Silica Gel: Purpose, Origin, How Is It Made, Types, and Uses

Silica gel is applied as a desiccant and used to control moisture and humidity levels in a spectrum of applications. Its primary function is to adsorb and retain airborne or contact-surface moisture. This serves to prevent the growth/progress of mold/mildew, corrosion, and other moisture-related damage issues in products.

There are several forms of silica gel, generally considered as indicating and non-indicating varieties. Indicating silica gel undergoes color changes, often from blue to pink, as the indicator chemical additive absorbs the moisture. Non-indicating silica gel doesn't change color but adsorbs moisture equally effectively. Silica gel is manufactured in a range of particle sizes and shapes for specific applications.

This article will discuss what silica gel is, how it is made, its purpose, origin, types, and uses.

What Is a Silica Gel?

Silica gel is a versatile and efficacious desiccant used to absorb and hold moisture from its local environment. It is a solid particulate material, but its name derives from the gelation process used to manufacture it. It consists of tiny, nano-porous beads or crystals of silicon dioxide.

The key characteristic of silica gel is its extreme ability to adsorb water vapor and virtually any aqueous substance. Its extraordinarily fine porosity results in a massive functional surface area, allowing it to trap and hold moisture molecules on its extensive surface. This essentially isolates the water from surrounding surfaces, preventing damage or degradation in products and materials thus protected. Its moisture-adsorbing capabilities make it a valuable tool for controlling humidity and protecting against the chemical and biological effects of moisture in most product and industrial contexts.

What Is the Other Term for Silica Gel?

An alternative name for silica gel is silicic acid gel, which is a more accurate description of the chemistry. Silica gel is the commercial nomenclature, whereas silicic acid gel is more precise and used in scientific or technical contexts.

Is Silica Gel and Silica Desiccant the Same?

Yes, silica gel and silica desiccant are considered in most contexts to be the same thing. Desiccant is a generalized term covering any substance or material used to absorb and remove moisture from its surroundings, and silica gel is the most commonly used but not the only desiccant chemical.

What Does Silica Gel Look Like?

Silica gel typically appears as small, translucent, or semi-translucent beads or crystals, in sizes ranging from particles as small as grains of sand up to small (2 mm) beads. It is naturally white or colorless but manufactured in various colors for specific applications. Figure 2 shows examples of a silica gel:

Some silica gel products contain indicator beads that alter in color as they become saturated, flagging the need for regeneration or replacement.

What Does Silica Gel Do?

Silica gel products primarily serve as desiccants. They absorb and retain moisture from their surroundings. The material is derived from its mineral sources in various forms and serves a purpose by moderating atmospheric and surface moisture. This helps to protect products, environments, and materials from the degradation that results from wet oxidation and biological growth.

Why Is Silica Gel Important in Manufacturing?

Silica gel is important in manufacturing for various related reasons as listed below:

1. Manufacturing processes often require precise control over or minimization of humidity levels. Silica gel helps maintain the target level, preventing issues such as powder clumping, deterioration of raw materials, and damage to finished products.
2. Used to preserve the quality of various materials, including chemicals, pharmaceuticals, and food products by preventing moisture-induced degradation from aqueous chemical or biological processes. 
3. Manufacturing equipment can be highly sensitive to moisture which results in corrosion. Silica gel helps protect such sensitive assets by desiccating the environment.
4. In electronics manufacturing, moisture control is critical to prevent defects and ensure product reliability, both at a component and product level.
5. Employed in the packaging of manufactured goods to control humidity risks in shipping and storage, maintaining optimal conditions.
6. In pharmaceuticals and semiconductor manufacturing, stringent environmental controls can be imperative. Silica gel helps maintain controlled humidity levels in cleanrooms and manufacturing environments.

What Is the Origin of Silica Gel?

Silica gel has been known since the mid-17th Century, but its first actual application was as an aqueous airborne toxin removal mechanism in gas masks (in which role it is still employed). A manufacturing process was first patented by Walter Patrick of Johns Hopkins University in 1919. The material found high-value use during the Second World War, employed as a catalyst for the production of gasoline with extreme octane levels and in the making of butadiene, the monomer used in the manufacture of synthetic rubbers.

What Is Silica Gel Made Of?

Silica gel is produced by chemically processing sodium metasilicate (Na2SiO3), sodium orthosilicate (Na4SiO4), and sodium pyrosilicate (Na6Si2O7) to form high-purity silicon dioxide (SiO2). The sodium silicates are a naturally occurring mineral group, commonly co-deposited with quartz, sand, and other minerals. The refined product is manufactured through an acidic gelation process followed by drying. Silica gel is silicic acid, alternatively silicon dioxide (SiO2).

What Are the Properties of Silica Gel?

The properties of silica gel are listed in Table 1 below:

Is It Possible To Make a DIY Silica Gel?

No. Creating DIY silica gel is challenging due to the precise chemical processes involved in its production. Attempting to replicate the manufacturing process at home is complex, demanding specialized equipment and chemicals and precise process control. 

What Are Silica Gel Packets Made Of?

Silica gel packets are typically made of a material called Tyvek® or other lower-cost, non-woven polypropylene or polyethylene fabrics. These materials are open to air and moisture transfer but have very fine pore size which prevents powder escape. The fabric is unaffected by moisture but may limit the regeneration temperature of the finished packet. The fabric packets are usually heat-sealed or ultrasonically sealed to contain the silica gel inside the fabric pouch. 

What Are the Different Types of Silica Gel?

The different types of silica gel are listed and discussed below:

1. Type A Silica Gel

Type A silica gel is generally available as very clear pellets that are nano-porous with typically 40 Å (Angstrom) pores. Applied in product packaging, this type of silica gel protects moisture-sensitive items from humidity-related damage. It is also employed in industrial settings for moisture control in manufacturing processes and for preserving the quality of various materials and products.

This material is important in chromatography and catalytic-support roles, ensuring extreme exposure of a target chemical/reaction to the catalyst by applying it on the extensive surface area that the silica gel’s nano-porosity provides. Silica gel's very high chemical stability prevents stray reactions in catalytic applications, as the gel is essentially inert in most contexts. This class of material is widely used in the gas separation columns of gas chromatographs.

2. Type B Silica Gel

Type B silica gel is translucent white and has nano-porosity in the range of 4.5–7.0 nm, which alters the transparency. Also applied as a desiccant, this material is lower cost and used whenever the pore size is appropriate or as a constituent in scent reduction applications such as cat litter, in which cost is a larger concern. In higher purity forms, it also serves in gas chromatography applications and as a catalyst exposure/support mechanism.

3. Type C Silica Gel

Type C silica gels have large pore sizes and a surface that is populated by silicon-hydride (Si-H) groups as opposed to silanols (Si-OH). They’re widely used as desiccants across most sectors and as catalyst carriers for the manufacture of butadiene synthetic rubber, melamine polymer (cyanamide), and acrylic nitrite.

These materials are frequently employed in petrochemical refining, adsorption of organics in gas and liquid states, and aqueous phase chromatography applications like high-performance liquid chromatography (HPLC).

4. Stabilizing Silica Gel

Stabilizing silica gel is specific to the stabilization and preservation of high volatility and contamination-sensitive compounds in the pharmaceutical and organic chemistry sectors. It presents a chemically modified surface that restrains interactions between the silica gel and the process materials, reducing reactive contaminant formation. Stabilizing silica gel plays a critical role in maintaining the quality and serviceability of high-sensitivity materials, as a tool for various industries.

5. Silica Alumina Gel

Silica alumina gel is a composite material that combines silica gel and alumina. It is used as a catalyst carrier agent or adsorbent in various chemical and industrial processes. This material is often employed in applications that require specific catalytic or molecular-sieve adsorption properties, such as in the petroleum and petrochemical industries for refining and chemical manufacturing by catalytic cracking, hydrocracking, and adsorption of impurities.

Silica alumina gel’s composition can vary, as the relative proportions of silica and alumina are adjusted to achieve specific performance criteria, such as: acidity, surface area, and pore-size distribution. This versatility makes silica-alumina gel valuable for a range of applications.

What Are the Uses of Silica Gel?

Silica gel has a wide range of uses due to its excellent moisture-absorbing properties and safety. Some of its key applications include:

1. Silica gel packets are commonly placed in product packaging to protect items sensitive to moisture, such as: electronics, pharmaceuticals, and food products.
2. Assist in the prevention of moisture damage and deterioration of important documents, photographs, and high-value items, and they are widely used in museums for this purpose.
3. Are extensively used in chemical processing and catalyst support roles, across the oil & gas, polymers, and organic chemistry industries.
4. As desiccants, they are used to protect sensitive electronic components and circuitry from humidity-related issues, ensuring product reliability. Moisture-induced excess oxidation of component solder points makes them immediately unusable in automated reflow and wave soldering applications, as the more aggressive fluxes used to remove such heavier oxidation are impractical in other regards.
5. Are employed to prevent fogging on camera lenses, eyeglasses, sealed double-glazing modules, and optical equipment in storage or internal to sealed assemblies. When saturated and exposed to elevated temperatures, evaporation and temporary condensation/fogging are real risks in sealed products.

How To Properly Use Silica Gel?

To apply silica gel effectively, the following tips should be observed:

1. Use an appropriate quantity of silica gel for the size of the container or area/volume you want to protect.
2. Ensure the grade selected is appropriate for the task. More complex tasks such as chemical catalysis and molecular sieve applications require very specific properties. 
3. Make sure the container or space is properly sealed to prevent moisture from entering. Rapid saturation in open environments with elevated humidity negates all use in the materials.
4. Monitor the silica gel regularly for color changes (for indicating types) and replace or regenerate it as needed.
5. To regenerate, heat the silica gel in an oven at the recommended temperature for a specific time (as per the manufacturer's instructions).
6. Avoid contact with eyes and the respiratory tract and ingestion. Store silica gel packets out of reach of children and pets.

Can Silica Gel be Used on Galvanized Steel?

Yes, silica gel can be used on galvanized steel to protect it from moisture-related issues, such as corrosion. Placing silica gel packets in sealed storage containers helps maintain a dry environment.

What Is the Recommended Amount of Silica Gel?

Recommendations as to the quantity of silica gel in desiccant applications depend on several factors, including: the size of the enclosed space, the humidity levels, and the specific moisture control requirements. A general guideline is to use about 28–85 grams per cubic meter of an enclosed space. Using too little silica gel may not provide sufficient protection, while using too much may lead to over-drying and unnecessary regeneration. In many cases, manufacturers will offer guidelines that can provide support in deciding quantity.

What Happens if Silica Gel Gets Wet?

When silica gel gets wet, it becomes saturated with moisture. As it wets, its moisture-absorbing capacity degrades progressively until it can no longer effectively adsorb. The gel may turn translucent or change color if it's an indicating type. If left wet for an extended period, it can develop mold and may become less effective or unusable as regeneration can leave organic detritus that reduces its porosity.

What Are the Precautions for Using Silica Gel?

When using silica gel, it's essential to take certain precautions to ensure people and environmental safety and the effectiveness of the product. These are:

1. Silica gel is not meant for consumption, so keep it away from children and pets.
2. The dust residue of the material can become airborne and will severely irritate the eyes and mucus membranes, so use caution (good quality PPE is required for prolonged contact or extensive exposure).
3. Handle silica gel and pack with clean, dry hands to maintain its effectiveness.
4. When not in use, store the packets in airtight containers to prevent premature moisture absorption.
5. If regenerating silica gel by heating, do so in a well-ventilated area to avoid inhaling fumes of adsorbed residues that will volatilize, potentially in concentrated amounts.
6. Dispose of silica gel by local regulations. Some types can be discarded with regular waste, while others may need special handling.

What Happens if Someone Eats Silica Gel?

Silica gel is considered to be non-toxic, but it is not meant for consumption. Eating it is not advisable, but if a small amount is ingested, it is unlikely to cause significant harm. It can result in digestive discomfort — irritation or mild gastrointestinal symptoms such as upset stomach or diarrhea. Although the material is graded as not highly toxic, it's wise to act with caution and seek medical advice, in the event of consumption.

Can Silica Gel Be Used To Store Food Safely?

No. Silica gel is not suited for direct contact with food, despite being considered non-toxic. Instead, it is securely packaged, generally in a non-woven fabric sleeve, and used to control moisture and humidity within the storage packaging of food items, to reduce the incidence/rate of moisture-related damage. Food-grade silica gel is specifically designed for this purpose, meeting strict safety standards for contact with food (when contained appropriately).

How Much Does Silica Gel Cost?

The retail/wholesale price of silica gel varies very widely, depending on several factors, including: the type, purity, quantity, and source. Small silica gel pockets for packaging and protecting consumer products can cost as little as a few cents each. When purchased in larger quantities, the cost per unit of silica gel decreases. Bulk quantities may range from a few dollars per pound or kilogram. Indicating silica gel is often slightly more expensive than non-indicating silica gel, due to the increased complexity of manufacture. Some specialized types of silica gel, such as stabilizing silica gel used in pharmaceuticals or chromatography column materials can be considerably more expensive due to their specific properties and applications. These can cost several hundred dollars per lb/kg.

What Are the Benefits of Silica Gel?

Silica gel offers various benefits that depend heavily on the nature of the application, such as:

1. Its most exploited benefit is its exceptional moisture-absorbing ability.
2. Serves to extend the shelf life and quality of products, from electronics to documents and collectibles.
3. Indicating silica gel provides a visual signal when it's saturated, indicating the need for replacement or regeneration.
4. These materials are safe and non-toxic, making them suitable for pharmaceutical and food-related applications.
5. Most types of silica gel can be regenerated and reused multiple times by heating to dry the material.
6. They are generally environmentally neutral materials and can be disposed of according to local regulations without pollution risk, depending on the nature of the application and contaminants.

What Are the Risks of Silica Gel?

While silica gel is generally safe for its intended purposes, there are a few risks associated with it such as:

1. Ingestion.
2. Eye, mucus membrane, and skin irritation.
3. Respiratory tract irritation.
4. Vapor release of captured materials during regeneration.

Is Silica Gel Reusable?

Yes. Most commercially available forms of silica gel are reusable by carefully heating it to remove the moisture (and any other chemicals) it has absorbed. The number of times you can regenerate and reuse silica gel depends on its quality and how well it's maintained. However, some silica gel products are designed for single use and cannot be regenerated, so it is wise to follow the manufacturers' guidance.

Is Silica Gel Flammable?

No. Silica gel itself is not flammable. However, if highly saturated with volatiles, as may be the case from a polymer catalyst or hydrocarbon purification process, the resultant evaporites may pose a flammability risk.

What Is the Difference Between Silica Gel and Molecular Sieve?

Silica gel and molecular sieves are both desiccants used for moisture control, but they have some key differences. Essentially, silica gel functions as a molecular sieve, along with a range of other chemistries as listed below:

1. Silica gel is generally high-purity silicon dioxide. Molecular sieves, on the other hand, tend to be made from crystalline aluminosilicates, with a more complex composition, often containing aluminum, silicon, and oxygen.
2. Molecular sieves have a uniform and closely controlled pore size in the order of nanometers (nm), allowing them to selectively adsorb molecules based on their size and shape. Silica gel has irregularly shaped pores, making it less selective.
3. Molecular sieves generally have higher adsorption capacities for specific molecules of a range of sizes from smaller than water to large hydrocarbons.
4. Molecular sieve materials are typically non-indicating, whereas silica gel often contains a saturation indicator.
5. Molecular sieves are more commonly used in gas and liquid purification processes, while silica gel is generally used as a storage desiccant.

Summary

This article presented silica gel, explained it, and discussed its origin and applications. To learn more about silica gel, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

Copyright and Trademark Notice

1. Tyvek® is a trademark of the E.I. DuPont de Nemours company

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