Cathodic protection of carbon steel in natural seawater: Effect of sunlight radiation

Cathodic protection of metals in seawater is known to be influenced by chemical–physical parameters affecting cathodic processes (oxygen discharge, hydrogen evolution and calcareous deposit precipitation). In shallow seawater, these parameters are influenced by sunlight photoperiod and photosynthetic activity. The results presented here represent the first step in studies dedicated to cathodic protection in shallow photic seawater. This paper reports on carbon steel protected at −850 mV vs. Ag/AgCl (oxygen limiting current regime) in the presence of sunlight radiation but in the absence of biological and photosynthetic activity, the role of which deserves future research. Comparison of results obtained by exposing electrochemical cells to daylight cycles in both biologically inactivated natural seawater and in NaCl 3.5 wt.% solutions showed that sunlight affects current densities and that calcareous deposit interfere with light-currents effects. Sunlight radiation and induced heating of the solution have been separated, highlighting results not otherwise obvious: (1) observed current waves concomitant with sunlight radiation depend fundamentally on solar radiation, (2) solar radiation can determine current enhancements from early to late phases of aragonite crystal growth, (3) a three-day-old CaCO₃ layer reduces but does not eliminate the amplitude of the current waves. Theoretical calculations for oxygen limiting currents and additional field tests showed that sunlight, rather than bulk solution heating, is the main cause of daily current enhancements. This was confirmed by polarizations performed at −850 and −1000 mV vs. Ag/AgCl (constant bulk temperature), during which the electrode was irradiated with artificial lighting. This test also confirmed O₂ discharge to be the cathodic process involved. A mechanism of radiation conversion to heat in the oxygen diffusion layer region is proposed.     

The influence of ageing of epoxy coatings on adhesion of polyurethane topcoats and protective properties of coating systems

The dependence of adhesion and protective properties of coating systems on surface properties of epoxy intermediate coatings, aged and non-aged before an application of polyurethane topcoats, were examined. The intermediate coatings were aged 500 h in UV chamber. The surface free energy and polar groups were estimated after ageing. After applying polyurethane topcoats on aged and non-aged epoxy coatings, resistance to salt spray and thermal shocks were tested as well as internal stresses were measured before and after corrosion tests.The results showed that adhesion in coating systems with polyurethane topcoats applied on aged epoxy coatings depends strongly on the degradation degree of epoxy intermediate coatings and the value of generated internal stresses. Coatings with good adhesion retention in corrosion environments have good protective properties even when temporary blistering has occurred.     

复合型防腐隔热漆的制备和性能研究

以水性丙烯酸树脂为成膜物质,配合防锈颜填料及以空心玻璃微珠为隔热填料,制备出了集防腐、隔热于一体的单组分水性防腐隔热漆.采用电化学阻抗测试技术及3%NaCl浸泡实验,确定涂料最佳颜基比为1.0.常规性能测试和隔热能力测试表明,玻璃微珠用量为8%(质量分数)时,涂层综合性能最优:附着力1级,柔韧性1 mm,抗冲击强度50 kg·cm;与不含微珠的底漆相比,温度低约6.8℃.     

微波通信站的防雷与接地技术探讨

微波通信站的防雷是一项系统工程,应强调全方位综合治理。本文针对微波站雷电防护,系统分析了泄放、隔离、屏蔽、均压等电位及联合接地设计等防雷原理和措施。     

尿素合成系统设备的腐蚀与防护

讨论了尿素合成系统设备的腐蚀机理、腐蚀现象和防护措施。尿素合成反应是在尿素合成塔中高温、高压下进行的,尿液和甲铵液对设备有强烈的腐蚀性。尿素合成塔的腐蚀情况,因不同的部位和操作条件,所产生的腐蚀现象与结果也不同。从材质的选择、材质的处理、采用合理的检漏设计和生产中的操作与控制进行防护。     

环氧乙烷氧化反应器化学钝化处理

通过环氧乙烷氧化反应器化学钝化处理的实践,讨论了碳钢设备采用含氨柠檬酸酸洗,再用亚硝酸钠钝化的几个关键技术,钝化应严格控制亚硝酸钠加入量,pH、温度、铁离子浓度与氧离子浓度等.     

化学转化膜的发展动态

出于节能、降耗、减排、可持续发展战略的需要,上世纪应用广泛的磷化和钝化技术,由于对环境的污染和对人类产生一定的危害,而逐步被新兴的转化膜技术所取代.本文介绍了几种新型代磷化、钝化工艺的化学转化膜技术,指出绿色防腐技术的开发、完善与成熟是大势所趋.     

离心机氮气保护防爆系统设计

离心机在国民经济许多领域如化工、制药等行业中应用极广,这些行业大多对离心机具有防爆等保护措施要求。介绍离心机在这些工业应用中,一种有效的保障安全生产的结合应用数字测氧仪的氮气保护防爆系统设计。     

脱水莴苣片的护色工艺研究

针对脱水莴苣片在贮藏过程中的变色问题进行研究,寻找出有效的护色方法。首先。通过研究最佳的热烫条件,保证酶活对颜色没有影响,并尽量减少热烫对颜色的损失,选择出最佳的热烫条件为95℃、4min。然后,采用各种护色方法进行试验,最终得出了糖和盐的渗透处理是最好的护色方法。并研究了渗透处理对莴苣片的其他影响,得出渗透处理不但提高了色素的稳定性,而且降低了水分活度。增加了产品的得率,提高了复水速率。     

中国钛白粉工业发展方向评述——硫酸法和氯化法前景分析

客观分析当前中国钛白工业的状况,分析未来发展趋向,以及相关政策的介绍,有助于对钛白工业的了解和未来前景的认知。