Silicon nitride nanofibers produced by the pyrolysis of SiCl4 in H2 and N2 media

Abstract

The synthesis of fibrous Si 3 N 4 nanostructures by gas-phase chemical deposition during the pyrolysis of silicon tetrachloride in a hydrogen and nitrogen atmosphere was investigated. It was shown that the products contained both amorphous Si 3 N 4 nanofibers and their a and b phases both with and without a silicon coating. In addition to the Si 3 N 4 nanofibers the products also contained nanoribbons.Silicon nitride (Si 3 N 4 ) has high hardness, strength, elasticity modulus, and high chemical stability and is resistant to thermal shock and creep [1]. On account of this set of properties the material is promising for high-temperature applications. The filamentary crystals of Si 3 N 4 are used as reinforcing elements for high-temperature ceramic matrices in order to increase their viscosity and strength [2][3].A technique for the production of Si 3 N 4 in the form of microfibers (whiskers) was developed in the sixties of the last century. Thus, a method for the production of Si 3 N 4 whiskers by carbothermic reduction-nitriding a mixture of SiO 2 and carbon was patented [4]. Such whiskers are single crystals, the diameter of which ranges from 0.5 to several micrometers.A catalytic method is also used for the manufacture of Si 3 N 4 whiskers. Transition metals are used as catalysts, NH 3 or N 2 as source of nitrogen, and SiO or SiH 4 as source of silicon [5].After the discovery of carbon nanotubes [6] researchers in many countries worked intensively on the manufacture of nanofibers and nanotubes from various materials, including silicon nitride. By using fibrous Si 3 N 4 , the diameter of which did not exceed 100 nm, it was possible to prepare composites with metallic and ceramic matrices having even higher strength characteristics. Over the last decade a series of publications have appeared on the development of technological processes and the investigation of the properties of nanofibers, nanorods, nanotubes, and nanoribbons from Si 3 N 4 .As noted by the authors of [7], nanofibers of silicon nitride were first produced in 1997 by Chinese scientists [8], who synthesized a-and b-Si 3 N 4 nanofibers by the reaction of carbon nanotubes with a mixture of Si and SiO 2 powders in an atmosphere of nitrogen at 1673 K for 1 h. The diameter of the nanofibers amounted to 4-40 nm, and the length amounted to several micrometers.At the same time one of the first papers on the production of silicon nitride nanofibers can be considered to be [9], the authors of which investigated the process leading to the formation of Si 3 N 4 fibers much earlier by nitriding silicon in ammonia. In this work a-and b-Si 3 N 4 fibers with lengths not exceeding 1 mm were produced at temperatures above 1573 K. Although the authors did not report the diameter of the fibers, to judge from the length of the fibers it can be assumed that we are talking here of nanofibers.

Surface modification of silicon nitride nanofibers with titanium nitride particles

“…It was established that anatase powders did not get nitrided after thermal treatment above 500°C. For a comparative analysis, we selected powders of titanium peroxyhydroxide Ti(O 2 )(OH) 2 and TiO(OH) 2 produced by the thermal hydrolysis of TiCl 4 with urea and urotropin, respectively. The powders were nitrided after drying at 70ºC for 4 h without addition of Si 3 N 4 fibers.…”

“…We used amorphous Si 3 N 4 nanofibers produced by chemical vapor deposition at the Frantsevich Institute for Problems of Materials Science [2]. As intermediate products for producing titanium nitride, we synthesized titanium oxyhydroxide TiO(OH) 2 in the presence of urea, titanium hydroxide Ti(OH) 4 in the presence of urotropin, and titanium peroxyhydroxide Ti(O 2 )(OH) 2 .…”

“…The mechanical characteristics of ceramic nanocomposites (primarily strength and fracture toughness) may be improved by reinforcing the material with elongated structures (nanofibers, nanotubes, or nanowhiskers). Current technologies permit obtaining elongated structures from most ceramic materials with preset sizes and constitution and also 'nanocomposing' nanoparticle-nanofiber systems to assure excellent functional characteristics [2]. Materials with 'structural mimicry' are relevant and promising.…”

Effect of the production temperature on the structure of Si3N4 nanofibers

“…Interest in aspects of the production and investigation of Si 3 N 4 nanofibers has not diminished to this day, as witnessed by the fairly large number of publications on the subject (e.g., see [4][5][6][7][8]). …”

“…Another promising method for the production of Si 3 N 4 nanofibers is the chemical gas-phase deposition method, in which silicon tetrachloride (SiCl 4 ) and also ammonia and/or nitrogen are used as reagents [4,9].…”