română ALINA BĂDĂNOIU, ELENA IORDACHE, RUXANDRA IONESCU, GEORGETA VOICU, ECATERINA MATEI
Abstract
In this study was assessed the possibility of geopolymers synthesis by alkaline activation of cathode ray tube (CRT) glass waste with/without fly ash addition. The nature of solid component and alkali activator (sodium or potassium hydroxide solution) combined with the curing conditions (initial curing at 60oC for different times – 1 up to 7 days) exert an important influence on the fresh mortars workability, microstructure and consequently on mechanical properties. The higher values of the compressive strength were obtained for geopolymers based on CRT glass waste activated with KOH solution cured the first 4 days at 60oC. The substitution of CRT glass waste with fly ash decreases the workability of fresh mortars and consequently the compressive strength values. The durability of this type of geopolymer is affected by water conservation but the substitution of CRT glass waste with 25% fly ash improves to a certain extent this property.
Keywords
Geopolymer, Cathode ray tube glass waste, Fly ash, Properties, Water stability
P.VALDEZ, G. FAJARDO, C.A. JUAREZ, A.DURAN-HERRERA, J.A.DEL REAL
Abstract
Mixtures were designed to produce hollow masonry units (blocks) conform to Mexican specification; these blocks were subjected to a 60°C temperature a 90% relative humidity steam curing in an atmosphere of 20% CO2 concentration. Thermo-gravimetric methods were used to evaluate the water vapor effect and carbonation in replicate pastes of the concrete blocks to determine portlandite, carbonates and CO2 concentration in the block. Results illustrate that the application of CO2 curing in activated fly ash-Portland cement masonry units can lead to 30% savings in cement consumption, to an average CO2 fixation of 7% without modification of the compressive strength.
Keywords
D. Concrete, B. Thermal analysis, D. Pozzolans, D. Lime, D. Portland cements
ADRIANA MOANŢĂ, VIOREL FUGARU, ROXANA TRUŞCĂ, MARIA GHEORGHE, MARIANA COARNĂ, IONELA PETRE
Abstract
The paper presents the results of laboratory researches regarding the possibility of using, as addition in the raw mix for cement of barite – alternative raw material with high specific weight. The raw mixes with barite constitute the base for prepare of the clinkers designated to obtaining the cements with capacity of attenuation of gamma radiations. Technological behavior of the raw mixes with addition of barite was investigated in comparison with those of a raw mix obtained from current raw materials, considered as reference sample.
It was investigated the influence of barite on clinkers characteristics, from chemical, mineralogical and structural point of view, using X-ray diffraction, scanning electron microscopy (SEM analyses) .
From obtained clinkers, cements type CEM I in accordance with SR EN 197-1were performed. These cements were characterized both regarding to usual physical-mechanical properties and of the capacity for attenuation of gamma radiations. In order to evaluate the capacity of gamma radiations attenuation it was determined the dose rate equivalent for different radioactive source (Ir-192, Cs-137, Co-60). The presence of barite, in raw mixes composition for the clinkers, determined the increase of the value for linear coefficient of attenuation and an increased capacity of gamma radiations attenuation, respectively.
Keywords
Clinker, Barite, Cement, Linear coefficient of attenuation
LIU HUI, WANG BAOMIN, HAN YU, QU JUN, GUO ZHIQIANG
Abstract
The influence of multi-walled carbon nanotubes (MWCNTs) mixed with silica fume (SF) on the mechanical property of cement-based composites was investigated. Results indicate that SF particles have a favorable dispersion effect on MWCNTs and MWCNTs can be dispersed uniformly in cement matrix when mixed with SF particles. MWCNTs mixed with SF can decrease the sample porosity and the amount of harmful pores and delay the formation process of micro cracks in the cement paste, improving the strength of specimens effectively. The compressive strength of the sample filled with 10% SF reaches maximum when the MWCNT addition is 0.15% and the flexural strength of the sample filled with 0.08% MWCNTs and 10% SF reaches maximum, the increase percent of flexural strength and compressive strength is both above 35%, displaying well reinforcement effect of MWCNTs mixed with SF particles on the mechanical properties of cement-based composites.
Keywords
Multi-walled carbon nanotubes; Silica fume; Cement-based composites; Mechanical properties
MARIA STEFANIDOU, VASILIKI PACHTA
Abstract
Coatings, such as plasters and renders have been continuously used for dwellings’ protection even from the Neolithic period. Diachronically, they present similar technological characteristics forming unwritten normes of manufacture. This paper focuses on the analysis and characterization of coatings from four monuments of Greece, dated through the 4th C BC. The physico-mechanical and chemical properties of samples were determined, leading to the characterization of their consistency and structure. Their stratigraphy showed that they consisted of two to four well compacted layers, the width of which decreased from the inner to the surface layer. The main binding system used was hydrated lime in combination with natural pozzolan, while the aggregates gradation as well the binder/aggregates ratio varied according to the coating’s stratigraphy.
Based on the results, it can be concluded that even from the 4th C BC the functional role of renders and plasters was clear and their technology definite. A carefully selected binding system was used, while additional parameters were taken into account in order to achieve the optimum performance and efficasy of the final material.
Keywords
Historic mortars, Renders, Plasters, Masonry, Stratigraphy, Technology
MIHAI BUDESCU, PETRU MIHAI, NICOLAE ŢĂRANU, IRINA LUNGU, OANA-MIHAELA BANU, IONUŢ-OVIDIU TOMA
Abstract
The paper presents a study on the concrete compression behaviour in the post-peak range, utilising an innovative system, conceived and patented at the Faculty of Civil Engineering and Building Services from Iasi. The designed mechanical system is attached to the universal testing machine and controls the deformation rate after reaching the peak stress. The theoretical bases related to this additional system are presented, along with its design and utilisation to the concrete testing aiming to determine the complete characteristic curve. The paper is finalised with a presentation of an extended experimental study related to the complete characteristic curve, determined by testing a series of concrete cylindrical specimens. A particular value of the stress relevant to the evaluation of the energy dissipation capacity is finally recommended.
Keywords
loading rate, specimen stiffness, displacement control, post-peak range
DAN GEORGESCU, RADU PASCU, RADU GAVRILESCU, TIBERIU PASCU
Abstract
The shrinkage deformations may lead to concrete cracking with adverse effects on structural reliability, durability and aspect of the reinforced concrete elements and structures. For preventing and mitigation of shrinkage effects measures must be taken in structural design in determining the composition and in concreting. The paper presents theoretical, practical and experimental aspects related to shrinkage strains calculation, pointing out the differences between the values computed using the provisions of SR EN 1992-1-1 -„Design of concrete structures” and measured values. Due to these differences we consider that a new approach for computing the shrinkage deformations is needed. This need is emphasized by the large number of cases in our country of cracked structural elements short time after the concrete was cast.
Keywords
Concrete, Shrinkage, Test methods
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
A.CANAKCI, T.VAROL, H. CUVALCI, F. ERDEMIR, S. OZKAYA
Abstract
In this study, novel CuSn10-B4C-graphite hybrid nanocomposite powders were synthesized by the solid-state powder processing technique of mechanical alloying. The effects of the addition of graphite particles, B4C distribution and milling time on the morphology, particle size and microstructure of CuSn10-graphite nanocomposite powders were investigated. It was found that the particle size of the nanocomposite powders was significantly lower than those of the CuSn10 alloy powders. Electron microscopy studies confirmed the formation of equiaxed graphite with a wide size distribution in the range of 100 to 200 nm.
Keywords
Mechanical alloying, Nanocomposite powders, Morphology, Electron microscopy
DOREL RADU, OVIDIU DUMITRESCU
Abstract
The type, proportion and chemical-structural characteristics of compounds that are formed as a result of chemical reactions between oxides are determined by the chemical-structural characteristics of the starting oxides and the processing conditions (genesis route).
In present paper, we investigate the influence of basicity on the values of some thermodynamic functions. The considered thermodynamic functions correspond to the forming reactions of the oxide compounds in the alkali-silicate systems.
It was shown that there was no strong correlation between the considered thermodynamic functions (standard enthalpy of formation, deltaH0298, standard Gibbs free energy of formation, deltaG0298) and the percentage of basicity, pB (%).
However, a strong correlation was determined between the ‘”specific” thermodynamic properties and pB%. The specific thermodynamic properties were calculated by dividing the values of the standard (classic) functions to the number of moles of oxide in the compound which resulted from the reaction.
Keywords
Standard Gibbs free energy, Standard enthalpy, Basicity, Alkali-silicate systems
AURELIA CRISTINA NECHIFOR, ABBAS ABDUL KADHIM KLAIF RIKABI, DANIELA DUMITRA CLEJ, SZIDONIA-KATALIN TANCZOS, CORNELIU TRIŞCĂ-RUSU, CRISTINA ORBECI
Abstract
This study focuses on developing a new method to obtain Fe3O4-TiO2 nanoparticles and on their use through photocatalysis in environmental applications. The procedure for the preparation of Fe3O4-TiO2 nanoparticles occurs according to an in situ TiO2 synthesis and magnetite covered process. After preparation, the Fe3O4-TiO2 nanoparticles were exhaustively characterised by XRD (SAED), EDAX, TEM/HRTEM. The catalytic performances of the Fe3O4-TiO2 nanoparticles in environmental applications, at different concentrations, were evaluated in relation to the degradation of the ampicillin and penicillin G antibiotics, using a photocatalytic reactor with continuous recirculation. The reactor was equipped with an exterior magnetic field necessary to support the Fe3O4-TiO2 nanoparticles in the volume of the solution. Different concentrations of Fe3O4-TiO2 nanoparticles were used. The initial concentrations of the antibiotics were equivalent to 400 mgO2/L. Monitoring the concentration of the organic substrate took place by taking off samples from the reactor, at pre-established times, and analysing them using Chemical Oxygen Demand (COD). The values for the studied process variables were: pH of the solutions at 3 and H2O2 concentration of 1.5 per stoichiometric ratio. The effect of Fe3O4-TiO2 in environmental applications showed good activity in a UV light, able to degrade 97.5% ampicillin and 95.0% penicillin G in 2.0 hours of reaction time.
Keywords
Fe3O4-TiO2, Ampicillin, Penicillin G, Photocatalytic oxidation
N.R. RAKHIMOVA
Abstract
The effects of ground used sand (GUS), ground fly ash (GFA) (class F), and microsilica (MS) on water requirement, setting time, and compressive and bending strength development of alkali-activated slag-blended cements (AASBC) were studied. Siliceous blending materials were found to be able to replace up to 50% of ground granulated blast furnace slag (GGBFS) and contributed to up to 90% improvement of strength of AASBCs, The granulation for GUS, granulation, curing conditions, and basicity of GGBFS for GFA, and curing conditions for MS have effects on the development of the properties of the AASBCs.
Keywords
Blast furnace slag, alkalis, activators, binding composite materials, setting time, mechanical properties
M.P.PEREIRA, J.B. AGUIAR, A. CAMÕES, P.LOURENÇO
Abstract
This study deals with the characterization of masonry mortars produced with different binders and sands. Several properties of the mortars were determined, like consistence, compressive and flexural strengths, shrinkage and fracture energy. By varying the type of binder (Portland cement, hydrated lime and hydraulic lime) and the type of sand (natural or artificial), it was possible to draw some conclusions about the influence of the composition on mortars properties. The results showed that the use of Portland cement makes the achievement of high strength classes easier. This was due to the slower hardening of lime compared with cement. The results of fracture energy tests showed much higher values for artificial sand mortars when compared with natural sand ones. This is due to the higher roughness of artificial sand particles which provided better adhesion between sand and binder.
Keywords
Masonry, composition, D.a. mortar, D.a. Portland cement, D.a. lime, D.d. sandstone
HAKAN BOLAT, OSMAN ŞIMŞEK
Abstract
This study aims to determine the energy absorption of concrete slabs (60×60×10cm) using polyester, polypropylene and steel fiber reinforced (SFRC, PYFRC, PPFRC) according to EN 14488-5. Significant differences in the energy absorption were observed between the concrete slabs strengthened with different fibers. The highest gain in energy absorption was observed in SFRC. Furthermore, concrete slabs strengthened with PPFRC and PYFRC showed 23.4% and 14.8% less energy to SFRC. Although the SFRC showed the highest energy absorption under directly negative conditions, it is important to evaluate the durability issues associated with SFRC, such negative conditions.
Keywords
Fiber reinforced concrete, steel fiber, synthetic fiber, energy absorption, slab test
CARMEN (GHEORGHE) OPROIU, GEORGETA VOICU
Abstract
The use of alternative fuels in the manufacturing of cement can influence the thermo-chemical processes in the kiln as well as the quality of the obtained clinker. Also, the use of alternative fuels has impact both from economic and environmental point of views.
In the present study are assessed the composition and microstructure of clinkers manufactured with conventional fuel i.e. coal-coke mixture, and alternative fuels - solid residual (SRF). The substitution rate of conventional combustible was 30%.
No significant differences were identify, in terms of composition (oxide and mineralogical) and microstructure for clinkers obtained using alternative (SRF) and conventional (coal-coke mixture) fuels.
Keywords
solid residual fuels (SRF), clinker quality,composition and microstructure, Riedveld method, scanning electron microscopy
Effect of alkaline activator on the main properties of geopolymers based on cullet glass and red mud
TAHA H. ABOOD AL-SAADI, ALINA BĂDĂNOIU, ŞTEFANIA STOLERIU, GEORGETA VOICU
Abstract
In this paper are presented results regarding the synthesis and properties of geopolymers based on glass powder, with/without red mud (solid part), activated with the solution resulted in the filtration process of red mud slurry (RF). The compressive strengths achieved by these materials are below 20 MPa, smaller as compared with those assessed on the geopolymers based on the same solid components but activated with NaOH 5M solution (up to 40MPa); these results can be explained by the lower alkalinity of RF. Nevertheless, for the materials activated with RF, the substitution of glass powder with 25% red mud powder (resulted by the drying of solid part separated from red mud slurry - R), determines an increase of compressive strength values - 15-100% with reference to the one assessed on the geopolymer based only on glass powder. This increase can be explained by the ability of red mud powder (R) to continuously release alkaline ions in RF solution.
Keywords
geopolymer, cullet glass, red mud, compressive strength, microstructure, hydrolytic stability
MÜNIR TASDEMIR, SEZGIN ERSOY
Abstract
Fillers, in the form of particulates and fibers, are often added to polymeric materials to improve their stiffness and strength. Polymers and their composites are being increasingly employed in view of their good strengths and low densities. Besides, a wider choice of materials and ease of manufacturing make them ideal for engineering applications. High density polyethylene filled with particulate fillers is of great interest in both research and industry. It is well known that HDPE has good process ability allowing accepting different types of natural and synthetic fillers. As fillers, mica, kaolin, calcium carbonate and talc are the most often used to reduce both the production cost and to improve the properties of the thermoplastics, such as rigidity, strength, hardness, flexural modulus, dimensional stability, crystallinity, electrical and thermal conductivity. In the present work, high density polyethylene based composites filled with glass spheres, talc and calcite particles were prepared. Fillers contents in the HDPE were 5, 10, 15, and 20 wt%. HDPE composites filled with glass spheres, talc and calcium carbonate were prepared using extrusion compounding and injection molding. The effects of filler contents on the mechanical, morphological and thermal properties of the polymer composites were studied. The modulus of elasticity, yield and tensile strength, % elongation, Izod notched impact strength, Shore D hardness, MFI, HDT and Vicat softening point of the composites were determined. The structure and properties of the composites are characterized using a scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS).
Keywords
Mechanical properties, high density polyethylene, talc, glass spheres, calcite, polymer composites
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
-
Issue
45 (2)
-
Pages
155-159
GABRIELA PURCEL, ADRIAN SURDU, ŞTEFANIA STOLERIU
Abstract
Silicon nitride attracts the attention of many researchers for its use in orthopedic and dental applications, but is not yet established as a biomaterial, the research is ongoing. Present paper deals with the obtaining of Si3N4 ceramics unconventional heat treatment (spark plasma sintering.
The sintering process was pursued through the variation of four influencing parameters: sintering temperature, the heating rate, the pressure applied during sintering and soaking time. The obtained ceramics were characterized using X-ray diffraction for the phases determination and scanning electron microscopy for microstructure characterization. Also, were determined ceramic and mechanical properties.
By testing the biocompatibility of these ceramics in contact with the physiological environment by following the evolution of pH and ionic conductivity on immersion of ceramics in SBF is found that pH values and ionic conductivity samples varies widely in the first days but after stabilizes around SBF values.
Regarding the antibacterial effect, the tests indicate a triple value of biofilm inhibition area for the Si3N4 samples, as comparing with pure titanium, measured under the same condition. Also, was evaluated the MG-63 cell proliferation (by lactate dehydrogenase method - LDH) and morphology.
Keywords
Si3N4, spark plasma sintering, biocompatibility
The influence of biomass use on CO2 emissions resulted from burning solid fuels in the energy sector
MONA BARBU, MIHAI BRATU, OVIDIU DUMITRESCU
Abstract
The issue of environmental protection focuses on preventing and reducing pollution phenomena caused by those human activities inducing negative effects such as global warming and the greenhouse effect. The energy sector has the greatest contribution to these phenomena in terms of greenhouse gases emissions.
The paper proposes an application in the energy sector for assessing CO2 emissions resulted from burning classic solid fuels and alternative and biomass fuels at a Combined Heat and Power (CHP) using two methods, either by calculations based upon data obtained from analytical laboratory investigations or by direct measurement at the source.
The investigations were carried out to highlight the influence of the addition of biomass (sawdust) to conventional solid fuel (lignite) for reducing CO2 emissions, recovering unburned carbon content present in the slag, improving the lignite energy properties, in order to use the biomass and slag waste and reduce the CO2 emissions.
Keywords
energy sector, coal, biomass, waste, carbon, CO2 emissions
MIRELA LAZĂR, DANIELA FIAT, GHEORGHE HUBCĂ
Abstract
In the recent years, the film-forming products obtained by adding a nanometric photocatalytic titanium dioxide pigment into their composition have drew the attention of both researchers and manufacturers.
The purpose of this paper is the development of new compositions based on organic binders in aqueous dispersion with different contents of nanometric photocatalytic titanium dioxide pigment and novelty lies in the study of their influence on the film-forming products properties. The study performed on these products revealed self-cleaning effect of the films after exposure to UV radiation and natural aging in urban-industrial environment and the improvement of certain properties, such as: coating power, adherence to support, water and watery-vapours permeability.
Keywords
titanium dioxide, self-cleaning, photocatalysis, film-forming product, aqueous dispersion.
MUSTAFA BASIM MOHAMMED AL TAMEEMI, DRAGOŞ GUDOVAN, RALUCA STAN, DAN MIHĂIESCU, CRISTINA OTT
Abstract
In this work it have been investigated the difference of the encapsulation efficiency and the release behavior of silica nanotubes and MCM-41 by using Ibuprofen as drug model. The highest encapsulation efficiency was in MCM-41, while the highest loaded Ibuprofen amount was in silica nanotubes. According to their larger size folded, silica nanotubes release percentage was around 80% which is higher than MCM-41 which was around 26%. It is worth mentioning that TEOS was used as silica precursor, and CTAB as a surfactant for the synthesis of both the nanostructured materials alike.
Keywords
MCM-41, silica nanotubes, Ibuprofen, Encapsulation efficiency, C-Silica, A-Sol-gel
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Year
2015
-
Issue
45 (2)
-
Pages
188-193
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
CONSTANTIN DORINEL VOINIŢCHI, RADU CONSTANTIN VOINIŢCHI
Abstract
This paper presents experimental work made in order to asses the influence of correction coefficients considered by a Romanian norm proposal for evaluating in situ compressive strength of concrete. It has been evaluated coefficients linked by influence of degraded end layer, the influence of nature of capping layer, cores humidity and presence of the reinforcement bars in the tested cores. Results show the luck of influence or contrary influences to that considered in Romanian norm proposal, generally in accordance with europen and american standards.
Keywords
concrete testing, in situ compressive strength, cores
KESTUTIS BALTAKYS, ANATOLIJUS EISINAS, JOLANTA DONELIENE, DEIMANTE MONSTVILAITE, AGNE BANKAUSKAITE, AURIMAS URBUTIS
Abstract
In this work the influence of Al2O3 on the formation of calcium aluminium silicate hydrates under hydrothermal conditions and the effect of this additive on the early hydration of Ordinary Portland cement (OPC) were investigated. The primary mixtures with molar ratios CaO/(SiO2+Al2O3) of 0.55 and Al2O3/(SiO2+Al2O3) of 0.05, 0.1 and 0.15 were mixed with water to obtain the water/solid ratio of the suspension equal to 10.0. Meanwhile, the hydrothermal synthesis of C-A-S-H has been carried out in air atmosphere at 130 °C temperature for 4–72 hours. It was determined that not only the amount of Al2O3 additive, but also the duration of hydrothermal synthesis strongly affect the formation of mentioned compounds. The largest amount of calcium aluminium silicate hydrates was obtained after 8 h of hydrothermal treatment, in the mixtures with a higher amount of Al2O3 (A/(S+A) = 0.15). Meanwhile, the formation of mentioned compounds is inhibited, when the duration of isothermal curing is extended from 16 to 72 h. It was determined that calcium aluminium silicate hydrates affect the early hydration of OPC. These compounds effectively shorten the induction period and accelerate the dissolution of C3S, C3A and the formation of ettringite.
Keywords
Calcium aluminium silicate hydrates, Hydrothermal synthesis, Portland cement hydration, Additives
SANJEEV KUMAR VERMA, SUDHIR SINGH BBHADAURIA, SALEEM AKHTAR
Abstract
In the last few decades, failure of concrete structures awakened researchers to focus on durability influencing parameters along with compressive strength. Factors like environmental or exposure conditions are found to be governing the service life of reinforced concrete (RC) structures significantly. One of the major processes influencing condition of steel bars is carbonation of concrete surrounding steel bars in RC structures. Hence, considerable researches on the carbonation of concrete in laboratory and field are carried out around the world. Present article reviewed several previous carbonation studies conducted by researchers and by utilizing the results of a field survey determines coefficient of carbonation ‘K’ for concrete structures located in the City of Bhopal, India and for other semitropical regions.
Keywords
concrete, carbonation, model, reinforcement, corrosion
The behaviour of the interface between carbon fibre reinforced polymer composite plates and concrete
NICOLAE ŢĂRANU, RUXANDRA COZMANCIUC, IOANA ENTUC, MIHAI BUDESCU, VLAD MUNTEANU, DORINA ISOPESCU
Abstract
The interface behaviour of fibre reinforced polymer carbon plates bonded to concrete represents a key issue in the efficiency of the strengthening solutions based on externally bonded composite plates.
An extensive research program was developed at the Faculty of Civil Engineering and Building Services from Iasi, to study the interfacial behaviour between carbon fibre reinforced polymeric composite (CFRP) plates and concrete. The study includes nine strengthened concrete elements which were tested under double shear pull testing set up. On the basis of the performed tests the recorded failure mode was the same for all tested specimens namely the interfacial failure. It essentially occurs in concrete close to the FRP plate-concrete interface.
The recorded data have been used to plot the load-slip curves and strains distributions along the composite bonded plates. Together, they served later on to calibrate the finite element method (FEM) based modelling accompanying the laboratory tests.
Keywords
externally bonded strips, carbon FRP plates, interface behaviour, finite element analysis
ANA-MARIA GHIŢĂ, HORIA ASANACHE
Abstract
The mathematical model of the semi-infinite massif was used to characterise building materials in case of thermal conduction in unidirectional non-stationary thermal regime. There were obtained informations about the evolution in time of the temperature inside the construction element. Thermal response was analyzed for the following building materials: cellular concrete block GBN35 masonry with thin joints, cellular concrete block Ytong A+ masonry with thin joints, solid brick masonry, reinforced concrete and cellular polystyrene. The results are useful for assessing the thermal insulation performance of building materials and improving the thermal comfort.
Keywords
thermal diffusivity, non-stationary thermal regime, thermal excitation of impulse-type
CRISTIAN OLIVIU BURADA, COSMIN MIHAI MIRIŢOIU, MARIUS MARINEL STĂNESCU, DUMITRU BOLCU
Abstract
In this paper, we have built some new composite sandwich platbands with polypropylene honeycomb core with the thickness of 10, 15 and 20 mm reinforced with two layers of glass fiber. We have chosen for the platbands the next width values: 45 and 60 mm. Starting from the dynamic response of these sandwich platbands with damping, that are in free vibration, we have established an experimental procedure to determine the damping factor per unit mass and unit length, loss factor, stiffness and the dynamic elasticity modulus.
Keywords
damping factor, loss factor, dynamic elasticity modulus, glass-fiber
NICOLAE DANIEL STOICA, MIRCEA BARNAURE
Abstract
For existing buildings masonry, numerical simulation of the seismic behaviour is difficult, involving complex nonlinear models. Testing large-scale models on shaking tables involves important costs and time. Still, the main purpose of testing or simulations is often to identify structural vulnerabilities probable failure modes so that the correct strengthening solution can be chosen. A simplified method for the assessment of the potential structural degradation pattern for simple masonry buildings is proposed. This method is based on energy dissipation and can be easily implemented by practicing engineers. Four case studies are performed using linear numerical models. The results are compared with observations on buildings tested on shaking tables.
Keywords
d. Masonry, d. Construction, c. Mechanical properties, b. Fracture, b. Modelling
RĂZVAN STATE, FLORICA PAPA, CORNEL MUNTEANU, IOAN BALINT, ALBERTO ION, ADRIAN VOLCEANOV
Abstract
Gold nanoparticles between 2 and 5 nanometers were synthesized using an easy obtaining method with good reproducibility using PVP as protective polymer and NaBH4 as reducing agent. The Au nanoparticles were characterized by TEM, XPS, XRD and UV-Vis. They are spherical with a very good dispersion making them suitable for a vast number of applications including catalytic and photocatalytic tests for nitrate and nitrite removal from water.
Keywords
gold nanoparticles, synthesis, characterization
SEZGIN ERSOY
Abstract
In the present work, the friction and wear property of high density polyethylene / Styrene - Butadiene Rubber polymer blends was studied. Styrene - Butadiene Rubber addition in the HDPE was 5, 10, 15, and 20 wt%. The result showed that the addition of fillers to the composite changed the friction coefficient and wear rate. All specimen wear loss increases with increasing load and sliding distance; meanwhile the friction (static and dynamic) coefficient increases. Wear rate of all HDPE composites are larger than that of pure HDPE. The results obtained in this study indicate that HDPE / Styrene - Butadiene Rubber polymer applied to the abrasion test indicate that road and load values to increase the effect of wear, but this effect by increasing the rate of Styrene - Butadiene Rubber additives lead to a reduction in wear is observed that value. In the friction test, the coefficients of friction are the rate of increase Styrene - Butadiene Rubber that the friction coefficient increases.
Keywords
Friction, wear, high density polyethylene, Styrene - Butadiene Rubber, polymer composites
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
IULIA ROATEŞI
Abstract
Dental implants (DI) are biocompatible structures made of alloplastic materials that are inserted surgically in the bone crest to become outstanding infrastructure for prostheses or dentures. Materials used in DI manufacturing are represented mainly by titanium and its alloys, but can be also manufactured by zirconia, safirbioceramics, etc. This article is dedicated to a 3D finite element modeling of various types of DI to calculate the stress and distribution of safety factor under masticatory forces, and therefore to assess risk factors for DI design. This work represents an original study of accurate geometric models of various types of DI and therefore for their using in calculation to evaluate the risk zones in the whole structure made up of bone, implant and ceramic crown.
Keywords
dental implants, biomaterials, bioceramics, three-dimensional finite element analysis, numerical modeling, implant stability
CONSTANTIN VLAD DENIS, ALEXANDRU CARÂP, BOGDAN SOCEA, ANTON FICAI, MĂDĂLINA GEORGIANA ALBU, GEORGETA PĂUNICĂ - PANEA
Abstract
The repair of the abdominal wall defects has always been a challenge. Good long term results (low percentage of recurrences) represent the purpose of different surgical techniques. Modern techniques use various types of alloplastic materials, making it possible for a lower recurrence rate, under a certain assumed and acceptable level. In the case of alloplastic repair, the tolerance of the organism towards the non-biologic material should be taken into consideration. Three types of meshes made of different synthetic materials were characterized by mesh density, pore size, pore shape, material composition by FT-IR microscopy and mechanical properties. The present study retrospectively analyzes the results obtained in our clinic within 3 years (October 2011- October 2014), using alloplastic repair of the abdominal wall defects. The recurrence rate and the occurrence of different complications (seroma, postoperative leakage, mesh rejection, neuromas with postoperative pain) were studied using the three meshes.
Keywords
synthetic meshes, pore size, mechanical strength, hernia repair
MIHAELA VIOLETA GHICA, ANTON FICAI , ŞTEFANIA MARIN, MINODORA MARIN, ANA-MARIA ENE, JENEL MARIAN PĂTRAŞCU
Abstract
The aim of this study was to develop and characterize some new drug delivery systems based on collagen, bioactive (apatite – β-wollastonite) glass ceramics and doxycycline in order to be used in infected bone defects. The composites with different amount of glass ceramics were prepared as hydrogels by crosslinking and then freeze-dryed in order to obtain porous structures which mimic bone. The hydrogels were characterized by rheological behaviour and the the spongious forms by Fourier transform infrared spectroscopy (FT-IR) and water up-take. The in vitro behaviour was determined by collagenase degradation; the doxycycline release from spongious composite systems was investigated and the kinetic mechanism was determined. The results of this study indicated that the obtained composites are promising biomaterials for treatment and prevention of infected bone.
Keywords
collagen, bioactive glass ceramic, composite, drug delivery systems
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Year
2015
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Issue
45 (4)
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Pages
307-314
VLAD GABRIEL VASILESCU, MIRUNA SILVIA STAN, ION PĂTRAŞCU, ANCA DINISCHIOTU, ELISABETA VASILESCU
Abstract
In vitro testing of materials biocompatibility provides information on cell behavior in relation to chemical composition and surface topography of materials. The studied biomaterial is a new one proposed to be used in oral implantology and therefore requires studying its biocompatibility compared to conventional materials commonly used in oral implantology.
The in vitro response induced by this bioalloy with surface characteristics conferred by casting, corrosion and anodizing was evaluated on G292 human osteoblasts. The experimental obtained surface after anodizing presented a stable and consistent oxide "gel-looking” layer well highlighted in scanning electron microscopy images. The results demonstrated the ability of the biomaterial to support attachment, growth and proliferation of human osteoblasts. As compared to the other materials tested and demonstrates the improved properties that facilitated rapid cellular adaptation to these surfaces.
Keywords
biomaterial, biocompatibility, cell adhesion, osteoblasts
RODICA ROGOJAN , ECATERINA ANDRONESCU, MIHAI HOTETEU
Abstract
The purpose of this paper is to assess whether calcium phosphate nanoparticles may be potential carriers of different cations. Recent advances in nanotechnology show that nanoscale particles may play an important role in tissue engineering in medicine or in their use as substrates for controlled drug release. The calcium phosphate nanoparticles were obtained from (NH4)2HPO4 0.3 M and Ca(NO3)2∙4H2O 0.5 M by coprecipitation technique and the hybrids calcium phosphates - copper ions were obtained by the similar cold-wet method, in the presence of ammonium hydroxide. The synthesized samples were analyzed by X-ray diffractometry, Fourier transform infrared spectrofotometry (FT-IR), energy dispersive X-ray analysis (EDAX) and the micrographs were determined by scanning electron microscopy (SEM). Calcium phosphates are widely used as implantable bioactive agent that replaces defect bone tissues and can serve, also, as substrate for binding of cations, for provide bioactivity and biological interactions or could be used as drug deliveries.
Keywords
copper ions, calcium phosphates, hydroxiapatite, nanoparticle
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
XIAOJIAN GAO, HUI WANG, SHUANGXIN LI, LIANG LU, YILUNG MO
Abstract
The addition of well-dispersed carbon nanofiber (CNF) can improve the mechanical and electrical property of concrete and the produced concrete (CNFC) shows a good piezoresistive effect, which is very useful for structural health monitoring. In order to confirm the feasibility of long-term application in real structures, the piezoresistive effects of CNFC samples were measured before and after different environment exposure test including freezing and thawing cycles, chloride penetration and drying under different relative humidity conditions. The results show that the electrical property of CNFC did not change obviously after 200 cycles of freezing and thawing, the resistivity of CNFC was increased by the addition of chloride during the mixing process possibly due to the accelerated cement hydration, and the resistivity of CNFC was increased and the polarization time was decreased with the decreasing relative humidity of exposure surroundings. However, the same or similar piezoresistive effects were found for all the concrete samples before and after different exposure treatment. Therefore, it is suggested that such CNFC can be used for the long-term monitoring of real structures.
Keywords
carbon nanofiber, piezoresistive effect, structural health monitoring, different environment exposure
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
UMUT YERLESEN, MÜNIR TASDEMIR
Abstract
The effect of zinc oxide (ZnO) and zinc borate (ZnHBO3) on the mechanical properties of high density polyethylene (HDPE) was investigated. Composites of HDPE with zinc oxide and zinc borate were prepared by melt mixing in a twin screw extruder and then the composites were molded by compression molding method. Filler contents in the HDPE were 5, 10 and 15 wt%.
The dispersion of zinc oxide and zinc borate particles in the matrix polymers was investigated using SEM. It was observed that the dispersion of ZnO and ZnHBO3 particles were relatively good with low ZnO and ZnHBO3 content but the aggregates of ZnO and ZnHBO3 particles in a polymer matrix increased with increasing content. The mechanical test showed that the elasticity modulus, hardness and density of HDPE composites increased with increasing ZnO and ZnHBO3 content. The addition of fillers to the HDPE changed the wear rate of the composites as well.
Keywords
High density polyethylene, zinc oxide, zinc borate, mechanical properties, wear
ZINA VULUGA, JENICA PACEAGIU , MICHAELA IORGA, MARIANA COARNĂ
Abstract
In the present work, polypropylene (PP) based composites filled with natural aluminosilicate materials were prepared. The volcanic tuff and kaolinite clay are used as filler in different proportions up to 15% by mass. PP composites filled with aluminosilicate materials were prepared using extrusion compounding and injection molding by dynamical melt processing.
The effects of filler content on the elasticity modulus and thermal conductivity of the composites were studied. Also, the morphology of the composites was evaluated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS).
The results showed that the elasticity modulus of composites improved with increasing the filler content. A better behavior is noticed in case of volcanic tuff using.
Keywords
polypropylene, volcanic tuff, clay, elasticity modulus, thermal conductivity
MIHAELA (NIŢUICĂ) VÎLSAN, AURELIA MEGHEA, MARIA SONMEZ, DANA GURĂU, MIHAI GEORGESCU
Abstract
The aim of this work was to obtain polyolefin polymer composites reinforced with chemically modified layered clay: polyolefin/rubber/compatibilizer /nanoparticles. The technology of making these polymer composites is extrusion-granulation, in strict compliance with the order of introduction of ingredients. Embedding montmorillonite nanopowders in the polymer composite mixture helps to increase the thermal resistance of the nanocomposite. The obtained polymer composites were tested in terms of physical-mechanical (hardness, elasticity, tensile strength normal state and accelerated aging for 168h at 70°C), resistance to solvents (immersion in iso-octane) and structural properties (FT-IR), according to standards in force.
Keywords
composites, EPDM- terpolymer rubber, hardness, reinforcing, montmorillonite
DOREL RADU, ZENO GHIZDĂVEŢ
Abstract
A comprehensive characterization of the particle size of polygranular powders can be done by:
- selecting the parameters to be used in the design, optimization and process control of various technological processes;
- establishing correlations between the properties of the mixtures and their particle size features.
One of the parameters to characterize powder mixtures is the particle size uniformity degree. For its evaluation, this paper gives two new indicators calculated by some factors coming from information theory: Shannon entropy - H - and Onicescu’s informational energy – E. Particle size uniformity calculated by these indicators (that are applicable to any granular materials) controls the specific surface area of the powder mixtures.
As applications, a series of quantitative relationships between the specific surface area of some Portland cements and their particle size uniformity were extracted. The results are characterized by a very good correlation for both several foreign cements as well as a set of local cements.
Keywords
informational energy, informational entropy, degree of uniformity, cement specific surface
IONUŢ-OVIDIU TOMA, NICOLAE ŢĂRANU , OANA-MIHAELA BANU, MIHAI BUDESCU, PETRU MIHAI, RAREŞ-GEORGE ŢĂRAN
Abstract
The growing amount of waste rubber produced from used tires has resulted in an environmental problem needed to be addressed. The paper investigates the effect of fine aggregate replacement by waste tyre rubber crumbs on the mechanical properties of concrete at different curing ages. The aim is to assess the suitability of the newly obtained material to load bearing elements in civil engineering.
The results presented in the paper are part of a larger research project related to the innovative use of all tyre components in concrete. The percentages considered were 40%, 60% and 80% by volume of fine aggregate. The general trend is a decreasing one in terms of mechanical properties. Even in such cases, the obtained values are above the minimum requirements, prescribed by norms, in terms of strength for some structural elements. The complete stress-strain curves determined at the age of 28 days show a softer descending trend for rubberized concrete compared to the reference mix. The embedded strain energy is larger in the post-peak region.
Keywords
rubberized concrete, modulus of elasticity, compressive strength, complete stress-strain curve
CARLOS CALADO , AIRES CAMÕES, TIBÉRIO ANDRADE, JOÃO RIBEIRO, BÉDA BARKOKÉBAS
Abstract
This study addressed the application, strength and durability of self-compacting concrete (SCC) in a large-scale construction site, comparing its performance with vibrated conventional concrete (CC) with similar characteristics, assessing its economic feasibility.
The studies were undertaken in the Arena Pernambuco project and involved the concreting during May, June and July 2012, for data collection, accompanying the routine concrete control tests and performing specific strength and durability tests.
The SCC compressive strength was on average 4% higher than the CC one, and its formwork reinforced to withstand greater lateral pressure of the fresh concrete. The durability indicators results were in favour of SCC, which cost was 13% higher than CC.
Keywords
self-compacting concrete (SCC), durability and applicability on a jobsite
NICOLAE DANIEL STOICA , MIRCEA BARNAURE
Abstract
Around the world there is a significant number of masonry buildings. Owing to the structural degradation during their existence, many of these structures require retrofitting interventions, especially those located in seismic areas. If masonry buildings have religious or cultural value, then the interventions should have a wider scope that aims to conserve the historical heritage. The Venice Charter of 1964 [1] includes two key principles guiding how this work should be carried out: the first principle is that structural interventions must be as less visible as possible, in order not to modify the aspect of the building; the second principle is that the action must be reversible, offering the possibility of dismantling should the interventions have poor efficiency. For this type of retrofitting works composite materials might offer several advantages. In particular, polymeric grids can ensure an enhanced resistance to the unreinforced masonry structures while not modifying their architectural aspect. The grids can be used for new buildings also, as they have some advantages with regard to the traditional solutions with steel reinforcement.
Keywords
d. Masonry, d. Construction, c. Mechanical properties, FRP, Polymeric grid, strength
SANJEEV KUMAR VERMA , SUDHIR SINGH BHADAURIA, SALEEM AKHTAR
Abstract
Premature deterioration and failure of reinforced structures in last 4 -5 decades deviated focus of researchers from compressive strength to durability and service life of structures. Several structures constructed before invention of modern cement and other advanced building materials are in service condition, whereas new structures were deteriorating faster than those old structures. Therefore, determination of remaining service life of concrete structures is significant. This article presents a service life model suitable for semitropical regions of India, developed using MATLAB for estimating residual service life of deteriorating structures and for predicting corrosion initiation time for new structures.
Keywords
concrete, carbonation, model, reinforcement, corrosion, deterioration, service life
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