Preparation and properties of porous ceramics from nickel slag by aerogel gelcasting

To further resource industrial solid waste, porous ceramics with high porosity were prepared by a gelcasting method using nickel slag and kaolin as raw materials and hydrophilic nontoxic SiO₂ aerogel as a gelling agent. The effects of nickel slag content, dispersant and solid content on the properties and microstructure of porous ceramics were investigated in detail in terms of density, compressive strength, porosity, phase composition and micromorphology. The results confirmed that a certain amount of nickel slag can effectively improve the porosity of porous ceramics, while the addition of dispersant can promote the flow of the slurry, enhanced the denseness of the raw billet and significantly improved the compressive strength. However, its excessive use had a negative effect on the ceramic density and porosity. At the same time, the solid content played a key role in the performance of porous ceramics prepared by gelcasting, and too much solid content was also not conducive to the generation of pores. When the nickel slag content was 55%, the amount of dispersant was 2%, and the solid content was 60 vol%, the porous ceramic had a better overall performance, the density of the porous ceramic was 510 kg/m³, the compressive strength was 1.3 MPa, and the porosity reached 80.1%. The major crystalline phases of porous ceramics prepared by nickel slag were cordierite and anorthite.     

汽车内饰用酚醛树脂/黄麻纤维复合材料的拉伸性能

采用正交试验方法,用5%Na OH溶液对黄麻毡进行预处理,利用模压成型工艺制备酚醛树脂/黄麻纤维复合材料,通过对正交试验结果进行极差分析和方差分析,研究树脂含量、模具温度、模具压力和保压时间4个工艺参数对复合材料拉伸性能的影响程度和显著性水平,并通过多指标综合评分法对材料的拉伸性能综合评价,分析各个工艺参数对材料拉伸性能的影响规律。结果显示,树脂含量和模具压力对复合材料的拉伸性能影响非常显著,当树脂含量为20%、模具温度为180℃、模具压力为10 MPa、模压时间为6 min时,复合材料的拉伸性能最好,此时拉伸强度为24.06 MPa,拉伸弹性模量为113.17 MPa。     

Study on preparing of ultrahigh-molecular weight polyethylene microporous materials by novel non-dense injection molding method

In this article, a novel method called non-dense injection molding with higher efficiency was proposed to prepare ultrahigh-molecular weight polyethylene (UHMWPE) microcellular open porous materials. The characteristics and the basic principle of the molding process were described, and the effects of shot size, injection pressure, and injection speed on microstructure, average pore size, porosity, and pore size distribution were further studied. The results showed that under the parameters of the shot size, injection pressure and injection speed set as 60%, 63.9 MPa, and 100%, the microporous UHMWPE materials were obtained with the average pore size 38.9 μm and porosity 38.3 vol% respectively, which were close to the microporous structure and properties of the commercial filter products prepared by traditional powder sintering method.     

Development of high strength,porous mullite ceramic hollow fiber membrane for treatment of oily wastewater

Ceramic hollow fiber membranes (CHFMs) are known for their excellent characteristics including high surface area, compact design, and good chemical, thermal, and mechanical stabilities. Despite these interesting attributes, CHFMs are also prone to certain limitations, such as brittleness and high cost that hinder them from being commercialized. To mitigate this drawback, we have developed a high strength, porous ceramic hollow fiber membrane, derived from mullite–kaolinite powder, for efficient oil–wastewater separation. The superhydrophilic, low-cost mullite-based (CHFM) was successfully fabricated through combined phase inversion and sintering techniques. Prior to the fabrication, the as-received mullite–kaolinite was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) analyses. Subsequently, operational parameters such as the effect of mullite content, sintering temperature, and air gap were optimized during the fabrication of mullite ceramic hollow fiber membrane. The resulting membranes were systematically characterized and evaluated in terms of morphology, porosity, mechanical strength, water flux, and oil–water separation. Increasing the mullite content, air gap, and sintering temperature enhanced the formation of microvoid structure. It is interesting to note that the mechanical strength of 86 MPa was obtained for the membrane containing 60 wt % of mullite sintered at 1450 °C and an air gap of 5 cm. The membrane induced a stable permeate water flux and oil rejection of mullite CHFM of 182 L/m²?h and 97.1%, respectively. As compared to kaolin ceramic counterparts, this porous mullite ceramic hollow fiber membrane can be used in various water treatment applications, including for the separation of oily wastewater due to its mechanical strength and water flux.     

Freeze casting of aqueous alumina slurries with glycerol for porous ceramics

Experiments have been performed to show that the mechanical properties of alumina porous ceramics may be improved by introducing glycerol into the raw slurries and then casting them under a constant cooling rate. The effects of glycerol on the freeze casting process and thereby on the microstructure and mechanical properties of porous ceramics obtained are investigated. It is shown that the addition of glycerol will increase both the slurry viscosity and sample sintered density. SEM images for microstructure of the final ceramics reveal that a good connection between ceramic lamellae has been promoted. This connection makes as-prepared porous ceramics obtain high mechanical properties. For the 30 vol.% alumina slurry with glycerol, the axial and radial compression strengths reach to, respectively, 255.1 MPa and 105.8 MPa.     

Effects of fiber aspect ratio and fabrication temperature on the microstructure and mechanical properties of elastic fibrous porous ceramics by press-filtration method

The inherent brittleness of fibrous porous ceramics (FPCs) results in their fragility, limiting their application in thermal protection. In this paper, a novel elastic fibrous porous ceramic (EFPCs) with quasi-layered structure were successfully prepared by facile press-filtration method. To further investigate the characteristics of EFPCs, the effect of fiber aspect ratio and fabrication temperature on the microstructures and properties were studied. Results demonstrated that both fiber aspect ratio and fabrication temperature had influence on the microstructure and mechanical properties on EFPCs. The prepared EFPCs exhibited low density (0.124–0.181 g cm^?3), relatively high compressive stress (0.096–0.377 MPa) compared to flexible fibrous ceramics, high porosity (91.73%–94.86%) and low thermal conductivity (～0.03 W m^?1 k^?1). According to these excellent properties, the EFPCs may have potential use in thermal insulation fields.     

Relationship between pore structure with residual pore and mechanical properties of expanded graphite nanocomposites at varying molding pressures

The main challenges of developing expanded graphite (EG) composites are to improve the diffusion of polymer chains into EG pores and consequently to reduce the residual pore as defects in the final composites. In this paper, composites of unsaturated polyester (UP) resin containing 0.75 wt% EG are prepared at varying molding pressures of 1, 10, 20, and 30 bar. The EG particles are prepared at different exfoliation temperatures in the range of 700 to 900°C to have EGs with different porous structures. The scanning electron microscopy (SEM) micrographs show that residual pores are observed in the composites prepared at a low pressure of 1 bar. However, when the molding pressure increases, the number of the residual pores decreases and consequently the flexural properties improve. The highlighted improvements achieved by increasing the molding pressure from 1 to 30 bar are a decrease in the value of the residual pore from 23% to 3%, an increase in the flexural modulus from 1523 to 1744 MPa, and an increase in the flexural strength from 30.6 to 54.5 MPa. Interestingly, applying higher molding pressure affects the composites containing EGs with the highest degree of porosity, or rather larger pores, more remarkably.     

Highly porous silica foams prepared via direct foaming with mixed surfactants and their sound absorption characteristics

The highly porous silica ceramics were fabricated by direct foaming with mixed surfactants and the influence of silicon nitride addition and solid content on the microstructures and properties were investigated. The results showed that silicon nitride can impede the formation of cristobalite and facilitates the sintering of silica ceramics. When the addition of silicon nitride powders reached 15 wt%, the highest compressive strength of silica ceramic foams could be obtained. The porosity of silica ceramic foams was tailored in the range of 84.61%–91.35% by adjusting the solid content, and the compressive strength of the obtained ceramic foams ranged from 5.89 MPa to 0.94 MPa. Sound absorption characteristics of silica ceramics foams were investigated. With the porosity of ceramic foams increased from 84.61% to 91.35%, the sound absorption coefficients in the entire sound wave frequency were enhanced due to the reduction of flow resistances, besides, the sound absorption peak varied from 4200 Hz to 2300 Hz, and became more intense and sharper.     

SiOC modified carbon-bonded carbon fiber composite with SiC nanowires enhanced interfibrous junctions

Carbon-bonded carbon fiber (CBCF) composites are promising lightweight and high efficient thermal insulators to be applied in aerospace area, but their practical applications are usually restricted by the low mechanical performance and poor oxidation resistance. To overcome these drawbacks, many efforts have been made in the fabrication of ceramic coated CBCF composites. However, the densities of these modified composites are usually very high, which would result in the reduction in their thermal insulation performance. Herein, we prepared a CBCF composite with SiC nanowires enhanced interfibrous junctions and SiOC ceramic coated carbon fibers (SiCNWs-SiOC-CBCF). Similar to CBCF, the SiCNWs-SiOC-CBCF exhibits a low density of 0.35 g/cm³ and an anisotropic and highly porous architecture. The SiCNWs-SiOC-CBCF possesses a compressive strength of 3.8 MPa and a compression modulus of 195.7 MPa in the X (or Y) direction, ~26.7% and 150% higher than those of CBCF respectively. It can also suffer from an isothermal treatment in air at 900°C for 120 minutes. The combination of these properties makes the SiCNWs-SiOC-CBCF a good candidate for thermal insulator to be applied in extreme conditions.     

Synthesis and characterization of porous Y2SiO5 with low linear shrinkage,high porosity and high strength

The emerging porous Y₂SiO₅ ceramic is regarded as a promising candidate of thermal insulator owing to its very low thermal conductivity. However, recent works on porous Y₂SiO₅ are confronted with severe problems such as large linear shrinkage (18.51–20.8%), low porosity (47.74–62%) and low strength (24.45–16.51 MPa) at high sintering temperatures (1450–1500 °C). In this work, highly porous Y₂SiO₅ ceramic with low shrinkage and excellent high-temperature strength was fabricated by in-situ foam-gelcasting method at 1550 °C. The as-prepared sample has unique multiple pore structures, low linear shrinkages of 6.3–4.5%, controllable high porosities of 60.7–88.4%, high compressive strengths of 38.2–0.90 MPa, and low thermal conductivities of 0.126–0.513 W/(m K) (porosity: 87.1–60.2%). The effects of relative density on relative strength, as well as porosity on thermal conductivity were quantitatively discussed. The present results indicate that porous Y₂SiO₅ is the potential high-temperature thermal insulation material of light weight, low thermal conductivity, and high strength.     

Effect of a Small Amount of Synthetic Fiber on Performance of Biocarbon-Filled Nylon-Based Hybrid Biocomposites

Advanced hybrid biocomposites are engineered from nylon 6, waste wood biosourced carbon (biocarbon) with a low content of synthetic fiber for lightweight auto-parts uses. The novel engineering process through direct injection molding of only 2 wt% synthetic fibers in the form of masterbatch with 20 wt% biocarbon, results outstanding performance of the resulting nylon biocomposites. Such uniquely developed biocomposites show tensile strength of 105 MPa and tensile modulus of 5.14 GPa with a remarkable heat deflection temperature (HDT) of 206 °C. The direct injection molding of synthetic fiber retains the length ≈3 times higher as compared to traditional extrusion and injection molding; resulting greater degree of entanglement and composite reinforcement effectiveness in the hybrid biocomposites. Highly dimensionally stable nylon 6 biocomposites with a very low coefficient of linear thermal expansion results through reinforcing ability of the sustainable biocarbon and small amount of synthetic fiber.     

Preparation and properties of anorthite-based ceramics by using metallurgical solid waste and fly ash

A large amount of metallurgical solid waste accumulation poses a serious threat to the environment. Study on synergistic reinforcement of synthetic process of metallurgical solid waste-based ceramics with fly ash is of great significance in reducing environmental pollution and resource utilization. A metallurgical solid waste-based ceramic used as building ceramic was developed with the erosion part of used MgO–C bricks and fly ash as main raw materials, and the amount of solid waste added to the prepared ceramics was at least 60 wt% and up to 90 wt%. The effects of fly ash content and sintering temperature on the crystalline phase transitions, morphologies, and the main physical and mechanical properties of ceramics were investigated by X-ray diffraction, scanning electron microscopy, and mechanical testing. The results show that the obtained ceramics presented maximum bending strength and minimum water absorption, 80.14 MPa and 5.04%, respectively, when the raw material proportions were the erosion part of used refractories accounted for 60 wt%, fly ash 20 wt%, pyrophyllite 10 wt%, and quartz sands 10 wt%, and the process parameters were the sintering temperature 1150°C, sintering time 120 min, and molding pressure 15 MPa.     

A novel cost-effective and near-net-shape fabrication process for SiO2f/SiO2 composites

In this study, we present a novel preparation process named vacuum-assisted slurry infiltration (VASI) for obtaining the SiO_2 f/SiO₂ composites. This method displays remarkably improvement in manufacturing cycles since it allows adopt the ceramic slurries with high solid content as well as low viscosity. Through the porous matrix design of combining coarse particles with fine particles, a homogeneous porous matrix is achieved. The SiO_2 f/SiO₂ composites prepared by the VASI method exhibit the rivaling flexural and tensile strength at 48.8 and 16.4 MPa, respectively. Meanwhile, such porous matrix can enable cracks deflecting and dissipating crack energy by fiber pullout and fiber debonding mechanisms. In comparison, composites fabricated via silica sol infiltration show lower mechanical properties and brittle fracture behavior due to the formation of some defects in the matrix. This work make the prospect for meeting the requirements of low-cost, short preparation cycles, and near-net-shape manufacturing technology for SiO_2 f/SiO₂ composites becomes realizable.     

PTFE／GF透波复合材料成型工艺与性能研究

为制备高性能聚四氟乙烯(PTFE)基透波复合材料,对玻璃布(GF)增强PTFE的成型工艺进行了研究。通过差示扫描量热法确定了PTFE/GF复合材料的烧结温度,考察了烧结时间、冷却速率、压制压力及组分配比等因素对复合材料性能的影响。结果表明,当GF质量含量为40%、压制压力为45MPa时,PTFE/GF复合材料的拉伸强度最大,可达81.2MPa,介电性能也满足透波复合材料的要求。     

单向玄武岩增强复合材料工艺与性能研究

采用正交试验方法,以冷却方式、成型压力、增强纤维百分含量、成型温度为影响因素研究以单向布为增强体结构的玄武岩增强硼酚醛树脂复合材料的工艺性能。结果表明,成型温度对复合材料的力学性能影响最大,且随着成型温度的提高而线性增强;增强纤维的百分含量对复合材料拉伸性能的有较大影响,但对弯曲性能的影响较小,且力学性能不随增强纤维含量的增加而线性增强;成型压力的增大有利于复合材料弯曲性能的改善,而对拉伸性能的影响较小;适当延长冷却时间有利于复合材料力学性能的提高。     

Influences of mullite fibers on mechanical and thermal properties of silica-based ceramic cores

Mullite fibers composite silica-based ceramic cores were successfully prepared by injection molding. The effects of mullite fibers on the mechanical and thermal properties of ceramic cores were investigated. The results indicated that the linear shrinkage was significantly decreased and the porosity was gradually increased with the increase of mullite fibers. In addition, the flexural strength for the room temperature and the simulated casting temperature of 1500°C was increased to a maximum value when the content of mullite fibers was about 1 wt.%, and then decreased with the increase of mullite fibers. The mullite fibers of 1 wt.% presented excellent mechanical properties with a linear shrinkage of .65%, a porosity of 6.96%, and a flexural strength of 17 MPa at room temperature and 34.83 MPa at the simulated casting temperature of 1500°C. Besides, the change in microstructure and properties in various contents of mullite fibers were analyzed.     

Preparation and performance of lightweight porous ceramics using metallurgical steel slag

In this paper, porous ceramics with high porosity and low bulk density were prepared by using steel slag and kaolin as main raw materials and polyurethane sponge as template. The effects of steel slag particle size, zirconia addition, the solid content of the slurry, and the addition of polycarboxylic acid water-reducing agent on the properties of ceramics were studied. In addition, by adding a surfactant (Sodium dodecyl sulfate) to form fine pores on the original framework of the three-dimensional network porous ceramic, the shortcomings of the single as well as the uncontrollable density and porosity of the porous ceramic, which are produced by the template method, are improved. When the grinding time of steel slag is 90 min, the content of zirconia is 3% wt, the solid content of ceramic slurry is 64% wt, and 0.6% wt polycarboxylic acid water-reducing agent and 0.4% of surfactant are added, the prepared porous ceramic skeleton is clear and good. The porous ceramic has a low bulk density (as low as 157.869 kg/m³), high porosity (about 94.05%) and high compressive strength (0.2 MPa). The crystalline phase of it is mainly composed of anorthite, gehlenite, forsterite and quartz. The addition of zirconia, water-reducing agent and surfactant only changes the macrostructure of porous ceramics, and does not change its crystal phase composition. The preparation of porous ceramics from steel slag not only solves the recycling problem of steel slag, but also provides a good substitute for main raw materials of porous ceramics.     

连续CF增强PEEK复合材料层压板的制备工艺

采用熔融浸渍法制备了连续碳纤维(CF)增强聚醚醚酮(PEEK)复合材料预浸带,并层压成型制备复合材料层压板。研究了成型温度、成型压力、成型时间、纤维含量等因素对复合材料层压板力学性能的影响。结果表明,在成型温度为370℃、成型压力为12 MPa、成型时间为70 min、纤维含量为61%的工艺条件下,连续CF增强PEEK复合材料层压板的力学性能达到最优值,弯曲强度和弯曲弹性模量分别达到(1 750.76±49.13)MPa和(107.54±6.35)GPa,层间剪切强度达到(100.04±6.88)MPa,缺口冲击强度为(84.44±1.54)k J/m2。随着冷却速率的增大,复合材料层压板的弯曲性能和层间剪切强度下降,而缺口冲击强度提高。SEM分析表明,复合材料层压板的界面粘结良好。     

Porous YbB6 Ceramics Prepared by In Situ Reaction between Yb2O3 and B4C Combined with Partial Sintering

Porous YbB₆ ceramic, a member of the ultrahigh‐temperature (UHT) family, is successfully prepared from Yb₂O₃ and B₄C powders by in situ synthesis combined with partial sintering method. Due to the fact that pores can be produced using the gases such as B₂O₃ and CO generated in reaction between Yb₂O₃ and B₄C, phase‐pure porous YbB₆ ceramics are obtained after sintering the Yb₂O₃/B₄C green bodies at 1750°C for 2 h in a flowing argon atmosphere under ambient pressure without addition of pore‐forming agent. Using this new and simple method, the porosity and volume shrinkage of porous YbB₆ ceramics are controllable by changing the green density. The prepared porous YbB₆ ceramic has homogeneous pore structure with very narrow pore diameter distribution. Furthermore, the porous YbB₆ possesses high compressive strength of ~21.34 MPa when the porosity is ~58.7% and the density is ~2.27 g/cm³. The combination of these favorable properties renders porous YbB₆ ceramic being a light‐weight structural and functional component for UHT applications.     

Additive manufacturing of Csf/SiC composites with high fiber content by direct ink writing and liquid silicon infiltration

Direct ink writing (DIW) provides a new route to produce SiC-based composites with complex structure. In this study, we additive manufactured short carbon fiber reinforced SiC ceramic matrix composites (Csf/SiC composites) with different short carbon fiber content through direct ink writing combined with liquid silicon infiltration (LSI). The effects of short carbon fiber content on the microstructure and mechanical properties of the DIW green parts and the final Csf/SiC composites were investigated. The results showed that the Csf content played an important role in maintaining the structure of the green parts. As the Csf content increases, the dimension deviation ratio of the sample decreased at all stages. With the Csf content of 40 vol%, the final Csf/SiC composite had low free Si content and high β-SiC content. The maximum density, tensile strength and bending strength of the Csf/SiC composites were 2.88 ± 0.06 g/cm³, 53.68 MPa and 253.63 MPa respectively. It is believed that this study can give some understanding for the additive manufacturing of fiber reinforced ceramic matrix composites.