ABSTRACT

The phase diagrams of the Mg(NO3)2-Ln(NO3)3 (Ln = Nd, Sm, Eu, Tb)-HNO3-H2O systems in the (-20%) HNO3 regions at T = 298.15 K were determined by using an isothermal solution saturation method. The Schreinemaker's wet residues method was used to determine the compositions of solid-phases. Both Mg(NO3)2-Nd(NO3)3-HNO3-H2O and Mg(NO3)2-Sm(NO3)3-HNO3-H2O systems are complicated with three equilibrium solid phases Mg(NO3)2*6H2O, Mg3Ln2(NO3)12*24H2O and Ln(NO3)3*6H2O (Ln = Nd, Sm). But the systems Mg(NO3)2-Eu(NO3)3-HNO3-H2O and Mg(NO3)2-Tb(NO3)3Tb-HNO3-H2O are simple eutonic type. The two new solid-phase compounds Mg3Nd2(NO3)12*24H2O and Mg3Sm2(NO3)12*24H2O are congruently soluble in an average medium of -20 mass % HNO3, and they were identified and characterized by the methods of powder X-ray diffraction, X-ray diffraction single crystal structure analysis, and thermogravimetric/differential thermogravimetric. The XRD diffraction patterns for the two new solid-phase compounds are identical due to their isomorphic structure. They belong to hexagonal systems, with space group R3. For Mg3Nd2(NO3)12*24H2O, a = b = (1.0993 +- 0.0005) nm, c = (1.7211 +- 0.0007) nm, V = (1.8012 +- 0.0013) nm3, Dc = (4.2532 +- 0.0024) g*cm-3, Z = 3; for Mg3Sm2(NO3)12*24H2O, (a = b = 1.1198 +- 0.0004) nm, c = (1.7257 +- 0.0006) nm, V = (1.8742 +- 0.0011) nm3, Dc = (4.1201 +- 0.0012) g cm-3, Z = 3. The standard molar enthalpies of solution of the compounds Mg3Nd2(NO3)12*24H2O and Mg3Sm2(NO3)12*24H2O in water (aq) were measured to be (101.26 +- 0.77) kJ mol-1 and (80.27 +- 0.81) kJ mol-1, and their standard molar enthalpies of formation were calculated to be - (12214.13 +- 2.5) kJ mol-1 and - (12183.6 +- 2.5) kJ mol-1, respectively.

Compounds

#	Formula	Name
1	N3NdO9	neodymium(III) nitrate
2	N3O9Sm	samarium(III) nitrate
3	EuN3O9	europium (III) nitrate
4	N3O9Tb	terbium (III) nitrate
5	HNO3	nitric acid
6	H2O	water
7	H48Mg3N12Nd2O60	trimagnesium dineodymium(III) nitrate tetracosahydrate
8	H48Mg3N12O60Sm2	trimagnesium disamarium(III) nitrate tetracosahydrate

Datasets

The table above is generated from the ThermoML associated json file (link above). POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied; the numbers refer to the table of compounds on the left.
Type	Compound-#	Property	Variable	Phase	Method	#Points
POMD	7	Mass density, kg/m3 ; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal	Crystal	X-ray diffraction	1
POMD	8	Mass density, kg/m3 ; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal	Crystal	X-ray diffraction	1
POMD	1 5 6	Mass fraction - 1 ; Liquid	Mass fraction - 5; Liquid Temperature, K; Liquid Pressure, kPa; Liquid	Liquid Crystal of intercomponent compound 1	Titration method	1
POMD	2 5 6	Mass fraction - 2 ; Liquid	Mass fraction - 5; Liquid Temperature, K; Liquid Pressure, kPa; Liquid	Liquid Crystal of intercomponent compound 1	Titration method	1
POMD	3 5 6	Mass fraction - 3 ; Liquid	Mass fraction - 5; Liquid Temperature, K; Liquid Pressure, kPa; Liquid	Liquid Crystal of intercomponent compound 1	Titration method	1
POMD	4 5 6	Mass fraction - 4 ; Liquid	Mass fraction - 5; Liquid Temperature, K; Liquid Pressure, kPa; Liquid	Liquid Crystal of intercomponent compound 1	Titration method	1
POMD	6 7	Molar enthalpy of solution, kJ/mol ; Liquid	Mole fraction - 7; Liquid Temperature, K; Liquid Pressure, kPa; Liquid	Liquid	Calvet calorimetry	1
POMD	6 8	Molar enthalpy of solution, kJ/mol ; Liquid	Mole fraction - 8; Liquid Temperature, K; Liquid Pressure, kPa; Liquid	Liquid	Calvet calorimetry	1

Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

Phase equilibria in Mg(NO3)2-Ln(NO3)3 (Ln = Nd, Sm, Eu, Tb)-HNO3 (~20%)-H2O systems at 298.15 K and thermodynamic properties of Mg3Ln2(NO3)12*24H2O (Ln = Nd, Sm)

Qiao, Zhan-Ping, Su, Meng-Yao, Dang, Yuan-Lin, Yang, Qi-Chao

ABSTRACT