Matters needing attention in the storage and use of chemicals in metallographic laboratory

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release time : 2020-06-01 15:10:15

Commonly used chemicals are toxic, corrosive, flammable and explosive. Therefore, the metallographic laboratory can only save a small amount of reagents for short-term use. Flammable solvents should be insulated; ideally stored in a metal cabinet on the ground. Materials that are easily oxidized must not be stored in the same cabinet as the oxidant.


(1) Precautions for using dangerous (toxic) substances


Be especially careful when using chemicals. Almost all chemicals and certain metals, even in small concentrations, often cause harm to the human body. Such harmful substances can enter the body from inside the respiratory and digestive organs, and from the skin and eyes. Therefore, the preparation of metallographic samples should in principle be the same as the safety rules of chemical laboratories.


Some important precautions are:


(1) All storage vessels must be clearly marked.


(2) It is not allowed to dump chemical products with high concentration, and pay attention to the environmental protection regulations of wastewater.


(3) All dangerous goods should be stored in a cool, fireproof and dark place.


(4) When handling corrosive substances (acids, alkalis, hydrogen peroxide, various salt solutions and molten salts), wear protective glasses, rubber gloves, and work clothes to protect your eyes and skin. The vapors of these items are also often toxic, so ventilators (ventilators) should be opened whenever possible. When generating toxic gases and vapors, you must work in an exhaust hood, and wear a gas mask if necessary.


(5) When preparing the etchant, put corrosive chemicals into the thinner (water, ethanol, glycerin, etc.) (for example: add water first, then add acid!).


(6) Combustible and explosive materials (benzene, acetone, acetic acid, perchlorate, nitrate, etc.) must not be heated or near an open flame.


(7) Toxic materials, such as coated materials and radioactive materials (uranium, strontium, cups, and alloys and compounds), should be worked in a protective box or so-called "lead wall protective room" when preparing the sample grinding discs.


There must be instructions for particularly harmful items! In addition, the following items should also be noted:


(1) Perchloric acid of higher concentration (over 60%) is flammable and explosive. The situation is especially severe in the case of organic matter or easily oxidized metals such as banknotes (Bi). Must avoid excessive concentration or heating. Care must be taken during electrolytic polishing and etching, and should not be stored in plastic bottles. In the mixture of perchloric acid and ethanol, the explosive alkyl perchlorate may be formed, and excessive concentration and heating must be avoided.




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(2) All solutions prepared with perchloric acid are flammable and explosive. Perchloric acid must be added to the solution with constant stirring. During mixing and during use, the temperature must not exceed 35T, so it needs to work in the cooling tank. Work behind the protective cover and wear protective glasses whenever possible!


(3) A mixture of ethanol and hydrochloric acid may react differently (aldehyde, fatty acid, explosive nitride, etc.). The explosiveness increases with the size of the molecule. The content of hydrochloric acid in ethanol must not exceed 5%, and in methanol must not exceed 35%. Do not save the mixture!


(4) The mixture of ethanol and phosphoric acid may be esterified. Some of these phosphates are highly toxic to the human nervous system and can be absorbed through the skin or breathed into the body, causing serious harm.


(5) Dimethyl sulfate may form in a mixture of methanol and sulfuric acid, which is odorless, odorless, but extremely toxic. Dimethyl sulfate absorbed by the skin or inhaled (also through a gas mask) can also reach a lethal dose. But the sulfates of higher alcohols are not dangerous poisons.


(6) The mixture consisting of oxidation (VI) and organic matter is explosive. Be careful when mixing, don't save!


(7) Both lead and lead salts are very toxic. The damage caused by lead poisoning does not diminish over time and can accumulate. Caution should also be exercised when using cadmium, xuan, shackles, mercury and other heavy metals and their compounds.


(8) All 氤 compounds (CN) are very dangerous because of the easy formation of hydroxyacid (HCN), which is a poison that acts quickly and in small concentrations and can be fatal.


(9) Hydrofluoric acid is not only toxic to skin and breath, but also an etchant to glass. Therefore, when using hydrofluoric acid, there is always a risk of damaging the front lens of the objective lens. After etching with a solution containing hydrofluoric acid and before taking a microscope photo, the sample should be thoroughly rinsed (at least 15 min!) And dried.


(10) Bitter acid tincture is explosive.


(―) Precautions for electrolytic etching


During electrolytic etching, the following points should be noted:


(1) Perchloric acid containing organic substances has the danger of explosion; the method of tank cooling should be adopted. Care should be taken when configuring cold electrolyte, and the current density should be low during operation.


(2) Ming acid and hydrofluoric acid are less dangerous but toxic; separate protective devices should be used to reduce the temperature of the tank by using strong ventilation shafts.


(3) Nitric acid containing organic compounds is toxic; separate protective devices must be used in strong ventilation shafts.


(4) Sulfuric acid and phosphoric acid are less toxic, but they still need to use strong ventilation shafts and separate protective devices.


(5) The boiled compound electrolyte contains strong poisons, so it can only be used if the special rules are followed.


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