CL‐20 Evaporative Crystallization under Reduced Pressure

The effect of parameters of the CL‐20 crystallization process carried out by solvent removal by evaporation in vacuo on shape, polymorph type, crystal size, and on their shock sensitivity was studied. The CL‐20 crystallization process by this technique was shown to allow a precise control of the crystallization process parameters and of the process run. The o‐xylene/ ethyl acetate system proved to be highly effective. Selecting suitable values of the parameters such as: pressure, process time, temperature, stirring rate, CL‐20 crystals were obtained in the ε form (even with no need for inoculation of the crystallization system with polymorph ε seeds) and of the shape close to a spherical one. The crystal growth modifiers added allowed to additionally control the shape and size of the CL‐20 crystals formed and to produce crystals of reduced impact and friction sensitivity.     

Study on Ultrasound‐ and Spray‐Assisted Precipitation of CL‐20

Ultrafine hexanitrohexaazaisowurtzitane (CL‐20) samples were prepared by a ultrasound‐ and spray‐assisted precipitation method. Raw CL‐20 and ultrafine CL‐20 samples were characterized by SEM, FT‐IR spectroscopy, XRD, and particle size analysis. The impact sensitivity and thermal stability of two CL‐20 samples were also tested and compared. The results indicate that by this recrystallization process, the mean particle size of CL‐20 is 470 nm, and the particle size distribution was in the range from 400–700 nm. The particle morphology is nearly spheric with a smooth surface. Compared with raw CL‐20, the impact sensitivity of the ultrafine sample is significantely reduced and the drop height (H₅₀) is increased from 12.8 to 37.9 cm. The critical explosion temperature of ultrafine CL‐20 decreased from 235.6 to 229.0 °C, which suggests that the thermal stability of ultrafine CL‐20 is lower than that of raw CL‐20.     

Preparation and Properties Study of Core‐Shell CL‐20/TATB Composites

The insensitive high explosive 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) was selected for coating and desensitization of hexanitrohexaazaisowurtzitane (CL‐20), another high explosive, after surface modification. About 2 wt‐% polymer binder was adopted in the preparation process to further maintain the coating strength and fill the voids among energetic particles. The structure, sensitivity, polymorph properties, and thermal behavior of CL‐20/TATB by coating and physical mixing were studied. Scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS) results indicate that submicrometer‐sized TATB was compactly coated onto the CL‐20 surface with coverage close to 100 %. The core‐shell structure of CL‐20/TATB was confirmed by observation of hollow TATB shell from the CL‐20 core dissolved sample. X‐ray diffraction (XRD) analysis revealed that the polymorph of CL‐20 maintained ε form during the whole preparing process. Thermal properties were studied by thermogravimetry (TG) and differential scanning calorimeter (DSC), showing effects of TATB coating on the polymorph thermal stability and exothermic decomposition of CL‐20. Both the impact and friction sensitivities were markedly reduced due to the cushioning and lubricating effects of TATB shell. The preparation of explosive composites with core‐shell structure provides an efficient route for the desensitization of high explosives, such as CL‐20 in this study.     

Voids and Density Distributions in 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐Hexaazaisowurtzitane (CL‐20) Prepared Under Various Conditions

The density distributions of six samples of CL‐20 were measured using the density gradient technique. This technique was used to determine which preparation procedure produced the highest average CL‐20 density. Assuming crystals with fewer flaws result in reduced sensitivity to shock initiation, higher average crystal density (closest to the theoretical maximum density) would imply the least number of voids or inclusions. Based on hot‐spot theory, better crystals, i.e., smaller number of flaws will reduce the shock sensitivity and perhaps other impact initiation mechanisms as well. Six samples from different synthesis and crystallization procedures gave average densities from 2.042 to 2.0230 g/cm³ as measured by density gradient. Assuming the voids have no density, the crystals were between 99.90 to 98.98% of the theoretical maximum density (TMD for ε‐CL‐20 is 2.044 g/cm³). An attempt was made to account for the density difference by identifying voids in the crystals using polarized light microscopy. This method also gave some insight into the different morphologies produced by different crystallization techniques. In 3 cases voids on the order of several micrometers could be resolved in large CL‐20 crystals.     

反应-溶析耦合结晶法提纯（（5-噻唑基）甲基）-（4-硝基苯基）碳酸酯

探索了反应-溶析耦合结晶法提纯抗艾滋病药物利托那韦中间体((5-噻唑基)甲基)-(4-硝基苯基)碳酸酯的新工艺,选用甲醇作为主溶剂,碳酸钾水溶液作为反应物和析出剂,测定了物系的溶解度关系,研究了结晶温度、析出剂量、加入方式等操作条件对产品收率和纯度的影响.试验证明,在结晶终点温度为20 ℃,V(5wt%碳酸钾水溶液)/V(甲醇)=3:1的条件下,采用反应-溶析耦合结晶法可从((5-噻唑基)甲基)-(4-硝基苯基)碳酸酯盐酸盐含量为93.42%的原料中,结晶得到纯度为99.81%的((5-噻唑基)甲基)-(4-硝基苯基)碳酸酯产品,收率可达93.72%.     

Attractive Nitramines and Related PBXs

At present, cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole (bicyclo‐HMX, BCHMX) and ε‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (ε‐HNIW, CL‐20) are a topic of interest from the attractive and the potentially attainable nitramines. They were chosen to be studied in comparison with 1,3,5‐trinitro‐1,3,5‐triazinane (RDX) and β‐1,3,5,7‐tetranitro‐1,3,5‐tetrazocane (β‐HMX). Marginal attention is devoted also to 4,8,10,12‐tetranitro‐2,6‐dioxa‐tetraazawurtzitane (Aurora 5). BCHMX, ε‐HNIW, RDX, and HMX were studied as plastic bonded explosives (PBXs) with elastic properties based on Composition C4 and Semtex 10 matrices. Also they were studied as a highly pressed PBXs based on the Viton A binder. The detonation parameters and sensitivity aspects of these nitramines and their corresponding PBXs were determined. Relative explosive strengths (RS) of these compositions are mentioned with mutual relationships between the measured RS values and some detonation parameters. These relationships indicate a possibility of changes in detonation chemistry of these mixtures filled mainly by HNIW. A sensitivity of RS‐CL20 (HNIW with reduced sensitivity) is reported and the new findings in the friction sensitivity are discussed.     

A Simple Method for the Purification of Crude Hexanitrohexaazaisowurtzitane (HNIW or CL20)

A simple method for purifying crude hexanitrohexaazaisowurtzitane (HNIW or CL20) to analytical purity is described. This involves filtering a solution of HNIW in heptane / ethyl acetate through a column of Darco activated carbon type G‐60 (∼20 g carbon/g HNIW). The method works extremely well for HNIW derived from 4,10‐diformyl‐2,6,8,12‐tetraacetylhexaazaisowurtzitane (final purity>99.95%, ∼90% recovery), and reasonably well for HNIW derived from 4,10‐dibenzyl‐2,6,8,12‐tetraacetylhexaazaisowurtzitane.     

Promising CL‐20‐Based Energetic Material by Cocrystallization

A novel cocrystal (NEX‐1) of CL‐20 and MDNT is presented herein. The CL‐20: MDNT cocrystal, obtained in high yield by resonant acoustic mixing, shows new properties versus the discrete components. This is the first example of cocrystallization of CL‐20 where the new material is less sensitive to friction than CL‐20 itself, while demonstrating similar impact and ESD sensitivity. The CL‐20: MDNT cocrystal shows promise in the production of new energetic materials of interest by the cocrystallization of well‐characterized components.     

Pressurized Nozzle‐Based Solvent/Anti‐Solvent Process for Making Ultrafine ϵ‐CL‐20 Explosive

CL‐20 explosive is one of the most recent and powerful explosives. It has very high potential in futuristic applications but at present it has limitations of sensitivity to mechanical stimuli. Among the four different polymorphs (α, β, γ, and ϵ), ϵ‐polymorph has better stability and shock/detonics properties. However, preparation of pure ϵ‐polymorph is a challenging task particularly in terms of repeatability and polymorphism. In our research work, pressurized nozzle based solvent/anti‐solvent process (PNSAP) was developed for the preparation of ultrafine ϵ‐CL‐20 explosives with high repeatability, purity, and yield. To get ultrafine particle size, shape, distribution and yield, various process parameters/ variables such as solvent type, anti‐solvent type, dosing rate, stirring rate, ultra‐sonication, and temperature were identified and prioritized using the weighted average method of Analytical Network Process (ANP) techniques. It was observed that ultrafine ϵ‐CL‐20 particle size in the range of 2 to 3 μm can be obtained using this process. The ϵ‐polymorph was confirmed by FT‐IR characterization. The main feature of this PNSAP process is that it is a laboratory scale table‐top pilot plant which is simple, cost‐effective, safe and repeatable for continuous batch production of ultrafine ϵ‐CL‐20 at the rate of 100 grams per hour.     

Preparation and Performances of Castable HTPB/CL‐20 Booster Explosives

HTPB/CL‐20 castable booster explosives were prepared successfully by a cast‐cured process. Scanning electron microscope (SEM) and the charge density test were employed to characterize the molding effect of HTPB/CL‐20 explosives. The propagation reliability, detonation velocity, mechanical sensitivity, thermal decomposition characteristics and thermal stability of the HTPB/CL‐20 explosives were also measured and analyzed. The results show that, when CL‐20 content is less than 91 wt.‐%, the charges with better molding effect were obtained easily. The critical diameter of HTPB/CL‐20 explosives is less than 1 mm, which exhibits good propagation reliability. When the density of HTPB/CL‐20 charge with 91 wt.‐% CL‐20 is 1.73 g cm⁻³, its detonation velocity can reach 8273 m s⁻¹. Moreover, this kind of explosives has low mechanical sensitivity and good thermal stability.     

Analytical Characterization of Impurities or Byproducts in New Energetic Materials

In the last years several new explosives have recently attracted attention as possible alternatives, e.g. for the nitramines RDX and HMX. Hexanitrohexaazaisowurtzitane (HNIW) also known as CL 20 is one of them. Objective of the study was to analyse three different CL 20 samples from different suppliers (ϵ-CL 20 from Thiokol, USA and ϵ- and β-CL 20 from SNPE, France) with chromatographic and spectroscopic techniques to characterize the chemical and polymorph purity of the materials in order to compare the different samples to each other. From IR-spectroscopic measurements it was determined that all three materials have polymorph purities >95%. To get informations about the chemical purity and possible byproducts or residual solvents the samples were analysed by HPLC, NMR and GC-MSD. For the last a new technique, the so called Solid Phase Micro Extraction, SPME was applied for sample preparation. The chemical purity estimated by HPLC analysis was for all CL 20 samples >96% while the ϵ-charge of SNPE had the highest purity (98.3%). From NMR-measurements an acetyl- or formyl-substituted byproduct was identified. From NMR as well as from GC-MSD analyses residual amounts of organic solvents have been detected (ethanol or tetrahydrofuran). Furthermore different spare amounts of other organic components were identified after SPME-treatment and characterization with GC-MSD.     

Comparative Investigation of Thermal Decomposition of Various Modifications of Hexanitrohexaazaisowurtzitane (CL‐20)

The thermal decomposition kinetics of different polymorphs of CL‐20 (α, γ and ε) has been investigated by thermogravimetry, IR spectroscopy and optical and electronic microscopy. The reactions proceed with self‐acceleration and can be described by a kinetic law of first order with autocatalysis. Already at the earliest stages of decomposition (≤1%) phase transitions take place from αγ and from εγ. For this reason the observed decomposition is related to the decomposition of γ‐CL‐20. On the other hand, the kinetics of decomposition depends on the initial polymorphic state, so that the thermal decomposition increases in the series: α<γ<ε. Experiments with different samples of α‐CL‐20 demonstrate that different rates of decomposition are observed for the same polymorph depending on the mean size and the size distribution of the crystals and their morphological features. In some cases the thermal stability of α‐CL‐20 can be increased by previous annealing. It is concluded that the thermal decomposition of CL‐20 is purely a solid‐state process. Microscopical and spectroscopical analysis of the condensed CL‐20 decomposition product (formed after prolonged heating at high temperature) show that it has a network structure and consists mainly of carbon and nitrogen.     

Fourier Transform Raman Spectroscopy of the Four Crystallographic Phases of α, β, γ and ε 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐hexaazatetracyclo[5.5.0.05,9.03,11]dodecane (HNIW,CL‐20)

Fourier transform Raman Spectroscopy (Nd : YAG laser at 1064 nm) was used to characterize the four stable phases of 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐hexaazatetracyclo[5.5.0.0^5,9.0^3,11]dodecane (HNIW, CL‐20). Raman spectra are reported over the region from 0–4000 cm⁻¹_, relative to the laser line. A tentative assignment of the most predominant Raman peaks was made with the aid of QM calculations at the B3LYP/6‐31G(d) level. A method for detecting polymorphic impurities in ε‐CL‐20 was also developed. The detection level for polymorphic impurities was determined to be below 2%. A method for producing γ‐CL‐20 is also presented.     

An improved ultrasound‐assisted extraction process of gossypol acetic acid from cottonseed soapstock

To investigate the extracted process of gossypol acetic acid (G‐AA) from cottonseed soapstock and explore the improvement of its yield and purity, a novel ultrasound‐assisted extraction and crystallization method was introduced to this process. Under the optimized conditions, preliminary G‐AA with the yield of 1300 mg and the purity of 95.9% could be obtained from 100 g of fresh soapstock by ultrasound‐assisted extraction. In addition, UV, IR, and NMR spectrum further confirmed the detailed chemical structure of G‐AA. Assay of inhibiting human prostate tumor cell line PC‐3 and human breast cancer cell line MDA‐MB‐231 revealed its biological activity, the values of IC₅₀ are 9.096 μmol/L and 14.37 μmol/L respectively. In comparison with the conventional solvent extraction, this novel process increases the content of G‐AA over 90%, reduces the time of crystallization by 75%, and retains the anticancer activity of gossypol. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Potential Use of CL‐20 in TNT/ETPE‐Based Melt Cast Formulations

An attempt was made to introduce CL‐20 in a TNT/energetic thermoplastic elastomer (ETPE)‐based melt cast formulation, to obtain an insensitive composition with reduced adverse environmental properties. A loading limit of 42% w/w of CL‐20 in melted TNT was observed, while it should have been around 70%. This paper describes the investigation that was undertaken to understand the observed phenomena. It was demonstrated that CL‐20 undergoes structural alterations in melted TNT. The relative solubility of CL‐20, RDX and HMX in melted TNT was determined and the α‐, β‐, γ‐ and ε‐CL‐20 were prepared and characterized using Raman spectroscopy and DTA. CL‐20 was mixed in melted TNT, as much as 4.2 g of CL‐20 dissolved in 100 g of TNT. This allowed a transformation from ε to β‐CL‐20 and a modification of CL‐20 particle size and distribution. The later modification induced a raise in CL‐20 specific surface and was responsible for the loading limit, while the transformation to β‐CL‐20 caused an increase in sensitivity and a decrease in density. This indicates that the use of CL‐20 in TNT melt cast is not promising. Our study also showed that CL‐20 is sensitive to morphological transformations, which should be taken into consideration in future processing using this compound.     

An Efficient and Facile Synthesis of CL‐20 from TADNO Using HNO3/N2O5 and Optimization of Reaction Parameters by Taguchi Method

Hexanitrohexaazaisowurtzitane (CL‐20) is an outstanding member of a promising new class of energetic compounds, which is applicable in both propellants and explosives. Herein, CL‐20 was synthesized in an efficient method from tetraacetyldinitrosohexaazaisowurtzitane (TADNO) using N₂O₅/HNO₃. The optimization reaction parameters were performed according to the Taguchi OA method. The yield of reaction at the optimized conditions was 97 % with 98.75 % purity.     

磷化渣废液除锌制备高纯度磷酸三钠

为了实现磷化渣碱溶后所得废液的综合利用,采用中和沉淀法和硫化钠沉淀法去除磷化渣废液中的杂质锌,对中和沉淀法和硫化钠沉淀法的工艺条件进行优化,并由此设计磷化渣废液除锌制备高纯度磷酸三钠的生产工艺。对于中和沉淀法,在反应体系pH=8.85,反应时间为10 min时,Zn2+去除率可达97.96%;对于硫化钠沉淀法,在反应体系pH=6.85,硫化钠投加量与Zn2+的摩尔比为1:1,反应时间为10 min时,Zn2+去除率可达99.80%。相比于中和沉淀法除锌制备磷酸三钠工艺,硫化钠沉淀法除锌制备磷酸三钠工艺具有更高的磷酸三钠纯度,为98.85%,固相产品中Zn2+含量更低,仅为0.0004%,符合化工行业分析纯标准。该工艺大幅度地回收了磷化渣废液中的PO43-离子和Na+离子,为实现磷化渣综合利用的工业化提供新思路。     

高效液相色谱测定CL-20纯度

用外标法单点校正峰面积定量，准确测定不同合成路线及精制阶段的ＣＬ－２０纯度。方法的准确度和精密度能满足产品分析的要求，用外标法测ＣＬ－２０精度更加简便、适用。     

Effects of calcium carbonate and its purity on crystallization and melting behavior,mechanical properties,and processability of syndiotactic polypropylene

Calcium carbonate‐filled syndiotactic poly(propylene) (CaCO₃‐filled s‐PP) was prepared in a self‐wiping, co‐rotating twin‐screw extruder. The effects of CaCO₃ of varying particle size (1.9, 2.8 and 10.5 μm), content (0–40 wt %), and type of surface modification (uncoated, stearic acid‐coated, and paraffin‐coated) on the crystallization and melting behavior, mechanical properties, and processability of CaCO₃‐filled s‐PP were investigated. Non‐isothermal crystallization studies indicate that CaCO₃ acts as a good nucleating agent for s‐PP. The nucleating efficiency of CaCO₃ for s‐PP was found to depend strongly on its purity, type of surface treatment, and average particle size. Tensile strength was found to decrease, while Young's modulus increased, with increasing CaCO₃ content. Both types of surface treatment on CaCO₃ particles reduced tensile strength and Young's modulus, but improved impact resistance. Scanning electron microscopy (SEM) observations of the fracture surfaces for selected CaCO₃‐filled s‐PP samples revealed an improvement in CaCO₃ dispersion as a result of surface treatment. Finally, steady‐state shear viscosity of CaCO₃‐filled s‐PP was found to increase with increasing CaCO₃ content and decreasing particle size. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 201–212, 2004     

A Novel Method to Prepare Nano‐sized CL‐20/NQ Co‐crystal: Vacuum Freeze Drying

Nano‐sized energetic co‐crystal consisting of the most powerful used military explosive 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (CL‐20) and a typical insensitive explosive used in propellants nitroguanidine (NQ) was prepared by vacuum freeze drying method. Material studio 6.1 was used to simulate the hydrogen bonds between CL‐20 and NQ molecules. Scanning electron microscopy (SEM) was used to reveal the morphology and size of the product. Fourier Transform infrared spectroscopy (FT‐IR) and X‐ray diffraction spectrum (XRD) proved the formation of the co‐crystal at the molecular level. Differential scanning calorimetry (DSC) was employed to characterize the thermal behavior of the co‐crystal. The result of mechanical sensitivity test indicated the sensitivity was effectively reduced compared to neat CL‐20.