Thixotropic rheology of concentrated alumina colloidal gels for solid freeform fabrication
Thixotropic rheology of concentrated alumina colloidal gels for solid freeform fabrication
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DOI：
10.1122/1.3573828
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发表时间：
2011-03
影响因子：
3.3
通讯作者：
Cheng Zhu;J. Smay
中科院分区：
文献类型：
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作者：
Cheng Zhu;J. Smay
提出了氧化铝（Al2O3）浓缩胶体凝胶触变流变的工程模型，并与流变实验结果进行了比较。用于基于挤出的固体自由成形制造中的浓缩胶体凝胶通常被建模为具有有限屈服应力的简单剪切稀化流体，使得它们的流变性质仅取决于瞬时剪切速率而不取决于剪切历史。虽然这是一个令人满意的稳态流动的观点，它缺乏考虑与瞬态过程，如模具进入和挤出过程中的出口或挤出长丝的形状演变，因为它来到一个低剪切环境中休息的现象的细节。在这里提出的流变模型认为，无论是弹性和粘性的水性Al2O3凝胶的胶体聚集体的微观结构的变化而变化，聚集体的结构是剪切速率和时间的函数。一阶结构动力学假设是用来量化的微观结构的凝胶网络在剪切流动过程中，剪切引起的磨损和扩散限制聚集的速率限制机制的演变。结合结构动力学，建立了描述非稳态剪切变稀行为的本构流动方程。通过剪切速率阶跃测量收集的数据被用来确定12个模型参数在建议的流变模型。该模型进行了比较和验证，通过与令人满意的协议，在双回路实验。这个模型是quasiempirical在这个意义上，粒子间的对电位的细节没有使用的配方。尽管如此，该模型可以在模拟胶体凝胶在挤出过程中的宏观流动行为的实际用途。具体而言，该模型提供了预测的弹性和粘性的胶体凝胶作为剪切history.A工程模型的氧化铝（Al2O3）浓缩胶体凝胶的触变流变学的函数的演变，并与流变学实验结果进行了比较。用于基于挤出的固体自由成形制造中的浓缩胶体凝胶通常被建模为具有有限屈服应力的简单剪切稀化流体，使得它们的流变性质仅取决于瞬时剪切速率而不取决于剪切历史。虽然这是一个令人满意的稳态流动的观点，它缺乏考虑与瞬态过程相关的现象的细节，如挤出过程中的模头进入和退出，或挤出长丝在低剪切环境中静止时的形状演变。在这里提出的流变模型认为，无论是弹性和粘性的水性Al2O3凝胶的胶体聚集体的微观结构的变化而变化，聚集体的结构是剪切速率和时间的函数。一阶结构动力学假设是用来量化的微观…
An engineering model for the thixotropic rheology of alumina (Al2O3) concentrated colloidal gels is proposed and compared to rheological experimental results. Concentrated colloidal gels used in extrusion-based solid freeform fabrication are often modeled as simple shear-thinning fluids with finite yield stress such that their rheological properties depend only on instantaneous shear rate and not on shear history. Although this is a satisfactory view for steady state flow, it lacks the detail to consider phenomena associated with transient processes such as die entry and exit in extrusion processes or the shape evolution of an extruded filament as it comes to rest in a low shear environment. The rheological model proposed here considers that both elastic and viscous properties of an aqueous Al2O3 gel vary with microstructure changes of colloidal aggregates and that the aggregate structure is a function of both shear rate and time. A first-order structural kinetics assumption is used to quantify the microstructure evolution of the gel network during shear flow, where shear-induced attrition and diffusion limited aggregation are the rate limiting mechanisms. A constitutive flow equation is developed by incorporating the structural kinetics to describe unsteady shear-thinning behavior. The data collected through shear rate step-change measurements are used to determine 12 model parameters in the proposed rheological model. The model is compared and validated through hysteresis-loop experiments with satisfactory agreement. This model is quasiempirical in the sense that details of interparticle pair-potentials are not used in the formulation. Nevertheless, the model could have practical uses in simulation of the macroscopic flow behavior of colloidal gels during extrusion processes. Specifically, the model offers predictions of elastic and viscous property evolution of colloidal gels as a function of shear history.An engineering model for the thixotropic rheology of alumina (Al2O3) concentrated colloidal gels is proposed and compared to rheological experimental results. Concentrated colloidal gels used in extrusion-based solid freeform fabrication are often modeled as simple shear-thinning fluids with finite yield stress such that their rheological properties depend only on instantaneous shear rate and not on shear history. Although this is a satisfactory view for steady state flow, it lacks the detail to consider phenomena associated with transient processes such as die entry and exit in extrusion processes or the shape evolution of an extruded filament as it comes to rest in a low shear environment. The rheological model proposed here considers that both elastic and viscous properties of an aqueous Al2O3 gel vary with microstructure changes of colloidal aggregates and that the aggregate structure is a function of both shear rate and time. A first-order structural kinetics assumption is used to quantify the micros...