氧化铝粉体在水悬浮液中的分散特性研究

采用Zeta电位表征Al_2O_3粉在悬浮液中的分散特性,研究了超声波分散时间、不同粒度Al_2O_3粉以及分散剂六偏磷酸钠的浓度和Al_2O_3粉体悬浮液pH值对Al_2O_3粉体Zeta电位的影响.研究结果表明:Zeta电位绝对值随超声波作用时间发生明显变化,在一定条件下存在一个最佳分散时间为4～6 min;悬浮液中Al_2O_3粉体颗粒的粒度对悬浮液的Zeta电位有重要影响;在Al_2O_3粉体悬浮液中添加分散剂六偏磷酸钠,Zeta电位随其浓度发生变化,存在一个最佳浓度0.5%;在不同pH值下,Al_2O_3粉体悬浮液的Zeta电位不同,在碱性条件下,粉体的分散性较好,且碱性越强,分散性越好.     

分散剂对纳米TiO2悬浮液稳定性的影响

选择不同的有机物为分散剂分别对纳米TiO2粒子进行了表面改性。通过采用重力沉降法、Zeta电位法等表征了其分散效果,研究了纳米TiO2悬浮液在不同PH值下的分散行为。结果表明:纤维素能使纳米TiO2悬浮稳定性明显提高。在纳米TiO2悬浮液中,纳米TiO2粉体表面的Zeta电位同水溶液的平衡PH有很大关系。提高颗粒表面电位(Zeta电位)是改善粉体分散体系稳定性的有效途径。     

含有α-氮化硅晶须的氮化硅流延浆料的制备

通过分析粘度、ζ-电位等参数,研究烧结助剂、分散剂、粘结剂等对含有α-氮化硅晶须陶瓷浆料的粘度的影响,并确定了最佳的工艺参数。结果发现:Si3N4悬浮粒子的等电点在pH=4.3,其最佳的ζ-电位在pH=11附近。分散剂的引入有效地提高悬浮粒子的ζ-电位等电点,改善浆料的分散性,最佳分散剂用量在1.9%～2.1%(质量分数)之间。制备了具有一定固相含量,流动性和稳定性良好的适合于流延工艺的陶瓷浆料,成型的膜片具有一定的柔韧性。     

酸洗处理对氮化硅浆料流变行为的影响

通过酸洗处理工艺对氮化硅粉体进行了表面改性,并研究了酸洗处理对粉体胶体特性及其浆料流动行的影响。结果表明：酸洗处理之后悬浮粒子的等电点升高;ＸＰＳ表面分析说明这是粉体表面氧化程度降低的缘故。     

纳米氮化硅粉体的表面改性研究

硅烷偶联剂KH550和KH560分别对纳米Si3N4粉体进行表面改性,通过测定改性后纳米Si3N4粉体的活化指数来筛选最佳改性工艺,并评价其分散性。用激光粒度分析仪和傅立叶变换红外光谱仪（FTIR）探测纳米Si3N4粉体的表面改性效果。结果表明：当KH560的添加量为Si3N4的10%,采用60℃×3h工艺改性,活化指数能达到85%以上,改性效果最佳。     

羟基磷灰石粉体表面Zeta电位变化研究

羟基磷灰石(HA、HA/TCP和TCP)的组成接近于生物体骨质的无机成分,具有良好的生物相容性和生物活性。但以往的研究仅局限于其合成工艺及其制品的烧结工艺等方面,有关羟基磷灰石粉体表面的电动特性的研究则甚少。羟基磷灰石粉体表面的电动特性主要表现在其Zeta电位的变化上,影响羟基磷灰石粉体表面的Zeta电位大小的因素有很多,如分散剂种类、溶液中的离子强度、烧结过程导致的粉体晶粒结构差异等。笔者通过研究不同条件下羟基磷灰石粉体在水中的Zeta电位变化,探讨了各种因素对粉体电动特性的影响。希望能通过羟基磷灰石粉体表面Zeta电位探讨体系的优选分散条件和烧结过程对羟基磷灰石表面电位的影响,为进一步探讨羟基磷灰石材料的生物活性提供理论基础。     

氯化钠和六偏磷酸钠对氧化铈抛光ZF7玻璃的协同增强作用

研究了添加NaCl或(NaPO3)6的氧化铈浆料对ZF7光学玻璃抛光的材料去除速率(MRR)及对应的粒子表面Zeta电位和悬浮稳定性的影响. 结果表明,加入NaCl使CeO2浆料的抛光速率下降,而(NaPO3)6则可有效提高MRR;同时添加NaCl和(NaPO3)6对MRR值有明显的协同增强作用. 用原子力显微镜测定了最大MRR值(351.26 nm/min)时抛光玻璃的表面粗糙度Ra为0.799 nm,完全可以满足高质量玻璃抛光的要求,比未加添加剂的MRR(199.36 nm/min)和Ra(0.754 nm)分别提高了76.2%和5.97%. MRR与粒子表面Zeta电位呈线性关系,证明可通过合理构筑粒子表面双电层来提高表面电性,进而提高抛光效果.     

分散剂用量和pH值对纳米氧化锆水基浆料稳定性的影响

在氧化锆陶瓷制作过程中采用凝胶注模成型工艺时,为了获得高分散性、低粘度的浆料,试图使用聚丙烯酸铵(PAA-NH4)作为分散剂,主要研究了氧化锆悬浮体的3个指标:Zeta电位、流变学行为、沉降度,在不同p H值和分散剂用量下的变化规律,并分析其影响机理。试验结果表明:PAA-NH4的加入能够明显提高氧化锆浆料的Zeta电位,用氨水调节悬浮体p H为11的情况下,当添加3.0 wt%的分散剂聚丙烯酸铵PAA-NH4时,Zeta电位为负值,达到最小,粘度和沉降高度也均达到最小值,此时,ZrO2水基浆料的分散性、稳定性和流变学行为达到最佳。     

改性纳米Si3N4在EPDM中的应用研究

用溶液聚合法合成BA—MAA—AN三元共聚物大分子表面处理剂对纳米Si3N4进行表面处理，大分子表面处理剂包覆在纳米Si3N4的表面，并与其发生了化学作用，可有效地阻止纳米Si3N4粉末的团聚；处理过的Si3N4粒径明显减小，可提高粉体在橡胶中的分散性。用经处理的纳米Si3N4填充三元乙丙橡胶（EPDM）制备了纳米橡胶复合材料，并研究了复合材料的力学性能。结果表明：改性纳米Si3N4的加入在一定程度上提高了EPDM的拉伸强度、撕裂强度、耐磨及动态耐久性能等，其中添加1．5份改性纳米Si3N4效果最好。     

碳化硅浓悬浮体的分散特性和流变性研究

通过对碳化硅粉体在有机单体介质中的Zeta电位，分散剂用量和浓悬浮体的粘度等的测试及其沉降试验，详细研究了粒径分布较宽的碳化硅粉体（0.2-250μm)的胶体分散特性，沉降行为以及浓悬浮体的流变行为。结果表明，选用适量的分散剂四甲基氢氧化铵可使SiC颗粒的Zeta电位绝对值提高近20mV，调整浆料pH至11．9附近可制备出固相体积分数高达70％的SiC浓悬浮体。该浓悬浮体中粗细SiC颗粒间能达到一稳定的分数，悬浮粒子不会产生明显地沉降，其流变行为符合Quemada模型。     

Electrokinetic and Rheological Properties of Aqueous TiN Suspensions with Ammonium Salt of Poly(methacrylic acid)

The study illustrates how rheology and electrokinetics can be utilized in the investigation and optimization of the properties of ceramic suspensions. Zeta potential studies show that the isoelectric point of TiN particulates is at pH=4, and for the pH range used, PMAA–NH₄ addition results in a more negative zeta potential value. The rheological behavior of titanium nitride in the presence of PMAA–NH₄ is strongly dependent on pH and three rheological types have been defined.     

Electrokinetic Properties of Colloidal Zirconia Powders in Aqueous Suspension

Pure zirconia, yttria, and three yttria-doped zirconia powders of submicrometer size have been dispersed in various aqueous solutions. The zeta potential (zeta) of the zirconia powders is determined primarily via streaming-current (SC) detection and is confirmed using electrophoretic spectroscopy techniques. The results reveal that the isoelectric point (IEP) of these zirconia powders is in the pH range of 5.6-7.2 and zeta is controlled primarily by the yttrium content of the zirconia powders and the type of electrolyte. In addition, the yttria content strongly affects the potential and SC in zirconia suspensions only at high solids contents (>1 vol%). The electrokinetic data reveal that the surface of the yttria-doped tetragonal zirconia powder (TZP) can be modified via the adsorption of ionic molecules or polymeric species in the suspension. The adsorption of an anionic polymer can stabilize zirconia particles in a solution that is almost neutral or weakly basic (in the IEP range of pure ZrO₂). The interaction of the zirconia and yttria particles with the electrolytes in an aqueous suspension will be discussed to reveal the roles of hydrated oxide formation and zirconia surface interaction with polymeric dispersants.     

Acoustophoretic studies of aqueous suspensions of alumina and 8 mol% yttria stabilised zirconia powders

The iso electric points (IEPS) of four alumina powders and three 8 mol% yttria stabilised zirconia powders were investigated using acoustophoresis to measure the zeta potential as a function of pH. All the powders were characterised by X-ray fluorescence spectroscopy for elemental composition and BET nitrogen adsorption for surface area. Initial experiments revealed that the IEPS of the alumina powders were independent of the volume fraction of the alumina suspensions. Further experiments investigated the effect of adjusting the pH with different bases, i.e. NaOH, KOH, and NH₄OH, on the IEPS of the alumina powders. The IEP of an individual powder was independent of the base used, however, the degree of hysteresis varied depending on the polarisability of the cation. The smallest degree of hysteresis was recorded with additions of NaOH. The differences in IEP between the alumina powders were attributed to the different surface chemistries of the powders. For the zirconia powders the IEP of each suspension was identified using HCl and NaOH to adjust the pH. Again the differences in the IEP were attributed to different surface chemistries of the powders. Two of the powders demonstrated an IEP of approximately 6.5; however the Tosoh powder suspension demonstrated considerable hysteresis and an IEP of 9.3. This was due to its natural pH being an approximate pH unit lower than the other two powders. At this lower natural pH, yttria dissolved out of the Tosoh powder, generating yttrium ions in solution. These precipitated onto the powder surface and altered the surface chemistry with time; i.e increased the zeta potential. Atomic absorption experiments on the supernatant confirmed the dissolution of the yttria from the Tosoh powder.     

Yield Stress of Alumina-Zirconia Suspensions

The yield stress of concentrated suspensions of alumina, zirconia, and mixed alumina-zirconia powders was measured by the vane technique as a function of solids loading, relative amounts of alumina and zirconia, and pH. At the isoelectric point (IEP), the yield stress varied as the fourth power of the solids loading. The relative ratio of alumina and zirconia particles was important in determining the yield stress of the suspension at the IEP. The yield stress of single and mixed suspensions showed a marked variation with pH. The maximum value occurred at or near the IEP of the suspension. The effect of electrical double-layer forces on the yield stress can be described on the basis of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. A normalized yield stress—that is, the ratio of the yield stress at a given pH to the yield stress at the IEP predicted by this model—showed good correlation with experimental data.     

The zeta potential and surface properties of asphaltenes obtained with different crude oil/n-heptane proportions

We have investigated some surface properties of asphaltenes precipitated from crude oil with different volumes of n-heptane. According to the crude oil/n-heptane proportions used, asphaltenes are identified as 1:5, 1:15 and 1:40. Zeta potential results indicate that the amount of n-heptane determines the electrokintetic behaviour of asphaltenes in aqueous suspensions. Asphaltene 1:5 exhibits an isoelectric point (IEP) at pH 4.5 whereas asphaltenes 1:15 and 1:40 show an IEP at about pH 3. Surface charge on asphaltenes arises from the dissociation of acid functionalities and the protonation of basic functional groups. The presence of resins remaining on the asphaltene molecules may be responsible for the different IEP of asphaltene 1:5. Both sodium dodecyl sulfate (an anionic surfactant) and cetylpyridinium chloride (a cationic surfactant) were found to adsorb specifically onto asphaltenes. They reverse the sign of the zeta potential under certain conditions. These surfactants may be potential candidates to aid in controlling the stability of crude oil dispersions. Critical micelle concentration, interfacial tension measurements, and Langmuir isotherms at the air-water interface confirm the different nature of asphaltene 1:5, which also showed more solubility and a larger molecular size.     

Relationship between the colloidal and rheological properties of mineral suspensions

The electrokinetic and rheological behaviour of lateritic aqueous suspensions has been analyzed as a function of samples chemical composition, pH of suspensions, and nature and concentration of electrolyte added to the aqueous suspensions. First, it was determined that the isoelectric point (IEP) of suspensions in the presence of non‐adsorbing electrolytes is a function of the ratio serpentine/ goethite present in samples. The flow properties of the suspensions are strongly dependent on pH, reaching the highest values of apparent viscosity at values around the isoelectric point. Specific adsorption of silicate and magnesium species on particles surface was revealed by a shift in the IEP. In particular, silicate anions shifted the IEP value to acidic pH whilst magnesium cations shifted the value to basic pH. A similar trend was displayed in the rheological behaviour of suspensions where the highest viscosity values were shifted to the same direction.     

Electrostatic and electrosteric stabilization of aqueous suspensions of barite nanoparticles

Electrostatic and electrosteric stabilization of aqueous suspensions of barite nanoparticles were investigated. The state of dispersion was evaluated in terms of zeta potential, apparent viscosity and the mean particle size of solid phase in the solution. Zeta potential, apparent viscosity and the mean particle size as a function of pH were performed in absence of dispersant. The result showed that electrostatic stabilization of the aqueous suspension of barite nanoparticles can be accomplished in low acidic and high basic range of pH. In presence of sodium polyacrylate (PAA-Na) dispersant, the isoelectric point (IEP) of the barite nanoparticles was shifted to lower pH and the negative zeta potential was increased in a large range of pH above the (IEP). The optimum amount of PAA-Na dispersant is discussed in the light of zeta potential and viscosity. It is found that the adsorption of PAA is correlated to the net surface charge of the barite nanoparticles and the fraction of dissociated polymer at pH 4, 8.5 and 10. At pH 4, the state of dispersion was achieved at higher amount of electrolyte due to the low fraction of negatively charged dissociated polymer and the positively charge particles. At basic pH, the fraction of dissociated polymer was high and the surface charge of particle was highly negative, therefore, the lowest viscosity was obtained at a small amount of PAA. In addition, the optimum amount of polymer decreased with the increase in pH of the suspension.     

Influence of Acidity on the Stability and Rheological Properties of Ionically Stabilized Alumina Suspensions in Ethanol

The ionic stability of alumina particles in moderately concentrated ethanol suspensions is studied. Surface chemistry and interparticle forces are manipulated by controlling the acidity of the suspensions without dispersants. The acidity of ethanol solution is determined using ion transfer functions, wherein the relationships between acidity, alumina particle surface charge, zeta-potential, stability, and suspension rheological behavior are established. Positive isoelectric point (IEP) shift is observed for alumina in ethanol on increasing the solids concentration. However, dilute and concentrated aqueous suspensions of alumina give the same IEP. The viscosity and flow curves for alumina/ethanol suspensions are acidity dependent. The flow curves of the suspensions follow the Casson model, and the Casson yield value is used to evaluate suspension stability.     

Properties of Porous Si3N4/BN Composites Fabricated by RBSN Technique

Reaction bonding of silicon nitride (RBSN) technique combined with slip-casting shaping process was used to fabricate porous Si₃N₄/BN ceramic composites. Si/BN slurry with chemical stability, good dispersibility, and viscosity was prepared using glycerol trioleate (GTO) covering on Si surface and poly(acrylic acid) (PAA) as dispersant. The hydrolysis of Si was strongly prevented by GTO coating. The dispersibility of covered Si and BN suspensions were improved by PAA dispersant. Twenty volume percent covered Si/BN slurries with low viscosity were successfully casted. The cast bodies were dried at room temperature, debindered at 750°C and nitrided below 1450°C. The nitrided samples mainly consist of α-Si₃N₄, β-Si₃N₄, and h-BN. The composites exhibit homogeneous microstructure consisting of faceted particles, α-Si₃N₄ nanowires and a large amount of pores. The porosity is 52.64% and the pore size is in the range of 60–300 nm. The composites show compressive strength of 16.6±1.5 MPa. The dielectric constant of the composite is about 3.1 and the dielectric loss is below 0.5% under different frequencies.     

The isoelectric point of BaTiO3

The value of the isoelectric point (IEP) of BaTiO₃ is highly significant for the development of a fully rational basis for the successful processing of BaTiO₃ powder by aqueous routes. We report here experimental evidence that the true IEP value for BaTiO₃ is in the neutral pH range (6–7). However, Ba²⁺ ions are also selectively adsorbed at BaTiO₃ particle surfaces, raising the ζ-potential; IEP values greater than pH 7 can occur when the concentration of Ba²⁺ in the aqueous phase is high. Studies of the effects of Ba²⁺ and CO₃²⁻ additions on the ζ-potential of BaTiO₃ and on the rheology of aqueous suspensions, indicate that the reason for the wide range of ζ-potential and IEP values found for BaTiO₃ is in large measure the presence of impurity BaCO₃ in the BaTiO₃ powders used. Fully dehydrated BaTiO₃ powder has a low IEP value (∼4), which slowly rises on ageing in water. The IEP appears not to be influenced by Nb₂O₅ doping at the levels normally used.