2 3.597 2 2 0 3.597. 26.27. 2 3.389 1 2 -1 3.391. 25.17. 2 3.535 2 -1 -1 3.535. 26.45. 6 3.367 3 0 1 3.366. 25.93 12 3.433 2 1 1 3.434. 26.51. 8 3.359 2 -2 0 3.359.
Phosphorus Research Bulletin (2002), Vol. 13, pp. 227-230
BINARY TETRAPHOSPHATES M(NH4)2P4O13 (M = Si, Ge, Sn, or Ti): SYNTHESIS IN THE AMMONIUM POLYPHOSPHATE MELT AND THERMAL BEHAVIOUR
A.F. SELEVICH, L.S. IVASHKEVICH, K.I. KHURS, A.S. LYAKHOV, AND A.I. LESNIKOVICH Physico-Chemical Research Institute of Belarusian State University, Leningradskaya 14, Minsk, 220050, Belarus Abstract Reactions of MO2–nH2O (M = Si, Ge, Sn, Ti, Zr, or Hf) with NH4PO3 have been studied in the 200º 400 ÅC range. Conditions of formation for tetraphosphates M(NH4)2P4O13 (M = Si, Ge, Sn, or Ti) have been elaborated. XRD studies have been performed for powder Ti(NH4)2P4O13 [triclinic, space group P 1 , with a = 15.03(1), b = 7.933(1), c = 5.079(2) A ; β= 99.15(3), γ = 97.05(3), ° = 83.41(3)°] and Sn(NH4)2P4O13 [triclinic, space group P 1 , with a = 15.15(1), b = 8.010(4), c = 5.107(7) A ; β = 99.90(2), γ = 96.82(3), ° = 83.87(7)°]. Thermal behaviour of the tetraphosphates has been investigated in the 20º 1000 °C range.
INTRODUCTION Binary metal-ammonium condensed phosphates provide high flame retardancy of interest in thermoplastics based on polyamides.1, 2 Ti(NH4)2P4O13 reveals the best flame retardant properties among investigated binary ammonium-containing phosphates.2 It was synthesized by reaction of TiO2–nH2O with NH4PO3.3 Two isotypical compounds, Si(NH4)2P4O13 and Ge(NH4)2P4O13, were obtained earlier by heating mixtures of (NH4)2HPO4 and corresponding hydrated oxide.4º 6 It was expected that these tetraphosphates also would reveal the fire retardant properties, however their physico-chemical characteristics were not studied. The aim of this work was to study the reactions of MO2–nH2O (M = Si, Ti, Ge, Sn, Zr, or Hf) with the NH4PO3 melt, to develop a convenient technique for synthesis of known and novel tetravalent metal-ammonium tetraphosphates, to characterize obtained M(NH4)2P4O13 compounds and to investigate their thermal behaviour. EXPERIMENTAL PROCEDURE Hydrated oxides MO2–nH2O (M = Si, Ti, Ge, Sn, Zr, or Hf) and NH4PO3 (APP) (all reagent-grade products) were used as starting materials. Reactions of MO2–nH2O with NH4PO3 were studied within the temperature range of 200º 400 ÅC at the molar ratio P2O5 : MO2 = (2º 5):1. Mixtures of APP with one of the above oxides were isothermally held at 200º 400 °C in air for several days. Progress of the reactions was monitored by periodic sampling using X-ray diffraction (XRD) and optical microscopy. Isolated compounds were identified by XRD, chemical analysis, and quantitative thin-layer chromatography. X-ray powder diffraction data were obtained with HZG 4A powder diffractometer (Carl Zeiss, Jena). The CuKβ radiation was selected by a Ni fil222
ter. The powder diffraction patterns were scanned in a step mode with step width of 0.02° (2香 ). Indexing of the diffraction pattern was performed with the programs ITO 7 and TREOR90.8 Standard procedures were used for chemical analysis of Si, Ti, Ge and Sn by gravimetry, red-ox titration or colorimetry; of ammonia by the Keldal method, of phosphorus by colorimetry.9 Thermal analysis was carried out by using the Mettler TA 3000 thermoanalyzer at a heating rate of 10 ÅC/min in steady-state air atmosphere. RESULTS AND DISCUSSION SiO2º NH4PO3 system. According to XRD, APP reacts distinctly with SiO2–nH2O over 220º 250 °C giving Si(NH4)2P4O13. However over 350 °C low-temperature monoclinic SiP2O710 was detected in the reaction products. It was found the 280º 340 ÅC range and the molar ratio APP:SiO2 = (6º 8):1 are optimal for Si(NH4)2P4O13 preparation. GeO2º NH4PO3 system. Reactions of APP with GeO2–nH2O are similar to those considered above. The 280º 320 °C range and the molar ratio APP:GeO2 = (5º 7):1 were found to be optimal for preparation of Ge(NH4)2P4O13. Low-temperature monoclinic GeP2O7 was detected in mixtures over 350 °C.11 TiO2º NH4PO3 system. The TiO2º NH4PO3 system differs slightly from those mentioned above. Ti(NH4)2P4O13 crystallizes over 220º 240 éC. However, over 320º 330éC traces of cubic TiP2O7 12 are also registered, its amount rising quickly with the temperature increasing. Probably, it was the reason why the correct powder XRD data of Ti(NH4)2P4O13 were not obtained earlier.3 The optimal conditions for preparation of Ti(NH4)2P4O13 are the 270º 310 °C range and the molar ratio APP:TiO2 = (5º 7):1. Powder XRD data of Ti(NH4)2P4O13 are shown in the Table 1. Main crystallographic characteristics are given in Table 2. A comparison of the XRD data of this compound with those of Si(NH4)2P4O13 and Ge(NH4)2P4O13 indicates that all they are isotypical. SnO2º NH4PO3 system. According to XRD data, the temperature range of crystallization of binary tin-ammonium tetraphosphate is essentially narrower than that in the systems discussed above. The 270º 300 ÅC range and the molar ratio APP : SnO2 = (5º 7):1 were found to be optimal for Sn(NH4)2P4O13 preparation. Over 310º 320°C cubic SnP2O7 12 is dominant crystalline phase in the system. The indexing procedure results of Sn(NH4)2P4O13 are presented in Table 1. Main crystallographic features of this salt are given in Table 2. A comparison of the XRD data of this tetraphosphate with those of M(NH4)2P4O13 (M = Si, Ge, or Ti) shows that all they are isotypical. Zr(Hf)O2º NH4PO3 systems. Main crystalline phase detected in the Zr(Hf)O2º NH4PO3 systems is cubic Zr(Hf)P2O7.12 XRD data allows to suggest that extremely metastable M(NH4)2P4O13 (M = Zr, Hf) are also presented in the reaction products. However, they could not be isolated in this investigation. Thermal behavior is an important characteristic of compound used as flame retardant additive. Figure 1 shows thermogravimetric curves of the binary tetraphosphates obtained. As seen, they are stable up to 380 °C (Si), 360 °C (Ge), 340º 345 °C (Ti and Sn). All compounds decompose similarly in two stages. They loss ammonia up to 500 °C (1st stage) giving mixtures of polyphosphoric acids and low-temperature monoclinic MP2O7 for M = Si, Ge and cubic MP2O7 for M = Ti, Sn. Polyphosphoric acids evaporate at the 550º 750 °C (2nd stage), final products of decomposition being cubic MP2O7 for M = Ti and Sn,12 triclinic GeP2O7 13 and high-temperature monoclinic SiP2O7.10 The data obtained allow to conclude that Si(NH4)2P4O13 as well as Ti(NH4)2P4O13 having high chemical stability may be used as flame retardant additives.
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TABLE 1 X-ray powder diffraction data of Ti(NH4)2P4O13 and Sn(NH4)2P4O13. Ti(NH4)2P4O13 2香 I, % dobs., A h k 11.34 2 7.796 0 1 11.91 100 7.424 2 0 13.33 2 6.636 1 -1 17.26 8 5.133 2 -1 19.66 5 4.512 0 1 1 1 20.35 3 4.360 2 0 21.41 1 4.147 2 1 22.18 1 4.004 3 -1 22.51 3 3.946 0 1 23.52 2 3.779 1 1 23.96 1 3.711 4 0 24.16 1 3.681 1 -2 24.57 2 3.620 3 1 24.73 2 3.597 2 2 25.17 2 3.535 2 -1 25.93 12 3.433 2 1 26.61 3 3.347 1 2 26.83 11 3.320 2 -2 27.71 9 3.217 3 2 2 2 28.38 10 3.142 4 0 28.70 2 3.108 4 1 29.42 3 3.033 3 1 30.02 1 2.974 3 2 30.52 3 2.926 3 -2 31.12
