基于显微CT技术的碳纤维复合材料体孔隙率测量

提出了一种基于显微CT技术的碳纤维复合材料体孔隙率测量的新方法,分析了采用显微CT技术测量孔隙率的实验原理,对实验结果进行了图像处理,并统计体孔隙率。实验结果表明,显微CT技术是一种行之有效的碳纤维复合材料体孔隙率测量技术,通过图像灰度进行阈值分割可以清晰地分辨材料内部基体与孔隙,且测量过程中应选择足够大的试样体积,测量值才能真实反映材料内部的体孔隙率。

造粒颗粒粒度级配对ZrO2陶瓷轴承坯体孔隙率的影响

为提高ZrO2陶瓷轴承坯体的成型致密度,采用倾斜式强逆流混合干法造粒机对ZrO2粉体进行造粒,用标准分样网筛筛分成20~30目、30~40目、40~50目、50~60目、60~70目和70~80目六种粒度,再按正态分布、平均分布和随机分布三种粒度级配配料,混合均匀后采用粉末压片机在40 MPa压力下分别保压60、90、120 s制成∅20.0 mm×4.0 mm的坯体试样,检测其孔隙率和表观密度,并观察其显微结构。结果表明:1)ZrO2造粒颗粒的粒度级配为正态分布时,ZrO2陶瓷轴承坯体试样的孔隙率明显小于另外两组试样的孔隙率。2)随着保压时间的延长,ZrO2陶瓷轴承坯体试样的孔隙率减小。

干压成型工艺参数对ZrO2干法制粒坯体孔隙率的影响

为改善ZrO2陶瓷干法制粒坯体孔隙率偏高等问题,探究干压成型工艺参数对坯体孔隙率的影响。自主搭建实验平台,对ZrO2粉体进行造粒,改变加压压力与保压时间,制备坯体试样。结合阿基米德法,分析孔隙率与体积密度、表观密度和真实密度的关系,修正孔隙率计算模型。采用SEM图对微观形貌进行表征,验证实验结果的准确性。结果表明:加压压力与保压时间对ZrO2坯体孔隙率有明显影响。为制备孔隙率低的ZrO2陶瓷,对工艺参数进行优化。当加压压力为60 MPa,保压时间为120 s时,制得孔隙率较低的ZrO2陶瓷坯体,孔隙率为6.41%。

多孔铝合金的孔隙率梯度及控制

应用图像识别与处理技术,描述了多孔铝合金的面孔隙率及体孔隙率;研究了渗流法制备的多孔铝合金沿长度方向的孔隙率梯度,并对整体孔隙率的均匀度进行了估计。研究结果表明:多孔铝合金的中上部孔隙率最高,顶端次之,底端最低。多孔铝合金的孔隙率梯度主要是由渗流驱动压力梯度与凝固顺序所决定,而颗粒的自然堆积密度影响相对较小。但通过振动控制方法,调整颗粒堆积密度,可以有效地改善多孔铝合金的孔隙率梯度,使孔隙率梯度绝对值平均由6.5%降至2.2%。

孔隙分布不均匀性对渗透率影响的MRTLBM法研究

孔隙率与渗透率是多孔介质非常重要的属性参数,采用MRT LBM研究孔隙率损失与渗透率损失相关性以及同孔隙率异构孔隙对渗透率特性的影响。结果表明:当存在使孔隙率均匀变小的沉积、沉降或结焦等因素时,渗透率损失率是孔隙率损失率的2倍左右;同孔隙率异构多孔体中,渗透率有巨大差异;同孔隙率异构多孔体中最大孔喉最小孔喉比越大渗透率越小;同孔隙率多孔体中迂曲度越大渗透率越小。

基于CT图像单轴受载煤样损伤计算

针对CT图像的特点,分别从像素与体素两种尺度定义了表面孔隙率与体孔隙率.利用数字地形模型方法计算表面孔隙率,给出了基于工业CT灰度图像体孔隙率的计算方法.对煤样单轴加载下不同阶段的CT图像进行分析,获得了煤样表面孔隙率与体孔隙率随应力变化关系曲线.两种孔隙率都能较好地反映煤样内部损伤变化,表面孔隙率反映的是像素级的孔隙,体孔隙率反映了像素内部的孔隙,更能体现CT图像的特点.

Effect of ore size and heap porosity on capillary process inside leaching heap

The capillary process coexists with gravity flow within leaching heap due to the dual-porosity structure. Capillary rise is responsible for the mineral dissolution in fine particle zones and interior coarse rock. The effect of particle size and heap porosity on the capillary process was investigated through a series of column tests. Macropore of the ore heap was identified, and its capillary rise theory analysis was put forward. Two groups of ore particles, mono-size and non-uniform, were selected for the capillary rise test. The result shows that particle size has an inverse effect on the capillary ultimate height, and smaller particles exhibit higher capillary rise. Meanwhile, the poorly graded group exhibits small rise height and velocity, while the capillary rise in the well-graded particles is much greater. The relationship between porosity and fitting parameters of capillary rise was obtained. Low porosity and high surface tension lead to higher capillary height of the fine gradation. Moisture content increases with the capillary rise level going up, the relationship between capillary height and moisture content was obtained.

轴向荷载作用下煤岩吸附瓦斯特性试验研究

为了揭示应力、气体吸附共同作用下煤岩的结构变化规律,对不同轴向载荷、不同瓦斯压力条件下的煤样进行CT扫描,基于CT图像定义了体素孔隙率α,分析了煤样体积应变、CT图像灰度及孔隙分布的变化规律。结果表明:体素孔隙率α可以反映应力、气体吸附共同作用下煤样内部不同尺度孔隙结构的变化;0<α≤20%时体素区域在瓦斯作用中起主导作用,α>40%时体素区域主要起着瓦斯运移通道作用;瓦斯吸附首先发生在0<α≤10%的体素区域,随着轴压的增大,吸附逐渐对10%<α≤20%的体素区域产生作用;应力比气体吸附对煤样孔隙结构的改变作用更为显著。

Ambient electrical conductivity of carbon cathode materials for aluminum reduction cells

The ambient electrical conductivity (AEC) of carbon cathode materials was investigated in respect to their open porosity, crystal structure and graphite content using hydrostatic method, four-probe technique and X-ray diffraction (XRD), respectively. The AEC is proportional to the specific conductivity (σ0) and the exponential of (1?ε) (ε is porosity) by a quasi-uniform formula based on the percolation theory. Theσ0 can reflect the intrinsic conductivity of the carbon cathodes free of pores, and it depends on the mean crystallite size parallel to the layer (002). The exponentn is dependent on the materials nature of the cathode aggregates, while an averaged value, 4.65, can practically work well with 5 types of cathode materials. The calculation ofσ0 can be extended to the graphitic cathodes containing different aggregates using the simple rule of mixture.

Volume change of macropores of titanium foams during sintering

The porosity of titanium foams obtained from the space holder technique was theoretically analyzed in the cases of volume shrinking, retaining and expanding during sintering. The relationship between porosity and spacer content was compared under different conditions. The kind of volume change of macropores during sintering was discussed. The results indicate that the relationship between porosity and spacer content depends on the decreased volume of macropores and the volume of micropores in cell-walls in the first case, while the porosity will be greater than the spacer content for the other two cases. It proves that the volume change of macropores during sintering decreases based on theory and practice.

Effects of pore size and porosity of surface-modified porous titanium implants on bone tissue ingrowth

The effects of surface-modified porous titanium implants with different porosities and pore sizes on osseointegration were investigated in vivo.Three porous titanium implants(A30,A40 and A50 containing volume fractions of space-holder NaCl being 30%,40%and 50%,respectively)were manufactured by metal injection moulding(MIM).The surface-modified implants were implanted into muscles and femurs of hybrid male dogs.Interface osteogenic activity and histological bone ingrowth of porous titanium implants were evaluated at 28,56 and 84 d.The results showed that when additive space-holder amount of NaCl increased from 30%to 50%(volume fraction),the general porosity and mass fraction of macropores of porous titanium rose from 42.4%to 62.0%and from 8.3%to 69.3%,respectively.Histologic sections and fluorescent labeling showed that the A50 implant demonstrated a significantly higher osteogenic capacity at 28 d than other implants.Bone ingrowth into the A30 implant was lower than that into other implants at 84 d.Therefore,the pore structure of A50 implant was suitable for new bone tissue to grow into porous implant.

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/cm3 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/cm3.

Gas Diffusion in Bi-disperse Porous Catalyst Pellets

A flux equation of diffusion for bi-disperse porous catalyst pellets was proposed by modifying the previously developed model equation over fractal trajectories. The proposed fractal model equation considered the same tortuous degree for both micro-and macro-pores. The experimental data of diffusion over a bi-disperse Ni/gamma-alumina pellet were obtained with a standard Wicke-Kallenbach diffusion cell for both carbon monoxide- ethylene and carbon dioxide-ethylene binary mixtures. The fitting between experimental results and the fractal model equation leads to a fractal dimension of 1.11. The prediction of diffusion flux over the bi-disperse Ni/gamma- alumina pellet by the proposed fractal model equation is much better than the traditional tortuosity-based model equation by comparison with the measured flux through the pellet.

Numerical investigation on freeze-drying of aqueous material frozen with pre-built pores

Freeze-drying of the initially porous frozen material with pre-built pores from liquid material was found experimentally to save drying time by over 30% with an initial saturation being 0.28 compared with the conventional operation with the initial saturation being 1, using mannitol as the solid material. In order to understand the mass and heat transfer phenomena of this novel process, a two-dimensional mathematical model of coupled mass and heat transfer was derived with reference to the cylindrical coordinate system. Three adsorption–desorption equilibrium relationships between the vapour pressure and saturation value namely, power-law, Redhead's style and Kelvin's style equation, were tested. Kelvin's style in exponential form of adsorption equilibrium relation gave an excellent agreement between the model prediction and experimental measurement when the equation parameter, γ, of 5000 was applied. Analyses of temperature and ice saturation profiles show that additional heat needs to be supplied to increase the sample temperature in order to promote the desorption process. Simulation also shows that there is a threshold initial porosity after which the drying time decreased with the increase in the initial porosity. Enhanced freeze-drying is expected to be achieved by simultaneously enhancing mass and heat transfer of the process.

Riser Simulation and Radial Porosity Distribution Characterization for Gas-Fluidized Bed of Cork Particles

Numerical simulations are carried out for gas-solid fluidized bed of cork particles, using discrete element method. Results exhibit the existence of a so-called anti core-annular porosity profile with lower porosity in the core and higher porosity near the wall for non-slugging fluidization. The tendency to form this unfamiliar anti core-annular porosity profile is stronger when the solid flux is higher. There exist multiple inflection points in the simulated axial solid volume fraction profile for non-slugging fluidization. Results also show that the familiar core-annular porosity profile still appears for slugging fluidization. In addition, the classical choking phenomenon can be captured at the superficial gas velocity slightly lower than the correlated transport velocity.