Humic Acid as Dispersant of an Alumina Suspension and its Rheological Behaviour

Humic acid was extracted and employed as a dispersant in an alumina suspension. The higher zeta potential for HA (-42 mV) was measured at pH 11 showing that an electrostatic repulsion might occur in the alumina/HA suspension. As a consequence of the long chain molecules of HA it was also expected a steric effect on deflocculation. The best dispersion conditions for the alumina suspension (28 vol%) were found with 0.016 wt% HA, close to the viscosity achieved with a commercial sodium polyacrylate. The rheological characterisation showed results beneficial for the slip casting process, such as slightly thixotropy and pseudoplastic behaviour. The excellent colloidal stability at pH 11 as evidenced through rheological and sedimentation tests was attributed to the polyelectrolyte nature of the HA. From deflocculated suspensions it was possible to obtain high density pieces by slip casting method.

本研究提取腐殖酸（Humic acid）并将其用作氧化铝悬浮液的分散剂。腐殖酸（HA）的ζ电势（zeta potential）在pH=11条件下达到最大值-42 mV，表明氧化铝/腐殖酸悬浮体系中可能存在静电排斥作用。由于腐殖酸具备长链分子结构，其在解絮凝（deflocculation）过程中还可产生空间位阻效应。当腐殖酸添加量为0.016 wt%时，28%体积分数的氧化铝悬浮液可达到最优分散效果，其粘度与商用聚丙烯酸钠（sodium polyacrylate）所能实现的粘度水平相当。流变学表征结果显示，该悬浮液的性能对注浆成型（slip casting）工艺较为友好，具体表现为轻微触变性（thixotropy）与假塑性（pseudoplastic）流变行为。通过流变学测试与沉降试验证实，该悬浮液在pH=11时具备优异的胶体稳定性，这一特性可归因于腐殖酸的聚电解质（polyelectrolyte）本质。借助解絮凝后的悬浮液，可通过注浆成型工艺制备出高密度坯体。