Polycrystalline ZSM-5 Aggregates Induced by Seed and Catalytic Performance in Methanol to Hydrocarbon

Synthesis of ZSM-5 zeolite typically utilizes small molecule polyamines or quaternary ammonium salts as organic structure guiding agent(OSDA).By contrast,the OSDA-free hydrothermal synthesis system eliminates the use of organic templates and the subsequent calcination procedure.This not only reduces the cost of synthesis,but also prevents environmental pollution from the combustion of organic templates,representing an eco-friendly approach.Despite this,literature suggests that even so-called template-free synthesis systems often involve trace amount of organic substances like alcohol.In the present work,a calcined commercial ZSM-5 zeolite was served as seed,with sodium aluminate as aluminum source and silica sol as silicon source,ensuring an entirely template-free synthesis system.Polycrystalline ZSM-5 aggregates consisted of rod-like nanocrystals were successfully prepared in the completely OSDA-free system.Effects of the Si/Al ratio in ZSM-5 seed,dosage and crystallization conditions such as crystallization temperature and crystallization time on ZSM-5 synthesis were investigated.The results show that a highly crystallinity ZSM-5 aggregate consisting of primary nano-sized crystals less than 100 nm is produced from a gel precursor with 5.6%(in mass)seed after hydrothermal treatment for 48 h.Furthermore,the Si/Al ratio in ZSM-5 seed has little effect on the topological structure and pore structure of the synthesized samples.However,the seeds with a low Si/Al ratio facilitate faster crystallization of zeolite and enhance the acidity,especially the strong acid centers,of the catalyst.The catalytic performance of the synthesized polycrystalline ZSM-5 was evaluated during dehydration of methanol and compared with a commercial reference ZSM-5r.The results exhibit that as compared with the reference catalyst,the fabricated sample has a longer catalytic lifetime(16 h vs 8 h)attributed to its hierarchical pores derived from the loosely packed primary nanoparticles.Additionally,the prepared polycrystalline catalyst also exhibits a higher aromatics selectivity(28.1%-29.8%vs 26.5%).

Growth Pattern and Its Indication of Spheroidal Nano-Micro Crystal Aggregates of Pyrite in the Baiyunpu Pb-Zn Polymetallic Deposit, Central Hunan

The Baiyunpu deposit lies in the southwest plunging Dachengshan anticline in central Hunan, which is a large Pb-Zn polymetallic deposit. The orebodies were surrounded by the Qiziqiao Formation limestone in the Middle Devonian, and its geological occurrence is consistent with the wall rocks. A large number of spheroidal pyrite aggregates are found unevenly distributed in the ores. The spheroidal aggregates are made up of kernels and concentric rings. The kernels are composed of approximately epigranular pyrite nanocrystals, while the rings are composed of accumulated pyrite microcrystals growing along the radial direction. The spheroidal pyrite aggregate and its outer zones can be divided into five areas（A–E）. The results of electron probe micro analysis（EPMA） show that from the zone A1 to B, Co/Ni 〈1, the sum of Co and Ni is 0.08%–0.26%, S/Fe increases from 2.06 to 2.15. While from the zone C to E, Ni cannot be detected and S/Fe decreases from 2.22 to 2.08. Powder X-ray diffraction（XRD） analysis in the micro zone shows obvious crystalline characteristics in the aggregates. Moving from the inside outwards, the maximum diffraction peak intensity of the（111） and（220） crystal planes of pyrite increases, and the crystallinity improves. The degree of change in the（111） plane is the most prominent. Considering the theory of crystal growth along with the geologic features of the depositional environment where the spheroidal pyrite aggregates developed, we confirm that the spheroidal aggregates are the result of nano-micro crystalline gathering and growth occurring by the following sequence of processes：nano-crystalline nucleation and growth, gathering into a ball, oriented growth of microcrystals, continuous accumulation, and adjustment of grain boundaries. The formation of the spheroidal pyrite aggregates in the late Qiziqiao Formation of the Middle Devonian occurred in a neutral to weak alkaline and reductive sedimentary environment in the normal oxygen-rich shallowwater carbonate platform edge. The variations in the S/Fe ratio and crystallisation characteristics indicate that during pyrite crystal growth, the sulphur fugacity was high locally and rose constantly, the degree of supersaturation decreased locally and the growth environment was stable relatively.

Forward-Light-Scattering Characterization of Pre-Crystalline Aggregates in Crystallizing Lysozyme Solutions

We present a method to characterize lysozyme pre-crystalline aggregates using a forward-light-scattering technique, which is highly sensitive to protein aggregates. The static light scattering properties at small angles of crystallizing lysozyme aggregates are discussed, and related to the crystallization conditions based on the concentration of added precipitant NaCl. Lysozyme solutions that started to crystallize because of precipitant exhibited profiles of forward light scattering that could be fitted by non-integer power laws, which indicated fractal aggregations of lysozyme had formed. Pre-crystalline solutions, in which lysozyme crystals later grew, had dense structural fractal clusters with fractal dimensions of D > 1.5. In contrast, solutions with aggregates in which crystals did not grow, had forward-light-scattering profiles that deviated from a power law or had lower power values.

A Study of Ca-Mg Silicate Crystalline Glazes——An Analysis on Forms of Crystals

In the study on Ca-Mg silicate crystalline glazes, we found some disequilibrated crystallization phenomena, such as non-crystallographic small angle forking and spheroidal growth, parasitism and wedging-form of crystals, dendritic growth, secondary nucleation, etc. Those phenomena possibly resulted from two factors: (1) partial temperature gradient, which is caused by heat asymmetry in the electrical resistance furnace, when crystals crystalize from silicate melt; (2) constitutional supercooling near the surface of crystals. The disparity of disequilibrated crystallization phenomena in different main crystalline phases causes various morphological features of the crystal aggregates. At the same time, disequilibrated crystallization causes great stress retained in the crystals, which results in cracks in glazes when the temperature drops. According to the results, the authors analyzed those phenomena and displayed correlative figures and data.

THE STRUCTURE OF AGGREGATION STATE AND ISOTHERMAL CRYSTALLIZATION KINETICS OF NYLON-1010

The structure of aggregation state and isothermal crystallization behavior of Nylon-1010 have been studied by WAXD, DSE, Variance-Range Function and density measurement. The results show that crystallization of Nylon-1010 has the most suitable annealing temperature, the crystals of the Nxlon-1010 are two-dimension heterogeneous nucleation. Both low treatment temperature and high crystallization te, temperature are disadvantageous for Nylon-1010 crystal growth.

Synthesization and crystallization mechanism of nano-scale γ-AlOOH with various morphologies

Nano-scale γ-AIOOH with various morphologies, such as whisker, bar, ball, and sheet, was synthesized successfully and control- lably through a facile hydrothermal method just by adjusting the pH value of the solvent. Based on the analysis of the experimental data, the growth mechanism of nano-scale γ-AlOOH in the hydrothermal process was established. It is proposed that the growth unit and the growth direction are determined by the pH value of the solution and the growth unit, respectively. One-dimensional γ-AlOOH, such as whisker and bar, is formed in lower pH ranges, while two-dimensional γ-AlOOH sueli as sheet is formed only in high pH environment following the plane expansion crystallization mechanism.

From crystalluria to kidney stones,some physicochemical aspects of calcium nephrolithiasis

Nephrolithiasis seems to be the result of crystal formation,aggregation and retention in the kidney during crystalluria.These processes have to occur within the short urinary transit time through the kidney being in the order of few minutes.Recently much work was done on rather qualitative aspects of nephrolithiasis like genetics,metabolism and morphology.In this review we try to provide some quantitative information on urinary supersaturation with respect to stone minerals,especially Ca oxalate(CaO x),on the formation and aggregation of Ca Ox crystals and on crystal retention in the kidney.The paper is centered on idiopathic Ca nephrolithiasis being the most frequent stone disease with only partially known pathogenesis.New aspects of the role of urinary macromolecules in stone formation and of the mechanism of crystal aggregation are provided.

Evolution of nitrogen structure in N-doped diamond crystal after high pressure and high temperature annealing treatment

In this paper, we have reported an investigation on the evolution of nitrogen structures in diamond crystals which contain nitrogen donor atoms in the range of 1500 ppm-1600 ppm following an annealing treatment at a high pressure of about 6.5 GPa and high temperatures of 1920 K-2120 K. The annealing treatment was found to completely transform nitrogen atoms originally arranged in a single substitutional form （C-center）, into a pair form （A-center）, indicated from infrared （IR） spectra. The photoluminescence （PL） spectra revealed that a small fraction of nitrogen atoms remained in C-center form, while some nitrogen atoms in A-center form were further transformed into N3 and H3 center structures. In addition, PL spectra have revealed the existence of two newly observed nitrogen-related structures with zero phonon lines at 611 nm and 711 nm. All these findings above are very helpful in understanding the formation mechanism of natural diamond stones of the Ia-type, which contains nitrogen atoms in an aggregated form.

Comparative experimental study on reactive crystallization of Ni(OH)2 in an airlift-loop reactor and a stirred reactor

The objective of this work is to study the reactive crystallization in an airlift-loop reactor （ALR） using the precipitation of Ni（OH）2 as a model reaction. The growth of Ni（OH）2 particles in an ALR and a stirred tank was quantified by scanning electronic microscope （SEM）, X-ray diffraction （XRD）, laser particle analyzer, tap densitometer and optical microscope, and the growth process of Ni（OH）2 particles is analyzed. It is found that the Ni（OH）2 particles prepared in an ALR have a better sphericity than those in a stirred tank and the growth of Ni（OH）2 particle tap density mainly depends on the size of crystallites： the bigger the size of crystallites, the bigger the tap density is. Based on these, the growth process of Ni（OH）2 particles in ALR is elaborated. Crystallites precipitated from solution aggregate to form large particles with much void. These constituting crystallites continue to grow up, that takes up the void inside particles and makes the tap densitv increase.

Synthesis, Structure and Aggregationinduced Emission Characteristics of Two Diaryquioxaline Derivatives

Two new diaryquioxaline derivatives, C21H10N2S3Br2（1） and C21H10Br2 N2OS2（2）,have been successfully synthesized. These two compounds have been determined by single-crystal X-ray diffraction analyses. Compound 1 crystallizes in monoclinic system, space group P21/n with a = 12.7896（3）, b = 6.0613（2）, c = 26.1153（7） ?, β = 94.1810（10）°, V = 2018.（97） ?3, Z = 4,C21H10N2S3Br2, Mr = 546.32, Dc = 1.797 g/cm3 and F（000） = 1072. The final R = 0.0343 and wR =0.785 for 3585 observed reflections with I > 2σ（I）. Compound 2 crystallizes in monoclinic system,space group P21/n with a = 7.8638（4）, b = 14.3447（7）, c = 17.8936（8） ?, β = 96.6980（10）°, V =2004.69（17） ?3, Z = 4, C21H10Br2 N2OS2, Mr = 530.25, Dc = 1.757 g/cm3 and F（000） = 1040. The final R = 0.0988 and wR = 0.1108 for 4613 observed reflections with I > 2σ（I）. By combination of diarylquinoxaline core and a 1,3-dithiole-2-thione unit, compound 1 is used as "turn on"chemosensors for Hg2+ by making use of the aggregation-induced emission（AIE） feature of diarylquinoxaline core and the specific reaction of 1,3-dithiole-2-thione with Hg2+.

DIPOLE POLARIZATION RELAXATION AND MOLECULAR STRUCTURE OF MAIN-AND SIDE-CHAIN LIQUID-CRYSTALLINE POLYMERS

Molecular mobility in thermotropic polyesters and side-chain polymers with different struc-ture of mesogens and spacers has been studied by dielectrical method in dilutesolutions. The results made it possible to establish the multiplicity of dielectric relaxationtransitions which reflects the small- and large-scale types of molecular motion. It was shownthat dielectric relaxation processes occurring in accordance with local mechanism (relaxationtimes 10^(-9)--10^(-7)s. and the activation energy 10--50kJ/mol) are due to the mobility of kineticchain elements of different length within a monomer units. It was found that the dielectricrelaxation process connected with a large-scale form of molecular motion (relaxation times10^(-5)--10^(-6)s. and the activation energy 100kJ/mol) did not depend on the molecular massbut was infiuenced by factors changing the conformational state of the macromolecule. It isestablished tha the cooperative reorientation mobility of associated mesogenic fragments isthe source of the large-scale process.

MELTING AND CRYSTALLIZATION BEHAVIOR OFAN AROMATIC POLY (AZOMETHINE ETHER) WITH NON-LINEARLY SHAPED MOLECULAR CONFORMATIONS

The melting and crystallization behavior have been investigated for an aromatic poly (azomethine ether)with non-linearly shaped molecular conformations. This polymer was found to undergo multiple melting processes and its phase transition behavior was influenced sensitively by the thermal history of sample. A significant difference between the polymer chain aggregation abilities of samples cooled from the different states was observed. The possible molecular morphology and aggregation models for describing the structures of this polymer were proposed and discussed. The crystallization behavior of the samples cooled from the partially isotropic state and the influence of cooling rate on it have also been examined with DSC.

CRYSTALLIZATION AND MELTING OF POLY(ETHYLENE OXIDE)CONFINED IN NANOSTRUCTURED PARTICLES WITH CROSS-LINKED SHELLS OF POLYBUTADIENE

Small fixed aggregates of a poly(ethylene oxide)-block-polybutadiene diblock copolymer(PEO-b-PB)in THFsolution were obtained by adding a selective solvent for PB blocks,followed by cross-linking the PB shells.Themorphologies of the nanostructured particles with a cross-linked shell were investigated by atomic force microscopy andtransmission electron microscopy.The average behaviors of the PEO crystallization and melting confined within thenanostructured particles were studied by using differential scanning calorimetry experiments.For the deeply cross-linkedsample(SCL-1),the crystallization of the PEO blocks was fully confined.The individual nanoparticles only crystallized atvery low crystallization temperatures(T_cs),wherein the homogenous primary nucleation determined the overallcrystallization rate.For the lightly cross-linked sample(SCL-2),the confinement effect was T_c dependent.At T_c(?)42℃,thecrystallization and melting behaviors of SCL-2 were similar to those of the pure PEO-b-PB diblock copolymer.At T_c>42℃,SCL-2 could form PEO lamellae thicker than those of the pure PEO-b-PB crystallized at the same T_c.

Influence of annealing treatment on as-grown Ib-type diamond crystal at a high temperature and high pressure

In this paper,we report on the influence of annealing treatment on as-grown Ib-type diamond crystal under high pressure and high temperature in a china-type cubic anvil high-pressure apparatus.Experiments are carried out at a pressure of 7.0 GPa and temperatures ranging from 1700 C to 1900 C for 1 h.Annealing treatment of the diamond crystal shows that the aggregation rate constant of nitrogen atoms in the as-grown Ib-type diamond crystal strongly depends on diamond morphology and annealing temperature.The aggregation rate constant of nitrogen remarkably increases with the increase of annealing temperature and its value in octahedral diamond is much higher than that in cubic diamond annealed at the same temperature.The colour of octahedral diamond crystal is obviously reduced from yellow to nearly colorless after annealing treatment for 1 h at 1900 C,which is induced by nitrogen aggregation in a diamond lattice.The extent of nitrogen aggregation in an annealed diamond could approach approximately 98% indicated from the infrared absorption spectra.The micro-Raman spectrum reveals that the annealing treatment can improve the crystalline quality of Ib-type diamond characterized by a half width at full maximum at first order Raman peak,and therefore the annealed diamond crystals exhibit nearly the same properties as the natural IaA-type diamond stones of high quality in the Raman measurements.

FRACTAL STRUCTURE OF COLLOIDAL SILVER AND ITS EFFECTS ON SERS INTENSITIES OF CRYSTAL VIOLET

The surface-enhanced Raman spectra (SERS) of crystal violet on colloidal silver particles of different sizes and shapes were measured and the structural effect of the silver aggregates on the SEPS intensities was discussed in terms of fractal geometry. It is found that the SERS band intensities of crystal violet change significantly with the fractal dimension (D) of colloidal silver at 1.25<D<1.65, but remains nearly constant at D>1.8.

Fabrication and structure of Langmuir-Blodgett films of ferroelectric liquid crystal

The molecular aggregation, orientation, and structure in Langmuir-Blodgett films of ferroelectric liquid crystal were studied by ultraviolet and Fourier transform infrared spectra. The results show that medium strong (H-aggregates) in the Langmuir-Blodgett films of ferroelectric liquid crystal are formed by chromophores where the alkyl chains are nearly perpendicular to the film surface. Compared with the cast films, the CO stretching bands, due to the rotational isomerism around the O—C axis of the chiral part, can be identified clearly in Langmuir-Blodgett films.

Kinetics and Mechanism of Spontaneous Crystallization of Potassium Nitrate from Its Supersaturated Aqueous Potassium Nitrate from Its Supersaturated Aqueous Solutions

Kinetics of spontaneous crystallization of potassium nitrate from its supersaturated aqueous solutions has been studied simultaneously by electrical conductance and optical transmittance methods. It was found that spontaneous crystallization of potassium nitrate was accompanied by aggregation of crystals. Growth of salt crystals was in the kinetic mode of the growth process, and was described by the equation of the first order regarding supersaturation of solution. The mechanism of aggregation and intergrowth of crystals during bulk crystallization via formation of nucleus-bridges between crystals found earlier for several salts was confirmed. Specific surface energy of potassium nitrate was evaluated on the basis of the above mechanism of aggregation and intergrowth of crystals. The established value of the specific surface energy was reasonable and agreed satisfactorily with the available literature data. Examination of crystal deposit after completion of crystallization allowed detecting crystal agglomerates of freakish and irregular forms, which may be considered as the direct confirmation of the above mechanism of intergrowth of crystals. Kinetics of crystallization, aggregation and size distribution of salt crystals after completion of crystallization have been satisfactory described by the earlier proposed model of the crystallization process. An excellent agreement was established between the experimental data on potassium nitrate solubility in aqueous solutions found in the present work and those available in the literature.

A NONCLASSICAL CONSTITUTIVE MODEL FOR CRYSTALPLASTICITY AND ITS APPLICATION

A nonclassical constitutive description for a slip system is formulated by using a simple mechanical model consisting of a spring and a plastic dashpot-like block. The corresponding constitutive model for a single crystal and the analysis for polycrystalline response is proposed based on the KBW's self-consistent theory. The constitutive model contains no yield criterion, so the corresponding numerical analysis is greatly simplified because it involves no additional process to search for the activation of slip systems and slip direction. A mixed averaging approach is proposed to obtain the response of polycrystalline material, which consists of the Gaussian integral mean for the omega which varies continuously within each face of the isosahedron and arithmetic mean for the spatially uniformly distributed twenty sets of 0 and phi determined by the normal of each face of the isosahedron. The main features 316 stainless steel subjected to typical biaxial nonproportional cyclic strain paths are well described. Calculation also shows that the developed model and the corresponding analytical approach are of good accuracy and efficiency.

CaP结晶体系中离子簇对磷回收效果的影响

为提高污水磷酸钙(CaP)结晶的磷回收效果,对CaP结晶体系中的离子簇进行了研究,探讨离子簇成簇和团聚对磷回收的影响.结果表明,采用Ca离子选择电极原位监测结晶体系游离态Ca浓度,结合结晶态P含量和产物Ca/P物质的量比的异位分析结果,可以实现对离子簇的定量分析.该方法操作简单,准确度较高.CaP结晶过程分为初期的离子簇成簇和团聚(0~20s)、中期的离子簇成簇(20~3000s)和后期的离子簇团聚(3000~7200s),3个阶段的磷回收率分别为11.1%、3.9%和28.5%.磷的回收主要是通过离子簇团聚实现.通过投加晶种,调控CaP离子簇的成簇和团聚过程,有望提升污水CaP结晶的磷回收效果.

Control over the aggregated structure of donor–acceptor conjugated polymerfilms for high-mobility organicfield-effect transistors

Donor–acceptor(D-A)conjugated polymers have demonstrated great potential in organicfield-effect transistors application,and their aggregated structure is a crucial factor for high charge mobility.However,the aggregated structure of D-A conjugated polymerfilms is complex and the structure–property relationship is difficult to understand.This review provides an overview of recent progress in controlling the aggregated structure of D-A conjugated polymerfilms for higher mobility,including the mechanisms,methods,and properties.Wefirst discuss the multilevel microstructures of D-A conjugated polymerfilms,and then summarize the current understanding of the relationship betweenfilm microstructures and charge transport properties.Subsequently,we review the theory of D-A conjugated polymer crystallization.After that,we summarize the common methods to control the aggregated structure of semi-crystalline and near-amorphous D-A conjugated polymerfilms,such as crystallites and aggregates,tie chains,film alignment,and attempt to understand them from the basic theory of polymer crystallization.Finally,we provide the current challenges in controlling the aggregated structure of D-A conjugated polymerfilms and in understanding the structure–property relationship.