The present invention discloses a method for decomposing medium-/low-grade scheelite, specifically comprising steps of: grinding medium-/low-grade scheelite, decomposing in an autoclave by using sodium phosphate and activated magnesium fluoride as leaching agents, and treating by solid-liquid separation to obtain crude sodium tungstate solution and residue. In this way, the medium-/low-grade scheelite is decomposed. Magnesium chloride is added in a sodium fluoride solution to prepare activated magnesium fluoride as a leaching agent. The present invention has the advantage that the high-efficiency decomposition of medium-/low-grade scheelite can be realized with low consumption of leaching agents, and the leaching cost can be greatly reduced in comparison to the existing decomposition processes using sodium hydroxide and sodium carbonate. This process is short in route, simple in operation, readily available and reliable in production equipment, and easy for industrialization.

Compositions suitable for reversibly storing heat in thermal energy systems (TES) include a salt hydrate represented by the formula: MX.sub.q.nH.sub.2O. M is a cation selected from Groups 1 to 14 of the IUPAC Periodic Table, X is a halide of Group 17, q ranges from 1 to 4, and n ranges from 1 to 12. The cation (M) may have an electronegativity of ≤ about 1.8 and a molar mass ≤ about 28 g/mol. The anion (X) may have an electronegativity of ≥ about 2.9 to ≤ about 3.2. A distance between a cation (M) and coordinating water molecules (H.sub.2O) is ≤ about 2.1 Å. Thermal energy systems (TES) incorporating such compositions are also provided that are configured to reversibly store heat in the thermal energy system (TES) via an endothermic dehydration reaction and to release heat in in the thermal energy system (TES) via an exothermic hydration reaction.

Compositions suitable for reversibly storing heat in thermal energy systems (TES) include a salt hydrate represented by the formula: MX.sub.q.nH.sub.2O. M is a cation selected from Groups 1 to 14 of the IUPAC Periodic Table, X is a halide of Group 17, q ranges from 1 to 4, and n ranges from 1 to 12. The cation (M) may have an electronegativity of ≤ about 1.8 and a molar mass ≤ about 28 g/mol. The anion (X) may have an electronegativity of ≥ about 2.9 to ≤ about 3.2. A distance between a cation (M) and coordinating water molecules (H.sub.2O) is ≤ about 2.1 Å. Thermal energy systems (TES) incorporating such compositions are also provided that are configured to reversibly store heat in the thermal energy system (TES) via an endothermic dehydration reaction and to release heat in in the thermal energy system (TES) via an exothermic hydration reaction.

A main object of the present disclosure is to provide an anode material that is used in a fluoride ion battery and can prevent the decrease in operating voltage while inhibiting occurrence of short circuit. The present disclosure achieves the object by providing an anode material to be used in a fluoride ion battery, the anode material comprising a Mg material containing a Mg element, and a fluoride ion conductive material containing at least one kind of metal element excluding a Mg element, and a F element.

An optical system includes a bulk material including a fluorine (F)-containing optical material. The bulk material is exposed to an environment at a pressure ranging from atmospheric to vacuum when the bulk material is under extreme ultra-violet (EUV), vacuum ultra-violet (VUV), deep ultra-violet (DUV) and/or UV radiation. The environment includes at least one type of gas or vapor. The at least one type of gas or vapor includes polar molecules.

An optical system includes a bulk material including a fluorine (F)-containing optical material. The bulk material is exposed to an environment at a pressure ranging from atmospheric to vacuum when the bulk material is under extreme ultra-violet (EUV), vacuum ultra-violet (VUV), deep ultra-violet (DUV) and/or UV radiation. The environment includes at least one type of gas or vapor. The at least one type of gas or vapor includes polar molecules.

An optical lens with an antireflective film includes: a lens substrate; and an antireflective film disposed on the lens substrate. The antireflective film is formed of layers each having a physical thickness of 140 nm or less. In order from an air side, the antireflective film has: a first layer formed as an MgF.sub.2 layer, a second layer, a fourth layer, a sixth layer, an eighth layer, and a tenth layer each having a refractive index of 2.0 or more and 2.3 or less, and a third layer, a fifth layer, a seventh layer, and a ninth layer each formed as an SiO.sub.2 layer.

An optical lens with an antireflective film includes: a lens substrate; and an antireflective film disposed on the lens substrate. The antireflective film is formed of layers each having a physical thickness of 140 nm or less. In order from an air side, the antireflective film has: a first layer formed as an MgF.sub.2 layer, a second layer, a fourth layer, a sixth layer, an eighth layer, and a tenth layer each having a refractive index of 2.0 or more and 2.3 or less, and a third layer, a fifth layer, a seventh layer, and a ninth layer each formed as an SiO.sub.2 layer.

An optical lens with an antireflective film includes: a lens substrate; and an antireflective film disposed on the lens substrate. The antireflective film is formed of layers each having a physical thickness of 140 nm or less. In order from an air side, the antireflective film has: a first layer formed as an MgF.sub.2 layer, a second layer, a fourth layer, a sixth layer, an eighth layer, and a tenth layer each having a refractive index of 2.0 or more and 2.3 or less, and a third layer, a fifth layer, a seventh layer, and a ninth layer each formed as an SiO.sub.2 layer.

An optical lens with an antireflective film includes: a lens substrate; and an antireflective film disposed on the lens substrate. The antireflective film is formed of layers each having a physical thickness of 140 nm or less. In order from an air side, the antireflective film has: a first layer formed as an MgF.sub.2 layer, a second layer, a fourth layer, a sixth layer, an eighth layer, and a tenth layer each having a refractive index of 2.0 or more and 2.3 or less, and a third layer, a fifth layer, a seventh layer, and a ninth layer each formed as an SiO.sub.2 layer.