Here is an English translation of the provided document. Due to its length, the translation is presented in an abridged yet accurate and logically structured form, covering key technical terms and concepts while preserving the original intent and sequence.
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Chapter 1: Introduction
1. Significance of Powder Technology
- Powders are foundational constituents or raw materials in numerous material systems.
- Powder processing is a key enabling technology for material synthesis.
- Ultrafine and especially nanopowders are increasingly vital in advanced material research.
- Powders allow mass production, uniform quality, low cost, and precise control, making them the preferred route for synthetic materials.
2. Definitions
- Particle: A geometric body within a defined size range (mm to nm); includes solid, droplet, or liquid forms.
- Powder: A collection of particles (a particle group); fine powders are termed "dust."
- Powder Science: Studies properties and processing of powders.
3. Powder Technology
- Includes preparation (physical, chemical, mechanical), processing (milling, classification, mixing, granulation, etc.), and characterization (geometric, mechanical, physical, chemical).
4. Classification of Powders
- By origin: natural vs. synthetic.
- By method: mechanical milling vs. chemical synthesis.
- By dispersion: primary, aggregated, agglomerated, flocculated.
- By size: coarse (>74 µm), medium, fine (10–74 µm), micro (<10 µm), nano (<100 nm).
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Chapter 2: Geometric Properties of Powders
1. Particle Size and Distribution
- Size definitions: linear dimensions (three-axis, directional, equivalent diameters).
- Distribution bases: number, length, area, weight.
- Methods: tabular, graphical, moment, and functional (most precise).
2. Shape Factors
- Shape index: dimensionless geometric ratios.
- Shape coefficient: ratios of surface area/volume to a reference diameter.
3. Measurement Techniques
- Sieving: >40 µm; pros: cheap, weight-based; cons: limited range.
- Microscopy: direct observation (optical: 250 µm; SEM/TEM: 5 nm).
- Laser diffraction: 0.1–500 µm; pros: fast, precise.
- Sedimentation: gravity (10–300 µm) or centrifugal (0.01–10 µm).
- Gas adsorption: specific surface area via adsorption isotherms.
4. Packing Structure
- Bulk density (ρb): mass per unit volume.
- Porosity (ε): void fraction; ε = 1 − ρb/ρp.
- Coordination number: contacts per particle.
- Wall effect: packing near walls differs from bulk.
- Optimal packing: multi-modal size distributions reduce porosity (e.g., 7:1:2 coarse/medium/fine ratio).
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Chapter 3: Mechanical Properties of Powders
1. Interparticle Forces
- Van der Waals, electrostatic, capillary, magnetic, mechanical interlocking.
2. Liquid Bridges
- Pendular, funicular, capillary, and slurry states; capillary force depends on liquid volume and wettability.
3. Friction Angles
- Internal friction angle: critical slope stability.
- Angle of repose: flowability indicator (≤30°: good; ≥40°: poor).
- Mass vs. funnel flow: mass flow (uniform, FIFO) preferred for consistent discharge.
4. Stress States
- Active/passive states: failure modes under gravity or compression.
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Chapter 4: Comminution (Size Reduction)
1. Definitions
- Crushing: coarse reduction (>100 mm → 3 mm).
- Grinding: fine reduction (3 mm → 5 µm).
2. Material Properties
- Strength, hardness, brittleness, toughness, grindability.
- Griffith theory: fracture from microcrack propagation under stress.
3. Comminution Models
- Volume: bulk breakage (impact/compression).
- Surface: surface abrasion (attrition).
- Uniform: rare, for loosely bonded aggregates.
4. Methods
- Low-temperature: for heat-sensitive materials.
- Hybrid milling: multi-component systems enhance efficiency via selective breakage.
5. Equipment
- Jaw/cone crushers: coarse.
- Planetary ball mill: micron-level via high-energy grinding.
- Jet mill: ultrafine via supersonic air streams.
6. Efficiency Factors
- Mechanical force, environment (dry/wet), media size, additives (surfactants to prevent agglomeration).
7. Mechanochemical Activation
- Increased surface energy and reactivity via lattice distortion, amorphization, and thermal effects.
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Chapter 5: Classification and Separation
1. Sieving
- Screen types: grizzly, plate, woven (high open area, short lifespan).
- Sequence: coarse-to-fine (efficient) vs. fine-to-coarse (simple).
- Equipment: vibrating, gyratory, drum screens.
2. Ultrafine Classification
- Principles: centrifugal, inertial, rapid classification to minimize agglomeration.
- Dry methods: cyclonic, inertial separators.
3. Gas-Solid Separation
- Cyclone: 5–50 µm; centrifugal force.
- Bag filters: >99% efficiency for 1 µm particles.
- Electrostatic precipitator: sub-µm via corona discharge.
4. Solid-Liquid Separation
- Sedimentation: gravity thickening (zones A–E).
- Centrifugation: density-based separation.
- Spray drying: atomization + hot air → instant powder formation.
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Chapter 6: Storage and Transport
1. Flow Patterns
- Mass flow: uniform discharge (FIFO).
- Funnel flow: core flow (LIFO), risk of arching/ratholing.
2. Arching Prevention
- Geometric design (hopper angle), aeration, vibrators, anti-stick coatings.
3. Segregation
- Causes: particle size/density differences, trajectory effects, vibration.
- Mitigation: inserts (baffles), controlled feeding, blending.
4. Conveying Systems
- Belt conveyors: long-distance, high capacity.
- Screw conveyors: enclosed, but degrades particles.
- Feeders: vibratory (precision), rotary valves (airlock).
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Chapter 7: Mixing and Granulation
1. Mixing Mechanisms
- Convective: bulk movement (e.g., ribbon blenders).
- Diffusive: random motion (e.g., tumbling mixers).
- Shear: inter-particle slip (e.g., high-speed paddles).
2. Mixing Quality
- Mixing index: heterogeneity decreases asymptotically to an optimal point, then reverses (demixing).
3. Granulation
- Purpose: improve flow, reduce dust, enhance compaction.
- Methods:
- Agglomeration: liquid binders (e.g., spray drying).
- Compression: tableting.
- Extrusion/spheronization: uniform pellets.
4. Bonding Mechanisms
- Solid bridges (sintering), liquid bridges (capillary), binders (polymers), van der Waals forces, mechanical interlocking.
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This translation condenses technical details while preserving critical terminology and procedural logic. For full equations or specific method protocols (e.g., ASTM standards), refer to specialized literature.
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