Kinetics and Combustion Behavior of Atomized Zn-Mg Alloy Powder.

Using pyrolants instead of warhead charges can release red light and thick smoke for target practice to highlight the safety of the impact point and dud disposal. In order to find the ideal material, the combustion and kinetic properties of two Zn-Mg alloys at critical proportions were investigated. Thermogravimetry/differential scanning calorimetry (TG/DSC) experiments in pure oxygen were conducted with atomized Zn-Mg alloy powder in the ratio of 7:3 and the ratio of 8:2 with three particle diameters under different heating rates. The kinetic parameters of the six materials were obtained by ASTM E698 and Ozawa-Flynn-Wall (OFW) methods, indicating that the activation energy (Eα) of the 7:3 Zn-Mg alloy powder was lower than that of the 8:2 Zn-Mg alloy powder when the particle size distributions are similar. By the method of nonlinear multivariate regression, the oxidation reaction of Zn-Mg alloy powder was divided into two steps. The proportion of mass gain of the first-step reaction of 7:3 Zn-Mg alloy powder was 0.462-0.518, and the proportion of mass gain of the first-step reaction of 8:2 Zn-Mg alloy powder was 0.138-0.228. Reaction mechanism functions of the two-step reaction of Zn-Mg alloy oxidation were derived as f(α) = (1 - α)n(1 + kcat·α). The results of combustion experiments showed that the pyrolants composed of 7:3 alloy can burn stably to produce satisfactory smoke and light signals, while the pyrolants composed of 8:2 alloy cannot achieve this. The 7:3 Zn-Mg alloy powder is an ideal ingredient for pyrotechnic compositions.

Quantitative Assessment Method of Muzzle Smoke in a Field Environment.

The muzzle of barrel weapons produces a large amount of smoke (muzzle smoke), a major source of pollution in the battlefield. Quantitative assessment of muzzle smoke is an important support for the development of advanced propellants. However, due to the lack of effective measurement methods for field experiments, most of the previous studies were based on a smoke box, and few studies have focused on muzzle smoke in the field environment. In view of the nature of the muzzle smoke and the conditions of the field environment, the characteristic quantity of muzzle smoke (CQMS) was defined based on the Beer-Lambert law in this paper. CQMS is used to characterize the danger level of muzzle smoke produced by the propellant charge, and theoretical calculations indicated that when the transmittance is e -2, the impact of the measurement errors on CQMS can be minimized. Seven firings with the same propellant charge of a 30 mm gun were carried out in a field environment to verify the effectivity of CQMS. The measurement uncertainty analysis on the experimental results showed that the CQMS of the propellant charge used in this study was 2.35 ± 0.06 m2, which indicates that CQMS can be used to quantitatively assess muzzle smoke.

Self-Propagating High-Temperature Synthesis of Magnesium Aluminate Spinel Using Mg-Al Alloy.

In this study, magnesium aluminate spinel (MgAl2O4) was synthesized by a self-propagating high-temperature synthesis method using Mg-Al alloy with a Mg/Al mass ratio of 50:50 as raw material. Synthesized MgAl2O4 was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, UV-vis diffused reflectance spectroscopy, photoluminescence, and thermogravimetric differential scanning calorimetry techniques. The results show that synthesized products are of high purity and excellent crystallinity. However, the particle size is not uniform and there is obvious agglomeration. The crystallite size of spinel phase is calculated to be 37.78 nm. In the UV band, the synthesized MgAl2O4 has a certain absorption capacity, and the extrapolated band gap is 4.02 eV. The synthesis mechanism was studied, and continued rupture and growth of the oxidation layer is thought to be responsible for grain refinement.

Tuning the Energetic Performance of CL-20 by Surface Modification Using Tannic Acid and Energetic Coordination Polymers.

The energetic performance of hexanitrohexaazaisowurtzitane (CL-20) was modulated with two energetic coordination polymers (ECPs), [Cu(ANQ)2(NO3)2] and [Ni(CHZ)3](ClO4)2, in this study by a two-step method. First, tannic acid polymerized in situ on the surface of CL-20 crystals. Then, [Cu(ANQ)2(NO3)2] and [Ni(CHZ)3](ClO4)2 were hydrothermally formed on the surface of CL-20/TA, respectively. Explosion performance tests show that the impact sensitivity of the coated structure CL-20/TA/[Cu(ANQ)2(NO3)2] is 58% less than that of CL-20 with no energy decrease. On the other hand, CL-20/TA/[Ni(CHZ)3](ClO4)2 can be initiated by a low laser energy of 107.3 mJ (Nd:YAG, 1064 nm, 6.5 ns pulse width), whereas CL-20 cannot be initiated by even 4000 mJ laser energy. This study shows that it is feasible to modify the performance of CL-20 by introducing energetic CPs with certain properties, like high energy insensitive, laser-sensitive, etc., which could be a prospective method for designing high energy insensitive energetic materials in the future.

[Expression of gene aiiA carrying the promoter of gene cry3Aa in Bacillus thuringiensis].

N-acyl-homoserine lactones (AHLs), are widely conserved signal molecules present in quorum-sensing systems of many Gram-negative bacteria. AHLs molecules mediate the expression of virulence genes of a range of bacterial pathogens. Recently, it has been reported that AiiA protein, which widely exists in Bacillus species, can inactivate the AHLs by hydrolyzing the lactone bond of AHLs, thus attenuate the diseases caused by the expression of virulence genes of bacterial pathogens. Bacillus thuringiensis, a type of Gram-positive bacteria, has been used extensively as a microbial insecticide in the last few decades. However, most of important insecticidal B. thuringiensis strains have not been exploited for bacterial disease control because they usually do not produce antibiotics that are effective against bacteria and fungi. The discovery of AiiA protein in B. thuringiensis shows the application potential of B. thuringiensis on biocontrol against bacterial diseases. In this study, in order to construct the B. thuringiensis recombinant strain that has high expression of AiiA protein, the promoter of insecticidal crystal protein coding gene cry3Aa of B. thuringiensis was selected. The promoter of gene cry3Aa is a non-sporulation promoter, it promotes the transcription earlier and longer than the promoters of other cry genes. The promoter of AiiA protein coding gene aiiA was replaced with the promoter of gene cry3Aa by overlapping PCR, resulting fusion gene pro3A-aiiA. The gene pro3A-aiiA was inserted into shuttle vector pHT304 at site BamH I / Sph I , resulting recombinant plasmid pBMB686. The plasmid pBMB686 was introduced into B. thuringiensis acrystalliferous strain BMB171, the resulting strain BMB686 had a higher and more stable expression level of protein AiiA comparing with the parental strain BMB171. Furthermore, the strain BMB686 exhibited stronger ability of AHLs inactivation and much more effective restraint to the potato's soft rot disease caused by Erwinia carotovora than those of the parental strain BMB171. From these results, it was concluded that the B. thuringiensis strain harvesting the fusion gene pro3A-aiiA may be utilized in the future to control bacterial diseases which are mediated by the AHL quorum-sensing signals.

[A novel resolution vector with Bacillus thuringiensis plasmid replicon ori44].

The resolution recognization sites of transposon Tn4430 of Bacillus thuringiensis was inserted into cloning vector pRSET B and pUC19, resulting recombinant plasmids pBMB1201 and pBMB1202. Both of the mini res fragments, BamHI/HindIII fragment in pBMB1201 and EcoRI/HindIII fragment in pBMB1202, were ligated to the 3.3 kb EcoRI/HindIII fragment of shuttle vector pHT3101, which contained the ori. Ec, ampr and emr antibiotic resistant genes, resulting recombinant plasmid pBMB1203. After deleted the BamHI and EcoRI sites which located ouside the two res sites, resolution vector pBMB1204 was resulted. There are multiple cloning sites between two copies of resolution sites which have the same direction. The plasmid replication origin ori44, which come from B. thuringiensis sub sp. kurstaki strain YBT-1520, was inserted into the multiple cloning sites of pBMB1204 and then resolution shuttle vector pBMB1205 was obtained. With spectinomycin resistant gene as target, it was found that the resolution rate is 100% and the stability of the resolved plasmid is 93%. Using this shuttle vector, antibiotic resistance markers and other non-B. thuringiensis DNA can be selectively eliminated after the selection of transformants by antibiotic resistance marker. This vector is very useful to solve the gene safety problem while has no effect on target gene expression.