Search Results

You are looking at 1 - 6 of 6 items for

  • Author or Editor: M. Férid x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

The aim of this work is to highlight the importance of controlling the residual water vapour pressure above the sample as well as the rate of the thermal decomposition during the thermal dehydration of cerium cyclotriphosphate trihydrate CeP3O9·3H2O. For this reason, the dehydration of the titled compound was followed by both techniques: the constant rate thermal analysis at P H2O = 5 hPa and the conventional TG-DTA in air. It has been shown that the pathway of the thermal dehydration depends strongly on the nature of atmosphere above the sample. However, in air atmosphere CeP3O9·3H2O decomposes in two well defined steps to give first an amorphous, phase in the temperature range 440–632 K, then the cerium polyphosphate Ce(PO3)3 crystallizing in orthorhombic system (C2221) at T>632 K. Whereas decomposition carried out at 5 hPa water vapour pressure, also occurring in two steps, leads first to a crystallized intermediate monohydrate at 259<T<343 K and second to a crystallized anhydrous cerium polyphosphate, at 343<T<791 K, with a structure different from those of all lanthanide polyphosphate known actually and particularly from that of Ce(PO3)3 obtained in air. The activation energy corresponding to the dehydration of the initial phosphate was also measured experimentally by means of two CRTA curves and was found equal to 81±5 kJ mol−1.

Restricted access

Abstract  

The preparation of a new acid lanthanide diphosphate is reported. The acid praseodymium diphosphate, obtained as a trihydrate salt, is investigated by chemical analysis, X-ray powder diffraction and IR spectroscopy. The study of the thermal behavior of HPrP2O7·3H2O shows that its dehydration begins at 367 K. A scheme of its decomposition is proposed.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
M. Férid
,
D. Ben Hassen-Chehimi
,
N. Kbir-Ariguib
, and
M. Trabelsi-Ayedi

Abstract  

The NaPO3−Pr(PO3)3 system was studied by microdifferential thermal analysis (DTA), IR and X-ray diffraction spectroscopies. The only new compound observed in the system is NaPr(PO3)4, which melts incongruently at 1149 K. A eutectic appears at 5% Pr(PO3)3 at 901 K. The new compound NaPr(PO3)4 was characterized by means of powder X-ray diffraction and IR absorption spectroscopy. NaPr(PO3)4 is a NaLa(PO3)4 isotype; it crystallizes in the monoclinic system P21/c witha=12.328(7),b=13.130(5),c=7.231(5) Å, β=126°, 18(5),Z=4,V=945 Ȧ3.

Restricted access

Abstract  

The formation of a new sulfate compound K4H2(SO4)3 is obtained by evaporation at 25C of an aqueous solution, which was formed by a mixture of K2SO4 and H2SO4. The characterization of this solid is carried out by X-ray diffraction, thermal and infrared analyzes. The heat treatment was carried out in interval 25–700C; the end product of the thermal evolution is K2SO4. The vibration bands relating to SO4 and OH groups were highlighted by the infrared spectroscopy.Moreover, one study of ionic conductivity on this solid compound was carried out according to the temperature in interval 25–80C. Its activation energy is 0.47 eV. The X-ray intensities collection obtained on a monocrystal of K4H2(SO4)3 gives the following cell parameters: a=7.035(5), b=19.751(4), c=23.466(2) , β=95.25(1).

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
F. Chehimi-Moumen
,
P. Llewellyn
,
F. Rouquerol
,
G. Vacquier
,
D. Ben Hassen-Chehimi
,
M. Ferid
, and
M. Trabelsi-Ayadi

Summary  

The aim of this work is the optimization of the preparation of anhydrous gadolinium hydrogen phosphate with good fluorescence properties. The products obtained by dehydration of gadolinium hydrogen phosphate trihydrate depend on the conditions chosen for the thermal treatment. For this reason, the dehydration was followed by Constant Rate Thermal Analysis whilst strictly controlling the water vapour pressure above the sample. Intermediate samples, obtained during dehydration were characterised by IR spectroscopy and X-ray diffraction. It has thus been shown that the thermal pathway taken for the dehydration depends on the water vapour pressure above the sample in the region from 10-2to 5 mbar. Under the lowest water vapour pressure (510-3mbar), the elimination of the crystallization water is carried out in a continuous way and produces a quasi-amorphous intermediate. Under higher water vapour pressure (5 mbar), well crystallized intermediate products are obtained. The results obtained suggest that the trihydrate contains zeolitic water which confirms a prior structural study.

Restricted access