please provide answers, not a snap from a book with no relevance. 3. In the shap

Question

please provide answers, not a snap from a book with no relevance.

3. In the shaping process of powder produced materials, the size of the particles is an important characteristic. Name two other characteristics of particles which are of significance and describe how these characteristics affect the material. (a) (b) What factors determine particle size in metal powder production by chemical reaction? (c) One method of determining particle sizes is to measure the velocity of descent when the particles are suspended in a fluid. (i) Describe two other methods.

Explanation / Answer

owder metallurgy is the manufacturing science of producing solid parts of desired geometry and material from powders. Commonly known as powder metallurgy.the properties are given below

Size And Distribution-Size of particles is a factor that will affect processing of metal powders. In manufacturing practice, powders are commonly measured using a series of screens with different sized openings.

Particle Structure-The structure, or shape, of particles is a major factor in a powder processing operation,Particle shape plays a large roll in powder density and flow characteristics, it is also a major factor in pressing and sintering. There are several types of basic powder particle shapes. These are ideal shapes, particles in reality are imperfect and may exhibit characteristics of more than one shape type(spherical,rounded,angular,spongy etc)

Porosity-Pores, or space, within the powder is in a large part determined by particle shape, (and size), since the shape dictates how particles will contact each other. Spaces that exist between particles of a powder and are open to the outside are called open pores. These spaces expose external surfaces of powder particles.During compaction of powder these spaces are eliminated. If any amount of this space remains after processing, it will result in porosity in the manufactured part. These open pores are permeable to the atmosphere.

(b) Chemical composition of the powder should be known. Powder chemistry is a major factor in manufacturing process design. Individual particles must be examined. Metal powders can be a pure element, a mixture of different elemental particles, or the particles themselves can be an alloy material, called pre-alloyed. Powder metallurgy is unique in its ability to alloy or combine materials that otherwise could not be produced by any other method. Often different materials are powdered and combined as powders. In this case individual powder particles will be all of one type of material or another. The particles will have different characteristics as well. The alloying of metal powders of different materials occurs latter during the sintering of the part. Sometimes nonmetallic powders, particularly ceramic powders, are mixed and combined with other materials.Surface chemistry of powder is critical, due to the high surface area to weight of powders. Oxides may form on particles and should be avoided. Organic materials or silica can develop surface films on powders. Moisture can permeate through open pores and substances within the water can react with particle surfaces, creating films. Surface films are undesirable in manufacturing powders. Typically they are rubbed off by particle motions during compaction and form inclusions in the material.

(c)The ability of a powder to flow will differ, depending upon the properties of that powder. Material flow will involve movement of particles over one another. Factors determining the ability of a particular powder to flow are particle size, particle size distribution, particle structure, particle surface, presence of moisture, material(s) and lubrication. Characteristics that decrease inter-particle friction will tend to increase a powder's ability to flow.

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