Correlation of electrical properties and internal friction in mixed conduction glasses containing ionic and electronic conduction (1) Fe2O3-Na2O-P2O5 glasses

The electrical properties and internal friction in (40–x)Fe₂O₃·xNa₂0.60P₂O₅ glasses were measured. Two or three peak on internal friction were observed in the temperature range of –100 to 300° C at a frequency of about 1 Hz. The peak area of internal friction could be explained quantitatively by the additivity law of diffusion of Na⁺ ion and hopping of electrons which are carriers similar to those of dielectric loss. Activation energy, peak temperature of dielectric loss and internal friction showed almost the same value. Both relaxation phenomena have the same mechanism which is due to the diffusion of Na⁺ion and the hopping of electrons between Fe²⁺ Fe³⁺. The high-temperature peak is assumed to result from the interaction between protons or alkali ions and non-bridging oxygen.     

Diffusion of alcohol-rhodamine 6G in polymethyl methacrylate

Rhodamine 6G (Rh6G) is impregnated in polymethyl methacrylate by concentration difference diffusion method. The diffusion behaviour of ethanoic and methanoic Rh6G in polymethyl methacrylate at temperatures between 35 and 70° C were studied. The following results were obtained: (a) Visually observed sharp boundary, characteristic of Case II transport, during diffusion of alcohol penetrates at a rate of 1.7×10^–6 cm sec^–1 with an activation energy of 23 kcal mol^–1 for ethanol-polymethyl methacrylate system and 1.0×10^–5 cm sec^–1, with 23 kcal mol^–1 for methanol-polymethyl methacrylate, respectively, at 60° C. (b) Diffusion of alcoholic Rh6G in polymethyl methacrylate is greatly hindered since internal stresses exist in the swollen region of the glassy polymer. (c) Diffusion of alcoholic Rh6G in swollen polymethyl methacrylate with equilibrium alcohol concentration followed Fickian kinetics. The diffusion coefficient of Rh6G at 60° C is determined as 5.2×10^–8 cm² sec^–1 with an activation energy of 41 kcal mol^–1 for the wet ethanol-polymethyl methacrylate and 6.1×10^–8 cm² sec^–1, with 34 kcal mol^–1 for the wet methanol-polymethyl methacrylate systems, respectively.     

The kinetics of crystallization of the metallic alloy Pd4Ge

The kinetic parameters for the crystallization of Pd₄Ge have been measured by differential scanning calorimetry (DSC). The effective activation energy was found to be 215 kJ mol^–1 (51 kcal mol^–1) and the heat of reaction was determined to be 13 kJ mol^–1 (3.1 kcal mol^–1). Preliminary investigation of the products of crystallization was undertaken using X-ray diffraction and electron microscope techniques. Some new phases for this alloy were observed.     

Chemorheology of epoxy resin Part I epoxy resin cured with tertiary amine

Epoxy resin was cured with a tertiary amine. The viscosity and dynamic mechanical properties during the curing reaction were measured by a cone-and-plate rheometer. A dual Arrhenius viscosity model was modified to predict the viscosity profile before gelation during the non-isothermal curing. The viscosity profile coincided with the experimental data. The activation energy of this system calculated using the modified model was 19.8 kcal mol^–1 for the first region, and 17.3 kcal mol^–1 for the second region. After gelation, the dynamic complex modulus was related to the reaction kinetics according to the rubber elasticity theory, and the activation energy was 15.3 kcal mol^–1. Furthermore, the gelling point can be estimated from the rheological measurements.     

Measurement of viscosity of the grain-boundary phase in hot-pressed silicon nitride

An internal friction technique has been used to measure the viscosity of the grain-boundary amorphous phase in commercial hot-pressed silicon nitride. The viscosity in the region of the glass transition (850 to 900° C) was approximately 5×10¹⁵ P per unit thickness (cm) of the grain boundary, with an apparant activation energy of 163 kcal mol⁻¹.     

Electrical resistivity,nucleation and crystal growth in amorphous Se100−x -Sb x ,

The process of nucleation and crystal growth has been studied, using the change of the electrical resistance with time, for the system Se_100–x -Sb _x , wherex = 5, 10 and 15. The X-ray analysis of different records was also used to investigate the same processes. The results show that the apparent activation energies of nucleation were 17.89, 19.88 and 24.25 kcal mol^–1 (74.90, 83.23 and 101.53 kJ mol^–1) for x = 5, 10 and 15, respectively. The values of the apparent activation energy of crystal growth were 39.78, 45.67 and 52.70 kcal mol^–1 (166.55, 191.21 and 220.64 kJ mol^–1 ) for the same respective samples. The activation energy of conduction and the electrical resistance were found to decrease as the antimony content increases in both amorphous and crystalline states.     

Compound growth in platinum/tin-lead solder diffusion couples

The two types of reactions that occur between 60/40 tin-lead solder and platinum were explored: (1) solid-state diffusion, in which the intermetallic compound PtSn₄ was observed to form; and (2) dissolution. Both bulk and thin-film couples were used and the extent of reaction in each was revealed by optical and scanning electron microscopy methods. Solid-state compound growth followed parabolic kinetics with an effective activation energy of 23 kcal mol^–1 (96.2 kJ mol^–1). Diffusion of platinum through PtSn₄ appears to limit compound growth. Dissolution of platinum wires in solder resulted in a linear decrease in wire diameter with time. The process occurred with an activation energy of 20.4 kcal mol^–1 (85.4 kJ mol^–1) and was attributed to Pt-Pt bond breaking assisted by strong chemical interaction with tin.     

A study of the oxidation kinetics of CuFeO2 in the Cu-Fe-O system

The oxidation kinetics of CuFeO₂ in the Cu-Fe-O system have been studied between 500 and 900° C in an atmosphere containing 1 vol% oxygen in a nitrogen stream using thermogravimetric analysis (TGA). It was found that addition of Fe₂O₃ to the CuFeO₂ caused a decrease in the oxidation rate while addition of CuO caused an increase. On increasing the concentration of Fe₂O₃ the activation energy was found to increase from ~ 18 kcal mol^–1 to ~ 45 kcal mol^–1 and the exponent n in Avrami's equationf=1-exp (–kt ⁿ) was also observed to increase, from 1.3 to 2.3. On adding CuO to the CuFeO₂ in the Cu-Fe-O system the activation energy decreased from ~ 18 kcal mol^–1 to ~ 8 kcal mol^–1. The variation in both values indicates changes in the oxidation mechanisms. The microstructural changes associated with oxidation have been studied using optical microscopy. A model has been proposed to explain the results.     

Effect of nitrogen on the dynamic strain ageing behaviour of type 316L stainless steel

The dynamic strain ageing (DSA) behaviours of type 316L stainless steels containing different nitrogen contents (0.01–0.15 wt% N) were studied in tension under varying strain rates (1 × 10^–2–2 × 10^–4s^–1) and the test temperatures (R.T.–1023 K). The temperature range for DSA was moved to higher temperature for increasing nitrogen contents. The critical strain, _c for the onset of serration increased with nitrogen content at 773 K and then became almost constant at 873 K. Type A and B serrations were observed at 873 K with the value of the strain required to effect the transition from type A to type B serration increasing for nitrogen contents upto 0.1 wt% and then becoming saturated. The activation energy for DSA was 23.4–26.2 kcal mol^–1 (97.8–109.5 kJ mol^–1) at the onset and 65.0–76.6 kcal mol^–1 (271–320.2 kJ mol^–1) at the end of serration. The lower activation energy was related to vacancy diffusion and the higher activation energy was attributed to the diffusion of chromium to dislocations. The activation energy for DSA was slightly increased with nitrogen addition. DSA was retarded by an increase in the nitrogen content since nitrogen reduced the chromium diffusion to dislocations due to a strong interaction between the nitrogen and chromium.     

Chemorheology of epoxy resin

A secondary hydroxyl group containing epoxy resin was reacted and cross-linked with polyurethane (PU). This PU-cross-linked epoxy resin was cured with a tertiary amine and the viscosity and dynamic mechanical properties were determined by a cone-and-plate rheometer. A dual Arrhenius viscosity model was modified to predict the viscosity profile with time before gelation during non-isothermal curing, and the calculated values coincided with the experimental data. The activation energy of this system (NCO/OH ratio=30 mol%) calculated by the modified model was 13kcal mol^–1 for the initial region, and 16.8 kcal mol^–1 for the final region. After gelation, the dynamic complex modulus was correlated to the reaction kinetics according to the rubber elasticity theory, and the activation energy calculated was 5.2 kcal mol^–1. These activation energies are all lower than those of the unmodified epoxy resin system. Consequently, the reaction rate of the PU-cross-linked epoxide system was less affected by temperature than that of the unmodified epoxide system. It was also found that the rate of increase of viscosity and dynamic moduli decreased with increasing PU content. The gelling point was estimated by rheological measurements.     

Indentation recovery of atactic polystyrene

Indentations made on the surface of atactic polystryene were annelaed for different lengths of time at various temperatures. The depths of these indentations were measured by using a modified Sloan surface profilometer. The variation of depth with time was found to follow second order kinetics at least for the later part of recovery. The activation energy associated with the second order rate constant was 163 kcal mol^–1 which is comparable to the value of 160 kcal mol^–1, measured in the same material for the recovery of coarse shear bands.     

Silica fracture

A quantitative model of environmentally sensitive crack growth of amorphous silica (a-silica) is based upon semiempirical molecular orbital (MO) calculations (AM-1 method) of a water molecule interacting with strained three- and four-fold silica rings and a five-fold ring-chain structure. The energy barrier for hydrolysis of strained 3-fold rings is only 7 kcal mol^–1, the energy barrier for hydrolysis of strained four-fold rings is 29 kcal mol^–1; for a five-fold ring-chain it is 39 kcal mol^–1. Thus, the MO model predicts that the energetics of Region 1 slow crack growth is controlled primarily by the distribution and hydrolysis of three-membered silica rings in the a-silica structure, and Region III is controlled by the distribution and energy of contraction of four and four + membered rings.     

Crystallization study of amorphous Fe40Ni40B20 by electrical resistivity measurement

The crystallization in amorphous Fe₄₀Ni₄₀B₂₀ alloy has been studied by electrical resistivity measurement. It shows a three stage compared to the more conventional two-stage crystallization behaviour in many metallic glasses. The Johnson-Mehl-Avrami equation was found to be operative only for 40% transformed crystallized volume for the highest measured isotherm (740 K). The Avrami exponent and activation energy were found to be 1.75 and 53 kcal mol^–1, respectively. The low activation energy in the amorphous alloy has been explained by the structural relaxation model.     

Silica fracture

A quantitative ring contraction model for the fracture of amorphous silica is described based upon AM-1 semiempirical molecular orbital calculations of strained three- and four-fold silica rings and a five-fold ring-chain structure. The fracture barrier for five-fold ring-chain structures is 103 kcal mol^–1. The barrier for fracture of a three-fold ring is 96 kcal mol^–1. Fracture by contraction of four-fold rings has a lower energy barrier of 77 kcal mol^–1 due to formation of pentacoordinate silicon transition states which produce trisiloxane rings and a broken siloxane bond. Thus, the ring contraction model predicts that a crack will follow a path which depends on the distribution of four-fold (or larger) rings in vacuum or fast fracture.     

Delayed failure in silica glass

Stable crack-propagation behaviour in silica glass as a raw material for optical fibres is studied under static tensile stress in various environments such as distilled water, NaCl aqueous solution, air and dry nitrogen gas, and the influence of these environments is discussed. The crack-growth rate in distilled water is obtained qualitatively as a function of the stress intensity factor and temperature, and the activation energy of the cracking process is determined as 97.6 kcal mol^–1. The growth rate seems to be unaffected by Na⁺ and Cl^– ions in an NaCl acqueous solution, but is influenced significantly by the humidity in the atmosphere. In a dry atmosphere, the growth rate in Region II cannot be expressed as a single function of the stress intensity factor. A plot of the log of time to failure against the initial stress intensity factor reveals a linear relationship in the environments tested. The critical fracture stress of an optical fibre is evaluated taking account of the crack size on the basis of fracture mechanics concept.     

Viscous creep deformation of polycrystalline CaTiO3 at elevated temperatures

Creep deformation of polycrystalline CaTiO₃ has been investigated in air at temperatures between 1100 and 1200° C and stresses between 4 and 13 MPa. The results indicate that the creep deformation of this material can be described by a threshold process with associated activation energy of 200 kcal mol^–1 (836.8 kJ mol^–1). It is tentatively concluded that creep deformation of polycrystalline CaTiO₃ within the ranges of experimental parameters investigated is rate-controlled by interfacial defect creation and/or annihiliation at grain boundaries.     

Preparation, characterization and applications of novel iminodiacetic polyurethane foam (IDA-PUF) for determination and removal of some alkali metal ions from water

The new type of ion chelating resin (IDA-PUF) has iminodiacetic group that was prepared from polyurethane foam (PUF) by the reaction between primary amine of PUF and monochloro-acetic acid. The IDA-PUF was characterized using infrared spectra, elemental and thermal analysis. The exchange properties and chromatographic behaviour of the new chelating resin were investigated for removal of some alkali metal ions (lithium, sodium and potassium) using batch and column processes. The maximum distribution coefficient (K_D) of trace alkali metal ions was in the pH range of 8–10. The kinetics of sorption of the alkali metal ions was found to be fast with average values of half-life of sorption (t_1/2) of 4.93 min. The values of ΔG, ΔS and ΔH were −3.86 kJ mol⁻¹, 57.73 J mol⁻¹ K⁻¹ and 14.41 kJ mol⁻¹, respectively, which reflects the spontaneous and endothermic nature of ion exchanger process. The average sorption capacity of IDA-PUF is 4.8 mmol/g for alkali metal ions, enrichment factors ≈40 and the recovery 95–100% were also achieved with average value of RSD% = 1.67. The proposed method has been successfully applied to preconcentrate, determinate and remove the alkali metal ions from different samples of water.     

Dissolution of calcite crystals in the presence of some metal ions

A constant composition method has been used for the study of the kinetics of calcium carbonate (calcite) dissolution in which the activities of ionic species in relatively undersaturated solutions are maintained constant. Over a range of relative undersaturation (0.032–0.158) the dissolution reaction appears to be controlled by a bulk diffusion process. The suggestion of a predominantly diffusion-controlled process was supported by the observed low activation energy (2.09 kcal mol^–1). The influence of a number of metal ions on the reaction rate has been investigated. The retardation effect of these additives has been attributed to the blocking of active sites by adsorption of metal ions at the crystal surfaces. Inhibition of dissolution by metal ions can be interpreted in terms of a Langmuir isotherm.     

Oxidation kinetics of silicon carbide whiskers studied by X-ray photoelectron spectroscopy

Silicon carbide whisker surfaces were characterized by X-ray photoelectron spectroscopy (XPS) to determine changes in the surface oxide film which occurred as a result of heating in air at temperatures from 600 to 800 °C. Equations were derived for the calculation of surface oxide film thickness from the SiC to SiO₂ 2p intensity ratios. Oxidation was found to follow a linear rate law in this temperature range for the first 10 nm of oxide growth. An activation energy of 17.2 ± 2.8 kcal mol^–1 (72 ± 12 kJ mol^–1) was measured.     

Hot-pressing kinetics of zirconium carbide

The hot-pressing kinetics of zirconium carbide were studied between 1700 and 2400° C in argon. The validity of different theoretical models due to Murray, Koval'chenko, Skorokhod, Scholz and Lersmacher was tested. For temperatures exceeding 2200° C, there is reasonably good agreement between kinetics and the whole set of models, but it has not been possible to classify them in order to draw conclusions on the sintering mechanism. The activation energy of ZrC hot-pressing was calculated, starting from the viscosity calculated by Murray's formula, as 41 kcal mol^–1 (171.7 kJ mol^–1).