Directed synthesis of alkaline aluminosilicate minerals in a geocement matrix

Geocements were created in accordance with a hypothesis put forward by Prof. V. Glukhovsky that the structure formation processes in the alkaline aluminosilicate binders corresponded to geological transformations of aluminosilicate minerals taking place in nature. At low temperatures, a type of hydration products depends on curing conditions and mix composition. An autoclave curing allows for an intensive synthesis of a well-crystallized zeolite structure, whereas other types of curing result in the formation of an amorphous structure with crystalline inclusions represented mainly by hydroxysodalite. On the contrary to this, after curing at high temperatures, a formation of nepheline, albite or α-cristobalite depends exclusively on the firing temperature and initial geocement composition. Mechanical strength of the geocements may reach 88.5 MPa after low temperature curing and 88.7 MPa after firing at 800 °C. Optimal thermo-mechanical properties of the metakaolin- and fly ash-based geocements may be reached in compositions with a microstructure represented by an average amount of thermostable zeolites, since just these phases are characterized by a smooth dehydration and subsequent re-crystallization into stable anhydrous alkaline aluminosilicates without destruction of a framework. Directed regulation of structure formation at low temperatures is a key question in obtaining a wide range of special materials such as acid-resistant, high-strength, quick hardening, with low leach rates, high adhesion, etc. At the same time, a structure formation at high temperatures is important with regard to creation of heat- and fire-resistant composite materials. Synthesis of analogies to natural aluminosilicate minerals ensures also high durability.     

Mechanochemical interaction of Ca silicate and aluminosilicate minerals with carbon dioxide

Processes induced by mechanical activation (MA) in a planetary ball mill of natural diopside CaMgSi₂O₆ and plagioclase (CaAl₂Si₂O₈)_0.745·(2NaAlSi₃O₈)_0.209·(2KAlSi₃O₈)_0.046 in CO₂ atmosphere have been studied. Plagioclase like diopside consumes CO₂ during MA in the form of distorted carbonate groups resulting in appearance of the double IR absorption band in 1400-1600 cm^?1 region corresponding to the stretching vibrations of CO^2? ₃ group. The degree of spitting of the double carbonate band for plagioclase is markedly higher than that for diopside indicating increased distortion of CO^2? ₃ group in the mechanically activated plagioclase. According to the XRD data after 25 min of MA the diopside and plagioclase samples are almost totally amorphous. The carbonization degree of the plagioclase is lower than that of diopside after MA at the same conditions. The differences in the mechanically induced CO₂ sorption ability by silicates can be explained on the basis of simple thermodynamic considerations involving standard Gibbs free energies of reactions of the crystalline minerals with carbon dioxide producing crystalline carbonates, silica and alumina. The results on thermal relaxation of the activated samples have been reported.     

Magnesium analogues of aluminosilicate inorganic polymers (geopolymers) from magnesium minerals

Attempts to synthesise magnesium-containing analogues of aluminosilicate geopolymers from the 1:1 and 2:1 layer magnesiosilicate minerals chrysotile and talc, as well as the magnesium mineral sepiolite are reported. The effect of pre-treating these starting minerals by grinding and/or dehydroxylation was also investigated by XRD, ²⁹Si and natural-abundance ²⁵Mg solid-state magic angle spinning (MAS) NMR spectroscopy. The products from sepiolite most closely resembled an aluminosilicate geopolymer, setting at 40 °C to an X-ray amorphous product containing a broad characteristic ²⁹Si MAS NMR resonance at ?90 ppm. The ²⁵Mg MAS NMR spectrum of this product also showed evidence that some of the Mg was located in tetrahedral sites, as expected for a conventional geopolymer. A similar ²⁵Mg MAS NMR result was obtained for chrysotile, but talc proved to be extremely resistant to geopolymer synthesis, requiring treatment at 120 °C for 3 days to set to a friable material retaining the XRD and NMR characteristics of the original talc or its crystalline dehydroxylation products. This lack of reactivity may be related to the 2:1 layer-lattice talc structure, or to the fact that a suitably reactive amorphous product is not formed upon dehydroxylation.     

Hydroerosion of steel in alkaline media

The article describes the results of a study of the resistance of St.45 and Cr18Ni10Ti steels to hydroerosion in sodium hydroxide solutions with pH=8–13 and in limewater with ph=11.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 5, No. 5, pp. 584–587, September–October, 1969.     

Preparation of aqueous magnetic liquids in alkaline and acidic media

The results of work on the preparation of aqueous magnetic liquids without using organic stabilizing agents is presented.     

Dissolution and precipitation behavior of ternary solid dispersions of ezetimibe in biorelevant media

Abstract

The effects of different formulations and processes on inducing and maintaining the supersaturation of ternary solid dispersions of ezetimibe (EZ) in two biorelevant media fasted-state simulated intestinal fluid (FaSSIF) and fasted-state simulated gastric fluid (FaSSGF) at different temperatures (25?°C and 37?°C) were investigated in this work.

Ternary solid dispersions of EZ were prepared by adding polymer PVP-K30 and surfactant poloxamer 188 using melt-quenching and spray-drying methods. The resulting solid dispersions were characterized using scanning electron microscopy, differential scanning calorimetry (DSC), modulated DSC, powder X-ray diffraction and Fourier transformation infrared spectroscopy. The dissolution of all the ternary solid dispersions was tested in vitro under non-sink conditions.

All the prepared solid dispersions were amorphous in nature. In FaSSIF at 25?°C, the melt-quenched (MQ) solid dispersions of EZ were more soluble than the spray-dried (SD) solid dispersions and supersaturation was maintained. However, at 37?°C, rapid and variable precipitation behavior was observed for all the MQ and SD formulations. In FaSSGF, the melting method resulted in better solubility than the spray-drying method at both temperatures.

Ternary solid dispersions show potential for improving solubility and supersaturation. However, powder dissolution experiments of these solid dispersions of EZ at 25?°C may not predict the supersaturation behavior at physiologically relevant temperatures.     

Hydrolytic degradation of PCL/PEO copolymers in alkaline media

PCL/PEO copolymers with different compositions were obtained from ring opening polymerization of -caprolactone in the presence of ethylene oxide and characterized by various analytical techniques. Data collected from DSC and X-ray diffractometry suggested that the copolymer chains possess a blocky structure, leading to both PCL and PEO-type crystalline structures. Hydrolytic degradation of these copolymers was carried out in a pH=10.6 carbonate buffer solution at 37 °C. Comparison was made with a PCL homopolymer and a PCL/PEG blend which had the same gross composition as one of the copolymers. The results showed that the presence of PEO sequences considerably enhanced the hydrophilicity of the copolymers as compared with PCL homopolymer. Nevertheless, the degradability of PCL chains was not enhanced due to the phase separation between the two components. These materials should be of great interest for biomedical uses such as matrices for sustained drug delivery because of the presence of both hydrophilic and hydrophobic microdomains. ©2000 Kluwer Academic Publishers     

Anomalous dissolution of steels during cathodic polarization in neutral and alkaline media

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 26, No. 6, pp. 34–38, November–December, 1990.     

Crack formation in iron-nickel alloys under stress in alkaline media

The corrosion resistance and the character of crack formation in iron, nickel, and iron-nickel alloys under stress in a boiling NaOH solution were studied. The character of fracture of two-phase alloys was found to be related to the presence of an -phase at the grain boundaries. In the absence of the ferrite constituent, Fe-Ni alloys fail by intercrystalline fracture and the time-to-rupture decreases with increasing stacking fault density.     

Utilization of organic by-products for the removal of organophosphorous pesticide from aqueous media

Sorption potential of rice (Oryza sativa) bran and rice husk for the removal of triazophos (TAP), an organophosphate pesticide, has been studied. The specific surface area were found to be 19+/-0.7 m(2)g(-1) and 11+/-0.8m(2)g(-1) for rice bran and rice husk, respectively. Rice bran exhibited higher removal efficiency (98+/-1.3%) than rice husk (94+/-1.2%) by employing triazophos solution concentration of 3 x 10(-5) M onto 0.2 g of each sorbent for 120 min agitation time at pH 6 and 303 K. The concentration range (3.2-32) x 10(-5) M was screened and sorption capacities of rice bran and rice husk for triazophos were computed by different sorption isotherms. The energy of sorption for rice bran and rice husk was assessed as 14+/-0.1 and 11+/-0.2 kJ mol(-1) and kinetics of the sorption is estimated to be 0.016+/-0.002 and 0.013+/-0.002 min(-1), respectively. Intraparticle diffusion rate was computed to be 4+/-0.8 and 4+/-0.9 nmol g(-1)min(-1/2). Thermodynamic constants DeltaH, DeltaS and DeltaG at varying temperatures (283-323 K) were also calculated.     

Formation of aluminosilicate geopolymers from 1:1 layer-lattice minerals pre-treated by various methods: a comparative study

Materials resembling aluminosilicate geopolymers have been prepared from the kaolinitic 1:1 layer lattice aluminosilicate clay mineral halloysite by reaction with sodium silicate solution under alkaline conditions. The effect on geopolymer formation of pretreating the clay mineral reactant by heating, high-energy grinding or exposure to acid or alkali was monitored by the ability of the samples to cure and harden, and by XRD, ²⁷Al and ²⁹Si solid-state MAS NMR spectroscopy. Only samples prepared from the fully thermally dehydroxylated clay showed the typical XRD and NMR geopolymer characteristics. Less complete reaction was found in samples pretreated by highly energetic grinding, whereas samples exposed to chemical pretreatment with dilute acid did not react to form viable geopolymers. Pretreatment with dilute alkali produced a zeolite which reacted with sodium silicate, but the hardened sample was not X-ray amorphous and showed subtle differences in its NMR spectra. These results are discussed in terms of the vital role played in the early stages of the reaction sequence by the presence of labile aluminium. The efficacy of the various pretreatment methods is related to their ability to render the aluminium source (the solid aluminosilicate clay) sufficiently soluble in alkali.     

Corrosion inhibition of AA6063 alloy by vanadates in alkaline media

Vanadium aqueous compounds are considered as promising environmentally friendly inhibitors for heterogeneous aluminium alloys. In this study, mechanism of corrosion inhibition of AA6063 in alkaline media by vanadate inhibitors is presented. A combination of weight loss and open circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy was used to compare corrosion behavior of AA6063 alloy in aerated pH 10 0.05 M sodium chloride solutions in the absence and presence of 0.003 mol/l sodium orthovanadate. Tetrahedrally coordinated mono‐ and polyvanadates, that are main forms in such solutions, cause a decrease in corrosion current density and significantly increase amplitude of impedance spectra and impedance modulus |Z| values due to mixed cathodic‐anodic inhibition effect mainly associated with the formation of adherent surface film on cathodic and anodic intermetallic particles of alloy.     

碱性纳米SiO2溶胶在化学机械抛光中的功能

纳米SiO2是一种性能优越的功能材料,化学机械抛光(CMP)过程的精确控制在很大程度上取决于对纳米SiO2功能的认识。但是目前对碱性纳米SiO2在CMP过程中的功能还没有完全弄清楚,探讨它在CMP中作用是提高CMP技术水平的前提。纳米SiO2溶胶的表面效应使其表面存在大量的羟基,在CMP过程中纳米SiO2表面羟基与碱反应生成硅酸负离子,硅酸负离子再与硅反应来降低纳米SiO2的表面能量,同时达到除去硅的目的。综上所述,碱性纳米SiO2在CMP的过程中不仅起到了磨料的作用,同时参加了化学反应,在此基础上提出了在碱性条件下纳米SiO2与硅的反应机理。     

Electrochemical and analytical investigation of passive films formed on stainless steels in alkaline media

Passive films were grown in potentiodynamic mode, by cyclic voltammetry on AISI 316 and AISI 304 stainless steels. The composition of these films was investigated by X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour and the chemical composition of the passive films formed by cyclic voltammetry were compared to those of films grown under natural conditions (by immersion at open circuit potential, OCP) in alkaline solutions simulating concrete. The study included the effect of pH of the electrolyte and the effect of the presence of chloride ions.The XPS results revealed important changes in the passive film composition, which becomes enriched in chromium and depleted in magnetite as the pH decreases. On the other hand, the presence of chlorides promotes a more oxidised passive layer. The XPS results also showed relevant differences on the composition of the oxide layers for the films formed under cyclic voltammetry and/or under OCP.     

Deciphering of advantageous electrocatalytic water oxidation behavior of metal-organic framework in alkaline media

Nano Research - Carboxylic acid-based metal-organic frameworks (MOFs) are normally passed for the “pre-catalysts” for oxygen evolution reaction (OER) due to the hydroxides constructed...     

Emissivity of aluminosilicate refractories

Experimental data was obtained on the dependence of the emissivity of refractories on temperature and chemical composition.Translated from Imzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 3, pp. 406–411, September, 1987.     

Cathodic detection of H2O2 using iodide-modified gold electrode in alkaline media

Oxidative chemisorption and cathodic stripping reductive desorption of iodide have been studied at a smooth polycrystalline gold (Au (poly)) electrode. Potential-dependent surface coverage of iodide has been controlled on the basis of its reductive desoprtion in 0.1 M KOH alkaline media and its quantitative oxidation to aqueous iodates in acidic media. The Au (poly) electrode surface catalyzes the decomposition of H2O2 to O2. Specific adsorption of iodide on the Au electrode inhibits fully the catalytic decomposition and electrochemical oxidation of H2O2 as well as the adsorption of unknown impurities and the oxidative degradation of the electrode surface by H2O2. A quantitative characterization/detection of H2O2 at the iodide-modified Au (poly) electrode in the alkaline media has, thus, been achieved. Performance of the electrode toward the detection of H2O2 with respect to response time and sensitivity as well as operational stability has been evaluated. It has a sensitivity of 0.272 mA cm(-2) mM(-1) in amperometric measurements with a detection limit of 1.0 x 10(-5) M H2O2, and the response time to achieve 95% of the steady-state current is <20 s. The effect of O2 in the air-saturated solution can be minimized by subtracting the additional current for the O2 reduction. Experimental measurements were based upon cyclic voltametric and amperometric techniques.