment temperature on the properties of the glass ceramic.
Keywords
cathode ray tubes, glass-ceramics, glass waste