Why are interstitial compounds tough to melt like Ti-c?

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Discussion Overview

The discussion centers on the melting point of interstitial compounds, specifically titanium carbide (TiC), and why such compounds exhibit higher melting points compared to their pure metal counterparts. The conversation explores the nature of bonding in these materials and the role of small atoms occupying lattice vacancies.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the melting point comparison between the metallic bond in pure titanium and the bonding in TiC, suggesting that the differences in bonding character contribute to the melting point disparity.
  • Another participant expresses skepticism about classifying TiC as an interstitial compound, noting the similarity in atomic radii between titanium and carbon and comparing its crystallization to that of NaCl.
  • A participant reflects on the ionic character of TiC, mentioning the electronegativity difference and suggesting that this contributes to its melting point.
  • Concerns are raised about the definition of interstitial compounds, with one participant noting the difficulty in determining when atoms transition from being interstitial to occupying normal lattice positions.
  • A later reply cites Wikipedia to support the classification of TiC as a prototypical interstitial carbide, although this reference is not considered authoritative by all participants.
  • One participant proposes that the electron deficiency of metals like titanium allows carbon to contribute electrons, enhancing the cohesion of the metal and potentially affecting the melting point.

Areas of Agreement / Disagreement

Participants express differing views on the classification of TiC as an interstitial compound and the reasons behind its melting point. There is no consensus on the definitions or the implications of the bonding characteristics discussed.

Contextual Notes

Participants acknowledge the complexity of defining interstitial compounds and the potential overlap with other types of bonding. There are references to specific atomic radii and electronegativity values, but these details remain unresolved within the discussion.

Who May Find This Useful

This discussion may be of interest to those studying materials science, particularly in the context of interstitial compounds, melting points, and bonding characteristics in transition metals.

leojun
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why are interstitial compounds tough to melt like Ti-c?
 
Last edited:
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Please elaborate, I don't get what your question (nor your attempt at explanation) is.
 
In my book,its given that Ti-c interstitial compound has higher melting point than that of pure metal Ti.i wanted to know why small atoms like( H,C,N,B) in the vacant spaces in the lattice of transition metals increase their melting point.
 
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You are comparing metal (with a metallic bond) with a compound (with slightly dominating ionic character). These are completely different, no wonder they have different melting points.

Besides, I am not convinced TiC classifies as interstitial compound. Radii of carbon and Ti are quite similar, and from what I understand TiC crystallizes just like NaCl does - fcc.
 
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Borek, i would also expect C in TiC to be rather interstitial. Which radii did you compare?
 
I can't locate the numbers I found earlier :(

That was my line of reasoning: I am reasonably sure about fcc (compare http://www.crystallography.net/5910091.html?cif=5910091). As electronegativity difference is around 1, I expected some ionic character, so smaller radius for Ti (cation) and a larger radius for C (anion). Lousy, but should be pointing in the right direction. And I found a page with ionic radii that seemed to confirm this line of thinking, unfortunately, I don't remember where it was.

I admit I have no idea where is the border between "still an interstitial compound" and "no longer an interstitial compound" - I mean, at some point it is hard to speak about "small atoms sitting in holes", they start to occupy not a hole (which happens when metal atoms stay in almost the same places they occupied before adding the other element), but just a normal place in the lattice (so the metal atoms have to move away to make place for newcomers).
 
Considering the original question, I would argue as follows: Metals, including Titanium are generally electron deficient materials, i.e. they have much more neighbouring atoms than they can form covalent bonds. The carbon atom delivers electrons which the metal can use to form bonds to it's neighbours thus increasing strongly the cohesion of the metal.
 
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