Colloidal Processing and Characterization of Aluminum-Doped Lanthanum Oxyapatite, La10AlSi5O26.5

Abstract

Lanthanum apatite is one of the most promising materials as electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFC), those operating close to 7001C. The complexity of microstructures, composition, and geometries of SOFC devices, make it necessary to have a precise control of processing parameters to obtain the desired combination of properties. This work involves the preparation and optimization of La 10 AlSi 5 O 26.5 materials by reaction sintering of the raw materials (La 2 O 3 , Al 2 O 3 , and SiO 2 ) to be used as IT-SOFCs electrolytes. Homogeneous mixed suspensions of those ceramic oxides were prepared. A heterocoagulation process was followed for ensuring a better reactivity during sintering. All the parameters involved in the process, such as deflocculant content, particle size of the initial powders, sonication time of the mixed suspensions, compaction, and sintering cycle were optimized. The effect of all these parameters were studied and discussed. Finally, La 10 AlSi 5 O 26.5 electrolytes with density values of B88% of the theoretical density and total conductivities of 1.7 Â 10 À2 S/cm at 7001C were obtained. This study opens a path for the preparation of concentrated suspensions for obtaining dense thin films.

Preparation of aluminium lanthanum oxyapatite tapes, La10AlSi5O26.5, by tape casting and reaction sintering

“…For Micro-Nano suspensions the viscosity increases slightly with the application of ultrasound due to the presence of nanosized powders; however, its application is required to obtained homogeneous samples, and longer or shorter ultrasound times led to inhomogeneous samples. 24 In general, suspensions show a shear thinning behaviour; however, 31 and 34 vol% Micro suspensions with 10 wt% binder content (M-31-U2-10BP and M-34-U2-10BP) show a near Newtonian behaviour (Fig. 4a).…”

“…Physical characteristics of those powders, except La 2 O 3 99.99%, are described elsewhere. 24 In the previous work, 24 Fig. 2 shows the evolution of zeta potential values of every powder with the deflocculant content.…”

Sinterability and conductivity of barium doped aluminium lanthanum oxyapatite La9.5Ba0.5Si5.5Al0.5O26.5 electrolyte of solid oxide fuel cells

“…Slightly doped oxygen stoichiometric composition has been found to be favorable for the fabrication of highly conducting lanthanum silicate apatite [19]. In particular, an enhancement of the sinterability and ionic conduction was found in aluminium lanthanum oxyapatite, La 9.33+x/3 Si 6−x Al x O 26.5 [6,[20][21][22]. Doping of La 10−x (Si,Al) 6 O 26±ı with iron increased the total conductivity and sinterability [22][23][24][25][26].…”

Colloidal processing and characterisation of lanthanum tungstate sheets, La5.5WO11.25, prepared by tape casting and reaction sintering

“…As explained before, at pH¼ 7 the charges of calcined-La 2 O 3 and WO 3 were opposite, then, an electrostatic attraction between them will occur leading to heterocoagulation. It has been demonstrated to be a suitable procedure to obtain core-shell structures and to coat bigger particles with smaller ones [25,26]. However, this may lead to agglomeration when particles have similar size and shape.…”

“…According to our previous results [25,27,28] and phase diagrams found in the literature [29], a two-step sintering cycle, 900 and 1600 1C, was selected. Previous attempts at lower final temperatures (from 1400 to 1550 1C) were performed, but un-reacted La 2 O 3 and impurities were detected by LXRPD.…”