Spodumene minerals

Spodumene And Its Use In Ceramics: An Overview

Spodumene is a mineral with an important role to play in modern ceramics: the addition of resistance to thermal shock and expansion - making for a longer ceramic lifetime.

Introduction

Spodumene is a pyroxene type mineral with the chemical formula LiAl(SiO3)2. It is primarily used as a source of lithium metal, which is isolated first by roasting the spodumene and then by leaching in acid. It is preferred over other methods owing to the higher amount of lithium that may be extracted. In other areas, spodumene finds uses in ceramics, as a fluxing agent and in medicine. In the home, spodumene found popular and widespread use as the crystalline phase of Corning Glass’ ‘Pyroceram’ glass-ceramic material for cooking. Possessing high thermal tolerance and low expansion at high temperatures, the material was incredibly popular from the late 1950’s. Spodumene, specifically the β-spodumene phase, is responsible for these impressive properties. Most of the naturally occurring spodumene exists as the α-spodumene crystal structure, with the stronger β variant attained through heating. The Democratic Republic of Congo has the largest proven reserves of spodumene.

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Uses In Ceramics

In Corning’s ‘Pyroceram’, the glass-ceramic appeared to be a milky white in colouration; allowing a moderate amount of light to pass; translucent. Spodumene based ceramics found their popularity due to the properties they bear, chefly resistance to thermal shock, tolerance of high temperatures and a resistance to thermal expansion. Additionally, spodumene ceramics are generally regarded for their strength and durability. In terms of manufacturing processes, spodumene sinters well.

Thermal Shock Resistance

Resistance to thermal shock refers to the ability of a material to not deform or rupture at a sudden and/or dramatic change in temperature. Because of its excellent thermal performance in its own right, β-spodumene is often included in other ceramics to aid in adding valuable shock resistant properties. For example, the addition of 15 wt% β-spodumene to alumina has been shown to produce ceramics with a high thermal expansion mismatch(1). Testing showed that the spodumene doped ceramic displayed minimal strength degradation under thermal shock conditions, compared to pure alumina which did not perform as well. This result compares favourably to other alumina composite ceramics.

In glass ceramics, spodumene and silica are used. Densities of the resultant glass ceramics are increased after 3.5 or more hours of sintering. In this process, the mean grain size increased from 0.55 to 0.67 µm with hardness increasing to 5.47 GPa, alongside a flexural strength increase of 158 MPa. There was a commensurate increase of residual strength and performance in thermal shock testing. Researchers explain this phenomenon by the increased crystallinity and elevated percentage of β-spodumene that comes with extended sintering/calcination durations(2). Thermal shock performance is therefore impacted favourably by flexural strength performance.

When used as a flux, spodumene is responsible for a densification effect in the resulting ceramics. In an example where researchers were developing cordierite-spodumene for solar heat transmission applications, adding just 10% of β-spodumene was sufficient to ensure bending strength after 30 heating and cooling cycles (rapidly from 1,100 °C to room temperature) decreased by only 6%. This highly resilient material retained virtually all of the spodumene after all of the cycles(3). Authors suggest this may be a promising material for heat transmission in solar thermal power generation. Building on the cordierite-spodumene work, the addition of 5% andalusite was found to increase thermal shock properties even further(4).

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Thermal Expansion Resistance

Coefficient of thermal expansion (CTE) is the measurement of how much a material expands at temperature, with lower numbers being preferred.

In silica ceramics with β-spodumene, the anisotropy of material expansion is greater with an increasing percentage of silica(5). The β-spodumene itself forms itself into spiral chains of Al-O tetrahedra in a screw axis arrangement, which although strained, the strain is relieved at high temperature by a reduction in bond angles in the tetrahedra. This causes a greater level of stability(6).

β-spodumene glass ceramics manufactured via a sol gel process followed by hot pressing have shown near-zero CTEs of -0.03 x 10-7 K-1 to -0.97 x 10-7 K-1  from room temperature to 1,200 °C(7). Researchers suggest that the reason for such incredible resistance to expansion is due to the highly stable crystal phases achieved and uniform crystallinity, which both depend on the excellent sintering behaviour of the spodumene. Such negative CTE values refer to a material that is dilatometric - i.e. the material contracts. This has been known to be the case for β-spodumene since 1951(8).

Especially low coefficient of thermal expansion in spodumene ceramics can be achieved by the use of a lithium oxide and germanium oxide sintering additive. Using just 3% by weight of this additive in an otherwise β-spodumene led process resulted in a ceramic with a CTE of just 7.0 x 10-7 K-1 from room temperature to 800 °C(9). For comparison, lithium aluminosilicate ceramic has a CTE of 3.2 x 10-7 K-1(10).

Negative CTE values are also observed in spodumene containing glass ceramics of a more exotic nature. In the case of nitrogen containing spodumene glass ceramics, nitrided β-spodumene rich compositions that crystallise at 1,200 °C have negative CTEs. Density and hardness of the resultant glass is vastly increased. The explanation for this phenomenon is that alongside the formation of β-quartz (see below), nitrogen atoms become incorporated into the lattice(11).

Considerations And Observations During Manufacturing

As with all ceramics, a heat treatment process is an essential part of manufacture. During heating, α-spodumene or amorphous spodumene converts into ɣ-spodumene, the stability of which depends on the rate of heating as well as the prior mechanical treatment of the sample (i.e. whether it has been ground). As calcination proceeds, ɣ-spodumene converts to β-spodumene, plus in some cases some β-quartz as a gangue, as some of the lithium and aluminium centres are substituted by silicon. As a general rule, starting with a finely ground sample will result in a more complete conversion to β-spodumene(12). Energy reduction can be achieved by processing the spodumene in a fluidised bed(13).

Researchers have noted that when forming spodumene ceramics, the body becomes much harder to form when calcination has caused the proportion of β-spodumene to exceed 50%. For more complex ceramic shapes with this material, it is therefore important to modulate the temperature carefully so as not to exceed the 50% level too soon(14). A potential method to alleviate this could include changing the content/addition of LiO2, which has more of an effect on sintering behaviour, alongside other oxides(15).

Impact On Other Ceramics

The addition of spodumene in the production of known ceramics has been shown to be beneficial in terms of adding desirable properties. In the manufacture of mullite ceramics, researchers have found that by using β-spodumene as a liquid phase sintering agent, density of the mullite increased (i.e. was less porous), the sintering behaviour was improved and the mullite is more easily formed at 1,550 °C(16). Additionally, the authors claim that the spodumene-modified mullite ceramic bears superior physical and mechanical properties compared to mullite alone.

These enhancement properties are largely echoed by researchers who doped liquid phase sintered aluminas with β-spodumene(17). They found that by adding β-spodumene, the ceramics produced contained a mix of crystalline spodumene and glassy material - which led to a strongly mechanically performing ceramic, rivalling any alumina ceramic commercially available.

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Spodumene Floatation And Recovery

An important factor in any modern production process is the minimisation of waste - and treatment of whatever waste there is to ensure safe disposal. With this in mind, spodumene floatation is an important process in the production of lithium metal (as mentioned, mostly from spodumene) and residual spodumene and lithium compounds may be extracted from lithium production tailings. As spodumene has a negative zeta potential in solutions that have a pH of less than 3(18), spodumene can potentially be removed from said tailings by cationic collection, such as with amines. Research has shown that 90% of spodumene from tailings can be extracted(19). Floatation is achieved by addition of sodium oleate (250 g L-1) and calcium chloride to the tailings(20). The recovered spodumene is perfectly suitable for use in ceramics(21), such as an example where floatation tailings, kaolin and low melting glass powder were combined to produce a highly porous ceramic with an enviable 5.60 MPa strength value(22).

Summary

  • Spodumene is a mineral with the formula LiAl(SiO3)2, which is primarily used as a source of lithium
  • In the ceramic and glass ceramic world, spodumene is valued for its excellent sintering properties
  • High resistance to thermal shock is explained by the increased crystallinity and strength produced by greater percentages of β-spodumene
  • In terms of thermal expansion, spodumene affords excellent characteristics to a ceramic, with some expansion coefficients even being negative
  • β-spodumene is largely responsible for the impressive strength and related properties, along with the formation of modest amounts of β-quartz in some systems
  • Recovery of spodumene sufficient for ceramic production is possible by way of spodumene floatation
  • Overall, spodumene is a valuable material for ceramics production

References

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2          H. Mohammad et al., Asian J. Ceram. Soc., 2021, 9, 507

3          C. Hu et al., Ceram. Int., 2016, 42, 13547

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5          J. P. Williams et al., J. Am. Ceram. Soc., 1968, 51, 651

6          C.-T. Li and D. R. Peacor, Z. Kristallogr. Krist., 1968, 126, 146
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8          E. J. Smoke, J. Am. Ceram. Soc., 1951, 34, 131
9          T. Ogiwara et al., J. Am. Ceram. Soc., 2013, 96, 2577

10        L. Xia et al., Ceram. Int., 2020, 46, 28668

11        H. Unuma et al., J. Am. Ceram. Soc., 1991, 74, 1291

12        M. Altarawneh et al., Miner. Eng., 2019, 140, 105883

13        E. Gasafi and R. Pardemann, Miner. Eng., 2020, 148, 106205

14        E. M. El-Meliegy, Ceram. Int., 2004, 30, 1059

15        S. Knickerbocker et al., J. Am. Ceram. Soc., 1989, 72, 1873

16        I. Low et al., J. Mater. Sci., 1997, 32, 3807

17        B. H. O’Connor et al., J. Am. Ceram. Soc., 1995, 78, 1895
18        J. Deng et al., Miner. Eng., 2015, 79, 40

19        L. Wang et al., Sep. Purif. Tech., 2016, 169, 33

20        S. Farrokhpay et al., Minerals, 2019, 9, 372

21        P. N. Lemougna et al., Ceram. Int., 2021, 47, 33286

22        L.-H. Xu et al., Trans. Non-ferrous Metal Soc. China, 2021, 31, 9