A poch poland altogether 05 mol of mgno32 6 h2o 99

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Unformatted text preview: nd if necessary also of a freshly prepared 2 M NaOH solutions (p.a., POCh, Poland). Altogether 0.5 mol of Mg(NO3)2· 6 H2O (99%, Aldrich), Ni(NO3)2· 6 H2O (Crystal, Aldrich) and Al(NO3)3· 9 H2O (99.997, Aldrich) were dissolved in 500 ml distilled water. The exact ratio of their amounts reflected the desired metal composition of the final HT. Due to their hydrate water the volume of the resulting metal nitrate solution was in all experiments about 600 ml, hence the metal concentration of the metal nitrate solution < 1 mol/l. After the reaction temperature was reached and the pH adjusted, the metal nitrates containing solution was continuously added dropwise to the reaction vessel by a peristaltic micro pump (Zalimp, Poland) at a speed of approximately 4 ml/min. The decrease in the pH value caused by the addition of the acidic metal nitrate solution was compensated by the pH controlled dropwise addition of a freshly prepared 2 M NaOH solution using a diaphragm pump (Cole Parmer, USA). The diaphragm pump was 2. Experimental 54 ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff automatically activated by the pH controller as soon as the pH value reached 7.9 and deactivated at pH 8.1. Following this procedure it was possible to keep the pH-value constant at pH 8 ± 0.2 during all coprecipitations. During the whole addition, which typically last 150 min the reaction mixture was stirred vigorously and the temperature kept at 60-70°C by a conventional 6 stage heating plate. After the addition the coprecipitated solid was aged by keeping the solution under energetic stirring for 120 min at 60-70°. Afterwards the suspension was allowed to settle and to cool down to 30°C before being filtered under water pump vacuum. For the effective removal of all the sodium salts (NaNO3, NaHCO3 and especially less soluble Na2CO3) possibly present in the precipitate, it was suspended in 500 ml distilled water under vigorous stirring and filtered again. As all these sodium salts are basic, the changes in the pH valu...
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