Adherent coatings

Zirconium metal exhibits passivity in air due to the formation of adherent coatings of oxide or nitnde. Even without the coating, it is resistant to the action of weak acids and acicl salts, but dissolves in HC1 (warm) or H2SO4 slowly, and more rapidly if F is present, forming compounds of Zr02+ ions, or fluorozneonates in the last case. 

Many metals on being heated in dry air or oxygen yield an adhering coat of oxide which tends to protect the underlying metal from attack. The rate at which oxidation proceeds at any temperature is given by the expression1... 

Adherent coatings of diborides can also be obtained by thermal decomposition of boron halides. 

Loose molybdenum disulphide powder has only a limited tendency to adhere to solid surfaces. Very fine powders will attach loosely to metal surfaces, but the coarser grades commonly used for lubrication will not. However, there are several techniques which will produce soft adherent coatings. 

The most straightforward technique for producing a thin uniform adherent coating is by the use of an adhesive binder, and bonded coatings were introduced very early in the modern development of molybdenum disulphide technology. They are probably now the most widely used form of molybdenum disulphide lubricant, and as long ago as 1968 Gresham estimated that over 95% of the solid lubricants commercially used were resin-bonded. 

In this context we might mention that surface preparation is a major factor in obtaining good, adherent coatings of any type. Degreasing, chemical cleaning and, in some cases, mechanical treatment are essential steps in the preparation of the surface for coating, which often consists of several layers, for optimum protection. 

Pre-coat microscope slides by adding 100 pL of 0.5% LMP agarose on to one end of each slide. Using another slide, spread the agarose thinly over each slide and dry at 37°C for approximately 2 h to form an adherent coating. 

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