Potassium Carbonate: A Cross-Sector Key Industrial Raw Material

In last month’s (September) content, we provided a detailed overview of potassium carbonate’s basic characteristics (physical and chemical properties), mainstream production processes (e.g., comparison of electrolysis vs. causticization), and its applications in agriculture (as a potash fertilizer to regulate soil potassium) and in animal husbandry (as a feed additive to supplement potassium).

For a recap, visit: https://www.kelewell.de/en/post/potassium-carbonate-a-multi-sector-key-raw-material-for-agriculture-food-and-industry

This article focuses on potassium carbonate’s diversified applications in industrial fields. As a basic chemical raw material that combines weak alkalinity, stability, and ease of purification, potassium carbonate plays core roles as a “performance modifier,” “raw-material precursor,” and “process aid” in key industrial scenarios such as glass, electronics, pharmaceuticals, and dyeing/printing. Its use directly affects the quality and functionality of end products.

Glass Manufacturing Industry

Potassium carbonate (K₂CO₃) is a key flux, clarifier, and performance regulator in glass manufacturing. Its core function is to lower the melting temperature and optimize the glass structure to produce glass with specific properties (e.g., high transparency, low thermal expansion, chemical corrosion resistance), and it is especially widely used in specialty glass. Dosage should be adjusted based on glass type (optical, pharmaceutical, daily-use) and used synergistically with raw materials such as silica sand (SiO₂) and soda ash (Na₂CO₃).

I. Core Functions of Potassium Carbonate in Glassmaking

The essence of glassmaking is to mix silica sand (main component SiO₂, melting point ≈ 1713 °C) with other raw materials, melt them at high temperature into a homogeneous melt, and then form and anneal to obtain the product. Adding potassium carbonate addresses issues such as “excessively high melting point of silica, high melt viscosity, and bubble formation,” with three specific functions:

1. Flux: Lowering Melting Temperature and Saving Energ

   Silica (SiO₂) alone requires temperatures above 1700 °C to melt—industrial implementation is difficult and highly energy-intensive. As a strong flux, potassium carbonate lowers the melting temperature via:

   
   

   At high temperature (decomposition begins ≈ 800 °C), K₂CO₃ releases CO₂ and forms K₂O (potassium oxide). Acting as a “network modifier,” K₂O disrupts the three-dimensional SiO₂ network (Si–O–Si bonds), weakening intermolecular forces;

   
   

   The generated K₂O reacts with SiO₂ to form “low-eutectic mixtures” (e.g., K₂O·SiO₂ with a melting point ≈ 976 °C), reducing the overall glass melt’s melting temperature from 1713 °C to about 1200–1400 °C and significantly cutting furnace energy consumption (typically saving 15%–25% in fuel);

   
   

   It simultaneously lowers melt viscosity (from 10⁶ Pa·s to 10³ Pa·s at high temperature), improving flowability for subsequent forming (e.g., blow-molding, pressing).

   
   

2. Clarifier: Eliminating Melt Bubbles to Improve Transparency

   During high-temperature melting, the glass melt readily generates bubbles due to raw-material decomposition (e.g., carbonates releasing CO₂) and moisture evaporation. If not removed, bubbles cause “haze” and defects that impair transparency and strength. Potassium carbonate clarifies by:

   
   

   CO₂ bubbles produced from K₂CO₃ decomposition, rising through the melt and “capturing” microbubbles (air, water vapor), coalescing into larger bubbles that quickly escape at the surface;

   
   

   Compared with soda ash (Na₂CO₃), K₂CO₃ decomposes more gradually (≈ 800–1000 °C vs. 700–850 °C), sustaining CO₂ release during the lower-viscosity stage (≈ 1200–1300 °C), extending clarification time and reducing residual bubbles;

   
   

   Especially suitable for glass with high transparency requirements (optical and pharmaceutical glass), enabling bubble contents ≤ 0.1 per cm².

   
   

3. Performance Modifier: Optimizing Physicochemical Properties

   The ionic radius of K⁺ (138 pm) is larger than that of Na⁺ from soda ash (95 pm). Introducing K⁺ alters the glass structure and thereby tunes key properties such as expansion coefficient, hardness, and corrosion resistance:

Performance Index	Mechanism	Application Value
Thermal expansion	K⁺ enhances network stability, lowering the coefficient of thermal expansion (typically, each 1% K₂O reduces CTE by 5×10⁻⁷/°C)	Producing “low-expansion” (heat-resistant) glass to prevent thermal shock cracking (e.g., lab beakers, microwave-safe glass)
Chemical stability	K₂O improves surface “hydrolytic resistance,” reducing water/acid attack on Si–O bonds	Producing pharmaceutical glass (ampoules, infusion bottles) to prevent ion leaching that contaminates drug solutions
Optical properties	K⁺ has low absorption in visible light and can adjust refractive index (e.g., K₂O addition raises n from 1.52 to 1.54)	Producing optical glass (lenses for glasses and cameras) to optimize transmittance and imaging quality
Mechanical strength	Densifies the glass network, increasing surface hardness (Mohs from 6 to 6.5)	Producing daily-use glass (cups, tableware) to reduce scratches and breakage

II. Main Application Scenarios (by Glass Type)

Use of K₂CO₃ is not universal but targeted to specific performance requirements—specialty glass is the core application:

1. Optical Glass (largest share)

   (e.g., eyeglass lenses, microscope/laser lenses) require high “transmittance, refractive index, and homogeneity,” with K₂CO₃ as a key raw material:

   
   

   Dosage: typically 10%–20% of the batch (adjusted per refractive-index needs), used with boric acid (H₃BO₃), alumina (Al₂O₃), etc.;

   
   

   Roles: (i) Lower melting temperature to mitigate raw-material volatilization (e.g., boric acid volatilizes at high temperatures; melting below 1400 °C reduces loss); (ii) Tune refractive index (more K₂O for high-index lenses; less for low-index); (iii) Increase transmittance (fewer bubbles/impurities, visible-light transmittance ≥ 92%).

   
   

2. Pharmaceutical Glass (high safety requirements)

   (e.g., ampoules, vials, IV bottles) must be “non-leaching and acid/alkali-resistant.” K₂CO₃ is a core partial substitute for soda ash:

   
   

   Traditional pharmaceutical glass uses Na₂CO₃ as flux, but Na⁺ readily leaches (especially during long-term storage), potentially reacting with drugs. K⁺ leaching is only about one-fifth that of Na⁺, greatly lowering risk;

   
   

   Dosage: 8%–15% of the batch; used with silica sand and limestone (CaCO₃) to produce “low-borosilicate” or “middle-borosilicate” pharmaceutical glass (the latter needs more K₂O to boost hydrolytic resistance);

   
   

   Key index: After 121 °C autoclaving, K⁺ leaching ≤ 0.5 µg/mL, meeting GB 12414 Pharmaceutical Glass Containers.

   
   

3. Heat-Resistant Glass (low expansion)

   (e.g., lab beakers, coffee pots, oven doors) must withstand sharp temperature swings (e.g., −20 °C to 150 °C) without cracking; K₂CO₃ is pivotal for low expansion:

   
   

   Principle: K₂O with SiO₂/Al₂O₃ forms a “low-expansion network,” cutting CTE to ≤ 3×10⁻⁷/°C (vs. ≈ 9×10⁻⁷/°C for ordinary glass);

   
   

   Dosage: 15%–25% of the batch; reduce Na₂O (raises CTE). Often paired with ZrO₂ to enhance heat resistance;

   
   

   Typical product: German “Pyrex” heat-resistant glass contains ≈ 20% K₂CO₃ and withstands rapid thermal cycling without failure.

   
   

4. Daily-Use Glass (practical performance)

   (e.g., cups, tableware, decorative glass), where K₂CO₃ typically serves as an auxiliary flux partially substituting soda ash:

   
   

   Dosage: 3%–8% of the batch, mainly to improve “gloss” and “impact resistance” (K₂O smooths the surface and reduces scratches);

   
   

   Advantage: Compared with soda ash, K₂CO₃ reduces devitrification (crystal precipitation on cooling), preventing “white spots” and improving appearance.

Purity and Impurity Control for Glassmaking

Impurities (chloride, heavy metals, sulfates) cause “bubbles, stones, and color specks.” Typical requirements:

Index Category	Glass Grade (Premium Industrial)	Regular Industrial Grade	Core Rationale
Main content	≥ 99.0%	≥ 98.0%	Ensure fluxing/clarifying efficacy; avoid dilution by impurities
Chloride (Cl⁻)	≤ 0.01%	≤ 0.1%	Cl⁻ forms HCl at high T, generating new bubbles
Sulfate (SO₄²⁻)	≤ 0.03%	≤ 0.2%	Forms CaSO₄ (m.p. 1450 °C) with Ca²⁺ → “stones”
Heavy metals (Pb/Cd)	≤ 0.001% (10 ppm)	≤ 0.01% (100 ppm)	Absorb visible light → color specks, lower transmittance
Iron (Fe₂O₃)	≤ 0.005% (50 ppm)	≤ 0.01% (100 ppm)	Fe³⁺ strongly absorbs blue light → yellow-green tint
Moisture	≤ 0.5%	≤ 1.0%	Prevent caking; ensure uniform mixing

5. Comparison and Synergy with Soda Ash (Na₂CO₃)

In glassmaking, K₂CO₃ is often used with Na₂CO₃. Both are fluxes, but they differ and must be combined per glass requirements:

Dimension	Potassium Carbonate (K₂CO₃)	Soda Ash (Na₂CO₃)	Synergy Strategy
Fluxing effect	Stronger (greater T reduction)	Moderate	Increase K₂CO₃ when large T drop is needed (e.g., optical glass)
Thermal expansion	Lowers CTE	Raises CTE	For heat-resistant glass, reduce Na₂CO₃ and increase K₂CO₃
Chemical stability	Better hydrolytic resistance (less K⁺ leaching)	Lower hydrolytic resistance (more Na⁺ leaching)	For pharma glass, partially replace Na₂CO₃ with K₂CO₃ (≈ 30%–50%)
Cost	Higher (≈ 2–3× soda ash)	Lower	For daily-use glass, use Na₂CO₃ as main, K₂CO₃ auxiliary (cost control)
Volatilization loss	Lower at high T (< 5%)	Higher at high T (< 10%)	For high-T melting (e.g., pot furnaces)

Electronics Industry

K₂CO₃ is a multifunctional basic chemical in electronics. Thanks to high-purity potential (refined to ≥ 99.9%) and properties (alkalinity, stability, solubility), it serves as both a direct raw material and a process aid.

1. Core Raw Material for Electronic-Grade KOH

   This is the primary electronics application. Through causticization or electrolysis, K₂CO₃ reacts with Ca(OH)₂ (or via water electrolysis routes) to produce high-purity KOH—critical for semiconductors and lithium batteries:

   
   

   Semiconductor fabrication: Wet etchant for selectively etching SiO₂ layers on wafers to form circuit patterns; cleaner to remove photoresist residues and metal contaminants.

   
   

   Cathode precursor synthesis for Li-ion batteries: Adjusts pH during NCM/NCA precursor formation, controls crystal growth, improving electrochemical performance (capacity, cycle life).

   
   

   PV cell texturing: With isopropanol to form uniform pyramidal textures on poly-Si wafers, enhancing light absorption.

   
   

2. Semiconductor Packaging & Lithography

   K₂CO₃ serves as a process aid in back-end packaging and lithography:

   
   

   Developer component: Low-concentration K₂CO₃ solution (≈ 0.2%–0.5%) can act as a developer for certain non-ionic resists, dissolving unexposed areas to form fine patterns (for specific wavelengths).

   
   

   Pre-bond cleaning: High-purity K₂CO₃ solutions clean chip surfaces before wire bonding, removing organic and oxide contaminants to ensure reliable bonds.

   
   

3. Electronic Components & MLCC Manufacturing

   K₂CO₃ is a key flux and composition modifier in electronic ceramics (notably MLCC):

   
   

   BaTiO₃ powder synthesis: Small K₂CO₃ additions (≈ 0.1%–1%) lower sintering temperature (≈ 1300 °C → ≈ 1100 °C), cut energy use, suppress grain overgrowth, and stabilize dielectric properties.

   
   

   Ceramic green-body forming: K₂CO₃ solutions act as binder aids to improve flowability and forming density, preventing cracking/layering.

   
   

4. Lithium Batteries & Energy Storage

   Beyond serving as a KOH precursor, K₂CO₃ is used directly:

   
   

   Electrolyte pH adjuster: ppm-level K₂CO₃ neutralizes acidic impurities (e.g., HF) in Li–S or solid-state electrolytes, suppressing electrode corrosion and improving cycle stability.

   
   

   Cathode doping: Trace K⁺ (from K₂CO₃) can dope LFP lattices, widening Li⁺ diffusion channels and improving rate (fast-charge) performance.

   
   

5. Photovoltaics & Displays

   PV glass coatings: Acts as a pH buffer in coating baths (e.g., SiO₂–TiO₂ AR films), stabilizing pH for uniform films with strong adhesion and lower reflectance.

   
   

   LCD glass cleaning: High-purity K₂CO₃ solutions can partially replace strong bases (NaOH), gently removing oils/scratches while reducing glass corrosion (K⁺ is less corrosive than Na⁺).

Key Technical Requirements for Electronic-Grade K₂CO₃

Index Category	Requirement (Electronic-Grade, ref.)	Rationale
Main content	≥ 99.9% (≥ 99.99% for high-end)	Avoid dilution by impurities
Heavy metals	Pb, Cd, Hg, As, Cr⁶⁺ ≤ 0.05 ppm	Prevent chip contamination/electrode poisoning; preserve mobility & electrochemistry
Alkali-metal impurities	Na⁺ ≤ 5 ppm, Li⁺ ≤ 1 ppm	Protect MLCC dielectric constant, IC conductivity; limit interface impedance in batteries
Anionic impurities	Cl⁻ ≤ 3 ppm, SO₄²⁻ ≤ 5 ppm, NO₃⁻ ≤ 2 ppm	Prevent electrode corrosion (e.g., PCB plating), bubbles during sintering, electrolyte decomposition
Moisture	≤ 0.2%	Prevent caking and bath-concentration drift; ensure lithography/ceramic stability
Particle size/form	Powder (10–50 µm) or granular, no visible foreign matter	Ensure uniform dissolution; avoid defects in coating/electrolyte

Pharmaceutical Field

Applications center on weak alkalinity, potassium supplementation, and chemical stability—primarily as a pharmaceutical excipient (>90%), and in limited cases as an active ingredient (strict dosing). Compliance with pharmacopeial standards is essential.

1. Excipient: Adjusting pH and Stability

   This is the main use—leveraging weak alkalinity (aqueous pH ≈ 11–12; milder than NaOH) to tune formulation pH, stability, solubility, and palatability:

   
   

   Oral solids (tablets/capsules): Many APIs are acidic (e.g., aspirin, ibuprofen; some antibiotics like amoxicillin) and degrade in acidic environments or irritate the gastric mucosa. Small amounts of K₂CO₃ (≈ 0.5%–5% of formulation) can:

   1. Neutralize residual acidity and adjust “micro-environmental pH” to near-neutral/alkaline (pH 7.0–8.5), slowing API degradation (e.g., extending aspirin tablet shelf life from 2 to 3 years);

   2. Serve as part of effervescent disintegrant systems with organic acids (citric/tartaric), generating CO₂ upon contact with water to accelerate disintegration (note: effervescent tablets typically use NaHCO₃; K₂CO₃ is used where sodium reduction is desired due to slightly astringent taste).

   
   

   Oral liquids (syrups/suspensions): For some APIs (e.g., certain alkaloids, B-vitamins) with low solubility or oxidative instability in acidic media, K₂CO₃ acts as a pH adjuster:

   
   

   For example, in vitamin B₁₂ syrups, adjusting pH to 4.5–5.5 increases solubility (≈ 0.1 g/L → ≈ 5 g/L), suppresses microbial growth, and avoids structural damage caused by strong bases like NaOH.

   
   

   Topicals (ointments/lotions): For fungal infections (e.g., tinea pedis), K₂CO₃:

   Neutralizes acidic metabolites (e.g., fatty acids), improving local pH (from ≈ 5.5–6.5 to ≈ 7.0–7.5) to inhibit fungal growth;

   
   

   Enhances penetration of topical antifungals (clotrimazole, terbinafine) by softening the stratum corneum.

   
   

2. Excipient: Improving Solubility and Absorption

   For poorly water-soluble APIs (e.g., dexamethasone, progesterone), K₂CO₃ enhances solubility via:

   
   

   Salt formation: Reacts with acidic groups (e.g., –COOH) to form potassium salts with far higher solubility (e.g., dexamethasone: ≈ 0.05 mg/L as free acid vs. up to ≈ 100 mg/L as potassium salt).

   
   

   Complexation: Binds divalent cations (Ca²⁺/Mg²⁺) to reduce insoluble precipitates (e.g., tetracyclines with Ca²⁺), preventing precipitation and improving GI absorption.

   
   

3. Active Ingredient: Potassium Supplement & Acid-Base Correction

   Used under medical supervision (as a drug rather than an excipient):

   
   

   Hypokalemia treatment: For losses due to vomiting/diarrhea/diuretics (serum K⁺ < 3.5 mmol/L), oral K₂CO₃ supplements K⁺ (1 g ≈ 13.4 mmol K⁺), maintaining osmotic balance and preventing arrhythmias and muscle weakness. Note: Use sustained-release K₂CO₃ tablets (e.g., 0.5 g per tablet) to minimize GI irritation.

   
   

   Metabolic acidosis correction: CO₃²⁻ combines with H⁺ to form CO₂ and H₂O (exhaled), raising blood pH. Concurrent K⁺ supplementation helps prevent the hypokalemia often accompanying acidosis (apparent normal serum K⁺ with intracellular depletion).

Core Quality Requirements for Pharmaceutical-Grade K₂CO₃

(Example: ChP 2025)

Index Category	Pharma Grade	Industrial Grade	Rationale
Main content	≥ 99.0%	≥ 98.0%	Ensure effective pH regulation/K⁺ supply; avoid impurity dilution
Heavy metals	Pb ≤ 0.001% (10 ppm), As ≤ 0.0002% (2 ppm)	Pb ≤ 0.01% (100 ppm)	Prevent cumulative toxicity (e.g., neurotoxicity of Pb, carcinogenicity of As)
Alkali-metal impurity (Na⁺)	≤ 0.5%	≤ 1.0%	Avoid excess sodium in hypertension/heart failure patients
Chloride (Cl⁻)	≤ 0.01%	≤ 0.1%	Prevent electrolyte disturbances (e.g., hyperchloremic acidosis)
Sulfate (SO₄²⁻)	≤ 0.01%	≤ 0.2%	Avoid CaSO₄ precipitation in vivo (stone risk)
Loss on drying	≤ 0.5%	≤ 1.0%	Prevent caking/content drift (e.g., slower tablet disintegration)
Solution clarity	10% aqueous solution clear, no visible particles	Not specified	Avoid insoluble particulates entering the body (e.g., thrombosis risk in injectables)

Safety Notes

Strictly distinguish excipient vs. active ingredient use to avoid misuse/overdose:

1. Excipient safety:

   Very low inclusion levels (< 5%), pharmacopeia-validated; generally no significant adverse effects under normal use. Note: Rare “potassium allergy” patients should avoid K₂CO₃-containing formulations.

   
   

2. Active-ingredient safety (medical supervision):

   Hyperkalemia: Excess K₂CO₃ (daily K⁺ intake > 200 mmol) may raise K⁺ > 5.5 mmol/L → arrhythmias (e.g., ventricular fibrillation), paralysis; life-threatening especially in renal impairment.

   
   

   GI irritation: Non-sustained-release forms can irritate gastric mucosa (nausea, vomiting, pain, ulcers). Use sustained-release or take with food.

   
   

   Drug interactions: With potassium-sparing diuretics (spironolactone) or ACEIs (enalapril), hyperkalemia risk increases—monitor serum K⁺.

   
   

3. Contraindications:

   Severe renal impairment (creatinine clearance < 30 mL/min)

   Hyperkalemia (serum K⁺ > 5.5 mmol/L)

   Addison’s disease (adrenocortical insufficiency impairing K⁺ excretion)

Difference from Similar Excipients (e.g., Sodium Bicarbonate)

K₂CO₃ is often confused with NaHCO₃; both are alkaline excipients but differ:

Dimension	Pharma-Grade K₂CO₃	Pharma-Grade NaHCO₃	Selection Basis
Alkalinity	Weak base (pH 11–12)	Weak base (pH 8.3–8.5)	Use K₂CO₃ for slightly stronger pH adjustment; NaHCO₃ for milder adjustment
Ions	Provides K⁺	Provides Na⁺	Choose K₂CO₃ for sodium-restricted patients; NaHCO₃ for potassium-restricted
Effervescence	Generates CO₂ with acids; slightly astringent taste	Generates CO₂; slightly sweet taste	Effervescents prefer NaHCO₃ (better taste); use K₂CO₃ when sodium must be limited
Stability	Stable (not easily decomposed)	Heat-labile (→ Na₂CO₃, CO₂, H₂O)	—

Essence: In industrial applications, potassium carbonate precisely matches chemical attributes (weak alkalinity, active K⁺) with industrial needs (cost reduction, quality improvement, functionalization). From tuning glass performance to safeguarding purity in electronic components, from stabilizing pharmaceutical formulations to enabling uniform dyeing/printing, K₂CO₃ functions as a universal raw material across sectors, continuously supporting the R&D and production of high-end industrial products—an irreplaceable basic chemical in modern industrial chains.