| الوصف: |
Grain oriented steels containing 3 % silicon are widely used as stacks of thin laminations in\ud transformers and other electrical devices. Phosphate coatings are applied to these laminations\ud in order in insulate between the sheets and hold them under tension, reducing the electrical\ud energy losses and making the transformers more efficient. This thesis explores the properties\ud of aluminium and magnesium phosphate, two commonly used coating materials. Using model\ud phosphate coatings it has been shown that an excess of phosphoric acid is required to cause the\ud condensation reaction that produces the metaphosphate, thought to be the cause of the\ud increased tension imparted on the steel.\ud The addition of chromium oxide was found to prevent this transformation by reacting with the\ud excess acid to form chromium pyrophosphate, which lead to a more stable coating which\ud imparted a greater tension upon the steel substrate.\ud XPS has been shown to be a useful technique for the characterisation of model phosphate\ud coatings, however it cannot be used to quantitatively analyse the systems (unlike other\ud phosphate systems) possibly due to the higher number of phases present within the samples. |