The kinetics of surface area reduction during isothermal sintering of hydroxyapatite adsorbent

Abstract

The behaviour of non-stoichiometric hydroxyapatite (HA) during the calcination in a solid bed was investigated. The structural properties are described in terms of the specific surface area. Calcination led to a significant decrease of the specific surface area by particle coalescence and densification. Hydroxyapatite begins to shrink near 780 • C and reaches 97% theoretical density at 1100 • C. The specific surface area and density variations are caused both by sintering and chemical reaction. Sintering data from these solids were correlated as a function of time and temperature. The rate of sintering is assumed to obey an Arrhenius equation. These results are compared with a number of literature models describing the mechanism of sintering kinetics using the specific surface area, and a good agreement is observed. The kinetic equation used is based on sintering driven by the curvature gradient in the interparticle neck region associated with initial stage sintering. Then, the decline in specific surface area is accurately described by the empirical equation of the form dS/dt = −B(T)k b. The changing value of b, also known as the "order" of the reaction, suggests that the diffusion mechanism for loss of surface area may be a function of the temperature.

CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments

“…A theoretical model which has been successfully used to interpret experimental results on the surface area loss of nascent CaO [30,32,33,45,50] (and other types of materials [26,51,52]) when subjected to short-timed isothermal heating is the German-Munir model [26].…”

Precipitation Process of Calcium Phosphate from Calcium Carbonate Suspension

“…Spray pyrolysis, freeze drying, gel diffusion, a sol-gel technique and electrochemical deposition have all also been used. Much work has been done on the synthesis of Ca-HA using different methods such as solid-solid reaction (Nakamura et al, 2001;Silva et al, 2003), ultrasonic spray freeze-drying (Itatani et al, 2000) or spray-drying techniques generating a Ca-HA powder of controlled morphology (Luo and Nieh, 1996), sol-gel technique (Anee et al, 2003;Bezzi et al, 2003;Salimi et al, 2012), precipitation in aqueous solution (Jarcho, and Bolen, 1976;Rodriguez-Lorenzo et al, 2001;Bailliez and Nzihou, 2004;Swain et al, 2012), emulsion route (Saha et al, 2009;Okada et al, 2012), microwaveassisted synthesis (Ipekoglu and Altintas, 2010) and synthesis under hydrothermal conditions (Vasile et al, 2012;Murakami et al, 2012). Among all these methods, precipitation is characterized by the simplicity of the process, its low cost and its easy application in industrial production (Liu et al, 2001).…”

Interactions between calcium phosphate and heavy metal ions in aqueous solution

“…Apatite is the name given to a group of crystals of the general chemical formula M 10 (RO 4 )X 2 , where R is most generally phosphorus, M could be one of the several metals, although it is usually calcium, and X is frequently hydroxide or a halogen such as fluorine or chlorine [7]. One of the most common apatite is calcium hydroxy apatite (Hap), whose theoretical formula is Ca 10 (PO 4 ) 6 (OH) 2 . Non stoichiometric Hap constitutes the mineral component of hard tissues (bone, dental enamel, etc.)…”

“…Non stoichiometric Hap constitutes the mineral component of hard tissues (bone, dental enamel, etc.) of mammals [6][7][8][9][10].…”