Properties of Ca–(Y)–Si–Al–O–N–F Glasses: Independent and Additive Effects of Fluorine and Nitrogen

Thirty glasses of composition (in equivalent percent) 20‐xCa:xY:50Si:30Al:(100‐y‐z)O:yN:zF, with x = 0, 10; y = 0, 10, 20, and z = 0, 1, 3, 5, 7 were prepared by melting and casting. All glasses were X‐ray amorphous. Glass molar volumes (MV) decreased with nitrogen substitution for oxygen for all fluorine contents and, correspondingly, glass fractional compactness increased. Fluorine substitution of oxygen had virtually no effect on molar volume or fractional glass compactness for the three nitrogen contents tested. Young's modulus and microhardness were virtually unaffected by fluorine substitution for oxygen while nitrogen substitution for oxygen caused increases in these two properties. Glass‐transition temperature and dilatometric‐softening point values all decreased with increasing fluorine substitution levels, while increasing nitrogen substitution caused values for these thermal properties to increase. Correspondingly, the thermal expansion coefficient increased with fluorine and decreased with nitrogen substitution levels. Using property value differences between glasses containing fluorine and the corresponding glass containing 0 eq.% F enabled 24 data points to be used to determine the effect of fluorine on T_g,dil and T_DS. The trends were linear with a gradient for both properties of the order of ?22°C (eq.% F)^?1. For the nitrogen effect, 20 data points were analyzed for trend effects. As expected from earlier work, all trends had good linearity. Gradients were for T_g,dil and T_DS +2.5°C (eq.% N)^?1, which are fairly similar to previous results in oxynitride systems. All of the data collected and its analysis clearly shows that the substitution effects of fluorine for oxygen and nitrogen for oxygen are independent and additive with the fluorine substitution. The property trends of the glasses are discussed in terms of their implications for glass structure.     

Effect of crosslink density on transport of industrial solvents through polyether based polyurethanes

Polyurethanes based on PPG 2000 with variable concentrations of TDI and TMP were prepared and used for sorption studies, employing homologous series of hydrocarbons such as benzene, toluene and xylene. The sorption was observed to be non-Fickian in nature. The solubility parameter of the polyurethane series was observed to be 9·7(calcm^-3)^1/2. The polymer solvent interaction parameter χ was found to be lowest in benzene, suggesting higher interaction with it. The sorption and diffusion coefficients were observed to increase with a decrease in the degree of crosslinking. Molecular weights between crosslinks were calculated using the Flory–Rehner equation and compared with those obtained theoretically. © 1998 Society of Chemical Industry     

Effects of crosslink density on mechanical properties of high glass transition temperature polycyanurate networks

Polycyanurate networks of different architecture were synthesized using different curing cycles. Networks with a variable extent of reaction were obtained; the small variation of the cyanate conversion (0.8 to 1) corresponds to a large variation of glass transition temperature (150–290°C) and crosslink density. The mechanical behavior at small and large deformations and the fracture toughness were examined at room temperature and related to the network structural parameters. To explain the puzzling variation of the yield stress and yield strain with the cyanate conversion, recovery experiments were conducted to discriminate anelastic deformation from plastic deformation. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2471–2479, 1997     

Mixed alkaline‐earth effect on the mechanical and rheological properties of Ca–Mg silicate glasses

In this article, we investigate the mixed alkaline‐earth effect in a silicate glass series with varying the molar ratio of [MgO]/([CaO]+[MgO]). This effect manifests itself as a minimum in Vickers microhardness (H_V), coefficient of thermal expansion (CTE), and isokom temperatures at 10¹²(T_g) and 10² Pa·s, and as a maximum in liquid fragility. To probe the structural origin of the mixed alkaline‐earth effect in CTE and H_v, we conducted the Raman measurements. In contrast to the aluminosilicate glasses, the present glass series exhibit a negative deviation of shift of peak position at ~1100 cm^?1 from a linear additivity, indicating the role of the aluminum speciation in affecting the vibration modes. By fitting the Vogel–Fulcher–Tamann equation to the high‐temperature viscosity data, we found a near‐linear increase of the fractional free volume with the gradual substitution of Ca by Mg, confirming the dynamic structural mismatch model describing the mixed modifier effect. This work gives insight into the mixed modifier effect in glassy systems.     

Influence of internal strain on change of crosslink density of natural rubber vulcanizates by thermal ageing

Change of crosslink density of natural rubber (NR) vulcanizates by thermal ageing at 60 °C has been studied under swollen conditions in solvents to investigate the influence of internal strain applied to the vulcanizate on the crosslink density change. The internal strain was controlled by swelling with various solvents such as n‐hexane, toluene, tetrahydrofuran (THF), methanol and water. The order of degree of the swelling is toluene ≈ THF > n‐hexane > methanol > water. The influence of curing system has been investigated with the vulcanizates cured by the conventional and EV cure systems. After thermal ageing, the apparent crosslink densities of the swollen vulcanizates in n‐hexane, toluene and THF decrease irrespective of the cure systems, while that of the swollen vulcanizate in water increases. For the swollen vulcanizates in methanol, the apparent crosslink density of the vulcanizate with the conventional cure system after thermal ageing increases while that of the vulcanizate with the EV cure system decreases. The decrement of the apparent crosslink density of the vulcanizate after thermal ageing becomes larger and larger upon increasing the internal strain. © 2001 Society of Chemical Industry     

交联密度对HNBR/聚甲基丙烯酸正丁酯IPN阻尼性能的影响

用序列法制备氢化丁腈橡胶(HNBR)/聚甲基丙烯酸正丁酯(PnBMA)互穿聚合物网络(IPN)材料,通过改变两网络的硫化剂用量得到不同交联密度的HNBR/PnBMA IPN。采用动态粘弹谱仪测试IPN的阻尼性能,结果表明HNBR/PnBMA IPN材料的阻尼特性与交联密度密切相关。随着第一网络交联密度的增加,阻尼曲线逐渐由双峰转变为单峰,阻尼峰宽降低。第二网络交联密度的增加使阻尼曲线整体下降,双峰形态不变。通过改变两网络的交联密度可调整阻尼峰的位置、宽度及阻尼峰值。     

Relationships of tensile strength with crosslink density for the high-carbon black-filled EPDM compounds with various softeners

Equilibrium swelling and rheological tests were adopted to systematically investigate the effects of softener type and dosage on the crosslink densities. The results turned out that the chemical crosslink density could be distinguished from the physical crosslink density by comparing the results of equilibrium swelling and rheological tests. The liquid butadiene (LB) as a softener leads to the greatest reduction in crosslink density, followed by polyethylene wax (PW) and paraffinic oil (PO). The tensile strength decreases with increasing PO content while shows peak values with increase of LB and PW contents. The dependencies of chemical crosslink density on the aging time under 150°C are quite different for the three softeners, which can be expected from the double crosslinking networks consisting of small softener and large main crosslinking networks. Further investigation has been performed to correlate the tensile strength with chemical crosslink density of ethylene propylene diene monomer elastomer vulcanizates. Three different linear relationships can be obtained for the softeners independent of the aging time. It can now be expected from this study that the role of some new softeners in rubber compounds is not only confined to plasticization but also forms crosslinking networks in the peroxide-cured rubbers.     

Effect of crosslink density on the refractive index of a polysiloxane network based on 2,4,6,8‐tetramethyl‐2,4,6, 8‐tetravinylcyclotetrasiloxane

Crosslink density is one of the factors which dictate the optical and mechanical properties of silicone‐based polymers. A series of hydrosilyl‐terminated polydimethylsiloxane cured with 2,4,6,8‐tetramethyl‐2,4,6,8‐tetravinyl cyclotetrasiloxane was prepared to form a crosslink network. They were clear gel forms whose elastomeric features were dependent on the end‐capper concentration, 1,1,3,3‐tetramethyldisiloxane, employed during their synthesis. The siloxane‐based polymers displayed excellent thermal stability whose decomposition temperature was around 480 °C. The refractive index was in the range 1.410–1.425. It was found that the refractive index is dependent on the crosslink density of the network. The effect of fractional free volume and ‘densification’ of the network was elucidated and found to contribute to this dependence. The Lorentz–Lorenz model was used to integrate these observations. © 2012 Society of Chemical Industry     

Influence of rubber composition on change of crosslink density of rubber vulcanizates with EV cure system by thermal aging

Variation of the crosslink density of a rubber vulcanizate depending on the rubber composition after the thermal aging was studied with single rubber, biblend, and triblend vulcanizates of natural rubber (NR), butadiene rubber (BR), and styrene‐butadiene rubber (SBR). The efficient vulcanization (EV) system was employed to minimize the influence of free sulfur in the vulcanizate on the change of the crosslink density. Thermal aging was performed at 40, 60, and 80°C for 20 days with 5‐day intervals. The crosslink densities of the vulcanizates after the thermal aging increase. For the single rubber vulcanizates, variation of the crosslink density by the thermal aging has the order: SBR > BR > NR. For the biblend vulcanizates, variations of the crosslink densities of the NR/SBR and SBR/BR blends are larger than that of NR/BR blend. Variation of the crosslink density of the vulcanizate increases by increasing the SBR content in the vulcanizate. Variation of the crosslink density of the rubber vulcanizate depending on the rubber composition was explained by miscibility of the blends, combination reaction of the pendent groups, and mobility of the pendent group. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1378–1384, 2000     

Mechanical properties and crosslink density of rare earth‐modified high‐abrasion furnace‐filled powdered natural rubber

High‐abrasion furnace‐filled powdered natural rubber [P(NR/HAF)] has more advantages than traditional HAF‐filled bale NR (NR/HAF) because of its better environmental performance and easier processing quality, but its lower mechanical properties are disadvantageous. To improve the mechanical properties, rare earth‐modified HAF‐filled powdered NR [P(NR/HAF‐Ln)] (Ln = Sm,La,Pr) was prepared by means of coacervation–coprecipitation, using rare earth‐modified HAF as separant and filler. The effect on mechanical properties of P(NR/HAF‐Ln) vulcanizate exerted by the emulsifier/HAF ratio, powdering temperature, Ln/HAF ratio and type of Ln, and HAF content were studied. The results indicated that when optimum formulation, the mechanical properties of P(NR/HAF‐Ln) vulcanizate were better than P(NR/HAF) vulcanizate. In addition, the relationship of the apparent crosslink density and HAF content of P(NR/HAF‐Ln), P(NR/HAF), NR/HAF vulcanizates was also investigated, along with their SEM microphotographs of tensile fracture surface, which indicated that the excellent mechanical properties of P(NR/HAF‐Ln) vulcanizate was attributed to correct amount of Ln that could increase crosslink density and reinforce the interface structure of NR matrix/HAF‐Ln particle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1755–1762, 2006     

A density functional theory study on the deformation behaviors of fe-si-B metallic glasses

Density functional theory has been employed to investigate the deformation behaviors of glassy Fe-Si-B model systems prepared by ab initio molecular dynamics. The atomistic deformation defects which are closely related to the local dilation volumes or excess volumes and unstable bonding have been systematically analyzed. It has been found that the icosahedral structures are relatively stable under shear deformation until fracture occurs. Plastic flow is indicated by interruption of percolating icosahedral structures, caused by unstable Fe-Si bonding of p-s hybridization in nature.     

Effects of crystal structures on luminescent properties of Eu doped Ca–Al–O systems

To investigate the correlations between the structural transformations of calcium aluminates and luminescent properties, Eu doped Ca–Al–O system phosphors were synthesized by solid-state reaction process in H₂ atmosphere with CaCO₃, Al₂O₃, Eu₂O₃, and a flux, H₃BO₃ as starting materials. Various phases such as CaAl₂O₄, CaAl₄O₇, Ca₃Al₂O₆, and Ca₁₂Al₁₄O₃₃ were achieved depending on firing temperature, flux amounts, and the mixing ratio of CaO to Al₂O₃. Among various phases, only CaAl₂O₄ contributed to a strong blue emission at 440 nm with an excitation wavelength of 330 nm.     

热固性聚合物的交联密度测试方法研究进展

综述了热固性聚合物交联密度测定方法的研究进展,重点介绍了平衡溶胀法、应力-应变法、动态机械热分析法、流变法、核磁共振法5种常用方法。     

Influence of the COOH and COONa groups and crosslink density of poly(acrylic acid)/montmorillonite superabsorbent composite on water absorbency

A novel poly(acrylic acid)/montmorillonite superabsorbent composite with a water absorbency of 1100 times its own weight was synthesized by the graft copolymerization of acrylic acid with a cross‐linking agent in the presence of montmorillonite ultrafine powder. The influence of the amount of crosslinker and montmorillonite on water absorbency has been investigated. It was found that a crosslinker concentration of 0.03 wt% and 30 wt% montmorillonite gave the best results. The collaborative absorbent effect of sodium carboxylate and carboxylic acid groups was superior to that of sodium carboxylate or carboxylic acid groups alone, and the composite with a ratio of about 2/3 for sodium carboxylate to carboxyl acid groups possessed the highest water absorbence. © 2001 Society of Chemical Industry     

Dispersion and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure

The dispersion behavior and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure were investigated. The Si–C powders synthesized by a mechanical alloying (MA) process had a near‐spherical shape with an average particle size of 170 nm. A solid loading of 62 vol% was achieved using polyethyleneimine (PEI) as a dispersant. The optimum dispersant amount was 1 wt% based on zeta potential, sedimentation, and viscosity analysis data. The high zeta potential value (73 mV) compared with that of the commercially available SiC (65 mV) was caused by modified surface properties and consequent promotion of the cationic dispersant adsorption. A Si–Al–C slurry containing 6.5 wt% of sintering additives with a solid loading of 60 vol% was also prepared. The relative density of the dried Si–Al–C slurry was 63.3% without additional compaction, which could be densified at 1650°C at a pressure of 20 MPa using a spark plasma sintering furnace.     

Compositional effects on the properties of high nitrogen content alkaline-earth silicon oxynitride glasses, AE = Mg, Ca, Sr, Ba

A series of alkaline-earth element containing high nitrogen content oxynitride glasses (AESiON), with AE = Mg, Ca, Sr, Ba, were prepared in order to investigate the compositional effects on the physical properties of the alkaline-earth element. The physical properties were found to change linearly with the concentration of AE elements. The density of the glasses increases substantially with an increase in the AE atomic mass and slightly with an increase in nitrogen ratio. Ba containing glasses shows the value of density 4.16 g/cm³. Glass transition temperatures are found to be higher for Mg glasses, ca. 1020 °C, in comparison with Ba glasses, ca. 895 °C. The hardness of Mg containing glasses shows high values, up to 12.2 GPa and decreases for Ca, Sr and Ba containing glasses. Ba, containing glasses shows high values of refractive index in comparison with the Sr, Ca and Mg containing glasses.     

Polymerization of butadiene with Co(acac)3–(i-Bu)3Al–H2O catalyst

The polymerization of butadiene in toluene using Co(acac)₃–(i-Bu)₃Al–H₂O catalyst system was studied. Presented are the effects of the addition order, aging time, and composition of catalysts on rates, polymer microstructure, and molecular weights. The polymerization was found to be initiated by the Co(acac)₃-hydrolized aluminum alkyl complex. The chain propagation proceeds according to a first-order reaction with respect to monomer and active species and is a strong function of Al/H₂O with an optimum ratio of 1.0, but independent of Al/Co. The nature of polymerization seems to change as Al/H₂O increases from less than 1 to greater than 1. Transfer reaction is significant. From the kinetic data it was found that the termination reaction is most likely to be by combination.     

Struktur und spektrale Eigenschaften des Pentamethinmerocyanins 5‐(Dimethylamino)pentadienal in Lösung – Eine kombinierte DFT–SCI–SCRF–Studie

In order to estimate the solvent effect on molecular structure and on NMR and UV spectral data of 5‐(dimethylamino)penta‐2,4‐dien‐al(1) ( 1 , R = Me) the compound was calculated by first‐principles methods. Density functional theory was employed for structural optimization with solvent effects simulated by the recently refined COSMO continuum model. According to the calculations the molecular structure of 1 (R = Me) is noticeably affected by polar solvents resulting in a reduced bond length alternation. The relaxation of the molecular geometry in polar solvents is clearly reflected in the calculated ¹³C NMR chemical shifts calculated by GIAO‐DFT and in the absorption wave numbers of the intense lowest‐energy electronic transition calculated by SCI. Although the optimum geometry of the solute molecule in the solvents was calculated the magnitude of the solvatochromic shift is underestimated. The calculated solvatochromic effect in water is enhanced if the specific solvent‐solute interactions are considered by addition of one water molecule to 1 (R = Me) in the solvent cavity.     

La–Si–O–N glasses: Part I. Extension of the glass forming region

The nitrogen-rich part of the glass forming region in the La–Si–O–N system has been the subject of a comprehensive study. Glasses were prepared by heating powder mixtures of La metal, Si₃N₄ and SiO₂ in a nitrogen atmosphere at 1650–1800 °C. By this new synthesis route, glasses containing up to 68 e/o of N and 62 e/o of La were prepared, showing that the glass forming region is significantly larger than previously reported. The glasses were characterized by elemental analysis, differential thermal analysis, X-ray powder diffraction, and scanning electron microscopy. They were found to be X-ray amorphous and homogenous, with the majority of them containing small amounts of crystalline La silicides and elemental Si. Glass transition temperatures (T_g) were found to vary between 900 and 1100 °C and crystallization to occur typically 120 °C above T_g. The forming of the glasses was investigated by characterizing samples taken out at various steps of the heating cycle. The results indicate that the glass formation is strongly dependent on reaction kinetics. A strong exothermal reaction occurs at temperatures 900–1100 °C, leading to the formation of assemblies of amorphous and crystalline (oxy)nitride phases that melt upon further heating at 1650–1800 °C.     

Effect of fluorine and nitrogen content on the properties of Ca-Mg-Si-Al-O-(N)-(F) glasses

X-ray amorphous glasses of composition (in equivalent percent) 15Ca:15Mg: 55Si:15Al:(100-x-y)O:xN:yF with x=0, 10, 15 and y=0, 1, 3, 5, were prepared by melting and casting. The effects of oxygen substitution by fluorine and/or nitrogen on the physical, mechanical, thermal and optical properties of the glasses have been investigated. Molar volume, fractional glass compactness, microhardness, Young's Modulus, glass-transition temperature, dilatometric-softening point and refractive index increased linearly with nitrogen substitution for oxygen, whereas molar volume and thermal expansion coefficient decreased linearly with nitrogen increase. In contrast, all properties except glass-transition temperature and dilatometric-softening point, are virtually unaffected by fluorine substitution for oxygen. Significant and linear, decreases in thermal properties occurred with increasing fluorine substitution level. All the data collected and its analysis clearly showed that the substitution effects of fluorine for oxygen on the studied properties of the glasses of the system with general formula Ca-Mg-Si-Al-O-(N)-(F) are totally independent and additive with respect to the substitution effects of nitrogen for oxygen on glass properties.