Abstract: The present invention provides, in the preparation of a hot press molded board from a lignocellulose or an inorganic material as a main raw material, an isocyanate-based binder composition with which a board having eternally good releasability from a hot press plate, excellent physical properties and a low hygroscopic linear expansion coefficient can be obtained with improved productivity. The binder composition comprises (A) a compound having at least two isocyanate groups, (B) a low molecular weight polyethylene and (C) water as indispensable components.

Abstract: NF.sub.3 gas containing N.sub.2 F.sub.2 as an impurity is purified by heating said NF.sub.3 gas at specified temperatures in a vessel the inner wall of which is coated with a strong and passive film of nickel flouride. According to this method, the rate of NF.sub.3 loss is low and the rate of removing N.sub.2 F.sub.2 is high. Therefore, when the NF.sub.3 gas thus purified is further purified with a known adsorbent, a highly pure NF.sub.3 gas can be easily and safely produced which is suitable for materials for semiconductor dry etching agents and the like.

Abstract: A process of the present invention can effectively decompose, particularly, dinitrogen difluoride present in a nitrogen trifluoride gas to remove it from the gas.This process for purifying the nitrogen trifluoride gas is characterized by comprising the step of heating the nitrogen trifluoride gas containing at least dinitrogen difluoride as an impurity at a temperature of 150.degree. C. to 600.degree. C. in a metallic vessel the inner wall of which is lined with a solid fluoride, or in a packing layer of the solid fluoride in the vessel.