chemistry

Nickel hydride

Nickel hydride is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Nickel hydride rather than just read about it. In short: Nickel hydride is either an inorganic compound of the formula NiHx or any of a variety of coordination complexes. It was discovered by Polish chemist Bogdan Baranowski in 1958.

Key takeaways

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

Reference excerpt

Nickel hydride is either an inorganic compound of the formula NiHx or any of a variety of coordination complexes. It was discovered by Polish chemist Bogdan Baranowski in 1958.

Binary nickel hydrides and related materials "The existence of definite hydrides of nickel and platinum is in doubt". This observation does not preclude the existence of nonstoichiometric hydrides. Indeed, nickel is a widely used hydrogenation catalyst. Experimental studies on nickel hydrides are rare and principally theoretical. Hydrogen hardens nickel (as it does most metals), inhibiting dislocations in the nickel atom crystal lattice from sliding past one another. Varying the amount of alloying hydrogen and the form of its presence in the nickel hydride (precipitated phase) controls qualities such as the hardness, ductility, and tensile strength of the resulting nickel hydride. Nickel hydride with increased hydrogen content can be made harder and stronger than nickel, but such nickel hydride is also less ductile than nickel. Loss of ductility occurs due to cracks maintaining sharp points due to suppression of elastic deformation by the hydrogen, and voids forming under tension due to decomposition of the hydride. Hydrogen embrittlement can be a problem in nickel in use in turbines at high temperatures. In the narrow range of stoichiometries adopted by nickel hydride, distinct structures are claimed. At room temperature, the most stable form of nickel is the face-centred cubic (FCC) structure α-nickel. It is a relatively soft metallic material that can dissolve only a very small concentration of hydrogen, no more than 0.002 wt% at 1,455 °C (2,651 °F), and only 0.00005% at 25 °C (77 °F). The solid solution phase with dissolved hydrogen, that maintains the same structure as the original nickel is termed the α-phase. At 25°C, 6 kbar of hydrogen pressure is needed to dissolve in β-nickel, but the hydrogen desorbs at pressures below 3.4 kbar.

Surface Hydrogen dissociates on nickel surfaces. The dissociation energies on Ni(111), Ni(100), and Ni(110) crystal faces are respectively 46, 52, and 36 kJ/mol. The H2 dissociates from each of these surfaces at distinct temperatures: 320–380, 220–360, and 230–430 K.

High pressure phases Crystallographically distinct phases of nickel hydride are produced with hydrogen gas at 600 MPa; or electrolytically. The crystal form is face-centred cubic or β-nickel hydride. Hydrogen to nickel atomic ratios are up to one, with hydrogen occupying an octahedral site. The density of the β-hydride is 7.74 g/cm3. It is grey. At a current density of 1 amp per square decimeter, in 0.5 mol/liter of sulfuric acid and thiourea a surface layer of nickel will be converted to nickel hydride. This surface is replete with cracks up to millimeters long. The direction of cracking is in the {001} plane of the original nickel crystals. The lattice constant of nickel hydride is 3.731 Å, which is 5.7% more than that of nickel. The near-stoichiometric NiH is unstable and loses hydrogen at pressures below 340 MPa.

Molecular nickel hydrides A large number of nickel hydride complexes are known. Illustrative is the complex trans-NiH(Cl)(P(C6H11)3)2.

References

Worked examples

Example 1 — a first encounter with Nickel hydride

Start with the simplest possible case. Write down what Nickel hydride 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 Nickel hydride 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 Nickel hydride 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 Nickel hydride

In research: Nickel hydride 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 Nickel hydride 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: Nickel hydride is common in secondary-school and first-year university syllabi. It links to neighbouring topics Metal hydrides, Nickel alloys, Nickel compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Nickel hydride 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.

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How to study Nickel hydride in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nickel hydride 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 Nickel hydride out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nickel hydride in simple terms?

Nickel hydride is either an inorganic compound of the formula NiHx or any of a variety of coordination complexes. It was discovered by Polish chemist Bogdan Baranowski in 1958.

Why does Nickel hydride 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 Nickel hydride?

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 Nickel hydride.