Dynamics of scaling and corrosion in the natural environment: the long-term sustainability of geothermal energy technologies through exp

二氧化碳对碳钢的腐蚀是一种已知的降解机制，其表现在能源部门，特别是在地热能生产中。尽管进行了广泛的研究，但二氧化碳腐蚀过程的复杂性仍然留下了关于真实反应途径的方面，特别是腐蚀产物的生长和局部腐蚀机制尚未解决。尽管人们在加强对二氧化碳腐蚀机制的理解方面进行了广泛的研究，并开发了大量的预测腐蚀模型，但在文献关注方面存在明显的差异。大部分的努力都是为了理解和预测在没有保护性腐蚀产物的情况下的均匀腐蚀，而很少关注存在这种表面沉积物的局部腐蚀。一方面，考虑到局部腐蚀是能源部门最大的失效模式之一，这可能令人惊讶。然而，活性材料（如碳钢）的局部腐蚀机制似乎特别难以阐明和减轻。与被动材料中的局部腐蚀相比，这种过程几乎没有被很好地理解或表征，在被动材料中，机制通常已经很好地建立和接受。许多理论和有影响的参数被分配到碳钢在含二氧化碳环境中的局部腐蚀。其中许多建议围绕着表面化学或表面纹理/组成方面的局部异质性的存在或产生，这些异质性总是促进原电/浓缩细胞或有助于诱导酸化过程，从而加剧离散区域的腐蚀。一个已经被确定为局部腐蚀前兆的因素是与碳酸盐（FexCayCO3）腐蚀产物在钢表面的沉淀有关。当在适当的条件下形成时，这种层可以高度保护整体和局部腐蚀，在实验室研究中可以将腐蚀速率降低两个数量级。这是通过该层作为电化学活性物质的扩散屏障和/或阻断钢表面的活性位点来实现的。尽管腐蚀产物有明显的好处，但许多作者认为，这些层的零星、不均匀覆盖对管道的完整性是有害的，因为它有利于局部腐蚀的开始和扩展。事实上，许多研究论文提到了局部腐蚀的潜在机制与腐蚀产物的局部去除有关。虽然这可能是正确的，但有一些与这一说法相关的复杂性应该被探索，以充分了解这种机制的起源，并考虑可能的替代理论/解释。为了全面了解这些系统中不同的腐蚀模式、步骤和机制，应该了解腐蚀沉积物或部分覆盖的系统中局部腐蚀的实际驱动因素。只有了解所有可能发生的情况、它们的复杂性和这些反应的驱动因素，才能有效地控制这些过程，防止失败。

Carbon dioxide (CO2) corrosion of carbon steel is a degradation mechanism known for its manifestation within the energy sector, particularly in the geothermal energy production. Despite extensive research, the complexities of CO2 corrosion processes has still left aspects regarding the true reaction pathways and, in particular, corrosion product growth and localised corrosion mechanisms, unresolved. Despite widespread research efforts related to enhancing the understanding of CO2 corrosion mechanism, as well as the development of a plethora of predictive corrosion models, there is a clear disparity in literature focus. The majority of effort is directed towards understanding and predicting uniform corrosion in the absence of protective corrosion products, with less attention afforded to localised corrosion in the presence of such surface deposits. On the one hand, this may be surprising given that localised corrosion constitutes one of the greatest failure modes within the energy sector. However, the localised corrosion mechanism in active materials such as carbon steel appears to be particularly difficult to both elucidate and mitigate. Such processes are not nearly as well understood or characterised compared to localised corrosion in passive materials, where the mechanisms are generally well established and accepted. Numerous theories and influential parameters have been assigned to localised corrosion of carbon steel in CO2-containing environments. Many of those proposed revolve around the existence or generation of local heterogeneity in terms of either surface chemistry or surface texture/composition which invariably promotes galvanic/concentration cells or aids in inducing acidification processes which accentuate corrosion in discrete areas.One factor which has been identified as a pre-cursor to localised corrosion is that associated with the precipitation of carbonate (FexCayCO3) corrosion products on steel surfaces. Such layers can be highly protective against general and localised corrosion when formed under appropriate conditions, suppressing corrosion rate by up to two orders of magnitude in laboratory studies. This is achieved through the layer acting as a diffusion barrier to electrochemically active species and/or blocking active sites on the steel surface. Despite the clear benefits of corrosion products, many authors have suggested that the sporadic, non-uniform coverage of such layers is detrimental to pipeline integrity, as it is conducive to both the initiation and propagation of localised corrosion. In fact, a number of research papers refer to the underlying mechanisms of localised corrosion being associated with the local removal of corrosion products. Whilst this may be true, there are some intricacies associated with this statement which should be explored to gain a full appreciation of the initiation of such mechanisms, as well as consideration of possible alternative theories/explanations. The actual driver for localised corrosion in systems under corrosion deposits or where there is partial coverage should be understood in order to have a full appreciation of the different modes, steps and mechanism of corrosion in such systems. Only by having an understanding of all eventualities, their complexities and the drivers for such reactions can these processes be effectively controlled to prevent failures.