Study on Adhesive and Microstructure Properties of Rice Husk Ash-Based Geopolymer Hybrid Alkyd Coating

Figures & data

Table 1. Experimental range and levels of central composite design.

Factor	Symbol	Levels
		−1	−0.5	0	0.5	1
GP-RHA	A	10	20	30	40	50
Paint	B	50	60	70	80	90

Figure 1. GP-RHA hybrid coating showing (a) actual sample and (b) sample schematic diagram.

Table 2. Design compositions of GP-RHA.

Specimen	RHA (g)	Na₂SiO₃ (g)	NaOH (g)	Ratio Na₂SiO₃/NaOH	Ratio Liquid/Solid
GP-RHA	52	110	20	5.5	2.5

Table 3. Design composition and adhesion value for dry pull-off adhesion test.

	Composition				Composition
Sample	A	B	Adhesion (MPa)	Sample	A	B	Adhesion (MPa)
GPHC1	20.00	80.00	2.1	GPHC21	30.00	70.00	2.5
GPHC2	37.50	62.50	3.3	GPHC22	30.00	70.00	2.6
GPHC3	25.00	75.00	2.3	GPHC23	30.00	70.00	2.5
GPHC 4	25.00	75.00	2.0	GPHC24	12.50	87.50	1.7
GPHC 5	33.33	66.67	3.1	GPHC25	20.00	80.00	1.9
GPHC 6	33.33	66.67	3.3	GPHC26	41.67	58.33	3.9
GPHC 7	30.00	70.00	2.9	GPHC27	41.67	58.33	3.8
GPHC 8	30.00	70.00	2.7	GPHC28	40.00	60.00	3.4
GPHC 9	30.00	70.00	2.6	GPHC29	12.50	87.50	1.5
GPHC10	30.00	70.00	2.7	GPHC30	30.00	70.00	2.7
GPHC11	30.00	70.00	2.9	GPHC31	30.00	70.00	2.5
GPHC12	30.00	70.00	2.9	GPHC32	30.00	70.00	2.7
GPHC13	40.00	60.00	3.4	GPHC33	40.00	60.00	3.5
GPHC14	30.00	70.00	2.9	GPHC34	20.00	80.00	1.9
GPHC15	30.00	70.00	2.7	GPHC35	30.00	70.00	2.5
GPHC16	25.00	75.00	2.3	GPHC36	25.00	75.00	2.0
GPHC17	25.00	75.00	2.1	GPHC37	37.50	62.50	3.1
GPHC18	41.67	58.33	3.7	GPHC38	33.33	66.67	2.9
GPHC19	37.50	62.50	3.3	GPHC39	20.00	80.00	1.8
GPHC20	25.00	75.00	2.1

Table 4. ANOVA analysis for pull-off adhesion strength.

Source	Sum of Squares	DF	Mean Square	F-value	p-value
Model	13.01	2	6.51	249.49	<.0001	significant
A	10.86	1	6.91	265.01	<.0001
B	0.0000	0
AB	0.2040	1	0.2040	7.82	.0082
Residual	0.9388	36	0.0261
Cor Total	13.95	38

Figure 2. Effect GP-RHA and alkyd paint on adhesion strength contour plot.

Figure 3. Optimum conditions and response for adhesion strength.

Table 5. Ratio and responses for sample alkyd, GPHC₂₆ and GPHC₂₉ for pull-off adhesion test.

Sample	Ratio (wt. %)
	GP-RHA (A)	Paint (B)	Adhesion (MPa)
Alkyd	0	100	1.4
GPHC26	41.67	58.33	3.9
GPHC29	12.50	87.50	1.5

Figure 4. SEM micrograph of the sample GPHC₂₆ surface (a) at 500× of magnification (b) at 5000× of magnification.

Figure 5. SEM micrograph of the sample GPHC₂₉ surface (a) at 500× of magnification (b) at 5000× of magnification.

Figure 6. Cross Section SEM micrograph of the sample GPHC₂₆ (a) at 100× of magnification and (b) at 500× of magnification.

Figure 7. Cross Section SEM micrograph of the sample GPHC₂₉ (a) at 100× of magnification and (b) at 500× of magnification.

Figure 8. SEM and EDX analysis composition for sample GPHC₂₆.

Figure 9. SEM and EDX analysis composition for sample GPHC₂₉.

Table 6. EDX analysis for sample GPHC₂₆ and GPHC_29.

Element	GPHC26 (wt. %)	GPHC29 (wt. %)
C	37.19	44.72
O	37.44	27.27
Na	2.95	1.39
Al	1.43	1.54
Si	8.13	.63
Ca	2.47	4.02
Ti	3.74	6.99
Cr	1.46	2.45
Fe	.65	1.45
Pb	4.40	9.35

Figure 10. The pull-off adhesion test result for measuring the dry adhesion and wet adhesion strength.

Table 7. Ratio and adhesion strength for sample alkyd, GPHC₂₆ and GPHC₂₉ for pull-off adhesion test.

Sample	Ratio (wt. %)		Adhesion Strength (MPa)
	GP-RHA (A)	Paint (B)	Dry Adhesion	Wet Adhesion
Alkyd	0	100	1.4	1.0
GPHC26	41.67	58.33	3.9	2.5
GPHC29	12.50	87.50	1.5	1.3

Figure 11. Coating sample after 500 h immersion in 3.5 wt.% NaCl solution showing (a) efflorescent effect with crystalline deposits on the surface of alkyd paint, (b) swelling on on the edge part of GPHC₂₆ specimen and (c) no visual defect on GPHC_29.

Figure 12. SEM micrograph after wet environment test simulation showing (a) several cracks occurred on the coating surface for alkyd, (b) swelling and unreacted particles on GPHC₂₆ coating surface and (c) micro pores on the GPCH₂₉ coating surface.