Addition Of Si3N4 Research Articles

Preparation and Properties of β-Si<sub>3</sub>N<sub>4</sub>/Epoxy Matrix Composite

Thermally conducting, but electrically insulating, polymer-matrix composites exhibiting low dielectric constant are needed for electronic packaging. For developing such composites, this work used silicon nitride particles as fillers and epoxy as matrix. The thermal conductivity of Si3N4 particles epoxy-matrix composites was increased by up to 31.4 times than that of neat polymer by silane surface treatment of the particles prior to composites fabrication. The increase in thermal conductivity is due to decrease in the filler-matrix thermal contact resistance through the improvement of the interface between matrix and particles. At 45.4 vol. % silane-treated Si3N4 particles only, the thermal conductivity of epoxy-matrix composites reached 9.72W/ (m*K). The dielectric constant was also low (up to 5.0 at 1 MHz). However, Si3N4 addition caused the flexural strength and ductility to decrease from the values of the neat polymer.

Elimination of Grain Boundary Glass in α‐Sialon by Adding Aluminium Nitride

The elimination of residual glass in hot‐pressed Y‐α‐SiAlON was demonstrated by varying the nitride composition. This was readily achieved by adding excess aluminium nitride (AlN), while the addition of excess Si3N4 had little effect. The amount of excess AlN required for this purpose increased with increasing Al and O content in α‐SiAlON, and was higher if α‐SiAlON contained larger interstitial cations. These results were explained by the thermodynamics of α‐SiAlON precipitation. The elimination of liquid also led to suppressed grain growth, refined microstructure, and improved oxidation resistance. Grain coarsening by post‐sintering annealing was required to obtain high fracture toughness.

Enhanced Jc–B performance in MgB2/Fe tapes with nanometre Si3N4 addition

The Jc–B performance of MgB2/Fe tapes was enhanced in high magnetic field by the addition of an appropriate amount of nanometreSi3N4 particles. At 4.2 K and in 12 T, the optimum doped samples (1% and 1.67%) show almost twice the valueof Jc of that of the undoped tape. The enhancement in theJc–B performance is considered to come from the introduction of extra pinningcentres and the improved core density. It is noted that the dependence ofJc on the magnetic field does not change in differentSi3N4 doped samples, indicating that the flux pinning centres introduced by the addition of nanometreSi3N4 particles are limited.Considering the small Tc drop and the residual Si3N4 particles in the heat treated tapes, it is believed that theSi3N4 particles appearas additives in MgB2. The added and/or reaction induced nanometre particles might serve as effective pinningcentres.

Preparation, structure, and properties of (Bi, Pb)2Sr2Ca2Cu3O10+δ ceramics with Si3N4 additions

The microstructure, phase composition, texture, and superconducting properties (Tc, ΔTc, jc(T), and R(T) at H= 0 and 5 mT) of (Bi,Pb)2Sr2Ca2Cu3O10 + δ ceramics (sintering at 840°C for 36 h) with ultrafine Si3N4 additions (0.05–0.2 wt %) are studied. The introduction of 0.05–0.1 wt % Si3N4 is shown to reduce the width of the superconducting transition by 2–3 K and to raise the critical current density at temperatures below 95 K.

A Spodumene Silicon Nitride Complex with Zero Thermal Expansion at Ambient Temperature

The influence of Si3N4 addition on the thermal expansion and Young’s modulus of ceramics based on spodumene is investigated. Powders of β-spodumene and α-Si3N4 are sintered at 1523 K to form complex ceramics consisting of those two phases. The bulk density and Young’s modulus of the ceramics are significantly improved compared to those of an undoped β-spodumene ceramic. The averaged thermal expansion coefficient between 293 K and 300 K is −0.032×10-6/K for the ceramic doped with 23.1 mass% Si3N4.

Effect of SiC, Si3N4 and TiB2 additions on the oxidation resistance of TiAl alloys

The oxidation behavior of TiAl alloys containing dispersed particles of (5, 10, 15 wt.%) SiC, (3,5 wt.%) Si3N4 or (3, 5, 10 wt.%) TiB2 was studied between 800 and 1200°C in atmospheric air. The TiAl−(SiC, Si3N4) alloys oxidized to TiO2, Al2O3, and SiO2. The TiAl−TiB2 alloys oxidized to TiO2, Al2O3, and B2O3 which evaporated during oxidation. Improvement in oxidation resistance accompanied by thin, dense scale formation due to the addition of dispersoids originated primarily from the enhanced alumina-forming tendency, improved scale adhesion by oxide grain refinement owing to the beneficial effect of dispersoids, and the incorporation of SiO2 within the oxide scale in the case of TiAl−(SiC, Si3N4) alloys.

Frictional and Mechanical Properties of Fe5Si3-Particles-Dispersed Si3N4 Formed by the Reaction during Sintering.

Aiming at the development of Si3N4 based ceramics with low frictional coefficient, Fe5Si3-particles-dispersed Si3N4 ceramics were fabricated from a mixture of powders containing Fe3O4, Si3N4 and sintering additives. Microstructure, frictional and mechanical properties were investigated of the obtained ceramics, and it was confirmed that Fe3O4 consumed and granular Fe5Si3 phase generated with in the Si3N4 matrix by the reaction of Fe3O4 with other components during sintering. Sintered bodies were densified and high strength of 900MPa was obtained, when the amount of Fe3O4 addition was less than 10mass%. Whereas Fe3O4 addition exceeded 20mass%, the strength fell off remarkably due to agglomerated Fe5Si3 and big pores. Moreover, the 10mass% Fe3O4 added Si3N4 showed the lowest frictional coefficient. According to data of heat of immersion and contact angle measurement, this result was interpreted as being provided by the lubricant film formed on the ceramic surface.

Effect of .ALPHA.-Si3N4 Addition on Sintering of Mg-.ALPHA.-SiAlON Powders.

Using Mg-α-SiAlON powders synthesized by carbothermal reduction-nitridation, fabrication of Mg-α-SiAlON ceramics was attempted through gas pressure sintering method. Furthermore, the effect of Si3N4 addition on densification of the synthesized powders was investigated. As a result, as-synthesized powders were transformed into β-SiAlON and did not densify during firing. On the other hand, in the case of samples with α-Si3N4 powder, it was found that full densification occurred and the Mg-α-SiAlON phase did not change upon gas pressure sintering, namely, dense Mg-α-SiAlON ceramics, composed of fine and uniform grains, could be obtained through firing at 1950°C for 2h.

MgSiN2 Addition as a Means of Increasing the Thermal Conductivity of β‐Silicon Nitride

Si3N4 powders with the concurrent addition of Yb2O3 and MgSiN2 were sintered at 1900°C for 2–48 h under 0.9 MPa nitrogen pressure. Microstructure, lattice oxygen content, and thermal conductivity of the sintered specimens were evaluated and compared with Si3N4, Yb2O3, and MgO addition. MgSiN2 addition was effective for improving the thermal conductivity of Si3N4 ceramics, and a material with high thermal conductivity over 140 W·(m·K)−1 could be obtained. For both specimens, lattice oxygen content was decreased with sintering time. However, the thermal conductivity of the MgSiN2‐doped specimen was slightly higher than the MgO‐doped specimen with the same oxygen content.

Various Types of Bubble-Containing Silica Glasses Fabricated by Sintering Powder Mixtures of Silica with Silicon Nitride.

Bubble-containing silica glasses were fabricated by sintering amorphous silica powders with small amount of silicon nitride powders. Sintering was performed at 1800°C in N2 gas atmosphere. It was found that the addition of Si3N4 is effective for forming bubbles. By controlling the Si3N4 content, various types of bubble-containing silica glasses, such as the so-called the opaque silica glass and the foamed silica glass, could be obtained. Addition of 0.004mol% Si3N4 produced highly opaque silica glasses containing a large number of small bubbles, while 0.431mol% Si3N4 resulted in low-density foamed silica glasses containing large 1mm-sized bubbles. Wide variations of bubble size and density were observed on these glasses. Thermal conductivities were estimated and compared with several literature values. The relation between thermal conductivity and bubble density was discussed based on a model simulation.

The Effect of Si3N4 Additions on the Oxidation Resistance of TiAl Alloys

The oxidation kinetics of TiAl alloys with and without 3 and 5 wt.%additions of Si3N4 particles were studied at 1173 and1273 K in 1 atm of air. The Si3N4 dispersions wereunstable in the matrix phase, so that some of them reacted with titaniumduring sintering to form Ti5Si3 and dissolvednitrogen. The oxide scale formed on TiAl–Si3N4alloys consisted of an outer TiO2, an intermediate(Al2O3+TiO2), and an inner(TiO2+Al2O3) mixed layers. The enhancedalumina-forming tendency, the presence of discrete SiO2 particlesbelow the outer TiO2 layer, and the improved scale adhesion bySi3N4 dispersions were attributable mainly to theincreased oxidation resistance compared to the Si3N4-freeTiAl alloys. Marker experiments showed that, for TiAl–Si3N4 alloys, the primary mode of scale growth was the outward diffusion oftitanium ions for the outer scale and the inward transport of oxygen ionsfor the inner scale.

Development and characterization of SiC(f)/MoSi2–Si3N4(p) hybrid composites

Intermetallic compound MoSi2 has long been known as a high temperature material that has excellent oxidation resistance and electrical/thermal conductivity. Also its low cost, high melting point (2023°C), relatively low density (6.2 g cm−3 versus 9 g cm−3 for current engine materials), and ease of machining, make it an attractive structural material. However, the use of MoSi2 has been hindered due to its poor toughness at low temperatures, poor creep resistance at high temperatures, and accelerated oxidation (also known as ‘pest’ oxidation) at temperatures between approximately 450 and 550°C. Continuous fiber reinforcing is very effective means of improving both toughness and strength. Unfortunately, MoSi2 has a relatively high coefficient of thermal expansion (CTE) compared to potential reinforcing fibers such as SiC. The large CTE mismatch between the fiber and the matrix resulted in severe matrix cracking during thermal cycling. Addition of about 30–50 vol.% of Si3N4 particulate to MoSi2 improved resistance to low temperature accelerated oxidation by forming a Si2ON2 protective scale and thereby eliminating catastrophic ‘pest failure’. The Si3N4 addition also improved the high temperature creep strength by nearly five orders of magnitude, doubled the room temperature toughness and significantly lowered the CTE of the MoSi2 and eliminated matrix cracking in SCS-6 reinforced composites even after thermal cycling. The SCS-6 fiber reinforcement improved the room temperature fracture toughness by seven times and impact resistance by five times. The composite exhibited excellent strength and toughness improvement up to 1400°C. More recently, tape casting was adopted as the preferred processing of MoSi2-base composites for improved fiber spacing, ability to use small diameter fibers, and for lower cost. Good strength and toughness values were also obtained with fine diameter Hi-Nicalon tow fibers. This hybrid composite remains competitive with ceramic matrix composites as a replacement for Ni-base superalloys in aircraft engine applications.

Influence of Additives on Slag Resistance of Al2O3‐SiO2‐SiC‐C Refractory Bond Phases under Reducing Atmosphere

The microstructures of Al2O3–SiO2–SiC–C refractory matrices with aluminum, silicon, Si3N4, BN, B2O3, and B4C additives are characterized before and after a crucible slag test, and the phases present are compared to those expected at thermodynamic equilibrium. The carbon content dominates the resistance to CaO–MgO–Al2O3–SiO2 slag penetration, while the viscosity of liquid phases present has a significant influence when the matrix carbon contents are similar. Silicon and Si3N4 additives reduce slag penetration resistance because of indirect oxidation of carbon to form SiC. B4C, in particular, and B2O3 also reduce slag penetration resistance because of formation of a more fluid boron‐containing liquid, while aluminum and BN addition have no significant effect. Carbon and BN hardly react with the slag, while SiC partially reacts with it, leading to deposition of carbon as a dense layer. Corundum present in the refractories also readily dissolves in the slag. Microstructurally, slag penetration resistance is associated with the dense carbon layer located at the slag‐refractory interface.

Pest Resistant and Low CTE MoSi2-Matrix for High Temperature Structural Applications

AbstractThe objective of this investigation was to identify a pest resistant MoSi2-base matrix composition having properties suitable for SiC reinforcement. A 30 vol.% addition of fine Si3N4 particulates to MoSi2 significantly improved the low temperature accelerated oxidation resistance and thereby eliminated pest failure. Addition of Si3N4 also improved the high temperature oxidation resistance, strength and more importantly lowered the CTE of MoSi2 such that cracking was eliminated in a hybrid composite consisting of 30 vol.% Si3N4 and 30 vol. % SCS-6 fibers.

Production of Ti powders by calcio-thermic reduction of TiO2

The process of densification and development of the microstructure of mullite–ZrO2/Y2O3 ceramics from mixture of Al2O3, SiO2, ZrO2 and Y2O3 by gradually adding of α–β Si3N4 nanopowder from 1 to 5 wt% by traditional and spark plasma sintering were investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and some ceramic and mechanical properties. The processes of DTA for all samples are characterised by a low-pitched endo-effect, when gradual mullite formation and noticeable densification at temperatures of 1200–1400 °C is started. It is testified by shrinkage and density both for traditionally and by SPS-sintered samples. The influence of the Si3N4 additive on the density characteristics is insignificant for both sintering cases. For SPS samples, the density reaches up to 3.33 g/cm3, while for traditionally sintered samples, the value is 2.55 g/cm3, and the compressive strength for SPS grows with Si3N4 additives, reaching 600 N/mm2. In the case of traditional sintering, it decreases to approximately 100 N/mm2. The basic microstructure of ceramic samples sintered in a traditional way and by SPS is created from mullite (or pseudo-mullite) crystalline formations with the incorporation of ZrO2 grains. The microstructure of ceramic samples sintered by SPS shows that mullite crystals are very densely arranged and they do not have the characteristic prismatic shape. The traditional sintering process causes the creation of voids in the microstructure, which, with an increasing amount of Si3N4 additive, are filled with mullite crystalline formations.

Water atomization of Al-5Cr-2Zr-1Mn

The process of densification and development of the microstructure of mullite–ZrO2/Y2O3 ceramics from mixture of Al2O3, SiO2, ZrO2 and Y2O3 by gradually adding of α–β Si3N4 nanopowder from 1 to 5 wt% by traditional and spark plasma sintering were investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and some ceramic and mechanical properties. The processes of DTA for all samples are characterised by a low-pitched endo-effect, when gradual mullite formation and noticeable densification at temperatures of 1200–1400 °C is started. It is testified by shrinkage and density both for traditionally and by SPS-sintered samples. The influence of the Si3N4 additive on the density characteristics is insignificant for both sintering cases. For SPS samples, the density reaches up to 3.33 g/cm3, while for traditionally sintered samples, the value is 2.55 g/cm3, and the compressive strength for SPS grows with Si3N4 additives, reaching 600 N/mm2. In the case of traditional sintering, it decreases to approximately 100 N/mm2. The basic microstructure of ceramic samples sintered in a traditional way and by SPS is created from mullite (or pseudo-mullite) crystalline formations with the incorporation of ZrO2 grains. The microstructure of ceramic samples sintered by SPS shows that mullite crystals are very densely arranged and they do not have the characteristic prismatic shape. The traditional sintering process causes the creation of voids in the microstructure, which, with an increasing amount of Si3N4 additive, are filled with mullite crystalline formations.

The oxidation of cobalt based alloys containing partially dissolved particles of Si3N4 at 1000�C

The isothermal oxidation behavior of Co-Cr and Co-Cr-Si alloys with and without 5, 10, and 15 vol.% dispersions of unstable Si3N4 particles was studied in 1 atm of oxygen at 1000°C. The dispersion of Si3N4 which dissolved partially in the matrix, greatly reduced the oxidation rate of Co-Cr alloys. Silicon nitride was found to promote the formation of continuous Cr2O3 layers at low chromium concentrations. Furthermore, the unstable Si3N4 was more effective in reducing the oxidation rate than an alloy containing an equivalent amount of silicon. Additions of 15vol.% Si3N4 tended to increase the oxidation rate by forming nonprotective SiO2 particles which disrupted the protective Cr2O3 scale. The mechanism of oxidation was altered due to the Si3N4 additions. Marker experiments indicated oxygen diffusion inward via the CoO lattice, rather than a combination of both oxygen and metal ion motion which is encountered in Co-Cr alloys.

A preliminary study of alumina sintering by addition of Si3N4

On etudie l'influence de l'addition de 0,5 a 4,4% de Si 3 N 4 sur la microstructure et les proprietes mecaniques d'une ceramique d'alumine frittee. On etudie aussi l'influence de l'addition simultanee de Si 3 N 4 et AlN

The role of Si3N4 additions in the reaction bonding of silicon compacts

The role of Si3N4 additions in the reaction bonding of silicon compacts

Solar radiation: (France)R Michard, Le Vide, 19 (113), Sept/Oct 1964, 265–271

Electrical resistivities, thermal conductivities and thermal expansion coefficients of hot-pressed ZrB2–SiC, ZrB2–SiC–Si3N4, ZrB2–ZrC–SiC–Si3N4 and HfB2–SiC composites have been evaluated. Effects of Si3N4 and ZrC additions on electrical and thermophysical properties of ZrB2–SiC composite have been investigated. Further, properties of ZrB2–SiC and HfB2–SiC composites have been compared. Electrical resistivities (at 25 °C), thermal conductivities (between 25 and 1300 °C) and thermal expansion coefficients (over 25–1000 °C) have been determined by four-probe method, laser flash method and thermo-mechanical analyzer, respectively. Experimental results have shown reasonable agreement with theoretical predictions. Electrical resistivities of ZrB2-based composites are lower than that of HfB2–SiC composite. Thermal conductivity of ZrB2 increases with addition of SiC, while it decreases on ZrC addition, which is explained considering relative contributions of electrons and phonons to thermal transport. As expected, thermal expansion coefficient of each composite is reduced by SiC additions in 25–200 °C range, while it exceeds theoretical values at higher temperatures.