Anti-tarnish Characteristics and Formation Mechanism of Self-Assembled Monolayers on Surface of Silver Coins

作者：Liang Chenghao^*; Yang Changjiang; Huang Naibao; Jin Guangming

来源：Rare Metal Materials and Engineering, 2013, 42(7): 1411-1417.

• Silver coin
• anti-tarnish
• self-assembled monolayers
• formation mechanism

Octadecanethiol (C18SH) self-assembled monolayers (SAM) were prepared on the silver coin surface. The anti-tarnish characteristics of C18SH SAMs were investigated in 0.5 mol/L NaCl+0.01 mol/L Na2S solution by an electrochemical technique. The results indicate that silver's corrosion potential moves by 30 mV to positive direction after forming SAMs. C18SH SAMs could inhibit oxygen depolarization and silver sulfuration. The inhibition effect for cathode process is better than that for anode. After SAMs is formed on the surface of silver, the silver coin's charge-transfer resistance increases and double layer capacitance decreases. The formation of SAMs on silver is in accordance with a two-phase model. In the initial stage, the adsorption obeys two grade Langmuir equation, which is theta(t)= 1.706ct/1+ 1.706ct. In the latter stage, the adsorption is the process of reforming and recrystallization, and is in accordance with one grade Langmuir equation, which is theta(t) = 1-e(-0.547)ct The relationship between rate constant and temperature is ln(k)=-5826/T+26.5 during absorption. The apparent activation energy of self-assembled process is 48.4 kJ/mol and the self-assembled process is controlled by chemical adsorption.

• 出版日期2013-7
• 单位昆明理工大学; 大连海事大学