Search Results (3)

In order to obtain the chemical reaction mechanism of Al-rich Al/PTFE/TiH₂ composites in argon and oxygen atmosphere, Al/PTFE, PTFE/TiH₂, Al/TiH₂ and Al-rich Al/PTFE/TiH₂ with different contents of TiH₂ composites were prepared by using the wet mixing method. The pyrolysis behavior of the above composites was investigated by thermogravimetric differential scanning calorimeter (TG-DSC). In addition, the calorific value of the above composite was measured by an oxygen bomb calorimeter. The compositions of TG-DSC residues at different peak temperatures and 1000 °C and the residues of oxygen bomb experiment were analyzed by X-ray diffraction (XRD), The results show that the pyrolytic products of Al-rich Al/PTFE/TiH₂ materials under argon atmosphere can be divided into four stages. In the first stage (328.6–378.6 °C), the products are TiH_1.924, (C₂F₄)_n, (CF₂)_n, H₂(g), Al and TiH₂; in the second stage (510.8–534.3 °C), the products are Al, TiH_1.924, (C₂F₄)_n, (CF₂)_n, Ti, AlF₃, TiF₃, TiF₄(g), C and H₂(g). In the third stage (540.8–618.1 °C), the products are Al, C, Ti, (C₂F₄)_n, (CF₂)_n, AlF₃, TiF₃, TiF₄, CF₄(g), C₃F₆(g), C₄F₈(g), C₂F₆(g), Al₅Ti₂ and H₂(g); in the fourth stage (918.5–1000 °C), the products are AlCTi₂, Al₂Ti, AlTi, TiC, AlF₃, Al, TiF₃, TiC_0.957, TiC_0.981 and TiC_0.95. The calorific value of the combustion of Al-rich Al/PTFE/TiH₂ composite with 10% the content of TiH₂ is the highest and is 19,899 J/g, which is 3.776% higher than that of Al-rich Al/PTFE composite. When TiH₂ content is greater than zero and not more than 10%, the chemical reaction mechanism of Al-rich Al/PTFE/TiH₂ is almost the same under oxygen atmosphere. When the content of TiH₂ is higher than 10%, the mechanism of this material is different. Full article

Sintering process is an important part of the specimen preparation process, which directly affects the properties of materials. In order to obtain the best sintering control factors of Al-rich PTFE/Al/TiH₂ active materials, Al-rich PTFE/Al/TiH₂ active specimens with different sintering control factors were prepared using a mold pressing sintering method. A quasi-static compression experiment was carried out on a universal material testing machine, and a real stress-strain curve was obtained. The effects of sintering control factors on the properties of Al-rich PTFE/Al/TiH₂ active materials were analyzed by means of mechanical parameters such as compressive strength, failure strain and toughness. SEM and XRD were used to analyze the microstructure and phase of the sintered samples. The results show that: (1) With the increase of cooling rate, the density, yield strength, strain hardening modulus, compressive strength and toughness of Al-rich Al/PTFE/TiH₂ specimens decrease gradually, while the failure strain and pores of the specimens increase gradually. (2) With the increase of sintering temperature, the density, maximum true strain and toughness of the specimens first increase and then decrease, and the failure strain of the specimens gradually increases. When the sintering temperature is 360 °C, the PTFE matrix and particles inside the specimen are closely combined, a small number of particles are exposed on the PTFE matrix and there are a small number of voids. (3) With the increase of holding time at 360 °C, the strength and toughness of the material first decrease and then increase. When the holding time is 6 h, the interface between particles and matrix inside the specimen is the strongest, and the crack propagation inside the specimen is less. (4) When the sintering time increased from 1 h to 4 h at 315 °C, the compressive strength of the specimen increased by 1.62%, the toughness of the specimen decreased by 0.55% and the failure strain of the specimen decreased by 0.54%. The interface between PTFE matrix and particles is the strongest and the crack propagation is less in the specimen with a holding time of 4 h. (5) Above all, the optimum sintering parameters of Al-rich Al/PTFE/TiH₂ materials are cooling rate of 25 °C/h, sintering temperature of 360 °C, holding time of 6 h and holding time of 4 h at 315 °C. (6) The reactivity of Al-rich Al/PTFE/TiH₂ specimens with 10% content of TiH₂ under static compression is not significantly affected by sintering parameters. Full article

Preforming pressure and the pressure holding time are important parameters of the molding process, which directly affect the mechanical properties of materials. In order to obtain the best molding parameters of Al-rich Al/PTFE/TiH₂ composites, based on the quasi-static compression test, the influence of molding parameters on the mechanical properties of Al-rich Al/PTFE/TiH₂ composites was analyzed, and the microstructure characteristics of Al-rich Al/PTFE/TiH₂ specimens were analyzed by SEM. An X-ray diffractometer was used to analyze the phase of the residue after quasi-static compression experiment. The results show that: (1) With the increase in molding parameters (preforming pressure and the pressure holding time), the compressive strength, failure strain and toughness of Al-rich Al/PTFE/TiH₂ specimens first increase and then decrease. The best molding process parameters of Al-rich Al/PTFE/TiH₂ materials are preforming pressure 240 MPa and the pressure holding time 100 s. (2) For unsintering specimens, when the preforming pressure is less than 150 MPa, the porosity of the specimen increases slowly at first and then decreases. When the preforming pressure is greater than 150 MPa, the porosity of the specimen increases first and then decreases. When the pressure holding time is no more than 100 s, the porosity of the specimen decreases gradually. When the pressure holding time is more than 100 s, the porosity of the specimen increases first and then decreases. For sintered specimens, when the preforming pressure is less than 100 MPa, the porosity of the specimen decreases gradually. When the preforming pressure is greater than 100 MPa, the porosity of the specimen first increases and then decreases. With the increase in the pressure holding time, the porosity first increases and then decreases. For each preforming pressure specimen, compared with that before sintering, the porosity after sintering either decreases or increases. For each the pressure holding time specimen, the porosity increases after sintering compared with that before sintering. The microstructure of PTFE crystal inside the specimen is mainly planar PTFE crystal. The size and number of planar PTFE crystals are significantly affected by the molding parameters, which further affects the mechanical properties of Al-rich Al/PTFE/TiH₂ specimens. When the preforming pressure is less than 100 MPa, the planar PTFE crystals are small and few, which results in the worst mechanical properties of the specimens. When the preforming pressure is more than 100 MPa and does not contain 240 Mpa, the planar PTFE crystals are small and there are more of them, which results in better mechanical properties of the specimens. When the preforming pressure is 240 MPa, the planar PTFE crystals are large and numerous, which results in the best mechanical properties of the specimen. When the pressure holding time is 100 s, the planar PTFE crystals are large and there are more of them, which results in the best mechanical properties of the specimen. (3) The reactivity of Al-rich Al/PTFE/TiH₂ specimens with TiH₂ the content of 10% under quasi-static compression is not significantly affected by the molding parameters. Full article