Influence of surfactants on the structure of the adsorption layer in the system: Carboxymethylcellulose/alumina

The influence of surfactants: anionic SDS, nonionic Triton-100 and their mixture (SDS/TX-100) on the structure of the adsorption layer in the system: carboxymethylcellulose (CMC)/alumina (Al₂O₃) was measured. The surface charge density of alumina and its zeta potential were determined in the presence of the CMC macromolecules and the surfactant particles. In order to gain more information about the structure of adsorption layer the amount of CMC adsorption in the presence of surfactants as well as the thickness of the CMC adsorption layer were determined. It was proved that in the presence of surfactants mixture (SDS/TX-100) the amount of adsorption of CMC is the highest and the obtained adsorption layer is the thickest. On the other hand, when Triton X-100 is added to the measured system the polysaccharide conformation is closely packed. The amount of adsorption is large but the thickness of the adsorption layer is relatively low. In the presence of SDS macromolecules of CMC form conformation expanded towards the bulk solution. Such a conformation is characterized by the smaller amount of adsorption of polymer but the larger thickness of the adsorption layer.     

Effectiveness of a dispersant for the thickening of alumina slurries whilst retaining the fluidity

Concentrated alumina slurries were fluidized in an optimum amount of polyacrylates (PAA) in the content region where a good dispersion was obtained. Dispersion was necessary, but not sufficient for fluidization. The expected role of PAA in the thickening was retention of a water-reducing ability to retain the fluidity. Thickening of the alumina slurry to the limit of retaining the fluidity was achieved by the amount of PAA at which the flow point showed a minimum. The flow of alumina slurries around the limit was approximated by the Bingham model which was characterized by the yield stress and the Bingham viscosity. The flow curves of the slurries containing insufficient PAA had a yield stress which decreased with increasing amount of PAA and disappeared at an optimum amount of PAA to give a minimum flow point. The yield stress again increased retaining the low Bingham viscosity with increasing amount of PAA, to exceed the optimum amount for molecular weights smaller than 10 000. On the other hand, the Bingham viscosity increased without increasing the yield stress with increasing amount of PAA, to exceed the optimum amount for molecular weights larger than 20 000. The effect of PAA on the dispersion and flow behaviour could be explained by the electrostatic stabilization based on the Derjaguin-Landau, Verwey-Overbeek (DLVO) theory for the PAA with a molecular weight smaller than 10 000, and by the steric stabilization for the PAA with a molecular weight larger than 20 000.     

Dependence of the rheological behaviour of electrostatically stabilized alumina slurries on pH and solid loading

Alumina slurries with different solid loadings were prepared using aqueous solutions of hydrochloric acid the concentrations of which were predetermined as suitable for dispersing media; their rheological behaviour was investigated with respect to the pH of the slurry. In regions of low pH (below 3.5), the viscosity of the slurries gradually increased with decreasing pH of the slurry, irrespective of the amount of solid loading. Near the isoelectric point of alumina (about pH 8–8.5), the viscosities of the slurries were high and dependent on the solid loading. The pH range which exhibits the regions with low viscosity narrows on increasing the solid loading. These results were interpreted using an interparticle potential energy diagram for the slurry system. © 1998 Kluwer Academic Publishers     

Apatite formation on collagen fibrils in the presence of polyacrylic acid

Recently, we reported the formation of bone-like apatite on collagen fibrils by biomimetic method. Compounds containing carboxyl moieties are believed to be effective in the formation of apatite. Polyacrylic acid [-CH2CH(COOH)-]n (PAAc) is widely used in dentistry. In the present study, the effect of PAAc in the formation of apatite from revised simulated body fluid (R-SBF) on collagen fibrils was studied. Two different experimental approaches were tried to study the effect of PAAc present in the collagen and in the R-SBF solution. In the first, collagen gel was soaked with 1 mg/ml PAAc (molecular weights 25000 and 100000) for the time intervals of 30 min and 6 h. The gels were then dried in air and incubated in R-SBF. Characterization of the precipitates formed on the collagen fibrils in gel showed that the formation of apatite was inhibited when soaked in PAAc for 6 h. In the second experiment, when PAAc (0.1 and 1.0 mg/ml) was mixed with R-SBF the microstructure of the precipitates formed on collagen fibrils was affected partially. Hence, it is confirmed that the presence of PAAc in the biomimetic environment of collagen affects the mineralization of apatite.     

硼硅酸盐玻璃/陶瓷流延浆料体系优化设计与烧结性能研究

借助高效流延成型工艺,探讨了多种溶剂组合与分散剂对玻璃/陶瓷浆料体系流变性能的影响,通过对玻璃/陶瓷料、塑化剂与粘结剂等配制浆料的组成配比进行优化设计,详细研究了浆料中各组成含量对流延生料带体积密度,以及对烧成后玻璃/陶瓷致密度、物相等微观结构与性能的影响。结果表明,适当的浆料组成类型及含量对提高试样的烧成致密度、降低高频介电损耗、改善微观结构均有明显的影响;850℃烧结试样10MHz测试,相对介电常数为7.7,介电损耗2.0×10-4,25~500℃热膨胀系数(7.30~7.65)×10-6/℃,满足模块级LTCC大面积高密度封装要求。     

Electrostatic charge distribution in the dielectric layer of alumina electrostatic chuck

Electrostatic charge and its distribution in the dielectric layer of TiO₂- and Cr₂O₃-added alumina electrostatic chucks has been studied. The electrostatic potential was evaluated at various applied voltages by an electrostatic potential meter and it demonstrated the existence of charges with opposite polarities. Direct SEM observation and toner development of the charged ceramic surface was carried out to clarify the charge distribution. The charge contrast was not uniform on the ceramic microstructure and the charge was distributed in the form of grains. Taking into consideration these results, the relationship between electrostatic charge distribution and ceramic microstructure is discussed.     

Influence of polyacrylic acid on the protective properties of the KORSOL inhibitor

Polyacrylic acid (PAA) is a dispersant of hardness salts. Its anticorrosion properties are better than the anticorrosion properties of the dispersants produced by the Nalko Firm. In the KORSOL composition, it does not reveal the synergetic action but does not deteriorate the protective properties of the inhibitor.     

Synthesis of strontium ferrite nanoparticles by coprecipitation in the presence of polyacrylic acid

Strontium ferrite nanoparticles were prepared by coprecipitation in a PAA aqueous solution. The average diameter of the mixed hydroxide precipitates was 3.1 nm. From the thermal analysis by TGA/DTA and the phase analysis by XRD, it was shown that the appropriate molar ratio of Sr/Fe in aqueous solution was 1/8 and the precursor could yield pure strontium ferrite after calcination at above 700°C. The average diameters of the strontium ferrite nanoparticles calcined at 700 and 800°C were 34 and 41 nm, respectively. The magnetic measurements indicated that their saturation magnetization (57-59 emu/g) reached 85-88% of the theoretical one and increased with the decrease of temperature at 5-400 K. Their coercivity values (55-67 Oe) were much lower than those reported earlier, revealing the resultant nanoparticles were superparamagnetic. All the magnetic properties observed reflected the nature of nanoparticles and also concerned with their morphology and microstructure.     

Covalent coupling of polyacrylic acid coated magnetic-nanoparticles to multi-wall carbon nanotubes for manipulation targets

This research effort investigated the chemical heterojunction between magnetic nanoparticles coated with polyacrylic acid and multi-wall carbon nanotubes (MWCNTs). Here, magnetic nanoparticles were covalently attached to open-ended nanotubes in the presence of diclohexylcarbodiiimide. Initial evidence demonstrated that short functionalised multi-wall nanotubes can be continuously connected at their terminals ends to build-up relatively large nanostructures. It has also been shown that magnetic-carbon nanotubes (CNTs) systems exhibited defined arrangements due to the influence of magnetic fields. Indeed, linear arrays of CNTs interconnected through magnetic nanoparticles were prone to be manipulated in the presence of a magnetic device. A potential application of these kind of magnetic nanostructures was shown here by successfully manipulating agarose beads in a buffer solution. These results suggest that the use of continuously connected magnetic nanostructures with non-modified sidewall surfaces will find potential applications in the area of bio-sensing, force transduction and cancer screening-manipulation among many others.     

The erosive wear of mild and stainless steels under controlled corrosion in alkaline slurries containing alumina particles

The erosive wear in an alkaline slurry containing alumina particles of three typical engineering materials, the mild steel BS 6323 (Fe-C), the AISI 410 stainless steel (Fe-Cr-C), and the AISI 304 stainless steel (Fe-Cr-Ni), was carried out, by means of rotating cylinder, three-electrode erosion-corrosion test, with a view to investigation into the roles of the typical elements and the mechanical and chemical properties in the erosive wear under simultaneous controlled corrosion. The total weight loss of erosion-corrosion was obtained by precision weighing and the result was compared and interpreted, for each material, by a full microscopical examination of the erosion-corrosion scars using scanning electron microscopy (SEM). It was found that the overall performance under erosion-corrosion in an descending order was the stainless steels AISI 304, AISI 410, and the mild steel, although the precise difference in performance was dependent upon the process conditions. Such a ranking of performance was not in total consistence with that expected only from the mechanical or the chemical property differences of the materials concerned. The individual contribution of each erosion and corrosion process was thus further separated through corrosion charge conversion using the Faraday's second law and the results were interpreted by discussion, on basis of the experimental and microscopical evidences, of the main factors that influenced the mechanical and wear behaviour, in conjunction with those influencing corrosion and passivity. Finally, schematic diagrams were proposed to outline the typical erosion and corrosion features thus obtained for all the three materials during erosion-corrosion.     

耐盐性聚丙烯酸类高吸水性树脂的研究进展

从高吸水性树脂的吸水机理出发,介绍了提高聚丙烯酸类高吸水性树脂耐盐性的方法,包括在聚丙烯酸类高吸水性树脂主链上引入多种亲水基团、改变交联剂的种类、接枝引入天然亲水性高分子化合物和无机物,并对耐盐性聚丙烯酸类高吸水性树脂今后发展趋势进行了展望。     

电渗析法浓缩回收稀土矿铵盐废液

介绍了采用离子交换膜电渗析法对硫酸铵废水进行浓缩回收的研究 .对诸多影响电渗析法浓缩和脱盐效果的工艺参数进行了试验研究 .结果表明 ,采用该法浓缩处理稀土矿铵盐废水是一条颇有前途的新型处理方法 .     

Optimization of the metakaolin geopolymer preparation for maximized ammonium adsorption capacity

Geopolymers are functional materials that can be used in various environmental applications such as adsorbents in pollutant removal from wastewaters. Metakaolin geopolymer (MK-GP) has been proven to be especially suitable for ammonium (NH₄ ⁺) removal. In this research, the optimal reagent and raw material ratios in the preparation of MK-GP in terms of NH₄ ⁺ adsorption capacity were investigated. The response surface methodology based on the face-centered central composite design was used to optimize the levels of three factors: the amounts of hydroxide, silicate, and metakaolin. In addition, the effect of Na or K as the charge-balancing cation was studied. Empirical models were fitted to the experimental data using multiple linear regression. The significance of the models was confirmed by means of analysis of variance. Optimal NH₄ ⁺ removal efficiency was achieved when the amounts of hydroxide and silicate were maximized, the amount of metakaolin was minimized, and Na-based reagents were used. These trends are most likely a result of optimized conversion of metakaolin into MK-GP.     

Fluidity and dispersion of alumina suspension at the limit of thickening by ammonium polyacrylates

The limit of thickening of an alumina suspension by ammonium polyacrylates (PAA) and its molecular weight dependence of the limit were determined from the lowering of the flow point to be a measure of simultaneous promotion of the thickening and the dispersion. PAA of a smaller molecular weight gave a lower flow point minimum and a thicker alumina suspension retaining fluidity up to 85 wt % alumina for PAA of molecular weight 2500. The suspension thickened to the limit has the smallest gap between the flow point and the wet point, supporting Daniel's statement on good dispersion. The average water layer thickness, calculated by dividing the amount of water of suspension at the limit of thickening by the particle numbers, indicated no linearity with the chain length of the PAA. The thickening for PAA with molecular weights smaller than 21 000 resulted in a limit in the average water layer thickness of 30 nm being accompanied by dilatant flow. The suspension at high solid loadings showed various extension features on the glass plate with changes in the PAA concentration around the flow point minimum. The flow behaviour of the alumina suspension around the limit of thickening was characterized by the Bingham model with two parameters of the yield stress, ₀, and the Bingham viscosity, . Increase in the fluidity on PAA addition was strongly attributed to a greater lowering of ₀ than of . A balanced ratio between the two parameters in the apparent viscosity under a suitable shear rate was suggested to be necessary for the flow of the castable thick suspension.     

Effects of alkali-metal ions on the thermal decomposition of ammonium metavanadate supported on alumina

The thermal decomposition of ammonium metavandate (AMV) supported on -alumina (11 mol) and treated with alkali-metal ions was investigated using differential thermal analysis (DTA), thermogravimetric analysis (TGA), infrared (i.r.) absorption spectroscopy and X-ray diffraction (XRD). The results revealed that the presence of alkali-metal ions did little to affect the thermal decomposition processes of AMV supported on alumina. However, these ions enhanced creation of V⁴⁺ ions by heating the samples in air at 400 °C. The oxides produced underwent a solid-solid interaction at 500–700 °C, forming alkali-metal vanadates. The formation of these spinels was found to be strongly dependent on the degree of diffusion and the concentration of the alkali-metal ions. Moreover, the addition of a higher concentration of alkali-metal ions inhibits the formation of aluminium vanadate while enhancing the crystallinity of - to -alumina.     

Formation of ZnS nanorods entrapped in polyacrylic acid (PAA) film

A simplistic approach for synthesis of zinc sulphide (ZnS) nanorods is reported. The synthesis of ZnS nanoparticles involved mixing of zinc acetate, sodium sulphide and acrylic acid in appropriate ratio at proper conditions, which formed the core. These nanoparticles were trapped in PAA by in-situ polymerization of acrylic acid and carefully casted into the film which resulted into entrapped nanorods in the polymer matrix. The nanoparticles as well as nanorods entrapped in PAA were characterized using high resolution scanning electron microscopy (SEM) for morphological investigations; energy dispersive X-ray analysis (EDAX) for composition and its crystalinity was checked using X-ray diffraction (XRD). The length of nanorods was in the range of 2–4 μm and thickness between 50–200 nm.     

二甲基烯丙基木质素季铵盐-海藻酸钠两性聚电解质的絮凝性能研究

为了扩大碱木质素的相对分子质量以及其对阳离子染料的应用范围,研究了以二甲基烯丙基木质素季铵盐(DL)和海藻酸钠(SA)为原料,制备二甲基烯丙基木质素季铵盐-海藻酸钠两性聚电解质(DL-SA)。采用FT-IR、SEM和TG/DTG表征了产物的结构,并考察了其两性聚合物的特点——等电点,结果表明,DL和SA接枝成功,其等电点为4.42,具有两性化合物的特征。以对酸性黑ATT和亚甲基蓝为模拟染料,研究了DL-SA对两种不同类型的染料絮凝影响因素(投加量、pH值和温度),确定了对两种染料的最佳絮凝条件以及最佳脱色率为酸性黑ATT 86.24%,亚甲基蓝99.15%,并初步探讨了其絮凝机理。     

介孔氧化铝的制备及其对As~(5+)的吸附性能研究

以异丙醇铝为铝源,非离子表面活性剂P123为模板剂,采用溶胶-凝胶法于室温下制备出介孔氧化铝,并研究了该介孔氧化铝对As~(5+)的吸附性能。就材料焙烧温度、初始pH值、接触时间、吸附剂量和吸附温度对吸附性能的影响进行探讨。结果表明,介孔氧化铝对As~(5+)的吸附性能随材料焙烧温度的升高而降低;随吸附温度的升高吸附速率加快,吸附平衡时间缩短;吸附性能受溶液pH值影响较大,pH值=4.5时吸附容量达到最大,此时最大单分子层吸附容量为51.02mg/g。     

Effect of adsorption behaviour of polyelectrolytes on fluidity and packing ability of aqueous graphite slurries

The effect of surface hydrophobicity on the adsorption behaviour of polyelectrolytes is investigated using graphite and alumina powder slurries. Graphite slurries containing carboxymethylcellulose (CMC) have a relatively low apparent viscosity and afford a sediment with a relatively high packing fraction as compared to that obtained when using sodium polyacrylate (Na-PAA) as a dispersant, although both have the same functional group. As a greater amount of CMC is adsorbed, it is concluded that its adsorption mechanism involves hydrophobic interaction, thus making it a better dispersant for hydrophobic powders in aqueous media. In contrast, Na-PAA is more effective in dispersing relatively hydrophilic powders such as alumina, as it adsorbs mainly through electrostatic interactions.