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Vibrational Spectroscopy of the Hydrated Borates and Their Aqueous Solutions and Thermochemistry of Hydrated Ammonium Borates

Author: WangJiang
Tutor: GaoShiYang；ZhuLiXia
School: Institute of Qinghai Salt Lake
Course: Inorganic Chemistry
Keywords: Hydrated borate Aqueous solution Borate anion Vibrational spectrum Solution calorimetry
CLC: O611.3
Type: Master's thesis
Year: 2004
Downloads: 88
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Abstract


This thesis comprise the researches of FTIR and Raman Spectroscopic studies of hydrated borates and their aqueous solutions, as well as the thermochemistry of hydrated ammonium borates.The supersaturated aqueous solutions of potassium borate {n（K2O）:n（B2O3）=1:4} and ammonium borate {n[（NH4）2O]:n（B2O3）=1:3} were prepared. The FTIR difference spectra (1500cm-1400cm-1) and Raman spectra (1000cm-1400cm-1) of the supersaturated aqueous solutions, as well as their acidified solutions by using azeotropic hydrochloric and the solutions during crystallization process, were recorded at room temperature. Fundamental vibrational modes were . identified and the assignments for vibrational bands of borate anions in aqueous solution were tentatively made. According to both vibrational spectra and other experimental results, the interaction of borate anions were proposed. Compared with the supersaturated aqueous solutions, the FTIR difference spectra and Raman spectra for the saturated aqueous solutions of KB5O8·4H2O, β-NH4B5O8·4H2O, and （NH4）2B8O13·6H2O were also obtained, respectively. All of the results showed that there exist various borate anions in the borate aqueous solution, in which the main particles are B（OH）3, [B3O3（OH）4]-, [B5O6（OH）4]- , and [B4O5（OH）4]2- when pH = 79. The vibrational bands for [B（OH）4]- are weak in this range.Based on the characterization of vibrational spectra, the FBB of （NH4）2B8O13·6H2O, [B7O11（OH）·B（OH）3]2-= [B8O11（OH）4]2- was predicted, and the strong and sharp band around 516cm-1 in the Raman spectrum was tentatively assigned to the symmetric pulse vibration of this anion, firstly.The preliminary studies on the dissolution and transformation of Rb2Ca[B4O5（OH）4]2·8H2O were carried out. It is indicated that the tetraborate anion is depolymerized to B（OH）3 and [B（OH）4]- during the dissolution process. Some amorphous residue will be transformed into the crystal hydrated calcium triborate.The enthalpies of solution of （NH4）2B4O7·4H2O （cr） and β-NH4B5O8·4H2O （cr） inapproximately 1 moldm"3 aqueous hydrochloric acid solution, as well as the enthalpy of solution of NH4CI （cr） in aqueous （hydrochloric acid + boric acid） have been measured by using a microcalorimeter. From these results and other auxiliary data, the standard molar enthalpies of formation Af//°m of （NH4）2B4O7-4H2O（cr） and yS-NH4B5O8-4H2O（cr） have been derived to be （-4313.74 + 3.26） kJmol’1 and （-4703.56 + 4.03） kJ-mol"1 at 298.15K, respectively. Some other thermodynamic parameters of the hydrated ammonium borates, such as the standard molar entropies of formation and the standard molar entropies, have also been calculated.

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