Authors:Titus Vlase, Constantin Bolcu, Gabriela Vlase, Alin Mogoş, and Nicolae Doca
Samples of flexible PU foam were prepared from a polyol (Elastoflex W 5516/115) and an isocyanate prepolymer (Iso 145/8),
both commercial Elastogram products. For the thermooxidative stabilization, two phenolic compounds were used, separately or
in mixture. These compounds were: 2,6-di-t-butyl-4-methyl-phenol (non-reactive) (AO-1), 3,5-di-t-butyl-4-hydroxy-benzyl alcohol
(reactive, AO-2), used in total mass% of 0.3/1.5. The TG/DTG/DTA curves were drawn up in dynamic air, with a heating rate
of 10 °C min−1, until 500 °C. For the unstabilized sample a single thermodegradative TG step, with a maximum rate at 268–270 °C was observed,
whereas for the stabilized samples, supplementary steps at higher temperature were observed. The changes in the TG/DTG/DTA
parameters are not in a single relationship with the mass% of the stabilizator, due to the following: AO-1 is easily migrated
out from PV, especially, at higher concentrations. AO-2 had positive effect at all studied concentrations. But the most remarkable
effect is the synergetic effect of a 1:1 mixture of AO-1 and AO-2.
Authors:Adriana Fuliaş, Titus Vlase, Gabriela Vlase, and Nicolae Doca
The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate,
starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min−1. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min−1. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears.
These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic
analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates:
5, 7, 10 and 12 °C min−1. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a
nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion
dependence on the reaction rate and less speculative discussions on the kinetic model. All there methods had furnished very
near values of the activation energy, this being an argument for a single thermooxidative degradation at the beginning (192–200 °C).
Authors:Alexandra Ioana Bucur, Raul Bucur, Titus Vlase, and Nicolae Doca
Calcium phosphate biomaterials have long ago attracted the interest of world-wide scientists because they form the main inorganic constituent of the human bones and teeth. Classical approaches to synthesize this ceramic material did not give satisfactory results until present, so new approaches are required. In this article the tricalcium phosphate achievement by a method which is a combination of sol–gel and classic precipitation from solution is presented, starting from CaCl2 as calcium precursor and H3PO4 as phosphorus precursor, without pH adjustment. The reaction mixture was allowed to maturate for 2 months, the time influence on the precipitated material being presented in previous articles. Present studies aimed at the influence of temperature on the structural characteristics of precipitated and maturated material, by means of thermal analysis, X-ray diffraction, infrared spectroscopy, and high-temperature X-ray diffraction. A complex type thermal decomposition takes place while heating the sample to 1000 °C, with superposed and parallel processes. The sample goes through alternative amorphous and crystalline stages before final crystallization of β-tricalcium phosphate takes place. The high-temperature XRD studies offered the great advantage of being both a synthesis and a physico-chemical characterization technique, which along with thermal analysis and infrared spectroscopy, gave a lot of useful information in a very short time.
Authors:Oana Ştefănescu, Marcela Stoia, Mircea Ştefănescu, and Titus Vlase
Hybrid organic–inorganic materials, silica–diol, were synthesized by the sol–gel process from mixtures of tetraethylorthosilicate
(TEOS) and diols: ethylene glycol (HO–CH2–CH2–OH) and 1,3 propane diol (HO–CH2–CH2–CH2–OH), in acid catalysis. The gels have been synthesized for a molar ratio H2O:TEOS = 4:1 and different molar ratios diol/TEOS: 0.25; 0.5; 0.75; 1.0; 1.25 and 1.5. The resulting gels were studied by
thermal analysis and FT-IR spectroscopy, in order to evidence the interaction of diols with silica matrix. Thermal analysis
indicated that the condensation degree increases with the molar ratio diol/TEOS until a certain value. The thermal decomposition
of the organic chains bonded within the silica network in the temperature range 250–320 °C, leaded to a silica matrix with
modified morphology. The adsorption–desorption isotherms type is different for the samples with and without diol. Thus, the
specific surface areas have values <11 m2/g for the samples without diol and >200 m2/g for the samples with diols, depending on the annealing temperature.
Authors:Adina-Maria Bodescu, Cecilia Sîrghie, Titus Vlase, and Nicolae Doca
Synthesis, characterizations, and thermal behavior of Na2[MoO(O2)2(C2O4)] was studied. The thermally induced events will be observed by comparing the FT-IR spectra of the initial compound and of the char at 300 and 500 °C. The TG data were obtained at different heating rates: β = 2.5, 4, 5, and 10 °C min−1 in air and nitrogen (50 mL min−1), and the TG/DTG data were processed with the following methods: Friedman, Flynn–Wall–Ozawa, and modified NPK method.
Authors:Gheorghe Ilia, Madalina Drehe, Titus Vlase, Gabriela Vlase, Lavinia Macarie, and Nicolae Doca
Metal or metal oxide nanoparticles possess unique features compared to equivalent larger-scale materials. In this paper we
present the synthesis of grafted titania with phosphonic acids, their characterization and an extended non-isothermal kinetic
study. The obtained results show that there in no significant difference between acids and esters in grafting reaction. The
phosphorus content wary between 0.9 and 1.80% and is comparable with literature data. IR and AFM studies confirmed the formation
of grafted titania. Extended non-isothermal kinetic study using different methods confirmed the complexity of thermooxidative
degradation processes in non-isothermal conditions.