Das, Dulal (2022) Processing of oxide bonded porous silicon carbide ceramic membrane for microfiltration applications. PhD thesis, CSIR CGCRI and Jadavpur University.
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Porous silicon carbide (SiC) ceramics has been considered as an excellent engineering materials for various industrial application such as diesel particulate filter, mechanical seals, petroleum refining, catalytic supports, chemical refining, hot gas & molten metal filters, gas turbine system, heat exchanger, wastewater filtration etc. due to its excellent porous structure with narrow pore size distribution, high temperature mechanical strength, high hardness, high thermal conductivity value, low thermal expansion coefficient, good thermal shock resistance, excellent corrosion resistance and thermal shock value etc. However, a major problem with SiC based non-oxide ceramic materials is their low sinterability due to their strong covalent bonds between C and Si. Depending on the application of porous SiC ceramics, various methods were used to fabricate porous SiC ceramics. In most of these methods SiC need to be sintered at very high temperatures using selective sintering additives, expensive atmospheres, costly equipment and delicate instrumentation. Recently porous SiC ceramics are produced by most simple and cost effective oxide bonding method. In oxide bonding technique porous SiC compact is heat treated in presence of air and during heat treatment the oxidised silica coming from the surface of SiC reacts with oxide additives (such as Al2O3, MgO, CaO etc.) to form secondary bond phases between SiC particles. Considering the cost of raw materials, ease and repeatability of formation including low temperature formation possibility of the bond phases the oxide bonds are very popular for SiC systems of materials, substantial research work has been initiated all over the globe for the development of oxide bonded porous SiC ceramics; still there are many unresolved issues that need further attentions. For example, the evolution of the bond phase and the chemical reactions responsible for bond phase formation and the influence of burning of any carbonaceous pore former on bond phase formation of SiC and the cost of the final ceramics are the major global unresolved issues. Finally, effects of the processing parameters on the material and mechanical properties, permeation behaviour and waste water filtration behaviour of porous SiC ceramics need systematic investigations. The beginning materials must be well dispersed with the sintering additive and the pore former in order to achieve significant filter performance improvements. Inspired by these possibilities in this present thesis work, porous SiC ceramics bonded with silica and mullite phases were prepared by oxide bonding method at low temperature. In this work, SiC powder compact were prepared by taking desired amounts of SiC, Al2O3, Clay, Fly ash (source of bond phase additives) etc. powders. Different volume fractions of pore former were used for generation of porosity. Sintering involves burning out the pore former at a temperature higher than that at which it burns (mostly at 800°C) in order to create pores. Temperature higher than 700°C, the SiC particles under slow oxidation, leading to formation of silica and with increase in temperature, the process become fast. At temperatures (1000 to 1400°C) oxidation derived silica reacted with Al2O3 to form silica, mullite, which bonds SiC particles together and produced a rigid porous body. Also in this study, cordierite precursor were incorporated in porous SiC compacts by using an infiltration technique and developed of oxide bonded porous SiC ceramics following a low temperature sintering method. The reasons behind the selection of these bond phase systems are their useful properties, such as high refractoriness, low thermal expansion coefficient nearly with SiC, low oxygen diffusion coefficient, low dielectric constant, good thermal and chemical stability etc. The effect of amount of sintering additives, metal catalyst, sintering temperatures, pore formers, on the bonding phase formation and the properties of the final ceramics are evaluated. Air permeability, pure water permeability and waste water filtration studied were also studied by using this ceramic membrane. The thermal shock and corrosion resistance properties were evaluated. Mullite bonded SiC ceramic membranes were synthesized by recycling industrial waste fly ash as a source of bonding phase, SiC as raw materials, and MoO3 as sintering catalyst for growth of mullite at 1000°C by oxide bonding method. To investigate the effect of MoO3 catalyst on the mullitization reaction, microstructural and mechanical properties of the final ceramics, four different SiC ceramics compositions having different amount of MoO3 content were prepared. In the final mixture three different pore forming agent were used to increase the porosity of the ceramics and observed its effects on the permeability parameters and filtration characteristics. To characterise material properties of the final ceramics porosity, density and % oxidation were evaluated. XRD, Rietveld, SEM mechanical properties and pore size distribution pattern were analysed in order to identify major phases with their content, morphologies, mechanical strength and pore diameters of porous SiC ceramics. The porosity, flexural strength and the pore size of the final ceramics were varied from ~36-45 vol%, ~38-28 MPa, and ~2.9-4.0 µm respectively. TG-DTA data indicated that the mullitization reaction had occurred at comparatively lower temperature at 1000°C in presence of MoO3. From the air & water permeation study, the ceramics prepared in this work showed coefficient value k1, k2 and specific water permeability (SP) value in the range of 7.30×10-15 to 2.66×10-13 m 2 , 1.18×10-11 to 2.63×10-8 m, and 1532 to 6113 Lm-2 h -1 bar-1 respectively. The membranes showed a high separation efficiency of oil, COD, TDS and turbidity of ~93-89%, ~92-82%, ~91-89% and ~94-91% from kitchen wastewater and also it showed high turbidity removal efficiency 99.5% from synthetically prepared kaolinite turbid water. In another approach mullite-bonded porous SiC ceramics membranes also prepared using commercial SiC powder, alumina, alkaline oxide clay as sintering additives, and different sacrificial pore formers. The effect of pore formers on materials, microstructural properties, and air and water permeability of porous ceramic were investigated. A variation in porosity from 38-50 vol%, pore diameter 3.7- 6.5 μm, and flexural strength 28-38 MPa of the final ceramics were observed depending on the characteristics of the pore former. The Darcian (k1) and non-Darcian (k2) permeability evaluated from air permeation behaviour at room temperature was found to vary from 1.48 × 10−13 to 4.64 × 10−13 m 2 and 1.46 × 10−8 to 6.51 × 10−8 m, respectively. High oil rejection rates (89%-93%) were obtained by all membranes from feed wastewater containing 1557 mg/L oil. A very high pure water permeability of 13298 Lm-2 h -1 bar-1 was obtained with membrane having porosity of 48 vol% and mechanical strength of 31.5 MPa. To avoid the agglomeration of bond phase additives during powder processing method, another infiltration assisted method was considered to develop porous ceramics with homogeneous distribution of bond phases. Following infiltration technique, multi-oxide bonded porous SiC ceramics were prepared at 1300‐ 1400°C by sintering a powder compact of SiC and Al2O3, infiltrated with cordierite sol. The microstructures, phase components, mechanical properties and air permeation characteristics of multi-oxide bonded porous SiC ceramics were examined and compared with materials obtained via a powder processing route. A variation in sintering temperature affected porosity, average pore diameter, and flexural strength of the ceramics. For instance, porosity varied from 33 to 37 vol%, average pore diameter was ~12‐ 14 μm, and strength varied from 23-39.6 MPa. According to the Xray diffraction results, both cordierite and mullite content increased with the increase in sintering temperature. Furthermore, the presence of alumina powder in the final ceramics improved strength due to the formation of mullite in the bond phase in contrast to the samples prepared without alumina. A single collector efficiency model was used to theoretically determine the particulate filtration efficiency of the developed ceramics. The result indicated that the material developed in this study have strong application possibilities in pollution control. The impact of the amount of bond phase alumina additive and the sintering temperature on phase evolution, microstructure, pore size distribution, flexural strength, thermal shock resistance, and corrosion resistance properties of the in-situ mullite bonded porous SiC ceramics were also studied. The alumina content was varied from 5-10 wt%, and porous SiC ceramics were fabricated via reaction sintering at 1300-1500°C for 4h. Porous mullite bonded SiC ceramics prepared at 1400C with 10 wt% alumina additive exhibited highest mechanical strength of ~ 58 MPa at porosity level ~27 vol%. Temperature-dependent thermal shock resistance of porous SiC ceramics due to cooling was evaluated as a function of quenching temperature (from 0°-1200°C) and quenching frequency (up to 10 cycles) using the air and water-quenching technique. A laboratory corrosion study of SiC ceramics was conducted at 1000°C for 96–240 hours in presence of steam, coal ash, and both steam and coal ash. With corrosion duration and medium, the apparent change in mass, porosity, and density was recorded. The corroded samples were evaluated with SEM, XRD, and mechanical tests and the results indicated water vapour is the perpetrator for strength degradation. Thermal and other corrosion results indicated that the material has strong application possibilities in hot gas filtration. The oxide bonding technique and the utilization low cost starting materials were found to be an effective way synthesizes cost effective porous SiC membrane at lower temperature with improved mechanical, corrosion and thermal shock resistance properties. The methods developed in this study can be effectively utilized in the fabrication of porous SiC ceramics for various applications such as hot-gas filtration, wastewater filtration, catalytic support, etc.
| Item Type: | Thesis (PhD) |
|---|---|
| Additional Information: | Supervisor: Dr Nijhuma Kayal |
| Uncontrolled Keywords: | Recycling of fly ash, SiC membrane, Mechanical strength, Wastewater treatment, Permeability,fluid flow properties, membrane, microstructure, silicon carbide, microfiltration, Porous ceramic |
| Subjects: | Environment and Pollution |
| Divisions: | Ceramic Membrane |
| Depositing User: | Ms Upasana Sahu |
| Date Deposited: | 28 May 2024 07:19 |
| Last Modified: | 28 May 2024 07:19 |
| URI: | http://cgcri.csircentral.net/id/eprint/5718 |
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