Reversible phase transition of the 1:1 complex between 18-crown-6 and n-propylammonium triiodide

Solid-state structure of the crystalline 1:1 complex [C 3 H 10 N(18-crown-6)] + [I 3 ](1) between 18-crown-6 and n-propylammonium triiodide has been determined at 293 and 93 K,respectively,showing a change from monoclinic P2 1 /m to monoclinic P2 1 /a.Crystal structural analysis shows that in addition to van der Waals’ forces,conventional N-H···O hydrogen bonds are the key interactions.Measurements of unit cell parameters versus temperature show that the values of one of the three axes and the crystal volume change abruptly and remarkably at 220 K,indicating a first-order phase transition.The lack of the mirror plane in the low temperature structure is the most important differences between the two structural forms.Differential scanning calorimetry(DSC) measurement confirms that 1 undergoes a reversible phase transition at about 220 K with a thermal hysteresis of 3.5 K.The relatively large latent heat makes 1 a good candidate for phase change materials.The phase transition is accompanied by an anomaly of dielectric constant during heating and cooling process near the phase transition temperature.     

Molecular dynamics study on the relationships of modeling, structural and energy properties with sensitivity for RDX-based PBXs

In this paper,a primary model is established for MD(molecular dynamics) simulation for the PBXs(polymer-bonded explosives) with RDX(cyclotrimethylene trinitramine) as base explosive and PS as polymer binder.A series of results from the MD simulation are compared between two PBX models,which are represented by PBX1 and PBX2,respectively,including one PS molecular chain having 46 repeating units and two PS molecular chains with each having 23 repeating units.It has been found that their structural,interaction energy and mechanical properties are basically consistent between the two models.A systematic MD study for the PBX2 is performed under NPT conditions at five different temperatures,i.e.,195 K,245 K,295 K,345 K,and 395 K.We have found that with the temperature increase,the maximum bond length(L max) of RDX N N trigger bond increases,and the interaction energy(E N-N) between two N atoms of the N-N trigger bond and the cohesive energy density(CED) decrease.These phenomena agree with the experimental fact that the PBX becomes more sensitive as the temperature increases.Therefore,we propose to use the maximum bond length L max of the trigger bond of the easily decomposed and exploded component and the interaction energy E N-N of the two relevant atoms as theoretical criteria to judge or predict the relative degree of heat and impact sensitivity for the energetic composites such as PBXs and solid propellants.     

A thermal stable cathode buffer based on an inexpensive tetranuclear zinc(II) complex for organic photovoltaic devices

An inexpensive material,i.e.,tetranuclear zinc(Ⅱ) complex,(Zn4O(AID)6) [AID = 7-azaindolate],was utilized as a cathode buffer in organic photovoltaic(OPV) devices,leading to the improvement of device performance.Compared to OPV devices based on a conventional cathode buffer of TPBi(1,3,5-tris(2-N-phenylbenzimidazolyl)benzene),although the freshly prepared devices showed similar performance,when heated to a series of high temperatures under air,the short circuit current and the open circuit voltage of the Zn4O(AID)6 devices dropped more slowly,indicating the superiority of using Zn4O(AID)6 as a cathode buffer over TPBi in OPV devices.     

Chiral cyanide-bridged 1D Fe~Ⅲ-Mn~Ⅲ heterobimetallic chains: Synthesis, structures and magnetic properties

Two couples of enantiomerically pure chiral cyano-bridged heterobimetallic one-dimensional (1D) chain complexes: [Mn((R,R)-Salphen)Fe(Tp)(CN)3]n (1) and [Mn((S,S)-Salphen)Te(Tp)(CN)3]n (2) (Salphen = N,N’-1,2-diphenylethylenebis (salicylideneiminato) dianion, Tp = tris(pyrazolyl) hydroborate), [Mn((R,R)-Salphen)Fe(Tp*)(CN)3·2H2O]n (3) and [Mn((S,S)-Salphen)Fe(Tp*)(CN)3·2H2O]n (4) (Tp* = hydridotris (3,5-dimethylpyrazol-1-yl) borate), have been successfully synthesized by the reactions of MnIII schiff-base complexes with the tricyanometalate building block, [(LTp)Fe(CN)3]- (LTp = Tp or Tp*). All complexes are made up of neutral cyano-bridged zigzag double chains with (-Fe-C≡N-Mn-N≡C-)n as the repeating unit. Circular dichroism (CD) spectra confirm the enantiomeric nature of the optically active complexes. Magnetic studies demonstrate that ferromagnetic interactions are operative in these complexes. The ferromagnetic couplings become weak in the chains with the bending of the Mn-N≡C angles.     

Crystal formation and growth mechanism of inorganic nanomaterials in sonochemical syntheses

A clear understanding of the nucleation, growth, coarsening, and aggregation processes of nanomaterials is necessary to enable the preparation of highly controlled nanostructures. Among wet chemical synthetic methods, ultrasound-assisted preparation has become an important tool in material science. The formation and crystal growth mechanism under ultrasound is special compared with other wet chemical synthetic routes. In this review, we discussed the chemical and physical effect of ultrasound and summarized the ultrasonic effect on crystallization. The sonolysis of water and the cavitation-induced microjet impact and shockwave are the two key factors in the sonochemical formation of inorganic nanomaterials. The ultrasonic-assisted Ostwald ripening and oriented attachment processes have been reviewed for the possible crystal growth mechanisms in the fabrication of inorganic nanostructures.     

注凝成型制备氧化锆增韧氧化铝陶瓷

采用低毒单体N,N-二甲基丙烯酰胺(DMAA)制备了氧化锆增韧氧化铝(ZrO2/Al2O3,ZTA)陶瓷,氧化铝与氧化锆的质量比为3∶1,浆料的固相体积分数为50 vol%。讨论了不同干燥方式对干燥速率以及坯体性能的影响,研究了不同成型温度对坯体性能的影响。通过研究发现,在湿热烘箱中干燥的坯体强度最高,成型温度应控制在65℃附近。通过对不同单体含量的坯体烧结后陶瓷性能的对比,发现单体的加入量为10wt%左右较好,通过与干压成型陶瓷性能的对比,发现注凝成型得到的陶瓷强度和韧性分别提高了42.2%和23.5%,达到640 MPa和6.3MPa.m1/2,通过扫描电镜图片分析发现,注凝成型制得的陶瓷结构更均匀。     

0.2wt% Bi2O3、CuO、B2O3对5Ca0.6La0.267TiO3-5Ca(Mg1/3Nb2/3)O3微波介质陶瓷的性能影响

采用传统的固相反应法,研究了三种烧结助剂Bi2O3、CuO、B2O3对5Ca0.6La0.267TiO3-5Ca(Mg1/3Nb2/3)O3微波介质陶瓷的烧结性能和介电性能的影响。实验结果表明,掺入0.2wt%的Bi2O3、CuO、B2O3产生了液相,有效地降低了体系的烧结温度。Bi2O3和CuO的加入没有改变烧结体的微观形貌,它们介电常数和品质因数随烧结温度的变化趋势和体积密度趋于一致,均在体积密度最大时最高。当温度大于1300℃时,加入0.2wt%B2O3试样有柱状晶体生成,并随着烧结温度的升高而增多,柱状晶体的存在可能促使Q×f值较大的提高,当烧结温度过高时(1350℃),由于柱状晶体过多使得烧结体不均匀导致Q×f值下降。Bi2O3、CuO、B2O3的加入没有改变烧结体的晶相组成,因此所有烧结体均有近零的温度系数。结果表明,加入0.2wt%B2O3的5Ca0.6La0.267TiO3-5Ca(Mg1/3Nb2/3)O3在1325℃烧结温度具有最佳的介电性能:εr=54.87,Q×f=55 726 GHz,τf=-0.6 ppm/℃。     

Ba(Co1/3Nb2/3)O3微波介质陶瓷预烧温度研究

采用传统固相法制备Ba(Co1/3Nb2/3)O3微波介质陶瓷。研究了预烧温度对其物相组成、显微结构、烧结性能、微波介电性能的影响。结果表明:在不同预烧温度下制备的陶瓷样品主晶相为复合钙钛矿结构的Ba3CoNb2O9,900℃、1000℃有微量Ba3Nb5O15生成。最佳预烧温度为1100℃,在1380℃烧结4 h时,εr=31.8,Q×f=60164GHz,τf=-15×10-6/℃。合适的预烧温度能有效抑制第二相的生成,提升材料致密度,促使主晶相B位有序排列,进而降低介电损耗。     

AIC多晶硅薄膜的制备与其上HWCVD低温外延生长多晶硅薄膜的研究

铝诱导晶化法(AIC)是一种低温制备大晶粒多晶硅薄膜的重要方法。本文分别基于Al/Al2O3/a-Si叠层和a-Si/SiOx/Al叠层制备了AIC多晶硅薄膜,前者表面粗糙,后者表面光滑。以后者为籽晶层,在其上用HWCVD法300℃低温下外延生长了表面形貌与籽晶层相似的多晶硅薄膜。铝诱导晶化过程中,在原始非晶硅层中会形成多晶硅、非晶硅和铝的混合层,去除铝后残留的硅将使表面粗糙,而在原始铝层中则形成连续的多晶硅薄膜。Al/Al2O3/a-Si叠层和a-Si/SiOx/Al叠层的上层分别是非晶硅层和铝层,发生层交换后,前者上层是硅铝混合层,因此表面粗糙,后者上层是连续的多晶硅薄膜,因此表面光滑。在AIC多晶硅薄膜表面外延生长多晶硅薄膜等效于铝诱导多晶硅的晶核在垂直于薄膜方向上的继续生长,因此外延生长的薄膜与AIC多晶硅薄膜呈现相似的枝晶状形貌。     

Monolithic approach to thermal fluid-structure interaction with nonconforming interfaces

This paper presents a monolithic approach to the thermal fluid-structureinteraction(FSI) with nonconforming interfaces.The thermal viscous flow is governedby the Boussinesq approximation and the incompressible Navier-Stokes equations.Themotion of the fluid domain is accounted for by an arbitrary Lagrangian-Eulerian(ALE)strategy.A pseudo-solid formulation is used to manage the deformation of the fluid do-main.The structure is described by the geometrically nonlinear thermoelastic dynamics.An efficient data transfer strategy based on the Gauss points is proposed to guarantee theequilibrium of the stresses and heat along the interface.The resulting strongly coupledset of nonlinear equations for the fluid,structure,and heat is solved by a monolithicsolution procedure.A numerical example is presented to demonstrate the robustness andefficiency of the methodology.