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10Journal of Siberian Federal University. Chemistry 1 (2012 5) 18-23 УДК 532.614+546.873
Interaction of Leade Oxide -Germanium Oxide Melts with Platinum and Palladium
Viktor М. Denisova, Oksana V. Kuchumovaa, Liubov Т. Denisovaa*, Natalia V. Belousovaa, Liubov G. Chumilinaa and Sergey A. Istominb
a Siberian Federal University, 79 Svobodny, Krasnoyarsk, 660041 Russia b Institute of Metallurgy of UB of RAS 101 Amundsen str., Yekaterinburg, 620019 Russia 1
Received 2.03.2012, received in revised form 9.03.2012, accepted 16.03.2012
Contact interaction of leade oxide - germanium oxide melts with Pt and Pd was investigated. Good adhesion of these melts to the solid metals was observed.
Keywords: wetting, spreading, platinum, palladium, oxides of lead and germanium.
Introduction
Oxide compounds of PbO-GeO2 system are provoking interest thanks to their properties [1-4]. An investigation of interaction of oxide melts with Pt and Pd was conditioned by a set of reasons. Nanostructural oxide systems containing ions of rare-earth elements and noble metals are perspective materials for optoelectronics [5]. In addition, noble metals, as crucible materials, can have a substantial effect on properties of synthesized oxide compounds. For example, the color of the glasses based on heavy metal oxides depends on the crucible type used for their obtaining [6]. The intensity of many processes occurring when melts contact with crucible materials can be determined by the wetting. Because of this, the study of contact interaction of PbO-GeO2 melts with Pt and Pd is of scientific and practical interest.
Results and discussion
“Melt-substrate” contact interaction was investigated by the sessile drop method. The wetting of Pt and Pd by PbO-GeO2 melts were conducted in air at the separate heating of the sample and the substrate. Photographs of the drops obtained with a Canon EOC 400 Digital were processed using a
* Corresponding author E-mail address: [email protected]
1 © Siberian Federal University. All rights reserved
computer. The experimental procedure was similar to described one [7, 8]. The samples were prepared with the use of extrapure-grade PbO and GeO2.
The contact interaction was studied for each composition at melting temperature because preliminary experiments showed that its increase resulted in the complete spreading of drops within a small time interval.
Figure 1a shows the spreading kinetics of PbO-GeO2 melt containing 20 mol % of PbO on platinum. According to these data, for 7 sec; the contact angle decneased from 65° to 19° It shauld be remarked that with increasing t the value of 0 changed not so sharply. Such change of 0 = f(x) and the values of contact angles (t > 20 sec) are rather unexpected as platinum is a general material for the crucibles in which like oxides are melted. Though, we can note the followings. Firstly, PbO-GeO2 melts behave similarly on contact inte raction w itla Au and Ag [9]. Secondly, so low values of 0were also registe re d on Pt for other oxides [10]. Foe example, it was established that the contact interaction of LiNbO3 with Pt, Pt + 10 wt. % of Rh, Pt + 10 wt . % of Ic, Pt + 5 w t. % Au and Ir was characterized by the values cf 0 in the range of 12-14°. TOe exception is ihe allpy of Pt with Au, on which the contact angle is equal to 28°. Thirdly0, there zre compounds Pt3Od PtO2 (Tm = 72t K) and PrO STm = '7810 K) in the eystem Pt-O2 [11]. PtO and PtO2decompoye at T > 773 K and > 873 I0 [12], yespeciively. We calculated the Gibbs energy, AG, of reactions PbO + Pt = PtO + Pb, PbO2 + Pn = PtO + PbO, 2Pb O2 + Pt = PtO2 + 2PbO and determined that in the rangr of 773 -1273K AG of fi rst reattion is positive in vahie, while in hhe case; of second and third one s i) is small negatize. It is yot incozceivable that the above causes the good wetting of platinum by PbO-GeO2 melte.
We obtained analogous results on the contact interaction of Pt with other PbO-GeO2 melts (Fig.
1, b-d).
At equilibrium [t3]
where asg, ash are the surface tensions at the solid-gas, solid-liquid and liquid-gas boundaries,
respectively.
With the woik of adhesion
from Eq. (1) - (3) follows that
From Eq. (4), according to [13], foUows that the value of 0 is determined by the relation between the attractive forces of the liquid to the solid surface and the attractive mieraction foeces oe particles of the liquid. On intenaction of liquid with solid, the following cases aue possible: wetting (Wa > WS/2) and complete wetting (Wa > Wf) [13]. Based on 1he Eq. 14), it may be concluded that the emaller is Wc
(1)
Wa Gsg + Qsi G/g,
and the work of cohesion
(3)
9
E-
¿so
—I____________________I________________l_
o 1 1 & Mu w vu uo -,c
I «
€ m
40
ïû
20
10
Q
I
10 20 30 1000 3ÛOO JSÜ00 t,C
JO
20 -
&
p.
>■........
0 10 30 ÎU 1000 2MOÏOOO T. f
Fig. 1. Spreading kinetic s of PbO-GeO2 melts, containing a) 20, b) 30 , c) 40 and d) 60 mol % of PbO, on
platinum
and thus o1g, the better the liquid wets the solid. The surface tension ofPbO-GeO2 melts is likely to be uninvestigated. By virtue of the fact that the surface tension of liquid PbO is smaller than os of melted GeO2 [14= 15], it is brlieved that PbO is a surface-active component with respect to GeO2. Taking into account all things, one might expect the improving wetting as the content of PbO in the melt increases. As illustrated in Fig. 1, the change of content of melt from 20 to 50 mol % of PbO has little effect on the values of 0.
The sSudy of1 wetting of refractory metals (W, Mo, Nb) by the alumina-based melts (Al2O3-BeO, Al2O3- MgO, Al2O3-CaO, Al2O3-Cr2O3, Al2O3-ZrO2, Al2O3-TiO2, Al2O3-V2O5) showed that initial values of contact angles in all systems increased as the content of added oxide increased, but they passed through a maximum and then decreased [16]. This phenomenon can not be explained by the change of surface tension of the melt because, by Eq. (1), the contact angle augmentation assumes the increase of o,g while the addition of BeO, TiO2, V2O5, CaO to Al2O3 resulted in the reducing surface tension of the melt. The observed change of 0 when wetting the refractory metals by oxide melts was connected with the relevant change of os1 and adsorptive phenomena at the “solid metal - liquid oxide” boundary. It is not improbable that the behavior of Pt-(PbO-GeO2) system can be explained in a like manner. In this case it should be considered that the oxide surface is primarily formed by the oxygen anions the size of which is significantly greater than the size of metal cations. As a consequence, the interaction of the metal with some oxide is determined by the reaction of this metal with the oxygen of oxide [13]. In addition, the Pt surface, on being heated in air, is covered with an adsorptive oxygen layer, and then according to V.N. Eremenko’s principle, “similar matter wets similar thing” [17].
î
iiim—
600
(;uo izoo t, c
Fig. 2. Spreading kinetics of Pb+ 80 mol % of Ge02 melt on palladium
We can also point out the possibility of brittle failure of Pt on interaction with melts. This question was detailed in the monograph [18].
Fig. 2 shows results on the contact interaction of Pd with PbO + 80 mol % of GeO2 melt. From this figure we observe that for ~ 30 sec the melted drop is practically spreading over the palladium. In the coutse of time (~ 800 sec) a complete spire ading takes plac e.
There is one compound PdO (Te = 1150 K) in the palladium-oxygen system [11]. A Cesosptioit of oxygen from polycrystalline palladium in the range of temperatures from 500 to 1300 K was investigated in [19]. The obtained results argue for a strong interaction in the palladium-oxygen system.
We established that after experiment the drop compos ad of I3!) f 80 mol % of GeO2 eucaed red-orange inetead of practically transparent It can give an indication of “melt-substrale” chemical interaction [6].
A relation between the Gibbs energy of chemical reactions at the phase interface (ArG) and contact aegles in the metal-oxide systems was considered in [20]. The mthoo poiated out that ehis relatione could be conditioned 0y ao influe nce of chemical interaction on the work of adhesion. Ia analyeable models the contact angle depends on a degree of reaction product conversion; the correlation between ArG and 0 was found only for the case that the three-phase system attained the equilibrium state. In a general wao, nonrquilibrium sestems likewise can fe contidered. In this case the value of 0 will be determined immediately by the degree of reaction product conversion rather than by ArG [20].
The drop of PbO + 80 mol % of GeO2 was found to spread on Pd after a precursor layer which was arranged in front of the conditional three-phase contact line. A detailed analysis of this phenomenon was given in [21] and we will not discuse it heee. It should be noted that inis pfenomenon wms observed ocspreading PbO-GeO2 melts over silver [22].
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Взаимодействие расплавов оксидов свинца -оксидов германия с платиной и палладием
В. М. Денисов3, О.В. Кучумоваа, Л.Т. Денисова3, Н.В. Белоусова3, Л.Г. Чумилина3, С.А. Истомин6
a Сибирский федеральный университет, Россия 660041, Красноярск, пр. Свободный, 79 б Институт металлургии УрО РАН Россия 620019, Екатеринбург, ул. Амундсена, 101
Исследовано контактное взаимодействие расплавов оксидов свинца - оксидов германия с платиной и палладием. Установлено, что наблюдается хорошая адгезия таких расплавов к твердым металлам.
Ключевые слова: смачивание, растекание, платина, палладий, оксиды свинца и германия.
