Monopotassium phosphate (MKP) (also, potassium dihydrogen phosphate, KDP, or monobasic potassium phosphate) is the

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the formula KH₂PO₄. Together with dipotassium phosphate (K₂HPO₄^.(H₂O)_x) it is often used as a

fertilizer A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Man ...

food additive Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives, such as vinegar ( pickling), salt ( salting), smoke ( smoking) and sugar ( crystallization), have been used f ...

, and

buffering agent A buffer solution is a solution where the pH does not change significantly on dilution or if an acid or base is added at constant temperature. Its pH changes very little when a small amount of strong acid or base is added to it. Buffer solution ...

. The salt often cocrystallizes with the dipotassium salt as well as with

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, ...

Single crystal In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no Grain boundary, grain bound ...

s are paraelectric at room temperature. At temperatures below , they become

ferroelectric In physics and materials science, ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are also piezoel ...

Structure

Monopotassium phosphate can exist in several polymorphs. At room temperature it forms paraelectric crystals with tetragonal symmetry. Upon cooling to it transforms to a

phase of orthorhombic symmetry, and the transition temperature shifts up to when hydrogen is replaced by deuterium. Heating to changes its structure to monoclinic. When heated further, MKP decomposes, by loss of water, to potassium metaphosphate, , at .

Manufacturing

Monopotassium phosphate is produced by the action of

potassium carbonate Potassium carbonate is the inorganic compound with the formula . It is a white salt, which is soluble in water and forms a strongly alkaline solution. It is deliquescent, often appearing as a damp or wet solid. Potassium carbonate is mainly used ...

. It can then be crystallized into boules, large crystals by dissolving the KDP in hot water and salt, creating a growth solution, placing a seed crystal in the solution and then cooling the solution, done in a holden-type crystallizer, in what is known as solution growth.

Applications

Fertilizer-grade MKP powder contains the equivalent of 52% and 34% , and is labeled NPK0-52-34. MKP powder is often used as a

nutrient A nutrient is a substance used by an organism to survive, grow and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

source in the

greenhouse A greenhouse is a structure that is designed to regulate the temperature and humidity of the environment inside. There are different types of greenhouses, but they all have large areas covered with transparent materials that let sunlight pass an ...

trade and in

hydroponics Hydroponics is a type of horticulture and a subset of #Passive sub-irrigation, hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral Plant nutrition, nutrient Solution (chemi ...

Crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

s of MKP are used in optical modulators and for non-linear optics such as

second-harmonic generation Second-harmonic generation (SHG), also known as frequency doubling, is the lowest-order wave-wave nonlinear interaction that occurs in various systems, including optical, radio, atmospheric, and magnetohydrodynamic systems. As a prototype behav ...

(SHG). Potassium dideuterium phosphate (KDP), with slightly different properties, is also used in nonlinear frequency conversion of laser light. The replacement of protons with deuterons in the crystal shifts the third overtone of the strong OH molecular stretch to longer wavelengths, moving it mostly out of the range of the fundamental line at approximately 1064 nm of neodymium-based lasers. Regular KDP has absorbances at this wavelength of approximately 4.7–6.3% per cm of thickness while highly deuterated KDP has absorbances of typically less than 0.8% per cm. Monopotassium phosphate is also used as an ingredient in

sports drink Sports drinks, also known as electrolyte drinks, are non-caffeinated functional beverages whose stated purpose is to help athletes replace water, electrolytes, and energy before, during and (especially) after training or competition. The eviden ...

s such as

Gatorade Gatorade is an American brand of sports-themed beverage and food products, built around its signature line of sports drinks. The drink is owned and manufactured by PepsiCo and is distributed in over 80 countries. The beverage was develope ...

and

Powerade Powerade is a sports drink created in 1988 and distributed by the Coca-Cola Company. Its primary competitor is Gatorade, which is owned by PepsiCo since 2001. History Powerade was created by the Coca-Cola Company and first released in 1988. Th ...

. In medicine, monopotassium phosphate is used for phosphate substitution in

hypophosphatemia Hypophosphatemia is an electrolyte disorder in which there is a low level of phosphate in the blood. Symptoms may include weakness, trouble breathing, and loss of appetite. Complications may include seizures, coma, rhabdomyolysis, or soft ...

Gallery

Image:KDP crystal.jpg, A large KDP crystal, used in the form of slices at the

National Ignition Facility The National Ignition Facility (NIF) is a laser-based inertial confinement fusion (ICF) research device, located at Lawrence Livermore National Laboratory in Livermore, California, United States. NIF's mission is to achieve fusion ignition wit ...

Image:Monocristal dsc03676.jpg, Alternate angle, covered

References

External links

International Chemical Safety Card 1608EPA: Potassium dihydrogen phosphate Fact Sheet
{{Potassium compounds Second-harmonic generation Phosphates Potassium compounds Acid salts Nonlinear optical materials Transparent materials E-number additives Inorganic fertilizers