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Chemistry and Chemists № 2 2024 Journal of Chemists-Enthusiasts |
Titanium hydride TiH2 in propane burner flame Volodymyr M. Viter |
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I have certainly heard and read about titanium hydride. Five years of university, and seven years of work on a dissertation in inorganic chemistry. Although I was not working on hydrides, but on a completely different topic, hydrides interested me and still interest me. Unfortunately, it is impossible to keep all the information in your head. Therefore, when a colleague mentioned titanium hydride, I found that I did not remember anything about the properties of this compound and its preparation methods. The first thing that came to mind was that titanium hydride might be formed by the interaction of titanium metal and hydrogen upon heating at atmospheric pressure or at increased hydrogen pressure.
A long time ago, when I was studying at university, I would have had to go to the library, order monographs and journals with review articles on hydrides, and then wait an hour and a half for them to be brought. Oh, yes... In those days, the word 'library' did not refer to a site with electronic books or articles as it does now. Instead, it meant a special building containing many shelves with paper books and magazines, and nearby were boxes with paper catalogues. You came, looked in the catalogue (to make sure that the books/magazines you wanted were in the library) and ordered these books or magazines. Then a library employee brought them to you. Sometimes this took a few minutes, and no catalogue was required. For example, if you order the novel "Treasure Island" in the children's library, they bring it to you quickly. But in the Central Scientific Library, from ordering a book to its getting, you had to wait an hour and a half. They had a lot of books and few employees, and they had never heard of such a concept as "labour automation". Nowadays everything is simpler: I sit down at the computer and do a Google search. To begin with, I look on Wikipedia, a source of information that is not entirely reliable, but quite suitable for a preliminary search. It turns out that titanium hydride is formed by treating a titanium sponge with hydrogen under heating conditions at atmospheric pressure. Titanium hydride is brittle (unlike the metal itself), stable in air, and has a non-stoichiometric composition TiH2-x. The hydrogen content varies from 0.02% to 4.0%. Another name for the compound is titanium-hydrogen alloy. Titanium hydride is used to produce ceramics and alloys, as well as is applied as a "blowing agent" in the production of cellular solid compositions. The substance is also used in pyrotechnics, in ammunition, to produce porous titanium and as a chemical reagent in laboratories. Titanium powder is commercially available, and a tube furnace with a hydrogen atmosphere can be made or purchased. However, I did not plan to work with this compound. Making a laboratory setup for titanium hydride synthesis without a specific goal is irrational. One fine day, a scientist from a neighbouring institute came to us. We promised to give him cobalt powder treated in a certain way (for catalysts). I was not involved in work with cobalt, so I did not know where this powder was. But there were no colleagues nearby - I had to search. Soon, we found a package labelled "boron carbide B4C". This was a black powder similar to soot. Nearby stood a big bag of dark grey powder without a label. I read the name written on the first package out loud: "B - four - С." A guest from another institute was interested: - Boron carbide? I brought it to you last time. There must be titanium hydride in a big package nearby. - In this package without a label (I am showing)? - Yes, it is titanium hydride. I immediately took a marker and wrote "TiH2" so as not to forget. But how could you check that there was titanium hydride in the package? Words cannot be trusted these days. My laboratory was still at the organization stage, so only the simplest tests were available. But nothing complicated was required: just heat the powder in a flame. I weighed 1 g of titanium hydride, placed it on aluminium foil and directed the sharp flame of a miniature propane torch onto the powder. The powder heated up to a red and then to a yellow glow, but the burner power was not enough. When I removed the flame, the powder remained hot in some places, but soon it stopped glowing. I took a large torch and directed the flame onto the titanium hydride powder. The powder became hot and bright sparks flew. When I removed the burner, the titanium hydride remained hot, and in some places, it became even hotter (local flashes occurred). I carefully crushed the burning powder with a spatula. It turned out that combustion occurred mainly in the upper layer of the pile. Inside, the titanium hydride appeared to be unaffected. When the flow of propane was increased, the powder was carried away by the gases, creating bright sparks. To get sparks, titanium hydride powder was poured into the flame. Beautiful bright white sparks were formed, they are characteristic of titanium (and its hydride). Unfortunately, the titanium hydride powder clumped together, reducing spark formation. During the cooling process, grains of the combustion products were initially orange, then turned yellow. This colour change is characteristic of titanium dioxide (the oxide was formed as a result of the combustion of titanium hydride). Thus, we can say for sure that the grey powder contains titanium. Most likely, this is titanium hydride TiH2. However, the possibility cannot be ruled out that the grey powder is titanium metal rather than the hydride. To distinguish titanium hydride from titanium metal, a quantitative chemical analysis must be performed. |
Titanium hydride TiH2 in propane burner flame |