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Metallographic laboratory environmental safety measures

Writer:Anonymous   2020-02-26 11:51:39


(I) Basic requirements for environmental safety


The metallographic microscope should be placed in an acid-free, alkali-free, vibration-free, cool, dry room. The sample preparation laboratory room should be ventilated frequently. The humidity of toxic gases should not exceed the specified value. Information on precautions for chemical substances and emergency measures in case of burns and poisoning. The staff in the laboratory must be familiar with the performance of the reagents used and the corresponding precautionary safety measures. They must also be familiar with the first aid methods and fire suppression methods after an unfortunate accident. The tools used should be located nearby and checked for applicability within the specified period. The use of concentrated acids will increase the health hazards of workers. Especially when macro-etching samples, safety technology education should be conducted with special care, and corresponding written guidelines should be prepared for all processes. Workers should distribute work clothes and personal protective equipment in accordance with current standards, and pay special attention to ventilation facilities. Also note the following:


(1) The amount of reagents to be poured out and injected should not exceed the required amount for 2 to 3 days, and the remaining reagents should be stored in a specially established warehouse. All bottles must have a frosted stopper. The bottles must not be left open. Pay particular attention to the bottles containing reagents such as concentrated acids, ammonia and toxic liquids.


(2) Weighing and use of reagents must be performed in a well-ventilated environment or in an exhaust cabinet. Wear goggles, rubber gloves, and rubber apron. Flammable liquids such as ethyl acetate, alcohol, gasoline, benzene, etc. should not be placed in rooms with gas torches and small electric stoves.


(3) Explosive substances can be formed when certain reagents are deployed and used; collision, vibration and fire sources should be avoided when neutral sodium picrate is deployed; nitroglycerin may be formed when using nitric acid and glycerol.


(4) Many reagents are liable to form harmful vapors of fluorine and chlorine when heated and when they interact with metals. A similar situation applies to the use of various toxic substances, potassium or sodium sulfide, stele salts, and concentrated acid solutions, so an air extraction device must be used.


(5) Reagents that are highly absorbent and have a strong pungent odor must be stored in completely sealed containers, so that they can be stored in wax-sealed containers. For reagents that are easily decomposed in the light (pyrogallic acid, salt), dark glass containers should be used; for solvents that will corrode glass (such as HF), paraffin containers should be used.


(6) All poisons (KCN, HCN, HgCl2, stele salt, etc.) must be kept in a locked special sealed cabinet.


(7) After humans burn with HCQ, HF, HNO3, H2SO4, HC1 and other acids, the wound heals slowly. Some concentrated salt solutions (such as potassium bimonate, potassium iron halide, etc.) can corrode hands. When using the above substances, as with toxic substances, you must carry rubber gloves and carry out under a ventilation device.


(8) For first aid in metallographic experiments, linseed oil, or olive oil, lime water, 10% aqueous soda solution, 5% potassium ingotate solution, 3% ~ 6% Acetic acid solution, 1% ~ 2% hydrochloric acid solution, etc.


(-) Operational safety requirements


The laboratory shall formulate safe operating procedures, and shall also formulate safe operating rules for each device. Most operations should be performed in a fume hood with a protective plastic or non-breaking glass as a shielded sliding door. There is a water tank for cleaning and draining solution in the cabinet. Before pouring strong acid waste liquid into the sewer, it should be diluted with a large amount of water to reduce the danger of reacting with the chemical reagents contained in the pipeline. Chemical polishing fluids and etchant containing hydrofluoric acid (HF) are particularly harmful to pipelines. Care should be taken when discharging water-sensitive drugs such as anhydrous aluminum chloride or sodium metal. Fume hoods are generally separated by appropriate sections for placing acid and etchant vials (50 ~ 500mL), and the bottles are affixed with neat and eye-catching signs. Pay attention to the following points during specific operations:


(1) When cutting wheels, the cutting area should be isolated from the outside world. The main danger comes from the broken pieces flying out of the grinding wheel, but it is only limited to the sealed chamber. It is caused by the specimen not being clamped or forced too much. Of course, the specimen may be broken.


(2) Metal dust generated during grinding is often toxic, such as quilt, magnesium, lead, thallium and silver, etc. are highly toxic. Wet grinding is no exception. It is suitable for all samples in the field and has good results. Radioactive materials require special remote control devices, and safety precautions should be strictly observed.


(3) The drilling machine must be flattened when punching thin specimens, otherwise the specimen flying up will cause serious accidents. There is a danger of burns in the mounting machine or small heat treatment furnace. When heating up, a "hot" sign should be added in front of the furnace.


(4) Reagents are generally stored in glass bottles with glass stoppers, while glass bottles with plastic stoppers are used to hold pressure-generating solutions such as nitric acid and alcohol. However, a small hole must be drilled in the stopper to reduce the pressure, otherwise, the stopper will be automatically opened when the pressure build-up reaches a certain level.


(5) Most etchants or electrolytes are formulated by solids by weight and liquids by volume. Only in rare cases are the amounts of all components given by mass fraction. In terms of metallographic studies, the composition of the reagents is not critical. Weigh in a laboratory with a balance, and measure with a measuring cylinder. Large scale beakers are usually used for solution preparation. In case of HF, all containers should be made of polyethylene. Some reagents need to pay attention to the mixing order, which is especially important for dangerous goods. It is necessary to use distilled water when preparing, because most tap water contains minerals and reacts with it to form chlorides and fluorides. Not only the effect is not good, but it is easy to be unexpected. Cold water should be used in the preparation, and the reaction will be aggravated with warm water or heating during the preparation. Fill the container with a solvent such as water or alcohol, and then dissolve the specified salt or acid. The magnetic stirring device is very useful. Add dangerous reagents such as acid, and it should be added slowly while stirring. If sulfuric acid (HzSQQ) is listed, it should be added slowly afterwards and cooled if necessary.


(6) Metallurgical chemicals and solvents should be high-purity reagents. Although the price is higher, it is more suitable due to the small amount and safety and reliability. Chapter 3 [1 ~ 6] contains a large number of formulations with extremely dangerous etchants, chemical polishing solutions, and electrolytes. However, most did not include descriptions of safe operation and potential dangers. Fortunately, the amount is small, and it does not always lead to catastrophic consequences.