What Is Phosphate Supplementation?

Phosphate binder refers to an inorganic material with acid orthophosphate or polycondensate as the main compound and has gelling properties. It is a refractory binder formed by the reaction of phosphoric acid with oxides or hydroxides or alkalis. The binding form of the phosphate binding agent is a chemical reaction binding or a polymerization binding. Most of the binders formed by the reaction of phosphoric acid with alkali metal or alkaline earth metal oxides and their hydroxides are pneumatic binders, that is, coagulation and hardening can occur without heating at normal temperature. Most of the binders formed by the reaction of phosphoric acid with amphoteric oxides and their hydroxides or acidic oxides are thermosetting binders, that is, coagulation and hardening can occur after heating to a certain temperature to react. Phosphate used as a binder for refractory materials has a strong bonding strength in the medium and low temperature range before ceramic bonding, so it is widely used as a binder for amorphous and non-fired refractory materials.

Phosphate binder refers to acid orthophosphate or polycondensed phosphate as the main

The classification of phosphates is generally distinguished by the molar ratio (R = M ₂ O / P ₂ O ₅ ) of the metal oxide (M ₂ O) and phosphorus pentoxide (P ₂ O ₅ ) contained in the compound. See its classification in Table 1.

It is prepared by the reaction of orthophosphoric acid with magnesium materials. The available magnesium materials are magnesium oxide, magnesium hydroxide, and lightly burned magnesia. Among the magnesium phosphates produced by the reaction of orthophosphoric acid with magnesium oxide, only Mg (H ₂ PO ₄ ) ₂ is soluble in water, and its composition is 11% MgO and 89% H ₃ PO ₄ , so the magnesium phosphate cement is a solution of magnesium dihydrogen phosphate.

Preparation method of magnesium dihydrogen phosphate: According to MgO / P ₂ O ₅ = 1, pour the necessary amount of magnesium material into the orthophosphoric acid solution with a concentration of 60% in batches. Each batch of material must be carefully and continuously Stir until MgO is completely dissolved. A large amount of heat is released during this dissolution reaction, so the reactor must be cooled in flowing water. The cooled solution can be filtered to obtain a liquid magnesium phosphate binding agent, or the magnesium dihydrogen phosphate solution can be spray-dried to obtain powdery magnesium dihydrogen phosphate for use.

Magnesium phosphate binder can be used as a binder for refractory materials such as corundum, spinel and aragonite ^[2]

It is made by reacting orthophosphoric acid with chromium-containing materials. The chromium-containing materials used are chromic acid (CrO ₃ ), chromium oxide, chromium hydroxide, volatile acid salts or chromite. CrO ₃ can be prepared by adding CrO ₃ directly to phosphoric acid with a concentration of 60%. After the binder is heated, CrO _{3 is} reduced to Cr ₂ O ₃ , thereby generating chromium phosphate. When prepared with other chromium-containing materials, orthophosphoric acid with a density of 1.7 g / cm ³ can be mixed and heated to obtain a green liquid with good cementation.

Aluminium-chromium phosphate, magnesium-chromium phosphate, sodium-chromium phosphate, and other binders. Aluminium-chromium phosphate binders are prepared by mixing and stirring aluminum phosphate with 50% -60% chromium phosphate. The bonding agent of Al ₂ O ₃ · Cr ₂ O ₃ · 2P ₂ O ₅ has better cementing performance, and this bonding agent can be stored for a long time without affecting its bonding performance. Magnesium chromium phosphate binder is prepared by reacting a mixture of MgO and Cr ₂ O ₃ with orthophosphoric acid ^[3]

In the refractory industry, orthophosphate is mainly used as a binder for neutral and acidic refractories, and polycondensed phosphate is mainly used as a binder for alkaline refractories.

When orthophosphate is used as a binder for neutral or acidic refractory materials, a small amount of admixture can be used depending on the application. For example, when used as a binder for refractory castables, a coagulant such as aluminum must be added. Acid calcium cement, fused or sintered magnesia powder, NH ₄ F, etc., in order to set and harden after the completion of construction. For example, when used as a binder for plastic refractory materials, repair materials and ramming materials, a preservative such as oxalic acid, citric acid, tartaric acid, etc. must be added so that the acid phosphate does not match the refractory material during storage and transportation. The oxides (such as Al ₂ O ₃ ) react to form insoluble orthophosphate, which makes the mixture dry prematurely and lose workability.

Polycondensation phosphate reacts slowly with alkaline refractories, so they have sufficient construction time when used as a binder for alkaline refractories. The polycondensed calcium phosphate salt can be used as a binder for non-fired bricks (such as magnesium bricks, magnesia-aluminum bricks, magnesia-chrome bricks, etc.), and also as a binder for castables and spray-ups ^[3] .