In Ghana, subsequent governments have, in one way or another, tried to implement policies that would drive the country from a primarily agricultural economy to a mixed agricultural-industrial one [1] . This is because Ghana’s economy has since independence been agrarian. To be able to industrialize Ghana’s economy, its industrial capacities need to be adequately improved by targeting the expansion of the metal processing industries. According to Ahmed and Awareng [2] , the economic and industrial capacity of a nation is highly related to its metal processing capacity. This metal processing becomes incapacitated when basic equipment like crucibles is unavailable [2] . Crucibles are ceramic vessels used in areas of applications where high temperature of heat is required [3] . Crucibles are also reaction vessels in which high-temperature transformation takes place without interacting with the heating materials [4] . The major raw materials for producing crucibles are clay and other graphite materials [5] . In Ghana, the presence of this naturally endowed mineral resource is relatively abundant in the earth’s crust [6] . Despite its abundance, there is little or no documented evidence of locally produced clay-graphite bonded crucibles. There are few industries that import crucibles while the small and medium scale operators result in the use of cut-out compressor ports [7] . It is against this backdrop that the study seeks to find out the suitability of selected clays and other raw materials found at Assin Fosu in the Central Region of Ghana to develop a recipe for the local manufacturing of crucibles.

According to Aigbodian et al. [8] , a crucible is a ceramic or metal container in which metals or other substances are melted or subjected to a very high-temperature. Again, it can also be defined as a refractory container used in a furnace for glass, metal and pigment production as well as laboratory processes, which can resist high-temperature to melt or otherwise alter its content. Crucible is also a ceramic or metal container for which metals or other materials are melted or subjected to a very high-temperature [9] . Another definition given by Torres et al. [10] is that crucibles are ceramic vessels used for dry, that is, high-temperature reactions. In another development, Adeoti et al. [11] define crucibles as refractory open-mouth vessels used for melting steel, glasses, iron and others.

Even though crucibles were historically made from clay, they can also be made from any metal that withstands temperatures high enough to melt or otherwise other its contents [10] .

Crucible is used in laboratories to contain chemical compounds when heated to extremely high temperatures. Crucibles help to keep metals when being heated in it, keep heat and melt losses to a minimum and also help to avoid overheating of the metal [8] .

After various preliminary body tests, three (3) recipes were developed with the following compositions: 1) Cru_a consisting of 65% white clay, 15% kaolin, 5% quartz and 10% white grog, 2) Cru_b comprising 70% white clay, 15% kaolin, 5% quartz and 10% white grog; and lastly 3) Cru_c composing of 70% white clay, 20% kaolin, 8% quartz and 2% white grog. These compositions were experimented with their suitability and potency to serve as potential recipes for making crucibles. For the purposes of analysis, samples of the compositions were rolled into slabs (test pieces) and labeled as Cru_a, Cru_b and Cru_c. The test pieces were subjected to physical and chemical experiments to understand the various properties of the compositions.

Density test results: In determining the bulk density of the compositions, the test pieces were immersed in a graduated cylinder filled with water to regulate the volume of water displaced. The test pieces that were denser displaced a lot of water while the less dense pieces displaced relatively less water. It came to light that Cru_c was denser followed by Cru_b and the least dense was Cru_a as shown in Figure 16. A dense object weighs more than a less object that is the same size [13] .

Plasticity Test: It was conducted to determine the ability to work with the composed ceramic body. It was done by rolling samples into rope-like forms and then coiling them around the fingers to experience the level of cracks developed. It was realized that sample Cru_a had more cracks (low plastic), followed by sample Cru_b with little cracks (medium plastic), and sample Cru_c had no cracks (high plastic). Finally, the colours of the samples were noted and recorded as

shown in Table 1.

Shrinkage Test: In order to find out how the samples would shrink, a shrinkage test was carried out by forming 12 briquettes and 12 MOR bars, 5 cm diagonal lines were created on each of the briquettes with 4 for each composition (Cru_a, Cru_b and Cru_c) and were allowed to dry under room temperature for days. Afterward, dry shrinkage was conducted on each briquette to determine how each one has shrunk and recorded as highlighted in Table 2.

Dry shrinkage test was given by:

Dry shrinkage = wet measurement (WM) − dry measurement (DM)

Thus, dry shrinkage test = WM − DM

For Cru_a, slab No. 1: 5.00 cm − 4.70 cm = 0.30 cm, slab No. 2: 5.00 cm − 4.70 cm = 0.30 cm, slab No 3: 5.00 cm − 4.70 cm = 0.30 cm, slab No 4: 5.00 cm − 4.70 cm = 0.30 cm.

For Cru_b, slab No. 1: 5.00 cm − 4.80 cm = 0.20 cm, slab No. 2: 5.00 cm − 4.80 cm = 0.20 cm, slab No. 3: 5.00 cm − 4.80 cm = 0.20 cm, slab No. 4: 5.00 cm − 4.80 cm = 0.20 cm.

For Cru_c, slab No. 1: 5 cm − 4.9 cm = 0.1 cm, slab No. 2: 5 cm − 4.9 cm = 0.1 cm, slab No. 3: 5.00 cm − 4.90 cm = 0.10 cm, slab No. 4: 5.00 cm − 4.90 cm = 0.10 cm.

After drying, the samples were heated by firing to determine the fired shrinkage test at two different firing temperatures 1400˚C and 1500˚C respectively in a gas kiln. This was done to ascertain how further the samples could shrink and to adjust it when working with such materials as exhibited in Table 3.

Fired shrinkage test was also given by:

Dry measurement (DM) − fired measurement (FM)

Thus, dry shrinkage test = DM − FM

Calculating fired shrinkage at 1400˚C

For Cru_a, slab No. 1: 4.70 cm − 4.60 cm = 0.10 cm, slab No. 2: 4.70 cm − 4.60 cm = 0.10 cm.

For Cru_b,: slab No. 1: 4.80 cm − 4.70 cm = 0.10 cm, slab No. 2: 4.80 cm − 4.70 cm = 0.10 cm.

For Cru_c, slab No. 1: 4.90 cm − 4.80 cm = 0.10 cm, slab No. 2: 4.90 cm − 4.80 cm = 0.10 cm.

Calculating fired shrinkage at 1500˚C

For Cru_a, slab No. 3: 4.70 cm − 4.50 cm = 0.20 cm, slab No. 4: 4.70 cm − 4.50 cm = 0.20 cm.

For Cru_b, slab No. 3: 4.80 cm − 4.60 cm = 0.20 cm, slab No. 4: 4.80 cm − 4.60 cm = 0.20 cm.

For Cru_c, slab No. 3: 4.90 cm − 4.70 cm = 0.20 cm, slab No. 4: 4.90 cm − 4.70 cm = 0.20 cm.

From Table 3, it came to light that all the three (3) samples Cru_a, Cru_b and Cru_c had the same fired shrinkage results (0.10 cm) at 1400˚C and another same fired shrinkage results (0.20 cm) at 1500˚C. These results implied that the composed ceramic bodies had perfect shrinkage tests and could be used to make ceramic products including crucibles.

Furthermore, the study continued with the physical test on porosity. Porosity refers to the pore space within a fired clay body. Here, the sintered briquettes were weighed according to the sintered temperatures at 1400˚C and1500˚C; and soaked in water overnight.

The porosity was given by:

Porosity = soaked weight − fired weight

Thus, Porosity = soaked weight (SW) − fired weight (FW)

Calculating porosity at 1400˚C

For Cru_a, slab No. 1: 68.70 − 65.50 = 3.20, slab No. 2: 64.50 − 61.30 = 3.20.

For Cru_b, slab No. 1: 75.60 − 74.30 = 1.30, slab No. 2: 67.50 − 66.20 = 1.30.

For Cru_c, slab No. 1: 72.10 − 71.40 = 0.70, slab No. 2: 66.30 − 65.60 = 0.70.

Calculating porosity at 1500˚C

For Cru_a, slab No. 3: 70.40 − 68.30 = 2.10, slab No. 4: 63.5 − 61.4 = 2.10.

For Cru_b, slab No. 3: 80.10 − 79.00 = 1.10, slab No. 4: 73.20 − 72.10 = 1.10.

For Cru_c, slab No. 3: 78.30 − 77.80 = 0.50, slab No. 4: 69.00 − 68.50 = 0.50.

Calculating for percentage (%) porosity is given by:

% Porosity = soakedwight ( SW ) − firedweight ( FW ) soakedweight ( SW ) × 100

Therefore, calculating percentage (%) porosity for the samples at 1400˚C;

For Cru_a, slab No. 1:

% porosity = 68.70 − 65.50 68.70 × 100 = 3.20 × 100 68.70 = 320 68.70 = 4.70 %

Slab No. 2: % porosity = 64.50 − 61.30 64.50 × 100 = 3.20 × 100 64.50 = 320 64.50 = 4.96 %

For Cru_b, slab No. 1:

% porosity = 75.60 − 74.30 75.60 × 100 = 1.30 × 100 75.60 = 130 75.60 = 1.72 %

Slab No. 2: % porosity = 67.50 − 66.20 67.50 × 100 = 1.30 × 100 67.50 = 130 67.50 = 1.93 %

For Cru_c, slab No. 1:

% porosity = 72.10 − 71.40 72.10 × 100 = 0.70 × 100 72.10 = 70 72.10 = 0.97 %

Slab No. 2: % porosity = 66.30 − 65.60 66.30 × 100 = 0.7 × 100 66.30 = 70 66.30 = 1.05 %

Again, calculating percentage (%) porosity for the samples at 1500˚C;

For Cru_a, slab No. 3:

% porosity = 70.40 − 68.30 70.40 × 100 = 2.10 × 100 70.40 = 210 70.40 = 2.98 %

Slab No. 4: % porosity = 63.50 − 61.40 63.50 × 100 = 2.10 × 100 63.50 = 210 63.50 = 3.31 %

For Cru_b, slab No. 3:

% porosity = 80.10 − 79.00 80.10 × 100 = 1.10 × 100 80.10 = 110 80.10 = 1.37 %

Slab No. 4: % porosity = 73.20 − 72.10 73.20 × 100 = 1.10 × 100 73.20 = 110 73.20 = 1.50 %

For Cru_c, slab No. 3:

% porosity = 78.30 − 77.80 78.30 × 100 = 0.50 × 100 73.20 = 50 73.20 = 0.68 %

Slab No. 4: % porosity = 69.00 − 68.50 69.00 × 100 = 0.5 × 100 69.00 = 50 69.00 = 0.72 %

The values obtained for the porosity had been recorded in Table 4. From Table 4, it was realized that sample Cru_a had high porosity (3.20 at 1400˚C and 2.10 at 1500˚C), followed by Cru_b (1.30 at 1400˚C and 1.10 at 1500˚C) and Cru_c had the least porosity (0.70 at 1400˚C and 0.5 at 1500˚C). Therefore, the sample Cru_c fired at 1500˚C was suitable for the manufacturing of the proposed crucible because of its low porosity and percentage (%) porosity values of 0.68% and 0.72% which were all less than 1% and therefore appropriate percentage values of porosity for a good refractory material [14] [15] .

Addressing the chemical properties, major oxides in the clay samples were analyzed at the Geological Survey Laboratory Department in Accra. The oxides of the samples were determined by using X-Ray fluorescence (XRF) with an ARL 9800XP spectrometer and yielded the following results as detailed in Table 5.

From Table 6, the individual oxides showing their percentages in the sampled clays had been outlined. It indicated that the composition Cru_a contained 55.82% of Silica (SiO₂) and 37.61% with other minerals constituting 6.57% as shown in Figure 17.

For composition Cru_b, it consisted of 57.81% of Silica (SiO₂) and 36.82% of alumina (Al₂O₃) with other minerals covering 5.37% as seen in Figure 18.

For composition Cru_c, it had 60.57% of quartz (SiO₂) and 30.72% of alumina ((Al₂O₃) as well as other minerals containing 8.71% as highlighted in Figure 19).

From Table 5, the silica (SiO₂) content of Cru_c indicated 60.57% which was a

signal of required standard for a good refractory ceramic body and also more appropriate as a recipe for making crucibles and other refractory products. Therefore, the preliminary tests (physical and chemical) conducted guided the study to formulate the ceramic bodies for making the proposed crucibles as shown in Table 7.

From Table 6, the recipe Cru_a consisted of 65% white clay, 15% kaolin, 5% quartz and 15% white grog. Cru_b comprised 70% white clay, 15% kaolin, 5% quartz and 10% white grog. Last but not least, Cru_c is composed of 70% white clay, 20% kaolin, 8% quartz and 2% white grog. The individual recipes were mixed with equal volumes of water to determine their water plasticity (the amount of water needed to make a clay body workable or mouldable). It came out that sample Cru_c was the most plastic followed by Cru_b and then Cru_a. Therefore, the study adopted sample Cru_c as the recipe to produce the crucibles. The “throwing” technique was employed to fabricate various shapes, forms and sizes of crucibles on the potter’s wheel. This was because special refractories components depend on the forming method, since it has an important influence on properties especially in relation to porosity distribution and final grain size [16] . However, crucibles were also made from the recipes Cru_a and Cru_b for comparative discussions on the compositions. In the “throwing” process, the recipes were kneaded to remove any air bubbles and made into lumps as seen in Figure 20.

The balls of various recipes were then “thrown” on the potter’s wheel by adopting “centering” method as seen in Figure 21, followed by the “pulling” method which made the crucibles into the required shapes and forms as seen in Figure 22. These processes were repeated until enough crucibles were made as shown in Figure 23.

The manufactured crucibles were dried under room temperature and further dried in an electric oven at 100˚C for 24 hours. The crucibles were grouped into two and sintered in the gas test kiln at 1400˚C and 1500˚C respectively. Preheating was done for three (3) hours so as to prevent the crucibles from breaking in the cause of thermal transformation. The sintering was then gradually increased

at intermittent intervals, and later increased to the full sintering stage of 1400˚C and 1500˚C which both took six (6) and eight (8) hours respectively. Figure 24 and Figure 25 show different crucibles sintered at 1400˚C and 1500˚C respectively having different colours.

Table 7 indicates the physical appearance of the sintered crucibles at temperatures of 1400˚C and 1500˚C. It was revealed that Cru_a and Cru_b had almond white colours for both temperatures while Cru_c at 1400˚C also had almond white colour. However, Cru_c sintered at 1500˚C had off-white colour indicating the high content of kaolin in the developed recipe.

Testing for thermal shock in crucible production is very important and key to determining its functionality. This is because the thermal shock if the thermal shock successfully done, the crucible would be suitable for use. To ascertain this test, the manufactured crucibles were sintered in an electric test kiln to 1000˚C. With the aid of a mechanized metal tool, each crucible was brought out and back into the hot kiln as seen in Figure 26.

The purpose was to allow penetration of cold air into the pores of the hot crucible while hot air in the hot pores would also try to come out, resulting in contraction and expansion of the body which normally could result in cracks leading to thermal shock [17] . After the conducted test, none of the crucibles developed cracks as the sample is shown in Figure 27.

Again, the manufactured crucibles were subjected to scanning electronic microscope (SEM) analysis. The SEM revealed a white block-like level and indicated the chemical intermetallic composition of the recipe developed. The result confirmed what other studies had revealed that a good refractory body is rich in quartz (SiO₂) and alumina (Al₂O₃) as exhibited in block-like morphology [18] . The crucibles were also microscopically examined for microcracking and it came to light that the manufactured crucibles had no cracks. This also signified that the crucibles were of high quality. Figure 28 shows a sample of the manufactured crucibles that have passed the thermally induced microcracking test.

From Table 6, the refractoriness of the manufactured crucibles indicated that sample Cru_c sintered at 1500˚C had the highest form of refractoriness followed by sample Cru_b and then Cru_a. This result supports the claims made by Titiladunayo & Fapetu [19] and Aye & Oyetunji [20] that a good refractory body should have refractoriness in the range of 1500˚C - 1700˚C. Therefore, the sample Cru_c sintered at 1500˚C was within this range. Hence, the study was very successful. This also implied that kaolin was highly responsible for refractoriness of the crucibles. The physical, mechanical and thermal properties of the manufactured crucibles showed that the crucibles were of good value and fit for use at any high-temperature application. It was realized that these ceramic raw materials (white plastic clay, kaolin, silica and grog) in different percentages by weight, if well treated technically could be employed to make different refractory items in the ceramic industry in Ghana.

The study recommends further collaboration between the researchers and institutions responsible for clay research such as Ghana Geological Survey Authority (GGSA) and Centre for Scientific and Industrial Research (CSIR) to improve upon this innovative idea. This would go a long way to bring back some of the collapsing ceramic industries in Ghana into operation and help the country to save costs for importing crucibles and other high-fired products. Again, it could also help create jobs for upcoming ceramic technologists and artists in Ghana so as to reduce the rate of unemployment in the country.

There could be further research to ascertain if the recipe developed could be used to produce other highly refractory products especially, high ceramic technology products.

The authors declare no conflicts of interest regarding the publication of this paper.

Asante-Kyei, K., Addae, A. and Aflo, A. (2023) Developing Recipe from Local Ceramic Raw Materials for Making Crucibles in Ghana. Journal of Minerals and Materials Characterization and Engineering, 11, 92-113. https://doi.org/10.4236/jmmce.2023.114009