Effect of high temperature on the mechanical properties of hierarchical porous cenosphere/geopolymer composite foams

A hierarchical porous cenosphere/geopolymer composite foam (FHCs/KGP) was fabricated by the simultaneous incorporation of O₂ pore from hydrogen peroxide and cenosphere filler addition. Effects of both H₂O₂ content and high-temperature treatment on the microstructure, porosity and strength of porous FHCs/KGP foams were investigated systematically. The obtained FHCs/KGP foams showed typical amorphous structure and desirable porosity from 65 to 82%. The composites could crystallize in situ to FHCs/leucite foams above 1000℃. Compression strength of the FHCs/leucite foams showed a maximum value of 5 ± 0.3 MPa when treated at 1000°C. The improvement of mechanical properties for the composite foams was attributed to crack deflection, fractured microspheres and the good bond between the FHCs and matrix. This study could open opportunities to employ cellular foams as alternatives in structure and filtration applications.     

The effect of heat treatment on tensile properties of 2D C/SiC composites

Two-dimensional (2D) carbon fiber reinforced silicon carbide (C/SiC) composites with different initial strength were prepared by chemical vapor infiltration (CVI). After tensile property testing, results exhibited that as the heat-treatment temperature (HTT) increases to 1900°C, the tensile strength and toughness of the low strength specimen (LSS) increased by 110% and 530%, while the high strength specimen (HSS) increased by 5.4% and 550%, respectively. As observed from morphologies, the heat treatment increases the graphitization of the amorphous PyC interphase, which leads to the weakening of interfacial bonding strength (IBS). Meanwhile, the defects arising from heat treatment cause thermal residual stress relaxation. Therefore, the tensile strength and toughness of LSS with relatively high initial IBS increase significantly as HTT increases. For HSS with moderate initial IBS, the heat treatment slightly improves the tensile strength, but significantly improves the toughness. Consequently, the post-heat-treatment tensile properties of 2D C/SiC composites can be regulated by varying HTTs and different initial strength.     

Biowaste-derived hydroxyapatite reinforced with polyvinyl pyrrolidone/aloevera composite for biomedical applications

The present investigation focuses on the synthesis of crabshell-derived hydroxyapatite (CS-HAP)/ water-soluble synthetic polymer—polyvinylpyrrolidone(PVP)/aloevera(AV)—a natural biopolymer, as a composite for enhanced mechanical, antibacterial and biocompatible properties. The reinforcement of polymer has a significant function in increasing the mechanical property of the composite, whereas the incorporation of AV improves the antibacterial and biocompatibility. Phase composition, morphology, mechanical property, and hydrophilicity of CS-HAP/PVP/AV biocomposite with different concentrations of PVP and AV were examined by Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM-EDX), Vickers microhardness tests, contact angle, respectively. Furthermore, the antibacterial efficiency of the composite is assessed using Escherichia coli (E coli) and Staphylococcus aureus (S aureus). The biocompatibility of HOS MG 63 cells on the CS-HAP/PVP/AV composite is evaluated by MTT assay test. The obtained results evidence that the as-synthesized composite have appropriate mechanical, antibacterial and biocompatible properties. Overall, the combination of mechanical property of PVP, antibacterial and biocompatible property of AV in CS-HAP/PVP/AV, makes the composite a potential therapeutic material for various biomedical applications.     

Photocatalytic performance of Fe-substituted ZnAl2O4 powders under sunlight irradiation on degradation of industrial dyes

Using the sol–gel auto combustion method with diethanolamine (DEA) as fuel, a sequence of iron-substituted zinc aluminates, ZnFe_xAl_2-xO₄ powders, including variable Fe³⁺ ion concentrations (0 ≤ x ≤ 2) were effectively prepared. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the Brunauer–Emmett–Teller (BET) method, UV–visible diffuse reflectance spectroscopy (UV-DRS), and vibrating sample magnetometer (VSM) were employed to examine the structures, chemical bonds, morphologies, composition, surface area, and optical properties as well as the magnetic behavior of the obtained samples. A single-phase spinel structure was obtained for the calcined aluminate powders with different interplanar spacing and crystallite sizes, as revealed by the classification results. The bandgap energy (E_g) of adapted aluminates was in the range of 2.04-3.14 eV, identified as being much lower compared to the pure sample (5.60 eV). Thus, Fe³⁺-substituted ZnAl₂O₄ samples could be successfully photoexcited using both ultraviolet and visible light, as suggested by the results. Examination of how the four main pollutant types decay when irradiated by sunlight was carried out to assess the samples and establish photocatalytic activity. These contaminants included rhodamine B (RhB), methylene blue (MB), methyl orange (MO), and methyl red (MR). The performance of photocatalytic degradation reached 98% after 150 min for all optimal samples of organic dyes. Besides, each of the altered photocatalysts could be recycled and displayed high stability. The S-shaped curve of ferrimagnetism can result in those samples as found by the magnetic measurements, though pure ZnAl₂O₄ displays diamagnetic characteristics. The adapted samples show intense improvement in the remanent magnetization (M_r) when compared to pure ZnAl₂O₄, signifying that magnetic photocatalyst recovery by applying an external magnetic field is easy. Thus, these results offer a convincing sign that ZnAl₂O₄ powders replaced by Fe³⁺ could provide the ability to aid in the ecologically friendly collection of solar energy.     

重芳烃轻质化催化剂n（Ni）/n（Ni+Mo）的优化与分析

以β分子筛为载体,在保持金属总负载量不变的情况下,采用等体积浸渍法制备了4种不同n（Ni）/n（Ni+Mo）的催化剂。分别采用X射线衍射（XRD）、比表面积测试（BET）、氨程序升温脱附（NH₃-TPD）、氢程序升温还原（H₂-TPR）、氢程序升温脱附（H₂-TPD）和热重-差热分析（TG-DTG）等方法对催化剂进行了表征。结果表明,4种催化剂的酸量和酸强度相近,在n（Ni）/n（Ni+Mo）等于基准+0.2时,Mo与载体之间的相互作用最弱,其氢气吸附量最多且积炭量最少;采用某炼厂重整C₁₀⁺ 重芳烃对4种催化剂进行评价,结果表明n（Ni）/n（Ni+Mo）等于基准+0.2催化剂具有最优的催化活性和稳定性。上述结果表明,影响重芳烃轻质化催化剂活性和稳定性的关键因素是催化剂氢气吸附量的多少,氢气吸附量越多金属表面的溢流氢效应越明显,积炭前驱体被溢流氢及时消除,从而保护了催化剂的加氢活性中心不被积炭覆盖,有助于催化剂在较高活性下保持稳定。     

Ni/W比对NiWCx催化剂加氢性能的影响

过渡金属碳化物具有类似贵金属的电子结构和加氢性能。采用等体积浸渍法制备了不同Ni/W比的NiW/γ-Al₂O₃催化剂,以程序升温碳化法转化为NiW碳化物后对芳烃模型化合物和低温煤焦油中分离所得芳烃组分进行加氢处理。催化剂的N₂吸附、XRD、H₂-TPR和SEM表征表明,Ni的添加促进了载体表面WO₃物种的分散和还原,抑制了WO₃晶体的团聚和大晶粒的生成。萘的加氢实验表明,Ni/W原子比为0.6时催化剂的活性最佳,而添加苯酚和吡啶后的模型油加氢过程中萘的转化率和十氢萘的产率均明显下降,Ni/W原子比为0.47和0.6的催化剂性能相近,煤焦油中芳烃组分加氢后Ni/W原子比为0.47的催化剂性能更优。结果表明,Ni和W均具有良好的加氢活性,但Ni耐杂原子性能较差,二者存在一个最佳的配比以使加氢性能更优。有杂原子化合物存在时,如煤基芳烃组分的加氢,Ni/W原子比为0.47的NiW碳化物催化剂具有更好的加氢性能。     

等速升温流态化下CaO/生物质焦的SO2/NO联合脱除特性

燃煤锅炉污染物超低排放标准对电厂脱硫和脱硝系统提出了更高的要求。CaO作为脱硫剂可以实现循环流化床锅炉烟气中SO₂的高效脱除,焦炭作为还原剂直接还原NO,同时CaO的存在对焦炭还原NO起催化作用,可以实现燃煤烟气中SO₂/NO的联合脱除。为了探究连续温度变化对CaO/生物质焦联合脱硫脱硝性能的影响,在钙循环捕集CO₂技术背景下,研究了等速升温流态化下CaO/生物质焦的SO₂/NO联合脱除特性。探究了烟气中O₂和CO₂对CaO/椰壳焦脱除SO₂/NO的影响。结果表明,O₂通过对椰壳焦表面碳原子的活化作用降低了异相还原NO温度,在300~950℃等速升温过程中CaO/椰壳焦的NO脱除效率逐渐增加,780℃以上能实现100%脱硝。O₂也提高了CaO/椰壳焦的脱硫效率。CO₂与CaO的碳酸化反应以及与椰壳焦的气化反应对同时脱除SO₂/NO有明显抑制作用。O₂和CO₂共同作用下,在500~800℃内CaO/椰壳焦的脱硝效率随温度升高而增加,脱硫效率先降低后升高。NO促进了CaO/椰壳焦脱除SO₂,而SO₂对脱硝有抑制作用。800℃时CaO/椰壳焦同时脱除SO₂和NO的效率分别为97.7%和93.9%。     

TEM and DFT investigation of CVD TiN/κ-Al2O3 multilayer coatings

This paper investigates the interfacial structure in hot-wall CVD TiN/κ-Al₂O₃ multilayer coatings using both HREM and DFT modeling. Two multilayers with different thicknesses of the TiN layers (50 and 600 nm) separating the κ-Al₂O₃ layers are analyzed. The general microstructure of the two multilayers is relatively similar. The TiN layer in the thicker TiN/κ-Al₂O₃ coating is thick enough to be several TiN grains high. This means that epitaxial columns, which are often found in the thinner TiN/κ-Al₂O₃ coatings, are not present. However, the orientation relationships at the TiN/κ-Al₂O₃ interfaces are the same in both multilayers. The HREM investigations show that κ-Al₂O₃ (001) planes can grow directly on flat (111) TiN faces, without any other phases or detectable amounts of impurities, such as sulphur, present. Where the TiN layers are more curved, γ-Al₂O₃ can be grown, at least partly stabilized by the cube-on-cube orientation relationship between γ-Al₂O₃ and the underlying TiN. The DFT calculations show very similar adsorption strengths for an O monolayer positioned on Ti-terminated TiC(111) and TiN(111) surfaces, with preferred adsorption in the fcc site. O adsorption on N-terminated TiN(111) is much weaker, with preferred adsorption in the top site. Calculated elastic-energy contributions yield a higher stability for κ-Al₂O₃ on TiN(111) than on TiC(111) and a higher stability for κ-Al₂O₃ than for α-Al₂O₃ on both TiC and TiN. This indicates that the observed higher stability of κ-Al₂O₃ on TiC(111) than on TiN(111) is not due to the lattice mismatch, while the preferred epitaxial growth of κ-Al₂O₃ over α-Al₂O₃ can be partly attributed to the mismatch.     

Crack initiation and propagation induced by inclusions in a nickel-base P/M superalloy under fatigue load

1 IntroductionRecently the key components in advanced aircraftengines are widely made of nickel-base P/M super-alloy. However, non-metallic inclusions are intro-duced into this material during powder metallurgyprocessing. In industry, although many method…     

液压机本体柔性化设计相关技术的研究

针对液压机本体设计特点，在液压机本体CAD应用系统的开发中，引入了柔性化设计的概念，以Pro／E为建模后台、VB6．0为操作语言，研究了柔性化设计的相关技术，并提出了相关解决方案，并为以：Pro／E为后台的应用系统的开发提供了一种可行方案。