PI: Luís Vieira
Corrosion protection is of a great importance. The yearly losses because of corrosion are about 10% of the overall amount of the produced metals. Intensive studies aim either to create new effective protection materials or to improve the performance of those that are currently in use. Some of the efforts are directed towards the development of "smart" additives to coatings, capable of efficiently protect a metal surface if and only if the coating is damaged and corrosion conditions occur. One of the promising solutions pursued here is the use of layered or porous structures loaded with corrosion-inhibiting species. Since recently, layered double hydroxides (LDHs) have been considered as excellent containers for storage and controllable release of anions-inhibitors. The characteristic scale of the "layer-interlayer" structure in LDHs varies from about 0.7 to several nanometers, depending on the nature of the intercalated anions. Such nanocontainers can be incorporated into polymer protection coatings for metal surfaces. The nanocontainers based on Zn-Al and Mg-Al LDHs intercalated with inorganic anions-inhibitors have been shown to provide active protection for aluminium alloys, both by releasing inhibitors that suppress the corrosion reaction, and by trapping corrosion-active anions. However, these nanocontainers are rather inefficient for protection of steels and Al-alloy/steel combinations. More versatile nanocontainers using suitable combinations of organic or inorganic anions-inhibitors must be created. In addition, the unique ion sorption capability of LDHs may also be used for loading the outer surface of the nanocontainers with specific inhibiting species (e.g., Ce(III)-containing ones). In this way, synergetic effects of inhibitors that act along separate protection paths can be expected. Finally, the products of the decomposition of the nanocontainer itself may still provide additional useful effects. For example, under corrosion conditions, nanocontainers based on vanadium- and calcium-containing LDHs are expected to give rise to V(III) and Ca(II) based compounds that may prolong the protective effects beyond the time scale of the main protective action.
The conventional methods of preparation of LDHs are water- and time-consuming. Cheaper reagents and more efficient processes are needed. This project also aims to develop methods of production of nanocontainers, either by using Ca-containing bio-wastes or widely spread and easy available (CaCO3-based) minerals.
Due to its layered structure, the LDH crystallites and particles are strongly anisotropic and inclined to agglomeration. This may complicate the production of homogeneous distribution of LDH-nanocontainers in polymer layers (of the order of 1 um thick), and reduce the quality of the protective coatings. In this respect, we will continue our promising preliminary tests to explore the use of high-power sonication in appropriate media to help deagglomerate the particles. We will also try to make useful the intrinsic anisotropy of the particles. Nanocontainers with paramagnetic cations Co(II), Fe(III) and/or high polarizable cations, such as Sn(II) and Bi(III), have the potential to be driven and reoriented by the action of external magnetic or electric fields. This may represent an important tool to improve both the distribution and the arrangement of the particles in the protection polymer coatings.
In this project, a series of new LDH-based nanocontainers loaded with inorganic inhibitors for application in corrosion protection of Al-alloys, steels and their combinations will be produced. These nanocontainers are expected to have an extended functionality in terms of application range, protection performance, and capacity to be used in ultra-thin coatings. The research team has sufficient expertise and technical tools to prepare the materials, investigate their properties, and conduct preliminary tests of their practical application. The work plan includes a thorough analysis of crystal structure and vibrational spectra of some novel LDH compositions. This analysis aims to disclose the correlation between "cation content and ratio - properties", a necessary condition for making possible both the tuning of the nanocontainers properties and the definition of the most efficient compositions for specific corrosion conditions. This integrated effort is new and, most important, includes the search of practical solutions for specific problems. Field tests and trials made in collaboration with the industrial partner will therefore be essential in this project.
- UNIVERSIDADE DO MINHO
- UNIVERSIDADEDE AVEIRO
- SEW - EURODRIVE PORTUGAL S.A.
Orçamento Global: 187 800,00€
Orçamento UMinho: 20 400,00 €
Apoio Financeiro UM
FEDER: 17 340,00€
OE: 3 060,00€
Data início: 01/05/2016
Data Fim: 30/04/2019