The effect of microencapsulation with nitrocellulose on thermal properties of sodium azide particles

Based on the coacervation principle a solvent/non-solvent method has been used for microencapsulation of sodium azide (NaN₃) with fibrous nitrocellulose (NC). Scanning electron microscopy (SEM) was employed to examine the coating morphology. The thermal behavior of solid samples has been studied by means of thermogravimetry (TG) and differential scanning calorimetry (DSC). The results of TG–DTA analysis revealed that the main thermal degradation for the pure NC and NaN₃ occurs in the temperature ranges of 192–220 and 415–420 °C, respectively. The effects of some parameters, such as NC to NaN₃ weight ratio and volume and addition time of non-solvent, on coating quality and thermal properties have been investigated by SEM and thermal methods. The results of these experiments showed that the decomposition temperature of most stabilized coated sodium azide is about 50 °C higher than that of the pure sample. The DSC experiments were conducted to study the influence of the heating rate (5, 10, 15 and 20 °C/min) on the thermal decomposition processes of the pure NC, coated and pure NaN₃ samples. The results revealed that, as the heating rate was increased, decomposition temperature of the compounds was increased. Also, the kinetic parameters such as activation energy and frequency factor of the decomposition processes were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Our finding showed that coated NaN₃ has lower decomposition rate with respect to the pure one.     

Stabilizing of magnesium powder by microencapsulation with azidodeoxy cellulose nitrate

Surface of magnesium particles is highly reactive and may be oxidized easily during storage at ambient conditions. Coating the surface of metal particles with a layer of polymer could be a simple and efficient way to prevent oxidation. In this study, Taguchi robust design was employed as a statistical experiment design for coating of magnesium powder with azidodeoxy cellulose nitrate via solvent/non-solvent technique. FT-IR spectroscopy and scanning electron microscopy techniques were used to evaluate the surface morphology of coated particles. The effect of azidodeoxy cellulose nitrate coating on magnesium powder thermal stability has been investigated by means of thermogravimetry (TG) coupled with differential scanning calorimetry (DSC). The effects of procedure parameters, i.e., type of solvent, percent of polymer as the stabilizer, flow rate of non-solvent addition, and added non-solvent volume in the coating quality and thermal properties of magnesium powder have been studied by thermal analysis methods. Analysis of variance (ANOVA) was employed to evaluate quantitatively the effect of these parameters on thermal stability of coated magnesium particles. Thermal data showed that magnesium powder could be stabilized considerably by controlling coating process parameters including the percent of the stabilizer, flow rate of non-solvent addition, and type of solvent. Based on the ANOVA results, using of 3% stabilizer, 1 ml/min as non-solvent flow rate, and DMF as the solvent are optimum conditions for coating of magnesium particles with azidodeoxy cellulose nitrate leads to producing coated particles with higher thermal stability (567 °C); whereas, TG/DSC analysis results revealed that the main thermal oxidation of the pure magnesium powder starts at lower temperature ranges of 260 °C.     

Stabilization of ammonium azide particles through its microencapsulation with some organic coating agents

This work is devoted to reduce spontaneous sublimation of ammonium azide at ambient and elevated temperatures by means of two microencapsulation techniques involving solvent/non-solvent and solvent evaporation methods in which stearic acid, Viton and nitrocellulose (NC) have been tested as coating agents. Scanning electron microscopy (SEM) was employed to examine the coating morphology. The thermal behavior of pure and coated ammonium azide samples have been studied by using simultaneous thermogravimetery-differential thermal analysis (TG-DTA) and differential scanning calorimetry (DSC). The results showed that ammonium azide microparticle could be effectively coated with nitrocellulose through a solvent/non-solvent experiment in which the coating quality depends on some experimental factors such as coating agent to NH₄N₃ weight ratio and volume and addition time of non-solvent. The effect of these factors on coating quality and thermal properties of NH₄N₃ has been revealed by results of SEM and thermal experiments. The most stabilized coated ammonium azide was achieved by using 4.5% (w/w) of NC as stabilizer, and by addition of 30 ml n-hexane as non-solvent within 75 min, where the maximum sublimation temperature increases about 30 °C with respect to uncoated sample and reaches to 145.5 °C. The influence of the heating rate (5, 10, 15 and 20 °C/min) on the DSC behavior of the pure and coated ammonium azide particles at the optimum condition was verified, whereas sublimation temperature of the NH₄N₃ was increased as the heating rate was increased. Also, the kinetic parameters such as the activation energy and frequency factor of the sublimation processes for pure and coated ammonium azide were obtained from the DSC data by non-isothermal methods proposed by Kissinger and Ozawa. The results showed that, activation energy for sublimation of completely coated NH₄N₃ particles is considerably higher than (nearly 1.5 times) that of the pure one. Also, the first order rate constant of sublimation of completely coated sample is noticeably lower than that of pure sample (). The kinetic results led us to conclude that the applied microencapsulation technique caused efficient stabilization of volatile NH₄N_3.     

甲醇羰基化合成醋酸Ni/AC催化体系的正交设计与优化

对甲醇气相羰基化合成醋酸的镍基催化剂及其操作条件进行了筛选，选择可变因子设计了正交试验。采用SPSS对结果进行方差分析，找出了主要影响因素并优化了反应条件。在此反应条件下，醋酸收率达到35.2%，且碘甲烷用量相对减少20%。