Sol-gel synthesis of microcrystalline rare earth orthophosphates

Abstract

Studies of the reactions between rare earth salts and phosphoric acid in aqueous or ethanolic media have shown that in both cases stable gels can be formed. Upon drying, gels prepared in aqueous environments yield macrocrystalline REPO 4 products similar to those produced by conventional precipitation and drying. Gels prepared in ethanol, on the other hand, undergo dehydration to form dense microcrystalline products. This observation is based on optical and scanning electron microscopy, as well as on x-ray diffraction studies and infrared spectroscopy. These techniques, as well as differential thermal analysis, indicate that crystal growth of these products takes place around 600-700 ± C. The composition of the dehydrated gels produced in both the aqueous and ethanolic systems corresponds to an orthophosphate structure. Other characteristics of the microcrystalline REPO 4 products include high resistance to attack by water, absence of coloration upon exposure to gamma rays, and a high index of refraction.

Synthesis and microstructure studies of nano-sized cerium phosphates

“…The obtained curves show several weight loss regions. The first one occurred at ~100 о C and is attributed to the loss of the physosorbed water and it is confirmed by appearance of an endothermic peak at ~100 о C. The second stage recorded at ~250 о C is due to the loss of water of hydration as confirmed by the presence of small endothermic peak on the DSC curve [31]. This stage is corresponding to the conversion of the hydrated cerium phosphates, hexagonal rhabdophane to dehydrated phosphate according to the following equation [24], CePO4.nH2O  CePO4 + nH2O.…”

A Facile Sol–Gel Strategy for the Synthesis of Rod‐Shaped Nanocrystalline High‐Surface‐Area Lanthanum Phosphate Powders and Nanocoatings

“…[9,4c] Guo et al prepared micrometer-sized lanthanum phosphate from lanthanum nitrate and orthophosphoric acid in ethanol medium through a sol-gel route. [10] A colloidal route was adopted by Boakye et al to prepare colloidal rhabdophane for coating alumina fibers. [11] The mean particle size they obtained was 200 nm and even a slight excess or deficiency of phosphate in the coating precursor caused formation of AlPO 4 and LaAlO 3 , LaAl 11 O 18 , and La 3 PO 7 , respectively, at the coating-fiber interface which Synthesis of rod-shaped nanocrystalline lanthanum phosphate with an average length of 40 nm even after calcination at 400 C has been realized through a room-temperature aqueous sol-gel process.…”

Synthesis and microstructure studies of nano-sized cerium-zinc phosphates

“…The attributed to th d by a broad en e second wei e between 100 er of hydratio endothermic p hese results co zinc cations x = 0.2-0.8, ay be due to the us state to the s shifts to low this may be d cated by the X-r ry strong and y be due to the monoclinic or re [25] In this case a rod like shaped particles and monoclinic crystalline structure with particle size ranging from 30 to 38 nm occurred. The formation of the nano-rods structure may be due to homogent-nucleation.…”