Study of the influence of nano-silica particles on the curing reactions of acrylic-melamine clear-coats

In present study, the influence of presence of nano-silica particles having different surface modifications on curing reaction of a thermosetting acrylic-melamine clear-coat is clarified.Acrylic-silica nano-composites were made by grinding and dispersing of silica nano-particles in a thermosetting acrylic resin via milling. The resulting compositions were characterized in terms of curing reaction and the final film morphology. The cure reaction of the Neat and nano-particle containing clear-coats was monitored by differential scanning calorimetry (DSC). It was found that the presence of nano-silica particles, either hydrophilic or hydrophobic, reduces the activation energy of cure and increases the total heat of reaction. The morphology of the film is also extensively influenced by the presence of nano-particles.     

Effects of fly ash,phosphoric acid,and nano-silica on the properties of magnesium oxychloride cement

This study investigates the effects of fly ash, phosphoric acid, nano-silica additives on the hydration process, setting time, compressive strength, water resistance, and thermal stability of magnesium oxychloride cement (MOC). MOC samples incorporating different combinations of additives are prepared, and their hydration products and microstructures are studied via X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TGA-DSC), and scanning electron microscopy (SEM). Results indicate that the addition of nano-silica to MOC containing fly ash and phosphoric acid reduces initial and final setting times, decreases the thermal stability, and increases compressive strength. Furthermore, the water resistance of modified MOC pastes is significantly improved through the combined use of additives. Hydration mechanisms arising in MOC are elucidated, and the remarkable enhancement of water resistance is attributed to secondary hydration of the 5 Mg(OH)₂·MgCl₂·8H₂O (5·1·8 phase) and the formation of amorphous gel facilitated by nano-silica inclusion.     

Effect of sphalerite to wurtzite crystallographic transformation on microstructure, optical and mechanical properties of zinc sulphide ceramics

Zinc sulphide (ZnS) ceramics synthesized by chemical vapour deposition (CVD) were subjected to post CVD thermal treatments at 850 and 1050 °C in inert atmosphere under pressureless conditions. The samples were found to undergo cubic (sphalerite) to hexagonal (wurtzite) crystallographic transformation at around 1020 °C as confirmed by dilatometric and X-ray diffraction studies. The paper reports the effect of transformation in terms of structure - both crystallography and microstructure. Further, the effects of this transformation on the optical and mechanical properties are also analyzed. The increase in grain size was found to be beneficial for the IR transmission of sphalerite (cubic) phase while, the presence of wurtzite (hexagonal) was found to reduce the transmission significantly. A detailed evaluation of the nature and characteristics of the fracture revealed that the ZnS ceramics failed predominantly by low energy, quasi - cleavage fracture. It was also confirmed that the mechanical properties of this material vary with the extent (area fraction) of quasi - cleavage facets.     

The influence of nano-silica and zircon additions on the sintering and mechanical properties of in situ formed forsterite

The influence of nano-silica and zircon additions on the sintering and mechanical properties of in situ formed forsterite fired at 1550 °C for 2 h was investigated. The results indicated that, nano-silica improved in situ formed forsterite at the firing temperature, while zircon additions enhanced the sintering of the investigated samples. XRD analysis and SEM examination observed a good crystallinity of in situ formed forsterite with nano-silica and/or zircon additions. Densification parameter (BD ∼3.22 g/cm³ and AP ∼5.82%), cold crushing strength (CCS ∼285 MPa) and micro-hardness (Hv ∼660) were enhanced with zircon additions.     

Evaluation of durability of nano-silica containing clear coats for automotive applications

In automotive application, multilayer coating systems are typically used to guarantee protection from corrosion phenomena and aesthetic properties. A coating system's appearance and its durability is becoming increasingly important for automotive original equipment manufacturers. Clear coats are required to maintain long term aesthetic appearance, color and gloss stability to weathering and mechanical damage. One key property is scratch and mar resistance. The use of nano-fillers is a promising strategy to increase the abrasion resistance without affecting the optical clarity of high gloss coatings.     

Effect of composition on phase assemblage,microstructure, mechanical and optical properties of Mg-doped sialon

Mg-doped sialon (Mg_m/2Si_12−m−nAl_m+nO_nN_16−n) ceramics with different compositions of m = 2n = 0.6, 0.84, 1.0, 1.2, 1.6 were hot pressed at 1850 °C for 1 h. Phase assemblage, microstructure, mechanical and optical properties of these samples were investigated. All samples achieved/approached full densification. However, the densification of Mg-doped sialon ceramics with higher MgO/AlN content becomes more difficult. Additionally, the anisotropic growth of β-sialon grains was significantly inhibited. The unique characteristics of Mg-doped sialon ceramics intrinsically derive from the formation of Mg-containing AlN polytypoids, which consumed most of the high-temperature liquid. Furthermore, their high stability at high temperatures accounts for the difficulty in preparing single-phase Mg-α-sialon., The hardness of these samples gradually increases while indentation fracture toughness gradually decreases with increasing m = 2n value. Due to little residual glassy phase, high infrared transparency/translucency was more readily achieved in Mg-doped sialon. The m = 1.2 sample possesses the maximum transmittance of ∼50% at ∼2 μm.     

含纳米二氧化硅的PA6纤维的结构和性能研究

以差示扫描量热法、扫描电镜等研究了含纳米二氧化硅的PA6纤维的热性能、力学性能和形态结构。结果表明:质量分数为1％和3％的纳米二氧化硅可均匀分散在PA6中,质量分数为3％时PA6纤维的力学性能如拉伸强度、模量达最大值。纳米二氧化硅可起异相成核剂的作用,提高起始结晶温度,但对PA6纤维熔点无明显影响。     

The influence of filler surface modification on mechanical and material properties of layered double hydroxide‐containing polypropylene composites

The processing and properties of layered double hydroxides (LDHs)‐containing polypropylene (PP) composites have been studied extensively. However, no detailed studies have reported on how stearic acid (SA)‐intercalated and SA‐coated LDHs influence the properties of melt‐processed PP/LDH composites. Here, four different types of LDHs: synthesized (cLDH1) and commercial (cLDH2) SA‐coated LDH, SA‐intercalated LDH (iLDH), and unmodified LDH (nLDH), were used to fabricate composites using a master‐batch‐dilution technique in a twin‐screw extruder. The characterization results showed that microcomposites were formed when cLDH2 and nLDH were used, whereas nanocomposites were formed when iLDH and cLDH1 were used. Strong nucleating behavior was observed for the nLDH‐, cLDH1‐, and cLDH2‐containing composites, whereas iLDH delayed the crystallization process of the PP matrix. A significant improvement in modulus, with a balance of tensile and impact strengths, was observed in the case of the cLDH1‐containing composite, whereas the nLDH‐containing composite showed good improvement in temperature‐dependent load‐bearing capacity. On the other hand, the PP/iLDH composite showed a remarkable improvement in thermal stability and a reduction in the peak‐heat‐release rate. Therefore, this study gives us an opportunity to design PP composites with desired properties by the judicious choice of LDH, which further widens the application of PP matrices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45024.     

Investigating the variations in properties of 2-pack polyurethane clear coat through separate incorporation of hydrophilic and hydrophobic nano-silica

In the present study, a 2-pack polyurethane clear coat curable at ambient conditions was selected. Two different types of nano-silica (i.e. hydrophilic and hydrophobic nano-silica) were employed as fillers in order to vary the properties of the resultant nano-composite polyurethane coatings.     

Densification behavior,microstructure, mechanical and optical properties of Mg-doped sialon with fluoride additives

Mg-doped sialon ceramics with the composition of M_0.4Si_10.2Al_1.8O₁N₁₅ were fully densified by hot pressing at 1850 °C for 1 h, using 0.5 wt.% MgF₂ or CaF₂ as a sintering additive. Densification behavior, phase assemblage, microstructure, and mechanical and optical properties were investigated in detail. The addition of fluorides, especially MgF₂, not only resulted in more high-temperature liquid by promoting the dissolution of more N and other constituents but also reduced the viscosity of liquid due to the terminal effect of fluorine. Consequently, the densification was effectively improved. Additionally, the fluoride addition facilitated the formation of a small amount of β-sialon. Both the samples possessed high hardness (∼20 GPa) and fracture toughness (∼4.2 MPa m^1/2). The CaF₂-added sample exhibited higher infrared transmittance than its counterpart due to less residual glass phase. The present work implies that fluorides are also very effective sintering additives for densifying α-sialon.     

The influence of microstructure on the mechanical properties of polycrystalline diamond: a literature review*

ABSTRACT

Polycrystalline diamond (PCD) is an extremely high-performance cutting tool material used in the machining of rock, high-strength, non-ferrous metal alloys and carbon-fibre-reinforced composites. It is favoured for its exceptional hardness and wear resistance which results in at least an order of magnitude improvement in performance over previous technologies in almost all metrics. However, PCD suffers from unpredictable brittle fracture and degradation at high temperature during service which limits its capabilities in cutting applications. The literature on the link between its microstructure and its mechanical properties, including strength, toughness and flaw size distribution as measured by pseudo-static tests, is investigated. The conclusions of the seminal paper on this topic are re-examined in the light of modern ceramics research and an alternative explanation is put forth for the strength–grain size relationship published in this paper. All known literature values for strength and toughness vs. grain size and binder content are collated showing no overall trend in strength with binder content but moderate trends in all other combinations. The common claim of weak grain boundaries is brought into question in the light of the lack of any evidence of this fracture mode being evident in pseudo-static tests. The industrial literature on wear testing and failure modes of PCD in service and service-like tests is examined to bridge the gap between pseudo-static and dynamic, application-based experiments. Six main failure modes are recorded and summarised with intergranular fracture being the most conspicuously absent from the pseudo-static tests. It is suggested that the temperature generated by friction in dynamic tests causes the weakening of grain boundaries, resulting in a transition from transgranular to intergranular fracture and a call for further research in this area is made.     

Effects of sintering aids on microstructure,mechanical, and optical properties of AlON ceramics synthesized by SPS

Aluminum oxynitride (AlON) ceramics doped with different sintering aids were synthesized by spark plasma sintering process. The microstructures, mechanical, and optical properties of the ceramics were investigated. The results indicate that the optimal amount of sintering aids is 0.06 wt% La₂O₃ + 0.16 wt% Y₂O₃ + 0.30 wt% MgO. The addition of La³⁺ and Mg²⁺ decreases the rate of grain boundary migration in ceramics, promotes pore elimination, and inhibits grain growth. The addition of Y³⁺ facilitates liquid-phase sintering of AlON ceramics. Moreover, the addition of Mg²⁺ effectively promotes twin formation in the ceramics, which hinders crack propagation and dislocation motion when the ceramics are loaded. Hence, the AlON ceramic doped with 0.06 wt% La₂O₃ + 0.16 wt% Y₂O₃ + 0.30 wt% MgO exhibits a relative density of 99.95%, an average grain size of 9.42 μm, and a twin boundary content of 10.3%, which contributes to its excellent mechanical and optical properties.     

Microstructure and mechanical properties of 3D-printed nano-silica reinforced alumina cores

Ceramic cores are an important component in the preparation of hollow turbine blades for aero-engines. Compared with traditional hot injection technology, 3D printing technology overcomes the disadvantages of a long production cycle and the difficulty in producing highly complex ceramic cores. The ceramic cores of hollow turbine blades require a high bending strength at high temperatures, and nano-mineralizers greatly improve their strength. In this study, nano-silica-reinforced alumina-based ceramic cores were prepared, and the effects of nanopowder content on the microstructure and properties of the ceramic cores were investigated. Alumina-based ceramic cores contained with nano-silica were prepared using the vat photopolymerization 3D printing technique and sintered at 1500 °C. The results showed that the linear shrinkage of ceramic cores first increased and then decreased as the nano-silica powder content increased, and the bending strength showed the same trend. The fracture mode changed from intergranular to transgranular. The open porosity and bulk density fluctuated slightly. The weight loss rate was approximately 20%. When the nano-silica content was 3%, the bending strength reached a maximum of 46.2 MPa and 26.1 MPa at 25 °C and 1500 °C, respectively. The precipitation of the glass phase, change in the fracture mode of the material, pinning crack of nanoparticles, and reduction of fracture energy due to the interlocking of cracks, were the main reasons for material strengthening. The successful preparation of 3D printed nano-silica reinforced alumina-based ceramic cores is expected to promote the preparation of high-performance ceramic cores with complex structures of hollow turbine blades.     

Bio‐nanocomposites for food packaging applications: effect of cellulose nanofibers on morphological,mechanical, optical and barrier properties

The effect of the addition of various concentrations of cellulose nanofibers (CNF) on the thickness, solubility, morphology, mechanics, water vapor permeability and optical properties of biopolymers isolated from whey protein produced by the casting method was studied. The results show that the addition of CNF did not cause significant variation in the thickness of the films and resulted in nanocomposites with lower solubility and water vapor permeability. Scanning electron microscopy analysis showed that the films obtained with up to 4% of CNF showed good dispersion of the nanofibers in the whey protein matrix. The results of mechanical tests showed that the nanofibers acted as reinforcing material resulting in more resistant and less flexible films. © 2017 Society of Chemical Industry     

The influence of different SiC amounts on the microstructure,densification, and mechanical properties of hot-pressed Al2O3-SiC composites

The hot pressing process of monolithic Al₂O₃ and Al₂O₃-SiC composites with 0-25 wt% of submicrometer silicon carbide was done in this paper. The presence of SiC particles prohibited the grain growth of the Al₂O₃ matrix during sintering at the temperatures of 1450°C and 1550°C for 1 h and under the pressure of 30 MPa in vacuum. The effect of SiC reinforcement on the mechanical properties of composite specimens like fracture toughness, flexural strength, and hardness was discussed. The results showed that the maximum values of fracture toughness (5.9 ± 0.5 MPa.m^1/2) and hardness (20.8 ± 0.4 GPa) were obtained for the Al₂O₃-5 wt% SiC composite specimens. The significant improvement in fracture toughness of composite specimens in comparison with the monolithic alumina (3.1 ± 0.4 MPa.m^1/2) could be attributed to crack deflection as one of the toughening mechanisms with regard to the presence of SiC particles. In addition, the flexural strength was improved by increasing SiC value up to 25 wt% and reached 395 ± 1.4 MPa. The scanning electron microscopy (SEM) observations verified that the increasing of flexural strength was related to the fine-grained microstructure.     

The influence of substrate absorbency on coating surface chemistry

The composition of the top surface of a coating layer can influence its functional properties or subsequent processing steps. The effect of the substrate absorbency on the coating surface chemistry is reported. Different coating systems containing a kaolin clay pigment, fine or coarse precipitated calcium carbonates, and a common latex binder were examined. The influence of a soluble polymer added into the coating was characterized. The surface chemistry was measured with attenuated total internal reflectance (ATR) and X-ray photoelectron spectroscopy (XPS).

Absorbent substrates generate bulky coatings with high voids and low gloss. Rapid dewatering by the absorbent substrate pulls the small particles, like latex binder, away from the top layers causing a low latex concentration at the surface. On non-absorbent substrates, the addition of the soluble polymer generates coating layers with higher void volume, lower gloss, and lower latex concentrations at the coating surface. However, on absorbent substrates, polymer addition causes coatings with lower void volumes and higher gloss. In this case, the rapid dewatering and mobility of particles is reduced by the polymer, which helps to retain the small particles at the surface. As a result, latex concentration at the surface increases with polymer addition on absorbent substrates.     

The influence of dehydration on the interfacial bonding,microstructure and mechanical properties of poly(vinyl alcohol)/graphene oxide nanocomposites

The relationship between the interfacial bonding, microstructure and mechanical properties of the poly(vinyl alcohol)/graphene oxide nanocomposites (PVA/GO) has been investigated by controlling the water content through a dehydration process. The interfacial bonding in PVA/GO was predominantly by hydrogen bonds which were strongly affected by the dehydration process. Micro-voids in the microstructure formed after dehydration due to the shrinkage of the fibrils. A variety of hydrogen bonds including water–water, water–GO and water–PVA can be replaced with the strong PVA–GO interfacial bond resulting in a transition from ductile to brittle fracture. The tensile modulus and strength properties of the PVA and PVA/GO increased as the amount of residual water reduced, while the fracture strain was decreased. The surface mechanical properties of PVA/GO measured by nanoindentation showed broadly similar trends with water content as the bulk mechanical properties. However, there was a threshold value of approximately 3 wt.% water below which the surface mechanical properties decrease slightly. The indentation modulus was higher than the tensile modulus by a factor of at least three. The combined influence of the microstructure and the distribution of water in the nanocomposite is considered to be responsible for this.     

Effect of processing on the crystalline orientation, morphology, and mechanical properties of polypropylene cast films and microporous membrane formation

Cast films of a high molecular weight linear polypropylene (L-PP) were prepared by extrusion followed by stretching using a chill roll. An air knife was employed to supply air to the film surface right at the exit of the die. The effects of air cooling conditions, chill roll temperature, and draw ratio on the crystalline orientation, morphology, mechanical and tear properties of the PP cast films were investigated. The crystallinity and crystal size distribution of the films were studied using differential scanning calorimetry (DSC). It was found that air blowing on the films contributed significantly to the uniformity of the lamellar structure. The orientation of crystalline and amorphous phases was measured using wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR). The amount of lamellae formation and long period spacing were obtained via small angle X-ray scattering (SAXS). The results showed that air cooling and the cast roll temperature have a crucial role on the orientation and amount of lamellae formation of the cast films, which was also confirmed from scanning electron microscopy (SEM) images of the films. Tensile properties and tear resistance of the cast films in machine and transverse directions (MD and TD, respectively) were evaluated. Significant increases of the Young modulus, yield stress, tensile strength, and tensile toughness along MD and drastic decreases of elongation at break along TD were observed for films subjected to air blowing. Morphological pictograms are proposed to represent the molecular structure of the films obtained without and upon applying air cooling for different chill roll temperatures. Finally, microporous membranes were prepared from annealed and stretched films to illustrate the effect of the PP cast film microstructure on the morphology and permeability of membranes. The observations of SEM surface images and water vapor transmission rate of the membranes showed higher pore density, uniform pore size, and superior permeability for the ones obtained from the precursor films prepared under controlled air cooling.     

Effects of mechanical recycling on optical properties and microstructure of recycled high-density polyethylene pellets and bottles

The demand for recycling high-density polyethylene (HDPE) utilizing mechanical recycling technologies is currently felt strongly by both society and industry. However, thermal oxidation of the polymer during the recycling process may lead to irreversible changes in the material properties of recycled high-density polyethylene (rHDPE). The effects of mechanical recycling on the optical characteristics and microstructure of rHDPE pellets and bottles were investigated in this study. The results revealed that the apparent color of the rHDPE became more yellow and gray compared to the virgin HDPE (vHDPE), and showed a signal at 670–680 nm in the solar reflectance spectrum. The thermal oxidation of rHDPE considerably raised the absorption intensities of carbonyl, ester, and hydroxyl groups in attenuated total reflection Fourier transform infrared spectrum. In addition, the presence of carbonyl and hydroxyl unsaturated chemicals might make it challenging to recognize the distinctive peaks of vHDPE in the ultraviolet–visible diffuse reflectance (UV–Vis-DIR) spectra at wavelengths less than 400 nm. Thermal oxidation of rHDPE was also confirmed in the C OH, CO, and O CO valence structures of C1s and O1s. A characteristic valence band (VB) profile at 25 eV can be used as the recognizable information for the oxidation of rHDPE. The microstructure of the surface of rHDPE pellets exhibited rough and uneven morphological defects. The higher recycled content made rHDPE bottles' surface morphology rougher and their cross-section microstructure thinner and more porous than vHDPE bottles.     

Enhancement of flexographic print quality on bleached kraft liner using nano-silica from rice husk

Nano-silica from rice husk (nano-RHS) was synthesized and used in a coating agent to enhance the flexographic print quality of bleached kraft liner. The rice husk was refluxed with a 2 M HCl solution and calcined in a muffle furnace at 650 °C for 4 h. The particle size of the resultant rice husk ash was reduced to a very fine nano-RHS by hexadecyl trimethyl ammonium bromide. The synthesized nano-RHS in different proportions – 1%, 2%, 3%, 4% and 5% (w/w_resin) – was added to a water-based coating agent consisting of acrylic resin. The coating agent with nano-RHS additive was applied by gravure rolling onto the surface of a 170 g/m² bleached kraft liner 3–4 μm in thickness. The flexographic print quality was determined with printing details of 31.5 lpc using water-based process colors. The results indicated that the coating agent with 1% nano-RHS was the most promising for improving the flexographic print quality on the bleached kraft liner. At this fraction, the best print quality in terms of high sharpness of fonts and texts, line art, realistic image, and TVI curve (under the requirements of ISO 12647-6) were achieved. In addition, low tone-value and ΔE*_abwith a large, three-dimensional color profile and the widest color gamut were obtained.