A modified method for preparing guanidino acetic acid (GAA) involves reacting cyanamide with an excess molar amount of glycine in an aqueous reaction mixture, in the presence of a base. The method avoids high molar amounts of base or acid for pH control, and maintains the reaction selectivity and product yields.

In order to produce high yields of astatine-211 without contamination of chloride ions, provided is a method for producing astatine-211, including (1) a step of generating astatine-211 by irradiating bismuth with α rays; (2) a step of heating the astatine-211 generated in step (1) to vaporize; (3) a step of cooling the astatine-211 that has been vaporized in step (2) and collecting the astatine-211 with a volatile and polar solvent to obtain an astatine-211 solution; (4) a step of adding a weak acid salt to the astatine-211 solution obtained in step (3) to obtain an astatine-211 solution containing the weak acid salt; and (5) a step of removing the solvent from the astatine-211 solution containing the weak acid salt obtained in step (4).

In order to produce high yields of astatine-211 without contamination of chloride ions, provided is a method for producing astatine-211, including (1) a step of generating astatine-211 by irradiating bismuth with α rays; (2) a step of heating the astatine-211 generated in step (1) to vaporize; (3) a step of cooling the astatine-211 that has been vaporized in step (2) and collecting the astatine-211 with a volatile and polar solvent to obtain an astatine-211 solution; (4) a step of adding a weak acid salt to the astatine-211 solution obtained in step (3) to obtain an astatine-211 solution containing the weak acid salt; and (5) a step of removing the solvent from the astatine-211 solution containing the weak acid salt obtained in step (4).

Disclosed are a metal halide perovskite light-emitting material with controlled defects and wavelength converting body having the same, and light-emitting device. Monvalent organic cation (A.sub.2) contained in the perovskite nanocrystal can stabilize the perovskite nanocrystal and suppress the generation of defects in the crystal due to the entropy effect. Remnant A.sub.2 cations not included in the perovskite nanocrystal form a structure surrounding the perovskite nanocrystal particles, and passivate defects generated on the surface of the perovskite nanocrystal particles. Photoluminescence quantum efficiency, photoluminescence lifetime, and stability are improved through passivation of defects, and the metal halide perovskite light-emitting material can be effectively used in a light-emitting layer or a wavelength conversion layer of a light-emitting device.

Disclosed are a metal halide perovskite light-emitting material with controlled defects and wavelength converting body having the same, and light-emitting device. Monvalent organic cation (A.sub.2) contained in the perovskite nanocrystal can stabilize the perovskite nanocrystal and suppress the generation of defects in the crystal due to the entropy effect. Remnant A.sub.2 cations not included in the perovskite nanocrystal form a structure surrounding the perovskite nanocrystal particles, and passivate defects generated on the surface of the perovskite nanocrystal particles. Photoluminescence quantum efficiency, photoluminescence lifetime, and stability are improved through passivation of defects, and the metal halide perovskite light-emitting material can be effectively used in a light-emitting layer or a wavelength conversion layer of a light-emitting device.

A method for preparing a latent hardener includes, in the order recited, introducing a hardener into a dry mixer that is a high-energy-type mixer; injecting carbon dioxide gas or an inert gas into the dry mixer; and mechanochemically deactivating only a surface of the hardener using the dry mixer. The hardener may be an amine-based adduct, an imidazole-based adduct, dicyandiamide, a dihydride-based compound, a dichlorophenyl dimethylurea compound and combinations thereof. The inert gas may be helium, nitrogen, argon, neon, krypton, and combinations thereof.

A method for preparing a latent hardener includes, in the order recited, introducing a hardener into a dry mixer that is a high-energy-type mixer; injecting carbon dioxide gas or an inert gas into the dry mixer; and mechanochemically deactivating only a surface of the hardener using the dry mixer. The hardener may be an amine-based adduct, an imidazole-based adduct, dicyandiamide, a dihydride-based compound, a dichlorophenyl dimethylurea compound and combinations thereof. The inert gas may be helium, nitrogen, argon, neon, krypton, and combinations thereof.

A polymer comprising repeating units derived from a first monomer, typically acrylonitrile, and repeating units derived from a second monomer different from the first monomer, wherein the second monomer is a compound comprising an ethylenically unsaturated organic anion and an organic cation containing a C═N imine group; a process for producing carbon fibers using the said polymer; and carbon fibers made therefrom, are described herein.

A polymer comprising repeating units derived from a first monomer, typically acrylonitrile, and repeating units derived from a second monomer different from the first monomer, wherein the second monomer is a compound comprising an ethylenically unsaturated organic anion and an organic cation containing a C═N imine group; a process for producing carbon fibers using the said polymer; and carbon fibers made therefrom, are described herein.

Compositions and methods are presented that selectively dissolve calcium from a variety of cementitious materials without dissolving or otherwise degrading calcium silica hydrate (CSH). Preferably, contemplated compositions comprise guanidine bisulfate hydrochloride, which can be prepared from a reaction of urea, hydrochloric acid, and sulfamic acid. Therefore, it is especially contemplated that the compositions contemplated herein are particularly suitable to clean or otherwise condition surfaces of cured concrete, Portland cement-based material, or an aggregate containing CSH.