Amorphous Silicon Nitride Powders Research Articles

Analytical Electron Microscopy of Silicon Nitride Nanostructures Synthesized from the Vapor Phase

Silicon nitride, Si3N4 is a covalent compound with excellent physical and chemical properties such as corrosion resistance, low-specific weight and good thermal conductivity at ambient and elevated temperatures. Such properties are very attractive in application as advanced ceramics and in semiconductor devise [1]. Nano sized amorphous silicon nitride powders were synthesized at 300 °C by precipitation from the vapor phase reaction of SiCl4 and NH3 and Ar as carrier gas. Solid ammonium halogenide is formed as by-product, in addition to silicon nitride powder.

Abrasion resistance of Ni-B/Si3N4 composite layers produced by electroless method

Purpose: The paper presents the results of investigations of Ni-B/Si3N4 composite layers produced on steel substrate by electroless method. Design/methodology/approach: Amorphous silicon nitride powder (Si3N4) with nanometric particle sizes was used as a dispersion phase for the production of composite layers. Ni-B/Si3N4 composite layers were produced in baths of varying Si3N4 powder content. For comparative purposes, the study also includes results related to a Ni-B layer. The Si3N4 powder and the structure of the produced layers were characterized. The topography and morphology of the surface of the produced layers are presented. The adhesion of the layers to the substrate material was determined. Microhardness and tribological properties of test materials were determined. Findings: The results of the studies show that Ni-B/Si3N4 composite layers and Ni-B composite layers are characterized by compact structures and good adhesion to the substrate material. The incorporation of Si3N4 particles into the Ni-B layers increases the degree of surface development of the layers. The Ni-B/Si3N4 composite layer material exhibits less microhardness and less abrasive wear compared to Ni-B layers. However, the extent of wear damage of the Ni-B/Si3N4 is relatively small comparing to Ni-B layers.

Investigation of nano-silicon nitride ceramics containing an yttria sintering additive and the carbon thermal reduction reaction

Carbothermal reduction treatment (CRT) and spark plasma sintering (SPS) were employed to prepare nano-silicon nitride ceramics from an amorphous silicon nitride powder containing yttria (Y2O3) as an additive, and the effects of the Y2O3 contents and reducing agent additives on the ceramic densification and phase transformation behavior were examined. The results showed that specimens with 6wt% Y2O3 generated dense sintered bodies with sufficient liquid-phase contents. Specimens with 3wt% and 4wt% carbon black produced single-phase silicon nitride after the CRT and SPS processes. In addition, increasing the quantity of carbon black enabled the effective removal of the second phase of silicon oxynitride and allowed the grain size of the sintered body to be maintained at a nanoscale level. An excess of the carbon black additive resulted in insufficient liquid phase production, hindering the complete conversion of α-phase silicon nitride into β-phase silicon nitride, which in turn affects the density of the sintered bodies.

Crystallization Behavior of Amorphous Si3N4 and Particle Size Control of the Crystallized α-Si3N4.

Amorphous silicon nitride powder prepared by low-temperature vapor-phase reaction was heat treated at various temperatures for different periods of time to examine the crystallization behavior. The effects of the heat-treatment temperature and duration on the degree of crystallization were investigated along with the effect of the heat-up rate on the particle size, and its distribution, of the crystallized α-phase silicon nitride powder. A phase transition from amorphous to α-phase occurred at a temperature above 1400 degrees C. The crystallization. process was completed after heat treatment at 1500 degrees C for 3 h or at 1550 degrees C for 1 h. The crystallization process starts at the surface of the amorphous particle: while the outer regions of the particle become crystalline, the inner part remains amorphous. The re-arrangement of the Si and N atoms on the surface of the amorphous particle leads to the formation of hexagonal crystals that are separated from the host amorphous particle. The particle size and size distribution can be controlled by varying the heat-treatment profile (namely, the heat-treatment temperature, heating rate, and heating duration at the specified temperature), which can be used to control the relative extent of the nucleation and growth. The completion of most of the nucleation process by lowering the heat-up rate can be used to achieve a singlet particle size distribution. Bimodal particle size distribution can be achieved by fast heat-up during the crystallization process.

Growth mechanism of Si3N4nanowires from amorphous Si3N4powders synthesized by low-temperature vapor-phase reaction

A novel synthesis method to prepare Si3N4 nanowires from amorphous silicon nitride (a-Si3N4) powder synthesized by a low-temperature vapor-phase reaction method was investigated. Highly crystalline α-Si3N4 nanowires were synthesized by heat treatment of the a-Si3N4 powder under ammonia atmosphere. The surface of the nanowires was smooth and clean without any attached particles. The thickness of the nanowires was in the range of ∼200–300 nm with lengths of tens of micrometers. The nucleation of nanowires from the reaction between SiO and N2 occurs on the surface of the a-Si3N4 powder, which is covered by a thin layer of SiO2, and the nanowires grow from the rearrangement of Si and N atoms of the a-Si3N4 powder. The reduction of SiO2 to SiO by ammonia was promoted in the presence of a Ni catalyst; therefore, the growth was observed at a lower temperature when Ni was added to the a-Si3N4 powder than in the presence of added Fe. The growth of α-Si3N4 nanowires occurs along the [100, 101] direction and follows the vapor–solid–solid mechanism.

Optimization of reaction parameters for synthesis of amorphous silicon nitride powder by vapor phase reaction

Most silicon nitride powders, which are industrially used in various applications under extreme conditions, are produced by the diimide process. The synthesis of diimide is carried out at −50–0°C using liquid-phase reactants with organic solvent. This process, however, consumes a considerable amount of energy. One promising method for the synthesis of silicon nitride powder which is also energy-efficient is the vapor-phase reaction of SiCl4 with NH3. In this study, the processing parameters of the vapor-phase reaction for the synthesis of silicon nitride were investigated to use this method for producing diimide. The vapor-phase reaction was completed at room temperature with a down-top flow, and solid products were obtained at the bottom of the reactor. Si(NH)2 was decomposed at temperatures above 150°C according to the result of the TG analysis, which limited the reaction temperature. The reaction temperature was increased with an increase in the flow rates of the reactants and decreased with an increase in the flow rate of the carrier gas. The reaction yield decreased with an increase in the flow rate of the carrier gas. 87% yield was obtained with the optimized reaction condition.

Elastic–plastic analysis of ultrafine-grained Si2N2O–Si3N4 composites by nanoindentation and finite element simulation

Ultrafine-grained Si2N2O–Si3N4 composites are fabricated by hot-press sintering of amorphous nano-sized silicon nitride powders at 1600, 1650, and 1700°C with nano-sized Al2O3 and Y2O3 as additives. Sintered materials of increasing average grain sizes of 280, 360, and 480nm were obtained with increasing sintering temperature. Hardness and elastic modulus are tested by nanoindentation. Finite element simulations of the nanoindentation are performed to study the elastic and plastic mechanical properties based on the elastic modulus and P–h curve that were obtained through the nanoindentation tests. A theoretical method is proposed for calculating the stress–strain relationship of brittle ceramic materials based on the experimental nanoindentation data. Several relevant coefficients in the theoretical calculation formula are determined by comparing the calculation and simulation results.

Experimental Study on Combustion Reaction between Silicon and Nitrogen in Transport Bed

Combustion reaction between silicon powders and nitrogen in transport bed was studied. The reaction temperature ranged from 1523 to 1653 K, and the reaction time ranged from 0 to 2.7 min. The phase compositions, morphologies and chemical composition of the products were analyzed by X-ray diffraction, scanning electron microscopy and O/N determinater, respectively. The experimental results showed, in the case of silicon powders with particle size of 2.2 μm, the conversion rate of silicon was 61.9% at reaction temperature of 1653 K and reaction time of 2.7min, and the products mainly comprised amorphous silicon nitride powders.

Crystallization behavior of amorphous silicon nitride added with silicon powder

The additives may accelerate the crystallization process of amorphous powder and shorten the crystallization time. In this respect, special attention should be paid to the effects of additives on the crystallization process of amorphous silicon nitride powder. In this paper, silicon nitride crystalline powder is prepared by crystallization process of nanosized amorphous silicon nitride powder added with 5% silicon powder at temperatures in the range of 1300–1500 °C. The complete crystallization time of amorphous silicon nitride powder would be reduced from more than 6 h to 30 min by silicon powder and the factors such as temperature and duration on the crystallization process are investigated. The XRD results indicate that the added silicon powder accelerates the crystallization process of amorphous silicon nitride powder effectively and the final products are mainly α-Si3N4 and Si2N2O. The SEM results show that most of the crystallization products are in the morphologies of slender columnar and irregular rod. The mechanisms of amorphous silicon nitride crystallization induced by Si are discussed. The crystallization process occurs at the interface of the amorphous powder and the added Si powder.

Silicon Oxynitride Ceramics Prepared by Plasma Activated Sintering of Nanosized Amorphous Silicon Nitride Powder without Additives

Si2N2O ceramics were prepared by plasma activated sintering using nanosized amorphous Si3N4 powder without sintering additives within a temperature range of 1400°C–1600°C in vacuum. A mixed Si–N4−n–On (n = 0, 1…4) amorphous structure was formed in the process of sintering, and Si2N2O crystals were nucleated where the local structure was similar with Si2N2O. After sintering at 1600°C, the Si2N2O ceramic was composed of elongated plate‐like Si2N2O grains and amorphous phase. The Si2N2O grains showed a width of less than 100 nm and a very high aspect ratio.

Rapid crystallization of amorphous silicon nitride powder accelerated by liquid Si

The complete crystallization time of amorphous silicon nitride powder could be reduced from more than 6h to 30min by adding Si powder in N2 atmosphere. The crystallization process may be affected by the synergy of the reaction between Si and N2 and the liquid phase of Si due to the addition of Si. The α-Si3N4 produced by the added Si and nitrogen may be the seed of the crystallization process. The amorphous silicon nitride powder may be dissolved in the liquid phase and then precipitated as α-Si3N4. This article uses Ar instead of N2 to shield the reaction between Si and N2 in order to analyze the role of the two mechanisms. The added Si powder accelerates the crystallization process effectively in Ar. Powder of more than 70% crystalline phase content is produced by adding 5% Si annealing at 1400°C for 15min. The existence of liquid Si is the key factor to promote the crystallization process and the process follows the solution–precipitation mechanism. The final products are mainly α-Si3N4 and Si2N2O. The SEM results show that most of the products are irregular rod-like particles.

Cold Isostatic Pressing–Normal Pressure Sintering Behavior of Amorphous Nano-Sized Silicon Nitride Powders

The amorphous nano-sized silicon nitride powders were sintered by cold isostatic pressing –normal press sintering method. The sintering additives of Y2O3 and Al2O3 powders with average grain size less than 20nm were prepared by polyacrylamide gel method. Relative density of sintered materials rise and pore size reduce with increasing of cold isostatic pressing. When the pressure is 100MPa, the density is only 48% and average pores size is between 2μm and 20μm which obvious the first particle space. When the pressure is 200MPa, the density is 67% and agglomerated particle size reduce obviously as well as the pores size are between 0.1μm and 1.0μm which appears because of the second particle. Pressed compact with a relative density 74% and average pore size less than 0.5μm reach to a good density state at 300MPa pressure. Sintering material composites with Si2N2O and β-Si3N4 phases, compared with hot press sintering composites, which indicates that increasing of sintering press is conducive to the formation phase Si2N2O. Relative density is above 96% and average pore size is less than 500nm at sintering temperature 1800°C.

Cold Isostatic Pressing–Normal Pressure Sintering Behavior of Amorphous Nano-Sized Silicon Nitride Powders

Cold Isostatic Pressing–Normal Pressure Sintering Behavior of Amorphous Nano-Sized Silicon Nitride Powders

Rapid Crystallization Process of Amorphous Silicon Nitride

The crystallization of nanosized amorphous silicon nitride powder is one of the methods to produce sub‐micrometer/nanosized α‐Si3N4 powder. The application of this method is still limited by the long crystallization time, low output, and high cost. This article invents a new crystallization method of amorphous silicon nitride involving the addition of Si powder. The new process reduces the complete crystallization time from more than 6 h to 30 min, thus allowing efficient production of sub‐micrometer/nanosized α‐Si3N4 powder. Effects of factors such as additive, temperature, and duration on the crystallization process are investigated using XRD and FTIR. The experimental results showed that the added Si powder accelerates the crystallization process effectively. The final product is a mixture of α‐Si3N4 and Si2N2O. In this article, amorphous silicon nitride powder with added Si is annealed at 1450°C. Powder of nearly 100% crystalline phase content is produced either by adding 10% Si and annealing for 15 min or by adding 5% Si and annealing for 30 min.

Experimental Study on Continuous Preparation of Ultrafine Silicon Nitride Powders in Transport Bed

Ultrafine e grain amorphous silicon nitride (Si3N4) powders were produced via direct nitridation process of silicon powders in transport bed. The properties of the nitridation products, such as morphology, phase composition, chemical composition and structure, were examined using standard characterization techniques (SEM, XRD, FTIR, etc). The experimental results showed, in the case of silicon powders with particle size of 2.7μm, the conversion rate of silicon was 53.4% at reaction temperature of 1380°C and reaction time of 2.7minutes, and the products mainly comprised amorphous silicon nitride powders.

Spark Plasma Sintering of Nanosized Amorphous Silicon Nitride Powder with a Small Amount of Sintering Additive

Dense and fine‐grained β‐Si3N4 ceramics were successfully obtained with a small amount of sintering additives, 1.5 mass% Y2O3 and 0.5 mass% Al2O3, using nanosized amorphous Si3N4 powder by spark plasma sintering at temperatures of 1500°–1800°C and a pressure of 30 MPa under N2. The β‐Si3N4 ceramics were composed of equiaxed grains with an average size of 300 nm. A higher sintering temperature was required for the densification of submicrometer‐sized α‐Si3N4 powder with the small amount of the additives. The use of nanosized amorphous Si3N4 powder accelerated the densification and the transformation to the β‐phase.

Formation and vanishment of the intragranular microstructure in Si2N2O/Si3N4 nanocomposites

Si2N2O/Si3N4 nanocomposites were fabricated by liquid phase sintering of amorphous nano-sized silicon nitride powders. The intragranular microstructure was observed and researched. Intragranular microstructure’s β-Si3N4 was formed in Si2N2O matrix at the sintering temperature higher than 1650°C. It was discovered that intragranular microstructure could also disappear by transformation during high temperature annealing. Two possible mechanisms of the disappearance of intragranular microstructure were given. The effect of intragranular microstructure on main mechanical properties was also investigated.

Effect of additives on the sintering of amorphous nano-sized silicon nitride powders

Amorphous nano-sized silicon nitride powders were sintered by liquid phase sintering. The influences of the additives of Y2O3 and Al2O3 prepared by two different ways, the polyacrylamide gel method and the precipitation method, were investigated. The grain sizes of the additives prepared by the first method were finer than those of prepared by the latter method. When sintered at the same temperature, 1700°C, the average grain size of the silicon nitride is 0.3 μm for the sample with the former additives, which is much finer than the one with the latter additives. The density of additives prepared by precipitation method is clearly lower than those of prepared by polyacrylamide gel method.

Superplastic Sinter-Forging of Fine-Grained Si<sub>3</sub>N<sub>4</sub>-Si<sub>2</sub>N<sub>2</sub>O Composite at Low Temperature

The Si3N4- Si2N2O composites are fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering (LPS) method. XRD analysis shows sintered body consists of β-Si3N4 and Si2N2O. SEM experiment conforms that the average grain size of sintered body is less than 300nm. The complex-shape gears can be formed by a sinter-forging technology when the sintering temperature is 1600°C and the superplastic forging temperature is only 1550°C. Rod-shaped grains aligned along the perpendicular direction of pressure and the mechanical properties increase about 10% after the materials were forged.

Liquid Phase Sintering Behavior of Amorphous Nano-Sized Silicon Nitride Powders

The amorphous nano-sized silicon nitride powders were sintered by liquid phase sintering method. Si3N4-Si2N2O composites were in-situ fabricated. The Si2N2O phase was generated by an in-situ reaction 2Si3N4(s)+1.5O2(g)=3Si2N2O(s)+N2(g). The content of Si2N2O phase up to 60% was obtained at a sintering temperature of 1650°C and reduced when the sintering temperature increased or decreased, which indicates that the reaction is reversible. The mass loss, relative density and average grain size increase with increasing of sintering temperature. The average grain size is less than 500nm when the sintering temperature is below 1700°C. During the sintering procedure, there is a complex crystallization and phase transition: amorphous Si3N4 → equiaxial α-Si3N4→ equiaxial β-Si3N4 → rod-likeSi2N2O → needle-like β-Si3N4. Small round-shaped β-Si3N4 particles are entrapped in the Si2N2O grains and a high density of staking faults are situated in the middle of Si2N2O grains at a sintering temperature of 1650°C.