Effects of guide holes on the performance of a vertical turbo air classifier

The wide usage of guide parts makes it one of the most interesting research hot spots in the field of fluid machinery. To improve the flow field distribution of the vertical turbo air classifier, the guide holes in the air intake region are designed. The flow fields of the classifiers with and without guide holes are simulated using ANSYS-FLUENT. The gas-phase simulation results show that the guide holes have a ‘diversion’ effect on the airflow, decreasing the tangential velocity and increasing the radial velocity of the airflow. After the airflow passes through the guide holes, the small guide hole sizes cause the large radial velocity and the strong ‘diversion’ effect, which can improve the flow field distribution. The well-distributed flow field of the elutriation region and annular region are obtained when the guide hole size is 7 mm × 7 mm. The discrete phase simulation results show that the cut size of the classifier without the guide holes is 9.1 μm. The cut size is 13.4 μm when the guide hole size is 7 mm × 7 mm. With the increase in the guide hole size, the cut size increases. However, when the guide hole size is larger than 10.5 mm × 10.5 mm, the cut size is almost kept unchanged, which is 22.9 μm.     

High-purity stoichiometric Si3N4 ceramics through trimethylsilyl-substituted polysilazanes

Trimethylsilyl-substituted polysilazanes were designed and successfully synthesized. They were used to fabricate high-purity stoichiometric Si₃N₄ ceramics through pyrolysis process. Trimethylsilyl groups improved the stability of polysilazanes and easily escaped during pyrolysis, which effectively reduced oxygen and carbon content in the final polymer-derived Si₃N₄. The C content of Si₃N₄ ceramic was below 0.06 wt%, and the O content was below 1.2 wt%. The Si₃N₄ ceramics remained amorphous up to 1400°C, yet they were completely transformed into α-Si₃N₄ at 1500°C. Synergistic effect from low oxygen and carbon content contributed to highly stable amorphous state of Si₃N₄ till high temperatures. This amorphous Si₃N₄ ceramics could be used in cutting-edge technology where high purity is compulsory.     

SiCN ceramics with controllable carbon nanomaterials for electromagnetic absorption performance

Different kinds of carbon nanomaterials, free carbon (C_free), graphene, and N-containing graphene (NG), in single-source-precursors-derived SiCN ceramics, were in situ generated by modifying polysilazane with divinylbenzene, dopamine hydrochloride and melamine, respectively. Adjusting the carbon source brings phase structure and electromagnetic wave absorption (EMA) properties differences of SiCN/C ceramics. In situ C_free enhances the EMA capacity of SiCN ceramics by improving their electrical conductivity of 9.2 × 10⁻⁴ S/cm. The electrical conductivity of SiCN ceramics with 2D graphene sheets balloons to 2.5 × 10⁻³ S/cm, causing poor impedance match thus leading to a worse EMA performance. In situ NG in SiCN ceramics has a low electrical conductivity of 5.6 × 10⁻⁸ S/cm, making for excellent impedance match. The corrugated NG boosts dielectric loss, interfacial, and dipole polarization. NG-SiCN nanocomposites possess an outstanding EMA performance with RL_min of −61.08 dB and effective absorption bandwidth of 4.05 GHz, which are ∼2.4 times lower and ∼4 times higher than those of SiCN, respectively.     

Polydopamine-Assisted Bi-Functional Modification of NiO Anode for Enhanced Lithium-Ion Storage Performance

The blooming requirement of high-performance energy storage systems has aroused the thirst for advanced energy storage materials. As a high capacity anode, however, the application of NiO nanoparticles (NiO NPs) is hindered by intractable issues of dramatic volume change, intrinsic low electronic conductivity, and severe aggregation tendency during lithiation/delithiation. Herein, a polydopamine (PDA) assisted bi-functionalization strategy for fabricating of PDA@NiO-CNT composites for fast and durable lithium storage is reported. In this composite, CNTs intertwine to form a network to ensure sufficient electrolyte infiltration and act as a highly conductive system to motivate fast charge transmission. The strong binding affinity of PDA facilitates bonding between NiO NPs and CNTs, which not only forms uniform and flexible PDA coating but also ensures homogeneous distribution of NiO NPs on CNTs network. Therefore, the bi-functional modified PDA@NiO-CNT electrode possesses high conductivity, alleviates volume change and aggregation of NiO NPs during cycling, achieves a reversible capacity of 1326 mAh g⁻¹ at 100 mA g⁻¹, a rate capability of 215 mAh g⁻¹ at 2000 mA g⁻¹ and a cycling stability with 78% capacity retention after 250 cycles. This bi-functional modification approach manifests its prospective potential for architecting other electrode materials toward high-performance electrochemical devices.     

Fibrous ceramic membrane constructed by mullite whiskers for the treatment of oil-in-water emulsions

Ceramic membranes with high porosity and excellent separation efficiency are necessary for the efficient treatment of large-scale wastewaters. However, the conventional ceramic membranes are usually prepared by particles-packing, which inhibits the advances of separation efficiency because of the low porosity and connectivity. Here, a fibrous ceramic membrane with mullite whiskers-interlocked structure was prepared by gas-solid reaction. The effects of aluminum fluoride (AlF₃) on the formation and growth of mullite whiskers, and then the permeability and selectivity of the ceramic membranes were investigated. With the increase of AlF₃ contents, the mullite phase evolved from needle-like, rod-like to flake-like structure, thus the catalyst accelerated the growth of mullite whiskers in the diameter direction. For the ceramic membrane sintered at 1400°C, the porosity increased from 58% to 76% while the average pore sizes increased from 0.65 to 3.93 μm because of the whisker-constructed structures. For the ceramic membrane sintered at 1450°C, the emulsion flux increased stably from 295 L/(m²·h) to 992 L/(m²·h) with the increase of trans-membrane pressure, and the oil rejection exceeded 98%. Thus, this study provides a feasible strategy for the preparation of ceramic membranes with high porosity and excellent separation performances.     

A capillary bundle model for the forced imbibition in the shale matrix with dual-wettability

The forced imbibition during hydraulic fracturing is one of the main mechanisms of oil production in shale oil reservoirs. However, the shale matrix has complex structures of nanopores and is rich in organic matters. The wettability of nanopores in organics matters is different from the nanopores in inorganic matters, and the characteristic of dual-wettability leads to complex mechanisms of forced imbibition. This paper proposes a model for describing the imbibition in a dual-wettability shale oil reservoir based on the capillary tube model. The external displacement pressure gradient is also considered to study the forced and spontaneous imbibition of hydraulic fracturing liquid into oil-wet organic nanopores and water-wet inorganic nanopores. The slip effect in organic nanopores and the boundary-layer effect in inorganic nanopores are considered in this model. The analytical expressions for describing the location of the oil–water imbibition front in an oil-wet organic nanopore and a water-wet inorganic nanopore are derived, respectively. The semi-analytical solution for predicting flow rate in a shale core with an external pressure gradient is given and demonstrated with a case study.     

Silica islands regulated external Ti-site environment of TS-1 for enhanced performance of 1-hexene epoxidation

Rational regulation of the local environment of Ti-sites in TS-1 harbors tremendous industrial and scientific significance to epoxidation reactions. Herein, we report a facile and environment-friendly strategy to boost catalytic selectivity by covering the Ti-sites on an external surface of TS-1 (ITS-1) without sacrificing activity of internal Ti sites. By a quantitative analysis of d₃-acetonitrile and quinoline-DRIFTS, ¹H MAS NMR and XPS, it is found that the percentage of external Ti-sites decreased from 11% to 6% after depositing surface silica islands. This successfully inhibits ring-opening reaction of 1,2-epoxyhexane on catalyst surface, as demonstrated by slower kinetic decomposition rate of 1,2-epoxyhexane. Compared with conventional TS-1 catalyst, selectivity of 1,2-epoxyhexane over ITS-1 catalyst significantly increased from 83.5% to 98.5% while maintaining high 1-hexene conversion. Furthermore, overmuch surface silica coverage only leads to extremely low conversion (2%) due to inhibition of mass transfer. This work paves the way for rational construction of Ti-containing catalysts for 1-hexene epoxidation.     

Study on the evaluation and compensating strategy for the wear damage of non-return valve during injection molding process

Injection molding (IM) is one of the most essential forming methods for plastics. However, some potential risks which influence part quality may occur in the molding process. A non-return valve (NRV) is a major component on the screw head whose function is to seal during the injection process to prevent the backflow of the melt. The NRV will wear in this process and cause fluctuations in parameters and quality but the wear states of NRVs cannot be monitored without the disassembly of the injection barrel. In this study, we proposed an optimization method to compensate for the wear damage of the NRVs. The V/P switchover point in each molding cycle was recalculated and output to stabilize the part quality. As a result, the wear damage of the NRV on the current machine was able to be predicted and the part quality could be initially optimized in the condition that the NRV had a degree of wear. The experimental results reveal that our proposed compensation algorithm can monitor the type of wear of NRV online, and at the same time, it can compensate the axial wear of NRV and finally improve the consistency of product weight, which established a fundamental for further research in the future.     

Flame retardant and antibacterial properties of PLA/PHMG-P/APP composites

Poly(lactic acid) (PLA) has evolved into a commodity polymer with numerous applications. However, its high flammability limits its viability as a perfect alternative to petrochemical engineering plastics. In this study, PLA was modified using polyhexamethyleneguanidine phosphate (PHMG-P) and ammonium polyphosphate (APP). The flame retardant performance of PLA/PHMG-P/APP was investigated based on the limiting oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA), cone calorimetry (CC), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Raman Spectrometry. Qualitative and quantitative methods were used to determine the antibacterial properties of PLA composites. The LOI of PLA-10% (P:A = 1:4) was 31.7% and was rated V-0 in the UL-94 V-0 test. The antibacterial properties of the composites reflected the antibacterial effects of PLA-10% (P: A = 1:4) against Escherichia coli and Staphylococcus aureus, with the antibacterial rates reaching 93.41% and 93.26%, respectively. PHMG-P and APP had a synergistic flame-retardant effect and improved the flame retardancy of PLA while exhibiting excellent antibacterial properties.