- 學位論文
鎳磷與鈷磷合金電鍍
Electrodeposition of Nickel-Phosphorus and Cobalt-Phosphorus Alloys
摘要
鎳磷與鈷磷合金鍍層之性質取決於其磷含量和微結構。本研究分別於胺基磺酸鎳與胺基磺酸鈷溶液中添加0~40g/l亞磷酸，藉由直流電鍍製備鎳磷與鈷磷合金，發現鍍層磷含量會隨著鍍液中亞磷酸濃度增加而遞增，然而陰極電流效率卻隨鍍液中亞磷酸濃度增加而遞減。鍍層微結構之演變隨鍍層磷共鍍量的增加，依序從純鎳與純鈷之柱狀晶轉為層、柱共存的組織，再轉變為細緻的層狀結構，最後形成非晶質結構，鍍層微結構及電鍍過程中氫的還原會影響鍍層之硬度與內應力。鎳磷合金在低於400℃熱處理1小時後，硬度因含磷化合物的析出而增加，同時鍍層磷含量愈多會有較多含磷化合物的析出，阻礙晶粒成長而保有較高的高溫強度，熱處理溫度超過500℃時，鎳基地晶粒與Ni3P的成長導致鍍層硬度下降。鈷磷合金熱處理時，在鈷基地中會有大量的退火雙晶生成，所以鈷磷合金抗高溫軟化能力優於鎳磷合金。 脈衝電鍍能夠提高鍍層磷含量並改善電流效率與內應力。低負載率可製備高磷含量鍍層，同時保有高電流效率。低負載率為10%時，晶粒尺寸則隨著脈衝頻率的增加而變大，鍍層內應力隨著脈衝頻率的增加而有降低的趨勢。糖精的添加會改變鎳磷鍍層電化學的結晶行為，雖有助於降低鍍層內應力，但有機分子吸附在電極表面，使鍍液中亞磷酸根離子不容易吸附並還原，造成鍍層磷共鍍量大幅降低。
並列摘要
Properties of Ni-P and Co-P electrodeposits can be best related to the phosphorus content and microstructure of the deposit. In this study, Ni-P and Co-P deposits were electroplated using the direct current in nickel and cobalt sulfamate solutions, respectively, with the addition of 0~40 g l-1 phosphorous acid (H3PO3). Experimental results indicate that deposit phosphorus content increased, while the current efficiency decreased with increasing bath H3PO3 concentration. Concomitant with the increase in deposit phosphorus content, the structure of the deposit evolved from coarse columnar grains for pure Ni and Co deposits to the mixture of column and laminate, then fine laminates, and finally amorphous structure. Both the deposit microstructure and proton discharge during electroplating affected the hardness and internal stress of the deposits. The hardness of Ni-P electrodeposits increased after 1 h of annealing at temperatures less than 400℃. This increase is due to the precipitation of P-bearing compounds. More P-bearing compounds precipitated and effectively inhibited the growth of recrystallized Ni grains for the deposit with higher phosphorus contents. Consequently, the deposit with more phosphorus generally exhibited higher peak hardness after 1 h of annealing at distinct temperatures. When annealing at temperatures exceeding 500℃, growth of Ni grains and coarsening of Ni3P precipitates prevailed; thereby resulting in a decrease in deposit hardness. Co-P deposits generally had higher softening temperature than Ni-P deposits because after annealing numerous twins formed in Co grains, while Ni grains were rather free of crystalline defects. Unlike dc electroplating, pulse electroplating enhanced the codeposition of phosphorus. And most importantly, pulse plating improved the current efficiency and reduced the internal stress associated with the deposit. Deposits containing high phosphorus contents could be plated under high current efficiency using the low duty cycle pulse currents. Furthermore, for the pulse currents with low duty cycle, namely 10%, both the grain size and internal stress of the deposit decreased with increasing pulse frequencies. The presence of saccharin in the solution modified the electrocrystallization of Ni-P deposit and reduced the internal stress of the deposit. Adsorption of this organic molecule, however, impeded adsorption and subsequent reduction of H3PO3. Therefore, less phosphorus was codeposited when saccharin was added to the solution.