The last two posts discussed the mechanical, thermal, and electrical properties of boron nitride ceramics, specifically our HeBoSint® SL-N 300. Today, we will focus on chemical resistance and relative density.
Corrosion: Most people associate corrosion solely with metals, but corrosion actually refers to the chemical attack of a medium on a material. Wear, on the other hand, refers to the deterioration of a material due to tribological stress.
Chemical resistance
Types of corrosion: In general, four forms of corrosion are encountered in technical ceramics: surface corrosion, selective corrosion, pitting corrosion, and intergranular corrosion along grain boundaries. In practice, however, it is often difficult to clearly distinguish between these types, which is why we would like to take a closer look at the influencing factors of the application and the material, as well as their impact on potential corrosion.
Operating temperature: When considering high-temperature corrosion, particular attention must be paid to the thermal weakness of the material in question. Once the melting or decomposition temperature of the respective phase is reached, the likelihood of a corresponding chemical reaction—and thus of corrosion—increases.
Taking this into account, practical application shows that the SL-N 300 material is very well suited for use in metal casting. For metal melts, operating temperatures typically range from 1400 to 1600 °C. Here it becomes apparent that the temperature resistance of the two main phases of HeBoSint® SL-N 300—boron nitride and SiAlON—is sufficient to withstand potential chemical attack, as their temperature resistance is significantly higher than the melting temperature of the metals. In such applications, most oxide ceramics are already ruled out.
Reaction partners: To assess the potential for corrosion, the compounds and elements involved must be examined more closely. It turns out, for example, that base metals in particular are prone to oxidation. The absence of oxygen in non-oxide ceramics is therefore advantageous.
However, oxide ceramics offer an advantage in the presence of excess oxygen. Non-oxide ceramics tend to oxidize even at low temperatures, which is why HeBoSint® SL-N 300 is resistant to air exposure up to approximately 900°C. If, however, the surrounding atmosphere is inert—e.g., argon or nitrogen—a reaction is not expected until temperatures exceed 1800°C. This can be explained by the nitride character of SL-N 300.
Relative Density/Porosity: The reaction surface area is also a key factor in corrosion. This, in turn, is strongly influenced by porosity. This means that materials with low or no open porosity offer as little surface area as possible for chemical attack. In the field of boron nitride ceramics, HeBoSint® SL-N 300 is a material with little to no open porosity, which can represent a corrosion-resistant advantage in light of the aforementioned factors.
As described, corrosion is always influenced by multiple factors, which is why the selection of the most suitable material usually depends on a combination of several properties.
Conclusion and Outlook
In our three-part series on HeBoSint® SL-N 300, we have examined its mechanical, thermal, electrical, and now also chemical properties. A strong performer in every respect. A closer look at the individual properties reveals their interplay and mutual influence. With this material, we have succeeded in achieving a good balance, thereby bringing a composite ceramic to market that meets the highest standards.
If you would like to learn more or need advice, our technical sales team is happy to assist you. We would be happy to advise you and work with you to determine whether our HeBoSint® SL-N 300 is the right solution for you.