What non-metallic materials have good resistance to seawater corrosion?

To facilitate those interested, the components of seawater are listed here. Seawater is a very complex multi-component aqueous solution. Its chemical composition is quite complex. Various elements in seawater exist in certain physicochemical forms. In seawater, copper exists in complex forms, with the majority being in the form of organic complexes. Only a small portion of free ions exist as divalent cations; the majority appear as anionic complexes. Therefore, free copper ions account for only a small portion of the total dissolved copper. Seawater contains a very high amount of sodium, but its chemical behavior is quite simple; it exists almost entirely in the form of Na+ ions. The dissolved organic matter in seawater is very complex; it mainly consists of a substance called \"marine humus,\" whose properties are similar to those of humic acid and fulvic acid produced by the decomposition of vegetation in soil. The molecular structure of marine humus has not yet been fully determined, but it can form strong complexes with metals. The components in seawater can be divided into five categories: 1. Major components (abundant, major elements): those with a concentration in seawater greater than 1×106 mg/kg. Examples of these include five cations: Na+, K+, Ca2+, Mg2+, and Sr2+, as well as five anions: Cl¯, SO42¯, Br¯, HCO3¯ (CO32¯), and F¯. There is also H3BO3 in molecular form; together, these make up 99.9% of the salts in seawater. Therefore, they are called the main components. Due to the high concentrations of these elements in seawater, their concentration ratios remain approximately constant, and changes in biological activity or total salinity have little impact on them; hence they are known as conservative elements. The Si content in seawater is sometimes also greater than 1 mg/kg, but since its concentration is greatly influenced by biological activity and its properties are unstable, it is considered a non-conservative element; therefore, Si is not included when discussing the main components. 2. Gaseous components dissolved in seawater, such as oxygen, nitrogen, and inert gases. 3. Nutrient elements (nutrients, biogenic elements): These are mainly the elements related to the growth of marine plants, typically referring to N, P, and Si. The concentrations of these elements in seawater are often influenced by plant activity; when their levels are low, it can hinder the normal growth of plants. Therefore, these elements are of great significance to living organisms. 4. Trace elements: Those that are present in very low amounts in seawater but are not considered nutritional elements. 5. Organic substances in seawater: such as amino acids, humus, chlorophyll, etc. These are the main components of seawater. Seawater contains various salts dissolved in it, and the origin of these salts is a complex issue related to the formation of the Earth, as well as the development and evolution of the oceans. It is generally believed that salts mainly originate from the weathering products of crustal rocks and volcanic ejecta. Furthermore, rivers around the world deliver 5.5×1015 g of dissolved salts to the oceans each year, which is also one of the sources of salt in seawater. Based on its origin, seawater seems to contain all the elements on Earth; however, due to limitations in analytical capabilities, only over 80 elements have been identified so far. Some of the important elements are listed in the table below. Chemical forms and concentrations of the most important dissolved elements in seawater
Element | Average concentration | Unit (per kg of seawater)
Li | 174 μg |
Fe | 55 mg |
B | 4.5 mg |
Ni | 0.50 μg |
C | 27.6 mg |
Cu | 0.25 μg |
N | 420 μg |
Zn | 0.40 μg |
F | 1.3 mg |
As | 1.7 μg |
Na | 10.77 g |
Br | 67 mg |
Mg | 1.29 g |
Rb | 120 μg |
Al | 540 mg |
Sr | 7.9 mg |
Si | 2.8 mg |
Cd | 80 ng |
P | 70 μg |
I | 50 ng |
S | 0.904 g |
Cs | 0.29 μg |
Cl | 19.354 g |
Ba | 14 μg |
K | 0.399 g |
Hg | 1 ng |
Ca | 0.412 g |
Pb | 2 ng |
Mn | 14 ng |
U | 3.3 μg |
The components with higher concentrations in the table generally represent their average concentrations in seawater. Some elements with lower concentrations are difficult to measure, and there are few samples available for analysis; therefore, it is challenging to determine their average concentrations. Many metals of interest are present in extremely low concentrations in seawater, and can only be detected using sensitive testing instruments and techniques, while avoiding contamination during sample collection and analysis. Based on the above, I believe the simpler the polymer structure, the better, such as polyethylene and polypropylene. This post was last edited by QXZ-1966 on 2009-4-5 12:41]

Polyethylene is the better choice; propylene contains methyl groups and tends to age easily. . .

Ethylene; nylon is produced by polycondensation, and the ester groups are unstable

I don’t know what operating conditions it is for? If it is for manufacturing heat exchangers, graphite is the best choice.