Hydration of portland cement in the presence of aluminum-containing setting accelerators

Portland cement hydration in the presence of two different aluminum-containing compounds, highly dispersed amorphous Al(OH)₃ and aqueous solution of aluminum hydroxosulfate Al(OH)_1.78(SO₄)_0.61, was studied by solid-state ²⁷Al and ²⁹Si NMR spectroscopy.     

Hydration of Portland cement in the presence of high activity aluminum hydroxides

The effect of highly dispersed amorphous aluminum hydroxides on the hydration of Portland cement was studied by the solid-state ²⁷Al and ²⁹Si NMR spectroscopy. It was established that in the presence of aluminum hydroxides the decrease in the setting time of a cement paste is due to rapid formation of ettringite phase, with contribution of admixture material the main and contribution of aluminum-containing phases at this stage insignificant.     

Hydration of C3a in the presence of CaCO3

The hydration of C₃A with and without CaCO₃ was studied. The techniques used were X-ray diffraction, thermogravimetry, differential thermogravimetry and calorimetry.In the presence of CaCO₃, the hydration of C₃A is accelerated. The hexagonal hydrates are formed first. They react with CaCO₃ to form calcium carboaluminate hydrate. This reaction blocks formation of the cubic hydrate. The latter appears when CaCO₃ is completely consumed.     

A calorimetric investigation of the formation of a stereocomplex in poly(methyl methacrylate) solutions

The heat of formation ΔH of the stereocomplex of iso + syndiotactic poly(methyl methacrylate) in a 1 per cent solution in dimethylformamide and in toluene was measured. From the concentration dependence of ΔH it may be inferred that multimolecular aggregates are formed, with a composition given by the ratio syn: iso = 1·5: 1 to 2: 1. The measurements also indicate a strong dependence of the thermal effect on the quality of the solvent and on the tacticity of both polymer components.     

A calorimetric investigation of the assembly of gold nanorods to form necklaces

Interaction of gold nanorods with cysteine as well as 3-mercaptopropionic acid (MPA) has been investigated by isothermal titration calorimetry (ITC), in combination with electronic absorption spectroscopy and electron microscopy. The assembly process with MPA shows two steps, the first due to the binding of MPA to gold nanorods through the sulfur atom, and the second due to assembly of the MPA capped gold nanorods through the formation of cyclic hydrogen bonded dimers between the MPA molecules. In the case of cysteine only a single step is observed in ITC, due to the binding of the molecules to gold nanorods.     

A new approach to the calorimetric investigation of physical and chemical transitions

The theoretical basis for Modulated DSC is described and the additional information in can give over conventional DSC illustrated for some polymers.     

Hydration behaviour of a lime-pozzolan cement containing MSW incinerator fly ash

A lime-pozzolan cement was used to make pastes containing different quantities of MSW fly ash. After setting, the pastes were cured in water at room temperature from 1 h to 260 days. The hydration characteristics and the nature of the hydration products of the various pastes were studied by simultaneous TG/DSC thermal analysis and X-ray diffractometry. The MSW fly ash was found to induce a slowing of the hydration process in lime-pozzolan pastes, and after some days an evident acceleration of hydration reactions occurred. Sulphate and chloride in the MSW fly ash yield hydration products forming a cementitious matrix.The author is grateful to D. Calabrese for assistance with the thermal and XRD analyses.     

A parametric investigation of the friction performance of PC‐ABS parts processed by FDM additive manufacturing process

The friction performance is an important factor of parts processed by fused deposition modeling (FDM) for various engineering applications. It is one type of failure made of surface contact. The proper use of FDM process parameters can bring a significant reduction in friction and the amount of wear, thereby leading to a reduction in the material waste. To date, very little studies have been performed in this area. This paper investigates the effect of FDM manufacturing parameters on the friction performance of polycarbonate‐acrylonitrile butadiene styrene prototypes processed by FDM using definitive screening design and partial least squares method. The observation of surface morphology was obtained by the scanning electron microscopy to examine the effect of process parameters on the microstructure. The experimental results have shown that layer thickness, air gap, raster angle, and build orientation are the most influential factors affecting the friction performance of FDM manufactured parts. The proposed approach presented in this study provides an impetus to develop analytical modeling and functional relationships between FDM manufacturing parameters and friction performance. Copyright © 2017 John Wiley & Sons, Ltd.     

High-resolution calorimetric investigation of the existence of a nematic phase for the dodecylcyanobiphenyl liquid crystal

We have employed high-resolution calorimetric techniques in order to investigate the unresolved issue of the existence of a nematic phase for the liquid crystal dodecylcyanobiphenyl. Various heating and cooling runs were performed on dodecylcyanobiphenyl samples of different origin and their analysis did not reveal any signature of a nematic phase. The calorimetric results are presented in detail and they are additionally supported by optical polarising microscopy observations.     

Humidity controlled calorimetric investigation of the hydration of MgSO4 hydrates

The isothermal heat of hydration of MgSO₄ hydrates was studied by humidity controlled calorimetry. Two hydrates, starkeyite (MgSO₄·4H₂O) and a mixture of MgSO₄ hydrates with summary 1.3 mol H₂O were investigated. The solid-gas reactions were initiated at 30°C and 85% relative humidity. The heat of hydration was determined in a circulation cell in the calorimeter C80 (Setaram). The crystal phases formed after the hydration process were analyzed by thermogravimetry (TG) and X-ray powder diffraction (XRD). Starkeyite reacted with the water vapour to the thermodynamic stable epsomite and the MgSO₄ hydrate mixture with 1.3 mol water to hexahydrite. The hydration heats of starkeyite and the mixture were determined to be −169±3 and −257±5 kJmol⁻¹, respectively.     

Hydration forces between bilayers in the presence of dissolved or surface-linked sugars

We analyse the experimental evidence of the hydration force near phospholipid bilayers when the “solvent” is a solution of carbohydrates. Two cases must be clearly distinguished: when sugar is dissolved, depletion causes a supplementary attractive force, while in the case of sugar linked to the lipid the contact pressure increases by orders of magnitude. Attractive interaction inferred between bilayers is sometimes derived from indirect evidence, i.e. scattering, attraction between layers adsorbed, shape of phase boundary limits, and without the simultaneous determination of the osmotic compressibility. Generally, water molecules in the first hydration shell of sugar compete with water molecules bound (by more than one kT in free energy) to lipid head-groups. A general result is that the decay length of any repulsive effect remains close to 0.2 nm, even in concentrated sugar solutions. A tentative general explanation of this experimental fact is given together with consequences, such as the possibility of several types of critical points appearing in bilayer stacks. Decay length as well as effective contact pressure is considered with respect to carbohydrate activity.     

Evaluation of quantum yields in the presence of an absorbing additive

A method is proposed for the evaluation of quantum yields of photochemical reactions studied in the presence of absorbing additives using cylindrical sample tubes.

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Hydration of alkenes and cycloalkenes in the presence of chromium and copper complexes

Chromium and copper complexes catalyzed hydration of acyclic and cyclic olefins in the presence of carbon tetrachloride at 110–160°C (4–12 h) with formation of the corresponding alcohols.     

Novel calorimetric investigation of different degenerative disorders of the human hyaline cartilage

The purpose of this investigation was to further elucidate calorimetric properties of cartilage samples from femoral head necrosis and osteoarthritis from live surgeries. The natural course of this disease is one of steady progression with eventual collapse of the femoral head, followed by secondary osteoarthritis in the hip joint. All samples showed a clear denaturation peak on the calorimetric curve. Cartilage obtained from necrotic femoral head required the lowest amount of energy for decomposition. The use differential scanning calorimetry as part of thermal analysis was a reliable method for differentiating.     

Calorimetric study of the ionization process for 2,5-dihydroxybenzoic acid. Resonance effect. A calorimetric acidity scale for dihydroxy-substituted benzoic derivatives

A calorimetric study of the ionization process of 2,5-dihydroxybenzoic acid, in water—DMSO mixtures, ranging from pure water up to 0.8 mole fraction is presented.This compound shows a very different behaviour with respect to the 2,3-dihydroxy derivative because of the two hydroxyl groups which, in the relative para position, stabilize and delocalize the charge on the anion. For this reason, 2,5-(OH)₂PhCOOH is, with the exception of 2,6-(OH)₂PhCOOH, the strongest acid in an acidity scale of dihydroxy derivatives.     

Designing a safer process for the reaction of TFA with sodium borohydride in THF by calorimetric technique

Reaction of TFA with sodium borohydride in THF is a loss of thermal control involving the evolution of Hydrogen gas. The investigation of the process by RC1e and ARSST showed that the criticality class of the reaction is dependant on the addition of TFA. Heat of reaction (Q _r), adiabatic temperature rise (ΔT _ad), and MTSR data are obtained from RC1e experiment. Exothermic onset temperature, Pressure rise, and self heat rate data are obtained from ARSST experiments. The correlation of these data was utilized to define the criticality class of the reaction under different conditions. The reaction with uncontrolled addition of TFA falls in the undesirable criticality class 5. Vent size data are obtained from the adiabatic calorimeter for undesirable reaction. The criticality class can be changed to class 2 with controlled addition. Accordingly, interlock system to control the undesired reaction and appropriate vent relief system are provided.     

Gas hydrate phase equilibria for propane in the presence of additive components

A proper discussion on the possibility and feasibility of technological applications for gas hydrates requires knowledge of the phase behaviour and its relation to the gas hydrate structure and its occupation. This paper presents experimental data on gas hydrate phase equilibria for the system water+propane and for various systems of the kind water+propane+additive. The additives considered are tetrahydropyran, cyclobutanone and cyclohexane, which are assumed to occupy the large cavity of structure II (sII) hydrate, and methylcyclohexane that is a typical structure H (sH) hydrate former. All additives have in common that they are very poorly soluble in water and, therefore, an additional liquid phase is present in these systems. The pressure for the equilibrium hydrate–liquid water–vapour (H–L_w–V) in the system water+propane is reduced upon addition of each of these components. Simultaneously, the hydrate equilibrium hydrate–liquid water–liquid propane (H–L_w–L_C3H8) is shifted to lower temperatures. These observations can be explained in terms of mutual miscibility of propane and the additive component. However, it cannot be excluded that propane molecules are exchanged by additive molecules in occupying the large cavity of sII.