Calcium carbonate is limestone. Barn lime is used primarily to reduce slipping on concrete. It is not commonly used as a desiccant.
Years ago we used calcium chloride as a desiccant. It can be oven dried and reused. Cobalt chloride was often mixed with it, as it turned from blue to red when it had absorbed water and was a visual indicator of the need for rejuvenating.
More recently, silica gel is used as it is less corrosive. It is the stuff in the little packets that come inside electronic equipment packages. It can also be rejuvenated by heating in an oven and an indicator like cobalt chloride can be added for a visual end-of-use indicator.
I personally do not rely on desiccants for humidity control. They are OK when fresh but as they absorb water, they are functioning as a constant humidity source. We used them in the lab but we had a regular routine to replace them with fresh desiccant on a weekly basis. We also used desiccators sealed with silicone grease to prevent an exchange of humid air with the interior. Any desiccant which is exposed to outside air will continue to pick up moisture until it is saturated.
A better approach is to use a small oven to maintain a temperature well above the dew point. This is the method used to keep welding rod dry. We also used it to keep phenolic microspheres used in epoxy composites dry. An insulated box with an incandescent light bulb will maintain a temperature of more than 100ºF and is hot enough to prevent any condensation (we used an old refrigerator). 70% RH at 70ºF is only about 25% RH at 105ºF.
If used to prevent corrosion of metrology instruments, you will have to allow them to come to room temperature before use.
Years ago we used calcium chloride as a desiccant. It can be oven dried and reused. Cobalt chloride was often mixed with it, as it turned from blue to red when it had absorbed water and was a visual indicator of the need for rejuvenating.
More recently, silica gel is used as it is less corrosive. It is the stuff in the little packets that come inside electronic equipment packages. It can also be rejuvenated by heating in an oven and an indicator like cobalt chloride can be added for a visual end-of-use indicator.
I personally do not rely on desiccants for humidity control. They are OK when fresh but as they absorb water, they are functioning as a constant humidity source. We used them in the lab but we had a regular routine to replace them with fresh desiccant on a weekly basis. We also used desiccators sealed with silicone grease to prevent an exchange of humid air with the interior. Any desiccant which is exposed to outside air will continue to pick up moisture until it is saturated.
A better approach is to use a small oven to maintain a temperature well above the dew point. This is the method used to keep welding rod dry. We also used it to keep phenolic microspheres used in epoxy composites dry. An insulated box with an incandescent light bulb will maintain a temperature of more than 100ºF and is hot enough to prevent any condensation (we used an old refrigerator). 70% RH at 70ºF is only about 25% RH at 105ºF.
If used to prevent corrosion of metrology instruments, you will have to allow them to come to room temperature before use.
They are since gone .
