PDF(Pubmed)
Abstract：
Thirty-two short term (∼7.5 h) abiotic experiments were conducted with new ductile iron and copper coupons exposed to various water qualities, including pH (7 or 9), dissolved inorganic carbon (DIC, 10 or 50 mg C L-1) and phosphate (0 or 3 mg P L-1) concentrations and 4 mg Cl2 L-1 free chlorine or monochloramine. To quantify oxidant reactivity with the new metal coupons, microelectrodes were used to obtain oxidant (free chlorine or monochloramine and dissolved oxygen (DO)) concentration and pH microprofiles from the bulk water to near the metal coupon surface. From the microprofiles, apparent surface reaction rate constants (k) were determined for each oxidant. An ANOVA analysis evaluated if the five variables (Material, Oxidant, Phosphate, DIC, and pH) significantly affected estimates of k, finding that the Material and Oxidant variables and their interaction were statistically significant (p<0.05), but the effect of variables of Phosphate, DIC, and pH on k values were not significant in this study. In general, both ductile iron and copper coupons showed significant surface reactivity towards free chlorine and monochloramine. For ductile iron, DO consumption was greater than for copper, which showed minimal DO reactivity, and DO was less reactive towards the copper surface than either free chlorine or monochloramine. Furthermore, pH microprofiles provided insight into the complexity that might exist near corroding metal surfaces where the bulk water pH may be substantially different from that measured near metal surfaces which is significant as pH is a controlling variable in terms of scale formation and metal solubility. This study represents an important first step towards using microelectrodes to (1) understand and provide direct measurement of oxidant microprofiles from the bulk water to the metal surface; (2) determine pipe wall reactivity using the directly measured concentrations profiles versus estimated pipe wall reactivity from bulk water measurements, and (3) understand how variables measured by bulk water samples (e.g., pH) may be drastically different from what is occurring at and near the metal surface. Together, these insights will assist in understanding disinfectant residual maintenance, corrosion, and metal release.
摘要：
用暴露于各种水质的新型球墨铸铁和铜片进行了32项短期（〜7.5h）非生物实验，包括pH（7或9），溶解的无机碳(DIC，10或50mgCL-1）和磷酸盐（0或3mgPL-1）浓度和4mgCl2L-1游离氯或一氯胺。为了量化新金属试样的氧化剂反应性，微电极用于从主体水到金属试样表面附近获得氧化剂（游离氯或一氯胺和溶解氧（DO））浓度和pH微曲线。从微观轮廓来看，确定每种氧化剂的表观表面反应速率常数（k）。方差分析评估了五个变量(材料，氧化剂,磷酸盐,DIC,和pH)显著影响k的估计值，发现材料和氧化剂变量及其相互作用具有统计学意义(p<0.05)，但是磷酸盐变量的影响，DIC,在本研究中，pH对k值的影响不显著。总的来说,球墨铸铁和铜试样对游离氯和一氯胺均显示出显着的表面反应性。对于球墨铸铁，DO消耗大于铜，显示出最小的DO反应性，和DO对铜表面的反应性低于游离氯或一氯胺。此外，pH微曲线提供了对在腐蚀的金属表面附近可能存在的复杂性的洞察,其中主体水pH可能与在金属表面附近测量的显著不同,这是显著的,因为pH是结垢形成和金属溶解度方面的控制变量。这项研究代表了使用微电极的重要的第一步，以（1）了解并提供从主体水到金属表面的氧化剂微轮廓的直接测量;（2）使用直接测量的浓度分布确定管壁反应性与从主体水测量估计的管壁反应性，和(3)了解如何通过散装水样测量变量(例如，pH）可能与金属表面及其附近发生的情况大不相同。一起,这些见解将有助于了解消毒剂残留的维护，腐蚀,和金属释放。
