A negative thermal expansion material according to an embodiment is represented by a general formula (1): Cu.sub.2-xR.sub.xV.sub.2O.sub.7 (R is at least one element selected from Zn, Ga, and Fe) and includes an oxide sintered compact whose linear expansion coefficient is 10 ppm/K or less.

A negative thermal expansion material according to an embodiment is represented by a general formula (1): Cu.sub.2-xR.sub.xV.sub.2O.sub.7 (R is at least one element selected from Zn, Ga, and Fe) and includes an oxide sintered compact whose linear expansion coefficient is 10 ppm/K or less.

A vanadium recovery approach utilizes oil fly ash (OFA), in contrast to coal fly ash, for separation and recovery of vanadium. OFA is first carbon burned to reduce the volume for recycling, and also to provide a fuel for other industrial processes. Following an almost 90% weight reduction from carbon burning, the remaining material includes about 18% vanadium. A salt roasting performed at the same temperature (about 650 C.) as the carbon burning allows use of the same oven or furnace, reducing heat requirements for the overall process. Salt roasting generates a water-soluble material from which a water leaching process yields a vanadium leach solution containing recovered vanadium, avoiding a need for caustic or volatile leaching agents. Ammonium metavanadate is precipitated from the vanadium leach solution through addition of ammonium sulfate, and a calcination process used to generate vanadium oxide (V.sub.2O.sub.5).

The present invention relates to a method for preparing high-purity vanadium pentoxide from vanadium-bearing shale by all-wet process. The technical solution is: the Gradient continuous leaching system of vanadium-bearing shale is used to wet activate and compound leach vanadium-bearing shale to obtain vanadium-containing acid leachate. The pH adjusting device of the vanadium-containing acid leachate is used to adjust the pH of vanadium-containing acid leaching leachate. The post-treatment solution is subjected to hydroxime countercurrent extraction after oxidation, and the raffinate returns to the water using in the wet activation and electrodialysis after neutralization, and the loaded organic phase is regenerated by countercurrent reduction stripping. The regenerated organic phase directly returns to hydroxime countercurrent extraction. The pH is adjusted for vanadium precipitation with chemical valence conversion, and the mother liquor after vanadium precipitation is incorporated into the vanadium-containing acid leachate, and the vanadium-containing hydroxide is oxidized and roasted to prepare vanadium pentoxide.

A chalcogen-containing compound of the following Chemical Formula 1 which exhibits excellent phase stability even at a low temperature, particularly at a temperature corresponding to an operating temperature of a thermoelectric element, and also exhibits a significantly superior power factor and thermoelectric performance index due to its excellent electrical conductivity and low thermal conductivity caused by its unique crystal lattice structure, a method for preparing the same, and a thermoelectric element including the same. [Chemical Formula 1]V.sub.1-2xSn.sub.4Bi.sub.2-xAg.sub.3xSe.sub.7, wherein V is vacancy and 0<x<0.5.

Methods and systems for removing impurities from electrolyte solutions having three or more valence states. In some embodiments, a method includes electrochemically reducing an electrolyte solution to lower its valence state to a level that causes impurities to precipitate out of the electrolyte solution and then filtering the precipitate(s) out of the electrolyte solution. In embodiments in which the electrolyte solution is desired to be at a valence state higher than the precipitation valence state, a method of the disclosure includes oxidizing the purified electrolyte solution to the target valence.

Methods and systems for removing impurities from electrolyte solutions having three or more valence states. In some embodiments, a method includes electrochemically reducing an electrolyte solution to lower its valence state to a level that causes impurities to precipitate out of the electrolyte solution and then filtering the precipitate(s) out of the electrolyte solution. In embodiments in which the electrolyte solution is desired to be at a valence state higher than the precipitation valence state, a method of the disclosure includes oxidizing the purified electrolyte solution to the target valence.

Disclosed is a method of preparing an oxide for hydrogen storage, including a) mixing and calcining vanadium oxide and titanium oxide, b) impregnating the oxide obtained in step a) with a noble metal precursor aqueous solution, and c) subjecting the oxide obtained in step b) to heat treatment in a reducing atmosphere, wherein the oxide obtained in step a) has the composition of Chemical Formula 1 below and is composed of a single-phase TiO.sub.2 crystal phase:

V.sub.1-xTi.sub.xO.sub.2[Chemical Formula 1] (in Chemical Formula 1, 0.05x0.95).

Disclosed is a method of preparing an oxide for hydrogen storage, including a) mixing and calcining vanadium oxide and titanium oxide, b) impregnating the oxide obtained in step a) with a noble metal precursor aqueous solution, and c) subjecting the oxide obtained in step b) to heat treatment in a reducing atmosphere, wherein the oxide obtained in step a) has the composition of Chemical Formula 1 below and is composed of a single-phase TiO.sub.2 crystal phase:

V.sub.1-xTi.sub.xO.sub.2[Chemical Formula 1] (in Chemical Formula 1, 0.05x0.95).

This method for producing a vanadium compound has an alkaline leaching step for immersing incineration ash in an alkaline solution to cause vanadium to leach from the incineration ash into the alkaline solution and obtain a leachate slurry, a solid-liquid separation step for separating the leachate slurry obtained in the alkaline leaching step into a solid and liquid followed by removing insoluble matter to obtain a leachate, a pH adjustment step for adding acid to the leachate following solid-liquid separation to make the leachate acidic, an aging step for aging the leachate following pH adjustment until a precipitate forms in the leachate, and a separation step for separating the precipitate from the leachate following the aging step.