Modulating the microstructure and surface chemistry of carbocatalysts for oxidative and direct dehydrogenation: A review

The catalytic performance of solid catalysts depends on the properties of the catalytically active sites and their accessibility to reactants, which are significantly affected by the microstructure（morphology, shape, size, texture, and surface structure） and surface chemistry（elemental components and chemical states）. The development of facile and efficient methods for tailoring the microstructure and surface chemistry is a hot topic in catalysis. This contribution reviews the state of the art in modulating the microstructure and surface chemistry of carbocatalysts by both bottom‐up and top‐down strategies and their use in the oxidative dehydrogenation（ODH） and direct dehydrogenation（DDH） of hydrocarbons including light alkanes and ethylbenzene to their corresponding olefins, important building blocks and chemicals like oxygenates. A concept of microstructure and surface chemistry tuning of the carbocatalyst for optimized catalytic performance and also for the fundamental understanding of the structure‐performance relationship is discussed. We also highlight the importance and challenges in modulating the microstructure and surface chemistry of carbocatalysts in ODH and DDH reactions of hydrocarbons for the highly‐efficient, energy‐saving,and clean production of their corresponding olefins.

Effects of substituting La with M(M=Sm, Nd, Pr) on electrochemical hydrogen storage characteristics of A_2B_7-type electrode alloys

The partial substitution of M （M=Sm, Nd, Pr） for La was performed in order to ameliorate the electrochemical hydrogen storage performance of RE–Mg–Ni-based A2B7-type electrode alloys. The La0.8–xMxMg0.2Ni3.35Al0.1Si0.05 （M=Sm, Nd, Pr;x=0-0.4） electrode alloys were fabricated by casting and annealing and their microstructures were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The major phases （La, Mg）2Ni7 with the hexagonal Ce2Ni7-type structure and LaNi5 with the hexagonal CaCu5-type structure make up the basic microstructure of the experimental alloys. The discharge capacities of the as-cast and annealed alloys all gain their maximum values with the M （M=Sm, Nd, Pr） content varying. The electrochemical cycle stability of the as-cast and annealed alloys clearly rises with the M （M=Sm, Nd, Pr） content growing. Furthermore, the electrochemical kinetics of the alloys, including the high rate discharge ability, charge transfer rate, limiting current density and hydrogen diffusion coefficient, all present a increase trend at first and then decrease with the rising of M （M=Sm, Nd, Pr） content.

Microstructure of TA2/TA15 graded structural material by laser additive manufacturing process

TA2/TA15 graded structural material（GSM） was fabricated by the laser additive manufacturing（LAM） process. The chemical composition, microstructure and micro-hardness of the as-deposited GSM were investigated. The results show that the TA2 part of exhibiting near-equiaxed grains was Widmanst？tten α-laths microstructure. The TA15 part containing large columnar grains was fine basket-weave microstructure. The graded zone was divided into four deposited layers with 3000 μm in thickness. As the distance from the TA2 part increases, the alloy element contents and the β phase volume fraction increase, the α phase volume fraction decreases and the microstructure shows the evolution from Widmanst？tten α-laths to basket-weave α-laths gradually. The micro-hardness increases from the TA2 part to the TA15 part due to the solid solution strengthening and grain boundary strengthening.

Chemical etching process of copper electrode for bioelectrical impedance technology

In order to obtain bioelectrical impedance electrodes with high stability, the chemical etching process was used to fabricate the copper electrode with a series of surface microstructures. By changing the etching processing parameters, some comparison experiments were performed to reveal the influence of etching time, etching temperature, etching liquid concentration, and sample sizes on the etching rate and surface microstructures of copper electrode. The result shows that the etching rate is decreased with increasing etching time, and is increased with increasing etching temperature. Moreover, it is found that the sample size has little influence on the etching rate. After choosing the reasonable etching liquid composition （formulation 3）, the copper electrode with many surface microstructures can be obtained by chemical etching process at room temperature for 20 rain. In addition, using the alternating current impedance test of electrode-electrode for 24 h, the copper electrode with a series of surface microstructures fabricated by the etching process presents a more stable impedance value compared with the electrocardiograph （ECG） electrode, resulting from the reliable surface contact of copper electrode-electrode.

Effects of current density on microstructure and properties of plasma electrolytic oxidation ceramic coatings formed on 6063 aluminum alloy

Plasma electrolytic oxidation (PEO) ceramic coatings were fabricated in a silicate-based electrolyte with the addition of potassium fluorozirconate (K2ZrF6) on 6063 aluminum alloy, and the effects of current density on microstructure and properties of the PEO coatings were studied. It was found that pore density of the coatings decreased with increasing the current density. The tribological and hardness tests suggested that the ceramic coating produced under the current density of 15 A/dm2showed the best mechanical property, which matched well with the phase analysis. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves proved that the coating obtained under 15 A/dm2 displayed the best anti-corrosion property, which was directly connected with morphologies of coatings.

THE SECRETORY STIGMAS IN POPULUS: DEVELOPMENT, CYTOCHEMISTRY, ULTRASTRUCTURE AND THEIR RELATION TO INTERSECTIONAL INCOMPATIBILITY *

The stigmas of five species, Populus euphratica Oliv., P. alba L., P. simonii Carr., P. lasiocarpa Oliv. and P. nigra L. have been studied. Scanning electron microscopy re veals that exudates are present in the intercellular spaces, in the clefts between the multicel lular papillae and on the receptive surface. Release and movement of exudates can be visual ized when the fresh stigmas are stained with sudan Ⅲ and auramine O. Paraffin and semi thin resin sections of stigmas after glutaraldehyde osmium fixation evidence the lipidic nature of the exudates. Transmission electron microscopy reveals the glandular features of the stigmatic papillae cells, such as abundance of rough and smooth endoplasmic reticulum, polyribosomes, and well developed dictyosomes with secretory vesicles. Pellicle and epicuticular lamellate layers which have been considered as typical features of the dry type stigmas are also present in the species where stigmas appear extremely wet. It is concluded that stigmas in all of the five species are secretory at the receptive stage. Well developed generative and sperm cells were observed in the pollen tubes penetrating through the deep layers of the stigmatic tissue in the reciprocal crosses between P. euphratica and P. simonii, which indicated that there is no significant barrier in the stigma.

Microstructure, mechanical and oxidation characteristics of detonation gun and HVOF sprayed MCrAlYX coatings

Microstructure, mechanical property and oxidation resistance of MCrAlYX coatings prepared by detonation gun (D-gun) and HVOF spraying were investigated. Lamellar microstructure and uniform microstructure formed in D-gun sprayed MCrAlYX coating and HVOF sprayed coating, respectively. Element redistribution and formation of new phase took place during the detonation process. Besides, the porosity of D-gun sprayed coating was much lower than that of HVOF sprayed coating. On the mechanical property, the micro-hardnesses of the two coatings were in the same level (~HV 910). However, D-gun sprayed MCrAlYX coating exhibited larger standard deviation of microhardness due to its lamellar microstructure, and exhibited better bend bonding strength owing to the existence of residual compressive stress between the layers and particles. Meanwhile, due to the much more compact microstructure, D-gun sprayed MCrAlYX coating showed superior oxidation resistance to the HVOF sprayed coating. The continuous dense protective layer can form earlier in D-gun sprayed coating and thus suppress further oxidation and control the oxide thickness at a relatively low level.

A Higher Plant Myosin in Luffa cylindrica: Electron Microscopic Visualization

The molecular structure of a higher plant myosin with two 174 kD heavy chains purified from the tendrils of Luffa cylindrica (L.) Roem. was viewed by electron microscopy. The myosin exhibited actin_activated MgATPase activity and could be recognized immunologically by a monoclonal antibody against the skeletal muscle myosin. Electron micrographs of rotary shadowed images of this protein revealed that it had two heads with size and shape similar to those of the skeletal muscle myosin and a relatively short tail in comparison with the conventional myosin. Luffa tendril actin filaments were also visualized and occasionally other Luffa myosin_like proteins with globular structure at the tail ends were also observed. The structural similarity and immunological cross reactivity with antibodies against muscle myosin demonstrate that the 174 kD Luffa tendril myosin is a double_headed myosin. The possible involvement of myosin_actin interactions in Luffa tendril contact coiling will be the subject of further research.

Microstructure and Nonlinear Optical Properties of Very Small Size GaAs Nanogranulae Embedded in SiO_2 Matrix by Magnetron Co-Sputtering

Microstructure of GaAs/SiO 2 nanogranular thin films fabricated by radio frequency magnetron co sputtering technique and postannealing are investigated via atomic force microscope,X ray diffraction,and Rutherford backscattering spectroscopy.The results show that GaAs nanocrystals with average diameters from 1 5nm to 3 2nm (depending on the annealing temperature) are uniformly dispersed in the SiO 2 matrices.GaAs and SiO 2 are found in normal stoichiometry in the films.The nonlinear optical refraction and nonlinear optical absorption are studied by Z scan technique using a single Gaussian beam of pulse laser.The third order nonlinear optical refractive index and nonlinear absorption coefficient are enhanced due to the quantum confinement effects and estimated to be 4×10 -12 m 2/W and 2×10 -5 m/W respectively in nonresonant condition,while 2×10 -11 m 2/W and -1×10 -4 m/W respectively in quasi resonant condition.

Electroless plating and growth kinetics of Ni-P alloy film on SiC_p/Al composite with high SiC volume fraction

After Sn/Pd activating, the SiCp/Al composite with 65% SiC (volume fraction) was coated by electroless Ni?P alloy plating. Surface morphology of the composite and its effect on the Ni?P alloy depositing process and bonding action of Ni and P atoms in the Ni?P alloy were studied. The results show that inhomogeneous distribution of the Sn/Pd activating points results in preferential deposition of the Ni?P alloy particles on the Al alloy and rough SiC particle surfaces and in the etched caves. The Ni?P alloy film has an amorphous structure where chemical bonding between Ni and P atoms exists. After a continuous Ni?P alloy film formed, electroless Ni?P alloy plating is not affected by surface morphology and characteristics of the SiCp/Al composite any longer, but by the electroless plating process itself. The Ni?P alloy film follows linear growth kinetics with an activation energy of 68.44 kJ/mol.

Effect of Cation Proportion on the Structural and Magnetic Properties of Ni-Zn Ferrites Nano-Size Particles Prepared By Co-Precipitation Technique

Ferrites having general formula Ni1-xZnxFe2O4 with x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 were prepared by wet chemical co-precipitation method. The structural and magnetic properties were studied by means of X-ray diffraction, magnetization, and AC susceptibility measurements. The X-ray analysis confirmed the single-phase formation of the samples. The lattice parameter obtained from XRD data was found to increase with Zn content x. The cation distribution was studied by X-ray intensity ratio calculations. Magnetization results exhibit collinear ferrimagnetic structure for x≤0.4, and which changes to non-collinear for x〉0.4. Curie temperature TC obtained from AC susceptibility data decreases with increasing x.

Preparation of tricalcium silicate and investigation of hydrated cement

Tricalcium silicate cement(TSC)has been widely used in dental materials because of its self-setting behavior,good bioactivity,biocompatibility,osteoinductivity,and antibacterial effect.Tricalcium silicate(C3S)powder was prepared by Pechini technique with a calcining temperature of 1300℃ for 3 h.The influence of liquid/powder(L/P)rate on the setting time and the mechanical property of TSC was studied.Characterization methods including XRD,FTIR,SEM-EDS,TEM,and ICP-AES were utilized to study the properties of C3S powder and its hydrated cement.The bioactivity and biocompatibility of the cement were investigated by soaking test and cell culture,respectively.The results show that the L/P rate plays an important role in the setting time and the compressive strength of TSC.The surface of TSC was covered by hydroxyapatite deposition during the immersion experiment and the cells attachment on the surface of TSC was well,which indicated that TSC has good bioactivity and biocompatibility.In addition,TSC has excellent antibacterial properties against Staphylococcus aureus.In conclusion,TSC is a promising candidate for root canal filling materials.

Characterization of the Microstructure Changes of Polypropylene Induced by Pan-milling

The microstructure changes of polypropylene induced by a complex combination of shearing, friction, compression and stretching actions during pan-milling were revealed by spectroscopic techniques. X-ray diffraction analysis showed that the structure of polypropylene transferred from crystal into amorphous after undergoing enough milling operation. No transformation between crystal forms was observed. The study of the high-frequency region of the Raman spectrum between 2800 and 3100cm-1 of polypropylene indicated that molecular motion and chain deformation of PP led to amorphization and deterioration of packing regularity during pan-milling. By co-panmilling PP with bis-(2,2,6,6-tetramethyl-4-piperidinyl) sebacate under ambient condition, ESR signals of free radicals formed by mechanochemical scission of main chain were observed, and an increase of ESR intensity with milling was detected.

Isothermal annealing of cold-rolled Al-Mn-Fe-Si alloy with different microchemistry states

Microstructural evolution of a cold-rolled Al-Mn-Fe-Si alloy during annealing was studied. Except the as-cast variant, two other different homogenizations were considered, one gave a high density of fine dispersiods providing a considerable Zener drag influencing the softening behavior while the other gave a lower density of coarser dispersoid structure providing a much smaller drag effect. The gradual microstructural evolutions during annealing for the three variants were captured by interrupting annealing at different time. Effects of microchemistry state on recrystallization kinetics, recrystallized grain structure and texture were characterized by EBSD. It is demonstrated that the actual softening kinetics, final microstructure and texture are a result of delicate balance between processing condition and microchemistry state. Strong concurrent precipitation takes place in the case with high concentration of Mn in solid solution, which suppresses nucleation and retards recrystallization and finally leads to grain structure of coarse elongated grains dominated by a P texture component together with a ND-rotated cube component. On the contrary, when solute content of Mn is low and pre-existing dispersoids are relatively coarser, faster recrystallization kinetics is exhibited together with an equiaxed grain structure with mainly cube texture.

Supercritical Antisolvent Precipitation of Microparticles of Quercetin

Supercritical antisolvent (SAS) process is a recently developed technology to produce micro- and nano particles. This paper presents a continuous apparatus to conduct experiment of SAS process. With the apparatus, the effects of pressure, temperature and flow ratio of CO2 to the solution on the shape and size of particles are studied for the quercetin-ethanol-CO2 system. Spherical quercetin microparticles with diameters ranging form 1 μm to 6μm can be obtained while ethanol is used as organic solvent. The most effective fact on the shape and size of particles is pressure, the next is temperature and the last is the flow ratio of CO2 to solution.

Siderophores from Marine Microorganisms and Their Applications

In view of the fact that siderophores from microorganisms in different environments have received much attention in recent years because of their potential applications and diverse physiological functions, this review deals with side rophore producing marine microorganisms and the detection, chemical structure and potential applications of siderophores.

Ultrastructure and histochemistry of rat myocardial capillary endothelial cells in response to diabetes and hypertension

Insufficient growth and rarefaction of capillaries, followed by endothelial dysfunction may represent one of the most critical mechanisms involved in heart damage. In this study we examined histochemical and ultrastructural changes in myocardial capillary endothelium in two models of heart failure streptozotocin-induced diabetes mellitus （STZ） and NO-deficient hypertension in male Wistar rats. Diabetes was induced by a single i.v. dose of STZ （45 mg/kg） and chronic 9-week stage was analysed. To induce NO-deficient hypertension, animals were treated with inhibitor of NO synthase Lnitroarginine methylester （L-NAME） （40 mg/kg） for 4 weeks. Left ventricular tissue was processed for enzyme catalytic histochemistry of capillary alkaline phosphatase （A1Ph）, dipeptidyl peptidase IV （DPP IV）, and endothelial NO synthase/NADPH-diaphorase （NOS） and for ultrastructural analysis. In diabetic and hypertensive rats, lower/absent A1Ph and DPP IV activities were found in focal micro-areas. NOS activity was significantly reduced and persisted only locally. Quantitative evaluation demonstrated reduction of reaction product intensity of A1Ph, DPP and NOS by 49.50%,74.36%, 20.05% in diabetic and 62.93%, 82.71%, 37.65% in hypertensive rats. Subcellular alterations of endothelial cells were found in heart of both groups suggesting injury of capillary function as well as compensatory processes. Endothelial injury was more significant in diabetic animals, in contrast the adaptation was more evident in hypertensive ones. Concluding： both STZ-induced diabetes- and NO-deficient hypertension-related cardiomyopathy were accompanied by similar features of structural remodelling of cardiac capillary network manifested as angiogenesis and angiopathy. The latter was however, predominant and may accelerate disappearance of capillary endothelium contributing to myocardial dysfunction.

Fabrication of 3D structure by combining AFM and chemical etching on crystalline silicon surface

AFM is used for forming silicon dioxide as a layer (mask) on the silicon wafer surface (100) during the cutting process in ambient atmosphere. The silicon dioxide is made through reaction of silicon and oxygen in the atmosphere. As a result of the anisotropic behavior of single crystalline silicon, the etching rates in alkaline solution depend greatly on the various crystal orientations. The anisotropic etching behaviors in KOH solution and reasons of crystalline silicon are described. Effect of etching conditions such as etching temperature and KOH concentration of the alkaline solution on height of the micro-protuberances has been described.

Influence of Yb_2O_3 doping on microstructural and electrical properties of ZnO-Bi_2O_3-based varistor ceramics

ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4% （molar fraction） were obtained by a solid reaction route. The X-ray diffractometry （XRD） and scanning electron microscopy （SEM） were applied to characterize the phases and microstructure of the varistor ceramics, and a DC parameter instrument for varistor ceramics was applied to investigate their electrical properties and V-I characteristics. The XRD analysis of the samples shows that the ZnO phase, Bi2O3 phase, ZnTSbaOl2-type spinel phase and Zn2Bi3Sb3O14-type pyrochlore are present, and the Yb2O3 phases and Sb2O4 phases are found in varistor ceramics with increasing amounts of Yb2O3. The average size of ZnO grain firstly increases and then decreases with the increase of Yb2O3 content. The result also shows that the threshold voltage is between 656 V/nun and 1 232 V/mm, the nonlinear coefficient is in the range of 14.1-22.3, and the leakage current is between 0.60 μA and 19.6 μA. The 0.20% Yb2O3-added ZnO-Bi2O3-based varistor ceramics sintered at 900 ℃ have the best electrical characteristics.