Commercial Silicon Carbide Powder Research Articles

Additive Manufacturing of SiC Ceramics with Complicated Shapes Using the FDM Type 3D-Printer

Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this work, the additive manufacturing (AM) technique was examined to fabricated SiC ceramics with complicated hollow structures using the Fused Deposition Modeling (FDM) type 3D-printer. To mold the hollow structure for the applications such as heat exchangers, the “support-less” condition must be achieved. Thus, extruded SiC-phenol resin compounds must be cured immediately after molding to keep the molded shapes. To increase the thermal conductivity of the SiC compounds, the combinations of commercial SiC powders with different average diameters were examined for increasing the volume fraction of SiC particles to the phenol resin. SiC compounds with optimized rheological properties for the modified FDM-type 3D-printer were successfully obtained.

Influence of oxygen content on the microstructure and mechanical properties of SPS SiC

In this paper, two different commercial silicon carbide powders were treated by HF etching, aging and heat treating to obtain various oxygen contents. Fully dense silicon carbide ceramics (>99% th.density) were produced by spark plasma sintering technique at 1900 °C under an applied pressure of 50 MPa for 15 min holding time with boron carbide and carbon additions. Microstructure, polytype of SiC, density, Knoop hardness and fracture behaviors were examined to understand the effect of oxygen content on the properties of dense silicon carbide. The results show that oxygen content affects all of the measured mechanical and microstructural properties. High oxygen content is shown to be detrimental to the final density and hardness of SPS SiC.

Effect of High Boron Additive Content on SPS-Consolidation and Properties of Commercial Silicon Carbide Powder

Consolidation of commercial silicon carbide powder was performed by means of spark plasma sintering. It is shown that mechanical preactivation is a promising method for introducing a high content of boron additives into silicon carbide. The effect of the boron-additive amount on sintering, microstructure, and properties of the ceramic material was studied. A ceramic showing promise for use as a structural material in nuclear reactors and gas-turbine engines was obtained on the basis of silicon carbide with boron weight content 10%, density 3.12 g/cm3, hardness 31.9 GPa, and crack resistance 5.65 MPa·m1/2.

Investigation of heterostructures 3C-SiC/15R- SiC

The subject of study. Investigation results for 3C-SiC layers, obtained on single-crystal 15R-SiC substrates by sublimation epitaxy in vacuum are presented. Materials and methods. 15R polytype Lely crystals were used as a substrate; the growth was carried out on polar С (000 )1 and Si (0001) substrate faces. The growth temperature was 1950-2000 °C, and growth time was equal to 10 min. Commercial silicon carbide powder with a grain diameter equal to 10-20 µm was used as a growth source. The following methods were applied for the characterization of grown epitaxial layers: cathodoluminescence, optical microscopy and two-crystal X-ray diffraction. Main results. The possibility of obtaining epitaxial 3C-SiC on 15R-SiC substrate by sublimation epitaxy in vacuum was demonstrated. It is shown that, C-face is preferable for heteropolytype growth, since more uniform growth of cubic polytype is observed on it with a small percentage of spurious substrate polytype inclusions; the same situation appears in the case of 6H-SiC substrate application. Practical significance. Comparison of the results of heteropolytype growth for 3C-SiC on substrates of other polytypes (6HSiC, 15R-SiC, 4H-SiC) will give the possibility to understand more completely the transformation mechanism of the crystal lattice during epitaxial growth and to develop a theoretical model of the process.

Pressureless sintered silicon carbide with enhanced mechanical properties obtained by the two-step sintering method

The Two-step sintering (TSS) method was applied to the pressureless sintering of commercial silicon carbide powder doped with boron and carbon. The microstructural and mechanical properties of TSS-SiC were compared to those of sintered SiC obtained with the conventional thermal cycle (CS-SiC). TSS-SiC was densified (97.7% T.D.) at 2050 °C instead of 2200 °C needed for CS-SiC (97% T.D.). Furthermore, TSS-SiC showed finer microstructure and enhanced mechanical properties. In particular, flexural strength of the TSS-SiC materials greatly increased up to 556 MPa, much higher than 341 MPa reached by CS-SiC.

Production and characterisation of glass ceramic foams from recycled raw materials

Glass foams were produced exclusively from industrial residues, namely from sheet glass cullet and fly ashes from thermal power plant as the main components, and from burned wastes of silicon carbide (SiC) abrasive papers. The experimental results showed that homogenous microstructures of large pores could be obtained by adding an optimum amount (1 wt-%) of a commercial SiC powder (SiCC) after sintering at 950°C. The SiCC was then replaced by equivalent amounts of SiC abrasive paper ashes of different grain sizes. The SiC containing foams led to apparent density and compressive strength values of about 0⋅18–0⋅35 g cm–3 and 0⋅9–1⋅8 MPa. Good correlations between compressive strength, apparent density and microstructure (pore size, strut thickness and internal porosity) were observed.

Effects of powder processing on colloidal and microstructural characteristics of β-SiC powders

Three different powder processing methods for introducing sintering aids (yttria and alumina) into a commercial silicon carbide powder are studied: mechanical mixing, heterocoagulation and coprecipitation. The surface characteristics of the raw powders and powder mixtures are analysed by acoustophoretic measurements and compared. The effectiveness of the coprecipitation process for additivation is evaluated by the comparison of ESA measurements and by TEM observations. The powder mixtures are pressureless sintered in argon atmosphere and the microstructure of the sintered materials is analysed. The coprecipitation process allows a higher final density to be obtained in a shorter sintering time, with a finer and more homogeneous microstructure.

An Aqueous Gelcasting Process for Sintered Silicon Carbide Ceramics

An aqueous gelcasting process for the preparation of dense as well as porous‐sintered SiC ceramics has been described in this paper. A commercial silicon carbide powder coated with phenolic resin was used in this investigation. For the purpose of comparison, a pure SiC powder was also studied. ς potential and viscosity studies revealed that the pure SiC powder requires an electro‐steric stabilization, whereas the phenolic resin‐coated powder requires an electrostatic stabilization in order to produce their corresponding aqueous slurries with high solids content. Thermogravimetry and differential thermal analysis techniques have been used to study the decomposition behavior of phenolic resin. Aqueous slurries containing 25–50 vol% SiC powder were gelcast and sintered at 2150°C for 1 h. The sinterability of gelcast SiC samples was found to be highly influenced by the SiO2 formed on the surface of SiC during aqueous processing, as confirmed by the Fourier transform infrared spectroscopy study. The results obtained from various characterization techniques suggest that in order to make dense SiC parts with >3.13 g/mL bulk density (a theoretical density of 97.5%) by an aqueous gelcasting process, the starting phenolic resin (∼5%)‐coated SiC powder should possess a median particle size of <11.0 μm, surface area of >3.2 m2/g, a compact (green) density of >1.67 g/mL, and a B content of >0.5%. Further, by using polyethylene granules and organic foaming agents, sintered SiC foam with a porosity of >80%, a compressive strength of >16 MPa and a coefficient of thermal expansion of 4.574 × 10−6/°C between 30° and 700°C can be prepared by an aqueous gelcasting process, followed by sintering at 2150°C for 1 h.

Structural Changes during Milling of Silicon Carbide

The kinetics of milling and structural changes during milling of commercial silicon carbide powder in a ball mill lined with hard alloy are studied. Data are provided for the specific surface, x-ray patterns, and infrared spectra. It is shown that milling kinetics are described best of all by an exponential relationship and that milling of silicon carbide powder is accompanied by changes in polytype composition. The x-ray patterns and infrared spectra obtained make it possible to assume that during milling the 15R polytype content in the powder composition decreases while the content of structures with less layering (the 4H polytype and β-SiC) increases; in this case the number of absorption bands in the infrared spectra decreases.

Effects of additives on densification, microstructure and properties of liquid-phase sintered silicon carbide

Dense SiC ceramics were obtained by hot pressing of β-SiC powders using Al2O3-Y2O3 and La2O3-Y2O3 additive systems. The effect of the addition of an amount of ultrafine SiC to commercial silicon carbide powder was evaluated. Sintering behaviour and microstructure depended on type and amount of liquid phase, as densification proceeded via a classical solution-reprecipitation mechanism. A core/rim structure of SiC grains indicated that reprecipitation of a solid solution of SiC containing Al and O occurred on pure SiC nuclei. Grain boundary phase was constituted of crystalline YAG and amorphous silicates. Values of flexural strength up to ∼750 MPa at RT and up to ∼550 MPa at 1000 °C were measured. At 1300 °C a strong degradation of strength was attributed to softening of the amorphous portion of grain boundary phase. In highly dense materials toughness ranged from 2.95 to 3.17 MPa·m1/2 and hardness from 21 to 23 GPa.

Role of the clogging effect in the slip casting process

Particle segregation phenomena occurring during consolidation of the green bodies lead to non-homogeneous microstructures and poor reliability of the ceramic components. The two driving forces responsible for particle segregation in the slip casting process are the gravity force and the capillary suction of the plaster moulds. Both segregation mechanisms depend on other factors such as particle density, particle size distribution, particle interaction forces, and solid loading. The relative importance of each segregation mechanism was investigated by using two commercial silicon carbide powders having different particle size distributions, as well as different colours. The effects of the interparticle forces, solid loading and the driving force of the slip casting process were studied. The results obtained showed that for moderately concentrated suspensions and a driving force given by the capillary suction of the plaster moulds, the clogging effect plays the main role in particle segregation, whilst sedimentation predominates for low driving forces. Inadequacy of the existing models to explain the clogging effect is discussed and a new model is proposed.

Determination of Free Carbon in Silicon Carbide Powder

Free carbon in a silicon carbide raw material powder was determined by a combustion method. A sample of 0.5g was weighed out into a 3ml-quartz crucible, and the crucible was placed in a graphite-sealed quartz cell. The cell was raised into the induction furnace combustion tube and heated in oxygen flow at 850°C for 10min by controlling the voltage applied to the furnace. The amount of CO2 produced by the combustion of free carbon in silicon carbide was measured with a thermal conduction detector. Heating at 850°C induced oxidation of silicon carbide. Therefore, the amount of free carbon in silicon carbide was calculated by the correction method in ANSI (B74.15). We also used the correction method based on the change of oxygen concentration. For the sample dried at 105°C for 1h, the values obtained by two correction methods did not agree each other. When the samples were heated at 500°C in an argon atmosphere for 1h, the values obtained by the two correction methods agreed well. Free carbon in five commercial silicon carbide powders were determined to be 0.26-0.92wt%, and the precision (relative standard deviation) was 1-11%.