Papers by Keyword: Calorimetry

Abstract: Portland cement has been replaced with 50% ground, granulated blastfurnace slag (ggbs) of two types. The influence of 2 and 4% calcium nitrate accelerator on early hydration of such binders was investigated by isothermal calorimetry as well as X-ray diffraction and thermogravimetry. The strength development of mortar based on these binder blends has been followed up to 28 days and the influence of calcium nitrate discussed. One ggbs lower in SiO₂, A_l2O₃ and MgO yielded somewhat lower strength (about 90%) than the other. Addition of calcium nitrate led to lower strength at 1 day, but higher strength from 3 days on-wards. The blends with the two ggbs achieved similar strength at 7 and 28 days when blended with 4% calcium nitrate. Calcium nitrate led to more ettringite formation and AF_m phases (probably nitrate version) at 1-day sealed curing. However, the calcium hydroxide content was reduced. Potential explanations for calcium hydroxide reduction are discussed.

Abstract: The results of experimental studies on the effectiveness of insulation of electrical cables with fire-resistant coating are presented. Analysis of methods of cables products using shows a steady trend of increasing their using during the arrangement of premises. Fires and rapid spread of flame are possible during the exploitation of such structures. Statistics of cable products show a low level of safety due to using of combustible insulation, which is highly sensitive to high temperatures and fire. After the test, it is seen that the specimen of the cable without a fire-resistant coating supports self-combustion for more than 30 s, and the damage to the specimen is more than 100 mm. After testing the specimen with a fire-resistant coating, it is seen that the cable specimen doesn’t support self-combustion, and the damage to the specimen isn’t more than 40 mm. Inhibition of the process of ignition and propagation of flame for such specimen is associated with the decomposition of flame retardants under the action of temperature, which occurs with heat absorption and release of non-combustible gases (nitrogen, carbon dioxide), as well as changing the direction of decomposition towards non-combustible gases and flame retardant coke residue. This leads to an increase of the thickness of the coke layer and inhibition of heat transfer of high-temperature flame to the insulation material, which indicates the possibility of transition of combustible insulation of the cable with a fire-resistant coating to non-flammable materials, which aren’t spread a flame.

Abstract: Thermophysical parameters of Finemet-type initially amorphous alloy produced using rapid quenching technique were determined. The temperature intervals of phase and structure changes have been obtained using calorimetry and non-ambient X-ray diffraction methods. The electric resistance data were recalculated to alloy electrical conductivity which it was recalculated to heat conductivity using the Wiedemann–Franz law. Resulting parameters were used for heat processes simulation that occurs in amorphous material of built-up transformer core during annealing in nanocrystallization temperature interval. Heat treatment of different sizes twisted magnetic cores was optimized.

Abstract: An exothermic chemical reaction between cement and water or is called as hydration of cement produced heat in which gives significance impact to the cement or concrete produced. This hydration of cement is similar to geopolymerization as in geopolymerization, heat is liberated when any pozzolanic material mixes with alkaline solution. Heat released for both hydration of cement and geopolymerization can be measured in a form of calorimetric data. This paper reviews on the use of heat released information for a better understanding on the reaction kinetics of geopolymerization and correlating the heat released with several factors including concentration of alkaline solution, mixing designation and curing temperature.

Abstract: The purpose of this study is to investigate the rheological properties of alkali-activated slag prepared as a paste modified by various amount of polymer admixtures. Four commercial admixtures VINNAPAS^® 5023 L, 5111 L, 7016 F and 7220 E were used as polymer admixture in this study. These admixtures were incorporated to alkali activated slag pastes in quantities between 0.5 and 2% by mass of slag. Rheological properties as shear stress and viscosity of fresh pastes were examined by Discovery HR-1. Another main focus of this paper is the effect of selected admixtures on the heat of hydration of an alkali activated slag. Results indicate that addition of polymer admixtures affects the viscosity of the pastes and hydration process.

Abstract: This paper describes influence of milling on chemical properties of fly ash from Circulating fluidized Bed Combustion (CFBC). Specific properties of fly ash was determined using calorimetric measurement. It was determined heat properties and total content of calcium oxide CaO. The following methods of measurement were also performed: granulometric measurement and chemical analysis. The ash properties of non-milled and milled ashes were also described and evaluated and the ash reactivity was compared.

Abstract: The contribution focuses on the description of failure mechanism of atmospheric plasma sprayed multilayer thermal barrier coatings subjected to calcia-magnesia-alumino-silicate (CMAS) environmental attack. To identify exothermic and endothermic reactions which occurred during heating/cooling by means of calorimetry was also utilized initial yttria stabilized zirconia (YSZ) powder subsequently used for thermal spraying of multilayer thermal barrier coating system (TBCs), CMAS powder later on utilized for thin layer deposition and its mixture. Atmospheric plasma spray technique was used to produce the TBCs on a grit blasted nickel-based superalloy substrates, where CoNiCrAlY powder was used for deposition of a bond coat and YSZ powder was sprayed as a top coat. In accordance to the aerospace standard the thin layer of CMAS was deposited on as sprayed TBCs samples surface from its colloidal solution by paint brush method. Burner-rig test, utilizing direct propane-oxygen flame, was used for thermal cyclic exposition of the multilayer coated samples at the temperature of 1150 °C. Samples after thermal cyclic exposure test were investigated by means of materialographic analysis approaches. The significant reduction in life-time of CMAS coated YSZ top coat was observed due to lower melting point phase formation and molten silicate crystallization within the pores providing the spallation identified as a major mechanism of TBCs failure.

Abstract: The microstructure and mechanical properties were investigated in an industrial Al-Cu-Mg alloy processed by Equal Channel Angular Pressing ECAP and heating. The die used is formed by two channels intersecting at an angle 90°. Transmission Electron Microscopy (TEM) and orientation (ASTAR) imaging were used in addition to hardness measurements. After heating, a sub-micron grain size is retained. In addition, a further hardening is observed due to secondary precipitation. Differential Scanning Calorimetry (DSC) showed that the activation energy of θ’ precipitation is strongly lowered after ECAP.

Abstract: This paper describes chemical properties of fly ash from Circulating fluidized Bed Combustion (CFBC). There are shown thermal properties of fly ash using calorimetric measurement and the total content of calcium oxide CaO was determined. This paper describes the methods of measurement for determining these properties including granulometric measurement and chemical analysis. Also there were described and evaluated properties of fly ash and the reactivity of the fly ash was compared.

Abstract: Quenching is a critical step during the strengthening age hardening of Aluminium alloys. To obtain optimal technological results, parts should be quenched with the upper critical cooling rate. The precipitation behaviour of Al alloys during cooling from solution annealing and thereby the critical cooling rates are typically investigated by in-situ measurements with differential scanning calorimetry (DSC). Conventional DSCs are limited at cooling rates below 10 Ks^-1. Unfortunately, medium to high strength Al alloys typically have critical cooling rates between 10 and some 100 Ks^-1. Recently it was shown that dilatometry is generally able for in-situ detection of precipitation in Al alloys. Dilatometry allows controlled cooling up to some 100 Ks^-1 and therefore covers the cooling rate range relevant. In this work, we aim to show up and discuss possibilities and limitations of dilatometric detection of quench induced precipitates in 2xxx, and 7xxx Al alloys. The basic method will be presented and results will be compared with DSC work.