Silicon Carbide-based Ceramics Research Articles

Investigation of the Dependence of the Strength Characteristics of Silicon Carbide-Based Ceramics on the Initial Carbon Content

Investigation of the Dependence of the Strength Characteristics of Silicon Carbide-Based Ceramics on the Initial Carbon Content

Sol-gel synthesis of SiC@Y3Al5O12 composite nanopowder and preparation of porous SiC-ceramics derived from it

A sol-gel method with aluminium and yttrium alkoxoacetylacetonates as precursors was used to modify highly dispersed silicon carbide powder, with the formation of SiC@Y3Al5O12 with a low content of Y3Al5O12 ∼2 vol%. Two series of porous silicon carbide-based ceramics were produced by spark plasma sintering (SPS) of SiC and SiC@Y3Al5O12 powders at temperatures of 1,400–1,700°С (exposure time 5 min) and sintering pressures of 47 and 58 MPa. The relative density was 38–51 and 26–49% for materials obtained without and with modification, respectively. It was shown that the greatest influence of the sintering additive on the compaction process was observed at elevated SPS temperatures of 1,600–1,700°С. This was related to easier sliding of SiC particles during high-temperature sintering, due to the formation of a liquid Al2O3-Y2O3-SiO2 film on their surface under given temperature conditions. A significant (by 2.5 times) increase in compressive strength for modified samples, compared to ceramics obtained based on an individual, highly dispersed SiC powder, was observed at the maximum SPS temperature (1,700 °C); the microhardness value rose sharply (by 5.9 times) at an SPS temperature of 1,600 °C. The effect of sintering pressure increase at an SPS temperature of 1,500 °C was not so significant, and this was mainly observed for samples obtained by liquid-phase sintering of SiC@Y3Al5O12.

Service-Induced Damages of the Ceramic Thrust Bearing Pivot in the Seal Section of Electrical Centrifugal Pump System

The paper provides the results of studying the condition of the working pivot of thrust bearings made of reaction- sintered silicon carbide-based ceramics (SiSiC-ceramics) removed from the seal section of the electrical centrifugal pump system. The working surface of the pivot demonstrates numerous service-induced damages of different origin resulting from friction. Based on categorization of these damages, recommendations were made concerning the improvement of the ceramic thrust bearing design.

Liquid phase sintering and characterization of SiC ceramics

The present study focuses on the sintering of silicon carbide-based ceramics (SiC) by liquid phase sintering (LPS) followed by characterization of the produced ceramics. AlN/Re2O3 mixtures were used as additives in the LPS process. In the first step, the LPS-SiC materials were produced in a graphite resistance furnace in the form of discs at different temperatures. The conditions with the best results regarding real density and relative density were taken as reference for sintering in the form of prismatic bars. In the second step, these samples were evaluated regarding fracture toughness (KIC), by the Single Edge V Notch Beam – SEVNB – method, and flexural strength. KIC behavior was evaluated according to the depth and curvature radius of the notches. Reliable KIC values were presented when the ceramic displayed a small curvature radius at the notch tip. When the radius was large, it did not maintain the square root singularity of the notch tip. Tests were carried out to determine KIC values in atmospheric air and water. KIC results were lower in water than air, with a decrease ranging between 2.56% and 11.26%. The observations indicated a direct grain size correlation between KIC values and fracture strength of the SiC ceramics.

MICROSTRUCTURE AND SINTERING MECHANISM OF SiC CERAMICS REINFORCED WITH NANOSIZED ZrO2

Silicon carbide-based (SiC) ceramics has attracted quite broad attention due to their excellent mechanical, chemical and thermal properties. However, their widespread industrial application is hindered by difficulties in sintering and poor fracture toughness of sintered bodies. In this work, we present an alternative way to produce SiC-based ceramics with improved microstructure and mechanical properties. We incorporated ZrO 2 nanofibres into the ceramic matrix to achieve a combined reinforcing effect of partially stabilized zirconia, namely fibre and phase transformation strengthening. For comparison, we also prepared silicon carbide ceramics containing yttria stabilized zirconia (YSZ) particles. SiC-based green bodies containing 5 wt%, 10 wt% and 15 wt% ZrO 2 nanofibres and particles, respectively, were subjected to spark plasma sintering (SPS) at relatively low (1700°C) temperatures with high heating and cooling rates. The effects of nanofibres on mechanical properties were studied by determining the Vickers hardness and Young’s modulus of sintered ceramics from instrumented indentation tests. The microstructural patterns were investigated, as well.

Processing and mechanical properties of silicon carbide-based ceramics doped with short zirconia fibers

Processing and mechanical properties of silicon carbide-based ceramics doped with short zirconia fibers

핵연료 피복관용 다중층 SiC 복합체 튜브의 Hoop Stress 전산모사 연구

Silicon carbide-based ceramics and their composites have been studied for application to fusion and advanced fission energy systems. For fission reactors, SiC f /SiC composites can be applied to core structural materials. Multilayered SiC composite fuel cladding, owing to its superior high temperature strength and low hydrogen generation under severe accident conditions, is a candidate for the replacement of zirconium alloy cladding. The SiC composite cladding has to retain its mechanical properties and original structure under the inner pressure caused by fission products; as such it can be applied as a cladding in fission reactor. A hoop strength test using an expandable polyurethane plug was designed in order to evaluate the mechanical properties of the fuel cladding. In this paper, a hoop strength test of the multilayered SiC composite tube for nuclear fuel cladding was simulated using FEA. The stress caused by the plug was distributed nonuniformly because of the friction coefficient difference between the inner surface of the tube and the plug. Hoop stress and shear stress at the tube was evaluated and the relationship between the concentrated stress at the inner layer of the tube and the fracture behavior of the tube was investigated.

Operating Temperature Window for SiC Ceramics and Composites for Fusion Energy Applications

Limitations in operating conditions, primarily the steady-state operating temperature, of silicon carbide-based ceramics and composites for applications to structural and functional components in fusion blanket systems were critically examined based on the latest experimental results. Irradiation-induced high temperature swelling and irradiation creep were identified to be the likely factors limiting the upper temperature bound for structural applications, whereas irradiation-induced thermal conductivity degradation was identified to be the primary factor to limit the lower temperature bound when substantial heat flux is anticipated. For the application to flow channel inserts in liquid metal blankets, insulating properties will likely limit the upper temperature bound, whereas the lower temperature bound may be limited by swelling-induced secondary stress. Additionally, key scientific issues which need to be addressed for the better definition of design limitations were identified.

Analysis of nanoindentation tests on SiC-based ceramics

Two silicon carbide-based ceramics, with very different mean grain size, and a standard fused silica sample were characterized by nanoindentation. The values of hardness and Young's modulus were measured at several peak loads and calculated using the models developed by Oliver and Pharr (O&P) and by Cheng et al. (C&C). For all the materials, the values of hardness and Young's modulus were strongly dependent on the adopted model. In the silica specimen, the C&C Young's modulus and hardness were lower than those calculated by the O&P model. In the SiC ceramics, the differences between the two models were both qualitative and quantitative. The C&C Young's modulus values were lower than those calculated by the O&P model but the hardness values were higher. For most of the peak loads, the O&P model distinguished between the two SiC specimens while the C&C model did not.

Characterization of rare earth aluminosilicate glasses

Rare earth glasses are commonly used in lasers, sensors and radiation shield glasses. Rare earth aluminosilicate-based glasses have been successfully used as in vivo radiation delivery vehicles, in treatment of primary hepatocellular carcinoma, irradiation of diseased synovial membrane for the treatment of rheumatoid arthritis, and treatment of prostate tumors. These glasses have also been found useful to promote liquid-phase sintering of covalent ceramics and, specifically, silicon carbide-based ceramics. Usually, the SiO 2–Al 2O 3–RE 2O 3 system is used as sintering additives. In this work, several rare earth silicate glasses (RE = Y, La, Nd, Dy and Yb) were prepared based on 60%SiO 2–20%Al 2O 3–20%RE 2O 3 (mol%) compositions. These glasses were characterized by infrared spectroscopy and nuclear magnetic resonance. Moreover, the liquid phase sintering of silicon carbide ceramics was studied using dilatometric experiments with 10 vol.% additives of the 60%SiO 2–20%Al 2O 3–20%RE 2O 3 system.

Light Weight Biomorphic Silicon Carbide-Based Ceramics for High Temperature Structural Applications

Light Weight Biomorphic Silicon Carbide-Based Ceramics for High Temperature Structural Applications

Densification studies of silicon carbide-based ceramics with yttria, silica and alumina as sintering additives

Silicon carbide has been extensively used in structural applications, especially at high temperatures. In this work, Y2O3, Al2O3 and SiO2 were added to beta-SiC in order to obtain highly dense ceramics. Sintering was conducted in a dilatometer and in a graphite resistance furnace and the densification behaviour was studied. Sintered samples were characterised by density measurements, the crystalline phases were identified by X-ray diffraction. Microstructural observation of polished and polished/etched samples was carried out with help of scanning electron microscopy. Silicon carbide ceramics with more than 90% of the theoretical density were obtained by pressureless sintering if a suitable proportion of the additives is used.

Wear-resistant engineering ceramics

Engineering ceramics have a high application potential for wear-protection of different working parts used for extraction, processing, conveying, and dust collection equipment in mining and mineral industries, as well as some structural rotating parts. The high alumina (Al 2O 3 content from 91 to 99.5 wt.%), alumina–zirconia, zirconia, and silicon carbide-based ceramics (ABSC) have been studied. They have high mechanical properties, including hardness that is greater than many processed materials, and they are able to withstand high temperatures (greater than 1300°C) and thermal shocks. These ceramics successfully resist various solid and liquid abrasive and corrosive media transported at high velocities and pressures, and at cavitation; they may replace hard metals widely used for wear- and corrosion-protection. The features of the compositions, microstructure, and physical properties of these ceramics, as well as the wear resistance test results, are discussed. The factors affecting wear resistance of ceramics are emphasized; they may be subdivided by the factors dealing with microstructure and properties of ceramics, and by the factors dealing with application conditions (e.g. type of abrasive media, velocity, impingement angle, and others). Wear mechanisms for dense homogeneous oxide ceramics and for coarse heterogeneous ABSC are discussed.

Young's modulus and vibrational damping of sintered silicon carbide ceramics at high temperatures

Silicon carbide-based advanced ceramics have good strength, high thermal conductivity, and good creep and environmental resistance at high temperatures [1]. These attractive thermomechanical properties have made them widely used ceramic material for a number of applications in aeronautics, energy, electronics, nuclear, and transportation industries. In the aeronautical arena, these materials are being considered for applications in jet engine components. Applications in the energy industries include radiant heater tubes, heat exchangers, heat recuperators, and components for land based turbines for power generation. These materials are also being considered for use in the first wall and blanket components of fusion reactors, in furnace linings, and bricks, and in components for diffusion furniture (boats, tubes) in the microelectronics industry. There are a number of critical issues related to the use of these materials. For a number of engineering applications, high temperature elastic modulus and damping behavior becomes very important. In earlier publications, dynamic Young’s modulus and damping behavior of a wide variety of reaction bonded and reaction formed silicon carbide ceramics have been reported [2–6]. The aim of the present work is to characterize the elastic modulus and vibrational damping behavior of a sintered silicon carbide (Hexoloy-SA; Carborundum Co., Niagra Falls, NY) material. These materials were fabricated by the pressureless sintering of alpha SiC powders with boron carbide or aluminum carbide as sintering aids. For the modulus and damping measurements, bend bars were machined from the as-supplied plates. These bars had dimensions of 50 mm× 4 mm× 3 mm. The dynamic Young’s modulus and vibrational damping were measured as a function of temperature. The vibrational damping was measured as Q−1, where: Q−1= energy dissipated per cycle 2π∗(maximum energy stored per cycle)

A reaction forming method for joining of silicon carbide-based ceramics

A reaction forming method for joining of silicon carbide-based ceramics

Synthesis of thermosetting copolymer of polycarbosilane and perhydropolysilazane

A copolymer of polycarbosilane and perhydropolysilazane was obtained by reacting polycarbosilane with titanium n-butoxide and perhydropolysilazane. Titanium n-butoxide and perhydropolysilazane were essential for the polymer to show a thermosetting property. The thermosetting copolymers were converted into silicon carbide-based ceramics by pyrolysis in a stream of nitrogen to 1000 °C with about 80 wt% ceramic yield. The main phase of the pyrolysis product at 1500 °C in nitrogen was small crystallite β-SiC. Elemental carbon, based on rule-of-mixtures composition, in the final ceramics could be reduced by varying the ratio of polycarbosilane/perhydropolysilazane. The copolymer was dry spun and pyrolysed to produce ceramic fibre. Pyrolysis in nitrogen to 1500 °C yielded a silicon carbide-based fibre with low oxygen and low elemental carbon content. A tensile strength of 1.8 GPa and an elastic modulus of 220 GPa were obtained for the fibre which ranged from 10–12 μm in diameter. Crystallization to α-Si3N4, β-SiC, and β-Si3N4 proceeded on annealing in nitrogen at 1700 °C for 1 h.

A Review of the Efficacy of Silicon Carbide Hot-Gas Filters in Coal Gasification and Pressurized Fluidized Bed Combustion Environments

Reviews of relevant literature and interviews with individuals cognizant of the state of the art in ceramic filters for hot-gas cleaning were conducted. Thermodynamic calculations of the stability of various ceramic phases were also made. Based on these calculations, reviews, and interviews, conclusions were reached regarding the use of silicon carbide-based ceramics as hot-gas filter media. Arguments are presented that provide the basis for our conclusion that high-purity silicon carbide is a viable material in the integrated coal gasification combined cycle (IGCC) and pressurized fluidized-bed combustion (PFBC) environments we examined. Clay-bonded materials are, we concluded, suspect for these applications, their extensive use not-withstanding. Operations data we reviewed focused primarily on clay-bonded filters, for which a great deal of experience exists. We used the clay-bonded filter experience as a point of reference for our review and analysis.

An original route to poly[silylene-co-(2,4-disilapentane-2,4-diyl)] oligomers, efficient precursors of silicon carbide-based ceramics with variable C/Si ratios

Novel oligomers possessing a backbone formed of ( ?SP-CH 2 -Si ?) and (SS) n units were prepared by the copolycondensation of bis(chlorosilyl)methanes and various dichlorosilanes in the presence of sodium, in refluxing toluene. The effect of the respective molar ratios of comonomers on the yields and the structure of the copolymers was investigated. The role of substituents on silicon atoms in the ability of these materials to provide convenient ceramic precursors upon pyrolysis was examined. When ?Si-H bonds were present, thermal cross-linking was readily performed and ceramics possessing variable C/Si ratios were prepared.

Synthesis and Pyrolysis of Thermosetting Copolymer of Polysilastyrene and Perhydropolysilazane

Copolymer of polysilastyrene and perhydropolysilazane was obtained by the reaction of polysilastyrene with zirconium n-butoxide and perhydropolysilazane. Zirconium n-butoxide and perhydropolysilazane were essential to render the thermosetting property. The thermosetting copolymers were converted into silicon carbide-based ceramics by pyrolysis at 1000°C in a stream of N2 with about 80 mass% ceramic yield. The main phase of the pyrolysis product at 1500°C in N2 was small crystallite β-SiC. Free carbon, based on rule-of-mixtures composition in the final ceramics could be reduced by varying the ratio of polysilastyrene/perhydropolysilazane. The copolymer was dry spun and pyrolyzed to produce a ceramic fiber. Pyrolysis in N2 at 1500°C yielded a silicon carbide-based fiber. Tensile strength of 1.0 GPa and elastic modulus of 190 GPa were obtained for the fiber from 10 to 12μ in diameter. Crystallization to α-Si3N4, β-Si3N4, β-SiC, and ZrN proceeded on annealing in N2 at 1700°C for 1 h.

Coal slag corrosion of silicon carbide-based ceramics in a combustion environment

Coal slag corrosion of silicon carbide-based ceramics in a combustion environment