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1.
The effect of high-energy ball milling and subsequent annealing on the mixture of MgO and Nb2O5 has been investigated. X-ray diffraction (XRD) measurement indicates that an amorphous phase is produced after milling for 5 h, while traces of MgNb2O6 crystallized from the amorphous phase during prolonged milling. Significant crystallization of MgNb2O6 from the amorphous state is observed after annealing at 500 °C, while the reaction of the remaining MgO and Nb2O5 does not take place at this temperature. Single phase MgNb2O6 can be achieved for all the milled samples at 700 °C. No significant grain growth is observed when the milled powders were annealed at temperature below 900 °C. Almost fully dense MgNb2O6 ceramics are obtained after annealing at 1100 °C from the as-milled powders. 相似文献
2.
P.G. Li M. Lei Z.B. Sun L.Z. Cao Y.F. Guo X. Guo W.H. Tang 《Journal of Alloys and Compounds》2007,430(1-2):237-240
While there already exit some routes to prepare carbides, highly efficient and facile routes are still desired to meet the increasing demand on carbides. By a facile solid-state reaction process using graphite-like phase of C3N4 (g-C3N4) as the carbonizing reagent, we synthesized three technologically important carbides including cubic NbC and TaC, and hexagonal WC nanoparticles at relatively low temperature (1150 °C). The products were characterized by power X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The results show that g-C3N4 is a highly efficient carbonizing reagent and the oxides Nb2O5, Ta2O5 and WO3 are completely converted into the corresponding carbides at 1150 °C, which is significantly lower than that reported for the commercial preparation of the carbides, typically >1600 °C. The NbC, TaC and WC nanoparticles are found to have an average particle size of 4, 35 and 60 nm, respectively. An important feature of this solid-state reaction process is that g-C3N4 plays double roles as both efficiently reducing and carbonizing reagent. 相似文献
3.
Nobuko Hanada Takayuki Ichikawa Satoshi Hino Hironobu Fujii 《Journal of Alloys and Compounds》2006,420(1-2):46-49
Kinetics of hydrogen absorption and desorption reactions was investigated on the MgH2 composite doped with 1 mol% Nb2O5 as a catalyst by ballmilling. The composite after dehydrogenation at 200 °C absorbed gaseous hydrogen of 4.5 mass% even at room temperature under lower pressure than 1 MPa within 15 s and finally its capacity reached more than 5 mass%. On the other hand, the catalyzed MgH2 after rehydrogenation desorbed 6 mass% hydrogen at 160 °C under purified He flow, which followed the first order reaction. From the Kissinger plot, the activation energy for hydrogen desorption was estimated to be 71 kJ/mol H2, indicating the product was significantly activated due to the catalytic effect of Nb2O5. 相似文献
4.
Wilson Acchar Diva Wolff 《International Journal of Refractory Metals and Hard Materials》2001,19(4-6):405-408
Studies have shown that Al2O3–NbC composites present a good potential to be used for metalworking. Manufacturing of composite ceramic material derived from polymer reactive filler mixtures were investigated. The present study reports the preliminary results of reaction bonded niobium carbide derived from polymer (polysiloxane), inert filler (Al2O3) and reactive filler (Nb). Niobium powder, alumina and polysiloxane mixtures were homogenized in a planetary ball milling and pressureless sintered in inert atmosphere at temperatures up to 1600 °C. Depending on the niobium content and pyrolysis conditions, ceramic materials with a porosity of 20–40%, a weight loss of 5–15%, a linear shrinkage of 2–4% and a flexural strength of maximum 80 MPa were obtained. X-ray diffraction (XRD) of a sample containing 60 wt% polymer + 40 wt% Nb showed the presence of new crystalline phases such as NbC, Nb3Si and Nb5Si3. 相似文献
5.
Cathode material Sm0.5Sr0.5CoO3 (SSC) with perovskite structure for intermediate temperature solid oxide fuel cell was synthesized using glycine-nitrate process (GNP). The phase evolution and the properties of Sm0.5Sr0.5CoO3 were investigated. The single cell performance was also tested using La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) as electrolyte and SSC as cathode. The results show that the formation of perovskite phase from synthesized precursor obtained by GNP begins at a calcining temperature of 600 °C. The single perovskite phase is formed completely after sintering at a temperature of 1000 °C. The phase formation temperature for SSC with complete single perovskite phase is from 1000 to 1100 °C. The SrSm2O4 phase appeared in the sample sintered at 1200 °C. It is also found that the sample sintered at 1200 °C has a higher conductivity. The electrical conductivity of sample is higher than 1000 S/cm at all temperature examined from 250 to 850 °C, and the highest conductivity reaches 2514 S/cm at 250 °C. The thermal expansion coefficient of sample SSC is 22.8 × 10−6 K−1 from 30 to 1000 °C in air. The maximum output power density of LSGM electrolyte single cell attains 222 and 293 mW/cm2 at 800 and 850 °C, respectively. 相似文献
6.
P. B. Trivedi S. N. Patankar F. H. Froes E. G. Baburaj 《Journal of Alloys and Compounds》2002,340(1-2):231-235
While processing Y2O3 dispersed γ-TiAl, Y2O3 particles which dissolved during hot isostatic pressing (HIP’ing) were found to precipitate during the heat treatment in the form of a mixed Al–Y oxide. To understand the chemical reaction that occurs between Y2O3 and γ-TiAl during the heat treatment cycle, a powder mixture comprising of γ-TiAl and 10 wt.% Y2O3 was mechanically alloyed (MA’d) for 8 h and the milled powder was subjected to differential thermal analysis (DTA) at 1150 °C prior to analyzing it using X-ray diffraction technique. The present study clearly demonstrates that aluminum in the combined form either as γ-TiAl or Al2O3 reacts in a similar manner with Y2O3 when milled and heat treated at 1150 °C. In either case there is formation of Al2Y4O9 (2Y2O3.Al2O3). 相似文献
7.
Viseslava Rajkovic Dusan Bozic Milan T. Jovanovic 《Journal of Materials Processing Technology》2008,200(1-3):106-114
Copper matrix was reinforced with Al2O3 particles of different size and amount by internal oxidation and mechanical alloying accomplished using high-energy ball milling in air. The inert gas-atomised prealloyed copper powder containing 1 wt.% Al as well as a mixture of electrolytic copper powder and 3 wt.% commercial Al2O3 powder served as starting materials. Milling of Cu-1 wt.% Al prealloyed powder promoted formation of fine dispersed particles (1.9 wt.% Al2O3, approximately 100 nm in size) by internal oxidation. During milling of Cu-3 wt.% Al2O3 powder mixture the uniform distribution of commercial Al2O3 particles has been obtained. Following milling, powders were treated in hydrogen at 400 °C for 1 h in order to eliminate copper oxides formed at the surface during milling. Compaction was executed by hot-pressing. Compacts processed from 5 to 20 h-milled powders were additionally subjected to high-temperature exposure at 800 °C in order to examine their thermal stability and electrical conductivity. Compacts of Cu-1 wt.% Al prealloyed powders with finer Al2O3 particles and smaller grain size exhibited higher microhardness than compacts of Cu-3 wt.% Al2O3 powder mixture. This indicates that nano-sized Al2O3 particles act as a stronger reinforcing parameter of the copper matrix than micro-sized commercial Al2O3 particles. Improved thermal stability of Cu-1 wt.% Al compacts compared to Cu-3 wt.% Al2O3 compacts implies that nano-sized Al2O3 particles act more efficiently as barriers obstructing grain growth than micro-sized particles. Contrary, the lower electrical conductivity of Cu-1 wt.% Al compacts is the result of higher electron scatter caused by nano-sized Al2O3 particles. 相似文献
8.
The ternary phase equilibria of the Er---Al---B system have been investigated and determined at 1600 °C. The ternary phase Er1—xAl1—yB14 forms equilibria with ErB4, ErB12, ErB66, -AlB12 and ErAlB4. X-Ray diffraction technique, electron microprobe analysis and X-ray powder Rietveld refinements were used to study the phase equilibria. The presence of the ternary phase Er1—xAl1—yB14 with a homogeneity range around the composition Er0.57Al0.62B14 has been established. 相似文献
9.
Milan Skrobian Nobuaki Sato Masatoshi Saito Takeo Fujino 《Journal of Alloys and Compounds》1994,210(1-2):291-297
The reaction to synthetize neodymium sulphides from neodymium sulphate octahydrate in a stream of carbon disulphide gas was studied. The dehydration of the octahydrate in vacuum was finished at 300 °C. At 1050–1100 °C in air neodymium oxysulphide, Nd2O2SO4, was formed. Neodymium oxysulphide, Nd2O2S, was formed upon heating with a reducing agent such as annealed carbon. The reaction of neodymium sulphate with carbon disulphide commenced at 500–600 °C, resulting in formation of the disulphide, NdS2. The crystal structure of NdS2 heated at 500 °C was, however, different from that of the sample heated at 600 °C. In the temperature range 800–900 °C -Nd2S3 was obtained as a single phase after heating for at least 3 h in high flow rates of gas mixtures of nitrogen and high concentrations of carbon disulphide. The sesquisulphide, γ-Nd2S3 (or Nd3S4), was formed at temperatures as high as 1100 °C. The reaction conditions for the compounds mentioned above are discussed together with the analysis of their crystal structures by X-ray powder diffractometry. 相似文献
10.
Aluminium matrix composites reinforced with molybdenum aluminide nanoparticles were synthesized by ball milling and reactive sintering of the mixture of aluminium and 10 wt% hydrated molybdenum oxide powders. Sintering the as milled powder in air below 750 °C produced MoAl12 intermetallic compound nanoparticles, at 750 °C produced a mixture of MoAl5 and MoAl4 nanoparticles and at 800 °C under Argon atmosphere produced predominantly MoAl4 intermetallic nano-particles in the Al matrix. The powder compacts sintered in air below 750 °C produced MoAl12 whereas at 750 °C or above formed the Al matrix composite reinforced with the MoAl5 nanoparticles. These nanoparticles become agglomerated to take up some irregular shaped flakes in the metal matrix. The reaction between Al and hydrated Mo oxide powders was found to be a favorable way to produce predominantly a particular Mo–Al intermetallic compound at a particular temperature. The Al2O3 particles formed as another reaction product, in all the above reactions, remain distributed in these composites. The composites thus formed were characterized by SEM-EDS, DTA, XRD and TEM analysis. 相似文献
11.
Yee-Shin Chang Hui-Jan Lin Yin-Lai Chai Yu-Chun Li 《Journal of Alloys and Compounds》2008,460(1-2):421-425
Effects of precursor milling on phase evolution and morphology of mullite (3Al2O3·2SiO2) processed by solid-state reaction have been investigated. Alumina and silica powders were used as starting materials and milling was taken place in a medium energy conventional ball mill and a high-energy planetary ball mill. Milling in a conventional ball mill although decreases mullite formation temperature by 200 °C, but does not considerably change mullite phase morphology. Use of a planetary ball mill after 40 h of milling showed to be much more effective in activating the oxide precursors, and mullitization temperature was reduced to below 900 °C. Whisker like mullite was formed after sintering at 1450 °C for 2 h and volume fraction of this structure was increased by increasing the milling time. XRD results showed that samples mechanically activated for 20 h in the planetary ball mill were fully transformed to mullite after sintering at 1450 °C, whereas Al2O3 and SiO2 phases were still detected in the samples milled in the conventional ball mill for 20 h and then sintered at the same conditions. 相似文献
12.
High-energy dry ball-mill and post-anneal processing were applied to synthesize MgTiO3 and Mg2TiO4 single crystalline phases from the predetermined compositions of MgO–TiO2 powder mixtures. Also, the experiments were performed to show that it is possible to prepare MgAl2O4 single crystalline phase from the predetermined composition of MgO–Al2O3 powder mixture only by employing high-energy dry ball milling, i.e. without post-annealing the milled samples. In contrast, fully developed single crystalline powders of MgTiO3 and Mg2TiO4 were obtained after post-annealing the milled samples for 1 h at 900 and 1200 °C, respectively. 相似文献
13.
R. Gupta F. Agresti S. Lo Russo A. Maddalena P. Palade G. Principi 《Journal of Alloys and Compounds》2008,450(1-2):310-313
The catalytic effect of the addition of lanthanum oxide (La2O3), in the range 0.5–2.0 mol%, on the hydrogen storage properties of MgH2 prepared by ball milling has been studied. The addition of La2O3 reduces the formation during milling of the metastable orthorhombic γ-MgH2 phase. The desorption rate of samples with 1 and 2 mol% La2O3 comes out to be about 0.010 wt% per second at 573 K under an hydrogen pressure of 0.3 bar, better than for sample with 0.5 mol% La2O3. The presence of LaH3 after hydrogenation/dehydrogenation cycles has been observed in all samples. The sample with 1 mol% of La2O3 gives a lower hysteresis factor compared with sample with 2 mol%. 相似文献
14.
Liping Xue Zhang Lin Dagui Chen Feng Huang Jingkui Liang 《Journal of Alloys and Compounds》2008,458(1-2):144-150
The subsolidus phase relations in the ZnO–MoO3–B2O3, ZnO–MoO3–WO3 and ZnO–WO3–B2O3 ternary systems have been investigated by the means of X-ray powder diffraction (XRD). There is no ternary compound in all the systems. There are five binary compounds and five tie lines in the ZnO–MoO3–B2O3 system. This system can be divided into six 3-phase regions. There are three binary compounds and three tie lines in the ZnO–MoO3–WO3 system. This system can be divided into four 3-phase regions. There are four binary compounds and four tie lines in the ZnO–WO3–B2O3 system. This system can be divided into five 3-phase regions. The possible component regions for ZnO single crystal flux growth were discussed. The phase diagram of Zn3B2O6–ZnWO4 pseudo-binary system has been constructed, and the result reveals this system is eutectic system. The eutectic temperature is 1007 °C and eutectic point component is 70 mol% Zn3B2O6. 相似文献
15.
Formation of Ti3SiC2 was conducted by self-propagating high-temperature synthesis (SHS) from both the elemental powder compacts of Ti:Si:C = 3:1:2 and the TiC-containing samples compressed from powder mixtures of Ti/Si/C/TiC with TiC content ranging from 4.3 to 33.3 mol%. The effect of TiC addition was studied on combustion characteristics and the degree of phase conversion. For the elemental powder compacts, with the progress of combustion wave the sample experiences substantial deformation, including axial elongation and radial contraction. The extent of sample deformation and flame-front propagation velocity were considerably reduced for the samples with TiC addition, because the dilution effect of TiC lowered the reaction temperature. Two reaction mechanisms were adopted to explain the formation of Ti3SiC2, one involving the reaction of a Ti–Si liquid phase with solid reactants for the elemental powder compact and the other dominated by the interaction of solid-phase species for the TiC-containing sample. For all products synthesized in this study, the XRD analysis identifies formation of Ti3SiC2 along with a major impurity TiC and a small amount of Ti5Si3. The resulting Ti3SiC2 is typically elongated grains. Based upon the XRD profile, the Ti3SiC2 content at a level of 71.5 vol.% was obtained in the product from the elemental powder compact. With the addition of TiC, an improvement in the yield of Ti3SiC2 was observed and an optimal conversion reaching 85 vol.% was achieved by the sample with 20 mol% of TiC. However, further increase of the TiC amount led to a decrease in the Ti3SiC2 content, because of the low reaction temperature around 1150 °C. 相似文献
16.
This paper reports results of studies on the interaction of praseodymium oxide nanocrystals with an amorphous silica. Nano-sized (3–4 nm) amorphous precursor of praseodymium oxide synthesized using a microemulsion technique were supported onto a high surface SiO2 or occluded into SiO2 matrix. Solid state reactions occurring in these binary systems upon heat treatment in air, argon or hydrogen at 800–1100 °C were studied by TEM, XRD, FT-IR and UV–vis spectroscopy. It has been found that morphology of the sample as well as annealing atmosphere influence greatly the phase evolution. At temperatures above 900 °C, nanocrystalline praseodymium silicates of various morphology and crystal structure were obtained. In particular, a new polymorph of Pr2Si2O7, isostructural with I-type Ln2Si2O7 (Ln6[Si4O13][SiO4]2) Ln = Ce, La, has been identified. 相似文献
17.
Nano-crystalline SrAl2O4 with spinel structure was successfully prepared at 700 °C using amorphous SrAl2(diethylenetriaminepentaacetic acid (DTPA)1.6)(H2O)4 as precursor. The precursor was synthesized by a simple inorganic reaction and decomposed into SrAl2O4 at temperatures above 500 °C, which was proved by DTA–TGA and X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction (XRD) results illustrated that a crystalline SrAl2O4 phase can form at 700 °C, which is about 600 °C lower than that used in the traditional method. The crystalline SrAl2O4 prepared at 900 °C for 2 h had a crystal size of about 28 nm and a grain size of about 80 nm, and its BET surface area can reach 28.056 m2/g. Calcination temperature and time had a weak effect on crystal size. 相似文献
18.
The addition of 5 wt.% SiO2, a viscous second phase, to 8 mol% Y2O3 cubic stabilized ZrO2 (8Y-CSZ) made superplastic 8Y-CSZ. This material had a fine grain size of 0.4 μm and exhibited deformations in tension as large as 520% at 1430 °C with a strain rate of 1.0 × 10−4 s−1. 相似文献
19.
J.K.M.F. Daguano C. Santos R.C. Souza R.M. Balestra K. Strecker C.N. Elias 《International Journal of Refractory Metals and Hard Materials》2007,25(5-6):374-379
Zirconia and alumina based ceramics present interesting properties for their application as implants, such as biocompatibility, good fracture resistance, as well as high fracture toughness and hardness. In this work the influence of sintering time on the properties of a ZrO2–Al2O3 composite material, containing 20 wt% of Al2O3, has been investigated. The ceramic composites were obtained by sintering, in air, at 1600 °C for sintering times between 0 and 1440 min. Sintered samples were characterized by microstructure and crystalline phases, as well as by mechanical properties. The grain growth exponents, n, for the ZrO2 and Al2O3 were 2.8 and 4.1, respectively, indicating that different mechanisms are responsible for grain growth of each phase. After sintering at 1600 °C, the material exhibited a dependency of hardness as function of sintering time, with hardness values between 1500 HV (120 min) and 1310 HV (1440 min) and a fracture toughness of 8 MPa m1/2, which makes it suitable for bioapplications, such as dental implants. 相似文献
20.
Zeheng Yang Peijun Cai Luyang Chen Yunle Gu Liang Shi Aiwu Zhao Yitai Qian 《Journal of Alloys and Compounds》2006,420(1-2):229-232
V2O3 and VN nanocrystals have been synthesized by the decomposition of the precursor NH4VO3 and following nitridation in an autoclave with metallic Na flux at 450–600 °C. X-ray powder diffraction (XRD) recorded the evolution process of the reaction from precursor NH4VO3 to hexagonal V2O3 and then to NaCl-type VN. In addition, the products were characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). 相似文献