Effect of cerium on ignition point of AZ91D magnesium alloy

The surface and interior temperature-time curves of blocky cerium modified AZ91D magnesium alloy were measured during a non-protective heating and melting process. Two inflection points with rapid increase in temperature were found on both curves, which corresponded to the formation of ＂aulifiower＂ oxide on the surface and the occurrence of flame during melting. These two temperatures are therefore defined as oxidation point and ignition point, respectively. The interior temperature-time curve is similar to that measured on the surface except for a comparable time delay. The oxidation and ignition temperatures increase with Ce content, an average increase of 33℃ and 61℃ was found when Ce addition was about 1.0 wt %. However, the increasing rate of the oxidation and ignition temperature decreases with increasing Ce content. An addition of 0.6wt% Ce is recommended for ignition-resistant AZ91 magnesium alloy.

On ignition point of Mg-Ca alloy under nitrogen atmosphere

The production cost will be greatly reduced if nitrogen can be used instead of inert gas in the spray forming process of magnesium alloys, but the heat from the reaction between magnesium alloys and nitrogen makes magnesium alloy burn easily. To solve the problem above, the ignition point of Mg-Ca alloy under nitrogen atmosphere was studied using a home-made experimental device and DSC-DTA. Results show that under nitrogen atmosphere, Ca addition has a great effect on the ignition point of Mg alloy. The ignition point of the Mg-5Ca bulk even exceeds 1,030℃, and the alloy can be held for 30 min at 900℃ without burning;while the average ignition point of Mg-5Ca powders is lower than 700℃, and it increases with the increasing particle size. Moreover, the purity of nitrogen must be in a certain scope;Mg-Ca alloy shows a higher ignition point under nitrogen with a purity of 99.5%. Based on the experimental results, the best adding content of Ca and the purity of nitrogen were determined, and the security and economic performance of preparing magnesium alloys by spray deposition were improved with nitrogen as atomizing gas.

Effect of FeCl_3 on Ignition Point of Coals

The potential combustion-supporting agents for three kinds of coals were selected according to the Thermal Gravity Analysis (TG). The TG analysis shows that the addition of FeCl3 can reduce the ignition point of clarain and fusain from Guangxi and also the raw coal from Xinwen. The combustion-supporting effect of FeCl3 on the clarain is quite obvious, with the maximum reduction of ignition point reaching 90 ℃ and that of the burn-out point reaching 95 ℃. What is more, it can make the coal burn more completely. The relationship between the amount of FeCl3 and the ig- nition point was also investigated and the optimum amount of FeCl3 obtained. When FeCl3 is added in doses of 6%, 4%, 2%, and 1%, the reduction of ignition point is proportional to the amount of agent. If 6% of FeCl3 is added, the combus- tion-supporting effect is very significant; while if only 1% of FeCl3 is added, the combustion-supporting effect can be negligible. Therefore the optimum amount of FeCl3 is between 3% and 6% for achieving an obvious combus- tion-supporting effect. In addition, the combustion supporting mechanism of FeCl3 was also studied, which is the com- bined action of chloride and iron in the compound.

Nonlinear characteristics of induced spontaneous combustion process of sulfide ores

To investigate the relationship between nonlinear parameters and spontaneous combustion tendency of sulfide ores, nine different sulfide ore samples were taken from a pyrite mine in China, and induced spontaneous combustion experiment was carried out in the laboratory. Different stages of the induced spontaneous combustion process were studied by integrating wavelet technology and nonlinear dynamics theory. The results show that ignition points of all the ore samples are above 330 ℃, indicating that sulfide ores of the pyrite mine are difficult to combust spontaneously under normal mining conditions. Spontaneous combustion process includes three stages： incubation stage, development stage and approaching stage. The average temperature rising rate of the three stages are 1.0 ~C/min, 2.0 ~C/min and 4.2 ~C/min, respectively. During the spontaneous combustion process, mean values of approximate entropy and correlation dimension increase at first, and then decrease in the following stage. The mean value of the maximum Lyapunov exponent increases with the passage of reaction time. In a whole, correlation among the three nonlinear parameters firstly weakens, then enhances, and the best correlation period is at approaching stage. As ignition point increases, the maximum Lyapunov exponent of approaching stage decreases. Therefore, combustible tendency of sulfide ores could be qualitatively evaluated based on the maximum Lyapunov exponent of this stage.