Technique F: Use of Crucible
Section 1: Purpose of Technique
This technique describes how to use a laboratory crucible to safely heat a sample.
Section 2: Operations of Crucible
There are several types of crucibles that can be used for heating up materials. Possible types of crucibles are alumina, ceramic and porcelain. Most labs require the use of porcelain crucibles. Porcelain crucibles are glazed on the outside and inside, except there is usually no glaze on the bottom. Crucibles are meant to withstand high temperatures of 1020-1050oC. Crucibles can heat up a variety of materials like metals (cooper, cobalt, etc.), hydrates and glass.
Use crucible tongs to pick-up crucibles and prevent fingerprints.
Put crucible on a clay triangle that has been placed over an iron ring attached to a stand and placed above a Bunsen burner.
Make sure that the crucible is directly in the center of clay triangle to prevent it from falling over.
After the crucible is in place, turn on the Bunsen burner flame (CAUTION: DO NOT use immediate high heat on the crucible) and begin heating.
Section 3: Maintenance of Crucible
The proper way to prepare the crucible and lid is to wash it with laboratory water ONLY. Use a gentle flame and heat the crucible for two minutes or until water is evaporated. This will allow the crucible time to be completely water free prior to more intense heating.
Place the clean crucible and lid on the wire gauze. Do not place the clean crucible or lid on the countertop. Clean it again if it is placed on the countertop.
Section 4: Safety Precautions of Crucible
DO NOT USE broken or severely damaged crucibles. Thermal shock can break the crucibles if there are already defects in the crucible.
DO NOT overheat the crucible. It may cause materials to spatter or to adhere the bottom
USE ONLY crucible tongs to put on the lid when the crucible is over a flame.
DO NOT touch a hot crucible with your hands. It can burn your hands.
NEVER put down a hot crucible has been heated on the counter. USE a wire gauze.
NEVER directly pick-up the crucible after it has been heated up. Allow the crucible to cool down first before using crucible tongs.
DO NOT stand near the crucible, especially when material is heating up. Make sure to use the lid before turning up the flame on the material, as you DO NOT want the material to become ejected toward you.
DO NOT allow cold water to interact with the hot water inside the crucible, it can cause thermal shock.
DO NOT allow cold water to touch the crucible after it has been heated up. It can cause mechanical shock of the crucible.
Do use crucible tongs to pick up and put down the crucible and lid on the wire rack.
Do use crucible tongs to place the lid on the heated crucible.
Do place the lid and crucible after cleaning onto the wire gauze and when the crucible and lid are hot.
Do not place the crucible and the lid on the counter at ANYTIME during the cleaning and experiment.
Do not place the crucible on its side. Make sure it is centered on the clay triangle.