Talc powder, also known as hydrated magnesium silicate, is a white, light gray or light yellow powder processed by mechanically crushing talc ore to 325 mesh (or 400 mesh, 600 mesh, 800 mesh, 1000 mesh, 1250 mesh, etc.). It is soft and slippery in texture, and appears as irregular flat particles under microscopy. Under conventional conditions, its relative density is 2.7–2.8, particle size is 1–10 μm, Mohs hardness is grade 1. It is chemically stable, acid and alkali resistant, fire resistant, electrically insulating, oleophilic and hydrophobic. It is slightly soluble in dilute inorganic acids and insoluble in water and ethanol. It is widely used in pharmaceutical tablets, pharmaceutical powders (e.g., Aspirin, and Phenacetin Powder), sugar coatings, prickly heat powder, traditional Chinese medicine prescriptions, food additives, release agents, etc.
Experimental Purpose
Whiteness of talc powder refers to the reflectance of its powder to visible light under specific lighting conditions (e.g., standard light source D65 or light source A), usually expressed as a percentage. It is an important indicator for evaluating its color purity and appearance quality, directly reflecting the influence of impurity content, particle fineness and crystal structure of talc powder on light reflectivity.
Higher whiteness indicates that the talc powder is closer to pure white, with lower impurity content and better optical performance. As one of the core parameters for evaluating talc powder quality, whiteness directly affects its application value in high-end fields such as cosmetics, coatings, plastics and papermaking.
Experimental Equipment
① ST001D Liquid Crystal Whiteness Tester
② Auxiliary parts such as ceramic standard white plate, powder standard white plate, constant-pressure powder sample presser, etc.
Experimental Steps
① Inspect the instrument and accessories to ensure they are clean, dry and free of contamination.
② Connect the instrument power supply and turn it on; the instrument will enter self-checking. Place the black zero-setting plate at the measuring position, press the zero-setting button for calibration, and finish zero-setting when the screen reading stabilizes at 00.0.
③ Take out the standard white plate (standard whiteness value: 86.0), place it at the measuring position for instrument calibration. If there is a deviation, adjust gradually by pressing the calibration button until the reading stably shows 86.0.
④ Take the sample: mix the talc powder thoroughly, reduce the sample to a representative sample of not less than 500 g by quartering, and press it into a smooth, flat sample without unevenness using a constant-pressure powder sample presser.
⑤ Place the sample at the observation port, select the sample test mode; the instrument will measure automatically and display the result.
⑥ Repeat the test 1–3 times.
Experimental Results
The three measured whiteness values of the sample are all >94%, with an average value of 94.3%, meeting the requirements for pharmaceutical-food grade talc powder.
