Reaction-bonded Silicon Nitride Research Articles

Preparation and characterization of porous reaction bonded silicon nitride by paraffin emulsified suspension

Porous Si3N4 ceramics with an interconnected pore structure were prepared by a paraffin emulsified suspension method. The effects of the volume ratio of paraffin to silicon and Y2O3 addition on the structure and properties of porous Si3N4 were studied. Uniform dispersed pores introduced by the emulsified paraffine droplets can be observed in the green samples. With the increase of the volume ratio of paraffin to silicon, the bulk density and the strength of the sample were decreased, and the apparent porosity and Darcy permeability were increased. The formation of α-Si3N4 whiskers could be promoted by the addition of the Y2O3 during the nitriding process, and numerous nano whiskers could be obtained in the pores left by the paraffine droplets with suitable addition of the Y2O3. The porous Si3N4 with interconnected whiskers prepared via the paraffin emulsion method exhibited potential application for hot gas particular matter filtration.

Fabrication and properties of Si3N4f/RBSN porous ceramic composite

Porous Si3N4 has excellent properties such as high temperature resistance, corrosion resistance, high porosity, and high specific surface area, but the inherent brittleness limits the application of Si3N4 in some special environments. Si3N4f/RBSN porous ceramic composites were prepared by reaction bonding method using reaction-bonded silicon nitride(RBSN) as the matrix and continuous Si3N4 fibers (fiber mats) as the reinforcement. The results show that the composite with Si/Si3N4 = 70:30 in the raw material has a superior nitridation rate and flexural strength of 96.5% and 23.5 MPa, respectively. The nitridation process of the Si3N4f/RBSN matrix is dominated by the vapour-phase reaction between SiO and N2, and the products are mainly α-Si3N4 whiskers. The residual flexural strength of the composites is essentially unchanged after 10 thermal cycles in air at 800 °C. The composites have excellent thermal shock resistance and can be used as the reusable crucible.

Thermal conductivity prediction of sintered reaction bonded silicon nitride ceramics using a machine learning approach based on process conditions

Thermal conductivity (TC) of sintered reaction bonded silicon nitride (SRBSN) ceramics was predicted from process conditions using support vector regression (SVR) as a machine learning algorithm. A total of ten explanatory variables were selected from the process conditions for building a SVR model. The determination coefficient (R2) in the testing results of the trained SVR model reached a satisfactory level (R2 = 0.8 on average) when more than 100 data points were used as the training data. The relative importance scores of the explanatory variables revealed that sintering conditions (temperature and time) had the largest contribution to the TC prediction while those of oxygen impurity content in the main starting powder, types and concentrations of sintering additives and nitriding conditions were also influential to a certain extent.

Effects of sintering additives on dielectric breakdown strength of sintered reaction-bonded silicon nitride

We prepared sintered reaction-bonded silicon nitride (Si3N4) by using various lanthanide oxides and magnesia for sintering additives and evaluated their effects on the microstructure and dielectric breakdown strength (DBS). Both the microstructure and DBS varied by the types of the sintering additives, and artificial intelligence (AI) based determination was conducted for the DBS to separate the effect of microstructural factors from that of sintering additives. The results indicated that the DBS values varied mainly by the former effect. The microstructures of Si3N4 with Eu2O3 and La2O3 contained a large number of pores, leading to lowered DBS; on the contrary, those with Tm2O3 and Y2O3 possessed dense microstructures with large-elongated grains, showing higher DBS. On the other hand, the Si3N4 with Yb2O3 showed lower DBS than what AI-determined from the microstructures because the additive forms grain boundary phase with a low electrical resistance.

Sintered reaction-bonded silicon nitride ceramics for power-device substrates -review-

This review addressed the recent progress of sintered reaction‐bonded Si3N4 (SRBSN) ceramics which are expected to be used as ceramic substrates of the next-generation power devices. Following an overview of thermal conductivities of Si3N4 ceramics and their improvement strategies, we described the advantages of the SRBSN routes. Because of the low content of lattice oxygen, the SRBSN ceramics possess significantly high thermal conductivities, compared to Si3N4 ceramics prepared by conventional methods. This material also showed exceptionally high fracture toughness and the strong rising R-curve behavior. The properties of the SRBSN ceramics are largely affected by the nitridation conditions, including the temperature, pressure and heating rate, and the sintering additive ratios. The thermal fatigue tests revealed the excellent thermal fatigue resistance of the SRBSN substrates, compared with those of other ceramic substrates. The strength retention ratio after thermal fatigue was clearly proportional to the fracture toughness. The dielectric breakdown strength (DBS) of the SRBSN ceramics with large fibrous grains showed a thickness dependency reverse to the normal (lower DBS in thinner substrates).

Effects of heating rate on microstructure and property of sintered reaction bonded silicon nitrides

Effects of heating rate on microstructure and property of sintered reaction bonded silicon nitrides

Enhanced thermal conductivity and flexural strength of sintered reaction‐bonded silicon nitride with addition of (Y0.96Eu0.04)2O3

AbstractSintered reaction‐bonded silicon nitride (SRBSN) with high thermal conductivity was obtained using (Y0.96Eu0.04)2O3 and MgO as sintering additives. Green compacts were nitrided at 1400°C for 4 h. Post‐sintering was carried out at 1850 and 1900°C for 4 h, respectively. In reaction‐bonded silicon nitride (RBSN) doped with Y2O3 and MgO, the β‐Si3N4 content and nitridation degree were 51.1% and 93.8%, respectively. However, the β‐Si3N4 content and nitridation degree were 72.6% and 96.7% in a nitrided compact doped with (Y0.96Eu0.04)2O3 and MgO. After post‐sintering, the phase composition, microstructure, mechanical properties, and thermal conductivity were investigated. After sintering at 1900°C for 4 h, the thermal conductivity of SRBSN doped with (Y0.96Eu0.04)2O3 and MgO was increased by 16.5% compared to that of the samples doped with Y2O3 and MgO. The highest hardness of 1639 HV and the good flexural strength of 776.4 MPa were also achieved in the sample doped with 2‐mol.% (Y0.96Eu0.04)2O3 and 5‐mol.% MgO.

Effect of rotary ultrasonic machining parameters on surface integrity of advanced ceramics

The commercial use of advanced ceramics has been hampered by the lack of an efficient, low-cost machining process. Two of the most important requirements for making machining of ceramics economically viable are: i) obtaining high enough material removal rates and ii) developing a machining process that does not cause surface and subsurface damage to the ceramic component. Therefore, it is important to study, in-depth, machining processes that have the potential to machine advanced ceramics efficiently and reliably. In this study, two-level full factorial experiments were designed and run to determine the effect of rotary ultrasonic machining process parameters (grit size, vibration amplitude, and feed rate) on the process outputs (cutting force, surface roughness, and surface compressive residual stresses). The materials under investigation were sintered silicon nitride and sintered reaction-bonded silicon nitride. The experiments reveal the main effects as well as the interaction effects of the process parameters on the process outputs such as cutting force, surface roughness, and surface compressive residual stresses. Using a larger grit size has been found to decreases the tool axial force. Samples that had a rougher surface finish also showed the highest surface residual compressive stresses. Surface compressive residual stresses were present in all samples after rotary ultrasonic machining irrespective of the conditions used. The presence of surface residual compressive stresses was found to be independent of the direction of machining.

Material evaluation for engineering a novel crucible setup for the growth of oxygen free Czochralski silicon crystals

For manufacturing of several high performance electronic devices, e.g. insulated-gate bipolar transistors (IGBT), single crystalline silicon crystals with high purity and minimum oxygen (in the range of 1015 at/cm3) concentration are required. Such silicon crystals are typically grown by the Floating Zone technique (Fz), as the more common and cheaper Czochralski technique (Cz) uses silica crucible, which leads always to a relatively high oxygen concentration in the silicon crystals (>1017 at/cm−3). Therefore, in this work potential materials were evaluated with respect to the development of a novel oxygen-free crucible system, which should enable a cost effective growth of oxygen free Cz silicon ingots. For that purpose different graphite materials as well as nitride bonded silicon nitride (NSN) were tested in contact with liquid silicon due to their infiltration behaviour and occurrence of crack formation. Functional silicon nitride (Si3N4) coatings were applied by powder based spray coating of reaction bonded silicon nitride (RBSN) and chemical vapour deposition (CVD) on graphite and NSN crucibles. Characterization of the crucible/coating systems before and after crystal growth experiments in a lab-scale casting furnace reveal information about morphology, infiltration behaviour and adhesion strength on the crucible. Further, investigations on the grown silicon crystals give information about impurity incorporation coming from the novel crucible systems. The results indicated, that especially graphite materials with low porosity and a high mechanical strength as well as NSN with polysilazane sealing in combination with a CVD Si3N4 coating have definitely a potential for application as crucible system in silicon growth processes.

The effect of silicon particle size on the characteristics of porous sintered reaction bonded silicon nitride

The effect of silicon particle size on the β-phase ratio, microstructure and the flexural strength of porous sintered reaction-bonded silicon nitride(SRBSN) was systematically investigated. Six kinds of raw powders containing Yb2O3 addtive (5, 10 wt%), prepared with different particle size distribution, were prepared by planetary ball-milling duration of 0, 3, 24 h. The behavior of α-to-β phase transformation of Si3N4 sintered at 1650 °C and 1750 °C, was found to be in good relation with SiO2 molar ratio over all the oxide additives. High flexural strength of SRBSN over 400 MPa was obtained when the amount of SiO2 was less than 0.7 owing to having the rod-like β-particles. Otherwise, the flexural strength of SRBSN became lower due to major occurrence of the equiaxed β-particles. This significant difference was considered to be caused from the seeding effect of β-ratio of RBSN samples as well as the different solubility of nitrogen element in the eutectic liquid phase.

Investigation of the Effect of Sintering Additive on the Microstructure and the Antibacterial Behavior of Reaction Bonded Silicon Nitride Ceramics

Silisyum Nitrür (Si3N4) genellikle yüksek sıcaklık ve yapısal uygulamalarda tercih edilen, üstün özellikli bir oksit dışı seramiktir. Çok sert bir malzeme olmasının yanı sıra, çubuksu beta () tanelerin gelişimi ile seramik malzemeler içinde yüksek kabul edilebilecek tokluk değerleri elde etmek mümkün olabilmektedir. Bu özelliklerine ilave olarak biyo uyumluluğunun da anlaşılması ile birlikte özellikle, bu malzemenin biyoseramik olarak kullanım potansiyelini arttırmak amacıyla son on yılda yapılan çalışmaların sayısı da artmıştır. Bu çalışmada da reaksiyon bağlama tekniği ile, çevre biyolojik dokularla entegrasyon açısından avantajlı olan gözenekli Si3N4 seramiklerinin üretilmesi amaçlanmıştır. Sinterleme ilavesi olarak sisteme yapılan CaO, Y2O3 ve CeO2 katkılarının, elde edilen Si3N4 seramiklerin fiziksel ve mikroyapısal özelliklerine ve bunların sonucu olarak antibakteriyel davranışlarına etkileri incelenmiştir. Elde edilen sonuçlar CeO2’in hem E. coli hem de S. aureus açısından dezavantajlı bir sinterleme ilavesi olduğunu, Y2O3’in ise en avantajlı ilave olduğunu görülmüştür. CaO ilavesi yapılan sistem ise E. coli için düşük, S. aureus için yüksek oranda bakteri üremesi ile sonuçlanmıştır.

Tunable microwave absorption performance of carbon fiber-reinforced reaction bonded silicon nitride composites

The hybrid network of Si3N4 whiskers and conducting carbon fiber has great potential for microwave absoprtion applications. The high electrical conductivity of the carbon fiber helps to transform the microwave transparent Si3N4 into microwave absorbing materials. Herein, the microwave absorption performance of 5–20 vol % of carbon fiber reinforced reaction bonded Si3N4 (Cf-RBSN) composites have been discussed in detail. The Cf reinforcement tuned the X-band dielectric properties of the RBSN composites. The 5 vol % Cf-RBSN composite exhibit a minimum reflection loss (RLmin) of −36.16 dB (99.998% microwave absorption) at 11.89 GHz and a high specific reflection loss of 920 dB. g−1 for 5.9 mm thickness, while 20 vol % Cf-RBSN composites resulted in RLmin of −22.86 dB at 11.56 GHz with a low thickness of 1.5 mm. Thus, the superior microwave absorption performance of the prepared lightweight composites results from the multiple interfacial polarization, dipole polarization, and conduction loss due to the 3D network of interconnected Si3N4 whiskers and Cf.

Sintering Behavior and Properties of Reaction-Bonded Silicon Nitride

The influence exerted by the conditions of the preliminary synthesis of Si3N4 by nitridation at 1350 and 1400°С and additional high-temperature sintering at 1800 and 1900°С on the properties of reaction-bonded silicon nitride was studied. Secondary silicon nitride (β-Si3N4) formed in the course of nitridation consists of needle-like grains, which reinforce the material and impart to it additional mechanical strength. The microstructure and phase composition of the silicon nitride material at different initial ratios of silicon and silicon nitride were studied. The materials obtained approach liquid-phase-sintered and hot-pressed silicon nitride in the mechanical properties.

Characterization of porous sintered reaction-bonded silicon nitride containing three different rare-earth oxides

The effect of rare-earth oxides on the characteristics of porous sintered reaction-bonded silicon nitride (SRBSN) was investigated. Three types of raw Si powder mixtures containing different rare-earth oxide (La2O3, Er2O3, and Yb2O3) were prepared and nitrided in the form of compacts. The nitriding profiles of the respective raw powder mixtures with elevating temperature indicated that Yb2O3 clearly promoted the nitridation of Si compacts at low temperature compared with other rare-earth oxides, and the β-Si3N4 ratio after completion of the nitriding reaction was different at which temperature the major nitridation occurred. Yb2O3 was found to be the most effective additive to achieve a strong porous SRBSN, having the flexural strength of 441 MPa. The reason why Yb2O3 promotes the nitridation reaction and has excellent mechanical properties after post-sintering is that oxygen was removed during the nitriding reaction, which was supported by the analysis of oxygen content via the laser-induced breakdown spectroscopy.

A comparative study on nitridation mechanism and microstructural development of porous reaction bonded silicon nitride in the presence of CaO, MgO and Al2O3

ABSTRACT During the in-situ nitridation of Si in the presence of CaO, MgO and Al2O3 formation of reaction bonded silicon nitride ceramics (RBSN) having various microstructures indicated the possibility of different nitridation mechanisms operating. Experimental evidence suggested that, whereas the morphology of pores was controlled by nitridation of Si(g) in CaO-RBSN and SiO(g) in Al2O3-RBSN, a combination of these two reactions occurred during the nitridation of the MgO-RBSN. By inhibiting the growth of whiskers and maximizing the α/β ratio, the CaO addition led to the formation of matte grains creating clean spherical cavities with d < 40 µm and flexural strength of 0.8 MPa. In contrast, when using Al2O3 additions, a microstructure with a very low α/β ratio, fine inter-particle pores and 2.4 MPa flexural strength, reinforced with interlocking whiskers, was produced. The highest porosity (85%) and the lowest strength (0.3 MPa) occurred in the MgO-RBSN, which was composed of both matte grains and fine whiskers. Local supersaturation and low content of β-nuclei led to the formation of anisotropic β-grains with a bimodal microstructure in heat-treated CaO-RBSN while a unimodal microstructure was observed in heat-treated MgO-RBSN. No porosity loss or β-grain growth occurred in the heat-treated Al2O3-RBSN.

The effect of preliminary heat treatment on the durability of reaction bonded silicon nitride crucibles for solar cells applications

Silicon nitride crucibles have the potential to replace silica crucibles and reduce the cost of silicon crystallization because of their reusability potential. Till date, crucibles’ heat treatment before each use is a prerequisite to achieve non-wetting conditions that is needed to facilitate the ingot release and hence enable reusability. Yet, no studies have examined the heat treatment influence on the crucibles’ durability. The present investigation focuses on the crucibles’ heat treatment and its impact on the crucibles’ lifetime. Repeated heat-treatments of silicon nitride crucibles in the air at above 1100 °C leads to crucible fracture. Therefore, this study identifies the cause and the mechanism of such failures by applying different heat treatment procedures in the air. The mass gain and the oxidation rates of the crucibles at different temperatures are measured via Thermogravimetry (TG) and Differential Thermal Analyzer (DTA). The results show that the porosity and phase distribution along the crucible wall thickness, play a key role in the crucible’s behavior during oxidation. Moreover, excessive internal oxidation in the tested crucibles results in severe thermal stresses which cause cracking during cooling.

Controlling the width of particle size distribution of Si powder and properties of sintered reaction-bonded silicon nitride (SRBSN) ceramics with high thermal conductivity

Sintered reaction-bonded silicon nitride (SRBSN) for high-thermal-conductivity ceramic substrates was fabricated from waste Si scrap. To prepare homogenously sized Si powder, the width of the particle size distribution (WPSD) was selected for the first time as the main index to characterize the milled Si powder and was systematically controlled. The coarse and irregular shape of the as-received Si scrap was carefully pulverized by controlling planetary milling parameter and then processed. As the WPSD of Si powder was narrower, the thermal conductivity of SRBSN ceramics increased from 67 to 81 W/mK with enhancing grain growth under the same sintering condition. Furthermore, to fabricate SRBSN ceramics with higher thermal conductivity, the effects of the milling fluid and the amount of sintering additive were investigated. It was proven that a smaller amount of a sintering additive was effective for enhancing the thermal and mechanical properties of SRBSN. Selection of the fluid for milling Si powders was an important inflection point for the surface properties of Si powder, which greatly influence the nitridation and thermal conductivity of the SRBSN ceramics.

Variation of porosity and pore size during post-sintering of reaction-bonded silicon nitride doped with Y&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and MgO additives

Variation of porosity and pore size during post-sintering of reaction-bonded silicon nitride doped with Y&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and MgO additives

Porous Reaction-Bonded Silicon Nitride Ceramics: Fabrication Using Hollow Polymer Microspheres and Properties

A process has been proposed for the preparation of porous reaction-bonded silicon nitride (RBSN) via the addition of a pore former, uniaxial pressing, and subsequent reaction sintering in a vacuum furnace. As a pore former, we used a commercially available powder consisting of hollow polymer microspheres (Akzonobel) with an average diameter of 9 μm. We have studied the effect of pore former content in green compacts on the mechanical, dielectric, and thermophysical properties of the ceramics. The proposed process allows one to prepare porous RBSN with the following properties: σb = 48 MPa, e = 3.2, tan δ = 35 × 10–4 at a frequency of 10 GHz, and λ = 0.96 W/(m K) at 1100°C. The ceramic obtained in this study is potentially attractive for industrial application as a radar-transparent structural material with reduced thermal conductivity.

Making reusable reaction‐bonded silicon nitride crucibles for silicon casting from kerf‐loss silicon waste

AbstractSilicon kerf loss during wafer slicing and the broken quartz crucibles after silicon casting are two major solid wastes from photovoltaic (PV) industry. Especially, the recycle of kerf‐loss silicon has become an urgent issue because near 100 000 t of solid wastes are generated every year. One of the most meaningful recycle routes of the kerf‐loss silicon is to make silicon nitride crucibles to replace the quartz crucibles. In this study, we demonstrated how this is feasible through acid leaching refining, slip casting, and nitridation. The reaction‐bonded silicon nitride (RBSN) crucibles after oxidation were found pure enough for silicon ingot growth. More importantly, they could be reused after ingot growth. With the present examples, the potential of using the kerf‐loss silicon for fine ceramics is prominent.