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1.
Based on thermodynamic analysis, highly dense (TiB2 + TiC)/Ti3SiC2 composite ceramics with different TiB2 volume contents were in situ fabricated in situ by hot-pressing at 1500 °C. Laminar Ti3SiC2 grains, columnar TiB2 grains and equiaxed TiC grains were clearly identified from microstructural observation; grain boundaries were clean. The increase of TiB2 volume content significantly restrains the grain growth of the Ti3SiC2 matrix. As the content of TiB2 increases from 5 vol.% to 20 vol.%, the bending strength and fracture toughness of the composites both increase and then decrease, whereas the Vickers hardness increases linearly from 6.13 GPa to 11.5 GPa. The composite with 10 vol.% TiB2 shows the optimized microstructure and optimal mechanical properties: 700 MPa for bending strength; 9.55 MPa m1/2 for fracture toughness. These are attributed to the synergistic action of strengthening and toughening mechanisms such as particulate reinforcement, crack deflection, grain's pull-out and fine-grain toughening, caused by the columnar TiB2 grains and equiaxed TiC grains. 相似文献
2.
Mário H.P. Santana 《Electrochimica acta》2006,51(17):3578-3585
A systematic investigation was conducted on the mechanism and electrocatalytic properties of O2 and Cl2 evolution on mixed oxide electrodes of nominal composition: Ti/[Ru(0.3)Ti(0.6)Ce(0.1−x)]O2[Nb2O5](x) (0 ≤ x ≤ 0.1). For the oxygen evolution, a 30 mV Tafel slope is obtained in the presence of CeO2, while in its absence a 40 mV coefficient is observed. The intrinsic electrocatalytic activity is mainly due to electronic factors, as result of the synergism between Ru and Ce oxides. For chlorine evolution, the Tafel slope (30 mV) is independent on oxide composition. The best global electrocatalytic activity for ClER was observed in the absence of Nb2O5 additive. Variation of the voltammetric charge throughout the experiments confirms high CeO2 content compositions are fragile, due mainly to the porosity caused by CeO2 presence. On the other hand, Nb2O5 addition decreases considerably this instability. 相似文献
3.
Dense Ti3AlC2/TiB2 composites were successfully fabricated from B4C/TiC/Ti/Al powders by spark plasma sintering (SPS). The microstructure, flexural strength and fracture toughness of the composites were investigated. The experimental results indicate that the Vickers hardness increased with the increase in TiB2 content. The maximum flexural strength (700 ± 10 MPa) and fracture toughness (7.0 ± 0.2 MPa m1/2) were achieved through addition of 10 vol.% TiB2, however, a slight decrease in the other mechanical properties was observed with TiB2 addition higher than 10 vol.%, which is believed to be due to TiB2 agglomeration. 相似文献
4.
Zhirong Fan 《Polymer》2009,50(15):3431-34
Hyperbranched (hb) aromatic polyesters with phenolic end groups were synthesized according to the A2 + B3 approach both, by solution polymerization and by melt (bulk) polymerization with different monomer ratios (A2:B3). The hb polyesters produced from solution polymerization exhibited higher yields, molar masses and glass transition temperature (Tg) compared to the products prepared in the melt. The resulting hb aromatic polyesters from the A2 + B3 approach were also compared with their properties to hb aromatic polymers produced from the well known AB2 monomer 3,5-bis(trimethylsiloxy)benzoyl chloride. Both types of hb aromatic polyesters possess high Tg, high thermal stability and good solubility in common organic solvents. A typical melt viscosity behavior with shear thinning effect was also observed for both. Thus similar polymer properties compared to melt-condensed products were obtained with the A2 + B3 approach by solution polycondensation possessing the advantage of easy monomer availability and much milder polymerization conditions (at room temperature in solution) compared to the AB2 approach. 相似文献
5.
Material removal and surface damage of Ti3SiC2 ceramic during electrical discharge machining (EDM) were investigated. Melting and decomposition were found to be the main material removal mechanisms during the machining process. Material removal rate was enhanced acceleratively with increasing discharge current, ie, working voltage, ui, but increased deceleratively with pulse duration, te. Microcracks in the surface and loose grains in the subsurface resulted from thermal shock were confirmed, and the surface damage in Ti3SiC2 ceramic led to a degradation of both strength and reliability. 相似文献
6.
Near-fully dense Ti3Si(Al)C2/Ti5Si3 composites were synthesized by in situ hot pressing/solid–liquid reaction process under a pressure of 30 MPa in a flowing Ar atmosphere at 1580 °C for 60 min. Compared to monolithic Ti3Si(Al)C2, Ti3Si(Al)C2/Ti5Si3 composites exhibit higher hardness and improved wear resistance, but a slight loss in flexural strength (about 26% lower than Ti3Si(Al)C2 matrix). In addition, Ti3Si(Al)C2/Ti5Si3 composites maintain a high fracture toughness (KIC = 5.69–6.79 MPa m1/2). The Ti3Si(Al)C2/30 vol.%Ti5Si3 composite shows the highest Vickers hardness (68% higher than that of Ti3Si(Al)C2) and best wear resistance (the wear resistance increases by 2 orders of magnitude). The improved properties are mainly ascribed to the contribution of hard Ti5Si3 particles, and the strength degradation is mainly due to the lower Young's modulus and strength of Ti5Si3. 相似文献
7.
Lifeng Zhang 《Fuel》2009,88(3):511-24
Nickel-based catalysts supported on Al2O3 · SiO2 were prepared with modification of the second metal involving La, Co, Cu, Zr or Y, of which the catalytic behaviors were assessed in the ethanol steam reforming reaction. Activity test indicated that addition of La resulted in higher selectivity of hydrogen and lower selectivity of carbon monoxide, compared with Co-doped nickel catalyst. Influences of lanthanum amounts on catalytic performance were studied over 30NixLa/Al2O3 · SiO2 (x = 5, 10, 15), and characterizations by XRD, TPR and XPS indicated that low amount of lanthanum additives (5%) was superior to inhibit the crystal growth of nickel as well as beneficial to the reduction of nickel oxide. Finally 100 h test for the optimal catalyst 30Ni5La/Al2O3 · SiO2 indicated its good long-term stability to provide high hydrogen selectivity and low carbon monoxide formation, as well as good resistance to coke deposition at low temperature. 相似文献
8.
The present study aims to investigate synthesis of Ti3SiC2 from TiO2 and SiO2 powder mixtures by carbothermal reduction method. Equilibrium TiO2–SiO2–C ternary phase diagram was used to predict the conditions for the formation of Ti3SiC2 at 1800 K under Ar atmosphere. A reactant mixture with a TiO2:SiO2 molar ratio of 1.5 and a C content of 68.75 mol% (26.86 wt%) was initially selected among the thermodynamically favorable reactant compositions for the experimental studies. Two different C sources, graphite flakes and pyrolytic C coating, were used to synthesize Ti3SiC2 at 1800 K under Ar atmosphere. When graphite flakes were used, the products contained a trace amount of Ti3SiC2 phase along with major TiC and minor SiC phases. Whereas, pyrolytic C coating on the oxide particles resulted in the products with much higher Ti3SiC2 contents owing to the close contact between the reactants. Optimal C concentration for the C coated oxide mixtures with a TiO2:SiO2 molar ratio of 1.5 was determined to be 30.05 wt% under the experimental conditions studied. Ti3SiC2 content of the products obtained from this reactant was observed to increase with reaction time to 31 wt% at 75 min beyond which it gradually decreased. XRD studies indicated that the product with the highest ternary carbide content also contained TiC and a trace amount of SiC. SEM-EDS analyses showed that this sample essentially consisted of spherical fine TiC particles and Ti3SiC2 nanolaminates. Equilibrium thermodynamic analysis of the TiO2–SiO2–C system suggested that the reaction of solid Ti2O3 with SiO and CO gases may play a dominant role in the formation of Ti3SiC2. 相似文献
9.
Soft Ti3SiC2 ceramic is a new class of potential biomaterial for orthopaedic applications and dental implants. Introducing SiC into Ti3SiC2 can compensate for the relatively low hardness of the Ti3SiC2 implants. In this study, SiC reinforced Ti3SiC2-base composites were fabricated by reactive sintering of powder compacts. Mechanical properties and phase constitution of the prepared samples were studied. Biocompatibility of the composite was evaluated by implanting the material onto the shaft surface of the femur of a rabbit, while, biostability was studied by immersing the material into human blood plasma and also into a simulated body fluid (Hank's) for prolonged time. 相似文献
10.
We previously proposed that current oscillations occurred when there were both an active factor and a passive factor that depended on each other and influenced the anodic dissolution processes of metallic materials alternatively. In this study, an electrochemical system, Al|NaCl + NaNO2, was designed to verify this proposal. The chloride ions are aggressive ions (active factor), assisting the dissolution of the oxide film, while nitrite ions are inhibitive ones (passive factor), assisting the formation of the oxide film. The dissolution and the formation of the oxide film on the surface of the Al electrode occurred alternatively, and the current oscillations were observed to occur in this system, which proved the above point. The Al|NaCl + NaNO2 system is a new electrochemical oscillator, in which hydrogen evolves periodically from the surface of the electrode during the current oscillations. The results were discussed in terms of the formation and the dissolution of the oxide film. The current oscillations were induced by pitting corrosion of Al in chloride ions containing solutions. It is expected that more oscillatory systems can be found and further studies into the nonlinear dynamic behaviour of metallic materials can be conducted in the light of the proposal. 相似文献
11.
In this paper, Me double hydroxides (Me = Co and Ni)/TiO2 nanotube composites were synthesized by a simple chemical co-precipitation method. Electrochemical properties of the composites were examined by cyclic voltammetry, galvanostatic and impedance measurements. The highest specific capacitance values of 1053 F/g could be achieved with Me double hydroxides loaded on the TiO2 nanotube, which was comparable to that of hydrated ruthenium oxide. 相似文献
12.
Hui XianFeng-Li Li Xin-Gang Li Xing-Wen ZhangMing Meng Tian-Yong ZhangNoritatsu Tsubaki 《Fuel Processing Technology》2011,92(9):1718-1724
A series of the BaFeO3 − x perovskite catalysts was synthesized by a sol-gel method using citric acid and/or EDTA as complexants with a purpose to improve their sulfur-resistance by forming a uniform perovskite structure at a low calcination temperature, i.e. 750 °C. The thermogravimetry results show that almost no carbonate was formed after calcination of the xerogel precursor with the complexants' molar ratio of CA/EDTA ≤ 1.5, which was convinced by the in situ DRIFT spectra results of the Ba-Fe-1 catalyst during the SO2/O2 sorption. It indicates that, after adding EDTA into the complexants, the metal ions of the raw material could be mixed homogeneously and react stoichiometrically by calcination at 750 °C to form a uniform perovskite structure. Accordingly, the obtained Ba-Fe-1 perovskite presented a performed sulfur-resistance. Moreover, the seriously damaged structure of the BaFeO3 − x perovskite by reduction could be in situ regenerated by calcination under lean conditions at 400 °C, which is within the operating temperature zone of the aftertreatment system of diesel to meet the real commercial demands. 相似文献
13.
M.A. Olutoye 《Fuel Processing Technology》2010,91(6):653-659
The Mg-Zn interaction effect of KyMg1 − xZn1 + xO3 heterogeneous type catalyst and its performance on transesterification of palm oil have been studied using the response surface methodology and the factorial design of experiments. The catalyst was synthesized using the co-precipitation method and the activity was assessed by transesterification of palm oil into fatty acid methyl esters. The ratio of the Mg/Zn metal interaction, temperature and time of calcination were found to have positive influence on the conversion of palm oil to fatty acid methyl ester (FAME) with the effect of metal to metal ratio and temperature of calcination being more significant. The catalytic activity was found to decrease at higher calcination temperature and the catalyst type K2Mg0.34Zn1.66O3 with Mg/Zn ratio of 4.81 gave FAME content of 73% at a catalyst loading of 1.404 wt.% of oil with molar ratio of methanol to oil being 6:1 at temperature of 150 °C in 6 h. A regression model was obtained to predict conversions to methyl esters as a function of metal interaction ratio, temperature of calcination and time. The observed activity of the synthesized catalyst was due to its synergetic structure and composition. 相似文献
14.
Yanhui Yuan 《The Journal of Supercritical Fluids》2010,55(1):358-362
We have recently proposed a compressible lattice model for CO2 + polymer systems in which CO2 forms complexes with one or more functional groups in the polymer. Furthermore, we have shown that this model is able to simultaneously correlate phase equilibria, sorption behavior, and glass transition temperatures in such systems. In the present work, we extend the model to ternary CO2 + cosolvent + polymer systems and demonstrate that cloud point behavior in CO2 + dimethyl ether + poly (?-caprolactone), CO2 + dimethyl ether + poly (isopropyl acrylate), and CO2 + dimethyl ether + poly (isodecyl acrylate) systems can be predicted using parameters obtained from binary data. Our results also suggest that dimethyl ether may form weak complexes with poly (?-caprolactone), poly (isopropyl acrylate), and poly (isodecyl acrylate). 相似文献
15.
Dongquan Shen Xiuzhi LiZujian Wang Ying LiuChao He Tao LiXifa Long 《Journal of the European Ceramic Society》2012,32(5):1077-1083
A new ferroelectric solid solution of (1 − x)Ba(Lu1/2Nb1/2)O3-xPbTiO3 (BLN-PT) (0 ≤ x ≤ 1) has been synthesized by solid state reactions. Its structure and electric properties have been studied by X-ray diffraction and di-/ferro-electric measurements. Based on the investigation, a partial solid state phase diagram of the binary BLN-PT ceramics system has been established, which exhibits a morphotropic phase boundary (MPB) region in the composition range of 0.64 ≤ x ≤ 0.68. The Curie temperature is measured to be around 250 °C in the vicinity of the MPB region, which is much higher than that of PMNT or PZNT system. The dielectric behavior has been discussed based on Curie-Weiss Law and Lorentz-type quadratic relationship. With increasing PT content, a transformation from relaxor to ferroelectric phase has been demonstrated in the solid solution system. 相似文献
16.
Isomerization of n-hexane and n-pentane were studied using equivalent 5 monolayers of MoO3 deposited on TiO2. Addition of 2.5% Pt by weight of MoO3 on the Mo catalyst resulted in an increase in the catalytic activity of the system in favor of hydrocracking products. Surface characterization by XPS-UPS and ISS reveal that the sample surface contains Oxygen, Molybdenum, Platinum and Titanium. Apparently, the metallic properties of the deposited Pt favors the hydrocracking reactions and becomes dominant at reaction temperatures higher than 623 K. Balanced metal-acid functions in MoO2 − x(OH)y phase seems to be in optimized condition toward the hydroisomerization process. The contribution of Platinum addition to this catalytic reaction is not obvious. Combination of surface XPS-UPS, ISS and catalytic reactions carried out at similar experimental conditions enabled us to have better insight concerning the catalytic activities of the different chemical species present on the sample surface. 相似文献
17.
Huihua Wang Wenyuan Wu Shucheng Sun Xue Bian Ganfeng Tu 《Ceramics International》2011,37(7):2689-2693
TiB2/TiC nanocomposite powders were successfully prepared by high-energy ball milling of the powder mixtures of Ti and B4C. X-ray diffraction analysis showed that the TiC phase was not produced until the milling time was up to 24 h and only a minimal amount of TiB2 was generated, even after 48 h of milling. The critical grain size of Ti milled for the reaction between Ti and B4C was 31.2 nm. Transmission electron microscopy clearly indicated that the resulting powder mixture obtained after milling for 48 h and annealing at 800 °C for 30 min was composed of nanosized TiC and TiB2 particles. 相似文献
18.
Al2O3/Al2O3 joint was achieved using Ag-Cu-Ti + B + TiH2 composite fillers at 900 °C for 10 min. The evolution mechanism of interface during brazing was discussed. Effects of Ti and B atoms content on microstructure of joints were investigated. Results show that a continuous and compact reaction layer Ti3(Cu,Al)3O forms at Al2O3/brazing alloy interface. Ti(Cu,Al) precipitates near Ti3(Cu,Al)3O layer. In situ synthesized TiB whiskers evenly distribute in Ag and Cu based solid solution. The higher content of B powders in composite fillers increases TiB whiskers content, but decreases the thickness of Ti3(Cu,Al)3O layer, while the higher TiH2 powders content thickens Ti3(Cu,Al)3O layer. Ag and Cu based solid solutions become uniform and fine with the increasing of TiB whiskers content. Ti(Cu,Al) intermetallics content increase and they gradually distribute from Al2O3 side to the central of brazing alloy, but the content of Cu based solid solution decreases when the TiH2 content increases. 相似文献
19.
Ni + Mo + Si coatings were obtained by nickel deposition from a bath containing suspension of molybdenum and silicon powders. These coatings were obtained in galvanostatic conditions, at the current density of jdep = −0.100 A cm−2. For determination of the influence of phase composition and surface morphology of obtained coatings on changes of corrosion resistance, these coatings were modified in argon atmosphere by thermal treatment at the temperature of 1100 °C during 1 h. A scanning electron microscope was used for surface morphology characterization of the coatings. Chemical composition of obtained coatings was determined by X-ray fluorescence spectroscopy method. Phase composition investigations were conducted by X-ray diffraction method. It was found that the obtained coatings are composed of three phase structures, i.e., nickel, molybdenum and silicon. Phase composition for the Ni + Mo + Si coatings after thermal treatment is markedly different. The main peaks corresponding to the Ni and Mo coexist with the new ones corresponding to new phases: Mo5Si3, NiSi, Mo2Ni3Si and Ni6Mo6C1.06.Electrochemical corrosion resistance investigations were carried out in the 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy methods. On the basis of these investigations it was found that Ni + Mo + Si coatings after thermal treatment are more resistant in alkaline solution than Ni + Mo + Si as-deposited coatings. The reason of this is presence of silicides in the coatings. 相似文献
20.
以三元碳化物陶瓷Ti_3AlC_2为原料,在500°C~1000°C温度范围内氯化制备具有纳米孔结构的碳化物衍生碳(Ti_3AlC_2-CDC)。高温氯化制备得到的Ti_3AlC_2-CDC由无定形碳和石墨组成。氯化温度越高,石墨化程度越明显,石墨有序度越高。Ti_3AlC_2-CDC的结构与前驱体Ti_3AlC_2的层状结构保持一致。但随着温度升高,Ti_3AlC_2-CDC会逐渐裂解为单片层或多片层。采用N2吸附技术研究了700°C、800°C和1000°C下制备的Ti_3AlC_2-CDC的孔隙结构特征,通过分析试样的吸附等温线特征和孔径分布探讨了温度对CDC孔结构的影响。 相似文献