My ultimate goal was to form the dioxide of both elements. With that goal in mind, I performed a wide range of experiments but failed to obtain the goal in either case.
My tellurium came in crystalline chunks. These were extremely brittle and somewhat conductive of electricity. My selenium came in glassy beads. These were also brittle but did not conduct electricity. They are probably the black allotrope of selenium.
When either element is heated, it volatilizes before it burns. This is because neither of these elements are metals. Tellurium has a similar appearance to a metal but different properties. It melts at 450 C, well below the temperature necessary to burn it. Selenium is even worse. It has a melting point of about 220 C, and the fumes produced by the volatilization are very toxic. Therefore, it is practically impossible to create the oxide using the heat of a propane torch in an open atmosphere.
Here is the video of a piece of tellurium being heated on a piece of brick to prevent the highly mobile liquid tellurium from falling out of anything. Volatilization occurs, tellurium is deposited, but no oxidation occurs. The flame test of tellurium vapor is visible as a green coloration.
When tellurium is heated on an iron loop, it melts and quickly falls through the loop. Again, very little oxidation occurred. The hot tellurium only left the vapor behind, not any white oxide.
Tellurium, though conductive to some degree, does not form the dioxide when connected to the anode of an electrolysis apparatus. It does form an interesting purple ion when connected to the cathode. This reacts with water to produce a black water-insoluble solid. This solid is soluble in hydrogen peroxide. I thought that this might be a finely divided form of tellurium, but I do not see any insoluble tellurium dioxide precipitating out as the substance is oxidized. Selenium does not conduct electricity in this state so electrolysis is out of the picture. It is very difficult for tellurium due to its brittleness. Any gentle pressure on the metal causes it to fracture and crumble, making electrolysis a painstaking procedure and a waste of tellurium, of which I only have 1 gram.
Here is a video of the electrolysis of tellurium. The tellurium is in the solution and is being contacted with a carbon rod. Uniquely, most of the current flows into the tellurium. A faint smell of hydrogen telluride was noticeable. There was a film of elemental tellurium floating on the surface of the solution after the experiment was complete, indicative of the oxidation of the gas.
I next tried simple dissolutions. Tellurium did not appear to dissolve in a mixture of hydrochloric acid and hydrogen peroxide, nor did it dissolve in sodium hypochlorite, and hypochlorous acid. Selenium dissolved in sodium hypochlorite but did not appear to dissolve in hydrogen peroxide, or the hydrogen peroxide hydrochloric acid mixture. The red allotrope of selenium is supposed to dissolve in hydrogen peroxide, forming the dioxide. Because of this, I tried to form this allotrope. Blowing hot dilute selenium vapor onto a cold surface forms the red allotrope of selenium. However, this process consumes a tremendous amount of fuel and produces a large amount of highly toxic vapors. Because I am not equipped to do this, I wrote off this process as unattainable. So I tried to melt black selenium in a dish and pour it into water. This formed a small amount of red selenium on the surface of the re-formed black selenium beads. It dissolved in added hydrogen peroxide but there was no residue. This was expected due to the extremely small amount of this form of selenium.
After a few more experiments and repetitions of previous experiments, I gave up on finding an easy route to selenium dioxide with my limited equipment and materials. Until I obtain some barium nitrate and sulfuric acid to make nitric acid, I will hold off on any anticipated experiments with these metals. This shows the error in trying to use transition metal chemical pathways (acid dissolution, burning in air, etc.) to perform the same results on semimetals and nonmetals.