Silicon Nitride Particles Research Articles

Influence of processing method on the exfoliation process for organically modified clay systems. I. Polyurethanes

AbstractThe influence of different processing methods on the nature of the dispersion achieved in the creation of a polyurethane nanocomposite is presented. The nanocomposites were produced using two different types of organically modified montmorillonite clays and a sample of fine particles of silicon nitride as a reference material. Rheological data were used to assess the nature of the dispersion achieved using the different processing methods. The nature of the dispersion produced was characterized using wide‐angle X‐ray scattering measurements of the finally cured products. Dynamic mechanical thermal analysis was used to investigate the effect of the incorporation of clay platelets into the matrix of the polymer. The high‐temperature modulus provides evidence of the interaction between the polymer and the clay platelets; however, surprisingly, the glass transition temperatures of the filled and unfilled materials were almost identical. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1335–1343, 2004

Friction and wear of low nanometer Si 3N 4 filled epoxy composites

To prepare epoxy-based composites with low frictional coefficient and high wear resistance, nanometer silicon nitride particles were added. Dry sliding wear tests indicate that the composite materials exhibit significantly improved tribological performance and mechanical properties at rather low filler content (typically less than 1 vol.%). Unlike the severe wear observed in unfilled epoxy dominated by fatigue-delamination mechanism, the wear mode of nano-Si 3N 4 composites is characterized by mild polishing. It is believed that strong interfacial adhesion between Si 3N 4 nanoparticles and the matrix, reduced damping ability and enhanced resistance to thermal distortion of the composites, and tribochemical reactions involving Si 3N 4 nanoparticles account for the reduced frictional coefficient and wear rate of the composites.

Preparation of h-BN nano-film coated α-Si3N4 composite particles by a chemical route

In this study, α-Si3N4 particles were successfully coated with h-BN nano-film by a novel chemical route. Ammonium biborate was deposited onto the surface of silicon nitride particles to form NH4HB4O7·3H2O–Si3N4 composite powders by the heterogeneous precipitation method in anhydrous ethanol solution. The obtained composite powders were dried at room temperature, then nitrided in an ammonia flow at 900 °C and subsequently crystallized at 1600 °C to obtain h-BN nano-film coated α-Si3N4 composite particles. The prepared composite particles were characterized by IR, SAM, TEM, HRTEM, TG and DSC techniques. TEM and HRTEM micrographs showed that α-Si3N4 particles were well coated by BN ultrathin film in thickness of 1 nm.

Yield Stress Measurement of Silicon Nitride Suspensions

AbstractYield stress values of silicon nitride suspensions were measured via a novel slotted plate device and a constant stress rheometer and the results were compared. Test platform velocity, associated with the slotted plate method, was found to have a substantial effect on dynamic yield stress but not on static yield stress. The effects of suspension concentration and temperature on yield stress values were investigated. Yield stress measurements on mixtures of silicon nitride and alumina particles, as well as creep tests were performed.

6061 Al reinforced with silicon nitride particles processed by mechanical milling

This study focused on the characterization of a new graphene oxide (GO) reinforced Al–10Ni/GO metal matrix composite fabricated by mechanical alloying technique. The effect of ball milling time and sintering temperature on the microstructural evolutions, wear behaviour, mechanical and thermal properties of the fabricated composites were investigated. X-ray diffractometer and scanning electron microscope analysis showed that as the ball milling time increased, the particle size decreased, the homogeneity increased, and the Al3Ni2 intermetallic phase occurred after 40 h of ball milling. The thermal properties of the prepared powder composites were investigated with a differential thermal analyzer (DTA). DTA results showed a series of reaction peaks, which were attributed to the melting of the eutectic Al phase and the crystallization of the Al3Ni2 phase, in the temperature range of 560–655 °C. Also, as the ball milling time and sintering temperature increased, it was observed that the microhardness of the pressed powder alloys increased as a result of cold-welding of the reinforcement with the matrix material, and the occurred intermetallic phases. The maximum microhardness value of Al–10Ni/1 wt%GO composite, which was ball milled for 50 h and heat-treated at 600 °C, was found to be 315 ± 10 HV1. Furthermore, the wear behaviours were investigated under loads of 5–15 N. It was observed that as the load increased, the mass loss increased, and the mass loss decreased as the sintering temperature and milling time increased. In addition, the maximum and minimum coefficients of friction were found to be 0.50 and 0.27, respectively. As a result, it is observed that increasing the amount of GO reinforcement in the matrix from 1 wt% to 2 wt% adversely affects the properties of the composite.

Effect of Si/α-Si3N4Ratio on the Shape of Silicon Nitride Particles Produced by SHS Method

Si and α-Si₃N₄ powder mixtures added with 3 wt% Y₂O₃ were reacted under 5 MPa nitrogen pressure. The reaction products contained α-Si₃N₄ particles with elongated shapes. Length and width of the elongated grains were the maximum when the starting powder mixture of 50 wt% Si - 47 wt% α-Si₃N₄ and 3 wt% Y₂O₃ was used. Aspect ratio of the elongated grains were between 4.4 and 5. When the starting powder mixture contained 70 wt% Si, large particles with irregular shapes appeared. Meanwhile, the reacti on did not proceed when the starting powder mixture contained 30 wt% Si and less. The SHS product was easy to crush and the elongated particles obtained from the starting powder mixtures of 40 wt% Si - 57 wt% α-Si₃N₄ - 3 wt% Y₂O₃ and 50 wt% Si - 47 wt% α-Si₃N₄ - 3 wt% Y₂O₃ were good candidates for the seeds.

Comportamiento mecánico de compuestos de aluminio reforzados con partículas en función de la temperatura

The aluminium matrix composites materials reinforced by ceramic particles can be elaborated by powder metallurgy techniques, with extrusion processes. These can provide new materials, with a better mechanical behaviour and moreover when we need those properties at higher temperatures. Aluminium alloy reinforced composites with silicon nitride particles by powder extrusion process was done. Their mechanical properties were characterised at room and elevated temperatures.

Stability of colloidal silicon nitride suspension with poly-electrolyte

This investigation aimed at elucidating the polymer conformation of NH 4 + salt of poly(acrylic acid) (PAA–NH 4) and relating it to the stability of colloidal silicon nitride suspension as a function of pH values. Conformation of PAA–NH 4 on silicon nitride particle was monitored along with electrokinetic and stability responses at different PAA–NH 4 concentration. The conformation of PAA–NH 4 has been identified by the use of titration experiments, from which the values of α and their corresponding pH can be roughly characterized by four stability regions. The stability properties indicate that conformation of the PAA–NH 4 chain along with the electrostatic interactions is shown to be a major controlling factor in determining the stability of the slurries considered here. At the acidic pH range, polymer adsorption in the coiled form is demonstrated to have a positive contribution to the dispersion. Nevertheless, the residual polymer in the stretched form is detrimental to the stability properties in the alkaline pH range. ©

Microstructure and mechanical behavior of 6061Al reinforced with silicon nitride particles, processed by powder metallurgy

The present work reports strength-ductility synergy achieved in an Al–Cr–Fe–Co–Ni complex concentrated alloy (CCA) through utilizing the heterogeneous lamella (HL) structure produced by a simple two-step thermo-mechanical processing route (cold rolling + annealing). The as-cast microstructure consists of dendritic FCC phase and inter-dendritic BCC phase having coherent precipitation of B2 particles. Compared to the as-cast specimen, nearly all the processed materials in this study showed significant simultaneous enhancement in both strength and ductility, which has not been achieved previously on CCAs with this type of microstructure. In addition, their mechanical properties can be tuned by changing the annealing time and resulted in superior properties compared to other CCAs of similar phase constitution. Moreover, the multiphase HL structure also exhibited a stronger Bauschinger effect compared to other HL-structured materials with heterogeneity among the lamellae generated solely by grain size difference. The strategy demonstrated in this work provides a cost-efficient and less composition-dependent direction for fabricating high-performance structural materials.

Water-based Si3N4 suspensions: Part I. Effect of processing routes on the surface chemistry and particle interactions

Si3N4 powders manufactured by two different preparative routes were characterized for the solid–liquid interfacial reactivity and surface composition. Three mixing processes were tried to investigate the modifications of silicon nitride particle surface in aqueous suspensions. The surfaces of the starting powders and the dried mixed powders were investigated by x-ray photoelectron spectroscopy to determine the nature and ratios of surface groups. Electroacoustic measurements show that no change occurs in the isoelectric point for the mixed Si3N4 powders while the milling/mixing process has a great influence on the zeta potential magnitude and particle size distribution.

Development of Short‐Range Repulsive Potentials by Short‐Chain Surfactants in Aqueous Slurries

The effect of both cationic (n‐trimethylammonium bromide, CnTAB) and zwitterionic (phosphocholine, CnCnPC) surfactants on the properties of aqueous slurries of Si3N4 was studied. These surfactants were expected to adsorb to the surface of Si3N4 particles to produce short‐range repulsive interparticle potentials that might be useful for the colloidal processing of advanced ceramic powders. Electrophoretic, adsorption, and viscosity measurements showed that longer‐chain‐length surfactants (CnTAB, n≥ 12, and CnCnPC, n≥ 9) strongly adsorb. Surfactants with shorter chain lengths were highly soluble and did not adsorb. Although the CnTAB, n≥ 12, surfactants produced very weak particle networks with a low viscosity, the packing density during consolidation was very low, and the bodies were brittle (cracked before plastic deformation). The less‐soluble, longer‐chained CnCnPC, n≥ 9, surfactants did produce high particle‐packing densities but also produced brittle bodies. In all cases, it appeared that the surfactants could be pushed away from the surface during particle packing.

Chemisorption of Organofunctional Silanes on Silicon Nitride for Improved Aqueous Processing

Different chem‐adsorbed silane molecules have been used to produce weakly attractive silicon nitride particle networks for aqueous colloidal processing. Silanes with diamino and poly(ethylene glycol) hydrophilic heads yielded slurries with the lowest viscosity, longest sedimentation stability, and highest packing density. Chem‐adsorbed silane molecules protected silicon nitride and yttrium oxide, a common processing aid, from hydrolysis at pHs between 5.5 and 11. A novel approach was used to produce short‐range repulsive potentials necessary to yield the weakly attractive networks. Addition of salt to dispersed silicon nitride slurries with particles coated with poly(ethylene glycol)‐silane caused the collapse of the 22‐atom‐long chains and residual electrical double layer. This produced a weakly attractive network which persisted during consolidation to yield a plastic body with a flow stress that was dependent on the counterion size. When 0.5M tetramethylammonium chloride was used at pH 10, plastic bodies had a flow stress similar to clay, whereas lithium counterions produced bodies with a much higher flow stress.

Threshold conditions for dynamic fragmentation of ceramic particles

A framework of a particle-impact experiment was developed and used to study the dynamic fragmentation of brittle materials. In the experiment a small, spherical particle of a brittle material impacts against a thick, hard anvil. Unlike conventional particle-impact experiments, observations and measurements are focused on dynamic failure processes in the particle, minimizing, if not completely eliminating, damage to the target during the impact. The impact process is observed using high-speed photography. Results are presented for aluminum oxide and silicon nitride particles striking a titanium diboride anvil. The radius of the particles ranged from 0.40 to 3.18 mm. It is observed that above a certain threshold velocity the particle undergoes fragmentation upon impact. This threshold velocity depends on the particle material properties, and decreases with increasing particle radius. An elasto-dynamic finite element simulation of the particle-impact experiment was carried out. The finite element simulations showed that for these experimental conditions the stress amplitude within the particle, for a given impact velocity, is independent of the size of the particle. The size of the particle influences only the contact time, and thus the duration of the stress pulse applied to the particle. The size dependence of the threshold velocity was explained by using a cohesive zone model to represent the dynamics of the failure process. Thus, the experimental results allow the dynamic cohesive strength and the dynamic toughness of the material to be determined. In addition to reporting measurements of the threshold velocity, the observed pattern of particle fragmentation is described. This experiment provides a means of studying the threshold conditions for dynamic fragmentation of brittle materials, and illustrates some of the issues involved in the application of cohesive zone models to problems involving impact and dynamic fragmentation in brittle materials.

The Removal of Submicron Particles in Liquid-Based Cleaning

Megasonic cleaning is one of the most widely used wet-cleaning processes in the semiconductor, hard disk and flat panel display industries. Presented results involve different and new techniques for introducing the high frequency ultrasonic energy in the cleaning bath. The effects of power, temperature and time on the removal efficiency of Si3N4 particles in the size range from 0.1 μm to 1.0 μm from silicon wafers are presented. Results show that removal efficiencies near 100% for silicon nitride particles using deionized water could be achieved under the right conditions. The megasonic input power has a greater effect on the removal efficiency than does temperature.

Transient Growth Bands in Silicon Nitride Cooled in Rare‐Earth‐Based Glass

Silicon nitride (Si3N4) particles embedded in various R‐SiAl‐O‐N glasses (R = La, Nd, Gd, Yb) have been systematically studied by high‐resolution transmission electron microscopy and by analytical electron microscopy. The particles typically show an internal growth band, which is attributed to the enhanced growth of the particles in the supersaturated silicate liquid during cooling and reheating. The electron energy‐loss spectroscopy and energy‐dispersive X‐ray spectroscopy analysis reveal that the growth band typically contains lanthanide elements. This trapping, especially of the lighter lanthanide elements, within the lattice of the β‐SiAlON is obviously beyond the general expectation that the lighter lanthanide ions hardly form solid solutions with either α‐ or β‐Si3N4. This ultimately provides some clues regarding the mobility of the lanthanide ions in the liquids and also revives interest in the general question of the possible effect of a cooling stage on the structures and compositions of the intergranular film and of the grain/glass interface in the Si3N4‐based polycrystalline ceramics.

The effect of water vapor on the agglomeration of wear particles of ceramics

By means of environmental scanning electron microscopy (ESEM), an in situ observation technique was developed to observe the agglomeration process of wear particles of silicon nitride, silicon carbide and alumina and to study the effect of water vapor on the agglomeration of wear particles. The results show that the size of the deposit of wear particles becomes smaller with increasing water vapor pressure. Among the three ceramics, alumina shows the largest size of the deposit of wear particles, with silicon nitride next silicon carbide the smallest. Furthermore, friction coefficient increases linearly as wear particles agglomerate. The normalized diameter of the deposit, which is used to quantitatively estimate the agglomeration degree of wear particles, is considered to be related to following parameters: (1) adhesive energy— higher adhesive energy leads to a larger diameter of the deposit of wear particles; (2) electric conductivity—lower electric conductivity leads to larger triboelectrification which produces electrostatic force and results in a larger diameter of the deposit of wear particles.

Formation and Growth of Silicon Nitride Particles in a Laser-Driven Aerosol Reactor Investigated with Photon Correlation Spectroscopy and Electron Microscopy

ABSTRACT This paper investigates the formation and growth of silicon nitride particles in a laser-driven aerosol reactor. This investigation is done on-line with photon correlation spectroscopy (PCS) and off-line with electron microscopy. The results of the measurements are compared with each other and with a monodisperse growth model that incorporates the influence of particle shape. PCS proved to be a good and fast monitoring technique, but it provides limited information: the intensity-weighted average particle size and approximate velocity. Electron microscope studies of samples showed good agreement with both the spectroscopy and the modeling results. The incorporation in the model and in the determination of the PCS diameter of the extra information about particle size and phase from the electron microscope photographs increases their accuracy. This is necessary if PCS combined with growth model are to be used for process control. Although the analysis techniques and the model are applied to a specific case, they are applicable in all types of flame reactors.

Microstructure and Superplasticity in Al-Mg Alloy Composites Reinforced with Silicon Nitride Particles

Microstructure and Superplasticity in Al-Mg Alloy Composites Reinforced with Silicon Nitride Particles

Role of polyacrylate in modifying interfacial properties and stability of silicon nitride particles in aqueous suspensions

The role of ammonium polyacrylate in modifying the interfacial properties of silicon nitride powder was examined systematically in order to understand the basic mechanism of dispersion. The adsorption of the polyacrylate on silicon nitride powder was found to be dependent on both the pH and its residual (equilibrium) concentration. The interfacial charge properties of the silicon nitride powder can be modified to a large extent by the adsorbed polyacrylate and equilibrium pH. Well-dispersed silicon nitride suspensions can be obtained in both the neutral and alkaline pH range by the application of ammonium polyacrylate. The enhanced electrostatic repulsion between the dispersant-modified powder surfaces was found to be the primary mechanism governing the dispersion. Also, the steric interactions of the adsorbed polyacrylate with aqueous media were demonstrated in this work to have a positive contribution to the dispersion. The latter is attributed to the hydrophilic nature of the polyacrylate. The dispersing functions of the adsorbed polyacrylate were understood to arise from the two oxygen atoms in the carboxylic group of the polyacrylate. The charged oxygen atom in the carboxylic group was responsible for the measured interfacial charge properties of the dispersant-modified powder. The uncharged oxygen atom had an additional contribution to the hydrophilic nature of the adsorbed dispersant layer.

Synthesis of silicon nitride particles in pulsed radio frequency plasmas

Silicon nitride (hydrogenated) particles are synthesized using a pulsed 13.56 MHz glow discharge. The plasma is modulated with a square-wave on/off cycle of varying period to study the growth kinetics. In situ laser light scattering and ex situ particle analysis are used to study the nucleation and growth. For SiH4/Ar and SiH4/NH 3 plasmas, an initial very rapid growth phase is followed by slower growth, approaching the rate of thin film deposition on adjacent flat surfaces. The average particle size can be controlled in the 10–100 nm range by adjusting the plasma-on time. The size dispersion of the particles is large and is consistent with a process of continuous nucleation during the plasma-on period. The large polydispersity is also reported for silicon particles from silane and differs from that reported in other laboratories. The silicon nitride particle morphology is compared to that of silicon and silicon carbide particles generated by the same technique. Whereas Si particles appear as rough clusters of smaller subunits, the SiC particles are smooth spheres, and the Si 3N4 particles are smooth but nonspherical. Postplasma oxidation kinetics of the particles are studied with Fourier transform infrared spectra and are consistent with a hydrolysis mechanism proposed in earlier work with continuous plasmas. Heat treatment of the powder in an ammonia atmosphere results in the elimination of hydrogen, rendering the silicon nitride resistant to atmospheric oxidation.