Layered aluminum oxygen systems

Storage tanks and transfer lines of liquid oxygen systems must be well insulated to prevent the condensation of moisture or air with subsequent ice formation on the outside. Vacuum jackets, formed plastics, and alternate layers of aluminum foil and glass-fiber mats have been used successfully. 

Upon exposure to oxygen, all metals form surface metal oxide layers which vary in thickness and structure, depending on the identity of the base metal and the oxide formation conditions. Mercury and noble metals generally form very thin oxide films. On the other hand, most metals of primary commercial importance (i.e. aluminum, iron, zinc, etc.), tend to form oxide layers which are thick enough (40-80 A or more), so that the underlying metal atoms do not contribute in an appreciable way to the adhesion forces in metal/polymer systems U). 

In most formulas for potassium nitrate-based flitter effects, the sulfur content of the stars will be found to be below the stoichiometric requirements for the formation of sulfide from all of the potassium nitrate. In most of the formulas of this type there is insufficient carbon to perform the total reduction of the potassium nitrate to form sulfides. Potassium nitrate can react with sulfur to produce sulfate directly and this is common in flitter effects. In all cases flitter effects will be found to have insufficient molten sulfide melts to protect the aluminum from direct reaction with oxygen from air. A thin layer of potassium sulfide at the melting point is quickly oxidized and thus there is rapid loss of the sulfur content. A thin layer of potassium sulfide on aluminum is insufficient to cause delay. The oxidation of the aluminum takes place first through a rate moderating oxygen transport system liquid layer covering the aluminum and then must later take place within the solid jacket of potassium aluminate that forms over the aluminum. This explains the observation that most flitter sparks lose incandescence in a smooth decent of temperatures at the end of their burn. This can also explain why some formulas appear to produce sparks at more than one temperature. Adjustment of flitter effects is easily made with an understanding of the phenomenon involved. 

No Mutual Solubility or Intermetallic Compound Formation System The mechanical properties of interfaces can be predicted based on the form of the binary equilibrium phase diagram [103]. Weak interfaces result in phase systems which do not form compounds or exhibit solubility. This behavior results because the unlike atomic species repel each other, typical of a system like Cr-Cu (Fig. 27). The binary phase diagram shows these species do not exhibit solubility or compound formation, and that the metals do not mix in the liquid state for most compositions. Interfacial adhesion can be improved in these systems by the addition of a glue layer which reacts with both metals. For the Cr-Cu system, the glue layer can be oxygen or another metal such as aluminum. Alternatively, the adhesion can also be achieved... 

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