Hydrothermal Preparation of Apatite-Type Phases La9.33Si6O26 and La9M1Si6O26.5 (M = Ca, Sr, Ba)

Abstract

Apatite-type lanthanum silicates show a great potential to be used as an electrolyte for intermediate-to low-temperature (600-700 C) solid oxide fuel cells (ITSOFC). However, so far these materials need to be prepared using a very high-temperature method, thus there is a growing interest to prepare apatites at lower temperatures. This paper reports the synthesis of undoped La 9.33 Si 6 O 26 and doped apatites (La 9 CaSi 6 O 26,5 , La 9 SrSi 6 O 26,5 , and La 9 BaSi 6 O 26,5 ) from raw materials La 2 O 3 , Na 2 SiO 4 , BaCO 3 , CaCO 3 , and SrCO 3 using a hydrothermal method. The polycrystalline apatites were obtained as a white powder, after the basic solution of the reagent mixture was heated at 240 C in an autoclave for 3 days. Le Bail refinement of the X-ray powder diffraction data showed that the compounds have a hexagonal cell (P 6 3 /m space group). In this paper, the undoped La 9.33 Si 6 O 26 and La-doped apatite ionic conductivities are also presented.

Preparation and conductivity of composite apatite La9.33Si6O26 (LSO) - Zr0.85Y0.15O1.925 (YSZ)

“…R//CPE parallel arrangement showed a response to heterogeneous electrode reaction. Electrochemical response of YSZ-7LSO composite is described by an electric circuit consisting of three series R//CPE arrangement, as this series is similar to that applicable to the series of apatite compounds (LSO) as reported previously results, the synthesis of solid chemical reaction with the hydrothermal synthesis method [7]. This is possible because the composition of the LSO is more dominating on the composition of the composite.…”

“…Addition of YSZ on lantanum silicate apatite can reduce reactivity sintering powder with the atmospheric H 2 O and CO 2 [11] and sintering temperature. It has been reported frequently that dense sintered lanthanum silicates are difficult to obtain using solid state reaction [8] sol gel [12], and hydrothermal methods [7]. Density of YSZ-LSO composite greatly influenced by the content of YSZ, density of sintering composite increases from YSZ-9 LSO, YSZ-8 LSO to YSZ-7 LSO (Fig.…”

“…The extra oxygen atoms occupy channels running through the structure that are responsible for the high oxygen ion conduction [6]. In one of our previous studies we have successfully synthesized the oxide apatite silicate type (La 9,33 at 500°C [7]. However, the nature of the apatite is unstable and furthermore the homogeneity and density was not solid membrane, and therefore it is not appropriate for solid electrolyte fuel cells.…”

Konduktivitas Apatit Lantanum Silikat La9.33Si6O26 Hasil Sintesis Hidrotermal dengan Mineraliser NaOH dan KOH

“…Selain struktur elektrolit, preparasi material ini juga sangat mempengaruhi karakternya sehingga berpegaruh terhadap sifat fisiknya, seperti konduktivitasnya. Salah satu metode sintesis oksida apatit lantanum silikat adalah metode hidrotermal (Ferdov et al, 2006;Ferdov et al, 2010;Noviyanti et al, 2012b;Sansom et al, 2001). Pada awalnya, metode hidrotermal digunakan dengan tujuan untuk mendapatkan hasil sintesis dengan ukuran kristal yang besar, tetapi dengan adanya perkembangan pada bidang nanoteknologi, nano kristal yang berukuran lebih kecil lebih disukai dan dibuat menggunakan metode hidrotermal tersebut dengan mineraliser sebagai pengatur ukuran kristal.…”

“…La9,33+x(SiO4)6O2+3x/2 (tetrahedral = SiO4; bola biru = La 6h, bola coklat = La 4f, bola merah = O 2a. (Noviyanti et al, 2012b) Mineraliser berfungsi untuk mempermudah pelarutan reaktan-reaktan yang sukar larut, selain itu juga mineraliser dapat menentukan hasil oksida yang diperoleh seperti menghasilkan ukuran dan bentuk kristal (Dell'Agli et al, 1999). Penggunaan mineraliser LiOH, NaOH, KOH dan (CH3)4N + dengan konsentrasi tertentu (dari 0,01 sampai 3,0 M) pada kristaliasi gel zirkonia melalui metode hidrotermal juga mempengeruhi perbedaan fase kristal, luas permukaan dan ukuran kristal.…”