Preparation of a Duplex Nanocrystalline Coating by Magnetron Sputtering and Its Oxidation Performance.

A duplex nanocrystalline coating was prepared in this study by magnetron sputtering on N5 single-crystal super alloy (Ni: Bal, Co: 7.5, Cr: 7.0, Al: 6.2, Ta: 6.5, Re: 3.0, Mo: 1.5 and W: 5.0, wt%). The novel nanocrystalline coating consists of two layers, the inner layer having the same composition with the alloy substrate for avoiding elements inter diffusion while the outer layer has 7.6 wt% higher Al to quickly ensure the formation of a protective Al2O3 layer. Both two layers were deposited within one magnetron sputtering apparatus that contained two targets. The main target was having the same alloy substrate in composition and secondary target with pure Al. The difference in Al content between the two layers was achieved by controlling the secondary target during sputtering. This study revealed a way for preparing a series of similar coatings with varying compositions and improving performance. After oxidation at 1050 °C, a protective Al2O3 layer was quickly formed on the duplex nanocrystalline coating and no TCP phases were detected in the alloy substrate.

Effect of kerosene combustion atmosphere on the mild steel oxide layer.

In arson cases, accelerants were usually used by criminals to achieve the purpose of rapid arson. Therefore, fire investigators aim to determine whether accelerants was used in the fire scene. Metallic material has to react with corrosive gas around it at high temperature and the oxidation products may store the information of reactants. Accelerants present in fire scenes impart some oxidative characteristics on metallic materials. The aim of this work is to figure out the possibility to identify the presence of accelerant in a fire according to the oxidation patterns of metallic material. This paper researched the oxidation behavior of mild steel at high temperature in a simulated flame environment. The surface morphological and cross-sectional microstructural features of the samples were characterized by X-ray diffractions, X-ray photoelectron spectroscopy and scanning electron microscopy with energy-dispersive spectroscopy analysis after oxidation. The carbon in the combustion atmosphere had a carburizing effect on the metal oxide layer. It was mostly C-C, C-O and C=O of organic matter could be used as in fire investigation. Various oxidizing atmosphere composite systems promote the formation of metal oxide layers. And bidirectional oxidation mode in the oxide layer further accelerates the oxidation rate. The (wustite) FeO phase was not found in the oxide layer because of the strong oxidation of the combustion atmosphere. These results offer complementary information in fire characteristics, which combining the characterization of surface scale with traditional chemical analysis of recovering ignitable liquid residues from fire debris are expected to offer crucial information for determining the presence of combustion accelerants at a fire scene.

The Optimal Distance of the Electrode to the Lifting Film Surface when Lifting Dust Footwear Impressions Using an Electrostatic Dust Print Lifter.

Footwear impressions are one of the valuable physical evidence encountered at crime scenes and its identification can facilitate narrowing down the suspects and establishing the identity of the criminals. The technique of electrostatic lifting (ESL) dust shoeprints at crime scenes is well established with scenes of crime examiners. And in the procedure, the recovery of the original item containing the impression should be made as good as it can and not damage the marks. In this study, the different particle sizes of SiO2 were used to simulate dust and light soil residues, comparing different particle sizes and electrode positions were used to compare the adsorption ability on the surface of electrostatic lifting film in high-voltage electrostatic field for the collection of shoeprints. The results indicated that lifting film in electrostatic field will be pressed down to the dust surface, the compaction and electrostatic adsorption force will vary with the distance between the high-voltage electrode and film surface. Reducing the distance can increase the electric field strength near the lifting film, and the adsorption capacity of Mylar aluminum-plating film to dusts can be improved significantly. Adsorption capacity of the lifting film was related to the size of dust particles and significantly improved with the increase of the particle charge. The optimum distance which can get the best adsorption capacity between the electrode and film surface is from 10 to 15 mm.

Visual and oxide analysis for identification of electrical fire scene.

Three aluminum wires with different melted mark, which were found inside a burned distribution board from the electrical fire debris in rural areas of Northeast China were characterized to determine the cause of fire. By visual and microstructure/metallographic analysis, one melted bead shows typical morphology (microstructure/characteristics) as a result of overheating or electric short circuit (ESC) arc beads which was identified as the most possible ignition source. The macro-/micro-structure of the metallic wire, the chemical composition of the beads surface and the state of the polymer insulating sheath combining the tension state of the electric wire provided solid evidence on the exposure temperature and time of each aluminum wire. Consequently, the fire source was identified. Therefore, the characterization on the macro-/micro-structure and chemical composition of metallic surface with scientific technique is greatly helpful in determining heating process of metallic parts and subsequently the cause of fire.