离子液体[HMIM]Br和[HMIM]BF_4对SiO_2气凝胶制备的影响

利用离子液体[HMIM]Br、[HMIM]BF4作催化剂,TEOS作前驱体在常压下制备出了高孔隙率块状SiO2气凝胶,并研究了离子液体对气凝胶制备的影响。离子液体[HMIM]BF4比[HMIM]Br拥有更好的催化性能,可以大大缩短凝胶时间,且两种离子液体制备凝胶过程中,凝胶时间都随n(IL)/n(Si)的增加而逐渐延长。在n(IL)/n(Si)=1.5时,制得密度最小、孔隙率最大的气凝胶;n(IL)/n(Si)>1.5时,随离子液体的摩尔比率的增加,气凝胶的密度增大,孔隙率、成块性和透明性逐渐降低。     

Property of three-dimensional silica composites

Silica fibers-reinforced, fused silica composites were fabricated with repeated vacuum-assisted liquid-phase infiltration. The mechanical properties, thermal properties, and ablative properties of the samples were evaluated. The effect of the silica fiber content and treatment temperature on the flexural strength of the three-dimensional SiO2 （3-D SiO2） composites also was investigated. The SiO2 composites show good mechanical properties and excellent ablative performance. The flexural strength increases with an increase in silica fiber content, and decreases with an increase in treatment temperature. When the volume fraction of the silica fiber is 50vo1% and the treatment temperature is 700℃ the flexural strength of the composites reaches a maximum value of 78 MPa. By adding cyclohexanone surfactant, the infiltration property can be largely improved, resulting in the density of SiO2 composites increasing up to 1.65 g/cm^3. The fracture surfaces of the flexural specimens observed using SEM, show that the pseudoplasticity and the toughening mechanisms of the composites are caused by absorption of a lot of energy by interface debonding and fiber pulling out.     

Mechanical behavior and microstructure characterization of 3D stitched quartz fibers-reinforced silica composites

The mechanical properties of silica material in the monolithic form are ;far from acceptable levels. In this paper, 3D stitched quartz preform was used for the fiber reinforcement, and quartz fibers- reinforced silica composites were prepared by the silica sol-infiltration-sintering method. The density of the composite was up to 1.71 g/cm3 after 10 infiltration-sintering cycles. The flexural strength and the in-plane shear strength were 61.7 MPa and 20.3 MPa, respectively. The flexural stress-deflection curve exhibited mostly nonlinear behavior, which was different from that of monolithic ceramics. Because of the existence of the fiber in Z axis direction, shearing property between the different layers of 3D stitched composites were greatly enhanced. Toughness effect of the 3D stitched quartz preform was conspicuous. The as-fabricated composites showed non-catastronhic failure behavior resulting from weak fiber/matrix interface.     

聚氨酯/三聚氰胺甲醛树脂互穿网络硬质泡沫性能的研究

采用分步IPN法合成了一系列聚氨酯/三聚氰胺甲醛树脂互穿网络硬质泡沫,并通过表观密度、压缩强度、弯曲强度、阻燃性能和泡孔结构对其进行了表征。结果表明：随着聚氨酯的加入,泡沫塑料的表观密度降低,并有效提高泡沫塑料的力学性能。但在加入20%的聚氨酯之后,力学性能增加不明显,且泡沫塑料从高难燃材料、难燃材料,向易燃材料转变。     

Structural control of silica aerogel fibers for methylene blue removal

The development of efficient adsorbents is significant for the miniaturization and cost reduction of water purifying facility. In our previous study, a new kind of silica aerogel fibers(SAFs) with hierarchical structure and hollow structure were developed, which shows outstanding mass transport property and adsorption performance. Herein, we further control and study the hierarchical structure and hollow structure of silica aerogel fibers by changing the sulfuric acid concentration of ageing bath and spinning speed. For removing methylene blue, A0 W120 SAFs sample, with DI water as ageing bath and a winding speed of 120 mm/s,presents the best mass transport property and adsorption performance, as they possess larger pore sizes in the outer layer, thinner fiber wall and higher degree of hollowness. The removal rates of methylene blue by A0 W120 SAFs sample is up to 91.6% and 98.2% in 2 and 5 min, respectively, which are at least 30% higher than other comparable commercial adsorbents, while the adsorption capacity of methylene blue reaches up to 139.1 mg/g.     

挤出制备的小麦淀粉泡沫密度对力学性能的影响

本文对有关结构设计及优化小麦粉泡沫的力学性能与密度的对应关系的进行了研究.揭示了用不同加工条件可以制备不同密度的小麦淀粉泡沫,并对不同密度的泡沫材料进行了静压力学测试和动态缓冲曲线测试.相对压缩强度与相对密度呈幂函数关系,可用式子σc/σ5≈0.308(ρc/ρ5)1.5表示.动态缓冲性能也随泡沫密度的变化而变化.     

Preparation of precursor for stainless steel foam

The effects of polyurethane sponge pretreatment and slurry compositions on the slurry loading in precursor were discussed： and the,performances of stainless steel foams prepared from precursors with different slurry loadings and different particle sizes of the stainless steel powder were also investigated. The experimental results show that the pretreatment of sponge with alkaline solution is effective to reduce the jam of cells in precursor and ensure the slurry to uniformly distribute in sponge, and it is also an effective method for increasing the slurry loading in precursor; the mass fraction of additive A and solid content in slurry greatly affect the slurry loading in precursor, when they are kept in 9%-13% and 52%-75%, respectively, the stainless steel foam may hold excellent 3D open-cell network structure and uniform muscles; the particle size of the stainless steel powder and the slurry loading in precursor have great effects on the bending strength, apparent density and open porosity of stainless steel foam; when the stainless steel powder with particle size of 44 μm and slurry loading of 0.5 g/cm^3 in precursor are used, a stainless steel foam can be obtained, which has open porosity of 81.2%, bending strength of about 51.76 MPa and apparent density of about 1.0 g/cm^3.     

Mechanism of low thermal conductivity of xonotlite-silica aerogel nanoporous super insulation material

In an effort to incorporate the low thermal conductivity of the silica aerogel and the superior structure strength of the xonotlite,a composite material of these two was produced. It was synthesized under vacuum condition and dried by supercritical drying technique. The thermal conductivity of the new material,which is at 298K with the gas pressure ranging from 1.01×10^5 to 1×10^-2 Pa,was measured using the transient hot-strip method. The mechanism of the low thermal conductivity was studied. The results indicate that the low thermal conductivity mainly results from the significant decrease of gaseous thermal conductivity of the new material due to the restriction of the motion of gas molecules in its fine structures. The formation of the fine structures is because the new material takes the pore structure of the silica aerogel which consists of mainly nanometer-sized pores.     

Properties of water blown rigid polyurethane foams with different functionality

Water blown rigid polyurethane foams with different functionality were prepared. The physical properties of rigid foams were measured with rotational viscometer （NDJ-1 ）, universal testing machine （Instron3365）, scanning electron microscope （SEM） and differential scanning calorimeter （DSC）. The results show that the viscosity of polyether polyol increases exponentially from 62 mPa s to 6 000 mPa s with the increase of functionality from 2 to 5.6, respectively. The overall density of foam increases slightly from 31.7 kg/m^3 to 37.4 kg/m^3 with increasing functionality while core density exhibited little difference. Compressive strength of foam shows the similar behavior with density except for 2-functional sample. At the same time, dimensional stability becomes better with increasing functionality except for 5.6-functional foam that has worse stability than 4.8-functional foam. From the SEM results, the functionality is not an important factor in determining distribution of cell size of foam. According to the results of thermal analysis, the glass transition temperature （T） shifts to a higher temperature from 128.9 ℃ to 166.3 ℃ for the 2 to 5.6 functional foam, respectively.     

Preparation and adsorption property of phenyltriethoxysilane modified SiO2 aerogel

The hydrophobic silica aerogel (SiO₂ aerogel) was prepared by in situ polymerization sol-gel method and ethanol supercritical drying, with tetraethoxysilane (TEOS) as silica source, phenyltriethoxysilane (PTES) as modifier, ethanol as solvent and ammonia as catalyst. The effects of n(PTES)/n(TOES) were investigated on gel time, structure, and hydrophobicity. The SiO₂ aerogel was measured by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The effects of n(PTES)/n(TOES) were also studied on adsorption property of pentane, hexane, heptane, octane, benzene, toluene, o-xylene, nitromethane, nitroethane, and nitrobenzene. The adsorption intensity of SiO₂ aerogel was compared with that of activated carbon. The results show, with the increasing of n(PTES)/n(TOES), the surface area, pore volume, and pore size of SiO₂ aerogel decreased, gel time and hydrophobicity increased, and the contact angle could be 154° with n(PTES)/n(TOES)=0.7. The adsorption intensity of SiO2 aerogel with n(PTES)/n(TOES)=0.5 was bigger than that of activated carbon with an average 5.84 times of 10 organic liquid. The adsorption intensity of aerogel with n(PTES)/n(TOES) =0.1 was the best one in all samples with the average 8.33 times compared with that of activated carbon.     

模压条件对EVA边角料/天然橡胶复合发泡材料性能的影响

以乙烯-醋酸乙烯酯共聚物（EVA）边角料、天然橡胶（NR）、相应助剂和填料为主要材料进行共混混炼,再用模压法制备EVA边角料/NR复合发泡材料,研究了模压温度、模压时间和模压压力对复合发泡材料性能的影响. 实验结果表明:模压温度为145 ℃,模压时间为30 min,模压压力为12.5 MPa时,复合发泡材料的综合性能较好. 进一步测定了复合发泡材料的表观密度和发泡倍率曲线,以及硬度和撕裂强度曲线. 实验数据表明,模压温度可改变复合发泡材料的交联程度,模压时间综合影响复合发泡材料的交联程度和泡孔大小,模压压力则与复合发泡材料泡孔生长有关,影响泡孔分布情况.     

季戊四醇磷酸酯/尿素改性酚醛泡沫的性能研究

以苯酚、甲醛为原料,尿素和季戊四醇磷酸酯（PEPA）为改性剂,制备了一系列的季戊四醇磷酸酯/尿素改性酚醛泡沫（PEPA/UMPF）. 利用热重分析、极限氧指数、扫描电镜和万能试验机对改性酚醛泡沫材料的结构和性能进行了测试和表征. 结果表明,PEPA/UMPF的热稳定性和阻燃性显著提高,仅仅加入质量分数1%的PEPA和尿素,氧指数值就增加了14%. 当加入质量分数5%的PEPA和尿素时,酚醛泡沫的压缩强度和冲击强度分别提高了0.09 MPa和0.53 kJ·m-2. 同时,改性泡沫的粉化率和吸水率下降,泡孔结构致密厚实并且分布均匀.     

Mechanical properties of silica aerogels prepared from a mixture of TEOS and organo-alkoxysilanes of type R1SiX3

Silica aerogels were prepared from a mixture of tetraethylorthosilicate and organo- alkoxysilanes. The effects of organo-alkoxysilanes on the mechanical properties of the silica aerogels were studied. The flexibility of silica aerogels was significantly improved by incorporation of organo-alkoxysilanes. When MTES and TEOS were combined as precursors of silica areogels, with the increased amount of MTES, the apparent elastic modulus and apparent compressive strength monotonously rose. At the same organo- alkoxysilanes to TEOS ratio, the size of alkyl groups of the organo-alkoxysilanes had little effect on the mechanical properties. In series of MTES and TEOS, the lowest elastic modulus of silica skeleton and the highest compressive strength of silica skeleton were observed at MTES to TEOS ratio of around 50：50. At a certain organo-alkoxysilanes to TEOS ratio, the elastic modulus of silica skeleton increased and the compressive strength of silica skeleton decreased with the size increase of the alkvl grouns.     

Fabrication and Characterization of Nano- CaCO3/Polypropylene Foam Sheets

By applying the reinforcing and toughening effect of calcium carbonate （CaCO3） nanoparticles on polypropylene, foam sheets of good performance were successfully fabricated by extrusion. The equipment and conditions of the extrusion were explored. The mechanical properties of the produced foam sheets were tested. The effect of CaCO3 nano-particles on the mechanical properties and the cellular structure of the sheets was comprehensively studied. The experimental results show that the optimum content of CaCO3 nano-particles in the composite material was -4wt%. At this content, the nano-particles were well dispersed in the substrate, and the composite material had maximum tensile strength and impact strength. Surface treatment of the nano-particles only affected the impact strength of the composite material. CaCO3 micro-particles, on the other hand, showed little effect on the properties of the composite material when the micro-particles content was less than 5 wt%. At a content higher than 5wt%, the properties of the composite material significantly worsened.     

Preparation and characterization of natural rubber/silica nanocomposites using rule of similarity in latex

Rule of similarity and latex compounding techniques were combined for the first time to prepare natural rubber/nanosilica (NR/SiO₂) nanocomposite with core-shell nanosilica-poly (methyl methacrylate) (SiO₂-PMMA) particles and PMMA-modified natural rubber matrix (NR-PMMA). The microstructure of SiO₂ and nanocomposites with different SiO₂ contents was characterized by fourier transform infrared spectroscopy (FTIR); the morphology of nanocomposites was investigated with scanning electron microscopy (SEM); the tensile strength was characterized by tensile testing machine and the thermal stability of composites was studied by thermal gravimetric analysis. Results showed that PMMA chains have successfully grafted onto the surface of SiO₂, and the core-shell SiO₂-PMMA nanoparticles and NR-PMMA latex have been perfectly incorporated. SiO₂-PMMA nanoparticles are evenly distributed over the NR matrix with an average size in the range of 60–100 nm at the low content (SiO₂≤ 3 wt%), while aggregations are apparently observed when 5 wt% SiO₂ is loaded. In addition, NR/SiO₂ composities possess a considerable improvement in ageing resistance compared with the pure NR. The tensile strength of composite increases from 6.99 to 12.72 MPa, reaching the highest value at a 0.5 wt% SiO₂ loading, and then the figure decreases gradually because of the aggregation of SiO₂ nanoparticles. It is anticipated that the reported process is to provide a simple and economic way for preparing NR composites.     

Acoustic properties of sintered FeCrAlY foams with open cells (II): Sound attenuation

Open-celled metal foams fabricated through metal sintering offers novel mechanical, thermal and acoustic properties. Previously, polymer foams were used as a means of absorbing acoustic energy. However, the structural applications of these foams are inherently limited. The metal sintering approach provides a cost-effective means for the mass-production of open-cell foams from a range of materials, including high-temperature steel alloys. The low Reynolds number fluid properties of sintered steel alloy (FeCrAlY) foams were investigated in a previous study. The static flow resistance of the foams was modeled based on a cylinder and a sphere arranged in a periodic lattice at general incidence to the flow, with the resulting predictions correlating well to measurements. The application of the flow resistance in an acoustic model is the primary focus of the present study. The predictions for the static flow resistance of the sintered foams are first used in a theoretical model to determine the characteristic impedances, as well as the propagation constants of the foams. Subsequently, the predicted acoustic performance of the foams is compared to experimental results. Finally, the design space for a simple acoustic absorber incorporating sintered foams is examined, with the effects of absorber size, foam selection, and foam spacing explored. Supported by the National Basic Research Program of China (Grant Nos. 2006CB601202, 2006CB601204), the National 111 Project of China (Grant No. B06024), US Office of Naval Research (Grant No. N000140210117), the National Natural Science Foundation of China (Grant Nos. 10572111, 10632060), and the National H-Tech Research and Development Program of China (Grant No. 2006AA03Z519)     

Effect of Fly Ash and Silica Fume on Hydration Rate of Cement Pastes and Strength of Mortars

The effect of fly ash and silica fume on hydration rate and strength of cement in the early stage was studied. Contrast test was applied to the complex cementitious system to investigate the hydration rate. Combined with mechanical strength, the influence of fly ash and silica fume during the hydration process of complex binder was researched. The peak of the rate of hydration heat evolution and the mechanical strength decreased as the ratio of fly ash increased, however, as the ratio of silica fume increased, the peak of the rate of hydration heat evolution and the mechanical strength increased obviously. When the ratios of fly ash and silica fume are 10% and 5%, the peak of the rate of hydration heat evolution is the highest. At the same time 7 days of flexural and compressive strength are the highest as 8.89 MPa and 46.52 MPa, respectively. Fly ash and silica fume are the main factors affecting the hydration rate and the mechanical property.     

Alumina Ceramics Fabricated by in-situ Consolidation of Pre-gelling Starch

An in-situ consolidation method was developed and optimized to successfully fabricate alumina ceramics using pre-gelling starch. Our results showed that the obtained ceramics have more homogeneous microstructure, higher density, higher flexural strength, and favorable biocompatibility compared to the regular one. During the process, cornstarch granules swelled and deformed but no fracture was observed. After the cornstarch granules bursted, alumina particles were suspended uniformly in the three-dimensional network structure to generate a much smoother surface. Below 0.5 wt% higher cornstarch content increased the flexural strength of prepared ceramics, while above 0.5 wt% the mechanical properties were compromised. Therefore the cornstarch content of 0.5% was the optimal concentration to achieve the highest mechanical strength of the prepared ceramics, with a measured flexural strength of 341 MPa, and a relative density of 96.01%.     

Synergistic effects of expandable graphite and dimethyl methyl phosphonate on the mechanical properties,fire behavior,and thermal stability of a polyisocyanurate–polyurethane foam

In this study, a series of flame-retardant polyisocyanurate–polyurethane (PIR–PUR) foams were prepared using various concentrations (0–25% by weight) of expandable graphite (EG) and dimethyl methyl phosphonate (DMMP) (0–7% by weight). The effect of these additives on the properties of the PIR–PUR foams, including physico-mechanical, morphological, flame retardancy, and thermal stability, was studied. Increasing amounts of EG in the PIR–PUR foam caused a significant drop in the compression strength. However, DMMP caused the mechanical properties of PIR–PUR foam to improve compared to foam filled with EG alone. The flame retardancy of PIR–PUR foams containing both EG and DMMP was enhanced significantly compared to EG filled foams. Thermogravimetric analysis (TGA) indicated that EG enhances the thermal stability of PIR–PUR foams but that DMMP decreased it. The morphology of the residual char provided conclusive evidence for the weak thermal stability of foams filled with DMMP.     

Synthesis and characterization of multi-walled carbon nanotube doped silica aerogels

Multi-walled carbon nanotube doped silica aerogels(MWCNT-SAs) were synthesized from a wet gel of well-dispersed MWCNT by one-step solvent exchange/surface modification and ambient pressure drying(APD). Waterglass was employed as a precursor to prepare wet gel. The content of MWCNT varied from 0 to 15% volume by wet gel. The surface group, thermal stability and microstructure of pure silica aerogel and MWCNT-SAs were investigated by FTIR, DTA, and TEM. Experimental results show that MWCNT-SAs are hydrophobic when the temperature is below 400 ℃, MWCNT-SAs exhibit a mesoporous network structure, and they achieve the largest scale with least shrinkage and lowest density when doped with 5 vol% MWCNT.