Evolution of aluminum nitride nanostructures from nanoflower to thin film on silicon substrate by direct nitridation of aluminum precursor

Herein we demonstrate a convenient regulation of several aluminum nitride nanostructures through direct nitridation of aluminum precursor under different conditions. Different AlN nanostructures including conic nanoflowers, nanowires, quasi-aligned nanocones and polycrystalline thin film have been obtained on the Au-coated Si substrates just simply by decreasing the reaction temperature or changing the reaction procedure, and a four-stage growth mechanism is hereby deduced. The conic nanoflower composed of AlN nanocones is an interesting geometry. The photoluminescence and field emission measurement revealed that these AlN nanoflowers own a broad blue emission band and a rather good field emission property, suggesting the potential applications in light and field emission nanodevices.     

Reactions of metal chlorides with hexamethyldisilazane: Novel precursors to aluminum nitride and beyond

Metal nitrides are intensely investigated because they can offer high melting points, excellent corrosion resistance, high hardness, electronic and magnetic properties superior to the corresponding metals/metal oxides. Thus, they are used in diverse applications including refractory materials, semiconductors, electronic devices, and energy storage/conversion systems. Here, we present a simple, novel, scalable and general route to metal nitride precursors by reactions of metal chlorides with hexamethyldisilazane [HMDS, (Me₃Si)₂NH] in tetrahydrofuran or acetonitrile at low temperatures (ambient to 60°C/N₂). Such reactions have received scant attention in the literature. The work reported here focuses primarily on the Al-HMDS precursor produced from the reaction of AlCl₃ with HMDS (mole ratio = 1:3) characterized by matrix-assisted laser desorption/ionization-time of flight, Fourier-transform infrared spectroscopy, thermogravimetric analysis-differential thermal analysis, and multinuclear nuclear magnetic resonance spectroscopy (NMRs) for chemical and structural analyses. The Al-HMDS precursor heated to 1600°C/4 h/N₂ produces aluminum nitride, characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and magic-angle spinning NMR. On heating to 800–1200°C/4 h/N₂, the precursor transforms to an amorphous, oxygen-sensitive powder with very high surface areas (>200 m²/g) indicating nanosized particles, which can be used as additives to polymer matrices to modify their thermal stabilities. Al₂O₃ is also presented in the final product after heating, due to its high susceptibility to oxidation. This approach was extended via proof-of-concept studies to other metal chloride systems, including Zn-HMDS, Cu-HMDS, Fe-HMDS, and Bi-HMDS. The formed precursors are volatile, offering the potential utility as gas-phase deposition precursors for their corresponding metal nitrides.     

二维石墨相氮化碳纳米片的制备及其光催化性能

摘要：利用水热反应法,将三聚氰胺悬浊液在200 ℃下反应生成中间产物,然后煅烧中间产物直接制成了二维石墨相氮化碳g-C3N4纳米片（WCN）,并与本体g-C3N4(CN)、传统热氧剥离法得到的g-C3N4纳米片（OCN）进行了比较。采用SEM、XRD、FTIR、Raman、AFM、PL仪等对催化剂进行了表征,探讨了催化剂的光电化学性能和光催化性能。结果表明：两种方法均实现了对CN的剥离,WCN和OCN二维纳米片与CN 晶体结构和组成相同,WCN和OCN的比表面积分别是CN的4倍和3倍。光电化学分析显示WCN有更好的载流子的迁移与分离效率,具有较好的光催化活性。在可见光条件下,WCN对亚甲基蓝（MB）的光催化降解率达到82％,分别是OCN和CN的2.4 倍和6.7 倍,光催化降解过程符合一级动力学方程。WCN具有优良的稳定性和可重复利用性能。     

二维石墨相氮化碳纳米片的制备及其光催化性能

利用水热反应法将三聚氰胺悬浊液在200℃下反应生成中间产物,中间产物经煅烧直接制成了二维石墨相氮化碳(g-C3N4)纳米片(WCN),并与本体g-C3N4(CN)、传统热氧剥离法得到的g-C3N4纳米片(OCN)进行了比较.采用SEM、XRD、FTIR、Raman、AFM、PL对样品进行了表征,探讨了其光电化学性能和光催化性能.结果表明,两种方法均实现了对CN的剥离,WCN和OCN与CN的晶体结构和组成相同,WCN和OCN比表面积分别是CN的3.6倍和3.1倍.光电化学分析显示,WCN具有更好的载流子迁移与分离效率,具有较好的光催化活性.可见光照射下,WCN对亚甲基蓝(MB)的光催化降解率达到82.0％,分别是OCN和CN的2.4倍和6.7倍,光催化降解过程符合一级动力学方程.WCN具有优良的稳定性和可重复利用性能.     

Effects of phase separation on stress development in polymeric coatings

A cantilever deflection technique was used to monitor stress in situ during drying of cellulose acetate coatings. Porosity was introduced in some coatings using dry-cast phase separation. Stress and weight loss profiles for dense coatings, a coating that contained small (∼1 μm) pores, and a coating that contained small (∼1 μm) pores and macrovoids (∼200 μm) are compared. In-plane tensile stress after drying ranged from 30 MPa (dense coatings) to 5 MPa (macrovoid-containing coating). The stress profiles for dense coatings feature a period of rapidly and then slowly increasing stress due to constrained shrinkage. For a coating that formed small pores, drying and stress development are delayed, stress rises and then drops a small amount due to capillary pressure relief. The stress profiles for the small pore and macrovoid-containing coatings are similar, except for a stress plateau at early stages of drying, which may be caused by macrovoid growth.     

Mechanical and fatigue strengths of silicon nitride ceramics in liquid aluminum alloys

Although the silicon nitride ceramic (Si₃N₄) has a high mechanical strength even at high air temperature, much reduction in the material strength occurs in liquid aluminum alloys. The bending strength of the ceramic in molten Al alloys is about 20% lower than that obtained in an air temperature of 750 °C. Moreover, a significant reduction of the fatigue strength occurs in the Al alloy melt. The change of mechanical properties of Si₃N₄ ceramic in the melt also depends on the amount of iron in the molten aluminum alloy; a large amount of iron makes the fatigue strength low. The reduction in the material strength is attributed to the change of material properties caused by the chemical reaction between iron and silicon nitride. Details of the chemical reaction in Si₃N₄ ceramic are discussed in the present work.     

Preparation and properties of hollow BN fibers derived from polymeric precursors

Boron nitride (BN) complex precursors were synthesized from a mixture of 2,4,6-tri(methylamino)borazine ([CH₃(H)N]₃B₃N₃H₃) and tris(methylamino)borane ([B(NHCH₃)₃]). The reactions between the two mixtures aimed at producing polymeric green fibers via a melt-spinning process and producing novel hollow BN ceramic fibers with various shell thicknesses by curing and pyrolysis. The properties and pyrolytic process of the complex precursors were characterized by TG-DSC-FTIR-MS online coupling analysis. The microstructure, solid phase, and morphologies of hollow BN fibers were investigated using XRD, SEM, TEM, and elementary analysis. Results showed that the synthesized fibers were highly pure and uniform with a mean diameter of 9 μm. The dielectric properties of the BN fibers were excellent with a dielectric constant of 2.90 and a dielectric loss factor of 0.00064. These results confirm that the ceramic fibers synthesized using the novel complex polymeric precursors indicate their adequate properties as micro-wave transparence reinforcements.     

复合铝絮凝剂的制备及其脱色性能研究

以三氯化铝和有机高分子PGA为原料,制备了复合絮凝剂CPAC,并探讨了该种絮凝剂对模拟染料废水的脱色作用.研究表明,在同等铝盐投量的情况下,相对于PAC而言,CPAC脱色效率明显提高,且脱色率随PGA与铝盐的质量比(O/A)增高而上升.以活性艳红K-2BP染料为例,铝盐投加质量浓度6.8 mg/L时,PAC脱色率75.5%,CPAC(O/A=0.05)脱色率为81%,CPAC(O/A=0.1)脱色率为86%.3种染料中,CPAC对分散黄G的脱色效果最好,铝盐投加质量浓度为3.3 mg/L时脱色率达98%.     

Ion implantation induced phase transformation in carbon and boron nitride thin films

The mechanism behind energetic ion impact induced stress reduction in highly stressed tetrahedral amorphous carbon and cubic boron nitride thin films is investigated by real time in situ spectroscopic ellipsometry and ex situ electron microscopy. Highly stressed carbon and boron nitride films were grown by filtered cathodic vacuum arc and RF magnetron sputtering, respectively. The films were then implanted by 5–10 keV argon ions and the film optical properties and thickness monitored in situ by spectroscopic ellipsometry. In both cases the films were observed to expand due to a reduction in the density of the ion-modified layer. Cross-sectional transmission electron microscopy and electron energy loss spectroscopy of the carbon films showed that this reduction in density is associated with a conversion of diamond-like bonding to graphite-like bonding. In situ stress measurements performed on the boron nitride films revealed a simultaneous reduction in stress with expansion of the material.     

改性六方氮化硼/水性聚氨酯涂料的制备与性能

以聚甘油-10(PG)作为稳定剂,超声下对六方氮化硼(h-BN)进行剥离和改性制得PG功能化的少层h-BN纳米粒子(GB).利用GB与水性聚氨酯(WPU)共混得到WPU/GB.通过FTIR、TG、AFM和TEM对GB进行了表征,证实了少层GB的成功制备.动电位极化和电化学阻抗谱测试表明,WPU/GB涂层比纯WPU涂层具有更高的耐腐蚀性能.GB含量为1.0％(以WPU的质量为基准,下同)的WPU/GB1.0复合涂层的耐腐蚀性能最好,极化电阻为1.33×107?·cm2,阻抗|Z|可达到5.37×107?·cm2.此外,与纯WPU相比,WPU/GB1.0腐蚀电流密度从2.64×10–8 A/cm2减小至3.32×10–9 A/cm2,腐蚀电压从–0.309 V增大到–0.037 V,保护效率高达98.74％.     

Production of carbon nanostructures by arc synthesis in the liquid phase

The advantages of arc synthesis of carbon nanostructures in a liquid medium have been investigated. Changes in the chemical compositions of the reagents (electrodes and a medium), the high temperature and pressure of the medium, the high cooling rate and the growth of structures in the reaction zone allow the materials with unique properties to be produced. The production of a purer product makes this efficient method promising for the synthesis of carbon nanostructures for different applications.     

Effect of surface modification of aluminum nitride on electrical and thermal characterizations of thermosetting polymeric nanocomposites

Thermally conductive composites and nanocomposites composed of epoxy resin as base matrix and aluminum nitride (AlN) as micro and nanofiller have been studied at variable temperatures and loading of AlN. To improve the dispersion of the filler within the polymer matrix, AlN was surface modified with silane‐coupling agent. Thermogravimetric analysis confirmed the interfacial bonding of epoxy‐ and silane‐modified AlN. The dielectric properties of epoxy/AlN composites and nanocomposites have been studied at variable percentage of filler. Test result indicated an increase of thermal conductivity of the composites at 20 wt% of AlN. Also, silane‐treated composites exhibited improved electrical conductivity properties, whereas the electrical insulation property decreased in terms of dielectric strength and resistivity. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Effects of titanium and aluminum incorporations on the structure of boron nitride thin films

Boron nitride (BN)-based composite thin films have been prepared by ion-beam-assisted deposition (IBAD) employing two electron-beam evaporators. Approximately 3–5 at.% of either Ti or Al was incorporated into the BN composite films. Fourier-transform infra-red (FTIR) spectroscopy was used for phase identification of the BN composite films. The influences of the Ti and Al additions on the cubic phase formation in the BN films are reported. It has been found that Al incorporation has a strong negative effect on cubic BN (cBN) formation. No cubic phase can be obtained under the presently chosen ion-bombardment parameters. However, the disturbance of 3∼5 at.% Ti addition, depending on the preparation conditions for the BN thin films, only shifts the threshold of the ion/atom ratio of the IBAD process, which is required for cBN formation to a higher value. In order to understand the different behaviors of the Ti and Al incorporations, the chemical states of the Ti and Al additions in the BN composite films were examined by X-ray photoelectron spectroscopy (XPS), indicating preferential formation of TiB₂ and AlN, respectively.     

Preparation of silicon carbide-silicon nitride fibers by the pyrolysis of polycarbosilazane precursors: A review

The development of silicon carbide-silicon nitride (SiC-Si₃N₄) fibers by the pyrolysis of polycarbosilazane precursors that was carried out in this laboratory is reviewed. Precursor resin, which was prepared by heating tris(N-methylamino)methylsilane or tris(N-methylamino)phenyl-silane to about 520°C, was drawn into fibers from the melt and then made unmeltable by humidity conditioning at 100°C and 95 percent relative humidity. The humidity-treated precursor fibers were pyrolyzed to ceramic fibers with good mechanical properties and electrical resistivity. For example, SiC? Si₃N₄ fibers derived from tris(N-methyl-amino)-methylsilane had a tensile rupture modulus of 29 × 10⁶ psi and electrical resistivity of 6.9 × 10⁸ Ω-cm, which is 10¹² times greater than a value obtained for graphite fibers.     

Fabrication of aluminum nitride coatings by electrophoretic deposition: Effect of particle size on deposition and drying behavior

Electrophoretic technique was used to deposit micro- and nano-sized aluminum nitride coatings on stainless steel surfaces by using a well-dispersed stable suspension produced by addition of AlN powder plus a small amount of iodine to ethanol. Parabolic regime governed the deposition. Electrophoretic deposition for 240 s at 100 V resulted in formation of a uniformly dense film on the top, but a porous inhomogeneous layer at the bottom. This was attributed to fast deposition of coarse particles and/or agglomerates at large electric fields. After drying, micro-sized particles led to a uniform crack-free interface while nano-particles resulted in fragmented non-cohesive layers. Weight loss measurements revealed higher drying rates for micro-layer as compared to nano-cover. This seemed owing to the larger pore sizes and lower specific surfaces of the former. Stress inducement by lateral drying of small capillaries led to crack initiation from the edges and its propagation across the surfaces. This resulted in fragmentation of the samples due to their delamination. Effect of deposition rate on particles packability was also investigated.     

铝合金表面耐久性超疏水防护膜的制备与表征

通过酸刻蚀-沸水浴处理构筑微纳米分级结构,进而通过喷涂含有磷酸铝胶黏剂(AP)和低表面能物质——全氟辛基三氯硅烷(PFOTS)的悬浮液增强结合力并降低表面能,从而在国产7B04铝合金表面制备了耐久性超疏水防护膜。利用场发射扫描电子显微镜(FESEM)、X射线光电子能谱仪(XPS)、傅里叶变换红外光谱仪(FTIR)、接触角测试仪(CA)、电化学阻抗谱(EIS)等技术以及多种环境模拟实验对样品进行了表征,结果显示,制备的防护膜表面水静态接触角(WCA)高达158.4°,滑动角(SA)为0°,呈现出超疏水和低黏附性;膜层电阻(Rc)约为101.55 kΩ·cm2,在NaCl腐蚀介质中的电荷转移电阻(Rt)增大了近2个数量级,表现出优异的防护性能;样品可以经受多种破坏,具有理想的机械耐久性、化学耐久性和环境耐久性。     

Preparation and characterization of durable superhydrophobic protective coatings on aluminum alloy

The durable superhydrophobic protective coatings on the 7B04 aluminum alloy surface was prepared by using acid etching and boiling water bath to construct micro-nano hierarchical structure, and then spraying suspension containing aluminum phosphate adhesive (AP) and perfluorooctyltrichlorosilane (PFOTS) to increase adhesion and reduce surface energy. The samples were characterized by field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), contact angle measurement (CA), electrochemical impedance spectroscopy(EIS) and a variety of the environmental simulation experiments. The results showed that the static water contact angle (WCA) of the surface is 158.4° and the slide angle (SA) is about 0°, suggesting superhydrophobicity and low adhesion to water. The coating resistance (R_c) was as high as 101.55 kΩ· cm² and the charge transfer resistance (R_t) in NaCl corrosion medium increased by nearly two orders of magnitude, showing excellent protective performance. The sample can withstand a variety of damages, with ideal mechanical durability, chemical durability and environmental durability.     

UVA and UVC modification of photo polymeric surface and application for flexographic deposition of thin coatings

The object of this research was to perform, characterize, and apply the functional modification of flexographic photo polymeric printing plate surface by UVA and UVC post‐treatments. Photo polymeric printing plates have an important application in functional printing, where new printing inks/coatings and substrate formulations are used and the specific qualitative requirements must be met. The limitations of materials and processes often require expensive reformulations of the functional inks to achieve printability. Results of this research showed that the modification of the photo polymeric printing plate surface at the end of its production process can be used to precisely adjust the printing ink transfer to the printing substrate and thus eliminate the need for changing the ink/coating composition. By applying specific UV post‐treatment, one can create a flexographic coating deposition system of tailored properties adjustable to variable reproduction systems with high quality requirements. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43526.     

Multicomponent phase equilibria of thin liquid films and their vapour

Subject of the paper are multicomponent phase equilibria between extremely thin liquid films and their vapour phase on curved or planar solid surfaces. The solid surface is either heated or cooled, so that the liquid films are evaporating or the vapour is condensing.The curvature of the film surface and long range molecular forces due to the van der Waals attraction acting over distances of about 0.2- between solid and liquid film can lead to a composition shift in liquid and vapour phase compared to the composition that would be observed at planar and not extremely thin liquid films in equilibrium with their vapour phase.The Kelvin equation for the interfacial pressure is derived, as well as the equations for the composition shift. As a numerical example shows the van der Waals forces considerably influence the pressures at the liquid-vapour interface. Responsible for the composition shift is a dimensionless thermodynamic quantity . For small values D_i→0, liquid-vapour phase equilibria become identical with those of planar surfaces. For D_i?0 the vapour phase contains less and for D_i?0 more of the lighter volatiles than planar interfaces.     

Synthesis and optical properties of II-VI 1D nanostructures

1D nanostructures from II-VI semiconductors have been demonstrated to exhibit outstanding optical properties with strong promise for novel optoelectronic devices with augmented performance and functionalities. Herein, we present a comprehensive review discussing important topics pertinent to the fundamental properties and applications of II-VI 1D nanostructures. With practical applications in mind, the considerations, principles and experimental techniques on the sample preparation of high quality 1D nanostructures are highlighted. Fundamentals on the optical properties of II-VI materials, along with relevant investigation techniques and recent progress in the field, are also extensively discussed. With the steady development of their synthesis, characterization and device fabrication, it is strongly expected that II-VI 1D nanostructures will assume a unique position in future technology.