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1.
《Journal of the European Ceramic Society》2002,22(9-10):1587-1600
Interphase boundaries between SiC and h-BN grains in hot isostatically pressed Si3N4–SiC particulate composites made from both as-received powders and deoxidised powders, in which sub-micron size h-BN particles occur as a contaminant, have been characterised using transmission electron microscopy techniques. Most of the h-BN grains observed were aligned with respect to SiC grains so that (111) 3C SiC and (0001) α-SiC planes were parallel to (0001) h-BN planes. The h-BN–SiC interphase boundaries in the composites made from as-received powders were covered with thin silica-rich intergranular films, in contrast to the interphase boundaries in the composites made from deoxidised powders. These observations are discussed in the light of models for the formation of intergranular amorphous films in ceramic materials, geometric considerations for low interfacial energies and the possible bonding at h-BN–SiC interphase boundaries free of intergranular films. 相似文献
2.
《Journal of the European Ceramic Society》2002,22(5):769-775
Tensile creep behavior of hot pressed silicon nitride on the Si3N4–Yb4Si2O7N2 tie line was investigated at temperatures of 1300 and 1400 °C under an applied stress of 125 to 200 MPa. During the tests, the creep strain increased with time and the creep rate monotonically decreased both with time and strain. On the basis of minimum strain rates, the stress exponents for 1300 and 1400 °C were determined to be 3.1 and 1.7, respectively. All the specimens tested at 1400 °C lead to failure while exhibiting a large scatter in the time-to-failure data. The activation energy was determined to be 879 kJ/mol from a comparison between creep rates at different temperatures. The creep mechanism is discussed on the basis of the creep parameters and creep damage observation. 相似文献
3.
《Journal of the European Ceramic Society》1999,19(12):2145-2153
The dispersing behaviour of silicon, silicon carbide and their mixtures in aqueous media were monitored by particle size, sedimentation, viscosity and zeta potential analyses as a function of pH of the slurry. The pH values for optimum dispersion were found to be 4 and 8 for silicon, 10 for SiC and 9 for Si+SiC mixtures. Optimum slips of Si+SiC mixtures were slip cast to obtain green compacts which were nitrided once at 1450°C for 2 or 4 h or successively and cumulatively for 8 (2+6) and 10 (4+6) h in a resistively heated graphite furnace. The binding phases in the nitrided products were found to be fibrous/needle like α-Si3N4, flaky grains of β-Si3N4 and Si2ON2. The products containing 19–47% of silicon nitride as bond/matrix possessed flexural strength (three-point bending) values of 50–85 MPa. © 相似文献
4.
《Diamond and Related Materials》1999,8(8-9):1737-1740
Epitaxial β-SiC films have been grown on mirror-polished Si(111) substrates using bias-assisted hot filament chemical vapor deposition at a substrate temperature of 1000°C. A graphite plate was used as the carbon source, and the silicon source came from the silicon substrate itself. The gas phase in the system is hydrogen only. Atomic hydrogen produced by hot filaments reacted with the graphite to form hydrocarbon radicals, which further reacted with the silicon substrate and deposited as β-SiC. The effect of negative bias applied to the substrate is the key factor for epitaxial growth. Under the growth conditions without the negative bias applied, only polycrystalline β-SiC was obtained. 相似文献
5.
《Journal of the European Ceramic Society》2002,22(6):963-971
Silicon nitride–silicon oxynitride in situ composites were fabricated by plane-strain-compressing dense silicon nitrides, starting from 93 wt.% ultrafine β-Si3N4 and 7 wt.% cordierite, at 1600 °C under a constant load of 40 MPa and subsequent annealing at 1750 °C for 30 min. The resulting composites featured a microstructure of elongated Si2N2O grains (∼0.64 μm in diameter and ∼5.5 in aspect ratio) dispersed in a fine-grained β-Si3N4 matrix (∼ 0.30μm in diameter and ∼3.5 in aspect ratio), with the amount of Si2N2O, which had relatively strong textures, being strain-dependent. The mechanical properties were found to be improved due to the development of elongated Si2N2O grains, the texture formation, and the coarsening of β-Si3N4. Fracture toughness, however, was still low (∼5.2 MPa m1/2) for these composites in comparison to self-reinforced silicon nitrides, resulted from the strong Si2N2O-matrix interfacial bond and nearly equiaxed β-Si3N4 with a small grain size. Anticipated property anisotropies were clearly observed as a result of the textured microstructure. 相似文献
6.
《Journal of the European Ceramic Society》2005,25(2-3):99-110
Polysilazanes with chemical composition Si4N4CHx (x = 12–14) were obtained on two different reaction pathways. In the first route three equivalents of dichlorosilane, H2SiCl2, were mixed with one equivalent of methyldichlorosilane, H3CSiHCl2, and reacted with ammonia to yield [(SiH2–NH)3(H3CSiH–NH)]n (1) after appropriate work-up. In the second route, dichlorosilane was reacted with methylamine and ammonia in a 3:1 ratio to deliver [(SiH2–NH)3(SiH2–NCH3)]n (2). The raw products were further cross-linked by base-catalyzed dehydrocoupling reactions involving SiH and NH units to yield products 1a and 2a, respectively. The molecular structure of 1 and 2 was investigated by means of high resolution 1H, 13C{1H}, and 29Si{1H} NMR spectroscopy in C6D6 solution as well as by IR spectroscopy. Because of the insolubility of the cross-linked products 1a and 2a solid state 1H, 13C, and 29Si CP-MAS NMR in combination with IR spectroscopy were applied for their spectroscopic characterization. Chemical compositions were determined using elemental analysis.Thermolysis in an argon atmosphere up to 1400 °C of the cross-linked products delivered Si3N4/SiC ceramics in ∼94% yield. The absence of “free” carbon was revealed by mass spectra-coupled thermogravimetric analysis (TGA). These investigations indicated a one-step decomposition in the 250–700 °C range with predominant evaporation of hydrogen. In contrast, elimination of methane and ammonia (1) or methane and methylamine (2) was below 0.5 mass%. Additionally, neutron wide angle scattering proved the absence of a “free” carbon phase. High-temperature properties were investigated using high temperature TGA as well as XRD, EDX and TEM of annealed ceramic samples. The onset of crystallization in both materials was around 1500 and 1300 °C (1 atm N2), respectively, and α- as well as β-Si3N4 formed besides α/β-SiC. Above 1900 °C ceramics derived from both 1a and 2a decomposed to α/β-SiC/β-Si3N4/α-Si composites. 相似文献
7.
Alain Robin Júlio Cesar Pinheiro de Santana Antonio Fernando Sartori 《Journal of Applied Electrochemistry》2010,40(3):507-513
Silicon nitride particles were incorporated to electrolytic copper by co-electrodeposition in acidic sulfate bath, aiming
the improvement of its mechanical resistance. Smooth deposits containing well-distributed silicon nitride particles were obtained.
The current density did not show significant influence on incorporated particle volume fraction, whereas the variation of
particle concentration in the bath had a more pronounced effect. The microhardness of the composite layers was higher than
that of pure copper deposits obtained under the same conditions and increased with the increase of incorporated particle volume
fraction. The microhardness of composites also increased with the increase of current density due to copper matrix grain refining.
The composite coatings were slightly more corrosion resistant than pure copper deposits in 3.5% NaCl solutions. 相似文献
8.
In this study, silicon carbide powders were manufactured successfully by the method of preheating combustion synthesis in nitrogen atmosphere where it was introduced into an epoxy resin to produce a microwave absorber. The structure of the silicon carbide was characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Composite based on the various loadings of silicon carbide and epoxy resin specimens were prepared and the reflection losses of these composite samples were studied using the free space method. Based on the microwave measurements, microwave absorber specimens of silicon carbide with thermal plastic resin at frequencies between 2 and 18 and 18–40 GHz could be obtained from a matching thickness of 2.0 mm by controlling the content of silicon carbide. 相似文献
9.
Søren Foghmoes Jan Hoffmann Jørgensen Karsten Agersted Marianne Nielsen Michela Della Negra 《International Journal of Applied Ceramic Technology》2021,18(4):1164-1173
The present work describes a comparative study on a pool of 12 dispersants for the de-agglomeration and stabilization of silicon carbide in aqueous suspensions with solids loading relevant for dip coating applications. As silicon carbide slurries may include sintering aids, different functional groups, molecular weight, and stabilization mechanisms were considered for the dispersants to be able to stabilize both slurry components. Additionally, pH effect, toxicity, additive compatibility, and foaming properties were considered, giving all the necessary information for developing new aqueous formulation of SiC suspensions, including advantages and disadvantages of the different candidates. Different de-agglomeration procedures, powder surface area, and calcination temperature were also considered to study the effect of the SiC surface properties. The outcome is that slurry stabilization provided by an alkaline environment at pH larger than 8‒9 is significantly more effective than slurry stabilization by any of the tested dispersants. Alkaline environments facilitate a negative surface charge on SiC particles and provide a stable electrostatic stabilization mechanism not observed in neutral or acidic environments. One among the dispersant candidates (FA 4404) seems to broaden slightly the range of stability toward the acidic regime. Anionic surfactants or block co-polymers tested exhibited no significant interaction with the SiC particles. 相似文献
10.
11.
《Journal of the European Ceramic Society》1999,19(12):2173-2181
Solid-state bonding of reactive systems, such as Si3N4–Mo often results in the formation of excessively thick intermetallic layers that can be detrimental to the final strength of the joint. The objective of this work was to study the microstructural evolution of Si3N4–Mo interfaces, aiming at maximum joint strength via a balance between the fraction of bonded material and the amount of interfacial reaction. Joining was carried out under vacuum or nitrogen atmosphere for temperatures between 1100 and 1800°C. Microstructural analyses of the interfaces revealed the presence of Mo3Si and Mo5Si3 along with residual pores. The results from shear strength tests revealed a strong relationship between the microstructure of the interface and the mechanical strength of the joint. © 相似文献
12.
Rohit Malik Seung Hoon Jang Young-Wook Kim Toshiyuki Nishimura 《International Journal of Applied Ceramic Technology》2019,16(4):1304-1313
SiC–Zr2CN composites were fabricated by conventional hot pressing from β-SiC and ZrN powders with 2 vol% equimolar Y2O3–Sc2O3 as a sintering additive. The effects of the ZrN addition on the room-temperature (RT) mechanical properties and high-temperature flexural strength of the SiC–Zr2CN composites were investigated. The fracture toughness gradually increased from 4.2 ± 0.3 MPa·m1/2 for monolithic SiC to 6.3 ± 0.2 MPa·m1/2 for a SiC–20 vol% ZrN composite, whereas the RT flexural strength (546 ± 32 MPa for the monolithic SiC) reached its maximum of 644 ± 87 MPa for the SiC–10 vol% ZrN composite. The monolithic SiC had improved strength at 1200°C, whereas the SiC–Zr2CN composites could not retain their RT strengths at 1200°C. The typical flexural strength values of the SiC–0, 10, and 20 vol% ZrN composites at 1200°C were 650 ± 53, 448 ± 31, and 386 ± 19 MPa, whereas their RT strength values were 546 ± 32, 644 ± 87, and 528 ± 117 MPa, respectively. 相似文献
13.
Stuart Hampshire Tríona Kennedy 《International Journal of Applied Ceramic Technology》2022,19(2):1107-1125
This paper reviews investigations of silicon nitride–silicon carbide micro–nanocomposites from the original work of Niihara, who proposed the concept of structural ceramic nanocomposites, to more recent work on strength and creep resistance of these unique materials. Various different raw materials are described that lead to the formation of nanosized SiC within the Si3N4 grains (intragranular) and at grain boundaries (intergranular). The latter exert a pinning effect on the amorphous grain boundary phases in the silicon nitride and also act as nucleation sites for β-Si3N4, which limits grain growth during sintering. This finer microstructure results in strengths higher than for the monolithic silicon nitride. Intragranular SiC particles enhance strength and fracture toughness as a result of residual compressive thermal stresses within the nanocomposites. High temperature strength and creep resistance are also much higher than for monolithic silicon nitride and a few investigations of these topics are briefly reviewed and the proposed mechanisms are described. Within the context of other studies cited, work on Si3N4–SiC micro–nanocomposites by the current authors describes an aqueous processing route for better dispersion of commercial powders prior to sintering. 相似文献
14.
The wetting behaviour of silicon on diamond and the interaction of diamond with molten silicon were investigated. It was found that diamond is well wetted by molten silicon reaching a contact angle of about 20° after melting. The wetting is caused by the rapid formation of a SiC interlayer by nucleation of silicon carbide grains on the surface of the diamond. Investigations of the interaction of silicon with CVD diamond, using SEM, showed that the initial rate of SiC formation is very fast and is significantly reduced after the formation of a 4–6 μm thick dense SiC interlayer. At that stage further growth is likely to be controlled by the diffusion of Si and C through the grain boundaries of the silicon carbide interlayer. The results were compared with the interaction of silicon with glassy carbon. 相似文献
15.
《Journal of the European Ceramic Society》2014,34(7):1783-1790
Dense nanocomposites constituted from 70/30 vol% of hafnia–silicon carbide and were prepared by spark plasma sintering. Silicon carbide suppresses grain growth. The fracture strength of as prepared composites is 400–600 MPa. Oxidation up to 1600 °C in air for 10 h has minor influence on the mechanical strength, which is ascribed to the dense nature of the oxidation scale. The high density of the oxidation scale is attributed to a volume increase when silicon carbide oxidizes and reacts with hafnia to form hafnium silicate. The composite has a thermal conductivity of 14 W m−1 K−1 at room temperature. Design approaches for further enhancement of ultrahigh temperature properties of oxide/non-oxide composites are discussed. 相似文献
16.
《Journal of the European Ceramic Society》2014,34(10):2143-2151
The corrosion behaviour of the relatively new silicon carbide bonded diamond materials (ScD) was investigated in NaOH, H2SO4 and hydrothermal conditions and compared with that of conventional SSiC and SiSiC-materials. The corrosion resistance increases with decreasing diamond grain size. In H2SO4 all investigated materials show a very high corrosion resistance, whereas in NaOH and under hydrothermal conditions above 100 °C some leaching of residual silicon takes place. Nevertheless the fine grained ScD material exhibits a residual strength of 400 MPa after 200 h corrosion in NaOH at 90 °C. Under the same conditions the strength of the SiSiC-material reduces to 50 MPa. The silicon carbide-diamond composites demonstrate corrosion resistance superior to SiSiC and wear properties analogous to that of conventional superhard materials. This material would therefore be suitable for use in demanding corrosive wear applications. 相似文献
17.
Kai Liu Lei Qiu Yuzhen Zhang Yanying Du Ce Sun Song Zhang Rong Tu Yanjiao Wu Huajun Sun Yusheng Shi 《International Journal of Applied Ceramic Technology》2023,20(6):3455-3469
A material extrusion (MEX) technology has been developed for the additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic (Cf/SiC) composites. By comparing and analyzing the rheological properties of the slurries with different compositions, a slurry with a high solid loading of 48.1 vol% and high viscosity was proposed. Furthermore, several complex structures of Cf/SiC ceramic composites were printed by this MEX additive manufacturing technique. Phenolic resin impregnation–carbonization process reduces the apparent porosity of the green body and protects the Cf. Finally, the reactive melting infiltration (RMI) process was used to prepare samples with different Cf contents from 0 to 2 K (a bundle of carbon fibers consisting of 1000 fibers). Samples with Cf content of 1 K show the highest bending strength (161.6 ± 10.5 MPa) and fracture toughness (3.72 ± 0.11 MPa·m1/2) while the thermal conductivity of the samples with the Cf content of 1 K reached 11.0 W/(m·K). This study provides a strategy to prepare Cf/SiC composites via MEX additive manufacturing and RMI. 相似文献
18.
《Journal of the European Ceramic Society》2014,34(15):4095-4098
To date, solid-state pressureless sintering of silicon carbide powder requires sintering aids and high sintering temperature (>2100 °C) in order to achieve high sintered density (>95% T.D.). Two-step sintering (TSS) method can allow to set sintering temperature lower than that conventionally required. So, pressureless two-step sintering process was successfully applied for solid-state sintering (boron carbide and carbon as sintering additives) of commercial SiC powder at 1980 °C. Microstructure and mechanical properties of TSS-SiC were evaluated and compared to those obtained with the conventional sintering (SSiC) process performed at 2130 °C. TSS-SiC showed finer microstructure and higher flexural strength than SSiC with very similar density (98.4% T.D. for TSS-SiC and 98.6% T.D. for SSiC). 相似文献
19.
《Journal of the European Ceramic Society》2000,20(14-15):2673-2677
Silicon nitride was sintered with 3 wt.% silicon nitride whiskers that were aligned using tape casting. Sintering was carried out at temperatures between 1550 and 1850°C for 1 h. The α to β phase transformation was complete at 1750°C. XRD results also showed that the amount of β-phase grains in the matrix increased faster than growth rate of the whisker grains at the early stage of sintering. The intensities of the peaks diffracted from the whisker grains increased faster than those diffracted from the matrix β-phase grains after the α to β phase transformation was complete. Both XRD results and the etched microstructures indicated that the whisker grains grew preferentially in the length direction. 相似文献
20.
《Journal of the European Ceramic Society》2006,26(4-5):703-710
Thermal diffusivity, a, and thermal conductivity, κ, between room temperature and 600 K were investigated for SiC composites containing 0–50 mass% of Tyranno® SiAlC (SA) fibre (mean length: 394 μm) hot-pressed at 1800 °C for 30 min under a pressure of 31 MPa. The monolithic SiC specimen possessed κ of 32.1 W m−1 K−1 at room temperature; no significant changes were found for the SiC composite containing ≤20 mass% of SA fibre addition. However, further increases in the amount of SA fibre to 50 mass% improved κ to a maximum of 56.3 W m−1 K−1. The value of a for the SiC composite containing 40 mass% of SA fibre was 0.185 cm2 s−1 at room temperature and decreased to 0.120 cm2 s−1 at 600 K. In addition, SiC composites using 40 mass% of SA fibre with a carbon interface of approximately 100 nm were fabricated. The effect of this interface on a and κ was marginal. 相似文献