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1.
以成分为Nd28.5Fe余B1.0Ga0.3Nb0.3 (%)的钕铁硼合金锭作为原料,采用 HDDR 工艺制备各向异性钕铁硼磁粉。重点研究了HDDR工艺过程中钙添加量对磁粉氧含量和磁性能的影响。结果表明,在不改变原有HDDR工艺参数的基础上,添加少量金属钙即可显著降低磁粉的氧化程度,大幅提高磁粉的磁性能。钙添加量小于0.1%时,由于磁粉的氧含量仍然较高而导致内禀矫顽力Hcj和最大磁能积(BH)max低劣;钙添加量大于0.3%时,由于磁粉中残留的非磁性相过多以及颗粒团聚加重会导致磁性能指标全面下降;钙添加量为0.1 ~ 0.3%是适宜的,在钙添加量为0.2%时,磁粉的综合磁性能最佳,其Br为1.37 T、Hcj为1 296 kA/m、(BH)max为340 kJ/m3。  相似文献   
2.
再生骨料混凝土是一种环保材料,然而由于再生骨料的固有缺陷,导致其很难在结构工程中推广应用。纳米二氧化硅作为一种混凝土辅助胶凝材料,已经在普通混凝土中得到了充分的研究,但其用于改性再生骨料混凝土的研究较少。利用万能试验机、扫描电镜及X射线衍射仪,从工作性能、抗压性能、抗拉性能和微观形貌等方面,分析了不同掺量纳米二氧化硅对再生骨料混凝土改性的影响,深入探讨了利用纳米二氧化硅对再生骨料混凝土进行改性的可行性。试验结果表明:纳米二氧化硅具有高活性和填充效应,促进了水泥的水化反应,对再生骨料混凝土早龄期抗压性能提升明显;此外,纳米二氧化硅由于其颗粒尺寸较小,填充了再生骨料的微裂纹和孔隙,降低了再生骨料混凝土的脆性,对再生骨料混凝土后龄期抗拉性能提升显著。值得注意的是,纳米二氧化硅具有团聚效应,需要采用减水剂和预拌的方法提升其工作性能,从而推广其适用性。  相似文献   
3.
Thermal action in extraction process had effects on characteristic tryptic peptides identification and gelling properties of porcine gelatin. SDS-PAGE, HPLC-LTQ/Orbitrap high-resolution mass spectrometry, texture analyser and rheometer were used to evaluate collagen depolymerisation degree, characteristic tryptic peptides and gelling properties of gelatins prepared in various thermal actions. Results showed that with increasing temperature and time, depolymerisation degree enlarged, while gel strength, gelling and melting temperature decreased. Mass spectra showed that 47 and 49 common characteristic tryptic peptides were identified in gelatins extracted at 50 °C and 100 °C with various times, respectively. Moreover, 34 common characteristic tryptic peptides were identified in all gelatin samples. Further comparison between this work and our previous investigations yielded 20 common characteristic tryptic peptides, which stably exist in various thermal actions. These common characteristic tryptic peptides may be very helpful for the accurate authentication of porcine gelatin.  相似文献   
4.
采用2mT低磁场(low magnetic field,LMF)冷冻、0mT磁场(no magnetic field,NMF)冷冻和常规冷冻(conventional freezing,CF)技术对3 组鲢鱼肌原纤维蛋白进行为期28 d的冷冻实验。通过表面疏水性、巯基含量、溶解度、浊度、热稳定性、傅里叶变换红外光谱、内源性荧光光谱和紫外吸收光谱各项指标考察蛋白的结构和功能性质变化。结果表明:施加低磁场冷冻可以抑制蛋白聚集和内部疏水基团的暴露,且能抑制α-螺旋的展开,减弱α-螺旋向β-折叠转变的能力,并维持良好的二、三级结构稳定性;CF组的蛋白总巯基含量、溶解度和浊度与NMF组相比无显著差异,由于冷冻温度较低,对蛋白聚集和内部疏水基团的暴露有一定的抑制作用,同时也使得蛋白结构变得松散不稳定;与CF组相比,LMF组同样显示出对蛋白的结构和功能有较好的保护和改善作用。总体来说,低磁场冷冻可以抑制肌原纤维蛋白变性并维持良好的结构和功能,且与常规冷冻(-30 ℃)相比,低磁场冷冻(-20 ℃、2 mT)可以节约10 ℃的冷冻温差,预测其具有一定的节能潜力。  相似文献   
5.
Gelatin is one of the most important multifunctional biopolymers and is widely used as an essential ingredient in food, pharmaceutical, and cosmetics. Porcine gelatin is regarded as the leading source of gelatin globally then followed by bovine gelatin. Porcine sources are favored over other sources since they are less expensive. However, porcine gelatin is religiously prohibited to be consumed by Muslims and the Jewish community. It is predicted that the global demand for gelatin will increase significantly in the future. Therefore, a sustainable source of gelatin with efficient production and free of disease transmission must be developed. The highest quality of Bovidae-based gelatin (BG) was acquired through alkaline pretreatment, which displayed excellent physicochemical and rheological properties. The utilization of mammalian- and plant-based enzyme significantly increased the gelatin yield. The emulsifying and foaming properties of BG also showed good stability when incorporated into food and pharmaceutical products. Manipulation of extraction conditions has enabled the development of custom-made gelatin with desired properties. This review highlighted the various modifications of extraction and processing methods to improve the physicochemical and functional properties of Bovidae-based gelatin. An in-depth analysis of the crucial stage of collagen breakdown is also discussed, which involved acid, alkaline, and enzyme pretreatment, respectively. In addition, the unique characteristics and primary qualities of BG including protein content, amphoteric property, gel strength, emulsifying and viscosity properties, and foaming ability were presented. Finally, the applications and prospects of BG as the preferred gelatin source globally were outlined.  相似文献   
6.
采用Gleeble-2000热模拟试验机对Mn18Cr18N高氮奥氏体不锈钢进行高温拉伸试验,利用扫描电镜-能谱仪对拉伸试样断口形貌及断口附近的显微组织进行观察,用Thermo-Calc软件计算试验钢的相变及析出相,研究了Mn18Cr18N高氮奥氏体不锈钢的高温力学性能。结果表明,试验钢的第Ⅰ脆性区>1200 ℃,第Ⅲ脆性区为850~950 ℃,未出现第Ⅱ脆性区,第Ⅰ脆性区的出现主要是在加热过程中试验钢由γ奥氏体向δ铁素体转变引起的,第Ⅲ脆性区的出现是因为沿晶析出M23C6、M2(C, N)等硬脆相引起的;试验钢的抗拉强度随着拉伸温度升高而降低,断面收缩率在1000~1200 ℃温度范围内逐渐增大并表现出极佳的热塑性,断面收缩率均在70%以上,温度超过1200 ℃后断面收缩率急剧下降;Mn18Cr18N高氮奥氏体不锈钢的热锻温度应选择在1000~1150 ℃之间,在此温度范围内试验钢的断面收缩率均在70%以上,并且可以避开第Ⅰ与第Ⅲ脆性区。  相似文献   
7.
研究了Ti-5Al-4Zr-10Mo-3Cr合金经过β相区固溶(880 ℃)、不同温度时效(540~620 ℃)处理后次生α相(αs)析出形貌及其对力学性能的影响。结果表明:随着时效温度由540 ℃升高至620 ℃,合金中析出αs相片层厚度由0.030 μm增加到0.142 μm,屈服强度由1353 MPa降低至1074 MPa,断后伸长率由2.5%升高至11.4%,即时效析出的微米级片层αs能够显著调控合金的力学性能。此外,时效温度升高使合金的拉伸断裂由沿晶脆性断裂为主转变为韧窝穿晶为主的韧性断裂方式。Ti-5Al-4Zr-10Mo-3Cr合金时效析出的片层状αs相的厚度大于0.1 μm,合金的断后伸长率≥6%。当时效温度为600 ℃时,合金的硬度为387 HV10,抗拉强度为1182 MPa,伸长率为8.5%,具有良好的强塑性匹配。  相似文献   
8.
采用叠轧焊接方法制备Al/IF钢多层复合材料,随后进行300~450 ℃退火处理,并对叠轧态和退火态的微观结构及力学性能进行分析。结果表明:叠轧态Al/IF钢多层复合材料的抗拉强度介于纯Al和IF钢之间,断裂总延伸率相对较低,退火后Al和IF钢层的硬变均高于其原材料;随着退火温度的增加,抗拉强度逐渐降低,断裂总延伸率呈先增加后减小的趋势,在350 ℃退火时,复合材料的综合力学性能最优。退火温度对Al/IF钢多层复合材料力学性能的影响主要体现在对Al层的影响上。  相似文献   
9.
《Soils and Foundations》2022,62(2):101106
This study investigates three aspects of the dynamic response of earth-core rockfill dams (ECRDs) under earthquake loadings, including induced shear strain, increased fundamental period, and shear modulus reduction. A database of the recorded ground motions of ECRD cases in Japan is analyzed to carry out this study. The required response parameters as mentioned above are extracted by analyzing the acceleration time histories recorded at the dams’ crests and foundations. Subsequently, statistical analyses are performed to achieve the objectives of this study. A graph is developed describing the change in the dam’s fundamental period with the induced shear strain, and it is observed that the increase of the dam’s period is dependent on the increase in the shear strain levels. A relationship is established to estimate the anticipated levels of shear strain from the intensity measure (IM) of the earthquake signals. In the proposed predictive relationship, a new IM is used that can adequately characterize the severity of an earthquake. Finally, a curve and a range are suggested for the average shear modulus degradation of the ECRD’s core materials. The presented empirical graphs and relationships in this study are valuable tools to obtain an appropriate perception of dams’ nonlinear behaviour under strong earthquake excitations.  相似文献   
10.
《Ceramics International》2022,48(1):130-136
A two-step mechanical milling followed by a reactive sintering process was used to synthesize Nano TiC-Graphene-Cu composites from a mixture of Cu, Ti, and Graphene (GN) powders in four different compositions, and effects of reinforcements content on the microstructure and mechanical properties were studied. The results showed that a part of GN reacted with Ti atoms in the matrix, leading to the successful formation of hybrid nanocomposites. Uniform distribution of in-situ TiC with nanometer size and unreacted GN in the nanostructured Cu (Ti) solid solution were obtained. Addition of high percentage of the reinforcements led to an increase in the porosity and microhardness, coarsening of TiC nanoparticles, and decreasing the grain size of the matrix after sintering. The simultaneous presence of GN and TiC nanoparticles in the Cu matrix improved the hardness and wear resistance and reduced the friction coefficient by self-lubricating behavior. The nanocomposite with the nominal composition of Ti-40 vol % TiC showed the highest wear resistance and the lowest friction coefficient.  相似文献   
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