Palladium physical properties

Impurities in cmde metal can occur as other metals or nonmetals, either dissolved or in some occluded form. Normally, impurities are detrimental, making the metal less useful and less valuable. Sometimes, as in the case of copper, extremely small impurity concentrations, eg, arsenic, can impart a harmful effect on a given physical property, eg, electrical conductivity. On the other hand, impurities may have commercial value. For example, gold, silver, platinum, and palladium, associated with copper, each has value. In the latter situation, the purity of the metal is usually improved by some refining technique, thereby achieving some value-added and by-product credit. 

Copper [7440-50-8] Cu, produces a reddish color and reduces the melting pokit of the alloy. It produces heat-treatable compositions with gold, platinum, and palladium that result ki kicreased hardness, strength, and generally improved physical properties. The tarnish resistance of the alloy is usually decreased. The gold—copper, Au—Cu, system is the fundamental system of many dental gold alloys. Copper has a useful range of 0—20 wt %. 

On uptake of hydrogen, at lower temperatures distant enough from that of the critical isotherm, the physical properties of palladium or nickel re-... 

Palladium is a soft, silvery-white metal whose chemical and physical properties closely resemble platinum. It is mosdy found with deposits of other metals. It is malleable and ductile, which means it can be worked into thin sheets and drawn through a die to form very thin wires. It does not corrode. Its melting point is 1,554°C, its boiling point is 3,140°C, and its density is 12.02 g/cm. ... 

The physical properties of many macrocyclic polyethers and their salt complexes have been already described. - Dibenzo-18-crown-6 polyether is useful for the preparation of sharpmelting salt complexes. Dicyclohexyl-18-crown-6 polyether has the convenient property of solubilizing sodium and potassium salts in aprotic solvents, as exemplified by the formation of a toluene solution of the potassium hydroxide complex (Note 13). Crystals of potassium permanganate, potassium Lbutoxide, and potassium palladium(II) tetrachloride (PdClj + KCl) can be made to dissolve in liquid aromatic hydrocarbons merely by adding dicyclohexyl-18-crown-6 polyether. The solubilizing power of the saturated macrocyclic polyethers permits ionic reactions to occur in aprotic media. It is expected that this [)ropcrty will find practical use in catalysis, enhancement of... 

Microwave irradiation also shows a beneficial effect in the preparation of solid-supported palladium catalysts for hydrogenation reactions. Thus, alumina- and silica-supported palladium catalysts were synthesised by conventional and microwave heating, and their physical properties and catalytic activity in the hydrogenation of benzene were compared. The alumina-based system prepared under microwave conditions showed turnover numbers an order of magnitude higher than the conventionally prepared catalysts28. 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

In summary, linear phosphorus-containing poly(N-arylanilines) can be readily obtained by palladium-catalyzed C-P bond formation. Their physical properties strongly support electronic delocalization through o3-P centers along the polymer backbone, something that is switched off upon oxidation of the P atoms. 

The development of CFC alternatives has focused on non-chlorinated compounds, such as hydrofluorocarbons (HFCs), which have similar physical properties, but break down in the lower atmosphere.110 111 Consequently, hydrodechlorination is a simple method for the production of HFCs and also for destruction of CFCs108,109,112-114. Palladium is unique among the catalytic metals for its activity and selectivity in this process,102-108,115,116 but using Pd-Au/SiC>2 (Pd Au = 60 40) increased the selectivity for difluoromethane from difluorodichloromethane (CFC-12) shown by Pd/Si02 at 453 K from 40 to 95%.109,112-114... 

R. Rushforth, Superior physical properties make palladium an ideal dental metal,... 

Physical Properties of Compact Palladium.—Palladium is a silver-white metal, somewhat less ductile than platinum, but of equal or slightly greater hardness. It can be hammered into thin plates and drawn out into fine wire. It softens before reaching its melting-point, and can be welded below 1500° C. Its density is variously given,... 

Even though sc CO2 was used in order to increase mass transfer and diffusivity, the activated carbon supported 0.5 wt. % palladium fixed bed catalyst shows a lower hydrogenation activity compared to the 1 wt. % palladium on DELOXAN AP II catalyst tested in the conventional trickle bed hardening process. This result indicates the outstanding advantage of DELOXAN supported precious metal fixed bed catalysts, which can be ascribed to their unique chemical and physical properties. 

NMR STUDIES of ADSORBED CARBON MONOXIDE. In the n.m.r. investigation of molecules adsorbed on solid supported metals, such as palladium on silica or platinum on alumina, both the chemical shift and line width of the observed nucleus in the adsorbate are drastically affected by the physical properties of the sample. The chemical shift anisotropy of a nucleus in a molecule... 

TABLE 26-2. SOME PHYSICAL PROPERTIES OF THE PALLADIUM AND PLATINUM METALS... 

The physical properties have the expected trend, while the thermal instability of the palladium derivative appears anomalous and can perhaps be attributed to a combination of kinetic and thermodynamic factors. (Platinum should be thermodynamically more unstable but kinetically stable.) In any case, it appears that Ni(PF3)4 is more stable than nickel carbonyl, and this confirms that the palladium and platinum tetratri-fluorophosphine derivatives could be prepared. 

The conducting and physical properties can be modified by the use of 3-/4-substituents, or A-substituents in the case of pyrrole. The counter-ions can be incorporated into a side-chain (self-doping), as in the polymer of 3-(thien-3-yl)propanesulfonic acid. Oligo(thiophenes) are also useful in these applications and have been specifically synthesised up to 27 units long by palladium(0)-catalysed couplings or via the diacetylene synthesis (17.12.1.1). ... 

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