română MARIANA IVAN, MARCELA MUNTEAN, FLORENTINA POTECAŞU
Abstract
The main user of the refractories is the iron and steel industry segment related to transporting, processing and casting of the molten metal (iron and steel).
At present, masses with good thermal, mechanical and chemical properties are imported, As a result of the analysis of the wear influences which the refractories in contact to the hot metal and slag are subjected to (mechanical and erosion stress, abrasion, ferro-static pressure, radiation rate – temperature >1500°C, chemical stress – corrosion caused by the slag attack), new refractory plastic mud gun masses for covering the hot metal taphole and the slag notch have been obtained and tested in the laboratory.
Improvement of the properties of the present plastic masses was aimed by adding materials that could offer the new masses the best thermal, mechanical and chemical characteristics, thus being obtained environment-friendly anhydrous plastic refractory masses by replacing the tar with a inorganic binding matter.
Plastic refractory masses of different compositions have been obtained in the laboratory.Their physical, chemical and mechanical characteristics have been defined after heating and thermal treatment.
Keywords
refractory plastic masses, organic binders, taphole clay
VASILICA DIMA, MIHAI EFTIMIE, ADRIAN VOLCEANOV, GEORGETA VOICU, RAMONA DINCĂ
Abstract
This paper presents experimental results on cathode ray tubes – CRT - glass waste for recovery in glazes. We characterized the CRT glass waste and we obtained frits from it.
We determined the density, the hydrolytic stability, the wetting ability against temperature and the thermal expansion curves, both on waste and obtained glasses.
Glazes were prepared and applied on ceramic support (terracotta and sandstone) in laboratory. SEM micrography was performed to support-glazes interface.
Keywords
CRT glass waste, glazes, recovery
ANA MARIA MONCEA, MARIA GEORGESCU, ALINA BĂDĂNOIU, ECATERINA MATEI
Abstract
Portland cement and derived blended cements, represent binding matrices adequate for the immobilization of hazardous waste. The high pH of the intergranular pore solution in the cement stone along with the presence of calcium silicates hydrates with high specific surface area, as main hydrates, are key elements in the immobilization capacity of noxious elements in these matrices. Portland clinker free binding systems such as alkali activated slag have also a good immobilization capacity of toxic elements such as heavy metals.
The present study brings information regarding the immobilization of a glass waste with high Pb content (> 15%), derived from cathode ray tube glass (CRT) recycling, in three types of matrices: ordinary Portland cement (CEM I), slag cement (CEM III A) and alkali – activated slag binder. All binders showed a good immobilization capacity of the Pb waste (over 99%).
The mechanical strengths developed by the ordinary Portland cement were not adversely affected by the presence of CRT waste (dosed in amounts corresponding to 0.18-10% Pb content).
The compressive strength recorded for the slag cement with a high amount of waste (corresponding to 10% Pb) decreased with 25% and for alkali activated slag with 15% (with reference to the binder without waste).
Keywords
Portland cement, alkali – activated slag, waste, Pb immobilization, compressive strengths
FLORENTINA ALBU, CRISTIAN ŞEITAN, CHRISTU ŢÂRDEI, VIOLETA TSAKIRIS, GEORGETA VELCIU
Abstract
This paper presents experimental results obtained in developing ceramic composites based on SiC and Si3N4, sintered by plasma sintering method (Spark Plasma Sintering (SPS). Sintering process took place in a controlled atmosphere of nitrogen (N2), at a temperature of 18500C. The experiments aimed to obtain ceramic plates based on SiC and Si3N4 doped with different sintering additives (Al2O3, Y2O3) and their characterization.
Physical-mechanical parameters were determined (bulk density, apparent porosity, water absorption, tensile strength and hardness). Mineralogical composition analysis was also carried out by X-ray diffraction for both composites. The results reflect the benefits of obtaining by plasma sintering method, because of the superior characteristics results comparing with those materials obtained by the classical method.
Keywords
ceramic composites, SiC, Si3N4, SPS sintering, physico-mechanical parameters
ANA MARIA LUNGU, ANDREI SÂRBU, VICTOR FRUTH, FLORIANA CONSTANTIN, MIRCEA TEODORESCU, NARTZISLAV PETROV
Abstract
A series of new inorganic/organic composites were synthesized by polymerization of acrylic acid in a concentrated aqueous suspension of alumina powder, using N,N’-methylenebisacrylamide as crosslinker. The inorganic/organic composites were characterized by scanning electron microscopy (SEM), thermal analysis (TGA/DTG), infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Composite materials, with a volumetric shrinkage ranging from 50 to 87% depending on the acrylic acid concentration, were obtained. By increasing the acrylic acid concentration, the compressive strength increased up to 230 MPa. It was demonstrated that these composite systems can form porous alumina ceramic materials with ~80% porosity after burning off the organic network.
Keywords
gelcasting, polymeric composites, alumina, acrylic acid, sintering, porous ceramics
DANIELA AURELIA PÎRVU, BOGDAN MIHAI GĂLBINAŞU, ION PĂTRAŞCU, CRISTINA FLORENTINA PÎRVU, DAN NIŢOI
Abstract
Self- adhesive cements are the lmost recent class of cements based on resin composites designed to secure the prosthetic restorations to dental tissues. Comparatively to classic cements based on resins, they are more attractive to dentists because there is no requirement for a preconditioning of the substrates. Nevertheless, their adhesive performance has been less evaluated.
The purpose of this study is to evaluate and compare the shear bond strength of the three resin self- adhesive cements: MaxcemElite (Kerr)- ME, Biscem (Bisco)- BC, Rely XU100 (3MEspe)- RU and a classic version of resin cement - Variolink II ( Ivoclar)- VL to ceramic substrates: glass matrix and zirconia.
The results evaluated by one-way ANOVA test indicated no statistically significant differences among the four cements in terms of adhesion to glass ceramics – the means of the values were: 14.33 MPa (SD+4.16)- ME, 17.55 MPa (SD+6.45)- BC, 21.45 MPa (SD+5.46)- RU and 21.40 MPa (SD+4.38)- VL. There are differences among the means of the values of the four groups analyzed (probability p <0.0001), the adhesion to zirconia: 4.9 MPa (SD+0.61)- ME, 10.84 MPa (SD+0.25)- BC, 8.2 MPa (SD+0.24)- RU and 15.65 MPa (SD+1.07)- VL.
Keywords
composite cements, glass ceramics, zirconia, shear bond strenght
PETRU BALTĂ
Abstract
This communication, having a review character of the works developed in the frame of the department Science and Engineering of the Oxidic Materials and Nano-Materials, begins with a short remembering of the problems of the oxide glass structure in the middle of the last century. A special attention is given to the concept elaborated by Professor Şerban Solacolu under the name quasicrystalline structure of glass. In the current year, a Nobel Prize was given for a theory with a similar name, elaborated for non-crystalline metallic alloys. In the department were studied the ideas concerning the chemical equilibrium in oxidic melts, which determine at high temperatures, the formation of a nano-heterogeneous structure with a certain aggregates distribution theoretically calculable which may be correlated with some properties of the resulted glass. An important progress was realized when an experimental method was elaborated for determining the basicity of these structural elements with the possibility to estimate their compositions and distribution. The principle of the experimental method is presented. The distribution of the nano-heterogeneous elements offers interesting information concerning the structure of glass and make possible correlations with properties. So is outlined the possibility to follow, even at the industrial level, the influences of some components of technology on the structure and properties of the produced glass.
Keywords
Professors’ Solacolu quasicrystalline structure of glass, studies of glass structure in our department, new SBD method for determination of the nano-heterogeneous aggregates distribution in glass
IOAN LAZĂU, COSMIN VANCEA
Abstract
Foam glass as a building construction material is competing with insulating polymeric and fiber materials as it is a good insulator. The low flammability, thermal stability and high chemical durability are a distinct advantage over polymeric materials. The possibility to produce foam glass using industrial wastes was investigated in this paper: three types of recycled glass wastes (window panes, bottle glass and glassware) together with fly ash were the main raw materials while SiC was used as foaming agent. Two different weight ratios glass waste: fly ash: SiC (80:10:10 and 70:20:10) were used for the foam glass synthesis. The raw materials as powders were mixed together with and then pressed into cylinders using ethylene glycol as binder. The heat treatment was conducted at 900°C for 5 and 10 minutes respectively. Optical microscopy, apparent porosity and apparent density and chemical stability of the foam glasses were used in order to characterize the obtained products as insulator materials for the building industry. The foam glasses obtained from a 5 minutes heat treatment process had an apparent porosity of 37.8-41.3% and an apparent density of 1.03-1.22 g/cm3 compared to those obtained from a 10 minutes heat treatment process, having an apparent porosity of 66.7-69.5% and apparent densities of 0.51-0.55 g/cm3. The obtained results confirm the alternative producing foam glass from glass wastes.
Keywords
thermal treatment, porosity, glass wastes, optical microscopy, insulator
ALINA MELINESCU, MARIA PREDA
Abstract
Porcelain stoneware is a high performance product with high wear resistance, used for floor tiles in high traffic areas. The final product must have a higher proportion of crystalline phase compared with the traditional ceramic floor tiles in order to obtain a good resistance. For this reason the chemical composition was chosen based on alkaline-earth oxides, which have the ability to form compounds with high speed of crystallization. Theoretically cordierite and mulltite have been chosen as the main mineralogical components which were widely varied. Samples were synthesized by pressing then heated (sintered) at 1200-13500C with 2 hours plateau at maximum sintering temperature (thermal treatment temperature).
On the thermally treated samples the variation of vitrification characteristics according to the thermal treatment temperature was determined. An appropriate behaviour to vitrification was observed for the samples with theoretical content of cordierite of 30-50%. The X-ray diffraction shows that at low temperatures (the cordierite is a major phase, but in low proportions magnesium spinel and mullite occur). The latter is a nonequilibrium compound that occurs as an intermediate phase in the formation of cordierite and entirely consumed over 1300°C. At temperature of 1300-1350°C remain crystalline only two components of equilibrium. Texture studies performed with electron microscopy revealed the presence of mullite as neddle form and cordierite as tabular form.
Keywords
mullite, cordierite, RX, SEM, porcelain stoneware
ALEXANDRA LUCIA CARABĂŢ, DANIELA BERGER, ŞERBAN GEORGESCU, SILVIU NĂSTASE, ŞTEFANIA STOLERIU, CRISTIAN MATEI
Abstract
Eu-doped lanthanum orthophosphate samples were prepared by precipitation in aqueous solution of lanthanide ions using different precipitation agents or applying a hydrothermal treatment. The influence of the precipitation parameters on the structure and morphology of La0.95Eu0.05PO4 was studied analyzing the samples by XRD, FTIR and SEM. La0.95Eu0.05PO4 synthesized by precipitation method presented rhabdophane structure, whereas the hydrothermal method leads to rhabdophane phase when H3PO4 was added in the synthesis and a mixture of rhabdophane and monazite phases when KH2PO4 or Na2HPO4 were used. The annealing step at 550°C/1h led to the monazite phase stabilization. The luminescent properties of La0.95Eu0.05PO4 samples were investigated.
Keywords
Eu-doped lanthanum orthophosphate, precipitation technique, hydrothermal treatment
CRISTINA BUSUIOC, SORIN ION JINGA, ECATERINA ANDRONESCU
Abstract
Ba(Mg1/3Ta2/3)O3 (BMT) compound is one of the most studied complex perovskite oxide with adequate properties for microwave applications, such as filters or antennas. BMT thin films were obtained by a modified sol-gel method, using the spin coating technique. Pt-coated Si or α-Al2O3 plates were used as substrates. X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy and atomic force microscopy were employed for compositional, structural and morphological characterization of BMT samples. BMT thin films present single-phase compositions and cubic structure. The dielectric properties of BMT thin films were investigated at low frequency.
Keywords
Sol-gel; Thin films; Dielectrics; Microwaves
VLAD IONUŢ LUNTRARU, CRISTINA MIHAELA BAICEA, CORNELIU TRIŞCĂ-RUSU, AURELIA CRISTINA NECHIFOR
Abstract
This paper presents the synthesis and characterization of iron particles covered with colloidal titanium dioxide and the functionalization of the TiO2 coated surface with cyanuric chloride. The synthesized materials were structurally characterized using Scanning Electron Microscopy, FT-IR spectroscopy and Energy-Dispersive X-ray spectroscopy.
Keywords
magnetic particles, titanium dioxide, cyanuric chloride
SILVANA BORCĂNESCU, IOAN LAZĂU, CORNELIA PĂCURARIU, ALEXANDRA JURCA
Abstract
The paper presents the results obtained in the mullite synthesis using the sol –gel method, starting from Si(OC2H5)4 (TEOS) and aluminum nitrate, respectively the sol-gel method combined with the combustion method. The combination of the two methods was achieved by addition urea, corresponding to the reaction with aluminum nitrate. The initiation of the combustion process was made by introducing the mixtures in the oven pre-heated at 500°C. The mullite formation requires further annealing at 1200°C, so in the case of the sol-gel method and in the combined version. The major difference between the two methods consist in avoiding the NOx release by using the combined version.
Keywords
sol-gel, combustion synthesis, X-ray method, mullite
MARIA GOREA, IOANA OLIVIA RUJONI
Abstract
Cordierite, Mg2Al4Si5O18, has a very low thermal expansion coefficient, thus a high resistance to thermal shocks. Accordingly, it is used in applications where high resistances to thermal shock, as well as chemical stability at high temperatures are essential; such is the case of Diesel particulate filters (DPF). This paper concerns the synthesis of cordierite by using the sol-gel method starting from two silicon-rich precursors: hydrophil aerosil and TEOS. When starting with TEOS, a magnesium carbonate basic pentahydrate and aluminium nitrate, a monomineralic powder consisting of cordierite is obtained at temperatures lower than 1000˚C. In order to obtain corresponding ceramics, these powders were sintered at temperatures in the 1000–1350˚C range. The thermal expansion coefficient decreased with firing temperature increase. The ceramics fired at 1300˚C were submitted to chemical attack by an alkaline mixture (one mole Na2CO3 with 1.5 moles SiO2) under so-called “less-severe” conditions, i.e., 900˚C and then under “severe” conditions at 1000˚C for 5 minutes. The SEM images evidence no corrosion in the first case, and slight corrosion features under the circumstance of the “severe” attack.
Keywords
Cuvinte cheie (engleza)
L. PALL, J-L. BOBET, E. ANDRONESCU
Abstract
The compounds synthesized in the ternary systems La-TM-B, Gd-TM-B et Y-TM-B (TM=Ni, Fe, Co) were studied in terms of their crystal structure, chemical composition and hydrogen sorption properties. Most of the compounds obtained in these systems crystallize with a CeCo4B type structure, with lattice parameters close to those of the compound GdNi4B. A total replacement of Ni by Fe and/or Co is sometimes possible, meaning that a total solid solution exists between RENi4B and REFe4B or RECo4B. Also, the boron is assumed to partially occupy two different crystallographic sites, although only one of these is mainly occupied by boron. The new phase GdNi2.5B2.5 was also observed in this study for the first time. In addition, a pseudo-binary phase GdB3 is observed. Finally, it is reported that only the compound LaNi4B absorbs hydrogen, albeit irreversibly.
Keywords
intermetallics, borides, ternary compounds