Zinc phosphide

Key takeaways

Zinc phosphide belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Zinc phosphide to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Zinc phosphide from memory before moving on to harder problems.

Reference excerpt

Zinc phosphide (Zn3P2) is an inorganic chemical compound. It is a grey solid, although commercial samples are often dark or even black. It is used as a rodenticide. Zn3P2 is a II-V semiconductor with a direct band gap of 1.5 eV and may have applications in photovoltaic cells. A second compound exists in the zinc-phosphorus system, zinc diphosphide (ZnP2).

Synthesis and reactions Zinc phosphide can be prepared by the reaction of zinc with phosphorus; however, for critical applications, additional processing to remove arsenic compounds may be needed.

6 Zn + P4 → 2 Zn3P2 Another method of preparation include reacting tri-n-octylphosphine with dimethylzinc. Zinc phosphide reacts with water to produce highly toxic phosphine (PH3) and zinc hydroxide (Zn(OH)2):

Zn3P2 + 6 H2O → 2 PH3 + 3 Zn(OH)2

Structure Zn3P2 has a room-temperature tetragonal form that converts to a cubic form at around 845 °C. In the room-temperature form there are discrete P atoms, zinc atoms are tetrahedrally coordinated and phosphorus six coordinate, with zinc atoms at 6 of the vertices of a distorted cube. The crystalline structure of zinc phosphide is very similar to that of cadmium arsenide (Cd3As2), zinc arsenide (Zn3As2) and cadmium phosphide (Cd3P2). These compounds of the Zn-Cd-P-As quaternary system exhibit full continuous solid-solution.

Applications

Photovoltaics Zinc phosphide is an ideal candidate for thin film photovoltaic applications, for it has strong optical absorption and an almost ideal band gap (1.5eV). In addition to this, both zinc and phosphorus are found abundantly in the Earth's crust, meaning that material extraction cost is low compared with that of other thin film photovoltaics. Both zinc and phosphorus are also nontoxic, which is not the case for other common commercial thin film photovoltaics, like cadmium telluride. Researchers at the University of Alberta were the first to successfully synthesize colloidal zinc phosphide. Before this, researchers were able to create efficient solar cells from bulk zinc phosphide, but their fabrication required temperatures greater than 850 °C or complicated vacuum deposition methods. By contrast, colloidal zinc phosphide nanoparticles, contained in a zinc phosphide "ink", allows for inexpensive, easy large-scale production, by means of slot-die coating or spray coating. The testing and development of these zinc phosphide thin films is still in its early stages, but early results have been positive. Prototype heterojunction devices fabricated from zinc phosphide nanoparticle ink exhibited a rectification ratio of 600 and photosensitivity with an on/off ratio near 100. These are both acceptable suitability benchmarks for solar cells. Development still needs to be made on optimizing the nanoparticle ink formation and device architecture before commercialization is possible, but commercial spray-on zinc phosphide solar cells may be possible within ten years.

Pest control

Rodenticide Metal phosphides have been used as rodenticides. A mixture of food and zinc phosphide is left where the rodents can eat it. The acid in the digestive system of the rodent reacts with the phosphide to generate toxic phosphine gas. This method of vermin control has possible use in places where rodents are immune to other common poisons. Other pesticides similar to zinc phosphide are aluminium phosphide and calcium phosphide.

Zn3P2 + 6H+ → 3Zn++ + PH3 ↑ Zinc phosphide is typically added to rodent baits in amount of around 0.75-2%. Such baits have a strong, pungent garlic-like odor characteristic of phosphine liberated by hydrolysis. The odor attracts rodents, but has a repulsive effect on other animals. The baits have to contain sufficient amount of zinc phosphide in sufficiently attractive food in order to kill rodents in a single serving; a sublethal dose may cause aversion towards zinc phosphide baits encountered by surviving rodents in the future. Rodenticide-grade zinc phosphide usually comes as a black powder containing 75% of zinc phosphide and 25% of antimony potassium tartrate, an emetic to cause vomiting if the material is accidentally ingested by humans or domestic animals. However, it is still effective against rats, mice, guinea pigs and rabbits, none of which have a vomiting reflex.

Pest control in New Zealand The New Zealand Environmental Protection Authority has approved the import and manufacture of Microencapsulated Zinc Phosphide (MZP Paste) for the ground control of possums. The application was made by Pest Tech Limited, with support from Connovation Ltd, Lincoln University and the Animal Health Board. It will be used as an additional vertebrate poison in certain situations. Unlike 1080 poison, it cannot be used for aerial application.

Safety Zinc phosphide is highly toxic, especially when ingested or inhaled. The reason for its toxicity is the release of phosphorus compounds, usually phosphine, when it reacts with water and acids. Phosphine is very toxic and, with trace amounts of P2H4, pyrophoric. Phosphine is also denser than air and may remain close to the ground without sufficient ventilation.

References

External links Zinc Phosphide Pesticide Information Profile - Extension Toxicology Network EPA Proposed Risk Mitigation Decision for Nine Rodenticides Zinc phosphide in the Pesticide Properties DataBase (PPDB) Zinc phosphide properties and use in Michigan MD0173 - Pesticides in the military

Illustrations

Worked examples

Example 1 — a first encounter with Zinc phosphide

Start with the simplest possible case. Write down what Zinc phosphide claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Zinc phosphide before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Zinc phosphide ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Zinc phosphide

In research: Zinc phosphide appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Zinc phosphide in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Zinc phosphide is common in secondary-school and first-year university syllabi. It links to neighbouring topics Foul-smelling chemicals, II-V compounds, II-V semiconductors, so understanding it makes those chapters shorter.
In everyday life: Look for Zinc phosphide outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Zinc phosphide in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Zinc phosphide means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Zinc phosphide out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Zinc phosphide in simple terms?

Zinc phosphide (Zn3P2) is an inorganic chemical compound. It is a grey solid, although commercial samples are often dark or even black.

Why does Zinc phosphide matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Zinc phosphide?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Zinc phosphide.