română DOREL RADU, ZENO GHIZDĂVEȚ
Abstract
Both endogenous and exogenous factors influence mechanical strength of oxide glasses. Thus, this property depends on the chemical-structural particularities of the vitreous system, and, also, on the measurement procedures. Due to the influence of random factors, in practice, mechanical strength has distributed values. For its evaluation, different statistical laws can be used.
In the paper, for a flat glass, four types of statistics are tested: the normal law (Gauss-Laplace), the Gamma law, the log-normal law and the Weibull law. Based on the experimental data, a series of statistical indices are calculated, and it is decided which statistical law better model data distribution.
Keywords
statistical analysis, mechanical strength, flat glass, probability distributions
ALINA IULIA DUMITRU, GEORGETA VELCIU, DELIA PĂTROI, JANA PINTEA, TUDOR-GABRIEL DUMITRU, ILDIKO PETER
Abstract
In this paper, some compositions belonging to the 0.98Pb(Zr1-xTix)O3 – 0.02La(Fe3+0.5, Nb5+0.5)O3 system have been investigated. The considered materials have been obtained by solid state reaction technique at high temperatures (1100°C, 1150°C, 1200°C and 1250°C). Three values of x (one in tetragonal region, one in Morphotropic Phase Boundary-MPB- region and one in rhombohedral region) have been chosen for the study in the range of 0.42 - 0.58. Sintering behaviour of the ferroelectric compositions has been studied by the experimental determination of the density by the method Archimedes. These ferroelectric compositions have been investigated in terms of their structural behaviour using X-ray diffraction (XRD) analysis. The XRD results have evidenced the formation of the perovskite type structure for all the studied compositions. The influence of theZr4+/Ti4+ ratio correlated to the sintering temperature on the degree of incorporation of the elements in the solid solution have been studied too. All the considered ferroelectric compositions have been characterized by a high anisotropy. The PZT modified compositions reveal that the piezoelectric properties are governed by the Zr4+/Ti4+ ratio and the sintering temperature too. For the electromechanical coupling factor (kp) the maximum value kp = 0.67 has been obtained for the composition with x = 0.58 and sintered at 1200°C.
Keywords
lead zirconate titanate (PZT) ceramics, ferroelectric compositions, high anisotropy, piezoelectric properties, dielectric properties
DORINEL TĂLPEANU, MAGDALENA VALENTINA LUNGU, DELIA PĂTROI, ANCA COJOCARU
Abstract
In this study were achieved advanced materials through the processing of some titanium-hydroxyapatite (Ti-HAp) powders by spark plasma sintering (SPS) technique. The Ti-HAp powders containing 95 wt.% Ti and 5 wt.% HAp were mechanically milled for 40 hours and then sintered at 900°C, 1000°C, and 1075°C for 10 minutes by SPS. The surfaces of the SPSed samples were finished by mirror polishing so that the final sizes were 20±0.05 mm in diameter and 4±0.3 mm in height. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The density was determined by Archimedes’ method in distilled water, and the mechanical properties were investigated by instrumented indentation testing and Oliver & Pharr method. The surface roughness Ra was determined by contact profilometry. The tribological tests included the measurement of the coefficient of friction (COF) in dry conditions. All sintered samples revealed crystalline phases, homogeneous microstructure, high density (4.45-4.52 g/cm3), low surface roughness Ra (0.07-0.14 µm), high Vickers hardness (786-879 HV), Young’s modulus of 111-137 GPa, elastic contact stiffness between 6.48 N/µm and 6.9 N/µm, and mean COF of up to 0.47. The properties were enhanced with the increase of the sintering temperature due to the advanced features of the SPS technique. Ti-HAp powder sintered at 1075°C revealed the best properties that recommend this material as a promising candidate in the development of medical applications.
Keywords
titanium, hydroxyapatite, Ti-HAp powders, spark plasma sintering (SPS)
ALINA IULIA DUMITRU, GEORGETA VELCIU, DELIA PĂTROI, JANA PINTEA, VIRGIL MARINESCU, TUDOR-GABRIEL DUMITRU, ILDIKO PETER
Abstract
In this paper, some compositions described by the general formula Pb(ZrλTi1-λ)1-3x/4FexO3 have been considered and investigated. The compositions selected have been obtained by solid state reaction, where x=0.01 and λ corresponds to 0.42, 0.52 and 0.58. The samples have been thermally treated in the range of 11000C -12500C and holded for 2 hours at the maximum temperature.
The influence of the sintering temperature on the microstructure and on the electrical properties of Fe3+ doped Pb(ZrλTi1-λ)O3 system has been investigated. The crystallographic phase and microstructure of the sintered compositions has been studied in detail using X-ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM). The experimental results obtained by XRD reveled that all the sintered samples have a perovskite structure. In order to correlate the behavior of the sintered materials to their microscopic structure, the domain structures have been defined by SEM. The dielectric properties, as dielectric permittivity (εr) and dielectric loss (tanδ) have been measured. The hysteresis loops at room temperature of all un-poled sintered compositions reveal a similar behaviour with “hard” PZT ceramics. The piezoelectric properties like electromechanical coupling factors (kp and kt) and the anisotropy (kt/kp) have been investigated after polarization. The results obtained from such investigations pointed out that some sintered compositions can be successfully proposed as good candidate for targets, materials to be deposited, employed for different applications as ceramic coatings in some deposition technology.
Keywords
doped PZT, dielectric properties, piezoelectric properties, ferroelectric properties
NICOLAE CONSTANTIN, ADRIAN IOANA, DANIELA TUFEANU, LUCIAN PĂUNESCU, DRAGOȘ FLORIN MARCU, BOGDAN FLOREA
Abstract
The paper presents experimental results obtained in the manufacturing process of a glass foam obtained from the recycling of glass from cathode ray tubes (CRT). The glass foam samples were performed experimentally by the sintering-foaming process. The heating technique was unconventional, the energy provided by the microwave was used as a heat source. The process is different from the conventional techniques applied both in the manufacture of industrial glass foam and in the numerous small-scale experiments known in the literature. The glass foam samples obtained were characterized by traditional methods of analysis. The main characteristics were bulk density, porosity, thermal conductivity, compressive strength, water absorption and microstructural configuration of the samples. The experimental results proved that the applied process obtained a glass foam with good characteristics (porosity of 90%, thermal conductivity of 0.042 W / m-1 • K-1 and compressive strength of 2.1 MPa) usable in construction.
Keywords
separation, recycling, glass waste, microwave field
MARIA PREDA, ILEANA RĂU, ALINA CORNELIA BACIU, CRISTIAN COVACIU, ALINA MELINESCU
Abstract
Tialite (Al2TiO5) is a known compound for its excellent mechanical properties and it is used in many fields. However, it should be noted that this compound has a very good chemical stability against silicate melts, so lately it has been used for obtaining ceramic pigments. In this paper, three samples were synthesized in the ternary pseudosystem MgAl2O4-CoAl2O4-Al2TiO5, which were heat treated at temperatures between 1200 and 1450°C. The mineralogical composition of the samples was determined by X-ray diffraction. The pigments obtained were introduced into the matte glaze in a proportion of 2%. The chromatic characterization both pigments and the coloured glaze was realised by the CIELab method.
Keywords
aluminium titanate, pigment, DRX, CIELab