The crystal structure of Mn-anorthite synthesized by ion-exchange zeolite with LTA and FAU topology

Abstract

The most common zeolites which are used as precursors for ceramic materials are synthetic zeolites of LTA, FAU or GIS topology. Eberhard presented the first data for synthetic feldspars MnAl2Si2O8 [1], while Matsui and Kimata presented the structural results of investigation in the three component system MnAl2Si2O8−CaAl2Si2O8−SrAl2Si2O8 [2]. Thermally induced phase transformation of Mn-exchange LTA and FAU zeolites are followed in the range from room temperature to 1300 ºC. Both frameworks collapse into amorphous intermediate products after heating between 600 and 650 °C. Prolonged heating of the intermediate product over 1100°C results directly in formation of a disorder Mn anorthite LTA [a = 8.10 95(4) Å, b = 12.824(4) Å, c = 7.0674(4) Å, β = 115.89(3)] and Mn anorthite FAU [a = 8.0498(4) Å, b = 12.758(4) Å, c = 7.0356(4) Å, β =116.13(3)] phase. The phase conversions in the temperature range investigated were followed by thermal (DTA, TGA, and DSC) and FTIR analyses. The crystal structures of both anorthite phases are refined by Rietveld method against X- ray powder diffraction data (Figure 1).

Najčešći zeoliti koji se koriste kao prekursori za keramičke materijale su sintetički zeoliti sa LTA, FAU ili GIS topologijom. Eberhard je prvi publikovao strukturne podatke za sintetičke feldspate, sa formulom MnAl2Si2O8 [1], dok su Matsui i Kimata prvi predstavili strukturne podatke za trokomponentni sistem, sa bruto formulom MnAl2Si2O8−CaAl2Si2O8−SrAl2Si2O8 [2]. Termički indukovane fazne transformacije LTA i FAU zeolita sa izmenjenim Mn, praćene su u opsegu temperatura od sobne do 1300 ºC. Kolaps u amorfnim intermedijerima kod oba tipa zeolita se javlja nakon zagrevanja između 600 i 650 °C. Produženo zagrevanje intermedijernog proizvoda preko 1100 °C rezultatira direktnom formiranju disordera u Mn-anortit-LTA [a = 8.1095(4) Å, b = 12.824(4) Å, c = 7.0674(4) Å, β = 115.89(3)] i Mn-anortit-FAU fazi [a = 8.0498(4) Å, b = 12.758(4) Å, c = 7.0356(4) Å, β = 116.13(3)]. Fazni prelazi u ispitivanom temperaturnom opsegu praćena je primenom termalne (DTA, TGA i DSC) i FTIR analize. Kristalne strukture oba anortita su utačnjene korišćenjem Ritveldove metode (slika 1), primenjene na podatke prikupljene rendgenskom difrakcijom sa polikristalnih materijala.