Thermal decomposition and combustion characteristics of Al/AP/HTPB propellant

Journal of Thermal Analysis and Calorimetry - Aluminum(Al)/ammonium perchlorate(AP)/hydroxyl-terminated polybutadiene (HTPB) propellant is the most widely used propulsion system currently. Its...     

Development of zirconium and potassium perchlorate igniter for AP/HTPB composite propellant base bleed grain

Journal of Thermal Analysis and Calorimetry - For effective and reliable ignition of ammonium perchlorate and hydroxyl-terminated polybutadiene (AP/HTPB) solid composite propellant base bleed (BB)...     

Influence of tailored CuO and Al/CuO nanothermites on the thermocatalytic degradation of nitrocellulose and combustion performance of AP/HTPB composite propellant

Cellulose - Al/CuO nanothermites have displayed unique catalytic activities in accelerating the thermolysis of nitrocellulose (NC) and combustion characteristics of AP/HTPB propellant depending on...     

Effects of gamma irradiation and accelerated aging on GO/UHMWPE nanocomposites

This article investigates irradiated and accelerated aged graphene oxide (GO)/ultrahigh molecular weight polyethylene (UHMWPE) nanocomposites. The prepared GO/UHMWPE nanocomposites are gamma-irradiated at a high irradiation dose in a vacuum and then accelerated aging procedure is performed at 80°C in an air oven for 21 days. Irradiated and aged samples are characterized by Raman spectrum, Fourier transform infrared (FT-IR) spectrum, differential scanning calorimetry, contact angle, and gel content. Filling GO reduces the intensity of Raman spectrum of UHMWPE and irradiation or aging cannot affect vibrational modes of UHMWPE and GO/UHMWPE. The result of the FT-IR spectrum shows that UHMWPE and GO/UHMWPE basically have the same oxidation index values, whether with irradiation or accelerated aging. Irradiation or aging can slightly increase the melting temperature. GO, irradiation, or aging can significantly increase the crystallinity and improve wetting properties. In irradiated GO/UHMWPE, GO is able to maintain the efficiency of the cross-linking. However, after aging, the cross-linking density of GO/UHMWPE is reduced significantly. According to the above results, it is proposed that GO shows a very weak scavenging free radicals capacity in GO/UHMWPE composites and cannot display antioxidant capacity.     

Influence of accelerated aging on clay-reinforced polyamide 6

Organically modified clay-reinforced polyamide 6 was subjected to accelerated heat aging to estimate its long-term thermo-oxidative stability and useful lifetime compared to the virgin material. Changes in molecular weight, and thermal and mechanical properties were monitored and connected to the polymer modification encountered during aging. The incorporation of the clay filler was found to result in moderate polymer degradation during processing, which became more pronounced with aging time at elevated temperature, imparting discoloration. Post-crystallization was favoured by short periods of heat exposure, leading to an increase of crystalline content. Conversely, extended chain scission occurring after prolonged residence time negatively affected crystallites' size, lowering the degree of crystallinity. The aging-induced transformations of crystal structures correlated well with materials' mechanical performance, yielding initially hard and brittle specimens which gradually adopted a softening behavior. Relative to the unfilled polymer, the loss of ductility during aging was milder in the case of nanocomposite, indicating that the clay filler restricted degradation, prolonging durability.     

Chemiluminescence as a condition monitoring method for thermal aging and lifetime prediction of an HTPB elastomer

Chemiluminescence (CL) has been applied as a condition monitoring technique to assess aging related changes in a hydroxyl-terminated-polybutadiene based polyurethane elastomer. Initial thermal aging of this polymer was conducted between 110 and 50 °C. Two CL methods were applied to examine the degradative changes that had occurred in these aged samples: isothermal “wear-out” experiments under oxygen yielding initial CL intensity and “wear-out” time data, and temperature ramp experiments under inert conditions as a measure of previously accumulated hydroperoxides or other reactive species. The sensitivities of these CL features to prior aging exposure of the polymer were evaluated on the basis of qualifying this method as a quick screening technique for quantification of degradation levels. Both the techniques yielded data representing the aging trends in this material via correlation with mechanical property changes. Initial CL rates from the isothermal experiments are the most sensitive and suitable approach for documenting material changes during the early part of thermal aging.     

Changes in mechanical properties of impregnated Nomex papers 410 and 910 during accelerated aging

New materials are currently being developed for applications in transformer design. With the useful life of transformers now determined by solid insulation conditions, a better understanding of aging kinetics is important in order to improve electrical system management and planning from the technical and economic points of view. This paper summarizes an investigation of the effects of impregnating aramid and cellulose/aramid papers (Nomex 410 and 910) with insulation fluids (Nynas Polaris and Luminol Tri) at thermally accelerated conditions (170 °C) on their mechanical properties.It was found that Nomex 410 (100% aramid) showed only a small change in tensile strength (~5% decrease) after accelerated aging (around 7500 h). However, its elongation capacity was significantly reduced (~45–70% decrease for dry and wet Nomex 410, respectively) by the end of the aging process, probably due to hydrolysis. In addition, the interaction between water and aramid hydrogen bonds at high temperatures produced the rupture and then, the randomly rebuilt of these bonds in meta-aramid fibres, thereby reducing its plastic deformation capacity.In the case of Nomex 910 (aramid enhanced cellulose), its mechanical properties were maintained for a longer time than those of thermally upgraded Kraft paper (TUK), as measured by the retained percentage of tensile index. However, when the tensile index was used instead of the retained percentage, TUK showed a higher tensile index value than Nomex 910 during the initial stage, while the values for both papers became similar during the second stage. It is only at the end of the aging process that Nomex 910 presented an advantage over TUK paper due to the addition of the aramid fibres.It was also found that the inception fractures in Nomex 910, as a fibrous layered composite paper, start in the weakest part of the composite, probably in the central cellulose layer. The fracture line follows the weakest path, avoiding the aramid fibres.The results presented in this paper can be used as a benchmark for improving our understanding of aging and changes in the mechanical properties of these relatively new materials used in the solid insulation of power transformers. A better understanding of the aging characteristics (thermal degradation) of aramid-based papers should help better assess the condition of the new generation of power transformer fleets.     

Effects of accelerated aging on mechanical,thermal and morphological behavior of polyurethane/epoxy/fiberglass composites

Wind blades, an important application of polymeric composite materials, are subject to natural weathering. This study aims to evaluate mechanical, thermal and morphological behavior during accelerated aging in three thicknesses of epoxy and fiberglass polyurethane-coated composite plates used in wind turbines, in addition to testing with two acoustic emission techniques. An accelerated aging chamber simulated natural weathering mechanisms for 45, 90, 135 and 180 days. This degradation primarily reduced the mechanical properties of the thinner composites, with some damaged specimens exhibiting fiber-matrix debonding. Thermal properties deteriorated. There were no morphological changes on the polyurethane–epoxy interface; however, degradation occurred in the fiber-matrix interface on the surface exposed to radiation. The degree of chalking indicated coating deterioration on the external surface of the polyurethane. The acoustic wave propagation speed and attenuation coefficient measured prior to mechanical testing indicated the presence of damage areas.     

Correlation of antioxidant depletion and mechanical performance during thermal degradation of an HTPB elastomer

Thermal degradation studies of a stabilized HTPB based elastomer were conducted at temperatures from 50 °C to 110 °C. The concentration of extractable antioxidant (AO2246) in the polymer was quantified via AO extraction and a gas chromatography-based method using internal standards. The decrease in extractable AO levels as a function of time and temperature was evaluated and correlated with mechanical property changes. Most importantly, AO depletion features were found to be temperature dependent. At elevated temperatures (>80 °C) extractable AO levels decreased rapidly and faster than the concurrent loss in mechanical properties. While extractable AO concentrations decrease quickly, the material is able to maintain some useful mechanical properties, perhaps via non-extractable or grafted AO species formed during degradation providing additional protection. At lower aging temperatures extractable or free AO levels decreased more slowly than the mechanical properties. Therefore, for condition monitoring purposes a universal correlation between AO levels and aging state or material condition could not be established. Most importantly, however, loss of mechanical properties and oxidative degradation is observed at lower temperatures despite significant levels of free antioxidant in the material. The antioxidant appears to be limited in its effectiveness to completely prevent degradation reactions, or only fractions of the total AO available are actually involved in the inhibition process.     

In situ kinetics study of the accelerated aging of poly(ethylene oxide) using PhotoDSC

PhotoDSC has been applied to follow the global kinetics of chain scissions resulting from the UV light irradiation or from the thermal degradation of a high molecular weight PEO (4 x 10(6) g x mol(-1)). Infrared spectroscopy, XRD measurements and rheology experiments were performed to evidence the occurrence of chain scissions. Melting energy was used as a tool to quantify the extent of the degradation. It was found that the chain scissions reaction follows a first-order kinetic law for both photo and thermal degradation. The activation energies were found identical in both cases (41 kJ x mol(-1)), whereas the degradation rate was higher in the case of UV irradiation than in the case of thermoageing.     

HTPB/HDI本体聚合反应动力学研究

用基团分析方法对端羟基聚丁二烯（ＨＴＰＢ）／己二异氰酸酯（ＨＤＩ）体系的本体聚合反应的动力学进行了研究。探讨了催化剂二丁基二月桂酸锡（ＤＢＴＤＬ）对反应速度的影响。结果表明,催化体系的聚合反应速度完全满足双螺杆挤出机反应挤出停留时间的要求。『     

梯度温度分布下半焦/焦炭收缩规律的研究

利用炉侧安装了移动测量标尺的加热炉 (φ150mm×300mm),分别以三种加热速率(1.0℃/min、1.5℃/min和3.0℃/min)及两种堆密度(880kg/m3和1080kg/m3)模拟工业炼焦,研究了1500g的炼焦用煤在焦化过程中径向收缩与焦化时间、中心温度、焦化升温速率及梯度温度的关系。结果表明,中心温度为280℃～360℃时煤柱开始收缩,900℃左右收缩结束,径向收缩值5mm～8.5mm,收缩率7%～12%;加热速率和堆密度增大,煤柱径向温度梯度增大,径向收缩值减小;加热速率增大,开始收缩时的中心温度降低,第二收缩高峰逐渐减弱,各梯度温度降低,煤柱收缩系数减小;堆密度大,开始收缩时的中心温度和各梯度温度均较高,对收缩系数及收缩高峰无明显影响。在焦化的不同时期,煤柱不同位置的升温速率不同。     

Coordination behaviour of nicotinamide: an infrared spectroscopic study

A series of Hofmann-type complexes containing two nicotinamide(nia) molecules attached to transition metal (II) (M) tetracyanonickelate frame with the formula: M(nia)₂Ni(CN)₄ (where M=Mn, Co, Ni, Cu or Cd) have been synthesised for the first time. Metal (II) halide complexes of nicotinamide complexes of the type [M(nia)₂X₂ (M=Cd, Ni, Cu, Hg; X=Cl, Br) and Ni(nia)₄Br₂ nia=nicotinamide] have also synthesised. The FTIR spectra are reported in the 4000-400 cm⁻¹ region. Vibrational assignments are given for all the observed bands. The analysis of the vibrational spectra indicates that there are some structure-spectra correlations. A pronounced change was observed in the N-H stretching frequencies of the NH₂ group. It is proposed that the amide NH₂ group influence by the intramolecular hydrogen bond in the complexes. The coordination effect on the nicotinamide modes is analysed.     

Effect of accelerated thermal ageing on the thermal behaviour of the recently made parchments

To reveal the fire injuring of parchment, the changes in the thermal behaviour of some goat parchments, obtained from skins originating from different animals, as a result of thermal aging were determined by thermal analysis methods (DSC; simultaneous TG/DTG, DSC; micro hot table (MHT)). Thermal aging of parchments was revealed to bring about the decrease in shrinkage temperature, absolute value of enthalpy of denaturation in water and some changes in non-isothermal parameters characteristic for dehydration process in static air atmosphere. The results obtained by DSC analysis performed in N₂ and O₂ flows as well as those obtained by simultaneous TG/DTG, DSC analyses have shown that both softening (melting) process parameters and parameters of thermo-oxidative processes have not been changed by thermal ageing. The results obtained by thermal analysis methods were correlated with those obtained by microscopic investigation of parchment samples immersed in water and scanning electron microscopy (SEM). The application of these microscopic techniques has revealed the morphology changes in the investigated parchments as a result of thermal degradation.     

DSC study on the effect of isocyanates and catalysts on the HTPB cure reaction

The urethane forming cure reactions of hydroxyl terminated polybutadiene (HTPB) binder with three different isocyanate curatives, viz., toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) and 4,4-methylene bis(cyclohexyl isocyanate) (MCHI), were investigated by differential scanning calorimetry (DSC). The effect of two cure catalysts, viz., dibutyl tin dilaurate (DBTDL) and ferrric tris-acetylacetonate (FeAA) on the cure reactions was also studied. Cure kinetics was evaluated using the multiple heating rate Ozawa method. The reactivities of the three isocyanates and catalytic efficiencies were compared based on the DSC reaction temperatures, activation energies and rate constants. Viscosity build-up in these systems at isothermal temperature was also studied and compared with the results from DSC.     

O2/CO2煤粉燃烧时含铁矿物质转化行为的实验研究

通过乌兰木伦煤和哈拉沟煤在沉降炉中的燃烧实验,采用57Fe M(o)ssbauer谱仪,对煤中含铁矿物质及其在O2/N2和O2/CO2燃烧条件下生成的灰中含铁成分进行分析和比较,研究了O2/CO2煤粉燃烧时含铁矿物质的转化行为.结果表明,与O2/N2燃烧相比,O2/CO2燃烧对灰中生成的主要含铁矿物相种类没有影响,但显著地改变了灰中含铁矿物相的相对含量;O2/CO2燃烧更有利于内在黄铁矿和菱铁矿生成硅酸盐玻璃体而不是氧化成铁氧化物.灰中含铁矿物相的相对含量变化表明O2/CO2燃烧影响煤的结渣趋势,对于含内在含铁矿物较多的煤,O2/CO2燃烧会增加其结渣的趋势.     

Research on mechanical and dielectric properties of XLPE cable under accelerated electrical‐thermal aging

Research into the electrical‐thermal aging properties of cross‐linked polyethylene (XLPE) cable has great significance, because of its wide application. This study conducted accelerated electrical‐thermal aging tests on 10‐kV XLPE cable in order to assess the cable's mechanical and dielectric properties. After being aged by applying 34.8‐kV AC voltage at the four temperatures of 90, 103, 114, and 135°C, the cable samples were taken out in five stages according to the aging time and cut into slices. The slices were conducted experiments to test the breaking elongation, tensile strength, gel content, breakdown voltage, and frequency spectrums of the dielectric constant and dielectric loss. The results demonstrate that the mechanical strength and gel content of XLPE vary greatly under different aging temperatures, a finding that is associated with the crystallization characteristics of the material. The breakdown voltage shows a slight decreasing trend with aging time. The dielectric constant decreases with aging time in high‐frequency areas (10³–10⁶ Hz), while the dielectric loss factor increases with aging time at low frequencies (10^?2–0 Hz). These two parameters can be used to characterize the degree of aging in cable. Copyright © 2016 John Wiley & Sons, Ltd.