Preparation of the organic–inorganic double-shell microencapsulated aluminum hypophosphite and its improved flame retardancy and mechanical properties of epoxy resin composites

To develop the functional particles with better flame-retardant and compatibility with epoxy resin (EP) matrix, organic–inorganic double-shell microencapsulated aluminum hypophosphite (MSiAHP) was prepared by situ polymerization. The water contact angles of MSiAHP (62.4°) is significantly larger than that of aluminum hypophosphite (34.4°), which shows that the organic shell material of MSiAHP endows excellent hydrophobicity and water resistance. With the incorporation of MSiAHP, EP/30%MSiAHP composite exhibits limiting oxygen index value of 27.3% and V-0 rating. Furthermore, the cone calorimetry test reveals that MSiAHP reduces the peak heat release rate, total heat release and total smoke release of EP matrix by 33.3%, 24.4% and 56.6%, respectively. Besides, due to the unique organic–inorganic double-shell structure of MSiAHP particles, EP/30%MSiAHP composite achieves greater thermal stability and higher char yields than pure EP. The investigation of the products in the gas and condensed phase demonstrates that MSiAHP is beneficial to the generation of a high-density and compact carbon layer structure with a high graphitization degree, and delay the generation time of pyrolysis products in the gas phase, which can improve the fire safety of EP composites effectively. Furthermore, preeminent dispersion and compatibility of MSiAHP lead to EP/MSiAHP composites with excellent mechanical properties.     

Effect of zirconia content on mechanical and thermal properties of mullite–zirconia composite

Abstract

Mullite–zirconia composites were prepared by adding various zirconia contents in the mullite ranging from 0 to 30 wt-% and sintering at 1400–1600°C for 2 h. The phase composition examined by X-ray diffraction showed that mullite was the major phase combined with developed t-ZrO₂ and m-ZrO₂ phase as a function of zirconia content, especially at 1600°C, wherein m-ZrO₂ predominated. Density increased when the zirconia content and sintering temperature were increased ranging from 2·2 to 3·53 g cm^?3. The morphology of mullite grain showed elongated grains, whereas dispersed zirconia showed equiaxed and intergranular grains. Flexural strength was continuously improved by adding zirconia during the sintering temperature ranging from 1400 to 1500°C, whereas flexural strength was initially improved up to 5 wt-% of zirconia addition and deteriorated with more than 5 wt-% of zirconia content during sintering between 1550 and 1600°C. The maximum strength, 190 MPa, was obtained when sintering mullite with 30 wt-% of zirconia content at 1500°C. The degradation of strength at high sintering temperature may be a result from more occurrence of m-ZrO₂ phase. Thermal expansion of sintered specimens indicated linear change and hysteresis loop change. The hysteresis loop obtained with increased zirconia content resulted in the t–m phase transformation. Martensitic start temperature M_s was determined to be 530°C for 15 wt-% zirconia sintered at 1500°C, implying that the t–m phase transformation occurred.     

Effect of nanocarbon sources on microstructure and mechanical properties of MgO–C refractories

A study of microstructural evolution, mechanical and thermo-mechanical properties of MgO–C refractories, based on graphite oxide nanosheets (GONs), carbon nanotubes (CNTs) and carbon black (CB), was carried out by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), three-point bending and thermal shock tests. Meanwhile, these results were compared to the conventional MgO–C refractory containing 10 wt% flaky graphite prepared under the same conditions. The results showed that higher cold modulus of rupture was obtained for the composition containing GONs, and the composition containing CNTs exhibited larger displacement after coking at 1000 °C and 1400 °C. Also, the addition of nanocarbons led to an improvement of the thermal shock resistance; in particular, both compositions containing CNTs and CB had higher residual strength ratio, approaching the thermal shock resistance of the reference composition containing 10 wt% flaky graphite, as it was associated with the presence of nanocarbons and in-situ formation of ceramic phases in the matrix.     

Effect of polytetrafiuoroethylene on flame retardancy and mechanical properties of silicone rubber filled with Mg ( OH ) 2/Al ( OH ) 3 complex

研究了聚四氟乙烯(PTFE)对Mg(OH)2/Al(OH)3填充硅橡胶阻燃性能和力学性能的影响.结果表明,PTFE不但能够改善硅橡胶的阻燃性能,而且还能使力学性能尤其是撕裂强度得到显著提高.当PTFE用量为2.5份(质量),撕裂强度达17.1 kN·m-1,比不含PTFE的试样提高了51%,而且其极限氧指数也有一定增加.     

Thermal and combustion behavior of phosphorus–nitrogen and phosphorus–silicon retarded epoxy

A novel trizine ring-based phosphorus–nitrogen flame retardant, 1,3,5-tris(3-(diphenylphosphoryl)propyl)-1,3,5-triazinane-2,4,6-trione (PN), was synthesized by the reaction of diphenylphosphine oxide and triallyl isocyanurate with triethylborane as catalyst. Chemical structure of the target compound was confirmed by Flourier transform infrared spectrum, nuclear magnetic resonances, matrix-assisted laser desorption/ionization time-of-flight mass spectrum measurements. The newly developed PN was used in the flame retardancy of o-cresol novolac epoxy/phenolic novolac hardener system. For comparison, another analogous phosphorus–silicon flame retardant, [(1,1,3,3-tetramethyl-1,3-disiloxanediyl)-di-2,1-ethanediyl]-bis(diphenylphosphine oxide) (PSi), was also applied in the same system. Experimental results revealed that PN showed superior flame retardant efficiency to that of PSi. In addition, the incorporation of flame retardants was in favor of the char formation during the thermal degradation process of epoxy thermosets. With the same flame retardant content, the char residue of epoxy thermosets with PSi was higher than that of epoxy thermosets with PN at 750 °C. Cone calorimeter results indicated that PN contributed to gas phase flame retardancy while PSi was more likely to take part in flame retardancy in the condense phase. X-ray photoelectron spectroscopy data revealed that the binding energies of phosphorus changed in different ways in PN and PSi after combustion. This implied that phosphorus exhibited different combustion behaviors when combined with nitrogen or silicon.     

Preparation of organic–inorganic intumescent flame retardant with phosphorus,nitrogen and silicon and its flame retardant effect for epoxy resin

According to the requirement of fire life cycle assessment (LCA), chitosan ethoxyl urea phosphate (CEUP), an organic–inorganic intumescent flame retardant (IFR) containing phosphorus, nitrogen, and silicon, was synthesized by the reaction of chitosan, phosphorus pentoxide, and urea. FTIR, ¹H NMR, SEM, and XRD were employed to characterize the compounds. As a result, CEUP was successfully prepared with higher thermal stability, favorable to enhance fire resistance. Combined with OMMT, the organic/inorganic IFR was applied as EP flame-retardant agents. The combustion behavior of EP composite was investigated by LOI, UL-94, CCT, SEM, TGA, and TG-IR. It was observed that using 15% CEUP and 3% OMMT (EP3), LOI value reached 34.8% and passed the UL-94 V-0 rating, while THR and TSP of EP composite reduced 65 and 72% compared with pure EP. The char residue of EP composite was up to 22.4%. The thermal decomposition mechanism was traced from 100 to 600°C by TG-IR. It was suggestive that CEUP decomposition commenced at 100°C to create phosphoric acid and sublimation of urea occurred at 300°C. EP3 exhibited a strong thermal stability, namely even at 600°C, the volatile substances were detectable. Dense and expanded carbon layer was confirmed in SEM images.     

Effect of different zeolitic imidazolate frameworks nanoparticle-modified β-FeOOH rods on flame retardancy and smoke suppression of epoxy resin

A simple method was used to load zeolitic imidazolate frameworks (ZIFs) onto β-FeOOH nanorods to ameliorate the flame retardancy and smoke suppression of epoxy resin (EP). The morphology and structure of ZIF-8-β-FeOOH (Z8Fe) and ZIF-67-β-FeOOH (Z67Fe) nano hybrids were systematically characterized by field emission scanning electron microscope, Fourier transform infrared and X-ray diffraction (XRD) spectra, which proved the successful preparation of the hybrids. 3 wt% of Z8Fe and Z67Fe were added to the EP matrix, and their combustion properties were studied, respectively. The results showed that the composites' limiting oxygen index values were ameliorated to 27.3% and 28.1%, respectively. Their UL94 flame retardant rating was improved, their peak heat release rate and total heat release were reduced, their flame retardant performance was considerably improved, and their generation of toxic smoke was significantly suppressed. Further, through X-ray photoelectron spectroscopy, XRD and laser Raman spectroscopy analysis of the char residue, their potential mechanism of flame retardancy and smoke suppression were studied.     

Effect of ZrB2 on the microstructure,mechanical and tribological properties of Mo–Si–B matrix composites

Composites with good mechanical and tribological properties are in high demand for engineering applications. Toward this aim, the Mo–12Si–8.5B alloy with 2.5–10 wt% ZrB₂ ceramic was prepared. The effects of the ZrB₂ content on the microstructure, mechanical properties, and tribological behavior were thoroughly investigated. The composites exhibited reduced density and enhanced hardness and strength owing to the dispersion strengthening of ZrB₂ particles, thus resulting in improved wear resistance. The frictional properties are highly dependent on the ZrB₂ content and counterpart materials. When coupled with GCr15 steel, it shows much slighter abrasive and adhesive wear; therefore, it presents a more preferable anti-wear performance. The wear rate of the composite with 7.5 wt% ZrB₂ showed a minimum value of 2.71 × 10⁻⁷ mm³N⁻¹m⁻¹.     

Effect of Mo addition mode on the microstructure and mechanical properties of TiC–high Mn steel cermets

In TiC- and Ti(C,N)-based cermets, the wettability of the ceramic phase with the metallic binder is commonly increased through supplementation with Mo in the form of pure Mo powder or Mo₂C. Herein, TiC–high Mn steel cermets were fabricated by conventional powder metallurgy techniques using Fe–Mo pre-alloyed powders as binders to guarantee uniform Mo distribution, and the cermet preparation process was optimized and investigated in detail. The microstructures of the thus obtained cermets were observed by scanning electron microscopy and compared to those of a Mo-free cermet and a cermet prepared using pure Mo powder. The grain size of Fe–Mo powder cermets exceeded that of the Mo-free cermet but was much smaller and more homogeneous than that of the Mo powder cermet. For Fe–Mo powder cermets, angular and tetragonal TiC particles were observed at Mo contents of <1.2 wt%, while round shapes became dominant at higher Mo contents. The hardness of Fe–Mo powder cermets increased with increasing Mo content, as did transverse rupture strength, which was maximal (2264 MPa) at a Mo content of 2.4 wt%, while impact toughness was maximal (11.2 J/cm²) at a Mo content of 1.2 wt%. The above values exceeded those reported for similar conventional cermets, and the use of Fe–Mo pre-alloyed powder as a metallic binder was therefore concluded to be an attractive strategy of increasing the strength and toughness of TiC–high Mn steel cermets.     

Effect of Al2O3 particles on mechanical and tribological properties of Al–Mg dual-matrix nanocomposites

This article aims to manufacture homogenous dual-matrix Al–Mg/Al₂O₃ nanocomposite from their raw materials and give insight into the correlation between powder morphology, crystallite structure and their mechanical and tribological properties. Al–Mg dual-matrix reinforced with micro/nano Al₂O₃ particles was manufactured by a novel double high-energy ball milling process followed by a cold consolidation and sintering. Microstructure and phase composition of the prepared samples were characterized using FE-SEM, EDS and XRD inspections. Mechanical and wear properties were characterized using compression and sliding wear tests. The results showed that a milling of Mg with Al₂O₃ particles in an initial step before mixing with Al has the beneficial of well dispersion of Al₂O₃ nanoparticles in Al–Mg dual matrix. The Al–Mg dual matrix reinforced with nano-size Al₂O₃ showed 3.29-times smaller crystallite size than pure Al. Moreover, the hardness and compressive strength are enhanced by adding nano-size Al₂O₃ with Al–Mg dual matrix composite while the ductility is maintained relatively high. Additionally, the wear rate of this composite was reduced by a factor of 2.7 compared to pure Al. The reduced crystallite size, the dispersion of Al₂O₃ nanoparticles and the formation of (Al–Mg)_ss were the main improvement factors for mechanical and wear properties.     

Effect of diamond volume fraction on the microstructure and mechanical properties of SPS WC–Co/diamond composites

In this research, the effect of the volume percentage of diamond additive on the sintering behavior, microstructure, and mechanical properties of WC–Co was investigated. WC–Co/diamond composites with different percentages of 0%, 2.5%, 5%, 7.5%, and 10% by volume of diamond were made by spark plasma sintering at 1300°C and 40 MPa for 5 min. A small amount of phase transformation from the diamond phase to the graphite phase was observed. The amount of graphitization was low due to low temperature and short sintering time. The addition of diamond leads to a significant enhancement in both the hardness and fracture toughness of the composites, overcoming the trade-off between hardness and toughness typically observed in WC-based materials. The sample reinforced with 5% by volume of diamond showed simultaneously the highest hardness (22.9 GPa), the highest fracture toughness (22.7 MPa m^1/2), and the highest flexural strength (1896 MPa). The uniform dispersion, good bonding of the superhard diamond phase with the matrix, and the fine microstructure caused the high hardness and toughness of composite. The main effective mechanisms in increasing the fracture toughness of the composite were crack deflection, bridging, and blocking of crack propagation by diamond particles.     

Effect of PyC interphase thickness on mechanical and ablation properties of 3D Cf/ZrC–SiC composite

Three-dimensional (3D) C_f/ZrC–SiC composites were successfully prepared by the polymer infiltration and pyrolysis (PIP) process using polycarbosilane (PCS) and a novel ZrC precursor. The effects of PyC interphase of different thicknesses on the mechanical and ablation properties were evaluated. The results indicate that the C_f/ZrC–SiC composites without and with a thin PyC interlayer of 0.15 µm possess much poor flexural strength and fracture toughness. The flexural strength grows with the increase of PyC layer thickness from 0.3 to 1.2 µm. However, the strength starts to decrease with the further increase of the PyC coating thickness to 2.2 µm. The highest flexural strength of 272.3±29.0 MPa and fracture toughness of 10.4±0.7 MPa m^1/2 were achieved for the composites with a 1.2 µm thick PyC coating. Moreover, the use of thicker PyC layer deteriorates the ablation properties of the C_f/ZrC–SiC composites slightly and the ZrO₂ scale acts as an anti-ablation component during the testing.     

Effect of core–shell rubber toughening on mechanical,thermal, and morphological properties of poly(lactic acid)/multiwalled carbon nanotubes nanocomposites

The effect of core–shell rubber (CSR) toughening on mechanical and thermal properties of poly(lactic acid)/multiwalled carbon nanotubes (PLA/CNT) nanocomposites were investigated. The nanocomposites were prepared by direct melt blending method in a counter-rotating twin-screw extruder. The contents of CSR were varied between 5 and 20 wt % while the content of CNT was kept at 5 phr. The extruded samples were injection molded into the desired test specimens for mechanical and thermal properties analysis. The impact strength of PLA/CNT increased with increasing CSR content with concomitant decrease in tensile strength and modulus. Interestingly, the flexural strength increased at low CSR content before decreasing at 15 and 20% content. Differential scanning calorimetry analysis on the second heating cycle shows no crystallinity content for PLA/CNT and all CSR toughened PLA/CNT nanocomposites, while thermogravimetric analysis shows lower thermal degradation of all CSR toughened PLA/CNT as compared to PLA/CNT nanocomposite. This study reveals significant correlation between CSR loading with the mechanical and thermal properties of the nanocomposites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47756.     

Effects of vinyltrimethoxy silane on thermal properties and dynamic mechanical properties of polypropylene–wood flour composites

The viability of vinyltrimethoxy silane was investigated as a coupling agent for the manufacture of wood–plastic composites (WPC). The effect of silane pretreatment of the wood flour on the thermal and the dynamic mechanical properties and thermal degradation properties of the composites were studied. Moreover, the effect of organosilane on the properties of composites was compared with the effect of maleated polypropylene (MAPP). DSC studies indicated that the wood flour acts as a PP-nucleating agent, increasing the PP crystallization rate. In general, pretreatment with small amounts of silane improved this behavior in all the WPCs studied. Thermal degradation studies of the WPCs indicated that the presence of wood flour delayed degradation of the PP. Silane pretreatment of the wood flour augmented this effect, though without significantly affecting cellulose degradation. Studies of dynamic mechanical properties revealed that the wood flour (at up to 30 wt %) increased storage modulus values with respect to those of pure PP; in WPCs with a higher wood flour amount, there was no additional increase in storage modulus. Pretreatment of the wood flour with silane basically had no effect on the dynamic mechanical properties of the WPC. These results show that with small amounts of vinyltrimethoxy silane similar properties to the MAPP are reached. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of two-step sintering on microstructure and mechanical properties of ceria-stabilized zirconia-toughened alumina-added titania (CSZTA–TiO2)

Effect of two-step sintering (TSS) on microstructure and mechanical properties of ceria-stabilized zirconia-toughened alumina with added TiO₂ (CSZTA–TiO₂) was studied. A coprecipitation technique was used to produce the CSZTA–TiO₂ powders. The synthesized powders were compacted using a uniaxial hydraulic press and conventionally sintered in air. The phase and microstructure of sintered samples were studied using X-ray diffraction and scanning electron microscopy techniques. Phases were quantified using the Rietveld refinement method. Different TSS schedules were followed to optimize microstructure and mechanical properties. Mechanical properties of the CSZTA-4TiO₂ composite were evaluated and found as follows: Vickers's hardness of 1650 ± 9.6 HV10, indentation fracture toughness of 8.45 ± .14 MPa √m, compressive strength of 2088 MPa, and Young's modulus of 158 GPa.     

Effect of nitrogen sources on γ-linolenic acid accumulation in Spirulina platensis

The effect of ammonium phosphate on the growth, lipid content, and γ-linolenic acid accumulation was determined in the cyanobacterium Spirulina platensis. After 14 d on media containing 0.041 g N/L, γ-linolenic acid concentration of cultured cells increased up to 35.3±0.13%, w/w. In treatments containing NaNO₃, NH₄NO₃, and NH₄Cl, γ-linolenic acid concentration increased up to 31.2±0.23%, w/w. After the same period, lipid content in the dry biomass was 12.2±0.03%, w/w, with (NH₄)₂HPO₄ compared to about 14.1±0.12%, w/w, in treatments with NaNO₃. When (NH₄)₂HPO₄ concentration in the medium was increased to 0.082 g N/L, 30.8±0.28%, w/w, γ-linolenic acid had formed after 10 d and the lipid percentage in the dry cell mass was 16.7±0.16%, w/w. However, in treatments with NaNO₃, NH₄NO₃, or NH₄Cl, γ-linolenic acid concentration increased up to 30.6±0.23%, w/w, and the lipid content was found to be 18.0±0.17 to 18.9±0.03%, w/w. These data showed that (NH₄)₂HPO₄ is a suitable source of nitrogen for growth of S. platensis, with increased accumulation of γ-linolenic acid at lower N concentration.     

Effect of heat treatment on electroless ternary nickel–cobalt–phosphorus alloy

Ternary Ni–Co–P and binary Ni–P alloy coatings were deposited on mild steel panels from an alkaline bath in the presence and absence of cobalt sulfate using an electroless process. The effects of heat treatment on surface topography and crystal orientation of Ni–Co(11.17%)–P(3.49%) alloy coatings were studied in contrast to that of Ni–P ones. It was found that the as plated Ni–Co–P alloy is a supersaturated solid solution of P and Co dissolved in a microcrystalline Ni matrix with 111 preferred direction. Heat treatment induces structural changes. The formation of Ni₃P phase precipitates and recrystallization of nickel occur when the sample is treated at > 400 °C for one hour. It is observed that the Ni diffraction lines of treated Ni–Co–P alloy at > 400 °C are shifted to lower angles as compared to those of treated Ni–P or as plated Ni–Co–P alloys. The surface topography of Ni–Co–P alloy also changes with heat treatment temperature. The surface topography and crystal orientation were characterized by means of scanning electron microscopy and X-ray diffraction, respectively. The hardness and corrosion resistance, in 5 wt % NaCl solution, of heat treated Ni–Co–P samples were studied.     

Effect of Ni content on the microstructure,mechanical properties and erosive wear of Mo2NiB2–Ni cermets

This work revealed the effects of Ni content on the microstructure, mechanical properties and erosive wear of Mo₂NiB₂–Ni cermets. Four groups of Mo₂NiB₂–Ni cermets with different Ni contents were fabricated by reaction boronizing sintering in this study, and their mechanical properties were tested. The results show that the microstructure of the cermets can be obviously refined with the Ni/B increasing from 0.9 to 1.2, and the cermets of Ni/B 1.1 have the best mechanical properties (hardness HRA 90.3 and fracture toughness 24.3 MPa m^1/2). Moreover, under high-speed slurry (artificial seawater mixed with SiO₂ sand) erosive wear, the cermets of Ni/B 0.9 and 1.0 indicate high wear rate with the aggravated eroded surfaces. However, the cermets of Ni/B 1.1 achieve the minimum wear rate with relatively complete eroded surface, which is attributed to the interaction of Mo₂NiB₂ hard phase and Ni binder phase with appropriate ratio of two phases.     

Influence of nano–micrometre powder blends on microstructure and mechanical properties of silicon nitride

Abstract

A well known route to making tough silicon nitride compositions is to control the grain size and aspect ratio distributions. This is usually done by choosing the appropriate powder characteristics, sintering conditions, as well as sintering additives. The effect of hot pressing a blend of nano and micrometre scale silicon nitride powder is explored here. Microstructures and mechanical properties are determined for these hot pressed ceramics and are compared with a reference silicon nitride. Hardness and fracture toughness are determined at room temperature using hardness indents produced by a macro Vickers hardness indenter. Grain size and aspect ratio distributions and their impact on mechanical properties are presented. Blending of nano and micrometre scale powder is shown to result in a refined microstructure with an increase in the area/volume fraction of finer grains. Rising R curves are established for these ceramics demonstrating toughening behaviour. Crack bridging and crack path deviation are identified as possible toughening mechanisms.