Dispersion stability of a ceramic glaze achieved through ionic surfactant adsorption

The adsorption of cetylpyridinium chloride (CPC) and sodium dodecylbenzenesulfonate (SDBS) onto a ceramic glaze mixture composed of limestone, feldspar, quartz, and kaolin has been investigated. Both adsorption isotherms and the average particle zeta potential have been studied in order to understand the suspension stability as a function of pH, ionic strength, and surfactant concentration. The adsorption of small amounts of cationic CPC onto the primarily negatively charged surfaces of the particles at pH 7 and 9 results in strong attraction and flocculation due to hydrophobic interactions. At higher surfactant concentrations a zeta potential of more than +60 mV results from the bilayered adsorbed surfactant, providing stability at salt concentrations < or = 0.01 M. At 0.1 M salt poor stability results despite substantial zeta potential values. Three mechanisms for SDBS adsorption have been identified. When anionic SDBS monomers either adsorb by electrostatic interactions with the few positive surface sites at high pH or adsorb onto like charged negative surface sites due to dispersion or hydrophobic interactions, the magnitude of the negative zeta potential increases slightly. At pH 9 this increase is enough to promote stability with an average zeta potential of more than -55 mV, whereas at pH 7 the zeta potential is lower at about -45 mV. The stability of suspensions at pH 7 is additionally due to steric repulsion caused by the adsorption of thick layers of neutrally charged Ca(DBS)2 complexes created when the surfactant interacts with dissolved calcium ions from the calcium carbonate component.     

Preparation of hemispherical hollow silica microcapsules with different affinity surface by using spherical vaterite calcium carbonate as template

We developed a method to prepare hemispherical hollow silica microcapsules (HHSM) with different affinity surfaces using spherical vaterite calcium carbonate (SVCC) as a template. The preparation process composed of the adhesion of calcium carbonate onto the surface of methyl methacrylate (MMA) droplets followed by suspension polymerization, the partial etching of calcium carbonate on the polymethyl methacrylate (PMMA) mother particle, the formation of silicon dioxide powder by sol–gel reaction and their deposition onto the etched flat surface of calcium carbonate, the surface modification of deposited silicon dioxide with silane coupling agent, the removal of the mother particle with acetone, the formation of silicon dioxide powder by sol–gel reaction and deposition onto the exposed hemispherical surface of calcium carbonate, and the surface modification of deposited silicon dioxide with silane coupling agent. The synthesized microcapsules had a complete hemispherical structure and both hydrophilic and hydrophobic surfaces. Copyright © 2007 John Wiley & Sons, Ltd.     

改性硝酸铵爆轰安全性研究 Ⅰ.CaCO3和MgSO4对硝酸铵爆轰安全性的影响

将碳酸钙和硫酸镁改性的硝酸铵按照工业炸药配方配制成铵油(ANFO)炸药，以8号雷管起爆，对硝酸铵的爆轰安全性进行了评价。采用恒温热分解和示差扫描量热法，研究了改性硝酸铵及铵油炸药的热分解行为。测定了改性硝酸铵的比表面积以解释爆轰结果。得出如下结论：硝酸铵含40％的碳酸钙，或25％碳酸钙和5％硫酸镁的混合物，所配制的铵油炸药不能被8号雷管起爆。碳酸钙同硝酸铵发生复分解反应放出NH3、H2O和CO2气体，反应程度与碳酸钙的含量、温度和时间成正比。虽然硝酸铵中加入碳酸钙后提高了ANFO炸药的热稳定性，但由于上述气体的逸出增加了改性硝酸铵的比表面积。因此，在硝酸铵中加入少量的碳酸钙不能达到爆轰安全性的要求。硫酸镁与硝酸铵形成复盐，可减缓硝酸铵和碳酸钙之间复分解反应的速度．有利于降低硝酸铵的起爆感度。     

Comparison of surface properties between kaolin and metakaolin in concentrated lime solutions

The surface adsorption of calcium hydroxide onto kaolin and metakaolin was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clays to calcium hydroxide solutions of various concentrations. Both clays adsorb calcium and hydroxyl ions but differently. Kaolin adsorbs calcium hydroxide not only at the edges of the clay particles but also onto the basal faces. The adsorbed hydrated calcium ions form a layer on the clay particle surfaces, preventing further dissolution of the clay mineral platelet. Metakaolin shows high pozzolanic activity, which provides the quick formation of hydrated phases at the interfaces between metakaolin and lime solutions. The nature of the hydration products has been investigated using X-ray diffraction (XRD) and differential thermal analysis (DTA). The most important hydrated phases like CSH (hydrated calcium silicate) and C₂ASH₈ (gehlenite) have been identified.     

The Dispersion Properties of Precipitated Calcium Carbonate Suspensions Adsorbed with Alkyl Polyglycoside in Aqueous Medium

The zeta potentials and dispersion properties of precipitated calcium carbonate suspensions adsorbed with alkyl polyglycosides in aqueous medium were investigated. Within the investigated pH ranges, the adsorption curves of alkyl polyglycosides on calcium carbonates show sigmoidal shapes, and the zeta potential decreases as the amount of adsorption increases. At positively charged surfaces of low pH, the adsorption amounts were greater than those at negatively charged surfaces, indicating that alkyl polyglycosides were negatively charged in aqueous solutions. At low concentrations of alkyl polyglycosides, the dispersion stabilities of suspensions were very poor and showed no linearity with zeta potentials over the entire range of pHs, which may be attributed to the onset of hydrophobic interaction between particles due to the adsorption of surfactant molecules. This destabilization continued until monolayer coverage by the surfactant layer was complete. Based on the classical DLVO theory, there may be a strong hydrophobic interaction between particles. Beyond monolayer adsorption, the dispersion stability increases, probably by the formation of hemimicelle or admicelle. Therefore, it is believed that ionization of alkyl polyglycosides and admicelles of surfactants on particle surface plays a key role in the stability of dispersions and the abrupt increase in adsorption. Copyright 2000 Academic Press.     

Acid dissociation of surface bound water on cellulose nanofibrils in aqueous micro nanofibrillated cellulose (MNFC) gel revealed by adsorption of calcium carbonate nanoparticles under the application of ultralow shear

At ultralow shear rate (~0.01 s^?1), acting below the yield stress of the aqueous gel, adsorption of calcium carbonate nanoparticles (<~100 nm) onto cellulose nanofibrils is induced without pigment–pigment preflocculation. Dispersant-free and polyacrylate treated dispersed carbonate particles are compared. Initially, it is seen that the polyacrylate dispersed material does not adsorb, whereas the dispersant-free carbonate adsorbs readily under the controlled ultralow shear conditions. However, repeated cycles of ultralow shear with intermittent periods in the rest state eventually induce the effect as initially seen with the dispersant-free calcium carbonate. The fibril suspension in the bulk is slightly acidic. The addition of buffer to a controlled pH in the case of the dispersant treated particles maintained a similar delay in the onset of adsorption, but adsorption occurred eventually after repeated cycles. During this cycling process, in parallel, the pH gradually drops under repeated cycles of ultralow shear, opposite to expectation, given the buffering capacity of calcium carbonate. The conductivity, in turn, progressively increases slightly at first and then significantly. The action of surface bound water on the nanofibril is considered key to the action of adsorption, and the condition of ultralow shear suggests that the residence time of the particle in contact with the nanofibril, acting under controlled strain against diffusion in the gel, is critical. It is proposed that under these specific conditions the calcium carbonate nanoparticles act as a probe of the nanofibril surface chemistry. The hydrogen bonded water, known to reside at the nanofibril surface, is thus considered the agent in the carbonate-surface interaction, effectively expressing an acid dissociation, and the calcium carbonate nanoparticles act as the probe to reveal it. An important phenomenon associated with this acid dissociation behaviour is that the adsorbed calcium carbonate particles subsequently act to flocculate the otherwise stable cellulose material, leading to release of water held in the aqueous gel matrix structure. This latter effect has major implications for the industrial ease of use of micro and nanofibrillar cellulose at increased solids content. This novel mechanism is also proposed for use to enhance the dewatering capability in general of complex cellulose-containing gel-like water-holding suspensions.     

原位沉析法制备碳酸钙/壳聚糖三维复合材料的研究

将含有Ca²⁺的壳聚糖溶液与含有CO^2-₃的碱溶液用离子可渗透膜隔离,根据膜渗透原理,使膜内壳聚糖与碱液原位沉析,生成碳酸钙,得到具有高强度的碳酸钙(CaCO₃)/壳聚糖(CS) 三维复合材料. XRD测试结果表明,生成的碳酸钙以方解石晶型存在. 从SEM可以观察到碳酸钙颗粒尺寸约为5～10 μm,并且颗粒呈有序分布,它们以棒材的纵轴为中心,围绕中心呈环状分布. 对不同碳酸钙含量的复合棒材进行了弯曲性能测试,其弯曲强度随碳酸钙含量的增大先上升后下降. 在碳酸钙质量分数为10％时,弯曲强度达到最大值(约为113 MPa),弯曲模量为2.6 GPa.     

Aspects on the interaction between sodium carboxymethylcellulose and calcium carbonate and the relationship to specific site adsorption

The mechanisms of adsorption and association for sodium carboxymethylcellulose (NaCMC) in calcium carbonate suspensions have been determined from isothermal calorimetry and adsorption measurements. The equilibrium adsorption isotherms were determined by two different methods of separation; a depletion method and a serum exchange method. The enthalpy of dilution for NaCMC was determined on supernatants obtained from the calcium carbonate suspensions in order to investigate the interaction between NaCMC and dissolved species from the mineral. For comparison, NaCMC was injected into CaCl(2) solutions in order to determine the role of calcium ions in the adsorption process. The initial part of the adsorption isotherm showed a quasi-infinite slope indicating a high affinity for the NaCMC to the calcium carbonate surface, which was significantly reduced when anionic sodium polyacrylate was preadsorbed onto the calcium carbonate implying competitive adsorption. An endothermic enthalpy change was observed between the NaCMC and the calcium carbonate surface, suggesting attachment of the carboxylic acid groups onto the hydrated calcium sites. A similar endothermic enthalpy was observed when NaCMC was injected into CaCl(2) solutions or supernatants obtained from the calcium carbonate suspensions, indicating a complexation of carboxylic acid groups and hydrated calcium ions. It was concluded that the mechanisms of interaction of NaCMC in calcium carbonate suspensions are primarily an association between NaCMC and Lewis acid sites on the calcium carbonate surface and the formation of NaCMC-Ca(2+) complexes in the bulk solution, both of which will be affected by the amount of anionic sodium polyacrylate present.     

Coprecipitation of Nanocomposites Based on Colloidal Particles of Sulfur and Carbonates of Alkaline-Earth Metals from Polysulfide Solutions

It has for the first time been shown that the action of carbon dioxide on solutions of alkaline-earth metal polysulfides causes a reaction yielding nanoparticles of sulfur and calcium, barium, and strontium carbonates. It has been found that, initially, particles of sulfur and a corresponding carbonate are synthesized with average sizes of about 20–25 nm; then, the particles are enlarged (aggregated) with the precipitation of a composite, which consists of hydrophobic particles of sulfur and the carbonate (the latter become hydrophobic due to the adsorption of neonol present in the reaction mixture). It has been shown that only sulfur exhibits antifungal activity in the composites, while carbonates have no effect on pathogenic fungi. The composite consisting of sulfur and calcium carbonate nanoparticles has shown the highest biological activity during germination of wheat seeds.     

A physico-chemical investigation of poly(ethylene oxide)-block-poly(L-lysine) copolymer adsorption onto silica nanoparticles

The adsorption behavior of poly(ethylene oxide)-b-poly(L-lysine) (PEO(113)-b-PLL(10)) copolymer onto silica nanoparticles was investigated in phosphate buffer at pH 7.4 by means of dynamic light scattering, zeta potential, adsorption isotherms and microcalorimetry measurements. Both blocks have an affinity for the silica surface through hydrogen bonding (PEO and PLL) or electrostatic interactions (PLL). Competitive adsorption experiments from a mixture of PEO and PLL homopolymers evidenced greater interactions of PLL with silica while displacement experiments even revealed that free PLL chains could desorb PEO chains from the particle surface. This allowed us to better understand the adsorption mechanism of PEO-b-PLL copolymer at the silica surface. At low surface coverage, both blocks adsorbed in flat conformation leading to the flocculation of the particles as neither steric nor electrostatic forces could take place at the silica surface. The addition of a large excess of copolymer favoured the dispersion of flocs according to a presumed mechanism where PLL blocks of incoming copolymer chains preferentially adsorbed to the surface by displacing already adsorbed PEO blocks. The gradual addition of silica particles to an excess of PEO-b-PLL copolymer solution was the preferred method for particle coating as it favoured equilibrium conditions where the copolymer formed an anchor-buoy (PLL-PEO) structure with stabilizing properties at the silica-water interface.     

Heterogeneous uptake and reactivity of formic acid on calcium carbonate particles: a Knudsen cell reactor, FTIR and SEM study

The heterogeneous uptake and reactivity of formic acid (HCOOH), a common gas-phase organic acid found in the environment, on calcium carbonate (CaCO(3)) particles have been investigated using a Knudsen cell reactor, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). FTIR measurements show that the adsorption of formic acid on the surface of calcium carbonate results in the formation of calcium formate. Besides calcium formate, carbonic acid is also a reaction product under dry conditions (<1% RH). Under dry conditions and at low pressures, the initial uptake coefficient of formic acid on CaCO(3) particles is measured to be 3 +/- 1 x 10(-3) and decreases as the surface saturates with adsorbed products. The maximum surface coverage of formic acid under dry conditions is determined to be (3 +/- 1)x 10(14) molecules cm(-2). Under humidified conditions (RH >10%), adsorbed water on the surface of the carbonate particles participates in the surface reactivity of these particles, which results in the enhanced uptake kinetics and extent of reaction of this organic acid on CaCO(3) as well as opens up several new reaction pathways. These reaction pathways include: (i) the water-assisted dissociation of carbonic acid to CO(2) and H(2)O and (ii) the formation of calcium formate islands and crystallites, as evident by SEM images. The results presented here show that adsorbed water plays a potentially important role in the surface chemistry of gas-phase organic acids on calcium carbonate particles.     

Interaction of nicotine with magnesium aluminum silicate at different pHs: characterization of flocculate size, zeta potential and nicotine adsorption behavior

The purposes of this study were to prepare dispersions in various ratios of nicotine (NCT) and magnesium aluminum silicate (MAS) at different pHs and to investigate interaction of NCT with MAS by characterizing microscopic morphology, particle size and zeta potential of MAS-NCT flocculates. Moreover, the NCT adsorption onto MAS at different pHs were also investigated. At basic medium, incorporating NCT into MAS dispersion brought about a small decrease in the zeta potential of MAS, leading to a loose flocculate formation of MAS. This is likely to be due to an adsorption of unionized form of NCT onto MAS via intermolecular hydrogen bonding. The lower zeta potential, denser matrix structure and larger size of the flocculates was found at neutral and acidic media because the protonated species of NCT could interact with the negatively charged MAS by electrostatic force. In addition the flocculates formed at pH 4 possibly possessed a higher density than those formed at pH 7, suggesting that the diprotonated species of NCT at pH 4 caused stronger interaction with MAS. The adsorption isotherms of NCT onto MAS at different pHs can be described not only using the Langmuir model, but also using the Freundlich model. The higher affinity of NCT adsorption onto MAS at neutral and acidic media was found. However, the adsorption capacity to form NCT monolayer reduced with decreasing the pH of the dispersions because of an adsorption of hydronium ions and a decrease in surface area of adsorption site by flocculation. These findings suggested that the flocculation of MAS dispersion could be induced by incorporation of NCT. The characteristics, such as particle size and zeta potential, of the NCT-MAS flocculates and the adsorption isotherms of NCT onto MAS were depended upon pH of dispersion, in which the different charged species of NCT were formed.     

A multi-scale assessment of Pb(II) sorption on dolomite

Macroscopic sorption studies indicated that Pb sorption capacity was independent of pH over the pH range 5-7, while sorption as a function of reaction time up to two weeks for systems with no bulk precipitate phases showed continuous Pb uptake on dolomite. This could be due to diffusion of Pb into the micropores of dolomite as well as an increase in surface sites caused by particle size reduction during suspension mixing. Normalized XANES spectra for systems undersaturated with respect to Pb carbonate precipitates resembled the spectrum of Pb4(OH)4(4+), suggesting that Pb is mainly coordinated to dolomite as an inner-sphere surface complex. On the other hand, the XANES spectrum for 10(-3) M Pb at 1 atm CO2(g) in a 2 M Mg(NO3)2 background electrolyte solution resembled that of cerussite, while a sample at 5 x 10(-4) M Pb in equilibrium with air and 2 M Mg(NO3)2 resembled that of hydrocerussite. EXAFS analyses of sorption samples in chloride solutions showed that there were only first-shell contributions under 1 atm CO2(g), while higher shell contributions from Ca/Mg were seen at 10(-3.42) atm CO2(g). On the other hand, EXAFS samples prepared in nitrate solutions showed noticeable differences in speciation under different reaction conditions-from outer-sphere surface complexes at low Pb concentrations and pH, to inner-sphere surface complexes at moderate Pb concentrations and neutral pH, to the formation of Pb carbonate precipitates at the highest Pb loadings.     

The calcite/water interface II. Effect of added lattice ions on the charge properties and adsorption of sodium polyacrylate

The origin of the surface potential of calcium carbonate in aqueous dispersions and the dissolution of calcite in systems containing excess Ca(2+) and CO(3)(2-) have been the subjects of this study. In addition, stabilization of calcite particles with an anionic polyelectrolyte (sodium polyacrylate (NaPA)) and the effect on surface potential and dissolution of calcite have been studied. Preferential dissolution of either Ca(2+) or CO(3)(2-) from the surface, which is governed by the partial pressure of CO(2) in solution and the pH of the solution, mainly determines the surface potential. Both lattice ions (Ca(2+) and CO(3)(2-)) adsorb onto the surface and thus alter the surface potential. NaPA adsorbs strongly onto the calcite surface regardless of background electrolyte concentration, and reverses the surface potential to negative values. Chelation of the surface due to NaPA can be partly prevented by adding Ca(2+) to the dispersion.     

二次碳化法制备疏水链状纳米碳酸钙

以柠檬酸和十六酸的氨溶液为表面控制剂, 用二次碳化法制备了疏水链状纳米碳酸钙晶体. 用透射电子显微镜、X射线衍射、红外光谱、热重分析和接触角测试对产品进行了分析. 结果表明, 表面控制剂在反应过程中不但可以控制晶体的成核生长, 还能对碳酸钙表面进行修饰. 在不添加表面控制剂的溶液中得到立方体状表面亲水的纳米碳酸钙晶体; 添加柠檬酸和十六酸的氨溶液后所得纳米碳酸钙晶体为链状表面疏水. 将碳酸钙添加到聚乙烯中, 聚乙烯的初始热分解温度提高, 热力学稳定性增加.     

An investigation of electrorheological properties of calcium carbonate suspensions in silicone oil

In this study, electrorheological behavior of suspensions prepared from 0.9 and 5.0 µm calcium carbonate particulates, dispersed in insulating silicone oil medium was investigated. Sedimentation stabilities of suspensions (c = 5 wt %) prepared using these calcium carbonate powders were determined to be 6 and 4 days, respectively. Electrorheological activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. Shear stress of calcium carbonate suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions was decreased sharply with increasing shear rate and particle size, showing a typical shear thinning non-Newtonian visco-elastic behavior. Effects of elevated temperature and polar promoter onto electrorheological activity of calcium carbonate/silicone oil system were also investigated.__________From Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 268–273.Original English Text Copyright © 2005 by Yilmaz, Ünal, Yavuz.This article was submitted by the authors in English.     

A carbonate controlled-addition method for amorphous calcium carbonate spheres stabilized by poly(acrylic acid)s

Stable amorphous calcium carbonate (ACC) composite particle with a size-controlled monodispersed sphere was obtained by a new simple carbonate controlled-addition method by using poly(acrylic acid) (PAA) (Mw = 5000), in which an aqueous ammonium carbonate solution was added into an aqueous solution of PAA and CaCl2 with a different time period. The obtained ACC composite products consist of about 50 wt % of ACC, 30 wt % of PAA, and H2O. Average particle sizes of the ACC spheres increased from (1.8 +/- 0.4) x 102 to (5.5 +/- 1.2) x 102 nm with an increase of the complexation time of the PAA-CaCl2 solution from 3 min to 24 h, respectively. The ACC formed from the complexation time for 3 min was stable for 10 days with gentle stirring as well as 3 months under a quiescent condition in the aqueous solution. Moreover, the ACC was also stable at 400 degrees C. Stability of the amorphous phase decreased with an increase of the complexation time of the PAA-CaCl2 solution. No ACC was obtained when the lower molar mass PAAs (Mw = 1200 and 2100) were used. In the higher molar mass case (Mw = 25 000), a mixture of the amorphous phase and vaterite and calcite crystalline product was produced. The present results demonstrate that the interaction and the reaction kinetics of the PAA-Ca2+-H2O complex play an important role in the mineralization of CaCO3.     

水分散体系中由BPO或KPS引发的苯乙烯反向原子转移自由基聚合

分别以过氧化二苯甲酰 (BPO)和过硫酸钾 (KPS)为引发剂、1 ,1 0 邻二氮菲为催化剂配体、十二烷基磺酸钠为乳化剂 ,在水分散体系中进行了苯乙烯的反向原子转移自由基聚合反应 .结果表明 ,对于BPO引发的苯乙烯乳液聚合反应 ,必须由CuBr和CuBr2 形成复合催化剂体系才能达到较好的控制效果 ,其中CuBr可以是直接加入到催化剂体系中 ,也可以是由CuBr2 与Cu0 就地快速反应生成 .CuBr迅速地与BPO反应而实现活性聚合中所谓的“快引发” ,从而有效地控制苯乙烯的聚合反应 .对于KPS引发的苯乙烯乳液聚合体系 ,反应介质的pH值对聚合有很大的影响 ,反应速度随着反应介质pH值的升高而加快 .实验结果表明 ,由两种不同引发剂引发的苯乙烯的乳液的粒径及粒径分布也有很大的差异     

Precipitation of different calcite crystal morphologies in the presence of sodium stearate

The influence of sodium stearate (NaSt) on the precipitation of calcium carbonate during the semicontinuous process of slaked lime carbonation was studied in the systems in which process parameters, like concentration of total dissolved calcium, temperature, CO(2) flow rate and initial addition rate of slaked lime, were controlled. It was found that calcite was the only calcium carbonate polymorph that appeared under the investigated experimental conditions, while FT-IR spectroscopy and thermogravimetric analysis of samples confirmed the presence of stearate on the surface of precipitated calcium carbonate (PCC). Specific surface area of PCC increased with increasing stearate content: the highest value, s = 52.8 m(2) g(-1), was obtained at t = 20 degrees C, c(tot) = 17.0 mmol dm(-3) and the stearate content of m(NaSt)/m(CaO) = 0.03. It was also found that hydrophobic calcite crystals in the form of rhombohedral and scalenohedral morphology can be produced at m(NaSt)/m(CaO) > 0.01. The exception is the case of nanosized PCC production, when much higher concentration of NaSt is needed, m(NaSt)/m(CaO) = 0.22. Minimal amount of stearate necessary to build up the monolayer and corresponding cross sectional area of one stearate molecule were estimated for the obtained calcite morphologies.     

Nature identification and morphology characterization of anion-exchange membrane fouling during conventional electrodialysis

The aim of this work was to study the effect on the fouling of anion-exchange membranes (AEM) of (1) the pH value of the concentrate solution and (2) the composition in calcium, carbonate, and protein of the diluate solution to be treated by conventional electrodialysis. It appeared that after demineralization of solutions containing CaCl(2) using a concentrate solution maintained at a pH value of 7 or 12, mineral fouling appeared on the AEM surface in contact with the concentrate. The mineral deposits presented a cylindrical filament shape for conditions with a concentrate solution pH value of 7, while, for a pH value of 12, the mineral deposit had a crumbly and spongy texture formed by irregular aggregates. The nature of the fouling was identified as a calcium phosphate with or without calcium hydroxide. In addition, gel-like protein fouling was detected on the AEM surface in contact with the diluate after demineralization procedures using a concentrate pH value of 2 or 7, regardless of the mineral composition of the diluate.