Talk:Titanium hydride

Phase diagram

It would be nice to have a phase diagram inserted under Material properties. Plasmic Physics (talk) 07:34, 18 February 2013 (UTC)

Reliable sources

It is neccesary to independently verify your sources, Chemspider is not a useable source for chemical data or names, and apparently, neither is PubChem. This evident from the quality of the information added to the recently proposed chembox. The compound most certainly does not melt at the given temperature, nor does it have a definite formula, and hence, nor a stoichiometric systematic name. Plasmic Physics (talk) 23:57, 10 March 2013 (UTC)

It does not have a molar mass, it does not have a unilateral density at STP. It does not only come in powder form, it is also available as foil. It also is not an ionic salt as the identifiers suggest. Plasmic Physics (talk) 00:01, 11 March 2013 (UTC)

Rewrite

I have rewritten the article bringing back a chembox and removing the "alloy" definition. Most authorities say this is a compound as the metal sublattice changes when the non-stoichiometric hydride is formed.Axiosaurus (talk) 13:05, 3 February 2014 (UTC) Apologies to any readers - this article has been reverted to an old version with some minor amendments - if you want information on titanium hydride, the non stoichiometric compound, TiH₂ look at historical verisons of the page. Axiosaurus (talk) 11:42, 24 May 2014 (UTC)

A massive rewrite such as this requires consensus, which is clearly lacking. The appropriate action to take would be to revert to a stable previous version until a consensus is reached. Authorities is not defined, nor is the relevant factual statement referenced. In it's current form, the article delivers erroneous content detrimental to the fundamental understanding of the topic. Plasmic Physics (talk) 12:45, 24 May 2014 (UTC)

OK, Plasmic Physics, let us discuss it here. I admit that I did not go far enough back in the history, but I do not think that the history supports your case. The article was originally about TiH2. You changed it to be about something else starting, I think on October 1st, 2012. There was no discussion on this talk page then about this total change in focus of this article. I do not see any edit summaries about the change. What you did back then was wrong. If you want an article on the alloy you should have written a new article. This article started about TiH2 and it should continue to be about TiH2. I think Axiosaurus is correct. So why do you not explain, what you should of done in 2012, why this should not be about TiH2? --Bduke (Discussion) 03:30, 25 May 2014 (UTC)

The version by Axiosaurus seems pretty conventional and useful for those seeking information on this material. One approach to avoiding controversies is to aim mainly for non-primary references. Greenwood and Earnshaw, which many inorganic chemists view as a sort of a bible, describes the material as having an antifluorite structure. Being part of an encyclopedia, hopefully the article can mainly rely on major sources of that type. For the sake of our readership, fringe perspectives and esoteric nomenclature should be kept to a minimum. --Smokefoot (talk) 04:35, 25 May 2014 (UTC)

Any scientist should be careful to not to take everything at face value. Implicit trust in any particular source, is poor scientific habit. That is one of the reasons why it took so long for Ptolemaic epicycles to disappear. You should know better than to put blind faith in Greenwood and Earnshaw. Nullius in verba. Plasmic Physics (talk) 06:02, 25 May 2014 (UTC)

Nobody is putting blind faith in anything. We are writing an encyclopedia. We have to follow what secondary sources say. We are not writing a scientific paper or review so scientific habit has nothing to do with it. --Bduke (Discussion) 06:37, 25 May 2014 (UTC)

Smokefoot is implying that we should parrot the multitudinous inorganic chemists who do put blind faith in that Greenwood and Earnshaw, and by extension we must put blind faith in the authority of those chemists. Plasmic Physics (talk) 06:51, 25 May 2014 (UTC)

My original rewrite is too far in the past for it to be appropriate to be considered now in making an argument for or against. The topic is in fact an alloy. Axiosaurus's claim that it is a compound is outdated and fundamentally incorrect. Plasmic Physics (talk) 06:02, 25 May 2014 (UTC)

You make two claims there - "is in fact an alloy" and "is outdated and fundamentally incorrect". Both need a source. As for the past, this kind of article does not get a lot of notice and you did not help by not flagging a major change on the talk page and by not using edit summaries to explain what you were doing. Both help to attract more eyes on an article. We should decide what the best sources say and use those. --Bduke (Discussion) 06:37, 25 May 2014 (UTC)

If you would have a look at the references given in the my rewrite, you should also see these references which you now are requesting. I could have supplied more inline citations, however that would invite WP:OVERCITE. I can't very well add edit summaries retrospectively, can I? Musing about the past is pointless, in no way contributing to solving the current issue. Plasmic Physics (talk)

Plamic Physics has been promoting the idea of metal hydrides being alloys before, but to me it looked very much like original research. For titanium hydride alloy, this term seems to always refer to a nickel titanium alloy hydride. "Titanium hydrogen alloy" appears to be used a couple of times in the academic literature, but most occurrences on the web are copies of this article. "Hydrogen Titanium alloy" is also used about three times in academic literature. There are at least 1000 Google scholar articles that talk about titanium hydride that do not use the term alloy. So the article here should not be pushing the idea of alloy at all, as less than 1% of writing on the topic are saying it is an alloy. Graeme Bartlett (talk) 07:53, 25 May 2014 (UTC)

Do not simply search for terms such as "titanium hydride alloy". Search instead for texts which describe it as an alloy, or attribute its behavior as that of an alloy. Moreover, you must be able to discern trustworthy sources. The sum of occurrences of articles containing a particular concept in does not in itself prove that it is correct. You must find a source which contains a dedicated investigation of the matter. A quote comes to mind: "If you tell a lie big enough and keep repeating it, people will eventually come to believe it." Now this matter is not a big lie, but a more subtle misinterpretation. Nonetheless, it is an untruthful fact that has been repeated over and over, and virtually become a pseudotruth. Plasmic Physics (talk) 08:27, 25 May 2014 (UTC)

I will quote Fukai(The metal hydrogen system- 2d edition) here. As an authority in this particlar field his views should carry weight when we write an encyclopedia article. "In its narrow sense the term (sic hydride) is used only in cases where the structure of the metal lattice is changed by the absorption of hydrogen." But later he broadens his definition to "In short we designate all the pahses of metal hydrogen systems other than a random interstitial solid solution as hydrides" . In my own experience in industry -alloy is not a tightly defined term - in its broadest sense it can be a metal with "stuff added" which may contain solid solutions, precipitates of stoichiometric and non stoichiometric compounds or crystalline elements. The argument for hydrides being considered as alloys may revolve around the perceived protic nature of atomic hydrogen in many metal hydrides - the electron adding to the conduction band. A case where I have noticed the term alloy alloys being applied to hydrides is in the field of hydrogen storage when the absorption/desorption characteristics of a pure metal are the focus and the metal with absorbed hydrogen, (phases beta, gamma etc may be present), is termed an alloy. Axiosaurus (talk) 10:13, 25 May 2014 (UTC)

It should be noted that discussions such as this have taken place on most transition metal hydride articles (see: Titanium(IV) hydride, Copper hydride, Mercury(I) hydride, Mercury(II) hydride etc). Once cause (although there are others) is the literature: primary sources are old and often disagree with one another, secondary sources are virtually non-existent or only make a passing mention of a compound - This makes good pages hard to write, and I consider this fair warning to all of you (except Axiosaurus, he knows better than I) that that a lot of time can be spent here. I do, however, have some sympathy with PP on this matter, several crystallography papers (admittedly primary) discuss the Ti-H system (doi:10.1107/S0365110X56001649, doi:10.1107/S0365110X58000098, doi:10.1107/S0365110X61003740), these seem to back up the description of a non-stoichiometric compound with a CaF₂ structure which changes to face-centred tetragonal as the composition approaches MH₂ (with some temp dependency). By way of moving forward; titanium(II) hydride is commercially available through Aldrich, it would seem to me that the most encyclopaedic thing to do would be to have a page on that. To do so may require a page split to give one on the Ti-H system (should that prove important enough) and one on TiH₂, there is precedent for this, several discrete compounds in the iron-carbon system have there own pages (e.g. Cementite). Titanium hydride could then be converted to a disambig-page for these two plus TiH₄. Project Osprey (talk) 10:39, 25 May 2014 (UTC)

In reply to both Axiosaurus and Project Osprey: the Titanium(II) hydride with the approximate formula TiH
_1.95 as traded by suppliers like Sigma Aldrich, refers to only one particular local minimum of a few in the composition phase diagram, namely, a delta-titanium matrix with dissolved atomic hydrogen. The atomic hydrogen exhibits mobility, proportional to temperature, leading to outgassing, even at room temperature. Plasmic Physics (talk) 12:14, 25 May 2014 (UTC)

I found a 1950s paper that hypothesises that for compositions of TiH
_≥2, the alloy should convert to a truly stoichiometric, covalent network solid with bridging hydrogen centres, where excess dihydrogen form bubbles within the bulk network. Based on previous attempts at achieving such compositions, which proved futile, the conversion is suggested to have a particularly high enthalpy, not attainable at the gigapascal pressures used. Plasmic Physics (talk) 13:14, 25 May 2014 (UTC)

Secondary sources and especially those of the broad impact like Greenwood and Earnshaw should take precedent. Plasmic and Osprey are encouraged to publish a review paper on why the terminology should be changed. We are not here to right great wrongs, but to report in a way that most scientists find acceptable, as reflected in our canonical texts and reviews. I really worry that many of the hydride articles have or had been corrupted by reliance on esoteric primary sources that give WP:UNDUE emphasis on weird fetish-like perspectives. --Smokefoot (talk) 13:33, 25 May 2014 (UTC)

Your comment speaks for itself in showing your lack of understanding of the topic at hand. Not being an isolated incident, your continual unabashed exhibition of impertinent commentary on my edits, verges on the definition of harassment. Furthermore, you ignore key points in favour of pushing your personal point of view, this wholly unconstructive towards forming consensus. Please refrain from making such disruptive edits. Plasmic Physics (talk) 13:51, 25 May 2014 (UTC)

Smokefoot may have come over a bit strong here, but he is making the point that I made above. We are writing an encyclopedia using the quidelines and policies that have evolved for wikipedia. You do not have to be a scientific expert to edit here. We need sources such as textbooks, although I would prefer something more recent than G & E, and review articles, not just primary sources, where we have to make scientific judgements and may miss the current consensus in the field. I am a scientist, but this is not my field. However, I have yet to see sources that convinces me that your edits are not special pleading. In reaching consensus we have to follow WP policies and guidelines. --Bduke (Discussion) 21:12, 25 May 2014 (UTC)

Indeed, one does not need to be an expert to edit here, but relative competence is expected. Competence should, among many other things, lead one to understand that a substance cannot be both a pure compound and a mixture (alloy) simultaneously. Hence, it is illogical and confusing to use a mixture-description for a compound, or conversely, a compound-description for a mixture. This discussion would seem a farce, if the topic was brass instead.

Being aware of a topic is not the same as understanding it. Plasmic Physics (talk) 23:56, 25 May 2014 (UTC)

Plasmic, a lot of materials and compounds are nonstoichiometric. This is the reason that Axiosaurus was urging you to read up on the topic. Many binary oxides and sulfides are subject to this complication, e.g. FeO. With ternary and quaternary phases, things get even worse. A particularly famous example is YBa₂Cu₃O_7-x. In the latter case, depending on the value of x, the material is a high Tc superconductor or semiconductor. It seems that by tradition, Wikipedia-Chem usually combine discussions of related phases into single articles. --Smokefoot (talk) 01:09, 26 May 2014 (UTC)

I am not talking about (non)stoichiometry. Plasmic Physics (talk) 02:54, 26 May 2014 (UTC)

So, this covalent network solid, with a discrete formula of TiH
₂:H
₂, would thus be the analogue of cementite, not the delta-hydride with a variable composition. Note: in the iron-carbon system, cementite has the formula Fe
₃C:C
_n, wherein C_n represent carbon clusters of varying size. Plasmic Physics (talk) 13:51, 25 May 2014 (UTC)

If so desired, I can compile a comprehensive selection of sources which either treat titanium hydride as an alloy implicitly or explicitly, or avoid using compound terminology. Plasmic Physics (talk) 11:58, 26 May 2014 (UTC)

Somehow I dont think that many editors would find "implicit" sources very convincing.

• Chem Abs lists "4517 references were found containing "titanium hydride" as entered."
• refining these hits with "alloy" gives "refine "alloy" (1539)", i.e. 1539 hits

These hits appear to be about alloys made from titanium hydride, a major app for titanium hydride as mentioned in the article. The abstracts of the 20 most cited hits refer to alloys made from titanium hydride or else organometallic complexes. --Smokefoot (talk) 13:02, 26 May 2014 (UTC)

• Yes PP we will need non primary sources such as reviews or textbooks that confirm the categorisation as an alloy. Existence o the term nickel-titanium hydride alloy does not mean that people call titanium hydride an alloy. Implicit means nothing, as deriving that fact is original research. Graeme Bartlett (talk) 13:07, 26 May 2014 (UTC)

You're missing the entire point, "... a substance cannot be both a pure compound and a mixture (alloy) simultaneously. Hence, it is illogical and confusing to use a mixture-description for a compound, or conversely, a compound-description for a mixture." Despite being illogical and confusing, this is the current state of the article. Plasmic Physics (talk) 13:13, 26 May 2014 (UTC)

Indeed, nonstoichiometric compounds can be messy. I am sure that you agree that Wikipedia should not shy away from messy situations. We can anticipate that multiple CAS registration numbers have been assigned to TiH_2-x. In deference to our readers, however, we present an overview of this slightly messy area, explaining that a range of compositions exist. The specific issue of labeling TiH_2-x as an alloy seems like a fringe idea. There is nothing wrong with harboring fringe ideas - we all do - but we cannot impose such views on readers of Wikipedia. --Smokefoot (talk) 13:22, 26 May 2014 (UTC)

A compilation of sources as I suggested, can disprove it being a fringe idea. To my knowledge, there exists no secondary sources discussing the various phases of the titanium-hydrogen system. So where secondary sources would be ideal, it is impossible. Plasmic Physics (talk) 00:21, 27 May 2014 (UTC)

Regarding the Ti-H phase diagram, Fukai covers this on p 50- and this may be helpful. Regarding the description of alloys, a change in the metal lattice is often taken to distinguish the formation of a "compound" phase. Specifically the metal lattice in alpha-Ti is hcp, the metal sub-lattice in the delta-Ti,H phase is fcc. While this "definition" is implicit in Fukai's description of hydrides (as mentioned earlier), if a more explicit definition of this difference is desirable one needs to be found. As a word of caution the categorisation of ordered phases is generally a grey area I have seen intermetallic, phase and alloy all being used in similar circumstances and it appears to depend on the writers background/training and we need to be be aware of the influence of our own backgrounds. Regarding the bonding in titanium hydrides here I can see why calling them alloys has merit, the recent change to the article mentions "four-coordinate hydride ligands linking eight-coordinate Ti(II) centres" a conventional fomulation which in my view is misleading and at variance with the reference quoted. Regarding the hydriding of metal alloys, in this field some researchers avoid calling the product an alloy but distinguish it from the precursor alloy by calling it a hydride, see [1] as just one example. Axiosaurus (talk) 11:59, 27 May 2014 (UTC)