Ultrasound-enhanced milling in the synthesis of phase-pure,highly crystalline ZnAl-layered double hydroxide of low Zn(II) content

Dry milling followed by ultrasonic irradiation in the presence of small amounts of aqueous NaOH, was used to synthesise ZnAl-layered double hydroxide (LDH). The synthetic conditions were optimised and the Zn(OH)₂, ZnO, and Al(OH)₃ contaminants were removed by rinsing with aqueous NH₃ solution from the sample prepared in the optimum conditions. Thus, phase-pure ZnAl-layered double hydroxide was obtained with high crystallinity. All materials produced during the syntheses were characterised by X-ray diffractometry, and a rose-like morphology was observed by scanning electron microscopy in the phase-pure sample. By changing the initial Zn/Al ratio, it was revealed that an LDH with low zinc content was always formed, probably through substitution of some of the Zn²⁺ ions by Al³⁺ ions in the gibbsite lattice.     

Al(OH)3对聚丙烯腈粉火焰传播特性影响研究

为研究Al(OH)₃粉体抑爆剂对聚丙烯腈（polyacrylonitrile, PAN）粉尘爆炸的抑制作用,利用透明管道爆炸传播测试系统,研究不同含量的Al(OH)₃对PAN粉尘爆炸火焰传播形态、温度等参数的影响,并采用扫描电镜、热重分析仪、傅里叶红外光谱仪研究Al(OH)₃抑制PAN粉尘爆炸的微观特征,总结出Al(OH)₃对PAN粉尘爆炸的抑制机理。测试结果表明,随着Al(OH)₃质量分数的增加,PAN粉尘爆燃的最大火焰传播距离和传播速度逐渐减小。同时压力监控及温度监控结果显示,随着Al(OH)₃质量分数的增加,PAN粉尘的最大爆炸压力及最大温度均逐渐减小,由此验证了Al(OH)₃对PAN粉尘爆炸的抑制作用,且60%质量比的Al(OH)₃的抑制效果最好。通过对PAN粉尘爆炸固态产物表征及热分析的研究,从物理和化学两个方面分析了Al(OH)₃对PAN粉尘火焰的抑制机理,物理抑制包括包覆、吸热降温、气体惰化3种方式,化学抑制主要通过消耗维持燃烧爆炸连锁反应的关键自由基?O和?OH减少了自由基?H、?OH与?O之间的放热反应。     

Al2O3—40%TiO2和Cr2O3等离子喷涂层的摩擦磨损特性

研究了AC4C铸铝合金表面等离子喷涂Al2O3-40%TiO2和Cr2O3陶瓷粉末涂层的滑动摩擦磨损特性;采用划痕试验方法测定了涂层与基体之间的结合强度;用扫描电子显微镜观察分析了磨痕形貌和涂层显微组织特征.研究结果表明:Cr2O3涂层的摩擦学性能优于Al2O3-40%TiO2涂层;涂层的结合强度、硬度和表面空隙对磨损影响较大;Al2O3-40%TiO2涂层的磨损机理主要表现为塑性变形和层状剥离;而Cr2O3涂层则主要为磨粒磨损     

Improving thermal stability and light fastness of Acid Red 114 by incorporating its anions in a ZnAl-layered double hydroxides matrix

Incorporation of anions of Acid Red 114 dye (1,3-naphthalenedisulfonic acid, 8-[2-[3,3′-dimethyl-4′-[2-[4-[[(4-methylphenyl)sulfonyl]oxy] phenyl]diazenyl] [1,1′-biphenyl]-4-yl]diazenyl]-7-hydroxy-, disodium salt) (denoted as NPDA) into ZnAl-layered double hydroxides (LDHs) has been carried out by an anion-exchange method in an effort to improve their thermal stability and light fastness. After intercalation of NPDA anions, the interlayer distance of the LDHs increases from 0.87 to 2.18 nm, confirming their incorporation into the interlayer galleries of the LDHs host. Infrared spectroscopy and thermogravimetric analysis revealed the presence of host–guest interactions between LDHs layers and NPDA anions. The thermal stability of NPDA and ZnAl–NPDA–LDHs was compared by thermogravimetric-differential thermal analysis, UV–visible spectroscopy and infrared spectroscopy. It was found that the thermal stability of NPDA anions was markedly improved by incorporation into the ZnAl–LDHs matrix, while the light fastness was also enhanced.     

Al含量对FeCrNiCoCu高熵合金涂层组织结构及冲蚀性能的影响

采用放电等离子烧结(SPS)制备不同Al含量的Al_xFeCrNiCoCu(x=0,1,2,3)高熵合金涂层.通过XRD、SEM和冲蚀磨损等检测方法,研究了Al含量对该高熵合金涂层的组织及冲蚀磨损性能的影响.结果表明:FeCrNiCoCu高熵合金的微观组织主要为简单FCC结构的富Cu相及富Al相.随着Al元素增加,涂层的微观结构出现由FCC向BCC的转变.同时,涂层的硬度、耐冲蚀性也显著提高.随着冲蚀角度的增加,涂层的冲蚀磨损量逐渐增加,表现出脆性材料的冲蚀磨损特性.在冲蚀角度为90°时,随着Al元素的增加,涂层的主要冲蚀磨损机理逐渐由微切削和锻造挤压转变为犁削.     

Synthesis and characterization of PMMA/Al2O3 composite particles by in situ emulsion polymerization

In order to improve its dispersibility, superfine alumina (Al2O3) was encapsulated with poly (methyl methacrylate) (PMMA) by in situ emulsion polymerization. It was found that only when the concentration of sodium dodecyl sulfate (SDS) was much higher than its critical micelle concentration, could PMMA/Al2O3 composite particles with high percentage of grafting (PG) be prepared. The same results were obtained between the experimental and stoichiometric amounts of tris (dodecylbenzenesulfonate) isopropoxide (NDZ), indicating that single-molecule-layer adsorption had taken place between NDZ and Al2O3. Analysis using FTIR. TEM and XPS showed that PMMA/Al2O3 composite particles with core-shell structure had been successfully synthesized by in sire emulsion polymerization. Compared to Al2O3, thermal stability and dispersibility of the composite particles showed marked improvement.     

开口阻塞比对粉体抑制甲烷爆炸的影响研究

为了研究开口阻塞比φ对粉体抑爆特性的影响,采用质量浓度C为0、80、160、240 g/m3的Al (OH)₃和NaHCO₃粉体,分别抑制具有不同φ（0、0.2、0.4、0.6、0.7、1.0）值的5 L管道内甲烷/空气预混气爆炸。实验结果表明:火焰的破碎度随粉体抑爆效率的增大而增大;最大超压峰值p_max、爆燃指数K_st由燃烧速率和泄爆速率共同决定。φ=0.7是每条爆炸特征参数曲线的拐点。随着φ值增加,超压峰值下降率δ先增大后减小,在0.4和0.6之间达到最大;总体上,Al (OH)₃和NaHCO₃两种粉体的抑爆效率相近。但在某些阻塞比下,阻塞比引起的低湍流影响着粉体颗粒的沉降行为,使得Al (OH)₃抑爆效率优于NaHCO₃。当粉体质量浓度从80 g/m3增加到240 g/m3时,热阻增加,火焰的热量不能扩散到粒子云的中心,不利于内部粒子的吸热分解,致使浓度效应越来越弱。     

TiAl合金表面热障涂层的组织结构及其高温磨损性能研究

利用EB-PVD技术在TiA l合金表面制备了扩散铝/YSZ热障涂层.采用SEM、EDS和XRD分析了涂层的微观组织及其相组成,并测试了显微硬度和耐磨性.结果表明：涂层表面YSZ层为致密柱状晶结构,由非平衡四方相t＇-ZrO2组成;涂层结构由表及里依次为YSZ/A l2O3/TiA l3/TiA l2/TiA l;涂层的显微硬度和高温磨损性能显著提高,其高温磨损机理为轻微的犁削和严重的粘附转移,体积磨损率约为TiA l合金磨损率的1/10.     

磁控溅射Al靶功率对类金刚石薄膜的结构和摩擦学性能影响

本文采用中频磁控溅射金属Al靶,以CH4为反应气体,通过调整Al靶溅射功率,在p(100)单晶硅片和不锈钢基底上成功制备出不同Al含量的Al/a-C:H纳米复合薄膜。并利用HR-TEM、XPS、纳米压痕仪和摩擦磨损试验机等手段分析和研究了Al/a-C:H薄膜的结构、机械及摩擦学性能。结果表明：金属Al以纳米晶颗粒形式镶嵌在非晶碳网络中,使得所制备Al/a-C:H薄膜呈现出典型的纳米晶/非晶复合结构;同时,Al掺杂促进薄膜中sp2杂化碳形成,且有效地释放残余内应力。Al靶溅射功率为800 W时所制备的Al/a-C:H薄膜具有结构致密、内应力低、硬度高的特性;在大气环境中,该薄膜与Si3N4陶瓷球干摩擦时显示出优越的摩擦学性能,其摩擦系数约为0.055,磨损率约为2.9×10-16 m3/(N?m)。     

原位反应合成金属间化合物激光合金化层的组织及抗磨性能

以近等原子比的NiTi合金粉末为原料,利用连续波高功率Nd-YAG激光器在6061Al合金表面制备了Ni-Al和Ti-Al金属间化合物改性层,采用扫描电子显微镜、X射线能谱仪、X射线衍射仪、显微硬度计及摩擦磨损试验机分析了合金化层的组织形貌、结构、成分、硬度分布及磨损性能.研究结果表明,该激光表面改性层主要由Ni3Al和TiAl3金属间化合物组成;采用合适的保护措施和激光处理工艺参数,可控制改性层产生孔洞和裂纹倾向,从而获得与基体具有良好冶金结合的致密金属间化合物合金激光改性层;与此同时,Ni-Al和Ti-Al金属间化合物改性层可有效地改善铝合金的抗磨性能.     

MoO3-ZnO/镍基复合涂层制备及其摩擦学性能研究

利用等离子喷涂工艺制备了含氧化物(MoO₃-ZnO)的镍基复合涂层,通过UMT-3球盘式高温摩擦试验机评价了复合涂层在室温、400和800 ℃下的摩擦学性能,并采用扫描电镜(SEM)、能谱分析仪(EDS)、X射线衍射仪(XRD)以及拉曼光谱仪(Raman)等分析手段研究了涂层微观组织、物相组成以及磨损机理. 结果表明:在室温和400 ℃,复合涂层的摩擦系数和磨损率均高于Ni-5%Al金属基底,且随着氧化物含量的增加,润滑和耐磨性能均被削弱,主要表现为磨粒磨损和黏着磨损. 在800 ℃,MoO₃和ZnO的添加可以有效改善复合涂层的摩擦性能,随着其含量的增加,摩擦系数变化不明显,而磨损率逐渐增加. 特别是添加5%MoO₃和5%ZnO的复合涂层在800 ℃摩擦系数低至0.28,磨损率低至4.22×10?5 mm3/(N·m),其良好的高温润滑耐磨性能得益于摩擦表面二元氧化物(NiO、MoO₃和ZnO)和三元氧化物(ZnMoO₄和NiMoO₄)的协同作用.      

Al-DLC薄膜结构及其在水介质下摩擦学性能研究

采用磁控溅射技术,以Al为溅射靶材,甲烷为溅射气体,在不同射频功率下制备了一系列Al含量不同的类金刚石碳基薄膜(AL-DLC).分析了Al含量对薄膜成分、结构及机械性能的影响,并探讨了其在空气和水介质下的摩擦磨损行为.结果表明:Al掺杂使得薄膜中sp~3-C的生长受到抑制,sp~2-C增加,表面吸附水分子能力变强,在水介质摩擦过程中的剪切阻力变小,从而使得摩擦磨损减小.通过调整射频功率可以对薄膜中Al含量进行调控,在最优Al含量时,Al-DLC在空气和水介质中均具有优异的摩擦学性能.     

SINGULAR PERTURBATIONS FOR A CLASS OF BOUNDARY VALUE PROBLEMS OF HIGHER ORDER NONLINEAR DIFFERENTIAL EQUATIONS

ＳＩＮＧＵＬＡＲ　ＰＥＲＴＵＲＢＡＴＩＯＮＳ　ＦＯＲ　Ａ　ＣＬＡＳＳ　ＯＦ　ＢＯＵＮＤＡＲＹ　ＶＡＬＵＥ　ＰＲＯＢＬＥＭＳ　ＯＦ　ＨＩＧＨＥＲ　ＯＲＤＥＲ　ＮＯＮＬＩＮＥＡＲ　ＤＩＦＦＥＲＥＮＴＩＡＬ　ＥＱＵＡＴＩＯＮＳＳｈｉＹｕａｎｉｎｇ（史玉明）...     

非离子表面活性剂体系层状液晶中硫化锌纳米颗粒的抗磨性

利用层状液晶中溶剂厚度的限定性,在ＴｒｉｔｏｎＸ－１００／Ｃ１０Ｈ２１ＯＨ／Ｈ２Ｏ体系层状液晶中,分别各以０．１ｍｏｌ／Ｌ的Ｚｎ（ＣＨ３ＣＯＯ）２和Ｎａ２Ｓ水溶液代替组分水制备出粒径约为１０ｎｍＺｎＳ颗粒,并对层状液晶中ＺｎＳ纳米颗粒的抗磨性能进行了研究,结果表明,ＺｎＳ纳米颗粒能提高ＴｒｉｔｏｎＸ－１０Ｃ１０Ｈ２１ＯＨ／Ｈ２Ｏ体系层状液晶的抗磨性,但对极压性能无影响。     

Four-point explicit difference schemes for the dispersive equation

A class of three-level explicit difference schemes for the dispersive equationu_1=au_(xxx)are established These schemes have higher stability and involve four meshpoints at the middle level.Their local truncation errors are O(τ+h)and stabilityconditions are from|R|≤0.25 to|R|≤10,where|R|=|a|τ/h~3,which is muchbetter than|R|≤0.25.     

Properties of an Al/(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>+TiB<Subscript>2</Subscript>+ZrB<Subscript>2</Subscript>) hybrid composite manufactured by powder metallurgy and hot pressing

The properties and microstructure of an Al/(Al₂O₃ + TiB₂ + ZrB₂) hybrid composite made by using hot pressing of aluminum combined with different amounts of TiB₂, ZrB₂, and Al₂O₃ powders are studied. The mechanical properties of the composites are investigated on the basis of microhardness and compression tests. The results show that the microstructure of the composites is uniform and the particles are well distributed in the matrix.     

CH4/O2/CO2预混体系爆炸动力学研究

为探究甲烷在富氧条件下的火焰动力学规律,以CH₄/O₂/CO₂预混体系为研究对象,在小尺度方形透明管道中进行了一系列爆炸实验,探讨了初始环境温度波动对爆炸参数的影响,并对预混体系的燃烧机理进行分析。结果表明:在273 K的环境温度下,化学当量比φ=0.8~1.0且氧气相对比γ<0.30和φ=1.2且γ<0.35的预混体系不能被点燃,而其他预混体系均可被点燃,最终产生郁金香与非郁金香两种火焰类型,并且根据郁金香火焰独特的演变特征,又划分为T形郁金香火焰和不对称郁金香火焰;随着γ的增大,无量纲火焰传播速度v/(S_Lσ)的变化趋势由“两升两降”转变为“一升一降”。初始环境温度的升高并未对火焰传播速度和爆炸超压的变化趋势产生影响,但是会导致最大爆炸超压p_max和最大火焰传播速度降低。值得注意的是,初始环境温度对爆炸强度的影响随化学当量比的减小而增强。另外,与最大爆炸超压相比,最大火焰传播速度与层流燃烧速度之间的关系更紧密。从敏感性分析中可知:层流燃烧速度对自由基链式反应R38(即H+O₂=O+OH)表现出最大的正敏感度,对R52(即H+CH₃(+M)=CH₄(+M))表现出最大的负敏感度,并且对自由基OH的生成速率最敏感,当初始环境温度升高至303 K时,层流燃烧速度对R38(正)和R52(负)的敏感度降低;H、O和OH自由基总摩尔分数的增大会削弱热扩散的不稳定性,增强流体力学的不稳定性。     

Existence of Weak Solutions to the Equations of Non-Stationary Motion of Non-Newtonian Fluids with Shear Rate Dependent Viscosity

In the present paper we prove the existence of weak solutions to the equations of non-stationary motion of an incompressible fluid with shear rate dependent viscosity in a cylinder Q = Ω × (0,T), where denotes an open set. For the power-low model with we are able to construct a weak solution with ∇ · u = 0.     

惰性粉体对油页岩粉尘爆炸火焰的抑制性能和作用机理研究

为了研究惰性粉体对油页岩粉尘爆炸火焰的抑制性能和作用机理,利用粉尘爆炸火焰传播测试系统,选取了五种常用惰性粉体和两种不同油页岩粉尘进行了爆炸火焰抑制实验。通过对爆炸火焰长度、最低惰化比和火焰形态结构的分析,结合惰性粉体的TG-DTG-DSC热特性曲线,系统研究了惰性粉体对油页岩粉尘爆炸火焰的抑制性能和作用机理。研究结果表明,惰性粉体对两种油页岩粉尘爆炸火焰的抑制性能优劣排序为:ABC干粉＞Al(OH)₃＞Mg(OH)₂＞NaHCO₃>岩粉,且两种惰性粉体均对桦甸油页岩（HDOS）的抑爆性能优于龙口油页岩（LKOS）;本文建立了惰性粉体对油页岩粉尘爆炸火焰的抑制机理物理模型,并分析了作用机理,通过作用机理分析表明:高效抑爆粉体应具有热稳定性较好（分解温度在200～400 ℃）,吸热量大,且分解中间态产物能够与燃烧反应活性自由基相结合发挥化学抑制作用等特点。