ABSTRACT
We present a facile method for the preparation of bimetallic AuAg nanoparticles (NPs) with controlled size and composition rendering them ideally suitable for optical and catalytic applications. In analogy to methods for the generation of monometallic Au and Ag NPs, AuAg NPs were prepared inside polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block-copolymer micelles formed in toluene, by loading the P4VP cores of the micelles first with AgNO(3) and then with HAuCl(4). In contrast to the reverse sequence of loading, homogenously bimetallic AuAg particle arrays were achieved after reduction carried out in solution with hydrazine monohydrate as the reducing agent. TEM reveals that stable and spherical NPs can be prepared well separated from one another and with a narrow size distribution with diameters of â¼3 nm. The bimetallic NP composition was confirmed by energy-dispersive X-ray spectroscopy (EDX) of single NPs. The atomic ratio of Ag and Au contained in single particles is in good agreement with the relative concentrations of both metals used in the synthesis which was confirmed by atomic absorption spectroscopy. The atomic ratio Au : Ag was systematically varied between 3 : 1 and 1 : 3. For all ratios UV-vis spectra showed a single plasmon band. Its wavelength varied from 430 for Au : Ag = 1 : 3 to 515 nm for Au : Ag = 3 : 1, showing a linear dependence on the relative amount of gold within the range of plasmon wavelengths from monometallic gold (538 nm) to silver (415 nm).
Subject(s)
Gold/chemistry , Metal Nanoparticles/chemistry , Micelles , Polystyrenes/chemistry , Polyvinyls/chemistry , Pyridines/chemistry , Silver/chemistry , Metal Nanoparticles/ultrastructure , Particle Size , Polystyrenes/chemical synthesis , Polyvinyls/chemical synthesis , Pyridines/chemical synthesisABSTRACT
AIM: To evaluate two NiTi wires with different carbon and oxygen contents in terms of mechanical resistance to rotary bending fatigue (RBF) under varied parameters of strain amplitude and rotational speed. METHODOLOGY: The wires produced from two vacuum induction melting (VIM) processed NiTi ingots were tested, Ti-49.81 at%Ni and Ti-50.33 at%Ni, named VIM 1 and VIM 2. A brief analysis related to wire fabrication is also presented, as well as chemical and microstructural analysis by energy dispersive spectroscopy (EDS) and optical microscope, respectively. A computer controlled RBF machine was specially constructed for the tests. Three radii of curvature were used: 50.0, 62.5 and 75.0 mm, respectively, R(1), R(2) and R(3), resulting in three strain amplitudes ε(a) : 1.00%, 0.80% and 0.67%. The selected rotational speeds were 250 and 455 rpm. RESULTS: The VIM 1 wire had a high carbon content of 0.188 wt% and a low oxygen content of 0.036 wt%. The oxygen and carbon contents of wire VIM 2 did not exceed their maximum, of 0.070 and 0.050 wt%, according to ASTM standard (ASTM F-2063-00 2001). The wire with lower carbon content performed better when compared to the one with higher carbon content, withstanding 29,441 and 12,895 cycles, respectively, to fracture. CONCLUSIONS: The surface quality of the wire was associated with resistance to cyclic fatigue. Surface defects acted as stress concentrators points. Overall, the number of cycles to failure was higher for VIM 2 wires with lower carbon content.
Subject(s)
Dental Alloys/chemistry , Dental Instruments , Root Canal Therapy/instrumentation , Stress, Mechanical , Carbon/chemistry , Dental Stress Analysis , Equipment Failure , Materials Testing , Nickel/chemistry , Oxygen/chemistry , Titanium/chemistryABSTRACT
Primary esophageal melanoma is a rare tumor. A 35 year old male with primary malignant melanoma of the esophagus is reported. He presented with dysphagia and weight loss. At autopsy a fusiform polypoidal growth was seen in the middle third of the esophagus. Microscopic sections showed a malignant melanoma in an in situ as well as invasive form.
