Metal Nitrate Hydrate Phase Change Materials
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Solution Overview
Problem
Metal nitrate hydrates exhibit sub-cooling, which limits their application as phase-change materials (PCMs) due to kinetic trapping in a metastable liquid state, slow crystallization, and wide-ranging melting and crystallization temperatures, making them unsuitable for reliable thermal cycling and efficient heat storage.
Innovation Solution
The use of combinations of metal nitrates and hydrates, specifically calcium nitrate tetrahydrate with nucleation agents like magnesium nitrate and strontium nitrate, along with physical methods such as agitation and sonication, to induce nucleation and increase crystallization rates, thereby overcoming sub-cooling and tuning the melting transition temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If metal nitrate hydrates are used as phase change materials, then large latent heats of fusion can be stored, but sub-cooling occurs causing the material to remain in a liquid state below its melting point without spontaneous crystallisation
Solution Approach 1:
The patent applies preliminary action by pre-introducing nucleation centres (such as fine metal particles, oxide particles, or hydroxide particles) into the metal nitrate hydrate composition before use. These nucleation centres are prepared in advance to provide immediate crystallisation sites when the material is cooled, preventing sub-cooling from occurring. The nucleation centres are mixed with the metal nitrate hydrate in specific proportions (0.1-10 wt%) to ensure reliable spontaneous crystallisation at or near the melting point.
Solution Approach 2:
The patent uses intermediary substances as nucleation centres that mediate the phase transition process. These intermediaries (metal particles, oxide particles, hydroxide particles) provide a surface or interface that facilitates the transition from liquid to solid phase. The intermediaries act as a bridge between the metastable liquid state and the stable solid state, enabling controlled crystallisation without requiring significant sub-cooling.
2Use of energy by moving object
If metal nitrate hydrates are used as phase change materials, then heat storage capacity is increased, but crystallisation proceeds slowly limiting the thermal power output
Solution Approach 1:
The patent applies preliminary action by pre-distributing numerous nucleation centres throughout the metal nitrate hydrate composition before the phase change cycle begins. These pre-distributed nucleation centres provide multiple simultaneous crystallisation sites, dramatically increasing the overall crystallisation rate and thermal power output. The nucleation centres are dispersed in advance to ensure uniform crystallisation throughout the material volume.
Solution Approach 2:
The patent applies segmentation by dividing the crystallisation process into numerous parallel events occurring at different nucleation centres throughout the material. Instead of relying on a single crystallisation front, the material contains many dispersed nucleation centres (0.1-10 wt%) that initiate crystallisation simultaneously, segmenting the overall phase transition into many small, concurrent crystallisation events that sum to high total power output.
3Ease of manufacture
If metal nitrate hydrates are used as phase change materials, then low cost and non-toxic properties are achieved, but the melting and crystallisation temperatures are wide ranging and may be at points which are inopportune for certain applications
Solution Approach 1:
The patent applies parameter changes by systematically varying the composition of the metal nitrate hydrate system to adjust the melting and crystallisation temperatures to desired ranges. Different metal nitrates (calcium, strontium, barium, zinc, manganese, iron) and their hydrate forms are selected and combined in specific proportions to achieve target temperature ranges. The nucleation centre composition and concentration are also adjusted to fine-tune the phase transition temperatures and ensure they match application requirements.
Solution Approach 2:
The patent applies composite materials by creating multi-component systems that combine metal nitrate hydrates with various nucleation centres (metal particles, oxide particles, hydroxide particles). These composite compositions allow independent optimization of temperature range, crystallisation reliability, and cost. The composite nature enables selecting from multiple metal nitrate options and nucleation centre types to achieve the desired temperature profile while maintaining low cost and non-toxic properties.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the development of PCMs that can be reliably thermally cycled, minimizing sub-cooling, increasing crystallization rates, and allowing for the depression or tuning of melting and crystallization temperatures, making them suitable for various industrial applications including temperature control, refrigeration, and low-emission heating and cooling solutions.
Implementation Method 1
Nucleation is the initiation process that leads to the formation of a solid phase as molecules, atoms or ions arrange themselves into a continuous superstructure. The initial nucleation centre provides a site upon which dissolved or molten material at the solid/liquid interface can be arranged, and thus the crystal grows.
Implementation Method 2
As the solid melts it stores heat - latent heat of fusion (ΔH f ) - and when the liquid freezes it releases the stored heat.
Implementation Method 3
Nucleation centres can also be formed from physical processes, such as sonication.
Data Source
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AI summary
There is disclosed herein metal nitrate hydrates as phase change materials(PCMs). More particularly, there is disclosed herein metal nitrate hydrate PCMs containing group II metal nitrates as nucleation agents. A further disclosure herein is the combination of multiple chemical species in the PCM formulation which act together to induce nucleation of metal nitrate PCMs.Furthermore, physical mechanisms by which nucleation of metal nitrate hydrate based PCMs and crystallisation rate increased are disclosed.