Modification of bentonite with diphosphonium salts: Synthesis and characterization

Intercalations of diphosphonium salts (bis(triphenylphosphonium methylene) benzene-dichloride (TPhPMB) and bis(tributylphosphonium methylene) benzene-dichloride (TBuPMB)) into bentonite were carried out through the ion-exchange of a purified bentonite with a solution of diphosphonium salt. X-ray diffraction (XRD), ³¹P MAS NMR, thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were used to assess the effect of product exchange on bentonite surface and the exfoliation phenomenon of bentonite interlayer. Experimental results demonstrated that the purified bentonite has a basal spacing of 13.2 Å while the modified bentonites show a greater basal spacing of about 18 Å and has a good thermal stability (300-400 °C).     

Synthesis, characterization, thermal and explosive properties of potassium salts of trinitrophloroglucinol

Three different substituted potassium salts of trinitrophloroglucinol (H(3)TNPG) were prepared and characterized. The salts are all hydrates, and thermogravimetric analysis (TG) and elemental analysis confirmed that these salts contain crystal H2O and that the amount crystal H2O in potassium salts of H3TNPG is 1.0 hydrate for mono-substituted potassium salts of H3TNPG [K(H2TNPG)] and di-substituted potassium salt of H3TNPG [K2(HTNPG)], and 2.0 hydrate for tri-substituted potassium salt of H3TNPG [K3(TNPG)]. Their thermal decomposition mechanisms and kinetic parameters from 50 to 500 degrees C were studied under a linear heating rate by differential scanning calorimetry (DSC). Their thermal decomposition mechanisms undergo dehydration stage and intensive exothermic decomposition stage. FT-IR and TG studies verify that their final residua of decomposition are potassium cyanide or potassium carbonate. According to the onset temperature of the first exothermic decomposition process of dehydrated salts, the order of the thermal stability from low to high is from K(H2TNPG) and K2(HTNPG) to K3(TNPG), which is conform to the results of apparent activation energy calculated by Kissinger's and Ozawa-Doyle's method. Sensitivity test results showed that potassium salts of H3TNPG demonstrated higher sensitivity properties and had greater explosive probabilities.     

Long-acting antibacterial activity of quaternary phosphonium salts functionalized few-layered graphite

Tetradecyl triphenyl phosphonium bromide (TTP) functionalized few-layered graphite (FG) was prepared to investigate the effects of phosphonium salts usage on the characteristics, morphology, thermal stability and long-acting antibacterial property of TTP functionalized FG (TTP-FG) by introducing different content of TTP into FG. The results showed that the phosphonium salt was intercalated into FG, and the basal spacing of TTP-FG was enlarged with the increasing of phosphonium salt content. TTP-FG-3 with 33.7% (mass fraction) of TTP, displayed excellent thermal stability and long-acting antibacterial activity with the minimal inhibitory concentrations against E. coli and S. aureus of 580 mg L⁻¹ and 285 mg L⁻¹ after 72 h soaking, respectively.     

几种硫鎓盐类光产酸剂的合成与性质

硫鎓盐类光产酸剂因其较高的产酸效率和好的热稳定性而广泛应用于化学增幅光致抗蚀剂中。本论文选择不同的酚化合物为原料,使之与二甲基亚砜和氯化氢反应,合成了一系列硫鎓盐化合物,研究了其在有机溶剂中的溶解性、热稳定性、紫外吸收性质及其光解特性。以低压汞灯为曝光光源,测定了该类光产酸剂的光解量子效率在0.2—0.7范围。     

碱性染料与磷钨酸形成的新型电荷转移盐的制备与表征

报道了用Keggin结构的磷钨酸与碱性染料结晶紫、碱性藏红T和碱性湖兰BB反应形成的3种新型电荷转移盐。利用元素分析、差热-热重、变温红外、固体漫反射电子光谱对标题化合物的组成、热稳定性和光学性质进行了表征。     

Influence of ultrasonic dual mixing on thermal and tensile properties of MWCNTs-epoxy composite

Multiwalled carbon nanotubes (MWCNTs) reinforced epoxy based composites were fabricated by using an innovative ultrasonic dual mixing (UDM) process consists of ultrasonic mixing with simultaneous magnetic stirring. The effect of addition of varying amount of MWCNTs on thermal stability and tensile properties of the epoxy based composite has been investigated. It is found that the thermal stability, tensile strength and toughness of the epoxy base improves with the increase of MWCNTs addition up to 1.5 wt.% and UDM processing at certain capacity of the system. Tensile tests and thermal gravimetric analysis (TGA) were performed on each group of composites containing different amount of MWCNTs to determine their mechanical and thermal properties respectively. The dispersion of 1.5 wt.% MWCNTs fillers in epoxy nanocomposites was studied by transmission electron microscopy (TEM) as well as by field emission scanning electron microscopy (FESEM) applied on their tensile fracture surface.     

Synthesis, characterization and properties of nitrogen-rich salts of trinitrophloroglucinol

Five different nitrogen-rich salts of trinitrophloroglucinol (H(3)TNPG) have been prepared by the reaction of ammonia, aminoguanidine (AG), carbohydrazide (CHZ), semicarbazide (SCZ) and 5-aminotetrazo (ATZ) with trinitrophloroglucinol in aqueous solution through the heating method of water bath, with the yield up to 80%. These salts were characterized by elemental analysis, FT-IR, DSC and TG-DTG techniques. Their melting temperature is consistent with the thermal decomposition temperature. Their thermal decomposition process and kinetic parameters from 323 to 673K were investigated under a linear heating rate by DSC. The thermal decomposition of these salts undergoes an intensive exothermic decomposition stage to evolve abundant gas products and the enthalpies of exothermic decomposition reaction are high. The tests of sensitivity properties show these salts are insensitivity. All the properties of five nitrogen-rich salts appeared to depend on molecule structures and interconnection. It can be concluded that the five compounds are worthy of further in-depth studies as the gas-generating composition, emission reagents and propellants.     

Modification of multi-walled carbon nanotubes by Diels-Alder and Sandmeyer reactions

Random (L) and aligned (A) multi-walled carbon nanotubes (MWNTs) were modified by Diels-Alder (DA) [4+2] cycloaddition, Sandmeyer (SM) reaction and by catalytic oxidation (OX). The properties of modified carbon nanotubes were studied by dispersability tests, elemental analysis, thermogravimetry/mass spectrometry, X-ray photoelectron spectroscopy, and NMR spectroscopy. The cycloaddition reaction could only be successfully performed with the L-MWNTs in molten and in solution state by using an aluminum chloride homogeneous catalyst. The efficiency and thermal stability of the solution phase cycloaddition were much higher than in the case of modification in the molten phase. The functionalization of both types of MWNTs by Sandmeyer reaction was carried out by copper(I) and iron(ll) ions that helped in the radical decomposition of diazonium salts. Successful functionalization of nanotubes is achieved by a long decomposition time of the thermally activated diazonium salts. To the contrary, in the case of radical decomposition of diazonium salts, the time is not a decisive parameter. The dispersability tests have proved the changes in the physical features of modified carbon nanotubes depending on the hydrophobic and hydrophilic character of the solvents. The presence of the modifying groups and their fragments from the functionalized MWNTs has been demonstrated by thermogravimetry/mass spectrometry (TG/MS). Relatively high concentration of sulfur atoms was detected by X-ray photoelectron spectroscopy in nanotubes modified by sulfur substituent groups. In the case of catalytic oxidation, the X-ray photoelectron spectroscopic signal of oxygen bound to nanotubes showed considerable change as compared to pristine nanotubes. Due to the high thermal stability of modified multi-walled carbon nanotubes, the functionalized derivatives are applicable in several industrial fields.     

Hardening and phase stability in rapidly solidified Al–Fe–Ce alloys

Rapidly solidified (RS) Al–Fe–Ce alloys were prepared by melt spinning. The phases present and the thermal stability, at temperatures up to 500 °C, were then followed by X-ray analysis, chemistry, hardness and thermal analysis techniques. The results obtained indicated that the alloys studied have enhanced mechanical properties compared to commercial aluminium alloys and castings of the same alloy compositions, and the RS alloy also exhibit good stability up to about 300 °C; a result of stable second phase particles. It is suggested that these results indicate that there are two mechanisms responsible for the hardening and stability of the RS alloys: solid solution strengthening at lower temperatures, and semicoherent particles formed from supersaturated solid solution at higher temperature. The maximum hardness, after 2 h ageing occurred at about 300 °C. At higher temperatures the dispersed phase became incoherent with a dramatic loss in hardness.     

Modification of montmorillonite by novel geminal benzimidazolium surfactant and its use for the preparation of polymer organoclay nanocomposites

A new benzimidazolium derivative, the benzimidazolium-N,N′-hexadecane-2-hydroxy-ethyl bromide (Bz) featuring two geminal hexadecyl hydrophobic buttress has been synthesized and used for the functionalization of sodium montmorillonite (MMT-Na) via cationic exchange process. The resulting benzimidazolium-modified MMT (MMT-Bz) exhibits a large d-spacing of 3 nm between silicate layers and shows a high thermal stability compared to the commonly used clay modified alkyl ammonium salts (cloisite 20A and cloisite 20B). MMT-Bz was incorporated in high density polyethylene (HDPE) matrix via melt mixing method to produce HDPE/MMT-Bz nanocomposites. The microstructure and the morphology of these nanocomposites were studied by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The dispersion state of the organoclay within HDPE was monitored by UV–Vis spectroscopy and melt rheology. A more homogeneous dispersion or a greater content of the MMT-Bz in the matrix produced stronger solid-like and non-terminal behavior in the nanocomposites. Tensile properties and thermal stability were evaluated and discussed on the basis of the amount of clay incorporated within the nanocomposites. The intercalated structure in the nanocomposites, resulting from both the better dispersion/distribution of clay nano-platelets and their strong interaction with the polymer chains, provides the driving force to significantly enhance the HDPE properties.     

The effect of aluminum additive on structure evolution of silicon oxycarbide derived from polysiloxane

Silicon oxycarbide (SiOC) and aluminum-containing silicon oxycarbide (SiAlOC) glasses were obtained through pyrolysis in argon atmosphere at 1000 °C of a polymethyl(phenyl)siloxane resin and aluminum tri-sec-butoxide-derived siloxane networks. These glasses were further annealed at 1200, 1300, and 1400 °C in vacuum atmosphere to investigate their high-temperature behavior. The two types of glasses were characterized by X-ray diffraction, ²⁹SiMASNMR, ²⁷AlMASNMR, and chemical element analysis. The aluminum incorporated into structure plays a major role on the thermal stability of SiOC by hindering carbothermal reductions. It can be found that introducing aluminum into structure should be an effective way to enhance the thermal stability of SiOC glasses.     

On the crystallization behavior of amorphous Fe-Cr-Mo-B-P-Si-C powder prepared by mechanical alloying

The crystallization behavior and thermal stability of Fe-Cr-Mo-B-P-Si-C amorphous alloy, prepared by mechanical alloying (MA), were investigated by using differential scanning calorimetry (DSC). One exothermic peak was observed on DSC traces, implying that the crystallization process undergoes only one stage. The crystallization kinetic parameters, including activation energy (E_a), Avrami exponent (n) were determined with non-isothermal analysis method based on the DSC data. The results suggest that the crystallization mechanism is governed dominantly by a three-dimensional diffusion-controlled growth. In addition a relatively high value of activation energy of crystallization (386.04 ± 10 kJ/mol) was found, indicating that this amorphous alloy has high thermal stability.     

Thermo-mechanical properties of poly(vinylidene fluoride) modified graphite/poly(methyl methacrylate) nano composites

Poly(methyl methacrylate) (PMMA) nano composites were synthesized by melt compounding technique. Different graphite loadings were investigated, including some treated with poly(vinylidene fluoride) (PVDF). A homogeneous dispersion of graphite throughout the PMMA matrix was observed under microscopic analysis. Thermo-gravimetric analysis showed the incorporation of graphite resulted in improvement of thermal stability of neat PMMA. Dynamic mechanical thermal analysis also showed a significant improvement in the storage modulus over the temperature range of 25–150 °C. Coating the graphite with a small amount of PVDF was found to further extend the improvement in the modulus of the PMMA nano composite at 1 wt.% graphite loading.     

Characterization of potassium salts of 12-tungstophosphoric acid

Potassium salts of 12-tungstophosphoric acid with varying amounts of cation, K_xH_3 − xPW₁₂O₄₀ (x = 1, 2, 3) have been prepared and their characteristics investigated by thermal analyses, FT-IR and micro-Raman spectroscopy and SEM-EDS analysis. It was found that the number of replaced protons by potassium ions in the 12-tungstophosphoric acid structure has influence on the presence of different protonic species, their dynamic equilibrium and on the conductivity of salts. The results reported in this study have been applied to improve the structural model of insoluble acidic salts. It is shown that an acidic potassium salt presents a mixture of neutral salt and unreacted acid. The nature of this mixture depends on the number of replaced protons-oxonium ions by cations. Preliminary measurements with synthesized compounds as solid electrolytes in fuel cells have been done, too.     

Structure and properties of mixtures based on long chain polyacrylate and 1-alcohol composites

A series of phase change materials (PCMs) based on long chain polyacrylate and 1-alcohol, i.e., poly (stearyl methacrylate) and 1-tetradecanol (PSMA/C14OH) were prepared through the solution-mixing method. Thermal energy storage capacity, thermal stability and morphology of PSMA/C14OH PCMs were characterized by Fourier transform infrared spectroscopy (FTIR), polarized optical microscopy (POM), field emission scanning electron microscopy (FE-SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC results demonstrated that the heat of fusion of PSMA/C14OH PCMs increased from 85.9 to 172.3 J g⁻¹ with the weight fraction of C14OH increasing from 20 to 80 wt%. And, the thermal stability also enhanced with PSMA weight. The spherulite (ca. 250 μm) in PSMA/C14OH composites containing 60 wt% C14OH proved the compatibility between PSMA and C14OH, indicating the cocrystallization behavior of alkyl side groups appeared. The cocrystallization behavior contributes the enhanced thermal stability of PSMA/C14OH PCMs, and it is suitable as the thermal energy storage materials in the future.     

Experimental determination of the thermal diffusivity of molten alkali halides by the forced Rayleigh scattering method. II. Molten NaBr,KBr, RbBr,and CsBr

This is a companion to an earlier paper (on molten alkali metal chlorides) which gives experimental results for the thermal diffusivity of four molten alkali metal bromides: NaBr, KBr, RbBr, and CsBr. The measurements were performed with a forced Rayleigh scattering instrument at temperatures up to 1326 K. The overall uncertainty in the measured thermal diffusivity is estimated to be ±3 to ±11%, depending on the measured salts. The results converted to thermal conductivity show one of the smallest values among other earlier experimental data obtained mainly by the steady-state methods. It is also found that the temperature dependence of the thermal conductivity is weakly negative.     

Reinforcement of polyurethane composites with an organically modified montmorillonite

A clay with reactive activity prepared by treatment of natural montmorillonite with Methylene-bis-ortho-chloroaniline (MOCA) was incorporated into polyurethane matrix and a series of PU/clay nanocomposites were obtained by in situ polymerization. The microstructure of the nanocomposites with different content of the clay was examined by atomic force microscopy (AFM). The thermal and mechanical properties of the nanocomposites with different organic clay content were characterized by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). It was found that the moduli and thermal stability of the nanocomposites were improved with augment of clay, especially, for the PU/9 wt% MO-MMT nanocomposite, compared to pure PU, the storage modulus and the loss modulus were increased by about 300% and 667% at −45 °C, respectively.     

Second-order nonlinear optical properties of cross-linked silica films prepared through sol-gel process

In this paper, second-order NLO chromophores containing two reactive sites have been synthesized and characterized by ¹H NMR, FTIR and elemental analysis. The transparent films have silica network of matrix and covalently bonded chromophore of NLO segment were then fabricated via sol-gel process. The SHG coefficients (d₃₃) of the poled films were calculated to be around 50 pm/V by in situ second harmonic generation (SHG) measurement. The thermal stability of the NLO coefficient was investigated by the depoling experiment and temporal decay test, showing that the cross-linked films had a good thermal stability up to 160 °C.     

The permeability and stability of microencapsulated epoxy resins

Microcapsules containing self-healing agents have been introduced into polymer to self-heal the microcracks and toughen the brittle matrix. Poly(urea–formaldehyde) (PUF) microcapsules containing epoxy resins are potential for the self-healing and toughening polymer. The resistance to medium surroundings of microcapsules is required. In the present study, PUF microcapsules containing epoxy resins were prepared by in situ polymerization. The effects of diameter, surface morphology and wall thickness on the permeability and stability of microcapsules in thermal and solvent surroundings were investigated. The morphology of microcapsule was investigated using optical microscope (OM), metalloscope (MS) and scanning electron microscope (SEM), respectively. The composition on the surface of microcapsule was analyzed by using energy dispersive analysis of X-ray (EDAX). The thermal properties of microcapsules were investigated using differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The thermal permeability of core increases and the stability of microcapsule decreases with the enhancement of heating temperature mainly due to the expansion of epoxy resins below 251 °C and the decomposition of PUF above 251 °C. At room temperature, the permeability constants of core materials of microcapsules in acetone solvent are small and they are 1.20 × 10⁻³ m s⁻¹, 1.39 × 10⁻³ m s⁻¹ and 1.60 × 10⁻³ m s⁻¹ corresponding to the microcapsules with diameters of 400 ± 50 μm, 230 ± 40 μm and 120 ± 30 μm. Increasing the surface smoothness, diameter and wall thickness can decrease the permeability and improve the stability of microcapsules in thermal and solvent surroundings.     

Effects of thermal annealing on Zr-N doped magnetron sputtered copper

A barrierless metallization scheme was proposed using Cu-based materials with enhanced thermal stability. Cu(Zr-N) films were deposited on Si substrates by magnetron sputtering and annealed at temperature up to 500 °C in vacuum. The beneficial effects of a minor insoluble Zr-N on the grain refinement and thermal stability improvement were confirmed. By doping insoluble Zr-N into pure copper, some of the additive atoms precipitate at the grain boundaries, which can block the path of diffusion between copper and silicon, and inhibit the interaction between copper and silicon. In addition, ZrO₂ or Zr(N,O) development near the Cu(Zr-N)/Si interface during annealing also contributes to the thermal stability of Cu(Zr-N)/Si samples. The results of X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and sheet resistance measurement show that Cu(Zr-N) seed layers has better thermal stability after 500 °C annealing and is suitable for advanced barrierless metallization.