There are many varieties of desiccants in industry, such as silica gel, montmorillonite, molecular sieve, and calcium chloride. Commonly used ones include white silica gel, color changing silica gel, and montmorillonite desiccant.
Main performance indicators of silica gel desiccant:
A. Moisture absorption capacity. The most important indicator for characterizing the performance of silica gel desiccant. A-type silica gel desiccant has moisture absorption requirements under both high and low humidity conditions, and generally the higher, the better.
B. Moisture content. The important indicator for characterizing the usage status of silica gel desiccant refers to the amount of moisture (expressed as a percentage by mass) contained in the desiccant after drying under certain temperature conditions. A high moisture content indicates that the silicone has already absorbed moisture, and its moisture absorption capacity is inevitably low; If the moisture content is too low, the drying cost will be too high. The temperature for removing adsorbed water from silica gel is about 150 ℃.
C. The pH value of the aqueous solution is 8 and the specific resistance is 9. Important indicators for characterizing the impurity content and quality stability of silica gel desiccants. The pH value of ordinary silicone gel is between 4 and 8, and a more economical approach is to control it around 5; The indicator of silica gel needs to be stable in a strongly acidic environment, so the pH value will be relatively low, around 2.5. The specific resistance of silicone is generally in the range of several thousand to tens of thousands of Ω· cm.
D. Specification and particle size qualification rate. Due to different packaging requirements (such as different packaging sizes, packaging materials, and moisture absorption speed requirements), silicone gel with different specifications (particle size range ⑾, shape) is used; The number of particles in the raw material that meet the specification requirements is called the particle size qualification rate (expressed as a percentage by mass).
E. Bulk density. Characterize the volume occupied by a certain amount of desiccant, in grams per cubic meter. Also known as bulk density or packing density. The packing density plays an important role in the specification of desiccant packaging and the calculation of fixed volume desiccant dosage. The bulk density of A-type silicone is about 740~800g/L.
Characteristics and Applications:
A-type porous silica gel desiccant has stable chemical properties (does not react with other substances except hydrofluoric acid and strong alkali), stable physical properties (high mechanical strength, good wear resistance, less impurities), is harmless to the human body (the amorphous structure of silica gel generally does not cause diseases such as stones unless ingested in large quantities), has good moisture absorption ability under high and low humidity, and is relatively affordable. Therefore, it is widely used in the storage and transportation of food, medicine, art, electronic products, clothing, furniture and other products. Color changing silicone:
Color changing silicone gel is a commonly used functional silicone desiccant product, also known as indicator silicone gel, which is made by adding a certain proportion of water changing components (3-7%) on the basis of A-type silicone gel, so that the silicone gel can change color after absorbing water, indicating its moisture absorption state.
Due to the presence of a certain amount of indicator, some of the pores of the color changing silicone gel will be occupied, resulting in a certain degree of decrease in its moisture absorption performance, with a decrease of about 2-4%.
Color changing silicone can also be divided into several categories:
Name: Blue Gel Indicator, Color Change
Color changing silicone gel (low humidity high humidity) blue purple light purple red (light blue purple red light red)
Main components of indicator:Cobalt chloride process is the most mature and cost-effective
Characteristics and Applications:General application requirements for occasions
Orange gel (orange to green silicone, cobalt free color changing silicone) Orange yellow green dark green
(Light Orange Light Yellow Green Green) Indicator Main Ingredients: Ammonium Ferrous Sulfate
Characteristics and applications of copper chloride: cobalt free, relatively safe, used as a substitute for blue glue
Orange gel (orange to white silicone gel, new cobalt free color changing silicone gel) Orange light orange colorless indicator Main components: ammonium iron sulfate Ammonium ferrous sulfate
Characteristics and Applications:Free from harmful metal elements such as cobalt and copper
Widely used in European and American countries.
Main performance indicators of montmorillonite desiccant
A. Moisture absorption capacity. The moisture absorption performance of high-quality montmorillonite desiccant is similar to that of silica gel desiccant, and its moisture absorption ability under low humidity is even better than that of silica gel desiccant.
B. Moisture content (or thermal weight loss). The temperature requirement for removing adsorbed water from montmorillonite is slightly higher, around 180 ℃.
C. The pH and conductivity of the aqueous solution are 9. Montmorillonite has a weak alkaline pH, generally between 7 and 8, which is closer to neutrality compared to silica gel; Similar to silica gel, the conductivity of montmorillonite indicates the level of impurities in montmorillonite, with conductivity generally ranging from a few ms/m.
D. Specification and particle size qualification rate. Montmorillonite desiccants are generally irregular blocks made by crushing and sieving bentonite ore. Weisheng's montmorillonite mainly comes in two specifications: 0.5-2mm and 1-4mm. Montmorillonite has lower mechanical strength compared to silica gel, and irregular particles are more prone to generate dust. There are two methods to solve this problem: one is to use packaging materials with better strength and density, but the denser the packaging material, the poorer its breathability, which will affect the product's moisture absorption rate; The second is to use the adhesive properties of montmorillonite itself to produce spherical particles, but spherical montmorillonite has a reduced moisture absorption capacity due to the limited expansion space of montmorillonite. Weisheng's spherical montmorillonite mainly comes in two types: 1-2mm and 2-4mm. Suitable specifications of montmorillonite need to be used as raw materials according to different requirements.
E. Bulk density. The bulk density of montmorillonite is relatively high, between 900-1000g/L, and the bulk density of spherical montmorillonite is even higher, reaching over 1000g/L.
Characteristics and Applications
Montmorillonite, as a desiccant, does not require the addition of any other substances during raw material mining and processing, and does not corrode metal or other products. It is a safe and environmentally friendly desiccant raw material. Due to its moisture absorption performance similar to silicone and relatively low cost, montmorillonite desiccant is gradually replacing silicone in many drying fields, especially in the packaging and transportation operations of large and medium-sized machinery, glass products, metal parts and other products. Montmorillonite desiccant has occupied an absolute dominant position.
The general industrial desiccant mainly depends on what product you use it on, and the above is what we hope will be effective for you.
