Application of dilatometric analysis to the study of autoclaved calcium silicate materials

The process of shrinkage of calcium silicate hydrate was investigated by dilatometry up to 350 °C. The properties of this material are based on the formation of C–S–H phases during the reaction at temperatures between 180 and 205 °C and water vapor pressure lower than 16 bars. The main C–S–H phases are 11.3 Å tobermorite and xonotlite. 11.3 Å tobermorite converts to 9.3 Å tobermorite on air at temperatures around 300 °C. The hydrosilicate materials were prepared from quicklime and finely ground sand with different CaO/SiO₂ ratios under different hydrothermal conditions. The reaction time was 24 h. Materials based on xonotlite and tobermorite were produced, and the calcium silicate phases were characterized by XRD and TG/DTA methods. Dilatometry measurements were used to study the effect of heating conditions on sample shrinkage. Dehydration of hydrated calcium silicate minerals occurred during heating. The results show that sample shrinkage is dependent on the type and amount of C–S–H phases, the amount of bound water and formation of 9.3 Å tobermorite. All samples showed shrinkage after heating up to 350 °C, but this change was not irreversible for all samples after cooling to room temperature.

     

Agar-based heat-sensitive gel with linear thermal response over 65–80 °C

A nontoxic heat-sensitive gel containing 1.5 % (w/v) agar and 25 % (w/v) bovine serum albumin (BSA) was fabricated in this study. Optical density measurements with 808 nm near-infrared (NIR) laser indicated that, in spite of its BSA content, the current agar + BSA gel remained similar to agar only gel in terms of its optical response to NIR laser. The thermal response of the current agar + BSA gel to high temperatures was quantified using magnetic resonance imaging (MRI). According to the MRI measurements of T2 relaxation rate as a function of heating temperature, the current agar + BSA gel showed a linear response to heating temperatures between 65 and 80 °C, while it remained thermally stable at temperatures up to 80 °C. Therefore, the current agar + BSA gel can be used as thermal dosimeters or volumetric heat-sensitive gel phantoms in typical thermal therapy regime.     

Thermogravimetric analysis of cellulose insulation and determination of activation energy of its thermo‐oxidation using non‐isothermal,model‐free methods

The aim of the work was to determine the effect of heating rate on initial decomposition temperature and phases of thermal decomposition of cellulose insulation. The activation energy of thermo‐oxidation of insulation was also determined. Individual samples were heated in the air flow in the thermal range of 100°C to 500°C at rates from 1.9°C min^?1 to 20.1°C min^?1. The initial temperatures of thermal decomposition ranged from 220°C to 320°C, depending on the heating rate. Three regions of thermal decomposition were observed. The maximum rates of mass loss were measured at the temperatures between 288°C and 362°C. The activation energies, which achieved average values between 75 and 80.7 kJ mol^?1, were calculated from the obtained results by non‐isothermal, model‐free methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermal transformations up to 1200 °C of Al-pillared montmorillonite precursors prepared by different OH–Al polymers

Aluminum-pillared montmorillonites are useful materials for their application as catalysts, adsorbents and ceramic composites. The precursor is a pillared montmorillonite that is not thermally stabilized. The precursor preparation methods, textural properties and catalytic activity have been extensively investigated, but comparatively, studies concerning their thermal transformations at high temperature are limited. In this work, precursors were prepared using two types of montmorillonites, Cheto (Ch) and Wyoming (W), and using two different OH–Al polymer sources: hydrolyzed (H) and commercial (C) solutions. Structural and thermal transformations of the precursors with heating up to 1200 °C were determined by X-ray diffraction and thermogravimetric analysis. Thermal analysis of these precursors below 600 °C revealed the influence of OH–Al polymers from the two solutions. The major phases developed at 1200 °C from the original montmorillonites were mullite for W and cordierite for Ch. The content of these phases depended on the aluminum in the octahedral sheet of the pristine montmorillonites. Amorphous phase, cristobalite, spinel, sapphirine and others phases were also found. The intercalation of OH–Al polymers in montmorillonites caused an increase in amorphous content after treatment at 1030 °C; however, it favored mullite development above 1100 °C. Although total aluminum content of both W and Ch precursors was similar, the transformation to mullite was directly related to the octahedral aluminum/magnesium ratio. The phase composition of the products at 1200 °C was not dependent on the type of intercalated OH–Al polymers. The increase in mullite content of the thermally treated precursors contributes to its possible application as advanced ceramic products.     

Electronic Structure and Size of TiO2 Nanoparticles of Controlled Size Prepared by Aerosol Methods

Summary.  A complete characterization of nanostructures has to deal both with electronic structure and dimensions. Here we present the characterization of TiO₂ nanoparticles of controlled size prepared by aerosol methods. The electronic structure of these nanoparticles was probed by X-ray absorption spectroscopy (XAS), the particle size by atomic force microscopy (AFM). XAS spectra show that the particles crystallize in the anatase phase upon heating at 500°C, whereas further annealing at 700°C give crystallites of 70% anatase and 30% rutile phases. Raising the temperature to 900°C results in a complete transformation of the particles to rutile. AFM images reveal that the mean size of the anatase particles formed upon heating at 500°C is 30 nm, whereas for the rutile particles formed upon annealing at 900°C 90 nm were found. The results obtained by these techniques agree with XRD data. Received October 5, 2001. Accepted (revised) December 6, 2001     

Ferroelectric Properties of Modified Lead Titanate Thin Films Obtained by a Sol-Gel Method

Calcium substituted lead titanate thin films have been prepared by a sol-gel method, deposited by spin-coating, and thermally treated so as to obtain a perovskite structure. Two types of thermal treatments were given, differing in the heating rate, which in conventional treatments was of some 10°C/min, and in rapid treatments >500°C/min. With rapid heating, materials are obtained in which greater polarizations are commuted and bias fields are smaller. This, together with the fact that additional (undesired) phases are not observed by X-ray diffractometry when rapid treatments are used, shows that these are to be preferred over conventional treatments.     

Synthesis and study the liquid crystalline properties of compounds containing benzoxazole core and terminal vinyl group

Terminal vinyl-based benzoxazole liquid crystalline compounds, 2-(3-fluoro-4?-alkoxy-1,1?-biphenyl ?4-yl)-5-(2-propenyloxymethyl)-benzoxazole (nPPF(2)BP), were synthesised and their structures were confirmed by infrared (IR) spectra, proton nuclear magnetic resonance (¹H-NMR) spectra, gas chromatography with electron impact-mass spectrometry (GC/EI-MS), matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry and elemental analysis (EA). The compounds show enantiotropic smectic/nematic phases with mesophase ranges are 71–97 °C and 87–136°C on heating and cooling processes for nPPF(2)BP, respectively. They give low melting points due to lateral fluoro substituent and flexible terminal 2-propenyloxymethyl chain. It is found that the compounds nPPF(2)BP with shorter alkoxy chain (n = 3, 4) exhibit a wide range of nematic mesophase, which is ascribed to enhanced π–π interaction caused by terminal vinyl moiety, whereas further elongation of the terminal alkoxy chain results in supressing nematic phase and increasing smectic mesophase. Compared with methyl terminated analogues, 2-propenyloxymethyl terminated compounds nPPF(2)BP display much lower melting points and wider or comparable mesophase range both in heating and cooling.     

Thermal decomposition of nickel and zinc peroxotitanates to metatitanates

Methods of DTA, TG, X-ray phase analysis and IR spectroscopy were used to study the thermal dehydration and decomposition of Ni²⁺ and Zn²⁺ peroxotitanates to the corresponding metatitanates. The course of the process was established and the intermediate phases were identified. The information obtained was utilized to determine the optimum temperatures of heating the initial peroxotitanates for conversion to metatitanates with a fairly high degree of crystallinity (for ZnTiO₃ the optimum temperature is 600°C, while for NiTiO₃ it is 550°C).     

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.     

Raman spectra of titanium dioxide

First-order Raman spectra have been recorded at room temperature for the anatase and rutile phases of polycrystalline titanium dioxide using an argon ion laser as exciter. The high-temperature rutile phase was found to be stabilized at temperatures below 450°C. Anatase transforms to rutile phase at ～750°C. All the Raman active fundamentals predicted by group theory are observed.     

Determination of thermophysical properties of high temperature alloy IN713LC by thermal analysis

The presented paper deals with the study of thermophysical properties of cast and complex alloyed nickel based on superalloy Inconel 713LC (IN713LC). In this work, the technique of Differential Thermal Analysis was selected for determination of the phase transformation temperatures and for the study of the effect of varying heating/cooling rate at these temperatures. The samples taken from as-received state of superalloy were analysed at heating and cooling rates of 1, 5, 10, 20 and 50?°C?min^?1 with the help of the experimental system Setaram SETSYS 18_TM. Moreover, the transformation temperatures at zero heating/cooling rate were calculated. The recommended values for IN713LC after correcting to a zero heating rate, are 1,205?°C (T _?á?,solvus), 1,250?°C (solidus) and 1,349?°C (liquidus). Influence of heating/cooling rate on shift of almost all temperatures of phase transformations was established from the DTA curves. Undercooling was observed at the cooling process. The samples before and after DTA analysis were also subjected to the phase analysis by scanning electron microscopy using the microscope JEOL JSM-6490LV equipped with an energy dispersive analyser EDAX (EDS INCA x-act). Documentation of the microstructure was made in the mode of secondary (SEI) and backscattered (BEI) electron imaging. On the basis of DTA analysis and phase analysis it may be stated that development of phase transformations of the alloy IN713LC will probably correspond to the following scheme: melting?????? phase; melting???????+?MC; melting????eutectics ??/?á?; melting???????+?minority phases (e.g. borides); and matrix ???????á?.     

Low temperature relaxation in polypyromellitimide

The effect of heat treatment at temperatures above 300°C on the low temperature relaxation of poly(4,4′-oxydiphenylenepyromellitimide) (Kapton H-film) was studied by wide-line nuclear magnetic resonance (NMR), mechanical, and dielectric measurements. In the NMR line spectrum of the as-received film, a narrow component above ?60°C and a broad component which begins to narrow at about ?100°C were observed. It is proposed that the narrow component is associated with absorbed water, because it disappeared in the heat-treated film at 300°C in N₂. On the other hand, the behavior of the broad component was not influenced by heating to 300°C in N₂. Mechanical and dielectric loss peaks were observed at ?75°C (11 Hz) and ?65°C (1 kHz), respectively, in the as-received film. These loss peaks did not change in intensity with heating to 300°C in N₂. It is proposed that the mechanical and dielectric loss peaks corresponding to the narrowing of the NMR broad component are associated with the local-mode motion of the diphenylether portion of the polypyromellitimide chain. It was found that crosslinks are formed by heating to 374°C in air through coupling of the diphenylether portions of the molecular chains. With the formation of crosslinks the dielectric loss peak shifted toward higher temperature and the intensity decreased through restriction of the local-mode motion of the diphenylether portion of the molecular chain.     

ArF laser photolytic deposition and thermal modification of an ultrafine chlorohydrocarbon

MW ArF laser irradiation of gaseous cis-dichloroethene results in fast decomposition of this compound and in deposition of solid ultrafine Cl- and H-containing carbonaceous powder which is of interest due to its sub-microscopic structure and possible reactive modification of the C-Cl bonds. The product was characterized by electron microscopy, and FTIR and Raman spectra and it was revealed that HCl, H₂, and C/H fragments are lost and graphitic features are adopted upon heating to 700°C.     

Flour starch thermal characteristics Modulated scanning calorimetric study

Thermal characteristics of refined wheat flour blend made with 90% Ohio soft red winter wheat and 10% Canadian Hard Red Winter Wheat are explored using a series of modulated differential scanning calorimeter conditions. Influences of pan type, period, amplitude of the thermal modulation, and underlying thermal heating rate on flour starch thermal transitions are presented. Wheat flour was blend 1:1 with water, and then heated at various heating rates while the amplitude and period of the instantaneous heating rate was modulated between ±0.5 and ±1.0 °C amplitude and 60 s to 80 s period. Study shows faster heating rates favor increased total heat flow and results in proportional increases in both reversing and non-reversing thermokinetic events of recrystallization. Slower overall heating rates (e.g., 2.5 °C min⁻¹) produced better resolution of thermal events related to preexisting structural phases, but allowed more time for creation of new events such as recrystallization, annealing.     

Thermal transformations of lead oxides

Differential scanning calorimetry, differential thermogravimetry, X-ray analysis and electronic microscopic studies of thermal transformations of PbO₂ were carried out. Formation of fine dispersed (less than 100 nm) particles of α-PbO was observed at PbO₂ thermal decomposition at heating to 580°C. Reverse reaction of Pb₃O₄ formation from PbO was found at cooling and annealing at 400°C in air. At heating of α-PbO to 650°C the particle growth to 1 μm with formation of β-PbO took place. Thermal decomposition with formation of β-PbO particles with size from 0.3 to 1 μm at PbO₂ heating to 650°C was observed. Transition from PbO to Pb₃O₄ at cooling of sample heated to 650°C was not detected. Interpretation of observed phenomena from the point of view of particle size influences on the shift of α-PbO↔β-PbO phase transition temperature and on the chemical activity of phases are presented.     

Calorimetric Investigation of Conversion to The Most Stable Subgel Phase of Phosphatidylethanolamine-water System

The conversion of either the gel or the liquid crystal phase to the most stable subgel phase in dimyristoylphosphatidylethanolamine (DMPE)-water system at a water content of 25 mass% was studied by differential scanning calorimetry and isothermal calorimetry. The calorimetric experiments were performed for two samples depending on whether the thermal treatment of cooling to -60°C was adopted or not. In DSC of varying heating rate, exothermic peaks due to the partial conversion were observed at either temperatures just below the gel-to-liquid crystal phase transition at 50°C or temperatures where the liquid crystal phase is present as a metastable state. The enthalpies of conversion for both the gel and the liquid crystal phase were measured directly by the isothermal calorimetries at 47 and 53°C, respectively, where the exothermic peaks were observed by DSC and were compared with the enthalpy difference between the gel and subgel phases and that between the liquid crystal and subgel phases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural investigation of water‐induced phase transitions of poly(ethylene imine). III. The thermal behavior of hydrates and the construction of a phase diagram

The thermal behavior of poly(ethylene imine) (PEI) hydrates in a water vapor atmosphere was investigated through temperature‐dependent measurements of infrared spectra and X‐ray diffraction. Almost perfectly dried anhydrate melted at about 60 °C during the heating process. Anhydrate containing a small amount of water showed a phase transition to a mixture of hemihydrate and sesquihydrate around 40 °C, at which point the ethylene imine (EI)/water ratio was 1/0.5 in the hemihydrate and 1/1.5 in the sesquihydrate. The hemihydrate transferred to the sesquihydrate around 60 °C, and the latter melted above 80 °C. When the starting PEI sample contained a greater amount of water and consisted of hemihydrate and sesquihydrate, the hemihydrate transferred to the sesquihydrate via heating, and the latter melted around 75 °C. For a sample of dihydrate (EI/water ratio = 1/2) containing an appreciably large amount of water, it transferred to the sesquihydrate around 65 °C, and the latter melted above 90 °C. A sample of dihydrate with a much higher water content existed up to 110 °C and then melted; during this period, no transition to the sesquihydrate was observed. In this way, the starting crystalline phases were found to change for anhydrate and various types of hydrates. Their transition behaviors varied according to the water content. From these data, a phase diagram was successfully derived as a function of the temperature and water content. This phase diagram allowed us to predict the transition behavior during the hydration process at various constant temperatures. For example, at 60 °C, a molten sample should crystallize into a mixture of hemihydrate and sesquihydrate at first, and the hemihydrate should transfer to the sesquihydrate with increasing water content. The latter should change to the dihydrate in the final stage. This prediction was checked with time‐resolved measurements of X‐ray diffraction and infrared spectra during the hydration process at the corresponding temperature; this led to the establishment of the phase diagram. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2937–2948, 2003     

Heat affected zones in polymer laser marking

Laser marking is based on the laser heating of the subjected material, the heating being below the melting temperature or thermal degradation starting point. Within and nearby the mark, the material is chemically, physically and mechanically affected. This means that the main characteristics are changing in such a way that the material is ageing. Thermal and mechanical analysis can be used to determine the modification of the material, which is important and necessary to know for predicting its use lifetime. This paper investigates the physical and mechanical modification of the polymer HDPE100, when laser marking is applied. Burst stress, elongation and relaxation modulus were determined for the base material, within the heat affected zone and within the laser burned mark. Information on the crystallization rate and on the elongation viscosity is also reported. According to the results, the polyethylene has very fast crystallization and that affects the marking process if lower than appropriate maintaining during heating process is applied. It becomes stabile after 0.23 min, when it is tested at 103 °C. The elongation viscosity was analysed and values of 10⁵ Pa s were recorded for 10 s, which is a usual time of applying pressure. The performed analysis revealed about 10 % difference between the relaxation modulus of the irradiated and non-irradiated HDPE.     

Synthesis of yttrium orthoborate powders

Yttrium orthoborate YBO₃ is synthesized by calcining precursors precipitated with aqueous ammonium hydroxide from yttrium nitrate or yttrium chloride solutions (with concentrations ranging from 4.8 × 10^?3 to 0.0165 mol/L) and with a more than tenfold excess of boric acid. Single-phase YBO₃ is obtained at pH 5–6. Higher pHs result in the formation of mixtures of yttrium orthoborate and yttrium hydroxide phases. Dehydration occurs up to 288°C as shown by differential thermal analysis. Further heating induces crystallization. Addition of surfactants (polyvinylpyrrolidone (PVP) or ammonium polyacrylate (APA)) to the starting solution in an amount of 1 wt % of the yttrium salt affects the sizes and shapes of the precipitated particles. YBO₃ platelets with nanometer thicknesses are obtained. The temperature of the low-temperature ? high-temperature vaterite phase transition in YBO₃ is 977°C upon heating and 640°C upon cooling.     

An integrated low-power thin-film CO gas sensor on silicon

An approach to an integrated semiconductor gas sensor is presented. The major reasons considered for developing a semiconductor oxide gas sensor on silicon are the accurate local temperature control of the sensing area and the low level of the heating power required, together with an appropriate integrated structure. Thermal loss measurements show that the integrated gas sensor can operate up to 400 °C with less than 200 mW heating power. Depending on the deposition conditions, catalyst addition or surface conditioning, the SnO_x thin films are known to have an optimal sensitivity to CO between 250 °C and 400 °C. The sensitivity for CO gas and the response time of the device are presented for sputtered thin films of SnO_x, deposited on top of an isolated resistive heater, separated from silicon by a thin thermally-isolating membrane.