牦牛绒过氧化氢/过硫酸铵脱色体系工艺优化及其机制

针对现有商业化牦牛绒脱色过程复杂、脱色时间长等问题,提出新型过氧化氢/过硫酸铵体系牦牛绒脱色工艺。在尽可能提高纤维白度的前提下尽量减少纤维损伤,通过单因素试验确定了脱色时间、过硫酸铵用量和试剂pH值,对脱色工艺进行探讨并与商业化脱色牦牛绒进行比较。结果表明:采用过硫酸铵质量浓度为400 g/L,试剂pH值为9,在室温下脱色为180 min可达到商业脱色牦牛绒的效果,脱色时间节省至原来的1/8;脱色机制分析发现,脱色过程中硫酸根自由基起主要作用,羟基自由基起次要作用。该脱色工艺简单,为牦牛绒高值化利用提供了新的解决方案。     

我国食品安全问题的社会学分析

以近几年来我国频发的食品安全事件为鉴，从社会学视角分析了其产生的原因，并提出了相应的预防和解决问题的对策。     

Magneto-optical imaging deviation model of micro-gap weld joint

Seam tracking is important for butt joint laser welding. A magneto-optical imaging approach is proposed to detect the micro-gap weld whose width is less than 0.2 mm. The symmetry of the magnetic field above the weld joint is an important precondition to ensure the detection accuracy of the magneto-optical imaging method. However, in actual complex industrial scene, it is difficult to guarantee complete symmetry of the magnetic field. This paper proposes an effective method for solving the problem of magneto-optical imaging deviation under an asymmetric magnetic field. Two possible factors causing the asymmetry of magnetic field above weld joint are firstly investigated using finite element analysis. By analyzing the characteristics of the magneto-optic medium used in the sensor and measuring the magnetic field distribution of weld joint at different lift-off height and different excitation voltage, the prediction model of deviation between the weld position detected by magneto-optical imaging and the actual weld position is built by back propagation (BP) neural network. The experimental result of weld seam tracking based on magneto-optical imaging shows that the change of the lift-off height will affect the detection accuracy of the weld position, and sufficient accuracy can be ensured after correcting the deviation according to the prediction model of magneto-optical imaging deviation.     

On the compatibility of dual phase BaCe0.65Zr0.2Y0.15O3-based membrane for hydrogen separation application

Among dense ceramic membranes for H₂ separation, the ceramic-ceramic composite ones have recently gained the interest of the scientific community thanks to their enhanced performances. However, the ceramic phases constituting the composite must show high chemical and thermomechanical compatibility to form a crack-free and robust membrane. This work reports the compatibility between the BaCe_0.65Zr_0.2Y_0.15O_3−δ (BCZY) proton conductive system and various electron conducting systems belonging to four different families: ceria-based (CeO₂ and Ce_0.8Gd_0.2O_1.9), lanthanum nickelate cobaltite (La_0.95Ni_0.6Co_0.4O_3−δ), strontium titanate (Sr_0.9La_0.1TiO_3−δ) and the non-oxidic α-SiC. This work highlights how the coupling of BCZY with chemically different electron-conductive ceramics represents a challenging task, since La_0.95Ni_0.6Co_0.4O₃, Sr_0.9La_0.1TiO₃ and α-SiC react with the proton conductive perovskite producing many secondary phases in air and in reducing atmosphere after 4 h of permanence at 1400 °C. As may be expected, BCZY is chemically compatible with CeO₂ and Ce_0.8Gd_0.2O_1.9 in air and in reducing atmosphere after 4 h of permanence at 1400 °C. Dilatometric results prove the thermomechanical compatibility between BCZY and the ceria-based systems in the operation temperature range.     

Hollow fiber membranes with polyimide matrix for sulfur-free hydrogen source

Sulfur-free hydrogen production is significant for sustainable energy such as fuel cell to avoid poisoning catalysts. The hollow fiber membrane is proposed as sulfur trapper for the hydrocarbon fuels. Hollow fiber membranes with polyimide (PI) matrix and adsorptive zeolites fillers are fabricated by dry–wet spinning with subsequent imidization process. By detailed investigation of FT-IR, thermal degradation cures, morphology and sulfur trapping performance, the molecular structure, thermostability and adsorption channels of membranes have been analyzed. The hollow fiber membranes have abundant pores, and the zeolites particles are incorporated in the three-dimension polymer matrix. The inlet fuel can be desulfurized to below 0.1 mg L⁻¹, which means that the outlet fuel can be used as sulfur-free hydrogen source for fuel cell applications. Excellent sustainability of the system with hollow fiber configuration show attractive on-board application potential.     

Triblock copolymer-assisted synthesis of hierarchical ZIF-67 in the presence of 1,3,5-trimenthylbenzene

A hierarchically porous ZIF-67 was successfully synthesized by using non-ionic block copolymers P123 as a supramolecular templating surfactant and 1,3,5-trimethylbenzene (TMB) as a swelling agent. It was noted that TMB was an effective swelling agent to expand the pore size. Pore size distribution analyses reveal that the as-synthesized hierarchical ZIF-67 has a typical trimodal pore size distribution showing simultaneous micro-, meso- and macropore channel systems. Due to the effect of TMB and P123, the diameter of ZIF-67 nanoparticles was about twice of that synthesized with P123 only and larger pores were formed among the enlarged nanoparticles. This strategy is expected to be a facile and efficient method for the preparation of hierarchical ZIF-67.     

Synthesis,structure, and substitution reactivity of a new bi-oxo capped molybdenum cluster: [Mo3(μ3-O)2(μ-O2CCH2Cl)6(H2O)2(OH)]+

A new bi-oxo capped molybdenum carboxylate, [Mo₃(μ₃-O)₂(μ-O₂CCH₂Cl)₆(H₂O)₂(OH)]⁺, was synthesized by refluxing [Mo₃(μ₃-O)₂(μ-O₂CCH₃)₆(H₂O)₃]^2 + in chloroacetic acid for 20 h (T = 110 °C). Using ion-exchange chromatography (0.5 M NaClO₄ eluant), the trinuclear molybdenum ion was isolated and allowed to crystallize slowly (T = 4 °C) as the perchlorate salt (yield 23%). Upon dissolution of the compound in methanol-d₄, substitution of the terminal ligands for solvent occurs readily in which the observed exchange rate constant is k_obs^298K = 5.3 × 10^− 5 (± 0.3) s^− 1 and activation parameters equal to ΔH³ = 130 (± 10) kJ mol^− 1 and ΔS³ = 111 (± 33) J mol^− 1 K^− 1. From the kinetic data, we find that ligand substitution follows a dissociative pathway and that rates of substitution are faster than expected when compared to the molybdenum acetate analog. Herein, we report the synthesis, crystallographic study, and substitution reactivity of a new molybdenum bi-oxo capped cluster with bridging chloroacetate ligands.     

Chemical vapour infiltration and mechanical properties of carbon open-cell foams

In order to improve their mechanical properties, carbon open-cell foams of two different pore sizes were infiltrated with pyrocarbon by chemical vapour deposition at reduced pressure and using pure propane as precursor. The optimal conditions in terms of deposition rate and uniformity in coating thickness, structure and anisotropy were first investigated. Foam specimens were infiltrated at various stages, with two pyrocarbons of distinct microtextures and their morphology, relative density and geometrical features were evaluated.Compressive crushing tests were conducted to determine the influence of the pore size, the pyrocarbon type and the relative density on the mechanical properties of the pyrocarbon-infiltrated foams. They retain their non-brittle and dissipating behaviour up to relative densities of 0.15. The stiffness, crushing strength and dissipated energy increase significantly with the relative density. The crushing behaviour of the pyrocarbon-foam specimens can be essentially explained using simple structural models and failure mechanisms, according to the Gibson & Ashby’s approach for brittle cellular solids.     

Innovative electrodes for direct methanol fuel cells based on carbon nanofibers and bimetallic PtAu nanocatalysts

Direct methanol fuel cells are very promising power sources, but the easy poisoning of the platinum anode electrocatalyst by CO-like reaction intermediates, restricts their industrial application and commercialization. The development of Pt-based alloys or bimetallic catalysts, in which the second metal acts as Pt poisoning inhibitor, is one of the main promising solutions to this problem. In this work we have combined the use of unconventional methods to deposit the catalyst nanoparticles with unconventional carbon supports. Innovative electrodes made of platelet carbon nanofibers, directly grown on graphite paper, as substrate for electrodeposited platinum and gold bimetallic nanoparticles, have been developed. These electrodes allow having a single layer with both the diffusive and catalytic function, and a considerable decrease of noble metals amount (about five times), with consequent large cost reduction. Moreover, the replacement of the conventional ink deposition methods with electrodeposition for platinum and gold dispersion, considerably increases the catalytic activity. The electrocatalytic performance results were encouraging. Gold allows increasing the catalyst poisoning tolerance and then the electrode long term stability. The innovative electrodes show a performance improvement up to three times compared to a commercial carbon substrate electrode (Vulcan XC-72R) with ink-spray deposited PtRu nanoparticles as catalyst.     

Nanotip-induced ultrahigh pressure-sensitive composites: Principles,properties and applications

Spiky spherical nickel powders with sharp nanotips on their surface are excellent fillers for developing pressure-sensitive composites. The sharp nano-tips are responsible for generating field-assisted tunneling conduction, which leads to the strong responses of electrical conductivity of the composites to external force or deformation. The nanotip-induced ultrahigh pressure-sensitive composites can be used to develop new sensors, switches and controls for a wide range of applications including electronics, transport, space, medicine, defense, textiles, oil and gas, and civil engineering. In this paper, we examine a systematical review of research progress on the nanotip-induced ultrahigh pressure-sensitive composites, with attentions to mechanism of pressure-sensitivity, sensing performances, and applications of the composites. Future challenges in the development and application of the nanotip-induced ultrahigh pressure-sensitive composites are also discussed.