溶胶-凝胶法原位生成SiO_2改性硅基耐烧蚀材料

建立了在硅基耐烧蚀材料中用溶胶-凝胶法原位生成SiO2的方法.首先将硅橡胶、气相白炭黑、纤维等原料混炼硫化制备出硫化胶.然后将硫化胶依次浸入四氢呋喃、原硅酸乙酯和正丁基胺水溶液中进行预溶胀处理、物理扩散和化学反应,得到原位生成SiO2.SEM照片显示,在硅基耐烧蚀材料中原位生成的SiO2颗粒呈球形,粒径在40~60 nm,但分布不均匀,在硫化胶表层存在富集现象.实验结果表明,原位生成SiO2平均含量增加,硅基耐烧蚀材料的抗拉强度增加,线烧蚀率下降;含13.7%原位生成SiO2硅基耐烧蚀材料抗拉强度为5.82 MPa,线烧蚀率为0.071 mm/s.     

辐射在CH泡沫中传输的数值模拟

 利用一维多群辐射输运程序对辐射在CH泡沫中的传输过程进行了数值模拟,给出一些细致的物理图像和定量结果。在一定的入射辐射流条件下，密度变化对辐射传输特征、辐射加热介质的热力学平衡弛豫过程有重要影响。随着密度下降，辐射由亚声速传输转变为超声速传输，辐射在传输过程中的能谱形状也不同。     

IR laser ablative decomposition and depolymerisation/repolymerisation of poly(ethylene succinate)

Pulsed IR laser ablation of poly(ethylene succinate) results in the formation of volatile products (mainly carbon oxides, hydrogen, C₁-C₄ hydrocarbons) and affords deposition of polymeric films. Composition, structure and molecular weight distribution of the latter products were examined by EDX-SEM, FTIR, UV and NMR spectroscopy and gel permeation chromatography and revealed to be virtually identical to the initial poly(ethylene succinate). The deposited films and poly(ethylene succinate) decompose in the same way, as proved by TGA analysis. The formation of the volatile products is accounted for by random cleavages of the polymer backbone. The deposition of the polymeric products is judged to be due to molecular ester group interchange and/or a sequence of the C-C bond homolysis and recombination of the produced radicals.     

Temperatures, pressures and stresses during laser shock processing

Mathematical models are developed to calculate the temperatures, pressures and stresses during laser shock processing for time-modulated (ramp-up, ramp-down and rectangular) laser pulses. Three different shock processing configurations are also considered: non-ablative exposure, ablative exposure and confined ablation with coating. The results for iron show that the plasma pressure reaches an average value of 9 GPa in direct ablation configuration and plays a dominant role for all three types of laser pulses. In the case of confined geometry, the plasma pressure reaches an average value of 20 GPa. All calculated pressures and stresses exceed the yield strength of the workpiece, indicating plastic deformation. It is also shown that pulses with short rise times yield higher plasma pressures.     

Synthesis and surface functionalization of silica nanoparticles for nanomedicine

There are a wide variety of silica nanoformulations being investigated for biomedical applications. Silica nanoparticles can be produced using a wide variety of synthetic techniques with precise control over their physical and chemical characteristics. Inorganic nanoformulations are often criticized or neglected for their poor tolerance; however, extensive studies into silica nanoparticle biodistributions and toxicology have shown that silica nanoparticles may be well tolerated, and in some case are excreted or are biodegradable. Robust synthetic techniques have allowed silica nanoparticles to be developed for applications such as biomedical imaging contrast agents, ablative therapy sensitizers, and drug delivery vehicles. This review explores the synthetic techniques used to create and modify an assortment of silica nanoformulations, as well as several of the diagnostic and therapeutic applications.     

Effect of polyphenylsilsesquioxane on the ablative and flame-retardation properties of ethylene propylene diene monomer (EPDM) composite

Polyphenylsilsesquioxane (PPSQ) microspheres with ladder structure synthesized in the laboratory have been incorporated into ethylene propylene diene monomer (EPDM) composite in order to study the effect of PPSQ on the ablative and flame-retardation properties of EPDM composites. The results showed that PPSQ microspheres serve as an effective ablative additive and flame retardant for EPDM composites. Thus, PPSQ greatly improved the ablative properties of EPDM composites, with a 4.8 wt% loading leading to a remarkable reduction in the linear ablation rate of EPDM by about 50%. Moreover, this loading of PPSQ improved the flame retardancy and smoke suppression, and significantly reduced the PHRR of EPDM composite from 504 kW/m² to 278 kW/m². Moderate tensile strength could be obtained and the breaking elongation was improved for the EPDM/PPSQ composites. TGA results showed that PPSQ had little influence on the thermal decomposition of EPDM. SEM, CONE, and TG-FTIR tests showed that the char structure of EPDM composites was the primary factor through which PPSQ affected the ablative and flame-retardation properties of EPDM. The chars formed during the ablation of EPDM composites containing PPSQ had better structural stability and thermal stability, owing to the fact that they were denser, remained intact, and had an ordered arrangement of holes.     

IR laser ablative and conventional decomposition of poly(vinyl phenyl ketone): Different processes and different products

Pulsed IR laser ablation of poly(vinyl phenyl ketone) results in the formation of CO, C₁-C₄ hydrocarbons, benzene, styrene and phenylacetylene and affords deposition of polymeric films that were examined by EDX-SEM, FTIR, UV and NMR spectroscopies and gel-permeation chromatography. It is revealed that the structure of the films is affected by laser fluence and their M_w distribution is almost identical to that of poly(vinyl phenyl ketone). The formation of the products is accounted for by cleavages of both polymer backbone and pendant group. Conventional heating of poly(vinyl phenyl ketone) yields CO, formaldehyde, methanol and benzene as major volatile products and affords a solid fraction showing substantial fragmentation of the polymer. The different degradation products from both processes are ascribed to different modes of heating and to the wall effect.     

Comparison of contact and radiant ablative pyrolysis of biomass

Ablation characterizes the phenomena occurring when a solid, submitted to a high external heat flux density, gives rise to solids, liquids and/or gases that can be rapidly and continuously eliminated. Ablation can be exploited for carrying out the fast pyrolysis of materials such as biomass. This paper describes and compares, on a fundamental point of view, two methods of biomass ablative pyrolysis. In the first one, biomass is pressed against a hot surface (contact ablative pyrolysis). In the second one, biomass intercepts a concentrated radiation (radiant ablative pyrolysis). The comparison is made on the basis of the values of ablation thickness and velocity (derived from experiments and modelling), and of product fractions and compositions. The results can be very different in spite of the fact that biomass may be subjected to similar heat flux densities in both cases. The paper shows the advantages, drawbacks and complementarities of each technology.