Thermal decomposition of the synthetic hydrotalcite iowaite

The thermal stability and thermal decomposition pathways for synthetic iowaite have been determined using thermogravimetry in conjunction with evolved gas mass spectrometry. Chemical analysis showed the formula of the synthesised iowaite to be Mg_6.27Fe_1.73(Cl)_1.07(OH)₁₆(CO₃)_0.336.1H₂O and X-ray diffraction confirms the layered structure. Dehydration of the iowaite occurred at 35 and 79°C. Dehydroxylation occurred at 254 and 291°C. Both steps were associated with the loss of CO₂. Hydrogen chloride gas was evolved in two steps at 368 and 434°C. The products of the thermal decomposition were MgO and a spinel MgFe₂O₄. Experimentally it was found to be difficult to eliminate CO₂ from inclusion in the interlayer during the synthesis of the iowaite compound and in this way the synthesised iowaite resembled the natural mineral.     

Thermoanalytical Study of the Dehydration of Cyclodextrin Inclusion Complexes of Clofibric Acid

Hydrated inclusion complexes of the hosts β-CD (CD=cyclodextrin), γ-CD and permethylated β-CD with the guest clofibric acid were analysed by TG and DSC methods to characterise their dehydration behaviours. Activation energies for dehydration of the β- and γ-CD clofibric acid complexes, determined by isothermal thermogravimetry, are significantly lower (∼20-25%) than those for the corresponding uncomplexed hydrated CDs. These data can be reconciled with X-ray structural data which show that H₂O molecules in the complexes occupy different crystal sites from those occupied in the parent CDs. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Kinetic Study of the Dehydration of VOPO4.2H2O by Thermal Methods

The dehydration of VOPO₄.2H₂O hasbeen studied by thermogravimetric analysis (TGA),differential thermal analysis (DTA) and differentialscanning calorimetry (DSC). From the shift of the DTA,DTG, and DSC peaks, activation energies of thedehydration processes have been calculated based onKissinger's method. The most suitable kinetic modelsfor two-step dehydration have been found.     

聚乙烯醇-戊二醛水凝胶的脱水行为

本文对聚乙烯醇－戊二醛水凝胶的脱水行为进行了研究。脱水与凝胶的交联密度有关。突发脱水后的过程可以用一级反应动力学描述。考察了油田应用环境下影响脱水的诸因素。     

Dehydration of polymeric hydrogels designed for gelcasting method in ceramics

Key issue in the gelcasting method is the way water is released from the ceramic–hydrogel system. It is the first step to the formation of ceramic materials called green body. The purpose of the presented investigations is to establish the range of temperatures in which dehydration of the various hydrogels takes place, and at what temperatures the eight prepared hydrogels are disintegrated. The set of hydrogels polymers was obtained by radical polymerization from ionic and non-ionic monomers. The polymers were solved in water causing formation of clear gels. The dehydration and thermal decomposition of the obtained hydrogel samples was studied using thermal analysis techniques. The amount of water contained in hydrogels was determined as well as the temperature and products of polymer disintegration. Enthalpies of dewatering were also determined.     

乙醇脱水演示实验问题的教学探究

对苏教版中乙醇脱水制取乙烯的演示实验中存在的问题进行了研究,改进了实验条件,提出了更合理的实验方案:采用磨口有机玻璃仪器,调整反应物之间的投料比,使用气压差方式等进行有害气体的吸收,体现绿色化学的实验理念,使课堂教学焕发出新的生机和活力。     

Effect of ultrasound and centrifugal force on carambola (Averrhoa carambola L.) slices during osmotic dehydration

Osmotic dehydration (OD) of carambola slices were carried out using glucose, sucrose, fructose and glycerol as osmotic agents with 70 °Bx solute concentration, 50 °C of temperature and for time of 180 min. Glycerol and sucrose were selected on the basis of their higher water loss, weight reduction and lowers solid gain. Further the optimization of OD of carambola slices (5 mm thick) were carried out under different process conditions of temperature (40–60 °C), concentration of sucrose and glycerol (50–70 °Bx), time (180 min) and fruit to solution ratio (1:10) against various responses viz. water loss, solid gain, texture, rehydration ratio and sensory score according to a composite design. The optimized value for temperature, concentration of sucrose and glycerol has been found to be 50 °C, 66 °Bx and 66 °Bx respectively. Under optimized conditions the effect of ultrasound for 10, 20, 30 min and centrifugal force (2800 rpm) for 15, 30, 45 and 60 min on OD of carambola slices were checked. The controlled samples showed 68.14% water loss and 13.05% solid gain in carambola slices. While, the sample having 30 min ultrasonic treatment showed 73.76% water loss and 9.79% solid gain; and the sample treated with centrifugal force for 60 min showed 75.65% water loss and 6.76% solid gain. The results showed that with increasing in treatment time the water loss, rehydration ratio were increased and solid gain, texture were decreased.     

水合金属卤化物脱水的方法和条件

分析了从水合金属卤化物脱水制备无水金属卤化物的几种方法和条件,如直接加热脱水法,在保护气氛或真空中加热脱水法,先制备成复盐然后加热脱水法,用脱水剂脱水法,以及用有机配位溶剂脱水法等。     

A novel inverse numerical modeling method for the estimation of water and salt mass transfer coefficients during ultrasonic assisted-osmotic dehydration of cucumber cubes

The objective of this paper was to study the moisture and salt diffusivity during ultrasonic assisted-osmotic dehydration of cucumbers. Experimental measurements of moisture and salt concentration versus time were carried out and an inverse numerical method was performed by coupling a CFD package (OpenFOAM) with a parameter estimation software (DAKOTA) to determine mass transfer coefficients. A good agreement between experimental and numerical results was observed. Mass transfer coefficients were from 3.5 × 10⁻⁹ to 7 × 10⁻⁹ m/s for water and from 4.8 × 10⁻⁹ m/s to 7.4 × 10⁻⁹ m/s for salt at different conditions (diffusion coefficients of around 3.5 × 10⁻¹²–11.5 × 10⁻¹² m²/s for water and 5 × 10⁻¹² m/s–12 × 10⁻¹² m²/s for salt). Ultrasound irradiation could increase the mass transfer coefficient. The values obtained by this method were closer to the actual data. The inverse simulation method can be an accurate technique to study the mass transfer phenomena during food processing.     

Thermo‐Raman spectroscopy of selected layered double hydroxides of formula Cu6Al2(OH)16CO3 and Zn6Al2(OH)16CO3

Raman spectroscopy using a hot stage was used to characterise layered double hydroxides (LDHs) of the formula (Cu,Zn)₆Al₂(OH)₁₆(CO₃)^·4H₂O. The spectra were used to assess the molecular assembly of the cations in the LDH structure. The sharp band at 1058 cm⁻¹for the Zn₆Al₂(OH)₁₆(CO₃)^·4H₂O is assigned to the ν₁CO₃²⁻ symmetric stretching mode. This band shifts to higher wavenumbers and is observed at 1103 cm⁻¹at 600 °C. It is proposed that metal carbonate species formed during the decomposition of the hydrotalcite structure is responsible for the increase in the band position. The Cu–Al hydrotalcite did not show the same trend. The symmetric stretching mode of carbonate is observed at around 1110 cm⁻¹, and at temperatures above 200 °C a shoulder appears at around 1210 cm⁻¹, suggested to be due to CuCO₃. Copyright © 2008 John Wiley & Sons, Ltd.