In this paper, we demonstrate that the behavior of a set of eight large-sized negatively solvatochromic pyridinium N-phenolate betaine dyes reflects the principle transformations, occurring in aqueous micellar solutions of three cationic surfactants. As surfactants, cetyltrimethylammonium bromide (CTAB), n-octadecyltrimethylammonium chloride (OTAC), and N-cetylpyridinium bromide (CPB) were used. Normally, for such probes coupled with micelles, a red shift of the vis absorption band is expected as a result of a hydrophobization ("drying") of the micellar interface. However, under addition of electrolytes with anions such as tosylate, salicylate, and some n-alkanesulfonates or n-alkanecarboxylates to the micellar solutions, an unexpected effect was observed. Instead of a red shift, a blue shift of the vis absorption band of some of the dissolved betaine dyes was registered, as compared with the spectrum measured in pure aqueous micellar solutions of CTAB, OTAC, or CPB (Deltalambda(max) up to ca. 80 nm). This blue shift, indicating an increase in the polarity of the dye microenvironment, is explained by displacing the large dye dipoles from the thinned micelles toward the aqueous phase. The effect is well expressed at concentrations of C(betaine dye) approximately 10(-5) M, C(cationic surfactant) approximately 0.001 M, and C(organic anion) approximately 0.01 M. Transmission electron microscopy of dried samples confirms the distinct changes occurring in the studied micellar systems upon the addition of organic anions. The excess of inorganic salts [C(NaBr, KBr, or KCl) = 0.5-4.0 M] restored the position of the vis absorption band or even shifted it toward the red. Moreover, some of the betaine dyes studied (i.e., the more hydrophobic ones) stay in the micellar pseudophase or precipitate under the aforementioned concentration conditions. The peculiarities of the behavior of these betaine dyes are in agreement with their molecular structure.
The recent developments in the production of large-sized and intricate refractory products by casting from aqueous suspensions [1][2][3][4][5] call for an improved technology of obtaining the casting suspensions and an increased strength of the unfinished castings.The conventional method of obtaining A1203 suspensions includes milling the powder in steel mills, subsequently washing off the milled iron contaminant, and suspending the milled products in the optimum pH range [4][5][6]. However, this method involves a lengthy process (multiple decantation requiring a total duration up to 30 days) and a significant consumption of hydrochloric acid (up to 0.5 liter per i kg of material). Besides this, the castings obtained from such suspensions exhibit a relatively high shrinkage during the process of drying (up to 3-4%) and low strength [7,8] because of which it is not possible to produce large-sized intricate components. Furthermore, the low strength makes machining of the unfinished (raw) products difficult. Machining of the underfired or sintered products leads to an increased consumption of diamonds.Furthermore, the conditions have been established [9-13] for obtaining ceramic suspensions possessing considerable binding properties that ensure high strength of castings. Thus, a new method was proposed [13] for obtaining heat-resistant binders (including those based on A1203) by introducing small amounts of highly active additives having low values of ionic potential (BaO, SrO, CaO) into the composition of the low-activity materials (having high values of ionic potential) and for obtaining the suspensions by wet milling the materials in corundum-lined mills using corundum grinding bodies at predetermined pH values. The ultimate bend strength of the raw castings based on the additiveless GK alumina that was prepared using the new method was found to be 2-4 MPa and after drying it increased up to 5-8 MPa [13].Wet milling at elevated temperatures (owing to the occurrence of heat liberating processes) and optimum (for thinning) pH values forms the main condition for obtaining such suspensions. This makes it possible to carry out the process at the maximum possible concentration of the solid phase. In this case, one obtains polydispersed granular composition (size distribution) and a low content of the bound (bonded) liquid that subsequently determine the density of the semifinished product. This paper deals with the evaluation of three methods of preparing the suspensions: the commonly used method of suspending a powder milled in a vibrational mill and subsequently washed for removing the iron contaminant; suspending a powder milled in a corundum-lined vibrational mill using corundum balls; and suspending a powder wet-milled in a corundumlined ball mill using corundum balls under the optimum values of the moisture content and pH. In all the cases, the material:balls ratio was maintained at 1:6; and during wet milling, the material:balls:water ratio was equal to 1:6:0.5.An aluminous frit (sinter) containing a glass phase...
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