Tag: XRD

  • Same Powder, Same Instrument, Sizes From 4 nm to 1,371 nm

    Same Powder, Same Instrument, Sizes From 4 nm to 1,371 nm

    The qualification file holds two certificates for the same natural hydroxyapatite. One reports a crystal size near 60 nanometres. The other, from an equally reputable lab, reports over a micron. Neither lab made an error, and both worked from the same X-ray diffraction data. The difference is a line of arithmetic.

    How can one XRD pattern give twenty different sizes?

    A 2020 study in Nanomaterials ran the comparison explicitly on natural hydroxyapatite from three sources. Using the classic Scherrer equation across all available peaks, “the sizes of crystallites obtained by the XRD patterns in each method for hydroxyapatite from cow, pig, and chicken were 1371, 457, and 196 nm.” The same patterns, run through the Halder–Wagner method, returned “4 nm for all samples.” And a corrected Scherrer model — a straight line forced through the origin — “gave 60, 60, and 53 nm, which shows much improvement.”

    From 4 nm to 1,371 nm, on identical data. The authors are blunt about the worst offender: the all-peaks Scherrer fit “led to unreasonable values.” Their corrected model, by contrast, landed within a few nanometres of an independent BET surface-area cross-check (56, 52 and 49 nm) — which is what validation looks like.

    Which number belongs on a certificate?

    The honest answer: none of them, without the method attached. A “crystallite size” figure is not a property of the powder alone; it is a property of the powder plus a peak set, a fitting model, and a set of assumptions about strain. Quote the figure without those, and a buyer comparing two suppliers may be comparing arithmetic, not materials.

    There is a second trap stacked on the first. Crystallite size is not particle size. As the paper puts it, “calculation of nanoparticle size extracted by XRD patterns is not possible because a particle has several nanoscale or microscale crystals.” A datasheet that slides from an XRD crystallite number to a “particle size” claim has changed subject mid-sentence — particle size belongs to laser diffraction, DLS or microscopy, each with its own disagreements.

    None of this is exotic knowledge inside a good analytical lab — the methods are decades old and their disagreements are documented. The problem is what survives the journey from instrument to certificate: a single number, shorn of its peak set and fitting model, rounded into false precision. By the time it reaches a purchasing spreadsheet it looks as objective as a weight. Two such numbers from two suppliers get compared as if they measured the same thing, and a sourcing decision quietly inherits an assumption nobody made on purpose.

    The question that sorts suppliers

    So when two drums arrive with two sizes, the discriminating question is not “which number is right?” It is: which method, which peaks, which model — and was it cross-checked against anything independent? A supplier who answers with “Scherrer” and nothing else has given you a word, not a measurement. A supplier who can name the model, show the fit, and point to a BET or TEM cross-check has given you something a specification can be built on.

    Consistency between lots is only detectable when the measuring stick itself holds still. The size number is where that discipline shows first.

    Sources

    Rabiei M, Palevicius A, Monshi A, Nasiri S, Vilkauskas A, Janusas G. “Comparing Methods for Calculating Nano Crystal Size of Natural Hydroxyapatite Using X-Ray Diffraction.” Nanomaterials, 2020;10(9):1627 (open access) — ncbi.nlm.nih.gov/pmc/articles/PMC7557758.

  • 98.5% Hydroxyapatite. The Other 1.5% Came From the Shell.

    98.5% Hydroxyapatite. The Other 1.5% Came From the Shell.

    Indonesia produced 67,201,200 kg of eggshell waste as the world’s eighth-largest egg-producing nation in 2017. Most of it goes to landfill, where it decomposes into ammonia, hydrogen sulfide and amines, and attracts what that attracts. Converting that stream into a biomaterial is a genuinely good idea, and it is the idea this entire industry rests on.

    It also means the feedstock is an agricultural product, with an agricultural product’s variability. So the useful question is not whether eggshell makes good hydroxyapatite. It is what else comes along.

    What a shell is made of

    El Milla, Hartami, Priyanto and Adrian, working at Universitas Brawijaya in Malang, published exactly that measurement in the Malaysian Journal of Medicine and Health Sciences in April 2023.

    They start with the shell itself. Calcium carbonate makes up 94–97% of an eggshell’s chemical components, with 3–4.5% organic content. Alongside it sit small quantities of other things: MgO at 0.83%, SO₃ at 0.66%, SrO at 0.43%, plus P₂O₅, Al₂O₃, K₂O, SiO₂ and Cl₂O₃.

    Their material was made by the hydrothermal route from Golden Comet chicken eggshells collected in Serang, Banten — milled to 100 mesh, calcined at 1000 °C for five hours to convert the carbonate to calcium oxide, then reacted with diammonium hydrogen phosphate at a Ca/P mole ratio of 1.67 and held at 230 °C for 48 hours. Particle size analysis put the average grain size at 243.4 ± 5 nm.

    98.5, and the remainder

    The X-ray diffraction result is a good one. The synthesised material came out at 98.5% hydroxyapatite.

    The remaining 1.5% was silica — and the paper does not leave its origin ambiguous. The impurity, it says, “came from the egg shell which was used as the starting material for the synthesis.”

    That is the sentence worth keeping. The contaminant was not introduced by poor handling or a dirty vessel. It was in the feedstock, it survived 1000 °C and 48 hours of hydrothermal synthesis, and it arrived in the product. There were also peaks in the diffractogram the authors could not assign — “not compounds of the elements Ca, Si, O, H, and P” — which they marked and reported rather than quietly smoothing away.

    Their own conclusion notes the material is a good candidate “but other strategy needed to eliminate the impurities especially for tissue regeneration material.”

    Why the trace table exists

    Set this beside ISO 13779-1, which caps arsenic at 3 mg/kg, cadmium at 5, mercury at 5 and lead at 30, with a total ceiling of 50 mg/kg for metals with adverse biological reactions.

    Those limits can look like bureaucratic furniture until you have read a paper that traces a product impurity directly back to the raw material it was made from. A biogenic feedstock inherits its source’s composition — the beneficial trace elements everyone advertises, and the ones nobody puts on a label, by the same mechanism. Magnesium and strontium are sold as advantages. Silica arrived by exactly the same route and is sold as nothing at all.

    None of which argues against eggshell as a source. It argues against treating “naturally derived” as though it settled the purity question, when it is the reason the question has to be asked.

    Chickens are fed differently in different places, and their shells reflect it. Which makes the composition of the feedstock a supplier variable like any other — one that a serious producer measures per lot, and an unserious one describes in a marketing sentence.

    Sources

    El Milla L, Hartami E, Priyanto R, Adrian AGW. “Synthesis and Characterization of Eggshell Based Hydroxyapatite Nanoparticles: X-ray Diffraction and Spectroscopy Analysis.” Malaysian Journal of Medicine and Health Sciences, 19(SUPP5):15–18, April 2023 (open access) — medic.upm.edu.my. Trace-element limits from ISO 13779-1:2008(E), Table 1 — iso.org/standard/43826.html.

  • The Datasheet Says Hydroxyapatite. The Diffractogram Says Two Minerals.

    The Datasheet Says Hydroxyapatite. The Diffractogram Says Two Minerals.

    Two drums arrive on the same pallet, from the same supplier, six weeks apart. Both certificates read the same: hydroxyapatite, eggshell-derived, calcined. The incoming-goods check passes both. It is only downstream, when one lot behaves differently in a suspension that had been stable for a year, that anyone goes looking for what the certificate did not say.

    What happens at 900 degrees

    The conversion of eggshell into hydroxyapatite is not exotic chemistry. Eggshell is mostly calcium carbonate; heat drives it to calcium oxide, which becomes the calcium source for a precipitation step, and the product is calcined again to crystallise it. The whole route hinges on how hot that second step runs.

    In 2024, Bayram, Dikmen and Malkoç published a study in the Eskişehir Technical University Journal of Science and Technology A doing the obvious controlled experiment: synthesise hydroxyapatite from waste eggshell, then calcine it at 500 °C, 700 °C, 900 °C, 1000 °C and 1100 °C, and put every sample through X-ray diffraction.

    Their conclusion was clean. “XRD patterns show that the most suitable calcination temperature for HAp is 900 °C.” The calcium-to-phosphorus ratio at that temperature came out at 1.73 — the paper notes this is “close to the expected stoichiometric ratio of 1.67.”

    So far this reads like a recipe. Run it at 900 °C.

    The sentence next to the conclusion

    Read one line further and the recipe acquires a caveat that the certificate on your pallet almost certainly does not carry. The same paper reports that the samples calcined at 900 °C, 1000 °C and 1100 °C “contain peaks belonging to biphasic HAp and β-TCP phase.”

    Not the failures. Not the over-fired samples. The optimum, too.

    β-tricalcium phosphate is a different mineral with a different solubility profile — it dissolves faster than hydroxyapatite under the same conditions, which is exactly why biphasic materials are engineered deliberately in bone grafting. Arriving uninvited in a cosmetic or oral-care powder, it is not a contaminant in the toxicological sense. It is something more awkward: a second material with its own behaviour, present in a proportion nobody wrote down.

    And the Ca/P figure tells the same story from another direction. 1.73 is close to 1.67. It is not 1.67. The gap is the part of the sample that is not stoichiometric hydroxyapatite.

    What the certificate should have said

    Which brings the two drums back into focus. Nothing in that study suggests either lot was made badly. It suggests that a process run correctly, at the temperature the literature endorses, produces a mixture — and that the ratio inside the mixture can move between runs while every word on the certificate stays true.

    “Hydroxyapatite, eggshell-derived, calcined” is a description of a route. It is not a specification of a product. A specification names the phases present and their proportions, states the Ca/P ratio as a measured number with a tolerance, and comes with the diffractogram attached rather than summarised.

    That is the difference between a supplier who knows what varies in their process and one who has never been asked. The question that separates them is not whether the material is good. It is whether the next drum is the same as this one — and only a supplier who measures the second phase can answer it.

    Sources

    Bayram N, Dikmen S, Malkoç S. “Effect of different calcination temperatures on synthesized hydroxyapatites from waste eggshell.” Eskişehir Technical University Journal of Science and Technology A — Applied Sciences and Engineering, 2024 (open access) — dergipark.org.tr/en/pub/estubtda/article/1539308.