Fabrication of Eu-coated silica particles by homogeneous precipitation method

The Stabilization Mechanism of Nano-SiO2 Precursor Solution

The issues associated with the fabrication of nano-silica (NS) mineral powder, such as high cost and agglomeration, can be effectively mitigated by using a precursor solution of NS as the external mixture of cement-based materials. Based on the liquid-phase preparation of NS mineral powder, its preparation technology was thoroughly investigated herein. The precursor solution of NS was synthesized using acid media (HCL, HNO₃, HBO₃, HCOOH, CH₃COOH)-the acetic acid concentration was 1~15%-and siliceous materials. (The concentration of sodium silicate was 20~38%). In addition, the pH value (pH4~pH8) of the precursor solution was measured using a pH detector. The indexes of NS, such as precipitation time, morphology, and distribution, were observed to formulate a preparation technique for the precursor solution of NS that possessed the best results for the precipitation of nanoparticles. From the acquired results, it was demonstrated that acetic acid solution (concentration ≤ 3%) and sodium silicate solution (concentration ≤ 25%) were mixed into a solution with pH = 6, which was the optimum mixing ratio for the precursor solution of NS. The prepared precursor solution of NS was also added to the Ca(OH)₂ saturated solution, and the precursor solution became active from a stable state. Then, NS particles were precipitated in an alkaline solution and reacted with Ca(OH)₂ to form calcium silicate gel, which made the solution increasingly turbid and generated many visible and uniformed flocculating substances. With time, gels were continuously produced, which then turn white. Similarly, NS particles can be precipitated when the precursor solution is added to cement paste, which reacts with the Ca(OH)₂ to generate CSH gel and improve the compactness of the cement paste.

pH-dependent surface charging and points of zero charge. IV. Update and new approach

The recently published points of zero charge (PZC) and isoelectric points (IEPs) of various materials are compiled to update the previous compilation [M. Kosmulski, Surface Charging and Points of Zero Charge, CRC Press, Boca Raton, FL, 2009]. Unlike in previous compilations by the same author [Chemical Properties of Material Surfaces, Dekker, New York, 2001; J. Colloid Interface Sci. 253 (2002) 77; J. Colloid Interface Sci. 275 (2004) 214; J. Colloid Interface Sci. 298 (2006) 730], the materials are sorted not only by the chemical formula, but also by specific product, that is, by brand name (commercially available materials), and by recipe (home-synthesized materials). This new approach indicated that the relatively consistent PZC/IEP reported in the literature for materials having the same chemical formula are due to biased choice of specimens to be studied. Specimens which have PZC/IEP close to the "recommended" value are selected more often than other specimens (PZC/IEP not reported before or PZC/IEP reported, but different from the "recommended" value). Thus, the previously published PZC/IEP act as a self-fulfilling prophecy.