Microstructures, Properties Of Porous Aluminum Sticks By Powder Metallurgy And Effects On Reduction Of Temperature And Harm Of Cigarettes

The release of harmful substances of cigarettes during smoking is closely related to the combustion cone temperature. However, the effect of existing cigarette cooling technology is not obvious and other harmful substances may generate. Because porous aluminum has some excellent properties, such as lower density, large specific surface area and high thermal conductivity, it becomes a research hot-spot in heat exchange materials. The traditional processes to prepare porous aluminum are complex, expensive and their products usually contain impurities, so they are not suitable for the preparation of porous aluminum sticks which will be used in cigarette. In this work, porous aluminum sticks were prepared by loose sintering and pressing-sintering, these processes are simple and the cooling effects of these porous aluminum sticks on cigarette are obvious. The effects of processing parameters on microstructure, mechanical properties and thermal conductivity of porous aluminum sticks were mainly investigated. The porous pure aluminum sticks were then added to cigarettes, and the cooling and harm reducing effects were studied. At the same time, the heat transfer mechanisms of composite cigarettes were also discussed. The main results are as follows:The porosity of porous aluminum prepared by powder loose sintering is moderate, its mechanical property and thermal conductivity is low. Average particle size, sintering temperature and holding time have a significant effect on microstructures, relative density, and hardness of porous aluminum sticks. Relative density and hardness of aluminum sticks increase with the increasing of average particle size firstly, then decrease slightly, and increase again finally. Under the conditions of the average particle size about 48μm, the sintering temperature of 600℃ and the holding time of 120 min, the relative density of porous pure aluminum stick is 61.7%, the micro-hardness is 33.89 HV and the thermal conductivity is 22.79W/(m?K). The relative density and the hardness of aluminum sticks increase with the increasing of sintering temperature which ranges from 525℃ to 625℃. The values of relative density range from 60% to 63% and hardness with 20~50HV. When the holding time is lower than 120 min, The relative densities of aluminum sticks increase slightly with the increasing of holding time.Compared with the porous aluminum stick prepared by powder loose sintering process, the porous aluminum stick prepared by powder pressing-sintering has many different features. Such as the porosity is lower, the mechanical property and heat conductivity is higher. The relative density, micro-hardness and yield strength of aluminum sticks increase with increasing pressing pressure firstly, then decrease slightly. The thermal conductivity increases with increasing pressing pressure. The relative density ranges from 81.2% to 92.6%. When the pressing pressure is 150 MPa with the sintering temperature of 600℃ and the holding time of 60 min, the relative density of porous aluminum sticks reaches to 91.9%. The micro-hardness reaches to 40 HV, the yield strength reaches to 132 MPa, and the thermal conductivity reaches to 43.25W/(m?K). Relative density, micro-hardness, yield strength and thermal conductivity increase with increasing sintering temperature when the pressing pressure is 150 MPa. When the sintering temperature is 600℃, the effects of holding time on the properties of porous aluminum sticks are very small.The cooling and reduction effects of porous aluminum prepared by different processes on cigarettes were studied. The results show that compared with the blank cigarette, the cooling effect of combustion cone of a cigarette added with a porous aluminum stick prepared by loose sintering is obvious and the temperature of the filter changes little. The temperature reduction of a combustion cone of a cigarette added with a porous pure aluminum stick prepared by pressing-sintering is more than 150℃, the release quantities of CO, Nicotine and tar decrease significantly by 26%、26% and 17% respectively.The heat transfer mechanisms during smoking of a composite cigarette were also discussed. Conduction, convection and radiation heat transfer are the main three basic heat transfer mechanisms for a cigarette. The combustion cone temperature of composite cigarette depends on the conduction effect caused by the heat conduction rod and the forced convection caused by the flue gas.