Color in glazes and enamels
Transcript of Color in glazes and enamels
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Sources of color in glazes• Transition metal ions• The precipitation of crystal: titania and zirconia• Insoluble crystal or crystals that are colored
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• Lattice energy� determined almost totally by the nearest-neighbor cation-anion distances
• Coordination polyhedra� radius ratio• Electrostatic neutrality
Crystal chemistry of pigments
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Oxide pigments
• Opacifiers = white pigments– Tin oxide (refractive index 2.04)
– Zirconia (refractive index 2.40)– Zircon (refractive index 1.85)
– Titania (R.I =2.5, 2.7 for anatase and rutite)
• Color pigments / stains
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Black and grey pigments
• CoO, Mn2O3, NiO, Fe2O3, Cr2O3, FeO, CuO
• Black spinel pigments:– CuO-Cr2O3
– FeO-CoO– FeO-CoO-Cr2O3
– Mn2O3-Fe2O3
– Cr2O3-FeO-NiO
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Brown pigments
• Zinc-iron-chromitespinels
• Zinc-iron-chrome-aluminate
• Chrome-iron-tin-brown
• Iron-manganese brown
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Pink, purple and maroon pigments
• Chrome alumina pink
• Maganesealumina pink
• Zircon-iron system
• Chrome-tin system
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• Cr 3+ , Cr 6+
• Cr 3+ ����� ������ก � ����������� �������������������ก� ����ก� ��� �� ����!"��ก� #�$� SiO2 %$&��ก��' RO ��
• Cr 6+ #&��(��ก� ����(�!���)��� #*"���" )"�ก*+,��-�%. ������+ ก#�$�ก�$� ���
• Cr2O3 �'������ก� ������ ��
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%* ������� ���ก� #�$�ก.� )"���!$��/�ก ��ก����
• Mn 2+ (�!� Mn 3+
• Mn 3+ �'������ก� #&��(��ก� ���� �� � �%��� )"�ก*+� �� � ����'-�.� ������+ ก#�$��0����1��'ก�+�����!�+�� �
• Mn 2+ �����!�+/'�(����"&�%��2�� ��'*ก3+ Mn 2+ �����!�+#�$�4��++��ก2.��-*$�
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• Fe 2+ (�!� Fe 3+
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Zr
Ca,Pb,Sn
Zn, Zr
Zn, Zr
Zr
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Zn, B, alkali1250 OFZr-Si-Fe��� (Coral)
Zn,B1250 OFSn-Ca-Si-Cr��� (maroon)
1300 OF
1350 OF
Zn-Cr-Fe-Al-Sn
Zn-Cr-Fe�"&�%��
Pb, Zn,Ca,B
alkali
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Tablewares
SinksChemical apparatusjewellry
Refrigerator, washing machines
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Properties of enamels and coatings
• Mechanical properties– Elasticity– Tensile strength, compressive strength, bending strength, hardness
• Thermal properties – Thermal conductivity (�.����#�$��3��� /'�&�� �����%$&� #&��(�#�%��ก������$������
� �������)– Thermal expansion (�.����� �� COE %$&�ก ����('(�!�-."����#�$/'���!�+)– Thermal shock resistance,TSR (�.�������� TSR ���������� convex )
• Optical properties– Reflection – color
• Electrical properties– Insulator
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Elasticity
• *���� ���(�!�� ��� ����$�����ก(�!������!$������)�(�!����ก�ก�'#&�%�� *����*"�
• ��� modulus %$&� /'� elasticity ��
• �!$� Elasticity �� �.����/'#�%�� strain ��
=∆
ES
Pll
∆ll
S P
E = modulus of elasticity
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Strains in the enamel layer
• Bonding between metal and enamel
• Shape of surface and radius of curvature
• COE
• Softening temperature of enamels
• Thickness of enamel
• Elasticity of enamel and metal
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• Acid oxides: Silica, boric oxide ����ก� Quartz, sand, boric oxide
• Basic oxides: alkalis and alkaline-earth metals) ����ก� (.�7:��� ��1 ZnO, MgO, PbO
• Amphoteric oxides: mainly alumina
• Acid+basic oxides (������ ก*�): Feldspar, clay and kaolin, borax
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