Surface modification of nanocrystalline cellulose and its application in natural rubber composites

As a biopolymer with high mechanical strength, nanocellulose was generally considered as a green filler for reinforcing polymer. In this study, nanocrystalline cellulose (NCC) isolated from softwood pulp was successfully modified by cetyltrimethyl ammonium bromide (CTMAB), a cationic surfactant, and the modified nanocrystalline cellulose (m-NCC) was used to reinforce natural rubber (NR). In this composite architecture, it was found that when the filler content was 5 or 10 phr, the surface modification of NCC improved the dispersion state of NCC in NR matrix and the interfacial interaction between NR and NCC. Therefore, the NR/m-NCC composites exhibited outstanding mechanical properties, and its tensile strength, elongation at break and tear strength was increased by 132.8, 20, and 66.1%, respectively, compared to pristine NR composites. Besides, the modified NCC could accelerate the vulcanization and improve wet-skid resistance and aging resistance of NR composites. It is envisioned that the modified NCC has the potential to be generalized to manufacturing other polymer matrix composites strengthened with nanocellulose.     

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.     

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。     

城市竞争力和城市经营与城市规划之间的关系

论述了城市经营与城市竞争力之间的连锁关系,反驳了一些对城市经营怀疑的观点,指出城市政府并不是参与竞争,而是引导竞争,提出只有制度创新才能使城市政府真正适应市场经济条件的城市经营任务,从而为城市竞争降低成本,实现对城市公共资源的合理运作,最大程度地发挥其效能。     

晶粒尺寸对纳晶双峰材料断裂韧性的影响

为了描述由纳晶基体和粗晶颗粒组成的纳晶双峰材料的断裂韧性,通过建立一个粘聚力模型来研究纳晶双峰材料的临界应力强度因子K_(IC)(表征材料断裂韧性)。考虑到纳晶双峰材料的一个典型情况:裂纹位于2个纳晶颗粒的交界面处,裂纹尖端与粗晶粒的晶界相交,假设粘聚区的尺寸等于纳晶颗粒的尺寸d。裂纹的钝化和扩展过程受位错和粘聚力的共同影响,刃型位错是从粘聚力裂纹的尖端发射,该过程对裂纹产生屏蔽效应。模型计算结果显示:当粗晶颗粒尺寸D确定时,K_(IC)随着纳晶材料晶粒尺寸d的增大而增大;当纳晶材料晶粒尺寸d确定时,K_(IC)随着粗晶材料晶粒尺寸D的增大而增大;相对于纳晶颗粒的尺寸,断裂韧性对粗晶晶粒的尺寸更加敏感。     

纳米晶Cu-50Ag合金在酸性溶液中腐蚀行为研究

与粉末冶金法(PM)制备的常规尺寸合金对比,研究了通过热压液相还原法(LPR)和机械合金化法(MA)合成的Cu-50Ag合金粉末制备的块体纳米晶Cu-50Ag合金在酸性溶液中的腐蚀行为。结果表明:在Na_2SO_4溶液中加入H_2SO_4后,3种合金的腐蚀速度均加快。随着H_2SO_4浓度的增加,PMCu-50Ag和LPRCu-50Ag合金的腐蚀速度均未发生明显变化,而MACu-50Ag合金的腐蚀速度则加快。在Na_2SO_4溶液中,3种合金均未出现钝化现象,随着H_2SO_4的加入,合金出现了钝化现象。3种合金的腐蚀速率按PMCu-50Ag,LPRCu-50Ag和MACu-50Ag合金的顺序增加,其中LPRCu-50Ag合金的腐蚀速度略大于PMCu-50Ag合金,但明显小于MACu-50Ag合金。     

Ti-5.8Al-4.8Sn-2Zr-1Mo-0.35Si-0.70Nd合金中富钕稀土相研究

针对Ti-5.8Al-4.8Sn-2Zr-1Mo-0.35Si-0.70Nd粉末冶金高温钛合金中富钕稀土相的形成、尺寸、分布、形态、长大及结构特征进行了系统研究。结果表明:快速凝固态高温钛合金粉末中稀土相为液态析出相,其尺寸大部分在50~250 nm之间,弥散分布在基体中;晶内稀土相多为球状,晶界稀土相多为椭球状,其长轴平行于晶界;TEM观察到的稀土相的尺寸和分布与理论计算相符合;快速凝固高温钛合金粉末经过700~1000℃/110 MPa/0.5 h热等静压成形后,快速凝固过程中已析出的稀土相尺寸变化不大;同时细小的稀土相从过饱和的基体中大量固相析出;经过1200℃/140 MPa/3 h热等静压成形后,稀土相颗粒尺寸大部分在150~500 nm之间,有明显长大;稀土相的高分辨图像及同心衍射环花样表明,快速凝固高温钛合金粉末中的稀土相由5~10 nm的纳米晶组成,经过1200℃热等静压成形处理后的稀土相仍由纳米晶组成,而且纳米晶的尺寸没有明显变化;但是稀土相的"基体"上明显出现富Sn元素的"第二相"颗粒,结构变得复杂。     

纳米金刚石膜的成核及生长特性研究

采用直流等离子体喷射化学气相沉积(DC arc pla sma jet)系统制备了纳米金刚石膜(NCD),研究了不同的金刚石成核剂溶液对NCD 膜的成核及生长的影响。研究表明,在成核剂溶液中添加二甲基亚砜(DMSO)后成核密度明显 得到提高,而 且制备的NCD膜晶粒分布均匀、致密。当金刚石粉体作为成核剂时,随着其粒径 的增大,NCD膜成核密度下降,晶粒的尺寸均匀性也变差,而粒径为5nm的金刚石纳米粒 子作为成核剂时,NCD膜晶粒间结合致密、颗粒分布均匀。最后,选择5nm的金刚石纳米 粒子和丙酮/DMSO配制的分散液作为成核剂配方,经过60min的生长 ,制备了粒径为50～70 nm的结晶性和品质良好的NCD膜,适用于高频声表面波(SAW)器件及各种光学窗口的研制。