self propagating high temperature synthesis of ultrafine tungsten carbide powders

... Preparation of nano-size ZrB2 powder by selfpropagating high- temperature synthesis J Eur Ceram Soc 2009, 29:1501-1506 15 Nersisyan HH, Lee JH, Won CW: Self- propagating high- temperature synthesis of nano-sized ... the synthesis of TiB2 powder by a self- propagating high- temperature synthesis technique Mater Lett 2004, 58:733-738 13 Khanra AK, Pathak LC, Mishra SK, Godkhindi MM: Self- propagating- hightemperature ... into the self- propagating high- temperature synthesis process Mater Res Bull 2011, 46:995-999 18 Lia XK, Westwood A, Brown A, Brydson R, Rand B: A convenient, general synthesis of carbide nanofibres...

Ngày tải lên: 21/06/2014, 00:20

... pressure of 50 MPa The characteristics of the reactant powders are given in Table Three grams of Al, S, and MnO2 powder mixture in the mass ratio of 1:1:1 was pressed into a pellet with dimensions of ... with argon gas at room temperature, heated to 180 °C, and then purged for a second time Heating of the reactor continued after introducing of MPa of argon gas The reaction of the igniter was started ... 3b shows the high magnification of the zone I in the Fig 3a The corresponding SAED of the I zone (Fig 3c) and the II zone (Fig 3d) results confirm the existence of the two phases of the eutectic,...

Ngày tải lên: 22/06/2014, 01:20

... Synthesis and characterization of nanocrystals of barium titanate, toward a generalized synthesis of oxide nanoparticles J Am Chem Soc 2001, 123:12085-12086 Urban JJ, Yun WS, Gu Q, Park HK: Synthesis ... modeling of aqueous and hydrothermal synthesis of barium titanate (BaTiO3) Chem Mater 2005, 17:5346-5356 doi:10.1186/1556-276X-6-466 Cite this article as: Qi et al.: Direct synthesis of ultrafine ... line of 637, 488, and 325 nm The rate of measured temperature rise is 15°C/min Results and discussion A large quantity (23.0 g) of barium titanate nanoparticles is directly synthesized at room temperature...

Ngày tải lên: 21/06/2014, 01:20

... supersaturation of the tungsten source, promoting the growth of tungsten oxide nanowires [11] At higher concentration, the highly saturated WCl6 could prohibit the growth of tungsten oxide nanowires ... (b) EDX profile of bundles synthesized at concentration of 0.007M 440 MA TE RI A L S CH A R A CT ER IZ A TI O N 60 ( 20 ) 7– 4 products synthesized at high concentrations are a mixture of different ... respectively The high specific surface area of the bundled nanowires can be ascribed to a combination of the ultra-thin feature of individual nanowires and the unique packing characteristic of the bundles...

Ngày tải lên: 20/03/2014, 13:08

... microscope Discussion 3.1 Influence of reaction temperature on the morphologies of ZnO powders The influence of the reaction temperature on the morphologies of ZnO powders was studied, and the results ... when the temperature was too high, the structures were broken down and yielded out micro-rods 3.2 Influence of the OHÀ/Zn2þ mol ratio on the morphologies of ZnO powders The influence of the OHÀ/Zn2þ ... structures were reaction temperature 150  C, OHÀ/Zn2þ mol ratio and reaction time 10 h 3.4 XRD patterns of ZnO powders and EDS pattern of flower-like structure The XRD patterns of ZnO of flower-like particles,...

Ngày tải lên: 06/05/2014, 13:26

... http://www.nanoscalereslett.com/content/6/1/397 Page of Figure Crystal structures of CuO products (a-b) XRD pattern and FESEM image of the CuO powders, respectively (c-d) Low magnification TEM and HRTEM images of an individual ... to a reversible capacity of 290 mA h g-1 after 20 cycles Recently, Xiang et al reported the synthesis of shuttle-shaped CuO particles with a length of μm and a thickness of 100-200 nm at 90°C using ... detrimental phenomenon may also have Figure Voltage profiles of CuO Galvanostatic discharge/charge voltage profiles of CuO-interlaced nanodiscs at a rate of C/5 Seo et al Nanoscale Research Letters 2011,...

Ngày tải lên: 21/06/2014, 03:20

... quality of MWCNTs obtained by mechanothermal makes it a suitable promising method of synthesis for the production of MWCNTs or other graphitic nanocarbons Indeed, because of the simplicity and high ... transitions of nanocarbon as functions of its size and temperature through systematically considering the effects of surface stresses and surface energies The fine nanosize amorphous structure of pure ... unstable, owing to the high amount of free energy Therefore, crystallization at a temperature regime might be expected The milled powders had an average crystalline size of about 5–10 nm as determined...

Ngày tải lên: 22/06/2014, 01:20

... of materials because of the microwave energy transfers to the thermal energy by collision between rotating materials Therefore, the generation of localized high temperatures in the presence of ... XRD patterns, crystalline of synthesized nanoparticles was improved Figure shows XRD patterns of synthesized powders using conventional heating In the XRD pattern of the powders after heating at ... nanoparticles of samples prepared at shorter time have higher surface activity with which can absorb more water than that of samples prepared at longer heating time The content of crystal water of two...

Ngày tải lên: 22/06/2014, 22:20

... Total Combination of Structural Peculiarities of High- temperature Deformation 40 Summary 41 Physical Mechanism of Strain at High Temperatures Physical Model and Theory 43 Velocity of Dislocations ... Variation of the Subgrain Size 71 System of Differential Equations 71 Results of Simulation 71 Density of Dislocations during Stationary Creep 77 Summary 80 High- temperature Deformation of Superalloys ... structural peculiarities of the metals, which have been deformed at high- temperatures, are formulated In the fourth chapter the physical mechanisms of the high- temperature deformation of pure metals and...

Ngày tải lên: 10/08/2014, 12:21

... investigation and detailed proofs of correctness of physical models An in situ investigation of metals is necessary in order to address the problem of the physics of the high- temperature deformation ... intersection of a node of the reciprocal lattice and the Evald sphere (c) Directions of erosion of the reciprocal lattice node due to the divergence of the initial beam χ and to the finite size, l, of ... planes of the dislocations The dislocation density, N , in the specimens was measured after the interrupted high- temperature tests by means of the intercept method The number of intersections of...

Ngày tải lên: 10/08/2014, 12:21

... is of great importance for our understanding of the physical mechanism of high- temperature deformation Fig 3.16 Histograms of the distribution of distances between jogs in screw components of ... situ at least to crystallites of or specimens of each material under each set of external conditions (temperature and stress) The substructure formation during high- temperature strain in vanadium ... observed very often in the structure of the high- temperature tested metals Dark-field analysis makes it possible to determine the sign and the type of loops The loops have been found to be of the vacancy...

Ngày tải lên: 10/08/2014, 12:21

... Mechanism of Strain at High Temperatures Now we can calculate the rate of the steady-state high- temperature deformation ε Three groups of physical parameters are needed: ˙ • • • External parameters: temperature ... influence of the tungsten additions (by three or four orders of magnitude at 850–1050K) 4.6 Formation of Jogs Fig 4.10 Comparison of the temperature dependence of the creep rates ε under stress of ... Physical Mechanism of Strain at High Temperatures where ρm is the rate of the density increase due to the dislocation multipli˙d cation, ρm is the rate of the density change on account of the sub-boundary...

Ngày tải lên: 10/08/2014, 12:21

... 4.7 Significance of the Stacking Faults Energy 4.7 Significance of the Stacking Faults Energy The processes of high- temperature strain are dependent upon the nature of a metal, especially, ... theory of the rates of reactions [25] the dislocation can be regarded as a linear crystal with D/b degrees of freedom The number of thermal activations per unit of time 4.8 Stability of Dislocation ... The area of temperature and stress where the proposed mechanism of hightemperature deformation takes place, is shown in normalized coordinates in Fig 4.18 Construction diagrams (maps) of this...

Ngày tải lên: 10/08/2014, 12:21

... value of λ and increased value of D lead to the strain rate decreasing when the applied stress is relatively low 81 83 High- temperature Deformation of Superalloys 6.1 γ Phase in Superalloys The high- temperature ... One of the most important requirements is resistance to high- temperature deformation This has created a need for alloys that can withstand higher stresses and temperatures for the hot zones of ... 3-527-313389-9 84 High- temperature Deformation of Superalloys Fig 6.1 Crystal structure of the γ phase The face-centered cubic cell contains atoms of B-type (6 atoms/2 adjacent cells) and atom of A-type...

Ngày tải lên: 10/08/2014, 12:21

... process of the γ structure occurs because of development of diffusion coarsening Now the incoherent irregular rafted 91 92 High- temperature Deformation of Superalloys Fig 6.11 Electron micrographs of ... used the results of measurements of the particle sizes and the data of the strain rate tests 99 100 High- temperature Deformation of Superalloys Finally, the minimum strain rate of a superalloy ... activation energy of an elementary event of the high- temperature strain (creep) is denoted differently by different authors, as Q, Qc , ∆Qapp , ∆U 101 102 High- temperature Deformation of Superalloys...

Ngày tải lên: 10/08/2014, 12:21

... 104 High- temperature Deformation of Superalloys An energetically efficient mechanism of an elementary diffusion event in the γ phase consists of a certain cycle of a vacancy shift The nodes of ... hardening phase the higher the creep strength of a superalloy Methods of prediction of the properties of new superalloys are being developed on the basis of integrated databases of superalloy composition ... strengthening phases of superalloys with the rate of the steady-state creep ε of the same ˙ alloys The superalloy EI437B with u2 = 460 pm2 at 1023K has the least A high- temperature strength of the three...

Ngày tải lên: 10/08/2014, 12:21

... Single Crystals of Superalloys 7.3 Deformation of Single-crystal Superalloys at Higher Temperatures and Lower Stress Increase in temperature up to 1223K results in a change in the shape of the curves ... rupture life of single crystals is found with a γ fraction as high as 60 to 75% 7.5 Rafting At temperatures above 1273K the γ morphology becomes unstable Under the combined influence of high temperature ... at Lower Temperatures Fig 7.7 The orientation of the CMSX-4 superalloy specimens within the stereographic triangle The effect of misorientation on the behavior of specimens at lower temperatures...

Ngày tải lên: 10/08/2014, 12:21

... Science Ltd carbide possesses the highest melting point Tungsten rhenium–hafnium carbide alloys seem to be promising for operation at high temperatures Fig 8.11 Effect of annealing temperature ... The minimum strain rate of niobium and molybdenum is dependent exponentially on the applied stress at high temperatures The mean value of the activation energy of the high- temperature strain for ... energy of high- temperature strain for molybdenum Fig 8.8 The strain rate map for molybdenum with a grain size of 100µm Reprinted from Ref [26] 8.2 Alloys of Refractory Metals Fig 8.9 The effect of...

Ngày tải lên: 10/08/2014, 12:21

... equations of strain rate 95–100, 137–140 – physical mechanism of strain 96–98 – prediction of properties 106–108 – trends of development 129 v vacancies – energies of formation 46, 52 – energy of diffusion ... years of her participation in numerous experiments I am grateful to Dr V.I Babenko for his participation in the development of equipment for in situ X-ray studies High Temperature Strain of Metals ... 96, 116–120, 124, 125 – at higher temperatures 124 – at lower temperatures 116 – dislocation splitting 112, 120–122, 129 – equations 99, 100 – influence of orientation, temperature and stress 111–120...

Ngày tải lên: 10/08/2014, 12:21

... Time evolution of the radius of gyration (nm) of the unfolding process, at least in respect of CI2 and the homeodomain of engrailed [7] It is also much higher than the melting temperature determined ... Moreover, a few folding simulations of have been carried out using implicit solvation models [4-6] In this article, the results of a high- temperature unfolding simulation of the Trp-cage mini-construct ... significant jump in the radius of gyration The distribution of the radius of gyration was determined for each of the three states and for the entire time-evolving system For each of the three ensembles...

Ngày tải lên: 13/08/2014, 22:22