Elastic modulus of nanocrystalline cemented carbide

The purposes of this work were to obtain the accurate elastic modulus of the nanocrystalline WC–Co cemented carbides, and to propose the mechanism for the difference of elastic modulus between the nanocrystalline and conventional polycrystalline cemented carbides. The nanocrystalline cemented carbide was prepared by spark plasma sintering (SPS) technique. The conventional polycrystalline cemented carbides were prepared by SPS and sinter-HIP techniques as references, respectively. The sintered cemented carbides were characterized by X-ray diffractometry, scanning electron microscopy and the transmission electron microscopy with precession electron diffraction technology. The elastic modulus was obtained by averaging the values measured with the continuous stiffness measurement method of the nanoindentation technology. The results show that the nanocrystalline cemented carbide has a relatively low modulus, which could be attributed to the more interface area and higher fraction ratio of the hcp cobalt phase caused by the rapid heating and cooling process during SPS.     

纳米微晶纤维素的表面基团及其改性

纳米微晶纤维素(Nanocrystalline Cellulose,NCC)是一种纤维素经酸水解后获得的棒状晶体,由于其原料丰富、可再生、生物兼容性好以及机械性能优良等特点,已成为纳米材料研究领域的热点。本文为探索其进一步改性应用,重点分析了NCC表面存在的基团种类,对其化学改性方法进行了概括,并对其进一步发展应用进行了展望。     

The influence of small hydrogen addition on the structural and magnetocaloric properties of high-purity nanocrystalline terbium

Hydrogen absorption often induces changes of various properties of rare-earth metals. In this paper, we study the influence of hydrogenation on the structural, magnetic and magnetocaloric properties of high-purity nanocrystalline terbium. Strong (00l) texture present in the parent Tb sample is practically destroyed after the hydrogenation procedure. We observe formation of agglomerates of different sizes and shapes depending on the hydrogen content in the samples. We find traces of β-hydride (TbH₂) in the main α-hydride TbH_x phase. For TbH_x with x = 0.25 and 0.5 at.H/f.u. The effect of hydrogenation on the magnetocaloric properties is studied in magnetic fields up to 9 T. The magnetocaloric effect decreases after hydrogenation. The -ΔS_M(T) curves feature a table-like effect in the vicinity of the magnetic phase transitions in magnetic fields exceeding 1 T.     

玉米纳米淀粉/纤维素纳米晶复合膜制备工艺优化

以玉米纳米淀粉为基质,甘油为增塑剂、纤维素纳米晶(CNC)为增强剂采用流延成膜法制备玉米纳米淀粉/CNC复合膜,成膜基质和干燥温度对纳米淀粉成膜影响较大,聚氯乙烯基质板对纳米淀粉成膜较好,干燥温度25℃,成膜平整光滑;单因素探讨了玉米纳米淀粉、甘油和CNC含量对纳米淀粉/CNC复合膜强度性能的影响,在该基础上进行三因素三水平正交试验,正交优化研究表明,对玉米纳米淀粉/CNC复合膜的抗张强度影响为:CNC甘油玉米纳米淀粉,正交试验优化结果为CNC 2%,甘油8%,玉米纳米淀粉10%,制备的玉米纳米淀粉/CNC复合膜抗张强度达20.18 MPa;FTIR分析表明玉米纳米淀粉、甘油、CNC混合均匀,形成了均一稳定的纳米淀粉/CNC复合膜。该玉米纳米淀粉/CNC复合膜在食品药品可食性包装领域具有较好的应用前景。     

纳米晶NiCrC涂层长时加热的显微组织和硬度变化

目的 探讨纳米晶NiCrC涂层长时高温条件下的显微组织和硬度演变规律。方法 采用超音速火焰（HVAF）喷涂低温球磨纳米晶合金粉末（液氮介质）制备了纳米晶NiCrC涂层，在650 ℃空气环境中对涂层进行总时长200 h的等温热处理。采用扫描电子显微镜、X射线衍射仪、透射电子显微镜、维氏显微硬度计等方法，对涂层样品的显微组织、物相构成、晶粒尺寸和显微硬度进行了测试分析，同时对原料粉末也进行了相同条件下的对比分析。结果 NiCrC涂层显微组织的主要特征为：纳米晶金属相基体中弥散分布着细小的碳化物颗粒。在保温过程中，纳米晶涂层发生了再结晶和晶粒长大，并伴随有合金基体的脱溶及碳化物的析出、相变和后续生长等现象。该涂层显示出优良的高温热稳定性，在650 ℃保温50 h后，晶粒平均尺寸由初始态的41 nm增长至相对稳定值约100 nm。保温后涂层的硬度总体有所提升，由初始的697HV300（15 s）先升高至最大值801HV300（15 s），而后降至相对稳定值729HV300（15 s）左右。纳米晶粉末的组织和硬度变化特点与涂层相似。结论 在650 ℃保温过程中，纳米晶NiCrC涂层中的合金相脱溶和晶粒长大导致涂层金属相基体的软化，但细小碳化物颗粒的析出强化以及由相变（Cr7C3→Cr23C6）引起的体积分数增加，不但补偿了基体的软化，而且使涂层的整体硬度有所提高。     

纳米粉体粒度特性表征方法讨论

实验中采用不同的方法对四种ZrO2纳米粉体的颗粒特性进行了表征。对颗粒呈现球形、不发生硬团聚的微小粒子，例如YSZ—KD试样，一次颗粒粒度为10～15nm，比表面为64．2m^2／g，采用XRD获得的微晶粒子尺寸与TEM和BET方法获得的颗粒尺寸相一致。由于比表面高，颗粒之间容易发生静电力、范德华力和液桥力的作用而软团聚在一起，其团聚系数较大为62．5，粒度分布宽度为14．58。TEM和BET与XRD方法获得的颗粒尺寸出现偏差，说明YSZ—HW1、YSZ—TH试样中出现了基元为2～3的多晶颗粒，多晶颗粒存在使得颗粒体偏离球形。团聚系数为25．71，粒度分布宽度为18．94的YSZ—HW1试样中仍存在较多的软团聚体，团聚系数为6．89，粒度分布宽度为8．91的YSZ—TH试样中软团聚状况明显较少。YSZ—HW2试样中TEM和BET与XRD方法获得的颗粒尺寸出现很大偏差，说明其中存在较多的硬团聚体，硬团聚体使得颗粒呈现不规则外形，其比表面小，活性低，表现为团聚系数小，粒度分布窄。     

Fe73.5Cu1Nb3Si13.5B9纳米晶软磁粉体的制备工艺与微波电磁性能

研究热处理工艺、材料粒度对Fe73.5Cu1Nb3Si13.5B9材料微波电磁性能的影响,对该类材料的微波电磁性能和吸波性能进行测试。结果表明:热处理工艺对材料的微波电磁性能产生较大的影响,达到晶化条件的热处理工艺有利于提高材料的电磁性能;随着材料粒度的减小,微波电磁性能提高,电磁参数之间的匹配性提高;Ⅴ级粒度材料的最低反射率达到-12 dB,低于-5 dB的频宽达12.5 GHz。     

NCC负载纳米TiO2复合膜的表征

采用交替沉积自组装的方法制备聚乙烯醇（PVA）/纳米纤维素（NCC）-纳米TiO2/PVA复合膜,用傅里叶变换红外光谱（FT-IR）和扫描电子显微镜（SEM）表征,结果表明PVA/NCC-纳米TiO2/PVA复合膜形貌规整,NCC负载纳米TiO2粒子只是物理共混,没有化学键合.性能分析结果表明PVA/NCC-纳米TiO2/PVA复合膜在紫外光区有较强吸收,较高的拉伸强度109.5 MPa,且比PVA膜热稳定性好,热分解温度提高约20℃.     

Fe82Nb6B12合金表面纳米多孔结构的形成及电催化析氢性能的研究

目的增加条带表面积,提高电催化析氢活性。方法采用真空激冷装置制备Fe_(82)Nb_6B_(12)前驱体条带,通过控制铜辊转速得到α-Fe纳米晶/非晶双相结构。利用α-Fe纳米晶与非晶基体在0.5 mol/L H_2SO_4溶液中腐蚀性能的差异,通过脱合金法得到非晶纳米多孔结构。使用XRD、DSC、SEM、EDS等表征手段以及电化学测试方法,研究铜辊转速、脱合金时间对物相、成分、形貌及电催化析氢性能的影响。结果 1kr/min样品完全晶化,2~3 kr/min样品为α-Fe纳米晶/非晶双相合金,且随着铜辊转速增大,前驱体条带中α-Fe纳米晶含量减少。脱合金后成功制备了非晶纳米多孔结构,铜辊转速越大,孔径越小,比表面积越小。4 kr/min样品为非晶态,脱合金后没有得到多孔结构。2 kr/min多孔结构的析氢性能最好,在电流密度为10 mA/cm~2时的过电位为220 mV,塔菲尔斜率为105 mV/dec。结论采用甩带法可以制备具有α-Fe纳米晶/非晶双相结构的Fe_(82)Nb_6B_(12)合金。通过α-Fe纳米晶的选择性腐蚀,在条带表面得到纳米多孔结构,条带比表面积显著改善,从而提高了其析氢性能。     

Synthesis of Dy2O3 nanoparticles via hydroxide precipitation： effect of calcination temperature

This work described the preparation of dysprosium oxide, Dy2O3, nanoparticles using the homogeneous precipitation method. Dy3+ ions were precipitated using NaOH solution. The obtained product was filtered, dried, and then calcined for 1 h at the temperature range of 300–700 °C in static air. The calcination temperature of the Dy-precursor was chosen based on its decomposition as indicated by the TGA analysis. The crystalline structure and surface morphology of the calcined solids were studied by X-ray diffraction(XRD), field emission scanning electron microscopy(FE-SEM), transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy(XPS). The obtained results revealed that Dy2O3 with crystallites size of 11–21 nm was formed at 500 °C. Such value increased to 25–37 nm for the sample calcined at 700 °C.