# PCM Cartridge Proposal Reconciliation

**Applies to:** `NanoArc_Zoey&Rumi_PCM_Thermal_Cartridge_Proposal_Rev0.pdf`  
**Related:** `NanoArc_RevB_RevC_PCM_Development_Proposal.pdf`  
**Date:** 2026-08-12  
**Status:** Reconciliation note; not a fabrication release or chemistry freeze

## Purpose

The thermal-cartridge proposal was written around a beeswax cartridge and
describes RevC/Rumi as the target. The newer PCM development proposal expands
the candidate set to beeswax, pure sodium acetate trihydrate (SAT), and a
screening SAT composite. The cartridge concept remains usable, but the PCM and
revision wording must be reconciled before engineering requirements are frozen.

## Corrected revision relationship

- **RevB is the prototype and characterization platform.** Build the first
  non-electrical cartridge and dummy-heater fixture against RevB-representative
  thermal geometry and available instrumentation.
- **RevC/Rumi is the intended integration target.** Do not credit the cartridge
  with RevC duty-cycle improvement until the RevB measurements support the
  thermal model and the RevC thermal boundary is defined.
- **RevA remains unchanged.** No RevA board, connector, firmware contract, or
  high-energy path is modified by this reconciliation.

## Corrected PCM relationship

### Configuration note — PCM-C versus the current crystallization route

`PCM-C` remains exactly **97.5 wt% SAT / 2.0 wt% DHPD / 0.5 wt% CMC**. Its
composition and formulation identity have not been silently changed or
retired. The newer `SAT/NanoArc_SAT_Crystallization_Route_Plan_Rev0.md` is the
current experimental development path: it first investigates chemical
nucleators, retained SAT seed, and on-demand triggering without depending on
DHPD, and introduces CMC only after a nucleation route passes independently.

The crystallization-route document is a draft unless Tristan's approval record
says otherwise. `PCM-C` remains a later historical/comparator branch and may be
revisited after the route work. Any substitute nucleator, hydrate, or changed
composition receives a new formulation ID and does not become `PCM-C`.

This configuration note reconciles programme routing; it does not select a
winning nucleator, approve the draft route, or change any experimental gate.

The cartridge should be treated as a **PCM-agnostic replaceable cartridge
envelope** during development. Use identical or deliberately documented
geometries for the initial specimen set:

| Specimen | Role | Cartridge status |
|---|---|---|
| PCM-A: beeswax | Baseline control | First mechanical fill and control |
| PCM-B: pure SAT | Salt-hydrate control | Candidate fill after containment review |
| PCM-C: 97.5 wt% SAT / 2.0 wt% DHPD / 0.5 wt% CMC | Modified SAT screening candidate | Candidate fill after mixing and hydration review |

The existing metal shell, flat contact face, thermal matrix, isolated airflow
tube, sensor pocket, removable clamp, and fan-assisted recharge concept remain
valid for all three specimens. What changes is the material-specific test and
containment evidence.

## Consequences for the cartridge proposal

1. Replace “beeswax PCM cartridge” with “replaceable PCM cartridge” wherever
   the text describes the general architecture.
2. Retain beeswax as the first control and simplest handmade prototype.
3. Add SAT and PCM-C only after the same fixture is characterized and the
   container, headspace, hydration retention, leakage, and corrosion behavior
   are understood.
4. Do not assume the beeswax temperature bands apply to SAT. Each PCM requires
   its own measured melt/plateau, freeze onset, supercooling, recovery, and
   allowable thermal limits.
5. Keep the fan as a recovery aid, not a safety dependency. A failed, blocked,
   or disconnected fan must still leave the passive thermal path within its
   characterized safe duty cycle.
6. Treat any salt-hydrate fill as a containment and materials-compatibility
   change, not merely a replacement pour.

## Revised prototype sequence

### RevB Phase 1 — thermal dummy and beeswax control

Build the small metal shell, isolated air tube, matrix, sensor pocket, and fan
mount. Use a controlled dummy heater rather than the Weld Energy Stage. Measure
contact repeatability, melt/softening behavior, fan-on/fan-off recovery, mass
loss, leakage, and blocked-airflow response.

### RevB Phase 2 — SAT controls

Use the same documented cartridge geometry for pure SAT and PCM-C, with separate
labelled fills. Record water/mass retention, visible separation, crystallization
and supercooling behavior, corrosion or residue, thermal plateau, recovery, and
cycle drift. Do not infer SAT performance from beeswax data.

### RevB Phase 3 — candidate comparison

Compare all candidates per gram, per cartridge volume, peak temperature
suppression, recovery time, containment burden, and repeatability. Select a
candidate only if it provides a system-level benefit over beeswax.

### RevC/Rumi decision

Only after RevB bench data exists should the design decide whether RevC/Rumi
uses beeswax, pure SAT, PCM-C, another PCM, or no PCM cartridge. Any selected
chemistry must receive extended cycling and orientation testing before it is
credited in the Rumi duty-cycle model.

## Requirements that remain material-independent

These requirements survive unchanged:

- The passive metal thermal path remains useful with the fan absent.
- The cartridge is removable and mechanically clamped through a flat contact
  face.
- The airflow path is isolated from the PCM cavity.
- The cartridge cannot drip or vent material toward ACE electronics, connectors,
  switches, vents, or pulse conductors.
- Temperature validity, cooldown recovery, and fresh operator action are
  required before another permitted output cycle.
- No cartridge is safety-critical until measured and reviewed evidence supports
  that claim.

## New PCM-specific open items

- SAT hydration retention and permissible headspace;
- salt residue or leakage containment;
- corrosion compatibility of shell, tube, matrix, and fasteners;
- PCM-specific transition and freeze behavior;
- supercooling and crystallization reproducibility;
- material mass/volume after cycling;
- cartridge cleaning or replacement procedure; and
- whether one chemistry can serve both RevB and RevC/Rumi thermal envelopes.

## DHPD sourcing contingency

DHPD remains the defined PCM-C nucleator. If CAS `10039-32-4` material cannot
be obtained from an individual-accessible supplier, discuss contingency
formulations separately before purchasing or mixing substitutes.

Any substitute nucleator or different hydrate must receive a new formulation
ID, exact component identity, mass fraction, hydrate state, supplier/lot
record, and separate thermal-cycle dataset. Do not silently replace DHPD with
another phosphate, calcium salt, or anhydrous material and continue calling the
result PCM-C. Pure SAT remains the valid fallback experiment while the
modified-SAT branch is unresolved.

### Candidate Plan-B shortlist (screening only)

These are contingency candidates, not replacements for PCM-C and not yet
approved formulations. Each would need its own formulation ID, weighed
composition, exact hydrate state, supplier/lot record, and repeat thermal
cycling in the RevB fixture.

| Candidate | Identity | Why screen it | Main reservation |
|---|---|---|---|
| PCM-CaCl2 | Calcium chloride dihydrate, CAS `10035-04-8` | A 2024 SAT nucleator screen observed reproducible crystallization with this hydrate. | Chloride-bearing, hygroscopic, and potentially corrosive to the cartridge and hardware. |
| PCM-MgCl2 | Magnesium chloride hexahydrate, CAS `7791-18-6` | The same screen observed SAT crystallization with this hydrate. | Greater hygroscopic/corrosive risk; second-line only. |
| PCM-PP | Sodium pyrophosphate decahydrate, CAS `13472-36-1` | Prior SAT composite work reports it as a nucleating additive. | Different phosphate chemistry and hydrate stability; verify independently. |
| PCM-BX | Sodium tetraborate decahydrate (borax), CAS `1303-96-4` | Reported as a SAT nucleator and possible binary-screen component. | Borate handling and matrix-interaction questions; not a DHPD drop-in. |
| PCM-SS | Anhydrous sodium sulfate, CAS `7757-82-6` | Recent work reports it as an accessible SAT nucleator candidate. | Newer evidence; hydrate balance and cycling remain unproven here. |

Recommended order is **pure SAT control → PCM-CaCl2 → PCM-MgCl2 only if
needed**, with PCM-PP/PCM-BX/PCM-SS reserved as second-line screens. Do not
screen several additives at once: a failed result must remain attributable.
Chloride candidates must stay isolated from ACE and pulse hardware during
bench characterization.

### Retrieved study documents

The local reference copies are stored under `Chemistry/References/`:

- `Li_2024_SAT_Nucleating_Agents.pdf` — open author manuscript of the 2024
  Crystal Growth & Design screening study. It tested 36 agents; calcium
  chloride dihydrate was the most reliable result and magnesium chloride
  hexahydrate was also effective, with performance degrading at low additive
  loading.
- `2018_Modified_SAT_Nucleators_Thickeners.pdf` — open study screening
  disodium hydrogen phosphate, tetrasodium pyrophosphate decahydrate,
  anhydrous sodium acetate, sodium tetraborate decahydrate, and sodium
  metasilicate nonahydrate as SAT nucleator candidates, alongside several
  thickeners.

These documents support the shortlist but do not establish a Rumi-ready
formulation. The Plan-B list above remains the controlled candidate set; the
additional agents named in the 2018 paper are literature leads only until
Tristan authorizes expanding the screening matrix.

Reference retrieval status is tracked in `../References/REFERENCE_GAPS.md`, and
material-documentation gaps are tracked in `../SDS/SDS_GAPS.md`.

## Reconciliation result

The cartridge engineering concept is retained as a **RevB prototype envelope
for three PCM candidates**, not as a beeswax-only RevC design. RevB produces the
thermal and containment evidence; RevC/Rumi receives only the PCM and geometry
that survive that evidence. No RevA change, high-energy routing change, or
chemistry freeze is implied.