Stability Of Alumina Suspension Research Articles

Improvement in dispersion stability of alumina suspensions and corresponding chemical mechanical polishing performance

The dispersion stability of alumina suspensions is an obstacle to its large-scale application for chemical mechanical polishing (CMP) since the aggregation of particles will cause scratches on the wafer surface during polishing. Therefore, this study was devoted to improving the physicochemical properties of alumina suspensions using different polymeric dispersants, including polyethylene glycol (PEG) with nonionic properties, sodium polyacrylate (PAAS) with anionic properties, and their triblock copolymer poly(acrylic acid)-b-PEG-b-poly(acrylic acid) (PAEG). The characterization results of dispersion stability showed that, compared with PEG and PAAS, the suspensions containing a suitable dosage of PAEG exhibited the advantages of low-viscosity (Viscosity < 3 mPa·s), good-stability (Zeta potential < -50 mV), and monodisperse (Polydispersity index < 0.1). The adsorption isotherm indicated that the adsorption of dispersants on alumina particles was consistent with Langmuir model. Furthermore, the total potential energy between particles in suspension was calculated for theoretical analysis of the inter-particle interactions. Besides, the dispersion mechanisms of PEG, PAAS, and PAEG were proposed as steric stabilization, electrostatic stabilization and electrosteric stabilization, respectively. Finally, CMP experiments showed that the suspension prepared by using PAEG as a dispersant to polish SiC substrates resulted in better removal rates (382 nm/h) and lower surface roughness (Ra: 1.85 nm).

Stabilizing properties of fucoidan for the alumina suspension containing the cationic surfactant

The paper presents the influence of fucoidan (FD) on stability of alumina suspensions in the presence of cationic surfactant hexadecyltrimethylammonium bromide (CTAB). The research results show that fucoidan adsorbs on the alumina surface and that the adsorption decreases in the CTAB presence. This is due to formation of the polymer-surfactant complexes characterized by lower affinity for the alumina surface than pure fucoidan. The complex formation was confirmed by the tensiometric studies where the increase of the CTAB/FD surface tension in comparison to pure CTAB was observed. It was established that fucoidan possesses great stabilizing efficiency regardless of pH. Furthermore, stability of the fucoidan/alumina system increased after CTAB addition due to the presence of non-adsorbed complexes between the alumina particles. The results indicate that fucoidan could be successfully used as a stabilizer of colloidal suspensions where the presence of surfactant is required, that is in cosmetic and pharmaceutical industries.

Complexes of fluorinated, silicone and hydrocarbon surfactants with carboxymethylcellulose and their influence on properties of the alumina suspension

The aim of this study was to investigate the influence of different types of surfactants on the adsorption, stability, and electrokinetic properties of the carboxymethylcellulose/alumina system as well as the interactions between the surfactants and the polymer. The authors decided to use fluorinated and silicone surfactants besides the conventional hydrocarbon ones. The obtained results showed that carboxymethylcellulose (cmc) adsorption increased in the presence of surfactants due to the formation of polymer-surfactant complexes (the increase of the adsorption from about 0.020 mg m−2 for pure cmc to 0.030 mg m−2 for MTAB/cmc and SJ2/cmc mixtures). The obtained complexes of 0.00336% MTAB/cmc and 0.004% S-106a/cmc reduced the surface tension of water more efficiently than pure surfactants of the same concentration (from 70.06 to 62.39 mN/m and 71.06 to 64.26 mN/m respectively). Stability of the alumina suspension was studied as well. The obtained results indicate that the addition of carboxymethylcellulose, surfactants, and the cmc-surfactant complexes leads to the increase of alumina suspension stability. The mechanism responsible for stabilization was electrosteric one. The largest stability was observed for the systems containing the mixture of cmc and surfactants. The reason for this is the formation of the adsorption layer composed of alternately arranged regions of polymer and surfactant complexes. Electrokinetic measurements of the studied systems allowed to describe the structure of the electrical double layer and to determine the point of zero charge of alumina (pHpzc ≈ 7.5). The addition of the polymer as well as surfactants leads to the charge reversal of alumina.Graphical abstract.

Stability of aqueous suspensions of alumina particles with adsorbed (carboxymethyl)cellulose

The influence of the counterion condensation on the colloid stability of alumina suspension with added carboxymethylcellulose (CMC) is investigated by electric light scattering and microelectrophoresis. The electrophoretic mobility μ and the interface ion polarizability γ are used as criteria for the effective charge of CMC-alumina particles. The light scattering intensity I0 and the field-strength dependence τ(E2) of the relaxation time τ are used as criteria for aggregation. The polymer-concentration dependences μ(CCMC), γ(CCMC) and I0(CCMC) under and above the recharging point are measured at different degrees of proton dissociation α and fraction φ of counterions condensed on the adsorbed polyelectrolyte chains: α≈1/2, φ=0 at pH 4.5, and α≈1, φ≈1/3 at pH 6.0. The results show out that the colloid stability is conditioned by the effective charge of CMC-alumina particles determined by the surface charge, the dissociated carboxylic groups of CMC chains and the condensed counterions. The particle aggregation about the recharging point (at 1:50 CMC/alumina) is explained with hetero-coagulation by polyelectrolyte chain bridging conditioned by the reduced total charge, surface charge-patches, low surface occupation and the high rigidity of CMC chains.

Investigation of Removal Possibilities of Colloidal Alumina from Aqueous Solution by the Use of Anionic Polyacrylamide

Purification of drinking and industrial water required usage of high molecular weight polymer to cause flocculation process of dispersed suspension of contaminants. Polyelectrolytes, including ionic polyacrylamide are especially appropriate for these purposes, because in this case the suspension stability can be controlled by both steric and electrostatic forces. Thus the influence of solution pH and hydrolysis degree (carboxyl groups content) of anionic polyacrylamide (PAM) on the alumina (Al2O3) suspension stability were studied. The turbidimetry was applied for determination of the examined systems stability. The mechanism of suspension stabilization or destabilization in the polymer presence was proposed on the basis of determined parameters: adsorbed amount of PAM, its adsorption layer thickness, linear dimensions of macromolecules in the solution and zeta potential of alumina particles covered with the polyacrylamide layer. The greatest decrease of the alumina suspension stability in the polymer presence in comparison to that without the polymer was obtained at pH 6 after the addition of PAMs with higher molecular weight (i.e. 14 000 0000) and hydrolysis degrees 20 and 30% (efficient neutralization of solid surface charge). In turn, the most unstable alumina system proved to be that prepared at pH 9 containing PAM with the highest molecular weight and the greatest hydrolysis degree (causing the most effective bridging flocculation).

Effect of the presence of cationic polyacrylamide on the surface properties of aqueous alumina suspension-stability mechanism

The effects of solution pH and the content of cationic groups in polyacrylamide (PAM) macromolecules on the stability mechanism of aqueous alumina suspension were investigated. The following experimental techniques were applied: spectrophotometry, potentiometric titration, microelectrophoresis, viscosimetry and turbidimetry. They enable determination of polymer adsorbed amount, surface charge density and zeta potential of solid particles in the presence and absence of PAM, as well as thickness of polymer adsorption layer, size of macromolecules in the solution and stability of the Al2O3–polymer systems, respectively. The obtained results indicate that adsorption of PAM increases with the increasing pH, whereas the thickness of polymeric adsorption layer decreases. Additionally, the greater the number of cationic groups in the PAM chains is, the higher adsorption was found. The polymer presence influences on the alumina suspension stability. At pH 3 and 6 the slight deterioration of stability conditions of solid particle covered with polyacrylamide was observed. At pH 9 the systems containing polymer are unstable, similarly to the suspension without PAM, but the mechanism of their destabilization is different.

Carboxymethyl Chitosan: Preparation and Use in Colloidal Ceramic Processing

The use of natural macromolecules from rejects of the fishing industry, such as chitosan and derivatives, may be advantageous in replacing synthetic polymers to stabilize ceramic suspensions. In this paper, a carboxymethylated chitosan (CMCh) was synthesized, characterized with FTIR, 1H NMR and SEC methods, and tested as stabilizing agent of alumina suspensions. Close to the point of zero charge (pzc) of the alumina suspensions (approximately pH 7), the incorporation of only 0.2 wt% of CMCh (DS, degree of substitution, 0.8) caused the suspension viscosity to decrease from ca. 40 × 103 Cps to approximately 16 × 103 Cps. This decrease in viscosity was accompanied by a decrease in particle size, as the incorporation of CMCh led to a narrower distribution of smaller particles. Furthermore, at the pzc of the aqueous alumina suspension, negative zeta potentials were measured when CMCh was added. Upon combining information from viscosity, particle size and zeta potential, it was possible to infer that CMCh induced the stabilization of alumina suspensions via steric and electrosteric effects. Because the latter can be tuned by changing parameters of the suspensions as well as of the CMCh derivatives, one may envisage further applications of alumina suspensions with tailored properties.

Influence of pH Value and Dispersants on the Alumina Suspension Stability

Alumina microparticles were synthesized by sol-gel method with aluminum isopropoxide as raw material, octanol and acetonitrile as solvent. The influence of pH value and three kinds of dispersants on the alumina suspension stability were discussed in water system. We find that The optimal pH value range of application for alumina suspension is 4-5 or 10-11, which has the biggest absolute value of Zeta potential, and alumina suspension has a good dispersion when Span-20 used as dispersant.

Investigation of the stability of an alumina suspension in the presence of ionic polyacrylamide

The influence of solution pH on the adsorption mechanism of polyacrylamide (PAM) on the alumina surface and stability of its suspension in the presence of polymer were investigated. The structure of polymer adsorption layer was determined from the spectrophotometric, viscosity, surface charge and zeta potential measurements which enable determination of adsorbed amount of polymer, thickness of the polymer adsorption layer, surface charge density and zeta potential of Al2O3 particles in the absence and presence of PAM. The measurements of stability of alumina suspension without and with adsorbed polyacrylamide were also carried out using two methods: spectrophotometry and turbidimetry. The obtained results indicate that solution pH influences the structure of PAM adsorption layer (decrease of adsorbed amounts of polymer and increase of its adsorption layer thickness with the increasing pH). These conformational changes of polyacrylamide molecules with the rising pH have an impact on stability of the alumina suspension. The most pronounced effect of polymer on the stabilization properties of investigated systems is observed for PAM addition at pH 6 resulting in a great destabilization of the alumina particles by bridging flocculation.

Studies of the Alumina Suspension Stability in the Presence of Anionic Polymer—Influences of Polymer Molecular Weight, its Concentration and Solution pH

The effect of an anionic polymer—polyacrylic acid (PAA) adsorption on the alumina (Al2O3) suspension stability was studied. The influence of the following parameters was examined: polymer molecular weight, its concentration and solution pH. Two methods were used to monitoring the suspension stability: turbidimetry and spectrophotometry. The conformational changes of macromolecules, both adsorbed and non-adsorbed, determine the stabilization—flocculation properties of the alumina suspension in the presence of the polymer.

The Spectrophotometric Investigation of Nonionic Polymer Adsorption (Polyethylene Glycol (PEG), Polyethylene Oxide (PEO) and Polyvinyl Alcohol (PVA)) Influence on the Alumina Suspension Stability – Effects of Polymer Type, its Molecular Weight and Solution pH

The effect of nonionic polymer adsorption on the stability of alumina (Al2O3) in the pH range 3–9 was examined. The influences of polymer type and its molecular weight, as well as solution pH, were studied. The following macromolecular substances were used: polyethylene glycol (PEG), polyethylene oxide (PEO) and polyvinyl alcohol (PVA). The spectrophotometry method was applied to obtain the stability curves (dependence of suspension absorbance vs. time). The obtained results indicate that the addition of the polymer influences alumina suspension stability. The addition of the polymer at pH 3 improves the stability conditions of investigated systems. At pH = 6 the decrease of Al2O3 suspension stability (except PEG 2 000) was obtained. On the other hand, at pH 9 the presence of polymer improves the stability properties of the alumina. The higher the molecular weight of the polymer, the more pronounced effects were observed. Moreover, adsorption of polyvinyl alcohol whose macromolecules contain ionizable acetate groups causes greater changes in alumina suspension stability in comparison to the systems containing polyethylene glycol and polyethylene oxide.

Carboxymethyl lignin as stabilizing agent in aqueous ceramic suspensions

Identifying new uses for residues of industries that process large quantities of biomass, as in bioethanol production, is essential for a sustainable development with reduced impact on the environment, which is the reason why many efforts have been devoted to find noble uses for lignins. In this study, a lignin obtained from sugarcane bagasse in a bioethanol producing plant was carboxymethylated to yield the water-soluble carboxymethyl lignin (CML), which was then used as stabilizing agent in aqueous alumina (Al2O3) suspensions. CML had a degree of substitution 0.46±0.01, in relation to the C9 unit of lignin, and behaved as a polyelectrolyte in a large pH range owing to the dissociation of carboxylic groups. The action of CML as stabilizing agent of alumina aqueous suspensions was investigated using viscometry, zeta potential, and photon correlation spectroscopy (PCS) measurements, mainly as a function of pH and time. Overall, the results showed that CML had a good performance as a deflocculating agent, because it led to dispersions with low viscosity and small change in particle size as a function of time. The positive effect from the addition of CML was confirmed in the morphological features of the material obtained from the alumina suspensions after elimination of water, as indicated by scanning electron microscopy. The stabilization of alumina suspensions afforded by CML opens the way for similar applications of modified lignins, whose electrical and structural properties may be tuned for specific uses in various industries, including the ceramic industry.

Effect of D-sorbitol on Rheology of Aqueous Alumina Suspensions with Poly(Acrylic Acid)

研究了D-山梨醇(D-sorbitol)对聚丙烯酸(poly(acrylic acid))(PAA)稳定的水基氧化铝(Al 2 O 3 )悬浮液流变性能的影响. 实验发现: 在pH为9.0时, 对于固含量为30vol% ~ 40vol%的Al 2 O 3 悬浮液, 少量D-山梨醇的加入皆能明显提高其分散稳定性. 当D-山梨醇的添加量占分散剂总量(0.5wt%)的20%时, 悬浮液粘度最低. 且添加二元分散剂PAA/D-山梨醇的悬浮液具有更好的抗电解质性能. 分别对单一PAA分散的Al 2 O 3 及二元分散剂分散的Al 2 O 3 进行了红外光谱表征. 结合流变与红外实验结果, 分析了山梨醇的作用机理: 部分山梨醇吸附在Al 2 O 3 颗粒表面, 部分山梨醇与PAA以氢键形式结合, 增大了颗粒间的空间位阻, 提高了悬浮液的流变性能.

Investigating the Dispersion State of Alumina Suspensions: Contribution of Cryo-Field-Emission Gun Scanning Electron Microscopy Characterizations

We illustrate in this paper the interest of cryo-field-emission gun scanning electron microscopy (cryo-FEGSEM) to investigate the stability of alumina suspensions. The stability is investigated through viscosity, zeta potential, total organic carbon measurements, and cryo-FEGSEM observations. We focus on two examples: the effect of the quantity of ammonium polyacrylate as dispersant and the effect of its chain length on alumina particles dispersion with a solid content of 32 vol%. In the first example for some suspensions, we measure values of viscosity or zeta potential too similar to discriminate the best state of dispersion. To overcome this problem, we directly observe the suspensions with cryo-FEGSEM. We take advantage of the recent developments of the technique, which provide now extremely high cooling rates and ensure that the freezing step does not induce observations artifacts related to the formation of ice. This technique provides an accurate vision of particles dispersion, agglomeration in ceramic suspensions, and it is possible to visualize the excess of dispersant. In the second example, the longer dispersant appears to be the more effective to obtain the best state of dispersion. Through both examples, we demonstrate that to have the best interpretation of results, it is useful to combine direct observations by cryo-FEGSEM and the usual properties measurements.

Derivatives of biomacromolecules as stabilizers of aqueous alumina suspensions

AbstractThe stabilization of alumina suspensions is key to the development of high‐performance materials for the ceramic industry, which has motivated extensive research into synthetic polymers used as stabilizers. In this study, mimosa tannin extract and a chitosan derivative, that is, macromolecules obtained from renewable resources, are shown to be promising to replace synthetic polymers, yielding less viscous suspensions with smaller particles and greater fluidity, that is, more homogeneous suspensions that may lead to better‐quality products. The functional groups of tannin present in mimosa extract and N,N,N‐trimethylchitosan (TMC) are capable of establishing interactions with the alumina surface, thus leading to repulsion between the particles mainly due to steric and electrosteric mechanisms, respectively. The stabilization of the suspension induced by either TMC or mimosa tannin was confirmed by a considerable decrease in viscosity and average particle size, in comparison with alumina suspensions without stabilizing agents. The viscosity/average particle size decreased by 49/84% and 52/87% for suspensions with TMC and mimosa tannin, respectively. In addition, the increase in the absolute zeta potential upon addition of either TMC or mimosa tannin extract, especially at high pHs, points to an increased stability of the suspension. The feasibility of using derivatives of macromolecules from renewable sources to stabilize aqueous alumina suspensions was therefore demonstrated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Interaction and dispersion stability of alumina suspension with PAA in N,N′-dimethylformamide

The alumina suspension in N,N′-dimethylformamide (DMF) was studied in the presence of a polyacrylic acid (PAA) dispersant. The sedimentation measurements of the suspensions show that PAA can impart favorable dispersion stability to alumina in DMF over a wide apparent pH (pH a) range. The adsorption of PAA on alumina and the zeta potential of the suspension are pH a dependent. FTIR-ATR spectroscopic studies reveal that the different interaction mechanisms between PAA and alumina work as a function of pH a. But the observable difference of dispersion between pH a values of 2.6–12.7 is small according to the sedimentation experiments. This can be explained by a combination of the static effect of PAA dispersant and different sizes of steric barrier resulting from the configurational variation of PAA with changing pH a values.

Influences of polyacrylic acid adsorption and temperature on the alumina suspension stability

The temperature influence on the alumina (Al 2O 3) suspension stability in the absence and presence of polyacrylic acid (PAA) was studied. The investigated temperature range was 15–35 °C. Stability measurements were carried out by the use of Turbiscan Lab Expert with a thermostatic system. Additionally, at 25 °C the suspension stability was determined from the spectrophotometric data. The obtained data and calculated values of Turbiscan Stability Indexes (TSI) suggest that for the alumina suspensions without polymer, the values of TSI and the rates of solid particles settling as well as the thickness of sediment were the lowest at all investigated temperatures. Moreover the PAA adsorption causes pronounced decrease of system stability at 15 and 35 °C while at 25 °C polyacrylic acid adsorption slightly improves the alumina stability. The conformational changes of adsorbed polymer macromolecules are responsible for such behaviour of the investigated systems. At all investigated temperatures the solid suspension is not stable in the presence of PAA. In the case of PAA 2 000 the coagulation by charge neutralization takes place, whereas in the case of PAA 240 000 the bridging flocculation is the most probable process. The destabilization of systems by the adsorbed polymer occurs with the lowest effectiveness at 25 °C.

Stability of alumina suspensions in the presence of Tiron

The stability of alumina suspensions in the presence of Tiron was studied and discussed in the light of surface properties of alumina powder used, ionization chemistry of Tiron, and sedimentation behavior of the suspensions. The point of zero charge of alumina with and without addition of Tiron was determined using a batch equilibration method. The sedimentation of the suspensions was evaluated via screen sedimentation tests as a function of pH and Tiron concentration. The dissociation constant, p K a1, of the hydroxyl groups of the Tiron molecule was determined by potentiometric titration carried out in water and KNO 3 as a background electrolyte. Tiron was shown to adsorb specifically onto the alumina surface in the examined pH range 4–10, but impart stability to the suspensions only at pH ≥ 6.

Dispersing Properties of Copolymers Able to Act as Binders

Macromolecules, containing both charged groups (COO− and SO3−), in order to ensure powder dispersion, and neutral groups (vinyl alcohol and ethyl hydroxyl acrylate), in order to obtain enough strength in the green parts, were synthesized to be used in the dry pressing process. The evaluation and the comparison of the capacity of these synthesized copolymers with disperse alumina particles in aqueous media are considered in this paper. Both COO− and SO3− ionized groups are responsible for strong adsorption onto alumina surface and can promote sufficient electrostatic repulsive forces to achieve a good state of dispersion. The role of the copolymers in the stabilization of alumina suspensions was found to be greatly affected by the nature and by the fraction of groups in the macromolecular chains. A low concentration of copolymers (0.5 wt% on alumina basis) containing 35% of carboxylic groups and 65% of vinyl alcohol groups (PV35) or containing 55% of carboxylic groups and 45% of hydroxy ethyl acrylate groups (EH2A55) leads to stable alumina suspensions with a low viscosity similar to that obtained with a classical ammonium polymethacrylate (between 10 and 20 mPa·s for 27 vol% alumina suspensions). Copolymers containing sulfonate groups are less efficient.

Effects of poly(acrylic acid) and poly(ethylene oxide) adsorption on the stability of alumina suspension

The effect of adsorbed polymer on the stability of alumina suspension was investigated. Poly(ethylene oxide) (PEO), poly(acrylic acid) (PAA) and similar kinds of polymer salts were used as a dispersant. The amount of polymer adsorbed on alumina surface and the suspension stability was measured. The pH, molecular weight, and concentration were considered as experimental parameters. PEO shows low affinity on the alumina surface while PAA has high affinity. In the case of PAA adsorption, the surface charge change by polymer adsorption influences suspension stability strongly, but not in the case of PEO adsorption. In simultaneous adsorption of PEO and PAA, the PAA concentration was fixed and PEO concentration was varied. The stability of suspension increased with increasing PEO concentration, and this is partly due to the steric stabilization by adsorption of PAA-PEO complex or adsorption of PEO through pre-adsorbed PAA and the depletion effect of non-adsorbed polymer. Suspension adsorbing sodium salts of PAA and poly(methacrylic acid) (PMA) each showed similar stability. But, when the PEO and these kinds of salts were added together to the suspension, the one with PAA sodium salt could keep a higher stability even with lower molecular weights of PEO compared with suspension with PMA sodium salt.