Erlend Lunde Runestad, 19 år, Trondheim
SHS synthesis and analysis of TiB2 and WB4 using powder XRD and SEM
This project is a culmination of several years of extracurricular work with self-propagating high temperature synthesis of metal rich borides. Self-propagating high temperature synthesis (SHS), is a type of chemical reaction that involves a self-sustaining exothermic process. In this study, the reaction between titanium or wolfram and two different allotropes of boron was carried out, to produce titanium diboride and wolfram borides, respectively.
Ti(s)+2B(s) -> TiB2(s)
W(s)+4B(s) -> WB4(s)
The experiments were set up to investigate the validity of the reactions and also the composition and properties of the resulting material. This also includes investigating the difference between reactions carried out with metallic or amorphous boron and also with the use of varying ignition sources. SHS reactions are carried out at very high temperatures. For example, the ignition temperature for an SHS reaction to produce titanium diboride is approximately 1000°C.
Three methods for ignition and heating were used: An oxygen-acetylene torch, an electric muffle furnace, and also an electric arc with wolfram electrodes. In addition to this, two main methods of analysis were used, including powder x-ray diffraction and scanning electron microscopy. The products of these reactions were mostly porous, except the samples from the electric arc method. Only the reactions with amorphous boron were noted to be self-propagating, as the metallic boron (β-boron) was much less reactive.
The SEM pictures revealed hexagonal TiB2 crystals, and also the presence of hollow hexagonal crystal formations. This means that the sample was porous at both a macroscopic and microscopic level. The XRD analyses proved three major points. Firstly, all three methods and both boron allotropes were able to produce titanium diboride. However, the methods using amorphous boron produced the most pure and uniform samples of titanium diboride, while the metallic boron methods contained many oxide and nitride impurities. Secondly, the methods using metallic boron and electric arc heating seemed to produce different amounts of nitride impurities depending on their exposure to air. This concludes that these reactions should be performed in an inert atmosphere. Lastly, the wolfram tetraboride tests suggested that most of the wolfram did not react and also formed W2B5 instead of WB4.
For future experiments, it could be beneficial to recreate the muffle furnace experiments, to further study the hollow hexagonal crystals created. The hollow crystals could potentially give an extremely porous material with an enormous surface area, which is very beneficial for catalytic purposes.