Posted tagged ‘Crystalline’

CRYSTAL SYSTEM

August 23, 2011

Crystalline Materials:

  • A crystalline material is one in which the atoms are situated in a repeating (or) periodic array over large atomic distances.

01-space-lattice-unit-cell-represenatation

 

 

Non Crystalline Materials:

  • Materials that do not crystallize are called non-crystalline (or) Amorphous materials

 

Space Lattice:

  • Lattice is the regular geometrical arrangement of points in crystal space.

01-lattice-crystal structure

 

  • The atoms arrange themselves in distinct pattern in space is called a Space Lattice.
  • Atoms in crystalline materials are arranged in a regular 3 – Dimensional repeating pattern known as Lattice Structure.
  • They are divided by network of lines in to equal volumes, the points of intersection are known as Lattice Points.

 

Unit Cell:

01-unit cell

  • It is the smallest portion of the lattice which repeated in all directions.
  • 3D visualization of 14 Space Lattices are known as Bravai’s Space Lattice.
  • If a unit cell contains lattice points only at it’s corners, then it is called Primitive Unit Cell (or) Simple Unit Cell.
  • Three edge length x,y, & z and three interaxial angles α, β, & γ are termed as Lattice Parameters.

 

Crystal System:

  • It is a scheme by which crystal structures are classified according to unit cell geometry.

 

Types of Crystal Systems:

    • Cubic
    • Tetragonal
    • Hexagonal
    • Orthorhombic
    • Rhombohedral
    • Monoclinic
    • Triclinic

 

Crystal Systems

image


Simple Crystal Structure:

Body Centered Cubic Structure (BCC)

  • Unit cell contains 2 atoms
  • Lattice Constant a= 4r / √3, where r is atomic radius
  • Atomic packing factor APF = 0.68
  • Metals are Vanadium, Molybdenum, Titanium, Tungsten

0I-bcc-structure-body center cubic02-bcc-structure-body center cubic

03-bcc-structure-body center cubic

 

Face Centered Cubic (FCC)

  • Unit cell contains 4 atoms
  • Lattice Constant a= 4r / √2, where r is atomic radius
  • Atomic packing factor APF = 0.72
  • FCC structures can be plastic deformed at severe rates
  • Metals are Copper, Aluminum, Phosphorous, Nickel, Cobalt etc

02-fcc-structure-face center cubic-unit cell

0I-fcc-structure-face center cubic-unit cellHexagonal Closed Packed Structure (HCP)

  • Unit cell contains 3 atoms
  • Axial ratio c/a, where ‘c’ is Distance between base planes, ‘a’ is Width of Hexagon
  • Axial Ratio varies from 1.58 for Beryllium to 1.88 for Cadmium (Therefore  a=2.9787, c=5.617)
  • Atomic packing factor APF = 0.74
  • Metals are Zinc, Cadmium, Beryllium, Magnesium etc

0I-hcp-structure-Hexagonal close packed-unit cell

0I-hcp-structure-hexagonal close packed

0I-hcp ball-structure-Hexagonal close packed-unit cell

 

 

Crystallographic Planes and Directions

The Layers of atoms in the planes along which atoms are arranged is known as “Atomic” (or) “Crystallographic planes”.

Miller Indices:

Miller Indices is a system of notation that denotes the orientation of the faces of a crystal and the planes and directions of atoms within that crystal.

Miller Indices for Planes:

1. The (110) surface

02-miller indices-crystalographic planes

 

Intercepts :   a , a , ∞

Fractional intercepts :   1 , 1 , ∞

Miller Indices :   (110)

 

2. The (111) surface

03-miller indices-crystalographic planes

 

Intercepts :   a , a , a

Fractional intercepts :   1 , 1 , 1

Miller Indices :   (111)

The (100), (110) and (111) surfaces considered above are the so-called low index surfaces of a cubic crystal system.

 

3. The (210) surface

04-miller indices-crystalographic planes

 

Intercepts :   ½ a , a , ∞

Fractional intercepts :   ½ , 1 , ∞

Miller Indices :   (210)

X RAY DIFFRACTION

August 23, 2011

It’s useful for studying Crystal structure

This method have the details about

    • Grain size (or) Crystal size
    • Orientation of the crystal
    • Cold worked, Distorted and Internally stressed crystals
    • Re-Crystallization
    • Preferred orientation etc

Methods of Examining and Measuring the condition of Crystal Structure

    1. The Laue back reflection method
    2. The Rotating Crystal method
    3. The DeBye- Scherrer (or) Powder method:

The Laue back Reflection method:

It’s applicable to single crystals (or) poly-Crystalline masses.

When a beam of Mono chromatic (i.e. of Single Wavelength) X-Ray is directed as a narrow pencil at a specimen of a metal diffraction takes place at certain of the crystallographic planes.


03-laue method- x-rays sheild

01-laue back reflection- method-X-ray-diffraction

01-electron-waves-travel-x-rays03-LaueBack reflection

02-lauemethod

The Rotating Crystal method:

It’s a useful method for determining angles and positions of planes.

Crystallographic planes are brought in to reflecting positions by rotating a crystal (Specimen) about one of it’s axis while simultaneously radially it with a beam of mono chromatic x-Rays.

If crystal orientation planes are known, the angles and directions can be calculated.

04-rotating-crytal-method-x-ray-diffration-crystal-structure

05-diffractometer-x ray detector-rotation crystal

The DeBye- Scherrer (or) Powder method:

The narrow pencil of monochromatic X-Rays is diffracted from the powder and recorded by the photographic film as a series of lines of varying armature.

By the Bragg Equation:

nλ=2d Sinθ

Where,

λ– Wave length of X-ray

d- Spacing of the atomic planes

θ – Angle of reflection

06-debye-scherrer-powder-method

 

 

 

 

 

07-debye-scherrer-powder-method

X RAY DIFFRACTION

August 23, 2011

It’s useful for studying Crystal structure

This method have the details about

    • Grain size (or) Crystal size
    • Orientation of the crystal
    • Cold worked, Distorted and Internally stressed crystals
    • Re-Crystallization
    • Preferred orientation etc

Methods of Examining and Measuring the condition of Crystal Structure

    1. The Laue back reflection method
    2. The Rotating Crystal method
    3. The DeBye- Scherrer (or) Powder method:

The Laue back Reflection method:

It’s applicable to single crystals (or) poly-Crystalline masses.

When a beam of Mono chromatic (i.e. of Single Wavelength) X-Ray is directed as a narrow pencil at a specimen of a metal diffraction takes place at certain of the crystallographic planes.


03-laue method- x-rays sheild

01-laue back reflection- method-X-ray-diffraction

01-electron-waves-travel-x-rays03-LaueBack reflection

02-lauemethod

The Rotating Crystal method:

It’s a useful method for determining angles and positions of planes.

Crystallographic planes are brought in to reflecting positions by rotating a crystal (Specimen) about one of it’s axis while simultaneously radially it with a beam of mono chromatic x-Rays.

If crystal orientation planes are known, the angles and directions can be calculated.

04-rotating-crytal-method-x-ray-diffration-crystal-structure

05-diffractometer-x ray detector-rotation crystal

The DeBye- Scherrer (or) Powder method:

The narrow pencil of monochromatic X-Rays is diffracted from the powder and recorded by the photographic film as a series of lines of varying armature.

By the Bragg Equation:

nλ=2d Sinθ

Where,

λ– Wave length of X-ray

d- Spacing of the atomic planes

θ – Angle of reflection

06-debye-scherrer-powder-method

 

 

 

 

 

07-debye-scherrer-powder-method

PLASTIC-2

August 23, 2011

What are Plastics?

Plastics are a material that is made up mainly of macromolecules, that can be made fluid by the action of heating and pressurizing, and that can be processed into end products with any useful shape you want to make.

01-plastic products-plastic household products-Chemical-in-Plastics-to-Cause-Breast-Cancer

Classification of Plastics

Plastics can be classified into:

1. Thermoplastics and Thermo sets
2. Amorphous Thermoplastics and Crystalline Thermoplastics
3. Commodity Plastics and Engineering Plastics

Thermoplastics Vs Thermo sets


01-thermo plastics vs thermosets-difference between thermo plastics and thermosets

Thermoplastics Elastomer

• TPE – thermoplastic elastomer
• Resemble rubber at room temperature
• Can be melt-processed like other thermoplastics
• Become elastic like rubber when cooled

Amorphous Thermoplastics Vs. Crystalline Thermoplastics

01-Amorphous thermoplastics-crystalline thermoplastics

Thermo sets Classifications

01-thermo sets-thermo sets classifications- thermo setting plastics-examples of thermo sets

Commodity Plastics Vs Engineering Plastics

01-difference between commodity plastics and engineering plastics-examples of commodity plastics, examples of engineering plastics

PLASTIC-2

August 23, 2011

What are Plastics?

Plastics are a material that is made up mainly of macromolecules, that can be made fluid by the action of heating and pressurizing, and that can be processed into end products with any useful shape you want to make.

01-plastic products-plastic household products-Chemical-in-Plastics-to-Cause-Breast-Cancer

Classification of Plastics

Plastics can be classified into:

1. Thermoplastics and Thermo sets
2. Amorphous Thermoplastics and Crystalline Thermoplastics
3. Commodity Plastics and Engineering Plastics

Thermoplastics Vs Thermo sets


01-thermo plastics vs thermosets-difference between thermo plastics and thermosets

Thermoplastics Elastomer

• TPE – thermoplastic elastomer
• Resemble rubber at room temperature
• Can be melt-processed like other thermoplastics
• Become elastic like rubber when cooled

Amorphous Thermoplastics Vs. Crystalline Thermoplastics

01-Amorphous thermoplastics-crystalline thermoplastics

Thermo sets Classifications

01-thermo sets-thermo sets classifications- thermo setting plastics-examples of thermo sets

Commodity Plastics Vs Engineering Plastics

01-difference between commodity plastics and engineering plastics-examples of commodity plastics, examples of engineering plastics

PRESSURE FORMING

August 22, 2011

01-pressure forming-products-intricate contours-tight radii-


Material & Description

ABS

Good general purpose material, very tough yet very hard and rigid, good impact and electrical. Available in gauges from .040 to .475 with several extruded textures. Comes opaque and can be matched in custom colors.

ABS/PC

A blend or alloy of ABS and polycarbonate that thermoforms well, weathers well, good color retention, very hard, excellent impact.

ABS/PVC

Flame retardant, tough.

Acrylic

Outstanding weather resistance, excellent optics and electrical properties, poor impact, high gloss and deep luster. Available in standard gauges from .080 to over 1″. Available in clear, transparent and opaque colors.

Acrylic, cell cast

Excellent optics and hot strength, more expensive. Acrylic, continuous and extrusion cast.
Large volume use and best price, good optics.

Acrylic film

3 or 6 mil film for laminating, decorating, and weathering of extruded ABS.

DR Acrylic

Modified acrylic with higher impact properties.

Acrylic/PVC

A blend of acrylic and PVC that is a tough, chemical-resistant material that weathers well and is flame resistant. Available in custom colors.

HDPE (high-density polyethylene)

Crystalline, very tough materials, good weather resistance with UV inhibitors, resistant to many chemicals. Available in standard gauges from .040 to .500. Available in opaque custom colors. Tough and stiff. Good low temperature. Economical.

HMWPE (high molecular weight)

Excellent environmental stress crack properties, thermoforms well, good low temperature.

HIPS (high impact polystyrene)

Good general-purpose material, rigid. Available in clear but usually opaque custom colors from .030 to .350, low cost.

PVC (vinyl)

Good general-purpose material, good abrasion and chemical resistance. Available in clear but usually opaque custom colors from .030 to .125.

Expanded PVC

Stiff, light, flat, thermoformable. Available in stock colors and gauges, generally 3 and 6 mm but others also available.

PETG

Clear, higher impact than acrylic, easy to form. Available in gauges from .030 to .500.

01-pressure forming-blow forming-Thermoform-Console-automobile parts

Pressure Forming:

Pressure Forming is the method used to produce injection mold quality, high definition plastic component parts, housings and containers without the huge expense of tooling. It involves positive pressure to force the heated plastic into the mold cavity. This is called pressure thermoforming or blow forming

Pressure Forming Working Operation:

01-pressure forming-20-150 psi pressure-temperature controlled mold cavity

The highly versatile pressure forming process utilizes air pressure, from 20 to 150 psi, to force the heated sheet into a temperature controlled mold cavity. Vent holes are provided in the mold to exhaust the trapped air. The final part features sharp definition of intricate contours and tight radii. Textures and accurate details are built right into the tooling. Low-cost, highly aesthetic plastic parts of varying sizes are possible due to the application of air pressure, as well as more sophisticated process controls that better monitor tool and sheet temperatures while controlling material shrinkage during forming.

01-pressure forming-products-intricate contours-tight radii-

Types Of Molding operation:

  • Positive Mold
  • Negative Mold

01-pressure forming process-positive molds-cost advantages-pressure forming over thermo forming

Negative molds  have concave cavities. A positive mold has a convex shape.

Pressure Forming over Thermo Forming:

The basic advantage of Pressure Forming over Thermo forming is the cost advantage for small production items. The mould cost for thermo forming is considerably higher in comparison to pressure forming thus for a lower quantity precision job the best suitable method used is pressure forming.

Application:

Pressure forming is used to create in a wide array of plastic products used for packaging of food trays, blisters, covers, internal parts, housings equipment, bezels, bases, and spare parts for use in business machines, electronics, computers and peripherals, bio-medical applications, and instruments.

Features:

Pressure forming achieves features beyond the capabilities of vacuum forming including louvers, ribs, recessed areas, crisp details and logos.

Pressure forming is ideal for small to medium sized production runs that do not justify the high cost of injection molding dies. Additionally, because the aluminum tooling used in pressure forming has an unlimited lifecycle, due to the non-abrasive process versus injection, it saves a great deal of money over many years of continued use. Pressure form tooling usually costs less than 10% the cost of an injection tool. There is also a significant time savings (sometimes 25%) in tooling lead time. Sheet gauges .020″ – .500″ are capable of being pressure formed.