Spec Sheet vs Batch COA: A Modulus Window the Plant Treats as Final

Plant QA at Zhongzhi Chemical treats two files as different jobs. The specification is the window the purchase order locks. The batch COA is the assay for the lot about to ship from Changyi. A brochure typical sits in neither file. Trust is the habit of comparing them line by line before a container is booked through Qingdao, and of holding a lot whose modulus sits outside the buyer’s window.

Illustrative industrial scenario (composite): Rewritten from factory training. A European buyer locked Na₂O, SiO₂, and a modulus window. A cheaper COA reported modulus 1.15. The buyer’s window was about 0.95–1.05. Same teaching figures already used on this site. No customer is named. No price is stated.

Three files, three jobs

Industry grade language sits underneath those files. HG/T 2568-2021 is the public Chinese chemical-industry standard for industrial sodium metasilicate — one line in the Changyi portfolio, not the whole plant. Zhongzhi’s predecessor took part in drafting that standard; the record is on company history. A teaching note already on this site: the standard layer for pentahydrate Superior may be discussed as Na₂O ≥28.5%. That sentence is a standard-layer reminder. It is not a new Fe limit and not a new Na₂O promise beyond what the COA on your lot prints.

Why modulus 1.15 misses a 0.95–1.05 window

Modulus is the molar ratio SiO₂ / Na₂O. Metasilicate sits near 1:1. A COA at 1.15 can still be “a silicate” and still miss the alkalinity the formula was validated on. In the composite, the side that kept the order did nothing clever with price. They lined the factory COA up against the buyer’s specification, confirmed the lot could sit inside the window, and committed to a COA on every batch.

Zhongzhi’s release practice on this point:

1. Write the buyer’s Na₂O, SiO₂, and modulus window into the order before the lot is scheduled.
2. Assay the lot. Compare every line. Modulus outside the window holds the lot.
3. Ship the batch COA with the goods. A sample COA on Downloads is a format example, not the shipment certificate.
4. For a repeat supply, set consecutive lots side by side and watch modulus, SiO₂, and Fe move in a narrow band.

Iron and whiteness are their own lines. A color complaint starts on the COA as well — see yellow powder: check the COA first. Published anhydrous grade bands already used on this site remain Superior Fe ≤0.010% and First Fe ≤0.02%. This article does not add a new iron figure.

What to send so QA can lock the window

• Form and mesh, and the specification rows you will claim against
• Modulus window, if your formula has one (state the numbers you already use)
• Whether you need COA history across several lots for qualification
• Packing and destination (FOB Qingdao when that is the agreed term)
• Volume as a request for the current supply plan

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