PAA-PEO和PAA对α-Al2O3-H2O悬浮液流变性能的影响

比较一种新型的分散剂--聚丙烯酸-聚氧化乙烯[poly(acrylic acid)-poly(ethylene oxide), PAA-PEO]梳型共聚物和PAA类分散剂对α-Al2O3-H2O悬浮液的流变性能的影响.研究结果表明:PAA-PEO分散剂在pH 2.0～12.0的范围内能使Al2O3浆料稳定,在剪切速率为102.4 s-1时,30%(体积分数)的α-Al2O3-H2O悬浮液的粘度保持在8～12 mPa·s之间,解决了在弱酸条件下PAA对Al2O3粉体不能分散的问题.无论是在酸性还是在碱性条件下,PAA-PEO都能保持其"梳状"结构,由于"梳齿"PEO支链频繁地接枝在"梳背"PAA主链上,这些"梳齿"状支链控制了分散剂在水溶液中构型的变化,产生了较强的空间位阻效应.     

过量PAA-PEO对α-Al2O3-H2O悬浮液流变性能的影响

利用一种新型的分散剂一梳型共聚物poly（acrylic acid）-poly（ethylene oxide）（PAA—PEO），研究了分散剂的添加量以及过量分散剂的添加对α-Al2O3-H2O悬浮液的流变性能的影响，并用常用的分散剂PAA与之比较。结果表明：随着分散剂添加量的增加，浆料的粘度变低，分散剂的添加量存在最佳值。但对于分散剂PAA，过量添加后，会使已经稳定的浆料又重新絮凝。而过量添加的PAA—PEO仍能使浆料保持稳定状态，这是在以往的研究中所没有发现的现象。     

PAA-PEO对ZrO2-H2O悬浮液流变性能的影响

利用一种新型的分散剂—梳型共聚物poly（acrylic acid）-pofy（ethyfene oxide）（PAA—PEO）,研究了pH、分散剂的添加量及固含量对ZrO2-H2O悬浮液的流变性能的影响。结果表明：在pH为3、PAA-PEO的添加量为0．3wt％,ZrO2-H2O悬浮液的粘度最低;固含量在31vol％以下时,浆料都保持稳定状态;随着固含量的增加,浆料的粘度也增加,当固含量达到33vol％时,浆料呈现出明显的剪切变稀行为。     

PAA-PAMPS对Al2O3-H2O体系的流变性影响的研究

研究了丙烯酸与2-丙烯酰胺-2-甲基丙磺酸共聚物(PAA-PAMPS)和聚丙烯酸铵盐(PANH4)在pH3-11条件下对水基氧化铝悬浮液流变行为的影响.研究结果表明,PAA-PAMPS对悬浮液的稳定效果要优于研究广泛的PANH4,尤其在酸性条件下,PAA-PAMPS分散剂仍然可以为体系提供很强的静电位阻作用,这种强静电位阻稳定作用使得氧化铝悬浮液稳定分散.     

聚乙烯吡咯烷酮对PESA-H2O-SiC悬浮液流变性能的影响

研究了聚乙烯吡咯烷酮(PVP)对聚环氧琥珀酸(PESA)稳定的水基碳化硅(SiC)悬浮液流变性能的影响.结果表明,在pH值为9.0时,添加一定比例的少剂量的二元分散剂即可改善SiC悬浮液的分散性.当分散剂总添加量为0.4wt％,PESA与PVP的质量之比为3∶1时,悬浮液的流变性最佳.固含量为40vo1％时,PESA稳定的SiC悬浮液完全絮凝,而添加PVP作为第二分散剂可使体系较好的分散.此外,添加二元分散剂PESA/PVP显著提高了SiC悬浮液的抗电解质性能.     

α-Al2O3-H2O-聚丙烯酸悬浮液的抗电解质性能

研究了电解质对α-Al2O3-H2O-聚丙烯酸(polyacrylic acid,PAA)浆料流变性的影响以及α-Al2O3-H2O-PAA悬浮液的抗电解质性能.结果表明:在pH值为6.5,PAA溶液添加质量分数为0.5%时,NaCl浓度提高,悬浮液的流变性下降.但在0.1～0.2 mol/L的浓度之间时,悬浮液的流变性能基本不随电解质浓度的变化而变化.在不同pH值条件下,PAA溶液最小添加量受电解质浓度影响的程度以及稳定浆料抗电解质能力显著不同.在酸性介质中,更有利于制备具有抗电解质性能的稳定悬浮液.     

分散剂用量对碳化硅浆料流变性能的影响

使用四甲基氢氧化铵(TMAH)作为分散剂,研究了分散剂用量对SiC浆料流变性能的影响,并分析了其原因。结果表明：TMAH能够显著提高SiC粉体的zeta电位,降低浆料粘度,从而显著优化浆料的流变性能。在pH为10左右,加入质量分数为0．3％和o．6％NTMAH后zeta电位分别提高了11.7mV和21mV。实验中,在不同体积分数SiC浆料中,加入0．6%TMAH时能够达到最优性能,浆料粘度都达到最低。过量的分散剂则会增加浆料中的离子浓度而导致双电层厚度减小,从而恶化浆料的流变性。     

SiO_2微粉悬浮液的流变性能

利用流变仪按旋转法研究了高固含量SiO2微粉悬浮液的流变性,考察了固含量(其质量分数分别为50%、60%)、分散剂(六偏磷酸钠、高效减水剂FS20)和悬浮液温度(分别为20、40、60、80℃)对SiO2微粉悬浮液流变性的影响。结果表明:SiO2颗粒表面的Si—OH键对其流变性影响很大,固含量、分散剂和温度都能影响Si—OH键,改变颗粒间的作用力,从而改变悬浮液的流变性;高固含量的SiO2微粉悬浮液属于塑性流体,在低剪切区内,悬浮液流变特性满足Casson模型,黏度降低主要发生在这个区域;六偏磷酸钠和FS20的加入都能有效改善SiO2微粉悬浮液的流变性,而FS20的分散效果更好;20~40℃时,提高温度促进了悬浮液流变性,40~80℃时颗粒间发生脱水缩合反应使悬浮液流变性不稳定,在80℃时,脱水缩合反应剧烈且趋于完成,流变性能又趋于稳定。     

聚环氧琥珀酸/聚乙烯吡咯烷酮对Al_2O_3/SiC悬浮液流变性能的影响

利用阴离子型分散剂聚环氧琥珀酸(polyepoxysuccinic acid,PESA)/非离子型分散剂聚乙烯吡咯烷酮(polyvinylpyrrolidone,PVP)复配为二元分散剂,对Al2O3/SiC悬浮液的流变性能进行了研究。结果表明:在碱性条件下,添加复合分散剂PESA/PVP的Al2O3/SiC悬浮液比加入单一分散剂的体系有更好的分散性。当复合分散剂总添加量为0.4%(质量分数)、PESA与PVP质量比为3∶1时,Al2O3/SiC悬浮液的黏度最低。添加二元分散剂的Al2O3/SiC悬浮液能在25%(体积分数)~45%的固含量范围内保持稳定。添加PESA/PVP作为分散剂的Al2O3/SiC悬浮液的抗电解质性能优于单一PESA作为分散剂的悬浮液。PESA与PVP通过静电斥力与空间位阻的协同效应,极大提高了Al2O3/SiC悬浮液的稳定性。     

分散剂对超细α-Al2O3浆料流变性的影响

以66％丁酮(质量分数,下同)和34％乙醇的共沸混合物为溶剂,测定了α-Al_2O_3超细粉体在该溶剂系统中所得浆料的流变性。研究了三油酸甘油酯(GTO)、蓖麻油(CTO)以及它们的混合物对α-Al_2O_3粉体在该溶剂中的稳定性的影响。实验发现,在0～300 s~(-1)的剪切区,不同条件下测得的流变曲线均符合Casson模型。实验结果显示,同时加入GTO与CTO的浆料,当GTO所占比例在2/3到5/6的范围内时,其流变性明显优于由单种分散剂分散的浆料。     

聚丙烯酸酯包覆铃兰醛纳米胶囊的流变性研究

对聚丙烯酸酯包覆铃兰醛缓释香精体系的流变特性进行研究。动态测试结果表明,随着固含量、香精用量和测试温度的提高,体系的黏弹性能会减弱;而随着乳化剂用量及引发剂用量增加,体系的动态模量随之增强。稳态测试结果表明,随着剪切速率的增大,体系的表观黏度随之下降,体系呈现出假塑性流体剪切变稀的流变特征;随着固含量、乳化剂用量、引发剂用量的增大,体系的表观黏度上升,而香精用量及测试温度提高会导致体系的表观黏度下降。     

Influence of Sucrose Addition on Rheology of Alumina Slurries Dispersed with a Polyacrylate Dispersant

The effect of sucrose addition on rheology of alumina slurries, dispersed with a polyacrylate dispersant (Darvan 821 A), was studied for different alumina loading. Smaller amount of sucrose addition (10 wt%) had a more significant influence on rheological behavior of the slurries than the incremental addition to 30 wt% sucrose. Addition of sucrose resulted in a decrease in the apparent yield stress, viscosity, thixotropy, and increase in non-Newtonian index as compared with the slurries containing just the polyacrylate, indicating weakening of the inter-particle network. Weakening of the inter-particle network arose from the enhanced steric hindrance because of the presence of sucrose molecules in association with the polyacrylate molecules adsorbed on alumina particle surfaces. This association is because of intermolecular hydrogen bond formation between free hydroxyl (−OH) groups of sucrose and carboxylate ions of polyacrylate molecules. Use of sucrose resulted in cast green bodies with higher strength.     

Effect of Polyvinylpyrrolidone Additions on the Rheology of Aqueous,Highly Loaded Alumina Suspensions

The control of the rheological behavior of highly loaded ceramic/polymer suspensions affords the development of near‐net shape forming techniques. In this study, suspensions containing sub‐micrometer diameter alumina (up to 56 vol%) were fabricated using an anionic dispersant (≈4 vol%) and water‐soluble polyvinylpyrrolidone (PVP). The amount and ratio of molecular weights of PVP in the suspension were varied to influence flow behavior. The final pH of the system, ≈9.5, was higher than the isoelectric point (IEP) of alumina implying that the alumina powder possesses a negative surface charge. In the case of alumina at this pH, PVP does not adsorb onto the surface of the powder. The flow behavior of the PVP‐containing suspensions displayed yield‐pseudoplastic characteristics that closely agreed with the Herschel–Bulkley fluid model. The addition of PVP significantly changed the rheology of the system, increasing the shear yield stress and altering flow behavior. Interparticle interaction approximations of the suspensions were modeled to correlate with experimental observations.     

In Situ Rheological Investigation of the Coagulation in Aqueous Alumina Suspensions

Electrostatically stabilized alumina suspensions can be destabilized by the enzyme-catalyzed decomposition of urea (direct coagulation casting). Depending on the conditions, this reaction can shift the pH of a suspension to the buffer pH of the reaction products or increase the ionic strength at the buffer pH. The coagulation for both mechanisms was investigated using in situ rheological measurements. Using a vane tool in oscillation mode, the measuring conditions were optimized to find a reasonable method for time-dependent measurements. Constant parameters (stress or strain) proved to be unsuitable, because the linear viscoelastic region shifted considerably during the coagulation. Furthermore, the gel structure produced on coagulation via increase of ionic strength (Δ I ) was very sensitive to the oscillation. Therefore, for long-time experiments, a short continuous measurement with a low strain was followed by amplitude sweeps with increased intervals to determine the linear values of G ' and G ". In this way, the increase of the moduli G ' and G " could be followed for longer times, and it was possible to demonstrate two results. First, the final G ' of the network was about 10 times higher for Δ I -coagulated material than for suspensions coagulated via pH shift (ΔpH). Second, particle rearrangement processes took place in Δ I -coagulated networks even after the chemical changes were finished, whereas ΔpH-coagulated samples were "frozen-in" when approaching the isoelectric point and showed no further physical changes afterward.     

Rheology of Cross-Linked Chitosan–Alumina Suspensions Used for a New Gelcasting Process

The rheological behavior of a low-toxicity, aqueous, Al₂O₃–chitosan–2,5-dimethoxy-2,5-dihydrofuran (DHF) system was examined over a temperature range of 20°–98°C. At room temperature, a high-volume-fraction solids, shear-thinning suspension was produced. The suspension remained in a liquidlike state for ∼24 h. By contrast, at elevated temperatures, DHF became active as a cross-linking agent for chitosan, and a rapid transition from liquidlike to solidlike suspension behavior was apparent. The rate of gelation and the gel strength increased with increased temperature and increased DHF concentration. Gelation occurred at pH 1.4–4.5, which is a complex function of pH. At pH above ∼4, rapid gelation was not possible because of the low-pH solution conditions required for the cross-linking reaction. An examination of the strength and shape-forming properties of several Al₂O₃–chitosan–DHF systems showed them to be suitable for production of strong, reliable, complex-shaped ceramic components. In particular, small, dense Al₂O₃ pseudorotors were formed and found to be of sufficient strength for mold removal and subsequent handling. In all formulations examined, chitosan concentrations of <0.5 wt% (by weight of ceramic) were required; therefore, the need for a discrete binder burnout process was eliminated.     

Additive Manufacturing of Dense Ceramic Parts via Direct Ink Writing of Aqueous Alumina Suspensions

Additive manufacturing of near‐net‐shaped dense ceramic components has been established via room‐temperature direct writing of highly loaded aqueous alumina suspensions in a layer‐by‐layer fashion. The effect of alumina solid loading on rheology, specimen uniformity, density, microstructure, and mechanical properties was studied. All suspensions contained a polymer binder (~5 vol.%), dispersant, and 51–58 vol.% alumina powder. Rheological measurements indicated all suspensions to be yield‐pseuodoplastic, and both yield stress and viscosity were found to increase with increasing alumina solid loading. Shear rates ranging from 19.5 to 24.2/s, corresponding to viscosities of 9.8 to 17.2 Pa·s, for the 53–56 vol.% alumina suspensions were found to produce the best results for the 1.25‐mm tip employed during writing. All parts were sintered to >98% of true density, with grain sizes ranging from 3.2 to 3.7 μm. The average flexure strength, which ranged from 134 to 157 MPa, was not influenced by the alumina solid loading.     

反相悬浮法合成高分子量聚丙烯酸钠

探讨了体系乳化剂、中和度对聚合稳定性的影响 ,研究引发体系、链转移剂、交联剂等与分子量、凝胶含量的关系。结果表明 ,当选用 Span- 6 0作为乳化剂、单体中和度为 93%时体系稳定性较好。用一定配比的过硫酸铵氧化还原体系为引发剂 ,以异丙醇作链转移剂 ,在适量的交联剂 N ,N'-亚甲基双丙烯酰胺和盐类的存在下 ,聚合得到了粒径为 5 0～ 2 0 0μm、分子量高达 10 0 0× 10 4 左右的聚丙烯酸钠透明粒子 ,并且解决水溶液聚合后期体系粘度大、搅拌和传热困难等问题。     

Plasticizing Aqueous Suspensions of Concentrated Alumina with Maltodextrin Sugar

Aqueous suspensions of submicrometer, 20 vol% Al₂O₃ powder exhibited a transition from strongly flocculated, thixotropic behavior to a low-viscosity, Newtonian-like state upon adding small amounts of maltodextrin (0.03 g of maltodextrin/(g of Al₂O₃)). These suspensions could be filter pressed to highly dense (57%) and extrudable pastes only when prepared with maltodextrin. We analyzed the interaction of maltodextrin with Al₂O₃ powder surfaces and quantitatively measured the resulting claylike consolidation, rheological, and extrusion behaviors. Benbow extrusion parameters were comparable to, but higher than, those of kaolin at approximately the same packing density of 57 vol%. In contrast, Al₂O₃ filter cakes without maltodextrin at 57 vol% density were too stiff to be extruded. Measurements of rheological properties, acoustophoresis, electrophoresis, sorption isotherms, and diffuse reflectance Fourier infrared spectroscopy supported the hypothesis that sorbate-mediated steric hindrance, rather than electrostatic, interparticle repulsion, is important to enhancing the consolidation and fluidity of maltodextrin–Al₂O₃ suspensions. Viscosity measurements on aqueous maltodextrin solutions indicated that free maltodextrin in solution does not improve suspension fluidity by decreasing the viscosity of the interparticle solution.     

水分散型TiO2/聚丙烯酸酯纳米复合材料的制备

通过聚醚型非离子表面活性剂对TiCl4水解后的纳米TiO2进行保护处理,制得能够稳定分散的纳米TiO2胶体,并用此胶体与聚丙烯酸酯乳液直接共混,共混物有较好的分散性及稳定性。