1. Application

This applies to the silica program test method.

2. Definition

Silica program is a chemical analysis of green sand consisting of the series of tests described in the following.

3. Chemicals, instrument and apparatus

3.1 Chemicals

1. Methylene blue solution The solution defined in TJFS-205 (Green sand active clay test method) is used.
2. 2% sodium pyrophosphate solution The solution defined in TJFS-205 (Green sand active clay test method) is used.
3. 50% hydrochloric acid A volume of first class concentrated hydrochloric acid (HCl) is diluted in pure water of the same volume.
4. 30% hydrofluoric acid solution 100 volume of 47% hydrofluoric acid solution is diluted by 56 volume of pure water.
   Note: It is recommended to purchase a commonly marketed hydrofluoric acid of 47% concentration. Hydrofluoric acid is a toxic material and needs utmost care for safety.
5. Safety wares such as glasses, mask containing absorbent of hydrofluoric acid, rubber gloves, or apron should be worn in handling. Hands should be washed well in running water. Sodium bicarbonate and magnesia emulsion (emulsion of magnesia in glycerin) are prepared for emergency. If skin happens to be in contact with hydrofluoric acid, sodium bicarbonate is coated on the skin and washed well in water, and then magnesia emulsion is spread over the skin. After these emergency treatmenst, doctor is consulted immediately.

3.2 Tools

1. Conical beaker
   One of 200ml size is used.
2. Automatic burette
   One of 50ml size is used.
3. Furon stirrer
   One of 5mm diameter and 25 to 30mm length is used.
4. Beaker 1
   One of 300ml size is used.
5. Beaker 2
   Teflon one of 100ml size is used.
6. Porcelain crucible 1
   One of 50ml size is used.
7. Porcelain crucible 2
   One of 30ml size is used.
8. Glass dish
   One of 100mm diameter is used.
9. Sieve 1
   One of nominal mesh size 22 μm is used.
10. Sieve 2
    One of nominal mesh size 53 μm is used.
11. Stirrer
    Teflon one of 5mm diameter and 200mm length is used.
12. KOMAGOME pipette
    Teflon one of 15ml size is used.
13. pH test paper
    Among the marketed pH papers, one that is fit for measuring pH 5 to 7 is used.

3.3 Apparatus

1. Balance 1
   One of the precision of 0.01g is used. If not specified otherwise, this one is used.
2. Balance 2
   A chemical balance of the precision of 0.0001g is used.
3. Supersonic disperser
   One of frequency 25 to 30kHz and output power of 150 to 200W is used.
4. Magnetic stirrer
   One of beaker size of 500ml is used.

3.4 Inspection

The precision should be occasionally checked to assure the precision of the apparatus used in this method.

4. Testing procedure

4.1 Determination of active clay

Active clay is measured by the method in TJFS-205 (Green sand active clay test method).

4.2 Determination of loss on ignition

4.2.1 Loss on ignition of the sample sand

1. The green sand is dried at 105±5 degree C until reaching a constant weight, and cooled in a desiccator. About 3g is ground fine in a mortar.
2. 1g of the ground sample is measured by the balance 2 and put in a 30ml porcelain crucible of a known weight. The crucible containing the sample is heated in an electric furnace at 1000 degree C for 1 hour.
3. After cooling in a desiccator, the crucible with the sample is weighed by the balance 2.
4. The loss on ignition of the sample is calculated by the following equation.
   \[L.O.I. = { ( W_1 - W_2 ) \over W_3 } \times 100 \]
   where
   \[ \left\{ \begin{array}{l} L.O.I. &= loss on ignition (％) \\ W_1 &= weight \ of \ the \ sample \ and \ crucible \ before \ heating \ (g) \\ W_2 &= weight \ of \ the \ sample \ and \ crucible \ after \ heating \ (g) \\ W_3 &= W_1 \ subtracted \ by \ the \ crucible \ weight \ (g) \end{array} \right. \]

4.2.2 Loss on ignition of the silica sand

Loss on ignition of the silica sand that is used in the sample green sand is measured in the same way.

4.2.3 Loss on ignition of the bentonite

Loss on ignition of the bentonite used in the sample green sand is measured in the same way.
Note: It is noted that the loss on ignition measurement described here is different from that of TJFS-206(Green sand loss on ignition test method).

4.3 Amount of carbonaceous material

The quantitative carbonaceous material is calculated by the following equation.

\[ C = L.O.I. - { ( AC - B.L.O.I. ) \over 100 } \times S.L.O.I. \]

where

\[ \left\{ \begin{array}{l} C &= carbonaceous \ material \ (％) \\ L.O.I. &= loss \ on \ ignition \ (％) \\ AC &= Active \ clay \ (％) \\ B.L.O.I. &= loss \ on \ ignition \ of \ the \ bentonite \ (％) \\ S.L.O.I. &= loss \ on \ ignition \ of \ the \ silica \ sand \ (％) \end{array} \right. \]

Note; The calculation of carbonaceous material here is different from that of TJFS-209 (Green sand fixed carbon calculation method).

4.4 Total clay

The total clay is determined by either of the following methods.

4.4.1 Total clay determination by TJFS-204 (Green sand total clay test method).

4.4.2 Total clay determination by sieving

1. The green sand is dried at 105±5 degree C until reaching a constant weight, and cooled in a desiccator. 25g is measured as a sample and put in a 300ml beaker.
2. 250ml of 2% sodium pyrophosphate solution is added to the sample and the sample is treated by a supersonic disperser for 10 minutes while occasionally being stirred with a glass rod. Otherwise, the boiling method described in 4.4.1 may also be used.
3. The dispersed sample is placed on a sieve of nominal mesh size of 22μm. It is washed by running water of an appropriately adjusted flow rate until the outflow water becomes clear.
4. The sample remained on the sieve is moved to a beaker and left still until the sample is settled on the bottom. Then the beaker is decanted carefully so as not to spill out the sample.
5. The sample is dried at 105±5 degree C until reaching a constant weight, and cooled in a desiccator. Then the sample weight is measured.
6. The total clay is calculated by the following equation.
   \[TC = 4 \times ( 25 - W ) \]
   where
   \[ \left\{ \begin{array}{l} TC &= total \ clay \ (％) \\ W &= weight \ of \ the \ sample \ remained \ (g) \end{array} \right. \]
   Note: Other items are handled in the same manner as in 4.4.1.

4.5 Determination of metallic substance

1. The sample after total clay determination is put in a porcelain crucible of a known weight. The crucible containing the sample is heated for 2 hours in an electric furnace of 1000 degree C, cooled in a desiccator, and weighed after cooling.
2. The sample after heating is transferred into a 300ml beaker and 175ml of hydrochloric acid is added. It is put in a glass dish with a cover and boiled for 2 hours in a sand bath in a draft chamber. Note: A sand bath consists of silica sand of a depth of 20 to 30mm in a steel container (preferably made of stainless steel) that is placed on an electric resistance heater.
3. After boiling and cooling, the sample, including those attached on the dish wall is washed into a beaker. Water is carefully added into the beaker to dilute hydrochloric acid. The beaker is left still until the sample has been settled.
4. After settling, the beaker is tilted and the upper layer water is decanted carefully not to spill out the sample. Then water is again added. The same process is repeated 4 times to dilute hydrochloric acid.
5. The sample is transferred onto a sieve of nominal mesh size of 53μm, processed in the same manner as in 4.4.2 (Total clay determination by sieving), and the residual sample on the sieve is weighed.
6. The metallic substance is calculated by the following equation.
   \[M = 4 \times ( W_1 - W_2 ) \]
   where
   \[ \left\{ \begin{array}{l} M &= metallic \ substance \ (％) \\ W_1 &= sample \ weight \ after \ heating \ (g) \\ W_2 &= residual \ sample \ weight \ (g) \end{array} \right. \]

4.6 Determination of dead clay

Dead clay (fine powder) is calculated by the following equation.

\[M = 4 \times ( W_1 - W_2 ) \]

where

\[ \left\{ \begin{array}{l} DC &= dead \ clay \ (％) \\ W &= sample \ weight \ after \ hydrochloric \ acid \ treatment \ as \ in \ 4.5(Determination \ of \ metallic \ substance) \\ AC &= active \ clay \ (％) \\ C &= carbonaceous \ substance \ (％) \\ M &= metallic \ substance \ (％) \end{array} \right. \]

4.7 Determination of Oolitic

1. 5g of the sample after hydrochloric acid treatment is transferred into a Teflon beaker of 100ml size.
2. 30ml of 30% hydrofluoric acid is added using a KOMAGOME pipette made from Teflon. Immediately after the addition, the solution is stirred for 1 minute with a Teflon stirrer and left still for 1 minute. Then it is stirred for another 1 minute. Note: Hydrofluoric acid may dissolve silica sand. The amount of dissolution, however, is small enough to be ignored, if the treating time specified here is followed. Therefore, the treating time must be followed rigorously.
3. 60 to 70ml of water is added to the solution, and the solution is left still for 1 minute. Then the beaker is carefully tilted to spill out the clear upper layer. Another 60 to 70ml of water is added, left for 1 minute, and the upper layer is flowed out. The same is repeated for 2 times.
4. The pH of the upper clear layer is measured with a pH test paper. If the pH is found less than 6, the treatment of 3) is repeated.
5. The water washing treatment is finished when pH becomes 6 or over. The residual sample in the beaker is dried at 105±5 degree C until reaching a constant weight, cooled, and weighed.
   Oolitic is calculated by the following equation.
   \[ O ={ HW \times ( 5 - FW ) \over 1.25 } \]
   where
   \[ \left\{ \begin{array}{l} O &= oolitic \ (％) \\ HW &= sample \ weight \ after \ the hydrochloric \ acid \ treatment \ as \ in \ 4.5 \ (Determination \ of \ metallic \ substance) \\ FW &= sample \ weight \ after \ hydrofluoric \ acid \ treatment \ (g) \end{array} \right. \]

4.7 Determination of quartz content

Quartz content is calculated by the following equation.

\[ Q ={ HW \times FW \over 1.25 } \]

where

\[ \left\{ \begin{array}{l} Q &= quartz \ content \ (％) \\ HW &= sample \ weight \ after \ the \ hydrochloric \ acid \ treatment \ as \ in \ 4.5 \ (Determination \ of \ metallic \ substance) \\ FW &= sample \ weight \ after \ hydrofluoric \ acid \ treatment \ (g) \end{array} \right. \]

Explanation: The present method, which has been substantially modified from an earlier method, is explained in the following.

1. Total clay determination
   To simplify the operation, the sieving method has been added. This method is simpler and quicker than TJFS-204 (Green sand total clay test method). The result of the sieving method, however, is dependent on the particle size and not on particle density, and hence, may somewhat different from that by TJFS-204 (Green sand total clay test method).
   According to a comparative study using samples of N=30, the average value by the sieving method is 0.51 % smaller than that by TJFS-204, the range of difference being 0 to 0.9% at the maximum. The total clay is normally above 10%, and hence, the difference of this amount was judged to be permissible. Thus the sieving method was adopted.
2. Change of acid in oolitic determination
   Phosphoric acid treatment had been used in the conventional oolitic determination. The phosphoric acid treatment, however, requires solution time over 20 hours, and solution is often not complete within the time conventionally specified.
   Therefore, a study was made for shorter testing time and correct results. Hydrofluoric acid, already adopted in Europe, was examined and the treatment procedure was established after various experiments.
   According to a comparative study using samples of N=30, the result of quartz by the hydrofluoric treatment was 6% smaller in average than the value by the phosphoric acid treatment, the range of difference being -4.5% to 14.9% maximum¹⁾.
   Note¹⁾: In three samples, quartz by the hydrofluoric acid was larger than that by the phosphoric acid treatment. X-ray diffraction analysis, however, indicated quartz to be even less in all the samples tested. This revealed that non-quartz components such as feldspar are not removed sufficiently by the phosphoric acid treatment. Therefore, it was judged that the hydrofluoric acid method gives better results than the phosphoric acid method, and thus the present method was adopted.