Steel particles

The steel particles are covered with an AI2O3 layer before hot isostatic pressing [3.58]. 

Magnetic particles may form much more stable beds when subjected to a magnetic field. Saxena and Shrivastava(51) have examined the complex behaviour of spherical steel particles of a range of sizes when subjected to fields of different strengths, considering in particular the bed pressure drop, the quality of fluidisation and the structure of the surface of the bed. 

The ignition process is basically the same for any tubed firework, but when the sparks start to fly, the chemistry becomes very different. Sparks are self-luminous but they need atmospheric oxygen to sustain the high temperature oxidising reaction with the steel particles or other emitters that are present, as described in the previous chapter. 

In operation, the mealed gunpowder provides the gas and heat necessary for the combustion of the other fuels and oxidisers that are present. The potassium sulfide that is formed produces orange-red sparks, whereas the steel particles contribute with gold ones. Pine needle-shaped sparks may also be seen when a spark suddenly breaks up into smaller particles. This phenomenon is said to be the result of residual carbon particles exploding in a glowing, active material. 

Fig. 10.13 Fraction of hematite particles deposited on steel as a function of pH at 25°C (solid line). For each point 50 cm of the hematite sol (dmodai = 170 nm and 10 particles cm ) was passed through the bed at a flow rate of one cm min Dashed lines represent the electrophoretic mobilities of the hematite and of the steel particles (Matijevic, 1980, with permission).

The effect of powder concentration was not remarkable with stainless steel particles, but the model indicates the possibility of spherical deformation with materials of smaller strength. 

Figure 13.3.10 shows the typical spheroidal deformation of stainless steel particles with treatment time. As compared with the result of copper particles, the rate of spheroidal deformation was lower. Thus, the stainless steel particles were easier for stepwise adjustment of the shape index with treatment time. 

Fig. 13.3.10 SEM pictures of stainless steel particles prepared for different treatment times (a) t = 0 s (b) t = 30 s (c) t = 33 s (d) t = 1200 s. Key 15-20 p,m stainless steel particles were used. (From M Odani. Hokkaido Industrial Research Institute, and K Shinohara, Graduate School of Hokkaido University, with permission.).

Considerable caution must be exercised in contacting perchloric add with metals, e.g. the catalytic action has been reported [69] of steel particles in reducing the explosion temperature of mixtures of perchloric acid vapour and hydrogen [69],... 

Occasional explosions experienced during use of hot perchloric acid to dissolve steel samples for analysis [1] were attributed to formation of hydrogen—perchloric acid vapour mixtures and their ignition by steel particles at temperatures as low as 215°C [2],... 

Mechanism. Basically, fretting is a form of adhesive or abrasive wear, where the normal load causes adhesion between asperities and oscillatory movement causes ruptures, resulting in wear debris. Most commonly, fretting is combined with corrosion, in which case the wear mode is known as fretting corrosion. For example, in the case of steel particles, the freshly worn nascent surfaces oxidize (corrode) to FejO, and the... 

In powder metallurgy very high cooling rates are encountered. Calculations lead to an estimate of lO -ICH °C/s for the solidification of argon atomized steel particles [9], Welding and powder metallurgy are thus not directly covered by the experiments reported in the present work. 

One important field of application for dispersion-reinforced glass matrix composites is as biomaterials for implants and in orthopaedics. Bioactive sihcate and phosphate glasses and glass-ceramics are toughened by incorporating biocompatible second phases, for example titanium, silver or stainless steel particles or chopped fibres [20,24,54,76,77]. 

Consider a 1.2 mm in diameter spherical carbon-steel particle that is placed in the middle of an open to air microchamber (3.5 cm in length, 2.5 cm in width, and 2.5 mm in height) and in contact with deionized (DI) water. Two platinum electrodes located at the ends of the microchamber apply the desired voltages and produce 40 V/cm DC electric field from left to right. The carbon-steel sphere density is much higher than that of water and thus remains... 

Figure 4.32 Schematic structures of spinnerets (a) Laminar flow disturbed by drop of molten pitch formed on spinneret surface. Jet material with good wettability gives larger drop (b) Shape of spinneret hole with narrow and wider parts designed to convert from laminar to turbulent flow (c) Laminar flow disturbed by a plug of stainless steel particles or mesh. Source Reprinted with permission from Otani S, Oya A, In Kawata K, Umekawa S, Kobayashi A eds. Composites 86 Recent Advances in Japan and the United States. Proc Japan-US CCM III Jpn Soc Compos Mater, Tokyo, 1-23,1986. Copyright 1986, Japan Society of Composite Materials.

Figure 8.55 Mapping across a pharmaceutical tablet allows a buried steel particle to be visualized and identified. Contaminants such as this can be introduced from the manufacturing process and are typically caused by wear debris from mechanical mixing/compressing equipment. ( 2013 HORIBA Scientific, www.horiba.com/scientific. All rights reserved.)...

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