1. A process for preparing precipitated silica comprising aluminum, the process comprising conducting a precipitation reaction between a silicate and an acidifying agent, via which a suspension of precipitated silica is obtained, followed by a separation and drying of this suspension, in which:
the precipitation reaction is performed in the following manner:
(i) forming an initial feedstock comprising a silicate and an electrolyte, wherein a concentration of silicate (expressed as SiO2) in said initial feedstock is less than 100 gL and a concentration of electrolyte in said initial feedstock is less than 17 gL,
(ii) adding the acidifying agent to said feedstock until the reaction medium has a pH value of at least 7,
(iii) simultaneously adding acidifying agent and a silicate to the reaction medium,
drying a suspension with a solids content of not more than 24% by weight, said process comprising one of the following three operations (a), (b) or (c):
(a) simultaneously adding at least one compound of aluminum and a basic agent to the reaction medium, after step (iii),
(b) simultaneously adding a silicate and at least one compound of aluminum to the reaction medium, in place of step (iii),
(c) performing step (iii) simultaneously adding to the reaction medium acidifying agent, a silicate and at least one aluminum compound.
2. The process as described by claim 1, wherein:
the precipitation reaction is performed in the following manner:
(i) forming an initial feedstock comprising a silicate and an electrolyte, wherein a concentration of silicate (expressed as SiO2) in said initial feedstock is less than 100 gL and a concentration of electrolyte in said initial feedstock is less than 17 gL,
(ii) adding the acidifying agent to said feedstock until the reaction medium has a pH value of at least 7,
(iii) simultaneously adding acidifying agent and a silicate to the reaction medium,
and then performing the following steps:
(iv) simultaneously adding at least one aluminum compound A and a basic agent to the reaction medium, and then
(v) adding acidifying agent to the reaction medium, and
drying a suspension with a solids content of not more than 24% by weight.
3. The process as described by claim 1, wherein:
the precipitation reaction is performed in the following manner:
(i) forming an initial feedstock comprising a silicate and an electrolyte, wherein a concentration of silicate (expressed as SiO2) in said initial feedstock is less than 100 gL and a concentration of electrolyte in said initial feedstock is less than 17 gL,
(ii) adding the acidifying agent to said feedstock until the reaction medium has a pH value of at least 7,
(iii) simultaneously adding a silicate and at least one aluminum compound A to the reaction medium, and
drying a suspension with a solids content of not more than 24% by weight.
4. The process as described by claim 3, wherein that after step (iii), the process further comprises adding acidifying agent to the reaction medium.
5. The process as described by claim 1, wherein the aluminum compound A is an organic or an inorganic aluminum salt.
6. The process as described by claim 2, wherein the aluminum compound A is an aluminum sulfate.
7. The process as described by claim 2, wherein the separation comprises a filtration and a disintegrating of a cake resulting from the filtration, said disintegrating optionally being performed in the presence of at least one aluminum compound B.
8. The process as described by claim 7, wherein compound B is an alkali metal aluminate.
9. The process as defined by claim 1, wherein:
the precipitation reaction is performed in the following manner:
(i) forming an initial feedstock comprising a silicate and an electrolyte, wherein a concentration of silicate (expressed as SiO2) in said initial feedstock is less than 100 gL and a concentration of electrolyte in said initial feedstock is less than 17 gL,
(ii) adding the acidifying agent to said feedstock until the reaction medium has a pH value of at least 7,
(iii) simultaneously adding an acidifying agent, a silicate and at least one aluminum compound B to the reaction medium, and
drying a suspension with a solids content of not more than 24% by weight.
10. The process as defined by claim 9, wherein that, after step (iii), acidifying agent is added to the reaction medium.
11. The process as defined by claim 10, wherein compound B is an alkali metal aluminate.
12. The process as as defined by claim 9, wherein the separation comprises a filtration and a disintegrating of the cake resulting from the filtration.
13. The process as defined by claim 1, wherein the drying is performed by atomization.
14. The process described by claim 2, wherein the at least one aluminum compound A and the basic agent are added until the reaction medium has a pH value of from 6.5 to 10.
15. The process described in claim 14, wherein the pH value is from 7.2 to 8.6.
16. The process described in claim 2, wherein the acidifying agent is added to the reaction until the reaction medium has a pH value of from 3 to 5.
17. The process described in claim 16, wherein the pH value is from 3.4 to 4.5.
18. The process described in claim 4, wherein the acidifying agent is added until the reaction medium has a pH value of from 3 to 6.5.
19. The process described by claim 5, wherein the organic salt is a carboxylic acid salt or a polycarboxylic acid salt.
20. The process described by claim 5, wherein the inorganic salt is selected from the group consisting of a halide, an oxyhalide, a nitrate, a phosphate, a sulfate and an oxysulfate.
21. The process described by claim 8, wherein the alkali metal aluminate is a sodium aluminate.
22. The process described by claim 10, wherein the acidifying agent is added until the reaction medium has a pH of from 3 to 6.9.
23. The process described by claim 11, wherein the alkali metal aluminate is a sodium aluminate.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A radio frequency (RF) coil array for use in a magnetic resonance imaging (MRI) system, the RF coil array comprising:
at least first and second RF coils, each having a main body loop configured to at least one of transmit or receive RF energy at an operating imaging frequency in connection with acquiring MRI image data for an MRI system;
first and second cables configured to electrically couple the first and second RF coils, respectively, to a system interface; and
a common ground connection between the first and second cables having selectively positioned at a grounding point along lengths of the first and second cables to form a ground loop having a select self-resonance frequency (SRF) that differs from the imaging frequency of the MRI system.
2. The RF coil array of claim 1, wherein the RF energy includes a wavelength, the location of the grounding point based on the wavelength.
3. The RF coil array of claim 2, wherein the grounding point is located at a distance approximately one-fourth of the wavelength extending from the main body loop of at least one of the first or the second RF coils.
4. The RF coil array of claim 1, wherein the main body loops of the first and second RF coils each include a central portion extending approximately through a center of each respective main body loop, the first or second cables extending to and through the central portion of the respective main body loop.
5. The RF coil of claim 1, wherein the ground loop includes the first and second RF coils and the first and second cables, the select SRF of the ground loop being tuned by moving the grounding point along the lengths of the first and second cables.
6. The RF coil array of claim 1, wherein the first and second cables include an impedance, the position of the grounding point along the length of the first and second cables being set to define a select impedance along the ground loop in connection with setting the select SRF.
7. The RF coil array of claim 1, wherein the self-resonance frequency is less than the imaging frequency.
8. The RF coil array of claim 1, wherein the imaging frequency is approximately 128 megahertz.
9. The RF coil array of claim 1, wherein the first and second cables are arranged such that the first and second cables are approximately perpendicular to electric field lines generated by the main body loops of the first and second RF coils.
10. The RF coil array of claim 1, wherein the first and second cables include an outer conductor, the outer conductors electrically coupled to one another to from the common ground connection.
11. A method for tuning a radio frequency (RF) coil array for use in a magnetic resonance imaging (MRI) system comprising:
coupling a first cable to a first RF coil and a second cable to a second RF coil, the first and second RF coils having a main body loop configured to at least one of transmit or receive RF energy at an operating imaging frequency in connection with acquiring MRI image data for an MRI system;
coupling the first and second cables to a system interface;
positioning a common ground point along lengths of the first and second cables; and
forming a ground loop having a select self-resonance frequency (SRF) that differs from the imaging frequency of the MRI system.
12. The method of claim 11, wherein the RF energy includes a wavelength, the location of the grounding point based on the wavelength.
13. The method of claim 12, wherein the grounding point is located at a distance approximately one-fourth of the wavelength extending from the main body loop of at least one of the first or the second RF coils.
14. The method of claim 13, wherein the main body loops of the first and second RF coils each include a central portion extending approximately through a center of each respective main body loop, the first or second cables extending to and through the central portion of the respective main body loop.
15. The method of claim 11, wherein the ground loop includes the first and second RF coils and the first and second cables, the select SRF of the ground loop being tuned by moving the grounding point along the lengths of the first and second cables.
16. The method of claim 11, wherein the first and second cables include an impedance, the position of the grounding point along the length of the first and second cables being set to define a select impedance along the ground loop in connection with setting the select SRF.
17. The method of claim 11, wherein the location of the common ground point is selected such that the self-resonance frequency is less than the imaging frequency.
18. The method of claim 11, wherein the imaging frequency is approximately 128 megahertz.
19. The method of claim 11, wherein the first and second cables are arranged such that the first and second cables are approximately perpendicular to electric field lines generated by the main body loops of the first and second RF coils.
20. The method of claim 11, wherein the first and second cables include an outer conductor, the outer conductors electrically coupled to one another to from the common ground connection.