以電化學方法探討鐵粉之絕緣被覆層耐壓性

A Study of Examining the Compaction Ability of Insulating Coatings on Iron Powder Using an Electrochemical Method

鐵粉易氧化，一般需於表面做防蝕處理，常用的防蝕處理是在鐵粉表面形成磷酸鐵被覆層，也可以再被覆一層樹脂做成雙層被覆鐵粉。鐵粉表面被覆層的耐壓性是重要的課題，本研究將鐵粉成形成鐵錠之後，以恆電位儀量測其極化曲線並探討其耐蝕性。未經表面處理的鐵粉耐蝕性差，而表面被覆磷酸鐵的鐵粉腐蝕率大幅下降，腐蝕電位也大幅提升，但磷酸鐵是易破裂的脆性材料，當鐵錠成形壓力大於270 MPa時磷酸鐵層產生破裂，腐蝕率大幅上升。若將磷酸鐵層之上再被覆一層氨基矽烷，此雙層被覆鐵粉的腐蝕率隨成形壓力增加而明顯下降，顯示矽烷層可保護底下的磷酸鐵層不易因壓力而發生破裂，且矽烷層與磷酸鐵層隨著加壓而逐漸緻密，更進一步提升了鐵粉的防蝕能力。

Iron powder is prone to be oxidized and is thus necessary to be subjected to anti-corrosion treatments. Iron powder is usually coated with ferrous phosphate for anti-corrosion, and, in some cases, it is also feasible to coat iron powder with resins after phosphating treatment. The compaction ability of the coating layers appears to be important to the performance of iron powder. In this study, iron powder was pressed into disks followed by the measurements of polarization curves in order to examine its corrosion resistance. The non-treated iron powder would be easily oxidized. On the other hand, the corrosion rate of the phosphate-coated powder was obviously suppressed and its corrosion potential has been largely increased. However, the ferrous phosphate was found to be brittle. When the pressure of compaction was larger than 270 MPa, the phosphate layer cracked and the corrosion rate grew greatly. Interestingly, as the phosphate layer was covered with an amino-polysilane, the corrosion rate of the doubly-coated iron powder decreased with increasing compaction pressure. This suggested that the existence of the silane film has protected the phosphate layer from cracking during pressing. Besides, as the polysilane and phosphate layers became denser, the capability of anti-corrosion has been further improved.