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Journal of the European Ceramic Society 36 (2016) 1455–1468 Contents lists available at www.sciencedirect.com Journal of the European Ceramic Society jo ur nal home p ag e: www. elsevier.com/locate/jeurceramsoc Experimental investigation of phase relations and thermodynamic properties in the system ZrO 2 –Eu 2 O 3 –Al 2 O 3 O. Fabrichnaya a,, I. Saenko a,b , M.J. Kriegel a , J. Seidel c , T. Zienert a , G. Savinykh a , G. Schreiber a a Institute of Materials Science, Technical University Bergakademie Freiberg, Gustav-Zeuner-Str. 5, D-09599 Freiberg, Germany b A.A Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Leninskiy Prospect 49, 119991 Moscow, Russia c Institute of Physical Chemistry, Technical University Bergakademie Freiberg, Leipziger-Str. 29, 09599 Freiberg, Germany a r t i c l e i n f o Article history: Received 9 October 2015 Received in revised form 7 December 2015 Accepted 12 December 2015 Available online 31 December 2015 Keywords: Phase diagram Electron microscopy X-ray methods Thermal analysis Thermodynamic modeling a b s t r a c t Phase relations in the Eu 2 O 3 –Al 2 O 3 and ZrO 2 –Eu 2 O 3 –Al 2 O 3 systems were studied experimentally using X-ray diffraction (XRD), scanning electron microscopy combined with dispersive X-ray spectrometry (SEM/EDX) and differential thermal analysis (DTA). The stability ranges of Eu 4 Al 2 O 9 phase were estab- lished as 1748–2095 K. Peritectic character of Eu 4 Al 2 O 9 melting was confirmed. Temperatures and compositions of eutectic reactions were measured. Heat capacities of EuAlO 3 and Eu 4 Al 2 O 9 were mea- sured by differential scanning calorimetry (DSC) in the range 298.15–1400 K. Thermodynamic description of Eu 2 O 3 –Al 2 O 3 system has been derived based on own results and data from literature. Isothermal sections of the ZrO 2 –Eu 2 O 3 –Al 2 O 3 system at temperatures 1523–2073 K were constructed based on experimental study and thermodynamic calculations based on binary extrapolations. Temperatures and compositions of two eutectic reactions were measured. Based on obtained experimental results thermo- dynamic parameters in the ZrO 2 –Eu 2 O 3 –Al 2 O 3 system have been optimized using CALPHAD approach. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction The phase relations in the ZrO 2 –Eu 2 O 3 –Al 2 O 3 system and ther- modynamic properties of constituent phases present interest for several industrial applications. One of possible application of this system is thermal barrier coating. The co-doping of yttria stabi- lized ZrO 2 with various rare earths is the way to produce coatings having lower thermal conductivity and therefore to increase effi- ciencies of gas turbines. The other possible application of the ZrO 2 –Eu 2 O 3 –Al 2 O 3 and Eu 2 O 3 –Al 2 O 3 systems is the directionally solidified eutectics [1]. These in situ composites are of inter- est because of their excellent mechanical properties at elevated temperatures and homogeneous microstructure being stable and resistant to corrosion [2]. The Al 2 O 3 -based directionally solidified eutectics find applications as structural ceramics at high temper- atures, as optical and electronic materials. The pyrochlore phase Corresponding author. Fax: +49 3731 393657. E-mail addresses: [email protected], [email protected] (O. Fabrichnaya). Eu 2 Zr 2 O 7 in the ZrO 2 –Eu 2 O 3 system is interesting for a variety of applications such as thermal barrier coating [3], temperature sensors, host materials for fluorescence centers, nuclear materials, matrices for immobilization of actinides and fuel cell electrolyte materials [3–7]. The phase relations in the ZrO 2 –Eu 2 O 3 system have been recently studied and thermodynamic description of the system was developed [8]. The thermodynamic description of ZrO 2 –Al 2 O 3 system was derived by [9,10] based on phase equilibrium data. The found in literature information about phase relations in the Eu 2 O 3 –Al 2 O 3 system is contradictory [11,12]. Timofeeva et al. [11] identified phase EuAl 11 O 18 with -alumina structure, while Mizuno et al. [12] found the Eu 4 Al 2 O 9 phase with monoclinic structure. Melting temperature of perovskite EuAlO 3 phase was substantially lower according to [11] compared to [12]. Two eutec- tic reactions were found in the work of Timofeeva et al. [11] as well as in Mizuno et al. [12]. However the reactions found in these works were different that probably caused substantial differences in mea- sured temperatures. Thermodynamic description obtained by Wu and Pelton [13] was based mainly on data [12]. Wu and Pelton assumed that the Eu 3 Al 5 O 12 phase with garnet structure was stable http://dx.doi.org/10.1016/j.jeurceramsoc.2015.12.010 0955-2219/© 2015 Elsevier Ltd. All rights reserved.
14

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Page 1: Journal of the European Ceramic Society - imet.ac.ru · Journal of the European Ceramic Society 36 (2016) 1455–1468 Contents lists available at Journal ... Electron experimental

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Journal of the European Ceramic Society 36 (2016) 1455–1468

Contents lists available at www.sciencedirect.com

Journal of the European Ceramic Society

jo ur nal home p ag e: www. elsev ier .com/ locate / jeurceramsoc

xperimental investigation of phase relations and thermodynamicroperties in the system ZrO2–Eu2O3–Al2O3

. Fabrichnayaa,∗, I. Saenkoa,b, M.J. Kriegela, J. Seidel c, T. Zienerta, G. Savinykha,

. Schreibera

Institute of Materials Science, Technical University Bergakademie Freiberg, Gustav-Zeuner-Str. 5, D-09599 Freiberg, GermanyA.A Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Leninskiy Prospect 49, 119991 Moscow, RussiaInstitute of Physical Chemistry, Technical University Bergakademie Freiberg, Leipziger-Str. 29, 09599 Freiberg, Germany

r t i c l e i n f o

rticle history:eceived 9 October 2015eceived in revised form 7 December 2015ccepted 12 December 2015vailable online 31 December 2015

eywords:

a b s t r a c t

Phase relations in the Eu2O3–Al2O3 and ZrO2–Eu2O3–Al2O3 systems were studied experimentally usingX-ray diffraction (XRD), scanning electron microscopy combined with dispersive X-ray spectrometry(SEM/EDX) and differential thermal analysis (DTA). The stability ranges of Eu4Al2O9 phase were estab-lished as 1748–2095 K. Peritectic character of Eu4Al2O9 melting was confirmed. Temperatures andcompositions of eutectic reactions were measured. Heat capacities of EuAlO3 and Eu4Al2O9 were mea-sured by differential scanning calorimetry (DSC) in the range 298.15–1400 K. Thermodynamic description

hase diagramlectron microscopy-ray methodshermal analysishermodynamic modeling

of Eu2O3–Al2O3 system has been derived based on own results and data from literature. Isothermalsections of the ZrO2–Eu2O3–Al2O3 system at temperatures 1523–2073 K were constructed based onexperimental study and thermodynamic calculations based on binary extrapolations. Temperatures andcompositions of two eutectic reactions were measured. Based on obtained experimental results thermo-dynamic parameters in the ZrO2–Eu2O3–Al2O3 system have been optimized using CALPHAD approach.

© 2015 Elsevier Ltd. All rights reserved.

. Introduction

The phase relations in the ZrO2–Eu2O3–Al2O3 system and ther-odynamic properties of constituent phases present interest for

everal industrial applications. One of possible application of thisystem is thermal barrier coating. The co-doping of yttria stabi-ized ZrO2 with various rare earths is the way to produce coatingsaving lower thermal conductivity and therefore to increase effi-iencies of gas turbines. The other possible application of therO2–Eu2O3–Al2O3 and Eu2O3–Al2O3 systems is the directionallyolidified eutectics [1]. These in situ composites are of inter-st because of their excellent mechanical properties at elevatedemperatures and homogeneous microstructure being stable and

esistant to corrosion [2]. The Al2O3-based directionally solidifiedutectics find applications as structural ceramics at high temper-tures, as optical and electronic materials. The pyrochlore phase

∗ Corresponding author. Fax: +49 3731 393657.E-mail addresses: [email protected],

[email protected] (O. Fabrichnaya).

ttp://dx.doi.org/10.1016/j.jeurceramsoc.2015.12.010955-2219/© 2015 Elsevier Ltd. All rights reserved.

Eu2Zr2O7 in the ZrO2–Eu2O3 system is interesting for a varietyof applications such as thermal barrier coating [3], temperaturesensors, host materials for fluorescence centers, nuclear materials,matrices for immobilization of actinides and fuel cell electrolytematerials [3–7].

The phase relations in the ZrO2–Eu2O3 system have beenrecently studied and thermodynamic description of the systemwas developed [8]. The thermodynamic description of ZrO2–Al2O3system was derived by [9,10] based on phase equilibrium data.The found in literature information about phase relations in theEu2O3–Al2O3 system is contradictory [11,12]. Timofeeva et al.[11] identified phase EuAl11O18 with �-alumina structure, whileMizuno et al. [12] found the Eu4Al2O9 phase with monoclinicstructure. Melting temperature of perovskite EuAlO3 phase wassubstantially lower according to [11] compared to [12]. Two eutec-tic reactions were found in the work of Timofeeva et al. [11] as wellas in Mizuno et al. [12]. However the reactions found in these works

were different that probably caused substantial differences in mea-sured temperatures. Thermodynamic description obtained by Wuand Pelton [13] was based mainly on data [12]. Wu and Peltonassumed that the Eu3Al5O12 phase with garnet structure was stable
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456 O. Fabrichnaya et al. / Journal of the Eur

p to 2080 K to fit liquidus data [12]. This assumption is in contra-iction with experimental work [14], where metastable characterf Eu3Al5O12 phase synthesized at 1098–1108 K was proved by itsomplete decomposition and formation of EuAlO3 phase at 1573 K.he EuAlO3 enthalpy of formation at room temperature obtained byrop solution calorimetry [15] is the only available thermodynamic

nformation in the Eu2O3–Al2O3 system.There is no available experimental information for the

rO2–Eu2O3–Al2O3 system so far. The liquidus surface of thisystem was predicted by [16] based on the comparison of liq-idus surfaces of ZrO2–Sm2O3–Al2O3, ZrO2–Gd2O3–Al2O3 andther similar systems. Therefore the aim of the present work isnvestigation of phase relations and thermodynamic properties inhe quasi-binary system Eu2O3–Al2O3 and quasi-ternary systemrO2–Eu2O3–Al2O3.

. Experimental

.1. Sample preparation

Co-precipitation procedure was described in previous work ofabrichnaya et al. [10]. The zirconium acetate solution in acetic acid,r(CH3COO)4 (99.99%, Sigma–Aldrich), Eu(NO3)3·6H2O (99.99%,lfa Aesar) and Al(NO3)3·6H2O (99.99%, Alfa Aesar) were used as

he starting chemicals. In the first step, the Eu(NO3)3·6H2O andl(NO3)3·6H2O were separately dissolved in distilled water and the

nitial zirconium acetate solution was diluted. The concentrationf initial solutions was determined by Inductively Coupled Plasma

Optical Emission Spectrometry (ICP-OES) spectrometry, with anxperimental accuracy of ±2 at.%. The solutions were mixed to get3 g of oxide sample of desired composition. The obtained pre-

ursor solution was dropped from a buret at a low speed (around ml min−1) into a big beaker containing about 500 ml of distilledater. The pH value was maintained above 9.0 by adding ammo-ia aqueous solution. The precipitation occurred during droppingnd stirring. The obtained suspension was heated up and held at33 K for 1–2 h. The precipitate was filtered and then dried at 353 K.o control completeness of co-precipitation the filtrates and sam-le after drying were analysed by ICP-OES spectrometry. Finally,he dried precipitate powder was annealed at 1073 K for 3 h inir. The powder after pyrolysis was pressed into cylindrical pelletsnd sintered in air atmosphere in Pt-crucibles using NABERTHERMurnace to reach the equilibrium state. The duration of heat treat-

ents was selected depending on temperature and it was in theange of 36 h at 1973 K and 240 h at 1523 K. Synthesis of EuAlO3nd Eu4Al2O9 phases for heat capacity measurements was per-ormed for 100 h at 1523 and 1873 K, respectively. Lowest eutecticeaction in the ZrO2–Eu2O3–Al2O3 system was additionally studiedn the NABERTHERM furnace at air conditions by heat treatmentst several temperatures starting from 1898 K with the step 25 Kor 4 h each time to observe at which temperature sample was

elted. Purity of the obtained samples was ensured by purity ofnitial reagents (99.99%) and additionally checked by ICP-OES andEM/EDX.

.2. Sample treatment and characterization

The samples were analysed by X-ray diffraction (XRD), scanninglectron microscopy combined with an energy dispersive X-raypectrometry (SEM/EDX) and differential thermal analysis (DTA).

The XRD measurements of powdered specimen were recorded

sing the URD63 diffractometer (Seifert, FPM, Freiberg, Germany).he goniometer working in the Bragg–Brentano geometryquipped with the graphite monochromator in the diffractedeam and the CuK� radiation (� = 1.5418 Å) was used for the

Ceramic Society 36 (2016) 1455–1468

measurements. All measured diffraction patterns were refinedusing the Rietveld algorithm to obtain the volume fractions ofpresent phases as well as lattice parameters. For the Rietveld refine-ment, the programs BGMN [17] and Maud [18] were used.

The microstructures of sintered samples were examined by SEM(Leo1530, Carl Zeiss) equipped with EDX (Bruker AXS MikroanalysisGmbH) to obtain the chemical compositions of sample. Ratio ofmetal elements were recalculated into the Al2O3, Eu2O3 and ZrO2content with an accuracy of ±4 mol.%.

Most of DTA investigations were performed using SETARAMinstrument SETSYS EVOLUTION 2400 (DTA-TG) in W crucibles inHe atmosphere at temperatures up to 2373 K. The heating rate wasof 20 K min−1 up to 1473 K and then of 10 K min−1; cooling rate wasof 30 K min−1. Temperature calibration of SETSYS EVOLUTION 2400was made using melting points of Al, Al2O3 and solid phase trans-formation in LaYO3 as discussed elsewhere [8]. Linear equation wasobtained for temperature correction. DTA curves resented in thiswork are obtained after taking into account temperature correc-tion. Temperature of transformation was accepted as on-set point,because calibrations were made using on-set points. However tem-peratures of first deviations from base-line were also indicated.

Solid state transformations in the range between 298 and 1973 Kwere investigated in SETSYS EVOLUTION 1750 (TG-DTA) deviceusing PtRh10% crucible and Ar (or He) atmosphere.

2.3. Calorimetric measurements

The heat capacity of samples with EuAlO3 (EAP) and Eu4Al2O9(EAM) nominal compositions were measured in Ar atmosphere inthe temperature range from 573 to 1373 K by differential scan-ning calorimetry (DSC; NETZSCH Pegasus 404C, Pt/Rh crucible). Theclassical three-step method (continuous method) with a constantheating rate of 10 K/min was used to measure specific heat. The sys-tem was calibrated using a certified sapphire standard material. Themass and radius of sample pellet was kept the same as for standardmaterial 84.1 mg and 5 mm. The measurements of two differentsamples were repeated three times with maximal uncertainty 2%.It should be mentioned that the CP measurements at temperatureabove 1200 K by described DSC equipment are becoming less reli-able due to increase of heat radiation which decrease registeredsignal.

The heat capacity measurements in the temperature rangefrom 298.15 K to 353.15 K were carried out using two differentinstruments C80 and SENSYS DSC. The measurements in the C80calorimeter (SETARAM, France; stainless steel cells, sample weight∼2 g) were made in static air. The instrument software assisted CPby step method (steps of 2 K at the measuring temperature for sam-ple, blank and reference material) was applied. The measurementsin the Sensys DSC (SETARAM, France; alumina crucibles, sampleweight ∼600 mg) were performed in pure Ar gas at a flow rate of20 ml/min. The instrument software assisted CP by step method(steps of 10 K at the measuring temperature for sample, blank andreference material) was applied. Synthetic sapphire was also usedas reference material in both calorimeters (data were taken fromRef. [19]).

It should be mentioned that samples were investigated byDTA before heat capacity measurements to check for phasetransformations. According to review of Vasylechko et al. [20]the orthorhombic perovskite EuAlO3 is stable in the range oftemperatures investigated in DSC and undergo reversible phasetransformations at ∼1600 K, i.e., at temperatures above measured

range. The phase Eu4Al2O9 is metastable in the range of measure-ments, but heat capacity measurements are possible if this phasedoes not transform to stable assemblage during heat capacity mea-surements. Thus DTA confirmed possibility for CP measurements.
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opean Ceramic Society 36 (2016) 1455–1468 1457

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Fig. 1. Heat capacities of (a) EuAlO3 (EAP) and (b) Eu4Al2O9 (EAM).

O. Fabrichnaya et al. / Journal of the Eur

. Thermodynamic modeling

Solid phases in the Eu2O3–Al2O3 system practically do not haveny homogeneity regions and therefore they are modeled as stoi-hiometric compounds. Thermodynamic parameters of EAP, EAMnd liquid phases were re-assessed based on new experimentalata obtained in the present work. The thermodynamic descrip-ions for the ZrO2–Eu2O3 (set 1) and ZrO2–Al2O3 systems wereccepted from works [8] and [10], respectively. Solid phases sta-le in the ZrO2–Eu2O3–Al2O3 system which have homogeneityegions were described by the sublattice model in the form ofompound energy formalism [21]. Liquid phase was describedy partially ionic model [21]. Model of phases and abbreviationsre given in Table 1. Thermodynamic parameters were assessedased on experimental data obtained in the present work for theu2O3–Al2O3 and ZrO2–Eu2O3–Al2O3 systems. The assessment ofhermodynamic parameters and phase diagram calculations wereerformed using Thermo-Calc program set [22].

. Results and discussions

Nominal sample compositions, method of synthesis, results ofCP measurements of co-precipitated sample and results of XRDxamination are presented in Table 2. Lattice parameters of EAPnd EAM phases after heat treatments at 1523, 1673 and 1873 Kespectively are presented in Table 3.

.1. Heat capacity for perovskite EuAlO3 and monoclinic phaseu4Al2O9

Sample EA2 heat treated at 1523 K and EA4 heat treated at873 K have been used for heat capacity measurements. It cane seen from Table 2, that practically single phase samples werebtained in these conditions. This was additionally confirmedy SEM/EDX investigation of these samples. The heat capacityeasurements of the EuAlO3 (EAP) and Eu4Al2O9 (EAM) per-

ormed in the present work in the temperature ranges range of93–353 K and 600-1400 K are compared with calculations basedn Neumann–Kopp rule [23] in Fig. 1a and b. The calculations basedn Neumann–Kopp rule show very good agreement with experi-ental results at room temperature for both EuAlO3 and Eu4Al2O9.

or the EuAlO3 the experimental results are slightly below calcu-ations using Neumann–Kopp rule, while the difference increases

ith the temperature and reaches 4% at 1400 K. The calculationsing the Neumann–Kopp rule are slightly higher than experi-ental results for the Eu4Al2O9 phase in the range from room

emperature to 700 K while at higher temperature the calculationsre slightly below than measurements with maximal deviations 1%t 1400 K. Therefore the differences are within uncertainty limitsor both compounds. The experimental results of the temperatureependence of the heat capacity in the temperature interval from93 to 1300 K are fitted to the Mayer–Kelly expression

uAlO3 : CP

(Jmol−1K−1

)= 127.23 + 0.0104T − 2, 670, 000/T2

u4Al2O9 : CP

(Jmol−1K−1

)= 381.49 + 0.0548T − 7, 080, 000/T2

here temperature T is in K.

.2. Phase relations in the Eu2O3–Al2O3 system

The information for invariant reactions in the Eu2O3–Al2O3ystem was obtained from DTA and SEM/EDX investigations. Thexperimental results obtained in the present study are com-ared with data from literature [11,12] in Table 4. The results of

Fig. 2. Heating and cooling DTA curves for sample EA1.

thermodynamic calculations performed in the present work are

also presented in Table 4.

The DTA heating and cooling curves for sample EA1 are shownin Fig. 2. The heat effect is observed at 1997 K. Slight undercooling

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1458 O. Fabrichnaya et al. / Journal of the European Ceramic Society 36 (2016) 1455–1468

Table 1Phases, their names abbreviations, crystal structure and model used for thermodynamicmodelling.

Phase (abr.) Model Space group

Fluorite (F) (Zr4+, Eu3+, Al3+)2(O2− , Va)4 Fm-3mTetragonal (T) (Zr4+, Eu3+, Al3+)2(O2− , Va)4 P42/nmcMonoclinic (M) (Zr4+, Eu3+, Al3+)2(O2− , Va)4 P121/c1Pyrochlore (Pyr) (Eu3+,Zr4+)2(Eu3+,Zr4+)2(O2− ,Va)6(O2−)1(O2− ,Va)1 Fd-3mC–Eu2O3 (C) (Eu3+, Zr4+)2(O2–)3(O2–, Va)1 Ia-3B–Eu2O3 (B) (Eu3+, Zr4+)2(O2–)3(O2–, Va)1 C2/mA–Eu2O3 (A) (Eu3+, Zr4+)2(O2–)3(O2–, Va)1 P-3m1H–Eu2O3 (H) (Eu3+, Zr4+)2(O2–)3(O2–, Va)1 P63/mmcX–Eu2O3 (X) (Eu3+, Zr4+)2(O2–)3(O2–, Va)1 Im-3mAl2O3 (Al2O3) (Al3+)2(O2–)3 R-3cHMonoclinic (EAM) (Al3+)2(Eu3+)4(O2–)9 P121/c1Perovskite (EAP) (Al3+)(Eu3+)(O2–)3 PnmaLiquid (L) (Zr4+, Eu3+)P(O2–, AlO3/2)Q

FDt

eilso[

1awdatfpp2e2ifn

soHblm

Fig. 4. Heating and cooling DTA curves of sample EA2 (a) heated up to 1773 K (b)heated up to 2373 K.

ig. 3. Microstructure of sample EA1 after melting in DTA.ark phase is primary Al2O3 and bright phase is EAP. The white points correspond

o the tungsten.

ffect is observed in cooling curve. The microstructure presentedn Fig. 3 indicates that Al2O3 is primary crystallisation phase andarge areas of eutectic crystallisation (L = Al2O3 + EAP). The mea-ured composition of eutectic composition is 76.6 mol.% Al2O3. Thebtained results are in a good agreement with data of Mizuno et al.12] for this reaction.

The DTA investigation of sample EA2 in SETSYS EVOLUTION750 indicates reversible transformation at 1601 K. The heatingnd cooling curves are shown in Fig. 4a. This effect can be relatedith phase transformation of orthorhombic EuAlO3 to rhombohe-ral modification. Temperature measured using DTA is in perfectgreement with data of Coutures and Coutures [24] who observedhis effect at 1603 K using high-temperature XRD. The same trans-ormation was reported at lower temperature 1420 K based onolarised Raman spectra [25]. The results of DTA study at high tem-eratures are shown in Fig. 4b. The melting effect was observed at182 K. This result is in better agreement with data of Timofeevat al. [11] who determined melting temperature of EuAlO3 (EAP) as213 K than with data of Mizuno at al. [12] who determined melt-

ng at 2320 K. The microstructure investigation show mostly EAPormation with small crystals of EAM due to small deviation fromominal composition (see Fig. 5).

The DTA results (heating and cooling curves) for EA3 and EA4amples are presented in Fig. 6a and b. The observed temperaturesf heat effects in these samples are 2132 and 2085 K, respectively.

owever if we assume that liquidus curve of Mizuno et al. [12]etween EAP and EAM is correct, the EA3 sample should melts at

ower temperature than EA4. In case of peritectic character of EAMelting the temperature of heat effect should be the same in both

samples. It can be seen that crystallisation of both samples occurredwith large undercooling and occurred at 1991 and 1979 K. The SEMimages of samples EA3 and EA4 are presented in Fig. 7a and b. Themicrostructure investigation of sample EA3 shows two differenteutectics. One of them (white dots in gray matrix marked as a)is stable eutectic EAM + Eu2O3 and the second one (white dots inblack matrix marked as b) EAP + Eu2O3 is metastable. The eutec-

tic between EAM and EAP was not found. Compositions of stableeutectic was determined as 29 mol.% Al2O3 and metastable eutec-tic as 31 mol.%Al2O3. The microstructure of sample EA4 indicated
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O. Fabrichnaya et al. / Journal of the European Ceramic Society 36 (2016) 1455–1468 1459

Table 2Sample compositions and results its characterization by ICP and XRD.

Mixture Nominal composition (mol.%) Composition by ICP T (K) XRD (vol.%)

NN ZrO2 Al2O3 Eu2O3

EA-1 0 76 24 0 77.8 22.2 1523 52 Al2O3 + 48 EAP1673 53 Al2O3 + 47 EAP1873 59 Al2O3 + 41 EAP

EA-2 0 50 50 0 48.5 51.5 1523 99 EAP + 1 B1673 99 EAP + 1 B1873 91 EAP + 9 EAM

EA-3 0 38 62 0 36.3 63.7 1523 68 EAP + 32 B1673 67 EAP + 32 B + 1 EAM1873 18 EAP + 82 EAM

EA-4 0 33.3 66.7 0 33.8 66.2 1523 58 EAP + 38 B + 4 EAM1673 53 EAP + 39 B + 8 EAM1723 51 EAP + 34 B + 15 EAM1773 3 EuAP + 2 B + 95 EAM1873 100 EAM

EA-5 0 23 77 0 22.6 77.4 1523 34 EAP + 64 B + 2 EAM1673 31 EAP + 65 B + 4 EAM1873 28 B + 72 EAM

#1 30 40 30 32.2 36.8 31 1523 16 Al2O3 + 37 F + 47 EAP1673 20 Al2O3 + 29 F + 51 EAP1873 33 Al2O3 + 34 F + 33 EAP1948 23 Al2O3 + 35 F + 42 EAP2033 25 Al2O3 + 34 F + 41 EAP

#2 10 10 80 11.9 9.1 79 1523 15 EAP + 70C + 15 B1673 15 EAP + 59C + 26 B1873 22 F + 44 B + 34 EAM1973 23 F + 41 B + 36 EAM

#3 30 5 65 30.9 4.1 65 1523 6 EAP + 46C + 48 F1673 8 EAP + 52C + 40 F1873 53 F + 28C + 19 EAM1973 57 F + 14C + 19 EAM + 10 B2073 32 F + 24C + 26 EAM + 18 B

#4 40 5 55 40.8 3.3 55.9 1523 4 EAP + 18C + 78 F1673 6 EAP + 17C + 77 F1873 14 EAM + 86 F1973 11 EAM + 69 F + 10C + 9 Pyr + 1 EAP2073 17 EAM + 42 F + 33C + 8 Pyr

#5 60 10 30 59.8 8.3 31.9 1523 19 EAP + 64 F + 17 Pyr1673 22 EAP + 78 Pyr1873 22 EAP + 78 Pyr1973 21 EAP + 79 Pyr

#6 80 15 5 77.1 17.5 5.4 1523 48 F + 21 Al2O3 + 31 M1673 51 F + 20 Al2O3 + 29 M1873 67 F + 26 Al2O3 + 7 M

#7 75 10 15 72.4 12.7 14.9 1523 90 F + 10 Al2O3

1673 85 F + 15 Al2O3

1873 86 F + 14 Al2O3

#8 60 25 15 56.4 29 14.6 1523 76 F + 24 Al2O3

1673 4 EAP + 66 F + 30 Al2O3

1873 3 EAP + 68 F + 29 Al2O3

#9 10 30 60 11.1 29.4 59.5 1523 53 EAP + 5 F + 38C + 4 EAM1673 51 EAP + 5 F + 38C + 6 EAM1873 13 EAP + 26 F + 61 EAM

#10 20 68 13 17.5 71.8 10.7 1898 71 Al2O3 + 18 F + 11 EAP1958 71 Al2O3 + 16 F + 13 EAP

toewia

hat it crystallised mostly as metastable eutectic EAP + Eu2O3. Thebtained results can be interpreted in a following way. Due to non-

quilibrium character of solidification the composition of liquidas shifted in Eu2O3 rich composition and solidification finished

n L = EAM + Eu2O3 eutectic. The metastable eutectic L = EAP + Eu2O3ppears if EAM phase did not form due to kinetic reasons. Therefore

2023 72 Al2O3 + 18 F + 10 EAP

based on temperatures determined using DTA and microstruc-ture investigation it can be concluded that EAM phase melted by

peritectic reaction. It should be also noted that cooling curve ofEA3 indicated small effect at 2090 K due to primary phase crys-tallisation of EAP, while EA4 sample crystallized all as metastableeutectic.
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1460 O. Fabrichnaya et al. / Journal of the European Ceramic Society 36 (2016) 1455–1468

Table 3Lattice parameters of EAP and EAM phases.

Sample Temperature (K) of heat treatment Composition (mol.%) Eu2O3 Lattice parameters (nm)

Nominal EDX

EA-2 1523 50 49.74 a = 0.5275b = 0.5295c = 0.7464

1873 50 49.74 a = 0.5277b = 0.5230c = 0.7468

EA-4 1873 66.7 66.97 a = 0.7591b = 1.0690

FGt

Tota

TI

ig. 5. Microstructure of sample (a) EA2 after melting in DTA.ray phase is primary EAP and bright gray phase is EAM. The light points correspond

o the tungsten.

The heating curve of EA4 investigated in SETSYS EVOLU-

ION 1750 device is presented in Fig. 8a. Two heat effects arebserved: the first one at 1591 K due to polymorphic transforma-ion in EuAlO3 observed also in sample EA2 and the second onet 1874 K. SEM/EDX study after DTA indicated almost complete

able 4nvariant reactions in the system Eu2O3–Al2O3.

Reaction Type T (K)

Liq + X = H Peritectic 2543

Liq + H = A Peritectic 2413

Liq + A = B Peritectic 2323

Liq = EAP Congruent 2233

2195

2320

2213

Liq + EAP = EAM Peritectic 2081

– 2094

Liq = EAM Congruent 2223

Liq = B + EAM Eutectic 2072

2053

2133

1903

Liq = Cor + EAP Eutectic 2005

1998

1983

1923

EAM = EAP + B Eutectoid 1748

c = 1.1211 ̌ = 109.124

transformation into EAM phase. Small fractions of EAP and Eu2O3were also observed (see Fig. 8b). Hence it can be concluded that theformation of EAM phase was slightly uncompleted during DTA. Itshould be noted that XRD and SEM/EDX investigation of sampleEA4 heat treated at 1873 K indicated complete transformation intoEAM phase. Small fraction of Eu2O3 was observed due to small devi-ation of sample composition from the nominal. The prolonged heattreatments of sample EA4 at 1723 and 1773 K followed by XRDinvestigation of sample indicated that transformation occurredbetween these two temperatures. The transformation temperaturedifference between results of DTA and phase equilibrium studycan be explained by slow kinetics of solid phase transformation.It should be noted that due to slow kinetics solid phase transfor-mations in DTA often occur with overheating effect [8]. Thereforethe low temperature limit of EAM stability was accepted as 1748 Kbased on phase equilibration study.

The heating and cooling curves for sample EA5 are shown inFig. 9a. A large heat effect was observed at 2053 K during heating.Two effects were observed during cooling: a small effect of pri-mary crystallization was observed at 2041 K and then large effectat 1960 K. The SEM image for this sample is shown in Fig. 9b.

Microstructure investigation of sample EA5 shows both stableand metastable eutectics similar to sample EA3. Primary crystalsof B-Eu2O3 can be seen in microstructure as phase with whitecontrast.

Composition Al2O3 (at.%) References

0.059 This work, calc.0.1290.179

0.500 This work, calc.0.500 This work, exp.0.500 [1977Miz]0.500 [1969Tim]

0.333 This work, calc.0.333 This work, exp.

0.333 [1977Miz]

0.292 This work, calc.0.290 This work, exp.0.220 [1977Miz]0.290 [1969Tim]

0.746 This work, calc.0.766 This work, exp.0.750 [1977Miz]0.710 [1969Tim]

0.333 This work, calc.

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O. Fabrichnaya et al. / Journal of the European Ceramic Society 36 (2016) 1455–1468 1461

4E

wouEofopdTte(tccl

4

omEt

Fig. 7. Microstructure of samples after melting in DTA (a) EA3 and (b) EA4.Light phase is B-Eu2O3, gray phase is EAM and dark phase is EAP. The stable eutecticbetween B-Eu2O3 and EAM phases is marked as a. The metastable eutectic between

Fig. 6. Heating and cooling DTA curves for sample (a) EA3 and (b) EA4.

.3. Assessment of thermodynamic parameters in theu2O3–Al2O3 system

The thermodynamic parameters of the Eu2O3–Al2O3 systemere assessed based on the phase equilibrium data and DTA

btained in the present work. Data from other works [11,12] weresed in case of consistency with the results of present work.xperimental data for thermodynamic values (i.e., heat capacityf EAP and EAM phases from the present work and enthalpy oformation of EAP [15]) were used in the present assessment. Theptimized parameters were standard entropies of EAP and EAMhases as well as mixing parameters of liquid phase. The thermo-ynamic description for the Eu2O3–Al2O3 system is presented inable 5. The calculated phase diagram for the system Eu2O3–Al2O3ogether with experimental data is shown in Fig. 10 together withxperimental data. Comparison of calculated invariant reactionstemperature and liquid composition) with experimental data fromhe present work and literature is presented in Table 4. It can beoncluded from this comparison that reasonable consistency of cal-ulated and experimental data was achieved within uncertaintyimits.

.4. Phase relations in the ZrO2–Eu2O3–Al2O3 system

Preliminary thermodynamic database was combined based

n binary extrapolations into a ternary description. The ther-odynamic databases for ZrO2–Al2O3 [10], ZrO2–Eu2O3 [8] and

u2O3–Al2O3 from the present work were combined into descrip-ion of the ZrO2–Eu2O3–Al2O3 system without including ternary

B-Eu2O3 and EAMis marked b.

mixing parameters. It should be noted that according to prelimi-nary calculations liquid appeared as stable phase already at 1873 K.Based on liquidus surface data for the systems ZrO2–Sm2O3–Al2O3[26] and ZrO2–Gd2O3–Al2O3 [27] stability of liquid at such lowtemperature does not look very realistic. Therefore ternary mixingparameter should be introduced into liquid description to makeliquid less stable.

Several compositions in the ZrO2–Eu2O3–Al2O3 system wereselected for experimental investigations based on preliminarycalculations. The prolonged heat treatments were performedat 1523, 1673 and 1873 K. The results of XRD analysis arepresented in Table 2. The sample microstructures after heattreatments were investigated by SEM/EDX and phase compo-sitions were determined. They were used for additional phaseidentification and compared with XRD results. The calculatedisothermal sections at 1523, 1673 and 1873 K with suspendedliquid phase are presented in Fig. 11a–c together with resultsof XRD and SEM/EDX investigations. The agreement with cal-culations is quite good except for the two things: in samples#7 and #8 two phases were found in equilibrium at 1523 Kinstead of three as expected from calculations and phaseassemblage found at 1873 K in sample #3 is in contradic-tion with phase assemblage found in sample #2. According toZrO2–Eu2O3 phase diagram B phase is stable at 1873 K andtherefore in both samples #2 and 3 B + EAM + F assemblage

should be stable. Even if stabilisation of C phase in ternary sys-tem is assumed stability of both phase assemblages F + EAM + Band F + EAM + C is not possible. To reach equilibrium sam-ples #2 and 3 were heat treated at higher temperatures of
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1462 O. Fabrichnaya et al. / Journal of the European Ceramic Society 36 (2016) 1455–1468

Table 5Thermodynamic parameters assessed in the present work.

Phase/temperature range in K Model/parameter (J/mol)

Ionic Liq (Eu3+, Zr4+)P(O2–, AlO3/2)Q

298–6000 0L (IONIC LIQ, Eu3+:O2–, AlO3/2) = −170,628298–6000 1L (IONIC LIQ, Eu3+:O2–, AlO3/2) = −99,015298–6000 0L (IONIC LIQ, Eu3+,Zr4+:O2–, AlO3/2) = 554,000 − 240 × T

Eu4Al2O9 EAM (Al3+)2(Eu3+)4(O2–)9

298–6000 G (EAM, Al3+:Eu3+:O2–) = −5,169,736.7 + 2250.0929 × T − 381.48591 × T × ln(T) – 0.027406924 × T2 + 3,540,981.4/TEuAlO3 EAP (Al3+)(Eu3+)(O2–)3

298–6000 G (EAP, Al3+:Eu3+:O2–) = −1,743,297.6 + 762.49097 × T − 127.22575 × T × ln(T) − 0.0051984965 × T2 + 1,336,251.9/T

Fig. 8. (a) Heating and cooling DTA curves for sample EA4 heated up to 2073 K, (b)Microstructure of this sample after DTA. Light phase is B-Eu2O3, gray phase is EAM,d

1Hpfloagiflm

Fig. 9. (a) Heating and cooling DTA curves for sample EA5, (b) Microstructure of thissample after melting in DTA. Light phase is B-Eu2O3 and dark phase is EAP. Stable

ark phase is EAP and black areas are pores.

973 and 2073 K. The formation of B phase was confirmed.owever five phases instead of three were identified in sam-le #3 after heat treatment at 2073 K. It can be concluded thatuorite phase partially decomposed to pyrochlore and C-phasen cooling. The SEM image of sample #3 after heat treatmentt 2073 K is presented in Fig. 12. White phase is B-Eu2O3, darkray EAM, gray phase in several places covered by white dots

s fluorite with C-Eu2O3. Area of eutectoid decomposition ofuorite to pyrochlore and C-Eu2O3 are indicated as a in theicrostructure. The composition of eutectoid reaction 53.45%

eutectic L = EAM + Eu2O3 is marked as a and metastable eutectic L = EAP + Eu2O3 ismarked as b.

Eu2O3 and 46.15% ZrO2 is in a perfect agreement with calculationsfor the ZrO2–Eu2O3 system [8]. The SEM image of samples #3 and#4 are similar.

DTA heating and cooling curves for sample #1 are presented inFig. 13a and microstructure formed during solidification of sample#1 is shown in Fig. 13b. The first heat effect on heating curve wasobserved at 1935 K and the second one at 2014 K. It can be seen fromcooling curve that crystallisation of sample #1 was complex andconsisted of several stages. This was confirmed by microstructureexamination. It can be seen that EAP (light gray phase) crystallised

first. The fluorite phase is observed as inclusions in EAP and can bedistinguished as slightly different gray contrast. SEM confirm thatthis phase was fluorite containing 1.22 mol.% of Al2O3, 20.73 mol.%
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O. Fabrichnaya et al. / Journal of the European Ceramic Society 36 (2016) 1455–1468 1463

Fm

Eawd

Fig. 12. Microstructure of sample #3 after heat treatment at 2073 K: a in the eutec-

ig. 10. Calculated phase diagram of the Eu2O3–Al2O3 system along with experi-ental data of the present study and from Refs. [11,12].

u2O3 and 78.05 mol.% ZrO2. Corundum, Al2O3 was also presents black phase. Unexpectedly metastable garnet phase Eu3Al5O12as also found as dark gray contrast. Composition of eutectic wasetermined as 66.67 mol.% Al2O3, 19.82 mol.% ZrO2 and 13.51 mol.%

Fig. 11. Calculated isothermal section of the ZrO2–Eu2O3

toid decomposition of fluorite into pyrochlore and C-Eu2O3.

Eu2O3. Sample #1 was also melted in air. It was heat treated at sev-eral temperatures and then investigated by XRD and SEM/EDX. Thetemperature of melting was found in agreement with DTA dataand composition of eutectic was also consistent with the resultsobtained after DTA. However XRD and SEM/EDX did not show

formation of garnet phase Eu3Al5O12. The SEM image for samplemelted in air is shown in Fig. 13c.

–Al2O3 system at (a) 1523, (b) 1673 and (c) 1873 K.

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1464 O. Fabrichnaya et al. / Journal of the European Ceramic Society 36 (2016) 1455–1468

Fig. 13. (a) Heating and cooling DTA curves for sample #1, (b) Microstructure of sample #1 after melting in DTA, (c) Microstructure of sample #1 after melting in air, (d)Heating and cooling DTA curves for sample #10, (e) Microstructure of sample #10 after melting in DTA, (f) Microstructure of sample #10 after melting in air.a

LthDtawo8o

is ternary eutectic Al2O3 + EAP + Fluorite, b—binary eutectic Fluorite + Al2O3.

For additional investigation of eutectic reaction = EAP + F + Al2O3 new sample #10 with the same composi-ion as determined for eutectic in sample #1 was prepared. It waseat treated at different temperatures in air and investigated byTA. The DTA heating and cooling curves for sample #10 heat

reated in air at 1873 K are shown in Fig. 13d. Only one heat effectt slightly lower temperature (1933 K) compared to sample #1

as detected on heating. Practically no undercooling effect was

bserved for sample #10—temperature of crystallization was only K below than melting temperature. The SEM/EDX investigationf sample #10 melted in DTA and in air showed that it was mostly

crystallised as eutectic containing primary grains of Al2O3. XRDand SEM/EDX indicated three phases fluorite, EuAlO3 and Al2O3.Microstructures of sample #10 after melting in DTA and in air areshown in Fig. 13e and f, respectively. The eutectic compositionwas slightly different than for sample #1:59.29 mol.% Al2O3,20.98 mol.% ZrO2 and 19.73 mol.% Eu2O3 and agreed well with[16]. The composition determined in sample #10 was accepted as

composition of eutectic reaction L = EAP + F + Al2O3.

The same eutectic reaction was found in sample #6 after melt-ing in DTA. DTA heating and cooling curves as well as SEM imageafter melting are presented in Fig. 14a and b, respectively. Melting

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O. Fabrichnaya et al. / Journal of the European Ceramic Society 36 (2016) 1455–1468 1465

Fig. 14. (a) Heating and cooling DTA curves for sample #6, (b) Microstructure ofsample #6 after melting in DTA.

twtflnfloActe

atEtTiSZ

Tseiaa

Fig. 15. (a) Heating and cooling DTA curves for sample #9, (b) Microstructure of

tions. Experimental data for two eutectic reactions E2 and E1

emperature was determined as 2048 K. Crystallization occurredith large undercooling effect at 1892 K. The large gray grains with

races of decomposition are tetragonal zirconia, light gray phase isuorite phase. Probably these large grains of T and F phases wereot completely melted. Black phase is corundum. At the edges ofuorite phase and around fields of eutectic crystallization the flu-rite phase is substantially enriched by Eu2O3 (the white phase).lso small grains of metastable EAG phase were found. Therefore itan be assumed that sample melted according to transitional reac-ion L + T-ZrO2 = F + Al2O3, while the crystallization was finished inutectic reaction L = F + EAP + Al2O3.

DTA heating curve for sample #9 and corresponding SEM imagefter DTA are presented in Fig. 15a and b. According to XRDhe sample #9 heat-treated at 1873 K was tree phase assemblageAP + EAM + F (Table 2) and the eutectic microstructure containinghe same phases was found in the sample after DTA investigation.emperature of melting was determined as 2080 K and melt-ng occurred by eutectic reaction L = EAM + EAP + F. According toEM/EDX data the composition of this eutectic was 15.92 mol.%rO2, 61.55 mol.% Eu2O3 and 22.53 mol.% Al2O3.

DTA heating and cooling curve for sample #3 is shown in Fig. 16a.he transformation at 2184 K on heating can be attributed to tran-itional reaction L + B = EAM + F. Cooling occur with undercoolingffect. In the microstructure of sample #3 after melting presented

n Fig. 16b the same eutectic is observed as in sample #9. There arelso areas with the fluorite decomposition to pyrochlore and Eu2O3ccording to eutectoid reaction F = Pyr + Eu2O3. Separate grains of

sample #9 after melting in DTA.

Eu2O3 and Eu2Zr2O7 pyrochlore were also observed as well as blackgrains of EAP. The other fine area of small gray sports in Eu2O3matrix is probably due to U reaction L + B=F + EAM presents crystal-lization of liquid interacting with B-Eu2O3.

Microstructure investigations of sample #4 are presented inFig. 16c and d. Large area of fluorite phase with gray contrast canbe observed. There are also areas with the fluorite decomposi-tion according to eutectoid reaction F = Pyr + Eu2O3. Separate grainsof Eu2O3 and Eu2Zr2O7 pyrochlore were also observed as well asslightly darker grains of EAM and black grains of EAP. The smallarea of the same eutectic as in samples #3 and 9 was also found.Joint crystallization areas of EAM and fluorite are also present inthe microstructure.

4.5. Assessment of thermodynamic parameters in theZrO2–Eu2O3–Al2O3 system.

The isothermal sections of ZrO2–Eu2O3–Al2O3 phase diagramat temperatures 1523–1873 K indicated good agreement withexperimental phase equilibria (Fig. 11a–c) and therefore ternaryparameters were not introduced in solid solutions. Ternary mix-ing parameter L0(Zr+4, Eu+3:O−2,AlO1.5) was introduced into liquiddescription to increase melting temperature of invariant reac-

(temperature and composition) as well as temperature of tran-sitional reaction were used for optimization. However it wasfound that increasing of mixing parameter resulting in reduce of

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1466 O. Fabrichnaya et al. / Journal of the European Ceramic Society 36 (2016) 1455–1468

Table 6Invariant reactions in the ZrO2–Eu2O3–Al2O3 system.

Reaction Type T (K) Composition of the liquid phase, in at.% Reference

Al2O3 Eu2O3 ZrO2

Liq + X = H + F Transitional U1 2353 4.54 72.49 22.96 Calc. this workLiq + H = A + F Transitional U2 2282 10.01 71.16 18.83 Calc. this workLiq + A = B + F Transitional U3 2190 16.26 68.36 15.38 Calc. this workLiq + B = EAM + F Transitional U4 2020 25.81 63.83 10.35 Calc. this workLiq = EAP + EAM + F Eutectic

E1

2016 27.08 61.54 11.39 Calc. this work2080 22.53 61.55 15.92 Exp. This work

Liq + Pyr = EAP + F Transitional U6 2063 36.76 41.95 21.30 Calc. this workPyr + Liq = EAP + F Transitional U7 2066 34.80 44.57 20.64 Calc. this workLiq = Cor + EAP + F Eutectic

E2

1890 60.41 23.75 15.83 Calc. this work1933 59.29 19.73 20.98 Exp. This work

Liq + T-ZrO2 = Cor + F

TransitionalU5

1991 63.15 17.45 19.40 Calc. this work2048 – – – Exp. This work

Liq = Pyr + F Eutectic e1 2089 34.34 43.75 21.91 Calc. this workLiq = EAP + Pyr Eutectic e2 2063 36.66 42.07 21.27 Calc. this work

F mple #a M + F;

simsmT

ig. 16. (a) Heating and cooling DTA curves for sample #3, (b) Microstructure of sa is the eutectoid reaction F = Pyr + C-Eu2O3; b is the eutectic reaction Liq = EAP + EA

tability of liquid phase also results in miscibility gap formationn Al2O3 rich compositions. This does not correspond to experi-

ental observations in the ZrO2–Eu2O3–Al2O3 system and other

imilar systems. Therefore optimization was stopped at maximalixing parameter which does not lead to miscibility gap formation.

he calculated liquidus and solidus surfaces of ZrO2–Eu2O3–Al2O3

3 after melting in DTA. (c) and (d) Microstructure sample #4 after melting in DTA. c is the transition reaction L + B = EAM + F; d is EAM + F.

system are presented in Fig. 17a and b. The calculated temperaturesand liquid composition are compared with experimental results inTable 6. As mentioned above temperature of invariant reactions

are systematically below (∼40 K) than measured ones. Calculatedcompositions for E1 and E2 agree quite well with experimentaldata.
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O. Fabrichnaya et al. / Journal of the European

Fs

5

gXwtD2iaamoLppbiTmccf

[

ig. 17. Calculated (a) liquidus and (b) solidus surface of the ZrO2–Eu2O3–Al2O3

ystem optimized based on experimental data of the present study.

. Conclusions

The phase relations in the Eu2O3–Al2O3 system were investi-ated in the temperature range between 1523 and 1873 K usingRD and SEM/EDX. Formation of EAM phase from EAP and Eu2O3as observed during heating in DTA and by heat treatments. Low

emperature stability limit of EAM was established as 1748 K. TheTA investigation showed the upper stability limit of EAM as095 K. SEM/EDX investigation of sample with EAM composition

ndicated peritectic character of its melting. Two eutectic reactionsnd were determined: L = Al2O3 + EAP at 1997 and 76.6 mol.%Al2O3nd L = EAM + Eu2O3 at 2055 K and 29 mol.% Al2O3. Congruentelting of EAP was determined at 2182 K. Comparison with data

f Mizuno et al. [12] confirms the results for eutectic reaction = EAP + Al2O3. The melting temperature of EAP determined in theresent work is consistent with data of Timofeeva et al. [11]. Thehase with �-Al2O3 structure found by [11] is not confirmed. Sta-ility limits of EAM phase and character of its melting determined

n the present work are in contrast with data of Mizuno et al. [12].he temperature of eutectic reaction L = EAM + Eu2O3 was deter-

ined at lower temperature than by Mizuno et al. [12]. Eutectic

omposition measured in the present work contained more Al2O3ompared to Mizuno et al. [12]. Based on experimental studies per-ormed in the present work phase diagram of the Eu2O3–Al2O3

[

Ceramic Society 36 (2016) 1455–1468 1467

system was established. Additionally heat capacities of EAP andEAM phases were measured in the range 298.15–1400 K. Thermo-dynamic parameters in the Eu2O3–Al2O3 system were derived byCALPHAD methods.

The phase relations in the ZrO2–Eu2O3–Al2O3 system havebeen investigated for the first time. The phase identificationin samples after heat treatment at 1523, 1673 and 1873 K aregenerally in a good agreement with thermodynamic calculationsbased on binary extrapolations into ternary system. Based onmelting investigation using DTA followed by SEM/EDX investiga-tion temperature and composition of two eutectic reactions wereestablished. The temperature of eutectic reaction L = EAP + Al2O3 + Fwas determined at 1933 K and liquid composition was59.29Al2O3–20.98ZrO2–19.73Eu2O3 (mol.%). Temperature andliquid composition in eutectic reactions L = EAP + EAM + F weredetermined as 2080 K and 61.55Eu2O3–22.53Al2O3–15.92ZrO2(mol.%).

The obtained experimental results were used to optimize ther-modynamic parameters in the system ZrO2–Eu2O3–Al2O3. Thecalculations with this dataset reproduce experimental resultswithin uncertainty. The derived thermodynamic database can beused to calculate different phase diagrams which were not studiedin the present work (e.g., vertical sections) and used for planning ofnew experimental studies. It should be noted that additional ther-modynamic information e.g., melting enthalpy of EAP, enthalpy offormation of EAM, activity data for liquid phase would be useful toimprove the thermodynamic description of Eu2O3–Al2O3 system.Activity measurements for liquid phase in ternary system would bealso important for better modeling of the system.

Acknowledgments

This work was performed in the frame of diploma thesis of I.Saenko and financially supported by TU Bergakademie Freiberg.Authors are thankful to Prof. Leineweber for discussions and to Mrs.Bleiber for technical support in SEM/EDX investigations.

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1 opean

[

[

[

[

[

[[[

[

[

[

[

[

[

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