Nanostructured surfaces

Obtaining zirconium-silicate aerogels by alco-thermal
treatment of hydrogels
M.V. Kravchenko, A.V. Redkina, N.D. Konovalova, V.V. Strelko
Institute for Sorption and Problems of Endoecology, Ukr ainian National Academy of Sciences, 13 General Naumov Street, Kyiv 03164, Ukraine, 
E-mail: email.of. corresponding nikolaikravchenko32@gmail.com

Zirconium-silicate aerogels with high porosity and high specific surface, low density and low thermal conductivity, strong energy of Zr-O-Si bind can serve as excellent sorbents, catalyst carriers and thermoinsulating materials. In this work, an attempt was made to obtain Zr-Si–aerogels from spherically granulated hydrogels synthesized by the direct sol-gel method by alternating their hydrothermal, alcohol, and alco-thermal treatments. The thermal stability of samples was evaluated by the change their density and structural-adsorption properties, measured by N2 adsorption / desorption, after they were calcined in air. The results are shown in the table.

Parameters of spherically granulated gels 0,6 Zr-Si after various treatment 
Preliminary processing	SBET, 
m2/g	Vpore, 
сm3/g	Rpore 
DFT, Е	W,
g/сm3	SBET, % wastage	
Drying at 130 oC  (D)	389,3	0,25	12,52	1,33		
Calcination at 600 oC  (C)	219,9	0,16	14,39		43,51	
НTТ* at 270 oС - 5 h. (D)	517,5	0,60	28,41	1,05		
НTТ - 5 h. (D, C)	414,7	0,49	35,16		19,86	
НTТ - 2 h. Ethanol. (D)	540,8	1,15	47,08	0,40		
НTТ - 2 h. Ethanol. (D, C)	450,3	0,83	47,08		16,59	
НTТ - 2 h. Ethanol + 2 % petrol. (D) 	549,1	1,98	126,2	0,26		
НTТ - 2 h. Ethanol + petrol. (D, C)	485,8	1,81	136,9		11,53	
ATТ** in Ethanol +2 % petrol - 5 h. (D)	511,0	2,26	136,9	0,22		
ATТ in Ethanol +2 % petrol - 5 h. (D, C)	494,3	2,00	136,9		3,27	
*- hydrothermal treatment at 270 oС; **- alcothermal treatment at 270 oС.

It is shown that strengthening the gel structure by its НТТ contributes to the growth of the surface area, volume and width of pores and more than doubles its thermal stability. Additional decantation with ethanol leads to a substantial increase in the volume and width of the pores, an increase in thermal stability of the samples, and reduces their density, even with a shorter duration of the НТТ. The introduction of petrol impurities into ethanol, and even more ATТ of samples in this mixture, leads to production of thermostable materials with a density < 0.3 g/cm3 and pores D > 27 nm, which is characteristic of metal oxide silica aerogels.