Nejia Kbir-Ariguib

Relationships between structural and luminescence properties in Eu3+-doped oxyphosphate–silicate apatite Ca2+xLa8−x(SiO4)6−x(PO4)xO2

The present paper reports the Eu 3+ fluorescence in the continuous solid solution Ca 2+x La 8 x(SiO4) 6-x (PO 4 ) x O 2 (x = 0,3,6) of the apatitic phosphate-silicates M 10 (XO 4 ) 6 Y 2 with M = Ca, La/X = P, Si and Y = O. Selective UV laser excitation, site-selective-laser excitation in the 5 D 0 level have been performed at 300 and 77 K 5 D 0 level decay times have been reported. In, these compounds, Eu 3+ can be observed in the three crystallographic positions Ca(I), Ca(II) and La(II) of the two cationic sites labeled M(I) (4f) C 3 symmetry and M(II) (6h) C s symmetry. The dominant one is found M(II) clue to an Eu - O privileged bonding with Eu 3+ located in (6h) positions either in La(II) or in Ca(II).

Effect of pH on the rheological behavior of pure and interstratified smectite clays

The effects of pH and ionic strength on the rheological behavior of aqueous suspensions of both crude and purified Wyoming bentonite and natural interstratified illite-smectite from Tunisia were investigated. Flow tests were performed on the four clay suspensions at a 10% clay concentration at different pH values. They showed that the rheological properties were highly sensitive to pH and the nature of the clay. The evolution of the yield stress as a function of pH is characterized by the presence of maxima and minima attributed to changes in the mode of association of the particles. The effect of pH on the behavior of clay suspended in NaCl solutions was also studied. The results show that the presence of NaCl has very little effect on the pH and yield stress values of the four materials.

Investigation of the CaO–La2O3–SiO2–P2O5 quaternary diagram. Synthesis, existence domain, and characterization of apatitic phosphosilicates

Abstract The CaO–La 2 O 3 –SiO 2 –P 2 O 5 phase diagram was investigated in order to determine a domain inside which all points correspond to pure apatitic oxyphosphosilicates with the general formula Ca x La y (SiO 4 ) 6− u (PO 4 ) u O t . The prepared compounds were chemically analyzed and then characterized by X-ray diffraction method, infrared absorption, and Raman diffusion spectroscopies. The bands present in the IR and Raman spectra were identified and assigned to the corresponding vibration modes of SiO 4 and PO 4 anions. The Eu 3+ luminescence study of some doped samples was carried out and their color points were determined. The present data show that a continuous solid solution is obtained inside the apatitic defined domain. Among the Eu 3+ -doped samples, the Ca 2 La 8 (SiO 4 ) 6 O 2 :Eu(2%) can be used as a red phosphor.

Synthesis and characterization of new oxyboroapatite. Investigation of the ternary system CaO–P2O5–B2O3

Abstract The CaO–P 2 O 5 –B 2 O 3 phase diagram was investigated at 1200 °C in order to determine the existence domain of pure apatitic oxyborophosphates with the general formula Ca x (PO 4 ) y B z O t . The prepared compounds were chemically analyzed and then characterized by X-ray diffraction, infrared absorption and Raman scattering spectroscopies. 11 B and 31 P magic angle spinning (MAS) NMR experiments suggest that boron is introduced as 2-fold coordinated boron BO 2 − in the channels of the apatitic structure and as triangular BO 3 3− groups in the channels and substituting for PO 4 groups. The present data show that a continuous solid solution is obtained inside the apatitic defined domain.

Etude du systeme TlPO3LaP3O9

Abstract The TlPO 3 LaP 3 O 9 system has been studied for the first time by differential thermal analysis, X-ray diffraction and IR spectroscopy; the new compounds observed within the system are: Tl 2 La(PO 3 ) 5 and TlLa(PO 3 ) 4 which melt incongruently at 650 and 820°C, respectively. Tl 2 La(PO 3 ) 5 is isotypic with (NH 4 ) 2 La(PO 3 ) 5 ; it belongs to the triclinic system P 1: a = 7.28(2) A, b = 13.30(4) A, c = 7.39(1) A; α = 91°60(8), β = 108°2(1), γ = 89°51(4); Z = 2. The compound TlLa(PO 3 ) 4 crystallizes in three systems. 1. TlLaP 4 O 12 is isotypic with tetrametaphosphate, RbLaP 4 O 12 ; it belongs to the monoclinic system C 2/ c : a = 7.83(2) A, b = 12.79(6) A, c = 10.69(3) A; β = 112°4(2); Z = 4. 2. TlLa(PO 3 ) 4 is monoclinic P 2 1 polyphosphate: a = 8.88(2) A, b = 9.19(2) A, c = 7.19(1) A; β = 99°5(2); Z = 2. It is isotypic with CsLa(PO 3 ) 4 . 3. TlLa(PO 3 ) 4 is monoclinic P 2 1 / n polyphosphate: a = 10.39(3) A, b = 9.04(2) A, c = 10.98(2) A; β = 105°9(2), Z = 4. It is isotypic with RbLa(PO 3 ) 4 . The chemical preparation, crystallographic data and IR spectra for these compounds are given.

Etude du diagramme d'equilibre du systeme KPO3-Er(PO3)3 et des formes allotropiques des phosphates condenses KEr(PO3)4

Abstract KPO 3 -Er(PO 3 ) 3 system has been investigated for the first time by DTA, X-ray diffraction and IR spectroscopy. It has shown the existence of one compound KEr(PO 3 ) 4 ( P 2 1 / c ) which melts incongruently at 985 K. A eutectic point appears at 905 K, corresponding to a concentration of 19% molar Er(PO 3 ) 3 . The intermediate compound presents two monocrystalline forms: the former has a chain structure KEr(PO 3 ) 4 ( P 2 1 / c ) ( a = 10.773(5) A, b = 8.838(5) A, c = 12.684(9) A, β = 128°.91(3), Z = 4); the latter has a cyclic anion KErP 4 O 12 ( C 2/ c ) ( a = 8.05(2) A, b = 12.45(2) A, c = 10.72(1) A, β = 109°.8(1), Z = 4). The method of synthesizing single crystals of these compounds is explained, and the diffraction data and IR absorption spectra are given.