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.
Authors:Vera Soares, L. Batista, and Rosane San Gil
incorporated into montmorillonite (MMT) though the controlled formation of
Mg(OH)2 followed by calcination. The evidence for Mg2+
in MMT before calcination was concluded from TG curves where two different
temperature ranges for Mg(OH)2 dehydroxylation suggested that the location
of Mg2+ at its internal and external surfaces.
FTIR by diffuse reflectance technique of calcined sample showed a typical
MgO band. XRD indicated a decrease in structural order and no collapse of
clay structure. The organic compounds adsorption to MMT modified with MgO
as suggested by increased degradation temperatures occurred at internal and
external clay surfaces besides in an area formed probably by MgO and MMT layers.
CuO based water nanofluid pool boiling heat transfer coefficient was about 35% compared to water as a baseline case. In the present work, the pool boiling heat transfer performance using deionized water and magnesiumoxide nanoparticles MgO based
Water, magnesium acetate,
magnesium chloride, acetic acid and hydrochloric acid were used as hydrating
agents for an industrially obtained MgO sample. The influence of these different
hydrating agents on the pH of the hydrating solution, degree of hydration
to Mg(OH)2, and product surface area was studied as
a function of the temperature of hydration. When compared to the hydration
in water, all hydrating agents improved the degree of hydration between 5
and 50% at all temperatures. MgCl2 and a mixture of
HCl and Mg(CH3COO)2 seemed to
be the most effective hydrating agents below 60C, while at temperatures
above 60C Mg(CH3COO)2 formed
the largest percentage Mg(OH)2. Mg(CH3COO)2
was the hydrating agent that showed the strongest temperature dependence.
The mechanism of the hydration reaction seems to be dependent of the availability
of Mg2+ ions and the increased formation of Mg(OH)2
as temperature increases.
The radioactive tracer technique was used to investigate the adsorption behaviour of 47 ions onto hydrous magnesium oxide. Detailed studies on Co(II), Zn(II), La(III) and Ce(III) reveal that the adsorption isotherms of these ions obey Langmuir's law. Radiochemical separation using hydrous magnesium oxide was applied to the RNAA of NBS standard reference materials, and satisfactory results were obtained. Hydrous magnesium oxide was also used to adsorb various ions from aqueous solution for the purpose of preconcentration which was followed by NAA or ICP-AES analysis. Satisfactory results have been observed in both methods.
The reaction between SiO2 and MgO at temperatures up to 1500°C was studied using thermal analysis, with X-ray diffraction being used to identify reaction
products. The reaction is slow and results in the formation of Mg2SiO4 and MgSiO3, with minor amounts of SiO2·nH2O and residual amounts of unreacted SiO2 and MgO. Complete reaction of the starting materials to form Mg2SiO4 can only be achieved by maintaining the mixture at 1500°C for extended periods of time (>1 h).
Authors:T. Ahmad, A. Sattar, S. Atta, A. Zeb, A. Ahmad, and S. A. Nagra
Rapeseed oil was used for frying of potato fillets (French fries) for 4 consecutive days at a rate of 20 minutes per day. The quality constants such as peroxide value (POV), anisidine value (AV), free fatty acid polar compounds (FFA%) and colour index (as OD at 420 nm) were determined before and after frying. The results showed an increasing pattern in the values of quality parameters. The POV increased from 4.42 to 17.00 meq kg-1, AV from 8.37 to 65.60, FFA from 0.02 to 1.90% and colour (absorbance at 420 nm) from 0.16 to 2.20. Fried rapeseed oil was mixed separately with 3 levels of MgO (2, 4 and 6% w/w) and activated charcoal (2, 6 and 10% w/w). For all the treatments the average % improvement of quality indices was statistically analysed. Increasing levels of both activated carbon and MgO significantly affected (P<0.05) the different quality parameters tested so far.
Authors:E. van der Merwe, Christiena Strydom, and A. Botha
Medium reactive magnesium oxide reacts incompletely with available water to form magnesium hydroxide. To enhance the hydration
of medium reactive magnesium oxide, the effect of magnesium acetate as hydrating agent was studied. The extent to which different
parameters (concentration of magnesium acetate, solution temperature and solid to liquid ratio of MgO to magnesium acetate)
influence the hydration rate of a medium reactive industrial sample of magnesium oxide were evaluated. The degree of rehydration
measured as percentage Mg(OH)2being formed, increases from approximately 56% using 0.5 M magnesium acetate solutions at 25C to 64% at 50C, to more than
70% at 70C. The major part of rehydration of the medium reactive MgO sample occurs within the first few minutes of the reaction
for all three temperatures studied.
It was found that trace amount of various ions could be effectively adsorbed onto hydrous magnesium oxide from aqueous solution. Attempts were made to investigate the feasibility of using hydrous magnesium oxide as preconcentration agent for neutron activation analysis (NAA). The procedure was successfully applied for the measurements of trace amounts of elements in the surface water of a number of large rivers which play very important roles in the lives of local people. Some of them are polluted rather badly. In order to improve the living standards it is rather important to establish reliable analytical methods so that more effective surveillance may be enforced on pollution control problems. NAA is generally accepted as one of the most suitable methods for simultaneous and multielemental determination of trace amounts of elements. In this work polluted surface waters were investigated by NAA using Tsing Hua Open-pool Reactor (THOR).
Authors:R. Mortier, C. Vandecasteele, J. Hoste, and F. den Hartog
The determination of boron in magnesium oxide using the10B/p, /7Be,10B/d, n/7Be, and10B/d, n/11C reactions is described. Lithium interferes the nuclear reactions leading to beryllium-7. Combination of a proton and deuteron irradiation, each followed by measurement of the induced beryllium-7 activity, allows a simultaneous determination of boron and lithium. The10B/d, n/11C reaction is free from nuclear interferences. The boron concentration ranges from 1.5 to 850 g g–1. The results obtained by the two methods are in good agreement.