Small crucible for big use

Different from the crucible used to make magic medicine in Harry Potter, the crucible in the real laboratory is mainly used to evaporate, condense or crystallize the solution and burn the solid matter Chemical materials with shorter chemical bond can stand higher temperature, and those with longer chemical bond can easily obtain enough energy to break them Therefore, some of the chemical bonds are short, and the materials forming the spatial network structure are also wear-resistant materials The crucibles commonly used in the laboratory must have been seen or used by everyone Have all kinds of crucibles been used for children's shoes? Ha ha, let's take a look at the types of crucibles! Different crucibles, due to different use conditions, need to pay attention to many different places! PS: there are some questions at the end of the article The common metal crucibles are: first, platinum crucible, also known as platinum, is more expensive than gold Because of its many excellent properties, it is often used The melting point of platinum is as high as 1774 ℃, and its chemical properties are stable After burning in the air, platinum does not undergo chemical changes or absorb water Most chemical reagents have no corrosive effect on it 1 Characteristics: it can resist the corrosion of hydrofluoric acid and molten alkali metal carbonate Platinum is different from glass and porcelain in its important properties, so it is often used for precipitation, burning and weighing, hydrofluoric acid melting sample and carbonate melting treatment Platinum is a little volatile at high temperature, so it needs to be corrected after burning for a long time The loss of 100 cm 2 platinum is about 1 mg when it is burned at 1200 ℃ for 1 h, and it is almost non-volatile below 900 ℃ 2 The use of platinum containers shall comply with the following rules: (1) a strict system shall be established for the collection, use, consumption and recovery of platinum (2) platinum is soft, even the alloy containing a small amount of rhodium and iridium is also soft, so do not use too much force when taking platinum containers to avoid deformation During the debonding process, sharp objects such as glass rods shall not be scraped from the platinum vessels to avoid damage to the inner wall; nor shall hot platinum vessels be suddenly put into cold water to avoid cracks The deformed platinum crucible or vessel can be corrected by the water model with the same shape (but the brittle part of platinum carbide shall be corrected by uniform force) (3) Platinum containers should not contact with any other metals when heated, because platinum is easy to form alloy with other metals at high temperature Therefore, the platinum crucible must be placed on the platinum tripod or on the supports of ceramics, clay, quartz and other materials for burning, or on the electric heating plate or electric furnace lined with asbestos plate for heating, but it cannot directly contact with the iron plate or electric furnace wire The crucible tongs used should be covered with platinum head Nickel or stainless steel tongs can only be used at low temperature 3 Cleaning method of platinum containers: if Platinum containers have spots, they can be treated separately with hydrochloric acid or nitric acid If it is not effective, potassium pyrosulfate can be used to melt in a platinum vessel at a lower temperature for 5-10 min after the melt is poured out, the platinum vessel can be immersed and boiled in hydrochloric acid solution If it is still invalid, sodium carbonate melting treatment can be tried again, or wet fine sand (passing 100 mesh sieve, i.e 0.14 mm sieve hole) can be used for gentle friction treatment 2 The price of gold in gold crucible is cheaper than that of platinum, and it is not eroded by alkali metal hydroxide and hydrofluoric acid, so it is often used to replace platinum vessels, but the melting point of gold is low (1063 ℃), so it cannot withstand high temperature burning, and it must be used below 700 ℃ Ammonium nitrate has an obvious erosive effect on gold, and aqua regia can not contact with the gold utensil The use principle of gold ware is basically the same as that of platinum ware 3 Silver crucible 1 Characteristics: the price of silver crucible is relatively low, and it is not eroded by potassium hydroxide (sodium) In the melting state, it only slightly erodes near the edge of air The melting point of silver is 960 ℃, and the use temperature is not more than 750 ℃ After heating, a layer of silver oxide will be formed on the surface, which is unstable at high temperature, but stable below 200 ℃ The silver crucible just taken out from the high temperature shall not be cooled with cold water immediately to prevent cracks Silver is easy to react with sulfur to form silver sulfide, so it is not allowed to decompose and burn sulfur-containing substances in silver crucible, and alkaline sulfuration reagent is not allowed Molten aluminum, zinc, tin, lead, mercury and other metal salts can make silver crucible brittle Silver crucibles are not used to melt borax When using sodium peroxide flux, it is only suitable to sinter, not to melt 2 Do not use acid when extracting and washing molten materials, especially concentrated acid When cleaning silver utensils, use slightly boiling dilute hydrochloric acid (1 + 5), but it is not suitable to heat the utensils in acid for a long time The mass of silver crucible will change after burning, so it is not suitable for the weighing of precipitation IV the melting point of nickel crucible is 1450 ℃, which is easy to be oxidized by burning in air, so Nickel Crucible cannot be used for burning and weighing precipitation Nickel has a good resistance to the erosion of alkaline substances, so it is mainly used in the melting treatment of alkaline flux in the laboratory 1 Basic fluxes such as temperature controlled sodium hydroxide and sodium carbonate can be melted in a Nickel Crucible, and the melting temperature is generally not more than 700 ℃ Sodium oxide can also be melted in the Nickel Crucible, but the temperature should be lower than 500 ℃, and the time should be short, otherwise the erosion will be serious, which will increase the content of nickel salt brought into the solution and become the impurity in the determination 2 Pay special attention to the acid solvents such as potassium pyrosulfate, potassium bisulfate and the solvent containing sulfide can not be used in Nickel Crucible If sulfur compounds are to be melted, they should be carried out in an oxidizing environment with excessive sodium peroxide Molten aluminum, zinc, tin, lead and other metal salts can make the Nickel Crucible brittle Silver, mercury, vanadium compounds and borax can not be burned in a nickel crucible The New Nickel Crucible should be burned at 700 ℃ for several minutes before use, so as to remove oil contamination and form oxide film on its surface, so as to prolong its service life The crucible after treatment should be dark green or gray black After that, wash it with water before use If necessary, add a small amount of hydrochloric acid to boil it for a while, then wash it with distilled water and dry it for use V iron crucible the use of iron crucible is similar to nickel crucible It is not durable as nickel crucible, but it is cheap and suitable for the melting of sodium peroxide It can replace Nickel Crucible Iron crucible or low silicon steel crucible shall be passivated before use First, soak it in dilute hydrochloric acid, then rub it with fine sandpaper, wash it with hot water, then soak it in 5% sulfuric acid + 1% nitric acid mixed solution for several minutes, then wash it with water, dry it, and burn it at 300-400 ℃ for 10 minutes Vi the porcelain dish used in the porcelain crucible laboratory is actually a glazed pottery It has a high melting point (1410 ℃) and can withstand high temperature burning For example, the porcelain crucible can be heated to 1200 ℃, and its quality changes little after burning, so it is often used for burning and weighing precipitation The high type porcelain crucible can process the sample under the condition of air isolation Note: the coefficient of thermal expansion of the porcelain dish used in the laboratory is (3 ~ 4) × 10-6 During the operation of high temperature evaporation and burning, the sudden change of temperature and uneven heating should be avoided to prevent breakage The stability of porcelain dish to acid and alkali is better than glassware, but it can't contact hydrofluoric acid Ceramic crucibles are not resistant to caustic soda and sodium carbonate corrosion, especially they cannot be melted Some substances that do not interact with porcelain, such as MgO and C powder, are used as fillers, and basic flux is wrapped in a quantitative filter paper in a porcelain crucible to melt silicate samples, which can partially replace platinum products Porcelain dishes are widely used because of their strong mechanical properties and low price 7、 Characteristics: transparent quartz glass is made of natural colorless and transparent crystal by melting at high temperature Translucent quartz is made of natural pure quartz or quartz sand, which is translucent because it contains many bubbles that are not discharged during smelting The physical and chemical properties of transparent quartz glass are better than that of translucent quartz It is mainly used to make laboratory glass instruments and optical instruments The coefficient of thermal expansion of crystal quartz crucible quartz glass is very small (5.5 × 10-7), only one fifth of that of extra hard glass Therefore, it can withstand the hot and cold After the transparent quartz glass is burned to the red heat, it will not burst when it is put into the cold water The softening temperature of quartz glass is 1650 ℃, which has high temperature resistance Quartz crucible is usually used for the melting of acid flux and sodium thiosulfate, and the service temperature shall not exceed 1100 ℃ Its acid resistance is very good, except hydrofluoric acid and phosphoric acid, any concentration of acid has little interaction with quartz glass even at high temperature Quartz glass is not resistant to hydrofluoric acid corrosion, phosphoric acid can also act on it above 150 ℃, strong alkali solution including alkali metal carbonate can also corrode quartz, but the corrosion is slow at room temperature, and the corrosion is accelerated when the temperature increases The appearance of quartz glass instrument is similar to that of glass instrument It is colorless and transparent, but it is more expensive, brittle and fragile than that of glass instrument Special care must be taken when using it It is usually stored separately from glass instrument and kept properly ————————————————————————————————————————————Don't think there is no plastic crucible except for metal, ceramics and quartz 8 Polytetrafluoroethylene crucible 1 Characteristics Polytetrafluoroethylene is a thermoplastic with white color, wax like feeling, stable chemical properties, good heat resistance, good mechanical strength, and the maximum working temperature of 250 ℃ Generally, it is used below 200 ℃, which can be used to treat hydrofluoric acid instead of platinum vessel In addition to molten sodium and liquid fluorine, it can resist the corrosion of all concentrated acids, bases and strong oxidants, and it can not change when boiling in aqua regia In terms of corrosion resistance, it can be called "King" of plastics Polytetrafluoroethylene crucible with stainless steel cover has been used in the treatment of ore samples and digestion of biomaterials Polytetrafluoroethylene has good electrical insulation and can be machined 2 Pay special attention to the sharp decomposition above 415 ℃, and release toxic perfluoroisobutylene gas CBG's own Teflon crucible IX and corundum crucible natural corundum are almost pure alumina Artificial corundum is made of pure alumina by high temperature sintering It has high temperature resistance, melting point of 2045 ℃, high hardness, and considerable corrosion resistance to acid and alkali Note: corundum crucible can be used for melting and sintering of some basic fluxes, but the temperature should not be too high, and the time should be as short as possible In some cases, it can replace the nickel and platinum crucible, but it can not be used when the determination of aluminum and aluminum interferes with the determination Is as one / yasuwang square corundum crucible very simple? But the actual operation is easy to make mistakes, only memorize the key points, carefully operate in accordance with the requirements and succeed steadily Of course, the crucible is also a consumable, especially the ceramic crucible The cracks in the crucible mean that it is not far from the garbage can Use and maintain it carefully