ABSTRACT

In this paper, we report synthesis and characterization of thorium and strontium substituted synthetic monazite solid-solutions of general formula La1-xSrx/2Thx/2PO4 (0less than=xless than=1) using solid-state synthesis route and described the influence of charged coupled (Sr2+, Th4+) substitution in place of La3+ on their thermodynamic stability. High temperature calorimetry has been employed to determine the standard molar enthalpy of formation of La1-xSrx/2Thx/2PO4 (0less than=xless than=1) compounds. The isobaric molar heat capacities of the compounds were measured employing differential scanning calorimetric technique. Based on these experimental data and the available thermodynamic data for the component oxides, thermodynamic properties of the La1-xSrx/2Thx/2PO4 (0less than=xless than=1) have been derived. The negative value of excess enthalpy of formation deltaHE indicates that the substitution of La by Sr, Th charge couple in the monazite host structure increases their relative stability. Such strong negative interaction parameter is an indication of short-range cation ordering, which found to be more evident at x = 0.3. Based on the experimental results thermodynamic functions for the solid solutions have been generated.

Compounds

#	Formula	Name
1	La	lanthanum
2	P	phosphorus
3	O2	oxygen
4	Sr	strontium
5	Th	thorium
6	LaO4P	lanthanum orthophosphate
7	O2Zr	zirconium oxide
8	O8P2SrTh	strontium thorium(IV) phosphate

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	Constraint	Phase	Method	#Points
POMD	6	Mass density, kg/m3 ; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal		Crystal	X-ray diffraction	1
POMD	6	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	DSC	12
POMD	7	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	DSC	50
POMD	8	Mass density, kg/m3 ; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal		Crystal	X-ray diffraction	1
POMD	8	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	DSC	12
POMD	6 8	Mass density, kg/m3 ; Crystal	Mole fraction - 6; Crystal	Pressure, kPa; Crystal Temperature, K; Crystal	Crystal	X-ray diffraction	6
POMD	6 8	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal Mole fraction - 6; Crystal	Pressure, kPa; Crystal	Crystal	DSC	72
RXND	1 2 6 3	Molar enthalpy of reaction, kJ/mol				Solution calorimetry	1
RXND	4 5 2 8 3	Molar enthalpy of reaction, kJ/mol				Solution calorimetry	1

Thermodynamics Research Center / ThermoML | Thermochimica Acta

Thermodynamic investigation of thorium and strontium substituted monazite solid-solution

Rawat, D., Phapale, S., Mishra, R., Dash, S.

ABSTRACT