Si3N4 Powders Research Articles

Structure and mechanical properties of electrodeposited Ni-AlN/Si3N4 composite coating

N1-AIN/Si3N4 composite coatings were successfully deposited on tungsten carbide by electrodeposition process. The influence of Si3N4 powder concentration on the microstructure, crystal structure and mechanical properties was investigated by using Scanning Electron Microscopy, Energy Dispersive Spectroscopy, X-Ray Diffraction and Vickers hardness tester, respectively. The results revealed that variation of Si3N4 concentration influenced the structure and mechanical properties of Ni-AlN/Si3N4 composite coatings. The fine surface morphology of composite was due to the inclusion of AlN and Si3N4 particles while it is rougher as the Si3N4 concentration was increased due to agglomeration effect and Ni crystal growth. The increase of microhardness is related to the particles dispersion- strengthening.

Microstructure and wear properties of multi ceramics reinforced metal-matrix composite coatings on Ti–6Al–4V alloy fabricated by laser surface alloying

ABSTRACTTo improve the wear resistance of titanium alloy, self-lubricating metal-matrix composite coatings reinforced by multi ceramic phases were designed and fabricated by laser surface alloying with the mixed powders of Ni, B4C, graphite and Si3N4 on Ti–6Al–4V alloy. Microstructure and wear resistance of the coatings were investigated. The coatings were mainly composed of TiB2, SiC, TiC0.7N0.3 and the phases containing Ni. There was residual graphite in the coatings. The average hardness of the coatings was 1385–1687 HV, equivalent to 3.7–4.5 times of the substrate. The coatings displayed superior wear resistance under dry sliding wear test condition at room temperature, compared to the substrate (over 13 times better than the substrate). The coating fabricated with the mixed powders of Ni:B4C:C(graphite):Si3N4 = 1:1:1.5:0.2 (mole ratio) exhibited the best wear resistance due to the good matching relationship of the high hardness, good lubrication and certain toughness. The wear mechanism of the coatings was discussed.

Microstructure Study and Mechanical Testing of Al 6061-Si3n4 Metal Matrix Composites

In these days exceptional properties are needed for wide range of applications like aerospace, medical, and automobile to improve strength, corrosive resistance and weight reduction. For these purposes composites have been developed. Metal matrix composite (MMC) is one of them, and aluminium composites have been using in various fields because of its less weight, thermal and electrical conduction and corrosive resistance. Here we are introducing silicon nitride (Si3N4) as reinforcement which is a ceramic in aluminium 6061 which is effectively used in many applications these days. Our composite has been made using Stir casting method for proper dispersion. Mechanical testing methods like Brinell’s, Charpy impact tests are carried out to identify properties of composite and microstructure is also been figured out through SEM. Properties of both 5% and 15% Si3N4 powder composition of MMC are compared with each other and discussions are made.

Microstructural evolution mechanism of porous reaction bonded silicon nitride ceramics heat-treated in two powder beds

Porous Si3N4 with various grain morphologies was prepared by direct nitriding of silicon powder and subjected to heat-treatment while embedded in a Si3N4 powder bed. The influence of MgO, added either to the starting silicon or to the powder bed, on the microstructural transformation and morphology of pores at temperatures between 1425 °C and 1700 °C are discussed. In the presence of MgO, α-Si3N4 grains with equiaxed morphology resulted in an interconnected microstructure with spherical pores. By contrast, in the absence of MgO, an α-whisker-dominant microstructure resulted in pores of various morphologies. During the post heat-treatment process, the α-whiskers gradually vanished, and grains recrystallized as very fine β-Si3N4 rods. Consequently, pores became spherical, large and whisker-free. In agreement with the results of SEM-EDX along with XRD analysis, the observed morphology transition and full phase transformation occurred by vapor phase transport of MgO from the powder bed and a subsequent solution-precipitation mechanism. The presence of volatile MgO in the powder bed caused a substantial decrease in weight losses, while enhancing β phase formation, grain coarsening and linear shrinkage. The development of coarse β-rods from α-matte grains in a Si–Mg–O–N glassy phase was related to the presence of substantial liquid phase during the growth mechanism. Compared to the granular morphology, whiskers with high aspect ratio gave rise to a high sintering driving force and led to a maximum value of ≈2% linear shrinkage and porosity of ≈30 vol%. Consequently, this ceramic exhibited the highest compressive strength of ≈10 MPa.

Effect of Si particle size and NH4Cl additive on combustion synthesis of α-Si3N4

High α-phase content Si3N4 powders were fabricated by combustion synthesis method using coarse Si powder with NH4Cl additive. The effects of Si particle size and NH4Cl additive on the macrokinetic feature, phase composition, microstructure of combustion synthesized α-Si3N4 powder were investigated. Without the addition of NH4Cl, the content of α-Si3N4 in the products first decreases under a critical Si particle size of 7.8 μm, and then increases with increasing Si particle size. With the addition of 6 wt% NH4Cl, high α-phase content Si3N4 powder (>90 wt%) was obtained by using coarse (19.6 μm) Si powder. The addition of NH4Cl reduces the maximum combustion temperature and retention time of liquid Si by promoting the gasification of Si, which lead to the increase of α-Si3N4 content in the product. The use of coarse Si powder is of great significance for the low-cost production of high-quality α-Si3N4 powder.

Electromagnetic interference shielding properties of polymer derived SiC-Si3N4 composite ceramics

SiC-Si3N4 composite ceramics are successfully fabricated by pyrolysis of ferrocene-modified polycarbosilane (PCS) mixed with inert filler Si3N4 powders, followed by thermal treatment from 1100 °C to 1400 °C in Ar atmosphere. The porosity of SiC-Si3N4 ceramics decreases to 6.4% due to the addition of inert filler Si3N4. And the content and crystallization degree of free carbon and SiC derived from PCS are improved simultaneously with the increase of thermal treatment temperature. Finally, the free carbon and SiC interconnect, forming the conductive network. As a result, the electromagnetic interference (EMI) shielding performance of the as-prepared ceramic annealed at 1400 °C reaches up to 36 dB, meaning more than 99.9% of EM energy is shielded. The low porosity and high EMI shielding performance enable SiC-Si3N4 composite ceramics to be a promising electromagnetic shielding and structural material.

Modification of Si3N4 ceramic powders and fabrication of Si3N4/PTFE composite substrate with high thermal conductivity

Abstract Si3N4 filled polytetrafluoroethylene (PTFE) composites were prepared for microwave composite substrates. The analyses of Si3N4 powder by XPS and FTIR confirmed the successful grafting of Si3N4 powder by F8261. The effects of Si3N4 content on the microstructure, density, moisture absorption, thermal conductivity and microwave dielectric properties (er, tan δ) of Si3N4/PTFE composites were investigated. With an increase of Si3N4 content, the density, dielectric constant and moisture absorption increase. The composite filled with the modified ceramic powders have better dielectric properties, and the powders are more compatible with PTFE. Different models are used to predict the thermal conductivity of the composite substrate. When the content of Si3N4 ceramic filler is 62 vol% (70 wt%), the prepared Si3N4/PTFE composite exhibits excellent low dielectric loss (tan δ = 0.0014), low dielectric constant (er = 4.03), high thermal conductivity (λ = 1.3 W/m·K) and relatively low water absorption (0.032%).

Fabrication of α-Si3N4 nanobelts assembled by Si3N4 microcrystals on the nanowires via crystallization of amorphous Si3N4 powders

Abstract In this paper, α-Si 3 N 4 nanobelts assembled by Si 3 N 4 microcrystals on the nanowires were synthesized from amorphous Si 3 N 4 powders that were prepared by thermolysis of silicon diimide powders. By prolonging the heating time at 1550 °C, the amorphous Si 3 N 4 powders were converted to hexagonal phase α-Si 3 N 4 microcrystals which were adhered to the surface of nanowires to obtain α-Si 3 N 4 nanobelts. The obtained α-Si 3 N 4 nanobelts were hollow in the centre with a width of ∼850 nm and a thickness of ∼150 nm. Microcrystals were deposited on the surface of 2–3 parallel nanowires. The diameter of the Si 3 N 4 microcrystals was 30–230 nm, and the diameter of the nanowires was 50–100 nm. Evaporation of the amorphous Si 3 N 4 powders released Si vapour and N vapour, which led to the formation of the Si 3 N 4 microcrystals. The nanowires grew on the surface of the amorphous Si 3 N 4 powders due to the nucleation and diffusion of Si and N atoms of amorphous Si 3 N 4 powders. The growth mechanism of the products with unique morphology can be considered as a combination of vapour-solid mechanism and secondary nucleation process.

Direct deposition of graphene nanowalls on ceramic powders for the fabrication of a ceramic matrix composite**Project supported by the National Natural Science Foundation of China (Grant Nos. 51602300 and 51602299) and the National Key Research and Development Program of China (Grant No. 2018FYA0305800).

Uniform mixing of ceramic powder and graphene is of great importance for producing ceramic matrix composite. In this study, graphene nanowalls (GNWs) are directly deposited on the surface of Al2O3 and Si3N4 powders using chemical vapor deposition system to realize the uniform mixing. The morphology and the initial stage of the growth process are investigated. It is found that the graphitic base layer is initially formed parallel to the powder surface and is followed by the growth of graphene nanowalls perpendicular to the surface. Moreover, the lateral length of the graphene sheet could be well controlled by tuning the growth temperature. GNWs/Al2O3 powder is consolidated by using sparking plasma sintering method and several physical properties are measured. Owing to the addition of GNWs, the electrical conductivity of the bulk alumina is significantly increased.

Preparation of α-Si3N4 nanorods assembled nanobelts by crystallizing amorphous Si3N4 powders

In this paper, a new nanomaterial, α-Si3N4 nanobelts assembled by high density nanorods were prepared via the crystallization of amorphous Si3N4 at 1450 °C for 12 h. The as-synthesized nanobelts exhibited a width of ∼900 nm and a thickness of ∼150 nm, and a depressed linear region in the central. α-Si3N4 nanorods on the nanobelts had a width of 8–16 nm and a length of 400–450 nm. The nanorods were single-crystal, growing along (101) plane. The nanobelt appeared to be initiated by α-Si3N4 nanorods constantly growing on the both sides of a nanowire which was caused by secondary nucleation and the growth of Si3N4 microcrystals. Growth mechanism related to the formation of the nanobelts was analyzed in detail on the basis of vapor-solid mechanism and secondary nucleation. The current work would provide new insights into α-Si3N4 nanobelts assembled by nanorods which play an important role in nanoscale devices and show widespread potential applications due to their special morphology.

Fabrication and properties of Si3N4 based ceramics using combustion synthesized powders

Silicon nitride (Si3N4) based ceramics were fabricated with β-SiAlON and Si3N4 powders synthesized by combustion synthesis method via power injection molding (PIM). In the PIM process, the solids loading for each material was first determined from the results of the torque rheometer experiment. The mixing process was repeated to produce the homogeneous feedstock, and homogeneity of feedstocks was evaluated by observing the shear viscosity with time at a constant shear rate. The rheological behavior of feedstocks was investigated using capillary rheometer. It found that both feedstocks have no problem in injection molding. The binder decomposition behavior was also investigated, and a wax-polymer binder system was nearly removed by the optimized solvent and thermal debinding processes. Thereafter, the debound samples were sintered at 1750 and 1800 °C for 4 h in nitrogen atmosphere. Regardless of sintering temperature, the relative density of higher than about 96% was achieved. When comparing mechanical properties including bending strength, Vickers hardness and fracture toughness, Si3N4 with 2 wt% Y2O3 and 5 wt% Al2O3 (Si3N4+2Y5A) had higher values than β-SiAlON with 4 wt% Y2O3 (β-SiAlON+4Y) regardless of sintering temperature. It was supported by observing the microstructures of the plasma-etched samples.

Investigation of structural and mechanical properties of silicon carbonitride thin films

Silicon Carbo-nitride (SiCN) thin films were deposited by using SiC and Si3N4 powder, and H2 and N2 as carrier gases by thermal chemical vapor deposition (CVD) on p-Si(100) substrates. The morphology, chemical bonding, structural analysis and mechanical properties of SiCN thin films were characterized by Atomic Force Microscope (AFM), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and nanoindentation techniques respectively. The AFM images reveal that the surface roughness of SiCN thin films decreased with increasing H2 flow rate. The Raman signature at 937 to 967 cm−1 indicated formations of SiCN phase in the SiCN thin films with an increase in H2 flow rate. The FTIR results indicated SiC and SiCN bonds were prominent bonding in the SiCN thin films. The XRD results reveal the crystallite size of (102) planes and lattice strain of SiCN thin films varied from 13.29 to 2.93 nm and +0.02328 to 0.00439 with variation in the H2 flow rate from 40 to 120 sccm. The estimated composition of Si, and N in the SiCN thin film was varied from 29.7 to 30.7 and 31.7 to 33.9 at. % respectively, moreover, carbon composition, decreased by 38.5 to 35.7 at. % respectively by increasing of H2 flow rate. Hardness and modulus of SiCN thin films 30 GPa and 300 GPa with an elastic recovery of 64–68% were achieved.

The effect of gelcasting parameters on microstructural optimization of porous [formula omitted] ceramics

In this article we are reporting the optimization of gelcasting process which enabled us to manufacture silicon nitride bodies with around 30–37% porosity and 182–250 MPa flexural strength. Owing to their potential applications mainly in biomedical and aerospace, porous Si3N4 ceramics have gained ever increasing interests. However, the main challenge has been ensuring their high strength while maintaining high porosity. Si3N4 bodies were prepared via a controlled gelcasting followed by pressureless sintering in a coke bed. Monomers including acrylamide (AM) and N,N' -methylenebisacrylamide (MBAM) were employed to formulate the primary slurry. Sub-micron Si3N4 powder of 35 vol% was used as solid loading where ammonium persulfate (APS) and N,N,N',N' -tetramethylethylenediamine (TEMED) were added to initiate and catalyze polymerization reactions. Sintering was carried out at 1650 °C for 2–6 h and at 1750 °C for 2 h where 6 wt% mixture of Al2O3−Y2O3 was included as a sintering aid. Phase characterization and microstructural evolution were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively; while mechanical evaluation was based on bending test. It was found that by optimizing the viscosity of slurry and the idle time of gelation, a well distribution of high porosity structure is developed. The high strength of the sintered bodies is related to a high volume and unique microstructure of fine and elongated β- Si3N4 grains evolved during optimized sintering conditions. At temperatures above 1650 °C and sintering times of more than 4 h, the strength is decreased due to coarsening of β- Si3N4 grains, however.

Получение нитрида и оксонитрида кремния газофазным пиролизом гексаметилдисилазана

The technique was developed, the installation was done, and the conditions for the production of Si3N4 and Si2N2O by the method of gas-phase pyrolysis of hexamethyldisilazane (CH3)3-Si-NH-Si-(CH3)3 (HMDS) were experimentally studied. In the experiments, two different methods of inputting the raw material were used—the input of a vapor–gas mixture (bubbling feeder with heating to supply the HMDS vapor in a stream of carrier gases) and input as a gas-droplet stream (pneumatic nozzle). The effect of gas-dynamic synthesis conditions at temperatures up to 1100°C on the properties of silicon oxonitride and silicon nitride nanopowders was studied. The influence of the conditions of mixing the reactants, the volume ratio of nitrogen/ammonia, and the content of HMDS in the vapor–gas mixture on the yield of products was shown. The dependences of the degree of conversion of the feedstock on the gas flow rate and the concentration of ammonia in the gas phase were obtained. The optimal conditions for the pyrolysis process were found: temperature, the ratio of the components of the gas mixture, the conditions of mixing, and the contact times of the phases. X-ray amorphous Si3N4 and Si2N2O powders with particle sizes of 50–200 nm and a specific surface area of up to 15 m2/g and powders of alpha modification of silicon nitride Si3N4 in the form of threadlike crystals with a particle diameter of 50–200 nm were obtained.

Microwave synthesis of red-emitting Ca2Si5N8:Eu2+ phosphor and its photoluminescence properties for white-LEDs

A microwave synthesis method has been developed for synthesis of Ca2Si5N8:Eu2+ phosphor and its photoluminescence properties were investigated. Ca, Si, and Eu2O3 powders were used as the reactants serving as the sources of the Ca, Si and Eu. Addition of NaN3 NH4Cl and Si3N4 powders was found to increase significantly the product yield. These powders were mixed and pressed into a compact which was then embedded in AlN powder inside a BN crucible. The crucible was then placed at the center of the microwave cavity (TE103 single-mode). The microwave synthesis was performed at a microwave power (2.45 GHz) of 600 W for 1 h in a flowing 90%N2-10%H2 gas at one atmosphere. The effects of process parameters on the product yield were investigated and a reaction mechanism was proposed. The synthesized Ca2Si5N8:Eu2+ phosphor absorbs light in the region of 240–520 nm and shows a single broad band emission in the region of 550–700 nm (peaking at 596–606 nm). The peak emission intensity at an optimized Eu2O3 molar ratio (0.03) was measured to be ∼106% of the commercial YAG:Ce3+ (P46-Y3) phosphor.

Toughness Enhancement in TiN/CNTs Reinforced Si3N4 Ceramic Nanocomposites

This paper elucidated the effect of carbon nanotubes (CNTs) and TiN nanoparticles on the mechanical properties of silicon nitride(Si3N4) nanocermic matrix, on their own and together respectively. This was investigated by using the samples fabricated by hot-pressing nano-sized Si3N4 powders, carbon nanotubes and TiN nanoparticles. The addition of each nanostructure caused varying degrees of enhancement of mechanical properties, the incorporation of 2wt.% CNTs along with 10wt.% TiN shows the highest improvements in fracture toughness. Fractography of the samples revealed a mixed intergranular/transgranular fracture mode for reinforced nanocomposites. The toughening mechanism for the Si3N4 nanocomposites reinforced with CNTs and TiN nanoparticles was crack deflection, crack bridging and pull-out of CNTs.

Fabrication of complex shaped ceramic parts with surface-oxidized Si3N4 powder via digital light processing based stereolithography method

Si3N4 ceramic is difficultly fabricated by digital light processing (DLP) based stereolithography method, due to a large refractive index difference between Si3N4 powder and resin. In this paper, a surface oxidation approach of Si3N4 powder for improving cure depth is proposed. The results showed that, the amorphous SiO2 layer was uniformly attached onto the surface of Si3N4 powder by surface oxidation, and the absorbance of Si3N4 powder decreased as increasing oxidation degree. Moreover, the cure depth of the suspension significantly increased because of a smaller absorbance and a refractive index difference at the interface between oxidized Si3N4 powder and resin. At the exposure energy of 500 mJ/cm2, the cure depth of the raw Si3N4 powder was 34 µm. After oxidizing at 1150 °C and 1200 °C for 1 h, the cure depth effectively increased to 42 µm and 51 µm, respectively. Finally, the complex-shaped Si3N4 parts were successfully fabricated using surface-oxidized Si3N4 powder via DLP method.

Effects of amino groups on dispersibility of silicon nitride powder in aqueous media

Silicon nitride (Si3N4) powders were subjected to amination modification by grafting γ-aminopropyltriethoxysilane (APTES) via a direct blending method in solution. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that the hydroxyl groups present on the surface of Si3N4 powder particles interacted with the silanols groups of APTES to combine through covalent bonding. Thermogravimetric analysis (TGA) suggested that the grafting of APTES on Si3N4 powder surface was successful with grafting content reaching up to 7%. Compared to native Si3N4, the surface hydrophilicity of amino Si3N4 powder was enhanced and dispersibility was improved. Overall, these findings indicated the promising aspects of amination modification and future potential use in environmental protection by using water instead of organic solvents during Si3N4 ceramic formation process.

Densification and mechanical properties of spark plasma sintered Si3N4/ZrO2 nano-composites

Fully dense Si3N4-ZrO2 nano-composites, where ZrO2 content varied from 0 to 30 vol%, were produced via Spark Plasma Sintering (SPS) at 1600 °C under the pressure of 30 MPa for 10 min. Si3N4, Y2O3-stabilized ZrO2 (YSZ), and Al2O3 (sintering aid) were used as starting powders and mixed with high energy planetary ball mill. The obtained nano-powders with an average particle size of 45 nm were employed for the sample preparation. XRD patterns of the sintered nano-composites showed that the entire ZrO2 constituent was successfully retained in tetragonal crystal structure, while neither monoclinic ZrO2 nor detrimental ZrN/ZrON phase was formed during the SPS process. Homogenous distribution of the tetragonal ZrO2 particles in Si3N4 matrix was observed by SEM analysis. By considering shrinkage behavior of the nano-composites as a function of sintering temperature and time, it was found that the addition of Y2O3-doped ZrO2 into the initial Si3N4 powder can noticeably facilitate densification process, decreasing sintering temperature of monolithic Si3N4 ceramic from 1600 °C to 1420 °C through 30 vol% YSZ utilization. The evaluation of mechanical properties indicated that the hardness of the Si3N4-base composites declined from 16.6 to 13.2 GPa, whereas the fracture toughness improved from 5.8 to 7.1 MPa m1/2 by increasing ZrO2 content from 0 to 30 vol%, which were explained based on the in-situ formation of β-Si3N4 and the stress-induced phase transformation from tetragonal to monoclinic ZrO2, respectively. Friction coefficient (μ) and specific wear rate (Kw) of Si3N4-ZrO2 nano-composites were estimated being in the range of 0.59–0.67 and 2.46 × 10−6-3.41 × 10−6 mm3/N m, respectively, demonstrating promising characteristics for tribological applications.

Biological response of human osteosarcoma cells to Si3N4-doped Bioglasses

In vitro and in vivo studies have recently shown that silicon nitride (Si3N4) is an osseoconductive and potential osseoinductive biomaterial. Even though the amount of bone mineral produced by Si3N4 was inferior when compared to commercial Bioglass®, it strongly stimulated the production of extracellular matrix and collagen tissues. Consequently, this study was designed to determine if appropriate mixtures of Bioglass® and Si3N4 might improve the ratio of mineral apatite to its biological matrix. Commercial 45S5 Bioglass® powder was mixed with 5 and 10 mol% Si3N4 powder, followed by melting, cooling, crushing, and comminution. The composite powders had modified morphologies and chemical structures including a reduced average particle size, a reduction of oxygen in the SiO backbone structure, and trapped CO2 gas which was converted into calcium carbonate. When exposed to human osteosarcoma cells within an osteogenic medium, the 5 mol% Si3N4 composite powder resulted in higher amounts of hydroxyapatite while the 10 mol% Si3N4 powder provided in a more balanced combination of collagen and mineral fractions closer to the natural composition of native human bone.