Platinum sulphide

Flower shaped crystalline deposit on the surface of the solid non-crystalline mass of platinum sulphide was probably due to the precipitation of elemental sulphur, which deposited as a floral growth on the non-crystalline platinum sulphide precipitate. Ultrasonic irradiation seemed to have broken tender sulphur flakes and cleaned the surface. The free sulphur, however, did not deposit further. This was probably due to the formation of other compounds of sulphur such as H2S, S02, etc. which could have been removed from the solution due to the phenomenon of degassing. 

When plates of platinum are kept in an alkaline solution of potassium permanganate for some twenty-four hours at the ordinary temperature they become superficially attacked, and on treatment with dilute potassium iodide solution and hydrochloric acid, red solutions are obtained, from which platinum sulphide may be precipitated on passage of hydrogen sulpiride.4... 

An obvious disadvantage lies in the fact that the bulk of the precipitate is increased, and of course the mercuric vapours evolved upon ignition are poisonous. For these reasons magnesium chloride has been recommended, since the presence of this salt in solution assists precipitation of the platinum sulphide, which is obtained in a pure state upon washing with acidulated water.4... 

Najdeker, E., Bishop, E. 1973. The formation and behaviour of platinum sulphide on platinum electrodes.. Electroanal. Chem. 41 79-87. 

Figure 1.6 A target structure, two secondary building units (SBU) and the synthon. The synthon defines the elicmical bonding that holds the building blocks (or tcctons) together and the SBU s define the geometry around each node. The tectons are what we mix in the reaction. These technical tenns are useful but will be used only sparingly in this text. Tlic resulting pts (for platinum sulphide) net has both tetrahedral and square planar nodes, and is thus binodal.

In the last example the cds net was built from two different types of nodes having the same basic geometry. We now turn to two nets that are constructed from nodes with different geometry, the square and the tetrahedron. First of these is the platinum sulphide or pts net, see Figure 5.16. 

Figure 5.18 The azide ion (NY) is not only potentially explosive but also a very versatile Imdging ligand as for example in this catcna tetrakis(g -A7ido-N.N )-dipyridyl-chr(Knium-dipyridyl-potassium] compound that contain one single pts or platinum sulphide net [37].

Niobium like tantalum relies for its corrosion resistance on a highly adherent passive oxide film it is however not as resistant as tantalum in the more aggressive media. In no case reported in the literature is niobium inert to corrosives that attack tantalum. Niobium has not therefore been used extensively for corrosion resistant applications and little information is available on its performance in service conditions. It is more susceptible than tantalum to embrittlement by hydrogen and to corrosion by many aqueous corrodants. Although it is possible to prevent hydrogen embrittlement of niobium under some conditions by contacting it with platinum the method does not seem to be broadly effective. Niobium is attacked at room temperature by hydrofluoric acid and at 100°C by concentrated hydrochloric, sulphuric and phosphoric acids. It is embrittled by sodium hydroxide presumably as the result of hydrogen absorption and it is not suited for use with sodium sulphide. 

It must be appreciated that at high temperatures platinum permits the flame gases to diffuse through it, and this may cause the reduction of some substances not otherwise affected. Hence if a covered crucible is heated by a gas flame there is a reducing atmosphere in the crucible in an open crucible diffusion into the air is so rapid that this effect is not appreciable. Thus if iron(III) oxide is heated in a covered crucible, it is partly reduced to metallic iron, which alloys with the platinum sodium sulphate is similarly partly reduced to the sulphide. It is, advisable, therefore, in the ignition of iron compounds or sulphates to place the crucible in a slanting position with free access of air. 

Z 1 Niobium 1 Nitrate 1 Osmium 73 a. I Perchlorate Phenols u a o Platinum o 0. 1 5 u 1 Rhodium 1 Rubidium Ruthenium Scandium 1 Selenium Silver I Sodium 1 Strontium 1 Sulphate Sulphides, organic Sulphur dioxide 1 Tantalum 1 Tellurium 1 Thallium Thorium e H 1 Titanium a u ab a 1- I Uranium 1 Vanadium 1 Yttrium 1 Zinc Zirconium... 

The metals are obtained from the metallic phase of the sulphide matte or the anode slime from electrolytic refining of nickel. In the traditional process for the platinum metals, their separation was facilitated by their solubility in aqua regia and convertibility into PdCl - or PtCl - salts. Nowadays, substantial amounts are obtained using solvent extraction. 

Very low asymmetric induction (e.e. 0.3-2.5%) was noted when unsymmetrical sulphides were electrochemically oxidized on an anode modified by treatment with (— )camphoric anhydride or (S)-phenylalanine methyl ester299. Much better results were obtained with the poly(L-valine) coated platinum electrodes300. For example, t-butyl phenyl sulphide was converted to the corresponding sulphoxide with e.e. as high as 93%, when electrode coated with polypyrrole and poly(L-valine) was used. 

In this area, the PGM are distributed in (a) disseminated sulphides, mostly in pyrrhotite, chalcopyrite and pentlandite. The predominant platinum minerals are Pt-Fe alloys, cooperate (PtS) and sperrilite (PtAs2) (b) massive sulphide ores where the predominant PGM are Pt-Fe alloys, rustenburgite (Pt3Sn) and sperrilite (PtAs2), occurring in fine inclusions in chalcopyrite and pyrrhotite and finally (c) disseminated veins and brecia ores that may consist of mainly chalcopyrite or pyrrhotite. The PGM in these ores is present as Pt-(cooperate) and Pd-(rysotkite) sulphides. 

The ores from this region are of tholeiitic intrusions hosting Cu-Ni sulphides with relatively low PGM content. In these ores, most of the palladium is associated with pentlandite, where the platinum and rhodium are mainly associated with pyrrhotite. Only sperrilite and Pt-Fe alloys have, so far, been found in these ores. 

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