铸钢用消失模涂料流变特性的研究

本文选用不同耐火骨料，以钙化钠基膨润土、CMC为悬浮剂与粘结剂，制备了水基消失模涂料，并测试了涂料的悬浮性、流变性与触变性。研究了耐火骨料的种类、CMC加入量和钠基膨润土加入量对涂料流变特性的影响。结果表明：耐火骨料的粒度和密度是影响消失模涂料悬浮性的主要因素，棕刚玉涂料的悬浮性最好，流变曲线最为平缓，滞后环面积最大，触变性最好。当CMC加入量小于0．4％时，钠基膨润土加入量〈4％时，涂料具有一定的屈服值，且流变曲线较平缓；当CMC的加入量为0．3％，钠基膨润土的加入量为3％时，涂料具有较好的触变性，将获得较好的综合性能。     

Rheology of lecithin dispersions

Dispersions of lecithin (1–25% solids, dry basis) in soybean oil or water were subjected to rheological measurement in a coaxial-cylinder viscometer. The different rheological characteristics determined included yield stress, flow behavior index, consistency index, and apparent viscosity. Pseudoplastic behavior was observed for all lecithin emulsions in oil and for dispersions in water. The flow behavior indices for lecithin-oil emulsions (0.855–0.875) were higher than for lecithin-water dispersions (0.472–0.584). Yield stresses were observed only for lecithin-water dispersions. An increase in the concentration of lecithin in oil or water increased yield stress, consistency index, and apparent viscosity. The apparent viscosities of the lecithin-oil emulsions were higher than those for corresponding lecithin-water dispersions. The power law model can adequately fit (r≥0.988, p≤0.01) the shear-rate vs. shear-stress data for lecithin-oil emulsions, whereas the Herschel-Bulkley model was suitable (r≥0.988, p≤0.01) for lecithin-water dispersions.     

Surface modification of sepiolite particles with polyurethane and polyvinyl alcohol

Sepiolite is a clay mineral that has many industrial applications due to its advantageous properties such as white color, low specific gravity, high absorption capacity, chemical composition and low thermal conductivity. In this study, the effect of the addition of polymers, polyvinyl-alcohol and polyurethane, on the rheological properties of the sepiolite dispersions have been investigated. The rheological parameters of clay suspensions can be used to examine particle–particle interactions. The polymers that have been added to the clay suspensions interact with clay particles, depending on their ionic or non-ionic character. Firstly, the sepiolite dispersions were characterized by the rheological properties, mineral structure and content. Then the effect of the polymers on the flow, structural, and surface properties of sepiolite dispersions was investigated by rheological, electrokinetical, and scanning electron microscopy (SEM) measurements. The measurements showed that polymer molecules bind on the surface of sepiolite particles and changed the flow properties of the dispersions as stable dispersions at some certain concentrations. It is also determined that PU polymer covered the surface of the sepiolite faster than PVA, but the coverage of the PVA was much more smoothly. The thermal properties of the sepiolite improved with PVA more than PU, as a result of the homogenous surface coverage.     

Rheological study of dispersions prepared with modified soybean protein isolates

Structural modifications of modified soy protein isolates (SPI) were distinguished by rheological behavior. SPI were prepared by acidic (pH 2.5) and thermal-acidic treatment without (pH 1.6) and with neutralization (pH 8.0). Dynamic properties of dispersions were determined through the variation of storage and loss moduli with frequency, and loss tangent behavior was analyzed. Changes in viscoelastic parameters with protein concentration (10–12% wt/vol) and time of heating (15–60 min) were also determined. Flow properties of dispersions were estimated through apparent viscosity and flow and consistency index measurements. Rheological behavior of dispersions was compared with those found by experiment with commercial mayonnaise, mustard, and salad dressing. The analysis of rheological parameters showed that thermally treated isolates formed dispersions with high elastic modulus and consistency index with a structure mainly stabilized by hydrophobic interactions, although no gelation process after cooling was observed. From the rheological point of view, it was deduced that thermally treated isolates could be used as ingredients in the formulation of salad dressings. The alkaline sample would be more versatile because, depending on protein concentration and thermal treatment, the consistency of its dispersions was like that in salad dressing, or similar to those of mustard and mayonnaise.     

超高性能混凝土流变特性及其调控研究

为了实现超高性能混凝土(UHPC)流变特性的高效调控,采用膨润土作为辅助胶凝材料并对制备的UHPC进行了性能评估,包括UHPC浆体的流动度、静态屈服应力、动态屈服应力、塑性黏度和触变性,并系统分析了不同掺量的膨润土对UHPC浆体流变性能的影响。结果表明:随着膨润土掺量增加,UHPC浆体的流动度整体表现为下降趋势,下降幅度逐渐增大;当膨润土掺量由0%增加到15.0%(质量分数)时,UHPC浆体静态屈服应力、动态屈服应力和塑性黏度均显著增大,分别提高了约17.05倍、5.78倍和1.16倍;随着膨润土掺量增加,滞回环面积和触变指数增大,触变性得到明显改善。同时,掺入膨润土后仍然满足UHPC的优异力学性能要求。     

Rheological,electrokinetic, and morphological characterization of alginate–bentonite biocomposites

We prepared biocomposite gel dispersions involving sodium alginate (Na‐Alg) and calcium bentonite (Ca‐B) with various solid concentrations and characterized their rheological, electrokinetic, and morphological properties. The flow properties, such as the apparent and plastic viscosities, shear stress, and yield value point, changed with increasing clay dosage. The viscosities of the homogeneous dispersions were represented by the Herschel–Bulkley model. The ζ‐potential results were examined in the light of different characterization methods (X‐ray diffraction, Fourier transform infrared spectroscopy, and atomic force microscopy) to understand the interactions between the Na and Ca ions of the alginate biopolymer and bentonite clay. A plausible structural model for the alginate–bentonite composite gel, known as the egg‐box model, is proposed. The presence of Ca ions in the Ca‐B partially crosslinked Na‐Alg may be regarded as an excellent example of a self‐assembling process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na2CO3-activated Kütahya bentonite

The effect of the Na₂CO₃ activation on the rheological properties of a bentonite from Kütahya (Turkey) was investigated. The bentonite was activated with Na₂CO₃ at different dosages (1–15 g Na₂CO₃/100 g bentonite). The activated samples were examined by chemical and X-ray diffraction analysis. The calcium bentonite was completely converted to sodium bentonite when the Na₂CO₃/bentonite ratio was 2.5%. The rheological values showed a maximum after addition of 2.5% Na₂CO₃ (bentonite concentrations 2–6% w/w). At 2.5 g Na₂CO₃/100 g bentonite, the shear stress was also measured at several NaCl and Na-hexametaphosphate concentrations. NaCl addition decreased the rheological properties up to NaCl concentrations of 0.005 mol l⁻¹. Further addition of NaCl increased the rheological properties again. The addition of Na-hexametaphosphate caused a decrease in the rheological properties to a constant value higher phosphate concentrations. The lowest yield stress was obtained around pH 7.     

Smectites as colloidal stabilizers of emulsions: II. Rheological properties of smectite-laden emulsions

Oil-in-water emulsions were prepared by dispersing aqueous dispersions of several bentonites, montmorillonites, and hectorites (2% solid content) in paraffin oil which contained 100 mg/25 ml of a coemulsifier (alkyl polyglucoside, glycerol monostearate, lecithin, tetra- and deca(ethylene oxide) hexadecyl ethers). The colloidal stabilizers were sodium montmorillonite from Wyoming (USA), sodium bentonite from Kimolos (Greece), soda-activated bentonite from Milos (Greece) and Kimolos, also after decomposition of the carbonate. Three samples of synthetic hectorites (as synthesized, after washing, and after impregnation with sodium polyphosphate) were also used as colloidal stabilizers. The processing steps had strong effects on the rheological properties of the clay mineral dispersions. The rheological behavior of emulsions reflected these properties of the dispersions. Due to the presence of the dispersed oil droplets, the shear stresses of the emulsions were distinctly higher than the corresponding values of the dispersions and increased with the oil volume fraction. Their behavior changed from antithixotropic to thixotropic with increasing oil volume fraction. The storage modulus G′ of the emulsions with alkyl polyglucoside and glycerol monostearate showed no linear viscoelastic regions indicating the destructive character of the oscillation experiments even at the smallest deformation and the lowest frequencies. The structure of the emulsion was more stable in the presence of lecithin and ethylene oxide ethers and resisted to the shearing forces during the oscillation experiments as indicated by the observation of linear viscoelastic regions.     

Influence of nonionic polymers on the rheological and electrical properties of Egyptian bentonite

The rheological properties of Egyptian bentonite suspensions in the presence of nonionic polymers were investigated. Two different types of nonionic polymers were studied: poly(ethylene glycol) (molecular weight = 6000 g/mol) and poly(vinyl pyrrolidone) (molecular weight = 40,000 g/mol). The rheological properties (plastic viscosity, apparent viscosity, and yield point) of concentrated clay suspensions (6–8% w/w) at different temperatures after 24 h were determined. As the nonionic polymer concentrations increased, the rheological properties of the bentonite suspensions showed a slight increase, especially at an 8% clay content. The electrical properties (electrophoretic mobility and ζ potential) of Egyptian bentonite in the presence of different nonionic polymers were measured with a ζ meter. The results showed that the ζ potential of this bentonite was higher with 200 mg/L poly (vinyl pyrrolidone) than with 1000 mg/L poly(ethylene glycol). Potential energy profiles for bentonite suspensions for these nonionic polymers were constructed to show that the net energy barrier for bentonite suspensions followed repulsion or attraction between particles. These profiles showed that the potential energy profile of a bentonite suspension with 200 mg/L poly(vinyl pyrrolidone) produced a high repulsion potential energy between clay surfaces; that is, the suspension stability improved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

纳米二氧化硅对卡波姆凝胶流变行为的影响

采用红外光谱(FTIR)和扫描电子显微镜(SEM)分析了气相法二氧化硅(FS)和沉淀法二氧化硅(PS)的表面性质,结果表明,FS表面比PS含有更多的羟基,在水中分散性更好。利用流变仪对比研究了FS和PS对卡波姆956凝胶流变行为的影响规律,结果表明,FS和PS的加入均能明显提高卡波姆凝胶的弹性模量、屈服应力、触变性等流变学性质;在纳米二氧化硅质量百分数≤4%,FS在卡波姆凝胶中分散粒径较小且更均匀,其对上述流变学性质的增强作用大于PS;纳米二氧化硅质量分数从4%增大到8%时,PS形成大团聚体,能更好地提高上述流变学性质。结合SEM的测试结果阐明了FS与PS同卡波姆之间不同的相互作用方式。     

Extensional viscosity of silica dispersions

The rheological behavior in extensional flow was investigated for silica dispersions in polymer solutions using the tubeless syphon technique. The flow field of tubeless syphon is unsteady in the Lagrangian sense; hence the data are taken under transient stress conditions. Due to the insensitive nature of the extensional rate to flow rate, the extensional viscosities at different flow rates lie very close to a single curve, once they are plotted against strain. Two important points are noted with regard to the behavior of the dispersions. First, the extensional viscosity decreases with increasing particle concentration. Second, the viscosity growth curves of the dispersions can be superimposed by a vertical shift, but the curve shape differs from that of the medium. This implies a change in the relaxation time.     

Physicochemical characterisation and flow properties of some bentonite muds

In civil engineering technologies, bentonites mixed with water are commonly used as bentonitic mud. The choice and the definition of criteria for mud selection are a difficult problem for industrials. This paper proposes a data set obtaining from the physicochemical and rheological investigation of 16 different commercial bentonites. Several analytical techniques are used to determine the mineralogical composition of those powders including X-ray diffraction, DTA and chemical analysis. Physical parameters such as particle size, specific surface area, swelling index, cationic exchangeable capacity and exchangeable bases are also studied. The viscosity of the mud is tested, thanks to the classic Marsh funnel viscometer and the rheological properties (yield stress, plastic viscosity and thixotropy) are measured by a high-resolution rheometer (Stresstech). Mineralogical data show that the bentonite appellation covers a very large variety of materials. Even if the main mineral is smectite, the global analysis of the powders shows that commercial bentonites contain secondary minerals, salts and sometimes polymers. Rheological data obtained for established flow allow to define two families of bentonite mud which difference seems to be due to industrial treatments. In fact, each bentonite develops its own behaviour depending on multicriteria. The results from this study show that it is necessary to characterize the mud from mineralogical and rheological points of view and to take into account, the nature of the excavated soils in order to choose the best bentonite.     

高分子聚合物调控膨润土造浆性能及机理研究

基于江苏某蒙脱石含量为43%的钠化膨润土,对其进行造浆性能检测,发现该膨润土Φ600为5 mPa·s,滤失量为27 mL,造浆性能指标无法满足国标用土的要求,进而提出添加不同高分子聚合物来改善其造浆性能的方案。本文通过单因素试验研究了高分子聚合物对膨润土造浆性能的影响,并采用扫描电镜、傅里叶变换红外光谱、X射线衍射以及Zeta电位等分析手段探究不同高分子聚合物影响膨润土造浆性能的机理,再通过正交试验及优化试验,得到最优的高分子聚合物组合及用量。结果表明:高分子聚合物可吸附在膨润土颗粒表面,这不仅有利于晶格表面氢键的形成,还可形成网状结构,使得泥浆黏度增大,滤失量降低。当添加高分子聚合物为0.1%(质量分数)的聚丙烯酸钠+0.4%(质量分数)的羧甲基淀粉时,膨润土的Φ600为60.5 mPa·s,滤失量为14.5 mL,其他性能也均满足国标对泥浆土的要求。     

Rheological and electrical properties of bentonite in anionic polystyrene sulfonate and nonionic poly(vinyl alcohol)

The flow properties of bentonite were studied with a combination of anionic polystyrene sulfonate (molecular weight = 70,000 g/mol) and nonionic poly(vinyl alcohol) (molecular weight = 50,000 g/mol). This combination had a significant effect on clay suspensions depending on the sequence of the polymer addition. The addition of 50 mg/L anionic polystyrene sulfonate followed by 200 mg/L nonionic poly(vinyl alcohol) improved the rheological properties with a 7% bentonite suspension, especially at 20°C and after 24 h of aging. However, by the reversal of this addition sequence, the rheological properties of bentonite suspensions were reduced. The ζ potential of bentonite suspensions of the individual polymers at the same concentration was ?42 mV for polystyrene sulfonate and ?63 mV for poly(vinyl alcohol). The combined effect of anionic polystyrene sulfonate followed by nonionic poly(vinyl alcohol) noticeably changed the ζ potential (?95 mV). With the reversal of the addition sequence, this parameter did not change. Potential energy profiles were constructed to investigate the suspension stability. Potential energy profiles of polystyrene sulfonate added to bentonite suspensions and followed by poly(vinyl alcohol) produced high repulsion potential energy between clay surfaces, reflecting high suspension stability. By the reversal of this sequence, a significant reduction of the energy barrier was observed. On the basis of the rheological and electrical properties of this system, the addition of polystyrene sulfonate followed by poly(vinyl alcohol) provides a promising tendency for a 7% clay concentration to meet desirable drilling mud properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3886–3894, 2007     

Flow of a Robertson-Stiff Fluid Between Two Approaching Disks

The rheological behavior of drilling fluids, bentonite suspensions, cement slurries, and polymer gels has been found to be best described by the Robertson-Stiff model. Such fluids are pseudoplastic and are characterized by a yield value. The steady, isothermal, incompressible flow of these fluids between two disks approaching each other with constant relative velocity under the action of a normal load has been analyzed. A basic characteristic of such fluids is the presence of a plug core of zero velocity gradient in the region under consideration. The nature, extent, and shape of the core have been determined for various values of the model parameters. The plug core occurs symmetrically in the middle of the region between the disks. The thickness of the core increases from the periphery to the center of the disks. The pressure drop and the maximum value of the applied load have been calculated for various values of yield number and flow behavior index.     

Gelation of water–bentonite suspensions at high temperatures and rheological control with lignite addition

The effectiveness of lignite addition to prevent gelation of 6.42% w/w water–bentonite suspensions exposed to high temperatures has been studied, using twenty six lignites from various basins in Greece with variable organic and inorganic contents at concentrations of 0.5% and 3.0%. The lignite-free bentonite suspensions thickened considerably when heated at 177 °C for 16 h, as was indicated by a two-fold increase of the yield stress, when compared to samples hydrated only at room temperature. However plastic viscosity did not change appreciably. Full flow curves showed a Herschel–Bulkley behavior of all suspensions. Addition of lignite maintained the stability of the suspensions exposed to high temperatures (177 °C) by keeping the yield stress low and did not affect plastic viscosity. Some of the Greek lignites performed equally well with a commercial lignite product and improvements of 80 to 100% of the stability of the suspensions, compared to lignite-free suspensions, have been found. Lignite addition also lowered yield stresses for the hydrated samples. No specific trends have been identified between the effectiveness of lignites to stabilize bentonite suspensions and their humic and fulvic acids and humins content. However, those lignites with highest humic and fulvic acid contents have maximum stabilization capacity. Similarly, no specific trends have been observed between the stabilization capacity of lignites and their inorganic components such as oxygen and ash content and also with the cation exchange capacity. The effectiveness of the Greek lignites to stabilize bentonite suspensions is very high and the minor differences in the efficiency of the different lignites cannot be attributed solely to any specific component.     

Effects of Organotitanate Additions on the Dispersion of Aluminum Nitride in Nonpolar Solvents

Organotitanate additives are known to reduce the viscosity of many filled polymer systems, including formulations of interest for ceramic powder injection molding. Mineral oil was used as a model solvent for these systems to examine the effects of Organotitanate additions on the stability and rheology of A1N dispersions. Addition of the titanate coupling agents neoalkoxy tri(neodecanoyl) titanate and neoalkoxy tri(dioctylphosphato) titanate resulted in better dispersion as measured by sedimentation tests and rheological characterizations. Excellent correlation of the sediment heights and measured viscosities with adsorption isotherms for the organotitanates was shown, with both lower sediment height and lower viscosity obtained when a monolayer of the titanate molecules was present on the powder surface. Comparison of the behavior of the mineral oil based systems with the viscosity of corresponding polypropylene based binder systems indicates that the titanate additions are effective in reducing particle-particle interaction effects in both systems.     

Model filled polymers. VII: Flow behavior of polymers containing monodisperse crosslinked polymeric beads

Steady shear viscosities and dynamic moduli of polymer composites, consisting of combinations of crosslinked beads and matrices of polystyrene (PS) and polymethacrylates (PMA), are measured in a cone and plate rheometer. Viscosities and moduli were very sensitive to chemical composition. Crosslinked beads of identical composition to the matrix exhibited the lowest viscosity enhancements at low shear rates and the lowest moduli in dynamic mechanical analysis. The effects of bead concentration on rheological behavior were compared for PS and PMMA beads in a PMMA matrix. PMMA beads produce small effects, whereas PS beads yield highly non-Newtonian systems in PMMA, showing a yield stress of 1100 Pa at 30 wt% filler loading and dynamic moduli independent of frequency. We suggest that rheological behavior reflects the state of dispersion of beads in the matrix. Beads identical in composition to the matrix yield uniform dispersions. We propose that uniform and stable bead dispersions exhibit the lowest viscosity and moduli. Beads that cluster in the matrix, such as PS beads in PMMA, exhibit highly non-Newtonian behavior.     

Rheological study of organoclays prepared from Indian bentonite: Effect of dispersing methods

Rheological properties of the organoclays prepared by cation exchange reaction of Indian bentonite with quaternary ammonium compounds viz. Hexadecyltrimethylammonium bromide, N-cetylpyridinium chloride and Stearyldimethylbenzylammonium chloride have been investigated. The basal spacing, particle size and bulk density of organoclays were affected by the chain length and/or carbon content (organic density) of quaternary ammonium compounds. The rheological behavior study revealed that all the toluene–organoclay-dispersions exhibited shear-thinning flow behavior, degree of shear-thinning, stability of the gel structures and yield stress. The incorporation of a mixture of 5 vol.% of H₂O in methanol as polar activator studied in the range of 33 to 100 wt.% of organoclay reinforced the rheological properties, viscosity and gel volume, and the degree of shear-thinning, stability of the gel structures and yield stress of the toluene–organoclay-dispersions. The organoclays with polar activator having 65 wt.% concentration exhibited optimum rheological reinforcement. The rheological properties were found to be more enhanced by ultrasonication relative to conventional stirring/shearing. Power-law and Casson equations have been used to describe the rheological properties of toluene–organoclay-dispersions.     

玉米粉蒸煮醪流变学研究

玉米粉蒸煮醪的流变特性不仅影响发酵过程的质量、动量和能量的传递 ,还影响发酵动力学过程。文中考察了玉米粉蒸煮醪的流变特性及其与质量分数和温度的关系 ,得出流变参数k、n与质量分数和温度的函数关系。结果表明 :玉米粉蒸煮醪在质量分数为 4 %时就具有良好的拟塑性 ,且随着质量分数的增大 ,拟塑性也越显著 ;随着温度的升高其稠度系数减小 ,流变指数基本上没有变化。其流变特性服从幂律指数模型