Residual Stress Distribution of Si_(3)N_(4)/SiC Gradient Material and the Effect of Residual Stress on Material Properties

The Si_(3)N_(4)/SiC gradient material with a gradient composition structure was prepared by a hot pressing sintering.The sinterability,distribution of residual stress and the effect of residual stress on mechanical properties of Si_(3)N_(4)/SiC gradient materials were studied.The research results show that,at 1750℃,Si_(3)N_(4)/SiC gradient materials with different ratios can achieve co-sintering,and the overall relative density of the sample reaches 98.5%.Interestingly,the flexural strength of Si_(3)N_(4)/SiC gradient material is related to its loading surface.The flexural strength of SiC as the loading surface is about 35%higher than that of Si_(3)N_(4)as the loading surface.The analysis of the residual stress of the material in the gradient structure shows that the gradient stress distribution between the two phases is a vital factor affecting the mechanical properties of the material.With the increase of SiC content in the gradient direction,the fracture toughness of each layer of Si_(3)N_(4)/SiC gradient materials gradually decreases.The surface hardness of the pure SiC side is lower than that reported in other literature.

放射性废阳离子树脂原位Fe_(2)O_(3)催化裂解减容研究

催化裂解能够有效减小放射性废树脂的体积,但温度过高有可能导致裂解过程中核素挥发。为降低裂解温度,本文采用原位Fe_(2)O_(3)对放射性废阳离子树脂进行催化裂解。结果表明,通过离子交换法将Fe^(3+)负载至阳离子树脂上,在裂解过程中原位生成Fe_(2)O_(3),能够使树脂的裂解温度降至650℃左右,比直接热裂解低130~150℃,且残渣率降低至15%(650℃)。对裂解残渣进行FT-IR、XRD、XPS和元素分析,结果发现Fe^(3+)原位生成的Fe_(2)O_(3)有效促进了磺酸基(-SO_(3)H)的转化及硫键(-S-)的断裂,树脂中83.1%的硫元素转化为SO_(2),16.9%的硫元素以硫酸盐的形式进入残渣中。上述实验结果表明,原位生成的Fe_(2)O_(3)能显著降低阳离子树脂的裂解温度和残渣率,能够实现放射性废树脂的有效减容。

Inner damage identification and residual strength assessment of a 3D printed tunnel with marble-like cementitious materials using piezoelectric transducers

Quantitative damage identification of surrounding rock is important to assess the current condition and residual strength of underground tunnels.In this work,an underground tunnel model with marble-like cementitious materials was first fabricated using the three-dimensional(3D)printing technique and then loaded to simulate its failure mode in the laboratory.Lead zirconate titanate piezoelectric(PZT)transducers were embedded in the surrounding rock around the tunnel in the process of 3D printing.A 3D monitoring network was formed to locate damage areas and evaluate damage extent during loading.Results show that as the load increased,main cracks firstly appeared above the tunnel roof and below the floor,and then they coalesced into the tunnel boundary.Finally,the tunnel model was broken into several parts.The resonant frequency and the peak of the conductance signature firstly shifted rightwards with loading due to the sealing of microcracks,and then shifted backwards after new cracks appeared.An overall increase in the root-mean-square deviation(RMSD)calculated from conductance signatures of all the PZT transducers was observed as the load(damage)increased.Damage-dependent equivalent stiffness parameters(ESPs)were calculated from the real and imaginary signatures of each PZT at different damage states.Satisfactory agreement between equivalent and experimental ESP values was achieved.Also,the relationship between the change of the ESP and the residual strength was obtained.The method paves the way for damage identification and residual strength estimation of other 3D printed structures in civil engineering.

Determination of <i>α</i>-1,3-Linked Mannose Residue in the Cell Wall Mannan of <i>Candida tropicalis</i>NBRC 1400 Strain

To investigate the chemical structure of cell wall mannan obtained from pathogenic yeast, Candida tropicalis NBRC 1400 (former antigenic standard strain, IFO 1400). As a result of two-dimensional NMR analysis, it was shown that the mannan of this strain is composed of α-1,6-, α-1,3-, α-1,2- and β-1,2-linked mannose residues. In this research, the mannan was subjected to three degradation procedures, acid-treatment, α-mannosidase, and acetolysis under two conditions in order to determine the chemical structure of the antigenic oligomannosyl side chains in this molecule. The 1H-nuclear magnetic resonance spectra of resultant oligosaccharides, pentaose and hexaose, demonstrated the existence of the oligomannosyl side chains corresponding to Manα1-3Manα1-2Manα1-2Manα1-2Man and Manα1-3Manα1-2Manα1-2Manα1-2Manα1-2Man, respectively, which have previously also been found in Candida albicans serotype A strain mannans. These findings indicate that C. tropicalis and C. albicans serotype A have no significant difference in the chemical structure of these cell wall mannans. Therefore, it can be interpreted that it is extremely difficult to distinguish both species by targeting the antigenic group in these mannans.

Impact of feeding flaxseed and microalgal residue on omega-3 fatty acids enrichment in hen eggs

To investigate the impact of dietary supplementation of different omega-3 polyunsaturated fatty acids (n-3 PUFAs) resources on PUFAs enrichment in hen eggs, two supplemental materials, flaxseed and oil-extracted microalgal residue of heterotrophic Schizochytrium, were added to the diet of laying hens in 3 groups. Results showed that supplementation with flaxseed and Schizochytrium residue gave rise to the increased, but different n-3 PUFAs levels in egg yolk, mainly α-linolenic acid (ALA) and docosahexaenoic acid (DHA). The ratio of n-6/n-3 PUFAs was reduced in all groups. After 14 days feeding of supplied PUFAs resources, n-3 PUFAs contents reached a plateau, and then remained constant during further supplementation in 3 experimental groups. Both the highest ALA level and DHA level were achieved in flaxseed group and microalgae group, reaching up to 353.69 (±68.15) mg/egg and 301.41 (± 26.76) mg/egg respectively. Moreover, the n-3 PUFAs enrichment efficiency was relatively low in flaxseed group when compared to other 2 groups. Laying rates of hens before entering peak production period could be improved by adding flaxseed but was not obviously affected by Schizochytrium residue. The egg weight, on the other hand, had no relationship with dietary supplementation. Thus, supplementation of flaxseed or Schizochytrium residue into standard feed offers an alternative choice for the production of n-3 PUFAs enriched eggs.

Residue Upgrading in Slurry Phase over Ultra-fine NiMo/γ-Al_2O_3 Catalyst

In this article, residual oil hydroconversion was studied in slurry phase in the presence of fine solid Ni Mo/γ-Al2O3 catalyst and the effects of operating conditions were carefully studied. The results showed that residue conversion was only affected by the reaction temperature and reaction time. The coke yield increased with a higher reaction temperature, a bigger catalyst particle size, a longer reaction time, a lower initial hydrogen pressure and a lower catalyst concentration. Heteroatoms removal rate increased with a higher reaction temperature, a longer reaction time, a higher initial hydrogen pressure, a higher catalyst concentration, and a smaller catalyst particle size. The role of catalyst in the slurry bed technology was discussed and its function could be stated as follows: the metal was applied to activate the hydrogen atoms for removing heteroatoms and saturating aromatics, while the support of the catalyst was used to prevent the mesophase coalescence for reducing coke formation.

AlN/YAlO_(3)复合陶瓷的抗热震性能

AlN陶瓷硬度高、脆性大,难以烧结致密,作为熔炼容器时会因高温变形或被温度变化引起热冲击破坏。将YAlO_(3)作为颗粒增强相加入AlN中,通过无压烧结方法制备AlN/YAlO_(3)复合陶瓷,研究不同温度下AlN/YAlO_(3)复合陶瓷的抗热震性能,分析热震前后AlN/YAlO_(3)复合陶瓷的物相结构、断口形貌和表面形貌,并阐明热震损伤机理。结果表明,在AlN陶瓷中加入YAlO_(3)能够促进AlN陶瓷的烧结,将致密度提升至98.37%,同时细化晶粒,提高AlN/YAlO_(3)复合陶瓷的抗弯强度和抗热震性能。在温度较高的热震试验中,当热震温度升高至600℃后,AlN/YAlO_(3)复合陶瓷的抗弯强度和残余强度保持率显著高于AlN陶瓷,表明添加YAlO_(3)能够有效提高AlN陶瓷的抗热震性能,这主要归因于微裂纹增韧及裂纹的偏折、分叉等机制的协同作用减缓了AlN/YAlO_(3)复合陶瓷抗弯强度的降低速度。此外,当热震温度达到1 000℃时,AlN发生氧化生成Al_(2)O_(3),导致AlN/YAlO_(3)复合陶瓷抗弯强度降低。

磁性Fe_(3)O_(4)/Mg-藻渣生物炭复合材料活化过硫酸盐处理甲基橙染料废水的应用

目的:探究不同条件下磁性Fe_(3)O_(4)/Mg-藻渣生物炭复合材料活化过硫酸氢钾对甲基橙染料废水的处理能力。方法:通过甲基橙溶液模拟染料废水,研究不同试验条件下(初始pH、甲基橙初始浓度、复合材料投加量、过硫酸氢钾投加量)磁性Fe_(3)O_(4)/Mg-藻渣生物炭复合材料活化过硫酸氢钾处理甲基橙染料废水的效果。结果:酸性条件下甲基橙染料废水降解速率随pH增大而减小,碱性环境下随pH增大而增大;甲基橙染料废水的去除效果与甲基橙初始浓度呈反比,与过硫酸氢钾的投加量呈正比;一定条件下增加复合材料投加量能提升对甲基橙的去除效果。结论:磁性藻渣生物炭复合材料活化过硫酸氢钾氧化甲基橙染料废水具有优异的性能,可作为一种高效的去除方法应用于染料废水处理领域。

PIEZOSPECTROSCOPIC STUDY OF RESIDUAL STRESSES AROUND INDENTATIONS IN SiC/Al_O_3 NANOCOMPOSITE

A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R lines in the fluorescence spectra va ry with the distance from the centre of indentation. The magnitude of load appli ed on the surface of the materials through the indenter influences the shifts of R lines to great extent. The luminescence of R lines of the materials before indenting is used to determine the residual stresses around the indentation in the materials, assuming that the stress tensor is transversely isotropic. Final ly, the term of hydrostatic stress is adopted to explain and compare different residual stresses around indentations with the increase of the indenting load an d the distance from the centre of indentations. <

8YSZ/Y_(3)Al_(5)O_(12):Ce^(3+)光敏复合热障涂层的等温氧化及光谱响应特性

为了监测热障涂层在氧化过程中陶瓷层内部的残余热应力,制备了Y_(3)Al_(5)O_(12):Ce^(3+)含量不同的8YSZ/Y_(3)Al_(5)O_(12):Ce^(3+)光敏复合热障涂层。研究了Y_(3)Al_(5)O_(12):Ce^(3+)不同含量下8YSZ/Y_(3)Al_(5)O_(12):Ce^(3+)光敏复合热障涂层等温氧化过程的失效机理,阐述了陶瓷层内部残余热应力与Y_(3)Al_(5)O_(12):Ce^(3+)的发射光谱的峰值波长之间的内在响应机制;同时研究了8YSZ/Y_(3)Al_(5)O_(12):Ce^(3+)光敏复合热障涂层陶瓷层发射光谱峰值波长偏移量与氧化时间的关系,并拟合了8YSZ/10%Y_(3)Al_(5)O_(12):Ce^(3+)光敏复合热障涂层等温氧化时间与光谱变化的传感方程。结果表明:1 050℃等温氧化100 h过程中8YSZ/Y_(3)Al_(5)O_(12):Ce^(3+)光敏复合热障涂层失效主要是陶瓷层内部残余热应力导致,且随氧化时间的增加,陶瓷层内部残余热应力增加,Y3Al5O12:Ce3+的发射光谱的峰值波长向短波方向偏移;8YSZ/10%Y_(3)Al_(5)O_(12):Ce^(3+)光敏复合热障涂层发射光谱峰值波长偏移量与氧化时间传感方程为:Δλ=155.785 07·t0.004 15-154.792 58。因此,可以通过发射光谱峰值波长的偏移规律表征氧化过程中陶瓷层内部的残余热应力。

厚度主导铝合金表面304不锈钢涂层组织结构及性能的演变行为

目的 评价不同沉积厚度对铝合金基体上304不锈钢涂层综合性能的影响。方法 采用超音速火焰喷涂在铝合金表面制备3种不同厚度(200、600、1 000μm)的304不锈钢涂层。利用附带能谱的扫描电镜(SEM)、X射线衍射仪(XRD)、维氏显微硬度计、纳米压痕仪、液压式万能试验机以及摩擦磨损试验机,研究涂层的微观结构、物相组成、残余应力、硬度分布、弹性模量、结合强度、弯曲性能和摩擦学行为。结果 304不锈钢涂层组织均匀、无裂纹,与基体结合良好。涂层主要由奥氏体相组成,其余为少量铁素体相和氧化物,且涂层中奥氏体晶粒相比粉末中发生晶粒细化。随着涂层厚度的增加,涂层孔隙率(C200≈0.5%、C600≈2.5%、C1000≈4.3%)、氧含量(C200≈2.4%、C600≈3.1%、C1000≈4.2%)增加,涂层残余压应力减小,显微硬度、弹性模量和结合强度均呈下降趋势;但涂层断裂刚度与其厚度成正比,断裂时裂纹主要沿未熔颗粒边界和氧化物聚集区域萌生和扩展。在干摩擦条件下,304不锈钢涂层的摩擦系数约为0.6,与铝合金相比,摩擦过程更加稳定,耐磨性提高3倍。随着涂层厚度的增加,涂层摩擦系数稳定性降低,磨损率增大,磨损机制以疲劳磨损和犁沟磨损为主。结论 与304不锈钢粉末相比,晶粒细化和残余压应力的存在致使涂层整体硬度提升。然而,随着涂层厚度增加,涂层中缺陷的增多以及残余压应力的减小又降低了涂层的综合性能。涂层断裂刚度与其断裂能有关,厚涂层体系具有更大的等效抗弯刚度。

PIEZOSPECTROSCOPIC STUDY OF RESIDUAL STRESSES AROUND INDENTATIONS IN SiC/AlO3 NANOCOMPOSITE

A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R lines in the fluorescence spectra va ry with the distance from the centre of indentation. The magnitude of load appli ed on the surface of the materials through the indenter influences the shifts of R lines to great extent. The luminescence of R lines of the materials before indenting is used to determine the residual stresses around the indentation in the materials, assuming that the stress tensor is transversely isotropic. Final ly, the term of hydrostatic stress is adopted to explain and compare different residual stresses around indentations with the increase of the indenting load an d the distance from the centre of indentations. 【

Si_(3)N_(4)陶瓷纵扭超声磨削表面残余应力及其试验研究

Si_(3)N_(4)陶瓷属于典型的硬脆材料,已加工表面易产生微裂纹,对陶瓷零件的使用性能影响较大。为获取高性能的Si_(3)N_(4)陶瓷零件,纵扭超声磨削被应用于其超精密加工中,为揭示纵扭超声振动磨削对Si_(3)N_(4)陶瓷零件独特的加工机理,建立了纵扭超声磨削单颗磨粒切削轨迹方程及其磨削表面残余应力模型,并进行Si_(3)N_(4)陶瓷纵扭超声磨削试验验证。结果表明:相同加工工艺参数下,普通磨削Si_(3)N_(4)陶瓷表面残余应力多为拉应力,而纵扭超声磨削Si_(3)N_(4)陶瓷表面多为残余压应力,进而纵扭超声磨削Si_(3)N_(4)陶瓷亚表面损伤深度比普通磨削最大可降低38%,且其理论仿真结果与试验结果误差不超过10%,可为Si_(3)N_(4)陶瓷高性能零件的超精密加工提供新的加工方法。

Extraction and kinetic analysis of Pb and Sr from the leaching residue of zinc oxide ore

NH4HCO3 conversion followed by HCl leaching was performed and proven to be effective in extracting Pb and Sr from zinc extracted residual.The mechanism and operating conditions of NH4HCO3 conversion,including molar ratio of NH4HCO3 to zinc extracted residual,NH4HCO3 concentration,conversion temperature,conversion time,and stirring velocity,were discussed,and operating conditions were optimized by the orthogonal test.Experimental results indicate that NH4HCO3 conversion at temperatures ranging from 25 to 85°C follows the shrinking unreacted core model and is controlled by inner diffusion through the product layer.The extraction ratios of Pb and Sr under optimized conditions reached 85.15%and 87.08%,respectively.Moreover,the apparent activation energies of Pb and Sr were 13.85 and 13.67 kJ·mol^−1,respectively.

Safe utilization of chromium-bearing vanadate residue by recovery of vanadium and chromium based on calcium circulation

A safe,economical treatment of hazardous chromium-bearing vanadate residue(CVR)will significantly benefit the clean production of chromate-bearing salts.This study investigated recovery of sodium vanadate and sodium chromate from CVR in sodium bicarbonate solution.Results indicate that the stability of calcium vanadate and calcium chromate depends on pH and[HCO3?].CaV2O6?4H2O transforms into CaV2O6?4H2O,CaV2O6?2H2O,CaV2O6,Ca2V2O7?2H2O,and Ca5(VO4)3(OH)when pH increases from 7.51 to 12.32.Increasing pH and reducing CVR dosage improve the vanadate extraction rate,and high V2O5 and Na2Cr2O7?2H2O extraction rates are achieved in dilute NaHCO3 solution.Moreover,addition of NaOH positively contributes to the recovery of vanadate and chromate from CVR.Over 95%V2O5 and Na2Cr2O7?2H2O in CVR can be extracted from 60 g/L NaHCO3 and 30 g/L NaOH solutions at 90°C for 2 h.In order to reduce the hazardous residue containing chromate after recovery of CVR,calcium circulation is presented.Results show that more than 60%lime can be saved with fresh residue addition to remove vanadate from sodium chromate solution due to the active CaCO3.Moreover,no lime is required in removal of vanadate when the roasting residue is added.Therefore,a novel process is developed for utilization of CVR.

3D Modal Solution for Tidally Induced Lagrangian Residual Velocity with Variations in Eddy Viscosity and Bathymetry in a Narrow Model Bay

In this study, we examine the results obtained by the Finite-volume Coastal Ocean Circulation Model(FVCOM) regarding the effects of eddy viscosity and bathymetry on the three-dimensional(3 D) Lagrangian residual velocity(LRV) in a narrow bay. The results are cast in terms of two nondimensional numbers: the ratio of friction to local acceleration(δ) and the ratio of the minimum depth over shoals to the maximum depth in the channel(ε). The ratio δ depends on the eddy viscosity and mean depth. For a given eddy viscosity, when ε > 0.5, the along-estuary LRV tends to be vertically sheared and when ε < 0.5, the exchange is laterally sheared. When ε << 1, the structure of the 3 D, depth-integrated, and breadth-averaged LRV changes only slightly as δ increases. For ε values between 0.33 and 0.5, the structure of the 3 D LRV is mainly laterally sheared. In the same ε range, the 3 D and depth-integrated LRV exhibit reversed structures from high to low δ values. In addition, the breadth-averaged LRV weakens the typical twolayered circulation when δ decreases. When ε is 1, the two-layered vertical structure reverses direction, and a three-layered vertical structure develops in the outer bay as δ decreases.

Cyanide removal for ultrafine gold cyanide residues by chemical oxidation methods

Because of the highly toxic cyanide in the gold cyanide residues,cyanide must be removed for environmental protection.The process mineralogy of residues was studied firstly,and then cyanide removal was carried out by three chemical methods.The results showed that the residue mainly contained Si,S and Fe.Pyrite was the main metallic mineral,and the iron-complex cyanides make cyanide removal difficult.The minerals in residues were in ultrafine particle size with high monomer dissociation degrees.In H_(2)O_(2)oxidation process,the self-decomposition and side reactions resulted in high consumption of H_(2)O_(2).In Na_(2)S_(2)O_(5)-air oxidation process,the time for complete process was long because of the reactions between Na_(2)S_(2)O_(5)and O_(2).Na_(2)SO_(3)oxidation method was found to be a new method for cyanide removal without air inflation device.The cyanide content was reduced to the national standard level in 90 min at pH 9.0 with optimum Na_(2)SO_(3)dose of 2.0 g/L.

功能性Fe_(3)O_(4)纳米颗粒在痕量农药残留分析中的应用研究进展

未被有效利用的农药经环境与膳食暴露,可能影响食品安全,进而在人体内形成微量残留,成为危害人体健康的潜在因素。相较环境水及水果蔬菜等常规样品而言,由于人体样本具有复杂的基质效应及农药痕量残留水平的特点,包括液-液萃取和固相萃取等在内的传统样品前处理方法很难实现对复杂基质中不同种类痕量农药的检测分析。为了解决复杂基质样本中痕量农药检测的难题,靶向性的纳米吸附剂被陆续开发出来。本文介绍了具备高效分离特性的纳米吸附剂——功能性Fe_(3)O_(4)纳米颗粒用于痕量农药残留分析的技术趋势,包括其磁核合成方式(化学共沉淀、热分解、溶剂热反应等)、功能基团修饰类型(天然高分子聚合物、碳基材料、金属有机框架材料和无机材料等)、应用基质(环境水、水果蔬菜及生物样本)以及适用农药种类和检测分析效率;重点介绍了该类纳米颗粒的靶向性制备原理、应用特点和最新研究进展,分析了目前基于功能性Fe_(3)O_(4)纳米颗粒分析痕量农药过程中尚待改进的问题和未来应用前景,以期为新型纳米吸附方法的拓展性应用提供理论参考。

RESIDUAL STRENGTH AND FATIGUE LIFE OF 2-D AND 3-D CARBON FABRIC COMPOSITES

The fatigue behavior and damage mechanisms of 2 D and 3 D carbon/epoxy composites with approximately the same 51% fiber volume fraction were investigated. A test program was conducted on fatigue residual strength and fatigue life under constant amplitude tensile fatigue loading. Equations of predicting the fatigue life for both 2 D and 3 D composites were provided. Comparison of the 2 D and 3 D composites indicated that due to the through thickness reinforcement, the 3 D composite has considerably better fatigue performance. Comparison of experimental data with calculation results shows good agreement, thus confirming the usefulness of the predictions.

Sand-bed defect recognition for 3D sand printing based on deep residual network

The 3D sand printing(3DSP),by binder jetting technology for rapid casting,has a pivotal role in promoting the development of the traditional casting industry as a result of producing high-quality and economical sand molds.This work presents an approach for monitoring and analyzing powder sand-bed images to serve as a real-time control system in a 3DSP machine.A deep residual network(ResNet)is used to classify the defects occurring during the powder spreading stage of the process.Firstly,a pre-trained network was applied as the initial parameter;then it was fine-tuned on the labelled defective sample dataset to accomplish the task,which defines the sand-bed defects induced in the 3DSP processing.Furthermore,the recognition and positioning of sand-bed defects were readily achieved by dividing the sand-bed images into blocks.Experiments show that the fine-tuned network has a 98.7%classification accuracy on the validation dataset of sand-bed defects and 95.4%recognition accuracy for the sand-bed images.