Studies on obtaining of aluminium phosphates modified with ammonium, calcium and molybdenum

Studies on obtaining of aluminium phosphates modified with ammonium, calcium and molybdenum were implemented. Reagent grade substrates (NH4)2HPO4, CaCO3, (NH4)6Mo7O24·4H2O, aqueous ammonia, and amorphous Al(OH)3 were prepared and used in the experiments. An influence of process parameters, i.e. reaction time (60 ± 30 min) and total salt concentration (50 ± 10 wt%) on the phase composition and product properties was determined. Statistical software STATISTICA 10 for planning and evaluation of the experiments was used. Based on the statistical evaluation of planned research by the plan fractional factorial design at three levels 3(k−p), process parameters allowing to obtain the material of with expected physicochemical properties were determined. The content of aluminium, calcium and molybdenum in the products was determined using ICP-AES technique. The phosphates and ammonium content was determined by means of a spectrophotometric method and ion selective electrode Orion 11–35 type, respectively. The phase composition of the obtained materials was studied using XRD analysis. The specific surface area was calculated using the BET method and the particle size was determined by LSM. The Tafel experiments for an uncoated mild steel (immersed in an aqueous phosphate extract in 3.5 wt% NaCl solution) were performed. The steel corrosion products as well as tested phosphates were examined by means of scanning electron microscope with a cold field emission coupled with the energy dispersive X-ray analyzer. The content of the individual components was in the range of 10.52–16.33 wt% (Al), 10.59–18.54 wt% (Ca), 0.59–5.28 wt% (Mo), 0.1–4.91 wt% (NH3), and 6.97–23.4 wt% (P2O5). The products were characterized by different physicochemical parameters. The surface area was in the range from 6 to 63 m2/g and the oil absorption was 36–71 g of oil/100 g of product, whereas the average particle size of products reached 221–319 nm. The Tafel tests revealed markedly higher anticorrosive properties of aluminium phosphates modified with ammonium, calcium, molybdenum in comparison to commercial aluminium phosphate and zinc phosphate.