Nano Sized Pd Particles in a SiO 2 Matrix by Sol-Gel Processing
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Pd nanoparticle containing Ormocers were prepared by the following route. 200 mg of Pd(ac) 2 was dissolved in 8 ml of acetone and an appropriate amount of the silane NH2(CH 2)2NH(CH 2)3Si(OR) 3 (DIAMO) in an alcoholic solution of ethanol, propanol and butanol with a volume ratio of 70: 15 : 15 was added to the Pd(ac) 2 solution at various ratios of Pd(ac) 2 : DIAMO = 1: y (with y=1,2,3,4,8,20). After 5 min. of stirring at room temperature 20 ml of GPTS/TEOS ('y-glycidoxypropyl trimethoxy silane / tetraethoxy silane) sol was added in order to obtain Pd nanoparticle containing powders, densified at temperatures up to 500 °C in N2-atmosphere. The GPTSITEOS sol was prepared by stirring 160 g of GPTS, 40 g of TEOS and 29 g of H20 in 290 ml of ethanol at 60 °C for 15 hours. The thermal decomposition of Pd(ac) 2 was examined 779 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
by thermal analysis airtight (DSC, Seiko DSC220C) and in Ar atmosphere (DTA/TG, Netzsch STA 409) as a function of the DIAMO concentration. For that Pd(ac) 2 was dissolved in acetone and the appropriate amount of DIAMO was added. The solvent was distilled at 100 mbar and 30 °C within 5 min and the resulting liqiud was dried at 60 °C for 12 h in air. The Pd colloid formation was observed by TEM (JEOL Jem 200 CX) and by WAXS measurements (Siemens D 500). RESULTS AND DISCUSSION
Pd(ac) 2 was chosen as Pd precursor, since other Pd salts like PdCI2, Pd(N0 3)2 or PdSO 4 are hygroscopic and form unsoluble brown oxohydrates 3 . As ligand, DIAMO has been used since it is known that amines easily form complexes with Pd (11)compounds and, in addition to this, the silane can be used for further condensation with other orthosilicates or other organosilanes like GPTS to form solid systems (coatings or powders). In ethanolic solution Pd(ac) 2 is reduced and a black precipitate of Pd is obtained within 5 min. In presence of DIAMO this reduction and precipitation is increasingly suppressed with increasing DIAMO concentrations. Pd(,\C)2 Acetone DIAMO
[Ethanol/Propanol/Butanol precipitation was observed,
whereas a ratio of I : 2 leads to precipitation after 12 hours. For ratios higher than 1 : 3 yellowish clear solutions are obtained that do not
H2N(CH,)2NH(CH2)3Si(OCH3)3
n eevaporation i Acetone
GPTH-H2 )SC -) sin,)TEOS H /H-CH2O(CH2),Si(OCH,)-,Si(OC2H)
Ormocersol Casting and slow solvent removal
Until 500 °C
For a Pd(ac) 2 : DIAMO ratio of 1 : 1 the solution turns black through a brownish state and after 30 min. only
Dip coating D
Until 500 'C N2, Ar, H2/N2
N2 -atmosphere
Fig. 1: Flow chart of the preparation for Pd colloid containing coatings and powders
780
show any precipitation during days. From resultseveral the conclusion canthis be drawn that DIAMO stabilizes the Pd(ac) 2 against reduction by ethanol. To investigate the influence of the stability /of the DIAMO on Pd(ac) 2, a
method for the preparation of
Pd containing inorganicorganic composites had been developed as shown in fig. 1. The experiment showed that no difference
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