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Metallic corrosion
Basic principies
The most pertinent form of corrosion related to metallic biomaterials is aqueous corrosion .The occurs when electrochemical reactions take place on a metallic surface in an aqueous eletrolyte.There are always two reactions that occur:the anodic reaction,which yields metallic ions, for example,involving the oxidation of the metal to its salt:
M---M(n+) +n(electrons) (1)
And the cathodic reaction,in which electrons so generated are consumed.The precise cathodic reation will depend on the nature of the electrolyte ,but two of the most important in aqueous environments are the reduction of hydrogen:
2H+ +2e-——H2 (2)
And the reduction of dissolved oxygen :
O2 +4H+ +4e——2H2O (3)
In acidic solutions or :
O2+2H2O+4e-——4OH- (4)
in neutral or basic solutions.
In all corrosion processes,the rate of the anodic or oxidation reaction must equal the rate of the cathodic or reduction reaction.This is a basic principle of electrochemically based metallic corrosion.It also explains how variations in the local environment can affect the overall rate of corrosion by influencing either the anodic or cathodic reactions.The whole corrosion process can be arrested by preventing either of these reactions.
From a thermodynamic point of view ,first consider the anodic dissolution of a pure metal isolated in a solution of its salt. The metal consists of positive ions closely surrounded by free electrons.When the metal is placed in a solution,there will be a net dissolution of metal ions since the Gibbs free energy(△G)for the dissolution reaction is less than for the replacement reaction.This leaves the metal with a net negative charge,thus making is harder for the positive ions to leave the surface and increasing the △G for the replacement reaction.At this point,a dynamic equilibrium is reached and a potential difference will be set up across the charged double layer surrounding the metal.The potential difference will be characteristic of the metal and can be measured against a standard reference electrode.When this is done against a standard hydrogen electrode in a 1 N solution of its salt at 25℃,it is defined as the standard electrode potential for that metal (Table 1).

金属腐蚀
基本principies
最相关的形式的腐蚀有关的非金属材料是水的腐蚀。时,就会发生电化学反应发生在金属表面,在一水eletrolyte.there始终是两种反应发生的:阳极反应,殖利率金属离子,例如,涉及氧化金属及其盐:
米---米( + ) + (电子) ( 1 )
和阴极反应,在其中电子,使产生的是consumed.the精确的阴极反应将取决于性质的电解质,但两个最重要的在水溶液中的环境是减少氢:
2小时+ 2 e ---与H2 ( 2 )
和减少溶解氧:
O2的4 H +的四专-2 h2o( 3 )
在酸性溶液中或:
O2的2 H2O的4 e --- 4oh - ( 4 )
在中性或基本的解决办法。
在所有的腐蚀过程,率或阳极氧化反应,必须平等率阴极或减少reaction.this是我国的一项基本原则,基于电化学金属corrosion.it还介绍了如何的变化在当地的环境可以影响整体率腐蚀的影响,无论是阳极或阴极reactions.the整个腐蚀过程可以被逮捕,以防止上述两种反应。
从热力学的角度来看,首先考虑阳极溶解纯金属孤立在一个解决方案,其盐。金属构成的正离子紧密包围免费electrons.when金属是放置在一个解决方案,将会净解散金属离子以来,吉布斯自由能( △克)解散的反应是少于为置换反应这叶片金属与净负电荷,从而使更难为正离子离开表面,并增加△克,用于更换reaction.at这一点,它是一个动态的平衡是达成和电位差将成立全国被控双层围绕metal.the电位差会的特点,金属和可衡量的标准参考electrode.when这样做是对的标准氢电极在1 n解决方案,其盐在25 ℃ ,定义为标准电极电位为金属(表1 ) 。
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第1个回答  2008-07-10
金属腐蚀
基本原理
最相关的形式的腐蚀有关的非金属材料是水的腐蚀。时,就会发生电化学反应发生在金属表面,在一水eletrolyte.there始终是两种反应发生的:阳极反应,殖利率金属离子,例如,涉及氧化金属及其盐:
米---米( + ) + (电子) ( 1 )
和阴极反应,在其中电子,使产生的是consumed.the精确的阴极反应将取决于性质的电解质,但两个最重要的在水溶液中的环境是减少氢:
2小时+ 2 e ---与H2 ( 2 )
和减少溶解氧:
O2的4 H +的四专-2 h2o( 3 )
在酸性溶液中或:
O2的2 H2O的4 e --- 4oh - ( 4 )
在中性或基本的解决办法。
在所有的腐蚀过程,率或阳极氧化反应,必须平等率阴极或减少reaction.this是我国的一项基本原则,基于电化学金属corrosion.it还介绍了如何的变化在当地的环境可以影响整体率腐蚀的影响,无论是阳极或阴极reactions.the整个腐蚀过程可以被逮捕,以防止上述两种反应。
从热力学的角度来看,首先考虑阳极溶解纯金属孤立在一个解决方案,其盐。金属构成的正离子紧密包围免费electrons.when金属是放置在一个解决方案,将会净解散金属离子以来,吉布斯自由能( △克)解散的反应是少于为置换反应这叶片金属与净负电荷,从而使更难为正离子离开表面,并增加△克,用于更换reaction.at这一点,它是一个动态的平衡是达成和电位差将成立全国被控双层围绕metal.the电位差会的特点,金属和可衡量的标准参考electrode.当这样做是对的标准氢电极在1 n解决方案,其盐在25 ℃ ,定义为标准电极电位为金属(表1 ) 。
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