română DAN GEORGESCU, ADELINA APOSTU, RADU GAVRILESCU
Abstract
The article presents the analysis and practical application modalities of certain modern methods to assess the characteristic compressive strength of the concrete manufactured in plants, using the concrete family concept, in accordance with CP 012-1/2007 “Practice Code for the manufacturing of concrete”, and the CUSUM analyses type (cumulative sum) according to ACI 214 R-02 “Evaluation of Strength Test Results of Concrete”. The concrete family system offers effective control means for a high number of different concretes. The analyses CUSUM type are extremely useful in the continuous pursuit of the quality of concrete manufactured in plants, being able to identify the negative tendencies in the evolution of concrete resistant values and therefore, there can be identified, for the reference concrete level, the causes of these evolutions.
Keywords
concrete, evaluation, conformity, compressive strength, concrete’s family, cumulative sum
LIANA TEREC, HENRIETTE SZILAGYI
Abstract
In order to obtain self-compacting concrete (SCC) for the construction industry, an important experimental program for the evaluation of the properties of fresh and hardened concrete was conducted at INCERC Cluj-Napoca Branch. The principal objectives of the research program were: to design the mix proportions for SCC, to assess the properties of fresh and hardened SCC and to study the behavior of SCC elements subjected to different loads. The fresh SCC evaluated properties were: slump flow, passing ability, viscosity and segregation resistance.
Keywords
construction (D, d), special concretes (D, a), compacting (A), limestone (D, d), organic polymers (D, a)
KSENIJA JANKOVIC, SRBOLJUB J.STANKOVIC, DRAGAN NIKOLIC, DRAGAN BOJOVIC, LJILJANA LONCAR
Abstract
The evaluation of the dynamic modulus of elasticity of twelve different concrete mix proportions as a function of the density and degradations due to freeze/thaw cycles is presented in this paper. Pore system and saturation are the main factors for concrete freeze-thaw resistance. The frequency analysis of ultrasonic waves in concrete after every 25 cycles was done. Dynamic modulus of elasticity was determination by resonance frequency analysis. This parameter is 35-50% smaller for concrete with recycled bricks as aggregate than ordinary concrete. For all concrete mixes dynamic and static (measured by destructive testing) modules of elasticity were compared.
Keywords
dynamic modulus of elasticity, ultrasonic waves, freeze-thaw resistance, recycled aggregate concrete
IOANA PAPAYIANNI, MARIA STEFANIDOU
Abstract
Binders are one of the basic constituent of mortars that plays an important role to their mechanical behavior and their behavior in physico-chemical interactions with the environment. The type, the quantity and the fineness of the binders result in different properties in the setting and in the hardening stage of mortars.
In the present paper very fine materials in the scale of nano were added to conventional binders such as lime and natural pozzolan. Properties of workability of the fresh mixtures, compression strength and porosity of the harden specimens were recorded in combination with structural observations using Scanning Electron Microscopy (SEM). Also, pore size distribution properties were recorded using Mercury Intrusion Porosimetry (M.I.P.). Based on the results, structural changes have been observed in nano-modified structures and early-age strength has been achieved in pozzolan mixtures. Pores, larger than 10μm have been reduced in mixtures with nanoparticles. The research is a precursor for the influence of nanoparticles to macro-scale properties of repair, lime-based mortars.
Keywords
D. mortars, B. nanoheterogenous structure
CRISTINA CIOBANU, STELIAN ILUC, IOAN LAZĂU, CORNELIA PĂCURARIU
Abstract
The effects of some commercial cellulose ethers type MHEC on some physico-mechanical properties (consistency, setting time and mechanical strength) of some mortars based on portland cement (CEM I 42.5 R), limestone filler and quartz sand were studied. It was observed that cellulose ethers increase setting time and the amount of water needed to achieve standard consistency while mechanical strength significant decreases. The intensity of these effects depends on the substitution degree of cellulose ethers and on the proportion in which they are added in mortars and less on the viscosity declared by the manufacturer.
Keywords
cellulose ethers, hydration, thermal analyse, setting time, mechanical properties
CORINA MITU, DOREL RADU
Abstract
In the flow technology of manufacturing Portland cement, operation of grinding the mixture of raw materials is decisive to obtain a certain particle size distribution with a prescribed degree of uniformity for providing good clinkerization reaction of the mixture of raw materials.
Uniformity degree can be considered an important technological parameter which can measure the change of the particles size of the raw materials mixtures during grinding.
This paper presents some correlation between the uniformity degree and a number of granulometric characteristics of some mixtures of raw materials from cement industry which is changing during the grinding.
Keywords
grinding, mixture of raw materials, particle size distribution, uniformity degree
KODURI RAMAM, K.CHANDRAMOULI
Abstract
A unique binary structured perovskite (Lead Lanthanum Zirconium Titante: PLZT) and tungsten bronze (Lead Barium Bismuth Niobate: PBBiN) piezoelectric material with Ordinary Portland Cement: OPC composites were fabricated by solid state reaction method. The composites were fabricated with ceramic to cement in the ratios of 25:75vol%, 50:50vol% and 75:25vol%, respectively. The X-ray diffraction patterns of these composites confirmed both perovskite and tungsten bronze phases. The scanning electron micrographs indicated homogeneity between ceramic and cement. These composites showed combined characteristics of perovskite and tungsten bronze ceramics with a high dielectric and piezoelectric properties. The dielectric constant (RT) and piezoelectric charge coefficient (d33) were found optimum at 75:25vol% composite which showed promising results that are potential for sensing and actuating in intelligent structures or structural health monitoring applications.
Keywords
A. Solid State Reaction; D. Composite Cement; b. Dielectric properties; b. Piezoelectric properties; Structural Health Monitoring
VICTOR FRUTH, CRISTIAN ANDRONESCU, CRISTIAN HORNOIU, ECATERINA ŢENEA, ADRIANA RUSU, RAREŞ SCURTU
Abstract
Sr and Mg doped lanthanum gallate perovskites (La1−xSrxGa1−yMgyO3−δ) shortened as LSGM are promising electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs).
The evolution of secondary phases, such as LaSrGa3O7 has been identified to be a problem in the preparation of LSGM. Actually, no mater what technical preparation route was adopted (wet-based or solid state-based method) the presence of the secondary phases, accompanying the main phase LSMG was reported.
The results regarding an attempt to obtain pure Sr and Mg doped LaGaO3 ceramics using a specific annealing treatment was reported in this work. The obtained ceramics were characterized using different techniques. Thermal analyses (DTA/TG) on the stoichiometric raw mixture and dilatometric measurements on sintered bodies were performed. Morphological and structural aspects were investigated by means of X-ray diffractometry, FT-IR spectroscopy and scanning electron microscopy. The electrical behavior of the obtained ceramic was characterized by complex impedance spectroscopy.
Choosing an appropriate annealing program, almost pure Sr and Mg doped LaGaO3 can be obtained.
Keywords
solid electrolytes, Sr and Mg doped LaGaO3, solid state technique, electric properties
ELENA CRĂCIUN, ANGHEL IONCEA, IOANA JITARU, MARIUS GHIUREA, OVIDIU OPREA
Abstract
In this paper a water based organo-inorganic dispersion as coating material has been prepared in the system polymer emulsion – inorganic filler – additive. The structure, topography, morphology and thermal stability of the film coating have been determined by SEM and TG analysis. The properties of the dried film like hardness, scratch abrasion, blocking resistance, elasticity, flexibility, dielectrical rigidity and optical aspect have been determined and compared with those of the conventional acrylic coating.
Keywords
nanofillers, nanocomposite, silica sol, abrasion
ZENO GHIZDĂVEŢ
Abstract
Based on the results of a comprehensive analysis made in the first part of the article, here we are handling the issue of developing prediction models on a large industrial dataset. The outcome of the first part is to ascertain, through a careful analysis, which of the process parameters will be selected as regressors and whom will be predictors. In this second part of the article they will be used in several models and the results will be assessed by their efficiency. Though formally distinct, these two parts should be read together, as they are mutually linked together. In practice, continuous exchange of information should be considered between these two parts.
Keywords
time series, prediction, industrial processes
ZORAN GRDIĆ, GORDANA TOPLIČIĆ ĆURČIĆ, NENAD RISTIĆ, IVA DESPOTOVIĆ
Abstract
The mechanical and rheological properties of concrete depend to a great extent upon the type of realized structure which can be viewed from the aspect of the relationship of the space between the grains in the aggregate and the quantity of the the cement paste in the concrete. The influence of the degree of filling of the cavities in the aggregate with the paste (ke) on the consistency type has to view in the light of the realized structure of concrete taking into consideration the particle size distribution and water-cement ratio. Generally, with the increase of the degree of filling of the cavities in the aggregate with the cement paste from 0.9 to 2.5 the consistency of concrete changes from stiff to very fluid. The maximum values of compressive strength are realized when the degree of filling of the cavities in the aggregate that can be considered as optimal is within the relatively narrow limits, and then the value of the parameter ranges between 1.2 to 1.4.
Keywords
cement paste, aggregate, concrete, rheologic properties, mechanical properties
ZENO GHIZDĂVEŢ, DOREL RADU, ANDREEA DAVID
Abstract
A mathematical model used to design clinkering plants is used here to explore the influence of the cooling air temperature and of the fuel selection on both heat and raw materials requirements and even on the required kiln length. The interest is not purely theoretical as cumulated differences over a long range, could reach important values.
Keywords
clinkering plants, combustion, mathematical model, design
IOAN ROBU, GABRIELA ILIE, IOAN PORDEA
Abstract
The utilization of thermo-power station ashes in construction is of major importance from a technical, economic and environmental viewpoint nationally and internationally.
Their limited utilization could be triggered also by their radioactivity. This paper researches the determination of radioactivity index for ashes originality from the main Romanian thermo-power stations for pastes, mortars and concretes made of cement with an ash component.
Keywords
thermo-power plant ash, puzzolanic activity, radioactivity index, radiologic risk
ALICE RĂDUCANU, ANGELA STANCA, AURELIA MEGHEA, CONSTANTIN GRIGORIU, CRISTIAN VIESPE
Abstract
The paper addresses the topic on morphostructural characterization of ultrafine particles generated in coal-based power plants, with special reference to Mintia-Deva power plant, Romania. The particles oxidic composition, concentration and size distribution were investigated. The concentration measurements have been performed based on light scattering for micro-sized particles and differential mobility analysis for nanometric scale. The highest values of oxide component concentration have been registered in the coal powders sampled from the work places at breaking room and on conveying belts. The dust composition mainly consisted of silica, and also iron, aluminum, calcium and magnesium oxides, with more than 25% SiO2, 10% Al2O3, 4%Fe2O3.
Keywords
ultrafine particles, dust, silica nanoparticles, power plant emissions
VICTOR LECA, ECATERINA ANDRONESCU
Abstract
The results of the influence of thermal and chemical treatments on the surface morphology of (110) NdGaO3 substrates are described in this paper. The treated surfaces were analyzed by Atomic Force Microscopy (AFM), in air, and by in-situ high pressure Reflection High Energy Electron Diffraction (RHEED). The thermal treatment of substrates resulted in a NdO1+x single terminated surface, while a surface with GaO2-x terminating layer and atomically flat terraces without etch pits could be obtained by chemical etching in a HF + NH4F + H2O solution, followed by an annealing step at high temperatures (900-1000oC) in air or in oxygen flow, for surface recrystalization.
Keywords
NdGaO3, surface morphology, AFM, RHEED, annealing, chemical treatment
OANA CADAR, MIRELA MICLEAN, CECILIA ROMAN, LUCIA GAGEA, LUDDOVIC FERENCZI
Abstract
Pigment dispersion properties are extremely important for paint, papermaking or plastic industries. To obtain multifunctional features like moisture resistance, antibacterial and self-cleaning properties, the dispersing ability of two alkali-modified styrene-maleic anhydride copolymers (StMa-X, X=Na, K) was studied. It was found that these copolymers showed excellent dispersion action on the M/ZnO (M = Ag, Au and Pt) nanopowders. Sedimentation tests were also performed to observe the compatibility between the M/ZnO nanopowders and copolymers. In addition, an agar plate method was used for the evaluation of antibacterial effect of these materials. Experiments were carried out using the following bacteria: Escherichia coli CCM 3954, Pseudomonas aeruginosa CCM 3955 and Staphylococcus aureus CCM 6188. The quantitative examination of bacterial activity was estimated by the antibacterial rate as calculated from the number of viable cells, which form colonies on the nutrient agar plates. The obtained results are discussed in order to justify their possible application in the field of coating materials with superior properties.
Keywords
antibacterial properties, copolymer, dispersing ability, nanopowder
CEZAR COMĂNESCU, PETRU PALADE, DENISA FICAI, CORNELIA GURAN
Abstract
The present paper presents the synthesis and characterization of some new functionalized SBA-15 silica, by an improved synthesis route leading to well-organized mesoporous materials belonging to p6mm symmetry group. In a one-pot co-condensation synthesis we obtained and characterized SBA-APTMS and SBA-APTES samples. Variation of the initial APTMS/TEOS and APTES/TEOS molar ratios and different TEOS pre-hydrolysis time were investigated. N2 sorption, FT-IR, NIR and XRD method were employed in determining the mesostructure characteristics of the obtained materials (SBA-15, SBA-APTMS x%, SBA-APTES x%, with x= 2, 4 and 8 % molar percent ).
Keywords
SBA-15, pre-hydrolysis, functionalization, APTMS, APTES
MIHAI BRATU, IOAN ROPOTĂ, OVIDIU VASILE, OVIDIU DUMITRESCU, MARCELA MUNTEAN
Abstract
The paper aims to introduce innovative systems to absorb and attenuate noise from industry or urban and extra-urban environment, efficient and sustainable, based on composite materials made by recycling solid wastes. The composite materials are obtained by including some materials considered wastes – pellets from plastic bottles, sawdust, ash from thermal plant and sterile municipal waste - in a polymer type organic matrix. Thus are obtained new organic materials which embed non-biodegradable waste, which can affect seriously the environment. The sound absorption capacity of these new composites varies depending on the proportion and nature of the waste used. The absorption coefficient which determines the phonic absorbing capacity of all new obtained materials is calculated for each sample. Samples are made of resin and reinforcement material in different proportions, which are tested to determine the absorption coefficient against frequency, using a device called KUNDT TUBE. Both for material preparation and sampling tests the in force standards are respected.
Keywords
Cuvinte cheie (engleza)
VASILICA DIMA, MIHAI EFTIMIE, ADRIAN VOLCEANOV, MARIA IONESCU
Abstract
Present paper deals with some experimental results obtained for fabrication of ceramic glazes from basaltic fibers waste and mixed with processed E-glass fibers waste, as well.
The use of basaltic fiber waste and of E-glass fiber waste in frits and glazes, taking advantage of oxide composition, energy content of glass and ecological effects, as well, may represent an efficient and effective solution from technical and economical point of view.
Keywords
vitreous glazes, basaltic fibers waste
GEORGETA VELCIU, ALINA MELINESCU, PETER STORCH, VIRGIL MARINESCU
Abstract
The purpose of this paper is to achieve a ceramic material based on cerium dioxide and copper as an attempt to optimize the properties of the anode used for intermediate temperature fuel cells SOFC-IT.
The synthesis of the material was accomplished by the precipitation method using the corresponding salts.The parameters of the precipitation route (solution pH as well as synthesis temperature) have been carefully contoled in order to obtain a homogenous material of cerium oxide particles uniformly coated with copper oxide nanoparticles. The obtained material was characterized by XR diffraction, scanning electron microscopy, measurements of specific surface area, density and
Keywords
anodes, solid electrolyte fuel-cell, precipitation method, copper oxide, ceria oxide
MILOŠ R. VASIĆ, ZAGORKA M. RADOJEVIĆ, MILICA V. ARSENOVIĆ, ŽELJKO B. GRBAVČIĆ
Abstract
The equation for drying kinetics is obtained, based on the analytical solution of the differential equation with a boundary condition in the form of the flux. This equation was initially developed by G. Efremov. In this paper a modification of the Efremov drying equation will be presented. Shrinkage correction will be included in that equation for the first time.
Two programs were designed to compute the effective diffusion coefficient. First program did not include shrinkage effect during drying into the computation algorithm while the second one has included it. Two models for predicting the drying behavior were obtained as the result of cited programs calculation. First model did not include shrinkage (model 1) and second one (model 2) has included it. The predicted values obtained from model 2 fit with experimental data. Results presented in this study showed that the values of effective diffusion coefficient determined by designed computer programs have similar values with values available in literature related to the same coefficient determined for different clays.
Keywords
effective diffusion coefficient, analytical solution, software
MARIA GEORGESCU, IRINA CĂTĂNESCU, GEORGETA VOICU
Abstract
The geopolymer binders are relative new materials with three-dimensional polymer structures having a preponderant amorphous character compositional similar, natural feldspar. These materials are synthesised by the processing of silico-aluminates materials like fly ashes, granulated blast furnace slag, metakaolinite, with alkaline solutions like hydroxides or silicates. The compositional characteristics and processing peculiarities influence the geopolymers synthesis and microstructure. These factors influence the development of mechanical strengths.
The present paper brings information concerning the microstructural and compositional characteristics of some geopolymers synthesized from fly ash and NaOH solution in different conditions of curing.
Keywords
Fly ash; Geopolymer; Microstructure; Mechanical properties
MIRELA MENICU, ADRIANA MOANŢĂ, DANIELA NĂSTAC, ADRIAN MOTOC, RADU PITICESCU
Abstract
In accordance with the requirements imposed to binder materials for performing of modern constructions, a multitude of new materials with added value are researched and introduced in practice. The article presents both the obtaining method of photo-catalytic component (TiO2 nano-structured), methods of photo-catalyst characterization and also the obtaining of photo-catalytic binder materials. In order to obtain photo-catalyst material, the hydrothermal synthesis was used, and this material was characterized by X-rays diffraction in order to establish the composition and crystallites dimensions and by optical microscopy in order to see powders morphology.
Photo-catalytic binder materials with TiO2 nano-structured were obtained. The own results obtained as consequence of characterization from physical-mechanical point of view (water for the slurry of normal consistency, setting time, stability, and also mechanical strengths at bending and compression) of these materials.
Keywords
photo-catalytic binder materials, nano-structured TiO2, binder materials with self-cleaning, anti-bacteriological, pollution decreasing
MARIA GHEORGHE, NASTASIA SACA, CĂTĂLINA GHECEF, RAMONA PINTOI, LIDIA RADU
Abstract
This paper presents experimental obtained data regarding the properties of self compacted concrete (SCC) with fly ash content, such as workability, compressive strength evolution over time in comparison with the reference (concrete without fly ash or concrete with limestone filler content). In this way, were realized two series of mixes: SCC with CEM I 52.5R and SCC with CEM II/B-M (S-LL) 42.5N.
Research realized showed that the addition of 20-34% fly ash of total powder amount is beneficial for the consistency and resistance to segregation of concrete in fresh state. SCC compressive strengths at early age were significantly diminished by fly ash addition, but these are increasing until 360 days.
Keywords
self compacting concrete, fly ash, workability, compressive strength.
KSENIJA JANKOVIČ, GORAN CIROVIČ, DRAGAN NIKOLIČ, DRAGAN BOJOVIČ
Abstract
Preparation and microstructure of ultra high performance concrete (UHPC) have been intensively analyzed in the last few years. The mechanical properties (compressive strength and flexural strength) were investigated under different curing conditions (standard and steam curing). Silica fumes have characteristics that make them necessary in cement composites with ultra strength properties. The search for substitute products thus appears important if the use of UHPC is to become more widespread in the concrete industry. Possibilities of making ultra high performance self compacting concrete (UHPSCC) with materials available in Serbia, based on experimental work are discussed in this paper. Three series of samples were made with different types of fine reactive additives (silica fume was replaced with metakaolin at 20% and 40% and with fine fly ash at 20%). The produced mixes had self compacted consistency. The 28th day compressive strength varied between 165 and 195 MPa for the heat treated specimens and between 135 and 150 MPa for the ones that had not been heat treated. Furthermore, this paper presents SEM micrographs of C-S-H phase formed after steam curing and super-heated steam under preassure.
Keywords
UHPSCC, Fine reactive additive, Steam curing regime, Super-heated steam under preassure
DAN GEORGESCU, ADELINA APOSTU, RADU GAVRILESCU
Abstract
The design of the service life of reinforced concrete structures can be performed using design approaches with different levels of complexity (full probabilistic, based on partial factor or deemed to satisfy). No matter the complexity, the results of the experimental researches in-situ and in the laboratory must provide the necessary data for such approaches, for different types of degradation mechanism of reinforced concrete.
The article presents the results of experimental researches performed on concretes prepared with cement type CEM III/A Carpatcement, as an example for obtaining the necessary data in order to establish the service life of constructions performed with a certain type of cement.
Keywords
concrete, service life design, chlorides, carbonation
GEORGETA VOICU, CRISTINA DANIELA GHIŢULICĂ, ELENA DINU, ECATERINA ANDRONESCU
Abstract
In the sol-gel synthesis of dicalcium silicate (Ca2SiO4 – C2S) the calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and trietoxysilane ( C6H16O3Si - TEOS) were used as precursors. The C2S was obtained at 800-1100°C.
Thermal analysis methods (DTA/TG), X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) were used to investigate the formation of dicalcium silicate.
The in-vitro behavior was also investigated by soaking of the dicalcium silicate powder in simulated body fluid (SBF) for 7 days. Our results indicated that dicalcium silicate formed in SBF hydrosilicates as principal mineralogical phases and bound a small proportion of the phosphor from liquid as phosphate phases.
Keywords
dicalcium silicate; sol-gel synthesis; in-vitro behavior
RALUCA STAN, CRISTINA OTT, GEORGETA VOICU, ADRIANA LUNGU, SORIN I. ROŞCA
Abstract
We report the synthesis of Cr-doped silica with different morphologies by sol-gel polymerization of tetraethoxysilicate in the presence of D-sorbitol derived organogelators (1,3:2,4-bis-O-benzylidene-D-sorbitol, DBS and its p-nitro and p-methoxy derivatives) and hexadecyltrimethylamonium bromide with S-(+)-1-phenylethylamine-tricarbonyl-chromium, acting both as chiral catalyst and source of chromium, for a 10 wt% Cr/SiO2 loading. Two different types of morphologies were observed: silica tubes with 300-500nm diameter and 10-15μm length for the nitro-substituted template and “necklace” type agglomerated silica granules for the other templates. EDX and XPS analyses revealed a uniform distribution of Cr ions on silica matrix consisting of 80% Cr3+ and 20% Cr6+.
Keywords
sol-gel, Cr-doped nanostructured silica, arene-tricarbonyl-chromium complexes, organogelator
Synthesis and characterization of calcia stabilized zirconia nano-powder, obtained by sol-gel method
RODICA ROGOJAN, ECATERIANA ANDRONESCU, IRINA ILIESCU, ROXANA TRUŞCĂ, BOGDAN ŞTEFAN VASILE
Abstract
The purpose of this study is to obtain nanometric zirconia powders, by sol-gel method, using precursors of different chemical nature - inorganic (ZrCl4) and organic (C12H28O4Zr). The obtained gels were dried at 100oC, and then heat treated to 1000oC for 2 hours. In order to identify obtained phases and their degree of crystallinity, powders were analyzed using X-ray diffraction. Analyses of scanning electron microscopy and transmission electron microscopy have been used to investigate the morphology and size of the obtained powders. Experimental analyzes show that, from different precursors (organic and inorganic), nanometric powders of partially stabilized zirconia with CaO are obtained.
Keywords
zirconia nanoparticles, sol-gel method, organic precursors, inorganic precursors
ELENA DINU, CRISTINA DANIELA GHIŢULICĂ, GEORGETA VOICU, ECATERINA ANDRONESCU
Abstract
The decreasing in particle size, from micro to nanometer dimensions, allows the development of new materials, with improved properties. The pyrolysis method is a modern, unconventional synthesis method of various powders which leads to the preparation of very small (few nanometers) particles. This method is based on the spray-pyrolysis technique - pyrolysis of an aerosol obtained by ultrasonic spray.
The present paper describes the evolution of the powders microstructure and composition with different processing parameters. Using different precursors, phosphate powders - hydroxyapatite (HAp) and β-tricalcium phosphate (βTCP) - were synthesized In order to obtain homogeneous and fine powders of calcium phosphates the following experimental parameters were modified: the concentration of the solution of precursors, the flow of carrying gas, the frequency of piezoelectric ceramics ultrasonic vibration and the temperature of the pyrolysis furnace.
The obtained powders were investigated using Thermogravimetric Analysis (or TGA) and Differential Thermal Analysis (or DTA) measurements, X-ray diffraction and scanning electron microscopy. The average crystallite size of powders was also estimated from diffraction data. The results are emphasizing that by the pyrosol method can be obtained powders with various compositions, consisting of spherical particles, with size within the nanometer range, which may have many medical applications.
Keywords
hydroxyapatite, β-tricalcium phosphate, spray-pyrolysis technique
ŞTEFANIA STOLERIU, ECATERIAN ANDRONESCU, ALEXANDRA LUCIA CARABĂŢ, BOGDAN ŞTEFAN VASILE
Abstract
The paper’s aim was to prepare and characterize ceramic powders of fully stabilized zirconia (with 8 mol% yttria), and alumina, obtained through co-precipitation starting from the corresponding chlorides. Co-precipitation was taken using water or ethanol as a solvent and considering the pH influence (7.5, 10.5 and 12.5 obtained by using ammonia solution) upon precipitation was analyzed. The obtained powders were dried at 80 °C for 24 h and afterwards calcinated at 350°C for 2 hours.
The powders were evaluated through thermal analysis, X-ray diffraction, scanning electron microscopy and transmission electron microscopy.
The XRD results show that 8YSZ calcinated powders is a tetragonal ZrO2 and, concerning alumina powder, besides -Al2O3, -Al2O3. The TEM examination shows that the tetragonal ZrO2 has a spherical like morphology with a size ranging from 5 nm to 12 nm. Also, it was observed that the best condition for nanopowders obtaining was using as solvent water and a pH value of 12.5.
Keywords
zirconia, alumina, nanopowders, (co-)precipitation
ALINA MELINESCU, GEORGETA VELCIU, VIRGIL MARINESCU, MARIA PREDA
Abstract
The IT-SOFC cells are consisting of three main components: solid electrolyte, cathode and anode. A solid electrolyte was synthesized based on solid solutions of CeO2 with strontium oxide, which was sintered at 1400°C. The solid electrolyte obtained has the relative density of 71% of theoretical density. The composition, La0,45Sr0,55MnO3 was used to obtain a cathode. The anode was prepared using a CeO2-CuO cermets. The heat treatment was performed at 1050°C for the cathode and at 970°C for the anode. By X-ray diffraction, was determined that the solid electrolyte consists of a solid solution with specific structure of cerium oxide and small amounts of SrCeO3 and the cathode is a solid solution of type La1-xSrxMnO3. The two electrodes were deposited by spraying on the solid electrolyte and the thickness of layers was 65-85 µm. By scanning electron microscopy there was found a good adhesion of the electrodes at solid electrolyte. No cracks were observed that may indicate mechanical incompatibility between the solid electrolyte and electrodes.
Keywords
solid electrolyte, XRD, SEM
DOREL RADU, RĂZVAN STATE
Abstract
In the field of advanced ceramics, the obtaining of some high strength ceramic materials is, nowadays, of interest for a series of practical applications. Their properties are highly correlated with their chemical composition and their processing methods.
In this article we try to highlight the main types of ceramic materials which are of interest for the targeted field. The mechanical and thermal properties of the ceramic compounds are determined by the electronic structure of their atoms and by their high degree of covalent chemical bonds.
Based on information from literature and from some own preliminary result, we have highlighted, for the Al2O3 ceramics, the interdependence between the main mechanical properties and their Al2O3 content.
Keywords
structural ceramics, correlation between properties and composition, ceramics with high mechanical strenght
DAN GEORGESCU, ADELINA APOSTU, RADU GAVRILESCU
Abstract
The environmental actions can cause deteriorations of concrete having as consequence an intensified reduction of the elements/construction structures’ performance. The design of the service life of certain structures is performed considering methods with different complexities which must consider a rigorous selection of materials as well as important execution, execution inspection, maintenance factors and status assessment during service life. No matter the complexity of the method used, the design process of the service life must be based on the results obtained from certain experimental researches, necessary for the assessment of the evolution of materials’ characteristics, depending on different environmental conditions. The freeze/thaw attack with /and without de-icing agents represents one of the actions with frequent occurrence, causing important deteriorations of concrete.
The paper presents an analysis of the main experimental methods related to the freeze/thaw action (Part 1) and the results of certain experimental researches performed by authors in order to determine the freeze/thaw resistance of concretes manufactured with different types of cement produced by CARPATCEMENT HOLDING S.A. – HEIDELBERGCEMENT GROUP which will be presented in Part II.
Keywords
concrete, freeze /thaw attack, service life, experimental methods
GABRIEL OPRIŞAN, NICOLAE ŢĂRANU, VLAD MUNTEANU, MIHAI BUDESCU, CIPRIAN COZMANCIUC, RUXANDRA OLTEAN
Abstract
Structural rehabilitation of concrete columns using confining with composite membranes has become a largely accepted technique. An extensive experimental program has been carried-out at the Faculty of Civil Engineering and Building Services, Iasi, aiming to evaluate the efficiency of the confining effect on concrete columns using fiber reinforced polymer (FRP) composite membranes. The results have established the effectiveness of wrapping solution, based on glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites, in increasing both strength and ductility. A predictive equation has been proposed by the authors, based on experimental results, in good agreement with existing models.
Keywords
hybrid confined columns, composite membranes, confinement pressure, wrapping, stress-strain curves, strength improvement
XIAOJIAN GAO, YINGZI YANG, HONGWEI DENG
Abstract
Shrinkage strains of high strength concretes with and without silica fume were measured at various depths from the drying surface by using linear variable differential transformer (LVDT) displacement sensors, and only one surface of the prism specimen was exposed to drying conditions (RH=75%, 54% and 33%) during the experiment. The results show that the internal shrinkage strain becomes lower with the increasing depth from drying surface. Such shrinkage difference gets severer with the longer drying time and the lower relative humidity of drying condition. There is a linear relationship between the reduction of internal relative humidity and shrinkage strain at every depth of specimen. However, the increased shrinkage at inner position is higher than that at outer position of each specimen when the same reduction of relative humidity happens.
Keywords
concrete, drying shrinkage, relative humidity, differential strain distribution
DANIELA LOREDANA BELEŞ, VLAD CODREA
Abstract
SO2 and VOC emissions belong to the first air pollutants which caused challenging experiences for cement industry. The reduction methods are particular for each cement plant, and are concerning the management of raw materials, combustibles or supplementary equipments and processes. The main raw material components responsible for SO2 and VOC emissions are the pyritic sulfur as well as the kerogen. Current paper describes the complete replacement of an organic and pyritic rich clay source with a non-contaminated new one and the corresponding impact on the emission level. Compared with the old clay deposit, the new clay type with very low pyrite and TOC content has determined a strong reduction of SO2 and VOC emissions.
Keywords
stack emissions, clayish materials, pyritic sulphur, sedimentary organic compounds
ILEANA MOHANU, MARIA GEORGESCU, DAN MOHANU, LIANA MANOLACHE, COSMIN DRĂGĂNOAIE
Abstract
The paper have information regarding the characteristics of some colored mortars based on lime –limestone-volcanic tuff-river sand, owned to some preservation-restoration works of the historical monuments plasters. Investigation was made regarding chemical, physical and chromatic properties of the raw materials. Different compositions of mortars were performed, being characterized from physical-mechanical point of view at terms of 28 and 56 days, and also aesthetic. Correlations were made between raw materials characteristics and those of mortars. It was stated that the type and limestone proportion modify in restricted limits physical-mechanical characteristics, imprinting to mortars, in the same time, different luminous, pastel tones.
Keywords
lime mortar, limestone, pozzolana, mechanical properties, colour
CORNELIA PĂCURARIU, RADU LAZĂU, IOAN LAZĂU
Abstract
Decorative aventurine glazes with Fe2O3 content have been synthesized. The crystallization of hematite in the synthesized glazes has been studied in non-isothermal conditions using DTA technique. The apparent activation energies of the crystallization processes were calculated using the Kissinger method. The influence of CaF2 and LiF addition on the activation energy of the crystallization process has also been investigated. The hematite presence in the samples has been confirmed by XRD analysis. The prepared glazes ensure a strong decorative effect and are suitable for faience and terracotta products.
Keywords
crystallization kinetics, aventurine glaze, thermal analysis, ceramics
ANAMARIA MIHĂILĂ, MARCEL BENEA
Abstract
Cârţa Cistercian Monastery was first attested at the beginning of the XIIIth century and is considered to be the first early gothic monument in Transylvania. It is located on the left side of the river Olt, between Sibiu and Făgăraş cities. The raw materials used at the construction of the monument are Miocene sandstones - litharenites with carbonate cement and bioclasts. The study focuses on the western portal of the monastery and the geminate window from the former chapter hall, on which we performed the mapping of the sandstone blocks. The paper presents the petrographic characteristics of the sandstones after detailed study on the polarised microscope: sorting degree, medium grain size and mineralogical composition, the latter one correlated also with XRD-analysis
Keywords
Building stones, Cârţa Cistercian Monastery, Sandstones, Miocene (Sarmatian).
RĂZVAN STATE, ADRIAN VOLCEANOV, ENIKÖ VOLCEANOV, ŞTEFANIA STOLERIU
Abstract
The structural ceramic materials are important because they are usually lightweight, harder than metals, resistant at higher temperatures and also present an impressive series of mechanical properties, including good mechanical strength in extreme conditions. The alumina based materials and composites are of great importance for ballistic protection. The aim of the present paper is focused on behavior of various alumina types after being sintered in different conditions.
The materials used in present study are α-Al2O3 powder (from 3 different sources) and additions of different rare-earth oxides (La2O3, Y2O3, Nd2O3) [1] in two proportions: 500 ppm and respectively 1000 ppm.
The Al2O3 dense ceramics were obtained by various sintering environments, using both traditional sintering ways at temperatures of 1500 ° C (electric furnace) and 1815° C (gas furnace) and a non-conventional technique (cold plasma sintering).
After sintering the samples were analyzed by X-Ray diffraction and scanning electron microscopy (SEM). Ceramic properties like contraction, absorption, porosity, and relative density were also determined.
The final conclusions highlight o series of interpretations and correlations of the sintering parameters with the properties of the sintered materials.
Keywords
ceramic composites, structural ceramics, cold plasma, alumina ceramics
BOGDAN ALEXANDRU SAVA, LUCICA BOROICA, MIHAI SAVA, MIHAI ELIŞA
Abstract
The present work investigates vitreous fertilizers for agricultural purposes. The studied compositions belong to K2O – MgO – P2O5 ternary system. The samples were investigated by IR and Raman spectroscopy, showing vibrations specific to P-O-P, PO32-, PO2 and P = O bonds. In the case of AG.5 sample, IR peaks are shifted, indicating that nitrogen replaces oxygen in a great extent that modifies the vitreous phosphate network. XRD plots revealed specific shapes for glassy state both for un-nitrided and nitrided samples. SEM investigations on powders show more homogeneous darker phases in the case of AG 5 sample comparatively to AG 2 series.
Keywords
phosphate glass, fertilizers, XRD, IR and Raman spectroscopy, SEM
ALEXANDRU MIHAI GRUMEZESCU, ECATERINA ANDRONESCU, ANTON FICAI, CRINA SAVIUC, DAN MIHĂIESCU, MARIANA CARMEN CHIFIRIUC
Abstract
The desired pharmacological activity with minimum side effects of different traditional chemical formulations is achieved by enabling the site-specific targeting and controlled release. In this study, magnetic diethylaminoethyl-cellulose (DEAE-Cellulose) has been prepared by magnetite nanoparticles deposition on the DEAE-Cellulose support. The primary method to analyze the surface modification was SEM. DEAE-Cellulose/Fe3O4 was loaded with different antibiotics and their antimicrobial efficacy against bacterial strains belonging to E. coli and S. aureus species were studied. DEAE-Cellulose/ Fe3O4/cephalosporins have been characterized by using FT-IR. Our study indicates that the materials of DEAE-Cellulose/Fe3O4/cephalosporins have generally increased the activity against tested strains, the antimicrobial effect being not significantly dependent of temperature treatment.
Keywords
Cephalosporins, hybrid material, DEAE-Cellulose, drug delivery, magnetic material, magnetic drug targeting
GEORGETA VELCIU, ALINA MELINESCU, PETER STORCH, VIRGIL MARINESCU
Abstract
The purpose of this paper is to achieve a ceramic material based on cerium dioxide and copper as an attempt to optimize the properties of the anode used for intermediate temperature fuel cells SOFC-IT.
Keywords
Cuvinte cheie (engleza)