Microstructure and mechanical properties of Fe/NbC composite layer prepared by in-situ reaction

NbC ceramic surface-reinforced steel matrix composites were prepared by an in-situ reaction method at different temperatures(1,050℃,1,100℃and 1,150℃)for different times(1 h,2 h and 3 h).The phase constitution,microstructure and fracture morphology of NbC ceramic surface-reinforced steel matrix composites were analyzed by XRD,SEM and EDS,and the effects of the in-situ reaction temperature and time on the mechanical properties were systematically studied.The results indicate that the NbC reinforcement layer is formed through the reaction between Nb atoms and carbon atoms diffused from the steel matrix to the Nb plate.The thickness of this reinforcement layer increases as the reaction time prolongs.Additionally,an increase in reaction temperature results in a thicker reinforcement layer,although the rate of increase gradually decreases.The relationship among the thickness of the Nb C reinforcement layer,the reaction time and temperature was established by data fitting.The optimal tensile performance is achieved at 1,100℃for 1 h,with a tensile strength of 228 MPa.It is also found that the defects between the reinforcement layer and the steel matrix are related to reaction temperature.At 1,100℃,these defects are minimal.Fracture mostly occurs in the NbC reinforced layer of the composites,and the fracture mode is characterized by typical intergranular brittle fracture.

Interfacial reaction behavior and mechanical properties of 5A06 Al alloy soldered with Sn-1Ti-xGa solders at a low temperature

Active soldering of 5A06 Al alloy was performed at 300 ℃ by using Sn-1Ti and Sn-1Ti-0.3Ga active solders, respectively. Theeffects of soldering time on the microstructure and mechanical properties of the joints were investigated. The results showed that the Sn-1Tisolder broke the oxide film on the surface of the Al substrate and induced intergranular diffusion in the Al substrate. When Ga was added tothe solder, severe dissolution pits appeared in the Al substrate due to the action of Sn-1Ti-0.3Ga solder, and many Al particles were flakedfrom the matrix into the solder seam. Under thermal stress and the Ti adsorption effect, the oxide film cracked. With increasing solderingtime, the shear strength of 5A06 Al alloy joints soldered with Sn-1Ti and Sn-1Ti-0.3Ga active solders increased. When soldered for 90 min,the joint soldered with Sn-1Ti-0.3Ga solder had a higher shear strength of 22.12 MPa when compared to Sn-1Ti solder.

Electrochemical properties of spinel LiMn_2O_4 and LiAl_(0.1)Mn_(1.9)O_(3.9)F_(0.1) synthesized by solid-state reaction

Two types of spinel cathode powders, LiMn2O4 and LiAl0.1Mn1.9O3.9F0.1, were synthesized by solid-state reaction, X-ray diffraction （XRD） patterns of the prepared samples were identified as the spinel structure with a space group of Fd 3^- m. The cubic lattice parameter was determined from least-squares fitting of the XRD data. The LiAl0.1Mn1.9O3.9F0.1 sample showed a little lower initial capacity, but better cycling performance than the LiMn2O4 sample at both room temperature and an elevated temperature. The Vanderbilt method was used to test the electrochemical conductivity of the LiMn2O4 samples. The electrochemical impedance spectroscopy （EIS） method was employed to investigate the electrochemical properties of these spinel LiMn2O4 samples.

Dielectric Properties of Porous Reaction-boned Si_3N_4 Ceramics with Controlled Porosity and Pore Size

This paper presents the microwave dielectric properties of reaction bonded porous silicon nitride ceramics with variant porosity and pore size, which were prepared by adding pore-forming agent grains into the silicon powders. The experimental results show that the dielectric constant and the dielectric loss of the samples reduce evidently with increasing porosity in the sample. When the porosity is constant, the dielectric constant and the dielectric loss of the ceramics decrease visibly as the pore size increases. Among all the obtained samples, the minimum dielectric constant is about 2.4.

Properties of a reaction-bonded β-SiAlON ceramic doped with an FeMo alloy for application to molten aluminum environments

An FeMo-alloy-doped β-SiA1ON （FeMo/β-SiA1ON） composite was fabricated via a reaction-bonding method using raw materials of Si, Al2O3, A1N, FeMo, and Sm2O3. The effects of FeMo on the microstructure and mechanical properties of the composite were investi- gated. Some properties of the composite, including its bending strength at 700℃ and after oxidization at 700℃ for 24 h in air, thermal shock resistance and corrosion resistance to molten aluminum, were also evaluated. The results show that the density, toughness, bending strength, and thermal shock resistance of the composite are obviously improved with the addition of an FeMo alloy. In addition, other properties of the composite such as its high-temperature strength and oxidized strength are also improved by the addition of FeMo alloy, and its corrosion re- sistance to molten aluminum is maintained. These findings indicate that the developed FeMo/β-SiA1ON composite exhibits strong potential for application to molten aluminum environments.

Effect of SiO_2 on the Preparation and Properties of Pure Carbon Reaction Bonded Silicon Carbide Ceramics

Effect of SiO 2 content and sintering process on the composition and properties of Pure Carbon Reaction Bonded Silicon Carbide (PCRBSC) ceramics prepared with C-SiO 2 green body by infiltrating silicon was presented.The infiltrating mechanism of C-SiO 2 preform was also explored.The experimental results indicate that the shaping pressure increases with the addition of SiO 2 to the preform,and the pore size of the body turned finer and distributed in a narrower range,which is beneficial to decreasing the residual silicon content in the sintered materials and to avoiding shock off,thus increasing the conversion rate of SiC.SiO 2 was deoxidized by carbon at a high temperature and the gaseous SiO and CO produced are the main reason to the crack of the body at an elevated temperature.If the green body is deposited at 1800℃ in vacuum before infiltration crack will not be produced in the preform and fully dense RBSC can be obtained.The ultimate material has the following properties:a density of 3.05-3.12g/cm3,a strength of 580±32MPa and a hardness of (HRA)91-92.3.

Preparation of new sunscreen materials Ce_(1-x)Zn_xO_(2-x) via solid-state reaction at room temperature and study on their properties

Superfine cerium-zinc oxides Ce1-xZnxO2-x with x = 0, 0.1, 0.3, 0.5, and 1.0 were obtained by grinding Ce（SO4）2·4H2O, ZnSO4·7H2O and NH4HCO3 under the condition of surfactant PEG-400 being present at room temperature, washing the mixture with water to remove soluble inorganic salts, drying at 80°C, and calcining.The precursor and its calcined samples were characterized using thermogravimetry and differential thermal analyses（TG/DTA）, UV-vis absorption spectroscopy, X-ray powder diffraction（XRD）, and scanning electron microscopy（SEM）.The results showed that superfine Ce1-xZnxO2-x behaved as an excellent UV-shielding material.The ZnO-doped CeO2 can facilitate the formation of crystalline state CeO2.The catalytic ability of products used in air oxidation of castor oil was investigated.The results showed that the catalytic abilities of products decreased with increasing zinc amount.

Oxygen vacancy boosting Fenton reaction in bone scaffold towards fighting bacterial infection

Bacterial infection is a major issue after artificial bone transplantation due to the absence of antibacterial function of bone scaffold,which seriously causes the transplant failure and even amputation in severe cases.In this study,oxygen vacancy(OV)defects Fe-doped Ti O2(OV-FeTiO2)nanoparticles were synthesized by nano TiO2and Fe3O4via high-energy ball milling,which was then incorporated into polycaprolactone/polyglycolic acid(PCLGA)biodegradable polymer matrix to construct composite bone scaffold with good antibacterial activities by selective laser sintering.The results indicated that OV defects were introduced into the core/shell-structured OV-FeTiO2nanoparticles through multiple welding and breaking during the high-energy ball milling,which facilitated the adsorption of hydrogen peroxide(H2O2)in the bacterial infection microenvironment at the bone transplant site.The accumulated H2O2could amplify the Fenton reaction efficiency to induce more hydroxyl radicals(·OH),thereby resulting in more bacterial deaths through·OH-mediated oxidative damage.This antibacterial strategy had more effective broad-spectrum antibacterial properties against Gram-negative Escherichia coli(E.coli)and Gram-positive Staphylococcus aureus(S.aureus).In addition,the PCLGA/OV-FeTiO2scaffold possessed mechanical properties that match those of human cancellous bone and good biocompatibility including cell attachment,proliferation and osteogenic differentiation.

Steam reforming of acetic acid over Ni/biochar of low metal-loading:Involvement of biochar in tailoring reaction intermediates renders superior catalytic performance

Biochar is a reactive carrier as it may be partially gasified with steam in steam reforming,which could influence the formation of reaction intermediates and modify catalytic behaviors.Herein,the Ni/biochar as well as two comparative catalysts,Ni/Al_(2)O_(3) and Ni/SiO_(2),with low nickel loading(2%(mass))was conducted to probe involvement of the varied carriers in the steam reforming.The results indicated that the Ni/biochar performed excellent catalytic activity than Ni/SiO_(2) and Ni/Al_(2)O_(3),as the biochar carrier facilitated quick conversion of the -OH from dissociation of steam to gasify the oxygen-rich carbonaceous intermediates like C=O and C-O-C,resulting in low coverage while high exposure of nickel species for maintaining the superior catalytic performance.In converse,strong adsorption of aliphatic intermediates over Ni/Al_(2)O_(3) and Ni/SiO_(2) induced serious coking with polymeric coke as the main type(21.5%and 32.1%,respectively),which was significantly higher than that over Ni/biochar(3.9%).The coke over Ni/biochar was mainly aromatic or catalytic type with nanotube morphology and high crystallinity.The high resistivity of Ni/biochar towards coking was due to the balance between formation of coke and gasification of coke and partially biochar with steam,which created developed mesopores in spent Ni/biochar while the coke blocked pores in Ni/Al_(2)O_(3) and Ni/SiO_(2) catalysts.

Investigation of electrophysical, photo- and gas-sensitive properties of ZnO–SnO_(2) sol–gel fflms

Thin nanocomposite fflms based on tin dioxide with a low content of zinc oxide(0.5–5 mol.%)were obtained by the sol–gel method.The synthesized fflms are 300–600 nm thick and contains pore sizes of 19–29 nm.The resulting ZnO–SnO_(2) fflms were comprehensively studied by atomic force and Kelvin probe force microscopy,X-ray diffraction,scanning electron microscopy,and high-resolution X-ray photoelectron spectroscopy spectra.The photoconductivity parameters on exposure to light with a wavelength of 470 nm were also studied.The study of the photosensitivity kinetics of ZnO–SnO_(2) fflms showed that the fflm with the Zn:Sn ratio equal to 0.5:99.5 has the minimum value of the charge carrier generation time constant.Measurements of the activation energy of the conductivity,potential barrier,and surface potential of ZnO–SnO_(2) fflms showed that these parameters have maxima at ZnO concentrations of 0.5 mol.%and 1 mol.%.Films with 1 mol.%ZnO exhibit high response values when exposed to 5–50 ppm of nitrogen dioxide at operating temperatures of 200℃ and 250℃.

Solid State Reaction Synthesis and Thermoelectric Properties ofMg_2Si doped with Sb and Te

Doped with Sb and Te, Mg2Si based compounds were prepared respectively by solid state reaction at 823 K for 8 h. Effects of dopants of Sb and Te on the structure and thermoelectric properties of the compounds were investigated. By calculating the values of the electrical conductivity for Sb-doped sample, the mechanism of electric conduction at 625 K is different. The figure of merit for sample doped with 0.4 wt% Te at500K is 2.4 × 10-3W/mK2,and it reaches 3. 3 ×10-3 W/mK2 at 650K for the sample doped with 0. 5wt% Sb. The values are more than 1.4 times and 2.3 times of the pure Mg2 Si sample.

Studies on the Inversion Phenomenon of Physical Properties Observed in the Huagang Formation Reservoir in the Xihu Sag Based on the Water-Rock Reaction Experiments

In the Xihu Sag,the reservoirs of the Paleogene Huagang formation have entered the middle diagenetic stage A and the rock physical properties of the water layer are considerably more suitable for the gas migration and storage than those of the present gas layer,indicating the inversion of the physical properties.In this study,core samples were collected from the corresponding reservoir to conduct water-rock reaction experiments in acidic,alkaline,and neutral systems under the specific temperature and pressure.The reasons for the inversion of physical properties were investigated based on the experiment results in reservoir diagenetic environments.The inversion of physical properties can be attributed to the fact that the diagenetic environment around the gas-water interface controls the water-rock reaction effect.With different types of acidic substances,two different situations corresponding to inverted physical properties were analyzed along with the corresponding mechanisms.When the pore fluid is acidic,the physical properties make the overall water layer a better reservoir space than the gas layer,which can be referred to as the overall inversion of physical properties.When the fluid were generally neutral or weakly alkaline and the gas layer was rich in CO2,only the physical properties of the water layer adjacent to the gas-water interface were more favorable for the gas migration than those of the gas layer.This phenomenon can be referred to as the near-interface inversion of physical properties.

Microstructure and mechanical properties of reaction-bonded B_(4)C–SiC composites

Reaction-bonded B_(4)C–SiC composites are highly promising materials for numerous advanced technological applications.However,their microstructure evolution mechanism remains unclear.Herein,B_(4)C–SiC composites were fabricated through the Si-melt infiltration process.The influences of the sintering time and the B_(4)C content on the mechanical properties,microstructure,and phase evolution were investigated.X-ray diffraction results showed the presence of SiC,boron silicon,boron silicon carbide,and boron carbide.Scanning electron microscopy results showed that with the increase in the boron carbide content,the Si content decreased and the unreacted B_(4)C amount increased when the sintering temperature reached 1650°C and the sintering time reached 1 h.The unreacted B_(4)C diminished with increasing sintering time and temperature when B_(4)C content was lower than 35wt%.Further microstructure analysis showed a transition area between B_(4)C and Si,with the C content marginally higher than in the Si area.This indicates that after the silicon infiltration,the diffusion mechanism was the primary sintering mechanism of the composites.As the diffusion process progressed,the hardness increased.The maximum values of the Vickers hardness,flexural strength,and fracture toughness of the reaction-bonded B_(4)C–SiC ceramic composite with 12wt%B_(4)C content sintered at 1600°C for 0.5 h were about HV 2400,330 MPa,and 5.2 MPa·m^(0.5),respectively.

The Reaction Sequence and Dielectric Properties of BaAl₂Ti₅O₁₄Ceramics

To investigate the correct reaction sequence of BaO-Al2O3-5TiO2 system, powders calcined at different temperatures are analyzed by x-ray diffraction. The results show that the source phase BaCO3 decomposes below 800°C, TiO2 and Al2O3 start to consume at 900 and 1100°C, respectively. BaTi4O9 phase appears at 1000°C while BaAl2Ti5O14 phase starts to reveal at 1200°C. As the temperature increases, the density, dielectric constant and quality factor of the BaAl2Ti5O14 ceramic increase and keep unchanged at 1350°C. The dielectric properties of BaAl2Ti5O14 ceramic sintered at 1350°C for 3h are: εr=35.8, Q×f=5130GHz, τf=-6.8ppm/°C.

A THEORETICAL STUDY OF THE THERMODYNAMIC AND KINETIC PROPERTIES FOR THE REACTION OF FORMYL CYANIDE DECOMPOSITION

We compute the thermodynamic and the kinetic properties for the reaction: HCOCN→HCH+CO using the statistical theory and the transition-state theory.The equi- librium constants and the rate coefficients of this reaction are also reported here,and the half lives of formyl cyanide at different temperatures are first estimated in this work.

Dependence of Nitrogen/Argon Reaction Gas Amount on Structural,Mechanical and Optical Properties of Thin WNx Films

WNxfilms are deposited by reactive chemical vapor deposition at different amounts of nitrogen in gas mixtures.Experimental data demonstrate that nitrogen amount has a strong effect on microstructure, phase formation,texture morphology, mechanical and optical properties of the WNxfilms. With increasing nitrogen a phase transition from a single WNxphase with low crystallinity structure to a well-mixed crystallized hexagonal WNxand face-centered-cubic W2N phases appears. Relatively smooth morphology at lower N2concentration changes to a really smooth morphology and then granular with coarse surface at higher N2concentration. The SEM observation clearly shows a columnar structure at lower N2concentration and a dense nanoplates one for higher nitrogen content. The hardness of WNxthin films mainly depends on the film microstructure. The absorbance peak position shifts to shorter wavelength continuously with increasing nitrogen amount and decreasing particle size.

STUDIES ON THE PROPERTIES OF SCHIFF BASE TYPE ARYLMERCURY COMPOUNDS Ⅲ TRANSMETALLATION REACTION OF SCHIFF BASE TYPE ARYLMERCURY COMPOUNDS WITH METALLIC TIN

The transmetallation reaction of 4 Schiff base type arylmercury compounds with metallic tin has been carried out in refluxing xylene.It was found that the reaction proceeds in the same manner as that of chloro[2-(phenylazo)phenyl]mercury(Ⅱ) to give dichlorobisaryltin(Ⅳ).The ~1H NMR spectra of the products provide evidence for the presence of N→Sn intramolecular coordination.The formation of dichlorobisaryltin(Ⅳ)as a unique product probably arises from the N→Sn intramolecular coordination which results in the increasing of the stability of the molecule.

Study on the Preparation,the Magnetic Performance,and the Oxygen Evolution Reaction of LaMnO_(3+δ)

In this paper,a series of LaMnO_(3+δ)(LMOs)were successfully prepared by adjusting the sintering temperature using the sol-gel method with ABO3-type LMO oxides as the object of study.The results showed that with the increase of sintering temperature,the O_(ads),oxygen vacancies,and Mn^(4+)content in the system gradually decreased,and the oxygen evolution reaction(OER)was subsequently weakened.Although the suitable Mn^(3+)/Mn^(4+)valence ratio(2.15:1)of the LMO700 sample created a strong ferromagnetic double-exchange effect,the high concentration of oxygen vacancies in LMO700 disturbed this effect and weakened its macro magnetism.This paper serves to contribute to the design and development of new magnetic perovskite electrocatalysts.

Effect of Homogenizing Procedures on the Properties of Reaction Sialon Suspension

Homogeneous, high concentrated ceramic suspensions wi th low viscosity are the key controlling factors for the production of ceramic c omponents through colloidal processing. A well-dispersed suspension can be obta ined by choosing suitable dispersant, solvent, particle size distribution etc. B esides these factors, the homogenizing procedure is also a key step. In this paper, reaction sialon suspensions were prepared using 3-wt% KD1 as dis persant in organic media composed of 60-vol% methyletheylketone and 40-vol% et hanol. Different homogenizing procedures have been used and compared, including planetary milling, low energy ball milling and ultrasonic disaggregation. The ef fects of different homogenizing routes and mixing times on the rheology and stab ility of suspensions, and on the microstructure of slip casting green bodies, ha ve been studied. The varying dispersion efficiencies observed could be attribute d to differences in deagglomeration degrees achieved and in adsorption amount of dispersant onto the surface of reaction sialon powders.

Synthesis of Ca_2ZnSi_2O_7:Eu phosphor by a modified solid-state reaction and its luminescent properties

This paper reports the detailed preparation and phosphorescence properties of Eu2+-activated Ca2ZnSi2O7 phosphors by a modified solid-state reaction.Phase-pure crystalline Ca2ZnSi2O7 is obtained at 600℃,a much lower temperature than by conventional solid-state reaction and the preparation process of Ca2ZnSi2O7 is simple.The obtained phosphors showed three emission peaks at 480,580 and 620 nm,respectively.Auxiliary activator R3+(R=Dy,Nd,Tm) would enhance their luminescent properties.