Development of low-loss lead-germanate glass for mid-infrared fiber optics: II. preform extrusion and fiber fabrication

For lead-germanate glass fibers, reducing the content of hydroxyl (OH) groups and the formation of metallic Pb species is essential to pave the way for their applications as low-loss mid-IR fiber optics since OH and metallic Pb species cause intense absorption and scattering loss, respectively, in the mid-IR spectral range. The first part of this study reported the optimization of the glass melting procedure to obtain low amount of OH while preventing formation of metallic Pb species in lead-germanate glass. Here, the second part of this study reports the investigation of the process conditions to fabricate low-loss lead-germanate glass fiber through further understanding of the co-effects of glass melting and heat treatment atmospheres on the formation of nano- and micron-scale metallic Pb species in both the as-produced and heat treated lead-germanate glasses. Finally, using this advance in knowledge, we successfully fabricated low-loss lead-germanate glass fibers with no presence of reduced metallic Pb particles by optimizing dehydration agent, glass melting, preform extrusion and fiber drawing conditions. The optimized fabrication conditions reduced the unstructured fiber loss by almost one order to <0.3 dB/m at 1.55 μm.     

Fabrication of Si3N4–SiC/SiO2 composites using 3D printing and infiltration processing

Si₃N₄–SiC/SiO₂ composites were prepared by employing three-dimensional (3D) printing using selective laser sintering (SLS) and infiltration processing. The process was based on the infiltration of silica sol into porous SLS parts, and silicon carbide and silicon nitride particles were bonded by melted nano-sized silica particles. To optimize the manufacturing process, the phase compositions, microstructures, porosities, and flexural strengths of the Si₃N₄–SiC/SiO₂ composites prepared at different heat-treatment temperatures and infiltration times were compared. Furthermore, the effects of the SiC mass fraction and the addition of Al₂O₃ and mullite fibers on the properties of the Si₃N₄–SiC/SiO₂ composites were investigated. After repeated infiltration and heat treatment, the flexural strength of the 3D-printed Si₃N₄–SiC/SiO₂ composite increased significantly to 76.48 MPa. Thus, a Si₃N₄–SiC/SiO₂ composite part with a complex structure was successfully manufactured by SLS and infiltration processes.     

风机主轴锻件锻后热处理工艺优化

通过对42CrMo4风机主轴结构尺寸、性能要求、材质特点等方面进行分析,对原有锻后热处理工艺进行优化,制定出既能达到锻后热处理效果又经济节能的工艺参数。     

Effect of thermal treatment on the antioxidant activity of egg white hydrolysate and the preparation of novel antioxidant peptides

Heat treatment will affect the nutritional properties and potential bioactivity of food materials. The aim of this work was to evaluate the effect of different thermal treatment (4, 56, 65 and 100 ℃) and in vitro gastrointestinal digestion on the antioxidant activity of egg white hydrolysate. The results demonstrated that egg white hydrolysate treated at 65 ℃ exhibited the highest antioxidant. Remarkably, the simulated digestion significantly increased antioxidant activity of egg white hydrolysate. Furthermore, we identified twenty-four potential antioxidant peptides by performing mass spectrometry and bioinformatic analysis. Six peptides were selected based on the activity prediction score of the online tool. The results showed that P6 (ACPECPK) possessed the most outstanding antioxidant properties and had low cytotoxicity and allergenicity. Bioinformatics technology combined with biochemical assays may offer a way for discovering novel antioxidant peptides from different kinds of food under various heat treatment conditions.     

Effect of heat moisture treatment on resistant starch content among carbohydrate sources: a meta-analysis

Resistant starch (RS) can be generated through heat moisture treatment (HMT). The HMT was conducted by modifying starch using different ratio of moisture content, high temperature and heating time. A number of studies showed that the effects of HMT on RS contents in cereals, pulses, tubers and fruits were inconsistent. This study aimed to analyse the impact of HMT on RS level in various carbohydrate sources through a meta-analysis approach. Study selection was conducted with the PRISMA method. There were 21 relevant studies and 67 data used for meta-analysis. The database was analysed by using Hedges’ d. The results showed that there was a significant impact of HMT on RS level of cereals, especially wheat. The highest increase in RS levels for various carbohydrate sources in starch was influenced by the interaction of treatment between water content at 15 ≤ x < 25%, heating time at 0.25 < x ≤ 6 h and temperature at 120 ≤ x ≤ 130 °C.     

Double pyrovanadates CaMgV2O7: Formation mechanism,phase structure,and thermodynamic properties

A double pyrovanadate CaMgV₂O₇ sample was synthesized via a facile solid-state route under an air atmosphere. The nonequilibrium formation pathways of the CaMgV₂O₇ were investigated via powder X-ray diffraction. A multistep reactions path (metavanadates–pyrovanadates–double pyrovanadate CaMgV₂O₇) was proposed to describe the formation of the CaMgV₂O₇ considering the thermodynamic and kinetic factors. The cell unit parameters of the CaMgV₂O₇ sample indicated the crystallization according to a monoclinic system with space group P12/c1(14), and the lattice parameters of a = 6.756 Å, b = 14.495 Å, c = 11.253 Å, β = 99.12, and V = 108.806 Å³. X-ray photoelectron spectroscopy also confirmed the +5 oxidation state vanadium in CaMgV₂O₇. The endothermic effects at 1033 and 1143 K were related to the incongruent melting and liquidus temperatures of CaMgV₂O₇, respectively. The comprehensive thermodynamic properties of CaMgV₂O₇ were established in both low- and high-temperature regions, utilizing a physical property measurement system and multi-high-temperature calorimetry (96 lines). The heat capacity (200 J mol K⁻¹) and entropy (198 J mol K⁻¹) at 298.15 K were computed based on the low-temperature heat capacity values, and the enthalpy of formation at 298.15 K was also estimated. The fitted high-temperature capacity can be used to obtain the changes in the enthalpy, entropy, and Gibbs free energy. This study is part of building a reliable thermodynamic database of the CaO–MgO–V₂O₅ system.     

Influence of Sm and Cd co-substitutions on physical,magnetic, Mössbauer,electric, and dielectric properties of Co2X hexagonal ferrites in presence of a hematite phase

X-type samarium-cadmium co-substituted hexaferrite with compositions Ba_2-xSm_xCo₂Cd_yFe_28-yO₄₆ (0.00 ≤ x ≤ 0.08, and 0 ≤ y ≤ 0.4) were prepared at 1340 °C using a simple heat treatment technique. All heated samples were characterized using FTIR, XRD, SEM, VSM, M?ssbauer, and low-frequency dielectric measurements. XRD analysis of prepared samples shows the formation of X as a major phase along with hematite. The M_S value varied from 67.01 Am²/kg to 50.43 Am²/kg; whereas the H_c value changed from 2.95 kA/m to 6.17 kA/m, A high value of M_S (67.01 Am²/kg) is observed in the pure sample, and a very low value of H_c (2.95 kA/m) is observed for x = 0.06, y = 0.3 compositions, but Mr/Ms < 0.5 confirm the multi-domain nature of prepared hexaferrites. Hysteresis loops of all samples are narrow, and confirmed that formed samples belong to magnetically soft. Mössbauer spectra of the three samples (S1, S3, and S5) show the existence of doublets. Significantly low values of coercivity, retentivity, and loss tangent in Sm–Cd substituted samples signified those prepared materials can be used to design electromagnets, transformer cores, electric motors, and maybe a potential candidate for lossless low-frequency applications.     

环形通道内液态铅铋合金流动换热特性实验研究

通过对环形通道内液态铅铋合金的流动换热特性进行实验研究，得到了气泡泵注气对液态金属流动的影响，并拟合出环形通道内液态铅铋合金的摩擦系数关系式和换热特性关系式。结果表明：采用气泡泵注气能有效提升铅铋合金的质量流速；相同Reynolds数下环形通道内液态铅铋合金的摩擦系数大于由布拉休斯公式计算得到的摩擦系数；液态铅铋合金对流换热过程中，导热项占主导地位，并且Nusselt数随Peclet数的增大而增大。