Zero Bubbles in Magnetic Slurry! High-Solids Defoaming Test

Solve bubble issues of high-solid slurries including ferrite, rare-earth permanent magnet and soft magnetic composite materials, and greatly improve the consistency of magnetic properties.


Magnetic slurry is a functional slurry mixed by high-performance magnetic powder (ferrite, NdFeB, SmCo, carbonyl iron powder, etc.) and binder carriers (epoxy resin, phenolic resin, solvents, etc.). It is the core raw material for manufacturing permanent magnets, soft magnetic components, magnetic recording media and magnetic sensors. Magnetic slurries generally feature high solid content (powder proportion 60-90wt%), high density, high viscosity and strong thixotropy. In addition, magnetic powder tends to agglomerate, so a large amount of air is easily trapped during stirring and hard to escape naturally. Residual bubbles will directly lead to uneven magnet density, decreased magnetic energy product, fluctuating coercivity and defects on coatings or molded parts. SIENOX provides high-efficiency defoaming solutions for various magnetic slurries through self-developed planetary stirring and defoaming technology.


◆ Material Properties

Magnetic Powder Type

Ferrite (Ba/Sr), NdFeB, SmCo, carbonyl iron powder, Fe-Si-Al powder

Binder / Carrier

Epoxy resin, phenolic resin, PVB, solvent-based dispersion system

Solid Content Range

60~90 wt%, much higher density than ordinary slurries

Viscosity Range

5,000~300,000+ cps, strong thixotropy & shear thinning

Process Temperature

Room temperature ~80℃. Preheating is required for some systems to reduce viscosity and improve fluidity

Defoaming Difficulties

High solid content + high-density powder agglomerates trapping bubbles; interaction between magnetic particles hinders bubble escape


◆ Mature Application Fields

🏭 Permanent Magnet Motors / Generators

Permanent magnet forming slurries (ferrite / NdFeB systems) for new energy vehicle drive motors, wind turbines and industrial servo motors

⚡ Soft Magnetic Composites

Fe-Si-Al / iron powder core, SMC soft magnetic composite slurries for high-frequency inductors and transformer cores (medium viscosity system)

💾 Magnetic Recording Media

Recording layer slurries for magnetic tapes, disks and magnetic cards, nano magnetic particle dispersion system (low viscosity & high uniformity)

📡 Magnetic Sensors

Magnetic film slurries for Hall sensors, magnetoresistive sensors and magnetostrictive sensors (precision coating, nano dispersion)

🔧 Inductor / Transformer Cores

Injection / compression molding slurries for ferrite cores and powder metallurgy magnetic cores (medium & high viscosity system)

🔒 Magnetic Sealing

Magnetic rubber / elastomer slurries for refrigerator door seals, magnetic sealing strips and magnetic gaskets (high viscosity & high filling system)

🖨️ 3D Printed Magnetic Materials

Slurries / inks for additive manufacturing of magnetic materials, photocuring or direct writing molding process (low viscosity & high leveling property)

🔋 New Energy Motor & Electronic Control

Magnetic steel bonding / potting slurries for new energy vehicle drive motors, requiring high magnetic energy product and high reliability

🏥 Medical Magnetic Applications

MRI contrast agent slurries, magnetic nanoparticle dispersions, targeted drug carrier slurries


◆ Core Problems Caused by Bubbles

📉 Degraded Magnetic Performance

Bubbles lead to uneven magnet density, (BH)max drops by 10-30%, coercivity Hcj fluctuates, large discreteness of magnetic performance between batches

⚡ Electrical Insulation Risk

Internal bubbles in soft magnetic cores reduce interlayer insulation, increase eddy current loss, temperature rise intensifies at high frequency and affects device reliability

🔘 Surface & Structural Defects

Pits and pinholes appear on molded parts / coating surfaces, mechanical strength of magnets decreases, prone to chipping or cracking during processing

📊 Poor Consistency & Low Yield

Random bubble distribution results in scattered product performance, difficult batch consistency control, high rework rate and yield below industry requirements


◆ Recommended Process — Planetary Stirring & Defoaming

Step 1 Batching & Pre-mixing

Weigh magnetic powder and binder carrier according to formula. Pre-mix at low speed to fully wet and disperse powder. High-viscosity systems can be preheated to 50-80℃ to reduce viscosity and improve powder dispersion

Step 2 Vacuum Stirring & Defoaming

Put pre-mixed slurry into defoaming cup, set vacuum degree -95KPa and planetary stirring parameters. High shear force generated by planetary motion breaks powder agglomerates and releases trapped bubbles. Vacuum environment accelerates bubble expansion and escape

Step 3 Forming / Casting / Coating

Perform forming operation immediately after defoaming: compression molding, injection molding, tape casting or coating. Avoid violent operation to prevent secondary air entrapment

Step 4 Curing / Sintering

Cure (resin binder system) or sinter (powder metallurgy system) as required by the process. Dense slurry after defoaming ensures no bubble expansion during curing / sintering and uniform product density


◆ Recommended Equipment

  1. MIX60 — Processing capacity 5~60g, suitable for laboratory formula R&D and small-batch magnetic slurry defoaming; excellent effect for low-viscosity magnetic ink / nano dispersion system (5,000~20,000cps)

  2. MIX90 — Processing capacity 20~500g, suitable for medium-batch production and medium-viscosity magnetic slurry (10,000~80,000cps) defoaming; ideal choice for ferrite core slurries

  3. MIX1000PLUS — Processing capacity 100~1,000g, suitable for mass production and defoaming of high-viscosity & high-solid permanent magnet slurries (50,000~300,000 cps)

  4. MIX2000 — Processing capacity 500~2,000g, suitable for industrial continuous production, batch defoaming of large permanent magnet / soft magnetic core slurries


◆ Test Cases

▶ Case 1: Ferrite Permanent Magnet Slurry Defoaming

Test Material

Anisotropic barium ferrite permanent magnet slurry (for motor magnetic tiles, solid content 75wt%, epoxy resin binder system)

Initial Viscosity

25,000 cps (25℃)

Test Model

MIX90

Vacuum Degree

-95 KPa

Rotating Speed

2,000 rpm

Defoaming Time

5 min

Slurry Temperature

40℃ (preheating for viscosity reduction)

✅ Defoaming Result: Mixing and defoaming finished in 5 minutes. Cross-section porosity of magnet<0.5%, magnetic="" energy="" product="">


▶ Case 2: Soft Magnetic Composite Slurry Defoaming

Test Material

Sendust soft magnetic composite slurry (for high-frequency inductor cores, solid content 80wt%, insulation coating + epoxy resin bonding)

Initial Viscosity

60,000 cps (25℃)

Test Model

MIX1000PLUS

Vacuum Degree

-95 KPa

Rotating Speed

2,500 rpm

Defoaming Time

6 min

Slurry Temperature

60℃ (preheating for viscosity reduction)

✅ Defoaming Result: Mixing and defoaming finished in 6 minutes. Cross-section porosity of magnetic core<0.3%, effective="" permeability="">


▶ Case 3: High-Solid Rare-Earth Permanent Magnet Slurry Defoaming

Test Material

NdFeB high-solid permanent magnet slurry (for new energy vehicle drive motors, solid content 88wt%, epoxy / phenolic composite binder system)

Initial Viscosity

120,000 cps (25℃)

Test Model

MIX1000PLUS

Vacuum Degree

-95 KPa

Rotating Speed

2,800 rpm

Defoaming Time

8 min

Slurry Temperature

60℃ (preheating for viscosity reduction)

✅ Defoaming Result: Mixing and defoaming finished in 8 minutes. Cross-section porosity of NdFeB magnet<0.3%, magnetic="" energy="" product="">


◆ Comparison Before & After Improvement

Comparison Item

Before Defoaming

After Defoaming

Magnetic Energy Product (BH)max

Bubbles cause uneven density and low magnetic energy product

Magnetic energy product increased by 15-18% and reaches design value

Coercivity Consistency

Hcj fluctuation ±8%, large batch discreteness

Hcj fluctuation reduced to ±2%, batch consistency controllable

Cross-section Porosity

Porosity 3-8%, uneven distribution

Porosity＜0.5%, dense and uniform

Eddy Current Loss (Soft Magnetic Parts)

Bubbles reduce interlayer insulation and lead to high eddy current loss

Eddy current loss reduced by 25%, high-frequency performance improved

Yield Rate

High rework rate, poor batch consistency

Yield＞99%, stable and controllable batches


🎯 Free Sample Testing    
      Send us your magnetic slurry samples. We will test defoaming parameters and issue a test report.