Mechanism Of Combustion Synthesis Research Articles

Preparation of low temperature cure polybenzoxazine coating with enhanced thermal stability and mechanical properties by combustion synthesis approach

This research aimed to develop a combustion synthesis method to decrease curing temperature of benzoxazine with enhanced thermal stability and mechanical properties. In(NO3)3 was selected as an oxidant and acetylacetone was employed as a fuel to form a combustion system. The mechanism of combustion synthesis that involved curing benzoxazine was studied, and thermal stability and mechanical properties of cured products were discussed. It was revealed that the proposed method could significantly reduce the curing temperature of benzoxazine, and the initial curing temperature dropped to below 100 °C. Compared with polybenzoxazine, proposed method indicated an improved thermal stability, and the highest carbon yield at 800 °C was increased by 25.0%. In addition, the possible effects of the proposed method on coatings were investigated. The impact resistance, hardness, and surface adhesion were significantly improved to 7J, 6H, and 5B, respectively, with excellent anti-corrosive properties including a corrosion rate of 1.39 × 10−3 mm/year, indicating its great application potential in coating. The formation of a high content of arylamine Mannich structures and a small amount of In2O3 after curing could justify the improvement of thermal stability and mechanical properties of polybenzoxazine. The proposed method not only provided a facilitate way to cure benzoxazine, but also showed to be significant for modulating the chemical structures and properties of cured benzoxazine.

Effect of ignition temperature and fuel amount on photocatalytic activity of solution combustion synthesized ZnO

Nanocrystalline zinc oxide (ZnO) photocatalyst has been synthesized by a simple solution combustion method using zinc nitrate as the oxidizer and urea as the fuel. Effect of fuel to oxidizer ratio and ignition temperature on the mechanism of combustion synthesis, crystallinity, morphology, surface area, and optical properties were investigated by thermal analysis, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Diffuse reflectance UV–Visible spectra and Photoluminescence analyses. Photocatalytic activity of the synthesized materials was evaluated by degrading an azo dye at ambient temperature and solution pH. The prepared photocatalysts at the fuel-rich condition possess small crystallite size and more surface area; consequently, a higher photocatalytic dye degradation capability.The powder samples synthesized at the fuel-oxidant ratio of 1.8 and the ignition temperature at 400 °C have shown the maximum percentage (99%) of dye degradation in 180 min. The pseudo-first order photocatalytic dye degradation rate constant of a catalyst sample synthesized at the fuel-oxidant ratio of 1.8 was 0.0253 min−1and it is 3.14 and 2.88 times higher than that of samples synthesized at fuel-oxidant ratios of 0.6 and 1.The outcomes of the present article help to design more pronounced experiments for the synthesis of photocatalysts by varying ignition temperatures and fuel amounts.

Mechanism and microstructural evolution of combustion synthesis of ZrB2–Al2O3 composite powders

Mechanism of combustion synthesis (CS) of ZrB2–Al2O3 composite powders was systematically analyzed by a combustion front quenching method (CFQM). The microstructural evolution during the CS process was investigated by field-emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectrometer (EDS). The combustion temperature and wave velocity were measured by the data acquisition system. Moreover, the phase constituents of the final product were examined by X-ray diffraction (XRD). The thermal behaviors of the stoichiometic powders under the thermal exposure were characterized using differential scanning calorimetry (DSC) and thermogravimetric (TG). The results showed that the combustion reaction started from the melting of the B2O3 and Al particles, which was followed by the formation of ZrO2–B2O3–Al solution. The ignition temperature of this system was determined to be around 800°C. B and Al2O3 were then precipitated from the solution. As the CS reaction proceeded, Zr and Al2O3 were produced by the reaction between ZrO2 particles and Al and precipitated from the solution. ZrB2 could then be formed by the direct reaction between Zr and B. Finally, the ZrB2–Al2O3 composite powders were obtained. Furthermore, a model corresponding to the dissolution–precipitation mechanism was proposed.

Mechanism of combustion synthesis of TiC–Fe composites under the action of an electric field

The combustion synthesis process of the 55 wt-%(Ti+C)–45 wt-%Fe system was studied under two different fields. The simplex thermal field was provided by differential scanning calorimeter and high temperature X-ray diffraction equipment, while the electric field was generated by a Gleeble thermal simulation instrument. With the aid of an electric field, the system is able to be ignited at 394°C, which is much lower than the ignition temperature of above 920°C required if only a simplex thermal field is used. This is because solid diffusion among reactant atoms could be accelerated at a lower temperature by the coeffect of an electric field and the self-generated thermal field. Microstructure study revealed the formation of instantaneous liquid phase in microzones during combustion. A four step model describing the mechanism for the combustion synthesis of TiC–Fe composites under an electric field is also proposed.

Mechanism of combustion synthesis of TiC-Ti cermet

In order to investigate the mechanism of combustion synthesis of TiC-Ti cermet, a mixture of Ti and C was used for a combustion front quenching test, and the microstructural evolution in the quenched sample was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). Also, a temperature-time profile of the combustion reaction was measured. Based on the experimental results, a reaction-dissolution-precipitation mechanism of the combustion synthesis of TiC-Ti was proposed.

Dual-solution-precipitation mechanism of combustion synthesis of TiC-Fe cermet with fine Ti powder

A Ti-C-Fe powder mixture with a finer Ti powder was used for a combustion front quenching test to investigate the effect of titanium particle size on the mechanism of the combustion reaction, and the microstructural evolution in the quenched specimen was then observed with scanning electron microscopy, and the combustion temperature was also measured. The results showed that the nature of the combustion reaction could be described with a dual-solution-precipitation mechanism and a correspondent model. The melting of the finer Ti particle prior to its reaction was attributed to a combined effect of two factors: a decrease of its size-controlled melting point, and a decrease of its composition-controlled melting point. The use of the finer Ti powder led to a more complete combustion reaction and hence a higher combustion temperature. As a result, the combustion-synthesized TiC-Fe cermet had a greater average size of TiC particles and layer-shaped pores that was confirmed to be a consequence of gathering of the evolved gases into the combustion wavefront.

Mechanism of combustion synthesis of TiC–Fe cermet

To investigate the mechanism of combustion synthesis of TiC–Fe cermet, a mixture of (Ti+C)+30 wt% Fe was used for a combustion front quenching test, and the microstructural evolution in the quenched sample was analyzed by scanning electron microscopy and energy dispersive spectrometry. The temperature-time profile of the combustion was measured, and the phase constituents of the product were inspected by X-ray diffraction. Based on these results, the mechanism of the combustion synthesis was analyzed, and a ternary-reaction-diffusion/solution-precipitation model was proposed. Asynchronism and incompleteness of the combustion are discussed also.

The influence of an electric field on the mechanism of combustion synthesis of tungsten silicides

The synthesis of tungsten silicides by self-propagating combustion has been successfully accomplished under the influence of an electric field. Materials with starting composition ranging from 6 to 30 wt. % Si were investigated by the method of field-activated combustion synthesis (FACS). A threshold field value was required to initiate a self-sustaining wave; the threshold value depended on composition. It was shown that the level of the applied field can influence the mechanism of silicide formation. The silicide W5Si3 could be formed only at relatively high field values while WSi2 can be formed at any field. The effect of the field on the silicide formation is discussed in terms of its role in liquid phase formation.