Nano-sized Si3N4 Particles Research Articles

Preparation by SHS-extrusion method of compact ceramic materials based on the Ti‒B system, modified with nanosized Si<sub>3</sub>N<sub>4</sub> particles

Compact ceramic materials based on the Ti‒B system modified with 5 wt. % of nanosized Si3N4 particles. The results of studies of the structure, phase composition, and physical and mechanical characteristics of the materials obtained are presented. It is shown that the addition of Si3N4 promotes the formation of new phases, in particular, titanium diboride and nitride in the final product. It was found that the introduction of modifying nanosized Si3N4 particles into the initial charge leads to an increase in hardness and microhardness by 15‒20 %, as well as to an increase in crack resistance by 1,5 times in comparison with unmodified samples.

Preparation of in-situ formed TiN0.3-Ti5Si3-TiN composites through reactive spark plasma sintering of Ti and Si3N4

In-situ intermetallic-ceramic composites have been prepared successfully via spark plasma sintering process using Ti and Si3N4 starting materials. 5, 10 and 15 wt% of nano-sized Si3N4 particles were mixed with Ti powders by milling in ethanol media for 2 h. Spark plasma sintering processes were performed at 1250 °C for each sample. It was observed that initial shrinkage of the sample with the lower amount of Si3N4 took place at the earlier time and the total shrinkage of this sample was higher than the other samples due to lower refractoriness of this composite. The phase formation was investigated by XRD and FESEM analyses. XRD analysis showed that the TiN0.3 and Ti5Si3 phases are formed for all samples after sintering process. It was also observed that in Ti-15%Si3N4 sample, the third phase of TiN was formed due to increasing of the N concentration in the composite and formation of a concentrated solid solution of N in Ti (50 at%). By increasing the Si3N4 content, the Ti5Si3 amount was increased due to increasing of Si concentration in the composite. Finally, the hardness and flexural strength of the composites were examined by Vickers hardness and 3-point bending strength tests. The results showed that increasing the content of Si3N4 in the composites leading to increasing of the hardness from 632 Hv to 1126 Hv due to formation of hard phases. Inversely, bending strength of the samples was decreased from 880 MPa to 710 MPa by increasing of Si3N4 content in the composites due to increasing of the composite brittleness.

SHS of ultrafine and nanosized Si3N4 powders: The effect of inorganic and organic additives on the microstructures, morphology, and phase compositions of products

The relationship between the microstructure and phase composition of a product obtained by selfpropagating high-temperature synthesis (SHS) and different reaction mechanisms is studied using the example of silicon nitride. The formation of nanosized silicon nitride particles upon the combustion of silicon in nitrogen and other phenomena typical of substances of this class, such as self-organization and self-assembly, are observed. The chemical condensation SHS of silicon nitride is studied in the presence of inorganic salts as modifying additives. The resulting Si3N4 powders have a structure of secondary spherical particles being composed of primary ultrafine and nanosized ones. The Si3N4 powders under study were fractionated depending on the particles size and microstructure by chemical dispersion. Ultrafine particles of the light fraction form as homogeneous rods by the conventional vapor–liquid–crystal mechanism. The fine-crystalline fractions are formed by hollow crystals assembled into globules. Microstructural analysis shows that the crystal walls consist of nanosized Si3N4 particles. The effects of organic additives introduced into the charge stock on the phase formation, microstructure formation, and particle size of SHS silicon nitride are studied. The combustion products are found to be composite powders whose phase compositions depend on the additive and the synthesis conditions. According to the data from X-ray powder diffraction and chemical analysis, the final products can contain up to 100% of β-Si3N4, up to 60% of α-Si3N4, up to 80% of SiC, and up to 70% of Si2N2O. It is shown that silicon nitride-based composite powders containing silicon carbide and/or silicon oxynitride can be obtained in one step. The role of ferric chloride hexahydrate as the SHS catalyst is studied. An ultrafine structurally homogeneous powder of β-Si3N4 is obtained in the presence of FeCl3 · 6H2O.

Study of Surface Modification of Nanosize Si3N4 with Macromolecular Coupling Agent LMPB-g-GMA in Different Solvents

A new macromolecular coupling agent, low-molecular-weight polybutadiene liquid rubber (LMPB)-glycidyl methacrylate (GMA), was synthesized using solution polymerization initiated by benzoyl peroxide (BPO). The molecular structure was confirmed by FTIR and NMR. This macromolecular LMPB-GMA was used for surface modification of silicon nitride (Si3N4) nanopowder in n-heptane, chloroform, ethyl acetate, and DMF, respectively. LMPB-GMA and modified nano-Si3N4 were systematically investigated by FTIR, NMR, TGA, and TEM. The results showed that LMPB-GMA bonded and formed an organic coating layer onto the surface of nanosized Si3N4 particles. The polarity of the solvents plays an important role in this process. Strong or weak polar both affect the results. The dosage loading of LMPB-GMA is 12 wt% of nanosized Si3N4. Nanosized Si3N4 modified in ethyl acetate has better dispersibility and stability than that modified in n-heptane or DMF. TEM pictures also reveal that modified nano-Si3N4 possesses good dispersibility.