The Ceramic Humidity Sensors on the Base of MgAL₂O₄

Application of New Organic Fuels in the Direct MgAl2O4 Combustion Synthesis

“…In addition, the sample displays another important weight loss at about 460°C, which can be assigned to the decomposition of unreacted Mg(NO 3 ) 2 ( Figure 4). This observation is in excellent consistency with the preliminary results according to which urea does not react with Mg(NO 3 ) 2 (Table 1). In this case, Mg(NO 3 ) 2 acts as an inhibitor, as a diluting medium, preventing the occurrence of the combustion reaction between Al(NO 3 ) 3 and urea.…”

“…Unlike Al(NO 3 ) 3 , which reacts very slowly with β-alanine or TETA, Mg(NO 3 ) 2 reacts very fast with TETA and explosively with β-alanine (Table 1). This experimental observation emphasizes once again that there are significant dis- In order to establish the most appropriate fuel for Mg(NO 3 ) 2 , it had been assumed that the average crystallite size of MgO obtained by using different fuels reflects the global effect of all the parameters which govern the nucleation and crystal growth processes specific to the combustion synthesis [Equation (15); D = average crystallite size, ∆ r H = reaction enthalpy, τ = duration of the combustion reaction, V = amount of combustion-generated gases].…”

“…From this point of view, these results are in consistency with those reported by other authors. [16,[23][24][25][26] The amorphous character of the powders obtained by using a single fuel represents conclusive evidence, which stands for the hypothesis that Mg(NO 3 ) 2 and Al(NO 3 ) 3 exhibit an essentially different behaviour with respect to the same fuel. As a result, when a single fuel is used for the synthesis of MgAl 2 O 4 , be it MEA -the most suitable fuel for Mg(NO 3 ) 2 -or be it urea -the most appropriate fuel for Al(NO 3 ) 3 -one of the two metal nitrates will act as a moderator or as an inhibitor of the combustion reaction.…”

“…Starting from the experimental results presented above, which have proven that Mg(NO 3 ) 2 and Al(NO 3 ) 3 exhibit a completely different behaviour with respect to the same fuel, the next step consisted in the MgAl 2 O 4 combustion synthesis. Nine procedures have ben designed: the first seven procedures correspond to the initial version of the combustion synthesis involving the use of a single fuel (reactions 16-22) whereas procedures 8 and 9 are the optimised ones, where two-fuel mixtures have been used: urea and MEA (reaction 23), urea and β-alanine (reaction 24).…”

“…Because of these valuable properties, MgAl 2 O 4 represents a ceramic material frequently used in many different applications: catalysts support, [1] humidity sensors, [2][3][4] nuclear technique, [5] refractory materials, [6,7] dentistry [8] etc. One of the major problems that appear during the fabrication of this kind of materials is related to the synthesis of cheap high-reactivity MgAl 2 O 4 powders.…”