Boron nitride fiber and process for production thereof

A process for producing a boron nitride fiber comprising boron nitride having a multi-layered structure consisting of planes (C planes) each formed by linkage of 6-membered rings in the plane, in which boron and nitrogen are positioned alternately and bonded to each other, which fiber has a tensile strength of at least 1,400 MPa, which process comprises:

• (a) reacting a boron trihalide-nitrile compound adduct with an ammonium halide or a primary amine hydrohalide in the presence of a boron trihalide to form a boron nitride precursor,
• (b) dissolving the boron nitride precursor in a solvent to prepare a boron nitride precursor solution,
• (c) spinning the boron nitride precursor solution to form a boron nitride precursor fiber,
• (d) preheating the boron nitride precursor fiber in an inert gas atmosphere at 100.degree.-600.degree. C.,
• (e) treating the preheated fiber by ammonia in an ammonia gas atmosphere at 200.degree.-1,300.degree. C., and
• (f) heating the fiber treated by ammonia in an inert gas atmosphere at 1,600.degree.-2,300.degree. C. with a tensile stress being applied to the fiber.

A process for producing a boron nitride fiber comprising boron nitride having a multi-layered structure consisting of planes (C planes) each formed by linkage of 6-membered rings in the plane, in which boron and nitrogen are positioned alternately and bonded to each other, which fiber has a tensile strength of at least 1,400 MPa, which process comprises:

• (a) reacting a boron trihalide-nitrile compound adduct with an ammonium halide or a primary amine hydrohalide in the presence of a boron trihalide to form a boron nitride precursor,
• (b) dissolving the boron nitride precursor and an acrylonitrile polymer in a solvent to prepare a boron nitride precursor solution,
• (c) spinning the boron nitride precursor solution to form a boron nitride precursor fiber,
• (d) preheating the boron nitride precursor fiber in an inert gas atmosphere at 100.degree.-600.degree. C.,
• (e) treating the preheated fiber by ammonia in an ammonia gas atmosphere at 200.degree.-1,300.degree. C., and
• (f) heating the fiber treated by ammonia in an inert gas atmosphere at 1,600.degree.-2,300.degree. C. with a tensile stress being applied to the fiber.

A process for producing a boron nitride fiber comprising boron nitride having a multi-layered structure consisting of planes (C planes) each formed by linkage of 6-membered rings in the plane, in which boron and nitrogen are positioned alternately and bonded to each other, which fiber has a degree of orientation of at least 0.74, which process comprises:

• (a) reacting a boron trihalide-nitrile compound adduct with an ammonium halide or a primary amine hydrohalide in the presence of a boron trihalide to form a boron nitride precursor,
• (b) dissolving the boron nitride precursor in a solvent to prepare a boron nitride precursor solution,
• (c) spinning the boron nitride precursor solution to form a boron nitride precursor fiber,
• (d) preheating the boron nitride precursor fiber in an inert gas atmosphere at 100.degree.-600.degree. C.,
• (e) treating the preheated fiber by ammonia in an ammonia gas atmosphere at 200.degree.-1,300.degree. C., and
• (f) heating the fiber treated by ammonia in an inert gas atmosphere at 1,600.degree.-2,300.degree. C. with a tensile stress being applied to the fiber.

A process for producing a boron nitride fiber comprising boron nitride having a multi-layered structure consisting of planes (C planes) each formed by linkage of 6-membered rings in the plane, in which boron and nitrogen are positioned alternately and bonded to each other, which fiber has a degree of orientation of at least 0.74, which process comprises:

• (a) reacting a boron trihalide-nitrile compound adduct with an ammonium halide or a primary amine hydrohalide in the presence of a boron trihalide to form a boron nitride precursor,
• (b) dissolving the boron nitride precursor and an acrylonitrile polymer in a solvent to prepare a boron nitride precursor solution,
• (c) spinning the boron nitride precursor solution to form a boron nitride precursor fiber,
• (d) preheating the boron nitride precursor fiber in an inert gas atmosphere at 100.degree.-600.degree. C.,
• (e) treating the preheated fiber by ammonia in an ammonia gas atmosphere at 200.degree.-1,300.degree. C., and
• (f) heating the fiber treated by ammonia in an inert gas atmosphere at 1,600.degree.-2,300.degree. C. with a tensile stress being applied to the fiber.