Presence Of Calcium Hydroxide Research Articles

The effect of high concentrations of calcium hydroxide in neutralised synthetic supernatant liquor—Implications for alumina refinery residues

The presence of calcium hydroxide in Bayer residue slurry inhibits the effectiveness of seawater neutralisation. An increase in the slurry pH, after neutralisation, is caused by the dissolution of calcium hydroxide and hydrocalumite (both components are found in the solid residue). At increased calcium hydroxide concentrations, additional hydrocalumite forms. Hydrocalumite has been found to be unstable when the solution pH is less than 10.5, releasing OH − ions and aluminium ions back into solution (pH and aluminium reversion). Through this mechanism, the concentration of calcium hydroxide in alumina refinery residues has an impact on seawater neutralisation process efficiency.

Co-generation of acetylene and hydrogen for a carbide-based fuel system

The co-generation of acetylene and hydrogen from the hydrolysis of calcium carbide and calcium hydride was investigated as part of a unique carbide-based fuel system intended for high-temperature fuel cells. To gain better control of this highly energetic reaction, glycerin was used to coat the reactant particles to form slurry prior to their reaction with water. This process was shown to moderate the rate of gas production, as well as to provide a means for preparing slurry that could be pumped into the reactor vessel. It was also observed that the presence of calcium hydroxide, a by-product of hydrolysis, lowered the solubility of acetylene resulting in a higher initial flow rate due to less acetylene being dissolved in solution. However, the buildup of calcium hydroxide with time inhibited the hydrolysis of both calcium carbide and calcium hydride causing the acetylene and hydrogen flow rates to decrease.

Activated platelets increase proliferation and protein synthesis of human dental pulp–derived cells

To evaluate the impact of activated platelets on the mitogenic expansion of human dental pulp-derived cells (DPC) in vitro. The effect of supernatants released from activated platelets (PRS) and the corresponding platelet membranes (MEM) on proliferation and protein synthesis of DPC was evaluated. The contributions of the phosphoinositide 3-kinase (PI3K)/AKT and mitogen-activated protein kinase (MAPK) pathways to the response of DPC were assessed using kinase inhibitors. Also examined was whether the presence of calcium hydroxide or the inflammatory mediators tumour necrosis factor alpha, interleukin-1, interleukin-6 and lipopolysaccharide of Escherichia coli modulated the expansion of DPC. Physiologic concentrations of PRS and MEM stimulated proliferation and protein synthesis by 18.4-fold (P < 0.01) and 2.9-fold (P < 0.01), respectively. This mitogenic expansion was paralleled by activation of AKT and the MAP kinases extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38. Inhibitor studies revealed that the mitogenic response of DPC involved PI3K/AKT, JNK and p38 signalling (P < 0.05). Calcium hydroxide and inflammatory factors did not significantly modulate the mitogenic response of DPC to PRS and MEM. Supernatants released from activated platelets and the corresponding platelet membranes stimulated DPC proliferation and protein synthesis involving PI3K/AKT and MAPK signalling. These findings may serve as a basis for preclinical studies that address the role of activated platelets in dental pulp repair.

The role of calcium hydroxide in the formation of thaumasite

It has recently been derived by thermodynamic calculation that the presence or absence of calcium hydroxide plays a vital role in the resistance of cement paste or concrete against the formation of thaumasite. To obtain experimental data on this matter, special binders have been mixed and used for the preparation of mortar bars. These specimens were exposed to moderate sulphate attack for a period of 18 months at a temperature of 8 °C. Mortar bars containing calcium hydroxide showed visual signs of attack a few months after exposure, leading to expansion, mass loss and complete failure. In contrast to this, no signs of attack were observed when no calcium hydroxide was present in the microstructure. These results confirm the conclusions of earlier thermodynamic calculations that the presence of calcium hydroxide has an important impact on the formation of thaumasite. Calcium-rich C–S–H formed in the presence of calcium hydroxide is vulnerable against sulphate attack and the formation of thaumasite. In the absence of calcium hydroxide, C–S–H has a much lower calcium/silicon ratio and a higher resistance against the formation of thaumasite.

Improved lean deNOx performance of Cu-ZSM-5 through alternative synthesis conditions for ZSM-5

A series of ZSM-5 samples with similar SiO2/Al2O3 ratio was synthesised using different aluminum sources and by including varying amounts of calcium hydroxide during the synthesis. The samples were subsequently ion-exchanged with Cu-ions, and evaluated with respect to deNOx activity in the absence and presence of water. The choice of aluminum source and the presence of calcium hydroxide during the zeolite synthesis affected the lean deNOx activity of Cu-ZSM-5.

Facile Synthesis of 1,3,7-Trihydroxyxanthone and Its Regioselective Coupling Reactions with Prenal: Simple and Efficient Access to Osajaxanthone and Nigrolineaxanthone F

A facile five-step synthesis of naturally occurring 1,3,7-trihydroxyxanthone has been described starting from 1,3,5-trimethoxybenzene via NBS-induced nuclear bromination, lithiation followed by an in situ benzoylation with methyl 2,5-dibenzyloxybenzoate, selective deprotection of the two benzyl groups, base-catalyzed intramolecular cyclization, and demethylations pathway with 62% overall yield. The regioselective coupling reactions of 1,3,7-trihydroxyxanthone with prenal in the presence of calcium hydroxide at room temperature and under thermal conditions at 140-150 degrees C have been demonstrated to exclusively obtain the natural products osajaxanthone in 75% yield and nigrolineaxanthone F in 98% yield, respectively.

A Study of the Influence of Organic Compounds during the Cement Hydration by Using XRD and DTA

Small amounts of toxic organics can be encountered in many industrial wastes and contaminated materials treated by cement solidification/stabilization. Besides, very low levels of organics make incineration processe very expensive and sometimes ineffective. The functional group of the organic compound can be important to determine the type of influence that occurs during the cement hydration process. Tetrachloroethylene, sodium acetate, ethylamine and phenol - four pollutant organics containing different functional groups were used in the experimental work. Three comparative concentrations (0,5; 5,0 and 10 weight percent of the total mix) and different curing times were tested. X-ray diffraction (XRD) has showed the presence of calcium hydroxide, ettringite, calcite and belite. Differential Thermal Analysis (DTA) results confirmed the calcium hydroxide formation that is formed during normal hydration of cements. Leaching tests correlated the Total Organic Carbon (TOC) levels in the leachates with the proportion of the organic compound additioned.

Selective production of benzene and naphthalene from poly(butylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) by pyrolysis in the presence of calcium hydroxide

Poly(butylene terephthalate) (PBT) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) were pyrolysed in a fixed bed reactor in the presence of calcium hydroxide (Ca(OH) 2) in order to obtain benzene and naphthalene, respectively. In these experiments different ratios of polymer and Ca(OH) 2 were used. Also the temperature was varied in a range between 600 °C and 800 °C. It was found that the highest yield of benzene (67%) was obtained at a temperature of 700 °C and a molar Ca(OH) 2/PBT ratio of 10. The amount of carbon, fixed in the reactor residue after the experiment, was reduced from 56% for pure PBT to 38% under these conditions. Aromatic byproducts were reduced, as well, while the amount of 1,3-butadiene increased. Tetrahydrofuran was just formed under the influence of Ca(OH) 2. For PEN, the optimal conditions were found at a temperature of 600 °C and a molar Ca(OH) 2/PEN ratio of 5. A naphthalene yield of 80% from PEN was obtained. The rise of the naphthalene yield was caused by a more effective decomposition of the polyester by Ca(OH) 2, which led to the reduction of carbon in the reactor residue after the experiment from 59% for pure PEN to 10% under optimised conditions. The part of aromatic byproducts changed just slightly.

Precipitation recovery of boron from wastewater by hydrothermal mineralization

It is well known that boric acid exhibits various toxic effects on plant, animal and human beings even at very low concentrations. Thus, the development of boron-removal technique from wastewater has been intensively investigated. In this study, a new hydrothermal treatment technique was developed to recover boron as recyclable precipitate Ca 2B 2O 5·H 2O from aqueous solutions. As a result, it was found that the hydrothermal treatment using calcium hydroxide as a mineralizer converted boron in the aqueous media effectively into calcium borate, Ca 2B 2O 5·H 2O. In the optimal hydrothermal condition, more than 99% of boron was collected from the synthetic wastewater of 500 ppm. Thus, the present hydrothermal treatment in the presence of calcium hydroxide is recommended as one of the effective techniques to recover boron from aqueous media.

03/02190 Hydrogen production from heavy oil in the presence of calcium hydroxide: Sato, S. et al. Fuel, 2003, 82, (5), 561–567

03/02190 Hydrogen production from heavy oil in the presence of calcium hydroxide: Sato, S. et al. Fuel, 2003, 82, (5), 561–567

Kinetics of slag hydration in the presence of calcium hydroxide : Biernacki, J. J. et al. Journal of the American Ceramic Society, 2002, 85, (9), 2261–2267

Kinetics of slag hydration in the presence of calcium hydroxide : Biernacki, J. J. et al. Journal of the American Ceramic Society, 2002, 85, (9), 2261–2267

Hydrogen production from heavy oil in the presence of calcium hydroxide ☆

A new hydrogen production method, the HyPr-RING process was applied to a vacuum residue of Arabian light crude oil to clarify the effects of added water, calcium hydroxide, which absorbs carbon dioxide, and the reaction temperature. It was determined that when a sufficient amount of calcium hydroxide was present, it provided enough water to produce hydrogen and additional water was not necessary. To consume all of the carbon dioxide in 1 mol of carbon from the feedstock, 25 mol% of calcium hydroxide was needed and hydrogen production was saturated at 50 mol%. Carbon conversion was dependent mainly on the temperature and was slightly dependent on water and pressure. The reaction pressure was as low as 4.2 MPa. Thermal decomposition of the feedstock was the dominant reaction below 600 °C, which produced methane.

Kinetics of Slag Hydration in the Presence of Calcium Hydroxide

The reaction between ground granulated blast furnace slag (GGBFS) having an empirical formula of C7.88S7.39M3A and calcium hydroxide (CH) was investigated. The kinetics of the reaction were explored. Thermogravimetric analysis was used to monitor the consumption of CH from which rate constants were determined. Based on Knudsen's kinetic model, activation energies of 14.5, 17.9, and 22.6 kJ/mol were determined for three different mass ratios of slag and CH reacted over a temperature range of 15° to 50°C and hydrated for a period of time from 0 to 32 days. A comparison of the kinetics of the slag/CH reaction was made with slag/portland cement hydration. The basic features of both appear similar.

Alkaline activation of metakaolin and calcium hydroxide mixtures: influence of temperature, activator concentration and solids ratio

Metakaolin is a highly reactive metastable clay that reacts with alkaline solutions forming a cementitious material with high mechanical performance. This material fixes alkalis as structural components. When metakaolin activation is carried out with highly concentrated alkaline solutions in the presence of calcium hydroxide, the main reaction product is a sodium aluminosilicate similar to that obtained when metakaolin is activated in the absence of calcium hydroxide. Additionally, the formation of CSH gel as a secondary product is also observed. The rate of polymer formation is influenced by parameters such as curing temperature, alkali concentration, initial solids content, etc. When the activator concentration increases, a delay in polymer formation is produced, whereas temperature accelerates its formation. The solids ratio (metakaolin/Ca(OH) 2) does not influence the rate of aluminosilicate formation, but it is demonstrated that larger product precipitation is produced when the solids ratio increases.

Kinetics of Tricalcium Aluminate Hydration in the Presence of Boric Acid and Calcium Hydroxide

Isothermal calorimetry has been used to study the hydration behavior of tricalcium aluminate (3CaO·Al2O3) in the presence of calcium hydroxide (Ca(OH)2) and boric acid (H3BO3). Hydration has been initiated with water and boric acid solutions of 0.18M‐0.89Mand at constant temperatures of 25°‐55°C. The resulting hydration products have been characterized via X‐ray diffractometry. Hydration of a 1:1 molar mixture of 3CaO·Al2O3 and Ca(OH)2 in water forms 3CaO·Al2O3·6H2O and produces ∼241 kJ/mol of heat. In boric acid solutions with concentrations of &gt;0.27M, well‐crystallized 4CaO·Al2O3·½B2O3·12H2O forms. The amount of heat that is generated increases as the H3BO3 concentration increases. At H3BO3 concentrations of &gt;0.70M, the total amount of heat that is generated remains constant at ∼330 kJ/mol. The rate curves that are associated with hydration in boric acid solutions of &gt;0.27Mare characterized by two reaction peaks, which are separated by an induction period. The first peak indicates initial and rapid hydration, which occurs during the first hour. The second thermal event reflects the remainder of the 3CaO·Al2O3 that is being consumed. The length of the induction period increases as the H3BO3 concentration increases and decreases as the temperature increases. Such behavior is indicative of diffusion‐controlled processes. An amorphous calcium borate layer is believed to precipitate around the active 3CaO·Al2O3 particles, which retards hydration. Higher temperatures and/or solutions of lower H3BO3 content favor the formation of highly crystalline reaction products. These conditions are associated with a short induction period. The rapid precipitation of 4CaO·Al2O3·½B2O3·12H2O under such conditions may cause “flash set.”

Use of wastes of the sugar industry as pozzolana in lime-pozzolana binders: study of the reaction

Mineralogical studies of different wastes of the sugar industry, mainly sugar cane bagasse ash and sugar cane straw ash, have shown that such by-products are likely to be pozzolanic. Their use in lime-pozzolana binders could become an interesting alternative for developing countries. This paper presents a study that was aimed at monitoring the reaction between lime and wastes of the sugar industry having pozzolanic properties by evaluating 1) content of calcium hydroxide, dependent on time; 2) development of the pore structure, dependent on time; 3) study of the reaction products at different stages; and 4) mechanical properties of hardened pastes. The presence of calcium hydroxide was confirmed by x-ray diffraction analysis and thermogravimetic analysis of powder from samples of hydrated lime-pozzolana pastes. The reaction products in hydrated pastes were observed in a scanning electron microscope, and the pore structure was assessed using a mercury intrusion porosimeter. The results of the study show that sugar cane bagasse ash does not act like a reactive pozzolana, mainly due to the presence of unburned material and carbon, whereas sugar cane straw ash shows good pozzolanic activity comparable to that of rice husk ash.

Imaging of ASR Gel by Soft X-Ray Microscopy

The soft x-ray transmission microscope XM-1 was used to examine alkali-silicate reaction (ASR) gel morphology in an experimental investigation of the alkali-aggregate reaction (AAR). The XM-1 microscope is operated by the Center for X-ray Optics on beamline 6.1 of the Advanced Light Source, a third generation synchrotron radiation facility operated by the Ernest O. Lawrence Berkeley National Laboratory. The instrument is unique as samples can be observed wet, with high resolution (43 nm), over time, as chemical reactions proceed. Soft x-ray microscopy was used to examine the in situ reaction of ground ASR gel, obtained from a large dam, and solutions of sodium hydroxide, calcium hydroxide, and combined sodium and calcium hydroxide. From this investigation, it appears that ASR gel combines with alkalis present in pore solution to produce a reaction gel capable of swelling, while the reaction of the ASR gel in the presence of calcium hydroxide and no alkalis results in the formation of a structure resembling C-S-H. It is theorized that the formation of C-S-H or a related compound will decrease the degree of swelling that would otherwise result from the formation of an alkali-aggregate reaction product. The C-S-H-like structure may also contribute strength. These hypotheses are currently under investigation.

Mechanism of ettringite and monosulphate formation

The kinetics of the hydration process of the sulphoaluminate phase Ca 4(Al 6O 12)(SO 4) in the presence of calcium hydroxide and gypsum were studied by differential calorimetry, optical microscope and X-ray phase analysis. The first period of reaction is characterized by the presence of ettringite even in the case of stoichiometric composition of monosulphate. The liquid interlayer on the surface of the sulphoaluminate phase plays an important role in the kinetics of hydration. The solubility of the sulphoaluminate phase is higher in the lower pH values of the surrounding liquid phase which causes acceleration of the hydration process. Ettringite was created at a certain distance ( δ i ) from the surface of the sulphoaluminate phase. This thickness δ i depends on the content of a dissoluting Ca 4(Al 6O 12)(SO 4) phase.

Selective formose reactions initiated by γ-irradiation

Formose reactions initiated by γ-irradiation in the presence of inorganic bases selectively produce ethylene glycol and pentaerythritol as major products at room temperature in the presence of calcium hydroxide. The yield ratio of ethylene glycol to pentaerythritol depends on the initial concentration of formaldehyde. At low concentration, the main product is ethylene glycol, whereas pentaerythritol increases at high concentration. The decomposition of formaldehyde is inhibited by ethanol, a hydroxyl-radical scavenger. These results suggest that radical reactions play an important role in radiation-initiated formose synthesis, in contrast to thermal formose reactions.

Normal Pressure Double Carbonylation of Aryl Halides Using Cobalt(II) Chloride in the Presence of either Sodium Sulfide or Sodium Borohydride

Abstract Tetracarbonylcobaltate ion generated by a treatment of cobalt(II) chloride with either sodium sulfide or sodium borohydride under a normal pressure of carbon monoxide was capable of catalyzing carbonylation of aryl halides in the presence of calcium hydroxide and methyl iodide to give arylglyoxylic acids in good selectivity.