Blog home Caesarean or natural birth — which is safer? Women should formally have the right to choose to give birth by caesarean section — but they must also be offered counselling to help them make their decision, the National Institute for Clinical Excellence has decided.
Galvanizing protects the underlying iron or steel in the following main ways: The zinc coating, when intact, prevents corrosive substances from reaching the underlying steel or iron. The zinc protects iron by corroding first.
For better results, application of chromates over zinc is also seen as an industrial trend. After all of the zinc in the immediate area is consumed, localized corrosion of the base metal can occur.
History and etymology[ edit ] Galvanized nails Named via French from the name of Italian scientist Luigi Galvanithe earliest use of the term was, in early 19th-century scientific research and medical practice, stimulation of a muscle by the application of an electric current.
The term "galvanized" continues to be used metaphorically of any stimulus which results in activity by a person or group of people. In modern usage, the term "galvanizing" has largely come to be associated with zinc coatings, to the exclusion of other metals.
Galvanic paint, a precursor to hot-dip galvanizingwas patented by Stanislas Sorelof Parisin December In the case of automobile bodies, where additional decorative coatings of paint will be applied, a thinner form of galvanizing is applied by electrogalvanizing.
The protection provided by hot-dip galvanizing is insufficient for products that will be constantly exposed to corrosive materials such as acidsincluding acid rain in outdoor uses.
For these applications, more expensive stainless steel is preferred. Some nails made today are galvanized.
Nonetheless, electroplating is used on its own for many outdoor applications because it is cheaper than hot-dip zinc coating and looks good when new. This means that for carsbicyclesand many other light mechanical products, the practical alternative to electroplating bolts and nuts is not hot-dip zinc coating, but making the fasteners from stainless steel or stronger but much more expensive titanium.
Galvanized surface with visible spangle The size of crystallites grains in galvanized coatings is a visible and aesthetic feature, known as "spangle". By varying the number of particles added for heterogeneous nucleation and the rate of cooling in a hot-dip process, the spangle can be adjusted from an apparently uniform surface crystallites too small to see with the naked eye to grains several centimetres wide.
Visible crystallites are rare in other engineering materials, even though they are usually present. Thermal diffusion galvanizing, or Sherardizingprovides a zinc diffusion coating on iron- or copper-based materials. The advance surface preparation of the goods can be carried out by shot blasting.
The process is also known as "dry galvanizing", because no liquids are involved; this can avoid possible problems caused by hydrogen embrittlement.
The dull-grey crystal structure of the zinc diffusion coating has a good adhesion to paint, powder coatings, or rubber. It is a preferred method for coating small, complex-shaped metals, and for smoothing rough surfaces on items formed with sintered metal.
Eventual corrosion[ edit ] Rusted corrugated steel roof Although galvanizing will inhibit attack of the underlying steel, rusting will be inevitable after some decades of exposure to weather, especially if exposed to acidic conditions.
For example, corrugated iron sheet roofing will start to degrade within a few years despite the protective action of the zinc coating. Marine and salty environments also lower the lifetime of galvanized iron because the high electrical conductivity of sea water increases the rate of corrosionprimarily through converting the solid zinc to soluble zinc chloride which simply washes away.
Galvanized car frames exemplify this; they corrode much faster in cold environments due to road saltthough they will last longer than unprotected steel.
Galvanized steel can last for many decades if other supplementary measures are maintained, such as paint coatings and additional sacrificial anodes. The rate of corrosion in non-salty environments is caused mainly by levels of sulfur dioxide in the air.
In developed countries most larger cities have several galvanizing factories, and many items of steel manufacture are galvanized for protection.
Hot dip galvanized steel is also used for making steel frames as a basic construction material for steel frame buildings. Galvanic corrosion In the early 20th century, galvanized piping replaced previously-used cast iron and lead in cold-water plumbing.
Typically, galvanized piping rusts from the inside out, building up layers of plaque on the inside of the piping, causing both water pressure problems and eventual pipe failure. These plaques can flake off, leading to visible impurities in water and a slight metallic taste.
The life expectancy of galvanized piping is about 70 years,[ citation needed ] but it may vary by region due to impurities in the water supply and the proximity of electrical grids for which interior piping acts as a pathway the flow of electricity can accelerate chemical corrosion.
Pipe longevity also depends on the thickness of zinc in the original galvanizing, which ranges on a scale from G40 to G,[ clarification needed ] and whether the pipe was galvanized on both the inside and outside, or just the outside.
Since World War II, copper and plastic piping have replaced galvanized piping for interior drinking water service, but galvanized steel pipes are still used in outdoor applications requiring steel's superior mechanical strength. The use of galvanized pipes lends some truth to the urban myth that water purity in outdoor water faucets is lower, but the actual impurities iron, zinc, calcium are harmless.
Galvanized piping will eventually need to be replaced if housing stock is to outlast a 50 to 70 year life expectancy, and some jurisdictions[ which? One option to extend the life expectancy of existing galvanized piping is to line it with an epoxy resin.Natural Caesarean section is safe, popular and feasible and is not encouraging maternal requests for C-section births Date: June 5, Source: ESA (European Society of Anaesthesiology).
In , Cragin popularized the dictum, “once a caesarean section, always a caesarean section”. That was the era of the classical CS. In the present era of lower segment caesarean section (LSCS), cesarean-related morbidity .
The armoured application is the origin of the metaphorical use of the verb "galvanize", meaning to reinforce. In modern usage, the term "galvanizing" has largely come to be associated with zinc coatings, to the exclusion of other metals.
Galvanic paint, a precursor to hot-dip galvanizing, was patented by Stanislas Sorel, of Paris, in December A Summary of the Logic of Natural Selection Three inductions from observation and two nec essary deductive conclusion If Inductions (derived directly from observation) are true t hen the Deductions (A & B) necessarily follow.
Luigi Galvani, (born September 9, , Bologna, Papal States [Italy]—died December 4, , Bologna, Cisalpine Republic), Italian physician and physicist who investigated the nature and effects of what he conceived to be electricity in animal tissue. WOA! World Population Awareness is a non-profit web publication seeking to inform people about overpopulation, unsustainability, and overconsumption; the impacts, including depletion of natural resources, water, oil, soil, fertilizers, species loss, malnutrition, poverty, displacement of people, conflict; and what can be done about it: women's advancement, education, reproductive health care.