Silicon Carbide Slurry Research Articles

Stabilizing high solid content slurries for SiC membrane preparation with enhanced separation performances

Silicon carbide (SiC) ceramic membranes are highly sought-after for their exceptional properties including high temperature resistance, corrosion resistance, good hydrophilicity, high flux, and high mechanical strength. However, achieving stable regulation of high solid content SiC slurries for membrane preparation remains a significant challenge. This study presents a novel approach to stabilize the dispersion of high solid content SiC slurries by controlling parameters such as solid content, pH, ball milling time and spray coating parameters. Furthermore, the impact of different milling durations on SiC particle size and membrane performance is systematically investigated, establishing, for the first time, a direct correlation between milling time and particle size. The investigations reveal that prolonged ball milling, specifically 18 h, results in a notable reduction in membrane pore size by approximately 40 %, accompanied by a remarkable enhancement in retention performance, as evidenced by a substantial increase in the average retention rate for 500 nm fluorescent microspheres from 54.61 % to 98.89 %. This study not only offers a practical method for the stable preparation of ceramic slurries, but also provide important reference for membrane morphology control and pore size regulation. These insights hold significant promise for advancing SiC membrane technology in applications such as wastewater treatment and resource recovery.

3D printing of high-purity complex SiC structures based on stereolithography

Complex Silicon carbide (SiC) structures are hardly achievable via traditional manufacturing methods, while stereolithography 3D printing technology effectively shapes sophisticated structures with high precision. However, it is a huge challenge to prepare SiC slurry for stereolithography 3D printing with excellent curing ability due to the increased light absorption of SiC powder. Therefore, a novel approach to fabricating high-purity SiC structures is proposed in this study based on the stereolithography 3D printing process, where SiO2 powder is used as an additive to increase the curing thickness from 27.8 μm to 53.0 μm. Moreover, phenolic epoxy resin (PEA) is introduced as a carbon source to transform SiO2 to SiC during sintering. As a result, there is almost no SiO2 phase or SiOC remaining in the final parts when the addition of PEA reaches 50 wt% related to the resin weight after sintering at 1600 °C for 4 h. Based on the SiC/SiO2/PEA slurry systems prepared, high-purity silicon carbide with complex structures can be successfully fabricated in one step without any pre-oxidation or precursor impregnation processes. This approach provides valuable insights into additive manufacturing of high-purity complex SiC structures.

Influence of Silane Coupling Agent and Anionic Dispersant on the Dispersion Effect of Silicon Carbide Particles.

Silicon carbide (SiC), as a widely used material, has great properties. To improve the flowability of ultrafine silicon carbide slurry, this study used sodium humate, tetramethylammonium hydroxide (TMAH), and N-(β-monoaminoethyl)-γ-aminopropyltrimethyl(ethoxysilane) (KH792) to modify the ultrafine silicon carbide powder produced by Qingzhou Micro Powder Company. The effects of different modifiers on improving the flowability of ultrafine silicon carbide slurry were investigated by means of viscosity tests, sedimentation experiments, and SEM observations. Their modification mechanisms were investigated by means of zeta potential tests, XPS tests, and so on. In this paper, the initial modification of SiC was carried out with KH792, followed by the secondary modification with anionic and cationic modifiers (tetramethylammonium hydroxide and sodium humate), and the optimal modification conditions were investigated by means of a viscosity test, which showed that the lowest viscosity of the modified SiC reached 0.076 Pa·s and that the absolute maximum value of the zeta potential increased from 47.5 at the time of no modification to 63.7 (maximum values) at the time of modification. This means it has an improved surface charge, which improves dispersion. The adsorption results of the modifier on the silicon carbide surface were also demonstrated by the XPS test results.

Effect of bimodal particle size distribution on the performance of SiC slurry for maskless vat photopolymerization

To address the concerns associated with the difficulties of the very limited light curing depth in the pure silicon carbide (SiC) printing slurry, a bimodal particle size distribution was investigated systematically. Powder mixtures of 1 µm SiC particles and 10.5 µm SiC particles with specific ratios were prepared for making the printing slurries of 55 vol% solid load. A comprehensive investigation was conducted on the rheological stability and photopolymerization properties of coarse and fine powders at different proportions, along with an exploration of the impact of powder proportion on the quality of sintering. It was observed that at a 40% proportion of fine powder in the mixed powder, the viscosity of the slurry reached its minimum value (4.7 Pa.s) at a shear rate of 10 s–1. Meanwhile, the settlement ratio V1/V0 reached the lowest value of 1.2%. The printed sample size closely matched the design size and the quality of ceramic samples obtained after sintering was excellent (134.78 MPa).

Fabrication of silicon carbide ceramics by combination of slip casting and spark plasma sintering

In this work, first, a systematic study has been done to optimize the rheological behavior of silicon carbide (SiC) slurries to produce 20 mm disc-shaped green bodies with the highest relative density by adding sintering aids and changing the most effective parameters of the slip casting process. In the second step, slip-casted SiC green bodies were sintered via spark plasma sintering (SPS) under the same conditions: at a heating rate of 200 °C/min and under a vacuum atmosphere (10−2 Torr), the temperature reached 1900 °C and was maintained for 15 min, then, a pressure of 50 MPa was applied, and sintering was performed for 15 min. Initial powders, as well as green bodies, were well characterized via different methods. Also, the microstructure, physical, and mechanical properties of sintered samples were investigated. Results showed that the optimal concentration of tetramethylammonium hydroxide (TMAH) as a dispersant agent for slurry with 60 wt% of SiC was 2 wt%. In addition, the optimal milling time for slurries containing sintering aids was 24 h. The sintered SiC samples containing a mixture of Al2O3 and Y2O3 powder as a liquid phase sintering aid in a range of 5–10 wt% showed low sinterability and as a result, their microstructures contained pores. In contrast, the use of B4C powder as a solid phase sintering aid in a range of 5–10 wt% resulted in forming of sintered SiC samples with completely uniform and dense structures without visible pores. The optimal percentage of B4C was 7 wt%, and the relative density and the hardness of the corresponding sintered sample were 99.5% and 3300 ± 20 Hv, respectively.

Room temperature enhancement of flexural strength in silicon carbide green body via the addition of cellulose nanofiber

Silicon carbide (SiC) green bodies fabricated using robocasting were strengthened by incorporating cellulose nanofiber (CNF) into a SiC slurry and just drying at room temperature. The measured flexural strength of a SiC green body modified via the CNF with a liquid phase weight ratio (water-to-CNF slurry) of 80:20 was 813 ± 37 kPa, 1.5 times larger than the strength of an unmodified green body. The strength was improved due to the increased number of hydrogen-bonding sites between the raw particles and CNF. After annealing at 250 °C, the lowering of the flexural strength indicated the occurrence of the bonding sites via water that was trapped on the CNF. The addition of CNF increased the viscosity and yield stress of the SiC slurry, which remained in the Bingham pseudoplastic behavior regardless of the CNF used. Moreover, this addition showed no effect on the relative densities, microstructures, and crystalline phases of the sintered SiC body. Therefore, the addition of CNF to the SiC slurry aided in handling the green body during processing and showed no detrimental effects on robocasting.

Preparation of silicon carbide ceramic slurry for stereolithography based additive manufacturing

Stereolithography-based additive manufacturing of ceramics has received tremendous attention in academic and industrial communities. In order to fabricate silicon carbide (SiC) components with complex shapes by stereolithography, a high SiC loaded ceramic slurry with low viscosity and excellent curing ability is required. However, it is challenging to meet these slurry requirements. In this work, the effects of resin formulation, dispersant, particle size, solid content and ball milling time on the properties of SiC ceramic slurry were systematically studied. The SiC slurries were prepared by using four precursor SiC powders having different particle sizes and modified by high temperature oxidation to reduce its UV absorbance. Additionally, the suitable SiC slurries for stereolithography were prepared by ball milling under appropriate processing parameters, and the geometrically complex SiC green bodies were subsequently fabricated.

Influence of high-temperature oxidation of SiC powders on curing properties of SiC slurry for digital light processing

Fabrication of silicon carbide (SiC) ceramics by digital light processing (DLP) technology is difficult owing to high refractive index and high ultraviolet (UV) absorptivity of SiC powders. The surface of the SiC powders can be coated with silicon oxide (SiO₂) with low refractive index and low UV absorptivity via high-temperature oxidation, reducing the loss of UV energy in the DLP process and realizing the DLP preparation of the SiC ceramics. However, it is necessary to explore a high-temperature modification process to obtain a better modification effect of the SiC powders. Therefore, the high-temperature modification behavior of the SiC powders is thoroughly investigated in this paper. The results show that nano-scale oxide film is formed on the surface of the SiC powders by short-time high-temperature oxidation, effectively reducing the UV absorptivity and the surface refractive index (<i>n</i>ʹ) of the SiC powders. When the oxidation temperature is 1300 ℃, compared with that of unoxidized SiC powders, the UV absorptivity of oxidized SiC powders decreases from 0.5065 to 0.4654, and a curing depth of SiC slurry increases from 22±4 to 59±4 μm. Finally, SiC green bodies are successfully prepared by the DLP with the the oxidized powders, and flexural strength of SiC sintered parts reaches 47.9±2.3 MPa after 3 h of atmospheric sintering at 2000 ℃ without any sintering aid.

Adsorption of anionic polyelectrolyte on an SiC surface and effects on dispersion stability

AbstractAluminum nitrate (Al(NO3)3) and sodium polystyrene sulfonate (PSS) were used to improve the dispersion of fine silicon carbide (SiC) powders. Effects of modification parameters on the viscosity of modified SiC slurry were studied by orthogonal experiments. Modified SiC slurry with the solid loading of 50 vol% reached the lowest viscosity of 34 MPa s. The adsorption processes of PSS on the as‐received and Al(NO3)3 premodified SiC surface were investigated. The results indicated that the adsorption between PSS and premodified SiC surfaces was a high affinity type and was mainly controlled by active sites on an SiC surface. The Langmuir model and the pseudo‐second‐order model could better fit the adsorption isotherm and kinetics data, respectively. The contact angle decreased from 32.8 to 15.2° and the wettability was improved by modification. The isoelectric point of modified SiC powder shifted to the acidic region and the maximum zeta potential was obtained at pH 11. Sedimentation results also showed that a stable dispersed suspension of modified SiC was achieved at pH 11. Density–pressure curves demonstrated that the flowability and formability of SiC powder were improved by modification. The dispersion effect of PSS on SiC and Al2O3 composite powder was verified by viscosity and sedimentation results.

Effect of octadecylamine polyoxyethylene ether on the adsorption feature of sodium polystyrene sulfonate on the SiC surface and the relevant dispersion stability of slurry

Silicon carbide (SiC) is a widely used advanced ceramic material. Due to the electrostatic repulsion between anionic polyelectrolyte and SiC surface, the adsorption capacity of anionic polyelectrolyte sodium polystyrene sulfonate (PSS) is small, so it is difficult to achieve good modification effect. It is very important to improve the adsorption capacity of PSS on SiC surface. In this paper, we used non-ionic surfactant octadecylamine polyoxyethylene ether (AC1830) and anionic polyelectrolyte PSS as dispersant to modify SiC powder. The adsorption of AC1830 is not affected by the surface charge and can shield part of the charge, which can be used as the adsorption site of PSS to promote the adsorption of PSS on SiC surface. The 50 vol% SiC slurry with viscosity of 0.039 Pa s was produced, which was suitable for slip casting. Zeta potential method showed that the isoelectric point (IEP) of SiC powder modified by this method shifts to the left obviously. The sedimentation experiment shows that the dispersion stability was significantly improved. Contact angle measurements showed that the modifier was successfully adsorbed on the surface of the powder and provided hydrophilic groups, which improved the wettability of the powder. The results of adsorption measurement showed that the isothermal adsorption model and kinetic adsorption model of PSS for SiC powder and SiC powder modified by AC1830 conform to Langmuir model and pseudo-second-order (PSO) model. The adsorption of AC1830 on SiC surface improves the adsorption capacity of PSS.

Dispersants for silicon carbide in water—A comparative study

AbstractThe 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.

Effect of SiC powder on the properties of SiC slurry for stereolithography

Silicon carbide (SiC) is a kind of structural ceramics with excellent properties and it is widely used in industrial fields. Stereolithography (SL) is a potential additive manufacturing technique to fabricate fine complex SiC components, the resin-based SiC slurry with superior rheological and photo-polymerization properties is important for SL. In this paper, we investigated the influence of SiC powder on the properties of the SiC slurries for SL. The physical characteristics of SiC powder such as particle size, size distribution and appearance were tested and observed, and their influence on the dispersion, sedimentation and photo-polymerization property of the SiC slurry were investigated and discussed in detail based on their correlative theory, we finally prepared SiC slurry with superior rheological and photo-polymerization properties, and fabricated the fine complex SiC green body with low defects, high accuracy and high bending strength successfully. The SiC slurry with the solid content of 40 vol% was fabricated by the SiC powder with the median diameter D50 ≈ 10.0 μm and a narrow particle size distribution, it is Bingham fluid with good fluidity and the viscosity of it is 464.40 mPa s under the shear rate of 51.08 s−1, the cured SiC parts with Z – axis dimension change of 0.75% was finally fabricated, the three points bending strength of it is 50.18 MPa. Our research work provides some fundamental understanding of the SL technique for fabricating fine complex SiC components, explored a suitable way to fabricate high quality SiC green parts through SL, and offers some valuable references for preparing SiC slurry with superior rheological and photo-polymerization properties.

Study on rheological behavior of Micro/Nano-silicon Carbide Particles in Ethanol by Selecting Efficient Dispersants.

A colloidal stability study of a nonaqueous silicon carbide suspension is of great significance for preparing special silicon carbide ceramics by colloidal processing. In this paper, three different chemical dispersants, which are amphiphilic, acidophilic, and alkaliphilic, are selected to compare their ability to stabilize nonaqueous slurries of silicon carbide. The analysis of the flow index factor is first used to estimate the colloidal stability of the suspensions. The results show that the addition of only 5 wt.% polyvinylpyrrolidone (PVP) forms a silicon carbide slurry with a low viscosity value of 17 mPa⋅s at 25 s−1. In addition, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS)measurements indicate that the PVP molecule is successfully adsorbed on the surface of silicon carbide. The different adsorption models are fitted, and the adsorption of PVP molecules on the surface of silicon carbide belongs to the Langmuir single-layer adsorption model. At the optimal PVP amount, the volume content of the suspension is as high as 22.27 vol.%, a Newtonian-like fluid still appears, and no agglomerate structure is formed in the system. After the volume content exceeds 22.27 vol.%, the flow index factor of the slurry begins to plummet, indicating that the slurry begins to transform from a Newtonian-like fluid to a shear-thinning fluid. The particles undergo inevitable agglomeration accompanied by the emergence of yield stress. Finally, a maximum solid loading of the system is predicted to be 46 vol.%, using the Krieger-Dougherty model.

The hydration resistance, evolution mechanism of sol-coated aluminum and its effect on mechanical properties of SiC reticulated porous ceramics

As the key component for porous media burner, the sufficient strength of SiC reticulated porous ceramics (RPCs) is necessary due to the scour of hot flue gas. However, SiC RPCs prepared with template replica method often exhibited serious oxidation and low strength when the foam was burnt out. In the present work, a sol-coated Al powder with high hydration resistance was introduced into the silicon carbide slurry to promote mullite formation in SiC skeleton, meanwhile reduce the SiC oxidation ratio of sample during the heat treatment. Firstly, the silica-sol coated Al with uniform silica-sol was successfully prepared via dip coating to improve the ability of hydration resistance of Al powder. Furthermore, sol-coated Al with spherical morphology improved rheological properties of silicon carbide slurry, including viscosity and rheological behavior. In addition, the evolution mechanism of sol-coated Al in SiC RPCs was revealed. The AlO2(g) and AlO(g) was first formed in the system, thus significantly reducing the SiC oxidation ratio in SiC RPC. The partial pressure of AlO(g) increased with the sintering temperature, the needle-shaped mullite formed at 1300 ○C when it dissolved in the microsilica, while lumpy mullite formed as SiC was the silica source in SiC RPCs. The addition of sol-coated Al was beneficial to optimize the microstructure of SiC skeleton, resulting in higher compressive strength of SiC RPCs.

Preparation of silicon carbide slurry for UV curing stereolithography

Abstract The present study was performed to investigate the optimum preparation conditions to obtain well-dispersed and fluidized silicon carbide (SiC) slurry with UV-curable resin, and to fabricate SiC sheets using the optimized SiC slurry. The rheological behavior of SiC slurries with UV-curable resin was examined and evaluated by adding suitable amounts of dispersant and selection of UV-curable resin. High solid concentrated SiC slurry with Newtonian flow and without yield stress were obtained by addition of 5 mass% dispersant for SiC. The slurry could be thickened to 75 mass% solid concentration. The composite sheet prepared from the optimized 75 mass% SiC slurries was successfully solidified using a stereolithography apparatus.

Wear and Corrosion Behavior of Tungsten Carbide Based Coating on Carbon Steel

High velocity oxy-fuel (HVOF) coating techniques are employed mainly to improve the service life of engineering components, which is exposed to wear, erosion, corrosion or combination of both; wear and corrosion. The aim of this study is to investigate the wear and corrosion behavior of WC-10Ni and WC-12Co coating deposited onto medium carbon steel (Cast steel BS 3100 GR A3) blade. The blade was used to stir the mixture of sulfuric acid (H2SO4) with ilmenite to produce titanium dioxide (TiO2) pigments. The microstructures of both coatings before and after wear and corrosion testing were evaluated using scanning electron microscope (SEM). Vickers microhardness testing was used to examine the coatings hardness. The three-body wear test with wet condition using silicon carbide (SiC) slurry was used to investigate the wear behavior for both coating. The experiment was based on weight loss of the sample and Archard’s law to determine the wear rate of the coating. In addition, the three-electrode electrochemical test was used to investigate the corrosion behavior of the coatings. The mixture of H2SO4 and ilmenite used as an electrolyte of the test. It is found that the wear rate will increase with increasing of the weight loss. This is consistent with decreases of the volume fraction loss and hardness of the coating. After corrosion test, it can be observed that the existence of the crack and porosity on the coating increasing the corrosion behavior of coating. With high volume fraction and hardness, WC-12Co shows higher wear resistance compared to WC-10Ni. However, the value of corrosion rate for both coating has a slight difference due to better corrosion resistance of Ni binder itself.

Study on Dispersion Stability of SiC Slurry and Its Membrane Properties

Silicon carbide (SiC) slurry with a low concentration was prepared, which was milled for 3 hours by mixing SiC powder with a certain amount of polyethylene glycol (PEG), tetramethyl ammonium hydroxide (TMAH), carboxymethyl cellulose sodium (CMC-Na), distilled water, and ethonal. The influence of the pH value on the Zeta potential and the additional components on the dispersion stability of the slurry were analyzed. The influence of various factors on slurry was studied by orthogonal experiment. The results showed that solid content had the greatest influence on viscosity and stability of slurry. After the slurry was coated on the surface of porous SiC ceramics and sintered at high temperature to form a SiC membrane, the micro-structure of SiC membrane and its pore size were characterized. The result showed that the pore size distribution of SiC membrane was narrow, and the average pore diameter was about 1µm. Meanwhile, the resultant grains tend to be round, uniform, single phase. Based on the above, we could know that the slurry has a good membrane-forming properties.

Study on Precision Polishing of Alumina Ceramics

The research is mainly to investigate the surface roughness by the mechanical polishing for the processing of alumina ceramic materials. In the experiment, the ceramic test piece was placed between the ceramic work ring and the grinding disc and then grinded firstly with an alumina grinding slurry with a particle size of 10 μm to make the original roughness of the test piece reach Ra value of 1.49 μm. Then the silicon carbide slurry polishing was employed to conduct the experiments by changing the concentration of the polishing, particle size, load, rotation and time to observe the polishing effect of ceramic materials under different parameters. The results showed that the silicon carbide particle size of 2μm, with the polishing time of 50 min, the disc speed of 90 rpm, the concentration of 35%, the original surface roughness of alumina ceramic Ra 1.49μm could be downed to 0.22 μm. The improvement rate could reach 94%. And the greater the specimen load with the better grinding efficiency, the smaller the load caused worse cutting force between alumina and the specimen surface. However, the better the surface roughness when the time kept going. Furthermore, alumina ceramic test piece after precision mechanical polishing by 3D surface roughness profiler and scanning electron microscope (SEM) analysis, the observation found that the wave of the original test piece rugged, after grinding and polishing wave front and grinding scratches had been removed, and a smooth surface was obtained.

Preparation and characterization of TiO2 embedded PVC ultrafiltration membranes

In this study, polyvinyl chloride membranes embedded with TiO2 nanoparticles were prepared via non-solvent induced phase separation method. The results of FESEM showed that all the membranes had sponge-like and asymmetric structure and the size of sponge-like as well as surface pores increased as the content of TiO2 increased. Backscattered FESEM results showed that nanoparticles were dispersed uniformly throughout the membranes even though agglomeration was observed for 2.0wt. % TiO2 embedded PVC membranes. Contact angle results revealed that hydrophilicity of membranes increased with increasing TiO2 content. Moreover, water flux of membranes increased with increasing TiO2 content as a result of increase in hydrophilicity. The results of abrasion test with silicon carbide slurry showed that weight loss of composite membranes were higher than that of neat PVC membrane meaning that incorporation of TiO2 had a negative effect on the abrasion resistance of PVC/TiO2 membranes. Fouling properties of membranes were investigated by filtration of BSA solution and the results showed that flux recovery of composite membranes improved due to the presence of hydrophilic TiO2 even though irreversible portion of fouling increased with increasing TiO2 content. However, rejection of BSA decreased as the content of TiO2 increased.

Fabrication of SiC reticulated porous ceramics with multi-layered struts for porous media combustion

Silicon carbide reticulated porous ceramics (SiC RPCs) with multi-layered struts were fabricated at 1450°C by polymer sponge replica technique, followed by vacuum infiltration. The effect of additives (polycarboxylate, ammonium lignosulfonate and sodium carboxymethyl-cellulose) on the rheological behavior of silicon carbide slurry was firstly investigated, and then the slurry was coated on polyurethane open-cell sponge template. Furthermore, alumina slurry was adopted to fill up the hollow struts in vacuum infiltration process after the coated sponge was pre-treated at 850°C. The results showed that the coating thickness on the struts and the microstructure in SiC RPCs were closely associated with the solid content of alumina slurry during vacuum infiltration. The typical multi-layered strut of SiC RPCs could be achieved after the infiltration of an alumina slurry containing 77wt% solid content. The compressive strength and thermal shock resistance of the infiltrated specimens were significantly improved in comparison with those of non-infiltrated ones. The improvement was attributed to the in-situ formation of reaction-bonded multilayer struts in SiC RPCs, which were characterized by the exterior coating of aluminosilicate-corundum, middle part of mullite bonded SiC and interior zone of corundum.