Preparation of amorphous aluminium ammonium phosphates
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Preparation of amorphous aluminium ammonium phosphates Barbara Grzmil, Kinga Łuczka and Marta Gleń West Pomeranian University of Technology, Szczecin, Institute of Chemical and Environment Engineering, 70-322 Szczecin, Pułaskiego 10, E-mail: [email protected] ABSTRACT A method for obtaining of amorphous aluminium ammonium phosphates is developed. The statistical program STATISTICA 9 is used for planning and evaluation of the experiments. Research is carried out according to the Box-Behnken model for the following values of independent variables (input factors): pH: 6.0 ± 2; concentration of reagents: 40 ± 10 wt%, molar ratio of NH4+:PO43- in substrates (2 ± 1:1) i.e. Al3+:NH4+:PO43- (0.66:1-3:1). On the basis of this research, process parameters are determined, in which materials with the expected physicochemical properties (chemical composition, specific surface area, oil absorption number) can be obtained. INTRODUCTION The most commonly used pigments having good anticorrosive properties are minium (mixture of lead oxides) and zinc chromate. Due to the environmental reasons these pigments are no longer desired. Other pigments providing coatings with suitable anticorrosive properties are borates, molybdates, ferrites, zinc powder, and phosphates (I, II and III generation) [1,2]. It is claimed that the introduction of the molybdenum anion brings a beneficial effect to the increase of effectiveness of the phosphate pigments [3,4]. The anticorrosive effectiveness of phosphate pigments is tested in various types of paints [5-11]. Zubielewicz and Gnot [6] conclude that calcium zinc phosphate and zinc ferrite have the best performance as a result of steel surface passivation. It is shown [8] that generation II phosphates (aluminium zinc phosphate, iron (II) zinc phosphate, zinc phosphormolybdate), used in acidic medium, are characterized by the improved corrosion inhibiting properties which are similar to zinc chromate. Aluminum phosphate is also used as an anticorrosive pigment. It is also used as a catalyst, catalyst support, high-temperature binder material, raw material for ceramics and optical glasses production or as an absorbent in medicine. Burrell et al. [11] pointed out the difficulty in obtaining of aluminum phosphates with repeatable properties. Mesoporous material with high surface area, narrow pore size distribution and high thermal stability is obtained [12]. In other publications [13-15], studies on the obtaining of amorphous, crystalline and nanocrystalline aluminum phosphate pigments are presented. Preparation and structure of aluminium ammonium dihydrate hydroxyphosphates used in molecular sieves are discussed [16]. Stability of aluminum phosphates in the NH3-Al2O3-P2O5-H2O system is studied [17]. In the publication [18], methods for obtaining of aluminium ammonium phosphates (NH4)2-x(H3O)x Al2(PO4)2(OH)2, (NH4)3Al2(PO4)3 and (NH4)3Al(PO4)2 are described. Anticorrosive properties of phosphates can result from their strong complexing power [5]. They can form complexes with both metal cations and
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