Recent progress on impact induced reaction mechanism of reactive alloys

In recent years,in order to improve the destructive effectiveness of munitions,the use of new types of destructive elements is an important way to improve destructive effectiveness.As a new type of reactive material,reactive alloy contains a large portion of reactive metal elements(Al,Mg,Ti,Zr,etc.),which breaks up under high-velocity impact conditions,generating a large number of high-temperature combustible fragments,which undergo a violent combustion reaction with air.Compared with traditional metal polymers(Al-PTFE)and other reactive composites,it has higher density and strength,excellent mechanical properties and broader application prospects.Currently,researchers have mainly investigated the impact energy release mechanism of reactive alloys through impact tests,and found that there are several important stages in the process of the material from fragmentation to reaction,i.e.,impact fragmentation of the material,rapid heating and combustion reaction.This paper focuses on three problems that need to be solved in the impact-induced energy release process of reactive alloys,namely:the fragmentation mechanism and size distribution law of the fragments produced by the impact of the material on the target,the relationship between the transient temperatures and the size of the fragments,and the reaction temperatures and size thresholds of the fragments to undergo the chemical reaction.The current status of the research of the above problems is reviewed,some potential directions to reveal the impact induced reaction mechanism of reactive alloy is discussed.

Size-Resolved Water-Soluble Ionic Composition of Ambient Particles in an Urban Area in Southern Poland

The ambient concentrations of PM-related anions (Cl-, NO3-, SO42-) and cations (Na+, NH4+, K+, Ca2+, Mg2+), total and contained in the PM fractions, were investigated in a typical urban area within the Silesian Agglomeration. A DEKATI low pressure impactor (DLPI) was used to sample PM and separate it into 13 fractions. The PM concentrations were determined gravimetrically, the ion content of the PM water extracts—by means of ion chromatography (Herisau Metrohm AG ion chromatograph). In general, sulfate, nitrate, and ammonia had the greatest ambient concentrations. PM1 contained over 60% of the PM-related sulfate and nitrate mass and 90% of the ammonia mass. Also the majority of Na+ and Cl- were bound onto fine particles. Instead, more of the PM-related K+, Ca2+ and Mg2+ mass were in PM2.5-10 than in PM2.5. In the fine particles (sub-fractions of PM1.6) sulfate, nitrate and ammonia occur mainly as (NH4)2SO4 and NH4NO3. In the sub-fractions of PM1.6-10 sulfate and nitrate might also occur as K2SO4, CaSO4, Ca(NO3)2 or NaNO3.

Characteristics of mass distributions of aerosol particle and its inorganic water-soluble ions in summer over a suburb farmland in Beijing

Agricultural activity is one of the most important sources of aerosol particles.To understand the mass distribu-tion and sources of aerosol particles and their inorganic water-soluble ions in a suburb farmland of Beijing,particle samples were collected using a microorifice uniform deposit impactor(MOUDI)in the summer of 2004 in a suburb vege-table field.The distribution of the particles and their inor-ganic water-soluble ions in the diameter range of 0.18-18 mm were measured.The dominant fine particle ions were SO_(4)^(2−),NO^(3−),and NH_(4)^(+).The association of day-to-day variation of the concentration of these ions with temperature,humidity,and solar radiation suggested that they are formed by the reac-tion of NH_(3) released from the vegetable field with the acid species produced from photochemical reactions.Fine particle K+is likely from vegetation emission and biomass burning.Coarse particles like Ca^(2+),Mg^(2+),NO_(3)^(−),and SO_(4)^(2−)are sug-gested to come from the mechanical process by which the soil particle entered the atmosphere,and from the reaction of the acid species at the surface of the soil particle.The results show that fertilizer and soil are important factors determining the aerosol particle over agricultural fields,and vegetable fields in suburban Beijing contribute significantly to the aerosol particle.