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V.R. DEJEU, R. BARABÁS, AL. POP, E.S. BOGYA, P.-Ş. AGACHI At pH = 8.5 the proposed model fits well with experimental data only until 20 % conversion (at 20 0 C) and until 40 % (at 50 0 C). η 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 exp20 teo20 exp50 teo50 pH=9,7 0 0.5 1 1.5 2 2.5 3 x 10 4 0 time [s] Figure 3. The variation of conversion in time at 20 0 C and 50 0 C at pH = 9.7 CONCLUSIONS Based on the kinetic study regarding the transformation process of beta-whitlockite in HAP the mathematical model of this process was established. The implementation of the model for three particular cases led to equations, which were used to calculate the numerical values of K1, K2 and K3 constants, based on experimental data. The process simulation using the mathematical model indicate that this could be described using the equation: − ⋅τ 2 K2 η =1-e , which corresponds to a combined macrokinetic mechanism: 2+ 3- transfer (transfer of Ca and PO 4 ions towards the HAP crystal surface) – mass transformation (formation and growing of HAP nuclei) EXPERIMENTAL SECTION For the synthesis of HAP and the kinetic study for the transformation of beta-whitlockite in hydroxyapatite, reactants of analytical purity were used: calcium nitrate tetra hydrate, bi-ammonia phosphate and ammonia solution 28 %.The concentration of the calcium nitrate solution was 0.5 mol/L and by adding ammonia solution the pH was turned to the value of 8.5. The concentration of the bi-ammonia phosphate solution was 0.3 mol/L and to this solution was added the necessary amount of ammonia to reach the pH values presented in Table 1. In all the experiments the phosphate solution 68
MATHEMATICAL MODELING FOR THE CRYSTALLIZATION PROCESS OF HYDROXYAPATITE … was added in drops over the calcium nitrate solution. The ammonia losses were avoided by fixing a closed ascending refrigerator and a hydraulic closing to the reaction vessel. The temperature was measured and maintained constant with a thermostat. From time to time, during the reaction, samples were taken, filtered, washed with distillated water and dried at 105 0 C until constant weight. The dried samples were crushed into fine powders with d p
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R /(mol m -2 s -1 ) 0.06 0.05 0.04
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ANA-MARIA CORMOS, JOZSEF GASPAR, AN
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Studia Universitatis Babes-Bolyai C
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6 PROFESSOR IOAN BÂLDEA AT HIS 70
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MARCELA ACHIM, DANA MUNTEAN, LAURIA
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Page 15 and 16: STUDIA UNIVERSITATIS BABEŞ-BOLYAI,
Page 17 and 18: STUDIES ON WO3 THIN FILMS PREPARED
Page 25 and 26: PREPARATION AND CHARACTERIZATION OF
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Page 35 and 36: C. CĂŢĂNAŞ, M. MOGOŞ, D. HORVA
Page 37 and 38: 38 ANA-MARIA CORMOS, JOZSEF GASPAR,
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Page 49 and 50: 50 EUGEN DARVASI, LADISLAU KÉKEDY-
Page 61 and 62: MATHEMATICAL MODELING FOR THE CRYST
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Page 71 and 72: STUDY OF THE CHROMATOGRAPHIC RETENT
Page 81 and 82: LOWER RIM SILYL SUBSTITUTED CALIX[8
Page 89 and 90: THE INTERACTION OF SILVER NANOPARTI
Page 97 and 98: OPTIMISATION OF COPPER REMOVAL FROM
Page 105 and 106: MELINDA-HAYDEE KOVACS, DUMITRU RIST
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IRON DOPED CARBON AEROGEL AS CATALY
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128 ANDRADA MĂICĂNEANU, HOREA BED
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ANDRADA MĂICĂNEANU, HOREA BEDELEA
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CRISTINA MIHALI, GABRIELA OPREA, EL
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144 CRISTINA MIHALI, GABRIELA OPREA
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146 Interfering ion, J - I - DBS -
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CONCLUSIONS 148 CRISTINA MIHALI, GA
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150 CRISTINA MIHALI, GABRIELA OPREA
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152 D. MIHU, L. VLASE, S. IMRE, C.
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154 Intens. x105 1.5 1.0 0.5 0.0 x1
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D. MIHU, L. VLASE, S. IMRE, C. M. M
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162 A. PETER, M. BAIA, F. TODERAS,
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164 (a) V relative [%] (c) V relati
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A. PETER, M. BAIA, F. TODERAS, M. L
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STUDIA UNIVERSITATIS BABEŞ-BOLYAI,
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BIOSORPTION OF PHENOL FROM AQUEOUS
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186 ANDREI ROTARU, MIHAI GOŞA, EUG
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ANDREI ROTARU, MIHAI GOŞA, EUGEN S
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194 OCTAVIAN STAICU, VALENTIN MUNTE
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ln(τ i / s) OCTAVIAN STAICU, VALEN
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204 MARIA ŞTEFAN, IOAN BÂLDEA, RO
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EXPERIMENTAL SECTION 210 MARIA ŞTE
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EQUILIBRIUM STUDY ON ADSORPTION PRO
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STRATEGIES OF HEAVY METAL UPTAKE BY
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CORROSION INHIBITION OF BRONZE BY A
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E / mV vs. SCE POTASSIUM-SELECTIVE
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POTASSIUM-SELECTIVE ELECTRODE BASED
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POTASSIUM-SELECTIVE ELECTRODE BASED
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256 CODRUTA VARODI, DELIA GLIGOR, L
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CODRUTA VARODI, DELIA GLIGOR, LEVEN
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PHARMACOKINETIC INTERACTION BETWEEN
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