Solution method for making molybdate and tungstate negative thermal expansion materials and compounds made by the method

A method for making substantially single-phase, crystalline NTE compounds having the formula A 4 + ⁢ M 2 6 + ⁢ O 8

• where A4+ is Zr4+, Hf4+, or mixtures thereof, and M6+ is Mo6+, W6+, or mixtures thereof, comprising:
• forming a liquid mixture comprising stoichiometric amounts of (1) a soluble source of Zr4+, Hf4+, or mixtures thereof, and (2) a sodium-ion-free tungstate salt, a sodium-ion-free molybdate salt, or mixtures thereof;
• adding a mineral acid to the liquid mixture;
• refluxing the liquid mixture at ambient pressure for a period of about 48 hours or more, or at pressures greater than ambient for a period of from about 1 to about 24 hours;
• separating a solid fraction from the mixture;
• and
• heating the solid fraction to a temperature within the temperature range of from about 500° C. to less than 700° C. to form a compound having the formula A 4 + ⁢ M 2 6 + ⁢ O 8 .

A method for making substantially single-phase, crystalline NTE compounds having the formula:

• A 4 + ⁢ M 2 6 + ⁢ O 8
• where A4+ is Zr, Hf, or mixtures thereof, and M6+ is Mo, W, or mixtures thereof, comprising:
• forming an aqueous mixture comprising stoichiometric amounts of (1) a zirconium oxyhalide, a zirconium oxynitrate, a hafnium oxyhalide, a hafnium oxynitrate, or mixtures thereof, and (2) sodium-ion-free ammonium tungstate, sodium-ion-free ammonium molybdate, or mixtures thereof;
• acidifying the aqueous mixture using a mineral acid to obtain a pH of about 0 or less;
• refluxing the aqueous liquid mixture at ambient pressures for a period of about 48 hours or more, or at pressures greater than ambient for a period of from about 1 to about 24 hours;
• separating a solid fraction from the aqueous mixture;
• and
• heating the solid fraction to a temperature of from about 500° C. to less than about 700° C. for a period of time sufficient to form a compound having the formula A 4 + ⁢ M 2 6 + ⁢ O 8 .

A method for making substantially single-phase crystalline NTE compounds having the formula:

• A 4 + ⁢ M 2 6 + ⁢ O 8
• where A4+ is Zr4+, Hf4+, or mixtures thereof, and M6+ is Mo6+, W6+, or mixtures thereof, the method comprising:
• forming a liquid mixture comprising stoichiometric amounts of (1) a soluble source of Zr4+, Hf4+, or mixtures thereof, (2) a sodium-ion-free tungstate salt, a sodium-ion-free molybdate salt, or mixtures thereof, and (3) a fuel material;
• adding an acid to the liquid mixture to acidify the liquid mixture;
• and
• heating the mixture within the temperature range of from about 500° C. to less than 700° C. to form a compound having the formula A 4 + ⁢ M 2 6 + ⁢ O 8 .

A method for making substantially single-phase NTE compounds having the formula:

• A 4 + ⁢ M 2 6 + ⁢ O 8
• where A4+ is Zr4+, Hf4+, or mixtures thereof, and M6+ is Mo6+, W6+, or mixtures thereof, the method comprising:
• forming an aqueous mixture comprising stoichiometric amounts of (1) a soluble source of Zr4+, Hf4+, or mixtures thereof, (2) a sodium-ion-free tungstate salt, a sodium-ion-free molybdate salt, or mixtures thereof, (3) a fuel material, and (4) HNO3;
• and
• heating the mixture at a temperature of from about 500° C. to about 600° C. for a period of time of less than about one hour, thereby forming a compound having the formula A 4 + ⁢ M 2 6 + ⁢ O 8 .

A method for making fine particle, crystalline ZrW2O8, comprising:

• forming 0.5M solutions of zirconium oxynitrate and ammonium metatungstate;
• heating a first volume of the ammonium metatungstate solution to a temperature of about 60° C.;
• adding a second volume which is about half the first volume of the zirconium salt solution to the ammonium metatungstate;
• adding 6M HCl to the mixture to form an acidified mixture;
• heating the acidified mixture at 60° C. until the mixture is concentrated at a slurry;
• transferring the slurry to a Parr bomb and heating the slurry in the Parr bomb and was heated at 180° C.;
• filtering and washing material removed from the Parr bomb;
• and
• sintering the material at a temperature of about 1200° C. for a period of time less than about thirty minutes.

A composition having a thermal expansion less than that of a material included in the composition, the composition comprising:

• a first material having low or negative thermal expansion and a formula of A 1 - x 4 + ⁢ A x ′4 + ⁢ M 2 - y 6 + ⁢ M y ′6 + ⁢ O 8
• where A4+ and A′4+ are Hf4+ or Zr4+, M6+ and M′6+ are W6+ or Mo6+, X is from 0 to 1, and Y is from about 0.05 to <2;
• and
• a second material, the second material exhibiting a positive thermal expansion.