Thermal stability and flammability of polyurethane foams chemically reinforced with POSS

Manganese ferrite nanopowder was prepared by a new solvothermal method, using 1,2 propanediol as solvent and KOH as precipitant. The as-synthesized powder, by solvothermal treatment in autoclave at 195 °C, for 12 h, consisted of fine manganese ferrite nanoparticles. The further thermal treatment of the initial manganese ferrite powder to higher temperature resulted in manganese ferrite decomposition due to Mn(II) oxidation to Mn(III), as observed by X-ray diffraction. FT-IR spectroscopy has evidenced that the oxidation takes place even at 400 °C. The oxidation of Mn(II) to Mn(III) was studied by TG/DSC simultaneous thermal analysis. It was shown that Mn(II) oxidation takes place in a very small extent up to 400 °C. The main oxidation step occurs around 600 °C, when a clear mass gain is registered on TG curve, associated with a sharp exothermic effect on DSC curve. The exothermic effect is smaller in case of the powder annealed at 400 °C, confirming the superficial oxidation of Mn(II) up to 400 °C. In order to avoid Mn(II) oxidation, the powder obtained at 400 °C was further annealed at 800 °C in argon atmosphere, without degassing, when manganese ferrite MnFe₂O₄ was obtained as major crystalline phase (69 %). All manganese ferrite powders showed a superparamagnetic behavior, with maximum magnetization of 51 emu g^?1 in case of the as-synthesized powder, characteristic of magnetic ferrite nanopowders.     

Study on the kinetics and reactivity at the ignition temperature of Jurassic coal in North Shaanxi

Thermal analysis of seven Jurassic coal samples from North Shaanxi in West China and three permo-carboniferous coal samples from East China was studied to identify ignition temperatures in the process of the oxidation and spontaneous combustion. The experiments were carried out under non-isothermal heating conditions up to 700 °C at the heating rates of 5, 10, 15, and 20 °C min^?1 in an air atmosphere. Through the FTIR spectrometer experiments, the absorbance peaks of functional groups of coal samples were analyzed at the ignition temperatures, pre-ignition of the 10 °C, post-ignition of the 10 °C at the heating rate of 10 °C min^?1. By the differential spectrum method, the changes of functional groups were discussed with the aim to determine characteristics and reactivity of the ignition temperature around. The results showed that ignition temperatures of experimental coal samples increased with the rising heating rates, and ignition temperatures of Jurassic coals were lower than that of the permo-carboniferous coal samples at the same heating rate. Apparent activation energy of experimental Jurassic coals at the ignition temperatures was calculated by Ozawa method based on the non-isothermal and differential heating rates, ranging from 80 to 105 kJ mol^?1, which were lower than that of the eastern permo-carboniferous samples. On the basis of Pearson correlation coefficient method which can signify the degree of correlations ranging from ?1 to 1, the correlation analyses were conducted between activation energy and functional groups variation within 10 °C before and after ignition temperature. It was concluded that the key functional groups of Jurassic coals in the oxidation and ignition reaction were methyl and alkyl ether within 10 °C before ignition temperature, and carboxyl and carbonyl within 10 °C after ignition temperature.     

Nanosized bismuth titanate (Bi4Ti3O12) system drive through auto-combustion process by using suspension titania (TiO2)

Bismuth titanate (Bi₄Ti₃O₁₂) was developed by means of titanium oxide (TiO₂) suspension in auto-combustion process at 220 °C to get nanosized (20 ± 5 nm) bismuth titanate (Bi₄Ti₃O₁₂) powder. Complete piezoelectric phase (tetragonal) was obtained after calcination at 700 °C. Dilatometery of compacts was performed to find out sintering temperature. On the basis of shrinkage results, compacts were sintered at 750, 800, and 850 °C for 2 h. After sintering single phase was obtained with orthorhombic structure analyzed by X-ray diffraction and also investigated by Rietveld method. High-resolution scanning electron microscopy revealed that fine plate-like structure which is a characteristic of BIT powder can be obtained at 850 °C. Sintering results indicate that density and average grain size increase with the increasing temperature. A maximum of about 90 % of the theoretical density was achieved for the sintered product at 850 °C.     

Influence of Gas Type on the Thermal Efficiency of Microwave Plasmas for the Sintering of Metal Powders

Microwave plasmas have enormous potential as a rapid and energy efficient sintering technology. This paper evaluates the influence of both plasma atmosphere and metal powder type on the sintering temperatures achieved and the properties of the sintered powder metal compacts. The sintering is carried out using a 2.45 GHz microwave-plasma process called rapid discharge sintering (RDS). The sintering of three types of metal powder are evaluated in this study: nickel (Ni), copper (Cu) and 316L stainless steel (SS). An in-depth study of the effects of the plasma processing parameters on the sintered powder compacts are investigated. These parameters are correlated with the mechanical performance of the sintered compacts to help understand the effect of the plasma heating process. The substrate materials are sintered in four different gas discharges, namely hydrogen, nitrogen oxygen and argon. Thermocouple, pyrometer and emission spectroscopy measurements were taken to determine the substrate and the discharge temperatures. The morphology and structure were examined using scanning electron microscopy and X-ray diffraction. The density and hardness of the sintered compacts were correlated with the plasma processing conditions. As expected higher densities were obtained with powders with lower sintering temperatures i.e. nickel and copper when compared with stainless steel. Under the power input and pressure conditions used, the highest substrate temperature attained was 1,100°C for Cu powder sintered in a nitrogen atmosphere. In contrast under the same processing conditions but in an argon plasma, the temperature achieved with SS was only 500°C. The effect of the plasma gas type on the sintered powder compact chemistry was also monitored, both hydrogen and nitrogen yielded a reducing effect for the metal in contrast with the oxidising effect observed in an oxygen plasma.     

Kinetics of isothermal oxidation of WC–20Co hot-pressed compacts in air

The present paper presents an isothermal analysis of the oxidation behavior in which hot-pressed compacts rather than powders are used over the temperature range 700–850 °C. This was done to better simulate the extent of oxidation occurring on use. WC–Co powders were first subjected to non-isothermal kinetic analysis to follow the oxidation mechanism. In the isothermal runs, a thermobalance was used to follow up the mass with time at different constant temperatures. The diameter of compacts was measured as function of time at these temperatures, and a simple model was proposed to relate the diameters to extent of oxidation. Two reactions were found to take place that are controlled by chemical reaction at interface: Oxidation of cobalt and oxidation of WC with the formation of WO₃ and CoWO₄. The activation energies for the two steps of oxidation were calculated and found to equal 157 kJ mol^?1 and 205 kJ mol^?1, respectively. These values are in reasonable agreement with published data for WC–Co powders.     

Pyrolysis of pine needles: effects of process parameters on products yield and analysis of products

Pyrolysis of pine needles was carried out in a semi-batch reactor. The effects of pyrolysis parameters such as temperature (350–650 °C), heating rate (10 and 50 °C min^?1), nitrogen flow rate (50–200 cm³ min^?1) and biomass particle size (0.25–1.7 mm) were examined on products yield. Maximum bio-oil yield of 43.76% was obtained at pyrolysis temperature of 550 °C with a heating rate of 50 °C min^?1, nitrogen flow rate of 100 cm³ min^?1 for biomass particle size of 0.6 < d _p < 1 mm. The characterization of pyrolysis products (bio-oil, bio-char) has been made through different instrumental methods like Fourier transform infrared spectroscopy, gas chromatography–mass spectrometry, nuclear magnetic resonance spectroscopy (¹H NMR), X-ray powder diffraction, field emission scanning electron microscope and Brunauer–Emmett–Teller surface area analysis. The empirical formula of the bio-oil and bio-char was found as CH_1.47O_0.36N_0.005 and CH_0.56O_0.28N_0.013 with heating value of 26.25 and 25.50 MJ kg^?1, respectively. Results show that bio-oil can be potentially valuable as a renewable fuel after upgrading and can be used as a feedstock for valuable chemicals production. The properties of bio-char reveal that it can be used as solid fuels, as a cheap adsorbent and as a feedstock for activated carbon production.     

Studies on the thermal behavior and decomposition kinetic of drugs cetirizine and simvastatin

Understanding the response of drugs and their formulations to thermal stresses is an integral part of the development of stable medicinal products. In the present study, the thermal degradation of two drug samples (cetirizine and simvastatin) was determined by differential scanning calorimetery (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the cetirizine occurs during two temperature ranges of 165–227 and 247–402 °C. The TG/DTA analysis of simvastatin indicates that this drug melts (at about 143 °C) before it decomposes. The main thermal degradation for the simvastatin occurs during two endothermic behaviors in the temperature ranges of 238–308 and 308–414 °C. The influence of the heating rate (5, 10, 15, and 20 °C min^?1) on the DSC behavior of both the drug samples was verified. The results showed that as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Based on the values of activation energy obtained by ASTM E696 method, the values of activation energy for cetirizine and simvastatin were 120.8 and 170.9 kJ mol^?1, respectively. Finally, the values of ΔS ^#, ΔH ^#, and ΔG ^# of their decomposition reaction were calculated.     

Diminishing hazardous air pollutant emissions from pyrolysis of furan no-bake binders using methanesulfonic acid as the binder catalyst

The formation of hazardous air pollutants (HAPs) in thermal decomposition of furan no-bake foundry binders was investigated using analytical pyrolysis techniques. Two furan binders cured with p-xylenesulfonic acid (conventional acid catalyst used in foundries) and methanesulfonic acid (alternative catalyst proposed for diminishing HAPs) were flash pyrolyzed in a Curie-point pyrolyzer at 920 °C and slowly pyrolyzed in a thermogravimetric analyzer from 50 to 800 °C with a heating rate of 20 °C min^?1. Similar HAPs (mainly benzene, toluene, and xylenes) were identified in the emissions of the two binders. However, the HAP yields were much higher for the binder cured with p-xylenesulfonic acid than for the binder cured with methanesulfonic acid (3.74 and 1.24 mg HAPs/g binder pyrolyzed, respectively). By analyzing the HAP formation pathways, it was concluded that for the binder cured with p-xylenesulfonic acid, the aromatic HAPs were originated mainly from the acid catalyst. In addition, some HAPs (predominantly benzene) could be formed from the recombination of furan-derived fragments (e.g., C₂–C₄ radicals generated from ring-opening of furans). The results suggest that by replacing the conventionally used catalysts (arylsulfonic acids) with methanesulfonic acid, the HAP emissions from furan no-bake molds can be decreased significantly in metal casting processes.     

A novel programmed shrinkage dilatometer for optimized sintering of powder ceramics

A fast-firing shrinkage rate controlled dilatometer was developed as a tool for optimizing sintering of powder compacts. The instrument described in this work features an infrared imaging radiation furnace and a low thermal mass dilatometer assembly which allowed controlled heating and cooling rates of up to 500°C min^?1. Shrinkage control was accomplished using a computer interfaced PID control algorithm. Adjustments were made to hardware and software which reduced specimen creep under dilatometer pushrod load, eliminated non-uniform pushrod expansion, fostered reproducible specimen temperature determination, accounted for thermal expansion during sintering, and generated instantaneous termination of sintering at the specified end of RCS. Tests performed on ZnO samples demonstrated very rapid thermal response and excellent shrinkage control.     

Dilatometry as a tool to study a new synthesis for calcium hexaluminate

By using a wet chemical route, pure calcium hexaluminate (CA₆) was yielded, significantly lowering the reaction temperature and shortening the synthesis time if compared to usual industrial procedures. owever, dilatometric studies performed on compacts made of the as-prepared powder, just after pre-heating at 450°C, has shown a superposition between sintering shrinkage and expansion related to CA₂ formation, an intermediate phase formed during calcination and phase evolution to CA₆. oupling of such opposite phenomena led to microcracking of the material, mainly if the heating rates (10°C min^-1) were high. However, lower heating rates (1-5°C min^-1) could quite avoid microcracking but also limit densification. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal behavior and decomposition kinetics of Formex-bonded explosives containing different cyclic nitramines

Thermal behavior and decomposition kinetics of Formex-bonded PBXs based on some attractive cyclic nitramines, such as 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Actually, cis-1,3,4,6-tetranitrooctahy droimidazo-[4,5-d]imidazole (BCHMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10, 12-hexaazaisowurtzitane (CL-20), was investigated by means of nonisothermal thermogravimetry (TG) and differential scanning calorimetry (DSC). It was found that the mass loss rate of PBXs involved in this research depends greatly on heating rate and the residue of the decomposition of these PBXs decreases with the heating rate. The onset of the exotherms was noticed at 215.4, 278.7, 231.2 and 233.7 °C with the peak maximum at 235.1, 279.0, 231.2 and 233.7 °C for RDX-Formex, HMX-Formex, CL-20-Formex, and BCHMX-Formex, respectively. Their corresponding exothermic changes were 1788, 1237, 691, and 1583 J g^?1. It was also observed that the dependence on the heating rate for onset temperatures of HMX- and BCHMX-based PBXs was almost the same due to their similar molecular structure. In addition, based on nonisothermal TG data, the kinetic parameters for thermal decomposition of these PBXs were calculated by isoconversional methods. It was shown that the Formex base has great effects on the activation energy distribution of nitramines. It was further found that the kinetic compensation effects occurred during the thermal decomposition of nitramine-based PBXs, and they almost have the same compensation effects due to similar decomposition mechanism.     

Polymorphism and melt crystallisation of racemic betaxolol, a β-adrenergic antagonist drug

We report the polymorphic behaviour, in melt cooling experiments, of racemic betaxolol, a low aqueous solubility selective β₁-adrenergic antagonist drug with a flexible molecular structure. A multidisciplinary approach is employed, using thermal analysis (differential scanning calorimetry, polarised light thermomicroscopy), spectroscopic methods (infrared spectroscopy, magic angle spinning ¹H NMR) and X-ray powder diffraction. A glass phase is obtained, T _g ~ ?10 °C, on cooling the melt, unless the cooling rate is ≤0.5 °C min^?1, while a new metastable form, polymorph II, T _fus = 33 °C, is generated in subsequent heating runs in a two step process. Although either partial crystallisation from the melt in the first step or the formation of an intermediate, metastable, low ordered phase may explain these observations, our results favour the second hypothesis. The stable polymorph I, T _fus = 69 °C, which crystallizes on further heating after form II melting, has also been obtained either from polymorph II or from the molten phase, on standing at 25 °C. The racemic betaxolol crystalline phases are found to exhibit some degree of disorder.     

Extraction of pertechnetates from HNO<Subscript>3</Subscript> solutions into ionic liquids

The effect of the oxidation temperature of sintered UO₂ pellets on the powder properties of U₃O₈ was studied in the temperature range 250–900 °C in air. The U₃O₈ was obtained at 450 °C after 180 min and its particle size and surface area are respectively, 35 µm and 0.7 m²/g. The reduction of the U₃O₈ powder resulted in UO₂ after 30 min with a surface area of 0.8 m²/g. This value was improved more than 3.5 times by applying five alternating oxidation–reduction cycles.     

Thermokinetic characterisation of tin(II) chloride

Thermokinetic behaviour of SnCl₂ was investigated using differential scanning calorimetry and thermogravimetry techniques under non-isothermal conditions in air, complemented by electron microscopy and Raman spectroscopy. According to the results obtained, the oxidation of SnCl₂ at the heating rates of 5 and 100 °C min^?1 leads to the in situ formation of highly crystalline SnO₂ nanostructures in the form of nanoparticles and nanorods, respectively. The oxidation of SnCl₂ was found to be a liquid–solid (LS) phase transition at the heating rates equal or lower than 10 °C min^?1 and a gas–solid phase transition at the heating rates equal or greater than 20 °C min^?1. The activation energy of melting, vaporisation and LS oxidation of SnCl₂ was determined to be 198, 93 and 91 kJ mol^?1, respectively.     

Thermal degradation kinetics study and thermal cracking of waste cooking oil for biofuel production

Thermal cracking of waste cooking oil (WCO) for production of liquid fuel has gained special interest due to the growing demand of renewable fuel, depleting fossil fuel reserves and environmental issues. In the present work, thermal cracking of WCO to produce liquid hydrocarbon fuels without any preprocessing has been studied. Moreover, non-isothermal kinetics of WCO using thermogravimetric analysis (TGA) has been studied under an inert atmosphere at various heating rates. According to TGA result, active thermal decomposition of WCO was found to be between 318 and 500 °C. Furthermore, the temperature at which the maximum mass loss rate attained was shifted to higher values as the heating rates increased from 10 to 50 °C min^?1 and the values were found to be approximately similar to that of R ₅₀. Besides, model-free iso-conversion kinetic methods such as Friedman (FM), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) were used to determine the activation energies of WCO degradation. The average activation energy for the thermal degradation of WCO was found to be 243.7, 211.23 and 222 kJ mol^?1 for FM, KAS and FWO kinetic methods, respectively. Additionally, the cracking of WCO was studied in a semi-batch reactor under an inert atmosphere and the influences of cracking temperature, time and heating rates on product distribution were investigated. From the reaction, an optimum yield of 72 mass% was obtained at a temperature of 475 °C, time of 180 min and a heating rate of 10 °C min^?1. The physicochemical properties studied were in accordance with ASTM standards.     

Thermal decomposition and kinetics studies on the 2,2-dinitropropyl acrylate–styrene copolymer and 2,2-dinitropropyl acrylate–vinyl acetate copolymer

In the present work, kinetics of thermal decomposition of 2,2-dinitropropyl acrylate–styrene copolymer (DNPA/St) and 2,2-dinitropropyl acrylate–vinyl acetate copolymer (DNPA/VAc) was investigated by differential scanning calorimetry (DSC). The influence of the heating rate (5, 10, 15, and 20 °C min^?1) on the DSC behavior of the copolymer was verified. The results showed that, as the heating rate was increased, decomposition temperature of the copolymer was increased. Also, the kinetic parameters such as activation energy and frequency factor of the copolymer were obtained from the DSC data by the isoconversional methods proposed by Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO). Average activation energy obtained by KAS and FWO methods for the thermal decomposition reaction of DNPA/St and DNPA/VAc are 157.38 ± 0.27 and 147.67 ± 0.57 kJ mol^?1, respectively. The rate constants for thermal decomposition calculated from the activation parameters showed the structural dependency. The relative stability of two copolymers under 50 °C was in this order: DNPA/St > DNPA/VAc. The results of thermogravimetry (TG) analysis revealed that the main mass changes for DNPA/St and DNPA/VAc occurred in the temperature ranges of 200–270 °C. The DSC-FTIR analysis of DNPA/St indicates that the band intensity of nitro and other groups increased haphazardly from 230 °C due to thermal decomposition.     

Study of carbon black obtained by pyrolysis of waste scrap tyres

Waste scrap tyres were thermally decomposed under various conditions. Decompositions were followed by the TGA method. Specific heating regimes were tested to obtain optimal structural properties of resulting pyrolytic carbon black produced by pyrolysis of scrap tyres and the process was characterized in temperature interval from 380 to 1,200 °C and heating rate 10, 20 and 50 °C min^?1 under nitrogen atmosphere. The original scrap tyres and pyrolytic carbon black were characterized by Raman and Fourier transform infrared spectroscopy methods. Textural properties were also determined. Effect of temperature and heating rate on process of pyrolysis of scrap tyres was observed. Shifting of temperature of maximum pyrolysis rate to lower value and spreading of DTG peak is caused by increasing heating rate. Temperature 570 °C was sufficient for total scrap tyres pyrolysis. Graphitic and disordered structure was distinguished in the formed carbon black by Raman spectroscopy. With increasing temperature, heating rate and weight loss, the amount of the graphitic structure was reduced at the expense of disordered structure. Destruction of nonporous scrap tyres and formation of porous structure took place at higher temperature. Porous carbon black is formed above 380 °C, specific surface area increased up to 88 m² g^?1 .     

Polymeric Schiff Bases. VII. Some Parameters in the Evaluation of the Thermal Stability of Poly(p-Xylylidene-p-phenylenediamine)

Thermogravimetric analyses of poly(p-xylylidene-p-phenylenediamine) in nitrogen, helium, and air yield stability values substantially identical to values obtained from tests in vacuo. The respective thermal stability values in nitrogen and in air are unchanged over a fourfold change in gas flow rates. Slightly lower values are found at heating rates of 5–15°C/min than at 30°C/min. Thermal stabilities are lower in oxygen than in air, but the values are still relatively high. Higher apparent thermal stability values are observed when a powder sample of 10 mg is evaluated as a single mass rather than as a fine powder. Calorimetric measurements indicate that Schiff base polymers which have been heated in nitrogen to 1000–1200°C have not been converted to graphite-type polymers. The Schiff base polymers are resistant to radiation; their stability is shown to be independent of dose rate and of the nature of the ionizing radiation.     

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.     

Influence of some lime-containing additives on the thermal behavior of urea

Urea is one of the main nitrogen fertilizers used in agriculture. But being well soluble in water, hardly 50% of its nitrogen is assimilated by plants. One possibility to eliminate this disadvantage is to use coating agents for modification of urea to obtain a controlled-realized fertilizer. The aim of this research was to study the influence of different lime-containing additives on the thermal behavior and decomposition kinetics of urea in oxidizing atmosphere. Commercial fertilizer-grade urea (46.4% N) and analytical-grade CaO, MgO, CaCO₃, MgCO₃ were used in the experiments. In addition, one Estonian limestone and one dolomite sample were used as additive or coating material. The experiments with a Setaram Setsys 1750 thermoanalyzer coupled to a Nicolet 380 FTIR Spectrometer by a heated transfer line were carried out under non-isothermal conditions up to 900 °C at the heating rate of 5 °C min^?1 and to calculate kinetic parameters, additionally, at 1, 2, and 10 °C min^?1 in the atmosphere containing 80% of Ar and 20% of O₂. The differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results obtained indicate that thermooxidative decomposition of urea as well as the blends of urea with lime-containing materials and urea prills coated with limestone or dolomite powder follows a complex reaction mechanism.