What is lab crucible?
is a cup-shaped vessel used in the laboratory to heat solids at high temperatures. Laboratory crucible
is an important part of chemical instruments. It is a vessel for melting and refining metallic liquids as well as solid-liquid heating and reactions and is the basis for ensuring that chemical reactions proceed smoothly.
Application of lab crucible
a. Cauterizing solid substances
b. Evaporation, concentration or crystallization of solutions (if evaporation dishes are available, they should be chosen. Crucibles
can also be used for evaporation, concentration or crystallization of solutions).
Type of lab crucible
Crucible lab equipment
A. Platinum crucible
Platinum has many excellent properties. The melting point of platinum is as high as 1774°C. It is chemically stable, does not undergo chemical changes after burning in air, and does not absorb water, and most chemical reagents have no erosive effect on it.
Platinum crucible can resist the corrosion of hydrofluoric acid and molten alkali metal carbonate is an important property of platinum different from glass, porcelain, etc., so it is often used for precipitation cautery weighing, hydrofluoric acid melt samples, and carbonate melt processing. Platinum is slightly volatile at high temperatures and burns for a long time to be corrected. A 100cm2 area of platinum is burned at 1200 ℃ for about 1h loss of 1mg, platinum at 900 ℃ below the basic non-volatile.
The following rules should be observed for the use of a platinum crucible.
a. A strict system should be established for the receipt, use, consumption, and recovery of platinum.
b. Platinum is soft, which means that even alloys containing small amounts of rhodium-iridium are soft, so don't use too much force when picking up a platinum vessel to avoid deforming it. When demelting, sharp objects such as glass rods should not be scraped from the platinum vessel to avoid damage to the inner wall; nor should hot platinum vessels be put into cold water suddenly to avoid cracking. The deformed platinum crucible or vessel can be corrected with a water mold that matches its shape (but the brittle part of the platinum carbide should be corrected with uniform force).
c. The platinum crucible must be heated on a platinum tripod or the support of ceramic, clay, quartz, etc. It can also be heated on an electric heating plate with asbestos sheets or on an electric furnace, but not directly with iron plates or electric furnace wires. The crucible tongs used should be covered with platinum tips, and nickel or stainless-steel tongs should only be used at low temperatures.
If the platinum ware is spotted, it can be treated with hydrochloric acid or nitric acid alone. If it is not effective, use potassium metabisulfite to melt the platinum vessel at a lower temperature for 5 to 10 min, pour off the melt, and then dip the vessel in the hydrochloric acid solution. If it is still not effective, you can try again to melt sodium carbonate treatment, but also available damp fine sand (through 100 mesh sieve that is 0.14 mm sieve) gently friction treatment.
B. Gold crucible
Gold crucible's gold price is cheaper than platinum, and not subject to alkali metal hydroxide and hydrofluoric acid erosion, so commonly used instead of platinum vessels, the melting point of gold is low (1063 ℃), so cannot resist high-temperature burning, generally must be less than 700 ℃ use. Ammonium nitrate has an obvious erosion effect on gold, aqua regia cannot be in contact with gold vessels. The use of gold vessels and platinum vessels is basically the same.
C. Silver crucible
Silverware is relatively inexpensive and is not subject to erosion by potassium hydroxide (sodium), and is only slightly eroded in the molten state at the edges close to the air. Silver melting point of 960 ℃, the use of temperature generally does not exceed 750 ℃ is appropriate, can not be directly heated on the fire. After heating, a layer of silver oxide is generated on the surface, which is unstable at high temperatures but stable below 200°C. The silver crucible just removed from the high temperature is not allowed to be cooled immediately with cold water to prevent cracks. Silver can easily interact with sulfur to produce silver sulfide, so it cannot be decomposed and burned in the silver crucible, and an alkaline sulfide reagent is not allowed. Metal salts of molten aluminum, zinc, tin, lead, mercury, etc. can make the silver crucible brittle. Silver crucible is not used for melting borax. When using a sodium peroxide melting agent, it is only suitable for sintering, not for melting.
No acid, especially not concentrated acid, should be used when using silver crucibles to leach molten material. When cleaning silver vessels, dilute hydrochloric acid (1+5) with a slight boil can be used, but it is not advisable to place the vessels in the acid for a long time and heat them. The quality of the silver crucible will change by cautery, so it is not suitable for weighing the precipitate.
D. Nickel crucible
Nickel has a melting point of 1450°C and is easily oxidized by burning in air, so nickel crucibles cannot be used for burning and weighing precipitates.
Nickel has good resistance to alkali erosion, so it is mainly used in the laboratory for the melting treatment of alkaline melts. Sodium hydroxide, sodium carbonate, and other alkaline melting agents can be melted in the nickel crucible, and their melting temperature generally does not exceed 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 is serious, so the nickel salt content brought into the solution increases and becomes an impurity in the determination.
Acidic solvents such as potassium metabisulfate, potassium bisulfate, and solvents containing sulfides should not be used in nickel crucibles. If sulfur-containing compounds are to be melted, this should be done in an oxidizing environment with an excess of sodium peroxide. Metal salts of aluminum, zinc, tin, lead, etc. in the molten state can make nickel crucibles brittle. Silver, mercury, vanadium compounds, and borax should also not be cauterized in nickel crucibles. New nickel crucibles should be cauterized at 700°C for a few minutes before use to remove oil and to generate oxide film on the surface to prolong service life. Afterward, the crucible should be boiled and washed with water before each use, and if necessary, a small amount of hydrochloric acid can be added dropwise and boiled for a moment, then washed with distilled water and dried for use.
E. Iron crucible
The use of an iron crucible is similar to that of a nickel crucible, it is not as durable as a nickel crucible, but cheaper, more suitable for sodium peroxide melting, and can replace a nickel crucible. The iron crucible or low silicon steel crucible should be passivated before use, soaked with dilute hydrochloric acid, then lightly rubbed with fine sandpaper and rinsed with hot water, then soaked in 5% sulfuric acid + 1% nitric acid mixed solution for several minutes, then washed with water, dried and scorched at 300~400℃ for 10min.
Use of crucible in laboratory
Crucible in laboratory
When a solid is to be heated over a high flame, a lab crucible must be used. Crucibles are usually used with the lid placed diagonally over the crucible to prevent the heated material from jumping out and to allow air to enter and exit freely for possible oxidation reactions. The crucible, because of its small bottom, usually needs to be set up on a clay triangle in order to be heated directly by fire. The crucible can be placed on an iron triangle in either a square or diagonal position, depending on the needs of the experiment.
The laboratory crucible should not be placed on a cold metal table immediately after heating in order to prevent it from breaking due to rapid cooling. Nor should it be placed on a wooden tabletop immediately to avoid burning the tabletop or causing a fire. The correct method is to leave it on a metal tripod to cool naturally or to place it on an asbestos net to cool slowly. Use crucible tongs to remove the crucible.
Precaution of lab crucible
a. It can be heated directly and cannot be cooled suddenly after heating; remove it with crucible tongs.
b. The crucible is placed on the iron tripod when heated.
c. Stir when evaporating; use residual heat to evaporate when nearly dry.
How to buy lab crucible?
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