How to Make Spherical Quartz Powder: A Comprehensive Guide

Spherical quartz powder (also called spherical silica powder) is a high-performance material with excellent fluidity, low thermal expansion coefficient, and high chemical stability, widely used in semiconductor packaging, electronic materials, and advanced composites. The core principle of spheroidization is melting angular particles and letting surface tension form perfect spheres during rapid cooling.

Core Production Methods Overview

Method 1: Flame Melting (Most Common Industrial Process)

Step 1: Raw Material Preparation & Purification

1. Source Selection: Use high-purity natural quartz sand (SiO₂ ≥99.9%) or fused quartz as base material
2. Physical Purification:
   • Magnetic separation to remove iron-bearing minerals
   • Flotation for non-silicate impurities
   • Gravity separation to eliminate heavy minerals
3. Chemical Purification:
   • Acid leaching (HNO₃, HF mixture) to dissolve metallic oxides (Fe₂O₃, Al₂O₃, Na₂O)
   • Deionized water washing until pH neutral
   • Drying at 110-150°C for 4-6 hours
4. Ultra-fine Grinding:
   • Jet milling or stirred media milling to achieve target particle size (0.5-50μm)
   • Air classification to ensure narrow particle size distribution (PSD)
   • Critical: Use ceramic-lined equipment to avoid metal contamination

Step 2: Flame Spheroidization Process

1. Equipment Setup:
   • Combustion system: Oxygen-acetylene, hydrogen-oxygen, or natural gas-oxygen burners
   • Powder feeding system: Pneumatic injector with precise flow control (10-50 kg/h)
   • Reaction chamber: Refractory-lined cylindrical furnace with temperature monitoring
   • Cooling & collection system: Quenching zone + cyclone separator + baghouse filter
2. Process Execution:

    

3. Angular quartz powder → Carrier gas (N₂/Ar) transport → High-temperature flame (1600-2000°C) → Instant melting (residence time: 0.5-2 seconds) → Surface tension-driven spheroidization → Rapid quenching (10⁴-10⁵°C/s) → Spherical particles collection

    

4. Key Parameters:
   • Flame temperature: 1700-1900°C (optimized for complete melting without overheating)
   • Powder feed rate: Matched to flame energy density (avoid under/over-melting)
   • Carrier gas flow: 5-20 m³/h (ensures uniform particle distribution in flame)
   • Quenching rate: Critical for maintaining spherical shape and amorphous structure

Step 3: Post-Treatment & Quality Control

1. Classification: Air classification to remove oversized/undersized particles and agglomerates
2. Secondary Purification:
   • Optional acid washing for residual metal removal
   • Deionized water rinsing and drying
3. Quality Testing:
   • Sphericity: ≥97% (using image analysis, circularity index >0.95)
   • Purity: SiO₂ ≥99.9% (XRF/ICP-MS analysis)
   • PSD: D10, D50, D90, D97 (laser diffraction)
   • Amorphous content: ≥99% (XRD)

Method 2: Plasma Spheroidization (For High-Purity Applications)

Step 1: Raw Material Preparation (Same as Flame Method, but stricter purity standards: SiO₂ ≥99.99%)

Step 2: Plasma Spheroidization Process

1. Equipment Setup:
   • Plasma generator: RF inductively coupled (3-50 MHz, 100-500 kW) or DC non-transferred arc torch
   • Working gases: Ar, Ar-H₂ mixture (improves spheroidization rate)
   • Powder feeder: Vibratory or screw-type with precise control (1-10 kg/h for lab scale)
   • Water-cooled reaction chamber (maintains pressure at 0.1-0.5 MPa)
   • Collection system: Water-cooled copper crucible or cyclone with bag filter
2. Process Execution:

    

3. Purified quartz powder → Carrier gas injection → Plasma zone (4000-7000°C) → Instantaneous melting (residence time: 0.1-0.5 seconds) → Spherical droplet formation → Rapid cooling (10⁵-10⁶°C/s) → Collection of high-purity spherical powder

    

4. Key Parameters:
   • Plasma power: 50-200 kW (balances energy efficiency and melting quality)
   • Gas composition: Ar-5-15% H₂ (enhances spheroidization and reduces oxidation)
   • Powder feed rate: 2-5 kg/kWh (optimizes energy utilization)
   • Chamber pressure: 0.15-0.2 MPa (affects plasma stability and particle trajectory)

Step 3: Post-Treatment & Quality Control (Same as Flame Method, but with stricter impurity limits: metallic contaminants <10 ppm)

Method 3: Spray Drying + Calcination (For Large Particles)

1. Precursor Preparation:
   • Mix organosilane (e.g., TEOS) with water and catalyst (NH₃·H₂O) for hydrolysis
   • Stir for 2-4 hours to form uniform silica sol (solid content: 10-20%)
   • Age for 12-24 hours to increase viscosity
2. Spray Drying:
   • Atomize sol into droplets (10-500μm) using centrifugal or pressure nozzle
   • Dry at 180-250°C in hot air stream (inlet temp: 200-300°C, outlet temp: 100-120°C)
   • Collect spherical xerogel particles
3. High-Temperature Calcination:
   • Heat in rotary kiln at 1200-1500°C for 2-4 hours
   • Removes organic matter, moisture, and hydroxyl groups
   • Enhances structural stability and density

Key Quality Control Parameters

Applications & Performance Advantages

Best Practices for Industrial Production

1. Raw Material Control: Use only certified high-purity quartz (≥99.9%) to minimize post-processing costs
2. Process Optimization:
   • For flame method: Optimize oxygen-fuel ratio for stable temperature field (1.1-1.3 stoichiometric)
   • For plasma method: Adjust power and gas flow to balance spheroidization rate and energy consumption
3. Contamination Prevention:
   • Use ceramic-lined equipment throughout the process
   • Implement closed-loop systems to avoid ambient contamination
4. Energy Efficiency:
   • Recover waste heat from flue gas for preheating raw materials
   • Optimize powder feed rate to maximize energy utilization