Investment materials developed in the first half of the twentieth century, to give clinically acceptable dental castings. But Wrongly, many assume that dental casting investment materials have reached a level of development that makes them completely fit for purpose and that the technology is stable. This is not the case. Casting titanium and it’s requirement for increased precision have given new challenges Silica exists in 22 different condensed phases. Five of these are amorphous, and 17 are crystalline; the latter are the polymorphs of silica. Of this group, only one phase, low-temperature quartz, is thermodynamically stable at normal temperature and pressure. Two more, tridymite and low-temperature cristobalite, exist under normal atmospheric conditions as metastable (but actually long-lived) phases In the investment powder, the binder is calcium sulfate hemihydrate. When the investment sets, the silica is unaffected; the hemihydrate binder combines with water to form dihydrate (gypsum).The set investment consists of fine particles of silica embedded in gypsum crystals. When this material is heated to the temperatures required for complete dehydration and sufficiently high to ensure complete castings, it shrinks considerably and occasionally fractures. The thermal expansion curves of the three common forms of gypsum products are shown in Figure. All forms shrink considerably after dehydration between 200" C and 400" C . A slight expansion takes place between 400" C and approximately 700, and a large contraction then occurs This shrinkage is most likely caused by decomposition and the release of sulfur gases, such as sulfur dioxide. This decomposition not only causes shrinkage but also contaminates the castings with the sulfides of the non-noble alloying elements, such as silver and copper. Thus it is imperative that gypsum investments not be heated above 700" C (1292" F). However, for gypsum products containing carbon, the maximum temperature should be 650" C (1202" F). In this way, proper fit and uncontaminated alloys are obtained.

1. “If you only do what you can do, you’ll never be
better than what you are.” - Shifu
Good Morning

2. Investment Material
&
Temporization, Cementation

3. Investment
Material
Uses
Composition
Properties
Definition
Types

4. Must expand to compensate for the alloy shrinkage
Should have a fine particle size
The manipulation should be easy.
Smooth consistency when mixed.
Must have adequate strength
Break away readily from the surface of the metal
A ceramic material which is suitable for forming a mold into which molten
metal or alloy is cast
Definition
Properties
Should not react chemically with it.
Material should be economical.
Should be porous enough.
The investment must not decompose.

5. Types
Gypsum bonded investments
Phosphate bonded investments
Ethyl silica bonded investments
Gold alloys
up to 700°C.
Metal ceramic & Cobalt chromium alloys
850 to 1100°C.
Base metal alloy partial dentures
> 1100°C.

6. Composition
REFRACTORY
Withstand high temperatures without decomposing or disintegrating
Quartz Trydimite Crystabollite Fused Quartz
Silica

7. Composition
BINDER
Set and bind together the particles of refractory substance
alpha-hemihydrate
Ethyl silicate,
Ammonium sulphate
Sodium phosphate
CHEMICAL MODIFIERS
Sodium Chloride, Boric Acid, Potassium Sulfate, Graphite, Copper Powder Or Magnesium Oxide

8. GYPSUM-BONDED INVESTMENT
ADA Specification No. 2 for casting investments for dental gold alloys encompasses three
types of investments
Type I - Inlays Or Crowns Thermal Expansion
Type II - Inlays, Onlays, Or Crowns Hygroscopic Expansion
Type III – Partial Denture
Inlay investment Denture investment (ISO 3)
Hygroscopic Expansion(ISO Type 2)Thermal Expansion (ISO Type 1)
Rapid-Heat Slow-Heat

9. Typical gypsum-bonded investments
Inlay investment, thermal expansion (ISO
Type 1)
Cristobalite Inlay (Kerr/Sybron)
Inlay investment, thermal expansion, rapid
heat (ISO Type 1)
Cristoquick (GC)
Inlay investment, hygroscopic expansion
(ISO Type 2)
Beauty-Cast (Whip Mix)
Denture investment (ISO Type 3) R&R Gray (Dentsply/Ransom and
Randolph)

10. Composition
α-hemihydrate of gypsum , quartz or cristobalite, allotropic forms of silica.
Greater Strength
The strength of the investment is dependent on the amount of binder present
25% to 45%

11. Quartz Trydimite Crystabollite Fused Quartz
Silica
Regulate The Thermal Expansion
55% to 75%.

12. When quartz, tridymite, or cristobalite is heated, a change in crystalline form occurs at a
transition temperature characteristic of the particular form of silica
575 °C
β-Quartzα-Quartz
200° & 270° C
α-Cristobalite β-Cristobalite
117° & 163° C
β-allotropic forms are stable only above the transition temperature noted, and an inversion
to the lower a form occurs on cooling in each case
α-Trydimite β-Trydimite

14. Modifiers
Reducing AgentsModifying Agents Coloring Matter
Provide A Nonoxidizing Atmosphere In The Mold
Not only regulate the setting expansion and the setting Time, but also prevent most of
the shrinkage of gypsum when it is heated above 300° c
Modifiers - Boric Acid And Sodium Chloride
Reducing Agents - Carbon And Powdered Copper

15. Properties
Particle size of the powder
The particle size affects the smoothness of the mold cavity surface
Manipulation time
Investing the wax pattern or pouring the investment cast must be completed while
the mix is still fluid.
Setting Time >25 minShould Not Be<5 min
Modern Inlay Investments Set Initially In 9 To 18 Min
< 75 um

16. A mixture of silica & calcinated gypsum (calcium sulfate hemihydrate) results
in setting expansion greater than that of the gypsum product used alone
Type I investment ≈ 0.6%.
Modern investments is ≈ 0.4%
The setting expansion in enlarging MOLD containing the
wax pattern may be related to the thermal expansion of
the WAX pattern
Investment
Wax
Pattern
SprueRing
Mold
EXPANSION
1) Setting Expansion - 0.1% to 0.6%.

17. The setting expansion of an investment with a comparatively high gypsum content is
more effective in enlarging the mold than is a product with a lower gypsum content.
It is Effective only to the extent that the exothermic heat is transmitted to the pattern
The amount of heat present depends on the gypsum content of the investment
Theory
It is one of the methods for expanding the casting mold to compensate for the casting
shrinkage of the gold alloy
Type II investments setting expansion in water -
Maximum 2.2%
Minimum 1.2%
2) Hygroscopic Setting Expansion - 1.3%

19. Factors Affecting Hygroscopic Setting Expansion
Effect of Composition
Effect of Water/Powder Ratio
Effect of Spatulation
Shelf Life of the Investment
Effect of Time of Immersion
Effect of Confinement
Effect of Added Water

20. Effect of Composition
Magnitude Of The Hygroscopic
Setting Expansion Silica Content Of The Investment
Finer The Particle Size Of The Silica Hygroscopic Setting Expansion
Investment should have enough hemihydrate binder with the silica to provide sufficient
strength after hygroscopic expansion. Otherwise, a shrinkage occurs during the
subsequent drying of the set investment.
At least 15% of binder is necessary to prevent a drying shrinkage

21. Effect of Water/Powder Ratio
The higher the water/powder ratio of the original investment water mixture, the less the
hygroscopic setting expansion.
Effect of Spatulation
Hygroscopic ExpansionMixing Time
Shelf Life of the Investment
Older The Investment, The Lower Its Hygroscopic Expansion
Effect of Time of Immersion
The greatest amount of hygroscopic setting expansion is observed if the immersion takes
place before the initial set

22. Effect of Confinement
The confining effect on hygroscopic expansion is more pronounced than the similar
effect on the normal setting expansion
Therefore the effective hygroscopic setting expansion is likely to be less relative
Effect of Added Water
The magnitude of the hygroscopic setting expansion can be controlled by the amount of
water that is added to the setting investment
No Further expansion is evident regardless of any amount of water added.
Hygroscopic expansion Amount of water added during the setting period

23. Thermal Expansion
Thermal Expansion Amount & Type of silica
A considerable amount of quartz is necessary to counter-balance the contraction of the
gypsum during heating
The contraction of the gypsum is entirely balanced when the quartz content is increased
to 75%
•The particle size of the quartz,
•The type of gypsum binder,
•The resultant water/powder ratio necessary to provide a workable mix.
The thermal expansion curves of quartz investments are influenced by -

24. Thermal expansion of the investment
25% POP & 75% of Quartz Crystabollite(Courtesy of G.C. Paffenbarger.)

25. Mold is usually heated to about 700°C in order to gain maximum mold expansion
The sulfur dioxide formed by the second reaction causes sulfide formation on the
gold-alloy casting, resulting in discoloration and embrittlement of the alloy
(O'Brien and Nielsen, 1959).
Sulfur dioxideCalcium Sulfate Carbon

26. Effect of the Water/Powder Ratio
Magnitude of thermal expansion is related to the amount of solids present.
Therefore it is apparent that the more water that is used in mixing the investment,
the less the thermal expansion achieved .
Effect of Chemical Modifiers
A disadvantage of an investment that contains sufficient silica to prevent any contraction
during heating is that the weakening effect of the silica in such quantities is likely to be
too great.
Addition of small amounts of sodium, potassium, lithium chlorides to the investment
eliminates the contraction caused by the gypsum and increase the expansion without
the presence of an excessive amount of silica.

27. Thermal Contraction
When an investment is cooled from 700" C, its contraction curve follows the expansion
curve during the inversion of the β-quartz or β-cristobalite to its stable a form at room
temperature.
Strength
Compressive strength < 2.5 MPa
However, when larger, complicated castings are made, a greater strength is necessary,
as required for Type III partial denture investment
Any investment that meets this requirement should possess adequate strength for the
casting of an inlay
The More Water That Is Employed In Mixing, The Lower The Compressive Strength
The greatest reduction in strength on heating is found in investments containing sodium
chloride

29. The selection of an investment is largely a matter of preference. Some investments
are formulated for casting inlays and crowns employing thermal expansion as the
main factor for casting shrinkage compensation, and some are designed for use with
hygroscopic setting expansion.
Consequently, the choice is dependent partly on the specific techniques for which
the investment is designed. Acceptable castings for the range of typical dental cavity
preparations can be made with a number of investments and techniques.

30. The investment should be weighed and the water should be measured according to the
proportion of the investment mix. Only in this manner can one expect to control the
setting or the thermal expansion in relation to the compensation needed for the casting
shrinkage and other important properties.

31. Item Beauty-Cast
Gypsum
Investment
Cristobalite
Investment
Material
Novacast
Investment
Material
Soldering
Investment
Compressive
Strength
700 psi (5 MPa) 700 psi (5 MPa) 950 psi (7 MPa) 1,200 psi (9 MPa)
Working Time 3 minutes 3 minutes 3 minutes 2 - 3 minutes
Set Time 14.5 minutes 16 minutes 15 minutes 15 minutes
Indication For Use Low Fusing Crown
and Bridge Alloys
Low Fusing Crown
and Bridge Alloys
Low Fusing Crown
and Bridge Alloys
Low and High
Fusing Precious
Metals
Liquid / Powder
Ratio
30 mL/100 g 30 mL / 100 g 34 mL / 100 g 24 mL / 100 g
Setting Expansion 0.4 % 0.5 % 0.45 % 0.25 %
Ready For Burnout 30 minutes 30 minutes 30 minutes 30 Minutes
Hygroscopic
Expansion
1.5 %
Thermal Expansion 480º C - 0.55%
650º C - 1.20%
650º C (1,200º F) -
1.25 %
650° C - 1.20 % 700° C (1,300° F) -
0.60 %

32. High-Temperature Investments

33. These investments are not gypsum based
The predominate compositions, used for the casting of high temperature
alloys and for creating veneering dies, are based on the use of a phosphate binder.
Silicate-bound systems are also used (Kondic, 1960)
But because of their difficult handling, their use tends to be restricted to the casting
of cobalt chromium alloys at temperatures above 1,425°C
Either entirely new systems or modifications
Titanium-based Alloys.

34. PHOSPHATE-BONDED INVESTMENT
The most widely utilized investment In dentistry. This is because a substantial amount
of cast dental structures today use high fusing noble or base metal alloys
Type
Type I Inlays, Crowns & Other Restorations,
Especially for alloys based on gold, platinum, palladium, cobalt-
chromium, and nickel-chromium
Type II Removable partial dentures.
The rapid growth in use of metal-ceramic and hot-pressed ceramic prostheses has
resulted in an increased use of phosphate or silicate-bonded investments.

35. PHOSPHATE-BONDED INVESTMENT
Powder
Aqueous Solution
Refractory Materials Glasses & Other Metal Oxides NH4H2PO4 MgO
Colloidal Silica
These investments are available as two-component systems that react to form a solid
when mixed together. (Takahashi et al, 1990)
Quartz Cristabolite

36. Cristobalite, Quartz, or a mixture of the two & in a concentration of approximately 80%
Provide High-temperature thermal shock resistance (refractoriness) and a high thermal
expansion.
Fillers
Particle size varies from a submicron level to that of a fine sand.
Binder
Magnesium Oxide & A Phosphate That Is Acid In Nature.
Contraction during solidification is also greater
This necessitates a greater expansion of the investment.
Colloidal Silica
For predominantly base metal alloys, a 33% dilution of the colloidal silica is required

37. Carbon
To produce clean castings and facilitate the divesting of the casting from the mold
Powder
Gold Alloy Silver-palladium alloys
Palladium-silver alloys
Base metal alloys
Evidence indicates that palladium reacts with carbon at temperatures above 1504°C.
Thus if the casting temperature of a high palladium alloy exceeds this critical point, a
phosphate investment without carbon should be used
Melting the alloyCarbon crucible

38. Setting Reactions
1
2

39. Setting and Thermal Expansion

40. However, some of the shrinkage is masked because of the expansion of the
refractory filler, especially in the case of cristobalite.
The early thermal shrinkage of phosphate investments is associated with the
decomposition of the binder, magnesium ammonium phosphate, and is accompanied
by evolution of ammonia, which is readily apparent by its odor
For gypsum investments the shrinkage is caused by the transformation of the
calcium sulfate from the hexagonal to the rhombic configuration

41. Working and Setting Time
The warmer the mix, the faster it sets.
The setting reaction itself gives off heat, and this further accelerates the rate of setting.
More efficient the mixing, The better the casting in terms of smoothness & accuracy.
Mechanical mixing under vacuum is preferred.
Another variable is the L/P ratio -
It can be very short (2 min Or less) when investment is mixed at the manufacturer
recommended L/P ratio, at high speed (1750 rpm) for the recommended time.
Working TimeL/P ratio

42. For the burnout process of the conventional Type I investment for inlays and crowns,
it is recommended that the mold be set in a furnace at room temperature, 1 hour after
trituration,
Recently, newer investments that allow insertion of the set investment directly into a
furnace at the burnout temperature (800°C) have been developed. These investments
are inserted 30 minutes after the powder has been mixed with the liquid.
It should be heated to 800°C over 1 to 2 hours (depending on the size of the mold)
and held at 800°C for 30 minutes before casting.

43. Effects of setting under air pressure on the number of surface
pores and irregularities of dental investment materials
(J Prosthet Dent 2014;111:150-153)
Conclusion -
Specimens set under positive pressure in a pressure chamber presented fewer surface
bubbles than specimens set under atmospheric pressure. Positive pressure is effective and,
therefore, is recommended for both gypsum-bonded and phosphate-bonded investment
materials.
Clinical Implications -
Setting investment materials in a positive pressure chamber led to fewer surface irregularities,
which makes the finishing and seating of the crown easier.

44. Advantages
They have both high green strength.
They can also provide setting and thermal expansions high enough to compensate for
the thermal contraction of cast-metal prostheses or porcelain veneers during cooling.
They have the ability to withstand the burnout process with temperatures that reach
900°C and they can withstand temperatures up to 1,000°C for short periods of time
(useful for fabricating porcelain veneers or performing metal-joining operations).

45. • High mold temperatures, result in mold breakdown and rougher surfaces on
castings.
• The high strength of these investments, although an advantage during casting, can
make divesting a difficult and tedious task .
• Further, when higher expansion is required, more of the silica liquid is used with
the result that a more dense and less porous mold is produced. This can result in
incomplete castings if a release for trapped gases is not provided.
Disadvantages

47. Increasing the special liquid/water ratio used for the mix markedly enhances
casting surface smoothness, but it can lead to oversized extra coronal castings
The phosphate investment now approaches that of the gypsum investments in
fineness.
However, their ability to improve the smoothness is dependent on the alloy and
casting procedure employed.

48. Although the basic binding reaction is the same for all of the phosphate-bonded
investments, there are some important differences in properties due to composition
High-temperature
Alloys
Contain Quartz And Cristobalite To Achieve Expansion
Soldering Investments Do Not Require Especially Fine Powders And Are Designed
Without High-expansion Fillers
Graphite Render Investment More Permeable After Burnout

49. BRAZING INVESTMENT
ANSI/ADA Specification No. 93 (IS0 11244) for dental brazing investments defines
two types of investment:
Type 1: Gypsum-bonded dental brazing investments
Type 2: Phosphate-bonded dental brazing investments

50. ETHYL SILICATE-BONDED INVESTMENT
Composition
Powder
Refractory Particles
Silicas & Glasses
Calcined Magnesium Oxide
Liquid
A Stabilized Alcohol Solution Of Silica Gel
Ethyl Silicate Denatured Ethyl Alcohol

51. ETHYL SILICATE-BONDED INVESTMENT
Binder is a silica gel that reverts to silica (cristobalite) on heating
When the pH of sodium silicate is lowered by the addition of an acid or an acid salt, a
bonding silicic acid gel forms. The addition of magnesium oxide strengthens the gel
An aqueous suspension of colloidal silica can also be converted to a gel by the
addition of an accelerator, such as ammonium chloride.
Methods
1

52. 2 Based on ethyl silicate
A colloidal silicic acid is first formed by hydrolyzing ethyl silicate in the presence of
HCL, ethyl alcohol, and water.
The sol is then mixed with the quartz or cristobalite to which is added a small amount
of finely powdered magnesium oxide to render the mixture alkaline
Soft gel is dried at a temperature below 168" C (334" F).
Green Shrinkage

53. The setting shrinkage is reduced to 0.1 %
The powder is added to the hydrolyzed ethyl silicate liquid, mixed quickly & vibrated into a
mold that has an extra collar to increase the height
The mold is placed on the platform of a special type of vibrator that provides a so-called
tamping action
The remaining cast is somewhat fragile because the amount of binder is quite low & is
essentially composed of silica
Compressive strength at room temperature shall not be less than 1.5 MPa.

54. Properties
Withstand higher temperatures than the phosphate-bonded investments
As a result, the top of the mold is prone to cracking due to greater drying shrinkage
from the evaporation of the ethyl alcohol, which results from the formation of the
silica gel.
During the vibration of the investment slurry into a casting ring around a pattern, a
separation occurs between the finer and coarser particles, The finer particles of the
investment rise to the top of the mold where the slurry acquires more liquid.
These cracks must be removed prior to the firing process. Otherwise, when the mold
is heated to burn out a pattern and achieve thermally induced expansion, the cracks
will grow and result in faulty castings.

55. Advantages
It offer the ability to cast high-temperature cobalt chromium and nickel-chromium
alloys,
Attain good surface finishes, low distortion, and high thermal expansion (good fit).
They are less dense (more permeable) than the phosphate-bonded investments, and thin
sections with fine detail can be reproduced.
Their low fired strength makes divesture easier than with phosphate-bonded investments
Precaution needed in handling the low strength fired molds.
The low strength and high thermal expansion require a more precise burnout
process and firing schedule to avoid cracking and, hence, destruction of a mold
Disadvantages

56. INVESTMENT FOR ALL-CERAMIC RESTORATIONS
Type
Type I The Cast Glass Technique
Type II Refractory Die Type Of Material
Refractory dies are made by pouring the investment into impressions
Refractory die spacer may be added
Porcelain or other ceramic powders are added to the die surface and fired

57. Item Formula 1 Universal
Investment
Cerami gold
Investment with
Carbon
PC 15 Phosphate
Bonded Investment
Compressive Strength 1.350 psi (9.2 MPa) 1,500 psi (10 MPa) 500 psi (3.4 MPa)
Working Time 6 - 8 minutes 6 - 7 minutes 7 - 9 minutes
Indication For Use Universal Investment for
All Alloys and Pressable
Ceramics
Crown and Bridge and
Ceramic Gold Alloys Pressable Ceramics
Liquid / Powder Ratio 22 mL / 100 g 16 mL /100 g 27 mL / 100 g
Setting Expansion 1.6 % 0.7 % 1 %
Ready For Burnout 15 minutes 60 minutes 15 minutes
Thermal Expansion 0.65 % 1.2 % 0.7 %
Material Type Phosphate Bonded
Investment
Phosphate Bonded
Investment
Fine Grain Phosphate
Bonded Investment

58. Item Cera-Fina Carbon-
Free Fine Grained
Investment
FastFire 15
Phosphate
Investment
Hi Temp Carbon-
Free Investment
PowerCast
Phosphate
Investment
Compressive
Strength
Wet - 600 psi (4
MPa)
Wet - 500 psi (3.4
MPa)
Wet - 1,500 psi (10
MPa)
Wet - 700 psi (5
MPa)
Working Time 8 - 10 minutes 7 - 9 minutes 7 - 8 minutes 8 - 9 minutes
Indication For
Use
High Fusing Alloys Universal Phosphate
Investment for All
Crown and Bridge
Alloys
High Fusing Alloys Casting Crown and
Bridge and Ceramic
Alloys
Liquid /
Powder Ratio
24 mL / 100 g 27 mL / 100 g 16 mL / 100 g 23 mL / 100 g
Setting
Expansion
0.25 % 1.0 % 0.7 % 0.8 %
Ready For
Burnout
90 minutes 15 minutes 60 minutes 45 minutes
Thermal
Expansion
1.3 % 1 % 1.2 % 1 %
Material Type Carbon-free
Phosphate Bonded
Investment
Fine Grain
Phosphate
Carbon-Free
Phosphate Bonded
Carbon-free, Fine-
grain Phosphate-
bonded Investment

59. Item X-20 Chrome
Phosphate
Investment
Carrara Universal
Dustless Investment
Polyvest Refractory
Die Material
V.H.T. Refractory
Investment
Compressive
Strength
Wet - 2,500 psi (17
MPa)
~2 MPa after 2h,
~6,7 MPa after
heating
6,000 psi (42 MPa) 2,500 psi (17 MPa)
Working Time 4 - 5 minutes 7 minutes 2 minutes 4 - 5 minutes
Indication For
Use
Casting Partials with
Chromium Dental
Alloys
Casting Precious
Metal Alloys and
Pressing Ceramics
Refractory
Investment - Direct
Firing Ceramics
Direct Firing
Ceramics
Liquid / Powder
Ratio
11 mL / 100 g 100 g / 24 mL 22 mL / 100 g 19 mL / 100 g
Setting
Expansion
0.2 % 0,3 - 2 % 0.8 % 0.3 %
Thermal
Expansion
700 -- 1,000° C
(1,300 -- 1,800° F) -
0.90 %
1.0 - 1.2 % 500° C, 2nd firing -
0.65%
500° C, 2nd Firing -
0.8 %
Material Type Phosphate Bonded Phosphate Bonded,
Carbon Free,
Universal Dustless
Investment
Refractory Die
Material
Refractory Die
Material

60. C
Other Systems

61. Composition
A variety of investment formulations for the casting of titanium have been developed
over the past several years
These investments might be classified as phosphate-bonded, ethyl silicate-bonded,
and "cemented" according to the source of the binder.
(Togaya, 1993; Miyazaki and Tamaki, 1993).
Silica (SiO2)
Refractories
Alumina (Al2O3) Magnesia (MgO) Zirconia (ZrO2)

63. Some modifications of phosphate-bonded investments have been explored for the
purpose of rendering them more compatible with molten titanium metals.
(Takahashi, 1993).
Phosphate Magnesia Quartz
Recommended for use as a room-temperature mold
Contamination Of Castings By Reaction With The Investment Was Still Encountered.

64. Contamination from the silica again becomes a problem.
Phosphate
Magnesia
•Good Heat Resistance
•Can be used as refractories
•Thermal expansions is low.
Colloidal Silica
Magnesia
Alumina
Large expansion
Spinel Reaction
MgO + Al2O3 -> MgO - Al2O3
1,150°C to 1,200°C
Highly Refractory
The spinel-forming temperature can also be reduced by mixing with magnesia acetate.

65. The zirconia formed is highly stable. Titanium castings from this investment were
reported to have smooth surfaces free of contamination from mold reaction
Another development is an investment using magnesia bonded by an aluminous
cement (CaO - Al2O3), which contains a mass fraction of 5% zirconium powder
(Togaya et al, 1985).
Aluminous CementBinder
MagnesiaRefractory
Sets by mixing with water
Oxidation of the zirconium powder to zirconia during the burnout process provides
irreversible expansion to compensate for shrinkage of the casting during cooling from
the solidification temperature

66. Another approach to obtaining the needed expansion is through the use of spodumen
(Li2O - Al2O3 - SiO2).
Spodumen expands irreversibly upon heating through the temperature range of 900°C
to 1100°C
(Okuda et al, 1991)
This is most likely due to the use of highly refractory oxides in the powder .
Reaction
ESBI Liquid Titanium PBI Liquid Titanium

67. Conclusion
• Of the three main type of casting investment materials, the Phosphate bonded
products are becoming most widely used.
• Silica bonded materials are rarely used now a days due to the fact that they are
less convenient to use & that the ethanol produced in the liquid can
spontaneously ignite or explode at elevated temperature
• The investment which is best able to retain it’s integrity at the casting
temperature & able to provide the necessary compensation for casting shrinkage
is chosen.