Method of manufacture of phosphate-bonded refractories

Details Method of manufacture of phosphate-bonded refractories Method of manufacture of phosphate-bonded refractories

1999-06-10

2001-07-10

Marcantoni, Paul (Department: 1755)

Compositions: ceramic

Ceramic compositions

Refractory

C501S127000, C501S142000, C501S153000

Reexamination Certificate

active

06258742

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to phosphate-bonded refractory compositions and to a method of manufacture.
Phosphate-bonded refractories have been extensively used in the iron, steel, aluminum and brass industries to line vessels for containment of molten metals and other applications for more than 50 years. These products are well known for their ability to withstand high temperatures and attack by molten metals and slags. They are further characterized by ease of forming, linear and volume stability, high strength both dried and fired, and excellent resistance to abrasion and to mechanical impact at high temperatures. The full range of phosphate-bonded refractories, including chemically bonded and fired brick, monoliths, and special shapes suitable for use in a wide range of high temperature applications, can be produced by the manufacturing method of the present invention.
SUMMARY OF THE INVENTION
This invention pertains to a method of manufacturing phosphate-bonded refractories having a proto aluminum orthophosphate chemical binder formed entirely during the mixing cycle by reacting orthophosphoric acid (H
3
PO
4
); finely divided aluminum hydroxide (Al(OH)
3
) and water. An aluminum orthophosphate (AlPO
4
) ceramic bond is formed progressively with the loss of combined water at temperatures from 212° F. to 1200° F. The true character of the proto aluminum orthophosphate is not known. It is believed, however, that the reaction product is an aluminum acid orthophosphate (AlHPO
4
) or an aluminum orthophosphate gel. The method discovered is a direct, simple and inexpensive way of manufacturing the broadest range of high performance phosphate-bonded refractories at low cost.
We have discovered that it is possible to react orthophosphoric acid with finely divided aluminum hydroxide and water in a refractory batch during the mixing cycle. The batch weights of aluminum hydroxide and orthophosphoric acid must be calculated to yield a proto aluminum orthophosphate which on drying and fired to a temperature of approximately 1200° F. will yield an aluminum orthophosphate ceramic bond. The three proportioned batch components—aluminum hydroxide, water and orthophosphoric acid—react in the pan to form a proto aluminum orthophosphate without generating the excessive heat which characterizes exothermic reactions. The ratio of phosphorus pentoxide (P
2
O
5
) in either 85% or 75% orthophosphoric acid (H
3
PO
4
) to aluminum oxide (Al
2
O
3
) in aluminum hydroxide (Al(OH)
3
) must be at least 1.3923 to 1. It is absolutely necessary to assure that a slight excess of aluminum hydroxide be present to prevent crystallization of aluminum metaphosphate (Al(PO)
3
). An excess of orthophosphoric acid will result in the development of aluminum metaphosphate directly proportional to the excess phosphoric acid available. The workability of the resultant phosphate-bonded product will be decreased as a function of time; that is, the product will have an attenuated “shelf life”.
Three batch components, aluminum hydroxide, water and orthophosphoric acid, react in the pan to form aluminum acid phosphate without generating excessive heat. After forming the finished product and upon heating to approximately 1200° F., the aluminum acid phosphate progressively loses chemically combined water ultimately forming aluminum orthophosphate.
A broad compositional range of sized refractory materials may be used to formulate phosphate bonded refractories. High alumina aggregates are the most commonly used in phosphate-bonded refractories. Zircon, silica, silicon carbide, chromium oxide and other non-alumina materials may also be incorporated to modify properties.
In practicing the present invention, standard procedures are followed in formulating, proportioning, batching and mixing. Finely divided aluminum hydroxide is introduced to the mixer with other dry batch components. The batch is dry mixed for the time required to distribute the aluminum hydroxide uniformly through the batch. In high efficiency mixers, one to two minutes are required to blend a one ton batch. Water is then added while mixing. In mixes, such as mortars and plasters containing greater than 7.0% water, the initial water addition is restricted to 7.0% of the total batch weight. The balance of the water is added after the orthophosphoric acid addition. Following the initial water addition, 75% or 85% orthophosphoric acid is added. The calculated ratio of 85% orthophosphoric acid to aluminum hydroxide by weight is less than 1.4782 to 1 and preferably 1.4078 to 1. The calculated ratio of 75% orthophosphoric acid to aluminum hydroxide by weight is less than 1.6757 to 1 and preferably 1.5955 to 1. The remaining water is added and mixing is completed. When using 75% orthophosphoric acid, the free water addition to the batch must be decreased by a factor of 0.1176 of the total weight of the 75% orthophosphoric acid addition. After forming the finished product and upon heating to at least 600° F. and preferably to 1200° F., the proto aluminum orthophosphate progressively loses water ultimately forming aluminum orthophosphate.


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patent: 1458340 (1989-02-01), None

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