升温速率和烧成温度对95多晶氧化铝纤维性能的影响

将甩丝后得到的凝胶纤维分别以0.5、1、1.5、2、2.5、3和4 ℃·min-1的升温速率升温至400℃,保温1 h后再以3℃·min-1的升温速率升温至600℃并保温1 h进行中温热处理,然后分别置入1 000、1 100、1 200、1 300和1 400℃的电炉中保温1 h烧成.测试中、高温处理后纤维的平均单丝拉伸强度,并采用SEM观测纤维表面形态.结果表明:中温段(400 ℃以下)升温速率为0.5～1℃·min-1时,600 ℃处理后纤维的平均单丝拉伸强度>1 000 Mpa,此时于1 000～1 100℃烧成的纤维平均单丝拉伸强度可达800 Mpa以上,纤维表面平整光滑,于1 200℃烧成的纤维内部开始出现α-Al2O3,于1 300℃及以上温度烧成的纤维内部α-Al2O3大量出现;升温速率>3℃·min-1时,中温处理后纤维出现了较明显的粉化现象.     

氟聚物的玻璃化温度与DMA测量频率关系的研究

采用动态力学分析（Dynamic mechanical analysis,DMA)方法,研究了F2314、F2311、F2603、F2463等四种氟聚物的动态力学的频率与玻璃化温度关系,并用最小二乘法对相关频率与玻璃化温度进行线性回归,得到了这四种氟聚物的动态力学活化能数据,这些活化能在一定程度上反映了氟聚物链段构象运动的受阻性。     

温升速率对混合煤样热解的影响及动力学分析

为了节约动力煤,降低电力成本,为锅炉燃烧提供理论指导。采用热重分析法和热差分析法对褐煤和煤矸石的混合物进行热解实验。通过改变实验条件(温升速率)可以得到不同情况下的TG曲线、DSC曲线和转化率曲线。实验选用褐煤和煤矸石的质量比为2∶3,温升速率分别为10、30、50℃/min。10℃/min和50℃/min的煤样总的放热面积相近,但30℃/min的放热面积较小,说明30℃/min的温升速率不利于放热。由动力学分析得知,由于温升速率不同,活化能、频率因子均不同,热解动力学参数均发生一定变化。     

Influence of cross-link density on the properties of ROMP thermosets

A norbornene-based cross-linker was synthesized and mixed at different loadings with two separate monomers for self-healing polymer applications: 5-ethylidene-2-norbornene (ENB) and endo-dicyclopentadiene (endo-DCPD). The monomer/cross-linker systems were polymerized by ring-opening metathesis polymerization (ROMP) with Grubbs' catalyst. The thermal-mechanical properties of the polymerized networks were evaluated by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) and the curing process was monitored by parallel plate oscillatory rheometry. The viscosities of the pre-polymer blends are shown to be adequately low for self-healing, and exhibit a high ROMP reactivity to form cross-linked networks with enhanced thermal-mechanical properties. The addition of cross-linker increases the glass transition temperature (T_g) and the storage modulus both above and below T_g. The storage modulus increase above T_g is used to estimate the molecular weight (M_c) between entanglements or cross-link sites for both ENB and endo-DCPD-based networks. The cross-linker also greatly accelerates network formation as defined by the gelation time.     

Thermal treatment and dynamic mechanical thermal properties of polyaniline

Thermal transitions of polyaniline in the emeraldine base form (Pani-EB) were studied by DMTA using two series of thermally treated samples. In the first series the specimens were annealed at 70 °C for 5, 15 min, 1 and 3.5 h. In the second they were submitted to annealing at 100 °C during the same periods of time plus a 24 h treatment. Two transitions were observed at sub-zero temperatures and were attributed to the motion of solvated water and solvent (NMP). The glass transition and the highest temperature relaxation, assigned to crosslinking depended on the degree of solvation resulting from the thermal treatment. A linear contraction of Pani-EB films with residual water evaporation was reported for the first time.     

接缝宽度对铝合金玻纤复合层板拉伸性能的影响

以铝合金玻纤复合层板为研究对象.从金属层接缝界面端应力场分析出发,建立有限元模型,确定位移边界条件和载荷边界条件.利用有限元方法模拟出不同接缝宽度在常温下的热残余应力.通过实验得出常温和高温条件下的各个接缝宽度试样的破坏拉伸载荷.考察接缝大小对残余应力的影响和分布,从而研究其对铝合金玻纤复合层板拉伸性能的影响.     

Tensile and dynamic mechanical properties of improved ultrathin polymeric films

Tensile and dynamic mechanical properties of improved ultrathin polymeric films for magnetic tapes are presented. These films include poly(ethylene terephthalate) or PET, poly(ethylene naphthalate) or PEN, and aromatic polyamide (ARAMID). PET film is currently the standard substrate used for magnetic tapes; thinner tensilized‐type PET, PEN, and ARAMID were recently used as alternate substrates with improved material properties. The thickness of the films ranges from 6.2 to 4.8 μm. Young's modulus of elasticity, F5 value, strain‐at‐yield, breaking strength, and strain‐at‐break were obtained at low strain rates by using a tensile machine. Storage (or elastic) modulus, E′, and the loss tangent, tan δ, which is a measurement of viscous energy dissipation, are measured by using a dynamic mechanical analyzer at temperature ranges of ?50 to 150°C (for PET), and ?50 to 210°C (for PEN and ARAMID), and at a frequency range of 0.016 to 29 Hz. Frequency–temperature superposition was used to predict the dynamic mechanical behavior of the films over a 28 decade frequency range. Results show that ARAMID and tensilized films tend to have higher strength and moduli than standard PET and PEN. The rates of decrease of storage modulus as a function of temperature are lower for PET films than those for PEN and ARAMID films. Storage modulus for PEN films are higher than that for PET films at high frequencies, but this relationship reverses at low frequencies. ARAMID has the highest modulus and strength among the films in this study. The relationship between polymeric structure and mechanical properties are also discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2225–2244, 2002     

Effect of demineralization and heating rate on the pyrolysis kinetics of Jordanian oil shales

The effect of mineral matter content on the activation energy of oil shale pyrolysis has been studied. Kerogen was isolated from raw oil shale by sequential HCl and HCl/HF digestion. Oil shale and kerogen samples were pyrolyzed in a Thermogravimetric Analyzer at different heating rates (1, 3, 5, 10, 30, and 50 °C/min) up to a temperature of 1000 °C. Total mass loss of all oil shale samples remained almost constant irrespective of the heating rate employed, whereas it decreased with the increase of heating rate for kerogen (74.5 to 71.4%). From the pyrolysis profile activation energy (Ea) was found to vary between 70 and 83 kJ/mol for oil shale, while 82-112 kJ/mol has been determined for isolated kerogen. An increase of both Ea and pre-exponential factor was observed with an increasing heating rate. It is concluded that the mineral matter in oil shale enhances catalytic cracking as is evident from the reduced Ea values of oil shale compared with those for kerogen.     

Effect of thermal shock cycling on the quasi-static and dynamic flexural properties of flax fabric-epoxy matrix laminates

The aim of the present work is to investigate the influence of thermal shock cycling on the quasi-static and dynamic flexural properties of epoxy matrix composites reinforced with natural flax fibers fabric. Polymer composite laminates reinforced with four plies of natural flax fiber fabric have been manufactured. The samples have been exposed to different number of thermal shock cycles (0, 50, 100, 200, 300, 400), at a temperature range from −40 °C to +28 °C. Dynamic mechanical analysis (DMA) tests were performed on both pristine and thermally shocked specimens in order to determine their viscoelastic response. Due to the thermal shock cycling and after 100 thermal shock cycles, a maximum decrease in storage and loss modulus on the order of 50% was observed. After 100 thermal shock cycles, no further degradation of dynamic properties was observed. On the contrary, damping factor and glass transition temperature values showed a minor variation as number of thermal shock cycles increased. In addition, the time–temperature superposition principle (TTSP) was successfully applied, confirming the fact that the flax fiber fabric-epoxy laminate is a thermo-rheologically simple material. Likewise, quasi-static three-point bending tests were executed and a maximum decrease of 20% in flexural strength was observed after 400 thermal shock cycles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48529.     

Structure and dynamic mechanical properties of highly oriented PS/clay nanolaminates over the entire composition range

A series of highly oriented model polymer/clay nanocomposites (nanolaminates) are prepared via a newly developed solvent deposition process with compositions ranging from neat polymer to neat organoclay. Morphology is analyzed via scanning electron microscopy (SEM) and wide-angle X-ray diffraction (WAXD) while thermogravimetric analysis (TGA) is used to confirm composition and solvent removal. Dynamic mechanical analysis (DMA) is used to examine the trends in stiffness and damping properties as the composition is shifted from polymer-rich to polymer-starved. The role of the organoclay modifier in determining the structure and properties of these nanolaminates is also reported. Experimental moduli are compared to relevant micromechanical models including Tandon-Weng and Halpin-Tsai. These comparisons allow for the identification of deviations from the behavior expected of conventional blends and composites, highlighting the effects of nanostructuration and the presence of the organic modifier on materials behavior.     

Influence of Mn doping on electrical conductivity of lead free BaZrTiO3 perovskite ceramic

Mn doped barium zirconate titanate lead free ceramic with formula BaZr_.045(Mn_xTi_1-x) _.955 O₃ for x?=?0.00, 0.01, 0.02 and 0.03 has been prepared by solid-state reaction method. The single phase tetragonal structure was confirmed by X-ray diffraction (XRD) pattern using Rietveld refinement. Scanning electron microscopy (SEM) shows an inhomogeneous distribution of randomly oriented grains with some voids. Electrical conductivity of Mn doped BZT ceramics was studied using impedance analyzer in the temperature range 493K–673K over wide frequency window. The dispersion behaviour in electrical conductivity obeys Jonscher's double power law for Mn free compound, while it follows single power law for Mn doped compositions. Various parameters viz. dc conductivity (σ_dc), pre-exponential factor (A), frequency exponent (s) and activation energy (E_a) have been estimated by the theoretical fitting of experimental data. The reciprocal temperature dependence of dc conductivity follows the Arrhenius law and specifies thermally activated conduction mechanism. The obtained value of activation energy (E_a) evidences the conduction mechanism is induced by the migration of oxygen vacancies and oxide ions. All samples shows Negative temperature coefficient of resistance (NTCR) and hence exhibit semiconducting behaviour. The environmental friendly lead free ceramic can be exploit to design advanced materials and suitable for the fuel cell electrolyte/electrode applications.     

Ultra-high heating rate densification of nanocrystalline magnesia at high pressure and investigation on densification mechanisms

The pressure-assisted densification method based on combustion reaction heating was applied to prepare dense nanocrystalline ceramics. The densification process of magnesia compact with a particle size of 50 nm was investigated, under the pressure range of 0–170 MPa, and the temperature range of 1620–1880 K with ultra-high heating rate (above 1600 K/min). The pressure was found to have an effect on enhancing densification while suppressing grain growth, and the higher sintering temperature lead to the larger grain size and lower density of the compact. Pure magnesia nanocrystalline ceramics with a relative density of 99.1% was obtained at 1620 K and 170 MPa, and the concurrent grain growth was almost completely restrained. Furthermore, the investigation on the pressure-dependent densification mechanisms including plastic flow, diffusion and power-law creep was also carried out. The result indicated the rate-controlling mechanism was the plastic flow accommodated by grain-boundary diffusion creep.     

Mechanical properties of geopolymer concrete exposed to dynamic compression under elevated temperatures

Through adoption of a self-designed high temperature SHPB apparatus herein, an experimental study is made on the mechanical properties of geopolymer concrete (GC) exposed to dynamic compression under elevated temperatures. As the results have turned out, the weight loss is remarkable within temperature ranges from room temperature to 200 °C as well as from 600 °C to 800 °C. The dynamic compressive strength of GC grows higher at 200 °C than at room temperature, but suffers a dramatic drop at 800 °C. The critical strain is higher at elevated temperature than that at room temperature. At 200 °C and 600 °C, respectively, its energy absorption property is superior to that at room temperature. However, at 400 °C and 800 °C, respectively, it is inferior to that at room temperature. The strain rate effect of the dynamic increase factor (DIF) obtained from test data can reflect the inherent nature of GC. The DIF assumes a linear relationship with the logarithm of strain rate.     

Influence of silane coupling agents on vulcanised natural rubber: dynamic properties and heat buildup

We explore the influence of surface modification of SiO₂ on dynamic properties and heat buildup of semi-ef?cient vulcanisates filled by both SiO₂ and carbon black. Compared with untreated-SiO₂-filled natural rubber (NR), vulcanisates reinforced by modified-SiO₂ presents not only better filler dispersity, mechanical properties and dynamic properties, as confirmed by scanning electron microscope and rubber processing analyser, but also lower heat buildup. Fourier infrared spectroscopy and cure characteristics indicates that silane coupling agent molecules grafted on the silica surface provoke an enhanced mobility of rubber chain and adsorb onto filler surface and then decrease the barrier of crosslink reaction. Moreover, composites with Si69-modified-SiO₂ show obviously the highest tear strength and lowest heat buildup attributed to that more sulphur released by Si69 also participate the vulcanisation reaction.     

升温速率对陶瓷化硅橡胶瓷化性能的影响

研究升温速率对陶瓷化硅橡胶瓷化性能和陶瓷化硅橡胶烧蚀所得陶瓷体性能的影响。结果表明,升温速率对陶瓷化硅橡胶的烧蚀质量损失率影响不大,当玻璃粉用量为45份时,烧蚀线性收缩率随升温速率的提高而增大;随着升温速率的提高,陶瓷体的三点弯曲强度和冲击强度先增大后减小;当升温速率为15℃·min~(-1)、玻璃粉用量为45份时,陶瓷体的三点弯曲强度和冲击强度达到最大值,相应的陶瓷体内部孔洞较小,微孔分布均匀,断面致密性较好。     

Influence of the wetting properties of polymeric adhesives on the mechanical behaviour of cork agglomerates

A series of adhesives, polyurethane prepolymers with alkane chains of different functionalities, were used in the production of cork agglomerates. The polymeric structure varied from long, linear chains in adhesive M1 (14% isocyanate groups) to short, branched chains in adhesive M4 (30% isocyanate groups). The wetting properties of the adhesives were studied through surface tension and contact angle measurements of the polymeric liquids deposited on cork substrates. The mechanical behaviour of the cork agglomerates was studied through compression and three-point bending tests, and the agglomerate structure was analysed by scanning electron microscopy (SEM). The relationship between the structural and wetting characteristics of the adhesives and the mechanical properties of the agglomerates was investigated. The experimental results indicate that it is the work of adhesion for the adhesive/cork system, and not only the contact angle, which determines the mechanical resistance of the cork agglomerate.     

Experimental and numerical studies on the effects of pressure release rate on number density of bubbles and bubble growth in a polymeric foaming process

A simulation of simultaneous bubble nucleation and growth was performed for a batch physical foaming process of polypropylene (PP)/CO₂ system under finite pressure release rate. In the batch physical foaming process, CO₂ gas is dissolved in a polymer matrix under pressure. Then, the dissolved CO₂ in the polymer matrix becomes supersaturated when the pressure is released. A certain degree of supersaturation produces CO₂ bubbles in the polymer matrix. Bubbles are expanded by diffusion of the dissolved CO₂ into the bubbles. The pressure release rate is one of the control factors determining number density of bubbles and bubble growth rate.To study the effect of pressure release rate on foaming, this paper developed a simple kinetic model for the creation and expansion of bubbles based on the model of Flumerfelt's group, established in 1996 [Shafi, M.A., Lee, J.G., Flumerfelt, R.W., 1996. Prediction of cellular structure in free expansion polymer foam processing. Polymer Engineering and Science 36, 1950-1959]. It was revised according to the kinetic experimental data on the creation and expansion of bubbles under a finite pressure release rate. The model involved a bubble nucleation rate equation for bubble creation and a set of bubble growth rate equations for bubble expansion. The calculated results of the number density of bubbles and bubble growth rate agreed well with experimental results. The number density of bubbles increased with an increase in the pressure release rate. Simulation results indicated that the maximum bubble nucleation rate is determined by the balance between the pressure release rate and the consumption rate of the physical foaming agent by the growing bubbles. The bubble growth rate also increased with an increase in the pressure release rate. Viscosity-controlled and diffusion-controlled periods exist between the bubble nucleation and coalescence periods.     

Bimodal grain structure effect on the static and dynamic mechanical properties of transparent polycrystalline magnesium aluminate (spinel)

Transparent polycrystalline magnesium aluminate (spinel) with bimodal and unimodal grain structures were prepared. The influence of grain size distribution on static and dynamic mechanical properties were systematically investigated. The results showed that bimodal grain structure spinel has larger flexural strength (236.31 MPa) compared to unimodal grain structure spinel (221.38 MPa). Whereas, their values of hardness are very similar (15.1 vs 14.7 GPa) and fracture toughness remains unchanged (1.1 MPa∙m^1/2 for both spinel). Although static compression strength of bimodal grain structure spinel (1236 MPa) is higher than that of unimodal one (1078 MPa) due to a smaller average grain size in the former, the negative effect of bimodal grain structure reduced the spinel strength compared to theoretically predicted value. Bimodal grain structure spinel shows slightly lower increment (49%) in compression strength from static to dynamic loading compared to that of unimodal one (57%) due to a decreased strain-rate sensitivity ascribed to bimodal grain structure. A brittle mode in inelastic deformation at Hugoniot elastic limit was demonstrated in both bimodal and unimodal grain structures. Bimodal grain structure has an influence on the Hall-Petch-like relation of yield strength under planar impact loading.     

造粒机性能对塑料生产率的影响

针对某厂塑料挤出机生产能力降低的问题 ,引用有关挤出理论 ,就影响挤出机生产率的原因作了分析 ,提出了解决问题的措施     

Effect of temperature and heating rate on the sintering performance of SiC-Al2O3-Dy2O3 and SiC-Al2O3-Yb2O3 systems

Samples of SiC+10 vol%(Al₂O₃+Dy₂O₃) and SiC+10 vol%(Al₂O₃+Yb₂O₃) mixtures were obtained by cold isostatic pressing and sintered for one hour in a dilatometer at 1800 °C and 1900 °C, applying heating rates of 10, 20 and 30 °C/min. The results of the complete sintering cycle indicated that the heating rates do not significantly influence the shrinkage, but that temperature and total sintering time may be relevant factors. The compacts sintered at 1900 °C shrank on average 9% more than those sintered at 1800 °C, and it was found that the sintering time can be reduced by 40–50% at faster heating rates. The maximum shrinkage rates occurred at temperatures lower than those of the sintering thresholds for the two mixtures, two temperatures and three heating rates. It was also found that after formation of the liquid, the mechanisms of particle rearrangement and solution-precipitation were not as fast as reported in the literature, even at high heating rates, for example 30 °C/min, but they are responsible for much of the shrinkage occurring throughout the sintering cycle.