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Heteroatom doping is a straightforward and smart strategy to improve the fluorescence efficiency of carbon dots (CDs). We synthesized the Si, N-codoped CDs (SiNCDs) with high quantum yield up to 29.7% through one-step hydrothermal method. The linear range for Fe3+ was between 0 and 200 μM, and the limit of detection was about 5 μM, which presented potential for Fe quantification in serum to diagnose Fe overload. In addition, the SiNCDs demonstrated good selectivity to Fe3+ among high concentrations of metal ions, amino acids and H2O2, so there is no need to mix additional reagents as the colorimetric method does in clinic, making SiNCDs more competitive in clinical application. Furthermore, we explored the practicability of SiNCDs by detecting Fe in serum from five healthy volunteers and three patients suffering Fe overload. The recovery rate was from 87.1 to 113.6%, which confirmed the application prospect of SiNCDs in clinical diagnostics. [ABSTRACT FROM AUTHOR]

Improving the photoluminescence quantum yields and air-stability of silicon nanocrystals is crucial to expanding their influence in optoelectronic devices and other burgeoning application areas. Here, a dual-plasma approach for the synthesis of silicon nanocrystals capped with silicon nitride is reported. The reactor consists of two plasma stages in series: a primary radiofrequency (rf) plasma for silicon nanocrystal growth from silane and argon gas followed by a secondary rf plasma for silicon nitride growth using nitrogen gas as the reactant. The core-shell nanocrystals were characterized using optical and structural analyses, and the plasma was characterized using optical emission spectroscopy. The resulting core-shell nanocrystals show a reduced susceptibility to ambient air oxidation as compared to bare silicon nanocrystals alone. This result is a step toward achieving highly efficient and air-stable photoluminescence from silicon nanocrystals while avoiding organic functionalization. [ABSTRACT FROM AUTHOR]

New AlGaN/GaN high electron mobility transistors (HEMTs) that their barrier layers under the gate are divided into two regions horizontally are presented in this work. Upper region is Si 3 N 4 (SI-HEMT) or un-doped AlGaN (UN-HEMT) and lower region is AlGaN with heavier doping compared to barrier layer. Upper region in SI-HEMT and UN-HEMT reduces peak electric field in the channel and then improves breakdown voltage considerably. Lower region increases electron density in the two dimensional electron gas (2-DEG) and enhances drain current significantly. For instance, saturated drain current in SI-HEMT is about 100% larger than that in the conventional one. Moreover, the maximum breakdown voltage in the proposed structures is 65 V. This value is about 30% larger than that in the conventional transistor (50 V). Also, suggested structure reduces short channel effect such as DIBL. The maximum g m is obtained in UN-HEMT and conventional devices. Proposed structures improve breakdown voltage and saturated drain current and then enhance maximum output power density. Maximum output power density in the new structures is about 150% higher than that in the conventional. [ABSTRACT FROM AUTHOR]

Si 3 N 4 has attracted much attention as the thermally conductive fillers owing to its high thermal conductivity, high electrical resistivity and low dielectric loss. This paper presented the preparation of well-dispersed columnar Si 3 N 4 particles by carbothermal reduction–nitridation (CRN) strategy with assistance of unique CaF 2 additive under an elevated N 2 pressure. The average diameter of columnar particles was 4 μm and aspect ratio was 3. The speculation for the inherent growth mechanism of the Si 3 N 4 particles was tentatively proposed. It was speculated that CaF 2 could promote the formation of β-Si 3 N 4 with columnar structure through a V-L-S (vapor-liquid-solid) route by forming Ca-containing liquid phase with SiO 2 . Moreover, appropriate content of CaF 2 are beneficial for fabricating Si 3 N 4 particles with good dispersity because of the proper the evaporation rate of Ca and F. [ABSTRACT FROM AUTHOR]

In situ observations are performed, for the first time, of stable crack propagation in nanocomposites of silicon nitride (Si 3 N 4 ) and reduced graphene-oxide (rGO) inside a scanning-electron microscope. Two different specimen geometries (wedge-splitting and double-cantilever beam) are used to observe crack interactions with rGO stacks in two different orientations (cross-section and in-plane). These observations provide new insights into the unique, effective pull-out of crack-bridging rGO stacks, which appears to be responsible for the extraordinary toughness in the Si 3 N 4 /rGO nanocomposites. These insights could be used to design and create future ceramic/rGO nanocomposites with superior mechanical properties. [ABSTRACT FROM AUTHOR]

This study investigates the preparation of samples with equimolar parts of silica and silicon nitride and the subsequent reaction synthesis of silicon oxynitride. The influence of the raw material and the processing parameters on the conversion yield was analyzed. In detail, the effects of the silica crystallinity and of the grain size of the silicon nitride were investigated. Furthermore, the reaction synthesis was activated by magnesium hydroxide or calcium hydroxide. The samples were prepared by slip casting in plaster molds. Firstly, the optimal dispersant type, a synthetic polyelectrolyte, was determined. For the batches with the finer silicon nitride the measured optimal amount was 0.6 wt%. For the batches with the coarser silicon nitride it was 0.18 wt%. From the cast and demolded samples, broken pieces were fired at 1550 °C for 1, 8 or 15 h in nitrogen atmosphere. The conversion yield of silicon oxynitride was analyzed by quantitative X-ray diffraction. The fraction of silicon oxynitride increased with extended holding time at the sintering temperature, by the use of fine silicon nitride, and by the addition of magnesium hydroxide as sintering additive. The silica crystallinity had no statistically significant effect. The obtained maximum conversion yield was 92 wt%. [ABSTRACT FROM AUTHOR]

High quality silicon nitride ceramics were fabricated by an oscillatory pressure sintering (OPS) process and the effect of sintering temperature on the microstructure and mechanical properties of Si 3 N 4 ceramics was investigated. Different from the specimen fabricated by the conventional hot pressing (HP) method, only β-Si 3 N 4 grains were detected in all the OPS-fabricated specimens. Driving forces of densification and grain growth were accelerated aided by oscillatory pressure. The optimum sintering temperature for silicon nitride ceramics under oscillatory pressure is considered to be 1770 °C; the highest average aspect ratio of β-Si 3 N 4 grains (4.74) was achieved from the highly densified compact (99.86% of theoretical density). The specimen prepared at this temperature accompanied with the highest flexural strength, hardness and fracture toughness of 1348 MPa, 16.04 GPa and 12.8 MPa m 1/2 , respectively. The presence of oscillatory pressure is detected to promote the elimination of defects and accelerate the densification and grain growth kinetics of grains, thus contributing to the improvement of mechanical properties. [ABSTRACT FROM AUTHOR]

AlON was successfully brazed to BN-Si 3 N 4 using a Ag-Cu-Ti filler alloy. SEM, TEM and XRD studies revealed that a TiN + TiB 2 + Ti 5 Si 3 reaction layer formed adjacent to the BN-Si 3 N 4 while a (Cu,Al) 3 Ti 3 O layer formed adjacent to the AlON. In addition, Ag-Cu eutectic, Cu(s,s) and AlCu 2 Ti were observed in the brazing filler. The effect of brazing temperature on the microstructure and mechanical properties of the joints was investigated. As the brazing temperature increased, the reaction layers became thicker, while the thickness of the brazing seam decreased. Meanwhile, the amount and the size of AlCu 2 Ti intermetallic compounds decreased. The shear strength of the joints first increased and then dropped with increasing the brazing temperature. A joint with a maximum strength of 94 MPa was obtained when it was brazed at 850 °C for 15 min. [ABSTRACT FROM AUTHOR]

In this study, Si 3 N 4 ceramic composites were fabricated by using ball-milling, titration preparation and urea preparation methods, respectively. The effect of different preparation methods on microstructure and mechanical properties of the Si 3 N 4 ceramic composites was investigated. Obviously, the Si 3 N 4 ceramic composite prepared by the urea preparation method (U-SN sample) showed better sintering behavior and higher mechanical properties than that prepared by the other two methods. Compared with the Si 3 N 4 ceramic composite by the titration preparation method (T-SN sample), we could avoid the complex titration process or uncontrollable pH value during the preparation process of the U-SN sample. Meanwhile, the coated Y-Al precursor layer in thickness of nanometers was more homogeneous than that prepared by the traditional titration method. B-SN represented the Si 3 N 4 ceramic composite prepared by the ball-milling method. These samples were all sintered from room temperature to 1750 °C via hot-pressing sintering. The U-SN specimen showed the optimal flexural strength and fracture toughness of being 817 MPa and 6.90 MPa/m 2 , respectively, which could be attributed to its smallest grain size (0.46 µm) among these three samples. [ABSTRACT FROM AUTHOR]

TiO 2 -MgO is proposed as new sintering additive for low temperature pressureless sintering of Si 3 N 4 ceramics to be circuit substrate in power electronic devices. The effects of additive content on densification, mechanical and thermal properties of Si 3 N 4 substrate were investigated systemically. Si 3 N 4 ceramics with density of 3.20 g cm −3 could be obtained with the addition of 10 wt% TiO 2 -MgO and sintered at 1780 °C. The flexural strength, fracture toughness and thermal conductivity were 668 MPa, 5.13 MPa m 1/2 and 55.3 W/(m K), respectively, and the highest thermal conductivity was 60 W/(m K) could be obtained after annealing. Phase compositions at different temperature were characterized by high temperature in-situ XRD. TiC 0.3 N 0.7 s phase was observed and its formation mechanism was investigated. Results showed TiO 2 -MgO to be effective sintering additive for developing Si 3 N 4 ceramics at low cost and with acceptable mechanical and thermal properties. [ABSTRACT FROM AUTHOR]

Ceramics are difficult to machine due to their high hardness and brittleness. As an effective method for machining ceramics, laser-assisted machining (LAM) has been studied by many researchers. In particular, many studies of methods to improve the machinability of silicon nitride using LAM have been performed. However, there is little research on the effect of the inclination angle of the workpiece, because varying the angle increases the difficulty of controlling the laser preheating and tool path. This paper investigates the effect of preheating temperature, spindle speed and inclination angle of the workpiece on edge chipping of silicon nitride in an effort to obtain an enhanced surface finish using laser-assisted milling (LAMill). The machining conditions were determined by considering the parameters that can reduce edge chipping using related theory. Experimental results showed a reduction in edge chipping based on increases in preheating temperature, spindle speed and inclination angle of the workpiece. Also, by increasing the spindle speed and the inclination angle of the workpiece, surface roughness was decreased due to reduction in the cutting force. The energy efficiency of LAMill by comparing the specific cutting energy according to the machining conditions is analyzed. [ABSTRACT FROM AUTHOR]

Nanoporous Silicon Nitride (NPN) is a new ultrathin (50 nm thick) membrane with potential applications in laboratory and industrial preparations of nanoparticles, antibodies, and other therapeutic biotechnology products. Like prior ultrathin silicon-based membranes (nanomembranes), NPN is capable of high separation resolution (∼10 nm) despite polydisperse pore distributions. Here we present a mathematical model that is predictive of the sieving curves seen in dead-end filtration with NPN. Interestingly, the model requires the inclusion of concentration polarization to predict sieving curves. The model also reveals a pressure dependence on sieving curves that is highly sensitive to membrane thickness: Thicker membranes require higher, often impractical, pressures for the same separations while thinner membranes achieve sharp separations at lower pressures. The pressure sensitivity of sieving behavior is confirmed experimentally by comparing the performance of NPN with 10 μ m thick nanoporous polycarbonate track etched membranes. The model illustrates that pore polydispersity limits the resolution of current silicon nanomembranes, suggesting that further manufacturing advancements are needed to realize the full potential of nanomembranes for size-based separations. Finally, the model further suggests that diffusion across ultrathin membranes aids separations, leading to higher resolutions. [ABSTRACT FROM AUTHOR]

The wear characteristics and an effect of lubrication regime between silicon nitride and steel balls sliding against reference material discs under lubricated conditions were studied. The mild wear was observed for silicon nitride balls and the worn out particles confirms the adhesive wear and simultaneous cutting action of worn-out particles. The worn-out surface analysis confirmed the material transfer from steel disc to silicon nitride ball. Eventually the coefficient of friction (COF) value was reduced by 25% for silicon nitride ball when compared to steel ball due to the formation of mixed oil regime between the contact surfaces. The more depletion of anti-wear additives and oxidation was observed for steel ball due to boundary lubrication. [ABSTRACT FROM AUTHOR]

Sintered reaction-bonded Si3N4 ceramics with equiaxed microstructure were prepared with TiO2-Y2O3-Al2O3 additions by rapid nitridation at 1400°C for 2 hours and subsequent post-sintering at 1850°C for 2 hours under N2 pressure of 3 MPa. It was found that α-Si3N4, β-Si3N4, Si2 N2O, and TiN phases were formed by rapid nitridation of Si powders with single TiO2 additives. However, the combination of TiO2 and Y2O3-Al2O3 additives led to the formation of 100% β-Si3N4 phase from the nitridation of Si powders at such low temperature (1400°C), and the removal of Si2N2O phase. As a result, dense β-Si3N4 ceramics with equiaxed microstructure were obtained after post-sintering at high temperature. [ABSTRACT FROM AUTHOR]

In this work, an efficient carbothermal reduction-nitridation (CRN) strategy was rationally designed to directly synthesize β-Si3N4 powders with eminent dispersity and granularity uniformity. With the aid of CaO additive, the obtained β-Si3N4 particles were endowed with approximate spherical morphology and smooth surface. The size of β-Si3N4 particles could be regulated in submicro and microscale by altering N2 pressures. More significantly, the underlying growth mechanism of the β-Si3N4 under elevated N2 pressure was comprehensively analyzed and tentatively put forward. Benefiting from the remarkable merits, the as-synthesized β-Si3N4 powders showed great potential for alternative fillers in the application of high thermal conductivity plastic packages. [ABSTRACT FROM AUTHOR]

Well-dispersed β-Si3N4 powders with a novel equiaxed structure and eminent crystal integrity were prepared by carbothermal reduction-nitridation (CRN) strategy with the assistance of CaF2 additive. The growth mechanism of Si3N4 particles in the CRN process was elucidated. It is proposed that the liquid phase formed by SiO2 and CaF2 additive is crucial to the formation of equiaxed β-Si3N4, and with an appropriate content of CaF2, Si3N4 powders with pure β phase, superior dispersity and crystal integrity can be obtained. [ABSTRACT FROM AUTHOR]

Silicon nitride (SiN) is a high demanded structural ceramic with exceptional mechanical, thermal and chemical properties. Poor surface integrity and limited material removal rate due to high tool wear and cutting forces are the main problems of grinding this material. A novel laser-assisted grinding process is developed to overcome the current technological constraints in the grinding of SiN. Ultra-short pulsed laser radiations are efficiently applied to create ablation, controlled thermal damages and enhance the material removal rate in the grinding process. Two different laser structures have been produced on gas-pressure-sintered SiN with various laser scan speeds and laser line spans. The high performance of the developed process is shown by experimental results. A substantial reduction in tangential and normal grinding forces and a slightly improved surface roughness have been achieved. The analysis of the surface integrity has shown a damage-free ground surface via laser assistance, where the pattern type of structures had a significant influence on the process results. [ABSTRACT FROM AUTHOR]

Si 3 N 4 ceramics with high porosity, complex shape and large dimension could be fabricated by carbothermal reduction of diatomite preforms. Take the fabrication of large tubular porous Si 3 N 4 ceramics as an example, the flow type and flow rate of nitrogen during sintering has little effect on the overall performance of the tubes, while impacts greatly on the composition, porosity and flexural strength at different locations of the tubes. When the nitrogen flow rate is in the range of 0.2–1.0 L/min, the tubes have a porosity of 73.7–79.6% and a flexural strength of 10.5–13.2 MPa when fabricated by conventional sintering, while possess a porosity of 73.2–81.3% and a flexural strength of 8.6–14.7 MPa when fabricated by directional sintering. As the nitrogen flow rate increases, the composition, porosity and flexural strength at different locations of the tubes fabricated by conventional sintering tend to be uniform, while the gradient of composition, porosity and flexural strength of the tubes fabricated by directional sintering becomes more obvious. [ABSTRACT FROM AUTHOR]

As a result of conducting numerical experiments a favorable effect is revealed for titanium carbide thickness on transformation of the stressed state of a surface layer of SiN-TiC-YO-ceramic. It is established that an increase in TiC-coating thickness leads to stable reduction in stresses σ, σ, σ, and σ in a surface layer of the main structural elements. [ABSTRACT FROM AUTHOR]

Self-propagating High-temperature Synthesis (SHS) is a cost effective process to synthesize advanced ceramic materials. In this work, the effect of reactant stoichiometry on the adiabatic temperature of the SHS of silicon nitride is studied and a 3-D time-dependent mathematical model based on the finite element analysis is developed to study the effects of the dimensions of the reaction system and ignition condition on the SHS process, including temperature and composition distributions as well as the production rate and conversion. Momentum transfer, heat transfer, reaction kinetics and temperature dependent thermodynamic properties are integrated in this model. The effects of pellet diameter, ignition time, ignition flux, green density of the reactant pellet, and composition of silicon nitride diluent on the initiation of the self-sustained reaction, temperature history and velocity of the reaction front movement are calculated using this model. The results of this work can be used to improve commercial production of nitride materials. [ABSTRACT FROM AUTHOR]

The contents and speciation of nitrogen, carbon, and hydrogen were determined in basalt-basaltic andesite melts in equilibrium with liquid Fe alloys at 1.5 Gpa, 1400°C, and oxygen fugacity ( fO) 1.4-1.9 log units below that of the Fe-FeO buffer (Δlog fO(IW) =-1.4 ...-1.9). Experiments were carried out on a piston- cylinder type apparatus using welded Pt capsules in the presence of excess С (graphite). Starting mixture consisted of natural ferrobasaltic glass and silicon nitride (SiN) as nitrogen source in the system. Experimental quench products representing glasses with spherical inclusions of iron alloy were analyzed using electron microprobe, Raman, and IR spectroscopy. With increase of SiN in the starting mixture and, respectively, decrease of fO, silicate melt forming during experiments became depleted in FeO and enriched in SiO. It was established that the nitrogen content in the glasses increases from 0.13 to 0.44 wt % with decrease of Δlog fO(IW) from-1.4 to-1.9, whereas C content in the first approximation remains constant within 1.18-1.13 wt %, while the total water content (ОН + НО) determined by IR spectroscopy decreases from 4.91 to 1.20 wt %. The N (0.13-0.48 wt %) and C (0.75-2.26 wt %) contents determined in the Fe alloy show no clear correlation with fO. The IR and Raman spectroscopic study of the glasses indicates the formation of molecules and complexes with bonds N-H (NH, NH , NH , NH ), Н-О (НО, OH), С-Н (СН) as well as N and Н molecules in silicate melts. IR spectra also reveal the presence of complexes with С=О, С-N bonds and СО molecules. Obtained data are compared with results of previous studies on the solubility and speciation of N, С, and Н in the model FeO-NaO-SiO-AlO melts in equilibrium with liquid iron alloys at 1.5 GPa (1400°C) and 4 GPa (1550°C) (Kadik et al., 2011, 2015). [ABSTRACT FROM AUTHOR]

The photoluminescence properties of silicon nitride and oxide superlattices fabricated by plasmaenhanced chemical vapor deposition are studied. In the structures annealed at a temperature of 1150°C, photoluminescence peaks at about 1.45 eV are recorded. The peaks are defined by exciton recombination in silicon nanocrystals formed upon annealing. Along with the 1.45-eV peaks, a number of peaks defined by recombination at defects at the interface between the nanocrystals and silicon-nitride matrix are detected. The structures annealed at 900°C exhibit a number of photoluminescence peaks in the range 1.3-2.0 eV. These peaks are defined by both the recombination at defects and exciton recombination in amorphous silicon nanoclusters formed at an annealing temperature of 900°C. The observed features of all of the photoluminescence spectra are confirmed by the nature of the photoluminescence kinetics. [ABSTRACT FROM AUTHOR]

Si 3 N 4 ceramics strengthened with molybdenum silicides seem to be potential candidates for (ultra-)high temperature applications. While Mo 5 Si 3 exhibits a higher melting point and a better creep resistance than MoSi 2 , its oxidation resistance is inferior due to accelerated pest oxidation at 700 °C in air. In order to protect Mo 5 Si 3 /Si 3 N 4 ceramic composites from pesting, in this work a composite material was developed using the inorganic precursor PHPS loaded with Mo particles as active filler. After pyrolysis, the resulting ceramic composite was coated with PHPS to generate a protective SiO 2 layer before the oxidation of Mo 5 Si 3 starts. The results demonstrated the in-situ formation of the silicide phase during pyrolysis at temperatures up to 1500 °C via solid-state reaction of the formed amorphous SiN phase and the Mo particles. As intended, the coated Mo 5 Si 3 /Si 3 N 4 ceramic composites exhibit a remarkably increased oxidation resistance up to 700 °C compared to the uncoated material. [ABSTRACT FROM AUTHOR]

Silicon nitride coated silicon (N-Si) has been synthesized by two-step DC sputtering on Cu Micro-cone arrays (CMAs) at ambient temperature. The electrochemical properties of N-Si anodes with various thickness of nitride layer are investigated. From the potential window of 1.2 V–0.05 V, high rate charge-discharge and long cycle test have been executed to investigate the electrochemical performances of various N-Si coated Si-based lithium ion batteries anode materials. Higher specific capacity can be obtained after 200 cycles. The cycling stability is enhanced via thinner nitride layer coating as silicon nitride films are converted to Li 3 N with covered Si thin films. These N-Si anodes can be cycled under high rates up to 10 C due to low charge transfer resistance resulted from silicon nitride films. This indicates that the combination of silicon nitride and silicon can effectively endure high current and thus enhance the cycling stability. It is expected that N-Si is a potential candidate for batteries that can work effectively under high power. [ABSTRACT FROM AUTHOR]

The aim of this work is to synthesize a net of interwoven β-Si 3 N 4 nanofibers and intertwined pea-pods and hand-fan like Si 2 N 2 O nanostructures by the chemical vapor deposition (CVD) method at a relatively low temperature (1300 °C) and short times (up to 4 h). A solid precursor (Na 2 SiF 6 ) was thermally decomposed at 400 °C into two new products: 2NaF and SiF 4 . Afterwards, the SiF 4 reacts with a flow of N 2 (9 cm 3 /min) with O 2 traces at 10 mbar and 1300 °C producing a net of β-Si 3 N 4 nanofibers with defined diameters (100–200 nm up to 3 h and 30–100 nm at 4 h) and intertwined pea-pods and hand-fan like Si 2 N 2 O micro and nanostructures on the back side of a particulate SiC preform. [ABSTRACT FROM AUTHOR]

Honeycomb-like structured porous Si 3 N 4 ceramics with exceptionally high number of cells per square inch were prepared by the self-organization method of alginate. The obtained samples have highly ordered channels, high porosity and well mechanical strength. It is found that the microstructure and properties of obtained porous Si 3 N 4 ceramics can be effectively controlled by choosing different kinds of alginates. And it is worth to note that the obtained ceramics possess interesting hierarchical pore structure, including the unidirectionally aligned channels with pore size of 50–120 µm (first pore structure) and the interlocked microstructure of fibrous β-Si 3 N 4 grains within channel walls with pore size of 0.8–2.6 µm (secondary pore structure), making it desirable for filter applications. [ABSTRACT FROM AUTHOR]

Nano-sized silicon nitride powders were synthesized through the reduction of silicon tetrachloride (SiCl 4 ) by sodium in liquid ammonia at around −40 °C.The product was in uniform particles of several nanometers, and in the amorphous form. The amorphous structure was stable up to 1200 °C and turned to the crystal structure of α-Si 3 N 4 at 1300 °C, and then to β-Si 3 N 4 structure when heated at temperatures higher than 1450 °C.Via spark plasma sintering (SPS) dense bulks with 97.9% relative density of theoretic value and the grain size of 100–300 nm was successfully fabricated at 1500 °C without any sintering additives. [ABSTRACT FROM AUTHOR]

The catalytic effects of Ni during the nitridation of Si from a molten salt and the morphologies of the nitridation products were investigated. The phase composition, particle size, and morphological structure of the α-Si 3 N 4 powder were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and a Brunauer–Emmett–Teller (BET) specific-surface-area analysis. The results showed that Ni significantly accelerated Si nitridation and the formation of the hexagonal plate-like α-Si 3 N 4 phase by the formation of Ni–Si in the eutectic salt at 1050–1350 °C. Further, the nitridation rate of the Si powder was increased to 93% after 5 h at 1250 °C with 2-wt% Ni used as the catalyst. The specific surface area of the α-Si 3 N 4 synthesized powder was 5.70–10 m 2 /g, exceeding that of 1.70 m 2 /g of the Si powder. [ABSTRACT FROM AUTHOR]

Mesoporous silicon nitride (Si 3 N 4 ), which is one of the most promising structural materials for applications in high-temperature filtration, was synthesized from the carbothermal reduction and nitridation of a pyrolyzed silica-containing phenol-resorcinol-formaldehyde (PRF) gel. The PRF gel was synthesized by combining sol–gel and polymerization of phenol, resorcinol and formaldehyde using sodium carbonate as a catalyst. Silica was incorporated into the gel by addition of 3-aminopropyl trimethoxysilane (APTMS) as a silica precursor. After aging and being freeze-dried, the silica/PRF composite was pyrolyzed under nitrogen gas to convert it into porous silica/carbon composite. The combination of phenol-formaldehyde (PF) and resorcinol-formaldehyde (RF) gels into PRF gel, allows further enhancement in porosity of the silica/carbon composite via pre-calcination in the range of 400–500 °C, since carbon derived from PF gel and that from RF gel have different thermal stability. The final product obtained after final calcination to remove residual carbon has a surface area as high as 194 m 2 /g, which is significantly much higher than the conventional Si 3 N 4 granules. Specific surface area of the product is affected by molar ratio of phenol-to-resorcinol, molar ratio of silica-to-carbon, and the pre-calcination temperature. [ABSTRACT FROM AUTHOR]

Silicon nitride nanofibers were prepared by direct nitridation of silicon powder, with an iron catalyst, under nitrogen flow. The as-prepared nanofibers have the α-SiN structure. Micromorphology and phase composition of the as-prepared α-SiN nanofibers were characterized by scanning and transmission electron microscopy and by X-ray diffraction analysis, respectively. The electronic structure of silicon nitride nanofibers was compared with that of SiN powder by X-ray photoelectron spectroscopy and X-ray emission spectroscopy. [ABSTRACT FROM AUTHOR]

Features are considered for preparing highly porous workpieces of silica by warm molding of elements prepared by cutting castings from thermoplastic slip based on silica with addition of plasma chemical synthesis silicon nitride and appropriate highly porous silicon nitride materials, and also methods by means of which a molded workpiece or sintered object may be given additional channel porosity for improving permeability. Material is suggested for use in power generation installations as a porous barrier for feeding natural fuel through porous material and combustion, capable of withstanding extreme situations. [ABSTRACT FROM AUTHOR]

A new kind of nanocomposites based on phthalonitrile resin reinforced with silicon nitride (SiN) nanoparticles was prepared by a hot compression molding technique. For different weight ratios ranging between 0% and 15%, the effect of nano-SiN particles on the thermal and thermomechanical properties has been studied. Results from thermal analysis revealed that the starting decomposition temperature and the residual weight at 800 °C were highly improved upon adding the reinforcing phase. At the maximum nano-SiN loading, dynamic mechanical analysis showed an enhancement in both storage modulus and glass transition temperature, reaching 4 GPa and 360 °C respectively. Scanning electron microscope analysis confirmed that these improvements are essentially attributed to the good dispersion and adhesion between the particles and the resin thanks to the particles treatment with silane coupling agent. [ABSTRACT FROM AUTHOR]

The gas-phase reaction thermodynamics in the chemical vapor deposition (CVD) process of preparing silicon nitride with the precursors of SiCl 4 –NH 3 –H 2 was investigated with a relatively complete set of 161 species, in which the thermochemistry data were calculated with accurate model chemistry at G3(MP2) and G3//B3LYP levels combined with standard statistical thermodynamics. The data include the heat capacities, entropies, enthalpies of formation, and Gibbs energies of formation. Two condensed phase, silicon nitride (Si 3 N 4 ) and silicon (Si) were taken into consideration. Based on these data, the distribution of the equilibrium concentration of the 161 species was obtained with the principle of chemical equilibrium. It was concluded that Si 3 N 4 could be produced at the initial temperature of 300 K up to the temperature 1560 K, and the ideal deposition ratio r = SiCl 4 /(SiCl 4 + NH 3 ) for Si 3 N 4 was found to be 0.5. [ABSTRACT FROM AUTHOR]

Silicon nitride nanowires were synthesized using silicon monoxide as raw materials and an alumina plate as substrate at 1500°C. The obtained nanowires were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and thermogravimetricdifferential scanning calorimetry. The results revealed that silicon nitride nanowires possess a diameter of about 200 nm and a length of several hundred micrometres. The preferred growth direction of the nanowires was [100]. The chemical and structural composition of the silicon nitride nanowires were also studied and were shown to have a composition of primarily α-Si3N4. The temperature for fierce oxidation in air was above 1135°C. The formation mechanism of silicon nitride nanowires was assumed to be a vapour-solid (VS) process. [ABSTRACT FROM AUTHOR]

This review covers some of the main trends in the field of synthesis and the applications of materials based on silicon nitride presented in publications over the past 10-15 years. Attention is paid to the technique for synthesizing nitride and oxynitride compounds and for the production of ceramic construction materials and phosphors in silicon nitride systems. [ABSTRACT FROM AUTHOR]

Crystalline silicon nitride (Si 3 N 4 ) wires have been synthesized by means of ball milling and nitridation route. The influence of temperature of reaction and starting condition of the powder (milled or unmilled) on the synthesis of Si 3 N 4 wires were studied. The reduced size of silicon particle during the milling process led to an increased degree of nitridation. Silicon powders with higher surface energy can react incessantly with nitrogen to form silicon nitride wires. The results show that the Si 3 N 4 was fully formed with two kinds morphologies including globular and wire with a width of 100–300 nm and a length of several microns at temperature of 1300 °C for 1 h by employing the milled silicon powder. The infrared adsorption of wires exhibit absorption bands related to the absorption peaks of Si–N band of Si 3 N 4 . [ABSTRACT FROM AUTHOR]

This work describes a new sonoelectrochemical synthesis method of novel composite materials based on silicon nitride (SiN) nanoparticles and intrinsically conducting polypyrrole (PPy). The sonoelectrochemical synthesis of polypyrrole coating and polypyrrole-silicon nitride (PPy-SiN) nanocomposite performed and corrosion behavior of these coatings on St-12 steel was studied by electrochemical methods. A design of experiment (DOE) technique using the Taguchi method has been applied to optimize the affecting factors on the sonoelectrochemical synthesis of PPy-SiN nanocomposite such as current density, synthesis time and amount of nanoparticles. The corrosion protection of St-12 steel by polypyrrole and polypyrrole-SiN nanocomposite coatings were investigated by open circuit potential (OCP) time trends, potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS) in NaCl 3.5% solution. The Kramers-Kronig transformation (KK) was applied to evaluate the validity of the experimental impedance data. The results prove that the addition of nanoparticles increased corrosion resistance of coatings and improved the surface morphology. Scanning electron microscopy (SEM) images reveal that the nanocomposite coatings form compact, homogenous and dense films on the St-12 steel surfaces. [ABSTRACT FROM AUTHOR]

The SiN-BN composites were prepared by gel-casting and precursor infiltration and pyrolysis route using borazine as the precursor. The composition, mechanical, microstructural, and dielectric properties of the composites were investigated. The composites are composed of h-BN, α-SiN, and β-SiN. The typical density, porosity, flexural strength, elastic modulus, and fracture toughness of the composites are 2.21 g/cm, 17.8%, 185.59 MPa, 69.13 GPa, and 2.47 MPa m, respectively. The dielectric constant and loss tangent of the composites are 4.507-4.635 and 1.06 × 10-1.97 × 10 at the frequency of 7-18 GHz. Desirable properties of the composites have been achieved. [ABSTRACT FROM AUTHOR]

Highlights: [•] Conventional and microwave carbothermal reduction was used to synthesize Si3N4. [•] Digested rice hulls were pyrolised and reacted under N2 flow. [•] The particles size of microwave Si3N4 was smaller than the conventional ones. [•] The phases obtained in the conventional powder were the same of microwave powder. [•] The reaction time was reduced about 90% using microwave energy. [Copyright &y& Elsevier]

Silicon nitride (Si3N4) powder with tunable α/β-Si3N4 relative contents was synthesized from waste silica fume using carbothermal reduction nitridation (CRN) at a relatively low temperature range of 1400–1500°C. The effects of the carbon source, CRN temperature and raw materials ratio (Carbon-to-Silica fume) on phase assembly and micro-morphology of the products were investigated. Fabrication of α-Si3N4/β-Si3N4 from waste silica fume by CRN was achieved at temperatures as low as 1400°C. Carbon black was found to be more suitable than coke and graphite for use as the reductant. Elevated temperature was beneficial for the formation of β-Si3N4, whilst excessive carbon black promoted the formation of α-Si3N4. Thus, the α-Si3N4/β-Si3N4 relative contents could be effectively tailored by adjusting the CRN temperature and carbon concentration of the initial mixtures. In addition, the bi-modal crystals of the whiskers and the short columns strongly influenced the morphologies of the product. [ABSTRACT FROM AUTHOR]

Abstract: Silicon nitride ultrafine powders were synthesized from a binary sol–gel route, in which tetraethoxysilane (TEOS) and saccharose were used to prepare a carbonaceous silica xerogel, and ferric nitrate was employed as an additive. The influence of reaction temperature and mass ratio of C to Si ( =0.1, 0.5, 1) on the synthesis of Si3N4 wires was studied. After purification, the Si3N4 sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectrum and Fourier transform infrared spectroscopy. The results show that the Si3N4 was fully formed with two kinds of morphologies including globular and wire with a diameter of 100–500nm and a length of several microns at reaction temperature of 1400°C for 10h in nitrogen flow (200ml/min) by employing the mass ratio of =0.5. [Copyright &y& Elsevier]

By gel casting with polymethylmethacrylate microbeads (PMMA) as pore-forming agent, porous boron nitride/silicon nitride (BN/SiN) composite ceramics were successfully prepared. The obtained ceramic shows bimodal hierarchical structures that composed of spherical-shaped micro pores depending on PMMA content and irregular sub-micro pores formed by the stacking of ceramic particles. Porosity of the porous BN/SiN ceramics can be well controlled from 53.0 to 60.6 % by the PMMA content from 10 to 40 wt%, as well as the mechanical and dielectric properties. Effect of PMMA content on phase composition and the relationship between microstructure and the basic properties of the porous BN/SiN ceramics was discussed in detail. Microstructure analysis reveals that the sub-micro pores acted as channels between micro pores. BN particles have a relatively denser distribution on the wall of spherical-shaped micro pores with a window between micro and sub-micro pores, and resulting in a half-closed micro pore structure, which is meaningful for material design with concentration of BN particles on the wall of pore structure. [ABSTRACT FROM AUTHOR]

Abstract: Alpha silicon nitride (α-Si3N4) crystallon has been synthesized by the solvothermal method with silica powder as the Si source, sodium azide (NaN3) as the N source, and thiosemicarbazide as the low-temperature additive at a low temperature of 180℃. The as-prepared sample has been characterized by x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence spectrum (PL, type F-7000, Hitachi, Japan). The as-prepared α-Si3N4 micron-rod crystallon is single crystal with a smooth surface and a uniformed size, the maximum diameter being 2.0µm. The main elements in the sample are Si and N with Si–N bonds and the ratio of Si and N are close to 3:4. The as-prepared α-Si3N4 micron-rod crystallon possesses good UV emission and its PL spectrum shows a strong ultraviolet emission at 380nm. [Copyright &y& Elsevier]

Abstract: A set of CrAlSiN coatings was synthesized in homogenous and graded composition via magnetron sputtering in mixed Ar and N2 ambient. The microstructures are investigated using glancing angle X-ray diffractometry, field emission scanning electron microscopy and transmission electron microscopy. With compositional grading, CrAlSiN coatings exhibit much improved scratch adhesion strength and better crack propagation resistance at a little expense of hardness. [Copyright &y& Elsevier]

Abstract: Graphene/silicon nitride (Si3N4) composites with high fraction of few layered graphene are synthesized by an in situ reduction of graphene oxide (GO) during spark plasma sintering (SPS) of the GO/Si3N4 composites. The adequate intermixing of the GO layers and the ceramic powders is achieved in alcohol under sonication followed by blade mixing. The reduction of GO occurs together with the composite densification in SPS, thus avoiding the implementation of additional reduction steps. The materials are studied by X-ray photoelectron and micro-Raman spectroscopy, revealing a high level of recovery of graphene-like domains. The SPS graphene/Si3N4 composites exhibit relatively large electrical conductivity values caused by the presence of reduced graphene oxide (∼1 S cm−1 for ∼4 vol.%, and ∼7 S cm−1 for 7 vol.% of reduced-GO). This single-step process also prevents the formation of highly curved graphene sheets during the thermal treatment as the sheets are homogeneously embedded in the ceramic matrix. The uniform distribution of the reduced GO sheets in the composites also produces a noticeable grain refinement of the silicon nitride matrix. [Copyright &y& Elsevier]

Abstract: The ZrN/SiNx double-layers with different density of SiNx layers, which was controlled by applying different substrate bias for depositing SiNx layers, were synthesized for investigating the interfacial electronic structure. Results indicated that the interfacial electrostatic polarization existed as the ZrN and SiNx bond with each other to form a heterojunction, since the electrons donated from ZrN layer to SiNx layer. Moreover, the degree of polarization was affected by the density of SiNx layer. The corresponding ZrN/SiNx multi-layers were deposited for studying the correlation between interfacial electronic structure and mechanical properties. The results of hardness test implied that the interfacial electrostatic polarization would enhance the hardness to a certain extent. [Copyright &y& Elsevier]

Abstract: β-Si3N4 powder was synthesized via carbothermal reduction nitridation (CRN) method using quartz as starting material. The influence of synthesis temperature, C/SiO2 molar ratio and amount of Fe2O3 additive on the phase transformation and micro-morphology of β-Si3N4 powder was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The results showed that the optimal experimental conditions for the CRN synthesis of β-Si3N4 powder were 3h sintering at 1600°C in flowing nitrogen atmosphere with C/SiO2 molar ratio of 2.0 and amount of Fe2O3 additive of 5.0wt.%. The prepared β-Si3N4 grains present a short hexagonal, rod-like morphology. Changes in experimental parameters affect the phase compositions and the morphology of the product. Excessive carbon promoted the formation reaction of β-SiC. Fe2O3 additive exerted a significant promotion on the formation of β-Si3N4 in CRN process by forming the low melting point eutectics. [Copyright &y& Elsevier]

The gas-phase reaction between the silicon nitride radical (SiN) and the prototypical olefin--ethylene--is investigated experimentally and theoretically for the first time. Silicon nitride (SiN) and the cyano radical (CN) are isoelectronic; however, their chemical reactivities and structures are drastically different from each other. Through the use of the cross molecular beam technique, we were able to study the notoriously refractory silicon nitride radical in reaction with ethylene under single-collision conditions. We investigated the similarities and also the distinct differences with the cyano radical--ethylene system. We find that the silicon nitride radical bonds by the nitrogen atom to the double bond of ethylene; in comparison, the cyano radical adds via its carbon atom. The silicon nitride addition is barrierless, forming a long-lived SiNCH2CH2 collision complex, which is also able to isomerize via a hydrogen shift to the SiNCHCH3 intermediate. Both isomers can emit a hydrogen atom via tight transition states to form the silaisocyanoethylene (SiNC2H3) molecule in an overall exoergic reaction. This presents the very first experiment in which the silaisocyanoethylene molecule--a member of the silaisocyanide family--has been formed via a directed synthesis under gas-phase single-collision conditions. In comparison with the isoelectronic cyano--ethylene system, the cyanoethylene (C2H3CN) isomer is formed. Therefore, the replacement of a single carbon atom by an isovalent silicon atom, i.e. shifting from the cyano (CN) to the silicon nitride (SiN) radical, has a dramatic influence not only on the reactivity with ethylene (carbon atom versus nitrogen atom addition) but also on the final reaction products. In the reactions of ethylene with silicon nitride and the cyano radical, the silaisonitrile over the silanitrile and the nitrile over the isonitrile reaction products are favored, respectively. This reaction provides rare experimental data for investigating the chemistry of bimolecular reactions of silicon nitride diatomics in chemical vapor deposition techniques and interstellar environments. [ABSTRACT FROM AUTHOR]

Abstract: Silver precursor ink was synthesised by a simple and environmentally friendly method based on chemical reduction. The stability, particle size, viscosity and surface tension of the ink were adjusted by adding polyvinylpyrrolidone (PVP) and ethylene glycol (EG). The silver patterns were fabricated on the silicon nitride substrate and were characterised by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrical measurements. The thickness of the sample printed three times was approximately 0.66μm, and it increased to 2.43μm after 12 printings. The ink-jet-printed silver patterns exhibited good conductivity when the samples were sintered at temperatures above 200°C. The resistivity value was observed to decrease to 3.1μΩcm after sintering at 500°C for 60min, twice the value of bulk silver (1.6μΩcm). The low resistivity of silver patterns suggests applications for ink-jet printing of electronics devices. [Copyright &y& Elsevier]

A mathematical model is presented for the numerical simulation of the flow, temperature, and concentration fields in an rf plasma chemical reactor. The simulation is performed assuming chemical equilibrium. The extent of validity of this assumption is discussed. The system considered is the reaction of SiCl and NH for the production of SiN. [ABSTRACT FROM AUTHOR]