Search Results

You are looking at 151 - 160 of 2,195 items for :

  • "treatment" x
  • Chemistry and Chemical Engineering x
  • All content x
Clear All
Journal of Thermal Analysis and Calorimetry
Authors: A. de Oliveira, J. Ferreira, Márcia Silva, Soraia de Souza, F. Vieira, E. Longo, A. Souza, and Iêda Santos

Abstract  

NiWO4 and ZnWO4 were synthesized by the polymeric precursor method at low temperatures with zinc or nickel carbonate as secondary phase. The materials were characterized by thermal analysis (TG/DTA), infrared spectroscopy, UV–Vis spectroscopy and X-ray diffraction. NiWO4 was crystalline after calcination at 350 °C/12 h while ZnWO4 only crystallized after calcination at 400 °C for 2 h. Thermal decomposition of the powder precursor of NiWO4 heat treated for 12 h had one exothermic transition, while the precursor heat treated for 24 h had one more step between 600 and 800 °C with a small mass gain. Powder precursor of ZnWO4 presented three exothermic transitions, with peak temperatures and mass losses higher than NiWO4 has indicating that nickel made carbon elimination easier.

Restricted access

Abstract  

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.

Restricted access

Abstract  

Bone provides an important source of forensic evidence. The storage conditions of bone have been recognised as a factor in maintaining the integrity of such evidence. Thermogravimetric analysis (TG) has been employed to examine the effects of storage environments and preparation methods on the structural properties of pig bones. A comparison of oven and freeze drying has been made to study the effect of storage conditions. A comparison has also been made of ground bone specimens with cut specimens. Freeze-dried hand ground specimens provided the most consistent results and, thus, this is the recommended method of preparation of bone specimens for TG analysis.

Restricted access

Abstract  

An extensive thermodynamic study has been carried out on aqueous solutions, obtained through the iteration of two processes: a dilution 1:100 in mass and a succussion. The iteration is repeated until extreme dilutions are reached (less than 1⋅10–5 mol kg–1 ) to the point that we may call the resulting solution an 'extremely diluted solution'. We conducted a calorimetric study, at 25C, of the interaction of those solutions with acids or bases. Namely, we measured the heats of mixing of acid or basic solutions with bidistilled water and compared them with the analogous heats of mixing obtained using the 'extremely diluted solutions'. Despite the extreme dilution of the latter solutions, we found a relevant exothermic excess heat of mixing, excess with respects to the corresponding heat of mixing with the untreated solvent. Such an excess has been found in about the totality of measurements, and of a magnitude being well beyond one that could arise any issue of sensibility of the instrumental apparatus. Here we thus show that successive dilutions and succussions can permanently alter the physico-chemical properties of the solvent water. The nature of the phenomena here described still remains unexplained, nevertheless some significant experimental results were obtained.

Restricted access

Separate stages of mathematical processing of thermogravimetric data, the difficulties most often encountered, and typical error sources are considered. A complex procedure of automatic acquisition and editing of experimental data, including calculation of effective kinetic parameters, is described and an appropriate algorithm for the 15 BCM-5 microcomputer is presented. The computer calculation of the kinetic parameters of the multistage thermal decomposition of a polyamide fibre is given as an example.

Restricted access

Abstract  

Properties of limestone related to SO2/SO3 reactivity were investigated. Limestone calcined under different conditions (temperature, time and with/without additives) yield calcines of distinctly different physical structures. The amount of pores and the size of the pores formed during calcination is important. The main purpose of the present work was to gain a better understanding and more reliable explanation of the temperature regime for gas desulphurization using Ca-based sorbents in atmospheric fluidized-bed combustors. Pore size, surface area and pore volume of each calcine were determined by mercury porosimetry and BET methods. At higher calcination temperature and during longer time, sintering became significant and the obtained calcine had a smaller internal surface area and thereby the average pore radius increased. The additives such as NaCl also accelerated sintering thus increasing the pore size. The measurements of porosity were supplemented by scanning electron microscopic observations employed for qualitative description of the pore structure. SEM micrographs are presented.

Restricted access

Abstract  

Since April 29, 1986, the radioactive contamination resulting from the accident of the Chernobyl reactor has been measured in various kinds of matrixes, with particular regard to Northern Italy. Here we present the data obtained for137Cs from several measurements effected on milk and dairy products over the period of one year. In particular, we have studied the transfer kinetics of137Cs from forage to milk by feeding dairy cows with forage of known activity and we have evaluated the body Cs absorption by measuring the percentages of Cs eliminated with milk as well as with urine and feces. Further, the decay rate of137Cs in milk has been assessed and the results of the kinetic, analysis are reported. We have also evaluated the efficacy of various clay materials in removing Cs from milk. Here we report the results of adsorption kinetics for the grey clay which resulted the most effective material.

Restricted access

Abstract

The thermal behavior of tin containing oxalate, EDTA, and inositol-hexaphosphate were investigated. The end products of synthesis were identified by Mössbauer-, XRD analyses, and FTIR studies. The thermal decompose of the samples was studied by DTA-TG analysis. The simultaneously obtained DTA and TG data makes it possible to follow the thermal decomposition of the investigated samples. The tin oxalate decomposed in the temperature range of 520–625 K through tin carbonate formation and finally yielded CO2 and SnO. The tin EDTA complex first lost its hydrate bound water till 520 K. The followed thermal events related to the pyrolysis of anhydrous salt. The intense exothermic process that exists in the temperature range of 820–915 K is due to the formation of SnO2. The tin sodium inositol-hexaposphate lost its hydrate bound water (∼10%), up to 460 K. The following sharp exothermic process, in the temperature range of 680–750 K is due to the decomposition and parallel oxidation of organic part of the molecule. At the end of this process, a mixture of phosphorous pentaoxide, sodium carbonate, and tin dioxide is obtained.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: M. Kubota, Y. Kanazawa, K. Nasu, S. Moritake, H. Kawaji, T. Atake, and Y. Ichiyanagi

Abstract  

MgFe2O4 (Mg-ferrite) nanoparticles encapsulated in amorphous SiO2 were prepared by the wet chemical method. The particle sizes were estimated, based on the X-ray diffraction peaks, to be between 3 and 8 nm, depending on the annealing temperature. The particle size increased as the annealing temperature increased. From the magnetization measurements, the blocking temperature, T b, was found to be between 30 and 60 K. The magnetization values varied with the annealing or quenching conditions. To clarify the process of crystal growth, thermogravimetric and differential thermal analysis (TG-DTA) measurements were performed and the results were compared with the X-ray diffraction patterns.

Restricted access

Abstract  

Apricot stone shells were carbonized under certain chemical and thermal conditions to produce sorbents having a quantitative affinity to retain some radioactive nuclei. The sorbent shows a thermal stability upto 500 °C. The diffraction patterns clarify that the sorbent is mainly amorphous in structure. Carbon in these shells was elementally analyzed and the data reveal a predominant content of acidic surface centers with hydrophilic properties. The isoelectric point (pHPZC) was determined and found to be 4.2 implying the acidic nature of the sorbent surface. The sorption of Cs+, Co2+ and Eu3+ on the prepared sorbent was studied from aqueous solution under different variables and the sorption capacity had values from 0.23-1.15 meq/g.

Restricted access