A practical guide to moisture content testing in ceramic manufacturing, including the oven-drying method and thermogravimetric analyzer (TGA) method.
Purpose of the Test
Moisture content testing in ceramic manufacturing is used to determine the percentage of water present in both raw materials and in-process ceramic products. This information is essential for:
- Calculating accurate batch formulations based on dry raw material weight
- Controlling drying and firing process parameters
- Reducing process defects
- Maintaining product quality and process consistency
Moisture can be present in raw materials for several reasons. Understanding the source of moisture helps improve raw material control and production accuracy.
1. Moisture from Mining
Raw materials excavated from mines may naturally retain moisture within the clay or mineral beds.
2. Incomplete Drying
If processed raw materials are dispatched before proper drying is completed, residual moisture remains in the material.
3. Moisture During Transport
Exposure to rain, humid storage, or poor transportation conditions can increase the moisture content of the raw material.
4. Process Moisture in Products
Formed ceramic products such as sanitaryware, tiles, tableware, and refractories also contain moisture at different process stages.
Why Moisture Testing Is Important
| Application | Why It Matters |
|---|---|
| Raw Material Formulation | Ensures correct dry weight calculation during body and glaze preparation. |
| Supplier Quality Control | Helps verify whether supplied materials are within agreed moisture tolerance limits. |
| Cost Control | Prevents manufacturers from paying for excess water instead of usable raw material. |
| Drying & Firing Process | Helps optimize drying and firing conditions to avoid cracks, blasts, and related defects. |
| In-Process Quality Monitoring | Useful for checking moisture before drying, after drying, or before firing. |
Equipment Required
- Dryer / Oven – Used to heat the sample to approximately 105°C
- Steel or Ceramic Crucible – Used to hold the sample during drying
- Weighing Machine – For accurate sample weight measurement before and after drying
- Desiccator – Prevents moisture reabsorption during cooling
Step-by-Step Procedure
Sample Collection
The sampling method depends on whether the test is for raw materials or in-process ceramic products.
For Raw Materials: Samples are generally collected from 5 to 10 different locations to ensure proper representation. These are then mixed thoroughly.
For In-Process Products: Moisture samples may be taken from different areas of the product, or in some cases, the full piece may be used depending on plant practice.
Weighing the Sample (W1)
Since moisture content is calculated as a percentage, any convenient sample weight may be used as long as it is representative. A 100 g sample is commonly used in ceramic labs.
Record the initial sample weight as W1.
Drying the Sample
Place the sample in a dryer or oven maintained at approximately 105°C. Dry the sample for 2 to 3 hours, or until all free moisture is removed.
Cooling the Sample
After drying, cool the sample in a closed environment such as a desiccator. This prevents the dried sample from absorbing moisture from the atmosphere.
Weighing Again (W2)
Once the sample reaches room temperature, weigh it again and record the final weight as W2.
Calculation
Moisture content is calculated using the following formula:
| Symbol | Meaning |
|---|---|
| W1 | Weight before drying |
| W2 | Weight after drying |
Thermogravimetric Analyzer (TGA) Method for Moisture Determination
A thermogravimetric analyzer (TGA) is commonly used to determine moisture percentage in ceramic raw materials. This method is faster, more convenient, and more user-friendly than the conventional oven-drying method because the instrument directly displays the moisture result.
Procedure
- Take approximately 3 to 5 grams of the raw material sample.
- Spread the sample evenly on the analyzer weighing pan.
- Close the analyzer after the initial weighing is completed.
- The instrument heats the sample, usually using a halogen bulb or sometimes an electric heater.
- Set the test temperature to 105°C.
- As the sample heats, moisture evaporates and the sample weight gradually decreases.
- The analyzer continuously tracks the weight loss during the drying process.
- Once the weight becomes constant, the instrument automatically stops the test.
- The moisture percentage is then displayed directly on the screen.
Advantages of the TGA Method
Fast Testing
Reduces testing time compared to conventional oven drying.
Easy to Use
Simple procedure suitable for routine lab operation.
No Manual Calculation
The instrument automatically calculates and displays the moisture percentage.
Suitable for Routine QC
Highly useful for regular moisture testing of ceramic raw materials.
Final Note
If you are working in sanitaryware, tiles, tableware, or refractories, maintaining proper moisture control can significantly reduce production defects and improve consistency.
Post Comment