Carbothermal synthesis of approximately spherical Si3N4 particles with homogeneous size distribution

Si₃N₄ particles with approximately spherical appearance, good dispersity, and homogeneous particle size distribution were successfully fabricated by a modified carbothermal method with the use of high-pressure N₂ and composite additives CaF₂ and Y₂O₃. The effects of parameters such as N₂ gas pressure, additive, and temperature on the carbothermal reduction-nitridation (CRN) process were examined in detail. Based on extensive investigations, the mechanism of formation of Si₃N₄ particles was revealed. It was found that the process of nucleation and growth of Si₃N₄via the vapour-liquid-solid (V-L-S) mechanism under sufficient liquid encapsulation was essential for synthesising uniform particles with approximately spherical morphology and good dispersity. Because of the favourable morphology, the as-prepared Si₃N₄ particles exhibited great potential as thermally conductive fillers for next generation thermal interface materials.     

Influence of vent air valve opening on combustion characteristics of a down-fired pulverized-coal 300 MWe utility boiler

Industrial experiments have been performed on a down-fired pulverized-coal 300 MWe utility boiler with vent air valve opening of 100% and 40%. The gas temperature distribution along the primary air and coal mixture flow, gas temperature distribution in the furnace, and gas components such as O₂, CO, CO₂ and NO_x in the near-wall region were measured for the first time. The influence of vent air valve opening on coal combustion in the furnace was determined. The results indicate that ignition of the primary air and pulverized-coal mixture is delayed. The position of the gas temperature peak is above the arches. Emission of NO_x is up to 2101 mg/m³ (at 6% O₂ dry) with vent valve opening of 40%.     

Effect of processing conditions on flash generation

Reduction of flash during injection molding is of great concern for manufacturers of electrical parts. In a previous report, we proposed a theoretical model for flash generation. The present study investigates the effect of processing conditions on flash generation and then attempts to analyze the flash data in terms of the flash model. Specifically, we carry out flow analyses to predict the temperature and pressure of materials when the flash generates. With the thus‐computed parameters, and material properties such as melt viscosity and crystallization temperature, a flash parameter defined in the model is calculated. In the end, it is shown that the flash parameter is correlated with the length of flash generated under various processing conditions. POLYM. ENG. SCI. 45:238–247, 2005. © 2005 Society of Plastics Engineers     

Influence of filler type and content on thermal conductivity and mechanical properties of thermoplastic compounds

Combining thermal conductivity with electrical isolation is a very interesting topic for electronic applications in order to transfer the generated heat. Typical approaches combine thermally conductive fillers with a thermoplastic matrix. The aim of this work was to investigate the influence of different fillers and matrices on the thermal conductivity of the polymer matrix composites. In this study, various inorganic fillers, including aluminum oxide (Al₂O₃), zinc oxide (ZnO), and boron nitride (BN) with different shapes and sizes, were used in matrix polymers, such as polyamide 6 (PA6), polypropylene (PP), polycarbonate (PC), thermoplastic polyurethane (TPU), and polysulfone (PSU), to produce thermally conductive polymer matrix composites by compounding and injection molding. Using simple mathematical models (e.g., Agari model, Lewis–Nielson model), a first attempt was made to predict thermal conductivity from constituent properties. The materials were characterized by tensile testing, density measurement, and thermal conductivity measurement. Contact angle measurements and the calculated surface energy can be used to evaluate the wetting behavior, which correlates directly with the elastic modulus. Based on the aforementioned evaluations, we found that besides the volume fraction, the particle shape in combination with the intrinsic thermal conductivity of the filler has the greatest influence on the thermal conductivity of the composite.     

Estimation of thermal conductivity of polymer multiphase composites

The thermal conductivities of a medium density polyethylene composites filled separately with two different thermal conductive fillers including graphite, cuprum, and aluminum oxide (Al₂O₃), an epoxy composites filled respectively with two different thermal conductive fillers including silicon nitride, aluminum hydroxide, Al₂O₃ and aluminum nitride, and a polypropylene composites filled with aluminum hydroxide and magnesium hydroxide were estimated using a thermal conductivity equation of polymer multiphase composites. This equation was based on a new heat transfer model, and the parameters were easily determined. It was found that the estimated thermal conductivities of the three composites systems were approximately close to the experimental measured data reported in literature. In addition, the predictions were roughly close to the estimations from the Agari model. POLYM. ENG. SCI., 57:965–972, 2017. © 2016 Society of Plastics Engineers     

Application of lime kiln dust as a filler in the natural rubber industry

Lime kiln dust (LKD) obtained from kraft chemical recovery systems by conversion of calcium carbonate (CaCO₃) back into calcium oxide (CaO) for reuse in the causticizing process, is mainly composed of CaCO₃. A two‐stage conventional mixing procedure was used to incorporate LKD into natural rubber (NR). For comparison purposes, four commercial fillers, stearic acid coated CaCO₃, ground CaCO₃, silica, and carbon black, were also used. The effect of these fillers on the curing characteristics and mechanical properties of NR materials at various loadings ranging from 0 to 60 phr were studied. The results indicate that the use of LKD filler resulted in a lower Mooney viscosity and shorter curing time in the NR materials. The incorporation of LKD into NR improved the Young's modulus and hardness but decreased the tensile strength and tear strength. However, LKD was better in processability than the commercial fillers. Scanning electron micrographs revealed that the morphology of the rubbers filled with reinforcing fillers, such as silica and carbon black, was finer and more homogeneous compared to the those of the rubbers filled with LKD and commercial CaCO₃. The dispersion of LKD and commercial CaCO₃ fillers in the rubber matrix was discontinuous, which in turn, generated a weak structure compared with the reinforcing fillers. According to these observations, LKD could be used as a cheaper filler for NR materials where improved mechanical properties are not critical. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of size-classified and slightly soluble mineral additives on hydration of tricalcium silicate

Early-age hydration of cement is enhanced by slightly soluble mineral additives (ie, fillers, such as quartz and limestone). However, few studies have attempted to systematically compare the effects of different fillers on cementitious hydration rates, and none have quantified such effects using fillers with comparable, size-classified particle size distributions (PSDs). This study examines the influence of size-classified fillers [ie, limestone (CaCO₃), quartz (SiO₂), corundum (Al₂O₃), and rutile (TiO₂)] on early-age hydration kinetics of tricalcium silicate (C₃S) using a combination of experimental methods, while also employing a modified phase boundary and nucleation and growth model. In prior studies, wherein fillers with broad PSDs were used, it has been reported that between quartz and limestone, the latter is a superior filler due to its ability to partake in anion-exchange reactions with C-S-H. Contrary to prior investigations, this study shows that when size-classified and area matched fillers are used—which, essentially, eliminate degrees of freedom associated with surface area and agglomeration of filler particulates—the filler effect of quartz is broadly similar to that of limestone as well as rutile. Results also show that unlike quartz, limestone, and rutile—which enhance C₃S hydration kinetics—corundum suppresses hydration of C₃S during the first several hours after mixing. Such deceleration in C₃S hydration kinetics is attributed to the adsorption of aluminate anions—released from corundum's dissolution—onto anhydrous particulates’ surfaces, which impedes both the dissolution of C₃S and heterogeneous nucleation of C-S-H.     

Similarity and grouping of perlite and zeolite abrasive fillers: A replacement test

Inverse gas chromatography was used to estimate surface activity expressed by the dispersive component of the surface free energy, γ, as well as parameters K_A and K_D describing surface ability to act as electron acceptor and donor, respectively. These parameters characterize the ability of the surface to specific interactions. The method was also applied to describe the magnitude of filler‐phenolic resin interaction by Flory‐Huggins parameter, χ′₂₃. Granulation, surface area and porosity were also determined. The minimum number of parameters required to complete characterization of filler properties has been selected by principal component analysis. The usefulness of the selection for the abrasive industry has been proven. Moreover, the similarities and deviations from “an average” filler was determined by chemometric methods. Principal component analysis (PCA) and a novel procedure based on sum of ranking differences (SRD) were successfully applied for selection of the best fillers, and of advantageous parameters for characterization of the fillers. Similar and diverse fillers have been chosen based on clustering pattern by PCA and SRD. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of different types of filler and filler loadings on the properties of carboxylated acrylonitrile–butadiene rubber latex films

The effects of different types of fillers and filler loadings on the properties of carboxylated nitrile rubber (XNBR) latex were identified. Silica, mica, carbon black (CB; N330), and calcium carbonate (CaCO₃) were used as fillers with filler loadings of 10, 15, and 20 parts per hundred rubber. Furnace ashing and Fourier transform infrared analysis proved that interaction existed between the fillers and XNBR latex films. The morphology of the filled XNBR films was significantly different for different types of fillers. Mica and CaCO₃ fillers showed uneven distribution within the XNBR film, whereas other fillers, such as silica and CB, showed homogeneous distribution within the films. In the observation, silica and mica fillers also illustrated some degree of agglomeration. The mechanical properties (e.g., tensile and tear strengths) showed different trends with different types of fillers used. For silica and mica fillers, the mechanical properties increased with filler loadings up to a certain loading, and decreased with higher filler loadings. For CB filler, the mechanical properties increased gradually with increasing filler loadings. CaCO₃ fillers did not increase the mechanical properties. The crosslinking density of the XNBR films increased when they were incorporated with fillers because of the presence of elastomer–filler and filler–filler interactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nonisothermal melt‐crystallization kinetics of syndiotactic polypropylene compounded with various nucleating agents

Nonisothermal melt‐crystallization behavior of syndiotactic polypropylene (sPP) compounded with 5% by weight (wt %) of some inorganic fillers [i.e., kaolin, talcum, marl, titanium dioxide (TiO₂), and silicon dioxide (SiO₂)] and 1 wt % of some organic fillers, which are some sorbital derivatives (i.e., DBS, MDBS, and DMDBS) was investigated and reported for the first time. It was found that the ability of these fillers to nucleate sPP decreased in the following sequence: DBS > talcum > MDBS > SiO₂ ～ kaolin ～ DMDBS > marl > TiO₂, with DBS being able to shift the crystallization exotherm by ～ 18°C on average, while TiO₂ was able to shift the crystallization exotherm by only ～ 6°C on average, from that of neat sPP. The Avrami analysis revealed that the Avrami exponent for sPP compounds varied between 2.9 and 4.3, with the values for neat sPP varying between 3.1 and 6.8. Lastly, the Ziabicki's crystallizability of sPP compounds was greater than that of neat sPP, suggesting an increase in the crystallization ability of sPP as a result of the presence of these fillers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 245–253, 2005     

Polymer composites with enhanced thermal conductivity via oriented boron nitride and alumina hybrid fillers assisted by 3-D printing

Herein, oriented boron nitride (BN)/alumina (Al₂O₃)/polydimethylsiloxane (PDMS) composites were obtained by filler orientation due to the shear-inducing effect via 3-D printing. The oriented BN platelets acted as a rapid highway for heat transfer in the matrix and resulted in a significant increase in the thermal conductivity along the orientation direction. Extra addition of spherical Al₂O₃ enhanced the fillers networks and resulted in the dramatic growth of slurry viscosity. This, together with filler orientation induced the synergism and provided large increases in the thermal conductivity. A high orientation degree of 90.65% and in-plane thermal conductivity of 3.64 W/(m∙K) were realized in the composites with oriented 35 wt% BN and 30 wt% Al₂O₃ hybrid fillers. We attributed the influence of filler orientation and hybrid fillers on the thermal conductivity to the decrease of thermal interface resistance of composites and proposed possible theoretical models for the thermal conductivity enhancement mechanisms.     

Plasma assisted novel production process of glass-ceramic spheres in the quaternary system CaO–SiO2–Al2O3–MgO

In this work, a novel transformation process of industrial byproducts into spherical glass-ceramic materials in the quaternary system CaO–SiO₂–Al₂O₃–MgO is presented. Byproducts used as precursor are blast furnace slags (BFS) generated by steelmaking industry located in northeastern Mexico. Several parameters for plasma projection process, such as Ar:He feeding flow and electric current were studied. Industrial Ar:He plasma projection equipment was used for vitrification and microstructural/morphological transformation of BFS. Precursor particles as well as produced glass-ceramic spheres were characterized by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XDS). In addition, density measurements from the generated powders were obtained using a Helium pycnometer.These new materials have a highly amorphous structure, and their final properties, such as porosity, density and size can be controlled by process parameters and therefore they could be modified to obtain special features for specific applications.     

The correlation between packing efficiency and tensile properties for polymer composites in SMC formulation

For polymer composites that find application as sheet-molding compounds (SMCs), the fiber aspect ratio l/d and the size ratio R (the ratio of the diameter of the spherical filler and the diameter of the fiber) are important parameters. A study of various composite formulations of different combinations of l/d and R has been made to examine the correlation between the packing efficiency of these fibers and fillers in air, and the properties of resulting composites. Samples containing a total of 32 wt% fibers and spherical fillers (in 1:3 proportion) were tested. The tensile modulus was seen to represent behavior similar to packing efficiency. Sources of experimental errors are discussed.     

Colored rubber vulcanizates with some magnetic properties

A new composite based on natural rubber vulcanizates loaded with the newly prepared iron oxide–aluminum oxide (Fe₂O₃·Al₂O₃) fillers were prepared and their physical and magnetic studies were investigated. The prepared fillers were evaluated as reinforcing fillers with some magnetic properties; these properties were dependent on the ratio of iron oxide to aluminum oxide in each prepared ratio of these fillers. Rheological properties of rubber mixes containing (1Fe₂O₃:3Al₂O₃) and (1Fe₂O₃:1Al₂O₃) fillers exhibited better properties than mixes containing (3Fe₂O₃:1Al₂O₃) and (α‐Fe₂O₃), which showed almost the same behavior. Physical properties such as tensile strength, stress at 100 and 200% strain, Young's modulus, and hardness were increased by increasing the volume fraction of the investigated fillers concentration in the mixed vulcanizates. Measured rheological and physical results were inversely related to the magnetic properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:494–505, 2006     

Carbon–Al2O3–Ag composite molecular sieve membranes for gas separation

Phenolic resins loaded with two different inorganic fillers (boehmite (γ-AlO(OH)) and silver (Ag)) were used to prepare composite carbon membranes. Polymer solutions containing γ-AlO(OH) and AgNO₃ were prepared and the effect of Ag on the transport properties of the composite membrane was evaluated. The polymer solutions were coated on α-Al₂O₃ tubes and carbonized in a single dipping-drying-pyrolysis step. After pyrolysis at 550 °C, γ-AlO(OH) yielded γ-Al₂O₃, and Ag agglomerated forming spherical nanoparticles of 30 nm in diameter. Ag loading enhanced the carbon membrane performance for several gas pairs of interest, especially for C₃H₆/C₃H₈ separation, where the C₃H₆/C₃H₈ permselectivity increased from a maximum of 15 to 38.     

Spheroidization of borosilicate glass powder by RF induction coupled plasma

The International Simple Glass (ISG) spherical particles were prepared by Ar–H₂ radio-frequency (RF) plasma, the effect of experimental parameters on the volatilization and size distribution of spherical particles was studied. The results show that the spherical powders can be obtained by RF plasma. The spheroidized powders (112 μm) have a smaller diameter than starting particles (124 μm). The high spheroidization (98%) was achieved under low flow rate of carry gas and low feed rate. In addition, the volatilization of B₂O₃ and Na₂O are 23.48% and 56.36%, respectively. The higher feed rate and flow rate of carry gas, the lower volatilization of B₂O₃ and Na₂O and well-spheroidization rate. Meanwhile, the particle surface is not completely smooth at low flow rate of carry gas. The distribution of elements was studied by Electro-probe Microanalyzer (EPMA), which shows the distribution of element is nearly homogeneous that provides a possibility for subsequent research.     

Theoretical and experimental studies on the gas transport properties of mixed matrix membranes based on polyvinylidene fluoride

The effects of the impregnation of three types of inorganic fillers into polyvinylidene fluoride (PVDF) polymer membranes on the gas permeability and selectivity of these membranes were studied theoretically and experimentally. Permeabilities of He, CO₂, O₂, and N₂ through three types of mixed matrix membranes (MMMs) based on PVDF, that is, PVDF/SiO₂, PVDF/MCM‐41, and PVDF/4A MMMs, were experimentally measured and theoretically predicted using Maxwell, Higuchi, Bruggeman, and Bottcher‐Landauer models. Theoretical permeabilities of the PVDF/SiO₂ MMMs using the above four models predicted the results in the following order: Maxwell model>Bruggeman model>Bottcher model>Higuchi model. However, this sequence was reversed for PVDF/MCM‐41 MMMs. The nonporous SiO₂, mesoporous MCM‐41 and zeolite 4A inorganic fillers had effects on the permeabilities of the challenge gases for the PVDF/SiO₂, PVDF/MCM‐41, and PVDF/4A MMMs but had no effects on the selectivities of the MMMs. The experimental permeabilities of the MMMs showed that there were no significant differences among the three types of MMMs despite that the inorganic fillers, that is, SiO₂, MCM‐41, and zeolite 4A, had distinct dissimilar properties such as pore structures and particle sizes. Density measurements indicated that some voids were present in the polymer/particle interfaces. Based on the density measurement results, the void volume fractions of the resulting MMMs were calculated. An equation is derived to determine the void thickness of the MMM in terms of its physical properties and hence this proposed equation can substitute the difficult task of measuring such void thickness through any microscopy techniques. The Maxwell, Higuchi, Bruggeman, and Bottcher‐Landauer models could not predict the actual gas permeabilities of the PVDF MMMs. By taking the effects of crystallinity and immobilization factor on gas permeability into consideration, the extended modified Maxwell model showed good agreement with the experimental gas permeabilities of the resulting MMMs, indicating that the model did capture the essence of the gas transport behaviors through the MMMs. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4715–4726, 2013     

Polymer Nanocomposite Membranes of Sulfonated Poly(Styrene‐Isobutylene‐Styrene) With Sulfonated Graphene Oxide for Fuel Cell and Protective Clothing Applications

Graphene oxide (GO) and its sulfonated analog (sGO) have been incorporated into sulfonated poly(styrene‐isobutylene‐styrene) (SO₃H SIBS) in order to enhance its water retention and proton conductivity, while aiming to block permeant passage through the material. The polymer nanocomposite membranes (PNMs) were tested for two applications: direct methanol fuel cell and chemical and biological protective clothing. The transport properties of the membranes were determined as a function of SIBS sulfonation level (i.e., 37, 61, and 88 mol%), filler type (i.e., GO and sGO) and filler loading (i.e., 1, 3, 5, and 10 wt%). Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) confirmed the functionalization and incorporation of the fillers into SO₃H SIBS. No significant changes were observed in the thermal stability or FTIR spectra of the PNMs after addition of the fillers. Dissimilar behaviors were observed for the ion exchange capacity, water absorption capabilities and transport properties of the membranes after incorporation of the fillers. Atomic force microscopy (AFM) phase images and Fenton's test results indicate that the oxidative stability of the PNMs is associated to the interconnectivity between the hydrophilic domains of the fillers and SO₃H SIBS. The PNMs presented low permeability and high proton conductivity and thus, functioned adequately for both applications. POLYM. ENG. SCI., 59:E455–E467, 2019. © 2018 Society of Plastics Engineers     

Highly thermal conductivity silicon nitride/carbon fibres/bismaleimide composites

Hybrid fillers of silicon nitride/carbon fibres (Si₃N₄/CFs) are performed to improve the thermal conductivities, mechanical and thermal resistance properties of the bismaleimide (BMI) composites. The thermally conductive coefficient of the Si₃N₄/CFs/BMI composites is improved to 1.68 W/mK with 50 wt% modified Si₃N₄ fillers. The flexural strength and interlaminar shear strength of the composites are optimal with 10 wt% modified Si₃N₄ fillers. The thermal resistance properties of the Si₃N₄/CFs/BMI composites are also improved with the addition of Si₃N₄ fillers. Surface modification of Si₃N₄ fillers exhibits positive effects on the thermal conductivities and mechanical properties of the Si₃N₄/CFs/BMI composites. POLYM. COMPOS., 37:468–471, 2016. © 2014 Society of Plastics Engineers     

Interaction effects and property retention in poly(vinyl chloride) compounds

The influence of thermodynamic interactions among the components of a polymer system on mechanical properties and their retention on aging has been investigated. The systems considered involve plasticized poly(vinyl chloride)(PVC), and CaCO₃ fillers. Inverse gas chromatography was used to measure interaction parameters, and to express these in terms of acid-base concepts. Interaction data were obtained over a wide temperature range. It was shown that the volume of plasticizers retained by the PVC correlates with the measured interaction parameters. Similarly, the interaction parameters identify a CaCO₃ filler preferred for reinforcing rigid PVC, and a different CaCO₃ filler for use in given PVC-plasticizer combinations. The mechanical properties of filled PVC (up to 40 phr CaCO₃), and particularly the ultimate properties of the compounds, correlate with interaction concepts, as do property retention data after accelerated aging of the compounds at 100°C. It is concluded that component interaction parameters may provide useful guidelines to the formulation of compounds with superior properties and reduced property losses due to aging.