A one-step salt-assisted general synthetic methodology for the controlled phase transformation of various types of 2H-phase transition metal dichalcogenides (2H-TMDs), yielding large-scale metastable 1T′-phase transition metal dichalcogenides (1T′-TMDs), including WS.sub.2, WSe.sub.2, MoS.sub.2, and MoSe.sub.2 is described. By tuning the reaction conditions, alloyed 1T′-TMDs such as WS.sub.2xSe.sub.2(1−x) and MoS.sub.2xSe.sub.2(1−x) are also obtained. Commercially-available metal salts such as K.sub.2C.sub.2O.sub.4.Math.H.sub.2O, Na.sub.2C.sub.2O.sub.4, K.sub.2CO.sub.3, Na.sub.2CO.sub.3, Cs.sub.2CO.sub.3, Rb.sub.2CO.sub.3, KHCO.sub.3, and NaHCO.sub.3, are demonstrated to be effective for the controlled phase transformation at elevated temperatures in a reducing atmosphere. The technique may be extended to the phase engineering of other materials with various polymorphs.

A one-step salt-assisted general synthetic methodology for the controlled phase transformation of various types of 2H-phase transition metal dichalcogenides (2H-TMDs), yielding large-scale metastable 1T′-phase transition metal dichalcogenides (1T′-TMDs), including WS.sub.2, WSe.sub.2, MoS.sub.2, and MoSe.sub.2 is described. By tuning the reaction conditions, alloyed 1T′-TMDs such as WS.sub.2xSe.sub.2(1−x) and MoS.sub.2xSe.sub.2(1−x) are also obtained. Commercially-available metal salts such as K.sub.2C.sub.2O.sub.4.Math.H.sub.2O, Na.sub.2C.sub.2O.sub.4, K.sub.2CO.sub.3, Na.sub.2CO.sub.3, Cs.sub.2CO.sub.3, Rb.sub.2CO.sub.3, KHCO.sub.3, and NaHCO.sub.3, are demonstrated to be effective for the controlled phase transformation at elevated temperatures in a reducing atmosphere. The technique may be extended to the phase engineering of other materials with various polymorphs.

Nanocrystalline metal powders comprising tungsten, molybdenum, rhenium and/or niobium can be synthesized using a combustion reaction. Methods for synthesizing the nanocrystalline metal powders are characterized by forming a combustion synthesis solution by dissolving in water an oxidizer, a fuel, and a base-soluble, ammonium precursor of tungsten, molybdenum, rhenium, or niobium in amounts that yield a stoichiometric burn when combusted. The combustion synthesis solution is then heated to a temperature sufficient to substantially remove water and to initiate a self-sustaining combustion reaction. The resulting powder can be subsequently reduced to metal form by heating in a reducing gas environment.

Nanocrystalline metal powders comprising tungsten, molybdenum, rhenium and/or niobium can be synthesized using a combustion reaction. Methods for synthesizing the nanocrystalline metal powders are characterized by forming a combustion synthesis solution by dissolving in water an oxidizer, a fuel, and a base-soluble, ammonium precursor of tungsten, molybdenum, rhenium, or niobium in amounts that yield a stoichiometric burn when combusted. The combustion synthesis solution is then heated to a temperature sufficient to substantially remove water and to initiate a self-sustaining combustion reaction. The resulting powder can be subsequently reduced to metal form by heating in a reducing gas environment.

A technique for exfoliating a transition metal dichalcogenide material to produce separated nano-scale platelets includes combining the transition metal dichalcogenide material with a liquid to form a slurry, wherein the transition metal dichalcogenide material includes layers of nano-scale platelets and has a general chemical formula MX.sub.2, and wherein M is a transition metal and X is sulfur, selenium, or tellurium. The slurry of the transition metal dichalcogenide material is treated with an oxidant to form peroxo-metalate intermediates on an edge region of the layers of nano-scale platelets of the transition metal dichalcogenide material. The peroxo-metalate intermediates is treated with a reducing agent to form negatively charged poly-oxo-metalates to induce separation of the transition metal dichalcogenide material into the separated nano-scale platelets of the transition metal dichalcogenide material.

A technique for exfoliating a transition metal dichalcogenide material to produce separated nano-scale platelets includes combining the transition metal dichalcogenide material with a liquid to form a slurry, wherein the transition metal dichalcogenide material includes layers of nano-scale platelets and has a general chemical formula MX.sub.2, and wherein M is a transition metal and X is sulfur, selenium, or tellurium. The slurry of the transition metal dichalcogenide material is treated with an oxidant to form peroxo-metalate intermediates on an edge region of the layers of nano-scale platelets of the transition metal dichalcogenide material. The peroxo-metalate intermediates is treated with a reducing agent to form negatively charged poly-oxo-metalates to induce separation of the transition metal dichalcogenide material into the separated nano-scale platelets of the transition metal dichalcogenide material.

Methods are provided for synthesizing high purity niobium or rhenium powders by a combustion reaction. The methods can include: forming a combustion synthesis solution by dissolving in water an oxidizer, a fuel, and at least one base-soluble, ammonium salt of niobium or rhenium in amounts that yield a stoichiometric burn when combusted; and heating the combustion synthesis solution to a temperature sufficient to substantially remove the water and to initiate a self-sustaining combustion reaction.

Methods are provided for synthesizing high purity niobium or rhenium powders by a combustion reaction. The methods can include: forming a combustion synthesis solution by dissolving in water an oxidizer, a fuel, and at least one base-soluble, ammonium salt of niobium or rhenium in amounts that yield a stoichiometric burn when combusted; and heating the combustion synthesis solution to a temperature sufficient to substantially remove the water and to initiate a self-sustaining combustion reaction.

The present invention relates to a process for the production of ammonium perrhenate (APR), which includes the use of Ca(OH)2 and to ammonium perrhenate which can be obtained by the method according to the invention.

The present invention relates to a process for the production of ammonium perrhenate (APR), which includes the use of Ca(OH)2 and to ammonium perrhenate which can be obtained by the method according to the invention.