Papers by Keyword: Reactivity

Abstract: Securing dense concrete structure and the intensification of cement hydration processes plays an important role in ensuring high concrete strength. The results of the applicability of dunite magnesian rocks of Central Aldan (Yakutia) for concrete production are presented. Petrographic and thermographic studies are conducted for the preliminary preparation of the charge. Pre-firing, fine intergrinding, and additional mechanical activation of the charge were applied. It is found that finely ground and pre-fired magnesium silicates act as both a micro-filler contributing to increased stone density and an active agent in forming robust crystallization structure. It is established that the use of pre-fired dunite powder with specific surface area of 8000 ± 200 cm²/kg in combination with the SP-1 superplasticizer allows obtaining autoclaved reactive powder concrete with a strength grade of up to B45.

Abstract: To activate the early-age hydraulic reactivity of steel slag powder (SS), a method of using acetic acid (AA)-anhydrous alcohol solution to modify the SS via dry chemical modification technology was proposed. The compressive strength and hydraulic reactivity of SS pastes and SS blended cement pastes were investigated, then the mineral composition, surface morphology and specific surface area of unmodified SS and AA modified SS were characterized. The results show that calcite, portlandite and dicalcium ferrite in SS react with AA to produce calcium acetate and pores in the modified process, thus leading to AA modified SS with the greater specific surface area and rougher surface. Water is easier to absorb onto the surface of modified SS and enters the inner of SS particles along the pores, resulting in higher dissolution heat and reaction heat of active minerals in SS. The result show that, the higher 72 h cumulative hydration heat, the 3 d, 7 d and 90 d compressive strengths of AA modified SS pastes and AA modified SS blended cement pastes are obtained, compared to the unmodified pastes.

Abstract: In the framework of method of the B3LYP hybrid density functional and the restricted Hartree-Fock method, quantum-chemical calculations of model compounds of lignin, i.e. derivatives of p-hydroxycinnamic alcohol were carried out. The structures and reactivity of coumaric, coniferyl and synapol alcohols were studied. Quantitative characteristics of the reactivity of these acids are given. It is found that the electronic structure of lignin is determined primarily by the charge distribution in its structural phenylpropane unit. In the molecules of all model compounds of lignin, the center for nucleophilic attack is the carbon of aromatic ring (E-ring) with a hydroxyl group, and in the molecule of synapol alcohol, this center is also the carbon of the aromatic ring (E-ring) with a methoxy group. In all three compounds, a center with an increased electron density appears on the С_β carbon atom.

Abstract: In this study, a magnesium oxide partially stabilized zirconia (Mg-PSZ) sample was prepared by granulation, molding, drying, and calcining. MgO was used as stabilizer, along with chemical-and electrofusion-made zirconium dioxide (ZrO₂) powder, as well as a different mixture of the two as the raw material. The effects of material reactivity on the sintering properties of the Mg-PSZ metering nozzle were studied by analyzing the physical properties and microscopic structure of the sample. The results show that, under the same sample preparation conditions, the electrofusion-made ZrO₂ had lower reactivity, resulting in a lower percentage of stable phase, loose adhesion among particles after sintering, more than 20% porosity, and poor antierosion and antiscouring performance. However, electrofusion-made ZrO₂ only had a shrinking percentage of 6%, leading to a higher sintering yield. However, compared with the electrofusion-made ZrO₂, chemical-made ZrO₂ had a higher reactivity, better sintering properties, more stable phase component, and approximately 75% less porosity. Chemical-made ZrO₂, however, had a shrinking percentage as high as 20%, causing serious sample cracking after sintering. Therefore, both types of ZrO₂ are not ideal as the only raw material for Mg-PSZ metering nozzles. Nonetheless, when a 1:1 mixture of the two types of ZrO₂ was used as the raw material, the calcined sample showed better property parameters in porosity and volume density, as well as compressive strength, satisfying the requirements for Mg–PSZ-based metering nozzles.

Abstract: The carbonate components effect of raw materials - chalk and limestone on the clinker properties has been determined. Studies have been carried out on the raw mix these components partial replacement with the Oskol electrometallurgical plant slag in the amount of 10 and 20%. The maximum decrease in the carbonate component amount was 10%. The grinding clinker individual stages, characterized by the material destruction certain processes have been analyzed. It has been established that by reducing the chalk content in the raw mix and replacing it with the Oskol electrometallurgical plant slag, the clinker grindability is improved. The duration of grinding of such clinker is reduced by 22%. A decrease in the limestone amount in the raw mix and an increase in the Oskol electrometallurgical plant slag content does not affect the synthesized clinkers grindability.

Abstract: Limestone is used in the flue gas desulphurization process due to its ability to form sulfur compounds. Different qualities of limestone absorbents can be used in the process and it is therefore important to measure the reactivity of these materials. A limestone with a 90 to 95% of calcium carbonate is used to prepare limestone slurry for the flue gas desulphurization. It is very important to explore the different properties of the raw material for a better understanding of the desulphurization process and also the impact on the economic aspect of the process [1-3]. This article presents a study about limestones reactivity, which is measured by the Bischof-Uhde method. At first the study monitors the impact of the milling of set of Czech limestones on their reactivity and furthermore deals with the influence of the genesis and porosity of the set of world limestones also on the reactivity of limestones in the desulphurization process.

Abstract: The main components of polymer carboxyl group are introduced.The effects of macromolecular carboxyl groups on the limestone-gypsum wet flue gas desulfurization (FGD) system of coal-fired power plants in China were studied by test method. The results showed that the macromolecular carboxyl groups can accelerate the chemical absorption of SO₂ under the action of active agents and crystallization agents, improve the desulfurization efficiency of about 2%, and shorten the limestone ablation time of more than 40%, catalytic calcium sulfite oxidation of calcium sulfate.

Abstract: Limestone as a natural rock tends to have various parameters. Variation in parameters, as well as firing temperature have significant impact on key properties of quicklime. Sedimentation volume and reactivity determine quality of quicklime in building industry. This paper is focused on monitoring the reactivity and sedimentation volume of quicklime prepared from various types of limestone at different temperatures. Selection of limestones with high purity collected from various quarries around the world were characterized by porosity, chemical and petrographic composition. To create quicklime, these samples were fired at 4 different temperatures. Reactivity measurements were made on quicklime with specific particle size. Sedimentation volume of hydrated slurry was determined. Obtained results suggest that there is tendency for slower reactivity and smaller sedimentation volume with increased firing temperature.

Abstract: The article contains a block diagram of the mechanical activation process of multicomponent shape memory materials, taking into account the variety of influencing factors. We proposed to evaluate the reactivity of the deposited material by using the energy criterion (energy intensity), determined by additivity concept as an amount of the basic material energy and energy accumulated during mechanical activation. The energy intensity of the basic material depends on the chemical and phase composition and is determined by the thermodynamic characteristics and is based on diagrams of the systems. The energy accumulated during the MA, is determined on the basis of X-ray structural analysis. We have shown experimentally that increase in fineness of grind leads to growth in the number of active centers. This enables nanopatterning of surface layers in high-velocity oxygen-fuel spraying (HVOF). Increasing the time of MA (1.5 h) promotes a more homogeneous structure during HVOF. The study results allow developing practical recommendations for effective implementation of multi-component SME materials with HVOF.

Abstract: The universal reactivity-mapping tool was developed for characterization and study on barrier properties of selected biopolymers. The reactivity of biocolloids (humic acids) was studied by both diffusion techniques (break-through diffusion technique and non-stationary diffusion). The rate of reactivity of humic acids was compared by the interactions with basic cationic organic dye (Methylene Blue) because of the positive interactions among anionic supramolecular humic acids and cationic organic dyes were expected. The reactivity and barrier properties of biocolloids were compared by determination of fundamental diffusion parameters such as effective diffusion coefficient, sorption capacity, break-through time (the time needed for penetration of chosen organic dye through hydrogel porous barrier) or the concentration of organic dye on the interface hydrogel-solution. The original combination of simple diffusion experiments of suitable diffusion probe (organic dye) with the advantages of hydrogel porous media (simple preparation of hydrogels, the diffusion is undisturbed by convection, etc.) provides very valuable information about the reactivity of chosen biocolloids.