Thermogravimetric characterization of some iraqi bitumens

The thermogravimetric analysis of various Iraqi bitumens was conducted by heating them in a stream of nitrogen or oxygen gas from room temperature to 800°C at a rate of 20°C mm^?1 while recording the partial weight loss at 100°C intervals in addition to the total weight loss Isothermal measurements in nitrogen gas were also performed by heating the bitumens from room temperature to 165°C and holding isothermally at this level for 250 min. The resulting thermogravimetric curves provided well-defined data for the characterization and identification of the bitumens studied.     

Effect of Heating Strategy on Power Consumption and Performance of a Pilot Plant Anaerobic Digester

The effect of heating strategy on power consumption and performance of a pilot plant anaerobic digester treating chicken litter, under thermophilic conditions, has been studied. Heating strategy was evaluated using three different spans (0.2 °C, 0.6 °C, and 1.0 °C) for triggering the temperature control system from target temperature (56.7 °C). The hydraulic retention time in the pilot plant digester was in the range of 32 to 37 days, varying the total solids concentration fed from 5% to 6%. The results showed that under the experimental conditions, heating was the most energy-demanding process with 95.5% of the energy used. Increments up to 7.5% and 3.8%, respectively, on mechanical and heating power consumption, were observed as the span, for triggering the temperature control system from target temperature, was increased. Under the experimental conditions studied here, an increment of 30.6% on the global biodigester performance index was observed when a span of 1.0 °C was compared to the one of 0.2 °C.     

DSC And X-Ray Diffraction Coupling

A new technique, that allows simultaneous time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) and high sensitivity DSC to be carried out in the same apparatus, has been developed. Microcalorimetry and XRDT scans can be performed at any rate between 0.01 and 10°C min^?1 with a 0.01°C temperature resolution in the temperature range, 30–130°C and at lower cooling rates but the same heating rates in the ?30–+30°C range. The use of a single and very small sample (1 to 20 μl) contained in a thin glass capillary for both measurements and simultaneous data collection prevents any temperature shift between recordings and any possible difference in the thermal histories of the samples.     

Polymerization of para-xylylene derivatives (parylene polymerization). II. Heat effects during deposition of parylene C at different temperatures

Thermal effects accompanying vacuum deposition of poly(chloro-para-xylylene) in the temperature range between ?196 and 0°C have been studied using two separate methods. One is based on the recording of the rate of evaporation of liquid nitrogen and it is used for the deposition at ?196°C, and the second involves the recording of changes in the substrate temperature and is used for the deposition in the range of ?162 to 0°C. These methods enable us to observe two distinct effects: fast (discrete), resulting in the appearance of sharp, exothermic spikes; and slow (continuous), resulting in the shift of the baseline. The shift of the baseline exhibits a well-defined maximum at about ?65°C and this temperature is attributed to the melting point of the monomer. The fast process always occurs below this temperature and is explained as a solid state, chain addition polymerization. The quantification of the heat effect at ?196°C strongly suggests that the quinonoid form of the monomer participates in the propagation step of this chain reaction. The fast (solid state) and the continuous modes of polymerization may occur simultaneously in the range of about ?140 and ?65°C. The frequency of the initiation which is the formation of dimer radical seems to control the occurrence of these two modes of polymerization.     

An apparatus for accurately measuring solubilities of gases in liquids at elevated temperatures and pressures

An apparatus for measuring solubilities of gases in liquids at elevated temperatures and pressures has been constructed. Using this apparatus, the solubilities of N₂ and CO₂ in some solvents have been determined in the temperature range between 20 and 230°C, and at pressures up to 130 atm. The experimental results obtained generally agree well with literature values. It is shown that this apparatus is reliable; attainment of equilibria needs only about 5 hours; precision of the measurements is ±0.2° o.     

Thermal compatibility between hydroquinone and retinoic acid in pharmaceutical formulations

Thermogravimetry (TG) and differential scanning calorimetry (DSC) are used in pharmaceutical studies for characterization of drugs, purity, compatibility of formulations, identification of polymorphism, evaluation of stability, and thermal decomposition of drugs and pharmaceutical formulations. Hydroquinone (HQ) and products containing HQ have been widely used as depigmentation agents for lightening the skin. Retinoids are compounds that have the basic core structure of vitamin A and its oxidized metabolites, or synthetic compounds that share similar mechanisms of action as naturally occurring retinoids. Depigmentants and excipients were analyzed by TG and DSC. The dynamic thermogravimetric curves were obtained on a SHIMADZU thermobalance, model DTG-60, using an alumina crucible, at the heating rate of 10 °C min^?1, in the temperature range of 25–900 °C, under an atmosphere of nitrogen at 50 mL min^?1. The sample's mass was 10 ± 0.05 mg. The DSC curves were obtained using Shimadzu calorimeter, model DSC-60, using aluminum crucible, at the heating rate of 10 °C min^?1, in the temperature range of 25–400 °C. The thermogravimetric and calorimetric curves were analyzed using TASYS software SHIMADZU. In this study were found the interaction between retinoic acid (RA) and the following excipients: cetyl alcohol(CA), cetostearyl alcohol (CTA), glycerin(GLY), and dipropylene glycol (DPG), and that between HQ and the excipient, DPG. Therefore, additional studies are necessary to evaluate final formulations. Thermal analysis is an effective and reliable technique that can be used in the control of raw materials and pharmaceutical products, and for evaluating their employment potential in the development and characterization of products.     

Origin of double melting peaks in drawn nylon 6 yarns

The differential scanning calorimetry (DSC) melting curves of drawn nylon 6 were studied from the standpoint of reorganization of the crystals during the heating process. A new method was presented to obtain the DSC curve associated with the growth and melting of the original crystals, and that with the recrystallization and final melting process, separately. The results obtained show that, in the case of a heating rate of 10°C/min, the original crystals in the sample start perfecting themselves at temperatures far below their initial melting temperature and melt out below 222°C, recrystallization starts at about 210°C, and the newly emerged crystals melt out at 228°C. The superposition of two such constructed DSC curves reproduces the observed DSC curve well. Therefore, the double melting peaks of the sample are considered to be the result of superposition of three processes which occur successively during heating; perfection of the original crystals, melting of the perfected crystals concurrently with recrystallization, and melting of the recrystallized crystals.     

A study of catalysts for desulphurization process by thermal analysis

A number of catalysts were prepared for the desulphurization process of tail gases. Their carrier was alumina oxide while the active phase was manganese. The catalysts were being tested in an lab apparatus. The effect of calcination temperature and process temperature of model gas (1 vol% of SO₂+99 vol% of N₂) were studied. The increase in the desulphurization temperature up to about 500°C causes the efficiency of the desulphurizing yield to be increased, a further increase of the temperature process decreases the SO₂ conversion. The DTA curves of catalysts after the desulphurizing process display the additional peak at a temperature of about 900°C being, perhaps, responsible for deactivation of the catalysts.     

Thermoelectric‐based temperature‐controlling system for in‐tube solid‐phase microextraction

A temperature‐controlling device for in‐tube solid‐phase microextraction was developed based on thermoelectric cooling and heating. This device can control the temperature of the capillary column from 0 to 100°C by applying a voltage to a Peltier cooler or stainless steel tube. The extraction temperatures for angiotensin I, propranolol, and ranitidine were optimized. In all cases, setting the temperature to 10°C for extraction achieved the best extraction efficiency. Desorption showed minimum peak broadening at 70°C, contributing to better chromatographic performance. Propranolol was selected as a model compound to compare the performance of temperature‐controlled in‐tube solid‐phase microextraction at optimized conditions. Calibration curves exhibited good linearity (R² > 0.999) over the studied range, and the limit of detection and limit of quantification were about three times lower than those obtained at standard conditions (30°C extraction and desorption).     

A new calorimeter for measuring rapidly thermal conductivities of the organic liquids and the electrically conducting liquids

A new calorimeter for measuring thermal conductivity of liquids has been constructed. It is wholly automatic under the computer control. The time of measurement is 1 s and the temperature rise due to heating is within 1°C. Six organic liquids and six aqueous solutions of electrolytes were employed as reference standards. The instrument was calibrated at 25°C. Its accuracy is better then 1% with a precision of about 0.2%.     

A high pressure electrical conductivity apparatus

A high pressure electrical conductivity (EC) apparatus. capable of operation at pressures from 1 to 170 atm in the temperature range from 25 to 500°C, is described. The effects of the sample holder geometry, pressure, and sample packing on the resulting EC curves are given. Operation of the apparatus is illustrated by the deaquation reactions of BaCI₂·2H₂0.     

Multi-frequency dynamic-mechanical thermal analysis of methyl methacrylate adhesive (MMA)

The paper presents the results of Dynamic-Mechanical Thermal Analysis (DMTA) for a selected methacrylate adhesive at the frequency range from 1 to 50?Hz and the heating rate of 1 and 3?°C/min, in the range from –70?°C to 180?°C. On the basis of the test results, the glass transition temperature was evaluated for three calculation methods. Master curves were also designated for three different reference temperatures: –20, +20 and +60?°C. Master curves were calculated using shift factors a_T - calculated by numerical method.     

Some Physico-chemical Properties of Doxazosin Mesylate Polymorphic Forms and its Amorphous State

Seven polymorphic modifications of doxazosin mesylate, designed as forms A, D, E, F, G, H, I, and the amorphous state were studied by thermal methods (TG and DSC), temperature resolved X-ray powder diffractometry, hot stage and scanning electron microscopy and by FT-IR spectroscopy. Amorphous form was obtained either by fast evaporation of the solvent or by fast cooling of the melt in the DSC. Polymorphs A and F were found to be stable in the temperature range from room temperature to their melting points at 277.9 and 276.5°C, respectively. Form G, which melts at 270.8°C, was found to be hygroscopic. Polymorph D undergoes irreversible solid–liquid–solid phase transition at 235.5°C to polymorph I which melts at 274.9°C. Form H, which melts at 258.0°C, was found to be unstable at high temperatures. DSC examinations revealed that form H is irreversibly transformed to polymorph F during heating above the temperature of about 240°C. The amorphous state was found to be stable at room temperature but when heating above the glass transition (T _g=144.1°C) it crystallizes at 221.6°C, what leads into a mixture of polymorphic forms. The new polymorphic form designed as E was identified in the mixture. The polymorph E is converted by heating to the more stable form F. The solubilities at 25°C for forms A, and F in methanol are 3.5 and 7.7 mg mL⁻¹and in water they are 3.8 and 6.2 mg mL⁻¹, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermodynamic cloud point assays

Analysis of cloud points and clouding curves by varying heating rates using a commercially available automated melting point apparatus is a method to obtain a corrected cloud point for polymers that have a lower critical solution temperature (LCST). Such assays also provide information about the effects of varying heating rates on LCSTs and similar stimuli‐responsive phase separation behavior. This melting point apparatus makes it experimentally simple to conduct such assays that probe the effect of varying heating rates, the effect of polymer structure, and the effect of solution components on the breadth and progress of the phase transition process over a wide temperature range. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 186–193, 2008     

Increase in dynamic modulus of nylon 6 fiber in repeated heating and cooling cycles under sinusoidal deformation

The repeated heating and cooling cycles under sinusoidal deformation have been investigated on nylon 6 fibers. The fibers zone-drawn twice at high temperatures were used, which have a crystallinity of 52.2% and a birefringence of 59.4×10^?3. The heating and cooling cycle was performed twice at a frequency of 110 Hz over a temperature range from 0°C to 180°C and 190°C. The crystallinity and birefringence of the treated fiber were 51.7% and 60.7×10^?3, respectively, indicating almost no changes in molecular orientation and crystallinity. However, the dynamic modulus, E′, increased steadily over whole temperature range measured. Finally, the E′ value reached 21 GPa at room temperature and 10 GPa ever at 180°C. The elongation of fiber after two cycles was only about 5%. © 1993 John Wiley & Sons, Inc.     

Electrical and optical properties of melting Au/Si eutectics on Si(111)

The Au/Si system exhibits an extremely low eutectic temperature of 363°?C. Thin gold films of 200 nm thickness were deposited on Si(111) single-crystals and the electrical and optical properties of the melting mixtures were investigated. The resistivity measurements were performed in situ in a combined LEED/Auger apparatus. A highly resolving spectroscopic ellipsometer was used for the optical analysis in the wavelength range 400–900 nm. The eutectic temperature was found to be lower than for bulk Au/Si samples. The structure analysis showed that small liquid Au/Si islands embedded in the silicon surface are formed by the melting process. Various heating/ cooling cycles show a characteristic hysteresis behaviour.     

Preheating and heat addition by LASER beam in hybrid LASER-ultrasonic welding

Heating during welding in electronics is limited because of the high difference between the properties of the components that are in the close neighbourhood of the welding area. The temperature should not exceed 240 °C. In the classic processes of soldering, depending on the soldering alloy types, the heat is up to 300 °C. Such temperature is producing thermal degradation of the neighbouring polymers. New hybrid heating process is proposed within the paper. A double source laser-ultrasonic vibration could be used as thermal source. Because of the concentration of the heat source, the duration of the process is sensitively reduced in time (from minutes down to 5–10 s). More, applying the heat in two sequences, a preheating of the base material can be done and the result is a decreasing of the hardness with about 10–15 %, so a decreasing of the brittleness is happening. After the preheating, the processing heating is applied. The thermal field was analysed and specific mathematical models of the field were built. The temperature of the process was reduced down to about 130–150 °C. A comparison between laser heating and hybrid laser-ultrasonic heating, from the thermal field point of view, is presented within the paper.     

Optical activity in CE6 A new metastable blue phase?

Abstract

The optical rotation of a mixture of 60 per cent of chiral and 40 per cent of racemic CE6 as an 18 μm thick sample placed between glass plates treated with PI has been measured. This mixture exhibits one blue phase (BP1) on heating over a temperature range of about 0·1°C. On cooling the sample on the other hand, the BP region is expanded to 0·6°C and is divided into two regions. One region (BP1) (of range about 0·38°C below the isotropic–blue phase transition) shows two Bragg wavelengths which increase with decreasing temperature. For the second region (BPS) (of range about 0·22°C above the cholesteric–blue phase transition), one Bragg wavelength decreases with decreasing temperature, and a third Bragg wavelength appears. At constant temperature both phases remained stable for a period of several days.     

Fast GC with a Small Volume Column Oven and Low Power Heater

A new apparatus for fast gas chromatography separations is described. It consists of a small volume oven containing a coiled fused silica capillary column that is heated by a flow of hot air. The oven can be heated at rates of 10 °C s^?1 with a 300 W heater. Benchmark studies at various temperature programming rates are described. Retention time relative standard deviations increase with increasing heating rate, but are at most about 1% when an 8 °C s^?1 heating rate is employed. The small size of the column oven makes it possible for it to be attached to a commercial GC instrument through an opening provided for installation of a second injector.     

Influence of γ-irradiation on the transition temperatures of crystalline polytetrafluorethylene

The influence of γ-irradiation on the melting and two solid-solid transitions, occurring near 19° and 30°C, of polytetrafluorethylene was studied by differential scanning calorimetry. A continuous depression of all three transition temperatures, with increasing dose was observed in a first scan of highly crystalline samples at a heating rate of 20°C/min. Additional information was obtained about the accompanying heats of transition. Values for the number of CF₂ units excluded from the crystal lattice per 100 eV energy deposition were calculated by using an equation for the depression of the melting point by chemical impurities. The value obtained of G(–units) = 3.3 ± 0.3 is in agreement with a value of G(chemically damaged units) = 3.0 ± 0.1 previously reported on the basis of scavenging techniques. It is concluded that chemical radiation-induced damage in this polymer may be estimated by reference to changes in the melting temperature. A value of G(–units) = 1.6 ± 0.2 was obtained by reference to the 19°C transition.