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1.
Titanium silicon carbide (Ti3SiC2) ceramic was synthesized by in-situ reaction of metal titanium and polycarbosilane. Reaction mechanisms which lead to the formation of Ti3SiC2 were suggested on the basis of XRD analysis. The content of Ti3SiC2 reached 93% in products obtained from heating the Ti/polycarbosilane green compact at 1400 °C in Ar. The morphology and compositions of the products were examined by SEM equipped with EDX. The typical laminate structure of Ti3SiC2 particles with 1-4 μm in thickness and 4-15 μm in length was observed. EDX results showed that the atomic ratio of Ti:Si:C of grains is close to 3:1:2, which agrees with Ti3SiC2 composition. 相似文献
2.
Si–C–Ti ceramics were synthesized by reactive pyrolysis of polycarbosilane (PCS) precursor filled with metal Ti powder. Pyrolysis of mixture with atomic ratio of Ti:Si through 3:1–3:2 was carried out in argon atmosphere at given temperature up to 1500 °C. The metal–precursor reactions, and phase evolution were studied using X-ray diffraction and scanning electron microscopy with EDX. The Ti3SiC2 phase was obtained firstly from reaction of PCS and Ti. Ti3SiC2 formation starts at 1300 °C and its amount increases significantly in a narrow temperature range between 1400 °C and 1500 °C. In addition, addition of CaF2 can promote the formation of Ti3SiC2 phase. 相似文献
3.
Ti/Si/TiC powder mixture with molar ratios of 2:2:3 were sintered at various temperatures from 700–1300 °C for 15 min by PDS technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for the evaluation of phase composition in different samples for the understanding of the sintering mechanism for this system. Results showed that Ti5Si3 formed as the intermediate phase during sintering. The reaction between Ti5Si3 and TiC as well as Si induces the formation of Ti3SiC2, and TiSi2 appears as the byproduct in this process. At temperature above 1000 °C, TiSi2 reacts with TiC to form Ti3SiC2. High Ti3SiC2 phase content bulk material can be synthesized at 1300 °C for 15 min. 相似文献
4.
Fabrication of monolithic Ti3SiC2 has been investigated through the route of reactive sintering of Ti/Si/2TiC mixtures. Significant phase differences existed between the surface and the interior of as-synthesized products due to the evaporation of Si during the reaction process. The use of a 3Ti/SiC/C mixture as a powder bed could control the evaporation of Si and develop monolithic Ti3SiC2. A reaction model for the formation of Ti3SiC2 in the Ti/Si/2TiC system is discussed.On leave from 相似文献
5.
Cuiwei Li Hongxiang Zhai Yan Ding Yang Zhou Shibo Li Zhili Zhang 《Materials Letters》2007,61(17):3575-3577
In this study, free Ti/Si/Al/C powder mixtures with molar ratios of 3:0.8:0.4:1.8 were heated in argon with various schedules, in order to reveal the possibility for the synthesis of high Ti3Si0.8Al0.4C1.8 content powder. X-ray diffraction (XRD) was used for the evaluation of phase identities of the powder after different treatments. Scanning electron microscopy (SEM) was used to observe the morphology of the Ti3Si0.8Al0.4C1.8 solid solution. XRD results showed that predominantly single phase samples of Ti3Si0.8Al0.4C1.8 were prepared after heating at 1450 °C for 5 min in argon and the lattice parameters of Ti3Si0.8Al0.4C1.8 lay between those of Ti3SiC2 and Ti3AlC2. SEM observation showed that the grains of Ti3Si0.8Al0.4C1.8 solid solution exhibited a lamellar shape, which is a characteristic feature of Ti3SiC2 and Ti3AlC2. 相似文献
6.
Ti/TiSi2/TiC powder mixtures with molar ratios of 1:1:4 (M1) and 1:1:3 (M2) were first employed for the synthesis of Ti3SiC2 through pulse discharge sintering (PDS) technique in a temperature range of 1100–1325 °C. It was found that Ti3SiC2 phase began to form at the temperature above 1200 °C and its purity did not show obvious dependence on the sintering temperature
at 1225–1325 °C. The TiC contents in M2 samples is always lower than that of the M1 samples, and the lowest TiC contents in
the M1 and M2 samples were calculated to be about 7 wt% and 5 wt% when the sintering was conducted at the temperature near
1300 °C for 15 minutes. The relative density of the M1 samples is always higher than 99% at sintering temperature above 1225
°C, indicating a good densification effect produced by the PDS technique. A solid-liquid reaction mechanism between Ti-Si
liquid phase and TiC particles was proposed to explain the rapid formation of Ti3SiC2. Furthermore, it is suggested that Ti/TiSi2/TiC powder can be regarded as a new mixture to fabricate ternary carbide Ti3SiC2.
Received: 5 September 2001 / Accepted: 11 September 2001 相似文献
7.
《Materials Science & Technology》2013,29(10):1252-1256
AbstractTernary carbide Ti3 SiC2 was first synthesised through a pulse discharge sintering (PDS) technique from mixtures of Ti, SiC, and C with different molar ratios. Sintering processes were conducted at 1200 – 1400°C for 15 – 60 min at a pressure of 50 MPa. The phase constituents and microstructures of the synthesised samples were analysed by X-ray diffraction (XRD) technique and observed by scanning electron microscopy (SEM). The results showed that, for samples sintered from 3Ti/SiC/C powder at 1200 – 1400°C, TiC is always the main phase and only little Ti3 SiC2 phase is formed. When the molar ratios Ti : SiC : C were adjusted to 3 : 1.1 : 2 and 5 : 2 : 1, the purity of Ti3 SiC2 in the synthesised samples was improved to about 93 wt-%. The optimum sintering temperature for Ti3 SiC2 samples was found to be in the range 1250 – 1300°C and all the synthesised samples contain platelike grains. The relative density of Ti3 SiC2 samples was measured to be higher than 99% at sintering temperatures above 1300?C. It is suggested that the PDS technique can rapidly synthesise ternary carbide Ti3 SiC2 with good densification at lower sintering temperature. 相似文献
8.
In this paper we have described the use of secondary-ion mass spectrometry (SIMS), solid state 29Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) to detect the existence of amorphous silica in Ti3SiC2 oxidised at 500–1000 °C. The formation of amorphous SiO2 and growth of crystalline TiO2 with temperature was monitored using dynamic SIMS and synchrotron radiation diffraction. A duplex structure with an outer TiO2-rich layer and an inner mixed layer of SiO2 and TiO2 was observed. Results of NMR and TEM verified for the first time the direct evidence of amorphous silica formation during the oxidation of Ti3SiC2 at the temperature range 500–1000 °C. 相似文献
9.
The joining of two pieces of SiC-based ceramic materials (SiC or Cf/SiC composite) was conducted using Ti3SiC2 as filler in vacuum in the joining temperatures range from 1200 °C to 1600 °C. The similar chemical reactions took place at the interface between Ti3SiC2 and SiC or Cf/SiC, and became more complete with joining temperature increases, and with the consequent increased joining strengths of the SiC and Cf/SiC joints. Based on the XRD and SEM analyses, it turns out that two reasons are most important for the high joining strengths of the SiC and Cf/SiC joints. One is the development of layered Ti3SiC2 ceramic, which has plasticity in nature and can contribute to thermal stress relaxation of the joints; the other is the chemical reactions between Ti3SiC2 and the base materials which result in good interface bonding. 相似文献
10.
Ti3AlC2 has good oxidation resistance at high temperatures owing to the formation of protective Al2O3 layer. However, as it is directly exposed to air at 500 °C and especially 600 °C, the scales formed on Ti3AlC2 exhibits poor protectivity because of the oxidation-induced microcracks, which limits the potential application of this technologically important material. In this work, the oxidation resistance of Ti3AlC2 at 500 °C and 600 °C was significantly improved by pre-oxidation at 1000–1300 °C for a short time of 2 h in air. The oxidation of the pre-oxidized Ti3AlC2 at 600 °C generally obeyed a parabolic rate law instead of the speed-up linear relation in the case without pre-oxidation. As revealed by X-ray diffraction, Raman spectroscopy results and SEM observations, the remarkable improvement of oxidation resistance after pre-oxidation was attributed to the protective layers formed on Ti3AlC2 during pre-oxidation, which inhibited the formation of anatase TiO2 that resulted in the oxidation-induced microcracks. Moreover, this work confirmed that the mechanism proposed previously for the anomalous oxidation of Ti3AlC2 in air at 500–600 °C was correct. 相似文献
11.
A novel fluctuation method for the synthesis of Ti3SiC2 powders was developed. The raw materials used in this process are Ti, Si, and graphite powders. Fluctuation synthesis utilized
Si as in-situ liquid forming phase (additive), which was formed by heating the powder mixtures to 1300°C and using the heat
released from the exothermic reaction for Ti3SiC2 formation. The result demonstrated that the reaction time for the formation of Ti3SiC2 was dramatically shortened using fluctuation method and the powders produced using this method contained more than twice
amount of Ti3SiC2 compared to the solid reaction synthesized powders. The powders prepared by fluctuation method are fiber-like in morphology
with dimensions of 0.8–2 μm in width and 5–10 μm in length. The growth direction of the fiber-like Ti3SiC2 particulate is {101–1}*. The lattice parameters for Ti3SiC2 were determined by a trial-and-error method and are a=3.067 ? and c=17.645 ?.
Received: 28 September 1998 / Reviewed and accepted: 1 October 1998 相似文献
12.
Pressureless-sintered SiC pieces and SiC single crystals were joined with foils of reactive metals at 1500° C (1773 K) for titanium and zirconium foils or at 1000° C (1273 K) for Al/Ti/Al foils. Bend testing at various temperatures up to 1400° C (1673 K), optical and electron microscopy, and electron-probe X-ray microanalysis studies were carried out on the specimens. From the results, it was concluded that the fairly high bond strength of titanium-foil joined SiC specimens might be attributed to the formation of a Ti3SiC2 compound, since good lattice matching between SiC and Ti3SiC2 was obtained in the SiC single crystals. Also in the Al/Ti/Al-foil joined SiC, high bond strength was obtained, but it decreased steeply at 600° C (873 K) because of a retained aluminium phase. The bond strength in the zirconium-foil joined SiC was low. 相似文献
13.
The effect of aluminum on synthesis of Ti3SiC2 by spark plasma sintering (SPS) from elemental powders was investigated in this paper. X-ray diffraction patterns and scanning electron microscopy photographs of samples with different content of aluminum indicated that proper addition of aluminum both favored the formation and accelerated the crystal growth of Ti3SiC2. The process parameters in the sintering course revealed that addition of aluminum decreased the temperature for the synthesis reaction of Ti3SiC2. Polycrystalline bulk Ti3SiC2 material with high purity and density could be fabricated by spark plasma sintering from the elemental powder mixture with starting composition of Ti3Si1–xAlxC2, where x = 0.05–0.2. SEM photographs showed Ti3SiC2 synthesized from elemental powders was in plane-shape with a size of about 10–20 µm in the elongated dimension. Solid solution of aluminum decreased the thermal stability of Ti3SiC2 and made the temperature at which Ti3SiC2 decomposed be as low as 1300°C. 相似文献
14.
The fine powders of Bi3.25La0.75Ti3O12 (BLT) were prepared by coprecipitaton method in aqueous medium at low temperature. The differential thermal analysis (DTA), thermo-gravimetric analysis (TG) and X-ray diffraction (XRD) were employed to evaluate the phase formation of BLT and TEM was used to characterize and observe the particle size and morphology of BLT powder obtained. The results show that the bismuth layer perovskite phase of BLT can begin to form at as low as 500 °C by the coprecipitation method. When the precipitates obtained were calcined at 600 °C for 2 h, the mono-phase and perfect BLT powder was synthesized. The BLT powder obtained consists of irregular or plate-like particles which are less than about 100 nm and is nearly aggregate free. 相似文献
15.
Xiaolin Hong Bingchu Mei Jiaoqun Zhu Weibing Zhou 《Journal of Materials Science》2004,39(5):1589-1592
Polycrystalline Ti2AlC samples were synthesized by hot pressing of Ti, Al, TiC and active carbon powder mixtures. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used for phase identification and microstructure evaluation. No other phase except Ti2AlC was detected in samples synthesized by hot pressing of the 0.5TiC/1.5Ti/1.0Al/0.5C powder mixtures at 1400°C for 1 and 3 h under a pressure of 30 MPa. The densities of these two samples were 96.1 and 98% of the theoretical value of pure Ti2AlC, respectively. The reason that the densities of these two samples were lower than the theoretical density of pure Ti2AlC is that pore existed in these two samples. At lower temperature of 1300°C, the speed of the reaction forming Ti2AlC was slow. While at higher temperature of 1500°C, Ti2AlC transformed to Ti3AlC2. So these two temperatures are not suitable for the fabrication of Ti2AlC. 相似文献
16.
The novel nano-ultrafine powders for the preparation of CaCu3Ti4O12 ceramic were prepared by the sol-gel method and citrate auto-ignition method. The obtained precursor powders were pressed, sintered at 1000 °C to fabricate microcrystal CaCu3Ti4O12 ceramic. The microcrystalline phase of CaCu3Ti4O12 was confirmed by X-ray powder diffraction (XRD). The morphology and size of the grains of the powders and ceramics under different heat treatments were observed using scanning electron microscopy (SEM). The relative dielectric constant of the ceramic sintered at 1000 °C was measured with a magnitude of more than 104 at room temperature, which was approaching to those of Pb-containing complex perovskite ceramics, and the loss tangent was less than 0.20 in a broad frequency region. The relative dielectric constant and loss tangent were also compared with that of CaCu3Ti4O12 ceramic prepared by other reported methods. 相似文献
17.
A microwave ceramic with general composition (1-x-y) BaTiO3 + x Cr2Ti3O9 + y Bi2O3 has been prepared by solid state synthesis at 1300-1400 °C. The phase composition, perovskite structural parameters and dielectric properties have been obtained by X-ray diffraction and dielectric measurements as a function of chemical composition and temperature. At low doping levels the formation of BaTiO3-based solid solution has been found. The precipitation of BaCrO3 has been detected at x = y = 2.0 mol%. A model of the incorporation of Cr3+ and Bi3+ ions into BaTiO3-based crystal lattice has been proposed. Diffused phase transition in the temperature range 100-140 °C have been revealed by dielectric measurements for different ceramic composition. As high dielectric constant as 7311 and as low dielectric loss as 0.02 have been found for the composition of 0.98BaTiO3-0.01Cr2Ti3O9-0.01Bi2O3. 相似文献
18.
Solid-state synthesis and characterization of the ternary phase Ti3SiC2 总被引:10,自引:0,他引:10
Ti3SiC2 is the only true ternary compound in the Ti-Si-C system. It seems to exhibit promising thermal and mechanical behaviour. With the exception of its layered crystal structure, most of its properties are unknown, owing to the great difficulty of synthesis. A new procedure of solid-state synthesis with several steps is proposed, which results in Ti3SiC2 with less than 5 at % of TiC. Ti3SiC2 is stable at least up to 1300 °C. Beyond this temperature, it can decompose with formation of non-stoichiometric titanium carbide and gaseous silicon, with kinetics highly dependent on the nature of the surroundings. As an example, graphite can initiate this process by reacting with silicon, while alumina does not favour the decomposition which remains very slow. The oxidation of Ti3SiC2 under flowing oxygen starts at 400 °C with formation of anatase-type TiO2 film, as studied by TGA, XRD, SEM and AES. Between 650 and 850 °C both rutile and anatase are formed, rapidly becoming protecting films and giving rise to slow formation of SiO2 and more TiO2. The oxidation kinetics is slower than for TiC, owing to a protecting effect of silica. By increasing the temperature, both oxidation processes (i.e. direct reaction and diffusion through oxide layers) are activated and an almost total oxidation is achieved between 1050 and 1250 °C resulting in titania (rutile) and silica (cristobalite). 相似文献
19.
Ti/Sn/TiC powder mixtures were first employed to synthesize Ti2SnC powder by pressureless sintering in the temperature range of 950–1250 °C at vacuum atmosphere. Ti2SnC began to form at 950 °C, its content increased with increasing temperature. High purity of Ti2SnC was obtained by sintering the mixtures with deficient Sn and TiC at 1200 °C for 15 min. A reaction mechanism was proposed to explain the formation of Ti2SnC. The Ti2SnC powder was characterized by scan electron microscopy (SEM) and X-ray diffraction (XRD). Using the above mixtures and process, the Ti2SnC ceramic powder can be obtained on a larger scale. 相似文献
20.
New compound ScTiNbO6 synthesized via phase transformation from anatase to srilankite-like structure
A new srilankite-like compound ScTiNbO6 was synthesized as a single phase at 900 °C via phase transformation using anatase-type nanoparticles that were directly formed from solution mixture of Sc(NO3)3, TiOSO4, and NbCl5 under mild and weakly basic hydrothermal condition at 180 °C for 5 h. Anatase-type Sc0.5Ti2Nb0.5O6 nanoparticles transformed into rutile phase at 1000 °C. The new phase that was appeared via phase transformation was identified as srilankite-like structure with a trace of symptomatic wolframite, α-PbO2 related structure. The optical band gap of ScTiNbO6 was 3.58 eV. This titania-base material has potential for application as catalyst and photoluminescence, etc. 相似文献