The Thermal Stability and Flammability of Expandable Graphite-Filled Polypropylene/Thermoplastic Polyurethane Blends

Polypropylene/thermoplastic polyurethane (PP/TPU) blends filled with two different particle sizes (45 and 150 μm) of expandable graphite (EG) were prepared by melt blending. Thermogravimetric analysis (TGA) was carried out to explain the effect of EG on the thermal stability of PP/TPU blends. In addition, the fire behavior of PP/TPU and PP/TPU/EG was investigated by a cone calorimeter. The char morphology and carbonation of the above systems were also characterized. The experimental results indicated that intumescent EG significantly enhanced the thermal stability and fire resistance of these blends. With the smaller particle size of EG, the thermal stability and flame retardancy were improved. The results from TGA and cone calorimeter demonstrated that the addition of EG could retard the degradation of the polymer materials above the temperature of 500°C by promoting the formation of a compact char layer. This char layer prevented further degradation of the polymer matrix and protected it effectively from heat penetrating inside, resulting in lower weight loss rate and better flame-retarded performances.     

A thermogravimetric method for the measurement of CO/CO2 ratio at the surface of carbon during combustion

This work presents a new method of measuring the CO/CO₂ ratio at the surface of carbon particles during combustion. This thermogravimetric method deduces the ratio of CO to CO₂ by comparing the rate of consumption of carbon with the rate of oxidation of an external reference material with fast oxidation kinetics, in this case Cu. The method is useful when combustion is controlled by external mass transfer, commonly encountered in large-scale processes. The viability of this method has been demonstrated experimentally with graphite and a lignite char. It was found that in an atmosphere of ～ 1% O₂, the graphite produced CO₂ between 700 and 900 °C whilst the lignite char produced a mixture of CO and CO₂ between 700 and 800 °C with the proportion of CO increasing with temperature, and above 850 °C, only CO was produced. It was also found that for this particular lignite char, the ratio of CO/CO₂ increased with decreasing pO₂ in the environment.     

Preparation and Thermal Properties of Boron-Containing o-Cresol-Formaldehyde Resin/Octa(aminophenyl)-POSS Nanocomposites

The boron-containing o-cresol-formaldehyde resin (BoCFR) and octa(aminophenyl) polyhedral oligomeric silsesquioxane (OAP-POSS) were synthesized, and the BoCFR/OAP-POSS nanocomposite prepared via an in-situ method. The curing process of the resin was characterized by Fourier transform infrared (FTIR). The thermal properties and dynamic mechanical properties of the nanocomposites were investigated. The results show that the maximal mechanical loss temperature (T_p) increased with increasing OAP-POSS content. When the content of OAP-POSS was 10 wt% the T_p was over 200°C, 27°C higher than the pure BoCFR. The BoCFR/OAP-POSS nanocomposite had better thermal stablitity than the pure BoCFR. The residual weight of the o-cresol-formaldehyde resin was only 6.13 wt% at 600°C. But the residual weight of the pure BoCFR was 55.73 wt% at 600°C, and the residual weights of the BoCFR nanocomposites were all higher than pure BoCFR. The residual weight of the BoCFR nanocomposite was 63.2 wt% at 600°C and 21.83 wt% at 900°C when the OAP-POSS content was 10 wt%. The weight loss of BoCFR/OAP-POSS nanocomposite can be divided primarily into two temperature stages, from 430°C to 550°C and from 550°C to 900°C. The main thermal degradation reaction follows first order kinetics.     

Activated carbon from coconut leaves for electrical double-layer capacitor

This study investigates the potential of coconut leaves as a precursor to obtain activated carbon. Coconut leaf-activated carbon (CLAC) has been prepared through gas activation process starting with carbonization at 400 °C in nitrogen flow for 3 h. The carbonized coconut leaves were milled using planetary ball milling followed by activation with carbon dioxide (CO₂) at different temperatures ranging from 700 to 1000 °C. The Brunauer–Emmett–Teller (BET) characterization reveals that the surface area of CLACs increases with the increase in activation temperature. Electrodes prepared from CLACs have been used to fabricate electrochemical double-layer capacitors (EDLCs) in order to study the electrochemical behavior using galvanostatic charge–discharge measurements and cyclic voltammetry. The carbon activated at 900 °C delivered the best specific capacitance of 133.4 F/g at current density of 200 mA/g.     

Advanced LiTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C anode by incorporation of carbon nanotubes for aqueous lithium-ion batteries

Inferior rate capability is a big challenge for LiTi₂(PO₄)₃ anode for aqueous lithium-ion batteries. Herein, to address such issue, we synthesized a high-performance LiTi₂(PO₄)₃/carbon/carbon nanotube (LTP/C/CNT) composite by virtue of high-quality carbon coating and incorporation of good conductive network. The as-prepared LTP/C/CNT composite exhibits excellent rate performance with discharge capacity of 80.1 and 59.1 mAh g^?1 at 10 C and 20 C (based on the mass of anode, 1 C = 150 mA g^?1), much larger than that of the LTP/C composite (53.4 mAh g^?1 at 10 C, and 31.7 mAh g^?1 at 20 C). LTP/C/CNT also demonstrates outstanding cycling stability with capacity retention of 83.3 % after 1000 cycles at 5 C, superior to LTP/C without incorporation of CNTs (60.1 %). As verified, the excellent electrochemical performance of the LTP/C/CNT composite is attributed to the enhanced electrical conductivity, rapid charge transfer, and Li-ion diffusion because of the incorporation of CNTs.     

Oxidation parameters determination of Cu–Al–Ni–Fe shape-memory alloy at high temperatures

In this study, isothermal oxidation behavior of a Cu–Al–Ni–Fe shape-memory alloy between 500 and 900 °C was investigated. Alloy samples were exposed to oxygen by TG/DTA for 1 h at a constant temperature, allowing for calculation of the oxidation constant and activation energy values of the oxidation process. The oxidation constant value increased with temperature, reaching saturation at 800 °C. The effect of oxidation on crystal structure, surface morphology and chemical composition of the Cu–Al–Ni–Fe alloy was determined by X-ray diffractometer (XRD) and scanning electron microscope (SEM)–energy-dispersive X-ray (EDX) analyses. With increasing oxidation temperature, number and intensity of the characteristic 18R martensite phase peaks were reduced while Al₂O₃ phase peaks were increased. In parallel to the XRD results, the same variations were also detected by SEM–EDX measurements.     

A study on the effect of stress state on damage evolution in hot deformation of free cutting steels using double notched bars

The effect of stress state on the initiation of damage for leaded free cutting steel has been investigated under hot rolling conditions. Double notched (DN) circumferential tension samples were designed and used to simulate damage development at different stress states and deformation conditions using a Gleeble (3800) thermal-mechanical testing system. Two DN sample geometries with varying notch profiles were used to account for different states of stress. To simulate the conditions of hot rolling the samples were tested at high temperatures (900–1200 °C) and moderate strain rates (0.1–1 s^?1). After testing to failure, which normally occurs at one notch of the specimen, the unfailed notch of each sample was sectioned to examine the sites where damage occurs since the material has been captured in a state very close to failure. Two of the cases examined have shown definitive damage paths occurring from ‘outside–in’ for a sharp notch deformed at T = 900 °C and from ‘inside–out’ for a blunt notch tested at T = 1200 °C for the same strain rate of 0.1 s^?1. The experimental results of the failure initiation sites were compared with computed values of the stress fields around the notch profiles, obtained from FE analysis using a set of viscoplastic constitutive equations calibrated for free cutting steel. The temperature profiles from high temperature mechanical testing were used in the FE calculations of the stress state.     

Kinetics of coal char gasification in a carbon dioxide medium

Solid fuel samples with different carbon contents are gasified by successively subjecting to pyrolysis in argon and oxidation in carbon dioxide at various temperatures to determine the rate of the chemical reactions and the activation energy required for simulating and optimizing the operation of gas generators. The samples were prepared from bituminous coal, lignite, and anthracite of the Kuznetsk and Kansk-Achinsk coal basins. The gasification of coal char samples in a carbon dioxide medium at 900–1200°C is analyzed by thermogravimetry. The temperature dependences of the weight change rate and gasification time of coal char samples are measured and used to calculate the preexponential factor and activation energy of the carbon oxidation reaction. It is found that, with increasing oxidizing medium temperature from 900 to 1200°C, the gasification time of the coal char samples obtained from anthracite and bituminous coal decrease 8- and 22-fold, respectively. A physicomathematical model of coal char gasification in a fixed bed, with the oxidizing gas diffusing through the ash layer formed, is proposed.     

Thermal Dehydration and Vibrational Studies of ZnK4(P3O9)2 · 6H2O

The thermal dehydration of ZnK₄(P₃O₉)₂ · 6H₂O was studied in the range 25–500°C by thermogravimetric analysis (TGA and DSC) and X‐ray diffraction. We found, based on the TGA and DSC scans, the dehydration of this salt takes place in three stages with a loss of the six water molecules. The infrared and Raman spectra of ZnK₄(P₃O₉)₂ · 6H₂O have been recorded and interpreted using a factor group analysis. The internal modes are assigned in terms of POP and PO₂ structural units using experimental and theoretical IR and Raman frequencies.     

Styrene Butadiene Rubber/Epoxidized Natural Rubber (SBR/ENR50) Nanocomposites Containing Nanoclay and Carbon Black as Fillers for Application in Tire-Tread Compounds

Nanocomposite vulcunizates based on a SBR/ENR50 (50/50%wt) rubber blend containing nanoclay (5 or 10 phr) with and without carbon black (CB 20 phr) were prepared by melt blending in an internal mixer. The compound containing 35 phr carbon black (only) was prepared as a reference sample. Microstructure of nanocomposite samples was investigated by using X-ray diffraction (XRD), melt rheo-mechanical spectroscopy (RMS), and scanning electron microscopy (SEM). The XRD patterns revealed that the distance between the clay layers were increased by adding CB to the nanocomposite samples; they caused better diffusion of chains between the layers and resulted in an intercalated structure. The RMS results also indicated the formation of the filler-filler networks. SEM images of fracture surfaces showed the presence of much roughness in the samples containing both nanoclay and CB compared to the other samples. The results obtained from application of the Flory–Rhener equation showed a high crosslink density for the sample with 10 phr nanoclay and 20 phr CB. Dynamic mechanical behavior, mechanical properties, and abrasion resistance of the nanocomposites were evaluated. The results indicated that the sample containing 10 phr nanoclay and 20 phr CB had an increased dynamic elastic modulus, reduced maximum loss factor (tanδ)_max,, and an improved tensile strength and abrasion resistance compared to the reference sample. Also, this sample showed the lowest maximum loss factor, at 50–60°C, so it can be a candidate for tire-tread application.     

Preparation and Characterization of Para-Aramid Fibers with the Main Chain Containing Heterocyclic Units

Abstract

A para-aramid fiber whose main chain contained heterocyclic units was prepared by low temperature copolycondensation, wet-spinning, and high temperature thermal treatment. The prepared fibers (named F-368) and two commercial aramid fibers, K49 (Kevlar 49, Dupont de Nemours Co., USA) and APMOC (Kamenskvolokno and Tver’khimvolokno, Russia), were characterized and analyzed in detail. Infrared spectroscopy (IR) and wide-angle X-ray diffraction (WAXD) were employed to characterize their chemical and aggregation structures, respectively. The results showed the introduction of heterocyclic units into the wholly para-aromatic polyamide backbone of K49 in the F-368 and APMOC reduced the crystallinity significantly. The tenacity of F-368 and APMOC were 32.2 and 30.5cN/dtex, which were about 68% and 59% higher than that of K49, respectively. Thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) were used to investigate their thermal properties; the results indicated that these aramid fibers showed exceptional thermal properties with glass transition temperatures of 240–260?°C, and decomposition temperatures at 510–560?°C, both in nitrogen and air. The TGA results also showed the decomposition mechanism of K49 and the heterocyclic aramid fibers in nitrogen and air were different. The decomposition temperature of K49 was higher than that of the heterocyclic copolyaramid fibers both in nitrogen and air. On the contrary, the char yields of the heterocyclic copolyaramid fibers at 800?°C were higher than that of K49 in both nitrogen and air.     

Effect of carbon nanotube addition on the thermite reaction in the Al/CuO energetic nanocomposite

Abstract

In this work, the Al/CNT/CuO nano-thermite samples are prepared by ultrasonic mixing with variable CNT content. The morphology of nano-thermites analysed by electron microscopy revealed that the CNTs are dispersed and there are intimate contacts between fuels (Al and CNT) and oxidiser (CuO) constituents of the nano-thermite. Raman spectroscopy technique is used to analyse the structural integrity of the CNTs in the nano-thermite. The thermite reaction characteristics are evaluated by simultaneous thermogravimetric analysis/differential scanning calorimetry technique. The exothermic enthalpy of the Al/CNT/CuO nano-thermite samples increased with increasing CNT content. The effect of Al particle size and Al/Cu molar ratio variation on the thermite reaction enthalpy is also analysed. The ignition temperature of the thermite reaction is also lowered by 71 °C than that of Al/CuO nano-thermite. The activation energy for thermite reaction of Al/CNT/CuO nano-thermite is also lowered by 23% to that of pure Al/CuO. The residues of the nano-thermites after the thermite reaction at 1010 °C are collected and analysed by the X-ray diffraction.     

Thermal and Spectral Dielectric Properties of Polypyrrole/Polymethylmethacrylate Composites

Thermal properties of polypyrrole/polymethylmethacrylate (PPy/PMMA) composites were analyzed by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). A decrease in the glass transition temperatures with PPy concentration reveals the increase of segmental motion. The dielectric properties of these composites were studied for several weight concentrations of PPy in the frequency range between 500 Hz and 0.2 MHz, over the temperature range 23–110°C. Jonscher's phenomenological model has been used for modeling the dielectric response of the composite materials. This study shows that the results obtained for the dielectric response are in good agreement with the results of TGA and DSC measurements.     

Catalytic cracking of tar derived from the pyrolysis of municipal solid waste fractions over biochar

The tars derived from the pyrolysis of four typical municipal solid waste fractions at 600 °C, namely pine wood (PW), tryptone (TP), polyethylene (PE) and polyvinyl chloride (PVC), were characterized and then catalytically cracked by activated biochar catalyst (ABC) at 700–900 °C. The ABC was produced from the pyrolysis of pine wood at 800 °C for 1 h, then activated by CO₂ at 900 °C for 20?min. The results showed that O-containing species, N-containing species, chain hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) were the main products in the raw tar from the pyrolysis of PW, TP, PE and PVC, respectively. The tar cracking efficiency by ABC was ordered as PW>TP>PE>PVC, which indicated that the biomass tars were easier to be converted by ABC than plastic tars. The highest tar conversion of 98.7% was achieved for PW at 900 °C. Besides, N-containing tars were more stable than O-containing tars. The coke deposition on the ABC was more serious after the cracking of plastic tars (PE and PVC) than that of biomass tars (PW and TP). After the catalytic cracking of TP and PVC tars at 900 °C, the nitrogen and chlorine contents in ABC increased by 3 times and 10.5 times, respectively.     

The iron mineral changes occurring in lignite coal during gasification

Representative lignite and gasified material samples were retrieved form a cooled down gasifier. The samples were taken at various heights in the gasifier that operated on lignite, under stable conditions. The proximate analyses, ash composition and temperature in the gasifier were determined according to standard procedures. The main minerals found in the present investigation were bassanite, illite, quartz, kaolinite, calcite and the only iron bearing mineral was found to be pyrite. The trend in the estimated particle surface temperature profile shows an increase in the drying, pyrolysis, gasification and combustion zones from about 300 °C to just over 900 °C. About 1/3 down the gasifier, an average particle temperature of about 400 °C and particle surface temperature of about 600 °C was measured where pyrite conversion started. About 2/3 down the gasifier, where an average temperature of about 700 °C and particle surface temperature of about 900 °C was measured, all the pyrite was converted and in the bottom part of the gasifier, oxidation of the iron started to play a role and hematite and an iron containing glass formed at an average temperature of > 800 °C and surface temperature of 900 °C.     

Preparation and Characterization of Novel Polyimides with Hydroxyl Groups

3,3′-diamino-4,4′-dihydroxybiphenyl (DADHBP) was synthesized and its chemical structure was confirmed by Fourier transform infrared (FT-IR) spectroscopy, ¹H-nuclear magnetic resonance (¹H-NMR), and differential scanning calorimetry (DSC). Then six poly(amic acid) (PAA) solutions were prepared by copolymerization of DADHBP, oxydiphthalicanhydride (ODPA), and 2,2-bis [4-(4-aminophenoxy)phenyl] propane (BAPOPP) in N,N-dimethylacetamide (DMAC) in different mole ratios. The polyimide (PI) films were obtained through thermal imidazation reactions of the thin layers of the above-mentioned precursor solutions. Chemical structures of all PI films were demonstrated by FT-IR. Thermal stabilities and decomposition behaviors of the PI films were tested by DSC and thermogravimetric analysis (TGA). Thermal measurements indicate that the polymers have high thermal stability and produce high char yields. The properties of the PI films were further studied by ultraviolet–visible spectroscopy, water absorption, surface energy, and mechanical measurements. Thermal analysis showed glass transition temperatures between 205.9°C and 276.7°C. Decomposition temperatures were higher than 360.2°C, with 10% weight losses in the range of 448.6°C～517.8°C. The prepared PI films also exhibited good UV absorption, low water absorption (<2%), low surface energy (<44.28 mJ/m²), and good mechanical properties.     

Flame retardance and thermal stability of carbon nanotube epoxy composite prepared from sol-gel method

Carbon nanotubes (CNTs) are functionalized by vinyltriethoxysilane (VTES) to incorporate the -O-C₂H₅ functional group and become VTES—CNT. The VTES—CNTs are added to the modified DGEBA epoxy resin that contains silicon to induce the sol-gel reaction. The final products are organic/inorganic nanocomposites. Thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) are used to study the thermal property of nanocomposites. The T_g was increased from 118 to 160 °C and char yield of composites that contained 9 wt% CNT at 750 °C was increased by 46.94%. The integral procedural decomposition temperature (IPDT) was increased from 890 to 1571 °C. The limiting oxygen index (LOI) and UL-94 tests were classified as the flame retardance. The LOI of composites was increased from 22 to 27 and the UL-94 changed from V-1 to V-0 when the contents were increased to 9 wt%. The nanocomposites had a higher char yield and were highly flame retardant. The products can meet to the requirements of halogen-free and phosphorus-free ecological flame retardant.     

Synthesis and Properties of Polyphenylsilsesquioxane Modified Phenolic Resin by in-situ Polymerization from Phenyltriethoxysilane Precursor

A series of phenolic resin-polyphenylsilsesquioxane (PR-PPSQ) composites were prepared by in situ formation from phenyltriethoxysilane (PTES) precursor during polymerization of the PR. The precursor was firstly hydrolyzed in a solution, and then the sol was added to the PR polymerization system. The structures of the composites were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and solid-state ²⁹Si nuclear magnetic resonance (Si-NMR). The PPSQs were spherical particles with a diameter of about 3 µm and nearly uniformly dispersed in the matrix, as revealed by scanning electron microscopy (SEM). The influence of PTES content on the thermal behavior of the PR was characterized by thermogravimetric analysis (TGA) in nitrogen and air atmospheres. The results showed that the onset temperature and residual weight of the composite containing 20 wt% PTES content were improved by 47°C and 8.4%, respectively, compared to the pure PR. The thermal oxidative stability was also greatly increased; the 50 wt% weight loss temperature rose from 567°C for PR to 601°C. The flexural strength of the composites was improved; in particular, the value of the composite containing 15 wt% PTES content was elevated by 32% (from 41.66 to 55.33 MPa).     

Thermal stability of second generation carbosilane dendrimers with peripheral ammonia groups

Spinel nickel zinc ferrite nanowires were successfully prepared in mesoporous silica SBA-15 as a host matrix. The powder was annealed at a range of temperatures (500–900 °C) with heating rate 0.5 °C/min. The required NiZnFe₂O₄ phase was obtained at 700 °C. The specific surface area S_BET data revealed that the surface area of the mesoporous silica after annealing was decreased from 821 to 90 m²/g which indicated that the spinal ferrite fills the channels of mesoporous materials. The one-dimensional spinel nanostructures were characterized by X-ray diffraction, infrared spectroscopy, vibrating sample magnetometer, and transmission electron microscopy before and after a selective removal of the silica template in aqueous solution of NaOH or HF. The presence of SBA-15 lowers the formation temperature of nickel zinc ferrite nanowires compared to the corresponding bulk material. The magnetic properties revealed a high saturation magnetization level (~43 emu/g) for the Ni–Zn nanowires at 900 °C.     

Deformation and annealing behaviour of a low carbon high Mn TWIP steel microalloyed with Ti

ABSTRACT

A low carbon high Mn, Ti microalloyed dual phase TWIP steel has been processed through cold rolling and annealing. X-ray diffraction reveals the maximum austenite (≈92%) in HRACST sample whereas, the 50CD sample shows 29% ferrite. The microstructure of HRAC and HRACST samples reveal austenite grains with annealing twins and deformation induced ferrite (DIF). The higher amount of DIF along with deformation twins form during cold deformation. Annealing at 500°C shows recovery, whereas at 700°C shows partial recrystallisation and at 900°C reveals almost full recrystallisation. TEM microstructures of the 900°C for 30?min samples reveal annealing twins with TiC particle. Strong Brass {110}<112> and Goss{110}<001> texture components are observed in HRAC, HRACST and 50CD samples. Goss Twin (GT) {113}<332> and Copper Twin (Cu-T) {552}<115> components are observed in 50CD sample. Addition of Ti results in an average grain size of 20?μm. Maximum YS (1176?MPa) and UTS (1283?MPa) values with the lowest ductility of 11% have been obtained for the 50CD sample which is related to the formation of extensive deformation twin and a higher fraction of DIF. 700°C-30?min and 700°C-60?min samples show an increase in ductility (23% and 34%, respectively) with a marginal decrease in tensile strength (1054?MPa). Annealing at 900°C shows ductility restoration up to 60% with higher tensile strength compared to HRACST sample. Ductile fracture of HRAC and HRACST samples transform to brittle fracture in the 50CD sample. Annealing at 900°C for 30?min shows ductile fracture with some (Fe, Mn)S and TiC particles.