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Dense Lanthanum Zirconate Ceramics
- 1. DENSE LANTHANUM ZIRCONATE CERAMICS PREPARED BY A NITRATE MODIFIED ALKOXIDE ROUT E Elena-Daniela Ion 1, 2 , Barbara Malič 1 , Marija Kosec 1 1 Jožef Stefan Institut e , Ljubljana, Slovenia 2 National Institute of Materials Physics, Bucharest-Magurele, Romania
- 6. ROH Zr( OR )( OAc ) 3 LNO . x H 2 O 1. Results: First Route Solution gelled in a few min. at RT ELECTRONIC CERAMICS DEPARTMENT - K5 J OZEF STEFAN INSTITUTE XRD spectra of La 2 Z r 2 O 7 precursor powders heat treated at different temperatures
- 7. ROH Zr( OR )( OAc ) 3 LNO . x H 2 O 1. Results: First Route Fast hydrolysis and condensation of Zr species Hindered reaction between La and Zr in solution! Hydrolysis: -Zr- OR + H 2 O -Zr- OH + ROH & Condensation: -Zr- OH + RO -Zr- -Zr- O -Zr- + ROH -Zr- OH + HO -Zr- -Zr- O -Zr- + H 2 O ELECTRONIC CERAMICS DEPARTMENT - K5 J OZEF STEFAN INSTITUTE Masive phase separation after heat treatment!
- 8. Results: Second Route XRD spectra of La 2 Z r 2 O 7 precursor powders heat treated at different temperatures LNO . x H 2 O M O EOH Zr( OR ) 4 2. Partial segregation of La 2 O 3 Partial hydrolysis and condensation of Zr species Zr( OR ) 4 + 4 M O EOH Zr( OE O M ) 4 + 4 ROH ( Alcohol exchange reaction ) ELECTRONIC CERAMICS DEPARTMENT - K5 J OZEF STEFAN INSTITUTE
- 9. XRD spectra of La 2 Z r 2 O 7 precursor powders heat treated at different temperatures Results: Third Route ELECTRONIC CERAMICS DEPARTMENT - K5 J OZEF STEFAN INSTITUTE Single phase La 2 Zr 2 O 7 We assume a reaction between La and Zr species in solution! LNO + Zr( OEOM ) 4 ? -La – O – Zr- LNO MEOH Zr( OR ) 4 3. MEOH Zr( OR ) 4 2. LNO . x H 2 O
- 10. SEM micrograph of a sample, pressed at 500 MPa (CIP) and sintered at 1400 o C for 2 h r =87.5% SEM image s of the powder heat treated at 900 o C/1h Results: Sintering of the as - prepared powder 5 m 10 m ELECTRONIC CERAMICS DEPARTMENT - K5 J OZEF STEFAN INSTITUTE 300nm
- 11. Results: Sintering of the milled powder Powder heat treated at 900 o C/1h and milled for 30 min in a planetary mill 5 m Pellet pressed at 500MPa (CIP) and sintered at 1400 o C/10h r =97.9% 5 m ELECTRONIC CERAMICS DEPARTMENT - K5 J OZEF STEFAN INSTITUTE
Notes de l'éditeur
- Good afternoon. My name is EDI and I will talk about DENSE LANTHANUM ZIRCONATE CERAMICS PREPARED BY A NITRATE MODIFIED ALKOXIDE ROUT E
- First a short introduction, aim of the work Experimental , Results , Conclusions
- L anthanum zirconate has been studied in relation with solid-oxide fuel cells SOFCs As reported preparation methods for powders are: hydrothermal and sol-gel method The lanthanul zirconate is very difficult to sinter as a ceramic . There are only a few references in which the relative density of La2Zr2O7 sintered ceramics is mentioned. 92% of theoretical density by sintering at 1650oC Almost theoretically dense ceramics we re obtained only by hot isostatic pressing at 1500oC .
- The aim of the work is First to s ynthesi ze of single phase La 2 Zr 2 O 7 powder The second to obtaine a Dense ceramic
- The method employed to prepare LZ powder is a nitrate modified alkoxide route. The chemicals : lanthanum precursor, Zr precursor ant the solvent are mixed. By drying the solution we got a precursor powder which by heat treatment gives a crystalline powder. The powder is then pressed and sintered to obtaine a ceramic. The characterization was done by XRD, SEM and Density.
- Three routes were used to prepare the lanthanum zirconate. In the first rout e we started from: lanthanum nitrate hydrate and acetic-acid-modified zirconium n-butoxide in n-butanol (The solution gelled in a few min at RT) The XRD pattern for the powder heat treated at 700oC, shows the presence of lanthanum hydroxide La(OH)3 phase . This means that the powder containe La2O3 which at Rt react with moisture from the air to form La(OH)3. At 900oC the La(OH)3 peaks are accompanied by the main reflection of the pyrochlore La2Zr2O7 phase . We propose that the solid-state reaction between the La2O3 and the zirconium-rich amorphous matrix takes place . Further heating to 1000oC leads to an increase in the crystallinity of both phases. Additionally, peaks of a zirconium-rich phase are identified. The phase separation is explained by the fast hydrolysis and condensation of the Zr species, which hinder the reaction between the La and Zr species and as a result we got a masive phase separation after heat treatment.
- Three routes were used to prepare the lanthanum zirconate. In the first rout e we started from: lanthanum nitrate hydrate and acetic-acid-modified zirconium n-butoxide in n-butanol (The solution gelled in a few min at RT) The XRD pattern for the powder heat treated at 700oC, shows the presence of lanthanum hydroxide La(OH)3 phase . This means that the powder containe La2O3 which at Rt react with moisture from the air to form La(OH)3. At 900oC the La(OH)3 peaks are accompanied by the main reflection of the pyrochlore La2Zr2O7 phase . We propose that the solid-state reaction between the La2O3 and the zirconium-rich amorphous matrix takes place . Further heating to 1000oC leads to an increase in the crystallinity of both phases. Additionally, peaks of a zirconium-rich phase are identified. The phase separation is explained by the fast hydrolysis and condensation of the Zr species, which hinder the reaction between the La and Zr species and as a result we got a masive phase separation after heat treatment.
- In the second route we decrease the reactivity of zirconium n-butoxide toward water by using 2-methoxyethanol as solvent . Namely the alcohol exchange reaction occured. the XRD spectra for lanthanum zirconate powder is a poorly crystall ine phase at 700oC. By increasing the heat-treatment temperature, the crystallinity of the pyrochlore phase is improved. Traces of La(OH)3 are present. The presence of these traces is due to a partial hydrolysis and condensation of Zr species by the water from lanthanum compound .
- For the third route we decided to remove the water from lantanum nitrate h y drate by distillation . X-ray diffraction patterns of LZ powder s show that: The sample is amorphous at 700oC and completely crystallized pyrochloreas single phase at 9 00oC and above this temperature. We assume that in solution a reaction between La nitrate and Zr alkoxide takes place and as a consequences we got a single phase lanthanum zirconate. We further used this powders for preparing ceramics.
- SEM image shows that t he powder is composed of flakes . They have a noticeably porous structure and are composed of very fine particles . The microstructure of the sample pressed and sintered at 1400oC for 2 h shows a relatively dense surface with a non-uniform porosity distribution, which is connected to the wide range of the fragments’ size of the powder.
- In the next step the powder was briefly milled . From the morphology we can see that there is a large decrease in particle size, to below 5 m icrons , this indicates that the original fragments are easily disintegrated. The milled powder was pressed into pellets and sintered at 1400oC for 10 h. The density increase to 9 8 % TD . The polished surface also shows a dense microstructure The uniform morphology of the powder is reflected in the uniform distribution of the pores observed in the microstructure.