That energy becomes thermal energy in the metal/acid solution. Before the spring dissolves, the energy it stores is actually found in the forces between adjacent metal atoms. The crystals in the metal are slightly distorted, bringing the atoms in these crystals a little too close or a little too far from one another. Since each of these displaced atoms has a little extra potential energy, it is a little more chemically reactive than normal. When the acid attacks one of these atoms and pulls it away from the crystal, the atom comes away a little more easily than normal because it brings with it a little extra energy. This extra energy enters the solution, making the solution a little warmer than it would have become had the spring not been compressed.
Near room temperature, heat pipes use working fluids such as HFCs (hydrofluorocarbons, the replacements for Freons), ammonia, or even water. At elevated temperatures, heat pipes often use liquid metals such as sodium.
If you take a compressed metal spring and place it in a container of metal disso…
Solvents and fuels produced from petroleum (e.g., benzene, toluene, mineral spirits, gasoline, jet fuel) can build up a charge when they are poured or flow through hoses. They tend to hold a charge because they cannot conduct electricity well enough to discharge when in contact with a conducting material, like a metal pipe or container, that is grounded. When enough of a charge is built up, a spark may result. If the vapour concentration of the liquid in air is in the "flammable range" and the spark has enough energy, a fire or explosion can result.
Transferring a liquid from one metal container to another may result in static electrical sparks. To prevent the build up of static electricity and prevent sparks from causing a fire, it is important to bond metal dispensing and receiving containers together before pouring. Bonding is done by making an electrical connection from one metal container to the other. This ensures that there will be no difference in electrical potential between the two containers and, therefore, no sparks will be formed.
Bond containers by securely attaching a special metal bonding strap or wire to both containers. Some liquid transfer pumps have self-bonding hoses. Bonding can also be done by keeping a solid metal-to-metal contact between the containers themselves or between a metal container and a conducting nozzle. These last two methods are usually not reliable because a good electrical contact is often hard to make and maintain during the entire transfer. In addition, while grounding conductors can be covered or insulated (e.g., with a plastic coated cable), uninsulated conductors are preferred as defects are easier to see.
In the flammable liquid storage and dispensing area, ground dispensing drums. Grounding is done by connecting the container to an already grounded object that will conduct electricity. This could be a buried metal plate, a metallic underground gas piping system, metal water pipes or a grounded, metal building framework. Bonding both containers and grounding one of them "drains off" static charges and prevents the discharge of sparks. All grounding and bonding connections must be bare metal to bare metal. Remove all dirt, paint, rust or corrosion from points of contact. Specially designed and approved bonding and grounding wire assemblies are available from safety equipment retailers.
For portable tanks, intermediate bulk containers and non-bulk containers, NFPA advises to ground any metal parts on the container (and nearby conductive surfaces that the container may come in contact) and fill the container from the bottom through a long, grounded metal pipe. This procedure will reduce the amount of static charge produced and will enable the generated charge to relax (dissipate) through the metal pipe. Use the smallest container for the job. The risk of fire from static electricity increases with the volume of the container and the volatility of the liquid being used.
When filling non-conducting portable containers, the NFPA recommends that a grounded dip pipe or grounded wire be in the liquid in the container while it is being filled. The filling rate should be minimized, especially if there is filter in the line. Any metal parts of the container and metal funnel, if one is used, should also be grounded. When filling containers with low-conductivity liquids (i.e., ones with a conductivity less than 50 picoSiemens, pS), one should keep the grounded dip rod in the liquid for around 30 seconds after the filling is completed.
Metal containers for different food products. a Plain three-piece enamelled metal can body, b beaded three-piece enamelled can body, c two piece aluminium can, d metal container for confections, e tin can for mustard oil with aluminium foil as sealant layer, f metal container for premium quality tea and roasted cocoa beans and g multi-layered carton with aluminium foil layer
Electrolytes play a major role in body functionality. Among various functions, they take part in metabolism, determine the cell membrane potentials and osmolarity of body fluids and so forth. Major cations include hydrogen, sodium, potassium, calcium and magnesium ions. Major anions include hydroxide, bicarbonate, chloride, phosphate and sulphate ions. Dissolved salts are probably the most influential components for implant corrosion in vivo. Chloride ions (and other halides) enhance the corrosion of almost all metals and interfere with many methods of corrosion protection.
When an implant is placed in vivo, the disruption of blood supply to the bone is often accompanied by severe pathological infections that might affect the healing and cause electrochemical variations in the equilibrium state [48]. In addition, the pH of the body fluid can drop from 7.4 to 5.5 and it could take 10 to 15 days to recover its normal value. Bacterial infection could result in even a wider range of pH in vicinity of the implant surface, from acidic to alkaline (4.0 to 9.0, respectively). Laing [49] reported that the pH around a newly inserted implant can drop to as low as 4.0 due to the build-up of hematomas, a condition that could last for several weeks. The local decrease in pH could result in severe localized corrosion of the metal implant. In addition, H2O2 may form during the initial stages of the inflammatory response to the placement of an implant in vivo [50,51]. The level of the aforementioned pathological changes depends on the biological activity of any corrosion products released from the implant as well as on the implant size and shape; it could vary across the surface of the implant, possibly leading to the development of electrochemical cells [52]. The risk of localized corrosion due to local variations in pH in vicinity of titanium alloys has also been reported based on in vitro studies [53].
The most important characteristics of body fluids that influence the corrosion of metal implants are the chloride, dissolved oxygen and pH levels. Body fluids may seem to be slightly less aggressive than seawater, based on the lower pitting resistance equivalent number (PREN) of 26 and greater recommended to prevent pitting corrosion of stainless steels in vivo, in comparison to the value of 40 usually required for stagnant seawater [54]. However, the dissolved oxygen levels in blood are lower than in artificial solutions exposed to air atmosphere due to combination with haemoglobin, which is the main component of red blood cells. The partial pressure of oxygen in blood varies between 100 to 40 mmHg for arterial and venous blood, respectively. The corresponding value in air is 160 mmHg. Because most biomaterials rely on oxygen to repassivate, repassivation of metal surfaces is more difficult under conditions of low dissolved oxygen concentration. Indeed, deaeration of the solution with high-purity nitrogen gas to maintain low O2 concentration was found to better predict the in vivo performance of metal implants [55]. Since the partial pressure of oxygen varies widely within the body, from about 2.67 102 to 1.33 104 Pa, an implant surface can be in contact with anatomical environments of widely different oxygen partial pressures, thus possibly establishing aeration cells. Another gas, carbon dioxide (CO2), influences the corrosion in vivo by affecting the pH [41]. Bicarbonate levels are about twenty times higher in blood than in seawater [56].
The Pourbaix diagrams have some limitations [46]. Since these are equilibrium diagrams, we can only learn from them what cannot happen. We cannot deduce which reaction will happen at a measurable rate, because these diagrams do not reflect the kinetics. The fact that at a certain pH and potential a metal can corrode according to its Pourbaix diagram is no proof that it actually will do so. Whether passivation will or will not form depends on the nature of the oxide and on the environment in contact with it. Furthermore, potential-pH diagrams are usually given for the pure elements, while many metallic biomaterials are alloys. The corrosion behaviour of an alloy is rarely, if ever, a linear combination of the corrosion behaviour of its components. Even for a given composition, the corrosion of an alloy usually depends on metallurgical factors such as the grain size and heat treatment of the material. An extreme example is the high corrosion resistance of some of the so-called glassy metals or amorphous alloys, compared to crystalline alloys of the same composition. Other limitations of the Pourbaix diagrams: (1) they typically refer to pure water, but in body fluids there are other ions that may affect equilibria. (2) Their shape is affected by the species that are taken into account, thus previous knowledge of the specific system is required. (3) The pH is that in vicinity of the metal surface, which could differ significantly from the pH of the bulk solution. 2ff7e9595c
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