Coatings are a very established way of protecting a surface from the environment, harsh substances, or substances that could readily oxidise the surface. But what happens when you use nanomaterials to make barrier coatings?
There are many benefits that nanomaterials bring to barrier coatings; and what the coating is made of is usually dependent on the degree of conformability required around the surface (which takes into account the geometry of the surface), the composition of the material being protected, the environment which the coating will be in, and the harmful molecules that the surface needs to be protected against. Barrier coatings is one application area where a range of nanomaterials have found great use, in a range of forms and for a range of specific applications/environments.
There are many ways in which nanomaterials can be used to form barrier coatings. Some of the most common methods include the bottom up fabrication of coatings using physical vapour deposition (PVD), chemical vapour deposition (CVD) and atomic layer deposition (ALD) methods, as well as formulated inks.
One of the main reasons that nanomaterials have become an option in barrier coating applications is due to their high stability. Whilst it can’t be said for all nanomaterials—as nanomaterials is a very wide-ranging field that encompasses both soft and hard materials—there are plenty of options out there which are highly stable under many conditions. Aside from being stable to many conventional environments, including those where water and moisture can cause corrosion to a surface, many are resistant to high temperatures, highly corrosive chemicals and high pressures. In addition to the inherent barrier properties brought about by their high stability, there are a select few which also exhibit a high degree of flexibility; and the combination of these barrier and flexibility properties make them an ideal choice for conformal-style coatings that can often mould to complex geometries. Additionally, there are nanomaterials which can be formulated into inks, which in turn can then either be printed, painted or coating on to a surface (depending on the area of the surface) to provide barrier properties.
So what applications do nanotechnology-based barrier coatings find themselves in?
There are many. Anti-corrosion and anti-fouling coatings are some of the most recent promising areas, with materials, such as graphene, being able to provide a stable barrier against water and moisture on the hulls of boats, and as a barrier against biological matter in medical prosthetics. There are also many nanomaterials, from nanosized clays to thin film inorganic oxides, that can be added into polymer matrices to produce many types of nanocomposites, which have use across the food packaging industry to keep out air and harmful bacteria. In food packaging applications, another benefit often seen is that the nanocomposites have anti-microbial properties, so they can better protect the internal environment inside the packaging and provide a barrier to the outside environment. Essentially any surface or internal environment (if encased) can be protected from air, moisture, water, and many other hazardous substances using nanomaterials in the coating.
Many of the inorganic-based nanomaterials (and graphene) also have a very high resistance to temperature. This is a very useful property in oil and gas applications, as well as in engines and turbines. Not only can nanomaterial-based coatings provide a thermal barrier to the high temperatures in oilfield and downhole drilling applications, they can double up as a barrier to the common corrosive substances found in these environments, such as hydrogen sulphide gas, and better protect and increase the longevity of the equipment used. Other applications where nanomaterials can provide a thermal barrier include aerospace engines and industrial gas turbines, where temperatures can reach above 1300 °C. In these high temperature environments, nanotechnology barrier coatings can reduce the thermal conduction in these systems and lower the overall operational temperatures, thus minimizing the possibility of the system overheating and/or damaging the surrounding parts.
Written by Liam Critchely