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Manuf > MIXING > Flashcards

MIXING Flashcards

1
Q

Unit operation that aims to treat two or more
components, initially in an unmixed or partially
mixed state, so that each unit (particle, molecule,
etc) of the components lies as nearly as possible in
contact with a unit of each of the other
components

A

Mixing

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2
Q

an ideal situation when each particle
lay adjacent to a particle of the other component

A

Perfect mix

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3
Q

where the probability of selecting
a particular type of particle is the same at all
positions in the mix, and is equal to the proportion
of such particles in the total mix

A

Random mix

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4
Q

Importance of Mixing

A
  • Ensure an even distribution of the active
    components
  • Ensure an even appearance
  • Ensure that the dosage form releases the
    drug at the correct site and at the desired
    rate
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5
Q

Types of Mixtures

A
  • Positive mixtures
  • Negative mixtures
  • Neutral mixtures
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6
Q

Formed from materials such as gases or miscible liquids which mix spontaneously
and irreversibly by diffusion, and tend to approach a perfect mix

A

positive mixing

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7
Q

No input of energy required

A

positive mixing

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8
Q

T/F: Materials that mix by positive mixing
present no problems during product
manufacture

A

T

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9
Q

Components will tend to separate out

A

Negative Mixtures

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10
Q

Energy must be continuously input to keep
the components adequately dispersed

A

Negative Mixtures

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11
Q

Generally more difficult to form and
maintain and require a higher degree of
mixing efficiency than do positive mixtures

A

Negative Mixtures

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12
Q

Static behavior

A

Neutral Mixtures

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13
Q

components have to
tendency to mix spontaneously or segregate
spontaneously once work has been input to
mix them

A

Neutral Mixtures

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14
Q

Mixed powders, pastes and ointments

A

Neutral Mixtures

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15
Q

Mathematical Treatment of the
Mixing Process

A
  • Standard deviation
  • Percentage coefficient of variation
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16
Q

Mechanisms of Mixing and Demixing for Powders

A

convection mixing, shear mixing
and diffusion mixing

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17
Q

Mechanisms of Mixing and Demixing for Liquids

A

bulk transport, turbulent mixing
and molecular diffusion

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18
Q

T/F: Powder segregation is a.k.a demixing

A

T

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19
Q

Transfer of relatively large groups of particles from one part of the powder bed to another, as might occur when a mixer blade or paddle moves
through the mix

A

Convection Mixing

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20
Q

Contributes mainly to the macroscopic mixing of
powder mixtures and tends to produce a large
degree of mixing fairly quickly

A

Convection Mixing

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21
Q

T/F: Convection mixing does not, however, occur within the group
of particles moving together as a unit,

A

T

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22
Q

In order to achieve a random mix in convection mixing, an ____________ is required

A

extended mixing
time

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23
Q

Occurs when a layer of material moves or flows
over another layer.

A

Shear Mixing

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24
Q

This might be due to the
removal of a mass by convective mixing creating an unstable shear/slip plane, which causes the powder bed to collapse

A

Shear Mixing

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25
Q

Shear Mixing occurs in high shear mixers or _____________

A

tumbling mixers

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26
Q

where the action of the mixer induces velocity
gradients within the powder bed and hence
shearing of one layer over another

A

high shear mixers or tumbling mixers

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27
Q

Movement of individual particles through
the voids created due to gravit

A

Diffusive Mixing

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28
Q

Potential to produce random mix, generally
results in a low rate of mixing

A

Diffusive Mixing

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29
Q

Analogous to the convective mixing of
powders

A

Bulk Transport

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30
Q

Involves the movement of a relatively large
amount of material from one position in the
mix to another, eg due to a mixer paddle

A

Bulk Transport

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31
Q

Arises from the haphazard movement of molecules

A

Turbulent Mixing

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32
Q

this means that induced turbulence is highly effective
mechanism for mixing

A

Constant changes in speed and direction of movement

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33
Q

Within a turbulent fluid there are, however, small
groups of molecules moving together as a unit,
referred as

A

Eddies

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34
Q

alone may therefore leave small
unmixed areas within the eddies and in areas near the
container surface which will exhibit streamlined flow

A

Turbulent mixing

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35
Q

Analogous to diffusive mixing in powder

A

Molecular Diffusion

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36
Q

Occur with miscible fluids wherever a
concentration gradient exits and will
eventually produce a well-mixed product

A

Molecular Diffusion

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37
Q

Opposite effect of mixing

A

Powder Segregation

38
Q

Components tend to separate out

A

Powder Segregation

39
Q

Will cause an increase in content variation in
samples taken from the mix and may cause a batch
to fail a uniformity of content test

A

Powder Segregation

40
Q

Particle size effects, particle density effects,
particle shape effects

A

Powder Segregation

41
Q

Ordered mixes can reduce or
prevent segregation, it occurs if

A
  • Carrier particles vary in size
  • There is competition for the active sites on
    the carrier particle
  • There are insufficient carrier particles
42
Q

Practical Considerations

A
  • Geometric dilution
  • Volume of powder in the mixer
  • Mixer should produce the mixing mechanism
    appropriate for the formulation
  • Mixer design – dust tight, easily cleaned, product can
    be fully discharged
  • Checking of the mixing process at different time to
    determine the most appropriate mixing time
  • Mixers should be earthed to dissipate the static
    charge and the process should be carried out at a RH
    > approx. 40%
43
Q

Mixers should be earthed to dissipate the static
charge and the process should be carried out at a RH
________________

A

> approx. 40%

44
Q

Mixer design should be

A

dust tight, easily cleaned, product can
be fully discharged

45
Q

Blenders

A

Tumbling Mixers

46
Q

Commonly used for the mixing/blending of granules or free
flowing powders but poor for cohesive or poorly flowing
powders

A

Tumbling Mixers

47
Q

blending lubricants,
glidants or external disintegrants with granules prior to tableting

A

Tumbling Mixers

48
Q

Can also be used to produce ordered mixe

A

Tumbling Mixers

49
Q

Double cone mixers, twin-shell mixers, cube mixers. Y-cone
mixers and drum mixers

A

Tumbling Mixers

50
Q

Mounted so that they can be rotated about an axis. When
operated at the correct speed, the tumbling action indicated is
achieved

A

Tumbling Mixers

51
Q

Common to use Intermediate bulk containers (IBCs) both as the
mixer bowl and to either feed the hopper of a tablet or capsule
machine or as the hopper itself

A

Tumbling Mixers

52
Q

Can both mix and granulate a product,
thereby removing the need to transfer the
product between pieces of equipment and so
reducing the opportunity for segregation to
occur

A

High Speed Mixer-Granulators

53
Q

Drying of granules or the coating of
multiparticulates

A

Fluidized Bed Mixers

54
Q

Used to mix powders prior to granulation in
the same bowl

A

Fluidized Bed Mixers

55
Q

Agitator Mixers depends on the motion of a blade or paddle
through the product, and hence the main mixing
mechanism is ___________

A

convection

56
Q

Mixing is achieved by the rotation of helical
blades in a hemispherical trough. D

A

Agitator Mixers

57
Q

Dead spots are
difficult to eliminate in this type of mixer and the
shearing action caused by the movement of the
blades may be insufficient to break up drug
aggregates

A

Agitator Mixers

58
Q

mix poorly
flowing material and is less likely to cause
segregation than a tumbling mixer

A

Agitator Mixers

59
Q

Mobile liquids with ________ are easily mixed
with each other

A

low viscosity

60
Q

Solid particles are readily suspended in ________, although the particles are likely to settle
rapidly when mixing is discontinued

A

mobile
liquids

61
Q

more difficult to stir and mix
but they reduce the sedimentation rate of
suspended particles

A

Viscous liquids

62
Q

Equipments used in mixing of mixcible liquids and suspensions

A

propeller mixer, turbine
mixers, In line Mixers

63
Q

Common arrangement for medium scale fluid mixing, which may be
clamped to the edge of a vessel

A

Propeller mixers

64
Q

has angled blades, which cause the fluid to circulate in both
an axial and radial direction

A

Propeller mixers

65
Q

(Propeller Mixers) An off centre mounting discourages the formation of a _________, which
may occur when the stirrer is mounted _______.

A

vortex; centrally

66
Q

(Propeller Mixers) forms when
the centrifugal force imparted to the liquid by the propeller blades
causes it to back up around the sides of the vessel and create a
depression at the shaft.

A

Vortex

67
Q

(Propeller Mixers) the speed of rotation is ___________, air may be
sucked into the fluid by formation of a vortex, this can cause frothing
and possible oxidation

A

increased

68
Q

(Propeller Mixers) Another method of suppressing the vortex is to fit _________ into
the vessel

A

vertical baffles

69
Q

(Propeller Mixers) Ratio of the diameter of a propeller stirrer to that of the vessel is ___________, operates at speeds of 1-20 rps

A

1:10 –
1:20

70
Q

Used for more viscous fluids

A

Turbine Mixers

71
Q

(Turbine Mixers) Impeller has _____ flat blades surrounded by perforated inner
and outer diffuser rings.

A

4

72
Q

(Turbine Mixers) draws the
liquid into the mixer head and forces the liquid through the
perforations with considerable radial velocity, sufficient to
overcome the viscous drag of the bulk of the fluid

A

rotating impeller

73
Q

absence of an axial component, but a different
head with the perforations pointing upwards can be fitted if
this is desired (Turbine Mixers)

A

Drawback

74
Q

As the liquids is forced through the small orifices of the
diffuser rings at high velocity__________ are
produced (Turbine Mixers)

A

large shear forces

75
Q

Will not cope with liquids of very high viscosity, as the
material will not be drawn into the mixer head

A

Turbine Mixers

76
Q

s an alternative to mixing fluids in batches
in vessels, mobile miscible components
may be fed through an inline mixer
designed to create turbulence in a flowing
fluid stream

A

Inline Mixers

77
Q

Continuous mixing process is needed

A

Inline Mixers

78
Q

Problems that arise during the mixing of semi-
solids (ointments & pastes) stem from the fact,
that, unlike powders and liquids, semisolids will
_____________

A

not flow easily

79
Q

T/F: Material that finds its ways to dead spots will
remain there.

A

T

80
Q

In mixing semisolids, suitable mixers must
have rotating elements with narrow clearances
between themselves and the mixing vessel wall
and they must produce a ___________, as diffusion and convection cannot occur

A

high degree of shear
mixing

81
Q

Mixer used in mixing semisolids

A

planetary mixers, sigma blade
mixer

82
Q

Commonly found in domestic kitchen and larger machines
which operate on the same principle are used in industry

A

Planetary Mixers

83
Q

Mixing blade is set off centre and is carried on a rotating
arm.

A

Planetary Mixers

84
Q

travels round the circumference of the mixing bowl
while simultaneously rotating around its own axis

A

Planetary Mixers

85
Q

This is
therefore a double rotation similar to that of a spinning
planet rotating around the sun

A

Planetary Mixers

86
Q

A small clearance between the vessel and the paddle gives
shear, but scraping down several times is necessary to mix
the contents well as some materials are forced to the top of
the bowl

A

Planetary Mixers

87
Q

Used to mix powders, particularly if a wet mass
granulation is required

A

Planetary Mixers

88
Q

Robust mixer that will deal with stiff pastes and
ointments and depends for its action on the close
intermeshing of the 2 blades which resembles the Greek
letter Sigma in shape

A

Sigma Blade mixer

89
Q

(sigma blade mixers) he clearance between the blades and the mixing trough
is kept _________ by the shape greek letter Sigma

A

small

90
Q

T/F: It is very difficult using primary mixers to completely
disperse powder particles in a semisolid base so that they
are invisible to the eye. (Sigma Blade mixer)

A

T

91
Q

The mix is usually subjected to
the further action of __________, so as to rub
out these particles by the intense shear generated by
rollers or cones set with very small clearance between
them. (Sigma Blade mixer)

A

roller mill or colloid mill

Manuf (12 decks)

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