Dr. Ralf Giskow, The Variety of Phosphates Jörg Lind, Erwin Schmidt Chemische Fabrik Budenheim KG, for Refractory and Technical D-55257 Buden- heim www.budenheim- Applications by the Example cfb.com of Aluminium Phosphates In 1669 the chemical element phos- Phase-I-content influences, for phorus was discovered by H. Brandt, example, the dissolution property of an alchemist. In 1694 Boyle made STPP in water. The choice of the the first phosphoric acid by dissolv- right phosphate can already be the ing phosphorus pentoxide (P2O5) in crucial point even with such a “sim- water. This was the start of the phos- ple“ phosphate like sodium tripoly- phorus chemistry. Since this time phosphate. phosphoric acid and its salts have a The next step into the direction firm place in chemistry and technical of complexity is a phosphate called applications. Phosphates are part of sodium hexametaphosphate (SHMP) our life and are used in a variety of in colloquial language. In fact, the ways also in industrial fields like chemical name is a mistake. The refractories, glass, ceramics, con- name sodium hexametaphosphate struction industry and for a lot of would stand for a sodium phosphate other technical purposes. with a ring structure (“meta”). But SHMP has a chaintype structure as can be proved. These melted glassy polyphosphates (SHMP) with pH-val- Fig. 1 Phosphates in Refractory phosphates are polyphosphates with ues between three and nine, most of FABUTIT 734, a modified STPP and Technical Industries different chain lengths. The average the products also in an instantised against a standard The most common and well known chain length and thus the properties quality (Fig. 2). STPP phosphates for technical applica- of the phosphate, like the pH-value The mentioned examples illustrate tions are sodium tripolyphosphate for example, are controlled by the the multiplicity of the phosphates. production process. Additionally the Beside STPP and SHMP, ammonium (Na5P3O10), sodium hexametaphos- final product can be refined, for phosphates, aluminium phosphates, phate [(NaPO3)n] or monoalumini- example by the process of instantis- boron phosphates, calcium phos- um phosphate (Al(H2PO4)3). These phosphates are used as defloccu- ing. This leads to sodium polyphos- phates, alkaline phosphates, magne- lants, additives or binders. Sodium phates which have an improved solu- sium phosphates or zinc phosphates tripolyphosphate, abbreviated STPP bility and dissolution speed. At the are used in different technical areas. (sodium tripolyphosphate), is a same time the hygroscopicity is re- To explain the variety of possible uses commonly used deflocculant for clay duced. The Chemische Fabrik for phosphates in the field of refracto- or materials containing clays in the Budenheim manufactures sodium ries, additives, glass or enamel, the ceramics industry, in refractories or in oil and gas prospect drilling. Already in these applications, phos- phates show their variety. STPPs are not all the same. Modifications exist, which have a remarkable influence on the properties. FABUTIT 734 is an example for a chemical modified sodium tripolyphosphate. This pro- duct has an improved solubility, which effects the liquefaction in a positive way. Fig. 1 shows the result of a comparing test between a modified product like FABUTIT 734 against a commercial standard STPP. In addition, STPP exists in two differ- ent crystal structures, a low and a high temperature phase. According Fig. 2 to the production process the BUDIT 3 to 9 as possible variations amount of the high temperature of sodium poly- phase can be adjusted. This so called phosphate cfi/Ber. DKG 81 (2004) No. 5 E 1 and modifications. Starting point is This intense exothermic reaction always the reaction between phos- must be controlled by the proper phoric acid and a source of alumini- manufacturing process. The result um, like aluminium hydroxide, is an aqueous solution marketed which leads to a monomer phos- with a concentration between 40 phate. The next step is the polymeri- and 60 %. sation process by temperature (Fig. The raw materials for the production 3). Polymerisation is the union of of monoaluminium phosphate are two or more molecules of given already important for the final quali- structure to form a new compound, ty. Chemische Fabrik Buden- usually accompanied by a thermal heim uses only a clear, white phos- loss of water which results into the phoric acid of food quality. In the formation of di-, tri- or poly-phos- production process care is taken to phates. ensure the correct basicity, the rela- In 1975 Tsuhako, Japan, summarized tion of Al2O3 to P2O5, which has to the formation of aluminium phos- be nearly exactly 1:3. This guaran- phates by thermal treatment (Fig. 4). tees that no free phosphoric acid is The following illustrates the relevant present in the monoaluminium aluminium phosphates in the areas phosphate. Fig. 3 group of aluminium phosphates has of refractories, ceramics, glass and Principle of poly- been chosen and will be described in merisation/types of accompanying technical applica- the following abstract. Monoaluminium Phosphate phosphates tions. The most well-known type of alu- – All Liquids are not Alike minium phosphate is of course the The use of the raw materials, the cor- monoaluminium phosphate. But the Monoaluminium rect manufacturing process and family tree of aluminium phosphates chemical modifications leads to is comprehensive and the possible Phosphate many chemical binders, which are all uses of aluminium phosphate are The manufacturing process of mono- covered by the generic term of extensive. aluminium phosphate from phos- monoaluminium phosphate. Mono- phoric acid and aluminium hydroxide aluminium phosphate produced Aluminium Phosphates – can be described by the following with technical phosphoric acid equation of reaction: Chemistry and Application always lead to technical monoalu- minium phosphates, which usually Aluminium phosphates exist in a 3 H3PO4 + Al(OH)3 are unstable solutions of bad stora- variety of stages of polymerisation --> Al(H2PO4)3 + 3 H2O bility, where impurities tend to floc- culate and sediment. A wrong basic- ity for example gives either a very unstable solution or very “reactive” solutions with a high amount of free phosphoric acid. Beside this, many technical monoaluminium phos- phate liquids contain impurities like sulphur, heavy metals or fluorine (!), which are according to experience detrimental to any installations and facilities. This is the main reason why the Chemische Fabrik Buden- heim only uses high-quality raw materials. The torture of choosing applies also to monoaluminium phosphate. The first monoaluminium phosphate liquid was produced in the roaring twenties and used as binder for chamotte. The outrider for the industrial use was the Metallge- sellschaft AG (later the Chemetall GmbH) with the development of a binder called “Feuerfestbinder 32”. This binder was based on a clever idea, covered by a publication with the headline “Mineralleim zur Bindung von Chamotten” (= engl. mineral glue to bind chamotte). This Fig. 4 “mineral glue” had a similar compo- The formation of sition as monoaluminium phos- aluminium phos- phates by thermal phate. The Metallgesellschaft turned treatment [Tsuhako] this proposal to advantage and E 2 cfi/Ber. DKG 81 (2004) No. 5 developed the chemical binder FFB Additional modifications are possi- 32 using a sludge from amblygonite, ble. Today many different concen- a lithium-aluminium-phosphate, trations of liquid monoaluminium and phosphoric acid. This was the phosphates are found, or the birth of phosphate-based bonding amount of free phosphoric acid is agents in Germany. adjusted. The production of a mono- FFB 32 still exists. It is a clear, pure aluminium phosphate in powder 50 % monoaluminium phosphate type form is also possible. The varied liquid for ceramics and refractories, use of such orthophosphate is re- produced by Chemische Fabrik markable. Budenheim, which took possesion of The most common and well known the binders activities of Chemetall at application for monoaluminium the end of 1999. Today monoalu- phosphate is the bonding of refrac- minium phosphate, like FFB 32, is tories. Besides raw materials based mentioned in the literature, but their Fig. 5 The effect of an widely used as bonding agent or on Al2O3, also basic raw materials existence has not yet been proved. It inhibited phosphor- coating. Monoaluminium phos- can be used, which form quick set- is to be accepted that such a dialu- ic acid coating on phate reacts with oxidic and non ting refractories. Among other minium phosphate is an unstable steel plates after oxidic raw materials by the forma- things the strong exothermal and intermediate stage of the polymeri- storing over night tion of phosphate salts, even at low very fast reaction between MgO and sation process. temperatures. This is one of the main monoaluminium phosphate is used Aluminium tripolyphosphate how- advantages of this sticky chemical to produce cold setting systems. ever exists in two different forms, an binder. Starting at about 100 °C, Examples for such self setting mate- anhydrous product and a dihydrate. bonded materials already have a rials are repair mixes or modern During the manufacturing process high strength, which constantly materials like self setting inorganic intermolecular water from the used inceases until the ceramic bond foams, which isolate and which are monoaluminium phosphate is dri- comes into effect. From 300 to fire proof (Fig. 6 ). ven off. The resulting