Abstract. A new conservation treatment for outdoor bronze sculptures based on inorganic-organic copolymers (ORMOCER| was designed which meets the special requirements defined for this field of conservation. Following a systematic research strategy, a great variety of starting compounds (main components: 3-glycidoxypropyitrimethoxysilane or 3/-methacryloxypropyltrimethoxysilane), curing conditions, hardeners and additives were considered for modifying the sol-gel materials. The characterization of the lacquers included IR, GPC and viscosity measurements as well as water and epoxy titrations. Screening was carried out by evaluation of the protective effect on bronze substrates. The material properties of the coatings were adjusted to optimize adhesion and resistance against weathering. Particular emphasis was given to curing the sol-gel polymer at ambient temperatures while retaining reversibility even after aging.
The average particle diameter can also be determined from X-ray diffraction experiments. X-ray powder diffraction diagrams of the isolated colloid show all reflections of metallic gold, which proves that the gold atoms in this case are arranged primarily in a cubic face-centered lattice, as in the bulk metal. The presence of significant amounts of icosahedral or polytetrahedral[161 structures, which were postulated earlier. can therefore be ruled out. The average particle size of the metal nuclei (17 nm) was determined from the halfwidth of the intense [ I l l ] reflection by use of the Scherrer formula." ' 1 Evaluation of the electron-microscopic image (Fig. I ) of a sample of the phosphane-stabilized cofloid gave nearly a [I41 The procedure is described in 131. 1151 V= M / e & , ( M = molecularweight,@,, = 19.32 gem-', N, = Loschmidt constant. d = ~$ M M /~~Q N , .[16] M. R. Harrison, P. P. Edwards in P. P. Edwards, C. N. R. kdz (Eds.): The MeiaNic and Nonmetallic SIales yf Molter, ydylor and Franus. London 1985. [**I This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. ;O VCH Verlagsgesellschafi mbH, 0-6940 Weinheim. I989 0570-0833/89jOrr0S-O7XI S OZ.50iO
complexed by axial Cle. The anodic shifts observed for p-octachlorination were once again on the order of 0.5 V.Analysis of current-voltage curves and half-wave potentials," 'I as well as spectroele~trochemistry,['~~ have shown that ferrous TPPs can complex with anions. The highly electron-deficient systems described here have been examined spectroelectrochemically. The weak binding of Cl0 to C1,TPPFe" compared to unsubstituted TPPFe" (KA; Table 2) may be due to steric effects of the bulky ortho-chloro substituents. The P-chlorinated porphyrins, on the other hand, exhibited high stability constants, suggesting that the electronegativity of the p-substituents far outweighs the steric effects of phenyl substitution.Preliminary studies have shown that these highly electronegatively substituted hemins are robust and effective catalysts for cytochrome-P450-related biomimetic studies. Received: March 12, 1990 [Z 3848 IE] German version: Angew. Chem. 102 (1990) 1073 \ a : Aryl = 2.4.6-trirnethylphenyl b : Aryl = Z3.5.6-tetramethylphenyl Me3Si Me& /C=B-Aryl 1 a,b r 1.U 7 L J 2 a,b a : R ' = H , R~= M b: R1=Me,R2=H Me3Si,[l] P. rataallene 4b, the unsymmetrical dimer of 2 b, as major product together with 3b as minor product.I2] The structureC3] of 3a is shown in Figure 1.
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