Hugh Hunt, Keeper of the Clock, explains how the Trinity College tower clock works and reaches 0.1 ppm precision, how gravity escapements work, and how John Harrison’s gridiron pendulum corrects for temperature by causing its #TCE to vanish through differential cancellation. cc-by-nd. #metrology #horology #hardware
on 02018-11-21#PDF #paper on #TCE, thermal coefficients of expansion, of different kinds of #glass #materials; B₂O₃ and MgO are 0.33 ppm/K at human temperatures, silica is 2.67, PbO and TiO₂ are 13, CaO and Al₂O₃ are 17, K₂O is 28, Na₂O is 33. Also they did their own linear regression, giving rise to a hairier model that is apparently twice as accurate. PbO’s 13 compares favorably to (from other sources) carbon steel at 10.8, aluminum at 23.1, and concrete’s at 12, but of course enormous compared to invar at 1.2 or crystalline quartz at 0.33.
on 02017-02-23#abstract on tunable-#TCE single-phase #materials made of tin/zirconium manganese oxide, down to zero-TCE.
on 02015-08-16Positive-#TCE Tin manganese oxide is closely related to negative-TCE zirconium manganese oxide, and so by adjusting proportions of tin and zirconium, you can get a single-phase near-zero thermal expansion material, but the material is metastable and tends to separate. This is #popsci; the research is by John Evans at U Durham.
on 02015-08-16"clearceram-z" is one of the few near-zero #TCE #materials like Sitall, and the curves in this #PDF suggest that that's because it has a local maximum expansion around room temperature, perhaps because it incorporates a negative-TCE phase. Apparently OHARA can’t afford to hire a person literate in English to write their brochure, though.
on 02015-08-16the #TCE range of different common #materials; e.g. fused silica is 0.55ppm/°, invar is 1.3, #silicon-nitride is 3.2, titanium is 9.5, copper is 16.7, polymers are 50–200, and silicone is 30–300.
on 02015-08-14Dan #Gelbart’s description of his 2010 #steam-engine. (Or maybe it's Tom Kimmel’s.) Includes a sort of zero-#TCE construction to keep the inside diameter of the cylinder constant: when the 440C stainless-steel cylinder expands, the graphite-filled #polyimide (Vespel) liner tries to expand even more, but can only do so toward the inside of the cylinder, thus counteracting the cylinder’s expansion. The piston itself is made of electroless-nickel-plated #Invar, which really seems like overkill, but whatever. The tabletop model reaches 10% efficiency.
on 02015-08-13Another overview #paper of negative-#TCE materials, again without mentioning metamaterials at all!
on 02015-08-1213-page overview #paper of negative-#TCE materials (including cubic zirconium tungstate and perovskites) without mentioning metamaterials at all!
on 02015-08-12Very brief negative-#TCE #metamaterials introduction.
on 02015-08-12A short, clear-seeming #paper about #metamaterials with tunable #TCE. #toread
on 02015-08-12Roderic Lakes’s #bibliography on composite #metamaterials that can have either negative or colossal thermal coefficients of expansion (#TCE) even if their components don’t. This is potentially useful for making nanometrically-precise #flexures without resorting to exotic materials like #Invar or maybe even metals.
on 02015-08-12negative thermal coefficients of expansion (#TCE) in normal temperature ranges are found in and water below 4°, but few other common #materials.
on 02015-08-12