Authors:T. Zmijewski, Barbara Pacewska, and J. Pysiak
The influence of calcination conditions on changes in phase composition and porous structure was studied for hydrous aluminium
oxide, obtained by leaching out potassium salts from the products of roasting basic aluminium-potassium sulfate in hydrogen
atmosphere at 600C. The product of calcination at 350C in vacuum has the most developed porous structure with most pores
of internal radius within 10–60 . Calcination in air atmosphere at temperatures 700, 800, 900, or 1000C resulted in decrease
of specific surface of aluminium oxide and increase of the share of pores with internal radius above 60 in the overall porosity
of the samples. The reconstruction of the porous structure proceeds mainly as a result of coalescent sintering.
Authors:K. Jesenák, L'. Kuchta, P. Hudec, and V. Fajnor
Differences in mass loss occurring in the course of dynamic and isothermal heating of SiO2-aerogel and changes of specific surface and hydrophylicity during calcination were studied by thermal analysis. SiO2-aerogel was prepared from tetramethoxysilane (TMOS) hydrolyzed by ammonia solution at 0C with molar ratio TMOS: H2O:NH4OH 4:1:0.01. Differences are caused mainly by oxidation of organic matter and by diffusion of products of the oxidation. Heat
transfer has none or little effect on the differences. Samples calcined at temperatures about 300C reach maximum hydrophilicity
though they still contain small amounts of residual organic matter.
Authors:R. H. Meinhold, H. Atakul, T. W. Davies, and R. C. T. Slade
The structural changes occurring during the dehydroxylation of kaolinite have been followed using flash calcination to produce kinetically frozen calcines. The percentage of dehydroxylation was varied by changing the furnace residence time or temperature and/or heating speed. These calcination conditions affected the reaction kinetics, but the products depended only on the extent of dehydroxylation.
Authors:B. Liu, P. Thomas, A. Ray, and J. Guerbois
of MgO obtained from calcination of magnesium carbonate at different temperatures
has been investigated by means of hydration in a constant relative humidity
environment at 40°C for periods up to 24 days. Natural magnesite and AR
grade basic MgCO3 calcined in the range of 500–1000°C
was characterised in terms of surface area, crystallite size, morphology,
and hydration rate.
It was found that the hydration rate is dependent
on the surface area and crystallite size where temperature was the main variable
affecting them. The most reactive MgO was produced at the lowest calcination
temperature with the highest surface area and the smallest crystallite size.
The basic MgO specimens showed higher degree of hydration compared to the
natural MgO specimens due to the smaller surface area and larger crystallite
size. The low MgO content of the starting natural magnesite is also attributable
to the lower reactivity. This preliminary study serves as a mean to investigate
potential utilisation of reactive MgO as a supplementary cementitious material
in eco-friendly cements.
Authors:S. Felder-Casagrande, H. Wiedemann, and A. Reller
The calcination of limestone is one of the oldest technical processes and it is still of actual interest. Very early calcitic
mortars from Turkey have been investigated and compared with materials of other early civilisations i.e. with Egyptian mortars
containing gypsum as well as medieval dolomite-based mortars from alpine regions. Contemporary calcination procedures, in
particular the cement production, range among the most important global industrial processes causing non neglectable environmental
problems. Sustainable, solar energy assisted calcination technologies and the conversion of product CO2 into useful commodities are discussed.
present study, the calcination of sulfur-rich calcareous oil shales from the Negev deposits of Israel is investigated. The Negev oil shales naturally contain a large amount of calcite, which may functioned as a sulfur-removing adsorbent. Therefore, the
Calcination conditions of the precursor powders, i.e. temperature, type of atmosphere and duration, were determined with a
view to obtain superconducting powders with the most advantageous physico-chemical properties. Investigated were powders in
the Y−Ba−Cu−O system prepared by the sol-gel method. Thermogravimetric examinations of the powders have revealed that the
decomposition kinetics of BaCO3 determines the formation rate of the superconducting YBa2Cu3O7−x (‘123’) phase. It follows from the decomposition kinetics of BaCO3 that the process is the most intensive in argon, whereas in static air and oxygen it is the slowest. The phase composition
analysis (XRD) and low-temperature magnetic susceptibility measurements of the calcinated powders, confirm the above mentioned
changes in the decomposition kinetics. The reaction of barium carbonate can be completed if the calcination process is conducted
at the temperature of 850°C for 25 h, yielding easily sinterable powders for obtaining single-phase superconducting bulk samples
with advantageous functional parameters.
The pozzolanic reactivity of thermally treated zeolites was studied on the basis of the Chapelle test combined with X-ray
diffraction (XRD) and Fourier Transform (FTIR) spectroscopy, as well as thermogravimetric analysis (TG/DTG) and differential
thermal analysis (DTA). The raw zeolite samples are from the Pentalofos area, Thrace, NE Greece. Their main mineral constituent
is 'heulandite type-II', an intermediate type of the heulandite-clinoptilolite isomorphous series. Calcination of the samples
was carried out up to 400, 500, 600, 700 and 1000C for 15 h. The changes were recorded using the above methods. The deformation
of the zeolite crystal lattice starts at about 400C and proceeds as the temperature of thermal treatment rises. The thermal
treatment of zeolite at 400C improves its pozzolanic reactivity and accelerates the reaction with Ca(OH)2.
Authors:C. A. Strydom, E. M. van der Merwe, and M. E. Aphane
Summary Magnesium oxide was produced through calcination of magnesite ore. A rehydration percentage of MgO to Mg(OH)2 of higher than 60% is obtained using calcination temperatures of 1000°C and below. At these temperatures medium reactive MgO was formed. The extend to which dead burnt MgO (obtained after calcination at 1200°C and higher) may be rehydrated is dependent on the calcination time, but even after 1 h and using magnesium acetate as a hydrating agent only 40% of the initial product has rehydrated to Mg(OH)2. After 4 and more hours of calcinations at 1200°C, a maximum of approximately 14% of the initial MgO is rehydrated back to Mg(OH)2. Thermogravimetric analysis was performed on the various compounds to determine the amounts of Mg(OH)2 that formed.
Calcination of sepiolite and of two sepiolite/CsCl mixtures, unground and air-ground was investigated by thermo-XRD-analysis.
At 200 °C sepiolite, neat, mixed or air-ground with CsCl lost interparticle and zeolitic water. The framework of sepiolite
persisted during the dehydration but became defected, mainly in the air-ground mixture, less in the unground mixture and little
in the neat clay. At 500 °C, with the loss of bound water, the neat clay was folded and transformed into sepiolite anhydride.
In sepiolite/CsCl mixtures the dehydrated variety persisted but the degree of crystal-imperfection increased in the air-ground
mixture more than in the unground mixture. At 700 °C the neat clay remained crystallized, but the CsCl mixtures became amorphous.
Some crystalline dehydrated sepiolite or sepiolite anhydride persisted in the unground and air-ground CsCl mixtures, respectively.
At 850 °C, the neat clay crystallized into protoenstatite with some enstatite and clinoenstatite. The amorphous fraction of
sepiolite in the unground sepiolite/CsCl mixtures crystallized into pollucite and forsterite and the crystalline fraction
was transformed into enstatite, protoenstatite, and clinoenstatite. In the air-ground mixture, the amorphous phase was transformed
into pollucite with some forsterite and the crystalline fraction into enstatite.