Laboratory work № 2 Definition of losses at baking

About 1,0g of kaolin, clay or fieldspar is dried in platinum or porcelain crucible during 10 - 15 minutes. After that temperature is gradually risen up to 1000 - 1200⁰ and hinge is kept during 30 minutes. Then crucible is cooled in the desiccator and weighed. Baking and weighing are repeated till receiving constant weight.

The losses at baking are defined under the formula:

B= a ∙ 100 - w٪ ,

Where a - loss of weight of a material at baking, g;

с - initial hinge, g;

w – content of hygroscopic moisture in a material, ٪

Devices and reagents

1. Porcelain crucible

2. Blind roaster

3. Exiccator

4. Kaolin, clay or feldspar

Questions for self-checking:

1. What includes losses at baking in usual chemical analysis?

2. To define composition of raw materials of ceramic masses and items a chemical analysis is widely used. What methods is chemical analysis made by?

3. Taking into consideration definition accuracy is only baking enough without testing the achieved constancy of the weight to solve appropriate technological tasks?

4. What accuracy is the size of losses at baking calculated with?

Laboratory work № 3 Mixing clay materials with water.

Aim of the work - mixing a clay materials with water.

Theoretical information

Production of plastic forming mass on the basis of clay and kaolins with properties necessary for normal proceeding of the of formation process is a complex task. The masses for plastic formation of whiteware products and some kinds of building ceramics except clays contain other components. The properties of masses are influenced by the content and kind of clay raw material, quantity, nature and dispersiveness of other components, way of processing and other factors. The most important parameter determining properties of weights is moisture.

The condition of weight containing clay, at which it can change the form under the hand of a man (loading 0,1 - 0,2 МPа), not sticking to hands or metal is called normal (working) consistence, and corresponding moisture content to it forming moisture.

Such condition of clay weight corresponds to formation of layers of water between all clay particles and creation of the advanced grid of coagulative contacts between them.

The definition of normal working consistence and, hence, water mixing in adhesion to a hand or metal is a rather subjective method depending on a set of factors. To increase objectivity of the analysis more exact methods are used.

The most important condition of accuracy and objectivity of received results is the way of preparation of samples. A researched material is previously dried up to air-dry condition at 105-110⁰С, ground by a wooden hammer (lump hammer) and sifted through a sieve №1 (size of apertures 1mm) and two ways of preparation of weight - plastic and dross are used.

At dross method: distilled water in quantity of 50-150 % from weight of dry clay is filled in a tank equipped by mixer. The crushed dried clay is added to water by small portions at working agitator. Time of preparation of suspension is 2-4 h.

If dross is prepared without using mixer, after adding all material it is periodically mixed by wooden shovel and passed through a sieve №1. Rest of weight is wiped through a sieve and washed with strained dross. Dross is kept not less than 48h and then added to the dry plaster forms, closed by damp cloth and plaster boards. Weight is periodically thoroughly flattened by hands. Selection of moisture is carried out till receiving weight of normal working consistence.

Technique of experiment

At a plastic way of preparation clay is moisted immedeatily necessary to receive normal forming consistence with quantity of water in 2-3 receptions with intervals in 30 minutes. Clay dough is kept not less than 10-15 h and flattened manually till disappearance of large lumps.

Prepared dough by same means or others are flattened to remove air lumps are formed, turned in a damp fabric and repeatedly (not less than 10 - 15 times) are beaten by wooden hammer. The best way is vacuum processing with the help of laboratory vacuum - mixer.

Processing of results

The result of definition is calculated by the formula:

The mass of water necessary to add to air-dry clay to receive clay of normal forming consistence is called absolute forming moisture (%) or water mixing Mw:

(1)