This study focuses on the friction and wear behaviors of reciprocatingly extruded Al–SiC composites. To increase the strength of metal matrix composites and refine the grains of the matrix some deformation processes can be applied, such as reciprocating extrusion (RE). For this reason, RE was carried out on a 6061 Al matrix by a SiC (20 μm) reinforced composite one. The billets were extruded under a pressure of 17.5 MPa at 573 K with a 10:1 extrusion ratio. The reciprocating extrusions were carried out by using up to 15 passes. 相似文献
A new amperometric urea biosensor based on gold nanoparticle embedded poly(propylene-co-imidazole) was developed for the determination of urea. The urease adsorbed on the polymeric film catalyzed the hydrolysis of urea to ammonium and bicarbonate ions and the ammonium was then electrooxidized on the gold electrode with the aid of gold nanoparticles at +0.2?V versus Ag/AgCl using differential pulse voltammetry. The biosensor provided a linear current response to urea concentration from 0.1 to 30?mM, a detection limit of 36?µM, a relative standard deviation of 2.43% (n?=?18), and excellent storage stability, as the current decrease was only 3% after 75 days. The operation of the biosensor was evaluated by the analysis of municipal sewage wastewater collected from the inlet pipe of the treatment plant of Zonguldak City in Turkey. The effects of possible interferants were also characterized. 相似文献
This paper presents an efficient method for stress measurement propagation. Pulse-echo method are used as stress measurement method on railway wheels. Hard service conditions and brake failures can lead to dangerous stress on the railway wheels. Stress measurements so important for wheels. Especially wheel expose to severe drag braking conditions in freight service. Residual stresses can significantly reduce the engineering properties and fatigue life of materials such as railway components. The paper presents results of stress state investigation of ER7 steel. Finally, the article briefly discusses how to adopt the pulse-echo method to railway wheels. Reducing cost of residual stress measurement investigated.
In this study, a new thermosensitive material was proposed as a carrier for gene delivery. The thermosensitive submicron particles were synthesized by the dispersion copolymerization of N-isopropylacylamide (NIPA) with a relatively new, cationic comonomer, N-3-dimethylaminopropylmethacrylamide (DMAPM) with higher ionization ability with respect to the commonly used cationic comonomers. To achieve particle sizes smaller than 1 microm, suitable for gene delivery, the total monomer concentration in the dispersion copolymerization was kept at a sufficiently low level. The size of poly(NIPA-co-DMAPM) particles was determined as 454 nm, by AFM in dry state. The poly(NIPA-co-DMAPM) particles showed both temperature and pH sensitivity in the aqueous media.The plasmid DNA adsorption onto the thermosensitive cationic particles was investigated at different temperatures and pHs. The adsorbed amount of plasmid DNA onto the particles was significantly increased by the introduction of cationic comonomer. The equilibrium plasmid DNA adsorptions up to 13 mg/g dry particles were achieved at physiological pH. Approximately 36% w/w of adsorbed plasmid could be desorbed from the cationic nanolatex. The results of biocompatibility studies performed with mouse fibroblast cells showed the suitability of thermosensitive cationic particles for intended application. 相似文献
A new solid-phase microextraction (SPμE) procedure has been developed for separation and preconcentration of Sn ions by using graphite furnace atomic absorption spectrometry (GFAAS). This technique is based on the complexation of Sn(IV) ions with 1-(2-pyridylazo)-2-naphthol (PAN). The poly (ε-caprolactone-b-4-vinyl benzyl-g-dimethyl amino ethyl methacrylate) polymer (PCL vacr) was used as an adsorbent, and it was loaded in micropipette tip of syringe system. Sn(IV) ions were adsorbed on polymer at pH 6. Different experimental conditions were optimized such as pH, amount of complexing agent, and amount of adsorbent. The detection limit (LOD), limit of quantification, preconcentration factor (PF), and relative standard deviation (RSD) were found as 4.5 ng L?1, 13.5 ng L?1, 100, and 3.3%, respectively. Certified reference materials were used to confirm the accuracy of the investigated procedure, and the procedure was successfully practiced for determination of entire concentration of tin within beverages and different food samples. 相似文献
A process for producing boric acid from ulexite and the recovery of the product by flotation is described. It was found that the degree of conversion of ulexite to boric acid decreased with rising HCl concentration. The undissolved mineral, together with other impurities such as clays, could be depressed by Quebracho, Orzan-S, Daxad-23 or starch, the first two being more effective. Concentrates assaying 97.1% H3BO3 were obtained without resorting to recrystallisation of the product. No flotation reagents other than the above-mentioned were necessary for the process. 相似文献
The effect of metal ions (Co, Cu, Ni, Pb, Zn) on the molecular weight distribution of humic substances (HSs) obtained from compost is studied. We believe this is the first of this type of study applied in this way to humic substances. Size exclusion chromatography is coupled with two on-line detection systems (spectrophotometric and ICPMS) to study the binding of metal ions by humic substances leached from compost. ICPMS provided highly specific, sensitive, and multielement analytical information that enabled obtaining direct experimental evidence for the participation of metal ions in molecular size distributions of humic compounds. The compost extract or its high molecular weight fraction (>5,000) was put in contact with EDTA or citrate ions, thereby competing with HSs for binding metals. The experiments were carried out by varying the pH maintained by Tris-HCl or CAPS buffer (pH 8.0 and 10.3) and keeping the ionic strength constant. The elution profile of humic substances using UV/ visible detection was compared with those from ICPMS detection of Co, Cu, Ni, Pb, and Zn in the same chromatographic runs. The results obtained suggested that both bridging between small molecules and complexation/ chelation by individual molecules are involved in metal ion binding to humic substances. The use of ICPMS to study the role of metal ions in aggregation/disassociation of humic substances proposed in this work is promising. Coupling element-specific detection with SEC or other separation systems allows better understanding of the mobility and bioaccessibility of elemental species in the environment and further elucidation of the dissolved humic structure. 相似文献