Lead oxide: properties, production, application, harm
Historyfor the First time white lead was described in the writings of the Greek writer Dioscorides in the fourth century before Christ. Already knew about the properties of lead and was able to produce paint. A little later the manufacturing technology of white, or, as they call them, cerussa, already described by Roman writers such as Vitruvius, Pliny and Theophrastus. In “new” the light of white lead first appeared in Holland in the Middle ages. Factory outlet white very quickly found a wide circulation, and their consumption is constantly growing. Despite this, the scientist Bergman only by the end of the eighteenth century could reveal the chemical composition of white.
as for Russia, the history of the use and the manufacture of white lead is not so ancient, a hundred years ago they began to produce in us. The paint is lead-based in large quantity produced in Yaroslavl, which is considered a center of production of white. Today there are several factories involved in the production of white brands, which are popular around the world.
Scopeit is Forbidden to use white lead as a solvent for other colors. The same applies to their use of the painting because of the high toxicity of the product. In exceptional cases the use of white lead for metal surfaces.
If, however, is the use of white lead in the work, strict observance of safety rules prescribed in the case of using such drugs. Due to the harmful effects on the human body even as a part of the paint shall be white lead.
due to the high toxicity the use of white is regulated at the legislative level. So, the laws of 1909 and 1926 years influenced the dramatic decrease in the annual production of these paints in France. Twelve paint factories in this country in the year produced more than 20,000 tons of white, at the same time, the volume does not exceed 1,000 tons. These laws, unfortunately, apply only to the territory of France, in other countries, the use of white lead is not confined to law.
Properties of white leadThey are produced in the form of a white heavy powder having a granular structure. If exposed to vapours of acetic acid on lead and white lead are formed. The color of them, judging by the title, white. Because of the peculiarities of the production process in the finished product contains a small amount of lead sugar. This affects the smell of white lead, they have a slightly sour flavor, and the ratio of primary acetic salts of lead shall not exceed 1% of the total number of impurities.
Mineral paints, including white lead, have a high hiding power and a short drying time. Up to 10% of the total weight of the paints is their oil absorption. Outdoor white very quickly harden, and it occurs throughout the thickness of the layer of paint. Due to this quality is so popular in painting in a layered technique and the production of oil coatings of ground white lead.
Structure, and, consequently, the ability to rapid drying of these paints are easily transferred to other materials, resulting in even a slow-drying paint dry out quickly throughout its layer. Of particular value they are acquired for podmalevka, as is suitable for subsequent dyeing, with good contact with the subsequent layers, and do not crack.
the Downsides to using white leadAlong with the obvious benefits of using lead paint, they have a number of significant drawbacks.
first and foremost it is worth noting the high toxicity of the powder. When rubbing is necessary to observe all safety rules, in order that the powder was not sprayed. Known not only for cases of severe poisoning, but deaths.
white Lead is able to change its light. When exposed to hydrogen sulfide paint it first starts to brown and then turns black. This happens only in the case if the whitewash to insufficient amount of the binder element. However, this process is reversible. To purchase the painted surface, the original form must paint treating with hydrogen peroxide, capable of converting the black sulphide of lead into white sulphate.
In an alkaline medium white is highly unstable, so they are not suitable for alkaline tempera and frescoes.
In the painting was observed such specificity. White lead ground with linseed oil, have the ability to change the light. If the painting is turned away from the window and toward the wall, the paint based on white lead yellow, but is able to return the initial color if some time she will be exposed to direct sunlight.
a Kind of whitetoday, there are different types of white. Lead, zinc and titanium are the most common.
Lead & ndash; the most ancient, they are often used by the old artists. The advantage of them is that you can apply transparent layers, and the paint dries very quickly. It has a flexible structure and is more resistant. But the main drawback is its toxicity.
Titanium white. They are not less popular among artists and characteristics similar to lead white. This paint by the tone of the white, but its drawback is that it is absolutely not transparent and completely fills other colors.
These white is very popular with pottery masters. They intervene directly in the clay, and if that's not enough then applied on top a thin layer.
Zinc oxide. They are not as thick as titanium white and therefore they are used for tinting and applying transparent layers. The downside of this paint remains for a long drying time.
DutchThis is the first and most ancient method for the production of white lead. For this method, the lead plate width of 2-3 mm and cut into strips up to a length of 6 cm and placed in a glazed clay pots at the same time turning the spiral. The pots should be about 1 liter, and in height not exceed 20 cm to the same pour 250 ml of vinegar. Rows of pots are placed in a brick chamber, and, interspersed with layers of horse manure, added. At the bottom make a layer of horse manure, it is the first layer of pots on top they are covered with lead plates and planks, and the spaces between the pots are also filled with manure. Thus the pots are set by the layers to the top.
During fermentation, manure generates heat that contributes to evaporation of acetic acid. Under catalyzation of oxygen from the air formed acetic-lead salt is converted into uglevonom, which is lead white. The process of separating the oxide from the lead plates of the most laborious, most often this involved machine. The most widely used for these purposes is the instrument horn.
German wayGerman Distinction of the method from the Dutch only in the details. Lead sheets shall be placed not in pots and hung in a brick and wooden cells. And the process of exposure to acetic acid and oxygen are identical. Most often, this method uses a device Major.
French wayTenar was offered to the French method of making white lead. Him first made a solution of acetic salts of lead, through which then pass carbonic acid. As a result, released white, and the average of the acetate-lead salt remains in solution. This method is continuous, as in the waste solution again dissolves the litharge, forming a basic salt.
EnglishThis method of extraction of white lead more complex, and that is why in recent times less is applied. Horizontal drums are placed litharge, moistened 1% solution of sugar of lead. There he with the help of the stirrer rotates. When this is treated with a jet of carbon dioxide.
For this method, it is extremely important that the litharge was not impurities, otherwise white can acquire an undesirable color.