Mahmood M. Barbooti

Thermal decomposition of citric acid

Abstract The thermal decomposition of citric acid is studied by thermogravimetry (TG) derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) techniques under various conditions. The thermal decomposition reactions of the acid are influenced by its particle size and the different heating rates used. Data obtained from the thermal curves were employed for mechanistic and kinetic studies using computer programs and manual computations. The decomposition follows the Jander diffusion mechanism and is of first order with an activation energy of

Thermochemical studies on hot ash corrosion of stainless steel 304 and inhibition by magnesium sulphate

200 k J mol−1.

Electrothermal atomic-absorption spectrophotometric determination of molybdenum

Abstract The accumulation of mineral ashes from residual fuel oil combustion on stainless steel surfaces causes fouling and corrosion resulting from the formation of low melting aggressive compounds. TG, DTA and weight loss experiments were carried out to study the effect of added MgSO 4 in depressing hot ash corrosion on stainless steel 304. Magnesium sulphate raised the melting point of the ash and inhibited the formation of sodium vanadate by formation of the more stable magnesium vanadates. The techniques employed help in determining the optimum amount of the chemical inhibitor to be added. When excesses of MgSO 4 were used, the iron was further protected; however, attack by chromium was relatively increased.

Effects of nickel(II) oxide on the thermal decomposition of alkali persulfates

The sensitivity for determining Mo by ETA-AA is dependent on the heating programme employed when the peak-height method is used, but not when the peak area is used for evaluation of the AA signals. The linear range is greater at lower heating rate. Molybdenum can be directly determined in up to 8% NaCl solution without chemical pretreatment or background correction by making use of the high ashing temperature allowed, at which the matrix NaCl can be totally removed. The minimum recovery is 94.5%. Amounts of alkaline earth metals greater than 4000 times the amount of Mo give scatter signals, but these are time-resolved from the Mo signal. Any small effect on the peak height or area can be compensated for by background correction. The interference of tungsten is significant even at low concentrations (2-5 mug/ml) owing to the formation of stable compounds. Mo is determined in brines and acid digests of phosphate rocks after preconcentration and separation with the APDC-MIBK system, by ETA-AA of the organic extracts with or without mineralization.

Use of silica gel in the preparation of used lubricating oil samples for the determination of wear metals by flame atomic absorption spectrometry

Abstract The thermal decomposition of Na 2 S 2 O 8 and K 2 S 2 O 8 has been studied derivatographically in the presence of NiO at various molar mixtures. Experiments have proved that the first decomposition stage (persulfate into pyrosulfate) is independent of the amount of the oxide present. During the second decomposition stage (pyrosulfate into sulfate) which occurs in the melt, NiO plays the role of lowering the melting, the initial and final decomposition temperatures of pyrosulfates. The lowest melting temperatures recorded for Na 2 S 2 O 8 and K 2 S 2 O 8 are 320 and 280°C, respectively. A mechanism has been proposed to describe the catalytic action of NiO on the thermal decomposition of alkali pyrosulfates. The mechanism makes use of the semiconductivity of NiO and the availability of electron-rich centers in the pyrosulfate group to help the formation of an adsorption complex between them. NiO reacts to some extent with alkali pyrosulfates forming the yellow NiSO 4 and alkali sulfates as separate products. NiO and NiSO 4 form eutectic mixtures with alkali sulfates melting at temperatures lower than those of the pure salts.

Determination of Trace Metals and Their Distribution in Heavy Crude Oil Distillates (350°C+) by Atomic Absorption Spectrophotometry:

Used lubricating oils were analysed for Cr, Fe, Mg and Pb using flame atomic absorption spectrometry after three types of sample preparation: direct dilution with an organic solvent, dry ashing-acid dissolution and dry ashing in the presence of a porous inert material (silica gel). The porous material prevented sputtering and volatilisation of the sample and hence a rapid charring-ashing programme could be employed. Results of the three methods of sample preparation indicated that direct dilution could be applied to highly volatile metals such as Pb which could be lost during the heating periods required for ashing. Dry ashing was particularly useful for all the metals studied provided that the rate of heating was slow. The proposed method, however, combines the advantages of dry ashing and rapid sample preparation because lubricating oil samples containing silica gel behave as solid samples and hence no loss of the metals occurs during heating, except for the highly volatile metals which could not be determined with sufficient precision using this method. The determination of metals in lubricating oils must be carefully carried out taking into account possible changes in their concentration during storage. In addition, metallic particles may precipitate on storage; hence vigorous shaking and other homogenisation procedures need to be employed prior to analysis.

Electrothermal atomic-absorption determination of vanadium

The concentration of Cu, Fe, Na, Ni, and V were determined in four heavy distillates from three heavy crude oils and one commercial crude oil by atomic absorption spectrophotometry. The distillates were extracted by DMF in order to estimate the porphyrinic (extract) and nonporphyrinic (residue) fractions of V and Ni contents. The V was distributed almost equally between the two types, while most of the Ni content was in the nonporphyrinic form. The asphaltene and resin fractions of the distillates were isolated and analyzed for their Ni and V contents. It appeared that about 90% of these metallic species of the distillates were concentrated in these two fractions, which in turn share these metallic compounds equally.

Thermoanalytical investigations on heterocyclic organic compounds. Part I. Thermal decomposition of pyrazolinoimides

Factors such as sample nature, matrix and heating programme have been found to influence both the sensitivity and precision of the determination of vanadium by electrothermal AAS. The reciprocal sensitivity, detection limit and precision (RSD) are 55 pg, 86 pg and 4%, respectively for aqueous solutions and 88 pg, 80 pg and 4% for organic solutions. Only tungsten and nitric acid have been found to interfere appreciably. Moderately concentrated sodium chloride solutions (6%) can be analysed for vanadium (0.05 mug/ml) without background correction, as can the acid digests of phosphate rocks and crude petroleum samples.

Non-isothermal kinetic studies on the effects of semi-conductive metal oxides on the thermal decomposition of barium perchlorate trihydrate

Abstract Pyrazolinoimides undergo denitrogenation reaction upon heating to form the cyclopropane derivatives and the corresponding olefins. They are studied by dynamic TG, DTG, DTA and DSC techniques. The enthalpies and kinetic parameters are evaluated. Further decomposition of the compounds led to carbon, and in some cases, polymeric products are suspected to be formed. The fluorene derivatives behave differently and undergo irreversible isomerization in the melt prior to decomposition. Practical mechanistic steps are postulated in order to explain the formation of the decomposition, rearrangement and isomerization products during thermal treatment.

Electrothermal atomic-absorption determination of barium in brines and caustic soda solutions

The evaluation of kinetic parameters and mechanism of the thermal decomposition of barium perchlorate trihydrate (BP) from non-isothermal analytical measurements using TG, DTG, and DTA have been obtained in the presence of β-MnO2 and Eu2O3. Both oxides catalyze the thermal decomposition of BP, and from the kinetic viewpoint they lower the activation energy by a factor of 2.5. Both of them remain chemically unchanged during the course of the decomposition of BP. A new mechanism has been proposed for the dehydration process to interpret the role of the oxide in it. Methods such as those of Freeman and Carroll and Coates and Redfern have been employed to estimate from TG curves, order of rection, activation energy, and pre-exponential factor for the thermal decomposition of BP, alone and in binary mixtures with each oxide. For the sake of checking, a modified computer program for the Coates and Redfern method has been introduced to compute the above mentioned parameters.