**3. Factors Affecting the Suitability of Kaolin Geopolymers in Ceramics**

Alumina is now used in the production of ceramic membranes. Kaolin, which is extensively used as a substitute for alumina due to its unique chemical and physical properties, provides a membrane with low plasticity and high refractoriness [22,30,49]. Additionally, kaolin shows hydrophilic properties. It possesses good chemical and fire resistance in addition to a comparatively high mechanical strength [50–52]. Therefore, geopolymers have the potential to be employed as construction and building materials that are environmentally beneficial. Under thermal activation, kaolin geopolymers become more stable, and kaolin clay transforms into the reactive phase of metakaolin. When metakaolin was employed as an aluminosilicate precursor [35,48], its characterization was simplified.

Ceramics cannot transfer high internal loads via plastic deformation due to their brittleness properties [53–55]. Despite all its benefits, ceramics as a building material also has several drawbacks. The basic structure of kaolin is a highly disturbed phyllosilicate network consisting primarily silicon and aluminium, which confer the major advantage of having a particle size distribution that is relatively homogeneous [22,50,56,57].

#### *3.1. Curing Process*

In general, efforts are undertaken to develop ceramics with superior mechanical qualities by incorporating amorphous phases, whiskers, fibres, particles, and even metallic phase and pores. Another method for improving the ballistic impact on a ceramic surface is to promote finer particle size, which prevents the initiation and spread of failures such as pores, flaws, fractures, and cracks [58,59]. Table 2 provides a review of prior research on geopolymer materials for diverse ceramic applications.


**Table 2.** Kaolin geopolymer on various ceramic applications.

Numerous studies of kaolin as a ceramic material show it is widely used for high performance ceramic materials, which are divided according to the end use application into electronic packaging industries [61], electroceramics (dielectric [64], insulator [63]), ceramic foam [62], ceramic grog [9], cementitious materials [15,60], soil construction [65], and ceramic coatings [66].

Kaolin has narrower interlayer spacing and less cation exchange capacity than other clay mineral materials [17,65,67]. Kaolin is the principal clay formed by chemical weathering; it is coarse in particle size and inflexible compared to other clays. It is the most researched clay mineral in this field, and its extensive use is attributed to its capacity to change into the metastable and more reactive phase of metakaolin following dehydroxylation at temperatures between 550 ◦C and 800 ◦C [52,62,68]. Similarly, kaolin's basic structure consists of a highly disturbed phyllosilicate matrix comprising primarily silicon and aluminium, with little variation in particle size [69,70].
