Influence of pencil lead hardness on voltammetric response of graphite reinforcement carbon electrodes

This work studied the voltammetric response of graphite reinforcement electrodes made of different pencil lead hardness. The studies showed that harder graphite leads, regardless of their manufacturer, are more appropriate as electrode material for voltammetric purposes due to their higher peak currents, increasing sensitivity and reproducibility, with ΔEp closer to the theoretical value for a reversible system.     

Extraction of cellulose nanocrystals and fabrication of high alumina refractory bricks using pencil chips as a waste biomass source

Extraction of “green” cellulose nanocrystals (CNCs) from waste biomass is a sustainable strategy for high valued valorization in the view of socio-economic and environmental issues. Herein, for the first time, waste pencil chips (PC) as a potential source of cellulose, were used for the extraction of CNCs. CNCs were successfully extracted from PC wastes using alkali and bleaching chemical treatments to remove hemicellulose and lignin followed by acid hydrolysis using concentrated sulfuric acid. The products after each step were characterized in terms of crystallinity, chemical structures, thermal properties, and morphologies. The XRD results showed that the crystalline index increased about 16% from PC (75%) to CNCs (91%). The FTIR analysis confirmed the removal of the hemicellulose and lignin from PC after alkali and bleaching treatments. The TGA analysis showed that the thermal stability of the CNCs is affected mainly by the dehydration reaction caused by sulfate groups. The SEM and FE-SEM images showed that after chemical treatments, defibrillation of fibers occurs and CNCs have a needle/rod like structure. Also, the specific surface aera was greatly increased from 0.495 for PC to 486.430 m²/g for CNCs. Herein, for the first time, lignin-containing cellulose extracted from PC was replaced with sawdust (SRB) in the production of alumina refractory bricks (RBs), as a pore former/binder. Interestingly, the prepared RBs (PC–NaOH/RB) had a greater amount of alumina (83%) and a lower density (0.75 g/cm³) than SRB. The classification temperature increased from 1650 for SRB to 1717 °C for PC-NaOH/RB.     

Machine learning predictions of Knoop hardness in lithium disilicate glass-ceramics

Predicting the effects of ceramic microstructures on macroscopic properties, such as the Knoop hardness, has long been a difficult task. This is particularly true in glass–ceramics, where multiple unique crystalline phases can overlap with a background glassy phase. The combination of crystalline and glassy phases makes it difficult to quantify the percent crystallinity and to predict properties that are the result of the chemical composition and microstructure. To overcome this difficulty and take the first step to build a system for characterizing glass-ceramics, we predict the Knoop hardness based on scanning electron microscopy images using two computational techniques. The first technique is a computer vision algorithm that allows for physical insights into the system because the features used in a predictive model are extracted from the images. The second technique is machine learning with convolutional neural networks that are trained through transfer learning, allowing for more accurate predictions than the first method but with the downside of being a black box. Discussion of the relative merits of the models is included.     

Preparation and characterization of novel ZnS/sulfur-containing polymer nanocomposite optical materials with high refractive index and high nanophase contents

A series of novel transparent bulk ZnS-polymer nanocomposites with high refractive index were successfully prepared via in-situ bulk polymerization in the presence of 2-mercaptoethanol (ME)-capped ZnS NPs. The polymerization mechanism combined the step-growth and free radical polymerization of different monomers of episulfide, m-xylylene diisocyanante (XDI), 2-hydroxyethyl methacrylate (HEMA) and N,N-dimethylacrylamide (DMAA). The high refractive index of episulfide compounds, including ESGMES, ESDGEBA and MPS, were synthesized and used as monomers in polymerization systems. The cured nanocomposites with 30 wt% nanoparticles show high refractive index and good transparency. The refractive index of the nanocomposites could be continuously regulated in the range from 1.59 to 1.65 by the content of ZnS NPs and the pencil hardness is round about 5H. The content of ME-ZnS NPs can affect the thermal stability, mechanical and optical properties of the resulting nanocomposites, and the relationship between them were studied by TGA, DMA, pencil hardness test, Charpy impact test.     

Preparation in presence of urushiol and properties of acrylate latex with interparticle bridges

Acrylate latices were prepared by seeded emulsion polymerization of methyl methacrylate (MMA) and butyl acrylate (BA) in presence of urushiol with multifunctional groups (0–6 wt%). The emulsion polymerization was strongly influenced by the urushiol content. With increasing urushiol content, the conversion rate of the monomers first increased then decreased, the stability of emulsion polymerization gradually declined, the average particle size of the latex increased from 115.9 to 175.3 nm, and a change from mono- to bimodal particle size distribution occurred. Interestingly, transmission electron microscopy (TEM) showed that some particles were connected by linear bridges in presence of urushiol. Based on results of ¹H nuclear magnetic resonance (NMR) analysis, such formation of interparticle bridges is due to participation of urushiol in the emulsion polymerization of the acrylate monomers. The content of urushiol also affected the properties of latex films. With increasing urushiol content from 0 to 3 wt%, the adhesion, pencil hardness, and contact angle were markedly improved from grade 6 to grade 2, from B to 3H, and from 22° to 61°, respectively, due to formation of interparticle bridges. When the content of urushiol exceeded 3 wt%, the adhesion and pencil hardness remained unchanged, but the water contact angle markedly declined because of higher surface roughness of the latex film. Furthermore, addition of urushiol enhanced the thermal stability of the latex films.     

Voltammetric behavior of nicotine at pencil graphite electrode and its enhancement determination in the presence of anionic surfactant

The electrochemical oxidation of nicotine was studied in aqueous as well as micellar media at a pencil graphite electrode using cyclic, differential pulse and square-wave voltammetric techniques. The compound was oxidized irreversibly at low positive potentials in one (in acidic and neutral media) or two (in alkaline media) oxidation steps. The response was evaluated with respect to pH, scan rate, addition of surfactant and other variables. For analytical purposes, very resolved voltammetric peaks at +0.84 V (versus Ag/AgCl) were obtained in phosphate buffer at pH 7.0 containing 2 mM sodium dodecylsulfate using square-wave mode. The process could be used to determine nicotine concentrations in the range of 7.6–107.5 μM with a detection limit of 2.0 μM (0.33 mg L⁻¹). The proposed method was applied to the determination of nicotine in different brands of commercial cigarettes.     

UV固化环氧丙烯酸酯-纳米Al2O3颗粒复合涂层的性能

制备了UV固化环氧丙烯酸酯-纳米Al2O3复合涂料. 对纳米复合涂层的硬度、附着力、耐腐蚀性及热稳定性等性能进行了表征,并考察了纳米Al2O3对涂层性能的影响规律. 结果表明,涂层硬度及附着力先随纳米Al2O3添加量增加而提高,添加量为2%时,涂层附着力达1级;添加量为3%时,涂层铅笔硬度达6H;添加量继续增大,涂层硬度及附着力均下降. 对纳米复合涂层的热重分析和电化学阻抗谱分析结果表明,加入纳米Al2O3能提高涂层的热稳定性,但加入未改性纳米Al2O3使涂层的耐腐蚀性下降.     

Pencil lead microelectrode and the application on cell dielectrophoresis

A microelectrode was fabricated by electrochemical etching of a pencil lead (0.5 mm in diameter) in 1.0 M NaOH aqueous solution. The pencil lead was dipped into the solution and then an ac voltage (3.0 V_rms for 10 min) was imposed against a stainless plate under mild stirring (450 rpm). The electrochemically sharpened pencil tip was about 10 μm in diameter (12 ± 3 μm, n = 5), and the lateral part was insulated within a polypropylene micro-pipette tip (2–200 μL volume range). The cyclic voltammograms conducted in 2.0 mM ferricyanide/ferrocyanide buffer solution (pH 7.0) are with low capacitive current and a typical sigmoidal signal of micro-sized electrodes.The microelectrode was used to perform dielectrophoresis of polystyrene latex microbeads (nominal diameter of 3 μm) and human red blood cells. A conducting glass (indium tin oxide coated glass, 40 mm × 40 mm × 1 mm) served as the counter electrode (0.5 mm beneath the microelectrode) to generate the asymmetrical electric field and also as the window for microscopic observation. With the sinusoidal bias voltage (30 V_rms) ranged from 20 Hz to 2 MHz, positive and negative dielectrophoretic phenomena were identified.     

High bio-based content waterborne UV-curable coatings with excellent adhesion and flexibility

A series of bio-based unsaturated polyesters was synthesized by melt polycondensation of itaconic acid with 1,4-butanediol and glycerol. Their chemical structures were confirmed by FT-IR, ¹H NMR, acid and hydroxyl values. Waterborne UV curable dispersion coatings based on these polyesters and acrylated epoxidized soybean oil (AESO) were formulated. The average particle size and their stability before curing as well as the coating properties after curing, including adhesion, flexibility, pencil hardness and solvent resistance, were investigated. Results demonstrated that the glycerol segment in the polyesters together with AESO led to the excellent coating properties in terms of highest grade of adhesion (5B), 0T flexibility, pencil hardness of 5H and excellent solvent resistance (no appearance change after 250 double rubs with ethanol and acetone). This work provided us the coating systems combining the merits of being bio-based, UV-curable and water dispersible.     

UV固化丙烯海松酸聚氨酯丙烯酸酯的合成及应用

以2,4-甲苯二异氰酸酯(TDI)、丙烯海松酸二甘醇聚酯二元醇和丙烯酸羟丙酯(HPA)为主要原料合成了可紫外光固化的涂料用丙烯海松酸聚氨酯丙烯酸酯(APAPUA)低聚物。对产物进行了红外表征,并考察了其光固化行为。测试了APAPUA固化膜的硬度、柔韧性及其他力学性能,同时考察了其热稳定性。结果表明,该低聚物固化膜铅笔硬度达到4H,附着力1级,耐冲击性55 cm,初始分解温度245℃,具有固化速度快,力学性能及耐热性优良等特点,可以作为价格低廉的耐热性低聚物应用于光固化涂料。     

对压痕硬度试验方法的分析研究

比较系统地分析了传统的布氏、洛氏、维氏、玻氏等七种常用压痕硬度试验法之间及它们与纳米压痕硬度试验法之间的异同,概括地分析了压痕硬度试验法研究的主要内容、现状及应用,讨论了压痕硬度试验法的研究重点——纳米压痕硬度试验法。这种试验方法主要是通过对卸载曲线的研究计算被测材料弹性模量及其它相关参数,它在薄膜材料及材料的微区域等方面的力学性能研究中表现出极大的优势。     

水性氨基烘漆的研制

研制了一种水性烘漆,该烘漆采用低甲醚化氨基树脂为固化剂,烘烤温度低。烘烤（130℃）15min后,漆膜的60°光泽〉90,铅笔硬度为2H,耐冲击性为50kg·cm,附着力一级,可用于金属的外表面涂装。并对影响水性烘漆性能的多种因素进行了分析,结果表明：选择合适的乳液、羟基树脂及固化剂是制备高性能水性烘漆的关键。     

Determination of amiloride using a ds-DNA-modified pencil graphite electrode based on guanine and adenine signals

A sensitive electrochemical procedure based on ds-DNA interaction with amiloride at a ds-DNA-modified pencil graphite electrode (PGE) was introduced as a promising tool for determination of amiloride. An adsorptive stripping voltammetry was applied for the immobilization of ds-DNA on PGE in acetate buffer (pH 4.8). Differential pulse voltammetry (DPV) was carried out to obtain the change in the oxidation signal intensity of guanine and adenine before and after interaction with amiloride. The decrease in intensity of the guanine and adenine oxidation signals was used as an indicator for the sensitive determination of amiloride. Under the optimum conditions, a linear dependence of the guanine and adenine oxidation signals was observed to the amiloride concentration in the range of 0.75-240 μmol L⁻¹ with a detection limit of 0.5 μmol L⁻¹. The relative standard deviations of 10 replicate measurements of 1.0 and 10.0 μmol L⁻¹ amiloride concentrations were 4.7% and 5.3%, respectively. UV-vis measurements combined with DPV were also carried out to propose the most plausible mechanism for the interaction of amiloride and ds-DNA. The influence of potential interfering substances on the amiloride determination was studied. Finally, the ds-DNA-modified PGE biosensor was applied for the determination of amiloride in tablets and urine samples with satisfactory results.     

Preparation and properties of dual-cure polyurethane acrylate

Dual-cure polyurethane acrylates (PUA) with different double bonds content were synthesized by using aliphatic polyisocyanate and 2-hydroxyethyl acrylate (HEA). The molecular structures were identified by Fourier transform infrared (FTIR) spectrum and nuclear magnetic resonance (NMR). Molecular weight (M_w) and glass-transition temperature (T_g) of PUA were measured by gel permeation chromatography and DSC, respectively. The pendulum hardness, pencil hardness, flexibility and abrasion resistance properties of dual-cure system were tested, the results indicated that the pendulum hardness, pencil hardness, and MEK resistance increased, but the flexibility reduced with the double bonds content increased. The mechanical properties of dual-cure system were greatly improved after the heat treatment.     

水性丙烯酸酯汽车涂料制备及其漆膜性能研究

合成了水性丙烯酸树脂并用其配制了汽车罩光清漆,研究了硬/软单体配比、丙烯酸单体的用量、芳香酯单体的用量、氨基树脂固化剂/丙烯酸树脂的配比及固化条件对漆膜性能的影响。结果发现,硬/软单体配比为39/35,丙烯酸质量分数为6%,甲基丙烯酸苄酯(BNMA)质量分数为12%,固化剂/树脂配比为40/100,固化温度及时间分别为140℃和30 min时,固化漆膜具有优良的综合性能,其光泽度达到98(60°),冲击强度为0.50 kJ/m,硬度为2H,附着力为0级,耐溶剂、耐紫外老化性能良好。FT-IR分析显示氨基树脂/丙烯酸树脂漆膜固化后表征羟基和甲氧基的吸收峰强度显著变弱,表明氨基树脂和丙烯酸树脂发生了交联固化。     

GPTMS/AlOOH透明硬涂膜制备

为获得高硬度透明复合涂膜,加快其工业应用,在水性条件下,以价格低廉的γ-(2,3-环氧丙氧基)丙基三甲氧基硅烷(GPTMS)和一水软铝石为主要原料,以硝酸溶液控制pH,通过硬度测试和红外定量分析,研究了GPTMS/AlOOH透明硬涂膜的制备工艺。结果表明:涂膜的硬度可由Si—O—Si和Si—O—Al含量控制。将质量比为100∶46∶50∶2.8的GPTMS水解产物、AlOOH、去离子水和硝酸溶液在80℃反应2 h,得到预聚物,将其在125℃热固化2.5 h,可得到铅笔硬度达4H的透明涂膜。     

Mechanical thinning to make few-layer graphene from pencil lead

Simple, fast and low cost production of graphene and few-layer graphene (FLG) with high yield is presented. The synthesis consists of mechanical ablation of pencil lead on a harsh glass surface with simultaneous ultrasonication followed by a purification to remove the inorganic binder present in the pencil lead. The combination of several characterization techniques, i.e. SEM, TEM and Raman show that FLG with lateral size of few micrometers, consisted of 1 up to 20 and occasionally up to fifty sheets is obtained by this process.     

Crystalline and amorphous PEO based ceramic coatings on AA6061: Nanoindentation and corrosion studies

Present study reports the detailed nanomechanical and corrosion behaviours of crystalline and amorphous plasma electrolytic oxidation (PEO) coatings developed on Aluminium alloy-6061. The concentration of sodium silicate in the electrolyte is tailored to achieve crystalline and amorphous natures of the PEO coatings. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoprofilometry techniques are utilized to investigate microstructural and morphological properties of the PEO coatings. XRD studies confirmed that crystalline ceramic phases are obtained at lower silicate concentration while amorphous nature occurred for comparatively higher concentration of silicate in the electrolyte. Nanoindentation technique is utilized to study the mechanical properties such as hardness (H) and Young's modulus (E) of the PEO coatings. The scatter of the data is treated with well-established Weibull statistical method. Finally, in depth corrosion behaviour of the coatings are investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Amorphous coatings exhibited superior mechanical properties compared to the crystalline coatings. This is possibly linked with the presence of aluminosilicate phases and difference in silicon content in the coatings. However, as expected crystalline PEO coatings offer better corrosion resistance than the amorphous coatings and this behaviour is explained in terms of porosity contents of the coatings.     

The effect of crystallinity on the scratch hardness of poly(ether ether ketone)

Summary This paper describes a study of the surface properties of the poly(ether ether ketone) (PEEK) using a scratch hardness technique. A comparison of the hardness values determined for amorphous and crystalline PEEK shows that the crystalline polymer is harder. In addition, comparison of the scratch frictional behaviour indicates several friction mechanisms apply for this polymer.     

Mechanisms of microstructural deformation governing Vickers hardness in phase-separated calcium aluminosilicate glasses

The impact of microstructure on hardness in phase-separated calcium aluminosilicate glasses is investigated. Changes in hardness are governed by microstructure deformations that occur during indentation. Phase separation leads to decreased hardness due to the incongruent yielding of the droplet and matrix phases. Moreover, the deformation of microstructures possessing dilute, spherical droplets did not have a significant impact on hardness. Microstructures characterized by concentrated, acicular droplets were found to deform through a process of droplet coalescence. This process absorbs additional energy during yielding and results in glasses that deform through droplet coalescence possessing improved hardness.